From Nature News, this is an excellent overview of what we know - and how much we do NOT know - about epigenetics. We are beginning to see the degree to which epigenetic variations can be transmitted from one generation to the next, but we still have very little idea how that process works.

[NOTE: the title of this article refers to a study with mice in which male mice were trained to be afraid of acetophenone, a sweet smelling substance, by pairing the scent with a mild electric shock. The male mice were later mated with females who had not experienced the conditioning. Their offspring showed an unusual sensitivity to the acetophenone scent, more so than other scents. And the grandchildren of the original male mice also showed an unusual sensitivity to acetophenone.]

Epigenetics: The sins of the father

The roots of inheritance may extend beyond the genome, but the mechanisms remain a puzzle.

Virginia Hughes
05 March 2014


20th Century Fox/The Kobal Collection
When Brian Dias became a father last October, he was, like any new parent, mindful of the enormous responsibility that lay before him. From that moment on, every choice he made could affect his newborn son's physical and psychological development. But, unlike most new parents, Dias was also aware of the influence of his past experiences — not to mention those of his parents, his grandparents and beyond.

Where one's ancestors lived, or how much they valued education, can clearly have effects that pass down through the generations. But what about the legacy of their health: whether they smoked, endured famine or fought in a war?

As a postdoc in Kerry Ressler's laboratory at Emory University in Atlanta, Georgia, Dias had spent much of the two years before his son's birth studying these kinds of questions in mice. Specifically, he looked at how fear associated with a particular smell affects the animals and leaves an imprint on the brains of their descendants.

Dias had been exposing male mice to acetophenone — a chemical with a sweet, almond-like smell — and then giving them a mild foot shock. After being exposed to this treatment five times a day for three days, the mice became reliably fearful, freezing in the presence of acetophenone even when they received no shock.

Ten days later, Dias allowed the mice to mate with unexposed females. When their young grew up, many of the animals were more sensitive to acetophenone than to other odours, and more likely to be startled by an unexpected noise during exposure to the smell. Their offspring — the 'grandchildren' of the mice trained to fear the smell — were also jumpier in the presence of acetophenone. What's more, all three generations had larger-than-normal 'M71 glomeruli', structures where acetophenone-sensitive neurons in the nose connect with neurons in the olfactory bulb. In the January issue of Nature Neuroscience1, Dias and Ressler suggested that this hereditary transmission of environmental information was the result of epigenetics — chemical changes to the genome that affect how DNA is packaged and expressed without altering its sequence.

Biologists first observed this 'transgenerational epigenetic inheritance' in plants. Tomatoes, for example, pass along chemical markings that control an important ripening gene2. But, over the past few years, evidence has been accumulating that the phenomenon occurs in rodents and humans as well. The subject remains controversial, in part because it harks back to the discredited theories of Jean-Baptiste Lamarck, a nineteenth-century French biologist who proposed that organisms pass down acquired traits to future generations. To many modern biologists, that's “scary-sounding”, says Oliver Rando, a molecular biologist at the University of Massachusetts Medical School in Worcester, whose work suggests that such inheritance does indeed happen in animals3. If it is true, he says, “Why hasn't this been obvious to all the brilliant researchers in the past hundred years of genetics?”.

One reason why many remain sceptical is that the mechanism by which such inheritance might work is mysterious. Explaining it will require a deep dive into reproductive biology to demonstrate how the relevant signals might be formed in the germ line, the cells that develop into sperm and eggs and carry on, at a minimum, a person's genetic legacy.

A mother might pass on effects of environmental exposures to a fetus during pregnancy. So, to study the phenomenon of transgenerational epigenetics cleanly, biologists are focusing on fathers, and have been looking at how sperm might gain and lose epigenetic marks. “In the past two to three years there's been a lot of new information,” says Michelle Lane, a reproductive biologist at the University of Adelaide in Australia. But proposals for how it all works are themselves embryonic. “It's a huge black box,” Lane says.


Monster plants and obese children
The epigenetics revolution hit in the early 2000s, when scientists began reporting that environmental factors — everything from neglectful mothering and child abuse to a high-fat diet and air pollution — can influence the addition or removal of chemical tags on DNA that turn genes on and off. This idea of an environmentally responsive genome still stirs debate (see Nature 467, 146–148; 2010). But the notion that epigenetic marks are transmitted across generations is even more provocative.

Swedish botanist Carl Linnaeus was among the first to spot changes resulting from this phenomenon. In the 1740s, he received a plant specimen that looked very similar to common toadflax (Linaria vulgaris), but with very different flowers. Linnaeus was shocked because this challenged his theory that plant species could be categorized by the structure of their flowers. “This is certainly no less remarkable,” he wrote, “than if a cow were to give birth to a calf with a wolf's head.” He named the plant Peloria, after the Greek word for 'monster'.

In the 1990s, plant biologist Enrico Coen at the John Innes Centre in Norwich, UK, found that in the monster plants, methyl groups litter a gene involved in flower structure called Lcyc, completely shutting it down. (DNA methylation usually turns genes off.) Coen's team also showed that these methyl marks pass through seeds to later generations4.

The public first started to take notice in the mid-2000s, after large epidemiological investigations in Europe began to show transgenerational effects in humans. One study of Swedish historical records showed that men who had experienced famine before puberty were less likely to have grandsons with heart disease or diabetes than men who had plenty to eat5. Similar work with children in Britain reported in 2005 that fathers who had started smoking before the age of 11 had an increased risk of having boys of above average weight6.

But many scientists remained sceptical. Epidemiological studies are often messy, and it is impossible to rule out all confounding variables. In the past few years, however, several studies in rodents have supported these observations and begun to attribute the transmission of various traits to changes in sperm.

Sperm signatures

Male rats fed a high-fat diet, for example, beget daughters with abnormal DNA methylation in the pancreas7. Male mice fed a low-protein diet have offspring with altered liver expression of cholesterol genes3. And male mice with pre-diabetes have abnormal sperm methylation, and pass on an increased risk of diabetes to the next two generations8.

“We and many other people have now shown these paternal effects,” says Rando, who led the low-protein study. “And we're all having a hell of a time figuring out how they work.”

