CD36 Promotes Podocyte Apoptosis by Activating the Pyrin Domain-Containing-3 (NLRP3) Inflammasome in Primary Nephrotic Syndrome

Activation of the inflammasome and pyroptosis cascade in podocytes of patients with minimal change disease

Background

In contrast to childhood minimal change disease (MCD), adult-onset MCD frequently recurs and requires prolonged immunosuppressive therapy. Accordingly, an investigation of the pathogenesis of adult MCD is required. MCD is usually accompanied by severe dyslipidaemia. Oxidized low-density lipoprotein (ox-LDL) is known to function in a damage-associated molecular pattern (DAMP) through CD36, triggering the NOD-like receptor thermal protein domain-associated protein 3 (NLRP3) inflammasome and programmed cell death called pyroptosis. However, the relationship between MCD pathogenesis and NLRP3 inflammasome/pyroptosis activation via CD36 is not fully understood.

Methods

We conducted comprehensive histological and clinical evaluations by analysing renal biopsy (RBx) specimens and urine samples obtained from 26 patients with MCD. These samples were compared with control kidneys from 15 transplant donors and urine samples from 15 healthy volunteers.

Results

The number of podocytes was lower in the MCD group than in the control group. Urinary ox-LDL levels were higher in the MCD group than in the control group. Immunofluorescence staining revealed that NLRP3 and CD36 were upregulated in MCD podocytes. Urinary interleukin (IL)-18 levels increased in patients with MCD. Steroid therapy performed before RBx appeared to maintain the podocyte number and reduce urinary ox-LDL and IL-18 levels.

Conclusion

In MCD, the NLRP3 inflammasome and pyroptosis cascade seem to be activated via upregulation of CD36 in podocytes, associated with increased urinary ox-LDL. Elevated urinary IL-18 levels suggest that pyroptosis may occur in MCD. Further research is required to confirm the significance of the podocyte NLRP3 inflammasome/pyroptosis in MCD.

Lipid metabolism disorder in diabetic kidney disease

Diabetic kidney disease (DKD), a significant complication associated with diabetes mellitus, presents limited treatment options. The progression of DKD is marked by substantial lipid disturbances, including alterations in triglycerides, cholesterol, sphingolipids, phospholipids, lipid droplets, and bile acids (BAs). Altered lipid metabolism serves as a crucial pathogenic mechanism in DKD, potentially intertwined with cellular ferroptosis, lipophagy, lipid metabolism reprogramming, and immune modulation of gut microbiota (thus impacting the liver-kidney axis). The elucidation of these mechanisms opens new potential therapeutic pathways for DKD management. This research explores the link between lipid metabolism disruptions and DKD onset.

Astragaloside IV attenuates renal tubule injury in DKD rats via suppression of CD36-mediated NLRP3 inflammasome activation

Background

In recent years, diabetic kidney disease (DKD) has emerged as a prominent factor contributing to end-stage renal disease. Tubulointerstitial inflammation and lipid accumulation have been identified as key factors in the development of DKD. Earlier research indicated that Astragaloside IV (AS-IV) reduces inflammation and oxidative stress, controls lipid accumulation, and provides protection to the kidneys. Nevertheless, the mechanisms responsible for its protective effects against DKD have not yet been completely elucidated.

Purpose

The primary objective of this research was to examine the protective properties of AS-IV against DKD and investigate the underlying mechanism, which involves CD36, reactive oxygen species (ROS), NLR family pyrin domain containing 3 (NLRP3), and interleukin-1β (IL-1β).

Methods

The DKD rat model was created by administering streptozotocin along with a high-fat diet. Subsequently, the DKD rats and palmitic acid (PA)-induced HK-2 cells were treated with AS-IV. Atorvastatin was used as the positive control. To assess the therapeutic effects of AS-IV on DKD, various tests including blood sugar levels, the lipid profile, renal function, and histopathological examinations were conducted. The levels of CD36, ROS, NLRP3, Caspase-1, and IL-1β were detected using western blot analysis, PCR, and flow cytometry. Furthermore, adenovirus-mediated CD36 overexpression was applied to explore the underlying mechanisms through in vitro experiments.

Results

In vivo experiments demonstrated that AS-IV significantly reduced hyperglycemia, dyslipidemia, urinary albumin excretion, and serum creatinine levels in DKD rats. Additionally, it improved renal structural abnormalities and suppressed the expression of CD36, NLRP3, IL-1β, TNF-α, and MCP-1. In vitro experiments showed that AS-IV decreased CD36 expression, lipid accumulation, and lipid ROS production while inhibiting NLRP3 activation and IL-1β secretion in PA-induced HK-2 cells.

