Epithelial-to-mesenchymal transition in podocytes mediated by activation of NADPH oxidase in hyperhomocysteinemia

Catalpol inhibits HHcy-induced EndMT in endothelial cells by modulating ROS/NF-κB signaling

BACKGROUND

Hyperhomocysteinemia (HHcy) is an independent risk factor for atherosclerosis (AS). Endothelial mesenchymal transition (EndMT) refers to the process in which endothelial cells lose endothelial cell morphology and characteristic gene expression, and acquire phenotypic characteristics and gene expression related to mesenchymal cells. Numerous studies have confirmed that EndMT is involved in the formation of atherosclerosis. Catalpol is one of the active components of Rehmannia, which has antioxidant, anti-inflammatory, anti-tumor, neuroprotective and other biological activities. Studies have shown that catalpol can reduce atherosclerotic plaque induced by high sugar or fat. However, the effect of catalpol on HHCY-induced EndMT is unclear.

METHODS AND RESULTS

In vitro HHcy-treated primary human umbilical vein endothelial cells (HUVECs) were used to construct a cell model, and the antioxidants N-acetylcysteine (NAC) and catalase alcohol were administered. In vivo C57BL/6N mice were given a diet fed with 4.4% high methionine chow to construct a HHcy mice model and were treated with catalpol. The results showed that hhcy could induce morphological transformation of endothelial cells into mesenchymal cells, increase intracellular ROS content, up-regulate α-SMA, N-cadherin, p-p65 protein expression, down-regulate VE-cadherin, CD31 protein expression, induce pathological changes of aortic root endothelium, and increase aortic endothelial ROS content. Catalpol reversed these hhcy induced outcomes.

CONCLUSIONS

Catalpol inhibits HHcy-induced EndMT, and the underlying mechanism may be related to the ROS/NF-κB signaling pathway. Catalpol may be a potential drug for the treatment of HHcy-related AS.

Astragaloside Ⅳ negatively regulates Gpr97-TPL2 signaling to protect against hyperhomocysteine-exacerbated sepsis associated acute kidney injury

BACKGROUND

Hyperhomocysteine (HHcy) plays an important role in promoting inflammation and cell death of tubular epithelial cells. However, the role of HHcy and Astragaloside IV (AS-IV) in sepsis associated acute kidney injury (S-AKI) remain unclear.

PURPOSE

A significant aspect of this study aimed to elucidate the effect of AS-Ⅳ treatment on HHcy-exacerbated S-AKI and reveal its potential mechanism.

METHODS

Male C57BL/6 J mice fed with specific diet containing 2% methionine were established as in vivo models, and AS-Ⅳ was orally administrated continuously for 3 weeks, and then LPS (10 mg·kg-1 bodyweight) was given by a single intraperitoneal injection. The renal morphological changes were evaluated by HE and PAS staining. RNA-sequencing analysis was applied to select key signaling. The NRK-52E cells exposed to Hcy or combined with LPS were used as in vitro models. The mRNA and protein expression levels of Gpr97-TPL2 signaling were examined by qRT-PCR and western blotting assays.

RESULTS

In vivo, HHcy mice developed more severe renal injury and prevalent tubular inflammation after LPS injection. In vitro, the levels of NGAL, Gpr97 and TPL2 were significantly increased in NRK-52E cells induced by Hcy (1.6 mM) or in combination with LPS. Notably, the effects of Hcy on TPL2 signaling was abolished by transfecting TPL2 siRNA or treating TPL2 inhibitor, without alterations in Gpr97. However, the enhancement of Gpr97-TPL2 signaling induced by Hcy was counteracted by Gpr97 siRNA. Subsequently, our findings demonstrated that AS-Ⅳ treatment can improve renal function in HHcy-exacerbated S-AKI mice. Mechanistically, AS-Ⅳ alleviated renal tubular damage characterized by abnormal increases in KIM-1, NGAL, TPL2, Gpr97, Sema3A and TNF-α, and decreases in survivin in vivo and in vitro mainly through suppressing the activation of Gpr97-TPL2 signaling.

CONCLUSION

The present study suggested that HHcy-exacerbated S-AKI was mediated mechanically by activation of Gpr97-TPL2 signaling for the first time. Furthermore, our research also illustrated that AS-Ⅳ protected against HHcy-exacerbated S-AKI by attenuating renal tubular epithelial cells damage through negatively regulating Gpr97-TPL2 signaling, proposing a natural product treatment strategy for HHcy-exacerbated S-AKI.

