HDACs are enzymes found in virtually all eukaryotic cells. Their principal job is to remove acetyl chemical groups from histones, the spool-like proteins around which DNA is wound. When histones are heavily acetylated, chromatin is loose and genes can be read; when HDACs strip those acetyl groups away, chromatin condenses and gene transcription is silenced. The enzymes also modify non-histone proteins, influencing protein stability and activity directly. Based on their similarity to yeast proteins, HDACs are sorted into four classes: Classes I, II, and IV are zinc-dependent enzymes, while Class III, the sirtuins, depend on the metabolic cofactor NAD+. Class I members HDAC1, 2, 3, and 8 operate within multiprotein complexes and have been linked to cancer, inflammation, and infection. Class II enzymes shuttle between nucleus and cytoplasm, with HDAC6 in particular targeting non-histone substrates such as alpha-tubulin and molecular chaperones, thereby regulating autophagy and cellular architecture.

What the new review makes clear is that HDAC family members are not uniformly disrupted in endometriosis; instead, each subtype follows its own pattern, and those patterns appear to map onto different stages and features of disease. HDAC1 is broadly upregulated. Studies of endometriotic stromal cell lines show elevated HDAC1 mRNA and protein compared with normal cells, and immunohistochemistry of human lesions reveals strong staining in ovarian, skin, and gastrointestinal implants, with ovarian lesions showing the highest levels. Experiments with exosomes derived from ovarian endometrioma tissue found that the long non-coding RNA HOTAIR upregulates HDAC1 by suppressing microRNA-761, and that these exosomes promote ectopic lesion growth in mice. Genetic work has even linked HDAC1 single nucleotide polymorphisms to endometriosis risk in South Indian women, and in mouse models HDAC1 staining intensity rises as lesions progress. In deep infiltrating endometriosis, the most aggressive form, HDAC1 levels correlate positively with the degree of fibrosis.

HDAC2 tells a more complicated story. Its expression is elevated in some cell models and in skin lesions and eutopic endometrial stroma, yet lower in ovarian and peritoneal implants, and one study found HDAC2 staining actually declines as mouse lesions progress while being significantly lower in deep infiltrating disease than in ovarian endometrioma. Functionally, however, silencing HDAC2 in endometriotic cells activates the HNF4A/ARID1A axis, curbing proliferation and invasion while promoting apoptosis, and reduces lesion size in animals. HDAC3, by contrast, is downregulated, particularly in women with infertility. In baboon models of the disease, HDAC3 expression falls as disease advances, and mice lacking HDAC3 specifically in the uterus show implantation failure and defective decidualization, tied to de-repression of collagen genes and impaired progesterone signaling. HDAC8, meanwhile, is upregulated and strongly linked to fibrosis: a specific HDAC8 activator accelerated lesion growth and scarring in mice, while the inhibitor PCI-34,051 dose-dependently suppressed lesions, eased fibrosis, and reduced pain.

Among the Class II and III enzymes, HDAC6 stands out for its dependence on lesion subtype and cellular context. A tissue microarray analysis of 168 endometriotic lesions confirmed that HDAC6 is significantly elevated in both epithelium and stroma of deep infiltrating disease and positively correlated with fibrosis, but unchanged in ovarian endometrioma. In cases lacking ARID1A expression, epithelial HDAC6 was higher still, suggesting a possible route toward malignant transformation. On the sirtuin side, SIRT1 is persistently expressed throughout the menstrual cycle in patients, whereas in healthy endometrium it appears only during menstruation. Mice engineered to overexpress Sirt1 in the uterus show implantation failure and downregulation of progesterone target genes, and the SIRT1/BCL6 axis has been implicated in the progesterone resistance that characterizes the disease. SIRT3, which governs mitochondrial energy metabolism and antioxidant defense, is reduced in ovarian endometrioma tissue, while SIRT7 is upregulated in ectopic lesions and drives a metabolic shift from mitochondrial respiration toward glycolysis through the TUFM/SIRT7 axis, promoting proliferation and lesion growth in mice.

