Inflammasome Activation in Chronic Glomerular Diseases.

BACKGROUND: The intracellular multiprotein complex termed the inflammasome functions as a platform of pro-inflammatory cytokine production such as IL-1ß and IL-18. Under certain conditions, however, the inflammasome produces non-canonical effects such as induction of cell death, pyroptosis and cell metabolism alterations. OBJECTIVE: In mammalian cells, several types of inflammasomes were identified, but the most widely studied one is the inflammasome containing NOD-like receptor with pyrin domain 3 (NLRP3), which has recently been reported as a central pathogenic mechanism of chronic degenerative diseases. Many activators or risk factors exert their actions through the activation of the NLRP3 inflammasome to produce a variety of functional changes in different cells including inflammatory, metabolic or survival responses. Several molecular signaling pathways are shown to mediate the activation of the NLRP3 inflammasome, and they are related to the modifications in K+ efflux, increased lysosome leakage and activation of cathepsin B or enhanced reactive oxygen species (ROS) production. In the kidney, inflammation is believed to mediate or promote the progression of glomerular sclerotic pathologies resulting in end-stage renal disease (ESRD). NLRP3 inflammasome activation may turn on glomerular inflammation and other cell damages, contributing to the onset of glomerular injury and ESRD. This inflammasome activation not only occurs in immune cells, but also in residential cells such as endothelial cells and podocytes in the glomeruli. SUMMARY: This review briefly summarizes current evidence of NLRP3 inflammasome activation and related molecular mechanisms in renal glomeruli. The possible canonical and non-canonical effects of this inflammasome activation and its potential implication in the development of different glomerular diseases are highlighted.

Protective Action of Anandamide and Its COX-2 Metabolite against l-Homocysteine-Induced NLRP3 Inflammasome Activation and Injury in Podocytes.

Recent studies have demonstrated that l-homocysteine (Hcys)-induced podocyte injury leading to glomerular damage or sclerosis is attributable to the activation of the nucleotide-binding oligomerization domain-like receptor containing pyrin domain 3 (NLRP3) inflammasome. Given the demonstrated anti-inflammatory effects of endocannabinoids, the present study was designed to test whether anandamide (AEA) or its metabolites diminish NLRP3 inflammasome activation and prevent podocyte injury and associated glomerular damage during hyperhomocysteinemia (hHcys). AEA (100 µM) inhibited Hcys-induced NLRP3 inflammasome activation in cultured podocytes, as indicated by elevated caspase-1 activity and interleukin-1ß levels, and attenuated podocyte dysfunction, as shown by reduced vascular endothelial growth factor production. These effects of AEA were inhibited by the cyclooxygenase-2 (COX-2) inhibitor celecoxib (CEL). In mice in vivo, AEA treatment attenuated glomerular NLRP3 inflammasome activation induced by hHcys accompanying a folate-free diet, on the basis of inhibition of hHcys-induced colocalization of NLRP3 molecules and increased interleukin-1ß levels in glomeruli. Correspondingly, AEA prevented hHcys-induced proteinuria, albuminuria, and glomerular damage observed microscopically. Hcys- and AEA-induced effects were absent in NLRP3-knockout mice. These beneficial effects of AEA against hHcys-induced NLRP3 inflammasome activation and glomerular injury were not observed in mice cotreated with CEL. We further demonstrated that prostaglandin E2-ethanolamide (PGE2-EA), a COX-2 product of AEA, at 10 µM had a similar inhibitory effect to that of 100 µM AEA on Hcys-induced NLRP3 inflammasome formation and activation in cultured podocytes. From these results, we conclude that AEA has anti-inflammatory properties, protecting podocytes from Hcys-induced injury by inhibition of NLRP3 inflammasome activation through its COX-2 metabolite, PGE2-EA.

Characterization and Activation of NLRP3 Inflammasomes in the Renal Medulla in Mice.

