Glucocorticoid uncoupling of antiogensin II-dependent phospholipase C activation in rat vascular smooth muscle cells

Synergistic effects of hormones on structural and functional maturation of cardiomyocytes and implications for heart regeneration

The limited endogenous regenerative capacity of the human heart renders cardiovascular diseases a major health threat, thus motivating intense research on in vitro heart cell generation and cell replacement therapies. However, so far, in vitro-generated cardiomyocytes share a rather fetal phenotype, limiting their utility for drug testing and cell-based heart repair. Various strategies to foster cellular maturation provide some success, but fully matured cardiomyocytes are still to be achieved. Today, several hormones are recognized for their effects on cardiomyocyte proliferation, differentiation, and function. Here, we will discuss how the endocrine system impacts cardiomyocyte maturation. After detailing which features characterize a mature phenotype, we will contemplate hormones most promising to induce such a phenotype, the routes of their action, and experimental evidence for their significance in this process. Due to their pleiotropic effects, hormones might be not only valuable to improve in vitro heart cell generation but also beneficial for in vivo heart regeneration. Accordingly, we will also contemplate how the presented hormones might be exploited for hormone-based regenerative therapies.

Intrarenal Renin Angiotensin System Imbalance During Postnatal Life Is Associated With Increased Microvascular Density in the Mature Kidney

Environmental stress during early life is an important factor that affects the postnatal renal development. We have previously shown that male rats exposed to maternal separation (MatSep), a model of early life stress, are normotensive but display a sex-specific reduced renal function and exacerbated angiotensin II (AngII)-mediated vascular responses as adults. Since optimal AngII levels during postnatal life are required for normal maturation of the kidney, this study was designed to investigate both short- and long-term effect of MatSep on (1) the renal vascular architecture and function, (2) the intrarenal renin-angiotensin system (RAS) components status, and (3) the genome-wide expression of genes in isolated renal vasculature. Renal tissue and plasma were collected from male rats at different postnatal days (P) for intrarenal RAS components mRNA and protein expression measurements at P2, 6, 10, 14, 21, and 90 and microCT analysis at P21 and 90. Although with similar body weight and renal mass trajectories from P2 to P90, MatSep rats displayed decreased renal filtration capacity at P90, while increased microvascular density at both P21 and P90 (p < 0.05). MatSep increased renal expression of renin, and angiotensin type 1 (AT1) and type 2 (AT2) receptors (p < 0.05), but reduced ACE2 mRNA expression and activity from P2-14 compared to controls. However, intrarenal levels of AngII peptide were reduced (p < 0.05) possible due to the increased degradation to AngIII by aminopeptidase A. In isolated renal vasculature from neonates, Enriched Biological Pathways functional clusters (EBPfc) from genes changed by MatSep reported to modulate extracellular structure organization, inflammation, and pro-angiogenic transcription factors. Our data suggest that male neonates exposed to MatSep could display permanent changes in the renal microvascular architecture in response to intrarenal RAS imbalance in the context of the atypical upregulation of angiogenic factors.

Phosphoinositide binding differentially regulates NHE1 Na+/H+ exchanger-dependent proximal tubule cell survival

Tubular atrophy predicts chronic kidney disease progression, and is caused by proximal tubular epithelial cellcaused by proximal tubular epithelial cell (PTC) apoptosis. The normally quiescent Na(+)/H(+) exchanger-1 (NHE1) defends against PTC apoptosis, and is regulated by PI(4,5)P(2) binding. Because of the vast array of plasma membrane lipids, we hypothesized that NHE1-mediated cell survival is dynamically regulated by multiple anionic inner leaflet phospholipids. In membrane overlay and surface plasmon resonance assays, the NHE1 C terminus bound phospholipids with low affinity and according to valence (PIP(3) > PIP(2) > PIP = PA > PS). NHE1-phosphoinositide binding was enhanced by acidic pH, and abolished by NHE1 Arg/Lys to Ala mutations within two juxtamembrane domains, consistent with electrostatic interactions. PI(4,5)P(2)-incorporated vesicles were distributed to apical and lateral PTC domains, increased NHE1-regulated Na(+)/H(+) exchange, and blunted apoptosis, whereas NHE1 activity was decreased in cells enriched with PI(3,4,5)P(3), which localized to basolateral membranes. Divergent PI(4,5)P(2) and PI(3,4,5)P(3) effects on NHE1-dependent Na(+)/H(+) exchange and apoptosis were confirmed by selective phosphoinositide sequestration with pleckstrin homology domain-containing phospholipase Cδ and Akt peptides, PI 3-kinase, and Akt inhibition in wild-type and NHE1-null PTCs. The results reveal an on-off switch model, whereby NHE1 toggles between weak interactions with PI(4,5)P(2) and PI(3,4,5)P(3). In response to apoptotic stress, NHE1 is stimulated by PI(4,5)P(2), which leads to PI 3-kinase activation, and PI(4,5)P(2) phosphorylation. The resulting PI(3,4,5)P(3) dually stimulates sustained, downstream Akt survival signaling, and dampens NHE1 activity through competitive inhibition and depletion of PI(4,5)P(2).