These expression anomalies feed into five interconnected pathological pathways. HDACs promote transcription of pro-inflammatory cytokines such as TNF-alpha, IL-1 beta, and IL-6, and weaken immune surveillance that would otherwise clear ectopic cells; exosomal miR-22-3p from peritoneal macrophages, for example, suppresses SIRT1 and activates the pro-invasive NF-kappaB pathway. HDAC1 and HDAC2 silence cyclin-dependent kinase inhibitors such as p21 and p57, pushing cells through the G1/S checkpoint, while SIRT1 upregulation is linked to reduced p53-mediated apoptosis. Invasion and migration are enhanced through epithelial-mesenchymal transition: HDAC1 suppresses RHOB, HDAC2 modulates the HNF4A/ARID1A axis, and HDAC6 remodels the cytoskeleton via alpha-tubulin deacetylation. HDAC1 also activates STAT3 to promote angiogenesis, and under hypoxia HDACs bind HIF-1 to drive adhesion, proliferation, and vessel-forming genes. Finally, HDACs regulate aromatase and estrogen receptor alpha, boosting local estrogen, and mediate epigenetic silencing of progesterone receptor B, the molecular basis of progesterone resistance.

The therapeutic logic follows directly. Histone deacetylase inhibitors, already established as anti-cancer drugs, can restore acetylation and reactivate silenced genes, and because epigenetic modifications are reversible, a single inhibitor can theoretically correct multiple pathological programs at once. Preclinical evidence is accumulating rapidly. Vorinostat, or SAHA, upregulated thioredoxin-binding protein-2 in endometrial stromal cells and promoted apoptosis through the TRX/TBP-2 system; in a mouse model of endometriosis-associated ovarian cancer it reduced tumor volume by inhibiting M2 macrophage polarization and lowering IL-10. Romidepsin, a Class I-specific inhibitor, inhibited HDAC activity in endometriotic epithelial cells with an IC50 of 6.5 nanomolar, induced histone acetylation, upregulated p21, and triggered caspase-dependent apoptosis. Trichostatin A reduced lesion area by 54.3 percent and relieved hyperalgesia in mice, suppressed NF-kappaB activation in endometriotic cells, which proved more than ten times more sensitive than normal cells, and induced apoptosis via NAG-1 in primary stromal cells.

Perhaps the most unexpected player is butyrate, a short-chain fatty acid produced by gut bacteria. Mouse studies showed endometriosis depletes butyrate-producing microbiota and colonic butyrate levels; fecal microbiota transfer confirmed that stool from diseased mice promotes lesion growth while normal stool inhibits it. Mechanistically, butyrate suppresses endometrial cell proliferation by activating GPR43 and GPR109A, inhibiting HDAC activity, and upregulating RAP1GAP, and it enhances ferroptosis sensitivity of ectopic cells through the FFAR2/PPAR-gamma/PINK1/Parkin axis. Serum butyrate in patients is reduced and inversely correlated with disease stage. Valproic acid, a widely used antiepileptic, also inhibits HDACs: in rats it dose-dependently shrank lesions and eased pain, and in human cells it silenced the CYP19 aromatase promoter, cutting estrogen synthesis, while reactivating the tumor suppressor C/EBPalpha. Selective HDAC8 inhibition with PCI-34,051 in a deep infiltrating disease model cut lesion weight by nearly two-thirds, reduced fibrosis, and relieved pain, hinting that subtype-selective drugs could avoid the off-target toxicity of pan-inhibitors.

Formidable obstacles remain before any of this reaches the clinic. No HDAC inhibitor is approved for endometriosis, and the known safety profile from oncology, including myelosuppression, thrombocytopenia, gastrointestinal symptoms, fatigue, and QT prolongation, is a serious concern for long-term use in benign disease. Reproductive safety is the thorniest issue: HDACs regulate gametogenesis, follicular development, implantation, and endometrial receptivity. Valproic acid carries a well-documented teratogenic risk of roughly 10 percent congenital malformation rate with pregnancy exposure, and embryonic exposure to butyrate or valproate can impair primordial germ cell development in mice. The review’s authors therefore call for subtype-selective inhibitors guided by single-cell expression maps, lesion-targeted delivery systems such as nanoparticles or exosomes to limit systemic exposure, combination strategies with hormonal, anti-inflammatory, or anti-angiogenic drugs, and biomarkers such as histone H3 acetylation states and circulating exosomal non-coding RNAs to stratify patients. If those pieces come together, epigenetic therapy could open the first genuinely new front against endometriosis in decades.