The animal studies have triggered some strong debate. The most controversial results have come out of Michael Skinner's lab at Washington State University in Pullman. Skinner's team exposed pregnant rats to large doses of pesticides and fungicides, which led to organ damage in their adult offspring. The sperm of male offspring showed changes in DNA methylation that persisted for at least four generations9.

But at least two groups failed to replicate the data, and in 2010, federal investigators found that one of Skinner's postdocs had fabricated data for a related paper, which the authors had retracted in 2009. Skinner says that some teams have replicated his results, and that those who have not were using inappropriate protocols. Last year, his own team reported successfully reproducing the results of the retracted paper10.

Methylation mechanism

Explaining how transgenerational epigenetics works has been difficult in part because most studies track outcomes — such as changes in glucose, cholesterol and fertility — that can be affected by a range of factors, making it tricky to tease out cause and effect. By contrast, Dias and Ressler's work with acetophenone takes advantage of specific biology: the chemical binds to a particular receptor in the nose that is encoded by a single gene, dubbed Olfr151. “This is the massive pro of their study,” Rando says.

Dias and Ressler do not claim to understand exactly what is going on, but they do have a working hypothesis. Somehow, the information about the frightening smell gets into a mouse's testes and results in lower methylation of the Olfr151 gene in sperm DNA. The researchers even ran experiments using in vitro fertilization to make sure that the father was not in some way passing on a fear of acetophenone through interactions with the mother. The epigenetic tweak in the sperm is perpetuated in the offspring's DNA, leading to increased expression of the receptor in the animals' noses and, ultimately, enhanced sensitivity to the smell.

But the chain of causation is loose. “There are a lot of disconnects there,” says William Kelly, a developmental geneticist at Emory. “It's not beyond the realm of possibility or plausibility. It's just right now we don't know enough about how information is transferred between generations.”

The first question is how the effects of environmental exposure become embedded in an animal's germ cells — in this case, the mouse's sperm. Germ cells have been shown to express olfactory receptors11. So it is possible that Olfr151 receptors in sperm respond to odorant molecules in the bloodstream and then change the methylation of the corresponding gene in sperm DNA.

Alternatively, after being exposed to the odour and the pain, a mouse might produce RNA molecules — perhaps in the brain — that make their way into the bloodstream and then selectively target the Olfr151 gene in sperm. Many studies in plants have hinted at this sort of systemic RNA shuttling. RNA molecules expressed in a plant's leaf, for example, can travel through its vascular system to many of its other tissues and affect gene expression12.

But creating an epigenetic mark in the sperm is only the first step. To pass down through multiple generations, the signal needs to survive multiple rounds of rigorous epigenetic reprogramming. In mammals, the first of these happens just hours after conception, when most methylation is stripped from sperm DNA in the single-celled embryo. Then, as the embryo develops and divides, and cells begin to differentiate into various tissue types, methylation is gradually re-established. But even if some signal from the father were to survive this process, the embryo's own primordial germ cells, those that eventually become its sperm or eggs, undergo a second round of epigenetic scrubbing (see 'Without a trace').

Some genes manage to escape these periods of major reprogramming. The best example is genes that are imprinted — whereby one copy from the mother or father is robustly methylated and effectively silenced. These silencing marks crop up in the egg or sperm and are retained in the embryo.

About 100 genes are known to be imprinted, but some non-imprinted genes may also escape the scrubbing through a similar mechanism. “There is a growing consensus that there are more regions than previously thought that escape reprogramming in sperm,” says Sarah Kimmins, an epigeneticist at McGill University in Montreal, Canada. “Why this is, and how, is not yet known, although studying imprinted genes may reveal clues.”

Then again, even if Olfr151 does escape reprogramming, it is hard to explain how that could lead to a noticeable difference in the behaviour of fully formed offspring. Dias and Ressler reported that in sperm samples from mice trained to fear acetophenone, about 86 out of every 100 sperm show Olfr151 methylation, whereas in mice trained to fear a different odour it is about 95 out of every 100. This difference is statistically significant, but fairly small. And yet the behavioural effects in the second generation were robust: about half of the acetophenone-trained animals' offspring showed increased sensitivity to the odour.

'Something goofball'?

Although many are scratching their heads over the holes in the proposed mechanism, few are suggesting that the underlying phenomenon is a fairy tale. “Impossible things are happening every day,” says Kelly, quoting a line from Rodgers and Hammerstein's Cinderella.

It is possible, for example, that the DNA-methylation tweaks reported in the odour study are simply a by-product of an altogether different mechanism.

One route might be chemical marks on histones, the proteins around which DNA wraps. Acetyl and methyl groups can attach to histones and affect the expression of nearby DNA. But during sperm-cell formation, DNA is stripped of most of its histones (and their attendant marks) and wraps instead around protamines, which pack it more tightly.

Nevertheless, about 10% of human histones — and about 1% of mouse ones — are retained. These sites might carry information from one generation to the next. In 2011, researchers reported that, in nematode worms, certain histone marks correlate with long life and can be passed down through several generations13. And last December, Kimmins and her colleagues showed that feeding male mice a diet low in folate — a nutrient that provides the raw materials for methylation — led to significantly reduced methylation of histone proteins in the animals' sperm and more birth defects in their offspring14.

Still other studies point to a mechanism involving short RNA molecules latching on to DNA and affecting gene expression. Twenty-eight microRNAs are expressed differently in the sperm of men who do and do not smoke, according to a study reported in 2012 (ref. 15). And these RNA patterns may persist through multiple generations. Last year, Lane's group found that obese male mice show abnormal expression of 11 microRNAs in their sperm — and that they pass on insulin resistance to the next two generations16.

Then there is the possibility that the mechanism is, as Rando puts it, “something goofball”. That might be prions — misfolded proteins that act as infectious agents — which have been shown to transmit heritable traits in budding yeast (see Nature 482, 294–296; 2012). Or it could be something in semen besides sperm. Researchers reported in January17 that mice born of fathers lacking seminal vesicles are fatter and have more metabolic problems than controls, suggesting that molecules in seminal fluid influence gene expression in sperm and the female reproductive tract.

