Metformin reduces proteinuria in spontaneously hypertensive rats by activating the HIF-2α-VEGF-A pathway

Unraveling the Complex Molecular Interplay and Vascular Adaptive Changes in Hypertension-Induced Kidney Disease

Angiogenesis, the natural mechanism by which fresh blood vessels develop from preexisting ones, is altered in arterial hypertension (AH), impacting renal function. Studies have shown that hypertension-induced renal damage involves changes in capillary density (CD), indicating alterations in vascularization. We aimed to elucidate the role of the apelin receptor (APLNR), neuronal nitric oxide synthase (nNOS), and vascular endothelial growth factor (VEGF) in hypertension-induced renal damage. We used two groups of spontaneously hypertensive rats aged 6 and 12 months, representing different stages of AH, and compared them to age-matched normotensive controls. The kidney tissue samples were prepared through a well-established protocol. All data analysis was conducted with a dedicated software program. APLNR was localized in tubular epithelial cells and the endothelial cells of the glomeruli, with higher expression in older SHRs. The localization of nNOS and VEGF was similar. The expression of APLNR and nNOS increased with AH progression, while VEGF levels decreased. CD was lower in young SHRs compared to controls and decreased significantly in older SHRs in comparison to age-matched controls. Our statistical analysis revealed significant differences in molecule expression between age groups and varying correlations between the expression of the three molecules and CD.

Autophagy and podocytopathy

Autophagy is a complex process of lysosomal-dependent degradation of unwanted cellular material. In response to endogenous or exogenous stimuli, autophagy is induced and regulated by two kinases: the AMP activated kinase and the mammalian target of rapamycin (mTOR). Cells activated by Unc-51-like kinase 1 form a double membrane complex that sequesters the cargo (phagophore) and elongates producing spherical vesicles (autophagosomes). These reach and fuse with lysosomes, which degrade the cargo (autolysosomes). The resulting macromolecules are released back and recycled in the cytosol for reuse. In the podocyte, autophagy is a homeostatic mechanism that contributes to the formation and preservation of the morphological and functional integrity of actin cytoskeleton. Podocytes, fenestrated endothelial cells and glomerular basement membrane compose the glomerular filtration barrier. Podocyte damage may cause dysfunction of the glomerular barrier, proteinuria and glomerulosclerosis in different glomerular diseases and particularly in so-called podocytopathies, namely minimal change disease and focal segmental glomerulosclerosis. Several drugs and molecules may activate autophagic function in murine models. Among them, aldosterone inhibitors, mineralocorticoid inhibitors and vitamin D3 were proven to protect podocyte from injury and reduce proteinuria in clinical studies. However, no clinical trial with autophagy regulators in podocytopathies has been conducted. Caution is needed with other autophagy activators, such as mTOR inhibitors and metformin, because of potential adverse events.

Silencing of ALOX15 reduces ferroptosis and inflammation induced by cerebral ischemia-reperfusion by regulating PHD2/HIF2α signaling pathway

OBJECTIVE

To investigate the potential mechanism of arachidonic acid deoxyribozyme 15 (ALOX15) in ferroptosis and inflammation induced by cerebral ischemia reperfusion injury.

METHODS

The mice and cell models of cerebral ischemia-reperfusion injury were constructed. Western Blot was used to detect the protein expression levels of ALOX15, glutathione peroxidase (GPX4), hypoxia-inducible factor-2α (HIF-2α), prolyl hydroxylase (PHD) and inflammatory factors (NLRP3, IL-1β, IL-18) in brain tissues and cells. Cell proliferation activity was detected by CCK-8 method. LDH assay was used to detect the release of lactate dehydrogenase. TTC staining was used to observe cerebral infarction.

RESULTS

In cerebral ischemia-reperfusion mice and cell models, the expression of ALOX15 protein was increased, the expression of GPX4, a key marker of ferroptosis was decreased, and silencing of ALOX15 down-regulated the GPX4 expression. HIF-2α expression was down-regulated in animal and cell models of cerebral ischemia reperfusion, and silencing of ALOX15 increased the HIF-2α expression by inhibiting PHD2 expression. Inhibition of ALOX15 expression reduced inflammatory factors levels (NLRP3, IL-1β, and IL-18) in cerebral ischemia. Inhibitor of PHD2 (IXOC-4) alleviating brain injury and cell death induced by cerebral ischemia reperfusion and stabilize HIF-2α expression in vivo.

CONCLUSION

The expression of ALOX15 was up-regulated in cerebral ischemia-reperfusion animals and cells model. Inhibition of ALOX15 up-regulated the GPX4 expression, and promoted HIF-2α expression by inhibiting PHD2, thus alleviating ferroptosis and inflammation caused by cerebral ischemia-reperfusion injury.