Elevated homocysteine level as an indicator for chronic kidney disease in community-dwelling middle-aged and elderly populations in Taiwan: A community-based cross-sectional study

Background

Hyperhomocysteinemia is an important factor for endothelial cell damage and a risk factor for cardiovascular diseases. Chronic kidney disease (CKD) is recognized as a leading burden in Taiwan’s healthcare system. This study aimed to investigate the association between homocysteine levels and CKD in middle-aged and elderly adults from a community in northern Taiwan.

Methods

A total of 396 middle-aged and elderly Taiwanese adults were enrolled and completed the health survey. We divided participants according to tertiles of homocysteine levels as first group (homocysteine level ≤ 11.1 μmol/L), second group (homocysteine level 11.2∼14.3 μmol/L), and third group (homocysteine level > 14.3 μmol/L). CKD was defined as estimated glomerular filtration rate (eGFR) < 60 (mL/min/1.73 m²) or urine albumin to creatinine ratio > 30 (mg/g). Pearson correlation was calculated between eGFR and other related risk factors after adjustment for age. The risk of CKD in the second and third groups compared to that in the first group was assessed by multivariate logistic regression after adjustment for age, sex, smoking, hypertension (HTN), diabetes mellitus (DM), body mass index (BMI), dyslipidemia, and uric acid. The Youden index and receiver operating characteristic (ROC) curve were calculated for the optimized cutoff value.

Results

Elevated plasma homocysteine levels were more likely to lower the eGFR and increase the prevalence of CKD. Pearson correlation showed a positive correlation between eGFR and high-density lipoprotein cholesterol, while a negative correlation was observed between homocysteine levels, waist circumference, systolic blood pressure, uric acid levels and BMI (all p < 0.05). In the logistic regression analysis, the prevalence of CKD increased, as well as the homocysteine level. The odds ratio of CKD under 95% confidence interval was 2.655 (1.284–5.490) for the third group compared with the first group after adjusting for age, sex, smoking, DM, HTN, dyslipidemia, uric acid, and BMI (p = 0.008). The area under the ROC curve was 0.662, and a cutoff value of 15.15 μmol/L for the homocysteine level was obtained for detecting subjects with CKD.

Conclusion

Our study findings revealed that elevated homocysteine levels were significantly associated with CKD and could be used as an indicator of CKD among the middle-aged and elderly populations in Taiwan.

Applications and Mechanisms of Tripterygium Wilfordii Hook. F. and its Preparations in Kidney Diseases

Tripterygium wilfordii Hook. f. (TwHF) is a Chinese botanical drug containing a large number of metabolites. The discovered and recognized anti-inflammatory and immune-regulating effects have made it attract more and more attentions in trials and clinical researches. The extraction and processing of TwHF for pharmaceuticals is a manifestation of the role of traditional Chinese medicine. However, TwHF is toxic. Optimization of TwHF preparations has become a requirement for the development of TwHF pharmaceuticals. Our article introduces the main preparations of TwHF on the Chinese market and their characteristics. In particular, we summarize the clinical applications and influential mechanisms of TwHF and its preparations in kidney diseases. Considering that nephropathy is closely related to immune inflammation and TwHF is a botanical drug with a high number of metabolites, the application of TwHF in kidney diseases may be much more complicated. By revealing the role and mechanisms of TwHF in kidney diseases, this study aims to provide more insights to basic and clinical studies about nephropathy.

Role of γ-adducin in actin cytoskeleton rearrangements in podocyte pathophysiology