Subject of Research: The role of histone deacetylases and their inhibitors in the pathogenesis and treatment of endometriosis

Article Title: Research Progress of Histone Deacetylase and Its Inhibitors in Endometriosis

Article References: Xiong, S., Xu, J., Pu, J., Zhao, S., & Jiang, L. (2026). Research Progress of Histone Deacetylase and Its Inhibitors in Endometriosis. Reproductive Sciences. https://doi.org/10.1007/s43032-026-02184-7

Image Credits: AI Generated

DOI: 10.1007/s43032-026-02184-7

Keywords: endometriosis, histone deacetylase, HDAC inhibitors, epigenetics, vorinostat, romidepsin, trichostatin A, butyrate, valproic acid, fibrosis, progesterone resistance, reproductive health

Valproic acid has long occupied an uncomfortable place in medicine. It is effective against seizures and certain psychiatric conditions, yet epidemiological studies have repeatedly associated prenatal exposure with an elevated likelihood of autism-related developmental impairments in children. Laboratory models built on embryonic valproate exposure reproduce core features of these outcomes, giving researchers a controlled window into how an environmental risk factor can reshape neural circuits. What has remained murky is the cellular mechanism, and in particular whether males and females differ in their vulnerability, since autism is diagnosed far more often in boys than in girls for reasons that are still poorly understood.

The new work, published in the journal Biology of Sex Differences, tackled both questions at once. The team exposed C57BL/6 mice to valproic acid either at embryonic day 12.5, a critical window of neural development, or at postnatal day 14, and then examined the animals during adolescence, a stage when social behavior and executive circuits are still maturing. Using the three-chamber social interaction test, the gold-standard assay for sociability in rodents, and the open field test for anxiety-like and exploratory behavior, the researchers found that both male and female offspring exposed to valproate showed reduced social preference and heightened anxiety. But the deficits were more pronounced in males, particularly on measures of sociability and social preference.

Behavioral changes alone do not reveal what is happening inside the brain, so the team turned to the microscope and the biochemistry bench. Histological staining with hematoxylin-eosin and Nissl methods revealed variable degrees of neuronal abnormality across three regions, the medial prefrontal cortex, the hippocampus, and the striatum. All three are implicated in social behavior, emotion, and reward processing, but the medial prefrontal cortex stood out as the most visibly damaged, with alterations appearing in both male and female offspring. The mPFC sits at the top of networks governing social decision-making and emotional regulation, so structural compromise there is a plausible substrate for the behavioral phenotype.

The deeper story emerged when the researchers probed ferroptosis, an iron-dependent form of regulated cell death defined by the accumulation of lipid peroxides in cell membranes. Unlike apoptosis, ferroptosis is driven by oxidative damage: when the lipid-repair enzyme glutathione peroxidase 4, or GPX4, is overwhelmed or depleted, lipid peroxides build up, membranes rupture, and cells die in a way that can spread inflammation through surrounding tissue. Biochemical assays in the exposed animals showed shifts in the classic ferroptosis indicators, including reactive oxygen species, malondialdehyde, a marker of lipid peroxidation, glutathione, the principal cellular antioxidant, and superoxide dismutase. Western blotting and immunofluorescence added molecular detail involving ferroptosis regulators such as ACSL4, an enzyme that tags fatty acids for peroxidation, and ferritin heavy chain 1, the iron-storage protein FTH1.

