Transmission of Polycystic Ovary Syndrome via Epigenetic Inheritance
Authors: Elisabet Stener-Victorin, Qiaolin Deng
Journal: Trends in Molecular Medicine (2021)

A recent study by Mimouni et al. shows that late gestation exposure to anti-Müllerian hormone (AMH) results in transgenerational transmission of a polycystic ovary syndrome (PCOS)-like phenotype in mice. Altered DNA methylation underlies transmission and was also observed in women with PCOS. Epigenetics-based therapy reversed some PCOS-like phenotypic traits when applied to F3 female mice. A recent study by Mimouni et al. shows that late gestation exposure to anti-Müllerian hormone (AMH) results in transgenerational transmission of a polycystic ovary syndrome (PCOS)-like phenotype in mice. Altered DNA methylation underlies transmission and was also observed in women with PCOS. Epigenetics-based therapy reversed some PCOS-like phenotypic traits when applied to F3 female mice. PCOS is the leading cause of female infertility and is associated with a high degree of comorbidities, including type 2 diabetes, psychiatric disorders, and endometrial cancer [1.Dumesic D.A. et al.Scientific statement on the diagnostic criteria, epidemiology, pathophysiology, and molecular genetics of polycystic ovary syndrome.Endocr. Rev. 2015; 36: 487-525Crossref PubMed Scopus (385) Google Scholar]. Worldwide, ~15% of women suffer from PCOS, leading to an annual multibillion Euro healthcare burden. Current management of PCOS is ad hoc and symptomatic, hindered by lack of insight into the origin and underlying mechanisms. Accumulating evidence has shown that PCOS runs in families, with an estimated heritability of 70% [1.Dumesic D.A. et al.Scientific statement on the diagnostic criteria, epidemiology, pathophysiology, and molecular genetics of polycystic ovary syndrome.Endocr. Rev. 2015; 36: 487-525Crossref PubMed Scopus (385) Google Scholar]. A register-based study of nearly 30 000 daughters of women with or without PCOS also found that daughters of women with PCOS have a fivefold increased risk of being diagnosed with the syndrome [2.Risal S. et al.Prenatal androgen exposure and transgenerational susceptibility to polycystic ovary syndrome.Nat. Med. 2019; 25: 1894-1904Crossref PubMed Scopus (60) Google Scholar]. However, how PCOS is inherited is unclear. Although family-based whole-genome sequencing studies have linked genetic variants involved in androgen biosynthesis and the actions of AMH with PCOS [3.Dapas M. et al.Distinct subtypes of polycystic ovary syndrome with novel genetic associations: an unsupervised, phenotypic clustering analysis.PLoS Med. 2020; 17e1003132Crossref PubMed Scopus (28) Google Scholar], the 19 PCOS risk loci identified by genome-wide association studies account for only 10% of the heritability [1.Dumesic D.A. et al.Scientific statement on the diagnostic criteria, epidemiology, pathophysiology, and molecular genetics of polycystic ovary syndrome.Endocr. Rev. 2015; 36: 487-525Crossref PubMed Scopus (385) Google Scholar]. Growing evidence suggests that nongenetic mechanisms such as developmental programming and epigenetic modification contribute significantly to the inheritance of PCOS. The hypothesis of Barker proposes that early adaptations to suboptimal conditions in utero translate into adverse health states later in life, laying the ground for the 'developmental origins of health and disease' (DOHaD) concept [4.Barker D.J. The origins of the developmental origins theory.J. Intern. Med. 2007; 261: 412-417Crossref PubMed Scopus (1460) Google Scholar]. Women with PCOS have abnormally high levels of circulating androgens and AMH throughout pregnancy which diminish placental aromatase activity [5.Piltonen T.T. et al.Circulating antimullerian hormone and steroid hormone levels remain high in pregnant women with polycystic ovary syndrome at term.Fertil. Steril. 2019; 111: 588-596Abstract Full Text Full Text PDF PubMed Scopus (23) Google Scholar,6.Maliqueo M. et al.Placental STAT3 signaling is activated in women with polycystic ovary syndrome.Hum. Reprod. 