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Activation of GPR120 in podocytes ameliorates kidney fibrosis and inflammation in diabetic nephropathy.

ABSTRACT: Diabetic nephropathy (DN) is one of the most common causes of end-stage renal disease worldwide. ω3-Fatty acids (ω3FAs) were found to attenuate kidney inflammation, glomerulosclerosis, and albuminuria in experimental and clinical studies of DN. As G protein-coupled receptor 120 (GPR120) was firstly identified as the receptor of ω3FAs, we here investigated the function of GPR120 in DN. We first examined the renal biopsies of DN patients, and found that GPR120 expression was negatively correlated with the progression of DN. Immunofluorescence staining analysis revealed that GPR120 protein was mainly located in the podocytes of the glomerulus. A potent and selective GPR120 agonist TUG-891 (35 mg · kg^-1 · d^-1, ig) was administered to db/db mice for 4 weeks. We showed that TUG-891 administration significantly improved urinary albumin excretion, protected against podocyte injury, and reduced collagen deposition in the glomerulus. In db/db mice, TUG-891 administration significantly inhibited the mRNA and protein expression of fibronectin, collagen IV, α-SMA, TGF-β1, and IL-6, and downregulated the phosphorylation of Smad3 and STAT3 to alleviate glomerulosclerosis. Similar results were observed in high-glucose-treated MPC5 podocytes in the presence of TUG-891 (10 μM). Furthermore, we showed that TUG-891 effectively upregulated GPR120 expression, and suppressed TAK1-binding protein-1 expression as well as the phosphorylation of TAK1, IKKβ, NF-κB p65, JNK, and p38 MAPK in db/db mice and high-glucose-treated MPC5 podocytes. Knockdown of GPR120 in MPC5 podocytes caused the opposite effects of TUG-891. In summary, our results highlight that activation of GPR120 in podocytes ameliorates renal inflammation and fibrosis to protect against DN.

SUBMITTER: Wei TT

PROVIDER: S-EPMC8027848 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundGlycolysis dysfunction is an important pathogenesis of podocyte injury in diabetic kidney disease (DKD). Foot process fusion of podocytes and increased albuminuria are markers of early DKD. Moreover, cytoskeletal remodeling has been found to be involved in the foot process fusion of podocytes. However, the connections between cytoskeletal remodeling and alterations of glycolysis in podocytes in DKD have not been clarified.MethodsmRNA sequencing of glomeruli obtained from db/db and db/m mice with albuminuria was performed to analyze the expression profiling of genes in glucose metabolism. Expressions of phosphofructokinase platelet type (PFKP) in the glomeruli of DKD patients were detected. Clotrimazole (CTZ) was used to explore the renal effects of PFKP inhibition in diabetic mice. Using Pfkp siRNA or recombinant plasmid to manipulate PFKP expression, the effects of PFKP on high glucose (HG) induced podocyte damage were assessed in vitro. The levels of fructose-1,6-bisphosphate (FBP) were measured. Targeted metabolomics was performed to observe the alterations of the metabolites in glucose metabolism after HG stimulation. Furthermore, aldolase type b (Aldob) siRNA or recombinant plasmid were applied to evaluate the influence of FBP level alteration on podocytes. FBP was directly added to podocyte culture media. Db/db mice were treated with FBP to investigate its effects on their kidney.ResultsmRNA sequencing showed that glycolysis enzyme genes were altered, characterized by upregulation of upstream genes (Hk1, and Pfkp) and down-regulation of downstream genes of glycolysis (Pkm, and Ldha). Moreover, the expression of PFKP was increased in glomeruli of DKD patients. The CTZ group presented more severe renal damage. In vitro, the Pfkp siRNA group and ALDOB overexpression group showed much more induced cytoskeletal remodeling in podocytes, while overexpression of PFKP and suppression of ALDOB in vitro rescued podocytes from cytoskeletal remodeling through regulation of FBP levels and inhibition of the RhoA/ROCK1 pathway. Furthermore, targeted metabolomics showed FBP level was significantly increased in HG group compared with the control group. Exogenous FBP addition reduced podocyte cytoskeletal remodeling and renal damage of db/db mice.ConclusionsThese findings provide evidence that PFKP may be a potential target for podocyte injury in DN and provide a rationale for applying podocyte glycolysis enhancing agents in patients with DKD.

