Cyclic GMP signaling in rat urinary bladder, prostate, and epididymis: tissue-specific changes with aging and in response to Leydig cell depletion.

Aging of the male reproductive system leads to changes in endocrine signaling and is frequently associated with the emergence of prostate hyperplasia and bladder dysfunctions. Recent reports highlight prostate and bladder as promising targets for therapeutic interventions with inhibitors of the cyclic GMP (cGMP)-degrading phosphodiesterase 5 (PDE5). However, the cGMP signaling system in these organs is as yet poorly characterized, and the possibility of age-related alterations has not been addressed.

Homologous and lysophosphatidic acid-induced desensitization of the atrial natriuretic peptide receptor, guanylyl cyclase-A, in MA-10 leydig cells.

The cardiac hormone atrial natriuretic peptide (ANP) signals via interaction with a plasma membrane receptor, which has guanylyl cyclase (GC) activity and is referred to as GC-A. Desensitization of GC-A is thought to represent a physiologically important regulatory mechanism, but the signaling pathways implicated and cell type-specific effects are still poorly understood. Here we demonstrate that sustained exposure to either ANP itself or the bioactive lipid lysophosphatidic acid (LPA) elicits GC-A desensitization in MA-10 Leydig cells.

Local regulatory factors in regulation of ovarian function: role of prorenin-renin-angiotensin-system.

During reproductive life in the female, there is a continuous flow of growth, maturation and demise of ovarian follicles, unless pregnancy occurs. Although ovarian function is primarily controlled by the hypothalamus-pituitary-axis, there is no doubt that a hormonal microenvironment specific for each individual follicle is established, that finally determines whether a follicle ovulates and becomes a corpus luteum or undergoes atresia. In this respect, autocrine and paracrine factors that act alone or modulate gonadotropins action are of paramount importance.

Comparative analysis between cyclic GMP and cyclic AMP signalling in human sperm.

The principal involvement of cyclic nucleotides in regulating sperm functions is well established, but the factors controlling their generation and actions have not yet been entirely resolved. In particular, specific roles for cyclic (c)GMP in mammalian sperm are poorly understood. In this study, we have characterized comparatively the cAMP and cGMP signalling systems in ejaculated human sperm.

Selective activation of protein kinase C isoforms by angiotensin II in neuroblastoma X glioma cells.

Differential activation of PKC isoforms by angiotensin II (AII) has been found in a variety of tissues in which this important octapeptide mediates its multitude of effects. To date, the PKC isoforms involved in mediating brain-specific effects are yet to be defined. In the present study, the identity of PKC isoforms coupled to AII stimulation was examined in the neuroblastoma X glioma hybrid cell line, NG108-15, by Western blot analysis.

Gonadotropin-mediated regulation of the murine VEGF expression in MA-10 Leydig cells.

Presence of vascular endothelial growth factor (VEGF) is not only limited to cells directly involved in angiogenesis but has also been demonstrated in steroidogenic cells like testicular Leydig cells. Because Leydig cells are subjected to regulation by gonadotropic hormones and produce steroid hormones, we have investigated here the effects of human chorionic gonadotropin (hCG) or steroid hormones on VEGF expression in cultured mouse tumor Leydig cells (MA-10 cells) and have then analyzed the underlying molecular mechanisms. Northern blot analysis and enzyme-linked immunosorbent assays revealed increases in VEGF mRNA and protein levels, respectively, over 3-20 hours in MA-10 cells after stimulation with hCG or 8-Br-cAMP.

Spatiotemporal regulation of the two atrial natriuretic peptide receptors in testis.

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.

Lysophosphatidic acid signals through mitogen-activated protein kinase-extracellular signal regulated kinase in ovarian theca cells expressing the LPA1/edg2-receptor: involvement of a nonclassical pathway?

We investigated the mechanism of lysophosphatidic acid (LPA) signaling in ovarian theca cells and observed that stimulation with this bioactive lipid markedly enhanced Thr/Tyr phosphorylation of the MAPK ERK1/2. Activation of ERK was transient, showing a peak at 5 min that declined thereafter, and was not associated with a concomitant nuclear translocation of the enzyme, suggesting that a cytosolic tyrosine phosphatase may be responsible for switching off the signal. Epidermal growth factor (EGF)-induced activation of the enzyme in the same cell system was more rapid (peaking at 1 min), sustainable for at least 60 min, and could be suppressed by prior treatment with either pertussis toxin or a noncompetitive inhibitor of Ras acceptor protein, manumycin A.