2015; 30: 692-700Crossref PubMed Scopus (40) Google Scholar], thereby further increasing the supply of androgen to the fetus. Prenatal androgen exposure (PNA), independently of diet-induced obesity, can result in transgenerational transmission of PCOS-like reproductive and metabolic traits [2.Risal S. et al.Prenatal androgen exposure and transgenerational susceptibility to polycystic ovary syndrome.Nat. Med. 2019; 25: 1894-1904Crossref PubMed Scopus (60) Google Scholar]. Transcriptional and mitochondrial disruption of oocytes accompanies this transmission, implying nongenetic inheritance of the syndrome [2.Risal S. et al.Prenatal androgen exposure and transgenerational susceptibility to polycystic ovary syndrome.Nat. Med. 2019; 25: 1894-1904Crossref PubMed Scopus (60) Google Scholar]. Importantly, several oocyte gene signatures identified by single-cell RNA sequencing were also detectable in serum from daughters of women with PCOS, as well as in serum and adipose tissue of unrelated women with PCOS. Mimouni et al. used the prenatal AMH (PAMH) mouse model [7.Tata B. et al.Elevated prenatal anti-Müllerian hormone reprograms the fetus and induces polycystic ovary syndrome in adulthood.Nat. Med. 2018; 24: 834-846Crossref PubMed Scopus (157) Google Scholar,8.Stener-Victorin E. et al.Animal models to understand the etiology and pathophysiology of polycystic ovary syndrome.Endocr. Rev. 2020; 41: 538-576Crossref Scopus (55) Google Scholar] to investigate PCOS transmission [9.Mimouni N.E.H. et al.Polycystic ovary syndrome is transmitted via a transgenerational epigenetic process.Cell Metab. 2021; 33: 513-530Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar]. They demonstrated that several PCOS-like traits, in compliance with the Rotterdam criteria, and PCOS-associated metabolic disturbances are transgenerationally passed on to daughters (F1), granddaughters (F2), and even great-granddaughters (F3) of exposed mothers (F0) [9.Mimouni N.E.H. et al.Polycystic ovary syndrome is transmitted via a transgenerational epigenetic process.Cell Metab. 2021; 33: 513-530Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar]. However, comparison between F3 control and F3 PAMH mice to ensure transgenerational transmission of phenotypes was lacking. Previously, Risal et al. reported that metabolic dysfunction in F3 female offspring was already present at 3 months of age, including increased fat mass and enlarged adipocytes which are strongly linked to insulin resistance, elevated liver triglyceride content and lipid droplets, and lower energy expenditure and respiratory exchange ratio [2.Risal S. et al.Prenatal androgen exposure and transgenerational susceptibility to polycystic ovary syndrome.Nat. Med. 2019; 25: 1894-1904Crossref PubMed Scopus (60) Google Scholar,8.Stener-Victorin E. et al.Animal models to understand the etiology and pathophysiology of polycystic ovary syndrome.Endocr. Rev. 2020; 41: 538-576Crossref Scopus (55) Google Scholar]. In the study by Mimouni et al. the onset of metabolic alterations, namely higher body weight, increased fat mass and lower lean mass, and elevated fasting glucose, first appeared at 6 months of age. Notably, the F1 PAMH female offspring had hypertrophic islets of Langerhans, resulting in increased insulin levels after 12 h of fasting, and this was transgenerationally transmitted to F3 offspring [9.Mimouni N.E.H. et al.Polycystic ovary syndrome is transmitted via a transgenerational epigenetic process.Cell Metab. 2021; 33: 513-530Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar]. All these findings suggest that developmental programming and germline moderation are involved in the transmission of PCOS-like traits across multiple generations, but the studies have some caveats. Transgenerational inheritance requires that the effects of environmental exposure during gestation are still present in the F3 generation, the first generation that is not directly exposed to the uterine environment, and thus inherits the phenotype via germline moderation. Moreover, a parallel control group is always required – namely the breeding of naïve female with naïve males following each generation to compare with the treatment group so as to exclude batch effects. The study by Risal et al. included parallel breeding of the control group from F1 to F3 [2.Risal S. et al.Prenatal androgen exposure and transgenerational susceptibility to polycystic ovary syndrome.Nat. Med. 2019; 25: 1894-1904Crossref PubMed Scopus (60) Google Scholar], whereas Mimouni et al. compared F3 treatment with F1 control animals [9.Mimouni N.E.H. et al.Polycystic ovary syndrome is transmitted via a transgenerational epigenetic process.Cell Metab. 2021; 33: 513-530Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar]. Both studies indicate that transgenerational transmission of PCOS could be mediated through germ cells, but they are also confounded by the effects of the altered in utero environment from the F0 mother. To further advance these findings, future studies will need to disentangle whether the increased disease risk in subsequent generations is due to the intrauterine environment, or to modified germ cells per se, by the use of in vitro fertilization, embryo transfer, and foster mothers. Nonetheless, these findings strengthen the DOHaD hypothesis that an adverse maternal/fetal environment in PCOS has lasting effects on the health of future generations. Moreover, Mimouni et al. dissected possible molecular mechanisms that underlie the transmission of PCOS-like phenotypes to F3 by performing comparative RNA sequencing and methylated DNA immunoprecipitation combined with sequencing (MeDIP-seq) of whole ovaries from F1 control mice and F3 offspring of the AMH-exposed mother [9.Mimouni N.E.H. et al.Polycystic ovary syndrome is transmitted via a transgenerational epigenetic process.Cell Metab. 