Endoplasmic reticulum stress and steroidogenic dysfunction in Leydig cells: Molecular mechanisms of UPR-mediated testosterone regulation.

This review aims to synthesize current evidence on how endoplasmic reticulum (ER) stress affects steroidogenic function in Leydig cells. It explores the mechanisms by which ER stress activates the unfolded protein response (UPR) and autophagy pathways, ultimately influencing testosterone production and cellular homeostasis. The central research question addresses how ER stress-induced signaling modulates the transcriptional regulation of key steroidogenic enzymes and contributes to age-related declines in androgen synthesis. A comprehensive literature review was conducted using recent findings from molecular, cellular, and animal studies focusing on ER stress signaling in Leydig cells. Studies examining the roles of UPR branches (PERK, IRE1, and ATF6), autophagy pathways, and pharmacological or natural compounds modulating ER stress were analyzed to identify the regulatory mechanisms being involved and potential therapeutic implications. Evidence indicates that unresolved ER stress impairs testosterone biosynthesis by suppressing the expression of genes related to steroidogenesis. Specifically, activations of XBP1, ATF4 and ATF6, as well as their nuclear translocations, may lead to the transcriptional repression of these genes. Conversely, pharmacological ER stress inhibitors and natural antioxidants may restore these protein levels, enhance testosterone production, and improve Leydig cell function. A thorough understanding of the UPR and autophagy in Leydig cells is critical for addressing male reproductive health. ER stress is established as a key factor in the pathophysiology of impaired steroidogenesis. Therefore, targeting these stress response pathways presents a promising strategy for developing novel therapeutic interventions for testosterone deficiency and associated reproductive disorders.