Conclusion

AS-IV alleviated renal tubule interstitial inflammation and tubule epithelial cell apoptosis in DKD rats by inhibiting CD36-mediated lipid accumulation and NLRP3 inflammasome activation.

Interplay of lipid metabolism and inflammation in podocyte injury

Podocytes are critical for maintaining permselectivity of the glomerular filtration barrier, and podocyte injury is a major cause of proteinuria in various primary and secondary glomerulopathies. Lipid dysmetabolism and inflammatory activation are the distinctive hallmarks of podocyte injury. Lipid accumulation and lipotoxicity trigger cytoskeletal rearrangement, insulin resistance, mitochondrial oxidative stress, and inflammation. Subsequently, inflammation promotes the progression of glomerulosclerosis and renal fibrosis via multiple pathways. These data suggest that lipid dysmetabolism positively or negatively regulates inflammation during podocyte injury. In this review, we summarize recent advances in the understanding of lipid metabolism and inflammation, and highlight the potential association between lipid metabolism and podocyte inflammation.

Quercetin-targeted AKT1 regulates the Raf/MEK/ERK signaling pathway to protect against doxorubicin-induced nephropathy in mice

BACKGROUND

Doxorubicin is an anthracycline antitumor agent commonly used in clinical practice, which has some nephrotoxicity and is often used to establish mouse models of kidney injury for basic medical research. This study will investigate the protective effect of quercetin on renal function in doxorubicin-induced nephropathy mice.

METHODS

C57BL/6 mice were divided into control, model, and quercetin low-, and high-dose groups. Serum and urine were collected to analyze markers of kidney function. H&E staining was used to detect pathological changes in renal tissues. Transmission electron microscopy was performed to observe the ultrastructural changes in renal tissues. Immunohistochemistry was performed to detect the changes of Ang II. RT-qPCR was performed to detect the changes of cytokines. ELISA was used to detect changes in serum inflammatory factors. Molecular docking was performed to verify the targeting relationship between quercetin and AKT1. Western blot was performed to detect Bax, Bcl-2, Cyt-c, AKT1, Raf, MEK, and ERK proteins.

RESULTS

Quercetin could induce the recovery of kidney function in kidney-injured mice; H&E results showed that kidney tissue damage and tissue fibrosis were reduced in kidney-injured mice under quercetin. The mitochondrial swollen structure was destroyed by doxorubicin, while the mitochondrial structure was restored under quercetin. The levels of abnormal apoptotic proteins Bax and Bcl-2 were regulated to normal by quercetin. The high expression of Ang II caused by doxorubicin was down-regulated by quercetin. Abnormal inflammatory factors caused by doxorubicin were reversed by quercetin. Western blot experiments showed that quercetin regulated the protein levels of AKT1 and Raf/MEK/ERK and inhibited the detrimental effects of doxorubicin.

CONCLUSION

Quercetin may mitigate doxorubicin-induced kidney injury in mice by regulating renal cell inflammatory factors and Raf/MEK/ERK signaling pathway through AKT1 to promote recovery of renal function.

Tripterygium glycosides improve abnormal lipid deposition in nephrotic syndrome rat models

OBJECTIVE

The purpose of this study was to determine the effect of tripterygium glycosides (TGs) on regulating abnormal lipid deposition in nephrotic syndrome (NS) rats.

METHODS

Sprague-Dawley (SD) rats were injected with 6 mg/kg doxorubicin to construct nephrotic syndrome models (n = 6 per group), and then administered with TGs (10 mg/kg·d^-1), prednisone (6.3 mg/kg·d^-1), or pure water for 5 weeks. Biomedical indexes, such as urine protein/creatinine ratio (PCR), blood urea nitrogen (BUN), serum creatinine (Scr), serum albumin (SA), triglycerides (TG), total cholesterol (TC)were investigated to evaluate the renal injury of rats. H&E staining experiment was used to assess the pathological alterations. Oil Red O staining was used to assess the level of renal lipid deposition. Malondialdehyde (MDA) and glutathione (GSH) were measured to assess the extent of oxidative damage to the kidney. TUNEL staining was used to assess the status of apoptosis in the kidney. Western blot analysis was performed to examine the levels of relevant intracellular signaling molecules.

RESULTS

After treatment with TGs, those tested biomedical indexes were significantly improved, and the extent of kidney tissue pathological changes and lipid deposition in the kidney was diminished. Treatment with TGs decreased renal oxidative damage and apoptosis. Regarding the molecular mechanism, TGs significantly increased the protein expression levels of Bcl-2 but decreased the levels of CD36, ADFP, Bax, and Cleaved caspase-3.

