Microsomal triglyceride transfer protein restricts progesterone production in Leydig Cells by regulating SREBP2 activity [ATAC-Seq]

Reduced serum testosterone or hypogonadism diminishes bone density, muscle mass, and sexual functions and increases obesity and CVD. Microsomal triglyceride transfer protein (MTP) is a lipid-transfer protein, primarily expressed in the liver and intestine, and is critical for apoB-containing lipoprotein assembly and secretion. MTP mRNA has been reported in the testis, but its function is unknown. Here, we report that MTP protein is present in the Leydig cells of human and mouse testes and plays a regulatory role in cholesterol metabolism and sex hormone production. Inhibition of the MTP activity by a specific inhibitor, knockdown, and gene ablation significantly increased progesterone secretion in mouse Leydig MA10 cells after stimulation with cyclic AMP. Molecular studies revealed that MTP enhanced the expression of genes in the uptake of lipoproteins, and in the synthesis and intracellular trafficking of cholesterol. Moreover, it enhanced the Lhcgr signaling as well as the expression of genes in the biosynthesis of progesterone. 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. MTP deficiency enhanced the expression and activity of Srebp2. ATAC sequencing revealed enhanced binding of Srebp2 to the promoters of several enzymes in the biosynthesis of cholesterol and sex hormones. Furthermore, cholesterol and progesterone biosynthesis pathways were significantly attenuated after Srebp2 knockdown in MTP-deficient cells to the levels seen in wildtype cells. In short, these studies showed that MTP regulates cholesterol and steroid biosynthesis in Leydig cells by modulating the activity of Srebp2. Inhibition of testicular MTP might be useful to treat hypogonadism in some patients.