Stress induces the expression of heterotrimeric G protein β subunits and the phosphorylation of PKB/Akt and ERK1/2 in rat brain

Various heterotrimeric G protein betagamma subunits (Gbetagamma) are region-specifically expressed in brain where associated with "stress-axis", however, the role of Gbetagamma-mediated signaling in regulating stress is unknown. This study was designed to examine the changes of Gbetagamma expression and Gbetagamma-mediated signaling in rat brain by stress. Experimental stress was induced by immobilization (2h/day for 7 days) and the level of mRNAs and proteins for Gbeta(1-5), and the phosphorylation of PKB/Akt (phosphatidylinositol 3-kinase-linked protein kinase B) and ERK1/2 (extracellular signal-regulated kinase 1/2) were measured in five different regions of rat brain including frontal cortex, striatum, hypothalamus, hippocampus, and cerebellum. As compared in not-handled non-stressed animals, the expression of both mRNAs and proteins for Gbeta(1-5) in brain regions associated with stress was increased in stressed animals. Especially, a significant increase in Gbetas immunoreactivity in the caudate putamen, the paraventricular nucleus of the hypothalamus (PVN), and the dentate gyrus of the hippocampus (DG) of stressed rats was observed. Stress significantly induced the phosphorylation of PKB/Akt and ERK1/2 in striatum, hypothalamus and hippocampus. Therefore, these results suggest that stress may activate, at least in part, the Gbetagamma-mediated PKB/Akt and ERK1/2 signaling pathway by increasing the expression of Gbetas to regulate the physiological responses.

Dexamethasone decreases phospholipase C beta1 isozyme expression in human vascular smooth muscle cells

The molecular characterization of the human PLC beta1 gene was just reported by Peruzzi et al. [Biochim. Biophys. Acta 1582 (2002) 46]. This prompted us to investigate the effects of dexamethasone on PLC beta1 expression in two types of human vascular smooth muscle cells--coronary artery smooth muscle cells (hCASMC) and aortic smooth muscle cells (hAoSMC), since glucocorticoids are known to affect the signaling pathways of Gprotein coupled receptors. Semi-quantitative RT-PCR was used to analyze mRNA expression and Western-blot for protein expression. Dexamethasone treatment in the two types of cells studied decreased (mRNA and protein) PLC beta1 isozyme expression. A rapid (2 h) fall in mRNA occurred in hCASMC after treatment, and hCASMC were more sensitive to dexamethasone (1 nM versus 100 nM) than hAoSMC. The major reduction (80%) was observed after 48 h of exposure in both VSMC. Treatment with mifeprisone, an antagonist of glucocorticoid receptors, blunted the dexamethasone effect on PLC beta1 mRNA and showed that this effect was mediated by glucocorticoids receptors.

