Branched chain amino acid sufficiency is necessary for proper luteinizing hormone response and testosterone synthesis.

Testosterone production by testicular Leydig cells (steroidogenesis) is vital to male fertility and overall male health. Information about how nutrition influences Leydig cell steroidogenesis is lacking. Branched chain amino acids (BCAAs - leucine, isoleucine, and valine) are essential amino acids and important regulators of protein synthesis and energy production. Circulating and tissue BCAA levels are tightly regulated by the enzyme branched chain a-keto acid dehydrogenase kinase (BCKDK), which inhibits their catabolism. This work explored how BCAAs, and especially leucine, modulate male fertility and testosterone production. In a mutant mouse model of Bckdk, breeding analysis showed reduced male fertility and circulating testosterone. Further, morphological evaluation demonstrated testicular and epididymal abnormalities consistent with abnormal testicular androgen signaling. Fertility was partially rescued by feeding a high protein diet while circulating testosterone was not. In wild type testes, Leydig cells were the primary cell type to express BCKDK. Leveraging a primary interstitial cell culture, cell survival and apoptosis analyses demonstrated Leydig cells are highly sensitive to leucine deprivation and this sensitivity is enhanced under steroidogenesis stimulating conditions. Lastly, using the same primary cell culture system, testosterone production was shown to be lost under leucine deprivation. In total, this work demonstrates Leydig cells are uniquely sensitive to BCAA status under steroidogenesis stimulation and that regulated BCAA catabolism may be important for optimal male fertility.