Peroxidase expression is decreased by palmitate in cultured podocytes but increased in podocytes of advanced diabetic nephropathy

Nrf2-Dependent Adaptation to Oxidative Stress Protects Against Progression of Diabetic Nephropathy

Aims: Adaptation to oxidative stress is essential for maintaining protein and redox homeostasis in mammalian cells. Palmitic acid (PA) plays a central role in oxidative stress and immunoproteasome regulation in podocytes and diabetes, and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have beneficial impact on diabetes. The role of Nrf2 in adaptation to oxidative stress and regulation of immunoproteasome by PA and EPA/DHA in podocytes and diabetic kidneys is not well defined. The present study describes the effect of PA- and EPA/DHA-induced oxidative stress in regulating Nrf2/immuoproteasome pathway in a model system relevant to diabetic nephropathy (DN). Results: Short PA exposure to podocytes promotes the upregulation of antioxidant proteins and immunoproteasome mediated by Nrf2, leading to acute transient oxidative stress adaptation. Both short- and long-term incubation of EPA or DHA in podocytes induced oxidative stress and activation of Nrf2, causing persistent oxidative stress adaptation. Long PA exposure to podocytes decreased the Nrf2 activity, and EPA/DHA attenuated these effects of PA. In db/db mice, feeding of EPA/DHA-rich fish oil increased oxidative stress in kidneys and induced renal cortical Nrf2 nuclear translocation and immunoproteasome overexpression, inhibiting the progression of DN. Innovation and Conclusion: We demonstrate an oxidative stress adaptation mechanism by PA and EPA/DHA regulated by Nrf2 in podocytes and kidneys of type 2 diabetes. This work provides an important insight into the pathogenetic mechanisms of DN by PA-induced oxidative stress. We conclude that activation of Nrf2-immunoproteasome signaling pathway by EPA/DHA plays a crucial role in abrogating the proteotoxic stress in DN. Antioxid. Redox Signal. 00, 000-000.

Qishen Yiqi Dripping Pill Protects Diabetic Nephropathy by Inhibiting the PI3K-AKT Signaling Pathways in Rats

This study aimed to explore the potential mechanisms of Qishen Yiqi dripping pill (QYDP) against diabetic nephropathy (DN) through network pharmacology and animal experiments. The components and targets of QYDP and DN-related targets were retrieved from public databases. A total of 116 compounds and 160 targets of QYDP anti-DN were obtained. The top 10 hub targets including AKT1, TNF, ALB, INS, PPARG, IL-6, IL-1B, VEGF-A, JUN, and MAPK3 were screened by Cytoscape software. Then, the key targets of QYDP were enriched in 1815 Gene Ontology (GO) entries (P < 0.01) and 159 Kyoto Encyclopedia of Genomes and Genomes (KEGG) pathways (P < 0.01), mainly including the AGE-RAGE signaling pathway in diabetic complications and the PI3K-AKT signaling pathway. In animal experiments, the results of an ELISA assay showed that QYDP could regulate the expression levels of kidney function-related indexes and reduce the expression of inflammatory factors. qRT-PCR and western blot results showed that QYDP regulated the expression of hub genes. In conclusion, this study shows that QYDP could treat DN by antioxidative and antiinflammatory activity and inhibiting the PI3K-AKT signaling pathway.

Research advance in the mechanism for oxidative stress-induced podocyte injury in diabetic kidney disease

Diabetic kidney disease (DKD) is one of the serious microvascular complications of diabetes mellitus (DM), and it is also the leading cause for the end-stage kidney disease (ESKD), but the clinical treatment for it is limited at present. The pathogenesis of DKD is complex. Many studies have shown that podocyte injury is the core event of DKD, and oxidative stress is closely related to podocyte injury in DKD. Oxidative stress mediates podocyte apoptosis and slit diaphragm damage in DKD through various pathways. The antioxidant drugs can slow down the progression of DKD through reducing podocyte injury and are expected to enter clinical trials. The research status of antioxidant drugs is very important, which will provide new strategies for the clinical treatment of DKD.