CONCLUSION

TGs alleviates renal injury and lipid deposition induced by doxorubicin, suggesting that it may be a new strategy for reducing renal lipotoxicity in NS.

Kidney lipid dysmetabolism and lipid droplet accumulation in chronic kidney disease

Chronic kidney disease (CKD) is a global health problem with rising incidence and prevalence. Among several pathogenetic mechanisms responsible for disease progression, lipid accumulation in the kidney parenchyma might drive inflammation and fibrosis, as has been described in fatty liver diseases. Lipids and their metabolites have several important structural and functional roles, as they are constituents of cell and organelle membranes, serve as signalling molecules and are used for energy production. However, although lipids can be stored in lipid droplets to maintain lipid homeostasis, lipid accumulation can become pathogenic. Understanding the mechanisms linking kidney parenchymal lipid accumulation to CKD of metabolic or non-metabolic origin is challenging, owing to the tremendous variety of lipid species and their functional diversity across different parenchymal cells. Nonetheless, multiple research reports have begun to emphasize the effect of dysregulated kidney lipid metabolism in CKD progression. For example, altered cholesterol and fatty acid metabolism contribute to glomerular and tubular cell injury. Newly developed lipid-targeting agents are being tested in clinical trials in CKD, raising expectations for further therapeutic development in this field.

Effect of Proprotein Convertase Subtilisin/Kexin Type 9 Inhibition on Podocytes in Mouse Nephrotic Syndrome

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is known to play a crucial role in dyslipidemia, and an increase in serum PCSK9 levels has also been reported in patients with nephrotic syndrome (NS). However, the specific effects of PCSK9 in kidney disease and the therapeutic potential of targeting PCSK9 in NS remain elusive. We thus investigated the effects of evolocumab (EVO) in mice with adriamycin (ADR)-induced NS. Male BALB/c mice were divided into the following 4 groups: Control, N = 11; EVO (monoclonal antibody for PCSK9), N = 11; ADR, N = 11; and ADR+EVO, N = 11. We also performed in vitro experiments using immortalized murine podocyte cells to validate the direct effects of PCSK9 on podocytes. EVO decreased urinary albumin levels and ameliorated podocytopathy in mice with ADR nephropathy. Further, EVO suppressed the Nod-like receptor protein 3 (NLRP3) inflammasome pathway in podocytes. PCSK9 expression upregulated CD36, a scavenger receptor of oxidized low-density lipoprotein (Ox-LDL), which in turn stimulated the absorption of Ox-LDL in vitro. EVO downregulated CD36 expression in podocytes both in vitro and in vivo. Immunofluorescence staining analysis reveals that CD36 and PCSK9 colocalized in the glomerular tufts of mice with ADR nephropathy. In the patients with focal segmental glomerulosclerosis, the CD36+ area in glomerular tufts increased compared with those diagnosed with minor glomerular abnormalities. This study revealed that EVO ameliorated mouse ADR nephropathy through the regulation of CD36 and NLRP3 inflammasome signaling. EVO treatment represents a potential therapeutic strategy for human NS.

Inhibiting NLRP3 signaling in aging podocytes improves their life- and health-span

The decrease in the podocyte's lifespan and health-span that typify healthy kidney aging cause a decrease in their normal structure, physiology and function. The ability to halt and even reverse these changes becomes clinically relevant when disease is superimposed on an aged kidney. RNA-sequencing of podocytes from middle-aged mice showed an inflammatory phenotype with increases in the NLRP3 inflammasome, signaling for IL2/Stat5, IL6 and TNF, interferon gamma response, allograft rejection and complement, consistent with inflammaging. Furthermore, injury-induced NLRP3 signaling in podocytes was further augmented in aged mice compared to young ones. The NLRP3 inflammasome (NLRP3, Caspase-1, IL1β IL-18) was also increased in podocytes of middle-aged humans. Higher transcript expression for NLRP3 in human glomeruli was accompanied by reduced podocyte density and increased global glomerulosclerosis and glomerular volume. Pharmacological inhibition of NLRP3 with MCC950, or gene deletion, reduced podocyte senescence and the genes typifying aging in middle-aged mice, which was accompanied by an improved podocyte lifespan and health-span. Moreover, modeling the injury-dependent increase in NLRP3 signaling in human kidney organoids confirmed the anti-senescence effect of MC9950. Finally, NLRP3 also impacted liver aging. Together, these results suggest a critical role for the NLRP3 inflammasome in podocyte and liver aging.