BACKGROUND/AIMS: Recent studies have indicated that local inflammatory mediators are importantly involved in the regulation of renal function. However, it remains unknown how such local inflammation is triggered intracellularly in the kidney. The present study was designed to characterize the inflammasome centered by Nlrp3 in the kidney and also test the effect of its activation in the renal medulla. METHODS AND RESULTS: By immunohistochemistry analysis, we found that inflammasome components, Nlrp3, Asc and caspase-1, were ubiquitously distributed in different kidney areas. The caspase-1 activity and IL-1ß production were particularly high in the renal outer medulla compared to other kidney regions. Further confocal microscopy and RT-PCR analysis showed that Nlrp3, Asc and caspase-1 were particularly enriched in the thick ascending limb of Henle's loop. In anesthetized mice, medullary infusion of Nlrp3 inflammasome activator, monosodium urate (MSU), induced significant decreases in sodium excretion and medullary blood flow without changes in mean arterial blood pressure and renal cortical blood flow. Caspase-1 inhibitor, Ac-YVAD-CMK and deletion of Nlrp3 or Asc gene abolished MSU-induced decreases in renal sodium excretion and MBF. CONCLUSION: Our results indicate that renal medullary Nlrp3 inflammasomes represent a new regulatory mechanism of renal MBF and sodium excretion which may not depend on classical inflammatory response.

Inflammation and hypertension: new understandings and potential therapeutic targets.

Research studying the role of inflammation in hypertension and cardiovascular disease has flourished in recent years; however, the exact mechanisms by which the activated immune cells lead to the development and maintenance of hypertension remain to be elucidated. The objectives of this brief review are to summarize and discuss the most recent findings in the field, with special emphasis on potential therapeutics to treat or prevent hypertension. This review will cover novel immune cell subtypes recently associated to the disease including the novel role of cytokines, toll-like receptors, and inflammasomes in hypertension.

Redox regulation of NLRP3 inflammasomes: ROS as trigger or effector?

SIGNIFICANCE: Inflammasomes are multiprotein complexes localized within the cytoplasm of the cell that are responsible for the maturation of proinflammatory cytokines such as interleukin-1ß (IL-1ß) and IL-18, and the activation of a highly inflammatory form of cell death, pyroptosis. In response to infection or cellular stress, inflammasomes are assembled, activated, and involved in host defense and pathophysiology of diseases. Clarification of the molecular mechanisms leading to the activation of this intracellular inflammatory machinery may provide new insights into the concept of inflammation as the root of and route to human diseases. RECENT ADVANCES: The activation of inflammasomes, specifically the most fully characterized inflammasome-the nucleotide-binding oligomerization domain (NOD)-like receptor containing pyrin domain 3 (NLRP3) inflammasome, is now emerging as a critical molecular mechanism for many degenerative diseases. Several models have been developed to describe how NLRP3 inflammasomes are activated, including K(+) efflux, lysosome function, endoplasmic reticulum (ER) stress, intracellular calcium, ubiquitination, microRNAs, and, in particular, reactive oxygen species (ROS). CRITICAL ISSUES: ROS may serve as a "kindling" or triggering factor to activate NLRP3 inflammasomes as well as "bonfire" or "effector" molecules, resulting in pathological processes. Increasing evidence seeks to understand how this spatiotemporal action of ROS occurs during NLRP3 inflammasome activation, which will be a major focus of this review. FUTURE DIRECTIONS: It is imperative to know how this dual action of ROS works during NLRP3 inflammation activation on different stimuli and what relevance such spatiotemporal redox regulation of NLRP3 inflammasomes has in cell or organ functions and possible human diseases.

Nod-like receptor protein 3 (NLRP3) inflammasome activation and podocyte injury via thioredoxin-interacting protein (TXNIP) during hyperhomocysteinemia.

NADPH oxidase-derived reactive oxygen species (ROS) have been reported to activate NLRP3 inflammasomes resulting in podocyte and glomerular injury during hyperhomocysteinemia (hHcys). However, the mechanism by which the inflammasome senses ROS is still unknown in podocytes upon hHcys stimulation. The current study explored whether thioredoxin-interacting protein (TXNIP), an endogenous inhibitor of the antioxidant thioredoxin and ROS sensor, mediates hHcys-induced NLRP3 inflammasome activation and consequent glomerular injury. In cultured podocytes, size exclusion chromatography and confocal microscopy showed that inhibition of TXNIP by siRNA or verapamil prevented Hcys-induced TXNIP protein recruitment to form NLRP3 inflammasomes and abolished Hcys-induced increases in caspase-1 activity and IL-1ß production. TXNIP inhibition protected podocytes from injury as shown by normal expression levels of podocyte markers, podocin and desmin. In vivo, adult C57BL/6J male mice were fed a folate-free diet for 4 weeks to induce hHcys, and TXNIP was inhibited by verapamil (1 mg/ml in drinking water) or by local microbubble-ultrasound TXNIP shRNA transfection. Evidenced by immunofluorescence and co-immunoprecipitation studies, glomerular inflammasome formation and TXNIP binding to NLRP3 were markedly increased in mice with hHcys but not in TXNIP shRNA-transfected mice or those receiving verapamil. Furthermore, TXNIP inhibition significantly reduced caspase-1 activity and IL-1ß production in glomeruli of mice with hHcys. Correspondingly, TXNIP shRNA transfection and verapamil attenuated hHcys-induced proteinuria, albuminuria, glomerular damage, and podocyte injury. In conclusion, our results demonstrate that TXNIP binding to NLRP3 is a key signaling mechanism necessary for hHcys-induced NLRP3 inflammasome formation and activation and subsequent glomerular injury.