Fas activation induces renal tubular epithelial cell beta 8 integrin expression and function in the absence of apoptosis

Cell fate following Fas (CD95) ligand or agonistic anti-Fas antibody stimulation is determined by multiple factors, including Fas expression level, microdomain localization, and modulating cytokines. Highly expressed Fas clusters and activates a canonical apoptosis signaling pathway. In less susceptible cells, Fas transduces apoptosis-independent signals, which are not well defined, but have been linked to inflammation, angiogenesis, and fibrosis. To identify apoptosis-independent Fas pathways, cultured renal tubular epithelial cells were stimulated with agonistic anti-Fas antibodies under conditions that did not cause cell death. Analysis of filter cDNA microarrays revealed beta(8) integrin subunit mRNA induction in Fas-stimulated cells. beta(8) integrin mRNA expression increased within 3-6 h of Fas ligation due to enhanced mRNA stabilization, and mRNA increases were sustained for 48-72 h. Expression of plasma membrane beta(8) integrin, as well as its heterodimer partner alpha(v), was increased by Fas activation with a similar kinetic pattern. Fas-induced alpha(v)beta(8) expression correlated with increased migration to vitronectin, the ligand for alpha(v)beta(8). Results from studies with function-blocking antibodies against other alpha(v)beta integrins or suppression of beta(8) integrin expression by RNA interference demonstrated that induced beta(8) integrin expression mediated Fas-stimulated migration. We conclude that alpha(v)beta(8) integrin induction defines an unexpected role for Fas in cell migration, rather than as a cell death receptor.

Retinoids inhibit the actions of angiotensin II on vascular smooth muscle cells

Retinoids are derivatives of vitamin A and powerful inhibitors of cell proliferation and inflammation. Angiotensin II (Ang II) contributes to vascular lesions by promoting cell growth of vascular smooth muscle cells (VSMCs). Therefore, we examined whether retinoids interfere with the proproliferative actions of Ang II in VSMCs via AT(1) receptor-dependent or activator protein-1 (AP-1)-dependent mechanisms. VSMCs express retinoid receptor proteins, ie, retinoic acid receptor (RAR) alpha and retinoid X receptor (RXR) alpha. Long-term exposure to 1 micromol/L all-trans retinoic acid (RA) dose-dependently inhibited Ang II-induced cell proliferation (P<0.005) as well as DNA and protein synthesis (P<0.001). All-trans RA blocked Ang II stimulation of transforming growth factor-beta(1) mRNA (P<0.005). All-trans RA inhibition of vascular VSMC growth was mediated both via RAR- and RXR-dependent pathways, as shown by receptor-specific synthetic retinoids. Transfection experiments revealed that inhibition of AP-1-dependent gene transcription is one mechanism by which all-trans RA inhibits Ang II action. RARalpha cotransfection enhanced the anti-AP-1 effects of all-trans RA dose-dependently. AP-1 activity was similarly inhibited by cotransfection with either RARalpha or RXRalpha. Ang II-induced gene expression of c-fos was abrogated by all-trans RA treatment (P<0.005). In VSMCs, all-trans RA downregulated AT(1) receptor mRNA (P<0.01) and reduced B(max) (P<0.001). All-trans RA repressed Ang II-stimulated AT(1) receptor promoter activity. The all-trans RA inhibitory effect was abolished when the AP-1 consensus site on the AT(1) receptor promoter was deleted. Our findings demonstrate that retinoids are potent inhibitors of the actions of Ang II on VSMCs. The findings support the notion that retinoids may interfere with proliferative vascular disease.

Sodium-potassium-adenosinetriphosphatase-dependent sodium transport in the kidney: hormonal control

Tubular reabsorption of filtered sodium is quantitatively the main contribution of kidneys to salt and water homeostasis. The transcellular reabsorption of sodium proceeds by a two-step mechanism: Na(+)-K(+)-ATPase-energized basolateral active extrusion of sodium permits passive apical entry through various sodium transport systems. In the past 15 years, most of the renal sodium transport systems (Na(+)-K(+)-ATPase, channels, cotransporters, and exchangers) have been characterized at a molecular level. Coupled to the methods developed during the 1965-1985 decades to circumvent kidney heterogeneity and analyze sodium transport at the level of single nephron segments, cloning of the transporters allowed us to move our understanding of hormone regulation of sodium transport from a cellular to a molecular level. The main purpose of this review is to analyze how molecular events at the transporter level account for the physiological changes in tubular handling of sodium promoted by hormones. In recent years, it also became obvious that intracellular signaling pathways interacted with each other, leading to synergisms or antagonisms. A second aim of this review is therefore to analyze the integrated network of signaling pathways underlying hormone action. Given the central role of Na(+)-K(+)-ATPase in sodium reabsorption, the first part of this review focuses on its structural and functional properties, with a special mention of the specificity of Na(+)-K(+)-ATPase expressed in renal tubule. In a second part, the general mechanisms of hormone signaling are briefly introduced before a more detailed discussion of the nephron segment-specific expression of hormone receptors and signaling pathways. The three following parts integrate the molecular and physiological aspects of the hormonal regulation of sodium transport processes in three nephron segments: the proximal tubule, the thick ascending limb of Henle's loop, and the collecting duct.

