Ultrastructural Features, Immune Response, and Junctional Proteins in the Seminiferous Epithelium of SARS-CoV-2-Infected Mice

During the COVID-19 pandemic, the prevalence of death in men was higher than in women. Using transgenic mice expressing the human angiotensin-converting enzyme 2 (hACE2), we demonstrated that SARS-CoV-2 infects Leydig cells and uses its steroidogenic machinery for replication. This study investigates the impact of SARS-CoV-2 in the seminiferous epithelium of K18-hACE2 mice, focusing on the immune response, junctional proteins, and spermatogenesis. The seminiferous tubules (STs) and epithelial (EA) areas were measured. The number of Sertoli cells (SCs), spermatocytes, and damaged ST was quantified. Ultrastructural analysis was performed under transmission electron microscopy. Angiotensin II levels and immunolocalization of hACE2, spike, and nucleocapsid were evaluated. TUNEL and immunoreactions for Ki-67, TNF-α, INF-γ, iNOS, NF-κB, and Conexin-43 were performed and correlated with <i>Jam-α</i>, <i>Stat1</i>, <i>Stat3</i>, and <i>iNOS</i> expressions. hACE2, spike, and nucleocapsid immunolabeling were detected in the epithelium along with high angiotensin II levels in the infected mice. The infection caused a significant reduction in ST, EA, spermatocytes, SCs, Ki-67+ cells, Cx43 immunoexpression, and <i>Jam-a</i> expression. In the epithelium, TNF-α, IFN-γ, iNOS, and nuclear NF-κB immunolabeling increased along with <i>Stat1</i> upregulation. These findings, combined with the increased epithelial hACE2 and high angiotensin II levels, confirm epithelial responsiveness to the infection and explain the spermatogenic failure and impaired junctional proteins. The presence of viral particles, increased TNF-α immunolabeling, and apoptotic features in Sertoli cells suggests that these sustentacular cells are targets for viral infection in the epithelium, and, due to their extensive projections and ability to phagocytize dying infected germ cells, they may disseminate the viruses throughout the epithelium.