PFKP Activation Ameliorates Foot Process Fusion in Podocytes in Diabetic Kidney Disease

Signaling through cAMP-Epac1 induces metabolic reprogramming to protect podocytes in glomerulonephritis

Unlike classical protein kinase A, with separate catalytic and regulatory subunits, EPACs are single chain multi-domain proteins containing both catalytic and regulatory elements. The importance of cAMP-Epac-signaling as an energy provider has emerged over the last years. However, little is known about Epac1 signaling in chronic kidney disease. Here, we examined the role of Epac1 during the progression of glomerulonephritis (GN). We first observed that total genetic deletion of Epac1 in mice accelerated the progression of nephrotoxic serum (NTS)-induced GN. Next, mice with podocyte-specific conditional deletion of Epac1 were generated and showed that NTS-induced GN was exacerbated in these mice. Gene expression analysis in glomeruli at the early and late phases of GN showed that deletion of Epac1 in podocytes was associated with major alterations in mitochondrial and metabolic processes and significant dysregulation of the glycolysis pathway. In vitro, Epac1 activation in a human podocyte cell line increased mitochondrial function to cope with the extra energy demand under conditions of stress. Furthermore, Epac1-induced glycolysis and lactate production improved podocyte viability. To verify the in vivo therapeutic potential of Epac1 activation, the Epac1 selective cAMP mimetic 8-pCPT was administered in wild type mice after induction of GN. 8-pCPT alleviated the progression of GN by improving kidney function with decreased structural injury with decreased crescent formation and kidney inflammation. Importantly, 8-pCPT had no beneficial effect in mice with Epac1 deletion in podocytes. Thus, our data suggest that Epac1 activation is an essential protective mechanism in GN by reprogramming podocyte metabolism. Hence, targeting Epac1 activation could represent a potential therapeutic approach.

Downregulating lncRNA MIAT attenuates apoptosis of podocytes exposed to high glucose

AIMS

Diabetic nephropathy (DN), a destructive complication of diabetes mellitus (DM), is one of the leading causes of end-stage renal disease (ESRD). This study aimed to investigate the role of long non-coding RNA (lncRNA) MIAT in high-glucose (HG)-induced podocyte injury associated with DN.

METHODS

Three human kidney podocyte (HKP) cultures were treated with HG to mimic DN. Expression of lncRNA MIAT, podocyte-specific and injury-related proteins, and apoptosis were assessed before and after MIAT knockdown using MIAT shRNAs.

RESULTS

MIAT expression was upregulated in HKPs in response to glucose stress. HG treatment resulted in a significant increase in the apoptotic rate, Bax level, and levels of injury-related proteins desmin, fibroblast-specific protein 1 (FSP-1), and smooth muscle α-actin (α-SMA), and a significant reduction in Bcl-2 levels and the levels of podocyte-specific proteins synaptopodin and podocin. Transfection of HKPs with shRNAs significantly reduced MIAT levels (p < 0.05) and attenuated apoptosis in HG-medium. Correspondingly, the levels of synaptopodin and podocin were upregulated, and desmin, FSP-1, and α-SMA were reduced (p < 0.05). Western blot analysis also showed that anti-apoptotic active caspase-3 and Bax and proapoptotic Bcl-2 were elevated and decreased, respectively, after MIAT knockdown, suggesting that apoptosis pathways are deactivated after MIAT downregulation.

CONCLUSIONS

High glucose upregulates MIAT level in HKPs and induces cellular injury. Knockdown of MIAT alleviates the injury likely via deactivating apoptosis pathways.

