Heat stress reduces poly(ADPR)polymerase expression in rat testis.

Poly(ADPR)polymerase (PARP) is a chromatin-associated enzyme with a presumptive role in DNA repair during replication and recovery from strand breaks caused by genotoxic agents. It catalyses the attachment and elongation of ADPribose polymers (pADPR) to a variety of acceptor proteins (including PARP itself, and histones) and is particularly active in the testis where its expression varies according to the stage of germ cell differentiation. PARP degradation is also one of the classic indicators of apoptosis. In this investigation we have examined the effects of heat stress on the adult rat testis with respect to the concentration and activity of PARP, the nature of the pADRP nuclear acceptor proteins, the length of ADPR polymers and the activity of the ADPR depolymerizing enzyme, poly(ADPR)glycohydrolase (PARG). Our results show a significant reduction in the concentration and activity of PARP 4 and 8 days after artificial cryptorchidism, but no significant changes were observed in PARG activity or in pADPR length. Unexpectedly, the apoptotic degradation of PARP was not detected following heat stress. These results confirm that PARP gene expression is developmentally regulated during spermatogenesis and indicate that it is suppressed coincidentally with the loss of meiotic spermatocytes during artificial cryptorchidism.