Mechanisms of Polystyrene Microplastics in Multipathway Disruption of the Blood–Testis Barrier

BACKGROUND: Polystyrene microplastics (PS-MPs) represent an emerging environmental pollutant, yet their potential threat to male reproductive health, specifically the integrity of the blood-testicular barrier (BTB), remains incompletely understood. OBJECTIVE: This study aimed to investigate the toxicological effects and underlying mechanisms of PS-MPs exposure on testicular structure and BTB function in a mouse model. METHODS: Four-week-old male ICR mice were exposed to PS-MPs at concentrations of 0, 500 µg/L, 5 mg/L, and 50 mg/L via drinking water for up to 5 weeks. Animals (n = 10 per group per time point) were sacrificed at weeks 1, 2, 3, 4, and 5 after initiation of exposure. A comprehensive assessment was performed, including evaluation of BTB permeability via biotin tracing, analysis of key junction protein (Connexin43, ZO-1, Occludin) expression and localization using western blot (WB), real-time quantitative polymerase chain reaction (RT-qPCR), and immunofluorescence, and immunofluorescent detection of macrophage activation (IBA-1). RESULTS: PS-MPs exposure significantly increased BTB permeability in a dose- and time-dependent manner. This was accompanied by a marked downregulation in the expression and disrupted localization of Connexin43, ZO-1, and Occludin. We observed an upregulation of IBA-1 within the testis, indicating macrophage activation. CONCLUSION: This study demonstrates that PS-MPs induce BTB dysfunction in association with multipathway responses. Macrophage activation, as indicated by IBA-1 upregulation, was closely associated with BTB injury and may represent a key component in this toxicological process, although its precise mechanistic role requires further investigation. These findings provide new insights into the reproductive toxicity of microplastics.