Introspection on the Value of Epigenetics for Psychiatry
Sally Seraphin, Moderator [via Zoom chat]: Dear friends, allow me to introduce to you: Dr. Brian G Dias, Assistant Professor, Department of Pediatrics, Division of Research on Children, Youth and Families USC Keck School of Medicine & Children’s Hospital Los Angeles Dr. Dias received his Ph.D. from UT-Austin. His research concerns the neurobiology underlying stress, depression, social behavior, and fear, in rats, lizards, birds, fruit flies, and mice. He is also experienced investigating the biological basis of behavioral states and neuropsychiatric disorders, in human and non-human primates. Interestingly, Dr. Dias uses molecular, cellular, genetic, epigenetic, physiological, and behavioral approaches to study how the biology of an organism and its responsiveness to stress or trauma is influenced by micro- (i.e., genome, epigenome, and hormones), and macro-environments (i.e., ancestral, intra-uterine and post-natal experiences).
Besides dozens of publications in peer-reviewed journals, such as Biological Psychiatry, Hormones & Behavior, Nature Neuroscience, and PNAS, his work has been featured in several news outlets, such as the BBC, La Recherche Magazine, and on BrainFacts. In addition to his distinguished service as a faculty member in the Emory Tibet Science Initiative, Dr. Dias has been decorated with many honors, such as membership in the Young Leader network at the Science & Technology in Society Forum in Kyoto, Japan (an invitation-only forum that includes world leaders and diplomats discussing how science and technology can address contemporary roadblocks to human progress) and a CIFAR Azrieli Global Scholar Award (competitive awards given to exceptional early-career investigators from around the world by the Canadian Institute for Advanced Research (CIFAR).
The amount of stress we experience is on a spectrum. An “optimal” level of stress is supported by animal literature (stress in one generation seems to confer some beneficial advantages to the next generation). But in humans many types of early life stress are risk factors for later psychopathology, including stress related to nutritional environment, immune system functioning (maternal activation), and air pollution. Importantly, age of exposure – critical periods – matters. Cultural differences in poverty can also play important roles in terms of whether or not behavior, such as neglect, is considered abuse.
The challenge is determining the significance for psychiatry of stress-related changes at the molecular and cellular levels, more specifically in terms of epigenetics (“the study of heritable changes in gene expression that occur independent of changes in the primary DNA sequence”).
What do generational legacies of stress look like?
- Adverse childhood experiences, including child abuse and overall neglect; mood disorders, behavior disorders, and substance abuse.
- In utero babies of mothers who developed PTSD had lower cortisol levels (a risk marker for later life PTSD) versus in utero babies of mothers who did not develop PTSD (similar results in Project Ice Storm). Likewise, descendants of Holocaust survivors have lower cortisol levels (similar intergenerational effects following Dutch hunger winter and famines in Sweden.
- Non-human animals
- There is naturally occurring variation in maternal care. In rats/non-human animals, a pup/progeny raised by an anxious, low-nurturing mother (fragmented maternal care) becomes an anxious adult.
How do they (legacies of stress) come about? (transmission)
Biological and social transmission routes are of equal importance. Mechanisms of how legacies of stress are perpetuated include:
- Social transmission of information from one generation to the next
- Maternal-fetal placental interface
- Biological inheritance via epigenetics (egg or sperm may bear imprints of trauma or stress/vectors)
Epigenetic mechanisms of inheritance in animal models:
- DNA methylation of stress hormone receptor (GR) is affected by quality of maternal care (licking and grooming): Methylation of the glucocorticoid receptor gene (GR) regulates HPA stress axis (Weaver et al., 2004).
- Fragmented maternal care in animals and humans – Tracked behaviors (nursing, licking/grooming, other) of rodent pups raised by different types of mothers (who experienced full bedding or limited bedding). Pups raised by anxious mothers exhibited more anxiety-like and depression-like behaviors and sleep disturbances (see Baram et al., 2012). Dias said unpredictability allows for anxiety-like and depression-like behaviors. He noted the work of neuroscientists Isabelle Mansuey and Tracy Bale, which showed these behaviors in pups following maternal separation across several generations.
Epigenetics and mammalian olfactory system/conditioning to aversive odor (Dias’s research)
- How genes in sperm register paternal experiences in mice: Olfr151, which encodes the M71 odorant receptor),is hypomethylated in sperm of F0-Ace males subjected to odor fear conditioning. Their sperm bears the imprint of the averse odor experience. Offspring are sensitive to same odor (Dias & Ressler, 2014), i.e., offspring had an enhanced neuroanatomical representation of the Olfr151 pathway.
- Inheritance of information (imprints of stress) rather than transmission of information confirmed with results from in-vitro fertilization.
- Similar results found in fruit flies and in worms (learned pathogenic avoidance).
NB: In humans, cognitive science research has shown that smell is culturally variable. There is a relationship between food and trauma/historical memory. Smell is marked well within a community. The calm associated with certain smells from early life (e.g., baking cookies) can be called up when a stressed adult bakes cookies to calm themselves.
