Insulin resistance in glomerular podocytes: Potential mechanisms of induction

Exploring the metabolic and antioxidant potential of solergy: Implications for enhanced animal production

Cell models are indispensable tools in biotechnology when investigating the functional properties of organic compounds. The emergence of various additives designed to enhance animal production has introduced the need for in-depth evaluations, which are often hindered by the complexities of in vivo testing. In this study, we harnessed cell-based models to scrutinize the impact of Solergy as a regulator of cellular metabolism with a particular focus on its modulation of glycogen and antioxidant effects. Our experiment was designed to include assessments of the influence of Solergy on the viability of both terrestrial and aquatic vertebrate cell models, which revealed the benign nature of Solergy and its lack of adverse effects. Furthermore, we examined the capacity of Solergy to modulate intracellular ATP concentrations and enhance glycogen accumulation. Notably, the antioxidant potential of Solergy and its ability to mitigate cellular aging were evaluated within the same cellular frameworks. The outcomes of our investigation suggest that Solergy is a potent metabolic regulator that elevates cellular activity while exerting an antioxidant effect. Importantly, our study demonstrates that Solergy does not induce changes in membrane oxidation. These findings indicate the potential of using Solergy to regulate glycogen synthesis, intracellular ATP concentrations, and oxidative stress in production animals. The multifaceted effects of this additive, which acts as both a metabolism enhancer and an antioxidant, open doors to the creation of custom diets tailored to meet specific production needs while maintaining stable production parameters.

Hyperglycemia - A culprit of podocyte pathology in the context of glycogen metabolism

Prolonged disruption in the balance of glucose can result in metabolic disorders. The kidneys play a significant role in regulating blood glucose levels. However, when exposed to chronic hyperglycemia, the kidneys' ability to handle glucose metabolism may be impaired, leading to an accumulation of glycogen. Earlier studies have shown that there can be a significant increase in glucose storage in the form of glycogen in the kidneys in diabetes. Podocytes play a crucial role in maintaining the integrity of filtration barrier. In diabetes, exposure to elevated glucose levels can lead to significant metabolic and structural changes in podocytes, contributing to kidney damage and the development of diabetic kidney disease. The accumulation of glycogen in podocytes is not a well-established phenomenon. However, a recent study has demonstrated the presence of glycogen granules in podocytes. This review delves into the intricate connections between hyperglycemia and glycogen metabolism within the context of the kidney, with special emphasis on podocytes. The aberrant storage of glycogen has the potential to detrimentally impact podocyte functionality and perturb their structural integrity. This review provides a comprehensive analysis of the alterations in cellular signaling pathways that may potentially lead to glycogen overproduction in podocytes.

ZFYVE28 mediates insulin resistance by promoting phosphorylated insulin receptor degradation via increasing late endosomes production

Insulin resistance is associated with many pathological conditions, and an in-depth understanding of the mechanisms involved is necessary to improve insulin sensitivity. Here, we show that ZFYVE28 expression is decreased in insulin-sensitive obese individuals but increased in insulin-resistant individuals. Insulin signaling inhibits ZFYVE28 expression by inhibiting NOTCH1 via the RAS/ERK pathway, whereas ZFYVE28 expression is elevated due to impaired insulin signaling in insulin resistance. While Zfyve28 overexpression impairs insulin sensitivity and causes lipid accumulation, Zfyve28 knockout in mice can significantly improve insulin sensitivity and other indicators associated with insulin resistance. Mechanistically, ZFYVE28 colocalizes with early endosomes via the FYVE domain, which inhibits the generation of recycling endosomes but promotes the conversion of early to late endosomes, ultimately promoting phosphorylated insulin receptor degradation. This effect disappears with deletion of the FYVE domain. Overall, in this study, we reveal that ZFYVE28 is involved in insulin resistance by promoting phosphorylated insulin receptor degradation, and ZFYVE28 may be a potential therapeutic target to improve insulin sensitivity.

