Insulin signaling to the glomerular podocyte is critical for normal kidney function

The bidirectional association between diabetes and periodontitis, from basic to clinical

The prevalence and severity of periodontitis are increased and advanced in diabetes. Severe periodontitis elicits adverse effects on diabetes by impairing insulin actions due to systemic microinflammation. Recent studies unveil the emerging findings and molecular basis of the bidirectional relationship between periodontitis and diabetes. In addition to conventional mechanisms such as hyperglycemia, hyperlipidemia, and chronic inflammation, deficient insulin action may play a pathogenic role in the progression of periodontitis under diabetes. Epidemiologically, from the viewpoint of the adverse effect of periodontitis on diabetes, recent studies have suggested that Asians including Japanese and Asian Americans with diabetes and mild obesity (BMI <25 kg/m2) should pay more attention to their increased risk for cardiovascular diseases. In this review, we summarize recent findings on the effect of diabetes on periodontitis from the viewpoint of abnormalities in metabolism and insulin resistance with novel mechanisms, and the influence of periodontitis on diabetes mainly focused on micro-inflammation related to mature adipose tissue and discuss future perspectives about novel approaches to interrupt the adverse interrelationship.

Cardiometabolic comorbidities and complications of obesity and chronic kidney disease (CKD)

Obesity and chronic kidney disease are two ongoing progressive clinical pandemics of major public health and clinical care significance. Because of their growing prevalence, chronic indolent course and consequent complications both these conditions place significant burden on the health care delivery system especially in developed countries like the United States. Beyond the chance coexistence of both of these conditions in the same patient based on high prevalence it is now apparent that obesity is associated with and likely has a direct causal role in the onset, progression and severity of chronic kidney disease. The causes and underlying pathophysiology of this are myriad, complicated and multi-faceted. In this review, continuing the theme of this special edition of the journal on " The Cross roads between Endocrinology and Nephrology" we review the epidemiology of obesity related chronic kidney disease (ORCKD), and its various underlying causes and pathophysiology. In addition, we delve into the consequent comorbidities and complications associated with ORCKD with particular emphasis on the cardio metabolic consequences and then review the current body of evidence for available strategies for chronic kidney disease modulation in ORCKD as well as the potential unique role of weight reduction and management strategies in its improvement and risk reduction.

The redox-sensitive GSK3β is a key regulator of glomerular podocyte injury in type 2 diabetic kidney disease

Emerging evidence suggests that GSK3β, a redox-sensitive transducer downstream of insulin signaling, acts as a convergent point for myriad pathways implicated in kidney injury, repair, and regeneration. However, its role in diabetic kidney disease remains controversial. In cultured glomerular podocytes, exposure to a milieu of type 2 diabetes elicited prominent signs of podocyte injury and degeneration, marked by loss of homeostatic marker proteins like synaptopodin, actin cytoskeleton disruption, oxidative stress, apoptosis, and stress-induced premature senescence, as shown by increased staining for senescence-associated β-galactosidase activity, amplified formation of γH2AX foci, and elevated expression of mediators of senescence signaling, like p21 and p16INK4A. These degenerative changes coincided with GSK3β hyperactivity, as evidenced by GSK3β overexpression and reduced inhibitory phosphorylation of GSK3β, and were averted by tideglusib, a highly-selective small molecule inhibitor of GSK3β. In agreement, post-hoc analysis of a publicly-available glomerular transcriptomics dataset from patients with type 2 diabetic nephropathy revealed that the curated diabetic nephropathy-related gene set was enriched in high GSK3β expression group. Mechanistically, GSK3β-modulated nuclear factor Nrf2 signaling is involved in diabetic podocytopathy, because GSK3β knockdown reinforced Nrf2 antioxidant response and suppressed oxidative stress, resulting in an improvement in podocyte injury and senescence. Conversely, ectopic expression of the constitutively active mutant of GSK3β impaired Nrf2 antioxidant response and augmented oxidative stress, culminating in an exacerbated diabetic podocyte injury and senescence. Moreover, IRS-1 was found to be a cognate substrate of GSK3β for phosphorylation at IRS-1S332, which negatively regulates IRS-1 activity. GSK3β hyperactivity promoted IRS-1 phosphorylation, denoting a desensitized insulin signaling. Consistently, in vivo in db/db mice with diabetic nephropathy, GSK3β was hyperactive in glomerular podocytes, associated with IRS-1 hyperphosphorylation, impaired Nrf2 response and premature senescence. Our finding suggests that GSK3β is likely a novel therapeutic target for treating type 2 diabetic glomerular injury.

Association of triglyceride glucose index with the risk of acute kidney injury in patients with coronary revascularization: a cohort study

BACKGROUND

The triglyceride glucose (TyG) index is a novel and reliable alternative marker for insulin resistance. Previous studies have shown that TyG index is closely associated with cardiovascular outcomes in cardiovascular diseases and coronary revascularization. However, the relationship between TyG index and renal outcomes of coronary revascularization is unclear. The purpose of this study was to investigate the correlation between TyG index and the risk of acute kidney injury (AKI) in patients with coronary revascularization.

METHODS

A retrospective cohort study was conducted to select eligible patients with coronary revascularization admitted to ICU in the medical information mart for intensive care IV (MIMIC-IV). According to the TyG index quartile, these patients were divided into four groups (Q1-Q4). The primary endpoint was the incidence of AKI, and secondary endpoints included 28-day mortality and the rate of renal replacement therapy (RRT) use in the AKI population. Multivariate Cox regression analysis and restricted cubic splines (RCS) were used to analyze TyG index association with AKI risk. Kaplan-Meier survival analysis was performed to assess the incidence of endpoints in the four groups.

RESULTS

In this study, 790 patients who underwent coronary revascularization surgery were included, and the incidence of AKI was 30.13%. Kaplan-Meier analysis showed that patients with a high TyG index had a significantly increased incidence of AKI (Log-rank P = 0.0045). Multivariate Cox regression analysis showed that whether TyG index was a continuous variable (HR 1.42, 95% CI 1.06-1.92, P = 0.018) or a categorical variable (Q4: HR 1.89, 95% CI 1.12-3.17, P = 0.017), and there was an independent association between TyG index and AKI in patients with coronary revascularization. The RCS curve showed a linear relationship between higher TyG index and AKI in this particular population (P = 0.078). In addition, Kaplan-Meier analysis showed a significantly increased risk of RRT application in a subset of AKI patients based on quartiles of TyG index (P = 0.029).

CONCLUSION

TyG index was significantly associated with increased risk of AKI and adverse renal outcomes in patients with coronary revascularization. This finding suggests that the TyG index may be useful in identifying people at high risk for AKI and poor renal outcomes in patients with coronary revascularization.

Contrasting consequences of podocyte insulin-like growth factor 1 receptor inhibition

Insulin signaling to the glomerular podocyte via the insulin receptor (IR) is critical for kidney function. In this study we show that near-complete knockout of the closely related insulin-like growth factor 1 receptor (IGF1R) in podocytes is detrimental, resulting in albuminuria in vivo and podocyte cell death in vitro. In contrast, partial podocyte IGF1R knockdown confers protection against doxorubicin-induced podocyte injury. Proteomic analysis of cultured podocytes revealed that while near-complete loss of podocyte IGF1R results in the downregulation of mitochondrial respiratory complex I and DNA damage repair proteins, partial IGF1R inhibition promotes respiratory complex expression. This suggests that altered mitochondrial function and resistance to podocyte stress depends on the level of IGF1R suppression, the latter determining whether receptor inhibition is protective or detrimental. Our work suggests that the partial suppression of podocyte IGF1R could have therapeutic benefits in treating albuminuric kidney disease.

Insulin resistance before type 2 diabetes onset is associated with increased risk of albuminuria after diabetes onset: A prospective cohort study

AIM

Reduced renal insulin signalling is implicated in the pathogenesis of albuminuria. We sought to investigate whether insulin action and secretion, measured before diabetes onset, are associated with the development of albuminuria after diabetes onset.

MATERIALS AND METHODS

Baseline body composition, insulin sensitivity by hyperinsulinaemic-euglycaemic clamp at submaximal and maximal insulin stimulation (240 and 2400 pmol/m2/min; M-low and M-high), and insulin secretion by intravenous glucose tolerance test [acute insulin response (AIR)] were measured in 170 Southwestern Indigenous American adults who subsequently developed diabetes. After diabetes onset and during the median follow-up of 13.6 years, 81 participants (48%) developed albuminuria (urine albumin-to-creatinine ratio ≥30 mg/g). Separate associations of M-low, M-high and AIR (per 1-SD change) with the risk of albuminuria were assessed by Cox regression models adjusted for age, sex and body fat (%).