Peroxiredoxins as Markers of Oxidative Stress in IgA Nephropathy, Membranous Nephropathy and Lupus Nephritis

IgA nephropathy (IgAN), membranous nephropathy (MN), and lupus nephritis (LN) represent important causes of chronic kidney disease. They belong to the immune-mediated glomerulonephritis (GNs), and have distinct pathogenesis, distinct clinical courses, and variable responses to treatment. Therefore, specific diagnostic procedures are necessary for more effective patient management. Recently, a role for oxidative stress has been proposed in various renal disorders. Thus, molecules related to oxidative stress, such as 2-Cys-peroxiredoxins (PRDXs), may represent plausible candidates for biomarkers in renal pathologies. The aim of this study was to assess whether there are differences between individual GNs and healthy controls in the context of PRDXs serum concentration. We enrolled 108 patients with biopsy-proven IgAN (47), MN (26), LN (35) and 30 healthy age- and sex-matched controls. The serum concentrations of PRDX 1-5 were measured with ELISA assays and correlated with demographic and clinical data. The PRDXs' concentration varied depending on the GN type. We also observed an association of PRDXs with lower estimated glomerular filtration rates, complement, hemoglobin, and body mass index. Our study indicates that individual PRDX can play roles in pathophysiology of selected GNs and that their serum concentrations may become useful as a new supplementary diagnostic markers in IgAN, MN as well as LN. The results of this study open a new avenue for prospective research on PRDXs in renal diseases.

The Antioxidative Role of Natural Compounds from a Green Coconut Mesocarp Undeniably Contributes to Control Diabetic Complications as Evidenced by the Associated Genes and Biochemical Indexes

The purpose of this study was to look into the effects of green coconut mesocarp juice extract (CMJE) on diabetes-related problems in streptozotocin- (STZ-) induced type 2 diabetes, as well as the antioxidative functions of its natural compounds in regulating the associated genes and biochemical markers. CMJE's antioxidative properties were evaluated by the standard antioxidant assays of 1,1-diphenyl-2-picrylhydrazyl (DPPH), superoxide radical, nitric oxide, and ferrous ions along with the total phenolic and flavonoids content. The α-amylase inhibitory effect was measured by an established method. The antidiabetic effect of CMJE was assayed by fructose-fed STZ-induced diabetic models in albino rats. The obtained results were verified by bioinformatics-based network pharmacological tools: STITCH, STRING, GSEA, and Cytoscape plugin cytoHubba bioinformatics tools. The results showed that GC-MS-characterized compounds from CMJE displayed a very promising antioxidative potential. In an animal model study, CMJE significantly (P < 0.05) decreased blood glucose, serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatinine, uric acid, and lipid levels and increased glucose tolerance as well as glucose homeostasis (HOMA-IR and HOMA-b scores). The animal's body weights and relative organ weights were found to be partially restored. Tissue architectures of the pancreas and the kidney were remarkably improved by low doses of CMJE. Compound-protein interactions showed that thymine, catechol, and 5-hydroxymethylfurfural of CMJE interacted with 84 target proteins. Of the top 15 proteins found by Cytoscape 3.6.1, 8, CAT and OGG1 (downregulated) and CASP3, COMT, CYP1B1, DPYD, NQO1, and PTGS1 (upregulated), were dysregulated in diabetes-related kidney disease. The data demonstrate the highly prospective use of CMJE in the regulation of tubulointerstitial tissues of patients with diabetic nephropathy.

Peroxiredomin-4 ameliorates lipotoxicity-induced oxidative stress and apoptosis in diabetic cardiomyopathy