Diesel vehicles-derived PM2.5 induces lung and cardiovascular injury attenuates by Securiniga suffruticosa: Involvement of NF-κB-mediated NLRP3 inflammasome activation pathway

Respiratory exposure to Particulate matter (PM), including Diesel exhaust particulate (DEP), causes oxidative stress-induced lung inflammation. Especially, fine particulate matter with an aerodynamic diameter less than 2.5 µm (PM2.5) is a serious air pollutant associated with various health problems including cardiovascular diseases. The present study aimed to examine the inhibitory effect of Securiniga suffruticosa (S. suffruiticosa) on DEP and PM-induced lung and cardiovascular diseases. Mice inhaled DEP by using nebulizer chamber for two weeks. Treatment with S. suffruiticosa reduced the expression of C-X-C motif ligand 1/2 in bronchoalveolar lavage fluid and Muc5ac, ICAM-1, TNF-⍺, IL-6 mRNA in lung were also attenuated by S. suffruiticosa. In thoracic aorta, DEP increased CAMs, TNF-⍺ and inflammasome markers such as NLRP3, Caspase-1, and ASC. However, S. suffruiticosa suppressed these levels. S. suffruiticosa inhibited PM2.5 induced production of intracellular reactive oxygen species (ROS); and inhibited the translocation of NF-κB p65 to the nucleus in human umbilical vein endothelial cells. Taken together, this study proved that exposure to PM2.5 induced both lung and vascular inflammation, however, S. suffruiticosa attenuated this injury via the downregulation of the NLRP3 signaling pathway. These findings suggest that S. suffruiticosa may have potential therapeutic benefit against air pollution-mediated lung and cardiovascular diseases.

Inflammasomes: Cause or consequence of obesity-associated comorbidities in humans

Inflammasomes are multiprotein intracellular complexes composed of innate immune system receptors and sensors; they activate the inflammatory cascade in response to infectious microbes and/or molecules derived from host proteins. Because of cytokine secretion, inflammasomes can induce amplified systemic responses, its dysregulation can exacerbate symptoms in infectious diseases, and it has been related to the development of autoimmune diseases, inflammatory disorders, and even cancer. Obesity is associated with a chronic low-grade inflammation, in which circulating proinflammatory cytokines are elevated. Some publications describe changes in inflammation markers as a consequence of obesity, but others suggest that chronic inflammation might cause obesity (e.g., C-reactive protein): these assumptions reflect the difficulty of identifying the appropriate role of inflammation as cause or consequence of obesity and its related complications. Obesity is recognized as a clinical risk factor for developing cardiovascular diseases including atherosclerosis, metabolic syndrome, insulin resistance, and diabetes mellitus. Changes in the expression of inflammasomes are described in some of these obesity-related complications, and moreover, its modulation might exert a beneficial effect in some cases. Despite some contradictory results, most publications suggest a promising clinical effect based on in vitro and in vivo experiments. In this review, we summarized recent publications about inflammasome dysregulation in humans and its relationship with obesity-related comorbidities.

Lipid metabolism disorders contribute to hepatotoxicity of ICR mice induced by nitrosamines exposure

Health risks caused by crucial environmental carcinogens N-nitrosamines triggered ubiquitous attention. As the liver exerted vital function through metabolic process, lipid metabolism disorders have been confirmed as potential drivers for toxicological effects, and the mechanisms of lipid regulation related to hepatotoxicity induced by N-nitrosamines remained largely unclear. In this study, we comprehensively explored the disturbance of hepatic lipid homeostasis in mice induced by nitrosamines. The results implied that nitrosamines exposure induced hepatotoxicity accompanied by liver injury, inflammatory infiltration, and hepatic edema. Lipidomics profiling analysis indicated the decreased levels of phosphatidic acids (PA), phosphatidylcholines (PC), phosphatidylethanolamines (PE), lyso-phosphatidylcholines (LPC), lyso-phosphatidylethanolamines (LPE), diacylglycerols (DAG) and triacylglycerols (TAG), the elevation of ceramides (Cer) and decomposition of free fatty acids (FFA) in high-dose nitrosamines exposure group. Importantly, nitrosamines exposure promoted fatty acid oxidation (FAO) by facilitating fatty acid uptake and decomposition, together with the upregulation of genes associated with FAO accompanied by the activation of inflammatory cytokines TNF-α, IL-1β and NLRP3. Furthermore, fatty acid translocase CD36-mediated fatty acid oxidation was correlated with the enhancement of oxidative stress in the liver caused by nitrosamines exposure. Overall, our results contributed to the new strategies to interpret the early toxic effects of nitrosamines exposure.

