The scientific backstory begins, fittingly, with the flu. Decades ago, epidemiologists noticed that mothers who contracted influenza during the second or third trimesters of pregnancy reported a higher incidence of psychiatric and neurodevelopmental disorders in their children. At the time, the observation was little more than a statistical curiosity. But when researchers later gained access to archived maternal blood samples, a clearer picture emerged: the risk appeared to track not with the virus itself but with the mother’s immune response to it. Chief among the suspects was interleukin-6, or IL-6, a signaling protein that stokes inflammation as part of the body’s defense against pathogens. Elevated IL-6 in the maternal bloodstream, it turned out, was the common thread. That discovery allowed scientists to build reliable rodent models of the phenomenon, in which a pregnant animal’s immune system is activated without any actual infection, reproducing the elevated risk of neurodevelopmental disorders in offspring.

What those models had largely lacked, however, was an epigenetic account of the damage. Most prior characterization of maternal immune activation in rodents was behavioral or electrophysiological—describing how the animals moved, responded to stimuli, or fired neuronal signals—without explaining what had changed inside the cells to produce those deficits. That gap is precisely what the Salk team, led by co-corresponding authors Margarita Behrens and Joseph Ecker, set out to close. Epigenetics refers to the layer of chemical tags and structural modifications that sits atop the base genetic sequence and determines which genes are turned on or off in a given cell. Unlike the genome itself, which is fixed at conception, the epigenome is malleable, making it a plausible target for environmental insults such as the inflammatory storm of maternal illness. If prenatal infection reshapes the developing brain, the epigenome is where that reshaping should leave its fingerprints.

To capture those fingerprints, the researchers used the field’s standard model of maternal immune activation: an injection of viral mimetic Poly(I:C), a synthetic double-stranded RNA that tricks the immune system into believing it has encountered an influenza virus. The treatment produces the same IL-6-driven inflammatory response as a genuine viral infection without introducing a pathogen. Using this model—referred to in the study as PIC-MIA—the team tracked epigenetic and transcriptional changes in the frontal cortex of mouse offspring from mid-gestation through two weeks after birth, comparing animals from immune-activated pregnancies with those from healthy pregnancies. The frontal cortex was the logical hunting ground: it is the brain region most associated with higher cognitive functions, and its development spans the entire window of vulnerability examined in the study.

The scale of the differences was striking. Across the developing cortex, the researchers documented thousands of epigenetic and gene-expression differences between the two groups. But the changes were not distributed evenly across all cell types. They concentrated, with remarkable specificity, in deep-layer neurons—a population of cortical cells that project long-range connections to other brain regions and are known to be generated during precisely the developmental window when maternal immune activation strikes. These cells form the structural backbone of cortical circuitry, and disruptions to their maturation ripple outward into the wiring of the entire brain.

At the molecular level, the team found that methylation patterns—the placement of small chemical methyl groups on the DNA—were especially altered in genomic regions that govern deep-layer neuron identity. The most consequential changes clustered at the binding sites of Tbr1, a transcription factor that serves as a master regulator of the developing brain, directing immature cells along the path to becoming deep-layer cortical neurons. Here the researchers encountered a genuine surprise. In the offspring of immune-activated mothers, Tbr1 was actually more abundant, and its binding sites were more heavily methylated than normal. Yet the genomic regions that Tbr1 typically regulates were downregulated, not upregulated. The explanation, the data suggest, is that the excess methylation was physically blocking Tbr1 from doing its job. The cell had produced more of its master architect, but methyl groups were sealing off the blueprints that architect needed to read. Deep-layer neuron development, deprived of proper Tbr1 direction, proceeded abnormally.

The implications deepened when the team cross-referenced their findings with the SFARI Gene Database, the reference catalog of autism-associated genomic alterations maintained for the autism research community. Among the high-confidence entries in that database—the genes scientists are most certain are genuinely linked to autism spectrum disorder—roughly twenty-five percent were dysregulated in the Salk dataset. In other words, the epigenetic disruptions caused by maternal immune activation were not scattered randomly across the genome; they landed preferentially on genes already known to matter for autism. That convergence between an environmental risk factor and a genetic risk landscape is exactly the kind of mechanistic bridge the field has been searching for, suggesting a route by which prenatal illness and inherited vulnerability may converge on the same developmental programs.