We recently reported that the enhanced susceptibility to chronic kidney disease (CKD) in the fawn-hooded hypertensive (FHH) rat is caused, at least in part, by a mutation in γ-adducin (ADD3) that attenuates renal vascular function. The present study explored whether Add3 contributes to the modulation of podocyte structure and function using FHH and FHH.Add3 transgenic rats. The expression of ADD3 on the membrane of primary podocytes isolated from FHH was reduced compared with FHH.Add3 transgenic rats. We found that F-actin nets, which are typically localized in the lamellipodia, replaced unbranched stress fibers in conditionally immortalized mouse podocytes transfected with Add3 Dicer-substrate short interfering RNA (DsiRNA) and primary podocytes isolated from FHH rats. There were increased F/G-actin ratios and expression of the Arp2/3 complexes throughout FHH podocytes in association with reduced synaptopodin and RhoA but enhanced Rac1 and CDC42 expression in the renal cortex, glomeruli, and podocytes of FHH rats. The expression of nephrin at the slit diaphragm and the levels of focal adhesion proteins integrin-α3 and integrin-β1 were decreased in the glomeruli of FHH rats. Cell migration was enhanced and adhesion was reduced in podocytes of FHH rats as well as in immortalized mouse podocytes transfected with Add3 DsiRNA. Mean arterial pressures were similar in FHH and FHH.Add3 transgenic rats at 16 wk of age; however, FHH rats exhibited enhanced proteinuria associated with podocyte foot process effacement. These results demonstrate that reduced ADD3 function in FHH rats alters baseline podocyte pathophysiology by rearrangement of the actin cytoskeleton at the onset of proteinuria in young animals.

Vitamin D3 reduces risk of cardiovascular and liver diseases by lowering homocysteine levels: double-blinded, randomised, placebo-controlled trial

The objective of this study was to evaluate the effect of vitamin D3 on total homocysteine (tHcy) and C-reactive protein (CRP) levels and liver and kidney function tests in overweight women with vitamin D deficiency. Therefore, a randomised, double-blind placebo, controlled clinical trial was conducted on 100 eligible women. Subjects were randomly divided into two groups: the placebo (n 50) and the vitamin D (n 50) which received 1250 µg vitamin D3 per week for 2 months. The participants' 25-hydroxyvitamin D (25(OH)D), tHcy, CRP, alanine aminotransferase (ALT), aspartate aminotransferase (AST), urea, creatinine and estimated glomerular filtration rate (eGFR) were measured and compared before and after treatment. Results showed that the tHcy, CRP, AST, ALT and eGFR levels after the 2nd month of vitamin D3 intervention were significantly (P < 0·001) decreased and the 25(OH)D, urea and creatinine levels were significantly (P < 0·001) increased in the treatment group. In the placebo group, no significant changes were identified throughout the follow-up period. In conclusion, vitamin D3 intervention with a treatment dose of 1250 µg/week for at least 2 months may help in lowering Hcy and CRP levels and may improve liver function tests, which in turn might help in minimising the risk of CVD and liver diseases among overweight women but negatively affect kidney function.

Protective effects of acarbose against vascular endothelial dysfunction through inhibiting Nox4/NLRP3 inflammasome pathway in diabetic rats

The cardiovascular efficacy of glucose-lowering drugs is needed due to the cardiovascular complication in type 2 diabetes mellitus (T2DM). Acarbose is an α-glucosidase inhibitor that suppresses postprandial hyperglycemia, however, the cardiovascular protection of acarbose has still remained controversial. NLRP3 inflammasome activation mediated tight junction disruption, a hallmark event of endothelial barrier dysfunction leading to endothelial hyperpermeability in diabetes. Given the anti-inflammatory property of acarbose, it was investigated that acarbose protected against vascular endothelial barrier dysfunction through inhibiting NLRP3 inflammasome in vascular endothelial cells in T2DM rats. The rat aortic endothelial cells (RAECs) were incubated with high glucose (HG, 30 mM) for 24 h in vitro. It was found that HG significantly induced the formation and activation of NLRP3 inflammasome, which was markedly blocked by acarbose treatment. Furthermore, acarbose blocked the Nox4-dependent superoxide (O₂^.-) generation, which regulated NLRP3 inflammasome in RAECs. Importantly, we found that acarbose remarkably enhanced the junction protein expression of ZO-1 and VE-Cadherin and consequently abolished vascular hyperpermeability, which was associated with inhibiting NLRP3 inflammasome in RAECs. In vivo, acarbose intervention relieved vascular leakage in the heart of diabetic rats injected with Evans blue dye and the vasodilatory response to acetylcholine, which was accompanied with the restoration of ZO-1, VE-Cadherin, Nox4 and NLRP3 inflammasome in the aortal endothelium of diabetic rats. Taken together, our data indicated that acarbose ameliorated endothelial barrier dysfunction by directly inhibiting NLRP3 inflammasome which was dependent on inhibiting Nox4 oxidase-dependent O₂^.- production. These properties might carry a potential significance for acarbose in cardiovascular protection in diabetic patients.

