Pathogenesis of diabesity-induced kidney disease: role of kidney nutrient sensing

Renal Mitochondrial ATP Transporter Ablation Ameliorates Obesity-Induced CKD

SIGNIFICANCE STATEMENT

This study sheds light on the central role of adenine nucleotide translocase 2 (ANT2) in the pathogenesis of obesity-induced CKD. Our data demonstrate that ANT2 depletion in renal proximal tubule cells (RPTCs) leads to a shift in their primary metabolic program from fatty acid oxidation to aerobic glycolysis, resulting in mitochondrial protection, cellular survival, and preservation of renal function. These findings provide new insights into the underlying mechanisms of obesity-induced CKD and have the potential to be translated toward the development of targeted therapeutic strategies for this debilitating condition.

BACKGROUND

The impairment in ATP production and transport in RPTCs has been linked to the pathogenesis of obesity-induced CKD. This condition is characterized by kidney dysfunction, inflammation, lipotoxicity, and fibrosis. In this study, we investigated the role of ANT2, which serves as the primary regulator of cellular ATP content in RPTCs, in the development of obesity-induced CKD.

METHODS

We generated RPTC-specific ANT2 knockout ( RPTC-ANT2-/- ) mice, which were then subjected to a 24-week high-fat diet-feeding regimen. We conducted comprehensive assessment of renal morphology, function, and metabolic alterations of these mice. In addition, we used large-scale transcriptomics, proteomics, and metabolomics analyses to gain insights into the role of ANT2 in regulating mitochondrial function, RPTC physiology, and overall renal health.

RESULTS

Our findings revealed that obese RPTC-ANT2-/- mice displayed preserved renal morphology and function, along with a notable absence of kidney lipotoxicity and fibrosis. The depletion of Ant2 in RPTCs led to a fundamental rewiring of their primary metabolic program. Specifically, these cells shifted from oxidizing fatty acids as their primary energy source to favoring aerobic glycolysis, a phenomenon mediated by the testis-selective Ant4.

CONCLUSIONS

We propose a significant role for RPTC-Ant2 in the development of obesity-induced CKD. The nullification of RPTC-Ant2 triggers a cascade of cellular mechanisms, including mitochondrial protection, enhanced RPTC survival, and ultimately the preservation of kidney function. These findings shed new light on the complex metabolic pathways contributing to CKD development and suggest potential therapeutic targets for this condition.

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.

Inhibition of Amino Acids Influx into Proximal Tubular Cells Improves Lysosome Function in Diabetes

Key Points

Collectrin serves as a chaperone for the trafficking of neutral amino acid (AA) transporters in the apical membranes of proximal tubular cells (PTCs). Cltrn knockout reduced AAs influx into PTCs, inactivated mTOR, activated transcription factor EB, improved lysosome function, and ameliorated vacuolar formation of PTCs in diabetic mice treated with streptozotocin and high-fat diet. The inhibition of neutral AA transporter, such as B0AT1 (SLC6A19), and transcription factor EB activator is a new therapeutic strategy against diabetic kidney disease.

Background

Inhibition of glucose influx into proximal tubular cells (PTCs) by sodium–glucose cotransporter 2 inhibitors revealed prominent therapeutic effects on diabetic kidney disease. Collectrin (CLTRN) serves as a chaperone for the trafficking of neutral amino acid (AA) transporters in the apical membranes of PTCs. We investigated the beneficial effects of reduced influx of AAs into PTCs in diabetes and obesity model of Cltrn−/y mice.

Methods

Cltrn+/y and Cltrn−/y mice at age 5 weeks were assigned to standard diet and streptozotocin and high-fat diet (STZ-HFD)–treated groups.

Results

At age 22–23 weeks, body weight and HbA1c levels significantly increased in STZ-HFD-Cltrn+/y compared with standard diet-Cltrn+/y; however, they were not altered in STZ-HFD-Cltrn−/y compared with STZ-HFD-Cltrn+/y. At age 20 weeks, urinary albumin creatinine ratio was significantly reduced in STZ-HFD-Cltrn−/y compared with STZ-HFD-Cltrn+/y. Under the treatments with STZ and HFD, the Cltrn gene deficiency caused significant increase in urinary concentration of AAs such as Gln, His, Gly, Thr, Tyr, Val, Trp, Phe, Ile, Leu, and Pro. In PTCs in STZ-HFD-Cltrn+/y, the enlarged lysosomes with diameter of 10 μ m or more were associated with reduced autolysosomes, and the formation of giant lysosomes was prominently suppressed in STZ-HFD-Cltrn−/y. Phospho-mTOR and inactive form of phospho-transcription factor EB were reduced in STZ-HFD-Cltrn−/y compared with STZ-HFD-Cltrn+/y.

Conclusions

The reduction of AAs influx into PTCs inactivated mTOR, activated transcription factor EB, improved lysosome function, and ameliorated vacuolar formation of PTCs in STZ-HFD-Cltrn−/y mice.

