Activation of TRPC6 by AngⅡ Induces Podocyte Injury and Participates in Proteinuria of Nephrotic Syndrome

Association of serum calcium levels with diabetic kidney disease in normocalcemic type 2 diabetes patients: a cross-sectional study

To explore the association between serum calcium levels within normal ranges and Diabetic Kidney Disease (DKD) in type 2 diabetes patients. In this cross-sectional study, we analyzed clinical data from type 2 diabetes patients admitted to the Endocrinology Department of the Affiliated Hospital of Qingdao University from January 1, 2021, to December 1, 2022. We measured serum calcium levels, corrected for albumin, and screened for diabetes-related complications, including DKD. The association between corrected serum calcium levels and DKD was evaluated using logistic regression, with adjustments made for potential confounders and a generalized additive model (GAM) to explore non-linear relationships, supplemented by subgroup analyses. Among the 3016 patients (52.55% male, 47.45% female), the mean corrected serum calcium was 2.29 ± 0.08 mmol/L. DKD was present in 38.73% of patients. A 0.1 mmol/L increase in corrected serum calcium was associated with a 44% increased risk of DKD (OR = 1.44, 95% CI 1.28-1.61, p < 0.0001). The GAM indicated a linear relationship between corrected serum calcium and DKD risk, consistent across subgroups. Corrected serum calcium levels were linearly associated with DKD risk in type 2 diabetes patients, underlining its potential role in risk assessment. These findings emphasize the clinical importance of monitoring serum calcium levels. However, the need for further prospective studies to confirm these findings is underscored by the study's cross-sectional design.

Klotho Stabilizes the Podocyte Actin Cytoskeleton in Idiopathic Membranous Nephropathy through Regulating the TRPC6/CatL Pathway

INTRODUCTION

The aim of this study was to explore the renoprotective effects of Klotho on podocyte injury mediated by complement activation and autoantibodies in idiopathic membranous nephropathy (IMN).

METHODS

Rat passive Heymann nephritis (PHN) was induced as an IMN model. Urine protein levels, serum biochemistry, kidney histology, and podocyte marker levels were assessed. In vitro, sublytic podocyte injury was induced by C5b-9. The expression of Klotho, transient receptor potential channel 6 (TRPC6), and cathepsin L (CatL); its substrate synaptopodin; and the intracellular Ca2+ concentration were detected via immunofluorescence. RhoA/ROCK pathway activity was measured by an activity quantitative detection kit, and the protein expression of phosphorylated-LIMK1 (p-LIMK1) and p-cofilin in podocytes was detected via Western blotting. Klotho knockdown and overexpression were performed to evaluate its role in regulating the TRPC6/CatL pathway.

RESULTS

PHN rats exhibited proteinuria, podocyte foot process effacement, decreased Klotho and Synaptopodin levels, and increased TRPC6 and CatL expression. The RhoA/ROCK pathway was activated by the increased phosphorylation of LIMK1 and cofilin. Similar changes were observed in C5b-9-injured podocytes. Klotho knockdown exacerbated podocyte injury, while Klotho overexpression partially ameliorated podocyte injury.

CONCLUSION

Klotho may protect against podocyte injury in IMN patients by inhibiting the TRPC6/CatL pathway. Klotho is a potential target for reducing proteinuria in IMN patients.

tRNA-Derived Small RNAs: A Novel Regulatory Small Noncoding RNA in Renal Diseases

Background

tRNA-derived small RNAs (tsRNAs) are an emerging class of small noncoding RNAs derived from tRNA cleavage.

Summary

With the development of high-throughput sequencing, various biological roles of tsRNAs have been gradually revealed, including regulation of mRNA stability, transcription, translation, direct interaction with proteins and as epigenetic factors, etc. Recent studies have shown that tsRNAs are also closely related to renal disease. In clinical acute kidney injury (AKI) patients and preclinical AKI models, the production and differential expression of tsRNAs in renal tissue and plasma were observed. Decreased expression of tsRNAs was also found in urine exosomes from chronic kidney disease patients. Dysregulation of tsRNAs also appears in models of nephrotic syndrome and patients with lupus nephritis. And specific tsRNAs were found in high glucose model in vitro and in serum of diabetic nephropathy patients. In addition, tsRNAs were also differentially expressed in patients with kidney cancer and transplantation.