Control of lysosomal TRPML1 channel activity and exosome release by acid ceramidase in mouse podocytes

The transient receptor potential mucolipin 1 (TRPML1) channel has been reported to mediate lysosomal Ca2+ release that is involved in Ca2+-dependent lysosome trafficking and autophagic flux. However, this regulatory mechanism of lysosomal TRPML1 channel activity in podocytes remains poorly understood. In the present study, we tested whether the TRPML1 channel in podocytes mediates lysosome trafficking, which is essential for multivesicular body (MVB) degradation by lysosomes. We first demonstrated the abundant expression of TRPML1 channel in podocytes. By GCaMP3 Ca2+ imaging, we characterized the lysosomal specificity of TRPML1 channel-mediated Ca2+ release in podocytes. Given the important role of acid ceramidase (AC) in lysosome function and podocyte injury, we tested whether AC regulates this TRPML1 channel-mediated Ca2+ release and consequent lysosome-dependent MVB degradation in podocytes. Pharmacologically, it was found that TRPML1 channel activity was remarkably attenuated by the AC inhibitor carmofur. Sphingosine, as an AC product, was demonstrated to induce TRPML1-mediated Ca2+ release, which was inhibited by a TRPML1 blocker, verapamil. Using a Port-a-Patch planar patch-clamp system, we found that AC-associated sphingolipids, sphingomyelin, ceramide, and sphingosine had different effects on TRPML1 channel activity in podocytes. Functionally, the inhibition of AC or blockade of TRPML1 channels was found to suppress the interaction of lysosomes and MVBs, leading to increased exosome release from podocytes. These results suggest that AC is critical for TRPML1 channel-mediated Ca2+ release, which controls lysosome-MVB interaction and exosome release in podocytes.

Ganoderma triterpenes Protect Against Hyperhomocysteinemia Induced Endothelial-Mesenchymal Transition via TGF-β Signaling Inhibition

Endothelial dysfunction is one of the most important pathological status in hyperhomocysteinemia (HHcy) related cardiovascular diseases. Whereas, the underlying mechanisms have not been fully elucidated yet, concomitant with the absence of effective treatment. The purpose of this study was to explore the main mechanisms involved in HHcy-induced endothelial injury and identify the protective effect of Ganoderma triterpenes (GT). Bovine aortic endothelial cells (BAECs) were applied as in vitro experimental model. The small molecular inhibitors were used to explore the signalings involved in HHcy-induced endothelial injury. The experimental results provided initial evidence that HHcy led to endothelial-mesenchymal transition (EndMT). Meanwhile, TGF-β/Smad, PI3K/AKT and MAPK pathways were activated in this process, which was demonstrated by pretreatment with TGF-β RI kinase inhibitor VI SB431542, PI3K inhibitor LY294002, p38 inhibitor SB203580, and ERK inhibitor PD98059. Furthermore, it was found that GT restrained the process of HHcy-induced EndMT via reducing oxidative stress and suppressing fore mentioned pathways with further inhibiting the activity of Snail. These results implicate that there is an untapped potential for GT as a novel therapeutic candidate for HHcy-induced EndMT through alleviating oxidative stress and canonical TGF-β/Smad and non-Smad dependent signaling pathways.

Homocysteine and age-associated disorders

There are numerous theories of aging, a process which still seems inevitable. Aging leads to cancer and multi-systemic disorders as well as chronic diseases. Decline in age- associated cellular functions leads to neurodegeneration and cognitive decline that affect the quality of life. Accumulation of damage, mutations, metabolic changes, failure in cellular energy production and clearance of altered proteins over the lifetime, and hyperhomocysteinemia, ultimately result in tissue degeneration. The decline in renal functions, nutritional deficiencies, deregulation of methionine cycle and deficiencies of homocysteine remethylation and transsulfuration cofactors cause elevation of homocysteine with advancing age. Abnormal accumulation of homocysteine is a risk factor of cardiovascular, neurodegenerative and chronic kidney disease. Moreover, approximately 50% of people, aged 65 years and older develop hypertension and are at a high risk of developing cardiovascular insufficiency and incurable neurodegenerative disorders. Increasing evidence suggests inverse relation between cognitive impairment, cerebrovascular and cardiovascular events and renal function. Oxidative stress, inactivation of nitric oxide synthase pathway and mitochondria dysfunction associated with impaired homocysteine metabolism lead to aging tissue degeneration. In this review, we examine impact of high homocysteine levels on changes observed with aging that contribute to development and progression of age associated diseases.