CD36 aggravates podocyte injury by activating NLRP3 inflammasome and inhibiting autophagy in lupus nephritis

A major cause of proteinuria in lupus nephritis (LN) is podocyte injury, and determining potential therapeutic targets to prevent podocyte injury is important from a clinical perspective in the treatment of LN. CD36 is involved in podocyte injury in several glomerulopathies and was reported to be a vital candidate gene in LN. Here, we determined the role of CD36 in the podocyte injury of LN and the underlying mechanisms. We observed that CD36 and NLRP3 (NLR family pyrin domain containing 3) were upregulated in the podocytes of lupus nephritis patients and MRL/lpr mice with renal impairment. In vitro, CD36, NLRP3 inflammasome, and autophagy were elevated accompanied with increased podocyte injury stimulated by IgG extracted from lupus nephritis patients compared that from healthy donors. Knocking out CD36 with the CRISPR/cas9 system decreased the NLRP3 inflammasome levels, increased the autophagy levels and alleviated podocyte injury. By enhancing autophagy, NLRP3 inflammasome was decreased and podocyte injury was alleviated. These results demonstrated that, in lupus nephritis, CD36 promoted podocyte injury by activating NLRP3 inflammasome and inhibiting autophagy by enhancing which could decrease NLRP3 inflammasome and alleviate podocyte injury.

Podocyte Bioenergetics in the Development of Diabetic Nephropathy: The Role of Mitochondria

Diabetic nephropathy (DN) is the leading cause of kidney failure, with an increasing incidence worldwide. Mitochondrial dysfunction is known to occur in DN and has been implicated in the underlying pathogenesis of disease. These complex organelles have an array of important cellular functions and involvement in signaling pathways, and understanding the intricacies of these responses in health, as well as how they are damaged in disease, is likely to highlight novel therapeutic avenues. A key cell type damaged early in DN is the podocyte, and increasing studies have focused on investigating the role of mitochondria in podocyte injury. This review will summarize what is known about podocyte mitochondrial dynamics in DN, with a particular focus on bioenergetic pathways, highlighting key studies in this field and potential opportunities to target, enhance or protect podocyte mitochondrial function in the treatment of DN.

Effect of Geumgwe-Sinkihwan on Renal Dysfunction in Ischemia/Reperfusion-Induced Acute Renal Failure Mice

Renal ischemia-reperfusion (I/R) injury is an important cause of acute renal failure (ARF). Geumgwe-sinkihwan (GSH) was recorded in a traditional Chines medical book named “Bangyakhappyeon” in 1884. GSH has been used for treatment for patients with diabetes and glomerulonephritis caused by deficiency of kidney yang and insufficiency of kidney gi. Here we investigate the effects of GSH in mice model of ischemic acute kidney injury. The mice groups are as follows; sham group: C57BL6 male mice, I/R group: C57BL6 male mice with I/R surgery, GSH low group: I/R + 100 mg/kg/day GSH, and GSH high group: I/R + 300 mg/kg/day GSH. Ischemia was induced by clamping both renal arteries and reperfusion. Mice were orally given GSH (100 and 300 mg/kg/day) during 3 days after surgery. Treatment with GSH significantly ameliorated creatinine clearance, creatinine, and blood urea nitrogen levels. Treatment with GSH reduced neutrophil gelatinase associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1), specific renal injury markers. GSH also reduced the periodic acid–Schiff and picro sirius red staining intensity in kidney of I/R group. Western blot and real-time RT-qPCR analysis demonstrated that GSH decreased protein and mRNA expression levels of the inflammatory cytokines in I/R-induced ARF mice. Moreover, GSH inhibited protein and mRNA expression of inflammasome-related protein including NLRP3 (NOD-like receptor pyrin domain-containing protein 3, cryoprin), ASC (Apoptosis-associated speck-like protein containing a CARD), and caspase-1. These findings provided evidence that GSH ameliorates renal injury including metabolic dysfunction and inflammation via the inhibition of NLRP3-dependent inflammasome in I/R-induced ARF mice.

Protective action of ultrasound-guided intraparenchymal transplantation of BMSCs in adriamycin nephropathy rats through the RIPK3/MLKL and NLRP3 pathways

BACKGROUND

Bone marrow stromal cells (BMSCs) are an effective new strategy for the treatment of kidney diseases. At present, noninvasive and efficient transplantation approaches to homing BMSCs to the renal parenchyma is still a serious challenge. The aim of this study was to investigate the feasibility and potential mechanism of ultrasound-guided intraparenchymal transplantation of BMSCs for the treatment of adriamycin nephropathy (AN) in rats.