Endothelial NLRP3 inflammasome activation and enhanced neointima formation in mice by adipokine visfatin.

Inflammasomes serve as an intracellular machinery to initiate inflammatory response to various danger signals. The present study tested whether an inflammasome centered on nucleotide oligomerization domain-like receptor protein 3 (NLRP3) triggers endothelial inflammatory response to adipokine visfatin, a major injurious adipokine during obesity. NLRP3 inflammasome components were abundantly expressed in cultured mouse microvascular endothelial cells, including NLRP3, apoptosis-associated speck-like protein, and caspase-1. These NLRP3 inflammasome molecules could be aggregated to form an inflammasome complex on stimulation of visfatin, as shown by fluorescence confocal microscopy and size exclusion chromatography. Correspondingly, visfatin significantly increased caspase-1 activity and IL-1ß release in microvascular endothelial cells, indicating an activation of NLRP3 inflammasomes. In animal experiments, direct infusion of visfatin in mice with partially ligated left carotid artery were found to have significantly increased neointimal formation, which was correlated with increased NLRP3 inflammasome formation and IL-1ß production in the intima. Further, visfatin-induced neointimal formation, endothelial inflammasome formation, and IL-1ß production in mouse partially ligated left carotid artery were abolished by caspase-1 inhibition, local delivery of apoptosis-associated speck-like protein shRNA or deletion of the ASC gene. In conclusion, the formation and activation of NLRP3 inflammasomes by adipokine visfatin may be an important initiating mechanism to turn on the endothelial inflammatory response leading to arterial inflammation and endothelial dysfunction in mice during early stage obesity.

Upregulation of cannabinoid receptor-1 and fibrotic activation of mouse hepatic stellate cells during Schistosoma J. infection: role of NADPH oxidase.

The endocannabinoid system (CS) has been implicated in the development of hepatic fibrosis such as schistosomiasis-associated liver fibrosis (SSLF). However, the mechanisms mediating the action of the CS in hepatic fibrosis are unclear. The present study hypothesized that Schistosoma J. infection upregulates cannabinoid receptor 1 (CB1) due to activation of NADPH oxidase leading to a fibrotic phenotype in hepatic stellate cells (HSCs). The SSLF model was developed by infecting mice with Schistosoma J. cercariae in the skin, and HSCs from control and infected mice were then isolated, cultured, and confirmed by analysis of HSC markers α-SMA and desmin. CB1 significantly increased in HSCs isolated from mice with SSLF, which was accompanied by a greater expression of fibrotic markers α-SMA, collagen I, and TIMP-1. CB1 upregulation and enhanced fibrotic changes were also observed in normal HSCs treated with soluble egg antigen (SEA) from Schistosoma J. Electron spin resonance (ESR) analysis further demonstrated that superoxide (O2(-)) production was increased in infected HSCs or normal HSCs stimulated with SEA. Both Nox4 and Nox1 siRNA prevented SEA-induced upregulation of CB1, α-SMA, collagen I, and TIMP-1 by inhibition of O2(-) production, while CB1 siRNA blocked SEA-induced fibrotic changes without effect on O2(-) production in these HSCs. Taken together, these data suggest that the fibrotic activation of HSCs on Schistosoma J. infection or SEA stimulation is associated with NADPH oxidase-mediated redox regulation of CB1 expression, which may be a triggering mechanism for SSLF.

Contribution of endogenously produced reactive oxygen species to the activation of podocyte NLRP3 inflammasomes in hyperhomocysteinemia.