To confirm that the molecular changes had functional consequences, the researchers performed electrophysiological recordings on deep-layer neurons after the animals were born. The recordings confirmed what the epigenomic data predicted: the maturation of these neurons was measurably impaired in offspring of PIC-MIA pregnancies. The electrical properties that define healthy, fully developed cortical neurons were disrupted, demonstrating that the altered methylation and gene expression translated into altered neuronal function—a defect in the brain’s hardware, not merely its chemical profile.

The findings also carry an important caveat about determinism, one the researchers are careful to emphasize. Maternal infection changes the odds of neurodevelopmental outcomes; it does not seal them. “Infection changes the odds of whether neurodevelopment is affected—not everyone who gets sick during pregnancy is going to definitively have a child with a neurodevelopmental disorder,” says Joseph Ecker, professor and Salk International Council Chair in Genetics at Salk and a Howard Hughes Medical Institute investigator. This framing matters both scientifically and for public communication. The study identifies a risk-modifying mechanism, not an inevitability, and understanding the mechanism opens the door to interventions that could shift those odds back in the child’s favor—whether through maternal therapeutics that dampen harmful inflammation or through fetal interventions that protect vulnerable developmental programs.

Much remains unknown. The researchers still do not know exactly when during brain development the epigenetic damage occurs, or which stretch of pregnancy represents the window of greatest vulnerability to severe illness. “We are closer now to understanding the consequences of maternal infection, but this is only just the beginning of the story,” Ecker says. Behrens, for her part, frames the work as the payoff of a decade of methodical groundwork. “It’s just the tip of the iceberg. We are distilling all these things that we have been doing for ten years—analyzing epigenomes for years and years to get to the point that we can ask these questions. Now we can approach questions with more detail. It’s going to be a lot of fun moving forward.” As single-cell epigenomic technologies continue to mature, the ability to ask where and when specific molecular events derail specific neuronal lineages will only sharpen, bringing the field closer to preventive strategies for a class of disorders that currently affects millions of families.

What makes the study resonate beyond the laboratory is its unifying logic. A mother’s feverish immune response, a chemical tag on DNA, a transcription factor locked out of its binding sites, a neuron that fails to mature, a brain whose circuitry carries the imprint into adulthood—these are not separate stories but a single causal chain, now traced end to end in a mammalian model. The work demonstrates the lasting impact of prenatal immune challenges on offspring health and adds a mechanistic foundation to a decades-old epidemiological observation. In doing so, it transforms a correlation once glimpsed in flu-season statistics into a testable, targetable biological pathway—one that may ultimately guide the development of maternal or fetal therapeutics designed to protect the developing brain from the collateral damage of the immune system’s own defense.

At the heart of the analysis is telomere length, one of the most widely used biomarkers of biological ageing. Telomeres are repetitive stretches of the DNA sequence TTAGGG that cap the ends of chromosomes and protect them from degradation and fusion. Because DNA polymerase cannot fully replicate chromosome ends, telomeres shorten with every cell division, and when they become critically short, cells enter senescence or die. Oxidative stress accelerates this process, because 8-oxoguanine lesions in telomeric DNA impede the replication fork, while chronic inflammation raises cellular turnover and reactive oxygen species production. A 2023 meta-analysis of 414 study samples covering more than 743,000 individuals estimated an average loss of roughly 38 base pairs of telomeric DNA per year across adulthood, with the steepest attrition in early childhood and a non-linear trajectory thereafter. Short telomeres are associated with cardiovascular disease, type 2 diabetes, neurodegenerative disorders, cancer, and all-cause mortality, which is why any factor that accelerates their erosion attracts intense scientific scrutiny.