Can we put brakes on these legacies? (i.e., can negative influences of stress be reversed?)
- Three core principles of effective early childhood programs from Harvard’s Center on the Developing Child: (1) reduce sources of stress, (2) strengthen core skills, and (3) support responsive relationships.
- In an extremely impoverished environment, foster care reversed the derailment of neurodevelopment in children.
- There is research looking at changes in epigenetic profiles over time as a result of compassion-based cultivation training for children in school.
- Non-human animals
- Extinction learning/training of F0 generation reverses behavioral/neuroanatomical/germline intergeneration influences of F0 stress.
- Rodent pups of a stressed mother can be cross-fostered by a different mother to disrupt social transmission of (stress) information.
Much of our epigenetic knowledge is from the understanding of epigenetic mechanisms and abnormalities in cancer biology. The fundamental question is if, and how, a precision-medicine approach in biology can help us address social structural problems related to psychopathology. The danger is essentializing individuals based on aberrant pathologizing biology. In searching for epigenetic mechanisms, we may disregard social structural influences, including impoverished environments of whole communities. Heightened stress reactivity may be necessary to adapt to local environment.
The meeting opened up for questions and comments. Lende said that he advocates for an ecological approach to understand the laboratory results. Rodents are very dependent on olfaction for their fitness. Lende said Dias is figuring out how the biological basis to get the Baldwin effect to work [NB: effect of learned behavior on evolution]. The Waddington landscape approach has differential effects on fitness. On the point of good versus bad rat mothers, neuroscientist Paul Plotsky’s work, using a maze to see where they go, on how rat mothers’ pathological behavior went away when the mothers were given options on where to go. Rats are social and adaptive creatures and ecologically, they behave adaptively, e.g., anxiously, in environments where there is predation and where novelty is bad. Dias strongly agrees.
In his paper in Genes, Brain and Behavior, Dias asked: Might there be an adaptive significance to this enhanced sensitivity to this odor? Rats learned this subthreshold. Dias said that this was adaptive, not all gloom and doom. There is task-specificity to adapt.
Aoued, H. S., Sannigrahi, S., Hunter, S. C., Doshi, N., Sathi, Z. S., Chan, A. W. S., Walum, H., & Dias, B. G. (2020). Proximate causes and consequences of intergenerational influences of salient sensory experience. Genes, Brain and Behavior, 19(4), e12638. https://doi.org/10.1111/gbb.12638
He mentioned a book from Thomas Boyce:
Boyce, W. T. (2019). The orchid and the dandelion: Why some children struggle and how all can thrive. Alfred A. Knopf.
Dias said what environment a child or mouse pup finds themselves in – they’re going to respond to that, negatively or positively. Lende said it depends on the species, that humans are more sensitive to touch than smell.
Tidwell said that thought about Tibetan medical practice and its use of nasal medicines for possession and psychiatric diseases. She said she is thinking about cultural approaches to fear mediation and the use of smell to evoke a different kind of embodiment. Smell is a very powerful mode to create and change memory and experience. In a question for Tidwell, Dias asked: For COVID smell training [NB: many people suffering from COVID lose their sense of smell], how does this transpose onto her point? Tidwell said that she is tracking mild, medium, and severe COVID cases treated with Tibetan medicine. The treatment is inhaling a concoction three times a day. There is a 10-day turnaround to regain smell for most cases. She said that she cannot look at the underlying mechanism for this but she is seeing interesting results from that therapy.
Snodgrass said that sperm as a vector for RNA made him think of epigenetics and that maybe there are a lot of vectors in RNA that can confound that transmission pathway, e.g., mother’s milk, sweat, blood, and mucus. With a more ecological approach, there could be many pathways of RNA. Epigenetics can be confounded by behavioral pathways, where shocks that change parents’ behaviors can then change children’s behaviors. Where is the field in thinking about all these different and possible biological and behavioral transmission pathways and how can they be disentangled? Dias said the field is more on the sperm bandwagon rather than the egg bandwagon. Dias said we will know more about eggs with more technology (get more profiles from eggs). Dias wondered: Are all sperm affected? Is it only an ovulating egg that is affected or all eggs affected by stress when a woman experiences a trauma? There is some biological stuff that is not passing on to the next generation because of social buffering. Dias said he does not know the answer to the vector question from Snodgrass. Exozomes and epididymosomes: Is it serendipity that they land up in sperm? How is an entire organism affected by stress in reproductive and non-reproductive ways for the next generation? Snodgrass said he’s been confused about how people use the term “epigenetics,” viewed by some loosely as gene expression and viewed in other ways by others. Snodgrass asked: What does “intergenerational” transmission mean because other processes are not always about sexual reproduction. Dias said that he agrees, but in rodents and flies, we can disentangle both of these. Dias said he does not discount social transmission route but his focus is on biological inheritance route. Dias said the social transmission is equally important.
