SAT-145 MTP Restricts Steroidogenesis in Leydig Cells by Regulating Srebp2

Abstract Disclosure: A. Chattopadhyay: None. M. Tirumalasetty: None. P. Thomas: None. M. Qing: None. M. Hussain: None. Reduced serum testosterone or hypogonadism affects almost 20-50% of men and is linked to several metabolic and physiological disorders including reduced bone density, muscle mass, obesity, CVD and sexual functions. Because of the negative feedback regulation of testosterone production by Leydig cells, exogenous testosterone administration may not be a suitable way to treat hypogonadism without affecting fertility. One approach may be to elevate intratesticular and serum testosterone by stimulating steroidogenesis in Leydig cell. Microsomal triglyceride protein (MTP) is a lipid-transfer protein, primarily expressed in the liver and intestine and is critical for the transport of lipids via apoB-containing lipoprotein assembly and secretion. In addition, MTP has been shown to support maturation of CD1 proteins in NKT cells and to regulate ATGL activity in adipocytes. MTP mRNA has been reported in the testis, but its role is unknown. Here, we report for the first time that MTP protein is in the Leydig cells of human and mouse testes and plays a regulatory role in cholesterol and sex hormone production. Inhibition of the MTP activity by lomitapide and sgRNA mediated knockdown significantly increased progesterone secretion in mouse Leydig MA10 cells after stimulation with cyclic AMP. Furthermore, MTP-deficient MA10 cell lines generated using CRISPR-cas9 showed significantly increased steroidogenesis. Molecular studies revealed that MTP enhanced the expression of genes in cholesterol biosynthesis, uptake and intracellular transport. Moreover, it upregulated the Lhcgr signaling, both ERK1/2 and PKA phosphorylation, as well as the expression of genes in the biosynthesis of steroids. Transcriptome analysis confirmed increased expression of cholesterol and steroid biosynthesis pathways in MTP deficient clones. To understand how MTP deficiency increases expression of genes in cholesterol and steroid biosynthesis, we looked for changes in transcription factors. Both RNA sequencing and qPCR studies showed that MTP deficiency enhances the expression of Srebp2. Furthermore, cholesterol and steroid synthesis pathways were significantly attenuated by knockdown of Srebp2 in MTP-deficient cells to the levels seen in wildtype cells. In short, these studies identify a negative regulatory role of MTP in steroidogenesis and show that MTP regulates steroidogenesis in Leydig cells by modulating the expression and activity of Srebp2. Inhibition of testicular MTP might be useful to treat hypogonadism in some patients. Presentation: Saturday, July 12, 2025