RESULTS

Participants who developed albuminuria were of similar age (26.4 ± 5.4 vs. 27.5 ± 6.1 years), sex (46% vs. 48% male), body fat (36.4 ± 7.5 vs. 35.7 ± 7.9%) and AIR [2.3 ± 0.3 vs. 2.3 ± 0.3, pmol/L (log)] as those who did not develop albuminuria but had lower insulin sensitivity [M-low: 0.33 ± 0.08 vs. 0.36 ± 0.12, p = .03; M-high: 0.87 ± 0.11 vs. 0.91 ± 0.12, p = .02; mg/kg-metabolic body size/min (log)]. In separate adjusted models, lower M-low and M-high were both associated with an increased risk for albuminuria [hazard ratio (HR) 1.51, 95% confidence interval (CI) 1.14, 2.00, p = .004; HR 1.31, 95% CI 1.06, 1.63, p = .01), whereas AIR was not (HR 1.15, 95% CI 0.87, 1.56, p = .3).

CONCLUSIONS

Lower insulin sensitivity is associated with the development of albuminuria, suggesting a role for insulin signalling in the pathogenesis of proteinuria.

Low molecular weight fucoidan restores diabetic endothelial glycocalyx by targeting neuraminidase2: A new therapy target in glycocalyx shedding

BACKGROUND AND PURPOSE

Diabetic vascular complication is a leading cause of disability and mortality in diabetes patients. Low molecular weight fucoidan (LMWF) is a promising drug candidate for vascular complications. Glycocalyx injury predates the occurrence of diabetes vascular complications. Protecting glycocalyx from degradation relieves diabetic vascular complications. LMWF has the potential to protect the diabetes endothelial glycocalyx from shedding.

EXPERIMENTAL APPROACH

The protective effect of LMWF on diabetic glycocalyx damage was investigated in db/db mice and Human Umbilical Vein Endothelial Cells (HUVEC) through transmission electron microscopy and WGA labelling. The effect of LMWF on glycocalyx degrading enzymes expression was investigated. Neuraminidase2 (NEU2) overexpression/knockdown was performed in HUVECs to verify the important role of NEU2 in glycocalyx homeostasis. The interaction between NEU2 and LMWF was detected by ELISA and surface plasmon resonance analysis (SPR).

KEY RESULTS

LMWF normalizes blood indexes including insulin, triglyceride, uric acid and reduces diabetes complications adverse events. LMWF alleviates diabetic endothelial glycocalyx damage in db/db mice kidney/aorta and high concentration glucose treated HUVECs. NEU2 is up-regulated in db/db mice and HUVECs with high concentration glucose. Overexpression/knockdown NEU2 results in glycocalyx shedding in HUVEC. Down-regulation and interaction of LMWF with NEU2 is a new therapy target in glycocalyx homeostasis. NEU2 was positively correlated with phosphorylated IR-β.

CONCLUSION AND IMPLICATIONS

NEU2 is an effective target for glycocalyx homeostasis and LMWF is a promising drug to alleviate vascular complications in diabetes by protecting endothelial glycocalyx.

Association between grip strength and albuminuria in the general United States population: NHANES 2011-2014

Background

Grip strength has been shown to be associated with chronic renal insufficiency, but the relationship between grip strength and albuminuria has not been confirmed. In this study, we used NHANES data to explore the association between grip strength and albuminuria in a US population.

Methods

In this analytical study, we utilized data sourced from the National Health and Nutrition Examination Survey (NHANES), specifically spanning the years 2011 to 2014. The dataset included 9,638 participants aged 20 years or older. After adjusting for potential confounders, multiple regression models were developed to infer the interrelationship between grip strength and albumin to creatinine ratio (ACR), and subgroup analyses were conducted.

Results

After adjusting for all covariates, ACR by 0.49 mg/g [-0.49 (95% CI: -0.93, -0.04)] for each 1 kg increase in grip strength decreased. Subgroup analysis showed that gender, age, hyperlipidemia, hypertension, diabetes mellitus, smoking, alcohol consumption and body mass index did not influence the negative correlation between grip strength and albuminuria.

Conclusion

There is a negative correlation between grip strength and albuminuria in the general U.S. population.

Metabolic Profiles of Type 2 Diabetes and Their Association With Renal Complications

CONTEXT

The components of metabolic syndrome (MetS) are interrelated and associated with renal complications in patients with type 2 diabetes (T2D).

OBJECTIVE

We aimed to reveal prevalent metabolic profiles in patients with T2D and identify which metabolic profiles were risk markers for renal progression.

METHODS

A total of 3556 participants with T2D from a hospital (derivation cohort) and 931 participants with T2D from a community survey (external validation cohort) were included. The primary outcome was the onset of diabetic kidney disease (DKD), and secondary outcomes included estimated glomerular filtration rate (eGFR) decline, macroalbuminuria, and end-stage renal disease (ESRD). In the derivation cohort, clusters were identified using the 5 components of MetS, and their relationships with the outcomes were assessed. To validate the findings, participants in the validation cohort were assigned to clusters. Multivariate odds ratios (ORs) of the primary outcome were evaluated in both cohorts, adjusted for multiple covariates at baseline.

RESULTS

In the derivation cohort, 6 clusters were identified as metabolic profiles. Compared with cluster 1, cluster 3 (severe hyperglycemia) had increased risks of DKD (hazard ratio [HR] [95% CI]: 1.72 [1.39-2.12]), macroalbuminuria (2.74 [1.84-4.08]), ESRD (4.31 [1.16-15.99]), and eGFR decline [P < .001]; cluster 4 (moderate dyslipidemia) had increased risks of DKD (1.97 [1.53-2.54]) and macroalbuminuria (2.62 [1.61-4.25]). In the validation cohort, clusters 3 and 4 were replicated to have significantly increased risks of DKD (adjusted ORs: 1.24 [1.07-1.44] and 1.39 [1.03-1.87]).

CONCLUSION

We identified 6 prevalent metabolic profiles in patients with T2D. Severe hyperglycemia and moderate dyslipidemia were validated as significant risk markers for DKD.

Association of physical activity with risk of chronic kidney disease in China: A population-based cohort study

BACKGROUND

Information on the association between physical activity (PA) and the risk of chronic kidney disease (CKD) is limited. We aimed to explore the associations of total, domain-specific, and intensity-specific PA with CKD and its subtypes in China.

METHODS

The study included 475,376 adults from the China Kadoorie Biobank aged 30-79 years during 2004-2008 at baseline. An interviewer-administered questionnaire was used to collect the information about PA, which was quantified as metabolic equivalent of task hours per day (MET-h/day) and categorized into 4 groups based on quartiles. Cox regression was used to analyze the association between PA and CKD risk.

RESULTS

During a median follow-up of 12.1 years, 5415 incident CKD cases were documented, including 1159 incident diabetic kidney disease (DKD) cases and 362 incident hypertensive nephropathy (HTN) cases. Total PA was inversely associated with CKD risk, with an adjusted hazard ratio (HR, 95% confidence interval (95%CI)) of 0.83 (0.75-0.92) for incident CKD in the highest quartile of total PA as compared with participants in the lowest quartile. Similar results were observed for risk of DKD and HTN, and the corresponding HRs (95%CIs) were 0.75 (0.58-0.97) for DKD risk and 0.56 (0.37-0.85) for HTN risk. Increased nonoccupational PA, low-intensity PA, and moderate-to-vigorous-intensity PA were significantly associated with a decreased risk of CKD, with HRs (95%CIs) of 0.80 (0.73-0.88), 0.85 (0.77-0.94), and 0.85 (0.76-0.95) in the highest quartile, respectively.

CONCLUSION

PA, including nonoccupational PA, low-intensity PA, and moderate-to-vigorous-intensity PA, was inversely associated with the risk of CKD, including DKD, HTN, and other CKD, and such associations were dose dependent.

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.

Outcomes With Finerenone in Patients With Chronic Kidney Disease and Type 2 Diabetes by Baseline Insulin Resistance

OBJECTIVE

To explore whether insulin resistance, assessed by estimated glucose disposal rate (eGDR), is associated with cardiorenal risk and whether it modifies finerenone efficacy.

RESEARCH DESIGN AND METHODS

In FIDELITY (N = 13,026), patients with type 2 diabetes, either 1) urine albumin-to-creatinine ratio (UACR) of ≥30 to <300 mg/g and estimated glomerular filtration rate (eGFR) of ≥25 to ≤90 mL/min/1.73 m2 or 2) UACR of ≥300 to ≤5,000 mg/g and eGFR of ≥25 mL/min/1.73 m2, who also received optimized renin-angiotensin system blockade, were randomized to finerenone or placebo. Outcomes included cardiovascular (cardiovascular death, nonfatal myocardial infarction, nonfatal stroke, or hospitalization for heart failure) and kidney (kidney failure, sustained decrease of ≥57% in eGFR from baseline, or renal death) composites. eGDR was calculated using waist circumference, hypertension status, and glycated hemoglobin for 12,964 patients.

