Proteasome subunit α4s is essential for formation of spermatoproteasomes and histone degradation during meiotic DNA repair in spermatocytes

Abstract

Meiosis, which produces haploid progeny, is critical to ensuring both faithful genome transmission and genetic diversity. Proteasomes play critical roles at various stages of spermatogenesis, including meiosis, but the underlying mechanisms remain unclear. The atypical proteasomes, which contain the activator PA200, catalyze the acetylation-dependent degradation of the core histones in elongated spermatids and DNA repair in somatic cells. We show here that the testis-specific proteasome subunit α4s/PSMA8 is essential for male fertility by promoting proper formation of spermatoproteasomes, which harbor both PA200 and constitutive catalytic subunits. Immunostaining of a spermatocyte marker, SYCP3, indicated that meiosis was halted at stage of spermatocytes in the α4s-deficient testes. α4s stimulated the in vitro degradation of the acetylated core histones, instead of non-acetylated histones, by the PA200-proteasome. Deletion of α4s blocked degradation of the core histones at DNA damage loci in spermatocytes, leading to meiotic arrest at metaphase I. Thus, α4s is required for histone degradation at meiotic DNA damage loci, proper progression of meiosis, and fertility in males by promoting proper formation of spermatoproteasomes. These results are important for understanding male infertility, and might provide potential targets for male contraception or treatment of male infertility.

Proteasome complexes experience profound structural and functional rearrangements throughout mammalian spermatogenesis

“…Here, increase in proteasome bound PA200 appears to be mainly the consequence of increased expression ( Supplementary Fig. S9 ), which is in accordance with the existing literature (Zhang et al ., 2021). However, given that we did not observe increased binding of PA200 to s20S in the whole testis interactome analysis, it remains difficult to draw conclusions about specific PA200 interactions.…”

“…This agrees with the increased proteolytic activities in SPC and SPT, compared to SPG and SER, and similar previous observations using whole testis lysate compared to muscle tissue (Qian et al ., 2013). Another study also showed high levels of 19S-containing species in post-meiotic germ cells (Gomez-H et al ., 2019) and in whole testes (Qian et al ., 2013; Zhang et al ., 2021). The increased association between s20S and activators during spermatogenesis is aligned with increased proteolytic requirements of this process.…”

“…Previous studies in PSMA8 −/− KO mouse models have established that the α4s subunit is essential for spermatogenesis (Gomez-H et al ., 2019; Zhang et al ., 2019). Functionally, mammalian s20S has been shown to degrade acetylated histones via association with PA200 and play a role in DNA damage repair in spermatocytes and the maturation of spermatids (Qian et al ., 2013; Zhang et al ., 2019, 2021). Double strand break (DSB) repair was shown to be dependent on s20S-mediated degradation of non-histone substrates (Ahuja et al ., 2017; Zhang et al ., 2021).…”

Le protéasome, la seconde vie d’une cible thérapeutique validée : aspects structuraux et nouveaux inhibiteurs

“…La particule a4s typique du spermatoprotéasome (Figure 3), contrairement à la particule a4, favoriserait l'association au PA200. Elle permettrait aussi le recrutement des sous-unités b1, b2 et b5 plutôt que celles de l'immunoprotéasome (Zhang et al, 2021). Le complexe ainsi formé est essentiel pour la réparation de l'ADN en métaphase I, la progression de la méiose et la fertilité masculine en favorisant, au moins partiellement, la dégradation des histones.…”

“…La signification des différences de composition des protéasomes 26S dans les cellules demeure à ce jour largement incomprise. Les protéasomes atypiques qui contiennent à la fois la particule régulatrice PA200 et la sous-unité a4s, jouent un rôle important dans la fertilité masculine (Zhang et al, 2021). Par ailleurs, dans des neurones cultivés d'hippocampe, la cryo-EM montre que 80 % des molécules de protéasome 26S se trouvent dans la forme appelée parfois « inactive », c'est-àdire sans substrat lié (Asano et al, 2015).…”