Double trouble for spermatogenesis: Polystyrene nanoplastics aggravate microcystin-LR toxicity by hijacking mitochondrial function in zebrafish

Microcystin-LR (MCLR) is a cyanobacterial toxin with demonstrated reproductive toxicity and frequently released during harmful algal blooms. In aquatic environments, MCLR is often present with polystyrene nanoplastics (PSNPs). However, the combined effects of these two pollutants on male reproduction and the underlying mechanisms remain poorly understood. To address this gap, adult male zebrafish (Danio rerio) were exposed to MCLR alone at 0, 2.4, and 24 μg/L or co-exposed with 100 μg/L PSNPs to investigate the effects of PSNPs on MCLR-induced spermatogenic impairment. We found that co-exposure with PSNPs exacerbated MCLR-induced spermatogenic impairment in zebrafish by increasing testicular MCLR accumulation and aggravating sperm defects. Transcriptomic profiling and subsequent functional analyses revealed that co-exposure broadly disrupted mitochondrial energy metabolism, particularly impairing both the tricarboxylic acid (TCA) cycle and oxidative phosphorylation, leading to compromised ATP production and elevated reactive oxygen species levels. Notably, the observed metabolic disruption was accompanied by reduced levels of the TCA cycle metabolite α-ketoglutarate (α-KG), decreased TET enzyme activity, and altered DNA methylation patterns of spermatogenesis-related genes, suggesting a potential link between mitochondrial metabolic disturbance and epigenetic dysregulation that may contribute to spermatogenic impairment. These findings uncover the carrier effect of PSNPs in enhancing MCLR reproductive toxicity and reveal a novel mechanism connecting mitochondrial metabolic disturbance to epigenetic dysregulation. Our study elucidates the joint reproductive toxicity of environmental pollutants and underscores the importance of considering mixture effects in ecological risk assessment.