Glucocorticoids inhibit superoxide anion production and p22 phox mRNA expression in human aortic smooth muscle cells

-Recent reports suggest that the increased production of reactive oxygen species (ROS) in the vascular wall may contribute to the functional and structural changes associated with hypertension and atherosclerosis. Although glucocorticoid therapy can promote atherosclerosis, protective effects of these compounds on vascular lesion formation have been reported. In the present study, we investigated whether ROS production in cultured human aortic smooth muscle cells (HSMCs) can be modulated by glucocorticoids. Pretreatment of HSMCs with dexamethasone for 24 hours attenuated the basal and platelet-derived growth factor (PDGF)-AB- and angiotensin II-induced superoxide anion (O2. -) production. PDGF-AB-stimulated O2. - production was also inhibited by prednisolone and hydrocortisone but not by other steroids, such as testosterone and norgestrel. Incubation of HSMCs with glucocorticoids for 24 hours decreased 2',7'-dichlorodihydrofluorescein (DCHF) oxidation, an indicator of intracellular ROS levels. Dexamethasone decreased the mRNA expression of p22 phox, one of the components of NADPH oxidase, but had no effect on the activity of superoxide dismutase. The effects of dexamethasone on DCHF oxidation, and p22 phox mRNA expression and PDGF-AB-stimulated O2. - production were inhibited by the glucocorticoid receptor antagonist RU486. These results indicate that glucocorticoids decrease O2. - production by HSMCs via a receptor-dependent pathway. This effect is likely to be mediated by a decrease in the generating system, such as downregulation of p22 phox mRNA, rather than an increased inactivation of O2. -. The inhibition of ROS production might contribute to the local protective effects that glucocorticoids have on vascular lesion formation.

G-protein-mediated signaling in cholesterol-enriched arterial smooth muscle cells. 2. Role of protein kinase C-delta in the regulation of eicosanoid production

PGI2 generation by the vessel wall is an agonist for cyclic-AMP-dependent cholesteryl ester hydrolysis. The process of enhanced PGI2 synthesis is stimulated, in part, by G-protein-coupled receptor ligands. Cellular cholesterol enrichment has been hypothesized to alter G-protein-mediated PGI2 synthesis. In the studies reported herein, cells generated PGI2 in response to AlF4-, GTPgammaS, and ATP in a dose-dependent manner. G-protein agonists stimulated eicosanoid production principally by activating phospholipase A2, but not phospholipase C. This is in contrast to PDGF, which stimulated phospholipase A2 and PLCgamma activities. Galphai subunits mediate G-protein agonist-induced PGI2 synthesis, since ATP- and PDGF-induced PGI2 synthesis was inhibited by pertussis toxin. Although cholesterol enrichment reduced arachidonic acid- and PDGF-induced PGI2 synthesis, cholesterol enrichment enhanced PGI2 release in response to AlF4-, GTPgammaS, and ATP. The enhancement of PGI2 release in cholesterol-enriched cells was augmented by mevalonate, which inhibits the ability of cholesterol enrichment to reduce membrane-associated G-protein subunits. Since cholesterol enrichment inhibited PDGF and AlF4--induced MAP kinase activity [Pomerantz, K., Lander, H. M., Summers, B., Robishaw, J. D., Balcueva, E. A., & Hajjar, D. P. (1997) Biochemistry 36, 9523-9531] (the major mechanism by which phospholipase A2 is activated), these results suggest that cholesterol enrichment induces other alternative signaling pathways leading to phospholipase A2 activation. A PKC-dependent pathway is described herein that is involved in enhanced eicosanoid production in cholesterol-enriched cells. This conclusion is supported by two observations: (1) G-protein-linked PGI2 production is inhibited by calphostin, and (2) cholesterol enrichment augments the specific translocation of the delta-isoform of PKC from the cytosol to the plasma membrane following treatment of cells with phorbol ester. These data support the concept that, in cells possessing normal levels of cholesterol, MAP-kinase-dependent pathways mediate eicosanoid synthesis in response to G-protein activation; however, under conditions of high cellular cholesterol levels, augmented G-protein-linked eicosanoid production results from enhanced PKCdelta activity.

