“If sexually naïve females have their formative sexually rewarding experiences paired with the same male, they will recognize that male and display mate-guarding behavior towards him in the presence of a female competitor. Female rats that display mate-guarding behavior also show enhanced activation of oxytocin and vasopressin neurons in the supraoptic and paraventricular hypothalamic nucleus.
We examined the effect of a lysine-specific demethylase-1 inhibitor to block the action of demethylase enzymes and maintain the methylation state of corresponding genes. Female rats treated with the demethylase inhibitor failed to show any measure of mate guarding, whereas females treated with vehicle displayed mate guarding behavior. Demethylase inhibitor treatment also blocked the ability of familiar male cues to activate oxytocin and vasopressin neurons, whereas vehicle-treated females showed this enhanced activation.”
General principles and their study-specific illustrations were:
“Histone modifications are a key element in gene regulation through chromatin remodeling. Histone methylation / demethylation does not have straightforward transcriptional outcomes as do other histone modifications, like acetylation, which is almost invariably associated with transcriptional activation.
What is of vital importance in regards to histone methylation / demethylation is the pattern of methylation that is established. Patterns of methylation incorporate both methylated and demethylated residues, and are what ultimately play a role in transcriptional outcomes.
In the present study, inhibiting LSD1 demethylase enzymes disrupted the ability of cells to properly establish histone methylation / demethylation patterns, thus creating a deficit in the cells’ ability to transcribe the gene products necessary for the enhanced induction of OT, AVP, and the subsequent mate-guarding behaviors we observed. This study is the first to demonstrate a definitive role of epigenetic histone modifications in a conditioned sexual response.”
This 2017 UC Irvine human review subject provided details of how fetalhypothalamic-pituitary-adrenal components and systems develop, and how they are epigenetically changed by the mother’s environment:
“The developmental origins of disease or fetal programming model predicts that intrauterine exposures have life-long consequences for physical and psychological health. Prenatal programming of the fetal hypothalamic-pituitary-adrenal (HPA) axis is proposed as a primary mechanism by which early experiences are linked to later disease risk.
Development of the fetal HPA axis is determined by an intricately timed cascade of endocrine events during gestation and is regulated by an integrated maternal-placental-fetal steroidogenic unit. Mechanisms by which stress-induced elevations in hormones of maternal, fetal, or placental origin influence the structure and function of the emerging fetal HPA axis are discussed.
Human gestational physiology and fetal HPA axis development differ even from that of closely related nonhuman primates, thereby limiting the generalizability of animal models. This review will focus solely on studies of prenatal stress and fetal HPA axis development in humans.”
Every time I read a prenatal study I’m in awe of all that has to go right, and at the appropriate time, and in sequence, for a fetus to be undamaged. Add in what needs to happen at birth, during infancy, and throughout early childhood, and it seems impossible for any human to escape epigenetic damage.
1. The reviewers referenced human research performed with postnatal subjects, as well as animal studies, despite the disclaimer:
This review will focus solely on studies of prenatal stress and fetal HPA axis development in humans.”
This led to blurring of what had been studied or not with human fetuses regarding the subject.
2. The reviewers uncritically listed many dubious human studies that had both stated and undisclosed severe limitations on their findings. It’s more appropriate for reviewers to offer informed reviews of cited studies, as Sex-specific impacts of childhood trauma summarized with cortisol:
“Findings are dependent upon variance in extenuating factors, including but not limited to, different measurements of:
presence and severity of psychopathology symptomology.”
3. It would have been preferable had the researchers stayed with their stated intention and critically reviewed only a few dozen studies with solid evidence of the review title: “Developmental origins of the human hypothalamic-pituitary-adrenal axis.” Let other reviews cover older humans, animals, and questionable evidence.
I asked the reviewers to provide a searchable file so that their work could be better used as a reference.