Metformin ameliorates calcium oxalate crystallization and stone formation by activating the Nrf2/HO-1 signaling pathway: Two birds with one stone

Deposition of calcium oxalate (CaOx) crystals and oxidative stress-induced injury of renal tubular epithelial cell are the primary pathogenic factors of nephrolithiasis. In this study we investigated the beneficial effects of metformin hydrochloride (MH) against nephrolithiasis and explored the underlying molecular mechanism. Our results demonstrated that MH inhibited the formation of CaOx crystals and promoted the transformation of thermodynamically stable CaOx monohydrate (COM) to more unstable CaOx dihydrate (COD). MH treatment effectively ameliorated oxalate-induced oxidative injury and mitochondrial damage in renal tubular cells and reduced CaOx crystal deposition in rat kidneys. MH also attenuated oxidative stress by lowering MDA level and enhancing SOD activity in HK-2 and NRK-52E cells and in a rat model of nephrolithiasis. In both HK-2 and NRK-52E cells, COM exposure significantlylowered the expressions of HO-1 and Nrf2, which was rescued by MH treatment even in the presence of Nrf2 and HO-1 inhibitors. In rats with nephrolithiasis, MH treatment significantly rescued the down-regulation of the mRNA and protein expression of Nrf2 and HO-1 in the kidneys. These results demonstrate that MH can alleviate CaOx crystal deposition and kidney tissue injury in rats with nephrolithiasis by suppressing oxidative stress and activating the Nrf2/HO-1 signaling pathway, suggesting the potential value of MH in the treatment of nephrolithiasis.

The expression of apoptosis related genes in HK-2 cells overexpressing PPM1K was determined by RNA-seq analysis

Chronic kidney disease (CKD) is a serious disease that endangers human health. It is reported that inhibiting renal cell apoptosis can delay the progress of CKD. Our previous study found that the mice with protein phosphatase Mg2+/Mn2+ dependent 1K (PPM1K) gene deletion had obvious symptoms of glomerular vascular and interstitial vascular dilatation, congestion and hemorrhage, glomerular hemorrhage and necrosis, interstitial fibrous tissue proliferation, decreased urinary creatinine clearance, and increased urinary protein level. In addition, studies have found that PPM1K is essential for cell survival, apoptosis and metabolism. However, no study has confirmed that PPM1K can inhibit renal cell apoptosis. In this study, PPM1K was overexpressed in human kidney-2 cells (HK-2), and the biological process of differentially expressed genes and its effect on apoptosis were comprehensively screened by RNA sequencing (RNA-seq). Through sequencing analysis, we found that there were 796 differentially expressed genes in human renal tubular epithelial cells transfected with PPM1K gene, of which 553 were down-regulated and 243 were up-regulated. Enrichment analysis found that differentially expressed genes may play an important role in amino acid metabolism and biosynthesis. In the GO analysis functional pathway list, we also found that multiple genes can be enriched in apoptosis related pathways, such as G0S2, GADD45A, TRIB3, VEGFA, NUPR1 and other up-regulated genes, and IL-6, MAGED1, CCL2, TP53INP1 and other down-regulated genes. Then we verified these differentially expressed genes by RT-PCR, and found that only the RT-PCR results of G0S2, VEGFA and NUPR1 were consistent with the transcriptome sequencing results. We believe that G0S2, VEGFA, NUPR1 and other genes may participate in the apoptosis process of HK-2 cells induced by PPM1K.In conclusion, these findings provide some data support for the study of HK-2 cell apoptosis mechanism, and also provide a scientific theoretical basis for further study of the effect of PPM1K on kidney disease.

Integrated Bioinformatics and Clinical Correlation Analysis of Key Genes, Pathways, and Potential Therapeutic Agents Related to Diabetic Nephropathy

Background

Diabetic nephropathy (DN) is a common microvascular complication of diabetes and a major cause of end-stage renal disease, resulting in a substantial socioeconomic burden around the world. Some unknown biomarkers, mechanisms, and potential novel agents regarding DN are yet to be identified.

Methods

GSE30528 and GSE1009 were downloaded as training datasets to identify differentially expressed genes (DEGs) of DN. Common DEGs were selected for further analysis. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses of DEGs were performed to explore molecular mechanisms and pathways. Protein-protein interaction (PPI) network of DEGs was used to identify the top 10 hub genes of DN. Expression profiles of the hub genes were validated in GSE96804 and GSE47183 datasets. The clinical correlation analyses were conducted to confirm the association between key genes and clinical characteristics in the Nephroseq v5 database. The Drug Gene Interaction Database was used to predict potential targeted drugs.

