Hypoxia-Inducible Factors and Diabetic Kidney Disease—How Deep Can We Go?

Unveiling the pathogenesis and therapeutic approaches for diabetic nephropathy: insights from panvascular diseases

Diabetic nephropathy (DN) represents a significant microvascular complication in diabetes, entailing intricate molecular pathways and mechanisms associated with cardiorenal vascular diseases. Prolonged hyperglycemia induces renal endothelial dysfunction and damage via metabolic abnormalities, inflammation, and oxidative stress, thereby compromising hemodynamics. Concurrently, fibrotic and sclerotic alterations exacerbate glomerular and tubular injuries. At a macro level, reciprocal communication between the renal microvasculature and systemic circulation establishes a pernicious cycle propelling disease progression. The current management approach emphasizes rigorous control of glycemic levels and blood pressure, with renin-angiotensin system blockade conferring renoprotection. Novel antidiabetic agents exhibit renoprotective effects, potentially mediated through endothelial modulation. Nonetheless, emerging therapies present novel avenues for enhancing patient outcomes and alleviating the disease burden. A precision-based approach, coupled with a comprehensive strategy addressing global vascular risk, will be pivotal in mitigating the cardiorenal burden associated with diabetes.

Special Issue IJMS-Molecular Mechanisms of Diabetic Kidney Disease

Diabetic kidney disease (DKD), as a major microvascular complication of both type 1 and type 2 diabetes mellitus (DM), accounts for over 40% of patients that reach end-stage renal disease and are referred to renal replacement therapies [...].

Identifying key genes related to the peritubular capillary rarefaction in renal interstitial fibrosis by bioinformatics

Renal interstitial fibrosis (RIF) is a key feature of progressive chronic kidney disease (CKD), characterized by tubular epithelial cell (TEC) hypoxia and peritubular capillary (PTC) rarefaction. However, the mechanisms underlying these processes remain poorly understood. To address this knowledge gap, we conducted a comparative transcriptome analysis of hypoxic and normoxic HK-2 cells, identifying 572 differentially expressed genes (DEGs). Subsequent Gene Ontology (GO), protein‒protein interaction (PPI) network, and hub gene analyses revealed significant enrichment of DEGs in the HIF-1 signaling pathway based on KEGG enrichment analysis. To further explore TEC modulation under hypoxic conditions, we performed chromatin immunoprecipitation (ChIP) sequencing targeting HIF-1α, identifying 2915 genes potentially regulated by HIF-1α. By comparing RNA sequencing and ChIP sequencing data, we identified 43 overlapping DEGs. By performing GO analysis and peak annotation with IGV, we identified two candidate molecules, VEGFA and BTG1, that are associated with angiogenesis and whose gene sequences were reliably bound by HIF-1α. Our study elucidates the molecular mechanisms underlying RIF, providing valuable insights for potential therapeutic interventions.

DPP-4i versus SGLT2i as modulators of PHD3/HIF-2α pathway in the diabetic kidney

RATIONALE

Renal hypoxia is one of the currently highlighted pathophysiologic mechanisms of diabetic nephropathy (DN). Both hypoxia-inducible factor-1α (HIF-1α) and HIF-2α are major regulators of renal adaptive responses to hypoxia.

OBJECTIVES

This study aims to compare the effects of vildagliptin (a dipeptidyl peptidase-IV inhibitor, DPP-4i) and empagliflozin (a sodium-glucose cotransporter 2 inhibitor, SGLT2i) on the differential expression of renal HIF-1α/2α. Tissue expression of prolylhydroxylase 3 (PHD3), a key regulator of HIF-2α stability, was also highlighted in a diabetic nephropathy rat model. Type 1 diabetes mellitus was induced and diabetic rats were treated with either Vildagliptin or Empagliflozin (10 mg/kg/d each) for 12 weeks. Improvements in the kidney functional and histopathological parameters were addressed and correlated to changes in the renal expression of HIF-1α/2α, and PHD3. Urinary KIM-1 concentration was tested as a correlate to HIF pathway changes.

FINDINGS

Both vildagliptin- and empagliflozin-treated groups exhibited significant improvement in the functional, pathological, and ultra-structural renal changes induced by chronic diabetes. Compared to the untreated group, renal gene expression of HIF-1α was decreased while that of HIF-2α was increased in both treated groups, with significantly greater effects observed with SGLT2i. Renal PHD3 immune-reactivity was also decreased by both drugs, again with better efficacy for the SGLT2i. Importantly, improvements in the diabetic kidney biochemical and structural biomarkers were significantly correlated to PHD3 reductions and HIF-2α increments.

CONCLUSIONS

Both DPP-4i and SGLT2i could delay the progression of DN through their differential modulating effects on the PHD3/ HIF-2α pathway with significantly better efficacy for SGLT2i.

Clinical Perspectives of Gut Microbiota in Patients with Chronic Kidney Disease and End-Stage Kidney Disease: Where Do We Stand?

The gut microbiota (GM) plays a vital role in human health, with increasing evidence linking its imbalance to chronic kidney disease and end-stage kidney disease. Although the exact methods underlying kidney-GM crosstalk are not fully understood, interventions targeting GM were made and lay in three aspects: diagnostic, predictive, and therapeutic interventions. While these interventions show promising results in reducing uremic toxins and inflammation, challenges remain in the form of patient-specific GM variability, potential side effects, and safety concerns. Our understanding of GMs role in kidney disease is still evolving, necessitating further research to elucidate the causal relationship and mechanistic interactions. Personalized interventions focusing on specific GM signatures could enhance patient outcomes. However, comprehensive clinical trials are needed to validate these approaches' safety, efficacy, and feasibility.

