TGFB1 and polycystic ovary syndrome: To summarize, IR in PCOS can be caused by serine phosphorylation of the cytochrome p450 17ɑ-hydroxylase enzyme involved in androgen synthesis, TNF-ɑ inhibition of tyrosine kinase function of the insulin receptor, a mutation in MTNR1B, insufficient vitamin D, and a decrease in NO and an increase in endothelin 1 resulting in vasoconstriction through TGFβ.