The central question the review tackles is whether bearing children ages mothers at the cellular level. The evidence, while heterogeneous, points in that direction. In a cross-sectional analysis of 1,954 US women aged 20 to 44 drawn from the National Health and Nutrition Examination Survey, women with a history of live birth had leukocyte telomeres that were 4.2 per cent shorter than those of women who had never given birth, equivalent to roughly 116 base pairs. That magnitude exceeded the shortening attributable to obesity or smoking. Work from the Sister Study of 1,048 postmenopausal women found that higher parity, particularly four or more births, was associated with shorter relative telomere length. In the Cebu Longitudinal Health and Nutrition Survey of young Filipino women, each additional pregnancy was linked to shorter telomeres and greater epigenetic age acceleration, and crucially, baseline telomere measures did not predict subsequent pregnancies, supporting a causal direction from reproduction to cellular ageing rather than the reverse. Notably, fathers show no equivalent effect, which supports the interpretation that it is the physical demands of gestation, birth, and lactation, rather than shared socioeconomic circumstances, that drive the association.

Pregnancy itself may be best understood as a transient episode of accelerated ageing. Using epigenetic clocks, computational models that estimate biological age from DNA methylation patterns, researchers have shown that maternal biological age rises across gestation and falls significantly by three months postpartum, though the reversal is only partial. This fits a broader biological principle demonstrated in animal models and humans alike: severe physiological stressors can transiently increase biological age, and recovery can restore it. Pre-pregnancy body mass index and breastfeeding emerged as key modifiers in a US pregnancy cohort, with higher BMI amplifying the pregnancy-associated ageing signal and exclusive breastfeeding partially reversing it after delivery. The authors of the review stress that this reframing matters clinically, because it suggests the biological costs of pregnancy are not fixed but modifiable through health behaviours and postpartum care.

The molecular toolkit behind these findings deserves explanation. Beyond direct telomere measurement by quantitative PCR or Southern blotting, researchers now use second- and third-generation epigenetic clocks. PhenoAge, trained on nine blood biomarkers from an Italian ageing cohort, predicts phenotypic age from 513 methylation sites and captures physiological health. GrimAge incorporates methylation-based surrogates for seven plasma proteins linked to inflammation and metabolic dysfunction, plus a smoking estimate, and predicts time to death. DunedinPACE, trained on two decades of longitudinal data from the Dunedin birth cohort, estimates not a static age but the current pace of ageing across cardiovascular, metabolic, renal, hepatic, immune, and pulmonary systems. A methylation-based telomere estimator, DNAmTL, uses 140 CpG sites to approximate telomere length in kilobases. These markers frequently diverge from one another, and the review is careful to note that they index components of ageing that are only partially overlapping, meaning the findings are best read as evidence that reproduction leaves a measurable molecular signature, not proof that telomere erosion itself causes maternal ageing.

Among the most striking findings is the role of timing. Women who have their last child later, at 34 or beyond, tend to have longer telomeres, with one study estimating that mothers delivering at age 40 or older carry telomeres equivalent to roughly nine years less biological ageing than those whose last birth occurred before 25. The most plausible interpretation, given cross-sectional designs, is not that late childbearing rejuvenates cells but that women with inherently robust telomere maintenance are biologically better equipped to sustain pregnancy into their late thirties, consistent with the telomeric theory of reproductive senescence in which telomere erosion in oocytes and granulosa cells limits ovarian reserve. Each additional pregnancy, meanwhile, has been estimated to shorten telomeres by roughly 0.011 kilobases, a cost detectable by sensitive multi-system biomarkers even in the mid-twenties.

The postpartum period emerges as a critical and chronically underexplored window. New mothers lose 40 to 60 minutes of sleep per night during the early postpartum months, with fragmentation that may be more physiologically disruptive than equivalent reductions in non-caregiving adults. Sleep loss elevates reactive oxygen species, activates the DNA damage response and the senescence-associated secretory phenotype, raises interleukin-6 and tumour necrosis factor-alpha, and disrupts cortisol and melatonin rhythms that regulate telomerase activity. In the Healthy Babies Before Birth study, mothers sleeping fewer than seven hours per night at six months postpartum showed accelerated epigenetic ageing and shorter methylation-estimated telomere length at twelve months, with effect sizes corresponding to multiple years of additional biological ageing. A pilot study also found that postpartum leukocyte telomeres were significantly shorter after caesarean delivery than after vaginal birth, and that poor sleep quality was the primary stressor associated with shorter telomeres across gestation. Mendelian randomisation analyses, which use genetic variants as natural experiments, lend causal weight to the sleep-telomere link.

