Dose-dependent testis infiltration of peritubular macrophages after MEHP exposure of Peri-pubertal rats and their role in the recovery of spermatogenesis.

We have previously reported that acute MEHP exposure resulted in a significant increase in peritubular macrophages along with differentiating spermatogonia. Here, we hypothesize that the recruitment of peritubular macrophages is MEHP dose-dependent and that the peritubular macrophages stimulate spermatogonial differentiation in response to MEHP-induced testicular injury. Peripubertal rats were exposed to a single dose of either 250 mg/kg or 500 mg/kg MEHP or 250 mg/kg MEHP for 3 consecutive days or 100 mg/kg for 7 consecutive days to study chronic exposure. Here, we report that an acute exposure to 500 mg/kg and a repeated 250 mg/kg exposure to MEHP resulted in significant loss of spermatocytes as well as increased numbers of peritubular macrophages and that this increase in peritubular macrophages corresponded closely with an observed increase in the numbers of differentiating (PLZF+) spermatogonia. Interestingly, a disruption of the blood-testis barrier (BTB) also corresponded closely with increased peritubular macrophage numbers after MEHP exposure. To delineate if the peritubular macrophages play a role in the repair and recovery of spermatogenesis after MEHP exposure, depletion of MEHP-induced increase in the numbers of peritubular macrophages via pre-treatment with clodronate resulted in a consequent decrease in number of PLZF-positive differentiating spermatogonia. Our findings are significant as it is the first demonstration of the infiltration of peritubular macrophages by a toxicant and is dose-dependent. Additionally, this recruitment of PTMO depends on the disruption of BTB and not germ cell loss. Furthermore, depletion of peritubular macrophages resulted in a decrease in the number of differentiating spermatogonia.