A review of fetal adverse events

This 2019 Australian review subject was fetal adversities:

“Adversity during the perinatal period is a significant risk factor for the development of neurodevelopmental disorders long after the causative event. Despite stemming from a variety of causes, perinatal compromise appears to have similar effects on the developing brain, thereby resulting in behavioural disorders of a similar nature.

These behavioural disorders occur in a sex‐dependent manner, with males affected more by externalizing behaviours such as attention deficit hyperactivity disorder (ADHD) and females by internalizing behaviours such as anxiety. The term ‘perinatal compromise’ serves as an umbrella term for intrauterine growth restriction, maternal immune activation, prenatal stress, early life stress, premature birth, placental dysfunction, and perinatal hypoxia.

The above conditions are associated with imbalanced excitatory-inhibitory pathways resulting from reduced GABAergic signalling. Methylation of the GAD1/GAD67 gene, which encodes the key glutamate‐to‐GABA synthesizing enzyme Glutamate Decarboxylase 1, resulting in increased levels of glutamate is one epigenetic mechanism that may account for a tendency towards excitation in disorders such as ADHD.

The posterior cerebellum’s role in higher executive functioning is becoming well established due to its connections with the prefrontal cortex, association cortices, and limbic system. It is now suggested that disruptions to cerebellar development, which can occur due to late gestation compromises such as preterm birth, can have a major impact on the region of the brain to which it projects.

Activation of the maternal hypothalamic-pituitary adrenal (HPA) axis and placental protection. Psychological stress is perceived by the maternal HPA axis, which stimulates cortisol release from the maternal adrenal gland.

High levels of maternal cortisol are normally prevented from reaching the fetus by the 11β-hydroxysteroid dehydrogenase 2 (HSD11B2) enzyme, which converts cortisol to the much less active cortisone. Under conditions of high maternal stress, this protective mechanism can be overwhelmed, with the gene encoding the enzyme becoming methylated, which reduces its expression allowing cortisol to cross the placenta and reach the fetus.”

The reviewers extrapolated many animal study findings to humans, although most of their own work was with guinea pigs. The “suggest” and “may” qualifiers were used often – 22 and 37 times, respectively. More frequent use of the “appears,” “hypothesize,” “propose,” and “possible” terms was justified.

As a result, many reviewed items such as the above graphic and caption should be viewed as hypothetical for humans rather than reflecting solid evidence from quality human studies.

The reviewers focused on the prenatal (before birth) period more than the perinatal (last trimester of pregnancy to one month after birth) period. There were fewer mentions of birth and early infancy adversities.

https://onlinelibrary.wiley.com/doi/abs/10.1111/jne.12814 “Perinatal compromise contributes to programming of GABAergic and Glutamatergic systems leading to long-term effects on offspring behaviour” (not freely available)

Organismal aging and cellular senescence

I’ll curate this 2019 German review through its figures:

“With the discovery of beneficial aspects of cellular senescence and evidence of senescence being not limited to replicative cellular states, a redefinition of our comprehension of aging and senescence appears scientifically overdue.

Figure 1. Current determinants and relevant open questions, marking the processes of aging and senescence as discussed in the text. Aspects represented in green are considered as broadly accepted or scientifically consolidated. Novel aspects that are yet unproven, or are under debate, are highlighted in red.

SASP = senescence-associated secretory phenotype. AASP = putative aging-associated secretory phenotype as suggested in the text.

Figure 2. Theories on the causality and purpose of aging. Graphically summarized are four contrasting concepts crystallized from current evidence addressing the inductive driving force of aging. Apart from a stochastic deleteriome, there are arguments for a pseudo-programmed, programmed or at least partially programmed nature of aging.

Figure 3. Comparative representation of the aging and senescence processes highlighting different levels of interaction and putative sites of interventions.