Dihydroxyacetone phosphate accumulation leads to podocyte pyroptosis in diabetic kidney disease

Diabetic kidney disease (DKD) can lead to accumulation of glucose upstream metabolites due to dysfunctional glycolysis. But the effects of accumulated glycolysis metabolites on podocytes in DKD remain unknown. The present study examined the effect of dihydroxyacetone phosphate (DHAP) on high glucose induced podocyte pyroptosis. By metabolomics, levels of DHAP, GAP, glucose-6-phosphate and fructose 1, 6-bisphosphate were significantly increased in glomeruli of db/db mice. Furthermore, the expression of LDHA and PKM2 were decreased. mRNA sequencing showed upregulation of pyroptosis-related genes (Nlrp3, Casp1, etc.). Targeted metabolomics demonstrated higher level of DHAP in HG-treated podocytes. In vitro, ALDOB expression in HG-treated podocytes was significantly increased. siALDOB-transfected podocytes showed less DHAP level, mTORC1 activation, reactive oxygen species (ROS) production, and pyroptosis, while overexpression of ALDOB had opposite effects. Furthermore, GAP had no effect on mTORC1 activation, and mTORC1 inhibitor rapamycin alleviated ROS production and pyroptosis in HG-stimulated podocytes. Our findings demonstrate that DHAP represents a critical metabolic product for pyroptosis in HG-stimulated podocytes through regulation of mTORC1 pathway. In addition, the results provide evidence that podocyte injury in DKD may be treated by reducing DHAP.

ALCAT1-mediated abnormal cardiolipin remodelling promotes mitochondrial injury in podocytes in diabetic kidney disease

BACKGROUND

Cardiolipin (CL) plays a critical role in maintaining mitochondrial membrane integrity and overall mitochondrial homeostasis. Recent studies have suggested that mitochondrial damage resulting from abnormal cardiolipin remodelling is associated with the pathogenesis of diabetic kidney disease (DKD). Acyl-coenzyme A:lyso-cardiolipin acyltransferase-1 (ALCAT1) was confirmed to be involved in the progression of Parkinson's disease, diet-induced obesity and other ageing-related diseases by regulating pathological cardiolipin remodelling. Thus, the purpose of this investigation was to determine the role of ALCAT1-mediated CL remodelling in DKD and to explore the potential underlying mechanism.

METHODS

In vivo study, the mitochondrial structure was examined by transmission electron microscopy (TEM). The colocalization of ALCAT1 and synaptopodin was evaluated by double immunolabelling. Western blotting (WB) was performed to assess ALCAT1 expression in glomeruli. Lipidomics analysis was conducted to evaluate the composition of reconstructed cardiolipins. In vitro study, the lipidomics, TEM and WB analyses were similar to those in vivo. Mitochondrial function was evaluated by measuring the mitochondrial membrane potential (MMP) and the production of ATP and ROS.

RESULTS

Here, we showed that increased oxidized cardiolipin (ox-CL) and significant mitochondrial damage were accompanied by increased ALCAT1 expression in the glomeruli of patients with DKD. Similar results were found in db/db mouse kidneys and in cultured podocytes stimulated with high glucose (HG). ALCAT1 deficiency effectively prevented HG-induced ox-CL production and mitochondrial damage in podocytes. In contrast, ALCAT1 upregulation enhanced ox-CL levels and podocyte mitochondrial dysfunction. Moreover, treatment with the cardiolipin antioxidant SS-31 markedly inhibited mitochondrial dysfunction and cell injury, and SS-31 treatment partly reversed the damage mediated by ALCAT1 overexpression. We further found that ALCAT1 could mediate the key regulators of mitochondrial dynamics and mitophagy through the AMPK pathway.

CONCLUSIONS

Collectively, our studies demonstrated that ALCAT1-mediated cardiolipin remodelling played a crucial role in DKD, which might provide new insights for DKD treatment. Video Abstract.