MATERIALS AND METHODS

A rat AN model was induced by 2 injections of doxorubicin. The rats were randomly divided into 4 groups (n = 10 animals in each group) : normal group (N group, no treatment), control medium group (CM group, transplant medium 1.0 mL), adriamycin nephropathy group (ADR group, phosphate buffered saline 1.0 mL), or BMSCs group (BMSCs fluid 1.0 mL). Intraparenchymal injection was completed under ultrasound guidance. After 4 weeks of treatment, blood samples were collected for serum biochemical measurements and ELISAs. The kidneys were removed for histopathological examination, electron microscopy, terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL), and western blot analysis.

RESULTS

No deaths occurred in any group after BMSCs transplantation through the renal parenchyma under ultrasound guidance. Compared with the N and CM groups, in the ADR group, blood serum creatinine (SCr), blood urea nitrogen (BUN) and urine albumin (ALb) were higher, glomerular and tubular dilatation was observed, the number of apoptotic cells was higher, and the protein levels of receptor-interacting protein kinase 3 (RIPK3)/mixed lineage kinase domain-like protein (MLKL) and nucleotide leukin-rich polypeptide 3 (NLRP3), key components of pathways in rat kidney, were significantly higher. Compared with those in the ADR group, the levels of SCr, BUN, ALb and serum proinflammatory cytokines in the BMSCs group were lower, the pathological structure of the kidney was improved, the number of apoptotic cells was lower, and the levels of RIPK3/MLKL and NLRP3 were significantly lower.

CONCLUSION

Ultrasound-guided intraparenchymal transplantation of BMSCs regulated the RIPK3/MLKL and NLRP3 pathways in a minimally invasive and safe manner, thereby inhibiting renal necrosis and inflammation and playing a protective role in rat AN.

Polybrominated Diphenyl Ether Quinone Exposure Induces Atherosclerosis Progression via CD36-Mediated Lipid Accumulation, NLRP3 Inflammasome Activation, and Pyroptosis

Polybrominated diphenyl ethers (PBDEs) are used worldwide in brominated flame retardants. Although due to the forbiddance of their application, PBDEs continuously exist in the environment due to their persistence. Therefore, it is important to expand the understanding of their potential toxicities and human risks. The underlying cardiovascular toxicological mechanisms of PBDEs are still largely unknown. Our previous studies indicated that PBDE quinone-type metabolite (PBDEQ) exposure causes reactive oxygen species (ROS)-driven cytotoxicity and various types of programmed cell death. Here, we first reported PBDEQ exposure induces atherosclerosis progression in bone marrow-derived macrophages (BMDMs) isolated from wild-type C57BL/6 or CD36-/- mice and J774A.1 macrophage models. First, we found that PBDEQ exposure induced lipid accumulation in oxidized low-density lipid (Ox-LDL)-treated J774A.1 macrophages. Consistently, in J774A.1 macrophages, PBDEQ exposure resulted in NLR family pyrin domain containing 3 (NLRP3) inflammasome activation and pyroptosis. CD36, a scavenger receptor responsible for the mediation of Ox-LDL uptake, was upregulated upon PBDEQ treatment. On the contrary, genetic knockout of CD36 or CD36 silencing by small interfering RNA efficiently attenuates PBDEQ-promoted lipid accumulation in BMDMs and J774A.1 macrophages. These findings highlight the effect of CD36 on the cardiovascular toxicity of PBDEs, which provides a better understanding of the pro-atherosclerosis effect of PBDEs.

New insights into renal lipid dysmetabolism in diabetic kidney disease

Lipid dysmetabolism is one of the main features of diabetes mellitus and manifests by dyslipidemia as well as the ectopic accumulation of lipids in various tissues and organs, including the kidney. Research suggests that impaired cholesterol metabolism, increased lipid uptake or synthesis, increased fatty acid oxidation, lipid droplet accumulation and an imbalance in biologically active sphingolipids (such as ceramide, ceramide-1-phosphate and sphingosine-1-phosphate) contribute to the development of diabetic kidney disease (DKD). Currently, the literature suggests that both quality and quantity of lipids are associated with DKD and contribute to increased reactive oxygen species production, oxidative stress, inflammation, or cell death. Therefore, control of renal lipid dysmetabolism is a very important therapeutic goal, which needs to be archived. This article will review some of the recent advances leading to a better understanding of the mechanisms of dyslipidemia and the role of particular lipids and sphingolipids in DKD.