Hyperhomocysteinemia (hHcys) is an important pathogenic factor contributing to the progression of end-stage renal disease. Recent studies have demonstrated the implication of nicotinamide adenine dinucleotide phosphate oxidase-mediated NLRP3 inflammasome activation in the development of podocyte injury and glomerular sclerosis during hHcys. However, it remains unknown which reactive oxygen species (ROS) are responsible for this activation of NLRP3 inflammasomes and how such action of ROS is controlled. This study tested the contribution of common endogenous ROS including superoxide (O2(-)), hydrogen peroxide (H2O2), peroxynitrite (ONOO(-)), and hydroxyl radical (OH) to the activation of NLRP3 inflammasomes in mouse podocytes and glomeruli. In vitro, confocal microscopy and size-exclusion chromatography demonstrated that dismutation of O2(-) by 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (Tempol) and decomposition of H2O2 by catalase prevented Hcys-induced aggregation of NLRP3 inflammasome proteins and inhibited Hcys-induced caspase-1 activation and IL-1ß production in mouse podocytes. However, scavenging of ONOO(-) or OH had no significant effect on either Hcys-induced NLRP3 inflammasome formation or activation. In vivo, scavenging of O2(-) by Tempol and removal of H2O2 by catalase substantially inhibited NLRP3 inflammasome formation and activation in glomeruli of hHcys mice as shown by reduced colocalization of NLRP3 with ASC or caspase-1 and inhibition of caspase-1 activation and IL-1ß production. Furthermore, Tempol and catalase significantly attenuated hHcys-induced glomerular injury. In conclusion, endogenously produced O2(-) and H2O2 primarily contribute to NLRP3 inflammasome formation and activation in mouse glomeruli resulting in glomerular injury or consequent sclerosis during hHcys.

Autophagy maturation associated with CD38-mediated regulation of lysosome function in mouse glomerular podocytes.

Podocytes are highly differentiated glomerular epithelial cells that contribute to the glomerular barrier function of kidney. A role for autophagy has been proposed in maintenance of their cellular integrity, but the mechanisms controlling autophagy in podocytes are not clear. The present study tested whether CD38-mediated regulation of lysosome function contributes to autophagic flux or autophagy maturation in podocytes. Podocytes were found to exhibit a high constitutive level of LC3-II, a robust marker of autophagosomes (APs), suggesting a high basal level of autophagic activity. Treatment with the mTOR inhibitor, rapamycin, increased LC3-II and the content of both APs detected by Cyto-ID Green staining and autophagolysosomes (APLs) measured by acridine orange staining and colocalization of LC3 and Lamp1. Lysosome function inhibitor bafilomycin A1 increased APs, but decreased APLs content under both basal and rapamycin-induced conditions. Inhibition of CD38 activity by nicotinamide or silencing of CD38 gene produced the similar effects to that bafilomycin A1 did in podocytes. To explore the possibility that CD38 may control podocyte autophagy through its regulation of lysosome function, the fusion of APs with lysosomes in living podocytes was observed by co-transfection of GFP-LC3B and RFP-Lamp1 expression vectors. A colocalization of GFP-LC3B and RFP-Lamp1 upon stimulation of rapamycin became obvious in transfected podocytes, which could be substantially blocked by nicotinamide, CD38 shRNA, and bafilomycin. Moreover, blockade of the CD38-mediated regulation by PPADS completely abolished rapamycin-induced fusion of APs with lysosomes. These results indicate that CD38 importantly control lysosomal function and influence autophagy at the maturation step in podocytes.

Contribution of NADPH oxidase to membrane CD38 internalization and activation in coronary arterial myocytes.

The CD38-ADP-ribosylcyclase-mediated Ca(2+) signaling pathway importantly contributes to the vasomotor response in different arteries. Although there is evidence indicating that the activation of CD38-ADP-ribosylcyclase is associated with CD38 internalization, the molecular mechanism mediating CD38 internalization and consequent activation in response to a variety of physiological and pathological stimuli remains poorly understood. Recent studies have shown that CD38 may sense redox signals and is thereby activated to produce cellular response and that the NADPH oxidase isoform, NOX1, is a major resource to produce superoxide (O2·-)) in coronary arterial myocytes (CAMs) in response to muscarinic receptor agonist, which uses CD38-ADP-ribosylcyclase signaling pathway to exert its action in these CAMs. These findings led us hypothesize that NOX1-derived O2·- serves in an autocrine fashion to enhance CD38 internalization, leading to redox activation of CD38-ADP-ribosylcyclase activity in mouse CAMs. To test this hypothesis, confocal microscopy, flow cytometry and a membrane protein biotinylation assay were used in the present study. We first demonstrated that CD38 internalization induced by endothelin-1 (ET-1) was inhibited by silencing of NOX1 gene, but not NOX4 gene. Correspondingly, NOX1 gene silencing abolished ET-1-induced O2·- production and increased CD38-ADP-ribosylcyclase activity in CAMs, while activation of NOX1 by overexpression of Rac1 or Vav2 or administration of exogenous O2·- significantly increased CD38 internalization in CAMs. Lastly, ET-1 was found to markedly increase membrane raft clustering as shown by increased colocalization of cholera toxin-B with CD38 and NOX1. Taken together, these results provide direct evidence that Rac1-NOX1-dependent O2·- production mediates CD38 internalization in CAMs, which may represent an important mechanism linking receptor activation with CD38 activity in these cells.