Glucocorticoids stimulate cholesteryl ester formation in human smooth muscle cells

The aim of the present study was to investigate the effect of synthetic glucocorticoid dexamethasone (Dex) on cholesterol esterification in cultured human smooth muscle cells (SMC). In labeled SMC, Dex stimulated the esterification of [3H]cholesterol in a dose-dependent manner. This effect was specific for glucocorticoid hormones and could be inhibited by cycloheximide (3 ng/mL), actinomycin D (10(-5) mol/L), and the specific glucocorticoid antagonist RU 486 (10(-8) mol/L). When plasma membrane was selectively labeled with trace quantities of [3H]cholesterol (0.25 microCi/mL, 1 hour, 10 degrees C), Dex (10(-8) mol/L) caused a net flux of free [3H]cholesterol into the cells. Moreover, Dex (10(-8) mol/L, 24 hours) stimulated the esterification of sterols, newly synthesized from [14C]mevalonate (10 microCi/mL, 4 hours) and lowered the amount of [14C]sterols susceptible for cholesterol oxidase. The incorporation of [14C]oleic acid into cholesteryl esters was markedly higher in Dex-pretreated SMC than in the control cells (2.1 +/- 0.07 and 1.4 +/- 0.1 pmol/h/microgram protein, respectively, P < .01). At the time, cholesteryl ester hydrolysis in Dex-treated cells was reduced (72 +/- 8 pmol cholesteryl esters/h per milligram versus 130 +/- 10 in the control cells). HDL3-mediated [3H]cholesterol efflux was also inhibited in Dex-treated cells; moreover, HDL3 (40 micrograms/mL, 24 hours) had practically no effect on [3H]cholesteryl ester content in Dex-treated SMC but caused a 50% reduction of [3H]cholesteryl esters in the control cells. Thus, in human SMC glucocorticoids alter the redistribution of cholesterol between the pools of free and esterified cholesterol, paralleled by the change in acyl coenzyme A: cholesteryl acyltransferase and neutral cholesteryl ester hydrolase activities, leading to the impaired HDL3-mediated cholesterol efflux.

Corticosterone alters G protein alpha-subunit levels in the rat hippocampus

The hypothalamic-pituitary-adrenal axis regulates the synthesis and secretion of corticosteroid hormones. The hippocampus, a component of the limbic system, contains the highest concentration of corticosteroid receptors in the brain and may play an important role in regulating hypothalamic-pituitary-adrenal axis activity and mediating physiological responses to stress. The corticosteroid hormone corticosterone alters the response elicited by activation of several different G protein-linked neurotransmitter receptors in the hippocampus. In the present study we used Western blot and immunohistochemical techniques to determine the effects of chronic adrenalectomy (ADX), low basal (CT) and high (HCT) corticosterone treatments on Gs, Gi1 and 2 and Go alpha-subunit levels and intracellular location in the rat hippocampus. CT treatment increased Gs alpha-subunit levels and HCT treatment increased the levels of Gs, Gi1 and 2 and Go alpha-subunits when compared to sham as detected on Western blots. No change in the intracellular location of the G protein alpha-subunits was detected using immunohistochemistry. Based on our results, we conclude that corticosterone alters G protein alpha-subunit levels in the rat hippocampus without altering their intracellular location. These results provide an important piece of information towards understanding how corticosteroids alter G protein-linked neurotransmitter receptor-mediated responses.