Knocking down TCF8 inhibits high glucose- and angiotensin II-induced epithelial to mesenchymal transition in podocytes

Epithelial to mesenchymal transition (EMT) is a physiological phenomenon in mammalian embryogenesis by which epithelial cells become mesenchymal stem cells. Studies have indicated that an inappropriate EMT plays a key role in a variety of pathogenic processes such as embryonic development and tumor metastasis. Moreover, recent studies have indicated EMT also plays an important role in renal fibrosis. In the current study, glucose and angiotensin II promoted EMT in podocytes as well as changes in the cellular morphology of podocytes. A high concentration of glucose and angiotensin II also promoted podocyte movement and migration. Moreover, a high concentration of glucose and angiotensin II promoted TCF8 expression. Inhibiting TCF8 expression with siRNA reversed EMT in podocytes in the presence of a high concentration of glucose and angiotensin. Inhibiting TCF8 expression also reversed changes in cellular morphology and podocyte movement and migration. Therefore, glucose and angiotensin II may promote EMT in podocytes via TCF8.

Hyperhomocysteinemia Exacerbates Cisplatin-induced Acute Kidney Injury

Hyperhomocysteinemia (HHcy) has been linked to several clinical manifestations including chronic kidney disease. However, it is not known whether HHcy has a role in the development of acute kidney injury (AKI). In the present study, we reported that HHcy mice developed more severe renal injury after cisplatin injection and ischemia-reperfusion injury shown as more severe renal tubular damage and higher serum creatinine. In response to cisplatin, HHcy mice showed more prevalent tubular cell apoptosis and decreased tubular cell proliferation. Mechanistically, a heightened ER stress and a reduced Akt activity were observed in kidney tissues of HHcy mice after cisplatin injection. Stimulating cultured NRK-52E cells with Hcy significantly increased the fraction of cells in G2/M phase and cell apoptosis together with decreased Akt kinase activity. Akt agonist IGF-1 rescued HHcy-induced cell cycle arrest and cell apoptosis. In conclusion, the present study provides evidence that HHcy increases the sensitivity and severity of AKI.

Strategy of integrated evaluation on treatment of traditional Chinese medicine as 'interaction of system to system' and establishment of novel fuzzy target contribution recognition with herb-pairs, a case study on Astragali Radix-Fructus Corni

To date, in the struggle against diseases and the development of TCM, what we lack is wisdom rather than knowledge. Studies on pharmacology of traditional Chinese medicine are facing critical challenges on how to select the proper parameters or targets to represent the pharmacological evaluation system. With seven steps of optimized modules established by ourselves, we can re-evaluate TCM in a panorama view with a proper pharmacological evaluation system. In this article, with the treatment of TCM as 'interaction of system to system', a novel and generally applicable approach called fuzzy target contribution recognition was established and agents from Astragali Radix-Fructus Corni in resisting diabetic nephropathy were successfully discovered for the first time. CG6, a promising agent from this herb-pair on the treatment of diabetic nephropathy, was finally acquired and its possible molecular mechanism was explored through a nuclear factor erythroid 2-Like 2 (NFE2L2) activation-dependent pathway.

Role of NADPH Oxidase in Metabolic Disease-Related Renal Injury: An Update

Metabolic syndrome has been linked to an increased risk of chronic kidney disease. The underlying pathogenesis of metabolic disease-related renal injury remains obscure. Accumulating evidence has shown that NADPH oxidase is a major source of intrarenal oxidative stress and is upregulated by metabolic factors leading to overproduction of ROS in podocytes, endothelial cells, and mesangial cells in glomeruli, which is closely associated with the initiation and progression of glomerular diseases. This review focuses on the role of NADPH oxidase-induced oxidative stress in the pathogenesis of metabolic disease-related renal injury. Understanding of the mechanism may help find potential therapeutic strategies.