Project description:Inflammatory pathways are central mechanisms in diabetic kidney disease (DKD). Serum amyloid A (SAA) is increased by chronic inflammation, but SAA has not been previously evaluated as a potential DKD mediator. The aims of this study were to determine whether SAA is increased in human DKD and corresponding mouse models and to assess effects of SAA on podocyte inflammatory responses. SAA was increased in the plasma of people with DKD characterized by overt proteinuria and inversely correlated with estimated glomerular filtration rate (creatinine-based CKD-EPI). SAA was also elevated in plasma of diabetic mouse models including type 1 diabetes (streptozotocin/C57BL/6) and type 2 diabetes (BTBR-ob/ob). SAA mRNA (Nephromine) was increased in human DKD compared with non-diabetic and/or glomerular disease controls (glomerular fold change 1.5, P=0.017; tubulointerstitium fold change 1.4, P=0.021). The kidneys of both diabetic mouse models also demonstrated increased SAA mRNA (quantitative real-time PCR) expression compared with non-diabetic controls (type 1 diabetes fold change 2.9; type 2 diabetes fold change 42.5, P=0.009; interaction by model P=0.57). Humans with DKD and the diabetic mouse models exhibited extensive SAA protein deposition in the glomeruli and tubulointerstitium in similar patterns by immunohistochemistry. SAA localized within podocytes of diabetic mice. Podocytes exposed to advanced glycation end products, metabolic mediators of inflammation in diabetes, increased expression of SAA mRNA (fold change 15.3, P=0.004) and protein (fold change 38.4, P=0.014). Podocytes exposed to exogenous SAA increased NF-?B activity, and pathway array analysis revealed upregulation of mRNA for NF-?B-dependent targets comprising numerous inflammatory mediators, including SAA itself (fold change 17.0, P=0.006). Inhibition of NF-?B reduced these pro-inflammatory responses. In conclusion, SAA is increased in the blood and produced in the kidneys of people with DKD and corresponding diabetic mouse models. Podocytes are likely to be key responder cells to SAA-induced inflammation in the diabetic kidney. SAA is a compelling candidate for DKD therapeutic and biomarker discovery.

Project description:Diabetic nephropathy (DN) as the primary cause of end-stage kidney disease is a common complication of diabetes. Recent researches have shown the activation of nuclear factor kappa light-chain enhancer of activated B cells (NF-κB) and NACHT, LRR and PYD domain-containing protein 3 (NLRP3) inflammasome are associated with inflammation in the progression of DN, but the exact mechanism is unclear. Long noncoding RNAs (lncRNAs) have roles in the development of many diseases including DN. However, the relationship between lncRNAs and inflammation in DN remains largely unknown. Our previous study has revealed that 14 lncRNAs are abnormally expressed in DN by RNA sequencing and real-time quantitative PCR (qRT-PCR) in the renal tissues of db/db DN mice. In this study, these lncRNAs were verified their expressions by qRT-PCR in mesangial cells (MCs) cultured under high- and low-glucose conditions. Twelve lncRNAs displayed the same expressional tendencies in both renal tissues and MCs. In particular, long intergenic noncoding RNA (lincRNA)-Gm4419 was the only one associating with NF-κB among these 12 lncRNAs by bioinformatics methods. Moreover, Gm4419 knockdown could obviously inhibit the expressions of pro-inflammatory cytokines and renal fibrosis biomarkers, and reduce cell proliferation in MCs under high-glucose condition, whereas overexpression of Gm4419 could increase the inflammation, fibrosis and cell proliferation in MCs under low-glucose condition. Interestingly, our results showed that Gm4419 could activate the NF-κB pathway by directly interacting with p50, the subunit of NF-κB. In addition, we found that p50 could interact with NLRP3 inflammasome in MCs. In conclusion, our findings suggest lincRNA-Gm4419 may participate in the inflammation, fibrosis and proliferation in MCs under high-glucose condition through NF-κB/NLRP3 inflammasome signaling pathway, and may provide new insights into the regulation of Gm4419 during the progression of DN.

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Activation of GPR120 in podocytes ameliorates kidney fibrosis and inflammation in diabetic nephropathy.

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