Embryonic Benzo[a]pyrene Exposure Induces Multigenerational Reproductive Effects on Adult Male Medaka: Phenotypic and Transcriptomic Insights

Benzo[a]pyrene (B[a]P), a ubiquitous environmental pollutant, poses a significant threat to male reproductive health, but the underlying latent molecular mechanisms remain virtually unknown. This study investigated the effects of embryonic B[a]P exposure on testicular function and spermatogenesis in F0 and F1 adult male medaka (<i>Oryzias latipes</i>). Embryos were exposed to sublethal concentrations (2.5, 20, and 80 μg/L) for 8 days and then raised in clean water until they reached adulthood. Transcriptomic analysis of F0 testicular tissues revealed widespread dysregulation of critical pathways. Exposure impaired the brain-pituitary-gonadal axis by disrupting GnRH signaling and downregulating genes encoding key steroidogenic enzymes (<i>CYP17A1</i>, <i>HSD3B2</i>), indicating suppressed testosterone biosynthesis. Concurrently, pathways essential for cellular energy metabolism (AMPK signaling, insulin signaling), amino acid biosynthesis, and cytoskeletal organization (actin cytoskeleton, focal adhesion) were profoundly altered. Furthermore, B[a]P activated apoptotic pathways and disrupted the balance between cell survival (PI3K-Akt signaling) and death, compromising spermatogenic cell fate. These molecular disruptions manifested in drastic physiological impairments, including a reduced gonadosomatic index, decreased sperm motility, and compromised fertilization success in F0 males, although these effects were recovered in the F1 generation. This study provides a comprehensive molecular basis for the long-term reproductive toxicity of early-life B[a]P exposure.