Enhancement of autophagy by simvastatin through inhibition of Rac1-mTOR signaling pathway in coronary arterial myocytes.

BACKGROUND/AIMS: In addition to their action of lowering blood cholesterol levels, statins modulate biological characteristics and functions of arterial myocytes such as viability, proliferation, apoptosis, survival and contraction. The present study tested whether simvastatin, as a prototype statin, enhances autophagy in coronary arterial myocytes (CAMs) to thereby exert their beneficial effects in atherosclerosis. METHODS AND RESULTS: Using flow cytometry, we demonstrated that simvastatin significantly increased the autophagsome formation in CAMs. Western blot analysis confirmed that simvastatin significantly increased protein expression of typical autophagy markers LC3B and Beclin1 in these CAMs. Confocal microscopy further demonstrated that simvastatin increased fusion of autophagosomes with lysosomes, which was blocked by autophagy inhibitor 3-methyladenine or silencing of Atg7 genes. Simvastatin reduced mammalian target of rapamycin (mTOR) activity, which was reversed by Rac1-GTPase overexpression and the mTOR agonist phosphatidic acid. Moreover, both Rac1-GTPase overexpression and activation of mTOR by phosphatidic acid drastically blocked simvastatin-induced autophagosome formation in CAMs. Interestingly, simvastatin increased protein expression of a contractile phenotype marker calponin in CAMs, which was blocked by autophagy inhibitor 3-methyladenine. Simvastatin markedly reduced proliferation of CAMs under both control and proatherogenic stimulation. However, this inhibitory effect of simvastatin on CAM proliferation was blocked by by autophagy inhibitor 3-methyladenine or silencing of Atg7 genes. Lastly, animal experiments demonstrated that simvastatin increased protein expression of LC3B and calponin in mouse coronary arteries. CONCLUSION: Our results indicate that simvastatin inhibits the Rac1-mTOR pathway and thereby increases autophagy in CAMs which may stabilize CAMs in the contractile phenotype to prevent proliferation and growth of these cells.

Protective role of growth hormone against hyperhomocysteinemia-induced glomerular injury.

The present study investigated the protective role of growth hormone (GH) against hyperhomocysteinemia (hHcys)-induced activations of reactive oxygen species/hypoxia-inducible factor (HIF)-1α, epithelial-mesenchymal transition (EMT), and consequent glomerular injury. A hHcys model was induced by folate free diet in mice. The urine protein excretion significantly increased while plasma GH levels dramatically decreased in hHcys. Real-time reverse transcription polymerase chain reaction showed that GH receptor (GHR) level increased in the cortex of hHcys mice, which mainly occurred in podocytes as shown by confocal microscopy. Recombinant mouse growth hormone (rmGH) treatment (0.02 mg/kg, once a day for 6 weeks) significantly restored the plasma GH, inhibited GHR upregulation and attenuated proteinuria. Correspondingly, rmGH treatment also blocked hHcys-induced decrease in the expression of podocin, a podocyte slit diaphragm molecule, and inhibited the increases in the expression of desmin, a podocyte injury marker. It was also demonstrated that in hHcys the expression of epithelial markers, p-cadherin and ZO-1, decreased, while the expression of mesenchymal markers, antifibroblast-specific protein 1 (FSP-1) and α-SMA, increased in podocytes, which together suggest the activation of EMT in podocytes. Nicotinamide adenine dinucleotide phosphate oxidase (Nox)-dependent superoxide anion (O2 (.-)) and hypoxia-inducible factor-1α (HIF-1α) level in the hHcys mice cortex was markedly enhanced. These hHcys-induced EMT enhancement and Nox-dependent O2 (.-)/HIF-1α activation were significantly attenuated by rmGH treatment. HIF-1α level increased in Hcys-treated cultured podocytes, which were blocked by rmGH treatment. Meanwhile, homocysteine (Hcys)-induced EMT in cultured podocytes was significantly reversed by HIF-1α siRNA. All these results support the view that GH ameliorates hHcys-induced glomerular injury by reducing Nox-dependent O2 (.-)/HIF-1α signal pathway and EMT.