RESULTS

Median eGDR was 4.1 mg/kg/min. eGDR

CONCLUSIONS

Insulin resistance was associated with increased cardiovascular (but not kidney) risk and did not modify finerenone efficacy.

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Key Words Collapse

MESH Headings

• Humans
• Diabetes Mellitus, Type 2/complications
• Diabetes Mellitus, Type 2/drug therapy
• Insulin Resistance
• Double-Blind Method
• Renal Insufficiency, Chronic/complications
• Glucose/therapeutic use
• Insulins/therapeutic use
• Naphthyridines

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Grants

• P30 DK111024 NIDDK NIH HHS
• Bayer

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Affiliation(s)

Thomas Ebert Medical Department III – Endocrinology, Nephrology, Rheumatology, University of Leipzig Medical Center, Leipzig, Germany
Stefan D. Anker Department of Cardiology of German Heart Center Charité; Institute of Health Center for Regenerative Therapies, German Centre for Cardiovascular Research partner site Berlin, Charité Universitätsmedizin, Berlin, Germany
Luis M. Ruilope Cardiorenal Translational Laboratory and Hypertension Unit, Institute of Research imas12, Madrid, Spain CIBER-CV, Hospital Universitario 12 de Octubre, Madrid, Spain Faculty of Sport Sciences, European University of Madrid, Madrid, Spain
Paola Fioretto Department of Medicine, University of Padua, Italy
Vivian Fonseca Tulane University Health Sciences Center, New Orleans, LA
Guillermo E. Umpierrez Division of Endocrinology, Emory University School of Medicine, Atlanta, GA
Andreas L. Birkenfeld Department of Diabetology, Endocrinology and Nephrology, University Clinic, Tübingen, Germany Institute for Diabetes Research and Metabolic Diseases, Helmholtz Center Munich, University of Tübingen, Tübingen, Germany German Center for Diabetes Research, Neuherberg, Germany
Robert Lawatscheck Clinical Research, Bayer AG, Berlin, Germany
Charlie Scott Data Science and Analytics, Bayer PLC, Reading, U.K
Katja Rohwedder Medical Affairs, Bayer AG, Berlin, Germany
Peter Rossing Steno Diabetes Center Copenhagen, Herlev, Denmark Department of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark
FIDELIO-DKD and FIGARO-DKD Investigators

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The role of endoplasmic reticulum-mitochondria-associated membranes in diabetic kidney disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease worldwide. The pathomechanisms of DKD are multifactorial, yet haemodynamic and metabolic changes in the early stages of the disease appear to predispose towards irreversible functional loss and histopathological changes. Recent studies highlight the importance of endoplasmic reticulum-mitochondria-associated membranes (ER-MAMs), structures conveying important cellular homeostatic and metabolic effects, in the pathology of DKD. Disruption of ER-MAM integrity in diabetic kidneys is associated with DKD progression, but the regulation of ER-MAMs and their pathogenic contribution remain largely unknown. Exploring the cell-specific components and dynamic changes of ER-MAMs in diabetic kidneys may lead to the identification of new approaches to detect and stratify diabetic patients with DKD. In addition, these insights may lead to novel therapeutic approaches to target and/or reverse disease progression. In this review, we discuss the association of ER-MAMs with key pathomechanisms driving DKD such as insulin resistance, dyslipidaemia, ER stress, and inflammasome activation and the importance of further exploration of ER-MAMs as diagnostic and therapeutic targets in DKD.

Triglyceride-glucose index change and chronic kidney disease progression in a Chinese hypertensive population

Background

The impact of triglyceride-glucose (TyG) index variations on chronic kidney disease (CKD) progression remains unexplored. To investigate the effects of the TyG index and its dynamic changes on CKD progression.

Method

This prospective cohort study included data from 8,418 hypertensive participants. The exposure variable in this study was defined as the difference between the TyG index at the last visit from that at baseline. The study's outcome variable was the progression of CKD, defined as follows: for subjects with an estimated glomerular filtration rate (eGFR) ≥60 mL/min, a ≥30% decrease in eGFR with a final follow-up value <60 mL/min; for those with an eGFR <60 mL/min, a ≥50% decrease in eGFR; or terminal renal failure requiring dialysis.

Results

During a median follow-up period of 48 months, 1077 patients were diagnosed with CKD progression. In the fully adjusted Model 3, patients with a change in the TyG index <0 exhibited a significantly decreased 13% risk of CKD progression (HR: 0.87, 95% CI: 0.76-0.98) compared to those with a change in the TyG index≥0 group. Subgroup analyses showed that changes in the TyG index significantly increased the risk of CKD progression only in patients with diastolic blood pressure (DBP) <90mmHg. In the path analysis, baseline TyG was associated with follow-up eGFR (the standard regression coefficient was 1.26 [95% CI, 0.45-2.06]).

Conclusions

Our findings suggest that TyG variability may serve as a useful tool for identifying individuals at risk of CKD progression, particularly hypertensive patients with normal DBP levels.

Association between the Triglyceride Glucose Index and All-Cause Mortality in Critically Ill Patients with Acute Kidney Injury

Introduction

The triglyceride glucose (TyG) index is a reliable alternative biomarker of insulin resistance, but the association between the TyG index and acute kidney injury (AKI) in critically ill patients remains unclear.

Methods

The data for the study were extracted from the Medical Information Mart for Intensive Care IV (MIMIC-IV) database. Cox regression and restricted cubic spline (RCS) analysis were performed to analyze the association between the TyG index and all-cause mortality. Besides, Cox regression was carried out in subgroups of age, gender, BMI, diabetes history, and dialysis status.

Results

A total of 7,508 critically ill participants with AKI from the MIMIC-IV database were included in this study, with 3,688 (49.12%) participants failed to survive. In Cox regression, after confounder adjustment, patients with a higher TyG index had a higher risk of all-cause mortality (HR = 1.845, 95% CI = 1.49-2.285, p < 0.001). In RCS, after confounder adjustment, the risk of death was positively correlated with the increased value of the TyG index when TyG index surpassed 10.014. This relationship was validated in age, gender, BMI, diabetes subgroups but not in the dialysis subgroup. Interestingly, RCS analysis demonstrated that, in patients undertaking dialysis, there is a "U"-shaped curve for the value of TyG index and risk of all-cause mortality. When TyG index is less than 10.460, the risk of all-cause mortality would decrease with the increased value of TyG index, while when TyG index is higher than 11.180, the risk of all-cause mortality would increase firmly with the increased value of TyG index.

Conclusion

Overall, a higher TyG index is associated with a higher risk of all-cause mortality in critically ill AKI. Interestingly, the relationship in the dialysis subgroup follows a "U"-shaped curve, indicating the importance of proper clinical blood glucose and lipid management in this particular population.

Communal interaction of glycation and gut microbes in diabetes mellitus, Alzheimer's disease, and Parkinson's disease pathogenesis

Diabetes and its complications, Alzheimer's disease (AD), and Parkinson's disease (PD) are increasing gradually, reflecting a global threat vis-à-vis expressing the essentiality of a substantial paradigm shift in research and remedial actions. Protein glycation is influenced by several factors, like time, temperature, pH, metal ions, and the half-life of the protein. Surprisingly, most proteins associated with metabolic and neurodegenerative disorders are generally long-lived and hence susceptible to glycation. Remarkably, proteins linked with diabetes, AD, and PD share this characteristic. This modulates protein's structure, aggregation tendency, and toxicity, highlighting renovated attention. Gut microbes and microbial metabolites marked their importance in human health and diseases. Though many scientific shreds of evidence are proposed for possible change and dysbiosis in gut flora in these diseases, very little is known about the mechanisms. Screening and unfolding their functionality in metabolic and neurodegenerative disorders is essential in hunting the gut treasure. Therefore, it is imperative to evaluate the role of glycation as a common link in diabetes and neurodegenerative diseases, which helps to clarify if modulation of nonenzymatic glycation may act as a beneficial therapeutic strategy and gut microbes/metabolites may answer some of the crucial questions. This review briefly emphasizes the common functional attributes of glycation and gut microbes, the possible linkages, and discusses current treatment options and therapeutic challenges.

