Genetic and Fetal Origins of Polycystic Ovary Syndrome

Abstract

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder that affects women of reproductive age. Although the syndrome affects over 10 percent women worldwide, its cause(s) remains unknown. Numerous studies have focussed on the genetic and fetal origins of the syndrome. However, the outcomes of genome wide association studies and candidate gene studies towards defining PCOS have, arguably, had almost no impact on the definition, diagnosis and treatment of the syndrome. This could be attributed mainly to the divergence of PCOS studies, as these studies have not collectively defined the molecular mechanisms involved in PCOS phenotypes observed. This thesis examined the role of genes in loci associated with PCOS and TGFβ signalling molecules, as well as their upstream regulators and mechanisms in the pathogenesis of PCOS. Genes in loci associated with PCOS (candidate genes) were shown to be dynamically expressed during bovine fetal ovary development. Notably, those genes expressed during the early stages of fetal development such as C8H9orf3, TOX3, FBN3, GATA4, HMGA2 and DENND1A are co-expressed with genes involved in mitochondria function and are regulated upstream by DAP3, MYC, PTEN, HNF4A, ESRRA/G, PSEN1, MYC, mitochondrial LONP1 and TP53. Those expressed in the second trimester or just after mid gestation such as YAP1, INSR, THADA and TGFB1I1 were co-expressed with genes involved in stroma expansion and are regulated upstream by TGF-β signalling molecules including TGFB1, TGFB2, TGFB3 and TGFBR2, coagulation factor II and fibroblast proliferation regulators including FGF2. Candidate genes expressed during the third trimester such as FDFT1, LHCGR, AMH, FSHR, ZBTB16 and PLGRKT are co-expressed with genes involved with folliculogenesis and steroidogenesis and are regulated upstream by SREBF2, INSIGI, TGFB1 and RPTOR among others. Thus, this study infers the possible role of these canonical pathways and upstream regulators in the pathogenesis of PCOS during fetal ovary development. The role of TGFB signalling molecules in the aetiology of PCOS was further examined. These molecules were also found to be dynamically expressed during fetal ovary development and could regulate some PCOS candidate genes in bovine fetal ovary fibroblasts. Across gestation, LTBP1/2/3/4, FBN1, TGFB2/3, TGFBR2/3 and TGFB1I1 expression levels increased, while FBN3, TGFBR3L, TGFBI and TGFB1 decreased and TGFBRAP1, TGFBR1 and FBN2 remained relatively constant. TGFβ1, but not androgens nor AMH, has previously been shown to inhibit expression of candidate genes (AR, INSR, C8H9orf3 and RAD50) but stimulate expression of androgen receptor co-factor, TGFB1I1, in cultured fetal ovarian fibroblasts. Additionally, we showed that expression of PCOS candidate genes ERBB3, NEIL2, IRF1 and ZBTB16 significantly decreased after TGFβ1 treatment in cultured fetal ovarian fibroblasts. These findings further confirm that TGFβ signalling could be involved in the pathogenesis of PCOS or at least in the establishment of polycystic ovaries. The role of candidate genes and TGFβ signalling molecules in various tissues including nonovarian tissues was assessed as PCOS does not only affect the ovary. Both were shown to be dynamically expressed in gonadal (ovary and testis), metabolic (heart, liver and kidney) and brain (brain and cerebellum) tissues during the first half of human fetal development and postnatally until adulthood. More so, some genes were significantly expressed in specific tissues at different time points pre-natally and/or post-natally. Notably, HMGA2, FBN3 and TOX3 were highly expressed during the early stages of fetal development in all tissues but least during adulthood. DENND1A, THADA, MAPRE1, RAB5B, ARL14EP, KRR1, NEIL2 and RAD50 were dynamically expressed in all postnatal tissues studied. Interestingly, correlation between expression of HMGA2/YAP1 and RAD50/YAP1 were significant in at least 5 of the 7 fetal tissues studied. Furthermore, HMGA2, YAP1 and RAD50 correlated significantly with most TGFβ signalling molecules in at least 4 tissues. We further showed that there is certainly a crosstalk within and between PCOS candidate genes and TGFβ signalling molecules during fetal development within each tissue. Considering the fact that HMGA2 and YAP1 are involved in the Hippo signalling pathway as well as epithelial mesenchymal transition (EMT) during embryogenesis through TGFβ signalling, their role in the aetiology of PCOS requires further studies. In conclusion, these findings confirm that genes in loci associated with PCOS and TGFβ signalling molecules are actively involved in the genetic and fetal origins of the syndrome and that there is a possible crosstalk between both in the development of multiple organs. This also infers that dysregulation of PCOS candidate genes and TGFβ signalling molecules during fetal development could initiate/lead to a cascade of molecular events in various tissues accounting for the various phenotypes of PCOS observed in adulthood.