Proton-secreting cells in various organs, such as the kidney and epididymis, regulate pH balance, maintain cellular homeostasis, and support key physiological processes. More recently, these specialized cells have emerged as key contributors to mucosal immunity, orchestrating immune activation. Epididymitis is an inflammatory condition that significantly impacts male fertility, often due to a lack of diagnosis and treatment. This study investigates the role of region-specific epididymal proton-secreting clear cells (CCs) in shaping immune responses during LPS-induced epididymitis in mice. We found that in response to lipopolysaccharide (LPS), CCs rapidly shifted to a proinflammatory phenotype, marked by the upregulation of cytokines and chemokines, alongside the downregulation of genes involved in sperm maturation. Morphological changes in CCs, including increased apical blebs and altered shape across different epididymal segments, suggest their active role in immune responses. Moreover, mononuclear phagocytes reduced their luminal-reaching projections in the proximal epididymis after the LPS challenge. This bacterial antigen triggered dendritic cell migration and neutrophil infiltration in the distal epididymis. These immune landscape alterations contributed to epithelial damage and impaired sperm maturation, as evidenced by decreased sperm motility following LPS intravasal-epididymal injection. Our findings indicate that proton-secreting cells are immune gatekeepers in the epididymis, initiating immune responses and disrupting sperm maturation. This research enhances the understanding of epithelial immunoregulation and will help to develop novel diagnostic and therapeutic strategies for epididymitis and male infertility. Furthermore, insights into CC-mediated immune responses could inform the development of new approaches for male contraception.

Although SARS-CoV-2 induces mucin hypersecretion in the respiratory tract, hyposalivation/xerostomia has been reported by COVID-19 patients. We evaluate the submandibular gland (SMGs) pathogenesis in SARS-CoV-2-infected K18-hACE2 mice, focusing on the impact of infection on the mucin production and structural integrity of acini, ductal system, myoepithelial cells (MECs) and telocytes. The spike protein, the nucleocapsid protein, hACE2, actin, EGF, TNF-α and IL-1β were detected by immunofluorescence, and the Egfr and Muc5b expression was evaluated. In the infected animals, significant acinar hypertrophy was observed in contrast to ductal atrophy. Nucleocapsid proteins and/or viral particles were detected in the SMG cells, mainly in the nuclear membrane-derived vesicles, confirming the nuclear role in the viral formation. The acinar cells showed intense TNF-α and IL-1β immunoexpression, and the EGF-EGFR signaling increased, together with Muc5b upregulation. This finding explains mucin hypersecretion and acinar hypertrophy, which compress the ducts. Dying MECs and actin reduction were also observed, indicating failure of contraction and acinar support, favoring acinar hypertrophy. Viral assembly was found in the dying telocytes, pointing to these intercommunicating cells as viral transmitters in SMGs. Therefore, EGF-EGFR-induced mucin hypersecretion was triggered by SARS-CoV-2 in acinar cells, likely mediated by cytokines. The damage to telocytes and MECs may have favored the acinar hypertrophy, leading to ductal obstruction, explaining xerostomia in COVID-19 patients. Thus, acinar cells, telocytes and MECs may be viral targets, which favor replication and cell-to-cell viral transmission in the SMG, corroborating the high viral load in saliva of infected individuals.

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 Jam-α, Stat1, Stat3, and iNOS 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 Jam-a expression. In the epithelium, TNF-α, IFN-γ, iNOS, and nuclear NF-κB immunolabeling increased along with Stat1 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.

Proton-secreting cells in various organs, such as the kidney and epididymis, regulate pH balance, maintaining cellular homeostasis, and supporting key physiological processes. More recently, these specialized cells have emerged as key contributors to mucosal immunity, orchestrating immune activation. Epididymitis is an inflammatory condition that significantly impacts male fertility, often due to a lack of diagnosis and treatment. This study explores the involvement of region-specific epididymal proton-secreting clear cells (CCs) in the immune response by interacting with the immune system during LPS-induced mouse epididymitis. We found that in response to LPS, CCs rapidly shifted to a proinflammatory phenotype, marked by the upregulation of cytokines and chemokines, alongside the downregulation of genes involved in sperm maturation. Morphological changes in CCs, including increased apical blebs and altered shape across different epididymal segments, suggest their active role in immune responses. Moreover, mononuclear phagocytes (MPs) reduced their luminal-reaching projections in the proximal epididymis after the LPS challenge. This bacteria antigen triggered the migration of dendritic cells and neutrophil infiltration in the distal epididymis. These immune landscape alterations contributed to epithelial damage and impaired sperm maturation, as evidenced by decreased sperm motility following LPS injection. Our findings indicate that proton-secreting cells are immune gatekeepers in the epididymis, initiating immune responses and disrupting sperm maturation. This research enhances the understanding of epithelial immunoregulation and will help to develop novel diagnostic and therapeutic strategies for epididymitis and male infertility. Furthermore, insights into CC-mediated immune responses could inform the development of new approaches for male contraception.

We examined SARS-CoV-2 infection in the epididymis of K18-hACE2 mice, focusing on the cauda region. Thirty mice were divided into control (CG), 2-day infection (2D), and 5-day infection (5D) groups. The animals were intranasally infected with SARS-CoV-2. The 5D group showed a significant increase in IL-6, TNF-a, and IL-1b, high mRNA levels of Ifna, Ifnb, and Ifng, and infiltration of CD8⁺ T cells. SARS-CoV-2 directly infects smooth muscle cells, leading to atrophy of the smooth muscle layer. The infection impaired the basement membrane and downregulated blood-epididymis barrier-related genes Ocln and Jam-a. Clear cells exhibited increased apical V-ATPase and immunoexpression of hACE2, spike, and nucleocapsid. Interestingly, the infected groups showed a greater number of juxtaposed clear cells with PCNA- and Ki67-positive nuclei. The findings also revealed a newly identified NF-kB-driven inflammatory-proliferative response in clear cells. By combining in vivo and in silico analysis of a parallel LPS-stimulation RNA-seq dataset, we uncovered significant co-enrichment of the TNF-a_NF-kB pathway alongside cell cycle pathways (G2/M, E2F). The protein-protein interaction network identified key nodes linking the inflammatory NF-kB pathway to the cell cycle machinery. This in silico model was confirmed in vivo, demonstrating co-localization of phosphorylated NF-kB and PCNA in the CC rows. Alterations in spermatozoa, including decreased PNA labeling, ultrastructural changes, and reduced Crisp1 mRNA, were also observed. Therefore, SARS-CoV-2 infection causes structural and functional changes in the epididymal cauda, leading to smooth muscle cell death and basement membrane disruption. Overall, the results suggest that SARS-CoV-2 infection induces dysfunction in the cauda, a microenvironment essential for sperm maturation and storage. Lay Summary SARS-CoV-2, the virus that causes COVID-19, can reach many organs beyond the lungs, including the male reproductive tract. We studied how this virus affects epididymis, a sperm- carrying tube where sperm are mature and stored, in a genetically modified mouse model that expresses the human ACE2 receptor, which allows SARS-CoV-2 infection. We demonstrated that infection triggers a strong local inflammatory response and impairs the muscular wall and spermatozoa. The virus also infects specialized clear cells that control the epididymal fluid pH where sperm are stored. Following infection, clear cell groups showed proliferation and possible acidification of the sperm storage microenvironment. All these combined changes suggest that the normal environment required for sperm maturation is disrupted. Our findings raise concern that severe COVID-19 may have lasting effects on male fertility and highlight the epididymis as an important but overlooked target organ of this infection.