Mechanical signal-mediated mitochondria-endoplasmic reticulum contacts modulate Leydig cell testosterone biosynthesis during testis development.

In males, 95% of testosterone is synthesized by Leydig cells, and a deficiency in this synthesis will cause metabolic disorders and multiple organ dysfunction. Testosterone deficiency is not only affected by aged or diseased Leydig cells, which have been studied extensively, but is also closely related to the development of the testis. At present, the focus on the mechanism of testis development includes epigenetic and hormone regulation. However, testicular development is constrained by the external tough tunica albuginea, suggesting that mechanical signals may also play an important role in the regulation of testis development; however, this is not yet well understood. In this in vitro study, we found that a gradual increase in extracellular substrate stiffness for testis development leads to the activation of mechanical signals to promote cytoskeleton remodeling. Eventually, the mechanical signal mediates changes in the mitochondrial-endoplasmic reticulum and affects the synthesis of testosterone in Leydig cells. Through organoid and animal experiments, we found that targeting mechanical signaling pathways that regulate testosterone biosynthesis is feasible. This provides a new angle for further exploration of testis development and new insights into how substrate stiffness affects the testis, raising new clues for clinical applications.