2021; 33: 513-530Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar]. Four of 102 differentially expressed genes were found to be directly regulated by differential methylation; these are implicated in Slit/Robo and Notch signaling, inhibition of cell proliferation, and inflammation. A total of 181 gene loci exhibited hypermethylation, in contrast to 866 gene loci with hypomethylation. Hypomethylated gene targets include Tet1, Uhrf1, Hdc, Cdkn1a, Sorbs2, and Robo1 in both mouse ovary and hypothalamus. Strikingly, four (TET1, ROBO1, CDKN1A, and HDC) of these candidate genes, together with two genes involved in the insulin pathway (IGFBPL1 and IRS4), were significantly hypomethylated in the blood of women with PCOS, and three (ROBO1, HDC, IGFBPL1) were significantly hypomethylated in the blood of daughters with PCOS compared with the control groups. These findings, together with those of Risal et al. [2.Risal S. et al.Prenatal androgen exposure and transgenerational susceptibility to polycystic ovary syndrome.Nat. Med. 2019; 25: 1894-1904Crossref PubMed Scopus (60) Google Scholar], indicate communication between ovaries, germ cells, and serum, and support the translational relevance of findings in mouse. The most remarkable and novel finding by Mimouni et al. is that treatment of F3 female offspring aged 6 months for 15 days with the universal methyl donor, S-adenosylmethionine (SAM), partially restored reproductive and metabolic traits. Although the methylation status of the targeted genes was not examined, the expression levels of several genes associated with inflammation, ovarian function, and insulin signaling, including some hypomethylated targets, were restored (albeit some not significantly) in ovary, visceral fat, and hypothalamus of PAMH F3 mice following 2 weeks of SAM treatment [9.Mimouni N.E.H. et al.Polycystic ovary syndrome is transmitted via a transgenerational epigenetic process.Cell Metab. 2021; 33: 513-530Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar]. Whether methyl donor supplementation can deliver specific treatment and potentially prevent transmission of PCOS-like traits in other mouse models remains to be investigated. Most importantly, it would be exciting to pursue such epigenetic therapy for the offspring of PCOS women. It is interesting to note that supplementation with a methyl donor – high-dose folate (5 mg daily by oral administration) – in obese adult women with PCOS improves their metabolic function and could hypothetically have positive effects on the health of their offspring [10.Asemi Z. et al.Metabolic response to folate supplementation in overweight women with polycystic ovary syndrome: a randomized double-blind placebo-controlled clinical trial.Mol. Nutr. Food Res. 2014; 58: 1465-1473Crossref PubMed Scopus (31) Google Scholar]. Although crucial questions remain (Box 1), the study by Mimouni et al. [9.Mimouni N.E.H. et al.Polycystic ovary syndrome is transmitted via a transgenerational epigenetic process.Cell Metab. 2021; 33: 513-530Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar] opens a path towards novel treatment strategies for PCOS-like phenotypic traits. Whether epigenetic therapy can prevent transmission of disease remains to be elucidated.Box 1Crucial Questions for Future Research(i)What are the key common and distinct downstream targets triggered by androgen and AMH pathways that drive PCOS transmission?(ii)Are the initial epigenetic modifications metastable or stable across generations?(iii)Can germ cells drive transgenerational transmission in the absence of initial fetal programming?(iv)Are both female and male offspring of PCOS women similarly affected in reproductive and metabolic traits?(v)Can rare genetic variants potentially predispose women (and men) to develop phenotypic changes triggered by adverse prenatal exposures? (i)What are the key common and distinct downstream targets triggered by androgen and AMH pathways that drive PCOS transmission?(ii)Are the initial epigenetic modifications metastable or stable across generations?(iii)Can germ cells drive transgenerational transmission in the absence of initial fetal programming?(iv)Are both female and male offspring of PCOS women similarly affected in reproductive and metabolic traits?(v)Can rare genetic variants potentially predispose women (and men) to develop phenotypic changes triggered by adverse prenatal exposures?