Attenuation by statins of membrane raft-redox signaling in coronary arterial endothelium.

Membrane raft (MR)-redox signaling platforms associated with NADPH oxidase are involved in coronary endothelial dysfunction. Here, we studied whether statins interfere with the formation of MR-redox signaling platforms to protect the coronary arterial endothelium from oxidized low-density lipoprotein (OxLDL)-induced injury and from acute hypercholesterolemia. In cultured human coronary arterial endothelial cells, confocal microscopy detected the formation of an MRs clustering when they were exposed to OxLDL, and such MR platform formation was inhibited markedly by statins, including pravastatin and simvastatin. In these MR clusters, NADPH oxidase subunits gp91(phox) and p47(phox) were aggregated and were markedly blocked by both statins. In addition, colocalization of acid sphingomyelinase (ASM) and ceramide was induced by OxLDL, which was blocked by statins. Electron spin resonance spectrometry showed that OxLDL-induced superoxide (O2(.-)) production in the MR fractions was substantially reduced by statins. In coronary artery intima of mice with acute hypercholesterolemia, confocal microscopy revealed a colocalization of gp91(phox), p47(phox), ASM, or ceramide in MR clusters. Such colocalization was rarely observed in the arteries of normal mice or significantly reduced by pretreatment of hypercholesterolemic mice with statins. Furthermore, O2(.-) production in situ was 3-fold higher in the coronary arteries from hypercholesterolemic mice than in those from normal mice, and such increase was inhibited by statins. Our results indicate that blockade of MR-redox signaling platform formation in endothelial cell membrane may be another important therapeutic mechanism of statins in preventing endothelial injury and atherosclerosis and may be associated with their direct action on membrane cholesterol structure and function.

Regulation of renin release via cyclic ADP-ribose-mediated signaling: evidence from mice lacking CD38 gene.

BACKGROUND/AIMS: Despite extensive studies, the intracellular regulatory mechanism of renin production and release is still poorly understood. The present study was designed to test whether CD38-ADP-ribosylcyclase signaling pathway contributes to the regulation of renin production and release, and to examine whether CD38 gene knockout (CD38(-/-)) can change this important renal endocrinal function. METHODS: ADP-ribosylcyclase activity was estimated utilizing HPLC, cADPR levels from western blot, plasma renin activity from RIA kit, urinary sodium and potassium excretion from fame photometry. RESULTS: The expression of CD38 and the activity of ADP-ribosylcyclase to produce cyclic ADP-ribose (cADPR) were nearly abolished in the kidney from CD38(-/-) mice, indicating that CD38 gene is a major enzyme responsible for the generation of cADPR in vivo. Mice lacking CD38 gene showed increased plasma renin activity (PRA) in either conscious or anesthetized status (P<0.05). Low salt intake significantly increased, but high salt intake significantly decreased renin release in both CD38(+/+) and CD38(-/-) mice. In acute experiments, it was demonstrated that plasma renin activity (PRA) significantly increased upon isoprenaline infusion in CD38(-/-) mice compared to CD38(+/+) mice. Accompanied with such increase in PRA, glomerular filtration rate (GFR), renal blood flow (RBF), urine volume (UV) and sodium excretion (UNaV) more significantly decreased in CD38(-/-) than CD38(+/+) mice. Similarly, more increases in PRA but more decreases in GFR, RBF, UV and UNaV were observed in CD38(-/-) than CD38(+/+) mice when they had a low renal perfusion pressure (RPP). CONCLUSION: CD38-cADPR-mediated signaling may importantly contribute to the maintenance of low PRA and participate in the regulation of renal hemodynamics and excretory function in mice.

Intracellular two-phase Ca2+ release and apoptosis controlled by TRP-ML1 channel activity in coronary arterial myocytes.

