Molecular Mechanisms Of Male Infertility In Transgenic Male Mice Overexpressing Aromatase (Cyp19a1)

Male infertility refers to a male’s inability to cause pregnancy in a fertility female after one year of unprotected intercourse. Male infertility accounts for almost40%-50%infertility cases. A numerous clinical studies have demonstrated that the balance between testosterone and estrogen is critical for the development of male infertility. A subset of infertility men exhibits reduced testosterone (T) and elevated levels of estradiol (E2). Although there are some advances in the studies of male infertility, the underlying etiology of the higher prevalence of male infertility with hormone remains poorly understood due to the lacking of good animal models which can mimic the pathology of male infertility. We used a transgenic male mouse model overexpressing human aromtase in the background of C57BL/6J (AROM+/6J) to investigate the molecular mechanisms of male infertility due to the imbalance of E2/T ratio.The imbalance of E2/T ratio was observed in AROM+/6J male mice with testes atrophy and male infertility. The immunohistochemical analysis PCNA and the whole testis Leydig cells (LCs) count showed that much more LCs were observed in2-month and5-month-old AROM+/6J male mice than WT mice, and testis macrophages activation were observed while the number of LCs shapely decreased at10-month-old AROM+/6J mice due to the engulfment by macrophage. LCs could produce testosterone, the depletion of testosterone-producing LCs by macrophage resulted in disrupted spermatogenesis, thereby leading to male infertility. The number of LCs, compared to WT, was found to be recovered in AROM+/6J male mice after ERα knockout by crossbred with ERa knockout mice, and macrophage inactivation. Meanwhile, the AROM+/6J male mice, treated by letrozole (aromatase inhibitor) or tamoxifen (ERα inhibitor), showed similar testis phenotype compared to WT. The results suggest that estrogen could induce LCs proliferation and macrophage activation though ERα signaling, and the activated macrophages engulf the living LC caused male infertility.Futhermore, E2/ERα signaling increases viable LCs soluble GAS6production, intracellular Ca2+and PLSCRs expression, which in turn induces PS exposure independent of apoptosis. GAS6is anchored on the surface of LCs by binding to the exposed PS and serves as an engulfment signal mainly for AXL on E2-activated macrophages. Moreover, by aliving cell imaging system, we confirmed the phagocytosis of LCs by testicular macrophages. We found that the expression CYP19, GAS6and TNFα were up-regulated in non-obstructive azoospermia (NOA) compared to obstructive azoospermia (OA) similar to AROM+/6J male mice. Significantly elevated serum E2and GAS6levels, decreased T levels and an increased E2/T ratio were found in NOA infertile subjects compared to normal healthy Chinese men, which confirmed the date from the mice.Taken together, E2/ERα signaling promotes macrophage activation and LCs proliferation, the activated macrophages engulf the living LCs. Further raise GAS6as a potential novel clinical marker for male infertility.