Regulation of angiotensin II receptor subtypes by dexamethasone in rat mesangial cells

The objective of this study was to examine the role of dexamethasone on the expression of angiotensin II (Ang II) receptors in cultured rat mesangial cells. Dexamethasone caused concentration- and time-dependent decreases in 125I-[Sar1,Ala8]Ang II binding that were prevented by glucocorticoid receptor inhibition with mifepristone. A lag time of 24 hours and a dexamethasone concentration of at least 10 nmol/L were necessary for this effect to occur. Dexamethasone-induced reduction of 125I-[Sar1,Ala8]Ang II binding resulted from decreased Ang II type 1 (AT1) receptor density. No change in the apparent dissociation constant was observed. Dexamethasone also markedly inhibited Ang II-dependent inositol phosphate accumulation. Both reverse transcription-polymerase chain reaction and Northern blot analysis using specific short probes from the 3' noncoding region of the cDNA demonstrated the presence of AT1A and AT1B receptor mRNAs in rat mesangial cells, with a slight predominance of AT1B. Therefore, we studied the effect of dexamethasone on the expression of these two subtypes in rat mesangial cells. Dexamethasone produced a time-dependent decrease of AT1B receptor mRNA that was apparent after 6 hours of incubation, whereas AT1A receptor mRNA did not change. Mifepristone also suppressed the dexamethasone-induced decrease in AT1B receptor mRNA. In conclusion, glucocorticoids diminish Ang II receptor density at the mesangial cell surface through a mechanism that implies successive interaction with the glucocorticoid receptor and specific reduction in AT1B receptor mRNA expression. This differential regulation of both AT1 receptor subtypes might allow glucocorticoids to exert adjusted effects in their various target tissues.

The antiglucocorticoid action of mifepristone

Glucocorticoid hormones influence the physiological activity of almost all cell types in the mammal. This is accomplished via a soluble receptor that, in the presence of an appropriate steroid, modifies the activity of RNA polymerase by binding to the site where different factors assemble for the initiation of cell transcription. The development of antiglucocorticoids has permitted the molecular elucidation of a number of underlying events. Contrary to the classical view, it is now clear that the affinity, stability and activability of the glucocorticoid receptor in the presence of a steroid are cell- and/or tissue-dependent events. The antiglucocorticoid RU 38486 can even activate transcription by binding to sites distinct from those that process transactivation by the agonist. Furthermore, glucocorticoids can sometimes activate the mineralocorticoid receptor, whereas mineralocorticoids can bind the glucocorticoid receptor. Since mifepristone is devoid of adverse toxicity, it has been used for the paraclinical diagnosis of the hypothalamus-pituitary-adrenal axis in normal volunteers, subjects with disorders of the behaviour, and the treatment of Cushing's disease. However, the whole spectrum of cell-specific processes that are antagonized by RU 38486 suggests wide ranging possibilities in the eventual application of antigluco-corticoids.

Corticosterone metabolism and effects on angiotensin II receptors in vascular smooth muscle

It has been postulated that mineralocorticoids can bind to corticosteroid receptors in the kidney, because glucocorticoids are metabolized to inactive compounds. The present study was performed to delineate glucocorticoid metabolism by rat vascular tissue and to determine the activity of these metabolites. Vascular segments converted 25% to 30% of corticosterone (compound B), the major glucocorticoid in the rat, to 11-dehydrocorticosterone (compound A) but not to aldosterone or 6 beta-hydroxycorticosterone. In cultured vascular smooth muscle cells, 10% of compound B was converted to compound A, whereas > 60% of compound A was converted to compound B. The 11 beta-hydroxysteroid dehydrogenase inhibitor carbenoxolone (1 mumol/L) completely blocked conversion in both directions. Whereas 6 beta-hydroxycorticosterone did not upregulate angiotensin II receptor binding (a marker for corticosteroid action in vascular smooth muscle), compound A caused concentration-dependent upregulation. Compound A was almost (75%) as effective and as potent as compound B in upregulating angiotensin II binding. Upregulation elicited by exposure to compound A persisted in the presence of 1 mumol/L carbenoxolone, which completely prevented the conversion of compound A to compound B. Compound A, even in the presence of carbenoxolone, effected other glucocorticoid actions by inhibiting cell growth and potentiating angiotensin II-stimulated inositol phosphate formation. In summary, compound B and compound A are interconverted in vascular tissue, and the latter displays significant glucocorticoid action. The concentration excess of compound B in the circulation and the activity of its metabolite compound A will make it difficult for mineralocorticoids to gain access to corticosteroid receptors in the vasculature.