Results

345 and 1228 DEGs were identified in GSE30528 and GSE1009, respectively; and 120 common DEGs were found. The biological process of DEGs was significantly enriched in kidney development. PI3K-Akt signaling pathway, focal adhesion, complement and coagulation cascades were significantly enriched KEGG pathways. The identified top10 hub genes were VEGFA, NPHS1, WT1, TJP1, CTGF, FYN, SYNPO, PODXL, TNNT2, and BMP2. VEGFA, NPHS1, WT1, CTGF, SYNPO, PODXL, and TNNT2 were significantly downregulated in DN. VEGFA, NPHS1, WT1, CTGF, SYNPO, and PODXL were positively correlated with glomerular filtration rate. The targeted drugs or molecular compounds were enalapril, sildenafil, and fenofibrate target for VEGFA; losartan target for NPHS1; halofuginone, deferoxamine, curcumin, and sirolimus target for WT1; and purpurogallin target for TNNT2.

Conclusions

VEGFA, NPHS1, WT1, CTGF, SYNPO, and PODXL are promising biomarkers for diagnosing and evaluating the progression of DN. The drug-gene interaction analyses provide a list of candidate drugs for the precise treatment of DN.

New Approaches to Diabetic Nephropathy from Bed to Bench

Diabetic nephropathy (DN) is the main cause of end-stage kidney disease (ESKD). DN-related ESKD has the worst prognosis for survival compared with other causes. Due to the complex mechanisms of DN and the heterogeneous presentations, unmet needs exist for the renal outcome of diabetes mellitus. Clinical evidence for treating DN is rather solid. For example, the first Kidney Disease: Improving Global Outcomes (KDIGO) guideline was published in October 2020: KDIGO Clinical Practice Guideline for Diabetes Management in Chronic Kidney Disease. In December of 2020, the International Society of Nephrology published 60 (+1) breakthrough discoveries in nephrology. Among these breakthroughs, four important ones after 1980 were recognized, including glomerular hyperfiltration theory, renal protection by renin-angiotensin system inhibition, hypoxia-inducible factor, and sodium-glucose cotransporter 2 inhibitors. Here, we present a review on the pivotal and new mechanisms of DN from the implications of clinical studies and medications.

Use of Anti-Diabetic Agents in Non-Diabetic Kidney Disease: From Bench to Bedside

New drugs were recently developed to treat hyperglycemia in patients with type 2 diabetes mellitus (T2D). However, metformin remains the first-line anti-diabetic agent because of its cost-effectiveness. It has pleiotropic action that produces cardiovascular benefits, and it can be useful in diabetic nephropathy, although metformin-associated lactic acidosis is a hindrance to its use in patients with kidney failure. New anti-diabetic agents, including glucagon-like peptide-1 receptor (GLP-1R) agonists, dipeptidyl peptidase-4 (DPP-4) inhibitors, and sodium-glucose transporter-2 (SGLT-2) inhibitors, also produce cardiovascular or renal benefits in T2D patients. Their glucose-independent beneficial actions can lead to cardiorenal protection via hemodynamic stabilization and inflammatory modulation. Systemic hypertension is relieved by natriuresis and improved vascular dysfunction. Enhanced tubuloglomerular feedback can be restored by SGLT-2 inhibition, reducing glomerular hypertension. Patients with non-diabetic kidney disease might also benefit from those drugs because hypertension, proteinuria, oxidative stress, and inflammation are common factors in the progression of kidney disease, irrespective of the presence of diabetes. In various animal models of non-diabetic kidney disease, metformin, GLP-1R agonists, DPP-4 inhibitors, and SGLT-2 inhibitors were favorable to kidney morphology and function. They strikingly attenuated biomarkers of oxidative stress and inflammatory responses in diseased kidneys. However, whether those animal results translate to patients with non-diabetic kidney disease has yet to be evaluated. Considering the paucity of new agents to treat kidney disease and the minimal adverse effects of metformin, GLP-1R agonists, DPP-4 inhibitors, and SGLT-2 inhibitors, these anti-diabetic agents could be used in patients with non-diabetic kidney disease. This paper provides a rationale for clinical trials that apply metformin, GLP-1R agonists, DPP-4 inhibitors, and SGLT-2 inhibitors to non-diabetic kidney disease.

Metformin Protects against Podocyte Injury in Diabetic Kidney Disease

Metformin is the most commonly prescribed drug for treating type 2 diabetes mellitus (T2D). Its mechanisms of action have been under extensive investigation, revealing that it has multiple cellular targets, either direct or indirect ones, via which it regulates numerous cellular pathways. Diabetic kidney disease (DKD), the serious complication of T2D, develops in up to 50% of the individuals with T2D. Various mechanisms contribute to the development of DKD, including hyperglycaemia, dyslipidemia, oxidative stress, chronic low-grade inflammation, altered autophagic activity and insulin resistance, among others. Metformin has been shown to affect these pathways, and thus, it could slow down or prevent the progression of DKD. Despite several animal studies demonstrating the renoprotective effects of metformin, there is no concrete evidence in clinical settings. This review summarizes the renoprotective effects of metformin in experimental settings. Special emphasis is on the effects of metformin on podocytes, the glomerular epithelial cells that are central in maintaining the glomerular ultrafiltration function.