Regulation of vascular endothelial growth factor production by Leydig cells in vitro: the role of protein kinase A and mitogen-activated protein kinase cascade.

We previously reported the presence of vascular endothelial growth factor (VEGF) in testicular cells, and high concentrations of VEGF have been measured in semen, although its role in male reproduction remains obscure. In the present study we focus on understanding the mechanism of VEGF production by mouse Leydig cells cultured in vitro. Production of VEGF protein in medium by testicular cells was markedly increased by the addition of hCG in a time- and dose-dependent manner.

Stimulatory effect of progesterone on the expression of steroidogenic acute regulatory protein in MA-10 Leydig cells.

The steroidogenic acute regulatory protein (StAR), by virtue of its ability to facilitate the intramitochondrial transport of cholesterol, plays an important role in regulating steroid hormone biosynthesis in steroidogenic cells. In agreement with published data, both StAR expression and progesterone production in MA-10 mouse Leydig tumor cells could be stimulated with hCG and 8Br-cAMP. Addition of aminoglutethimide, an inhibitor of cholesterol side chain cleavage (P450(scc)) enzyme, not only resulted in a drastic inhibition of progesterone production but also in an attenuation of StAR expression in response to either hCG or 8-Br-cAMP.

Characterization of VIP and PACAP receptors in cultured rat penis corpus cavernosum smooth muscle cells and their interaction with guanylate cyclase-B receptors.

Penile corpus cavernosum smooth muscle relaxation can be induced by both cyclic AMP and cyclic GMP-elevating agents, but possible interactions between these two signalling pathways are still poorly understood. Using in vitro cultured rat penile corpus cavernosum smooth muscle (CCSM) cells, we have characterized the local expression and functional activities of receptors for the cAMP-elevating peptides, PACAP and VIP, and for the cGMP-elevating peptides, CNP and ANP. Stimulation of the cells with various concentrations of PACAP(-27/-38) or VIP resulted in rapid and dose-dependent increases in cyclic AMP levels.

Lysophosphatidic acid-induced nuclear localization of protein kinase C delta in bovine theca cells stimulated with luteinizing hormone.

The amounts of lysophospholipase D (LPLD) and the ovarian protein kinase C delta (PKCdelta) increase during the course of pregnancy. Because LPLD is involved in the production of the bioactive phospholipid lysophosphatidic acid (LPA), we examined whether stimulation with LPA would influence PKCdelta in the ovary. We used immunoblotting and immunohistochemical methods to show that stimulation of bovine theca cells with LPA leads to an unexpected redistribution of PKCdelta from the cytosol to the perinuclear area and that in the presence of LH, LPA induces a complete nuclear translocation of PKCdelta.

The tunica albuginea of the human testis is characterized by complex contraction and relaxation activities regulated by cyclic GMP.

The mechanisms responsible for the initial transport of immotile sperm from the testis into the epididymis are still poorly understood. We show here by electron microscopy and immunohistochemical approaches that the tunica albuginea of the human testis contains abundantly contractile elements. This tissue is also distinguished by extraordinarily high concentrations of cyclic GMP (cGMP)-dependent protein kinase I, known to mediate cGMP-dependent relaxation.

Lysophosphatidic acid and its role in reproduction.

Lysophosphatidic acid (LPA) belongs to a new family of lipid mediators that are endogenous growth factors and that elicit diverse biological effects, usually via the activation of G protein-coupled receptors. LPA can be generated after cell activation through the hydrolysis of preexisting phospholipids in the membranes of stimulated cells. A dramatic elevation of LPA levels was found in serum of patients suffering from ovarian carcinoma.

Central nervous system-specific glycosylation of the type A natriuretic peptide receptor.

Physiological effects of atrial natriuretic peptide (ANP) are thought to be mediated by binding to and activation of a widely expressed membrane receptor, termed guanylyl cyclase (GC)-A. During comparative analyses of ANP receptor expression in various rat and bovine tissues, by UV light-induced affinity cross-linking to (125)I-ANP, we uncovered a size heterogeneity of GC-A, detectable as a 130-kDa protein in peripheral and as a 122-kDa protein in central nervous system tissues. This heterogeneity could be explained by differences in N-linked glycosylation, because treatments with N-glycosidase F reduced the apparent molecular weights of both receptor variants to the same value of 116,000.