Role of dynamic changes in human sperm heat shock protein A2 in male infertility

Male factors account for approximately 50% of infertility cases; however, the mechanisms underlying sperm dysfunction remain unclear. Heat shock protein A2 (HSPA2) is a biomarker associated with sperm fertilization; however, few studies have examined changes in its localization in vitro. This study investigated the in vitro localization dynamics of HSPA2 in sperm and its association with male infertility. Fertility status was determined according to the 2021 World Health Organization criteria. Semen samples were collected from 28 men with normal findings and 57 men with varicocele or oligozoospermia. Samples were subjected to density gradient centrifugation and the swim-up procedure, followed by a 24 h incubation. HSPA2 protein levels were analyzed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and western blotting, and localization patterns were evaluated using immunofluorescence staining. Western blot analysis showed that HSPA2 levels were significantly lower in samples from men with oligozoospermia (P < 0.01) and varicocele (P < 0.05) than in those from men with normal findings. Moreover, HSPA2 levels were correlated with total motile sperm counts and sperm motility. The percentage of sperm with HSPA2 localized in the acrosomal region immediately after sperm processing was lower (P < 0.01) and peaked later in samples from men with oligozoospermia and varicocele than in those from men with normal findings. These findings indicate that the reduced acrosomal localization of HSPA2 and delayed acrosomal localization dynamics after sperm processing represent a shared feature of male infertility rather than condition-specific differences and may be linked to impaired sperm function.