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Aquaporin-9 (AQP-9) regulates tissue hydration by promoting transmembrane exchanges of both water and solutes, such as lactate. The latter is a key metabolite of primary spermatocytes and of maturing haploid germ cells (h-GCs). The present investigation was aimed at immunolocalising human AQP-9 in both normal and varicocele testes. Histology and immmunocytochemistry were investigated in archival biopsies from 20 varicocele testes and in eight unaffected ones. AQP-9 immunostaining was performed using a rabbit antibody, and either focal or diffuse cell membrane labelling was recorded. Varicocele testes showed disarranged tubular compartments, with sloughing h-GCs, tissue hyperhydration, spermiogenesis failure and fibrosis. AQP-9 immunohistology of the control testes showed a diffuse cell membrane staining of the primary spermatocytes and h-GCs, without any positive reaction of spermatogonia and Sertoli cells. AQP-9 cell expression in the varicocele testes was focal or lacking in both adluminal and sloughing GCs. AQP-9 expression occurs in normal human testis, at cell membrane of primary spermatocytes and h-GCs, suggesting a possible role of AQP-9 in the water and lactate transport from Sertoli cells to GCs. AQP-9 is focal or lacking in adolescent varicocele testes, and this suggests AQP-9 to be downregulated in such testicular disorder, leading to lactate deprivation with subsequent hypospermatogenesis.

Summary Chronic testicular inflammation and infection have been regarded as important factors in the pathogenesis of azoospermia. As key effector cells in innate and adaptive immune system, mast cells (MCs) were observed in inflammation and autoimmune disease. Furthermore, increased expression of tryptase-positive MCs has been reported in testicular disorders associated with male infertility/subfertility. However, little is known about the potential relationship between MCs and chronic testicular inflammation in azoospermic patients. Moreover, the preferential expression of MCs' subtypes in testis of these patients is still far from being understood. Thus, this study aimed to investigate characteristics of testicular MCs as well as their subtypes in azoospermic men with chronic testicular inflammation (AZI, n = 5) by immunohistochemical techniques. Our results showed significant increase of MCs in AZI, and more importantly, considerable numbers of tryptase-positive/chymase-positive MCs could also be demonstrated in AZI, when compared to control groups representing azoospermia without chronic testicular inflammation (AZW, n = 5) and normal spermatogenesis (NT, n = 5) respectively. Most interestingly, immunofluorescence staining revealed autoimmune-associated interleukin (IL)-17-producing MCs in AZI, whereas co-expression of MC markers with tumour necrosis factor (TNF)-α, IL-10 and IL-1β could not be detected. In conclusion, AZI is associated with significant increase of tryptase-positive/chymase-positive MCs expressing IL-17, and these MCs might contribute to the pathogenesis of AZI.