Prostaglandin E2 promotes cell survival of glomerular epithelial cells via the EP4 receptor.
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Visceral glomerular epithelial cells (GEC) are crucial for glomerular permselectivity and structural integrity in the kidney. The current study addressed the role of cyclooxygenase (COX)-2 and its product prostaglandin (PG) E2 in GEC survival. We generated a subclone of cultured rat GEC, which overexpress COX-2 in an inducible manner. When COX-2 was induced, GEC survived better in serum-deprived conditions. Induction of COX-2 was correlated with increased PGE2 generation, increased activation of extracellular signal-regulated kinase, decreased apoptosis, and increased cell proliferation. Rat GEC abundantly expressed the EP4 isoform of PGE2 receptor. Induction of COX-2 and addition of exogenous PGE2 both lead to decreased serum deprivation-induced apoptosis, which was accompanied by activation of the survival kinase Akt. Anti-apoptotic effect of COX-2 induction was reversed by the specific inhibitor of the EP4 receptor, L-161982. PGE2 also inhibited puromycin aminonucleoside-induced GEC apoptosis in vitro. Acute puromycin aminonucleoside nephrosis (PAN) is a rat model of GEC injury and proteinuria. In rats with PAN, glomerular apoptosis, quantified as caspase-3 activity, as well as urinary protein excretion were significantly increased, compared with control rats. Administration of L-161982 in rats with PAN further exacerbated caspase-3 activation and proteinuria. Thus COX-2 and its product PGE2 may have anti-apoptotic/protective effect on GEC via the EP4 receptor of PGE2. (+info)
Cyclic guanosine monophosphate compartmentation in rat cardiac myocytes.
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BACKGROUND: Cyclic guanosine monophosphate (cGMP) is the common second messenger for the cardiovascular effects of nitric oxide (NO) and natriuretic peptides, such as atrial or brain natriuretic peptide, which activate the soluble and particulate forms of guanylyl cyclase, respectively. However, natriuretic peptides and NO donors exert different effects on cardiac and vascular smooth muscle function. We therefore tested whether these differences are due to an intracellular compartmentation of cGMP and evaluated the role of phosphodiesterase (PDE) subtypes in this process. METHODS AND RESULTS: Subsarcolemmal cGMP signals were monitored in adult rat cardiomyocytes by expression of the rat olfactory cyclic nucleotide-gated (CNG) channel alpha-subunit and recording of the associated cGMP-gated current (ICNG). Atrial natriuretic peptide (10 nmol/L) or brain natriuretic peptide (10 nmol/L) induced a clear activation of ICNG, whereas NO donors (S-nitroso-N-acetyl-penicillamine, diethylamine NONOate, 3-morpholinosydnonimine, and spermine NO, all at 100 micromol/L) had little effect. The ICNG current was strongly potentiated by nonselective PDE inhibition with isobutyl methylxanthine (100 micromol/L) and by the PDE2 inhibitors erythro-9-(2-hydroxy-3-nonyl)adenine (10 micromol/L) and Bay 60-7550 (50 nmol/L). Surprisingly, sildenafil, a PDE5 inhibitor, produced a dose-dependent increase of I(CNG) activated by NO donors but had no effect (at 100 nmol/L) on the current elicited by atrial natriuretic peptide. CONCLUSIONS: These results indicate that in rat cardiomyocytes (1) the particulate cGMP pool is readily accessible at the plasma membrane, whereas the soluble pool is not; and (2) PDE5 controls the soluble but not the particulate pool, whereas the latter is under the exclusive control of PDE2. Differential spatiotemporal distributions of cGMP may therefore contribute to the specific effects of natriuretic peptides and NO donors on cardiac function. (+info)
Phosphodiesterase 2A forms a complex with the co-chaperone XAP2 and regulates nuclear translocation of the aryl hydrocarbon receptor.
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Phosphodiesterase type 2A (PDE2A) hydrolyzes cyclic nucleotides cAMP and cGMP, thus efficiently controlling cNMP-dependent signaling pathways. PDE2A is composed of an amino-terminal region, two regulatory GAF domains, and a catalytic domain. Cyclic nucleotide hydrolysis is known to be activated by cGMP binding to GAF-B; however, other mechanisms may operate to fine-tune local cyclic nucleotide levels. In a yeast two-hybrid screening we identified XAP2, a crucial component of the aryl hydrocarbon receptor (AhR) complex, as a major PDE2A-interacting protein. We mapped the XAP2 binding site to the GAF-B domain of PDE2A. PDE assays with purified proteins showed that XAP2 binding does not change the enzymatic activity of PDE2A. To analyze whether PDE2A could affect the function of XAP2, we studied nuclear translocation of AhR, i.e. the master transcription factor controlling the expression of multiple detoxification genes. Notably, regulation of AhR target gene expression is initiated by tetrachlorodibenzodioxin (TCDD) binding to AhR and by a poorly understood cAMP-dependent pathway followed by the translocation of AhR from the cytosol into the nucleus. Binding of PDE2A to XAP2 inhibited TCDD- and cAMP-induced nuclear translocation of AhR in Hepa1c1c7 hepatocytes. Furthermore, PDE2A attenuated TCDD-induced transcription in reporter gene assays. We conclude that XAP2 targets PDE2A to the AhR complex, thereby restricting AhR mobility, possibly by a local reduction of cAMP levels. Our results provide first insights into the elusive cAMP-dependent regulation of AhR. (+info)
Detection of near-atmospheric concentrations of CO2 by an olfactory subsystem in the mouse.