Diabetic cardiomyopathy (DCM), one severe complication in the diabetes, leads to high mortality in the diabetic patients. However, the understanding of molecular mechanisms underlying DCM is far from completion. Herein, we investigated the disease-related differences in the proteomes of DCM based on db/db mice and verified the protective roles of peroxiredoxin-4 (Prdx4) in H9c2 cardiomyocytes treated by palmitic acid (PA). Fasting blood glucose (FBG) and cardiac function was detected in the 6-month-old control and diabetic mice. The hearts were then collected and analyzed by a coupled label-free and mass spectrometry approach. In vivo investigation indicated that body weight and FBG of db/db mice markedly increased, and diabetic heart exhibited obvious cardiac hypertrophy and lipid droplet accumulation, and cardiac dysfunction as is indicated by the increases of left ventricle posterior wall thickness in systole (LVPWd) and diastole (LVPWs), and reduction of fractional shortening (FS). We used proteomic analysis and then detected a grand total of 2636 proteins. 175 differentially expressed proteins (DEPs) were markedly detected in the diabetic heart. Thereinto, Prdx4 was markedly down-regulated in the diabetic heart. In vitro experiments revealed that 250 μM PA significantly inhibited viability of H9c2 cell. PA induced much accumulation of lipid droplet in cardiomyocytes and resulted in an increase of mRNA expressions of lipogenic genes (FASN and SCD1) and cardiac hypertrophic genes. Additionally, protein level of Prdx4 evidently reduced in the PA-treated H9c2 cell. It was further found that shRNA-mediated Prdx4 knockdown exacerbated PA-induced oxidative stress and cardiomyocyte apoptosis, whereas overexpressing Prdx4 in the H9c2 cells noteworthily limited PA-induced ROS generation and cardiomyocytes apoptosis. These data collectively reveal the essential role of abnormal Prdx4 in pathological alteration of DCM, and provide potentially therapeutic target for the prevention of DCM.

Lipotoxicity dysregulates the immunoproteasome in podocytes and kidneys in type 2 diabetes

Palmitic acid (PA) leads to lipotoxicity in type 2 diabetes and induces oxidative stress in podocytes. Oxidized cellular proteins are degraded by proteasomes. The role of proteasomes in PA- or oxidative stress-induced podocyte injury and pathogenesis of diabetic nephropathy (DN) is unknown. We investigated the effects of PA on expression of 20S and 26S proteasomes, proteasome activator 28 (PA28) regulators, and the immunoproteasome in cultured podocytes and renal cortical tissues of db/db and db/m mice using Western blot analysis. Glomerular areas and glomerular basement membrane (GBM) widths of db/db and db/m mice were examined using morphometry. Short-term incubation of PA or low levels of H₂O₂ upregulated only the immunoproteasome in cultured podocytes. Long-term exposure of podocytes to PA ultimately downregulated the immunoproteasome as with other proteasomes, whereas oleic acid (OA) or eicosapentaenoic acid (EPA) restored the PA-induced decreased protein levels. In db/db mice, renal cortical immunoproteasome expression with PA28α was significantly decreased compared with db/m mice, and glomerular areas and GBM widths were significantly increased compared with db/m mice. Feeding of an OA-rich olive oil or EPA-rich fish oil protected db/db mice against the reduced renal cortical immunoproteasome expression, glomerular enlargement, and GBM thickening. These results demonstrate that lipotoxicity downregulates the immunoproteasome in podocytes and kidneys in type 2 diabetes and that OA and EPA protected type 2 diabetic mice against decreased renal cortical immunoproteasome expression and the progression of DN. Given this, lipotoxicity-induced podocyte injury with impaired immunoproteasome expression appears to play an important role in the pathogenesis of DN.NEW & NOTEWORTHY In podocytes, PA rapidly induced immunoproteasome expression but ultimately decreased it, while OA and EPA restored the decreased immunoproteasome levels. In the renal cortex of type 2 diabetic mice, immunoproteasome expression was significantly decreased, whereas feeding of OA-rich olive oil or EPA-rich fish oil diets protected them against the reduced immunoproteasome expression and progression of diabetic nephropathy. Thus, lipotoxicity-induced podocyte injury with impaired immunoproteasome expression may be related to the pathogenesis of diabetic nephropathy.