Homocysteine in Chronic Kidney Disease

Hyperhomocysteinemia occurs in chronic- and end-stage kidney disease at the time when dialysis or transplant becomes indispensable for survival. Excessive accumulation of homocysteine (Hcy) aggravates conditions associated with imbalanced homeostasis and cellular redox thereby resulting in severe oxidative stress leading to oxidation of reduced free and protein-bound thiols. Thiol modifications such as N-homocysteinylation, sulfination, cysteinylation, glutathionylation, and sulfhydration control cellular responses that direct complex metabolic pathways. Although cysteinyl modifications are kept low, under Hcy-induced stress, thiol modifications persist thus surpassing cellular proteostasis. Here, we review mechanisms of redox regulation and show how cysteinyl modifications triggered by excess Hcy contribute development and progression of chronic kidney disease. We discuss different signaling events resulting from aberrant cysteinyl modification with a focus on transsulfuration.

Wnt/β-catenin signalling and podocyte dysfunction in proteinuric kidney disease

Podocytes are unique, highly specialized, terminally differentiated cells that are integral components of the kidney glomerular filtration barrier. Podocytes are vulnerable to a variety of injuries and in response they undergo a series of changes ranging from hypertrophy, autophagy, dedifferentiation, mesenchymal transition and detachment to apoptosis, depending on the nature and extent of the insult. Emerging evidence indicates that Wnt/β-catenin signalling has a central role in mediating podocyte dysfunction and proteinuria. Wnts are induced and β-catenin is activated in podocytes in various proteinuric kidney diseases. Genetic or pharmacologic activation of β-catenin is sufficient to impair podocyte integrity and causes proteinuria in healthy mice, whereas podocyte-specific ablation of β-catenin protects against proteinuria after kidney injury. Mechanistically, Wnt/β-catenin controls the expression of several key mediators implicated in podocytopathies, including Snail1, the renin-angiotensin system and matrix metalloproteinase 7. Wnt/β-catenin also negatively regulates Wilms tumour protein, a crucial transcription factor that safeguards podocyte integrity. Targeted inhibition of Wnt/β-catenin signalling preserves podocyte integrity and ameliorates proteinuria in animal models. This Review highlights advances in our understanding of the pathomechanisms of Wnt/β-catenin signalling in mediating podocyte injury, and describes the therapeutic potential of targeting this pathway for the treatment of proteinuric kidney disease.

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-1β 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-1β 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.

Activation of inflammasomes in podocyte injury of mice on the high fat diet: Effects of ASC gene deletion and silencing

Inflammasome, an intracellular inflammatory machinery, has been reported to be involved in a variety of chronic degenerative diseases such as atherosclerosis, autoinflammatory diseases and Alzheimer's disease. The present study hypothesized that the formation and activation of inflammasomes associated with apoptosis associated speck-like protein (ASC) are an important initiating mechanism resulting in obesity-associated podocyte injury and consequent glomerular sclerosis. To test this hypothesis, Asc gene knockout (Asc(-/-)), wild type (Asc(+/+)) and intrarenal Asc shRNA-transfected wild type (Asc shRNA) mice were fed a high fat diet (HFD) or normal diet (ND) for 12 weeks to produce obesity and associated glomerular injury. Western blot and RT-PCR analyses demonstrated that renal tissue Asc expression was lacking in Asc(-/-) mice or substantially reduced in Asc shRNA transfected mice compared to Asc(+/+) mice. Confocal microscopic and co-immunoprecipitation analysis showed that the HFD enhanced the formation of inflammasome associated with Asc in podocytes as shown by colocalization of Asc with Nod-like receptor protein 3 (Nalp3). This inflammasome complex aggregation was not observed in Asc(-/-) and local Asc shRNA-transfected mice. The caspase-1 activity, IL-1β production and glomerular damage index (GDI) were also significantly attenuated in Asc(-/-) and Asc shRNA-transfected mice fed the HFD. This decreased GDI in Asc(-/-) and Asc shRNA transfected mice on the HFD was accompanied by attenuated proteinuria, albuminuria, foot process effacement of podocytes and loss of podocyte slit diaphragm molecules. In conclusion, activation and formation of inflammasomes in podocytes are importantly implicated in the development of obesity-associated glomerular injury.

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-1β 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-1β 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.