Protein tyrosine phosphatase 1B is a regulator of alpha-actinin4 in the glomerular podocyte

Glomerular podocytes are instrumental for the barrier function of the kidney, and podocyte injury contributes to proteinuria and the deterioration of renal function. Protein tyrosine phosphatase 1B (PTP1B) is an established metabolic regulator, and the inactivation of this phosphatase mitigates podocyte injury. However, there is a paucity of data regarding the substrates that mediate PTP1B actions in podocytes. This study aims to uncover novel substrates of PTP1B in podocytes and validate a leading candidate. To this end, using substrate-trapping and mass spectroscopy, we identified putative substrates of this phosphatase and investigated the actin cross-linking cytoskeletal protein alpha-actinin4. PTP1B and alpha-actinin4 co-localized in murine and human glomeruli and transiently transfected E11 podocyte cells. Additionally, podocyte PTP1B deficiency in vivo and culture was associated with elevated tyrosine phosphorylation of alpha-actinin4. Conversely, reconstitution of the knockdown cells with PTP1B attenuated alpha-actinin4 tyrosine phosphorylation. We demonstrated co-association between alpha-actinin4 and the PTP1B substrate-trapping mutant, which was enhanced upon insulin stimulation and disrupted by vanadate, consistent with an enzyme-substrate interaction. Moreover, we identified alpha-actinin4 tandem tyrosine residues 486/487 as mediators of its interaction with PTP1B. Furthermore, knockdown studies in E11 cells suggest that PTP1B and alpha-actinin4 are modulators of podocyte motility. These observations indicate that PTP1B and alpha-actinin4 are likely interacting partners in a signaling node that modulates podocyte function. Targeting PTP1B and plausibly this one of its substrates may represent a new therapeutic approach for podocyte injury that warrants additional investigation.

Defective insulin-stimulated equilibrative nucleoside transporter-2 activity and altered subcellular transporter distribution drive the loss of adenosine homeostasis in diabetic kidney disease progression

AIM

Progression of diabetic nephropathy (DN) is linked to the dysregulated increase of adenosine and altered signaling properties. A major contribution to the maintenance of physiological extracellular adenosine levels relies on cellular uptake activity through plasma membrane nucleoside transporters. Because kidney cells are responsive to insulin, this study aims to determine how DN affects insulin regulation of the equilibrative nucleoside transporter-2 (ENT2).

METHODS

Human Podocytes and rat glomeruli were used to study ENT2 regulation. The effects of diabetes and insulin on ENT2 mediated transport activity were determined measuring the fraction of total adenosine uptake in sodium-free medium which is inhibitable by hypoxanthine. Alterations in ENT2 subcellular distribution were assessed in the kidney of people affected with DN and diabetic rats. The consequences of impaired ENT2 activity on the kidney were evaluated using dipyridamole in an animal model.

RESULTS

Insulin upregulates ENT2 uptake activity by increasing the Vmax, thus counteracting decreased adenosine uptake due to high d-glucose and achieving extracellular adenosine homeostasis. Insulin promoted ENT2 translocation to the plasma membrane dependent on PI3-kinase/Akt signaling and actin cytoskeleton integrity. However, in diabetic rats, the insulin-mediated induction of ENT2 activity was lost. Additionally, reduced Akt activation in response to insulin correlated with decreased ENT2 distribution at the plasma membrane. Kidney tissues from diabetic rats and human DN biopsies showed ENT2 redistribution to an intracellular pattern, evidencing dysfunctional adenosine uptake. Through ENT inhibition, we evidenced increased proteinuria and induced alpha-smooth muscle actin as a result of profibrotic activation of cells in the kidney.

CONCLUSION

Deficient insulin regulation of ENT2 activity contributes to chronically high adenosine levels and glomerular alterations that underline diabetic kidney disease progression.

Role of lysosomes in insulin signaling and glucose uptake in cultured rat podocytes

Podocytes are sensitive to insulin, which governs the functional and structural integrity of podocytes that are essential for proper function of the glomerular filtration barrier. Lysosomes are acidic organelles that are implicated in regulation of the insulin signaling pathway. Cathepsin D (CTPD) and lysosome-associated membrane protein 1 (LAMP1) are major lysosomal proteins that reflect the functional state of lysosomes. However, the effect of insulin on lysosome activity and role of lysosomes in the regulation of insulin-dependent glucose uptake in podocytes are unknown. Our studies showed that the short-term incubation of podocytes with insulin decreased LAMP1 and CTPD mRNA levels. Insulin and bafilomycin A1 reduced both the amounts of LAMP1 and CTPD proteins and activity of CTPD, which were associated with a decrease in the fluorescence intensity of lysosomes that were labeled with LysoTracker. Bafilomycin A1 inhibited insulin-dependent endocytosis of the insulin receptor and increased the amounts of the insulin receptor and glucose transporter 4 on the cell surface of podocytes. Bafilomycin A1 also inhibited insulin-dependent glucose uptake despite an increase in the amount of glucose transporter 4 in the plasma membrane of podocytes. These results suggest that lysosomes are signaling hubs that may be involved in the coupling of insulin signaling with the regulation of glucose uptake in podocytes. The dysregulation of this mechanism can lead to the dysfunction of podocytes and development of insulin resistance.

Stem Cell-Derived Islet Transplantation in Patients With Type 2 Diabetes: Can Diabetes Subtypes Guide Implementation?

Historically, only patients with brittle diabetes or severe recurrent hypoglycemia have been considered for islet transplantation (ITx). This population has been selected to optimize the risk-benefit profile, considering risks of long-term immunosuppression and limited organ supply. However, with the advent of stem cell (SC)-derived ITx and the potential for immunosuppression-free ITx, consideration of a broader recipient cohort may soon be justified. Simultaneously, the classical categorization of diabetes is being challenged by growing evidence in support of a clustering of disease subtypes that can be better categorized by the All New Diabetics in Scania (ANDIS) classification system. Using the ANDIS classification, 5 subtypes of diabetes have been described, each with unique causes and consequences. We evaluate consideration for ITx in the context of this broader patient population and the new classification of diabetes subtypes. In this review, we evaluate considerations for ITx based on novel diabetes subtypes, including their limitations, and we elaborate on unique transplant features that should now be considered to enable ITx in these "unconventional" patient cohorts. Based on evidence from those receiving whole pancreas transplant and our more than 20-year experience with ITx, we offer recommendations and potential research avenues to justify implementation of SC-derived ITx in broader populations of patients with all types of diabetes.

Dendrobium officinale polysaccharide decreases podocyte injury in diabetic nephropathy by regulating IRS-1/AKT signal and promoting mitophagy

BACKGROUNDS

High glucose (HG) caused oxidative stress and mitochondrial dysfunction, resulting in insulin resistance in podocytes, a key mechanism of diabetic nephropathy. Dendrobium officinale polysaccharide (DOP) was able to improve insulin resistance and antioxidant capability.

OBJECTIVE

The purpose of this study is to explore the mechanism by which DOP decreases the podocyte injury induced by HG.

METHODS

MPC5 cells were treated with HG, DOP, and IRS-1/2 inhibitor NT157. Afterwards, glucose consumption, generations of ROS and MDA were measured using the detection kits. Mitophagy was monitored using both MtphagTracyker and LysoTracker. The mitochondrial membrane potential was evaluated by JC-1 staining. DOP was also used in a mouse model of diabetes, with the measurements of urine albumin, blood creatinine and blood urea nitrogen.

RESULTS

Treatment with DOP suppressed the HG-induced reduction of glucose consumption, the phosphorylation of IRS-1 (phospho Y632), AKT (phospho Ser473 and Thr308) and Nephrin. In addition, HG-induced augment of ROS and MDA, formation of γ-H2A.X foci and translocation of AKT to nucleus were inhibited by DOP. DOP enhanced mitophagy, which was associated with decreased mitochondrial membrane potential and ROS production. DOP conferred protective effect on podocyte in the diabetic mouse by reducing the albumin/creatinine ratio and blood urea nitrogen, and restoring Nephrin expression in podocytes.

CONCLUSIONS

DOP alleviates HG-induced podocyte injuryby regulating IRS-1/AKT signal and promoting mitophagy.