The Vicious Cycle of Renal Lipotoxicity and Mitochondrial Dysfunction

The kidney is one of the most energy-demanding organs that require abundant and healthy mitochondria to maintain proper function. Increasing evidence suggests a strong association between mitochondrial dysfunction and chronic kidney diseases (CKDs). Lipids are not only important sources of energy but also essential components of mitochondrial membrane structures. Dysregulation of mitochondrial oxidative metabolism and increased reactive oxygen species (ROS) production lead to compromised mitochondrial lipid utilization, resulting in lipid accumulation and renal lipotoxicity. However, lipotoxicity can be either the cause or the consequence of mitochondrial dysfunction. Imbalanced lipid metabolism, in turn, can hamper mitochondrial dynamics, contributing to the alteration of mitochondrial lipids and reduction in mitochondrial function. In this review, we summarize the interplay between renal lipotoxicity and mitochondrial dysfunction, with a focus on glomerular diseases.

The emerging role of dyslipidemia in diabetic microvascular complications

PURPOSE OF REVIEW

To summarize recent advancements in our understanding of the impact of dyslipidemia on microvascular complications in type 2 diabetes (T2D), with an emphasis on peripheral neuropathy and nephropathy.

RECENT FINDINGS

Mounting evidence suggests that rigorous glycemic control only mitigates certain microvascular complications in T2D patients. Particularly, well regulated blood glucose levels only marginally improve peripheral neuropathy in the T2D setting. Dyslipidemia, an abnormal lipid profile, is emerging as a key factor in peripheral neuropathy. Furthermore, although glycemic control may prevent or slow nephropathy, recent developments demonstrate that dyslipidemia can also affect kidney outcomes in normoglycemic patients. Transcriptomic, epigenomic, and lipidomic investigations, as well as integrative approaches, are shedding light on potential pathomechanisms. These molecular studies are identifying possible targets for therapeutic intervention. Complementing molecular research, lifestyle interventions are on-going to assess whether dietary choices and/or exercise, weight-loss, or surgical interventions, such as bariatric surgery, can ameliorate peripheral neuropathy and nephropathy in T2D patients.

SUMMARY

Dyslipidemia is an emerging mechanism in microvascular complications in T2D. Elucidating the molecular pathomechanisms may pinpoint potential lipid-centric treatments. Interventional studies of dietary changes, exercise, or weight-loss surgery may also positively impact these highly prevalent and morbid complications.

Proteomics of human glomerulonephritis by laser microdissection and liquid chromatography-tandem mass spectrometry

Aim

Laser microdissection (LMD) and liquid chromatography‐tandem mass spectrometry (LC‐MS/MS) enable clinicians to analyse proteins from tissue sections. In nephrology, these methods are used to diagnose diseases of abnormal protein deposition, such as amyloidosis, but they are seldom applied to the diagnosis and pathophysiological understanding of human glomerular diseases.

Methods

Renal biopsy specimens were obtained from five patients with IgA nephropathy (IgAN), five patients with membranous nephropathy (MN) and five kidney transplant donors (as controls). From 10‐μm‐thick sections of formalin‐fixed, paraffin‐embedded specimens, 0.3‐mm² samples of glomerular tissue were subjected to LMD. The samples were analysed by LC‐MS/MS and investigated clinically and histologically.

Results

From the control glomeruli, we identified more than 300 types of proteins. In patients with IgAN, we detected significant increases not only in IgA1 and in C3, but also in the factors related to oxidative stress and cell proliferation in comparison to the controls. In patients with MN, levels of IgG1, IgG4, C3, C4a and phospholipase‐A2‐receptor were significantly elevated in comparison to the controls, as were the aforementioned factors related to oxidative stress and cell proliferations detected in IgAN.

Conclusion

Application of LMD and LC‐MS/MS to renal biopsy specimens enabled us to identify not only pathognomonic proteins for the diagnosis, but also several factors possibly involved in the pathogenesis of human glomerular diseases.

This paper examined the possible application of laser microdissection and liquid chromatography‐tandem mass spectrometry to renal biopsy specimens to clarify the pathogenesis of human glomerular diseases.

