Paternal BPA and BPS exposure induce testicular dysfunction in pubertal male offspring: roles of OCTN2 carnitine transporter disruption and exacerbated oxidative stress/apoptosis

Although numerous studies have reported the male reproductive toxicity of bisphenol A (BPA) and its substitute bisphenol S (BPS), the impacts of paternal exposure to these chemicals on the male reproductive system of offspring and the underlying molecular mechanism remain inadequately explored. In this study, we investigated male reproductive toxicity in pubertal offspring resulting from paternal exposure to environmentally relevant doses of BPA (0.45 μg/kg body weight [bw]/day) or BPS (0.15 μg/kg bw/day). Our results showed that paternal exposure to BPA or BPS reduced pubertal offspring testosterone levels and impaired testicular histomorphology and development. Concurrently, BPA and BPS decreased the activities of testicular marker enzymes (LDH and SDH), down-regulated the expression of spermatogenesis-related genes (Plzf, Pcna, and Sycp3), and were accompanied by reduced sperm quality and increased malformation rates. Notably, paternal exposure to BPA/BPS suppressed the expression of the key carnitine transporter OCTN2 and disrupted testicular carnitine transport homeostasis in offspring. The consequent reduction in testicular carnitine led to decreased expression of markers involved in mitochondrial β-oxidation (CPT1 and CPT2) and the respiratory chain (ND1, ND2, ND3, CYTB, COX1, and ATP6), resulting in severely impaired energy metabolism. Further investigation revealed that paternal BPA/BPS exposure also inhibited the activities of antioxidant enzymes (CAT, SOD, and GSH-Px) in offspring testes, leading to substantial accumulation of MDA. Elevated oxidative stress promoted intrinsic apoptotic signaling in offspring testes. This was characterized by the upregulation of pro-apoptotic markers, including increased Cleaved-CASPASE-3/9 levels and a higher BAX/BCL2 ratio. In summary, this study demonstrates that paternal BPA/BPS-induced dysregulation of the testicular carnitine transport system and disruption of carnitine homeostasis contribute to impairments in testicular energy metabolism in offspring. Concurrently, it induces oxidative stress and activates the intrinsic apoptotic pathway, collectively contributing to impaired testicular development and spermatogenesis in pubertal offspring.