Obesity is a major risk factor for male infertility, yet the molecular mechanisms linking obesity to impaired spermatogenesis remain poorly defined. Here we show that C1q/TNF-related protein 6 (CTRP6) is a Leydig cell–derived regulator of testosterone production whose local expression is reduced in obesity. High-fat diet (HFD) feeding selectively reduced CTRP6 expression and secretion in Leydig cells despite elevated circulating CTRP6 levels, indicating tissue-specific dysregulation within the testicular microenvironment. Leydig cell–specific CTRP6 overexpression markedly alleviated HFD-induced testicular atrophy, restored seminiferous tubule architecture, improved sperm parameters and reproductive outcomes, and rescued testosterone production. Conversely, Leydig cell–specific CTRP6 knockout impaired spermatogenesis and reduced male reproductive capacity under normal-diet conditions, supporting an important role for endogenous CTRP6 in reproductive homeostasis. The combined secretion, genetic and extracellular-protein experiments are consistent with an autocrine contribution. Transcriptomic analyses identified CYP51A1 as a candidate downstream mediator. CTRP6 associated with adiponectin receptor 1 (AdipoR1), and AdipoR1 knockdown attenuated rhCTRP6-associated changes in PI3K/Akt phosphorylation, SREBP2 and CYP51A1 abundance, cholesterol content and testosterone production. Notably, intratesticular administration of recombinant human CTRP6 (rhCTRP6) effectively rescued HFD-induced spermatogenic dysfunction in vivo. Together, these findings uncover a previously unrecognized local Leydig cell–derived CTRP6 signaling model linking obesity to male reproductive dysfunction.