If the mechanism involves DNA methylation, histones or RNA, the field is likely to make great progress in the next few years, Rando predicts. “But if it's something completely novel,” he says, “Maybe it will take decades to Figure out.”

Dias has his fingers crossed for the former. He is going to Boston, Massachusetts, in April for a Keystone meeting on epigenetic inheritance, to get a sense of the most promising mechanistic avenues to follow. “If science has taught me anything,” he says, “it is to not discount the myriad ways of becoming and being.”

Nature 507:22–24 (06 March 2014) | doi:10.1038/507022a

References

1. Dias, B. G. & Ressler, K. J. Nature Neurosci. 17, 89–96 (2014). Article
2. Manning, K. et al. Nature Genet. 38, 948–952 (2006). Article
3. Carone, B. R. et al. Cell 143, 1084–1096 (2010). Article
4. Cubas, P., Vincent, C. & Coen, E. Nature 401, 157–161 (1999). Article
5. Kaati, G., Bygren, L. O. & Edvinsson, S. Eur. J. Hum. Genet. 10, 682–688 (2002). Article
6. Pembrey, M. E. et al. Eur. J. Hum. Genet. 14, 159–166 (2006). Article
7. Ng, S.-F. et al. Nature 467, 963–966 (2010). Article
8. Wei, Y. et al. Proc. Natl Acad. Sci. USA 111, 1873–1878 (2014). Article
9. Anway, M. D., Cupp, A. S., Uzumcu, M. & Skinner, M. K. Science 308, 1466–1469 (2005).  Article
10. Skinner, M. K., Haque, C. G.-B., Nilsson, E., Bhandari, R. & McCarrey, J. R. PLoS ONE 8, e66318 (2013). Article
11. Goto, T., Salpekar, A. & Monk, M. Mol. Hum. Reprod. 7, 553–558 (2001).  Article
12. Dunoyer, P. et al. Science 328, 912–916 (2010). Article
13. Greer, E. L. et al. Nature 479, 365–371 (2011). Article
14. Lambrot, R. et al. Nature Commun. 4, 2889 (2013). Article
15. Marczylo, E. L., Amoako, A. A., Konje, J. C., Gant, T. W. & Marczylo, T. H. Epigenetics 7, 432–439 (2012). Article
16. Fullston, T. et al. FASEB J. 27, 4226–4243 (2013). Article
17. Bromfield, J. J. et al. Proc. Natl Acad. Sci. USA 111, 2200–2205 (2014). Article

Related stories and links

From nature.com

• Behaviour and biology: The accidental epigeneticist - 30 December 2013
• Fearful memories haunt mouse descendants - 01 December 2013
• Epigenetics posited as important for evolutionary success - 09 January 2013
• Fat fathers affect daughters' health - 20 October 2010
• Neuroscience: In their nurture - 08 September 2010
• Nature Reviews Genetics: Epigenetics
• Nature Insight: Epigenetics

Meaningful Happiness (Eudaimonia) Boosts the Immune System

Researchers identify two distinct forms of happiness or well-being - hedonic happiness is based on material or bodily pleasures, such as fine cuisine or great sex; eudaimonic happiness is based on a deeper satisfaction from activities that provide meaning or a sense of purpose, such as intellectual endeavors or charity work.

When researchers look at the ways each type of well-being influences gene expression, the find that there are very distinct ways genes are impacted.

People with a meaning-based or purpose-based outlook had favorable gene-expression profiles, whereas hedonic well-being, when it occurred on its own, was associated with profiles similar to those seen in individuals facing adversity.

Findings such these support the idea that volunteering is a great way to change our moods and our gene expression.

This is only one of the interesting findings from this Scientific American article that originally appeared in the journal Nature.

How Happiness Boosts the Immune System

Researchers have struggled to identify how certain states of mind influence physical health. One biologist thinks he has an answer.

By Jo Marchant and Nature magazine | Wednesday, November 27, 2013



Volunteers serve a Thanksgiving meal to homeless and needy families in New Bern, NC. Image: Wikimedia Commons/United States Marine Corps
When Steve Cole was a postdoc, he had an unusual hobby: matching art buyers with artists that they might like. The task made looking at art, something he had always loved, even more enjoyable. “There was an extra layer of purpose. I loved the ability to help artists I thought were great to find an appreciative audience,” he says.

At the time, it was nothing more than a quirky sideline. But his latest findings have caused Cole — now a professor at the Cousins Center for Psychoneuroimmunology at the University of California, Los Angeles — to wonder whether the exhilaration and sense of purpose that he felt during that period might have done more than help him to find homes for unloved pieces of art. It might have benefited his immune system too.

At one time, most self-respecting molecular biologists would have scoffed at the idea. Today, evidence from many studies suggests that mental states such as stress can influence health. Still, it has proved difficult to explain how this happens at the molecular level — how subjective moods connect with the vastly complex physiology of the nervous and immune systems. The field that searches for these explanations, known as psychoneuroimmunology (PNI), is often criticized as lacking rigour. Cole's stated aim is to fix that, and his tool of choice is genome-wide transcriptional analysis: looking at broad patterns of gene expression in cells. “My job is to be a hard-core tracker,” he says. “How do these mental states get out into the rest of the body?”

With his colleagues, Cole has published a string of studies suggesting that negative mental states such as stress and loneliness guide immune responses by driving broad programs of gene expression, shaping our ability to fight disease. If he is right, the way people see the world could affect everything from their risk of chronic illnesses such as diabetes and heart disease to the progression of conditions such as HIV and cancer. Now Cole has switched tack, moving from negative moods into the even more murky territory of happiness. It is a risky strategy; his work has already been criticized as wishful thinking and moralizing. But the pay-off is nothing less than finding a healthier way to live.

“If you talk to any high-quality neurobiologist or immunologist about PNI, it will invariably generate a little snicker,” says Stephen Smale, an immunologist at the University of California, Los Angeles, who is not affiliated with the Cousins Center. “But this doesn't mean the topic should be ignored forever. Someday we need to confront it and try to understand how the immune system and nervous system interact.”

The best medicine?

