Study of the multidrug resistance phenomenon in tumor cell lines has led to the discovery of the product of the multidrug resistance (MDR) type 1 genes, the plasma membrane P-glycoprotein (P-gp) that functions as an energy-dependent pump for the efflux of diverse anticancer drugs. P-gp was also recently identified in normal epithelial cells with secretory/excretory functions and in the endothelial cells of the capillary blood vessels in the brain and the testis. These endothelial cells are key elements of the blood-brain and blood-testis barriers, respectively. The aim of this study, in the rat, mouse, guinea pig, and human, was to determine whether testicular cells other than the capillary endothelial cells could express MDR type I genes. Immunohistochemistry on testicular sections revealed that P-gp is present in interstitial cells in the mouse, rat, and human testes, in early and late spermatids in guinea pig testis, and in late spermatids in the rat, mouse, and human. Reverse transcription-polymerase chain reaction analysis on isolated mouse, rat, and human cells showed that all somatic testicular cells (Leydig cells, macrophages, peritubular cells, and Sertoli cells) and the cytoplasmic lobes from rat late spermatids expressed MDR type I mRNAs, whereas spermatogonia, pachytene spermatocytes, and early spermatids did not. An ontogenesis study in the mouse reveals that type I MDR gene expression begins at 13.5 days postcoitum at the time when the seminiferous cords and the blood vessels appear and are maintained thereafter. Finally, two functional tests on isolated rat cells, the doxorubicin and rhodamine uptake assays, demonstrated that rat testicular macrophages, Leydig cells, peritubular cells, and Sertoli cells displayed a multidrug-resistance activity, whereas spermatogonia, pachytene spermatocytes, and early spermatids did not. Western blot experiments have revealed that a P-gp of 175 kDa is present in the human testis as well as in the rat Leydig cells, testicular macrophages, peritubular cells, and Sertoli cells, but is absent in spermatogonia, spermatocytes, and early spermatids. We conclude that P-gp is involved in the self-protection of the somatic cells and is most probably one of the molecules that confers its functionality to the blood-testis barrier. The absence of expression of MDR type I genes in mitotic and meiotic germ cells probably explains their particular vulnerability to various anticancer drugs. In contrast, expression of the P-gp in the haploid cells most likely reflects the ability of spermatozoa to assume their own antidrug defense.
Despite clear indications of interleukin-1 (IL-1) action on Sertoli and germ cells, previous studies failed to detect IL-1 receptors (IL-1R) within the seminiferous tubules. Here, we investigated the existence of the type I signaling receptor (IL-1RI) and the type II decoy receptor (IL-1RII) mRNAs within the testis. Polymerase chain reaction analysis showed the presence of both receptor mRNAs in isolated rat, mouse, and human somatic testicular cells (macrophages, Leydig, Sertoli, and peritubular cells). While also present in rat and mouse isolated pachytene spermatocytes and early spermatids, these receptor mRNAs were not found in human germ cells. The distribution of both IL-1R mRNAs was then examined in adult rat and mouse testis using light and electron microscopic in situ hybridization. No IL-1RI signal was detected in rat testis. In mouse testis, we did not find any signal for IL-1RII. In contrast, IL-1RI mRNA was detected in a wide variety of mouse testicular cells. Strong expression was observed in the rete testis area and high expression was seen over the epithelium of the epididymal duct and in interstitial cells, while lower labeling was detected in peritubular and Sertoli cells and in all germ cell types from spermatogonia to early spermatids; no signal was seen in late spermatids. That the IL-IR was also strongly expressed in the interstitium, the rete testis and efferent duct areas, and the epididymis was established using an autoradiography technique. Overall, our study strongly supports the hypothesis that IL-1 is a regulator of testicular function of prime importance.
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