Spatiotemporal regulation of the two atrial natriuretic peptide receptors in testis.
ABSTRACT By interacting with a guanylyl cyclase (GC) activity-containing receptor, termed GC-A, atrial natriuretic peptide (ANP) acts as a regulator of blood pressure and fluid volume homeostasis. High expression levels of GC-A in the testis and reported effects of ANP on testosterone secretion by Leydig cells are indicative of important local functions in this organ. Here we show, based on radioligand receptor labeling and immunological approaches, that seminiferous tubules rather than Leydig cells are the predominant GC-A expression sites in the rat testis. Functional activity was proved by ANP- induced cGMP accumulation in isolated seminiferous tubules. Although ontogenetic studies revealed a massive increase in GC-A levels during sexual maturation, the so-called natriuretic peptide clearance receptor, another type of ANP receptor proposed to locally control the availability of natriuretic peptides, was found to be expressed predominantly before puberty, exceeding the level of GC-A expression at this time. Natriuretic peptide clearance receptor also shows a distinct distribution pattern surrounding the seminiferous tubules. These findings raise the possibility of novel physiological roles for ANP and cGMP in the testis related to germ cell maturation and/or the regulation of the onset of puberty and suggest that the two ANP receptors function in a coordinated manner at this target organ.
Article: Calcineurin regulates homologous desensitization of natriuretic peptide receptor-A and inhibits ANP-induced testosterone production in MA-10 cells.[show abstract] [hide abstract]
ABSTRACT: Receptor desensitization is a ubiquitous regulatory mechanism that defines the activatable pool of receptors, and thus, the ability of cells to respond to environmental stimuli. In recent years, the molecular mechanisms controlling the desensitization of a variety of receptors have been established. However, little is known about the molecular mechanisms that underlie desensitization of natriuretic peptide receptors, including natriuretic peptide receptor-A (NPR-A). Here we report that calcineurin (protein phosphatase 2B, PP2B, PPP3C) regulates homologous desensitization of NPR-A in murine Leydig tumor (MA-10) cells. We demonstrate that both pharmacological inhibition of calcineurin activity and siRNA-mediated suppression of calcineurin expression potentiate atrial natriuretic peptide (ANP)-induced cGMP synthesis. Treatment of MA-10 cells with inhibitors of other phosphoprotein phosphatases had little or no effect on ANP-induced cGMP accumulation. In addition, overexpression of calcineurin blunts ANP-induced cGMP synthesis. We also present data indicating that the inhibition of calcineurin potentiates ANP-induced testosterone production. To better understand the contribution of calcineurin in the regulation of NPR-A activity, we examined the kinetics of ANP-induced cGMP signals. We observed transient ANP-induced cGMP signals, even in the presence of phosphodiesterase inhibitors. Inhibition of both calcineurin and phosphodiesterase dramatically slowed the decay in the response. These observations are consistent with a model in which calcineurin mediated dephosphorylation and desensitization of NPR-A is associated with significant inhibition of cGMP synthesis. PDE activity hydrolyzes cGMP, thus lowering intracellular cGMP toward the basal level. Taken together, these data suggest that calcineurin plays a previously unrecognized role in the desensitization of NPR-A and, thereby, inhibits ANP-mediated increases in testosterone production.PLoS ONE 01/2012; 7(8):e41711. · 4.09 Impact Factor
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ABSTRACT: In adult rat testes, the blood-testis barrier (BTB) in the seminiferous epithelium must "open" (or "disassemble") to accommodate the migration of preleptotene spermatocytes from the basal to the adluminal compartment that occurs at stage VIII of the epithelial cycle. However, the molecule(s) and/or mechanism(s) that regulate this event are unknown. In this report, C-type natriuretic peptide (CNP) was shown to be a regulator of BTB dynamics. Although Sertoli and germ cells contributed to the pool of CNP in the seminiferous epithelium, its receptor, natriuretic peptide receptor B, resided almost exclusively in Sertoli cells. CNP also expressed stage-specifically and localized predominantly at the BTB in the seminiferous epithelium at stage VIII of the epithelial cycle. A synthetic CNP-22 peptide, when added to Sertoli cell cultures, was shown to perturb Sertoli cell tight junction in vitro, causing disappearance of BTB-associated proteins (JAM-A, occludin, N-cadherin, and beta-catenin) from the cell-cell interface. This inhibitory effect of CNP on the tight junction was confirmed by transient overexpression of CNP in these cells, which was mediated, at least in part, by accelerating the internalization of BTB integral membrane proteins. To validate these in vitro findings, CNP-22 was administered to testes at a dose of 0.35 or 3.5 mug per testis, which was shown to perturb the BTB integrity In vivo when the barrier function was assessed by monitoring the diffusion of a small molecular probe across the BTB. In summary, CNP secreted by Sertoli and germ cells into the BTB microenvironment regulates BTB dynamics during spermatogenesis.Proceedings of the National Academy of Sciences 04/2007; 104(10):3841-6. · 9.68 Impact Factor