L-Kynurenine activates the AHR-PCSK9 pathway to mediate the lipid metabolic and ovarian dysfunction in polycystic ovary syndrome.

Dysregulated amino acid metabolism is a key contributor to polycystic ovary syndrome (PCOS). This cross-sectional study revealed that serum levels of L-kynurenine (L-Kyn) were significantly elevated in women with PCOS, whereas pyridoxal 5'-phosphate (PLP) levels were markedly reduced. Moreover, human serum L-Kyn levels exhibited a positive correlated with low-density lipoprotein cholesterol (LDL-C) and a negative correlation with high-density lipoprotein cholesterol (HDL-C). Additionally, letrozole (LET) induced PCOS-like mice displayed increased hepatic L-Kyn levels. Mechanistically, both in vivo and in vitro experiments demonstrated that the upregulation of indoleamine 2,3-dioxygenase (IDO1) activates the aryl hydrocarbon receptor (AHR) - proprotein convertase subtilisin/kexin type 9 (PCSK9) pathway in the liver of PCOS-like mice, thereby contributing to dyslipidemia. Treatment with epacadostat, an inhibitor of the enzyme IDO1, or PLP, a cofactor for L-Kyn catabolism, effectively restored ovarian function, improved glucose tolerance, and ameliorated lipid profile abnormalities in PCOS-like mice.