Renal Endocannabinoid Dysregulation in Obesity-Induced Chronic Kidney Disease in Humans

The endocannabinoid system (ECS) regulates various physiological processes, including energy homeostasis and kidney function. ECS upregulation in obese animals and humans suggests a potential link to obesity-induced chronic kidney disease (CKD). However, obesity-induced ECS changes in the kidney are mainly studied in rodents, leaving the impact on obese humans unknown. In this study, a total of 21 lean and obese males (38-71 years) underwent a kidney biopsy. Biochemical analysis, histology, and endocannabinoid (eCB) assessment were performed on kidney tissue and blood samples. Correlations between different parameters were evaluated using a comprehensive matrix. The obese group exhibited kidney damage, reflected in morphological changes, and elevated kidney injury and fibrotic markers. While serum eCB levels were similar between the lean and obese groups, kidney eCB analysis revealed higher anandamide in obese patients. Obese individuals also exhibited reduced expression of cannabinoid-1 receptor (CB1R) in the kidney, along with increased activity of eCB synthesizing and degrading enzymes. Correlation analysis highlighted connections between renal eCBs, kidney injury markers, obesity, and related pathologies. In summary, this study investigates obesity's impact on renal eCB "tone" in humans, providing insights into the ECS's role in obesity-induced CKD. Our findings enhance the understanding of the intricate interplay among obesity, the ECS, and kidney function.

Cannabinoid Signaling in Kidney Disease

Endocannabinoid signaling plays crucial roles in human physiology in the function of multiple systems. The two cannabinoid receptors, CB1 and CB2, are cell membrane proteins that interact with both exogenous and endogenous bioactive lipid ligands, or endocannabinoids. Recent evidence has established that endocannabinoid signaling operates within the human kidney, as well as suggests the important role it plays in multiple renal pathologies. CB1, specifically, has been identified as the more prominent ECS receptor within the kidney, allowing us to place emphasis on this receptor. The activity of CB1 has been repeatedly shown to contribute to both diabetic and non-diabetic chronic kidney disease (CKD). Interestingly, recent reports of acute kidney injury (AKI) have been attributed to synthetic cannabinoid use. Therefore, the exploration of the ECS, its receptors, and its ligands can help provide better insight into new methods of treatment for a range of renal diseases. This review explores the endocannabinoid system, with a focus on its impacts within the healthy and diseased kidney.

Management of diabesity: Current concepts

The global prevalence of obesity is increasing rapidly with an exponential rise in incidence of type 2 diabetes mellitus in recent years. ‘Diabesity’, the term coined to show the strong interlink between obesity and diabetes, is the direct cons-equence of the obesity pandemic, and poses significant challenges in the management of the disease. Without addressing the clinical and mechanistic complications of obesity such as metabolic-associated fatty liver disease and obstructive sleep apnoea, a rational management algorithm for diabesity cannot be developed. Several classes of anti-diabetic medications including insulins, sulphonylureas, thiazolidinediones and meglitinides are associated with the risk of weight gain and may potentially worsen diabesity. Therefore, appropriate selection of antidiabetic drug regimen is crucial in the medical management of diabesity. The role of non-pharmacological measures such as dietary adjustments, exercise interventions and bariatric procedures should also be emphasised. Unfortunately, the importance of appropriate and optimal management of diabesity is often overlooked by medical professionals when achieving adequate glycemic control which results in inappropriate management of the disease and its complications. This review provides a narrative clinical update on the evidence behind the management of diabesity.

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.

Kidney Proximal Tubule GLUT2-More than Meets the Eye

Tubulopathy plays a central role in the pathophysiology of diabetic kidney disease (DKD). Under diabetic conditions, the kidney proximal tubule cells (KPTCs) are exposed to an extensive amount of nutrients, most notably glucose; these nutrients deteriorate KPTCs function and promote the development and progression of DKD. Recently, the facilitative glucose transporter 2 (GLUT2) in KPTCs has emerged as a central regulator in the pathogenesis of DKD. This has been demonstrated by identifying its specific role in enhancing glucose reabsorption and glucotoxicity, and by deciphering its effect in regulating the expression of the sodium-glucose transporter 2 (SGLT2) in KPTCs. Moreover, reduction/deletion of KPTC-GLUT2 has been recently found to ameliorate DKD, raising the plausible idea of considering it as a therapeutic target against DKD. However, the underlying molecular mechanisms by which GLUT2 exerts its deleterious effects in KPTCs remain vague. Herein, we review the current findings on the proximal tubule GLUT2 biology and function under physiologic conditions, and its involvement in the pathophysiology of DKD. Furthermore, we shed new light on its cellular regulation during diabetic conditions.

Urinary metabolite profiling and risk of progression of diabetic nephropathy in 2670 individuals with type 1 diabetes

AIMS/HYPOTHESIS

This prospective, observational study examines associations between 51 urinary metabolites and risk of progression of diabetic nephropathy in individuals with type 1 diabetes by employing an automated NMR metabolomics technique suitable for large-scale urine sample collections.

METHODS

We collected 24-h urine samples for 2670 individuals with type 1 diabetes from the Finnish Diabetic Nephropathy study and measured metabolite concentrations by NMR. Individuals were followed up for 9.0 ± 5.0 years until their first sign of progression of diabetic nephropathy, end-stage kidney disease or study end. Cox regressions were performed on the entire study population (overall progression), on 1999 individuals with normoalbuminuria and 347 individuals with macroalbuminuria at baseline.