Activation of the death receptor Fas has been reported to produce a two-phase intracellular Ca(2+) release response in coronary arterial myocytes (CAMs), which consists of local Ca(2+) bursts via lysosomal transient potential receptor-mucolipin 1 (TRP-ML1) channels and consequent Ca(2+) release from the sarcoplasmic reticulum (SR). The present study was designed to explore the molecular mechanism by which lysosomal Ca(2+) bursts are coupled with SR Ca(2+) release in mouse CAMs and to determine the functional relevance of this lysosome-associated two-phase Ca(2+) release to apoptosis, a common action of Fas activation with Fas ligand (FasL). By confocal microscopy, we found that transfection of CAMs with TRP-ML1 small interfering (si)RNA substantially inhibited FasL (10 ng/ml)-induced lysosome Ca(2+) bursts and consequent SR Ca(2+) release. In contrast, transfection of CAMs with plasmids containing a full-length TRP-ML1 gene enhanced FasL-induced two-phase Ca(2+) release. We further demonstrated that FasL significantly increased the colocalization of the lysosomal marker Lamp1 with ryanodine receptor 3 and enhanced a dynamic trafficking of lysosomes to the SR. When CAMs were treated with TRP-ML1 siRNA, FasL-induced interactions between the lysosomes and SR were substantially blocked. Functionally, FasL-induced apoptosis and activation of calpain and calcineurin, the Ca(2+) sensitive proteins that mediate apoptosis, were significantly attenuated by silencing TRP-ML1 gene but enhanced by overexpression of TRP-ML1 gene. These results suggest that TRP-ML1 channel-mediated lysosomal Ca(2+) bursts upon FasL stimulation promote lysosome trafficking and interactions with the SR, leading to apoptosis of CAMs via a Ca(2+)-dependent mechanism.

NADPH oxidase-mediated triggering of inflammasome activation in mouse podocytes and glomeruli during hyperhomocysteinemia.

AIM: Our previous studies have shown that NOD-like receptor protein (NALP3) inflammasome activation is importantly involved in podocyte dysfunction and glomerular sclerosis induced by hyperhomocysteinemia (hHcys). The present study was designed to test whether nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-mediated redox signaling contributes to homocysteine (Hcys)-induced activation of NALP3 inflammasomes, an intracellular inflammatory machinery in podocytes in vitro and in vivo. RESULTS: In vitro confocal microscopy and size-exclusion chromatography revealed that upon NADPH oxidase inhibition by gp91(phox) siRNA, gp91ds-tat peptide, diphenyleneiodonium, or apocynin, aggregation of inflammasome proteins NALP3, apoptosis-associated speck-like protein (ASC), and caspase-1 was significantly attenuated in mouse podocytes. This NADPH oxidase inhibition also resulted in diminished Hcys-induced inflammasome activation, evidenced by reduced caspase-1 activity and interleukin-1ß production. Similar findings were observed in vivo where gp91(phox-/-) mice and mice receiving a gp91ds-tat treatment exhibited markedly reduced inflammasome formation and activation. Further, in vivo NADPH oxidase inhibition protected the glomeruli and podocytes from hHcys-induced injury as shown by attenuated proteinuria, albuminuria, and glomerular sclerotic changes. This might be attributed to the fact that gp91(phox-/-) and gp91ds-tat-treated mice had abolished infiltration of macrophages and T-cells into the glomeruli during hHcys. INNOVATION: Our study for the first time links NADPH oxidase to the formation and activation of NALP3 inflammasomes in podocytes. CONCLUSION: Hcys-induced NADPH oxidase activation is importantly involved in the switching on of NALP3 inflammasomes within podocytes, which leads to the downstream recruitment of immune cells, ultimately resulting in glomerular injury and sclerosis.

Cyclic ADP-Ribose and NAADP in Vascular Regulation and Diseases.

Cyclic ADP-ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP), two intracellular Ca2+ mobilizing second messengers, have been recognized as a fundamental signaling mechanism regulating a variety of cell or organ functions in different biological systems. Here we reviewed the literature regarding these ADP-ribosylcyclase products in vascular cells with a major focus on their production, physiological roles, and related underlying mechanisms mediating their actions. In particular, several hot topics in this area of research are comprehensively discussed, which may help understand some of the controversial evidence provided by different studies. For example, some new models are emerging for the agonist receptor coupling of CD38 or ADP-ribosylcyclase and for the formation of an acidic microenvironment to facilitate the production of NAADP in vascular cells. We also summarized the evidence regarding the NAADP-mediated two-phase Ca2+ release with a slow Ca2+-induced Ca2+ release (CICR) and corresponding physiological relevance. The possibility of a permanent structural space between lysosomes and sarcoplasmic reticulum (SR), as well as the critical role of lysosome trafficking in phase 2 Ca2+ release in response to some agonists are also explored. With respect to the molecular targets of NAADP within cells, several possible candidates including SR ryanodine receptors (RyRs), lysosomal transient receptor potential-mucolipin 1 (TRP-ML1) and two pore channels (TPCs) are presented with supporting and opposing evidence. Finally, the possible role of NAADP-mediated regulation of lysosome function in autophagy and atherogenesis is discussed, which may indicate a new direction for further studies on the pathological roles of cADPR and NAADP in the vascular system.