Actin-associated Proteins in the Pathogenesis of Podocyte Injury

Podocytes have a complex cellular architecture with interdigitating processes maintained by a precise organization of actin filaments. The actin-based foot processes of podocytes and the interposed slit diaphragm form the final barrier to proteinuria. The function of podocytes is largely based on the maintenance of the normal foot process structure with actin cytoskeleton. Cytoskeletal dynamics play important roles during normal podocyte development, in maintenance of the healthy glomerular filtration barrier, and in the pathogenesis of glomerular diseases. In this review, we focused on recent findings on the mechanisms of organization and reorganization of these actin-related molecules in the pathogenesis of podocyte injury and potential therapeutics targeting the regulation of actin cytoskeleton in podocytopathies.

Role of NADPH oxidase-mediated reactive oxygen species in podocyte injury

Proteinuria is an independent risk factor for end-stage renal disease (ESRD) (Shankland, 2006). Recent studies highlighted the mechanisms of podocyte injury and implications for potential treatment strategies in proteinuric kidney diseases (Zhang et al., 2012). Reactive oxygen species (ROS) are cellular signals which are closely associated with the development and progression of glomerular sclerosis. NADPH oxidase is a district enzymatic source of cellular ROS production and prominently expressed in podocytes (Zhang et al., 2010). In the last decade, it has become evident that NADPH oxidase-derived ROS overproduction is a key trigger of podocyte injury, such as renin-angiotensin-aldosterone system activation (Whaley-Connell et al., 2006), epithelial-to-mesenchymal transition (Zhang et al., 2011), and inflammatory priming (Abais et al., 2013). This review focuses on the mechanism of NADPH oxidase-mediated ROS in podocyte injury under different pathophysiological conditions. In addition, we also reviewed the therapeutic perspectives of NADPH oxidase in kidney diseases related to podocyte injury.

The signaling pathway of NADPH oxidase and its role in glomerular diseases

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (Nox), a major source of reactive oxygen species, is a critical mediator of redox signaling. It is well-documented that oxidative stress is associated with the development of glomerular diseases (GN). Hence, the Nox was also thought to be involved in the pathogenesis of GN. However, the expression of Nox in various GN was not consistent, the mechanisms by which the activity of the Nox enzymes in regulating renal cells remains unclear. Signaling pathways might be very important in the pathogenesis of GN. We performed this review to provide a relatively complete signaling pathways flowchart for Nox to the investigators who were interested in the role of Nox in the pathogenesis of GN. Here, we reviewed the signal transduction pathway of Nox and its role in the pathogenesis of GN.

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.

Sustained activation of N-methyl-D-aspartate receptors in podoctyes leads to oxidative stress, mobilization of transient receptor potential canonical 6 channels, nuclear factor of activated T cells activation, and apoptotic cell death

Atypical N-methyl-D-aspartate (NMDA) receptors are expressed in podocytes. Sustained (≥24 h) application of 50 to100 μM NMDA to immortalized mouse podocytes evoked a marked increase in the production of reactive oxygen species(ROS) such as H₂O₂. This effect of NMDA was associated with increased cell-surface expression of p47(phox), a cytosolic regulatory subunit of the NADPH oxidase NOX2. NMDA-evoked generation of ROS drove an increase in steady-state surface expression of transient receptor potential canonical (TRPC) 6 channels, which was blocked by the NMDA antagonist dizocilpine(MK-801) and by a membrane-permeable scavenger of ROS. The effect of NMDA on TRPC6 was observed using cell surface biotinylation assays and also with whole-cell recordings made under conditions designed to facilitate detection of current through TRPC6. NMDA mobilization of TRPC6 channels was blocked by concurrent treatment with the NMDA antagonist MK-801 and by a membrane-permeable scavenger ofROS. Mobilization of TRPC6 was also evoked by L-homocysteic acid. NMDA treatment also increased nuclear localization of endogenous nuclear factor of activated T cells, which could be blocked by MK-801, by scavenging ROS, by the calcineurin inhibitor cyclosporine, and by the TRPC channel inhibitor 1-[2-(4-methoxyphenyl)-2-[3-(4-methoxyphenyl)propoxy]ethyl]imidazole (SKF-96365). NMDA treatment also evoked robust activation of Rho but not Rac,consistent with previous studies of downstream effectors of TRPC6 activation. Exposing cells to NMDA for 24 h reduced total and cell surface expression of the podocyte markers nephrin and podocin, but there was no loss of cells. With longer NMDA exposure (72 h), we observed loss of cells associated with nuclear fragmentation and increased expression of caspase-3, caspase-6, and Bax, suggesting an apoptotic process.