Proteasome activators, PA28γ and PA200, play indispensable roles in male fertility

Abstract

Protein degradation mediated by the proteasome is important for the protein homeostasis. Various proteasome activators, such as PA28 and PA200, regulate the proteasome function. Here we show double knockout (dKO) mice of Psme3 and Psme4 (genes for PA28γ and PA200), but not each single knockout mice, are completely infertile in male. The dKO sperms exhibited remarkable defects in motility, although most of them showed normal appearance in morphology. The proteasome activity of the mutant sperms decreased notably, and the sperms were strongly positive with ubiquitin staining. Quantitative analyses of proteins expressed in dKO sperms revealed up-regulation of several proteins involved in oxidative stress response. Furthermore, increased 8-OHdG staining was observed in dKO sperms head, suggesting defective response to oxidative damage. This report verified PA28γ and PA200 play indispensable roles in male fertility, and provides a novel insight into the role of proteasome activators in antioxidant response.

Substrate receptors of proteasomes

“…BRD-like regions of PA200 and Blm10 specifically bind the acetylated core histones in vitro (Qian et al, 2013). Double deletion of PA200 and PA28γ in mice causes complete infertility in males with noteworthy defects in sperm motility due to decreased proteasome activity of the mutant sperm (Huang et al, 2016a). Thus, PA200 plays a vital role in spermatogenesis and could be a potential therapeutic target for human male infertility.…”

Novel functions of the ubiquitin-independent proteasome system in regulatingXenopusgermline development

“…Involvement of the ubiquitin-independent proteasome during germline development has been previously documented (Khor et al, 2006;Qian et al, 2013;Huang et al, 2016). In mice, compound mutants for PSME3 and PSME4 are completely infertile in males (Huang et al, 2016). So far, only acetylated core histones have been identified as substrates of ubiquitin-independent proteasomes during germline development (Qian et al, 2013).…”

“…PSME4 acts as a monomer to open the gate of the 20S CP (Hwang et al, 2011;Rechsteiner and Hill, 2005;Kish-Trier and Hill, 2013;Ben-Nissan and Sharon, 2014). Involvement of the ubiquitin-independent proteasome during germline development has been previously documented (Khor et al, 2006;Qian et al, 2013;Huang et al, 2016). In mice, compound mutants for PSME3 and PSME4 are completely infertile in males (Huang et al, 2016).…”

A conserved requirement forFbxo7during male germ cell cytoplasmic remodelling

“…Other proteasome-related knockout males (PA200, PA28γ) have defects in multiple stages of germ cell development, both pre-and post-meiotic. The post-meiotic phenotypes of these knockout models include delayed histone replacement during nuclear remodelling and delayed spermiation, neither of which was seen in Fbxo7 LacZ/LacZ testes (Qian et al, 2013;Huang et al, 2016). Moreover, unlike Fbxo7 LacZ/LacZ males, even the PA200/PA28γ double knockout males were able to produce substantial numbers of morphologically normal sperm in their epididymis (Huang et al, 2016).…”

“…The post-meiotic phenotypes of these knockout models include delayed histone replacement during nuclear remodelling and delayed spermiation, neither of which was seen in Fbxo7 LacZ/LacZ testes (Qian et al, 2013;Huang et al, 2016). Moreover, unlike Fbxo7 LacZ/LacZ males, even the PA200/PA28γ double knockout males were able to produce substantial numbers of morphologically normal sperm in their epididymis (Huang et al, 2016). A knockout of the spermatoproteasome-specific subunit PSMA8 has recently been shown to lead to meiotic abnormalities and early spermatid arrest [Gómez Hernández et al, unpublished data, preprint available at https://www.biorxiv.org/content/early/2018/08/03/384354], unlike the late stage spermatid loss described in the present study.…”