This 2018 Korean review discussed aspects of the hypothalamus and aging:
“A majority of physiological functions that decline with aging are broadly governed by the hypothalamus, a brain region controlling development, metabolism, reproduction, circadian rhythm, and homeostasis. In addition, the hypothalamus is poised to connect the brain and the body so that the environmental information affecting aging can be transmitted through the hypothalamus to affect the systematic aging of the peripheral organs.
The hypothalamus is hypothesized to be a primary regulator of the process of aging of the entire body. This review aims to assess the contribution of hypothalamic aging to the age-related decline in body functions, particularly from the perspective of:
circadian rhythm, and
and to highlight its underlying cellular mechanisms with a focus on:
“The hypothalamus is hypothesized to be a primary regulator of the process of aging.”
Almost all of the details discussed were from rodent studies.
I favor the “unintended consequence” explanation of aging. As detailed in How to cure the ultimate causes of migraines? and its references, the hypothalamus is a brain structure that lacks feedback mechanisms for several of its activities.
This structure develops shortly after conception and has an active prenatal role. The hypothalamus plays its part in getting us developed and ready to reproduce, with several feedback loops being evolutionarily unnecessary.
The hypothalamus perfectly illustrates the point of:
“When these programs are completed, they are not switched off.”
Hypothalamic activity not winding down when its developmental role is over shouldn’t be interpreted to construe a role that has some other meaning or purpose.
This 2018 Loma Linda review subject was gestational hypoxia:
“Of all the stresses to which the fetus and newborn infant are subjected, perhaps the most important and clinically relevant is that of hypoxia. This review explores the impact of gestational hypoxia on maternal health and fetal development, and epigenetic mechanisms of developmental plasticity with emphasis on the uteroplacental circulation, heart development, cerebral circulation, pulmonary development, and the hypothalamic-pituitary-adrenal axis and adipose tissue.
An understanding of the specific hypoxia-induced environmental and epigenetic adaptations linked to specific organ systems will enhance the development of target-specific inhibition of DNA methylation, histone modifications, and noncoding RNAs that underlie hypoxia-induced phenotypicprogramming of disease vulnerability later in life.
A potential stumbling block to these efforts, however, relates to timing of the intervention. The greatest potential effect would be accomplished at the critical period in development for which the genomic plasticity is at its peak, thus ameliorating the influence of hypoxia or other stressors.
With future developments, it may even become possible to intervene before conception, before the genetic determinants of the risk of developing programmed disease are established.”
Table 3 “Antenatal hypoxia and developmental plasticity” column titles were Species | Offspring Phenotypes of Disorders and Diseases | Reference Nos.
This review was really an ebook, with 94 pages and 1,172 citations in the pdf file. As I did with Faith-tainted epigenetics, I read it with caution toward recognizing 1) the influence of the sponsor’s biases, 2) any directed narrative that ignored evidence contradicting the narrative, and 3) any storytelling.
One review topic that was misconstrued was transgenerational epigenetic inheritance of hypoxic effects. The “transgenerational” term was used inappropriately by several of the citations, and no cited study provided evidence for gestational hypoxic effects through the F2 grandchild and F3 great-grandchild generations.
“One substance that fetuses are frequently exposed to is caffeine, which is a non-selective adenosine receptor antagonist. We discovered that in utero alteration in adenosine action leads to adverse effects on embryonic and adult murine hearts. We find that cardiac A1ARs [a type of adenosine receptor] protect the embryo from in utero hypoxic stress, a condition that causes an increase in adenosine levels.
After birth in mice, we observed that in utero caffeine exposure leads to abnormal cardiac function and morphology in adults, including an impaired response to β-adrenergic stimulation. Recently, we observed that in utero caffeine exposure induces transgenerational effects on cardiac morphology, function, and gene expression.”
Why was this review and its studies omitted? It was on target for both gestational hypoxia and transgenerational epigenetic inheritance of hypoxic effects!
It was alright to review smoking, cocaine, methamphetamine, etc., but the most prevalent drug addiction – caffeine – couldn’t be a review topic?
The Loma Linda review covered a lot, but I had a quick trigger due to the sponsor’s bias. I started to lose “faith” in the reviewers after reading the citation for the review’s last sentence that didn’t support the statement.