In 1964, magazine editor Norman Cousins was diagnosed with ankylosing spondylitis, a life-threatening autoimmune disease, and given a 1 in 500 chance of recovery. Cousins rejected his doctors' prognosis and embarked on his own program of happiness therapy, including regular doses of Marx Brothers films, and credited it with triggering a dramatic recovery. He later established the Cousins Center, which is dedicated to investigating whether psychological factors really can keep people healthy.

At the time, mainstream science rejected the idea that any psychological state, positive or negative, could affect physical well-being. But studies during the 1980s and early 1990s revealed that the brain is directly wired to the immune system — portions of the nervous system connect with immune-related organs such as the thymus and bone marrow, and immune cells have receptors for neurotransmitters, suggesting that there is crosstalk.

These connections seem to have clinical relevance, at least in the case of stress. One of the first researchers to show this was virologist Ronald Glaser, now director of the Institute for Behavioral Medicine Research at the Ohio State University in Columbus. “When I started working on this in the 1980s, nobody believed what stress could do, including me,” he recalls. He and his colleagues sampled blood from medical students, and found that during a stressful exam period, they had lower activity from virus-fighting immune cells, and higher levels of antibodies for the common virus Epstein–Barr, suggesting that stress had compromised their immune systems and allowed the normally latent virus to become reactivated.

The field of PNI has grown hugely since then, with medical schools worldwide boasting their own departments of mind–body medicine, of which PNI is just one component. It is now accepted that the body's response to stress can suppress parts of the immune system and, over the long term, lead to damaging levels of inflammation. Large epidemiological studies — including the Whitehall studies, which have been following thousands of British civil servants since 1967 — suggest that chronic work stress increases the risk of coronary heart disease and type 2 diabetes, for example. Low socio-economic status increases susceptibility to a wide range of infectious diseases, and there is considerable evidence that stress increases the rate of progression of HIV/AIDS. But researchers have a long way to go before they will understand exactly how signals from the brain feed into physical health.

Worried sick

PNI studies have mostly tended to look at levels of individual immune-cell types or molecular messengers — such as the stress hormone cortisol and the immune messenger proteins called cytokines — or the expression of individual genes. But Cole wanted to get a sense of how the whole system was working.

His first foray, published in 2007, looked at loneliness. Social isolation is one of the most powerful known psychological risk factors for poor health, but it is never certain whether it causes the health problems, or whether a third factor is involved: lonely people might be less likely than others to eat well, for example, or to visit their doctor regularly.

Cole and his colleagues looked at gene expression in the white blood cells of six chronically lonely people — people who had said consistently over several years that they felt lonely or isolated, and were fearful of other people — and eight people who said that they had great friends and social support. Out of the roughly 22,000 genes in the human genome, the researchers identified 209 that distinguished the lonely people from the sociable ones: they were either regulated up to produce more of an individual protein or regulated down to produce less. Any individual gene could easily look different by chance, but Cole was struck by the overall pattern. A particularly large proportion of the upregulated genes in the lonely group turned out to be involved in the inflammatory response, whereas many of the downregulated genes had antiviral roles. In sociable people, the reverse was true. It was a small study, but one of the first to link a psychological risk factor with a broad underlying change in gene expression.

The researchers have since replicated that result in a group of 93 people. Cole says that he has also seen a similar shift in gene expression in individuals exposed to various types of social adversity, from imminent bereavement to low socio-economic status.

The results make evolutionary sense, he says. Early humans in close-knit social groups would have faced increased risk of viral infections, so they would have benefited from revved-up antiviral genes. By contrast, people who were isolated and under stress faced greater risk of injuries that could cause bacterial infection — and thus would need to respond by ramping up genes associated with inflammation, to help heal wounds and fight off those infections. But modern stresses lead to chronic and unhelpful inflammation, which over time damages the body's tissues, increasing the risk of chronic diseases such as atherosclerosis, cancer and diabetes.

To a classical immunologist such as Smale, Cole's results are “intriguing, wonderful observations”, but not yet completely convincing. In future work, he wants to see the rest of the physiological pathway nailed down. “Until you put together a full understanding of that mechanism, you have this level of uncertainty and scepticism,” he says. That sentiment is echoed by Alexander Tarakhovsky, an immunologist at the Rockefeller University in New York City. Pinning down precise mechanisms — for example, which neurotransmitters cause which specific effects — is extremely difficult, he says, because the brain and the immune system are both so complex. Cole's research “makes you think about what the consequences of social hardship could be, but it doesn't really tell you how it works”.

Greg Gibson, director of the Center for Integrative Genomics at the Georgia Institute of Technology in Atlanta, wants to see larger studies but argues that the big-picture “genetic architecture” that Cole is uncovering is worth studying, even if not every detail of the mechanism is yet understood. “A lot of people are taking a whole-genome approach, but they focus only on a handful of 'top hits'. They are missing the wood for the trees.”

Don't worry, be happy

In 2010, Cole received an e-mail from Barbara Fredrickson, a friend from graduate school who was now studying emotional well-being at the University of North Carolina in Chapel Hill. “Remember me?” she said. She was interested in the biological correlates of happiness and other positive emotional states, and suggested that the pair collaborate. After years of looking at stress and adversity, Cole loved the idea. “I was bored as hell with misery,” he says.

If PNI as a whole has credibility issues, studying well-being is even trickier. It is more slippery to measure than stress — there is no biological marker such as cortisol to fall back on and no simple way to induce it in the lab, and mainstream biologists tend to look down on fuzzy methods of data collection such as questionnaires.

One approach is to test whether it is possible to reverse the adverse effects on gene expression caused by stress. Cole has collaborated in three small, randomized, controlled trials that attempt to do this. Studies involving 45 stressed caregivers and 40 lonely adults respectively found that courses in meditation shifted gene-expression profiles in the participants' white blood cells away from inflammatory genes and towards antiviral genes. A third trial, led by psycho-oncologist Michael Antoni at the University of Miami, Florida, involved 200 women with early-stage breast cancer. In those who completed a ten-week stress-management program, genes associated with inflammation and metastasis were downregulated compared with those of women in the control group, who attended a one-day educational seminar. Meanwhile, genes involved in the type I interferon response (which fights tumors as well as viruses) were upregulated in the women who took the stress-management course. “Our conclusion was that mood matters,” says Antoni. “If we change the psychology, physiological changes do parallel that.”