Key Messages

In the present review, we have summarized up-to-date works and reviewed the relationship and possible mechanisms between tsRNAs and kidney diseases.

Store-operated Ca2+ entry inhibition ameliorates high glucose and ANG II-induced podocyte apoptosis and mitochondrial damage

Hyperglycemia and increased activity of the renal angiotensin II (ANG II) system are two primary pathogenic stimuli for the onset and progression of podocyte injury in diabetic nephropathy. However, the underlying mechanisms are not fully understood. Store-operated Ca2+ entry (SOCE) is an important mechanism that helps maintain cell Ca2+ homeostasis in both excitable and nonexcitable cells. Our previous study demonstrated that high glucose (HG) enhanced podocyte SOCE (1). It is also known that ANG II activates SOCE by releasing endoplasmic reticulum Ca2+. However, the role of SOCE in stress-induced podocyte apoptosis and mitochondrial dysfunction remains unclear. The present study was aimed to determine whether enhanced SOCE mediated HG- and ANG II-induced podocyte apoptosis and mitochondrial damage. In kidneys of mice with diabetic nephropathy, the number of podocytes was significantly reduced. In cultured human podocytes, both HG and ANG II treatment induced podocyte apoptosis, which was significantly blunted by an SOCE inhibitor, BTP2. Seahorse analysis showed that podocyte oxidative phosphorylation in response to HG and ANG II was impaired. This impairment was significantly alleviated by BTP2. The SOCE inhibitor, but not a transient receptor potential cation channel subfamily C member 6 inhibitor, significantly blunted the damage of podocyte mitochondrial respiration induced by ANG II treatment. Furthermore, BTP2 reversed impaired mitochondrial membrane potential and ATP production and enhanced mitochondrial superoxide generation induced by HG treatment. Finally, BTP2 prevented the overwhelming Ca2+ uptake in HG-treated podocytes. Taken together, our results suggest that enhanced SOCE mediated HG- and ANG II-induced podocyte apoptosis and mitochondrial injury.NEW & NOTEWORTHY This study tested the hypothesis that overwhelming store-operated Ca2+ entry is a novel mechanism contributing to high glucose- and angiotensin II-induced podocyte apoptosis and mitochondrial injury.

Effects of a Losartan-Antioxidant Hybrid (GGN1231) on Vascular and Cardiac Health in an Experimental Model of Chronic Renal Failure

Drugs providing antihypertensive and protective cardiovascular actions are of clinical interest in controlling cardiovascular events and slowing the progression of kidney disease. We studied the effect of a hybrid compound, GGN1231 (derived from losartan in which a powerful antioxidant was attached), on the prevention of cardiovascular damage, cardiac hypertrophy, and fibrosis in a rat model of severe chronic renal failure (CRF). CRF by a 7/8 nephrectomy was carried out in male Wistar rats fed with a diet rich in phosphorous (0.9%) and normal calcium (0.6%) for a period of 12 weeks until sacrifice. In week 8, rats were randomized in five groups receiving different drugs including dihydrocaffeic acid as antioxidant (Aox), losartan (Los), dihydrocaffeic acid+losartan (Aox+Los) and GGN1231 as follows: Group 1 (CRF+vehicle group), Group 2 (CRF+Aox group), Group 3 (CRF+Los group), Group 4 (CRF+Aox+Los group), and Group 5 (CRF+GGN1231 group). Group 5, the CRF+GGN1231 group, displayed reduced proteinuria, aortic TNF-α, blood pressure, LV wall thickness, diameter of the cardiomyocytes, ATR1, cardiac TNF-α and fibrosis, cardiac collagen I, and TGF-β1 expression. A non-significant 20% reduction in the mortality was also observed. This study showed the possible advantages of GGN1231, which could help in the management of cardiovascular and inflammatory processes. Further research is needed to confirm and even expand the positive aspects of this compound.