Triglyceride glucose index and renal function decline in Han Chinese hypertensive patients

Elevated triglyceride glucose (TyG) index is associated with an increased risk of cardiovascular disease. The current study aimed to investigate whether the TyG index was correlated with renal function decline in patients with hypertension. Han Chinese participants with essential hypertension were included. The TyG index was calculated as ln[fasting triglycerides (mg/dL) * fasting glucose (mg/dL)/2]. Renal function decline was defined as >25% decline in estimated glomerular filtration rate (eGFR). The Cox proportional hazard regression model was used to examine the independent effect of the TyG index on renal events. In total, 548 Han Chinese hypertensive participants with a mean age of 62.1 ± 14.3 years were eligible for enrollment. During a mean follow-up period of 4.7 ± 3.1 years, 97 patients suffered from >25% decline in eGFR. When compared to those without eGFR decline, patients with eGFR decline had higher fasting triglyceride levels (P = .056), fasting glucose levels (P = .014), and TyG indexes (P = .014). The Cox proportional hazard regression model revealed that the TyG index (hazard ratio [HR] = 1.490; 95% confidence interval [CI] = 1.016-2.185, P = .041), office systolic blood pressure (HR = 1.013; 95% CI = 1.000-1.026, P = .047), diabetes mellitus (HR = 1.797, 95% CI = 1.026-3.147, P = .040), and baseline eGFR (HR = 1.015; 95% CI = 1.002-1.028, P = .025) were associated with renal events. In conclusions, an elevated TyG index is independently associated with an increased risk of eGFR decline in hypertensive patients.

Obesity-Related Kidney Disease: Current Understanding and Future Perspectives

Obesity is a serious chronic disease and an independent risk factor for the new onset and progression of chronic kidney disease (CKD). CKD prevalence is expected to increase, at least partly due to the continuous rise in the prevalence of obesity. The concept of obesity-related kidney disease (OKD) has been introduced to describe the still incompletely understood interplay between obesity, CKD, and other cardiometabolic conditions, including risk factors for OKD and cardiovascular disease, such as diabetes and hypertension. Current therapeutics target obesity and CKD individually. Non-pharmacological interventions play a major part, but the efficacy and clinical applicability of lifestyle changes and metabolic surgery remain debatable, because the strategies do not benefit everyone, and it remains questionable whether lifestyle changes can be sustained in the long term. Pharmacological interventions, such as sodium-glucose co-transporter 2 inhibitors and the non-steroidal mineralocorticoid receptor antagonist finerenone, provide kidney protection but have limited or no impact on body weight. Medicines based on glucagon-like peptide-1 (GLP-1) induce clinically relevant weight loss and may also offer kidney benefits. An urgent medical need remains for investigations to better understand the intertwined pathophysiologies in OKD, paving the way for the best possible therapeutic strategies in this increasingly prevalent disease complex.

Pit 1 transporter (SLC20A1) as a key factor in the NPP1-mediated inhibition of insulin signaling in human podocytes

Podocytes are crucially involved in blood filtration in the glomerulus. Their proper function relies on efficient insulin responsiveness. The insulin resistance of podocytes, defined as a reduction of cell sensitivity to this hormone, is the earliest pathomechanism of microalbuminuria that is observed in metabolic syndrome and diabetic nephropathy. In many tissues, this alteration is mediated by the phosphate homeostasis-controlling enzyme nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1). By binding to the insulin receptor (IR), NPP1 inhibits downstream cellular signaling. Our previous research found that hyperglycemic conditions affect another protein that is involved in phosphate balance, type III sodium-dependent phosphate transporter 1 (Pit 1). In the present study, we evaluated the insulin resistance of podocytes after 24 h of incubation under hyperinsulinemic conditions. Thereafter, insulin signaling was inhibited. The formation of NPP1/IR complexes was observed at that time. A novel finding in the present study was our observation of an interaction between NPP1 and Pit 1 after the 24 h stimulation of podocytes with insulin. After downregulation of the SLC20A1 gene, which encodes Pit 1, we established insulin resistance in podocytes that were cultured under native conditions, manifested as a lack of intracellular insulin signaling and the inhibition of glucose uptake via the glucose transporter type 4. These findings suggest that Pit 1 might be a major factor that participates in the NPP1-mediated inhibition of insulin signaling.

