Alteration of Poly(ADP-ribose) Metabolism Leads to Abnormal Nucleoprotein Exchange in Spermiogenesis of the Mouse.

Abstract

Chromatin integrity has been identified as an important prerequisite for normal sperm cell function. The etiology of male idiopathic infertility associated with high sperm nuclear histone content and residual DNA strand breaks is not well understood. Most likely this type of sperm cell defect will be caused by faulty or incomplete execution of chromatin remodeling steps and insufficient DNA strand break management during spermatid development. Based on earlier observations, we hypothesized that poly(ADP-ribose) (PAR) metabolism is required for chromatin remodeling steps involving DNA strand breaks during spermatid nuclear elongation. At least two members of the multifunctional family of poly(ADP-ribose) polymerases, PARP1 and PARP2, are intimately involved in DNA repair where their enzymatic activity is directly triggered by DNA strand breaks to produce PAR by cleavage of NAD. Only one enzyme is capable of rapid degradation of the unique biopolymer, poly(ADP-ribose) glycohydrolase (PARG) which exists in four isoforms encoded by alternatively spliced transcripts from a single gene. Using Parp1-/-, Parg(110)-/-, and double gene disrupted mice, which all have different forms of abnormal poly(ADP-ribose) metabolism, we showed that nuclear shaping and DNA integrity are compromised by modulation of this pathway. In the present study we investigated the exchange of histones and transition proteins by protamines in a similar panel of gene disrupted mice and by pharmacological targeting using PJ34 as a small molecule competitive inhibitor of PARP1 and PARP2. Abnormal degrees of histone retention in spermatozoa, associated with varying degrees of subfertility in these mouse strains support the view that PAR metabolism is carefully regulated during spermiogenesis and that pharmacological or genetic manipulation of both, PARP1 and PARP2 will lead to compromised sperm chromatin quality similar to that observed in clinical cases of increased sperm histone levels. This work has been supported by NIH HD048837 (RGM) and in part by intramural funding through the Mari Lowe Center for Comparative Oncology, Philadelphia. (platform)