My “faith” disappeared after not understanding why a few topics were misconstrued and omitted. Why do researchers and sponsors ignore, misrepresent, and not continue experiments through the F3 generation to produce evidence for and against transgenerational epigenetic inheritance? Where was the will to follow evidence trails regardless of socially acceptable beverage norms?
The review acquired the taint of storytelling with the reviewers’ assertion:
“..timing of the intervention. The greatest potential effect would be accomplished at the critical period in development for which the genomic plasticity is at its peak, thus ameliorating the influence of hypoxia or other stressors.”
Contradictory evidence was in the omitted caffeine study’s graphic above which described two gestational critical periods where an “intervention” had opposite effects, all of which were harmful to the current fetus’ development and/or to following generations. Widening the PubMed link’s search parameters to “caffeine hypoxia” and “caffeine pregnancy” returned links to human early life studies that used caffeine in interventions, ignoring possible adverse effects on future generations.
This is my final curation of any paper sponsored by this institution.
“Reduction of maternal behavior[nursing behavior, grooming, licking, carrying pups] was predictive of behavioral disturbances in PRS [prenatally restraint stressed] rats as well as of the impairment of the oxytocin and its receptor gene expression.
Postpartum carbetocin [an oxytocin receptor agonist unavailable in the US] corrected the reduction of maternal behavior induced by gestational stress as well as the impaired oxytocinergic system in the PRS progeny, which was associated with reduced risk-taking behavior.
Moreover, postpartum carbetocin had an anti-stress effect on HPA[hypothalamic-pituitary-adrenal] axis activity in the adult PRS progeny and increased hippocampal mGlu5 [type 5 metabotropic glutamate] receptor expression in aging.
Early postpartum carbetocin administration to the dam enhances maternal behavior and prevents all the pathological outcomes of PRS throughout the entire lifespan of the progeny..proves that the defect in maternal care induced by gestational stress programs the development of the offspring.“
This chart from Figure 4 summarized the behavioral performance of aged adult male progeny in relation to the experimental variables of:
Stress administered to the mothers three times daily every day during the second half of pregnancy up until delivery; and
The effects on the mothers’ behavior of daily carbetocin administration during postpartum days 1 through 7.
The symbols denote which of these relationships had statistically significant effects:
“* p [Pearson’s correlation coefficient] < 0.05 PRS-Saline vs. CONT-Saline;
# p < 0.05 PRS-Carbetocin vs. the PRS-Saline group.”
There are many interesting aspects to this study. Ask the corresponding coauthor Dr. Sara Morley-Fletcher at email@example.com for a copy.
One place the paper referenced the researchers’ previous studies was in this context:
“Postpartum carbetocin administration reversed the same molecular and behavioral parameters in the hippocampus, as does adult chronic carbetocin treatment, i.e. it led to a correction of the HPA axis negative feedback mechanisms, stress and anti-stress gene expression, and synaptic glutamate release. The fact that postpartum carbetocin administration [to the stressed mothers in this study] had the same effect [on the PRS infants in this study] as adult carbetocin treatment [to the PRS offspring in the previous study] indicates a short-term effect of carbetocin when administered in adulthood and a reprogramming (long-term) effect lasting until an advanced age when administered in early development.”
This group’s research seems to be constrained to treatments of F0 and F1 generations. What intergenerational and transgenerational effects would they possibly find by extending research efforts to F2 and F3 generations?
As the study may apply to humans:
The study demonstrated that stresses during the second half of pregnancy had lifelong impacts on both the mothers’ and offsprings’ biology and behavior. Studies and reviews that attribute similar human biological and behavioral conditions to unknown causes, or shuffle them into the black box of individual differences, should be recognized as either disingenuous or insufficient etiological investigations.
The study showed that prevention of gestational stress was a viable strategy. The control group progeny’s biology and behavior wasn’t affected by carbetocin administration to their mothers because neither they nor their mothers had experience-dependent epigenetic deficiencies.