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Carbon dioxide (CO2) is an important environmental cue for many organisms but is odorless to humans. It remains unclear whether the mammalian olfactory system can detect CO2 at concentrations around the average atmospheric level (0.038%). We demonstrated the expression of carbonic anhydrase type II (CAII), an enzyme that catabolizes CO2, in a subset of mouse olfactory neurons that express guanylyl cyclase D (GC-D+ neurons) and project axons to necklace glomeruli in the olfactory bulb. Exposure to CO2 activated these GC-D+ neurons, and exposure of a mouse to CO2 activated bulbar neurons associated with necklace glomeruli. Behavioral tests revealed CO2 detection thresholds of approximately 0.066%, and this sensitive CO2 detection required CAII activity. We conclude that mice detect CO2 at near-atmospheric concentrations through the olfactory subsystem of GC-D+ neurons. (+info)
Differential regulation of endothelial cell permeability by cGMP via phosphodiesterases 2 and 3.
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Endothelial barrier dysfunction leading to increased permeability and vascular leakage is an underlying cause of several pathological conditions, including edema and sepsis. Whereas cAMP has been shown to decrease endothelial permeability, the role of cGMP is controversial. Endothelial cells express cGMP-inhibited phosphodiesterase (PDE)3A and cGMP-stimulated PDE2A. Thus we hypothesized that the effect of cGMP on endothelial permeability is dependent on the concentration of cGMP present and on the relative expression levels of PDE2A and PDE3A. When cAMP synthesis was slightly elevated with a submaximal concentration of 7-deacetyl-7-(O-[N-methylpiperazino]-gamma-butyryl)-dihydrochloride-forskolin (MPB-forskolin), we found that low doses of either atrial natriuretic peptide (ANP) or NO donors potentiated the inhibitory effects of MPB-forskolin on thrombin-induced permeability. However, this inhibitory effect of forskolin was reversed at higher doses of ANP or NO. These data suggest that cGMP at lower concentrations inhibits PDE3A and thereby increases a local pool of cAMP, whereas higher concentrations cGMP activates PDE2A, reversing the effect. Inhibitors of PDE3A mimicked the effect of low-dose ANP on thrombin-induced permeability, and inhibition of PDE2A reversed the stimulation of permeability seen with higher doses of ANP. Finally, increasing PDE2A expression with tumor necrosis factor-alpha reversed the inhibition of permeability caused by low doses of ANP. As predicted, the effect of tumor necrosis factor-alpha on permeability was reversed by a PDE2A inhibitor. These findings suggest that the effect of increasing concentrations of cGMP on endothelial permeability is biphasic, which, in large part, is attributable to the relative amounts of PDE2A and PDE3A in endothelial cells. (+info)
Farnesol and dodecanol effects on the Candida albicans Ras1-cAMP signalling pathway and the regulation of morphogenesis.
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Candida albicans hypha formation which has been stimulated via the Ras1-cAMP-Efg1 signalling cascade is inhibited by farnesol, a C. albicans autoregulatory factor, and small molecules such as dodecanol. In cultures containing farnesol or dodecanol, hypha formation was restored upon addition of dibutyryl-cAMP. The CAI4-Ras1(G13V) strain, which carries a dominant-active variant of Ras1 and forms hyphae in the absence of inducing stimuli, grew as yeast in medium with farnesol or dodecanol; the heat shock sensitivity of the CAI4-Ras1(G13V) strain was also suppressed by these compounds. Neither Pde1 nor Pde2 was necessary for the repression of hyphal growth by farnesol or dodecanol. Two transcripts, CTA1 and HSP12, which are at higher levels upon mutation of Ras1 or Cdc35, were increased in abundance in cells grown with farnesol or dodecanol. Microscopic analysis of strains carrying CTA1 and HWP1 promoter fusions grown with intermediate concentrations of farnesol or dodecanol indicated a link between cells with the increased expression of cAMP-repressed genes and cells repressed for hypha formation. Because several cAMP-controlled outputs are affected by farnesol and dodecanol, our findings suggest that these compounds impact activity of the Ras1-Cdc35 pathway, thus leading to an alteration of C. albicans morphology. (+info)
Induction of functional photoreceptor phenotype by exogenous Crx expression in mouse retinal stem cells.
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