Changes in urinary exosomal protein CALM1 may serve as an early noninvasive biomarker for diagnosing diabetic kidney disease

BACKGROUND

The risk of the development and progression of diabetic kidney disease (DKD) was increased by abnormal calcium release. However, it is still unknown whether calcium signal pathway-related proteins are changed in urinary exosomes. This study aims to explore the changes in urinary exosomal proteins, which may provide novel biomarkers for diagnosing DKD.

METHODS

Urinary exosomes were isolated from 132 participants by size exclusion chromatography method and 72 participants were tested by LC-MS/MS (Discovery phase). Correlation and multivariate logistics analysis were applied to evaluate selected urinary proteins. Western blot and ELISA were used to validate the selected protein (Validation phase: n = 60). The diagnostic performance of the selected biomarker was evaluated by receiver operating characteristic curve analyses between the discovery and validation phases.

RESULTS

Sixteen calcium signal pathway-related proteins were identified, however, only Calmodulin-1(CALM1) was continuously increased. Different expression of CALM1 was found in patients with different level of estimated glomerular filtration rate (eGFR) in two cohorts. The level of CALM1 was correlated with eGFR and serum creatinine levels in two cohorts. Multivariate analysis revealed that serum albumin (ALB) levels and CALM1 were independent risk factors for DKD. A diagnostic model based on CALM1 and serum ALB levels that could significantly distinguish DKD was established and validated.

CONCLUSIONS

Significant changes in calcium signal pathway-related urinary exosomal proteins were observed. The CALM1 may serve as an early noninvasive biomarker for diagnosing DKD.

Inhibition of phosphodiesterase 5A by tadalafil improves SIRT1 expression and activity in insulin-resistant podocytes

A decrease in intracellular levels of 3',5'-cyclic guanosine monophosphate (cGMP) has been implicated in the progression of diabetic nephropathy. Hyperglycemia significantly inhibits cGMP-dependent pathway activity in the kidney, leading to glomerular damage and proteinuria. The enhancement of activity of this pathway that is associated with an elevation of cGMP levels may be achieved by inhibition of the cGMP specific phosphodiesterase 5A (PDE5A) using selective inhibitors, such as tadalafil. Hyperglycemia decreased the insulin responsiveness of podocytes and impaired podocyte function. These effects were associated with lower protein amounts and activity of the protein deacetylase sirtuin 1 (SIRT1) and a decrease in the phosphorylation of adenosine monophosphate-dependent protein kinase (AMPK). We found that PDE5A protein levels increased in hyperglycemia, and PDE5A downregulation improved the insulin responsiveness of podocytes with reestablished SIRT1 expression and activity. PDE5A inhibitors potentiate nitric oxide (NO)/cGMP signaling, and NO modulates the activity and expression of SIRT1. Therefore, we investigated the effects of tadalafil on SIRT1 and AMPK in the context of improving the insulin sensitivity in podocytes and podocyte function in hyperglycemia. Our study revealed that tadalafil restored SIRT1 expression and activity and activated AMPK by increasing its phosphorylation. Tadalafil also restored stimulating effect of insulin on glucose transport in podocytes with high glucose-induced insulin resistance. Additionally, tadalafil improved the function of podocytes that were exposed to high glucose concentrations. Our results display novel mechanisms involved in the pathogenesis of glomerulopathies in diabetes, which may contribute to the development of more effective treatment strategies for diabetic nephropathy.