Mental health adds a bidirectional dimension to the model. Postpartum depression affects an estimated 17 per cent of women worldwide, and telomere length at delivery correlates negatively with the severity of depressive symptoms at week 32 of pregnancy and six weeks postpartum. Persistent postpartum depression is associated with shorter telomeres, particularly among women with a high burden of adverse childhood experiences, and neither TERT nor TERC genotype moderated the effect, pointing to cumulative environmental rather than genetic influences. Most provocatively, shorter prenatal telomeres predicted greater postpartum depression symptom severity weeks later, independent of baseline psychosocial variables, suggesting that cellular ageing is not merely a consequence of perinatal stress but potentially an upstream biomarker of vulnerability. The review proposes a self-amplifying cycle: distress shortens telomeres, and shortened telomeres, through impaired stress regulation and heightened inflammation, predispose to further psychological deterioration.

The picture around menopause is subtler still. A study of more than 4,400 US women found that parity predicted biological age acceleration, measured by clinical composite indices, in postmenopausal but not premenopausal women, with ageing lowest among those reporting three to four live births. This hints that cellular markers register reproductive costs earlier and more sensitively than clinical measures, which only reveal them after menopause, when compensatory mechanisms of the reproductive years lapse. The oestrogen story is similarly complicated: although an oestrogen response element exists in the promoter of telomerase’s catalytic subunit, and longer reproductive lifespan is associated with longer telomeres in some studies, other large datasets show faster telomere attrition before menopause than after it, and no clear protective effect of exogenous oestrogen. The prevailing model is that the cumulative oxidative, immune, and energetic burden of repeated pregnancies and lactation outweighs any telomerase-stimulating benefit of oestrogen across the reproductive lifespan.

The authors conclude with a call for longitudinal studies tracking telomeres and epigenetic clocks from pre-conception through menopause, mechanistic work on the pathways linking sleep, delivery mode, lactation, and parity to telomere maintenance, and intervention trials that treat postpartum sleep and mental health support not as amenities but as measurable determinants of long-term maternal ageing. Given rising global caesarean rates and growing recognition that reproductive costs fall unevenly across socioeconomic and racial lines, the review argues that maternal cellular ageing should move from the margins of biogerontology to its centre. The biological price of motherhood, the evidence suggests, is real, quantifiable, and, at least in part, recoverable, provided the postpartum body gets the sleep, support, and care it needs to pay down the debt.

The liver, often referred to as the body’s metabolic hub, plays a pivotal role in a multitude of biological processes, including metabolism, detoxification, and hormone regulation. In understanding how sexual maturation affects liver functionality, researchers have meticulously mapped out sex-specific transcriptomes. This mapping not only emphasizes the distinctions between male and female hepatic profiles but also uncovers how these differences may impact health outcomes later in life, particularly in relation to obesity.

Maternal obesity has emerged as a significant public health concern, with subsequent generations potentially bearing the brunt of its effects. The study presented by Yadav and colleagues delves into this phenomenon by exploring the epigenetic changes caused by maternal obesity during pregnancy. The researchers argue that these epigenetic alterations are not just mere byproducts but rather factors that can potentially predispose offspring to metabolic disorders. The liver plays an integral role in these metabolic pathways, making it an essential focus for understanding the broader implications of maternal health.

At the core of this investigation are sex-specific differences that emerge in liver transcriptomes as subjects enter sexual maturity. Utilizing advanced genomic technologies, the researchers meticulously characterized the transcriptional landscapes of the livers from male and female models. This detailed examination revealed that distinct gene expression profiles are established, likely influenced by the hormonal milieu associated with sexual maturation. Such findings are pivotal in recognizing how sexual dimorphism manifests at the molecular level in crucial metabolic organs.

