Mechanistic Insights into Targeting APLN/APJ for Ameliorating Testosterone and Reproductive Disorders in Type 2 Diabetes (CUT&Tag)

About 10% of couples of reproductive age worldwide suffer from infertility, with male factors accounting for about 50%, and testosterone is essential for male fertility, but the mechanisms behind the poor sperm quality and abnormally low blood testosterone levels in diabetic patients are unclear. In this study, we found that the peptide Apelin (APLN) significantly inhibited testosterone secretion from Leydig cells (LCs), which in turn led to decreased sperm quality. APLN was found to be localized to leydig cells in the testes of several diabetic mice, and its expression was significantly increased. The addition of APLN to mouse leydig cells decreased testosterone content and decreased the expression of genes related to testosterone synthesis, but the addition of ML221, an APLN receptor inhibitor, significantly increased the expression of testosterone synthesis genes. Injecting ML221 into diabetic mice significantly increased testosterone levels in the blood, increased sperm count as well as enhanced sperm motility and ultimately increased live birth rate of mice after in vitro fertilization. Proteomics revealed that ML221 significantly increased the expression of NR2F2 and further activated the transcription of testosterone synthesis genes. This study will further use mouse and cellular models to completely unravel the specific mechanisms by which APLN inhibits testosterone secretion and elucidate the causes of decreased sperm quality in diabetic patients. This study provides a new clinical target for the development of drugs to improve fertility in diabetic patients.