The Role of Hypoxia on the Trimethylation of H3K27 in Podocytes

Epigenetic alterations contribute to the pathogenesis of chronic diseases such as diabetes mellitus. Previous studies of our group showed that diabetic conditions reduce the trimethylation of H3K27 in podocytes in a NIPP1- (nuclear inhibitor of protein phosphatase 1) and EZH2- (enhancer of zeste homolog 2) dependent manner. It has been previously reported that in differentiated podocytes, hypoxia decreases the expression of slit diaphragm proteins and promotes foot process effacement, thereby contributing to the progression of renal disease. The exact mechanisms are, however, not completely understood. The aim of this study was to analyze the role of hypoxia and HIFs (hypoxia-inducible factor) on epigenetic changes in podocytes affecting NIPP1, EZH2 and H3K27me3, in vitro and in vivo. In vivo studies were performed with mice exposed to 10% systemic hypoxia for 3 days or injected with 3,4-DHB (dihydroxybenzoate), a PHD (prolyl hydroxylase) inhibitor, 24 h prior analyses. Immunodetection of H3K27me3, NIPP1 and EZH2 in glomerular podocytes revealed, to the best of our knowledge for the first time, that hypoxic conditions and pharmacological HIFs activation significantly reduce the expression of NIPP1 and EZH2 and diminish H3K27 trimethylation. These findings are also supported by in vitro studies using murine-differentiated podocytes.

Why Is Iron Deficiency/Anemia Linked to Alzheimer's Disease and Its Comorbidities, and How Is It Prevented?

Impaired iron metabolism has been increasingly observed in many diseases, but a deeper, mechanistic understanding of the cellular impact of altered iron metabolism is still lacking. In addition, deficits in neuronal energy metabolism due to reduced glucose import were described for Alzheimer's disease (AD) and its comorbidities like obesity, depression, cardiovascular disease, and type 2 diabetes mellitus. The aim of this review is to present the molecular link between both observations. Insufficient cellular glucose uptake triggers increased ferritin expression, leading to depletion of the cellular free iron pool and stabilization of the hypoxia-induced factor (HIF) 1α. This transcription factor induces the expression of the glucose transporters (Glut) 1 and 3 and shifts the cellular metabolism towards glycolysis. If this first line of defense is not adequate for sufficient glucose supply, further reduction of the intracellular iron pool affects the enzymes of the mitochondrial electron transport chain and activates the AMP-activated kinase (AMPK). This enzyme triggers the translocation of Glut4 to the plasma membrane as well as the autophagic recycling of cell components in order to mobilize energy resources. Moreover, AMPK activates the autophagic process of ferritinophagy, which provides free iron urgently needed as a cofactor for the synthesis of heme- and iron-sulfur proteins. Excessive activation of this pathway ends in ferroptosis, a special iron-dependent form of cell death, while hampered AMPK activation steadily reduces the iron pools, leading to hypoferremia with iron sequestration in the spleen and liver. Long-lasting iron depletion affects erythropoiesis and results in anemia of chronic disease, a common condition in patients with AD and its comorbidities. Instead of iron supplementation, drugs, diet, or phytochemicals that improve energy supply and cellular glucose uptake should be administered to counteract hypoferremia and anemia of chronic disease.

Ferroptosis in diabetic nephropathy: Mechanisms and therapeutic implications

Diabetic Nephropathy (DN), the most common complication in diabetes mellitus, has been affecting the lives of people diabetic for a long time. Numerous studies have demonstrated the unbreakable connection between ferroptosis and kidney cell damage. Ferroptosis is a type of iron-dependent, non-apoptotic, regulated cell death, characterized by the buildup of intracellular lipid peroxides to lethal levels. Although the role of programmed cell deaths like apoptosis, autophagy, and necroptosis in the pathogenesis of DN has been demonstrated, the implication of ferroptosis in DN was least interrogated. Hence, the main aim of this review was to discuss the current understanding of ferroptosis focusing on its potential mechanisms, its involvement in DN, and emerging therapeutic opportunities.

The Role of Oxidative Stress-Mediated Inflammation in the Development of T2DM-Induced Diabetic Nephropathy: Possible Preventive Action of Tannins and Other Oligomeric Polyphenols

Diabetic nephropathy is manifested in more than 10% of people with diabetes. It is a common cause of kidney failure and end-stage kidney disease. Understanding of mechanisms underlying the initiation and development of diabetes-induced kidney injuries will allow for the development of more effective methods of prevention and treatment of the disease. Diabetic nephropathy is a wide-ranging complication of diabetes, and it is necessary to discuss the "weight" of pro-inflammatory pathways and molecules in the progress of renal injuries during the development of the disease. A large spectrum of pro-inflammatory molecules and pathways participate in different stages of the pathophysiological progression of diabetic nephropathy, including pro-inflammatory cytokines, chemokines, their receptors, adhesion molecules, and transcription factors. On the other hand, it is known that one of the consequences of hyperglycemia-induced ROS generation is the up-regulation of pro-inflammatory cascades, which, in turn, activate the transcription of genes encoding cytokines-chemokines, growth factors, and extracellular matrix proteins. It is a proven fact that a variety of plant secondary metabolites, such as tannins, flavonoids, and other polyphenols, demonstrate significant anti-diabetic, redox-modulating properties and effectively modulate the inflammatory response. Thus, this review is discussing the possible role of plant phenols in the prevention and treatment of diabetic nephropathy.