Cole and Fredrickson aspired to go further. Instead of looking at the benefits of blocking stress, they wanted to investigate what happens in the body when people are happy. To that end, they asked 80 participants 14 questions, such as how often in the past week they had felt happy or satisfied, and how often they felt that their life had a sense of meaning. The questions were designed to distinguish between the two forms of happiness recognized by psychologists: hedonic well-being (characterized by material or bodily pleasures such as eating well or having sex) and eudaimonic well-being (deeper satisfaction from activities with a greater meaning or purpose, such as intellectual pursuits, social relationships or charity work).

The researchers were surprised to find that the two types of happiness influenced gene expression in different ways. People with a meaning-based or purpose-based outlook had favorable gene-expression profiles, whereas hedonic well-being, when it occurred on its own, was associated with profiles similar to those seen in individuals facing adversity.

One interpretation is that eudaimonic well-being benefits immune function directly. But Cole prefers to explain it in terms of response to stress. If someone is driven purely by hollow consumption, he argues, all of their happiness depends on their personal circumstances. If they run into adversity, they may become very stressed. But if they care about things beyond themselves — community, politics, art — then everyday stresses will perhaps be of less concern. Eudaimonia, in other words, may help to buffer our sense of threat or uncertainty, potentially improving our health. “It's fine to invest in yourself,” says Cole, “as long as you invest in lots of other things as well.”

Perils of positive thinking

This is just the kind of advice that attracts some of the most vociferous criticisms of Cole's work. James Coyne, a health psychologist and emeritus professor at the University of Pennsylvania in Philadelphia, says that Cole and Frederickson's well-being study is simply too small to show anything useful. He also argues that the measures of eudaimonic and hedonic happiness are so highly correlated in the study as to be essentially the same thing. Coyne says that early results are being vastly over-sold. “They claim that if you make the right choices, you'll be healthy. And if you don't, you'll die.”

Coyne wants researchers across the field of PNI to stop publicizing claims about health benefits until the science is more solid. “They're turning it into books and workshops, telling people how to live their lives.”

Fredrickson, for example, is the author of two popular books, including Positivity: Top-Notch Research Reveals the 3 to 1 Ratio That Will Change Your Life (Crown Archetype, 2009), which posits that a specific ratio of positive to negative emotions (2.9013:1, to be precise) is linked to good health. The book has been praised by eminent psychologists such as Daniel Goleman and Martin Seligman, but the set of equations behind the ratio was criticized this year by Alan Sokal, a physicist at New York University (who famously published a deliberately nonsensical paper in the journal Social Text in 1996, intended to expose the lack of rigour in the field of cultural studies). He pointed out that the equations are based on parameters from a 1962 paper on air flow, with no connection to psychological data at all. Fredrickson acknowledges problems with the maths, which she based on a peer-reviewed paper on the complex dynamics of teams, but says that she stands by the fundamental principles described in the book. “There seems good enough evidence to suggest that emotions contribute to health.”

Cole and Fredrickson agree that their study is small and needs to be repeated. But they say that extensive previous research has validated the questionnaire they used and confirmed that it measures two distinct, albeit highly correlated, emotional states. They also note that correlation does not necessarily mean that two states are the same: height and weight are also highly correlated, for example, yet describe different things. Each type of happiness tends to encourage the other, says Fredrickson, “but we can try to understand which is leading the way towards health”.

The researchers are not the first from the PNI community to face accusations of wishful thinking. Indeed, the story of the field's founder — hailed in the press as proof of the power of positive emotions — has been questioned. Immunologists have suggested that Cousins was not suffering from ankylosing spondylitis at all, but from polymyalgia rheumatica, which often clears up on its own. His “health probably coincidentally remitted”, says Cole.

Despite the criticisms, and the fact that his work is in its early days, Cole says that he is struck by the evidence that positive emotions can override the biological effects of adversity — enough to make changes in his own life. Although he no longer has time to engage in the art trade, he has embraced the ways that his hobby helped him. “I have spent most of my career and personal life trying to avoid or overcome bad things,” he says. “I spend a lot more time now thinking about what I really want to do with my life, and where I'd like to go with whatever years remain.”

~ This article is reproduced with permission from the magazine Nature. The article was first published on November 27, 2013.

Aggression in Boys May Start Before Birth (McGill University)

This new(ish) study from McGill University looked at the epigenetic genesis of some behavioral issues in boys and discovered that the cause can often be traced back to the pregnancy.

Their study revealed that men who displayed chronic aggressive behavior between the ages of 6 and 15 had lower blood levels of four biomarkers of inflammation (cytokines) than in men who displayed "normal" levels of aggressive behavior in their youth (from the original paper).

Compared to the control group, males on a chronic physical aggression trajectory from childhood to adolescence had consistently lower plasma levels of five cytokines: lower pro-inflammatory interleukins IL-1α (T(28.7) = 3.48, P = 0.002) and IL-6 (T(26.9) = 3.76, P = 0.001), lower anti-inflammatory interleukin IL-4 (T(27.1) = 4.91, P = 0.00004) and IL-10 (T(29.8) = 2.84, P = 0.008) and lower chemokine IL-8 (T(26) = 3.69, P = 0.001).

This allowed researchers to distinguish between men with physically aggressive histories from men without such histories simply on the basis of four cytokines (IL-1α, IL-4, IL-6, and IL-8).

In a follow-up study with the same men with aggressive pasts, "the DNA encoding the cytokines showed methylation patterns different from those of the comparison group."

Methylation is an epigenetic modification of DNA in relation to imprinting by parents or caregivers. Methylation also plays a role in regulating gene expression (turning a gene on or off). 

According to the researchers, the prenatal and early postnatal environment may trigger these epigenetic shifts that cause reduced levels of the four specific cytokines associated with youthful aggression.