(1) As discussed in the text, causative mechanisms of aging are still not well understood, however, multiple factors including genetic, epigenetic and stress-related effects seem to have an orchestrated role in the progression of aging. Senescence on the other hand, is seen as a programmed response to different kinds of stressors, which proceed in defined stages. Whether, in analogy, aging also follows a defined program or sequential stages is not known.

(2) Senescence involves autocrine and paracrine factors, which are responsible for a ‘seno-infection’ or bystander effect in neighboring cells. There is currently no direct evidence for a similar factor composition propagating the aging process via a kind of ‘gero-infection’.

(3) Accumulation of senescent cells has been described as a hallmark of aging; however, whether they are a causative factor or a consequence of tissue and organismal aging is still unknown. As discussed in the text, it appears possible that aging and senescence mutually influence each other through positive feedback at this level, leading to accelerated tissue damage and aging.

(4,5) Clearance of senescent or aging cells might constitute putative targets for interventional approaches aimed to reduce or reverse the impact of aging and improve cell and tissue homeostasis by inducing a ‘rejuvenation’ process.

Figure 4. Pathological and beneficial functions of aging and senescence, according to current knowledge. In red are represented pathological consequences and in green beneficial functions of aging and senescence.

The impact of aging has mainly been described at the organismal level, since a complete cellular functional profile has not yet been established. Accordingly, whether beneficial consequences of the aging process exist at the cellular level is unclear.”

The reviewers’ position on Figure 2 was:

“In our view, recent evidence that senescence is based on an unterminated developmental growth program and the finding that the concept of post-mitotic senescence requires the activation of expansion, or ‘growth’ factors as a second hit, favor the assumption that aging underlies a grating of genetic determination similarly to what is summarized above under the pseudo-programmed causative approach.”

Their position on Figure 4’s beneficial effects of aging began with the sentence:

“If we assume that aging already starts before birth, it can be considered simply a developmental stage, required to complete the evolutionary program associated with species-intrinsic biological functions such as reproduction, survival, and selection.”

Cited studies included:

https://www.mdpi.com/2073-4409/8/11/1446 “Dissecting Aging and Senescence-Current Concepts and Open Lessons”

Do genes or maternal environments shape fetal brains?

This 2019 Singapore human study used Diffusion Tensor Imaging on 5-to-17-day old infants to find:

“Our findings showed evidence for region-specific effects of genotype and GxE on individual differences in human fetal development of the hippocampus and amygdala. Gene x Environment models outcompeted models containing genotype or environment only, to best explain the majority of measures but some, especially of the amygdaloid microstructure, were best explained by genotype only.

Models including DNA methylation measured in the neonate umbilical cords outcompeted the Gene and Gene x Environment models for the majority of amygdaloid measures and minority of hippocampal measures. The fact that methylation models outcompeted gene x environment models in many instances is compatible with the idea that DNA methylation is a product of GxE.

A genome-wide association study of SNP [single nucleotide polymorphism] interactions with the prenatal environments (GxE) yielded genome wide significance for 13 gene x environment models. The majority (10) explained hippocampal measures in interaction with prenatal maternal mental health and SES [socioeconomic status]. The three genome-wide significant models predicting amygdaloid measures, explained right amygdala volume in interaction with maternal depression.

The transcription factor CUX1 was implicated in the genotypic variation interaction with prenatal maternal health to shape the amygdala. It was also a central node in the subnetworks formed by genes mapping to the CpGs in neonatal umbilical cord DNA methylation data associating with both amygdala and hippocampus structure and substructure.

Our results implicated the glucocorticoid receptor (NR3C1) in population variance of neonatal amygdala structure and microstructure.

