Prokineticin 2 overexpression induces spermatocyte apoptosis in varicocele in rats

Varicocele is one of the most important causes of male infertility, as this condition leads to a decline in sperm quality. It is generally believed that the presence of varicocele induces an increase in reactive oxygen species levels, leading to oxidative stress and sperm apoptosis; however, the specific pathogenic mechanisms affecting spermatogenesis remain elusive. Prokineticin 2 (PK2), a secretory protein, is associated with multiple biological processes, including cell migration, proliferation, and apoptosis. In the testis, PK2 is expressed in spermatocytes under normal physiological conditions. To investigate the role of PK2 in varicocele, a rat varicocele model was established to locate and quantify the expression of PK2 and its receptor, prokineticin receptor 1 (PKR1), by immunohistochemistry and quantitative real-time PCR assays (qPCR). Moreover, H₂O₂ was applied to mimic the oxidative stress state of varicocele through coculturing with a spermatocyte-derived cell line (GC-2) in vitro, and the apoptosis rate was detected by flow cytometry. Here, we illustrated that the expression levels of PK2 and PKR1 were upregulated in the spermatocytes of the rat model. Administration of H₂O₂ stimulated the overexpression of PK2 in GC-2. Transfection of recombinant pCMV-HA-PK2 into GC-2 cells promoted apoptosis by upregulating cleaved-caspase-3, caspase-8, and B cell lymphoma 2-associated X; downregulating B cell lymphoma 2; and promoting the accumulation of intracellular calcium. Overall, we revealed that the varicocele-induced oxidative stress stimulated the overexpression of PK2, leading to apoptosis of spermatocytes. Our study provides new insight into the mechanisms underlying oxidative stress-associated male infertility and suggests a novel therapeutic target for male infertility.