The NLRP3 Inflammasome: Metabolic Regulation and Contribution to Inflammaging

In response to inflammatory stimuli, immune cells reconfigure their metabolism and bioenergetics to generate energy and substrates for cell survival and to launch immune effector functions. As a critical component of the innate immune system, the nucleotide-binding and oligomerization domain, leucine-rich repeat, and pyrin domain-containing 3 (NLRP3) inflammasome can be activated by various endogenous and exogenous danger signals. Activation of this cytosolic multiprotein complex triggers the release of the pro-inflammatory cytokines interleukin (IL)-1β and IL-18 and initiates pyroptosis, an inflammatory form of programmed cell death. The NLRP3 inflammasome fuels both chronic and acute inflammatory conditions and is critical in the emergence of inflammaging. Recent advances have highlighted that various metabolic pathways converge as potent regulators of the NLRP3 inflammasome. This review focuses on our current understanding of the metabolic regulation of the NLRP3 inflammasome activation, and the contribution of the NLRP3 inflammasome to inflammaging.

Inflammasome activation in podocytes: a new mechanism of glomerular diseases

INTRODUCTION

Inflammasome is a multi-protein complex which is an important constituent of innate immunity. It mainly consists of three parts, apoptosis-associated speck-like protein containing caspase recruitment domain (ASC), caspase protease, and a NOD-like receptor (NLR) family protein (such as NLRP1) or an HIN200 family protein (such as AIM2). Inflammasome is widely studied in many autoimmune diseases and chronic inflammatory reactions, such as familial periodic autoinflammatory response, type 2 diabetes, Alzheimer's disease, and atherosclerosis. Activation of inflammasome in the kidney has been widely reported in glomerular and tubular-interstitial diseases. Podocytes play a critical role in maintaining the normal structure and function of glomerular filtration barrier. Recently, it has been demonstrated that podocytes, as a group of renal residential cells, can express all necessary components of NLRP3 inflammasome, which is activated and contribute to inflammatory response in the local kidney.

METHODS

Literature review was conducted to further summarize current evidence of podocyte NLRP3 inflammasome activation and related molecular mechanisms under different disease conditions.

RESULTS

Podocytes are a key component of the glomerular filtration barrier, and the loss of podocyte regeneration is a major limiting factor in the recovery of proteinuria. Through a more comprehensive study of inflammasome in podocytes, it will provide new targets and possibilities for the treatment of kidney diseases.

Recent Progress on Lipid Intake and Chronic Kidney Disease

The incidence of chronic kidney disease (CKD) is associated with major abnormalities in circulating lipoproteins and renal lipid metabolism. This article elaborates on the mechanisms of CKD and lipid uptake abnormalities. The viewpoint we supported is that lipid abnormalities directly cause CKD, resulting in forming a vicious cycle. On the theoretical and experiment fronts, this inference has been verified by elaborately elucidating the role of lipid intake and accumulation as well as their influences on CKD. Taken together, these findings suggest that further understanding of lipid metabolism in CKD may lead to novel therapeutic approaches.

Crosstalk Between Lipids and Mitochondria in Diabetic Kidney Disease

PURPOSE OF REVIEW

The goal of this review is to review the role that renal parenchymal lipid accumulation plays in contributing to diabetic kidney disease (DKD), specifically contributing to the mitochondrial dysfunction observed in glomerular renal cells in the context of DKD development and progression.

RECENT FINDINGS

Mitochondrial dysfunction has been observed in experimental and clinical DKD. Recently, Ayanga et al. demonstrate that podocyte-specific deletion of a protein involved in mitochondrial dynamics protects from DKD progression. Furthermore, our group has recently shown that ATP-binding cassette A1 (a protein involved in cholesterol and phospholipid efflux) is significantly reduced in clinical and experimental DKD and that genetic or pharmacological induction of ABCA1 is sufficient to protect from DKD. ABCA1 deficiency in podocytes leads to mitochondrial dysfunction observed with alterations of mitochondrial lipids, in particular, cardiolipin (a mitochondrial-specific phospholipid). However, through pharmacological reduction of cardiolipin peroxidation DKD progression is reverted. Lipid metabolism is significantly altered in the diabetic kidney and renders cellular components, such as the podocyte, susceptible to injury leading to worsened DKD progression. Dysfunction of the lipid metabolism pathway can also lead to mitochondrial dysfunction and mitochondrial lipid alteration. Future research aimed at targeting mitochondrial lipids content and function could prove to be beneficial for the treatment of DKD.