Estrogen in the hippocampus affects learning, memory, neurogenesis, synapse density and plasticity. In the brain testosterone is commonly aromatized to estradiol and thus the estrogen receptor mediates not only the effects of estrogen, but also that of testosterone.”

https://onlinelibrary.wiley.com/doi/full/10.1111/gbb.12576 “Neonatal amygdalae and hippocampi are influenced by genotype and prenatal environment, and reflected in the neonatal DNA methylome” (not freely available)

Transgenerational epigenetic inheritance of thyroid hormone sensitivity

My 500th curation is a 2019 Portuguese human study of Azorean islanders:

“This study demonstrates a transgenerational epigenetic inheritance in humans produced by exposure to high TH [thyroid hormone] in fetal life, in the absence of maternal influences secondary to thyrotoxicosis. The inheritance is along the male line.

The present work took advantage of the relatively frequent occurrence of fetal exposure to high TH levels in the Azorean island of São Miguel. This is the consequence of a missense mutation in the THRB gene causing the amino-acid replacement R243Q, resulting in reduced affinity of the TH receptor beta (TRβ) for TH and thus RTHβ.

Its origin has been traced to a couple who lived at the end of the 19th century. F0 represented the third generation and F3 the sixth and seventh generation descendant.”

These researchers provided the first adequately evidenced human transgenerational epigenetic inheritance study! However, the lead sentence in its Abstract wasn’t correct:

“Evidence for transgenerational epigenetic inheritance in humans is still controversial, given the requirement to demonstrate persistence of the phenotype across three generations.”

Although found in this study, there is no “requirement to demonstrate persistence of the phenotype.” Observing the same phenotype in each generation is NOT required for human transgenerational epigenetic inheritance to exist!

Animal transgenerational studies have shown that epigenetic inheritance mechanisms may both express different phenotypes for each generation:

and entirely skip a phenotype in one or more generations!

  • Transgenerational pathological traits induced by prenatal immune activation found a F2 and F3 generation phenotype of impaired sociability, abnormal fear expression and behavioral despair – effects that weren’t present in the F1 offspring;
  • The transgenerational impact of Roundup exposure “Found negligible impacts of glyphosate on the directly exposed F0 generation, or F1 generation offspring pathology. In contrast, dramatic increases in pathologies in the F2 generation grand-offspring, and F3 transgenerational great-grand-offspring were observed.” (a disease phenotype similarly skipped the first offspring generation);
  • Epigenetic transgenerational inheritance mechanisms that lead to prostate disease “There was also no increase in prostate histopathology in the directly exposed F1 or F2 generation.” (a prostate disease phenotype skipped the first two male offspring generations before it was observed in the F3 male offspring); and
  • Epigenetic transgenerational inheritance of ovarian disease “There was no increase in ovarian disease in direct fetal exposed F1 or germline exposed F2 generation. The F3 generation can have disease while the F1 and F2 generations do not, due to this difference in the molecular mechanisms involved.” (an ovarian disease phenotype similarly skipped the first two female offspring generations before it was observed in the F3 female offspring).

Details of epigenetic inheritance mechanisms were provided in Another important transgenerational epigenetic inheritance study. Mechanisms from fetal exposure to the fungicide vinclozolin were compared with mechanisms from fetal DDT exposure, and summarized as:

The fetal exposure initiates a developmental cascade of aberrant epigenetic programming, and does NOT simply induce a specific number of DMRs [DNA methylation regions] that are maintained throughout development.

I emailed references to the studies in the first five above curations to the current study’s corresponding coauthor. They replied “What is the mechanism for the transgenerational inheritance you describe?” and my reply included a link to the sixth curation’s study.

Are there still other transgenerational epigenetically inherited effects due to fetal exposure to high thyroid hormone levels?

https://www.liebertpub.com/doi/full/10.1089/thy.2019.0080 “Reduced Sensitivity to Thyroid Hormone as a Transgenerational Epigenetic Marker Transmitted Along the Human Male Line”

Perinatal stress and sex differences in circadian activity

This 2019 French/Italian rodent study used the PRS model to investigate its effects on circadian activity:

“The aim of this study was to explore the influence of PRS on the circadian oscillations of gene expression in the SCN [suprachiasmatic nucleus of the hypothalamus] and on circadian locomotor behavior, in a sex-dependent manner.