Lipotoxicity in Kidney, Heart, and Skeletal Muscle Dysfunction

Dyslipidemia is a common nutritional and metabolic disorder in patients with chronic kidney disease. Accumulating evidence supports the hypothesis that prolonged metabolic imbalance of lipids leads to ectopic fat distribution in the peripheral organs (lipotoxicity), including the kidney, heart, and skeletal muscle, which accelerates peripheral inflammation and afflictions. Thus, lipotoxicity may partly explain progression of renal dysfunction and even extrarenal complications, including renal anemia, heart failure, and sarcopenia. Additionally, endoplasmic reticulum stress activated by the unfolded protein response pathway plays a pivotal role in lipotoxicity by modulating the expression of key enzymes in lipid synthesis and oxidation. Here, we review the molecular mechanisms underlying lipid deposition and resultant tissue damage in the kidney, heart, and skeletal muscle, with the goal of illuminating the nutritional aspects of these pathologies.

Astragaloside IV inhibits palmitate-mediated oxidative stress and fibrosis in human glomerular mesangial cells via downregulation of CD36 expression

BACKGROUND

The increased influx of free fatty acids (FFAs) into the kidney is a risk factor for diabetes nephropathy (DN). In the present study we investigated the effects of astragaloside IV (AS-IV) on FFA-induced lipid accumulation, oxidative stress, and activation of TGF-β1 signaling in human glomerular mesangial cells (HMCs).

METHODS

A DN model was induced in Sprague Dawley rats by the administration of a high-fat diet and streptozocin, and HMCs were stimulated with palmitate. Lipid accumulation and FFA uptake were detected using Oil Red O and BODIPY™ FL C₁₆ staining, respectively. The expression levels of TGF-β1, p-Smad2/3, FN, Col4 A1, NOX4, p22phox, and CD36 were evaluated by western blotting or immunofluorescence/immunohistochemistry. The level of reactive oxygen species (ROS) was detected using 2',7'-dichlorofluorescein diacetate and dihydroethidium.

RESULTS

Exposure to palmitate induced marked lipid accumulation in HMCs, whereas co-treatment with AS-IV significantly attenuated this phenomenon. Moreover, AS-IV suppressed palmitate-induced expression of TGF-β1, p-Smad2/3, FN, Col4 A1, NOX4, and p22phox, in addition to ROS production. Notably, AS-IV reduced the palmitate-induced expression of CD36 in HMCs and DN rats. Treatment of HMCs with the CD36 inhibitor, sulfo-N-succinimidyl oleate (SSO), significantly attenuated FFA uptake, oxidative stress, and fibrosis. Nevertheless, the combined use of SSO and AS-IV did not enhance the efficacy.

CONCLUSION

AS-IV inhibited palmitate-induced HMCs oxidative stress and fibrosis via the downregulation of CD36 expression, mediating FFA uptake and lipid accumulation.

Peroxidase expression is decreased by palmitate in cultured podocytes but increased in podocytes of advanced diabetic nephropathy

High levels of serum free fatty acids (FFAs) are associated with lipotoxicity and type 2 diabetes. Palmitic acid (PA) is the predominant circulating saturated FFA. PA induces mitochondrial superoxide and hydrogen peroxide (H₂O ₂) generation in cultured podocytes. To elucidate the role of PA in antioxidant defense systems in diabetic nephropathy (DN), cultured podocytes were exposed to 250 μM PA for 1–24 hr, and protein expressions of catalase, peroxiredoxins (Prxs), and glutathione peroxidase (GPx) were examined by western blot analysis. PA induced an early transient increase in the Prx1, Prx2, and GPx1 levels in podocytes, but not catalase. Long‐term exposure of PA to podocytes significantly decreased the protein levels of Prx1, Prx2, GPx1, and catalase. Coincubation of PA‐treated cells with oleic acid, however, restored the expression of these proteins. In advanced human diabetic glomeruli, H₂O₂ generation was elevated as shown by increased fluorescence of dichlorofluorescein. Strong immunostaining for Prx1, Prx2, GPx1, and catalase was observed in the podocytes of advanced human DN, wherein transforming growth factor‐β1 staining was also positive. These results suggest that podocytes are susceptible to PA‐induced oxidative damage with impaired peroxidase activity and that peroxidases have futile antioxidant effects in the podocytes in the late stages of DN. Given this, PA‐induced podocyte injury via inadequate peroxidase response to H₂O₂ appears to play an important role in the pathogenesis of DN.