RESULTS

Seven urinary metabolites were associated with overall progression after adjustment for baseline albuminuria and chronic kidney disease stage (p < 8 × 10^-4): leucine (HR 1.47 [95% CI 1.30, 1.66] per 1-SD creatinine-scaled metabolite concentration), valine (1.38 [1.22, 1.56]), isoleucine (1.33 [1.18, 1.50]), pseudouridine (1.25 [1.11, 1.42]), threonine (1.27 [1.11, 1.46]) and citrate (0.84 [0.75, 0.93]). 2-Hydroxyisobutyrate was associated with overall progression (1.30 [1.16, 1.45]) and also progression from normoalbuminuria (1.56 [1.25, 1.95]). Six amino acids and pyroglutamate were associated with progression from macroalbuminuria.

CONCLUSIONS/INTERPRETATION

Branched-chain amino acids and other urinary metabolites were associated with the progression of diabetic nephropathy on top of baseline albuminuria and chronic kidney disease. We found differences in associations for overall progression and progression from normo- and macroalbuminuria. These novel discoveries illustrate the utility of analysing urinary metabolites in entire population cohorts.

[Oxymatrine improves renal fibrosis and inflammation in diabetic rats by modulating CHK1/2 phosphorylation]

OBJECTIVE

To explore the role of cell cycle checkpoint kinase 1/2 (CHK1/2) in mediating the inhibitory effect of oxymatrine (OMT) against renal inflammation and fibrosis in diabetic rats.

METHODS

SD rats were randomly divided into normal control group, diabetes model group (DM) and OMT treatment group (n=6). HE and Masson staining were used to observe histopathological changes of the renal tissue, and the expressions of CHK1, CHK2, p-CHK1 and p-CHK2 were localized by immunohistochemical staining. The contents of interleukin-6 (IL-6) and IL-1β in the renal tissue were detected using ELISA, and the expression levels of CHK1, CHK2, p-CHK1, p-CHK2, type Ⅲ collagen (Col-Ⅲ), type Ⅳ collagen (Col-Ⅳ), and fibronectin (FN) were determined using Western blotting. The changes in the expressions of CHK1, CHK2, p-CHK1, p-CHK2, Col-Ⅲ, Col-Ⅳ and FN proteins were also examined with Western blotting in NRK-52E cells in response to high glucose exposure, OMT treatment and siRNA-mediated CHK1/2 knockdown.

RESULTS

In diabetic rats, OMT treatment significantly decreased the levels of blood glucose, serum creatinine and 24 h urinary protein (P < 0.05) and obviously improved inflammatory cell infiltration and fibrosis phenotype in the renal tissue (P < 0.05). CHK1 and CHK2 were mainly expressed in the cytoplasm and nuclei of renal tubule cells, and their phosphorylation levels were significantly higher in DM group than in the control group and OMT group. OMT treatment significantly decreased the protein expression levels of p-CHK1, p-CHK2, Col-Ⅲ, Col-Ⅳ and FN in the renal tissue of diabetic rats and in NRK-52E cells exposed to high glucose (P < 0.05). In NRK-52E cells, CHK1/2 knockdown resulted in significant reduction of the protein expressions of p-CHK1/2, Col-Ⅲ, Col-Ⅳ and FN (P < 0.05).

CONCLUSION

The inhibitory effects of OMT against renal inflammation and fibrosis in diabetic rats are mediated probably by lowered phosphorylation levels of CHK1 and CHK2, which result in reduced release of the downstream inflammatory mediators and decreased secretion and deposition of extracellular matrix.

Heterozygous Nme7 Mutation Affects Glucose Tolerance in Male Rats

Complex metabolic conditions such as type 2 diabetes and obesity result from the interaction of numerous genetic and environmental factors. While the family of Nme proteins has been connected so far mostly to development, proliferation, or ciliary functions, several lines of evidence from human and experimental studies point to the potential involvement of one of its members, NME7 (non-metastatic cells 7, nucleoside diphosphate kinase 7) in carbohydrate and lipid metabolism. As a complete lack of Nme7 is semilethal in rats, we compared morphometric, metabolic, and transcriptomic profiles of standard diet-fed heterozygous Nme7+/− on male rats vs. their wild-type Nme7+/+ controls. Nme7+/− animals showed increased body weight, adiposity, higher insulin levels together with decreased glucose tolerance. Moreover, they displayed pancreatic islet fibrosis and kidney tubular damage. Despite no signs of overt liver steatosis or dyslipidemia, we found significant changes in the hepatic transcriptome of Nme7+/− male rats with a concerted increase of expression of lipogenic enzymes including Scd1, Fads1, Dhcr7 and a decrease of Cyp7b1 and Nme7. Network analyses suggested possible links between Nme7 and the activation of Srebf1 and Srebf2 upstream regulators. These results further support the implication of NME7 in the pathogenesis of glucose intolerance and adiposity.