Gsk3a is Essential for Sperm Function and Male Fertility

Abstract

The signaling enzyme glycogen synthase kinase 3 exists as two isoforms – GSK3A and GSK3B. GSK3 is part of key signaling pathways in several cells and tissues. We have previously shown that both isoforms of GSK3 are present in sperm and testis. Increase or decrease in sperm motility in vitro resulted in changes in GSK3 phosphorylation. The enzyme was also shown to activate a mammal specific protein phosphatase isoform PP1γ2, a key enzyme essential for sperm function. Here we examined the role of Gsk3a in male fertility using a targeted gene knockout approach. Gsk3 (+/‐) male and female mice are fertile. However, global knockout of Gsk3a results in male infertility, while females are normal. Testis weights and sperm numbers of Gsk3a (‐/‐) mice are comparable to the fertile Gsk3a (+/‐) controls. However sperm motility in Gsk3a (‐/‐) appears to be compromised. Strikingly, forward motility of mutant sperm is altered, characterized by markedly attenuated amplitude of flagellar beat. Sperm ATP levels were lower in Gsk3a (‐/‐) mice compared to wild type animals. PP1γ2 protein levels were unaltered, but its catalytic activity was elevated in KO sperm. Remarkably, capacitation associated changes in tyrosine phosphorylation of proteins are absent or significantly lower in Gsk3a (‐/‐) sperm. Moreover the glycolytic enzyme, hexokinase, which is constitutively tyrosine phosphorylated in WT sperm, is not phosphorylated in Gsk3 (‐/‐) sperm. The GSK3B isoform was present and unaltered in testis and sperm of Gsk3a (‐/‐) mice suggesting that GSK3B is not able to compensate for the loss of GSK3A in testis and sperm. Our studies show that GSK3A, which has a highly conserved glycine rich N‐terminus in mammals, is essential for sperm motility and male fertility.Supported by NIH grant R15 HD068971