Transmission electron microscopy provided some of the most striking evidence. In the medial prefrontal cortex of valproate-exposed offspring, mitochondria, the organelles whose shrinkage and membrane damage are hallmarks of ferroptotic death, displayed characteristic abnormalities alongside vacuolization within the tissue. These ultrastructural signatures, combined with the biochemical shifts, indicated that ferroptosis-related processes were most evident precisely in the region that also carried the heaviest histological burden. Critically, the ferroptosis-related molecular changes followed a clear sex-differentiated pattern: the alterations were more pronounced in males than in females, mirroring the asymmetry in behavioral deficits and offering a candidate mechanism for the male-skewed vulnerability seen in autism epidemiology.

The study also asked whether timing matters. In a second cohort, male mice were exposed to valproic acid during early postnatal life rather than before birth, and the outcomes were compared with the prenatal group. Both exposure windows produced similar patterns of behavioral abnormality and similar ferroptosis-related molecular changes in the medial prefrontal cortex. That convergence is significant because it suggests ferroptosis-associated alterations are not a peculiarity of one developmental moment but may represent a shared molecular feature of valproate-induced neurodevelopmental disruption across distinct windows of vulnerability. For researchers trying to model autism risk in animals, that consistency strengthens the argument that iron-linked oxidative cell death is a meaningful convergent pathway rather than an incidental finding.

The findings place ferroptosis in a growing cast of cellular mechanisms implicated in autism spectrum disorder, alongside synaptic miswiring, immune signaling, and mitochondrial dysfunction. Ferroptosis has been studied most intensively in neurodegeneration, where vulnerable neurons in Parkinson’s and Alzheimer’s disease show lipid-peroxidation damage, so finding a ferroptosis signature in a neurodevelopmental model extends the concept into the prenatal and adolescent periods. It also offers a testable intervention target: ferroptosis can be chemically suppressed with agents that bolster GPX4 activity or scavenge lipid peroxides, and if the same pathway operates in humans, protecting the adolescent or prenatal prefrontal cortex from ferroptotic stress becomes a concrete therapeutic hypothesis.

The authors, led by Shatong Zhao and corresponding authors Jiangshan Li and Xiang Feng, are careful about the limits of inference. The work was conducted in mice, and behavioral assays such as the three-chamber test capture only a slice of the social phenomena relevant to human autism. Nor does the study establish that ferroptosis causes the behavioral deficits; it demonstrates a robust association, regionally specific and sex-dependent, that co-occurs with neuronal abnormality and mitochondrial damage. Distinguishing causation from correlation will require interventions that block ferroptosis and test whether the behavioral phenotype softens, as well as human tissue studies to confirm the pathway operates in people exposed to valproate in utero.

Even so, the study lands at a moment of intense interest in the biology of sex differences in the brain. If males sustain greater ferroptosis-related damage in the medial prefrontal cortex after an identical exposure, that asymmetry could help explain why autism diagnoses cluster in boys and could guide sex-stratified approaches to prevention and treatment. It also adds urgency to clinical guidance around valproic acid, which is already contraindicated in pregnancy in many jurisdictions for epilepsy and bipolar disorder. For the researchers, the next steps are clear: pin down why male brains are more susceptible to lipid-peroxidation injury during development, and determine whether shielding the medial prefrontal cortex from ferroptosis can preserve the social circuits that valproate exposure appears to erode.

Subject of Research: Sex differences in ferroptosis-related vulnerability to autism-like deficits in the adolescent mouse medial prefrontal cortex following prenatal valproic acid exposure

Article Title: Sex differences in ferroptosis-related vulnerability to autism-like deficits in the adolescent medial prefrontal cortex following embryonic valproic acid exposure

Article References: Zhao, S., Wang, J., Pan, Y., Yang, Y., Yin, Y., Li, W., Li, J., & Feng, X. (2026). Sex differences in ferroptosis-related vulnerability to autism-like deficits in the adolescent medial prefrontal cortex following embryonic valproic acid exposure. Biology of Sex Differences. https://doi.org/10.1186/s13293-026-00982-x

Image Credits: AI Generated

DOI: 10.1186/s13293-026-00982-x

Keywords: autism spectrum disorder, valproic acid, ferroptosis, sex differences, medial prefrontal cortex, neurodevelopment, GPX4, lipid peroxidation, mitochondria, prenatal exposure, mice, social behavior