Long noncoding RNA ENST00000436340 promotes podocyte injury in diabetic kidney disease by facilitating the association of PTBP1 with RAB3B

Dysfunction of podocytes has been regarded as an important early pathologic characteristic of diabetic kidney disease (DKD), but the regulatory role of long noncoding RNAs (lncRNAs) in this process remains largely unknown. Here, we performed RNA sequencing in kidney tissues isolated from DKD patients and nondiabetic renal cancer patients undergoing surgical resection and discovered that the novel lncRNA ENST00000436340 was upregulated in DKD patients and high glucose-induced podocytes, and we showed a significant correlation between ENST00000436340 and kidney injury. Gain- and loss-of-function experiments showed that silencing ENST00000436340 alleviated high glucose-induced podocyte injury and cytoskeleton rearrangement. Mechanistically, we showed that fat mass and obesity- associate gene (FTO)-mediated m6A induced the upregulation of ENST00000436340. ENST00000436340 interacted with polypyrimidine tract binding protein 1 (PTBP1) and augmented PTBP1 binding to RAB3B mRNA, promoted RAB3B mRNA degradation, and thereby caused cytoskeleton rearrangement and inhibition of GLUT4 translocation to the plasma membrane, leading to podocyte injury and DKD progression. Together, our results suggested that upregulation of ENST00000436340 could promote podocyte injury through PTBP1-dependent RAB3B regulation, thus suggesting a novel form of lncRNA-mediated epigenetic regulation of podocytes that contributes to the pathogenesis of DKD.

"Multiomics" Analyses Combined with Systems Pharmacology Reveal the Renoprotection of Mangiferin Monosodium Salt in Rats with Diabetic Nephropathy: Focus on Improvements in Renal Ferroptosis, Renal Inflammation, and Podocyte Insulin Resistance

We explored the protection of mangiferin monosodium salt (MGM) on kidney injury in rats with streptozotocin (STZ)-induced diabetic nephropathy (DN) by "multiomics" analysis combined with systems pharmacology, with a specific focus on ferroptosis, inflammation, and podocyte insulin resistance (IR) signaling events in kidneys. MGM treatment afforded renoprotective effects on rats with STZ-induced DN by alleviating systemic IR-induced renal inflammation and podocyte IR. These mechanisms were correlated mainly with the MGM treatment-induced inhibition of the mitogen-activated protein kinase/nuclear factor-kappa B axis and activation of the phosphorylated insulin receptor substrate 1(Tyr608)/phosphorylated phosphatidylinositol 3-kinase/phosphorylated protein kinase B axis in the kidneys of DN rats. MGM had an ameliorative function in renal ferroptosis in rats with STZ-induced DN by upregulating mevalonate-mediated antioxidant capacities (glutathione peroxidase 4 and ferroptosis suppressor protein 1/coenzyme Q10 axis) and weakening acyl-CoA synthetase long-chain family member 4-mediated proferroptotic generation of lipid drivers in kidneys. MGM may be a promising alternative strategy for the treatment of DN.

Ion channels and channelopathies in glomeruli

An essential step in renal function entails the formation of an ultrafiltrate that is delivered to the renal tubules for subsequent processing. This process, known as glomerular filtration, is controlled by intrinsic regulatory systems and by paracrine, neuronal, and endocrine signals that converge onto glomerular cells. In addition, the characteristics of glomerular fluid flow, such as the glomerular filtration rate and the glomerular filtration fraction, play an important role in determining blood flow to the rest of the kidney. Consequently, disease processes that initially affect glomeruli are the most likely to lead to end-stage kidney failure. The cells that comprise the glomerular filter, especially podocytes and mesangial cells, express many different types of ion channels that regulate intrinsic aspects of cell function and cellular responses to the local environment, such as changes in glomerular capillary pressure. Dysregulation of glomerular ion channels, such as changes in TRPC6, can lead to devastating glomerular diseases, and a number of channels, including TRPC6, TRPC5, and various ionotropic receptors, are promising targets for drug development. This review discusses glomerular structure and glomerular disease processes. It also describes the types of plasma membrane ion channels that have been identified in glomerular cells, the physiological and pathophysiological contexts in which they operate, and the pathways by which they are regulated and dysregulated. The contributions of these channels to glomerular disease processes, such as focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy, as well as the development of drugs that target these channels are also discussed.