Multi-omics analysis reveals the potential pathogenesis and therapeutic targets of diabetic kidney disease

Clinicians have long been interested in understanding the molecular basis of diabetic kidney disease (DKD)and its potential treatment targets. Its pathophysiology involves protein phosphorylation, one of the most recognizable post-transcriptional modifications, that can take part in many cellular functions and control different metabolic processes. In order to recognize the molecular and protein changes of DKD kidney, this study applied Tandem liquid chromatography-mass spectrometry (LC-MS/MS) and Next-Generation Sequencing, along with Tandem Mass Tags (TMT) labeling techniques to evaluate the mRNA, protein and modified phosphorylation sites between DKD mice and model ones. Based on Gene Ontology (GO) and KEGG pathway analyses of transcriptome and proteome, The molecular changes of DKD include accumulation of extracellular matrix, abnormally activated inflammatory microenvironment, oxidative stress and lipid metabolism disorders, leading to glomerulosclerosis and tubulointerstitial fibrosis. Oxidative stress has been emphasized as an important factor in DKD and progression to ESKD, which is directly related to podocyte injury, albuminuria and renal tubulointerstitial fibrosis. A histological study of phosphorylation further revealed that kinases were crucial. Three groups of studies have found that RAS signaling pathway, RAP1 signaling pathway, AMPK signaling pathway, PPAR signaling pathway and HIF-1 signaling pathway were crucial for the pathogenesis of DKD. Through this approach, it was discovered that targeting specific molecules, proteins, kinases and critical pathways could be a promising approach for treating DKD.

Baicalin ameliorates renal fibrosis by upregulating CPT1α-mediated fatty acid oxidation in diabetic kidney disease

BACKGROUND

Diabetic kidney disease (DKD) is a leading cause of end-stage renal disease (ESRD). The progression of DKD is often marked by heightened renal fibrosis due to hindered fatty acid oxidation within renal tubules. Baicalin (BA), a naturally derived compound, has exhibited the potential to mitigate the advancement of DKD. Delving deeper into the precise targets and mechanisms of BA's effect on DKD is crucial.

PURPOSE

This study sought to elucidate the specific mechanism through which BA moderates the progression of DKD.

METHODS

Renal tubular tissues from diabetic (db/db) and control (db/m) mice were subjected to mRNA sequencing to discern BA's influence on DKD. Immunohistochemical staining and Western blot were employed to assess the expression of CPT1α in DKD patients and db/db and db/m mice administered with either BA (50 mg/kg/day) or a vehicle for 12 weeks. In vitro, human proximal renal tubule cells (HK-2) were treated with 40 mM high glucose or 50 μM BA. The potential inhibitory mechanism of BA on renal fibrosis in DKD was evaluated using Oil Red O staining and oxygen consumption rate (OCR) measurements.

RESULTS

The results demonstrated that BA notably reduced lipid accumulation and renal fibrosis in db/db mice. Moreover, mRNA sequencing pinpointed a significant downregulation of CPT1α in DKD. In vitro assays revealed that both the overexpression of CPT1α and treatment with BA exerted similar influences on mitochondrial respiration, fatty acid oxidation, and renal fibrosis levels. Given the pronounced downregulation of CPT1α in DKD patients and its substantial correlation with clinical indicators, it was evident that CPT1α could serve as a therapeutic target for BA in addressing DKD.

CONCLUSION

Our findings demonstrated that BA potentially enhances FAO by augmenting the expression of CPT1α, subsequently diminishing renal fibrosis in DKD. As such, CPT1α emerges as a promising therapeutic target for DKD intervention.

Inhibition of PFKP in renal tubular epithelial cell restrains TGF-β induced glycolysis and renal fibrosis

Metabolic reprogramming to glycolysis is closely associated with the development of chronic kidney disease (CKD). Although it has been reported that phosphofructokinase 1 (PFK) is a rate-limiting enzyme in glycolysis, the role of the platelet isoform of PFK (PFKP) in kidney fibrosis initiation and progression is as yet poorly understood. Here, we investigated whether PFKP could mediate the progression of kidney interstitial fibrosis by regulating glycolysis in proximal tubular epithelial cells (PTECs). We induced PFKP overexpression or knockdown in renal tubules via an adeno-associated virus (AAV) vector in the kidneys of mice following unilateral ureteral occlusion. Our results show that the dilated tubules, the area of interstitial fibrosis, and renal glycolysis were promoted by proximal tubule-specific overexpression of PFKP, and repressed by knockdown of PFKP. Furthermore, knockdown of PFKP expression restrained, while PFKP overexpression promoted TGF-β1-induced glycolysis in the human PTECs line. Mechanistically, Chip-qPCR revealed that TGF-β1 recruited the small mothers against decapentaplegic (SMAD) family member 3-SP1 complex to the PFKP promoter to enhance its expression. Treatment of mice with isorhamnetin notably ameliorated PTEC-elevated glycolysis and kidney fibrosis. Hence, our results suggest that PFKP mediates the progression of kidney interstitial fibrosis by regulating glycolysis in PTECs.

