Testis Cell Pyroptosis Mediated by CASP1 and CASP4: Possible Sertoli Cell-Only Syndrome Pathogenesis

Abstract Background and aims: Sertoli cell-only syndrome (SCOS) is the most serious pathological type of non-obstructive azoospermia. In recent years, some genes related to SCOS have been identified, including FANCM, TEX14, NR5A1, NANOS2, PLK4, WNK3, and FANCA, but they cannot explain the pathogenesis of SCOS completely. This study attempted to explain the spermatogenesis dysfunction in SCOS through testicular tissue RNA sequencing and provide new targets for SCOS diagnosis and therapy. Methods and results: We analyzed differentially expressed genes (DEGs) based on RNA sequencing of 9 SCOS patients and 3 obstructive azoospermia patients with normal spermatogenesis. A total of 9406 DEGs were expressed (Log2|FC| ≥ 1 and adjusted P value < 0.05) in SCOS patients, and 21 hub genes were identified among the DEGs. Three upregulated core genes were found in our study including CASP4, CASP1, and PLA2G4A. Thus, we hypothesized that testis cell pyroptosis mediated by CASP1 and CASP4 might be involved in SCOS occurrence and development. We verified that CASP1 and CASP4 activities in the testes of patients with SCOS were significantly higher than those in patients with normal spermatogenesis using ELISA. Immunohistochemical results showed that CASP1 and CASP4 in the normal spermatogenesis group were mainly expressed in the nuclei of spermatogenic cells, Sertoli cells, and interstitial cells. CASP1 and CASP4 in the SCOS group were mainly expressed in the nuclei of Sertoli cells and interstitial cells because of the loss of spermatogonia and spermatocytes. At the same time, CASP1 and CASP4 expression levels in the testes of patients with SCOS were significantly higher than those in normal spermatogenic patients. Furthermore, the pyroptosis-related proteins GSDMD and GSDME in the testes of patients with SCOS were also significantly higher than those in patients with normal spermatogenesis. ELISA also showed that inflammatory factors IL-1 β, IL-18, LDH, and ROS were significantly increased in the testes of SCOS patients. Conclusion: For the first time, we found that cell pyroptosis-related genes and key markers were significantly increased in the testes of patients with SCOS, and we observed a large number of inflammatory and oxidative stress reactions in SCOS. Thus, we considered that testis cell pyroptosis mediated by CASP1 and CASP4 could participate in SCOS occurrence and development.