Deletion of protein tyrosine phosphatase SHP-1 restores SUMOylation of podocin and reverses the progression of diabetic kidney disease

Both clinical and experimental data suggest that podocyte injury is involved in the onset and progression of diabetic kidney disease (DKD). Although the mechanisms underlying the development of podocyte loss are not completely understood, critical structural proteins such as podocin play a major role in podocyte survival and function. We have reported that the protein tyrosine phosphatase SHP-1 expression increased in podocytes of diabetic mice and glomeruli of patients with diabetes. However, the in vivo contribution of SHP-1 in podocytes is unknown. Conditional podocyte-specific SHP-1-deficient mice (Podo-SHP-1-/-) were generated to evaluate the impact of SHP-1 deletion at four weeks of age (early) prior to the onset of diabetes and after 20 weeks (late) of diabetes (DM; Ins2+/C96Y) on kidney function (albuminuria and glomerular filtration rate) and kidney pathology. Ablation of the SHP-1 gene specifically in podocytes prevented and even reversed the elevated albumin/creatinine ratio, glomerular filtration rate progression, mesangial cell expansion, glomerular hypertrophy, glomerular basement membrane thickening and podocyte foot process effacement induced by diabetes. Moreover, podocyte-specific deletion of SHP-1 at an early and late stage prevented diabetes-induced expression of collagen IV, fibronectin, transforming growth factor-β, transforming protein RhoA, and serine/threonine kinase ROCK1, whereas it restored nephrin, podocin and cation channel TRPC6 expression. Mass spectrometry analysis revealed that SHP-1 reduced SUMO2 post-translational modification of podocin while podocyte-specific deletion of SHP-1 preserved slit diaphragm protein complexes in the diabetic context. Thus, our data uncovered a new role of SHP-1 in the regulation of cytoskeleton dynamics and slit diaphragm protein expression/stability, and its inhibition preserved podocyte function preventing DKD progression.

The unique structural and functional characteristics of glomerular endothelial cell fenestrations and their potential as a therapeutic target in kidney disease

Glomerular endothelial cell (GEnC) fenestrations are a critical component of the glomerular filtration barrier. Their unique nondiaphragmed structure is key to their function in glomerular hydraulic permeability, and their aberration in disease can contribute to loss of glomerular filtration function. This review provides a comprehensive update of current understanding of the regulation and biogenesis of fenestrae. We consider diseases in which GEnC fenestration loss is recognized or may play a role and discuss methods with potential to facilitate the study of these critical structures. Literature is drawn from GEnCs as well as other fenestrated cell types such as liver sinusoidal endothelial cells that most closely parallel GEnCs.

Insulin and the kidneys: a contemporary view on the molecular basis

Insulin is a hormone that is composed of 51 amino acids and structurally organized as a hexamer comprising three heterodimers. Insulin is the central hormone involved in the control of glucose and lipid metabolism, aiding in processes such as body homeostasis and cell growth. Insulin is synthesized as a large preprohormone and has a leader sequence or signal peptide that appears to be responsible for transport to the endoplasmic reticulum membranes. The interaction of insulin with the kidneys is a dynamic and multicenter process, as it acts in multiple sites throughout the nephron. Insulin acts on a range of tissues, from the glomerulus to the renal tubule, by modulating different functions such as glomerular filtration, gluconeogenesis, natriuresis, glucose uptake, regulation of ion transport, and the prevention of apoptosis. On the other hand, there is sufficient evidence showing the insulin receptor's involvement in renal functions and its responsibility for the regulation of glucose homeostasis, which enables us to understand its contribution to the insulin resistance phenomenon and its association with the progression of diabetic kidney disease.

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.

Estimated Glucose Disposal Rate Predicts Renal Progression in Type 2 Diabetes Mellitus: A Retrospective Cohort Study

Context

Insulin resistance is a feature of type 2 diabetes mellitus (T2DM). The estimated glucose disposal rate (eGDR), a validated marker for insulin resistance, is associated with complications of diabetes, but few studies have explored the relationship between eGDR and renal outcomes in T2DM.

Objective

This study investigated the value of eGDR in predicting renal progression in T2DM.

Methods

A total of 956 T2DM patients with a baseline estimated glomerular filtration rate (eGFR) ≥ 60 mL/min/1.73 m² and 5 years of follow-up were enrolled. Primary outcomes were rapid eGFR decline, eGFR <60 mL/min/1.73 m², and composite renal endpoint consisting of 50% eGFR decline, doubling of serum creatinine, or end-stage renal disease. A continuous scale with restricted cubic spline curves and a generalized linear model were applied to evaluate the associations between eGDR and primary outcomes.

Results

Rapid eGFR decline was experienced by 23.95% of patients, 21.97% with eGFR <60 mL/min/1.73 m², and 12.13% with the composite renal endpoint. The eGDR showed a relationship with follow-up eGFR and percentage change in eGFR (P < .001). An eGDR <6.34 mg/kg/min was an independent risk factor for rapid eGFR decline, eGFR < 60 mL/min/1.73 m², or the composite renal endpoint(P < .05). Compared with eGDR of 5.65∼6.91 mg/kg/min, eGDR levels >8.33 mg/kg/min decreased the risk of rapid eGFR decline by 75%, eGFR < 60 mL/min/1.73 m² by 60%, and the composite renal endpoint by 61%. Subgroup analysis was performed by sex, age, and diabetes duration, which showed that eGDR was associated with primary outcomes.

Conclusion

Lower eGDR is a predictive factor for renal deterioration in T2DM patients.

Role of insulin signaling and its associated signaling in glomerulus for diabetic kidney disease

The number of patients with diabetic kidney disease (DKD) has been rising significantly over the last several decades and is one of the most frequent causes of chronic kidney disease (CKD) in the United States. Hyperglycemia accelerates development of DKD, a direct result of increased intracellular glucose availability. Two large clinical studies, the Diabetes Control and Complications Trial in type 1 diabetes and the United Kingdom Prospective Diabetes Study in type 2 diabetes showed that intensive glycemic control delayed the onset and the progression of DKD. On the other hand, it is reported that glycemic control alone is not sufficient to control DKD progression. Recent data support that insulin signaling and its associated signaling contribute significantly to preserve glomerular function. However, little is known about the key regulators of insulin signaling in glomerular component cells. In this review, we summarize the novel knowledge regarding the reno-protective effects of insulin signaling or its associated signaling in glomerular constituent cells on DKD.

Diabetic vascular diseases: molecular mechanisms and therapeutic strategies

Vascular complications of diabetes pose a severe threat to human health. Prevention and treatment protocols based on a single vascular complication are no longer suitable for the long-term management of patients with diabetes. Diabetic panvascular disease (DPD) is a clinical syndrome in which vessels of various sizes, including macrovessels and microvessels in the cardiac, cerebral, renal, ophthalmic, and peripheral systems of patients with diabetes, develop atherosclerosis as a common pathology. Pathological manifestations of DPDs usually manifest macrovascular atherosclerosis, as well as microvascular endothelial function impairment, basement membrane thickening, and microthrombosis. Cardiac, cerebral, and peripheral microangiopathy coexist with microangiopathy, while renal and retinal are predominantly microangiopathic. The following associations exist between DPDs: numerous similar molecular mechanisms, and risk-predictive relationships between diseases. Aggressive glycemic control combined with early comprehensive vascular intervention is the key to prevention and treatment. In addition to the widely recommended metformin, glucagon-like peptide-1 agonist, and sodium-glucose cotransporter-2 inhibitors, for the latest molecular mechanisms, aldose reductase inhibitors, peroxisome proliferator-activated receptor-γ agonizts, glucokinases agonizts, mitochondrial energy modulators, etc. are under active development. DPDs are proposed for patients to obtain more systematic clinical care requires a comprehensive diabetes care center focusing on panvascular diseases. This would leverage the advantages of a cross-disciplinary approach to achieve better integration of the pathogenesis and therapeutic evidence. Such a strategy would confer more clinical benefits to patients and promote the comprehensive development of DPD as a discipline.

Triglyceride-glucose index is associated with the risk of chronic kidney disease progression in type 2 diabetes

OBJECTIVE

The study aimed to investigate the association of TyG index with chronic kidney disease (CKD) progression in type 2 diabetes mellitus (T2DM).

METHODS

A total of 179 T2DM patients with CKD were retrospectively included. CKD progression was defined as a doubling of baseline serum creatinine or onset of end-stage kidney disease (ESKD). Internal validation was performed by the Kidney Failure Risk Equation (KFRE) model and Net reclassification improvement (NRI).

RESULTS

The optimal cut-off value of the TyG index was 9.17. The cumulative incidence of kidney outcomes was significantly higher in the high-TyG group (v.s low-TyG group, P = 0.019). In addition, the high-TyG index was associated with a greater risk of CKD progression (HR 1.794, 95% CI 1.026-3.137, P = 0.040). And reclassification analyses confirmed the final adjusted model improved NRI (61.90% v.s model 2, 43.80% v.s model 1). The further RCS curves presented an inverted S-shaped relationship between the TyG index and the risk of CKD progression. Internal validation verified that a higher TyG index was associated with 2.10-fold increased odds of 2-year ESKD risk >10% (95% CI 1.82-8.21). Moreover, subgroup analysis suggested that the association was more pronounced in those at relatively early CKD stages (higher than stage 2) and with no medication history of oral hypoglycemic agents.