Seraphin said in chromatin remodeling, for eggs, methylation and phosphorylation occurs after fertilization to lock down or modify gene expression. Sperm is more open to revision by the mechanisms that Dias described. She asked: Is methylation and phosphorylation of the developing zygote edited maternally? Dias said eggs are arrested in a particular phase of the cell cycle, progress to the next phase in ovulation, and can get methylated or not, so the fetus develops in one way or another. Eggs and sperm of advanced age females and male have accumulation of marks that occur, in addition to chromosomal things happening (why there are developmental disabilities in offspring). Seraphin said there is a study that linked paternal stress to changes in myelination – not chromatin remodeling – linked to early postnatal experience. She wondered if Dias is talking about both genetic and environmental co-influencing of change of myelination of cortex. Dias said it affects oligodendrocytes and how they form myelin. In response to his comment about precision medicine, Seraphin said for a precision-medicine approach to address the social structural problems that perpetuate, e.g., family violence, you will need a crop duster for entire communities driven by despair. She said there is a danger of essentializing people based on aberrant pathologizing biology. Some communities have impoverished environments. She mentioned the late biological anthropologist, epidemiologist, and geneticist Ryk Ward, who found that differences in hypertension had a genetic basis as opposed to being a result of living in situations of discrimination and oppression [NB: Ward did actually look at effects of environment change on health]. Sometimes in looking for epigenetic mechanisms, we disregard social structural influences. Sometimes there is a need for heightened stress reactivity to adapt to the circumstances of where you live. [NB: brings back the previous point that not all stress or stress reactivity is maladaptive or negative] Dias said he does not see psychiatry going in the direction of cancer research; with psychiatry, you have to be doing it on a population level, but drug companies cannot bottle that.
Luhrmann asked Dias if he thought that “trauma” is a useful category to use in his work. Dias said he would be happy to use something else. He said in moving from non-human animal to human, one cannot think of another term beyond “trauma.” He gave an example of a retired US Army general whose mission was to change the perception of people in service from it being posttraumatic stress disorder (negative connotations) to a syndrome. Seraphin said, with the Dutch hunger winter and intergenerational transmission of trauma, how long before we see impacts of COVID quarantining on children in unsafe environments? Dias said a big factor of that is age of exposure. Dias said stability of social relationships is tough for his 2-year-old daughter, with effects later when she forms her own relationships. For his 7-year-old son, the effects of impulse control and forming relationships with agemates will appear in adolescence. Dias said it is all going to be about critical periods.
Kitayama said neurogenesis is very active throughout life for humans. Is this true for rats? Dias said yes. Dias said energetically wasteful to process something if it is not part of one’s environment. Kitayama from sexual reproduction and marriage, there is conditioning to the smell of a person. Smell is hidden in the psychology of all of this from evolutionary and psychology points of view. Kitayama asked, with regard to the Dutch famine in WWII, is it true that some cases of hunger happened in the grandchild’s generation? Kitayama said inflammation and stress response are very important and evolutionarily conserved.
Kitayama said human and rat life are complicated. What are domains that are biologically grounded and conserved in the expression of genes, if funds allow? With regard to cultural influence, Kitayama said that he is finding that different cultural groups have regional brain volume changes (an experience effect, e.g., London taxi cab drivers). Epigenetic changes lead to changes in the structure of the brain. What are cultural training effects at the epigenetic level? Dias said biomedical anthropologist and epidemiologist Tyralynn Frazier is doing research looking at changes in epigenetic profiles over time as a result of compassion-based cultivation training for children in school.
Positive and negative experiences leave marks. But, as Dias acknowledged, going from the cheek swab to the brain is a “herculean task.” With regard to Kitayama’s mention of changes in brain volume, Dias said he doesn’t know where to begin. Does something methylated in blood tell you something about how cultural experience may change the brain? Dias said his answers cannot rise up to the challenge to Kitayama’s questions.
Video Highlights (2.33 mins) / Using Olfaction
Dias, B. G. (2020, August 10). Halting legacies of trauma [Video]. TEDxEmory. https://youtu.be/OhrW08fqiP0
Reh, R. K., Dias, B. G., Nelson, C. A. III, Kaufer, D., Werker, J. F., Kolb, B., Levine, J. D., & Hensch, T. K. (2020). Critical period regulation across multiple timescales. PNAS, 117(38), 23242–23251. https://doi.org/10.1073/pnas.1820836117
Taylor, W. W., Imhoff, B. R., Sathi, Z. S., Garza, K. M., & Dias, B. G. (2020, September 2). Sex-specific calibration of memory recall by glucocorticoid receptors on cortical astrocytes. bioRxiv. https://doi.org/10.1101/2020.09.01.278556
Venkataraman, A., Brody, N., Reddi, P., Guo, J., Rainnie, D. G., & Dias, B. G. (2019). Modulation of fear generalization by the zona incerta. PNAS, 116(18), 9072–9077.