Store-operated Ca2+ channel signaling: Novel mechanism for podocyte injury in kidney disease

Studies over the last decade have markedly broadened our understanding of store-operated Ca2+ channels (SOCs) and their roles in kidney diseases and podocyte dysfunction. Podocytes are terminally differentiated glomerular visceral epithelial cells which are tightly attached to the glomerular capillary basement membrane. Podocytes and their unique foot processes (pedicels) constitute the outer layer of the glomerular filtration membrane and the final barrier preventing filtration of albumin and other plasma proteins. Diabetic nephropathy and other renal diseases are associated with podocyte injury and proteinuria. Recent evidence demonstrates a pivotal role of store-operated Ca2+ entry (SOCE) in maintaining structural and functional integrity of podocytes. This article reviews the current knowledge of SOCE and its contributions to podocyte physiology. Recent studies of the contributions of SOC dysfunction to podocyte injury in both cell culture and animal models are discussed, including work in our laboratory. Several downstream signaling pathways mediating SOC function in podocytes also are examined. Understanding the pivotal roles of SOC in podocyte health and disease is essential, as SOCE-activated signaling pathways are potential treatment targets for podocyte injury-related kidney diseases.

Efficacy and Safety of Zhenwu Decoction in the Treatment of Diabetic Nephropathy: A Systematic Review and Meta-Analysis

OBJECTIVE

To perform a systematic evaluation of the clinical efficacy and safety of Zhenwu decoction (ZWD) for the treatment of diabetic nephropathy (DN).

METHODS

PubMed, the China National Knowledge Infrastructure (CNKI), the China Science and Technology Journal Database (VIP), the Chinese Biomedical Literature Database (CBM), and the WanFang databases were searched, and a systematic review and meta-analysis of randomized controlled trials (RCTs) were subsequently conducted to compare the efficacy and safety of ZWD combined with conventional Western medicine (CWM) to conventional therapy alone in the treatment of DN. The Cochrane Handbook for Systematic Reviews of Interventions and GRADE criteria were utilized to assess the quality of the included literature, and RevMan 5.3 software was used for statistical analysis.

RESULTS

13 randomized controlled trials were included, involving 1347 patients with diabetic nephropathy assigned into two subgroups according to the disease duration. The results revealed that compared with conventional therapy alone, ZWD combined with CWM treatment significantly improved the total effective rate (OR = 3.88, 95% CI = (2.87, 5.26), P < 0.00001). Furthermore, ZWD combination therapy also decreased fasting blood glucose (MD = -0.72, 95% CI = (-0.97, -0.48), P < 0.00001), BUN (MD = -1.92, 95% CI = (-3.19, -0.64), P = 0.003), 24-hour urine protein (MD = -0.48, 95% CI = (-0.57, -0.39), P < 0.00001), and serum creatinine levels (MD = -51.17, 95% CI = (-66.95, -35.39), P < 0.00001). However,there was no statistical significance in the effect of combination therapy on creatinine clearance (MD = -0.64, 95% CI = [-8.21,6.92], P = 0.87). However, there was no statistical significance in the effect of combination therapy oncreatinine clearance (MD =-0.64, 95% CI=[-8.21,6.92], P=0.87).

CONCLUSION

ZWD combined with CWM outperformed conventional Western medicine in DN treatment. However, further investigations via multicenter RCTs with rigorous designs and higher quality are still warranted.

TRPC6 mediates high glucose-induced mitochondrial fission through activation of CDK5 in cultured human podocytes