CD36 identified by weighted gene co-expression network analysis as a hub candidate gene in lupus nephritis

Lupus nephritis (LN) is a severe manifestation of systemic lupus erythematosus (SLE), which often progresses to end-stage renal disease (ESRD) and ultimately leads to death. At present, there are no definitive therapies towards LN, so that illuminating the molecular mechanism behind the disease has become an urgent task for researchers. Bioinformatics has become a widely utilized method for exploring genes related to disease. This study set out to conduct weighted gene co-expression network analysis (WGCNA) and screen the hub gene of LN. We performed WGCNA on the microarray expression profile dataset of GSE104948 from the Gene Expression Omnibus (GEO) database with 18 normal and 21 LN samples of glomerulus. A total of 5,942 genes were divided into 5 co-expression modules, one of which was significantly correlated to LN. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were conducted on the LN-related module, and the module was proved to be associated mainly with the activation of inflammation, immune response, cytokines, and immune cells. Genes in the most significant GO terms were extracted for sub-networks of WGNCA. We evaluated the centrality of genes in the sub-networks by Maximal Clique Centrality (MCC) method and CD36 was ultimately screened out as a hub candidate gene of the pathogenesis of LN. The result was verified by its differentially expressed level between normal and LN in GSE104948 and the other three multi-microarray datasets of GEO. Moreover, we further demonstrated that the expression level of CD36 is related to the WHO Lupus Nephritis Class of LN patients with the help of Nephroseq database. The current study proposed CD36 as a vital candidate gene in LN for the first time and CD36 may perform as a brand-new biomarker or therapeutic target of LN in the future.

Inflammation Induces Lipid Deposition in Kidneys by Downregulating Renal PCSK9 in Mice with Adriamycin-Induced Nephropathy

BACKGROUND Previous studies of human and animal models indicate that inflammation alters lipid metabolism. The pro-protein convertase subtilisin kexin type 9 (PCSK9) plays an important role in lipid metabolism. MATERIAL AND METHODS We examined the effect of inflammation on PCSK9 expression and lipid deposition in the kidneys of mice with Adriamycin-induced nephropathy. RESULTS The results indicated an increased expression of inflammatory cytokines and lipid deposition over 12 weeks. During this time, the expression of PCSK9 and its transcriptional activator (hepatocyte nuclear factor 1alpha, HNF1alpha) decreased, and the expression of the low-density lipoprotein receptor (LDLR) and its transcriptional activator (sterol regulatory element binding protein-2, SREBP-2) increased. Exogenous inflammation appeared to further aggravate this process. CONCLUSIONS Our mouse model of nephropathy suggests that a key step in the inflammation-induced deposition of lipids in the kidneys is the downregulation renal PCSK9 expression.

CD36-Mediated Lipid Accumulation and Activation of NLRP3 Inflammasome Lead to Podocyte Injury in Obesity-Related Glomerulopathy

Podocyte injury critically contributes to the pathogenesis of obesity-related glomerulopathy (ORG). Recently, lipid accumulation and inflammatory responses have been found to be involved in podocyte injury. This study is to explore their role and relationship in podocyte injury of ORG. In animal experiments, the ORG mice developed proteinuria, podocyte injury, and hypertriglyceridemia, accompanied with deregulated lipid metabolism, renal ectopic lipid deposition, activation of NOD-like receptor protein 3 (NLRP3) inflammasome, and secretion of IL-1β of the kidney. The expression of adipose differentiation-related protein (ADRP), CD36, sterol regulatory element-binding protein 1 (SREBP-1), and peroxisome proliferator-activated receptor α (PPARα) in renal tissue were increased. In in vitro cell experiments, after cultured podocytes were stimulated with leptin, similar to ORG mice, we found aggravated podocyte injury, formatted lipid droplet, increased expression of ADRP and CD36, activated NLRP3 inflammasome, and released IL-1β. In addition, after blocking CD36 with inhibitor sulfo-N-succinimidyl oleate (SSO) or CD36 siRNA, activation of NLRP3 inflammasome and release of IL-1β are downregulated, and podocyte injury was alleviated. However, after blocking NLRP3 with MCC950, although podocyte injury was alleviated and release of IL-1β was decreased, there was no change in the expression of CD36, ADRP, and intracellular lipid droplets. Taken together, our study suggests that CD36-mediated lipid accumulation and activation of NLRP3 inflammasome may be one of the potential pathogeneses of ORG podocyte injury.