CONCLUSION

An elevated TyG index was associated with a higher risk of CKD progression in T2DM patients. Our findings suggested that timely targeting insulin sensitivity at the early stages of T2DM might be associated with declined future risk of CKD development.

Change in albuminuria as a surrogate endpoint for cardiovascular and renal outcomes in patients with diabetes

For the purpose of predicting clinical outcomes in patients with diabetes and chronic kidney disease, change in albuminuria is a good candidate to be a surrogate marker for future cardiovascular events and progression of kidney disease. Spot urine albumin/creatinine ratio is convenient and recognized as a viable alternative to 24-h albumin, with some limitations. Although there is sufficient evidence to validate its use in clinical trials as a surrogate endpoint for renal outcomes, this is not yet the case for cardiovascular outcomes. While change in albuminuria as a primary or secondary endpoint is trial-specific, its use should be encouraged, nonetheless.

Gut microbiota and its metabolites - molecular mechanisms and management strategies in diabetic kidney disease

Diabetic kidney disease (DKD) is one of the major microvascular complications of diabetes mellitus and is also one of the serious risk factors in cardiovascular events, end-stage renal disease, and mortality. DKD is associated with the diversified, compositional, and functional alterations of gut microbiota. The interaction between gut microbiota and host is mainly achieved through metabolites, which are small molecules produced by microbial metabolism from exogenous dietary substrates and endogenous host compounds. The gut microbiota plays a critical role in the pathogenesis of DKD by producing multitudinous metabolites. Nevertheless, detailed mechanisms of gut microbiota and its metabolites involved in the occurrence and development of DKD have not been completely elucidated. This review summarizes the specific classes of gut microbiota-derived metabolites, aims to explore the molecular mechanisms of gut microbiota in DKD pathophysiology and progression, recognizes biomarkers for the screening, diagnosis, and prognosis of DKD, as well as provides novel therapeutic strategies for DKD.

Atractylodes lancea and Magnolia officinalis combination protects against high fructose-impaired insulin signaling in glomerular podocytes through upregulating Sirt1 to inhibit p53-driven miR-221

ETHNOPHARMACOLOGICAL RELEVANCE

In traditional Chinese medicine, a long term of improper diet causes the Dampness and disturbs Zang-Fu's functions including Kidney deficiency. Atractylodes lancea (Atr) and Magnolia officinalis (Mag) as a famous herb pair are commonly used to transform Dampness, with kidney protection.

AIM OF THE STUDY

To explore how Atr and Mag protected against insulin signaling impairment in glomerular podocytes induced by high dietary fructose feeding, a major contributor for insulin resistance in glomerular podocyte dysfunction.

MATERIALS AND METHODS

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyze constituents of Atr and Mag. Rat model was induced by 10% fructose drinking water in vivo, and heat-sensitive human podocyte cells (HPCs) were exposed to 5 mM fructose in vitro. Animal or cultured podocyte models were treated with different doses of Atr, Mag or Atr and Mag combination. Western blot, qRT-PCR and immunofluorescence assays as well as other experiments were performed to detect adiponectin receptor protein 1 (AdipoR1), protein kinase B (AKT), Sirt1, p53 and miR-221 levels in rat glomeruli or HPCs, respectively.

RESULTS

Fifty-five components were identified in Atr and Mag combination. Network pharmacology analysis indicated that Atr and Mag combination might affect insulin signaling pathway. This combination significantly improved systemic insulin resistance and prevented glomerulus morphological damage in high fructose-fed rats. Of note, high fructose decreased IRS1, AKT and AdipoR1 in rat glomeruli and cultured podocytes. Further data from cultured podocytes with Sirt1 inhibitor/agonist, p53 agonist/inhibitor, or miR-221 mimic/inhibitor showed that high fructose downregulated Sirt1 to stimulate p53-driven miR-221, resulting in insulin signaling impairment. Atr and Mag combination effectively increased Sirt1, and decreased p53 and miR-221 in in vivo and in vitro models.

CONCLUSIONS

Atr and Mag combination improved insulin signaling in high fructose-stimulated glomerular podocytes possibly through upregulating Sirt1 to inhibit p53-driven miR-221. Thus, the regulation of Sirt1/p53/miR-221 by this combination may be a potential therapeutic approach in podocyte insulin signaling impairment.

Nutrient sensing, signaling transduction, and autophagy in podocyte injury: implications for kidney disease

Podocytes are terminally differentiated epithelial cells of the renal glomerular tuft and these highly specialized cells are essential for the integrity of the slit diaphragm. The biological function of podocytes is primarily based on a complex ramified structure that requires sufficient nutrients and a large supply of energy in support of their unique structure and function in the glomeruli. Of note, the dysregulation of nutrient signaling and energy metabolic pathways in podocytes has been associated with a range of kidney diseases i.e., diabetic nephropathy. Therefore, nutrient-related and energy metabolic signaling pathways are critical to maintaining podocyte homeostasis and the pathogenesis of podocyte injury. Recently, a growing body of evidence has indicated that nutrient starvation induces autophagy, which suggests crosstalk between nutritional signaling with the modulation of autophagy for podocytes to adapt to nutrient deprivation. In this review, the current knowledge and advancement in the understanding of nutrient sensing, signaling, and autophagy in the podocyte biology, injury, and pathogenesis of kidney diseases is summarized. Based on the existing findings, the implications and perspective to target these signaling pathways and autophagy in podocytes during the development of novel preventive and therapeutic strategies in patients with podocyte injury-associated kidney diseases are discussed.

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.

Sex-specific trajectories of insulin resistance markers and reduced renal function during 18 years of follow-up; TLGS

OBJECTIVE

To investigate the association between the dynamic course of insulin resistance and chronic kidney disease (CKD).

METHODS

In a longitudinal population-based Tehran Lipid and Glucose Study, 3071 eligible participants aged ≥20 years were followed for 18 years at three-year intervals. HOMA-IR and clinical surrogate markers of insulin resistance, including triglyceride-glucose index (TyG), visceral adiposity index (VAI), and lipid accumulation product (LAP), were calculated. Using latent variable mixture modeling, sex-specific trajectories were plotted for each insulin resistance marker. Trajectory group association of the insulin resistance markers with CKD was determined using the multivariate cox proportional hazards regression model.

RESULTS

For HOMA-IR, two distinct trajectory patterns (stable and increasing), and for TyG, VAI, and LAP, three trajectories (low, moderate, high) were identified. The participants with increasing HOMA-IR trajectory had a significantly increased risk of CKD in men (HR: 1.72, 95%CI: 1.06-2.79) and women (HR: 1.37, 95%CI: 1.00-1.89) after adjusting confounding variables. The high TyG and VAI trajectory classes were associated with a higher risk of CKD than the low TyG and VAI trajectory classes in both men (TyG: HR:1.97, 95%CI: 1.12-3.46; VAI: HR:1.66, 95%CI:1.06-2.62) and women (TyG: HR:1.50, 95%CI:1.06-2.12; VAI: HR:1.66, 95%CI:1.20-2.31). In contrast, the High LAP (HR: 3.38, 95%CI: 2.08-5.48) trajectory was associated with incident CKD only in women.

CONCLUSION

An increasing trend of HOMA-IR is associated with a higher risk of CKD in men and women. Among clinical insulin resistance surrogate markers, abnormal trajectory patterns of LAP in women and TyG and VAI in both sexes are associated with a higher risk of CKD.

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.

Activation of Stimulator of IFN Genes (STING) Causes Proteinuria and Contributes to Glomerular Diseases

BACKGROUND

The signaling molecule stimulator of IFN genes (STING) was identified as a crucial regulator of the DNA-sensing cyclic GMP-AMP synthase (cGAS)-STING pathway, and this signaling pathway regulates inflammation and energy homeostasis under conditions of obesity, kidney fibrosis, and AKI. However, the role of STING in causing CKD, including diabetic kidney disease (DKD) and Alport syndrome, is unknown.

METHODS

To investigate whether STING activation contributes to the development and progression of glomerular diseases such as DKD and Alport syndrome, immortalized human and murine podocytes were differentiated for 14 days and treated with a STING-specific agonist. We used diabetic db/db mice, mice with experimental Alport syndrome, C57BL/6 mice, and STING knockout mice to assess the role of the STING signaling pathway in kidney failure.

RESULTS

In vitro, murine and human podocytes express all of the components of the cGAS-STING pathway. In vivo, activation of STING renders C57BL/6 mice susceptible to albuminuria and podocyte loss. STING is activated at baseline in mice with experimental DKD and Alport syndrome. STING activation occurs in the glomerular but not the tubulointerstitial compartment in association with autophagic podocyte death in Alport syndrome mice and with apoptotic podocyte death in DKD mouse models. Genetic or pharmacologic inhibition of STING protects from progression of kidney disease in mice with DKD and Alport syndrome and increases lifespan in Alport syndrome mice.