Mitochondrial abnormalities contribute to the development of diabetic nephropathy (DN). However, the precise mechanisms of mitochondrial dysfunction in DN remain unclear. Transient receptor potential canonical channel-6 (TRPC6), a non-selective cation channel permeable to Ca²⁺, has been shown to regulate mitochondrial dynamics. This study was therefore aimed to explore the regulatory role and mechanisms of TRPC6 in high glucose (HG)-induced mitochondrial dysfunction in podocytes. Here we found that TRPC6 expression and TRPC6-induced Ca²⁺ influx were increased in HG-treated podocytes. Furthermore, the TRPC6 inhibitor and TRPC6 siRNA ameliorated mitochondrial dysfunction and apoptosis in HG-treated podocytes. BAPTA-AM, an intracellular calcium chelating agent, attenuated mitochondrial fission under HG conditions as well. Then, we found the activity of calpain and cyclin-dependent kinase 5 (CDK5) was markedly enhanced in HG-treated podocytes, which can be blocked by pretreatment with the TRPC6 inhibitor. Calpain-1 inhibition by calpeptin or by calpain-1 siRNA transfection not only attenuated HG-induced mitochondrial fission but also reduced the activity of CDK5. Additionally, the CDK5 inhibitor and its siRNA decreased mitochondrial fragmentation in HG-treated podocytes. Collectively, we revealed the essential role of TRPC6 in regulating HG-induced mitochondrial fission and apoptosis through the calpain-1/CDK5 pathway in human podocytes, which may provide new insights into the pathogenesis of DN.

Sirtuins as novel pharmacological targets in podocyte injury and related glomerular diseases

Podocyte injury is a major cause of proteinuria in kidney diseases, and persistent loss of podocytes leads to rapid irreversible progression of kidney disease. Sirtuins, a class of nicotinamide adenine dinucleotide-dependent deacetylases, can promote DNA repair, modify transcription factors, and regulate the cell cycle. Additionally, sirtuins play a critical role in renoprotection, particularly against podocyte injury. They also have pleiotropic protective effects on podocyte injury-related glomerular diseases, such as improving the immune inflammatory status and oxidative stress levels, maintaining mitochondrial homeostasis, enhancing autophagy, and regulating lipid metabolism. Sirtuins deficiency causes podocyte injury in different glomerular diseases. Studies using podocyte sirtuin-specific knockout and transgenic models corroborate this conclusion. Of note, sirtuin activators have protective effects in different podocyte injury-related glomerular diseases, including diabetic kidney disease, focal segmental glomerulosclerosis, membranous nephropathy, IgA nephropathy, and lupus nephritis. These findings suggest that sirtuins are promising therapeutic targets for preventing podocyte injury. This review provides an overview of recent advances in the role of sirtuins in kidney diseases, especially their role in podocyte injury, and summarizes the possible rationale for sirtuins as targets for pharmacological intervention in podocyte injury-related glomerular diseases.

Insulin Resistance and Type 2 Diabetes Mellitus: An Ultimatum to Renal Physiology

Insulin resistance (IR) is stated as diminished insulin action regardless of hyperinsulinemia. The usual target organs for insulin activities are the liver, skeletal muscle, and adipose tissue. Hence, the vasculature and kidneys are nonconventional target organs as the impacts of insulin on these are comparatively separate from other conventional target organs. Vasodilation is achieved by raising endothelial nitric oxide (NO) generation by initiating the phosphoinositide 3-kinase (PI3K) pathway. In insulin-nonresponsive conditions, this process is defective, and there is increased production of endothelin-1 through the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway, which predominates the NO effects, causing vasoconstriction. Renal tubular cells and podocytes have insulin receptors, and their purposeful importance has been studied, which discloses critical acts of insulin signaling in podocyte survivability and tubular action. Diabetic nephropathy (DN) is a prevalent problem in individuals with hypertension, poor glycemic management, hereditary susceptibility, or glomerular hyperfiltration. DN could be a significant contributing factor to end-stage renal disease (ESRD) that results from chronic kidney disease (CKD). IR and diabetes mellitus (DM) are the constituents of syndrome X and are accompanied by CKD progression. IR performs a key part in syndrome X leading to CKD. However, it is indistinct whether IR individually participates in enhancing the threat to CKD advancement rather than CKD complexity. CKD is an extensive public health problem affecting millions of individuals worldwide. The tremendous spread of kidney disease intensifies people’s health impacts related to communicable and noncommunicable diseases. Chronic disease regulator policies do not include CKD at global, local, and/or general levels. Improved knowledge of the character of CKD-associated problems might aid in reforming diagnosis, prevention, and management.