The study demonstrated a biological and behavioral cure for the PRS offspring by changing their stressed mothers’ behaviors during a critical period of their development. The above excerpt characterized improving the mothers’ behaviors as a long-term cure for the PRS descendants, as opposed to the short-term cure of administering carbetocin to the PRS children when they were adults.
What long-term therapies may be effective for humans who had their developmental trajectories altered by their mothers’ stresses during their gestation, or who didn’t get the parental care they needed when they needed it?
“Recent studies, primarily focused on the findings from human studies, to indicate the role of DNA methylation in the associations between childhood adversity and cardiometabolic disease in adulthood. In particular, we focused on DNA methylation modifications in genes regulating the hypothalamus-pituitary-adrenalaxis as well as the immune system.”
Recommendations in the review’s Epigenetics inheritance and preadaptation theory section included:
“Twin studies offer another promising design to explore the mediation effect of DNA methylation between child adversity and cardiometabolic outcomes..which could rule out heterogeneity due to genetic and familia[l]r environmental confounding.”
As it so happened, the below 2018 study provided some evidence.
“Tested the hypothesis that victimization is associated with DNA methylation in the Environmental Risk (E-Risk) Longitudinal Study, a nationally representative 1994-1995 birth cohort of 2,232 twins born in England and Wales and assessed at ages 5, 7, 10, 12, and 18 years. Multiple forms of victimization were ascertained in childhood and adolescence (including physical, sexual, and emotional abuse; neglect; exposure to intimate-partner violence; bullying; cyber-victimization; and crime).
Hypothesis-driven analyses of six candidate genes in the stress response (
) did not reveal predicted associations with DNA methylation.
Epigenetic epidemiology is not yet well matched to experimental, nonhuman models in uncovering the biological embedding of stress.”
One of the sad findings was that as the types of trauma inflicted by other people on the subjects increased, so did the percentage of subjects who hurt themselves by smoking. Two-thirds of teens who reported three or more of the seven adolescent trauma types also smoked by age 18. Self-harming behaviors other than smoking weren’t considered.
Another somber finding was:
“Childhood sexual victimization is associated with stable DNA methylation differences in whole blood in young adulthood.
These associations were not observed in relation to sexual victimization in adolescence.”
The researchers guided future studies regarding the proxy measurements of peripheral blood DNA methylation:
“The vast majority of subsequent human studies, including the present one, have relied on peripheral blood. This choice is expedient, but also scientifically reasonable given the aim of detecting effects on stress-related physical health systems that include peripheral circulating processes (immune, neuroendocrine).
But whole blood is heterogeneous, and although cell-type composition can be evaluated and controlled, as in the present study, it does raise the question of whether peripheral blood is a problematic surrogate tissue for research on the epigenetics of stress.
Comparisons of methylomic variation across blood and brain suggest that blood-based EWAS may yield limited information relating to underlying pathological processes for disorders where brain is the primary tissue of interest.”
1. The comment on “epigenetic epidemiology” overstated the study’s findings because the epigenetic analysis, although thorough, was limited to peripheral blood DNA methylation. Other consequential epigenetic effects weren’t investigated, such as histone modifications and microRNA expression.
“A main limitation with studies using the Illumina 450 K array is that the platform only covers ~1.5 % of overall genomic CpGs, which are biased towards promoters and strongly underrepresented in distal regulatory elements, i.e., enhancers.
WGBS [whole-genome bisulfite sequencing] offers single-site resolution CpG methylation interrogation at full genomic coverage.
Another advantage of WGBS is its ability to access patterns of non-CpG methylation.”
I’d expect that in the future, researchers with larger budgets would reanalyze the study samples using other DNA methylation techniques.
4. An outstanding opportunity to advance science was missed regarding intergenerational and transgenerational epigenetic inheritance:
Wouldn’t the parents’ blood samples and histories – derived from administering the same questionnaires their twins answered at age 18 – likely provide distant causal evidence for some of the children’s observed effects?
And lay the groundwork for hypotheses about aspects of future grandchildren’s physiologies and behaviors?