CONCLUSION

The activation of the STING pathway acts as a mediator of disease progression in DKD and Alport syndrome. Targeting STING may offer a therapeutic option to treat glomerular diseases of metabolic and nonmetabolic origin or prevent their development, progression, or both.

Renal insulin resistance in type 2 diabetes mellitus and progression of chronic kidney disease: potential pathogenic mechanisms

INTRODUCTION

A bidirectional association exists between insulin resistance (IR) and chronic kidney disease (CKD) in Type 2 Diabetes Mellitus (T2DM). Baseline measures of IR are predictive of CKD progression, and uremia in progressive CKD is itself, in turn, associated with a worsening of IR. Pre-clinical research reveals that intrinsic IR in glomerular podocytes and the renal tubule may serve as a pathogenic driver of CKD in T2DM.

AREAS COVERED

The present manuscript takes as its point of departure, the recently identified prognostic utility of severe insulin resistance as a predictor of CKD in T2DM. Findings from a series of studies describing the association of IR with pathological alterations in both established, and less commonly assessed dynamic measures of renal impairment are discussed. Drawing upon the pre-clinical mechanistic evidence base, the cellular and molecular basis of intrinsic renal IR as a promoter of CKD is considered.

EXPERT OPINION

Measurement of insulin sensitivity may add value to profiling of renal risk in T2DM. Rational selection of therapeutic strategies targeting the enhancement of insulin sensitivity merits special attention regarding the personalized management of CKD in insulin resistance predominant T2DM.

Deficiency of the Src homology phosphatase 2 in podocytes is associated with renoprotective effects in mice under hyperglycemia

Diabetic nephropathy (DN) is a significant complication of diabetes and the leading cause of end-stage renal disease. Hyperglycemia-induced dysfunction of the glomerular podocytes is a major contributor to the deterioration of renal function in DN. Previously, we demonstrated that podocyte-specific disruption of the Src homology phosphatase 2 (Shp2) ameliorated lipopolysaccharide-induced renal injury. This study aims to evaluate the contribution of Shp2 to podocyte function under hyperglycemia and explore the molecular underpinnings. We report elevated Shp2 in the E11 podocyte cell line under high glucose and the kidney under streptozotocin- and high-fat diet-induced hyperglycemia. Consistently, Shp2 disruption in podocytes was associated with partial renoprotective effects under hyperglycemia, as evidenced by the preserved renal function. At the molecular level, Shp2 deficiency was associated with altered renal insulin signaling and diminished hyperglycemia-induced renal endoplasmic reticulum stress, inflammation, and fibrosis. Additionally, Shp2 knockdown in E11 podocytes mimicked the in vivo deficiency of this phosphatase and ameliorated the deleterious impact of high glucose, whereas Shp2 reconstitution reversed these effects. Moreover, Shp2 deficiency attenuated high glucose-induced E11 podocyte migration. Further, we identified the protein tyrosine kinase FYN as a putative mediator of Shp2 signaling in podocytes under high glucose. Collectively, these findings suggest that Shp2 inactivation may afford protection to podocytes under hyperglycemia and highlight this phosphatase as a potential target to ameliorate glomerular dysfunction in DN.

Insulin controls cytoskeleton reorganization and filtration barrier permeability via the PKGIα-Rac1-RhoA crosstalk in cultured rat podocytes

Podocyte foot processes are an important cellular layer of the glomerular barrier that regulates glomerular permeability. Insulin via the protein kinase G type Iα (PKGIα) signaling pathway regulates the balance between contractility and relaxation (permeability) of the podocyte barrier by regulation of the actin cytoskeleton. This mechanism was shown to be disrupted in diabetes. Rho family guanosine-5'-triphosphates (GTPases) are dynamic modulators of the actin cytoskeleton and expressed in cells that form the glomerular filtration barrier. Thus, changes in Rho GTPase activity may affect glomerular permeability to albumin. The present study showed that Rho family GTPases control podocyte migration and permeability. Moreover these processes are regulated by insulin in PKGIα-dependent manner. Modulation of the PKGI-dependent activity of Rac1 and RhoA GTPases with inhibitors or small-interfering RNA impair glomerular permeability to albumin. We also demonstrated this mechanism in obese, insulin-resistant Zucker rats. We propose that PKGIα-Rac1-RhoA crosstalk is necessary in proper organization of the podocyte cytoskeleton and consequently the stabilization of glomerular architecture and regulation of filtration barrier permeability.

Spatial localization of β-unsaturated aldehyde markers in murine diabetic kidney tissue by mass spectrometry imaging

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease. Limitations in current diagnosis and screening methods have sparked a search for more specific and conclusive biomarkers. Hyperglycemic conditions generate a plethora of harmful molecules in circulation and within tissues. Oxidative stress generates reactive α-dicarbonyls and β-unsaturated hydroxyhexenals, which react with proteins to form advanced glycation end products. Mass spectrometry imaging (MSI) enables the detection and spatial localization of molecules in biological tissue sections. Here, for the first time, the localization and semiquantitative analysis of “reactive aldehydes” (RAs) 4-hydroxyhexenal (4-HHE), 4-hydroxynonenal (4-HNE), and 4-oxo-2-nonenal (4-ONE) in the kidney tissues of a diabetic mouse model is presented. Ionization efficiency was enhanced through on-tissue chemical derivatization (OTCD) using Girard’s reagent T (GT), forming positively charged hydrazone derivatives. MSI analysis was performed using matrix-assisted laser desorption ionization (MALDI) coupled with Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR). RA levels were elevated in diabetic kidney tissues compared to lean controls and localized throughout the kidney sections at a spatial resolution of 100 µm. This was confirmed by liquid extraction surface analysis–MSI (LESA-MSI) and liquid chromatography–mass spectrometry (LC–MS). This method identified β-unsaturated aldehydes as “potential” biomarkers of DN and demonstrated the capability of OTCD-MSI for detection and localization of poorly ionizable molecules by adapting existing chemical derivatization methods. Untargeted exploratory distribution analysis of some precursor lipids was also assessed using MALDI-FT-ICR-MSI.

Obesity-related glomerulopathy: Current approaches and future perspectives

Obesity-related glomerulopathy (ORG) is a silent comorbidity which is increasing in incidence as the obesity epidemic escalates. ORG is associated with serious health consequences including chronic kidney disease, end-stage renal disease (ESRD), and increased mortality. Although the pathogenic mechanisms involved in the development of ORG are not fully understood, glomerular hemodynamic changes, renin-angiotensin-aldosterone system (RAAS) overactivation, insulin-resistance, inflammation and ectopic lipid accumulation seem to play a major role. Despite albuminuria being commonly used for the non-invasive evaluation of ORG, promising biomarkers of early kidney injury that are emerging, as well as new approaches with proteomics and metabolomics, might permit an earlier diagnosis of this disease. In addition, the assessment of ectopic kidney fat by renal imaging could be a useful tool to detect and evaluate the progression of ORG. Weight loss interventions appear to be effective in ORG, although large-scale trials are needed. RAAS blockade has a renoprotective effect in patients with ORG, but even so, a significant proportion of patients with ORG will eventually progress to ESRD despite therapeutic efforts. It is noteworthy that certain antidiabetic agents such as sodium-glucose cotransporter 2 inhibitors (SGLT2i) or glucagon-like peptide-1 receptor agonists (GLP-1 RAs) could be useful in the treatment of ORG through different pleiotropic effects. In this article, we review current approaches and future perspectives in the care and treatment of ORG.

Metabolic Syndrome-Related Kidney Injury: A Review and Update

Metabolic syndrome (MetS) includes visceral obesity, hyperglycemia, dyslipidemia, and hypertension. The prevalence of MetS is 20-25%, which is an important risk factor for chronic kidney disease (CKD). MetS causes effects on renal pathophysiology, including glomerular hyperfiltration, RAAS, microalbuminuria, profibrotic factors and podocyte injury. This review compares several criteria of MetS and analyzes their differences. MetS and the pathogenesis of CKD includes insulin resistance, obesity, dyslipidemia, inflammation, oxidative stress, and endothelial dysfunction. The intervention of MetS-related renal damage is the focus of this article and includes controlling body weight, hypertension, hyperglycemia, and hyperlipidemia, requiring all components to meet the criteria. In addition, interventions such as endoplasmic reticulum stress, oxidative stress, gut microbiota, body metabolism, appetite inhibition, podocyte apoptosis, and mesenchymal stem cells are reviewed.