Epigenetic modification in diabetic kidney disease

Diabetic kidney disease (DKD) is a common microangiopathy in diabetic patients and the main cause of death in diabetic patients. The main manifestations of DKD are proteinuria and decreased renal filtration capacity. The glomerular filtration rate and urinary albumin level are two of the most important hallmarks of the progression of DKD. The classical treatment of DKD is controlling blood glucose and blood pressure. However, the commonly used clinical therapeutic strategies and the existing biomarkers only partially slow the progression of DKD and roughly predict disease progression. Therefore, novel therapeutic methods, targets and biomarkers are urgently needed to meet clinical requirements. In recent years, increasing attention has been given to the role of epigenetic modification in the pathogenesis of DKD. Epigenetic variation mainly includes DNA methylation, histone modification and changes in the noncoding RNA expression profile, which are deeply involved in DKD-related inflammation, oxidative stress, hemodynamics, and the activation of abnormal signaling pathways. Since DKD is reversible at certain disease stages, it is valuable to identify abnormal epigenetic modifications as early diagnosis and treatment targets to prevent the progression of end-stage renal disease (ESRD). Because the current understanding of the epigenetic mechanism of DKD is not comprehensive, the purpose of this review is to summarize the role of epigenetic modification in the occurrence and development of DKD and evaluate the value of epigenetic therapies in DKD.

Irisin Ameliorates Renal Tubulointerstitial Fibrosis by Regulating the Smad4/β-Catenin Pathway in Diabetic Mice

Background

The primary pathophysiology of diabetic kidney disease (DKD) is tubulointerstitial fibrosis (TIF), and an essential contributing element is excessive extracellular matrix deposition. Irisin is a polypeptide formed by splitting fibronectin type III domain containing 5 (FNDC5), which participates in a number of physiological and pathological processes.

Methods

The purpose of this article is to examine irisin's function in DKD and analyze both its in vitro and in vivo effects. The Gene Expression Omnibus (GEO) database was used to download GSE30122, GSE104954, and GSE99325. Analysis of renal tubule samples from nondiabetic and diabetic mice identified 94 differentially expressed genes (DEGs). The transforming growth factor beta receptor 2 (TGFBR2), irisin, and TGF-β1 were utilized as DEGs to examine the impact of irisin on TIF in diabetic kidney tissue, according to the datasets retrieved from the GEO database and Nephroseq database. Additionally, the therapeutic impact of irisin was also examined using Western blot, RT-qPCR, immunofluorescence, immunohistochemistry, and kits for detecting mouse biochemical indices.

Results

In vitro, the findings demonstrated that irisin not only down-regulated the expression of Smad4 and β-catenin but also reduced the expression of proteins linked to fibrosis, the epithelial-mesenchymal transition (EMT), and mitochondrial dysfunction in HK-2 cells maintained in high glucose (HG) environment. In vivo, overexpressed FNDC5 plasmid was injected into diabetic mice to enhance its expression. Our studies found that overexpressed FNDC5 plasmid not only reversed the biochemical parameters and renal morphological characteristics of diabetic mice but also alleviated EMT and TIF by inhibiting Smad4/β-catenin signaling pathway.

Conclusion

The above experimental results revealed that irisin could reduce TIF in diabetic mice via regulating the Smad4/β-catenin pathway.