The authors speculate in the discussion on the connection between specific cytokines and various brain chemicals, specifically serotonin and cortisol (from the original paper):

First, high cortisol levels were found to be associated with high levels of aggression in adolescent males from the same sample [41]. Cortisol levels are known to regulate immune and inflammatory responses [42]. Second, Vasopressin, a mediator of the HPA axis activity released in the brain enhances arousal and aggression [43]. Brain vasopressin is also involved in stress-induced suppression of immune functions in rats [44], [45]. Third, serotonin, a key player in aggressive behavior, is induced by cytokines, such as IL-6 and IL-1β, in brain and in blood [46]–[48]. Serotonin is also known to be involved in regulating IL-4, IL-8, IL-6, TNF-α and IL-1 expression and secretion through the CREB signaling pathway [49], [50]. Together, these studies suggest a link between known mediators previously shown to be involved in aggression and cytokines.

More importantly, the researchers suggest:

There is good evidence that the parents of children on a high trajectory of physical aggression had similar behavior problems and created early childhood family environments which did not support learning to regulate physically aggressive reactions [4], [10]–[14].

As is often the case, aggression is a family issue and is usually intergenerational. The fundamental question, as always, is causality: "Does chronic aggression during childhood result in lowered cytokine activity or does lowered cytokine activity result in more aggression?"

This is an excellent study and worth the time to read. Below is a summary of the research from Futurity, followed by the abstract of the original study.

Aggression in boys may start before birth

Posted by Cynthia Lee-McGill on September 23, 2013


"If our results show that behavioral problems originate from as far back as pregnancy, it means that we can reduce violence through preventive intervention from as early as pregnancy," says Richard Tremblay. (Credit: Peter Dutton/Flickr)

McGill University -- Original Study (PLoS ONE)

Chronic aggressive behavior exhibited by some boys from disadvantaged families may be due to epigenetic changes during pregnancy and early childhood.

A new study shows that men who displayed chronic aggressive behavior during childhood and adolescence have lower blood levels of four biomarkers of inflammation than in men who exhibited average levels of aggressive behavior in their youth, from 6 to 15 years of age.

“This means that using four specific biomarkers of inflammation, called cytokines, we were able to distinguish men with chronic physical aggression histories from those without,” says Richard Tremblay, professor emeritus at the University of Montreal.

In a second study, in the same men with aggressive pasts, the DNA encoding the cytokines showed methylation patterns different from those of the comparison group.

“Methylation is an epigenetic modification—hence reversible—of DNA, in relation to parental imprinting. It plays a role in regulating gene expression,”says Moshe Szyf, a professor at McGill University.

“The pre- and postnatal environment could cause these differences in biomarkers associated with chronic aggression,” Szyf says.

Various studies conducted with animals show that hostile environments during pregnancy and early childhood have an impact on gene methylation and gene programming leading to problems with brain development, particularly in regard to the control of aggressive behavior.

Begins with mom?

Previous work suggests that men with aggressive pasts have one thing in common: the characteristics of their mothers.

“They are usually young mothers at the birth of their first child, with low education, often suffering from mental health problems, and with substance use problems,” Tremblay says.

The significant difficulties these mothers experienced during pregnancy and the early childhood of their child may have an impact on the expression of genes related to brain development, the immune system, and many other biological systems critical for the development of their child.

For the two studies, published in PLOS ONE, researchers collected blood from 32 participants who took part in either of two longitudinal studies that began nearly 30 years ago. The first study followed young Quebecers from disadvantaged backgrounds, while the second involved a representative sample of children who were in kindergarten in Quebec in 1986-87.

It is important to note that in disadvantaged families, the rate of boys with chronic aggressive behavior represents about 4 percent of the population. This greatly restricts the selection of potential participants.

Disorganized lifestyles

“Once they are adults, they are difficult to find because they have disorganized lifestyles,” Tremblay says. “We are studying the impact of the socioeconomic environment on the third generation, now that these children are grown up and have children.”

While no study has yet been published on the subject, he anticipates “significant intergenerational ties, since we observed an association between parental criminality of the first generation and the behavior of their children.”

Nevertheless, Tremblay, who has conducted his work for decades with a prevention perspective, is optimistic.

“If our results show that behavioral problems originate from as far back as pregnancy, it means that we can reduce violence through preventive intervention from as early as pregnancy. We have already shown that support given to families of aggressive boys in kindergarten prevents school dropout and crime in adulthood.”

* * * * *

Here is the abstract of the original article from PLoS ONE, available as an open access publication and downloadable as a PDF.

Childhood Chronic Physical Aggression Associates with Adult Cytokine Levels in Plasma

Nadine Provençal, Matthew J. Suderman, Frank Vitaro, Moshe Szyf, Richard E. Tremblay 

Abstract

Background

An increasing number of animal and human studies are indicating that inflammation is associated with behavioral disorders including aggression. This study investigates the association between chronic physical aggression during childhood and plasma cytokine levels in early adulthood.

Methodology/Principal Findings

Two longitudinal studies were used to select males on a chronic physical aggression trajectory from childhood to adolescence (n = 7) and a control group from the same background (n = 25). Physical aggression was assessed yearly by teachers from childhood to adolescence and plasma levels of 10 inflammatory cytokines were assessed at age 26 and 28 years. Compared to the control group, males on a chronic physical aggression trajectory from childhood to adolescence had consistently lower plasma levels of five cytokines: lower pro-inflammatory interleukins IL-1α (T(28.7) = 3.48, P = 0.002) and IL-6 (T(26.9) = 3.76, P = 0.001), lower anti-inflammatory interleukin IL-4 (T(27.1) = 4.91, P = 0.00004) and IL-10 (T(29.8) = 2.84, P = 0.008) and lower chemokine IL-8 (T(26) = 3.69, P = 0.001). The plasma levels of four cytokines accurately predicted aggressive and control group membership for all subjects.

Conclusions/Significance

Physical aggression of boys during childhood is a strong predictor of reduced plasma levels of cytokines in early adulthood. The causal and physiological relations underlying this association should be further investigated since animal data suggest that some cytokines such as IL-6 and IL-1β play a causal role in aggression.

Full Citation: 
Provençal N, Suderman MJ, Vitaro F, Szyf M, Tremblay RE. (2013, Jul 26), Childhood Chronic Physical Aggression Associates with Adult Cytokine Levels in Plasma. PLoS ONE 8(7): e69481. doi:10.1371/journal.pone.0069481

Judith Shulevitz - Why Fathers Really Matter

From the New York Times, this is an excellent overview of the some of the most recent data on how big a role fathers play in the lives of their children, from the genetic to the emotional levels. It's good to see this is in a major newspaper.

