HSPA1A-BAG5 chaperone complex promotes spermatogenesis by driving ubiquitination-mediated degradation of ATF2

Male infertility represents a major global health challenge. Heat shock protein A1A (HSPA1A), a stress-inducible molecular chaperone, shows potential importance in spermatogenesis, though its precise mechanistic role remains undefined.

Analysis of human sperm transcriptome data (GSE6969) revealed HSPA1A expression in fertile versus infertile samples. Functional characterization involved the overexpression of HSPA1A in spermatogonia (GC-1 spg) and its knockdown in spermatocytes (GC-2 spd(ts)), assessing apoptosis, proliferation, and cell cycle progression. HSPA1A-interacting proteins were identified through immunoprecipitation-mass spectrometry and validated by co-immunoprecipitation. Downstream targets were investigated via bioinformatic analysis and proteomics. In vivo validation employed a mouse model of chronic HSP70 inhibition (VER-155008).

HSPA1A is highly expressed in fertile sperm, and its overexpression significantly inhibited apoptosis, enhanced proliferation, and induced S/G2 phase arrest, while HSPA1A knockdown produced opposite effects. BAG5 was identified as a primary HSPA1A interactor. Mechanistically, the HSPA1A-BAG5 complex promoted ubiquitination-mediated degradation of ATF2, subsequently downregulating apoptotic signaling. In vivo HSPA1A inhibition induced testicular atrophy, reduced sperm count, impaired sperm morphology and acrosome reaction, disrupted seminiferous tubule architecture, and elevated germ cell apoptosis. Concurrent upregulation of ATF2, p53, and reduced testosterone levels were observed.

The HSPA1A-BAG5 complex maintains spermatogenic cell survival and proliferation through ubiquitination-dependent ATF2 degradation. These findings elucidate a novel regulatory axis essential for spermatogenesis and position HSPA1A as a promising therapeutic target for male infertility.