Research on transcriptional rhythms has shown that more than half of all genes in the human and rodent genome follow a circadian pattern. We focused on genes belonging to four functional classes, namely the circadian clock, HPA axis stress response regulation, signaling and glucose metabolism in male and female adult PRS rats.

Our findings provide evidence for a specific profile of dysmasculinization induced by PRS at the behavioral and molecular level, thus advocating the necessity to include sex as a biological variable to study the set-up of circadian system in animal models.”

“There was a clear-cut effect of sex on the effect of PRS on the levels of activity:

  • During the period of lower activity (light phase), both CONT and PRS females were more active than males. During the light phase, PRS increased activity in males, which reached levels of CONT females.
  • More interestingly, during the period of activity (dark phase), male PRS rats were more active than male CONT rats. In contrast, female PRS rats were less active than CONT females.
  • During the dark phase, CONT female rats were less active than CONT male rats.

The study presented evidence for sex differences in circadian activity of first generation offspring that was caused by stress experienced by the pregnant mother:

“Exposure to gestational stress and altered maternal behavior programs a life-long disruption in the reactive adaptation such as:

  •  A hyperactive response to stress and
  • A defective feedback of the hypothalamus-pituitary-adrenal (HPA) axis together with
  • Long-lasting modifications in stress/anti-stress gene expression balance in the hippocampus.”

It would advance science if these researchers carried out experiments to two more generations to investigate possible transgenerational epigenetic inheritance of effects caused by PRS. What intergenerational and transgenerational effects would they possibly find by taking a few more months and extending research efforts to F2 and F3 generations? Wouldn’t these findings likely help humans?

One aspect of the study was troubling. One of the marginally-involved coauthors was funded by the person described in How one person’s paradigms regarding stress and epigenetics impedes relevant research. Although no part of the current study was sponsored by that person, there were three gratuitous citations of their work.

All three citations were reviews. Unlike study researchers, reviewers aren’t bound to demonstrate evidence from tested hypotheses. Reviewers are free to:

  • Express their beliefs as facts;
  • Over/under emphasize study limitations; and
  • Disregard and misrepresent evidence as they see fit.

Fair or not, comparisons of reviews with Cochrane meta-analyses of the same subjects consistently show the extent of reviewers’ biases. Reviewers also aren’t obligated to make post-publication corrections for their errors and distortions.

As such, reviews can’t be cited for reliable evidence. Higher-quality studies that were more relevant and recent than a 1993 review could have elucidated points.

Sucking up to the boss and endorsing their paradigm was predictable. Since that coauthor couldn’t constrain themself to funder citations only in funder studies, it was the other coauthors’ responsibilities to edit out unnecessary citations.

https://www.frontiersin.org/articles/10.3389/fnmol.2019.00089/full “Perinatal Stress Programs Sex Differences in the Behavioral and Molecular Chronobiological Profile of Rats Maintained Under a 12-h Light-Dark Cycle”

A drug that countered effects of a traumatizing mother

This 2019 US rodent study concerned transmitting poor maternal care to the next generation:

“The quality of parental care received during development profoundly influences an individual’s phenotype, including that of maternal behavior. Infant experiences with a caregiver have lifelong behavioral consequences.

Maternal behavior is a complex behavior requiring the recruitment of multiple brain regions including the nucleus accumbens, bed nucleus of the stria terminalis, ventral tegmental area, prefrontal cortex, amygdala, and medial preoptic area. Dysregulation within this circuitry can lead to altered or impaired maternal responsiveness.

We administered zebularine, a drug known to alter DNA methylation, to dams exposed during infancy to the scarcity-adversity model of low nesting resources, and then characterized the quality of their care towards their offspring.

  1. We replicate that dams with a history of maltreatment mistreat their own offspring.
  2. We show that maltreated-dams treated with zebularine exhibit lower levels of adverse care toward their offspring.
  3. We show that administration of zebularine in control dams (history of nurturing care) enhances levels of adverse care.
  4. We show altered methylation and gene expression in maltreated dams normalized by zebularine.