Why Fathers Really Matter

By JUDITH SHULEVITZ
Published: September 8, 2012

MOTHERHOOD begins as a tempestuously physical experience but quickly becomes a political one. Once a woman’s pregnancy goes public, the storm moves outside. Don’t pile on the pounds! Your child will be obese. Don’t eat too little, or your baby will be born too small. For heaven’s sake, don’t drink alcohol. Oh, please: you can sip some wine now and again. And no matter how many contradictory things the experts say, don’t panic. Stress hormones wreak havoc on a baby’s budding nervous system.

 

All this advice rains down on expectant mothers for the obvious reason that mothers carry babies and create the environments in which they grow. What if it turned out, though, that expectant fathers molded babies, too, and not just by way of genes?

Biology is making it clearer by the day that a man’s health and well-being have a measurable impact on his future children’s health and happiness. This is not because a strong, resilient man has a greater likelihood of being a fabulous dad — or not only for that reason — or because he’s probably got good genes. Whether a man’s genes are good or bad (and whatever “good” and “bad” mean in this context), his children’s bodies and minds will reflect lifestyle choices he has made over the years, even if he made those choices long before he ever imagined himself strapping on a Baby Bjorn. 

Doctors have been telling men for years that smoking, drinking and recreational drugs can lower the quality of their sperm. What doctors should probably add is that the health of unborn children can be affected by what and how much men eat; the toxins they absorb; the traumas they endure; their poverty or powerlessness; and their age at the time of conception. In other words, what a man needs to know is that his life experience leaves biological traces on his children. Even more astonishingly, those children may pass those traces along to their children.

Before I began reading up on fathers and their influence on future generations, I had a high-school-biology-level understanding of how a man passes his traits on to his child. His sperm and the mother’s egg smash into each other, his sperm tosses in one set of chromosomes, the egg tosses in another, and a child’s genetic future is set for life. Physical features: check. Character: check. Cognitive style: check. But the pathways of inheritance, I’ve learned, are subtler and more varied than that. Genes matter, and culture matters, and how fathers behave matters, too.

Lately scientists have become obsessed with a means of inheritance that isn’t genetic but isn’t nongenetic either. It’s epigenetic. “Epi,” in Greek, means “above” or “beyond.” Think of epigenetics as the way our bodies modify their genetic makeup. Epigenetics describes how genes are turned on or off, in part through compounds that hitch on top of DNA — or else jump off it — determining whether it makes the proteins that tell our bodies what to do.

In the past decade or so, the study of epigenetics has become so popular it’s practically a fad. Psychologists and sociologists particularly like it because gene expression or suppression is to some degree dictated by the environment and plays at least as large a role as genes do in the development of a person’s temperament, body shape and predisposition to disease. I’ve become obsessed with epigenetics because it strikes me as both game-changing and terrifying. Our genes can be switched on or off by three environmental factors, among other things: what we ingest (food, drink, air, toxins); what we experience (stress, trauma); and how long we live.

Epigenetics means that our physical and mental tendencies were not set in stone during the Pleistocene age, as evolutionary psychology sometimes seems to claim. Rather, they’re shaped by the life we lead and the world we live in right now. Epigenetics proves that we are the products of history, public as well as private, in parts of us that are so intimately ours that few people ever imagined that history could reach them. (One person who did imagine it is the French 18th-century naturalist Jean-Baptiste Lamarck, who believed that acquired traits could be inherited. Twentieth-century Darwinian genetics dismissed Lamarckism as laughable, but because of epigenetics, Lamarckism is staging a comeback.)

The best-known example of the power of nutrition to affect the genes of fathers and sons comes from a corner of northern Sweden called Overkalix. Until the 20th century, Overkalix was cut off from the rest of the world, unreachable by road, train or even, in wintertime, boat, because the frozen Baltic Sea could not be crossed. Thus, when there were bad harvests in Overkalix, the children starved, and when there were good harvests, they stuffed themselves.

More than a decade ago, three Swedish researchers dug up records from Overkalix going back to 1799 in order to correlate its children’s health data with records of regional harvests and other documents showing when food was and wasn’t available. What the researchers learned was extremely odd. They found that when boys ate badly during the years right before puberty, between the ages of 9 and 12, their sons, as adults, had lower than normal rates of heart disease. When boys ate all too well during that period, their grandsons had higher rates of diabetes.

When the study appeared in 2002, a British geneticist published an essay speculating that how much a boy ate in prepuberty could permanently reprogram the epigenetic switches that would govern the manufacture of sperm a few years later. And then, in a process so intricate that no one agrees yet how it happens but probably has something to do with the germline (the reproductive cells that are handed down to children, and to children’s children), those reprogrammed switches are transferred to his sons and his sons’ sons.

A decade later, animal studies confirm that a male mammal’s nutritional past has a surprisingly strong effect on his offspring. Male rats that are starved before they’re mated produce offspring with less blood sugar and altered levels of corticosterone (which protects against stress) and insulin-like growth factor 1 (which helps babies develop).

Southeast Asian men who chew betel nuts, a snack that contains a chemical affecting metabolic functioning, are more likely to have children with weight problems and heart disease. Animal studies have shown that the effects of betel nut consumption by a male may extend to his grandchildren.

Environmental toxins leave even more florid traces on grandchildren and great-grandchildren. Vinclozin, a fungicide that used to be sprayed all over America (it’s less common now), is what’s known as an endocrine disrupter; it blocks the production of testosterone. Male rats whose mothers receive a fat dose of vinclozin late in their pregnancy are highly likely to be born with defective testicles and reduced fertility. These problems seem to reappear in up to four generations of male rats after the mother is poisoned.