Acid sphingomyelinase gene knockout ameliorates hyperhomocysteinemic glomerular injury in mice lacking cystathionine-ß-synthase.

Acid sphingomyelinase (ASM) has been implicated in the development of hyperhomocysteinemia (hHcys)-induced glomerular oxidative stress and injury. However, it remains unknown whether genetically engineering of ASM gene produces beneficial or detrimental action on hHcys-induced glomerular injury. The present study generated and characterized the mice lacking cystathionine ß-synthase (Cbs) and Asm mouse gene by cross breeding Cbs(+/-) and Asm(+/-) mice. Given that the homozygotes of Cbs(-/-/)Asm(-/-) mice could not survive for 3 weeks. Cbs(+/-/)Asm(+/+), Cbs(+/-/)Asm(+/-) and Cbs(+/-/)Asm(-/-) as well as their Cbs wild type littermates were used to study the role of Asm(-/-) under a background of Cbs(+/-) with hHcys. HPLC analysis revealed that plasma Hcys level was significantly elevated in Cbs heterozygous (Cbs(+/-)) mice with different copies of Asm gene compared to Cbs(+/+) mice with different Asm gene copies. Cbs(+/-/)Asm(+/+) mice had significantly increased renal Asm activity, ceramide production and O(2.)(-) level compared to Cbs(+/+)/Asm(+/+), while Cbs(+/-/)Asm(-/-) mice showed significantly reduced renal Asm activity, ceramide production and O(2.)(-) level due to increased plasma Hcys levels. Confocal microscopy demonstrated that colocalization of podocin with ceramide was much lower in Cbs(+/-/)Asm(-/-) mice compared to Cbs(+/-/)Asm(+/+) mice, which was accompanied by a reduced glomerular damage index, albuminuria and proteinuria in Cbs(+/-/)Asm(-/-) mice. Immunofluorescent analyses of the podocin, nephrin and desmin expression also illustrated less podocyte damages in the glomeruli from Cbs(+/-/)Asm(-/-) mice compared to Cbs(+/-/)Asm(+/+) mice. In in vitro studies of podocytes, hHcys-enhanced O(2.)(-) production, desmin expression, and ceramide production as well as decreases in VEGF level and podocin expression in podocytes were substantially attenuated by prior treatment with amitriptyline, an Asm inhibitor. In conclusion, Asm gene knockout or corresponding enzyme inhibition protects the podocytes and glomeruli from hHcys-induced oxidative stress and injury.

Activation of Nod-like receptor protein 3 inflammasomes turns on podocyte injury and glomerular sclerosis in hyperhomocysteinemia.

Inflammasome is a multiprotein complex consisting of Nod-like receptor protein 3 (NALP3), apoptosis-associated speck-like protein (ASC), and caspase 1 or 5, which functions to switch on the inflammatory process. The present study hypothesized that the formation and activation of NALP3 inflammasomes turn on podocyte injury leading to glomerulosclerosis during hyperhomocysteinemia (hHcys). RT-PCR and Western blot analysis demonstrated that murine podocytes expressed 3 essential components of the NALP3 inflammasome complex, namely, NALP3, ASC, and caspase 1. Treatment of podocytes with l-homocysteine induced the formation of NALP3 inflammasome complex, an increase in caspase 1 activity, podocyte cytoskeleton rearrangement, and decreased production of vascular endothelial growth factor from podocytes, which were all blocked by silencing the ASC gene or inhibiting caspase 1 activity. In mice with hHcys induced by feeding them a folate-free diet, NALP3 inflammasome formation and activation in glomerular podocytes were detected at an early stage, as shown by confocal microscopy, size exclusion chromatography of the assembled inflammasome complex, and increased interleukin-1ß production in glomeruli. Locally silencing the ASC gene in the kidney significantly reduced NALP3 inflammasome formation and interleukin 1ß production in glomeruli of mice with hHcys. Pathologically, hHcys-associated albuminuria, foot process effacement of podocytes, loss of podocyte slit diaphragm molecules, and glomerulosclerosis at the late stage were significantly improved by local ASC gene silencing or by caspase 1 inhibition. In conclusion, NALP3 inflammasome formation and activation on stimulation of homocysteine are important molecular mechanisms triggering podocyte injury and ultimately resulting in glomerulosclerosis in hHcys.