Moreover, the researchers utilized H3K9me3, an epigenetic marker associated with transcriptional repression, to further delineate the changes in gene expression brought about by maternal obesity. This histone modification is known for its role in silencing genes, and its dysregulation could have profound implications on liver function and overall metabolic health. By analyzing H3K9me3 profiles, the study demonstrates how maternal obesity could potentially influence the developmental trajectory of hepatic gene expression in a sex-specific manner.

The implications of these findings reach far beyond the confines of laboratory research. As public awareness of obesity’s health implications grows, so does the urgency for scientific inquiry into its transgenerational effects. The relationship between a mother’s health and her offspring’s metabolic profiles is not only a biological concern but also a societal one. Educating expectant mothers about the ramifications of obesity could transform public health strategies aimed at reducing the prevalence of metabolic disorders in future generations.

In addition to the immediate relevance of these findings, the study raises compelling questions about the potential reversibility of epigenetic changes initiated by maternal obesity. Research into targeted interventions that could mitigate these adverse effects is needed to promote healthier outcomes for offspring. The role of lifestyle modifications, dietary interventions, and exercise in reversing or reducing the epigenetic marks caused by obesity warrants further exploration.

Moreover, the research provokes discussions about the complexity of gene-environment interactions. How might environmental factors, beyond maternal obesity, influence liver development and function, and subsequently, metabolic health? The interplay between these variables is crucial to comprehensively understanding sexual dimorphism and its implications for disease susceptibility.

As scientists continue to uncover the molecular underpinnings of metabolic health, emphasis on the timing of environmental exposures will be paramount. The window of opportunity for intervention may be narrow but critical, suggesting that early-life conditions set the stage for lifelong health trajectories. This research underscores the necessity for a multidisciplinary approach, integrating genetics, epigenetics, nutrition, and health education in tackling obesity-related health issues.

The innovation of utilizing sex-specific transcriptomic profiles represents a significant advancement in personalized medicine. By appreciating the unique biological mechanisms at play in different sexes, future research and clinical interventions can be tailored to optimize health outcomes. This individualized approach has the potential to revolutionize how metabolic disorders are treated, enabling healthcare providers to offer more precise and effective interventions.

In conclusion, the research carried out by Yadav and colleagues is a monumental step toward understanding the intricacies of liver physiology, sexual maturation, and the overarching impacts of maternal obesity. Their findings not only contribute to the scientific literature but also serve as a clarion call for public health initiatives aimed at educating mothers about the implications of their health on their children. As the field of epigenetics continues to evolve, it is crucial to harness these insights to improve health outcomes across generations.

The exploration of sex-specific differences in hepatic gene expression, particularly following maternal obesity, opens avenues for new research focused on preventive measures and therapeutic strategies. Understanding how epigenetic modifications can be mitigated or reversed will be critical in addressing the obesity epidemic and its wide-reaching effects on metabolic health.

Ultimately, this research is a reminder of the interconnected nature of health, environment, and genetic predisposition. The journey to deciphering the complexities of our biology is ongoing and presents exciting opportunities for future discoveries. As researchers delve deeper into the epigenetic landscape of health and disease, the potential to illuminate the pathways that lead to optimal health remains a tantalizing frontier.

Subject of Research: The impact of maternal obesity on sex-specific liver transcriptomes and H3K9me3 profiles during sexual maturity.

Article Title: Establishment of sex-specific liver transcriptomes and H3K9me3 profiles during sexual maturity: the impact of maternal obesity.

Article References:

Yadav, A.K., Harris-Kawano, A., Saxena, R. et al. Establishment of sex-specific liver transcriptomes and H3K9me3 profiles during sexual maturity: the impact of maternal obesity.
Biol Sex Differ 16, 81 (2025). https://doi.org/10.1186/s13293-025-00767-8

Image Credits: AI Generated

DOI: 10.1186/s13293-025-00767-8

Keywords: maternal obesity, liver transcriptomes, H3K9me3, sexual maturity, epigenetics, metabolic health, sex differences.