PTEN-induced kinase 1 deficiency alters albumin permeability and insulin signaling in podocytes

Alterations of insulin signaling in diabetes are associated with podocyte injury, proteinuria, and renal failure. Insulin stimulates glucose transport to cells and regulates other intracellular processes that are linked to cellular bioenergetics, such as autophagy, gluconeogenesis, fatty acid metabolism, and mitochondrial homeostasis. The dysfunction of mitochondrial dynamics, including mitochondrial fusion, fission, and mitophagy, has been observed in high glucose-treated podocytes and renal cells from patients with diabetes. Previous studies showed that prolonged hyperglycemia is associated with the development of insulin resistance in podocytes, and high glucose-treated podocytes exhibit an increase in mitochondrial fission and decrease in markers of mitophagy. In the present study, we found that deficiency of the main mitophagy protein PTEN-induced kinase 1 (PINK1) significantly increased albumin permeability and hampered glucose uptake to podocytes. We suggest that PINK1 inhibition impairs the insulin signaling pathway, in which lower levels of phosphorylated Akt and membrane fractions of the insulin receptor and glucose transporter-4 were observed. Moreover, PINK1-depleted podocytes exhibited lower podocin and nephrin expression, thus identifying a potential mechanism whereby albumin leakage increases under hyperglycemic conditions when mitophagy is inhibited. In conclusion, we found that PINK1 plays an essential role in insulin signaling and the maintenance of proper permeability in podocytes. Therefore, PINK1 may be a potential therapeutic target for the treatment or prevention of diabetic nephropathy.

ROCK2-induced metabolic rewiring in diabetic podocytopathy

Loss of podocytes is a common feature of diabetic renal injury and a key contributor to the development of albuminuria. We found that podocyte Rho associated coiled-coil containing protein kinase 2 (ROCK2) is activated in rodent models and patients with diabetes. Mice that lacked ROCK2 only in podocytes (PR2KO) were resistant to albuminuria, glomerular fibrosis, and podocyte loss in multiple animal models of diabetes (i.e., streptozotocin injection, db/db, and high-fat diet feeding). RNA-sequencing of ROCK2-null podocytes provided initial evidence suggesting ROCK2 as a regulator of cellular metabolism. In particular, ROCK2 serves as a suppressor of peroxisome proliferator-activated receptors α (PPARα), which rewires cellular programs to negatively control the transcription of genes involved in fatty acid oxidation and consequently induce podocyte apoptosis. These data establish ROCK2 as a nodal regulator of podocyte energy homeostasis and suggest this signaling pathway as a promising target for the treatment of diabetic podocytopathy.

ROCK2 is found to be activated in 3 diabetic models and patients with diabetes. ROCK2 deletion in podocytes protects against diabetic kidney injury, with the beneficial effect of ROCK2 inhibition observed due to rescued PPARα signaling, leading to a recovery of fatty acid metabolism.

Serum Level of Polyubiquitinated PTEN and Loss of Kidney Function in American Indians With Type 2 Diabetes

RATIONALE & OBJECTIVE

Fibrosis is a major driver of chronic kidney disease, and epithelial-mesenchymal transition (EMT) may contribute to its development. A polyubiquitinated form of phosphatase and tensin homolog (PTEN^K27polyUb) promotes EMT in vitro. Thus, it is a potentially useful biomarker of progressive kidney fibrosis and may predict loss of kidney function.

STUDY DESIGN

Observational cohort study.

SETTING & PARTICIPANTS

Southwest United States, American Indians (154 women, 80 men) with or at high risk for diabetic kidney disease (DKD).

PREDICTORS

Serum level of PTEN^K27polyUb.

OUTCOME

≥40% loss of glomerular filtration rate (GFR) or onset of kidney failure. Kidney structural measures in a subset of study participants who underwent research kidney biopsies (n = 77).

ANALYTICAL APPROACH

Cox proportional hazards models adjusted for age, sex, diabetes duration, hemoglobin A_1c (HbA_1c), blood pressure, use of renin angiotensin system (RAS) blockers, measured GFR, and albuminuria. Spearman correlations for associations with structural measures.

RESULTS

At baseline, the participants' mean age was 42.8 ± 10.5 (SD) years, diabetes duration 11.5 ± 7.1 years, mean arterial pressure 90.5 ± 9.5 mm Hg, HbA_1c 9.3 ± 2.4%, GFR 152 ± 45 mL/min, and median urinary albumin-creatinine ratio 38 (interquartile range, 14-215) mg/g. RAS blockers were being used by 64 participants (27.4%). A higher PTEN^K27polyUb value was associated with a greater risk of ≥40% loss of GFR during a median follow-up period of 6.3 years (HR for quartile 4 [Q4] vs Q1, 3.95 [95% CI, 2.23-6.98], P < 0.001). Serum PTEN^K27polyUb was associated with an increased risk of kidney failure over a median follow-up period of 15.8 years (HR for Q4 vs Q1, 5.66 [95% CI, 1.99-16.13], P = 0.001). Baseline serum PTEN^K27polyUb in the biopsy subset correlated with structural measures including glomerular basement membrane width (ρ = 0.370, P < 0.001) and mesangial fractional volume (ρ = 0.392, P < 0.001).

LIMITATIONS

Small study in single population.

CONCLUSIONS

Higher serum PTEN^K27polyUb is associated with increased risk for GFR decline and kidney failure in American Indians with type 2 diabetes.

Regulation of the Homeostatic Unfolded Protein Response in Diabetic Nephropathy

A growing body of scientific evidence indicates that protein homeostasis, also designated as proteostasis, is causatively linked to chronic diabetic nephropathy (DN). Experimental studies have demonstrated that the insulin signaling in podocytes maintain the homeostatic unfolded protein response (UPR). Insulin signaling via the insulin receptor non-canonically activates the spliced X-box binding protein-1 (sXBP1), a highly conserved endoplasmic reticulum (ER) transcription factor, which regulates the expression of genes that control proteostasis. Defective insulin signaling in mouse models of diabetes or the genetic disruption of the insulin signaling pathway in podocytes propagates hyperglycemia induced maladaptive UPR and DN. Insulin resistance in podocytes specifically promotes activating transcription factor 6 (ATF6) dependent pathogenic UPR. Akin to insulin, recent studies have identified that the cytoprotective effect of anticoagulant serine protease-activated protein C (aPC) in DN is mediated by sXBP1. In mouse models of DN, treatment with chemical chaperones that improve protein folding provides an additional benefit on top of currently used ACE inhibitors. Understanding the molecular mechanisms that transmute renal cell specific adaptive responses and that deteriorate renal function in diabetes will enable researchers to develop new therapeutic regimens for DN. Within this review, we focus on the current understanding of homeostatic mechanisms by which UPR is regulated in DN.

MicroRNAs and their delivery in diabetic fibrosis

The global prevalence of diabetes mellitus was estimated to be 463 million people in 2019 and is predicted to rise to 700 million by 2045. The associated financial and societal costs of this burgeoning epidemic demand an understanding of the pathology of this disease, and its complications, that will inform treatment to enable improved patient outcomes. Nearly two decades after the sequencing of the human genome, the significance of noncoding RNA expression is still being assessed. The family of functional noncoding RNAs known as microRNAs regulates the expression of most genes encoded by the human genome. Altered microRNA expression profiles have been observed both in diabetes and in diabetic complications. These transcripts therefore have significant potential and novelty as targets for therapy, therapeutic agents and biomarkers.

Cytoskeleton alterations in non-alcoholic fatty liver disease

BACKGROUND

Due to its extremely high prevalence and severity, non-alcoholic fatty liver disease (NALFD) is a serious health and economic concern worldwide. Developing effective methods of diagnosis and therapy demands a deeper understanding of its molecular basis. One of the strategies in such an endeavor is the analysis of alterations in the morphology of liver cells. Such alterations, widely reported in NAFLD patients and disease models, are related to the cytoskeleton. Therefore, the fate of the cytoskeleton components is useful to uncover the molecular basis of NAFLD, to further design innovative approaches for its diagnosis and therapy.

MAIN FINDINGS

Several cytoskeleton proteins are up-regulated in liver cells of NAFLD patients. Under pathological conditions, keratin 18 is released from hepatocytes and its detection in the blood emerges as a non-invasive diagnosis tool. α-Smooth muscle actin is up-regulated in hepatic stellate cells and its down-regulation has been widely tested as a potential NALFD therapeutic approach. Other cytoskeleton proteins, such as vimentin, are also up-regulated.

CONCLUSIONS

NAFLD progression involves alterations in expression levels of proteins that build the liver cytoskeleton or associate with it. These findings provide a timely opportunity of developing novel approaches for NAFLD diagnosis and therapy.