THAT food and poison change us is not all that surprising, even if it is surprising how far down the change goes. What is unexpected are the psychological dimensions of epigenetics. To learn more about these, I visited the Mount Sinai Medical Center laboratory of Dr. Eric Nestler, a psychiatrist who did a discomfiting study on male mice and what he calls “social defeat.” His researchers put small normal field mice in cages with big, nasty retired breeders, and let the big mice attack the smaller mice for about five minutes a day. If a mean mouse and a little mouse were pried apart by means of a screen, the torturer would claw at the screen, trying to get at his victim. All this subjected the field mouse to “a horrendous level of stress,” Dr. Nestler told me. This process was repeated for 10 days, with a different tormentor placed in each cage every day. By the time the torture stopped, about two-thirds of the field mice exhibited permanent and quantifiable symptoms of the mouse equivalents of depression, anxiety and post-traumatic stress disorder. The researchers then bred these unhappy mice with normal females. When their pups grew up, they tended to overreact to social stress, becoming so anxious and depressed that they wouldn’t even drink sugar water. They avoided other mice as much as they could. 

Dr. Nestler is not sure exactly how the mouse fathers’ trauma communicates itself to their offspring. It may be via sperm, or it may be through some more complicated dance of nature and nurture that involves sperm but also other factors. When instead of letting the “defeated” mice mate, Dr. Nestler’s researchers killed them, harvested their sperm and impregnated the female mice through artificial means, the offspring were largely normal. Perhaps the sperm was harvested at the wrong stage in the process, says Dr. Nestler. Or maybe the female mouse picked up some signal when she had sex with the dysfunctional male mouse, some telltale pheromone or squeak, that made her body withhold nutrition and care from his pups. Females have been known to not invest in the spawn of non-optimal males, an outcome that makes perfect evolutionary sense — why waste resources on a loser?

When it comes to the epigenetics of aging, however, there is little question that the chemical insults and social setbacks of everyday life distill themselves in sperm. A woman is born with all the eggs she’ll ever carry. By the time a man turns 40, on the other hand, his gonad cells will have divided 610 times to make spermatozoa. By the time he’s in his 50s, that number goes up to 840. Each time those cells copy themselves, mistakes may appear in the DNA chain. Some researchers now think that a percentage of those mistakes reflects not just random mutations but experience-based epigenetic markings that insinuate themselves from sperm to fetus and influence brain development. Another theory holds that aging gonad cells are more error-prone because the parts of the DNA that should have spotted and repaired any mistakes have been epigenetically tamped down. In any case, we now know that the children of older fathers show more signs of schizophrenia, autism and bipolar disorder than children of younger ones.

In a meta-analysis of a population study of more than a million people published last year, Christina Hultman of the Karolinska Institute of Sweden concluded that children of men older than 50 were 2.2 times as likely to have autism as children of 29-year-olds, even after the study had factored out mothers’ ages and known risk factors for autism. By the time the men passed 55, the risk doubled to 4.4 times that of 29-year-olds. Can the aging of the parent population explain the apparent spike in autism cases? A study published last month in Nature that used whole-genome sequencing on 78 Icelandic families made the strongest case to date that as fathers age, mutations in their sperm spike dramatically. Some of the mutations found by the researchers in Reykjavik have been linked to autism and schizophrenia in children.

In his Washington Heights laboratory at the New York State Psychiatric Institute, Jay Gingrich, a professor of psychobiology, compares the pups of young male mice (3 months old or so) to those of old male mice (12 to 14 months old). The differences between the pups, he told me, weren’t “earth-shattering” — they weighed about the same and there weren’t big gaps in their early development. But discrepancies appeared when the mice grew up. The adult offspring of the older fathers had less adventuresome personalities; they also reacted to loud noises in unusual ways that paralleled reactions evinced by schizophrenics who heard similar sounds.

Still, Dr. Gingrich said, “the differences were subtle” until he decided to pool the data on their behavior and graph it on a bell curve. A “vast majority” of the children of the older mice were “completely normal,” he said, which meant their score fell under the upside-down parabola of the curve. The real differences came at the tails or skinny ends of the bell curve. There was about a sixfold increase in likelihood that one of the “abnormal outliers,” mice with cognitive or behavioral handicaps, “would come from an older father.” Conversely, the super-high-performing mice were about six times more likely to come from a younger father. “I’m an inherently skeptical person,” Dr. Gingrich told me, but he was impressed by these results.

One unanswered question about autism and schizophrenia is how they crop up in generation after generation; after all, wildly dysfunctional individuals don’t usually flourish romantically. “I think we’re going to have to consider that advanced paternal age, with its epigenetic effects, may be a way of explaining the mysteries of schizophrenia and autism, insofar as the rates of these disorders have maintained themselves — and autism may be going up,” Dr. Gingrich said. “From a cruel Darwinian perspective, it’s not clear how much success these folks have at procreating, or how else these genes maintain themselves in the population.”

When you’re an older mother, you get used to the sidelong glances of sonogram technicians, the extra battery of medical tests, the fear that your baby has Down syndrome, the real or imagined hints from younger mothers that you’re having children so late because you care more about professional advancement than family. But as the research on paternal inheritance piles up, the needle of doubt may swing at least partway to fathers. “We’re living through a paradigm shift,” said Dolores Malaspina, a professor of psychiatry at New York University who has done pioneering work on older fathers and schizophrenia. Older mothers no longer need to shoulder all the blame: “It’s the aging man who damages the offspring.”

Aging, though, is only one of the vicissitudes of life that assault a man’s reproductive vitality. Think of epigenetics as having ushered in a new age of sexual equality, in which both sexes have to worry about threats to which women once felt uniquely exposed. Dr. Malaspina remembers that before she went to medical school, she worked in a chemical plant making radioactive drugs. The women who worked there came under constant, invasive scrutiny, lest the toxic workplace contaminate their eggs. But maybe, Dr. Malaspina points out, the plant managers should have spared some concern for the men, whose germlines were just as susceptible to poisoning as the women’s, and maybe even more so. The well-being of the children used to be the sole responsibility of their mothers. Now fathers have to be held accountable, too. Having twice endured the self-scrutiny and second-guessing that goes along with being pregnant, I wish them luck. 

Judith Shulevitz is the science editor for The New Republic.

A version of this op-ed appeared in print on September 9, 2012, on page SR1 of the New York edition with the headline: Why Fathers Really Matter.