These findings lend support to the hypothesis that epigenetic alterations resulting from maltreatment causally relate to behavioral outcomes.”

“Maternal behavior is an intergenerational behavior. It is important to establish the neurobiological underpinnings of aberrant maternal behavior and explore treatments that can improve maternal behavior to prevent the perpetuation of poor maternal care across generations.”

The study authors demonstrated intergenerational epigenetic effects, and missed an opportunity to also investigate transgenerational epigenetically inherited effects. They cited reference 60 for the first part of the above quotation, but that reviewer misused the transgenerational term by applying it to grand-offspring instead of the great-grand-offspring.

There were resources available to replicate the study authors’ previous findings, which didn’t show anything new. Why not use such resources to uncover evidence even more applicable to humans by extending experiments to great-grand-offspring that have no potential germline exposure to the initial damaging cause?

Could a study design similar to A limited study of parental transmission of anxiety/stress-reactive traits have been integrated? That study’s thorough removal of parental behavior would be an outstanding methodology to confirm by falsifiability whether parental behavior is both an intergenerational and a transgenerational epigenetic inheritance mechanism.

Rodent great-grand-offspring can be studied in < 9 months. It takes > 50 years for human studies to reach the transgenerational generation. Why not attempt to “prevent the perpetuation of poor maternal care across generations?”

Isn’t it a plausible hypothesis that humans “with a history of maltreatment mistreat their own offspring?” Isn’t it worth the extra effort to extend animal research to investigate this unfortunate chain?

https://www.nature.com/articles/s41598-019-46539-4 “Pharmacological manipulation of DNA methylation normalizes maternal behavior, DNA methylation, and gene expression in dams with a history of maltreatment”

Our brains are shaped by our early environments

This 2019 McGill paper reviewed human and animal studies on brain-shaping influences from the fetal period through childhood:

“In neonates, regions of the methylome that are highly variable across individuals are explained by the genotype alone in 25 percent of cases. The best explanation for 75 percent of variably methylated regions is the interaction of genotype with different in utero environments.

A meta-analysis including 45,821 individuals with attention-deficit/hyperactivity disorder and 9,207,363 controls suggests that conditions such as preeclampsia, Apgar score lower than 7 at 5 minutes, breech/transverse presentations, and prolapsed/nuchal cord – all of which involve some sort of poor oxygenation during delivery – are significantly associated with attention-deficit/hyperactivity disorder. The dopaminergic system seems to be one of the brain systems most affected by perinatal hypoxia-ischemia.

Exposure to childhood trauma activates the stress response systems and dysregulates serotonin transmission that can adversely impact brain development. Smaller cerebral, cerebellar, prefrontal cortex, and corpus callosum volumes were reported in maltreated young people as well as reduced hippocampal activity.

Environmental enrichment has a series of beneficial effects associated with neuroplasticity mechanisms, increasing hippocampal volume, and enhancing dorsal dentate gyrus-specific differences in gene expression. Environmental enrichment after prenatal stress decreases depressive-like behaviors and fear, and improves cognitive deficits.”

The reviewers presented strong evidence until the Possible Factors for Reversibility section, which ended with the assertion:

“All these positive environmental experiences mentioned in this section could counterbalance the detrimental effects of early life adversities, making individuals resilient to brain alterations and development of later psychopathology.”

The review’s penultimate sentence recognized that research is seldom done on direct treatments of causes:

“The cross-sectional nature of most epigenetic studies and the tissue specificity of the epigenetic changes are still challenges.”

Cross-sectional studies won’t provide definitive data on cause-and-effect relationships.

The question yet to be examined is: How can humans best address these early-life causes to ameliorate their lifelong effects?

https://onlinelibrary.wiley.com/doi/full/10.1111/dmcn.14182 “Early environmental influences on the development of children’s brain structure and function” (not freely available)