Podocyturia parallels proximal tubule dysfunction in type 2 diabetes mellitus patients independently of albuminuria and renal function decline: A cross-sectional study

Renal tubular Bim mediates the tubule-podocyte crosstalk via NFAT2 to induce podocyte cytoskeletal dysfunction

Diabetic nephropathy (DN) is mainly regarded as diabetic glomerulopathy, and its progression is tightly correlated with tubular epithelial lesions. However, the underlying molecular mechanisms linking tubular damage and glomerulopathy are poorly understood.

Methods: We previously reported that the upregulation of Bim mediated proximal tubular epithelial cell (PTEC) apoptosis and was crucial in the early stages of DN. Herein we modulated Bim expression in PTECs and subsequently determined podocyte (PC) cytoskeletal arrangement by building a Transwell co-culture system in high glucose (HG).

Results: Compared to normal glucose, exposure to 40 mM of HG for 48 h induced significant expression of Bim in PTECs and disorganization in the PC cytoskeleton. When cocultured with PTECs in HG, exacerbated filamentous actin (F-actin) rearrangement and reduced synaptopodin levels were detected in PCs. In contrast, gene knockdown of Bim in PTECs was correlated with the absence of PC cytoskeletal disorganization. NFAT2 level and its nuclear translocation in PTECs were decreased by suppressing Bim expression. Upregulating NFAT2 disrupted the beneficial effects on F-actin organization in PCs obtained by inhibiting Bim. LncRNA microarray analysis identified NONHSAT179542.1, which was implicated in Bim-mediated PC cytoskeletal disorder.

Conclusion: Our study clarified the functional role of Bim, a pro-apoptotic factor, which is involved in the crosstalk between PTECs and PCs. Bim promotes NFAT2 activation in PTECs, inducing the downregulation of lncRNA NONHSAT179542.1 in PCs, contributing to the cytoskeletal damage. Identification of the role of the Bim/NFAT2 pathway may represent a promising research direction for a better understanding of DN development.

Association between Renal Podocalyxin Expression and Renal Dysfunction in Patients with Diabetic Nephropathy: A Single-Center, Retrospective Case-Control Study

This retrospective study investigated whether podocalyxin expression in renal biopsies and urine of patients with diabetic nephropathy (DN) is associated with renal function. This retrospective study included 32 patients with nephropathy, secondary to type 2 diabetes treated at the First Hospital of Lanzhou University (January 2010 to January 2015). Compared with the control group, the DN group had a significantly lower renal expression of podocalyxin and higher urinary podocalyxin/creatinine ratio. Patients with DN were divided into the high and low expression groups according to podocalyxin expression in renal tissues. Patients in the low expression group had longer diabetes duration, lower plasma albumin and eGFR, higher glycated hemoglobin (HbA1c), 24 h urinary protein, serum creatinine, and urinary podocalyxin/creatinine ratio, and more severe glomerular, tubulointerstitial, and renal interstitial inflammation than patients in the high expression group (all P < 0.01). The renal survival rate was significantly lower in the low expression group than in the high expression group (P < 0.01). Single-factor Cox regression analysis showed that reduced podocalyxin expression and increased urinary podocalyxin excretion were associated with poor renal outcome. Measuring podocalyxin levels in renal tissues and urine could help evaluate the progression of DN.

Pro-inflammatory cytokines are associated with podocyte damage and proximal tubular dysfunction in the early stage of diabetic kidney disease in type 2 diabetes mellitus patients

AIMS

To evaluate if there is a link between inflammation (expressed by inflammatory cytokines) and the early stage of diabetic kidney disease (DKD), as shown by markers of podocyte damage and proximal tubular (PT) dysfunction.

METHODS

In this study were enrolled 117 type 2 DM patients (36-normoalbuminuria, 42-microalbuminuria, 39- macroalbuminuria), and 11 healthy subjects. Serum and urinary IL-1 alpha, IL-8, IL-18, urinary albumin:creatinine ratio (UACR), eGFR, biomarkers of podocyte damage (podocalyxin, synaptopodin, nephrin) and of PT dysfunction (KIM-1, NAG) were assessed.

RESULTS

In multivariable regression urinary Il-1 alpha correlated positively with podocalyxin and NAG (p < 0.0001, R²= 0.57); urinary IL-8 correlated directly with synaptopodin, NAG, nephrin, and KIM-1 (p < 0.0001, R² = 0.67); urinary IL-18 correlated directly with synaptopodin, NAG, and nephrin (p < 0.0001, R² = 0.59). Serum IL-1 alpha correlated positively with nephrin, synaptopodin, NAG (P < 0.0001, R² = 0.68); serum IL-8 correlated directly with synaptopodin and NAG (p < 0.0001, R² = 0.66); serum IL-18 correlated directly with NAG, KIM-1, and podocalyxin (p < 0.0001, R²=0.647).

CONCLUSIONS

Pro-inflammatory interleukins are associated with podocyte injury and PT dysfunction in early DKD. These could exert a key role in the pathogenesis of early DKD, before the development of albuminuria.

Risk factors and urinary biomarkers of non-albuminuric and albuminuric chronic kidney disease in patients with type 2 diabetes

BACKGROUND

A number of recent studies indicate a transformation in the natural course of chronic kidney disease (CKD) in type 2 diabetes (T2D) patients: an increasing prevalence of declined renal function without proceeding to the accompanying elevation of albuminuria. It has been suggested that albuminuric and non-albuminuric CKD patterns could be different in their phenotypes and pathogenic mechanisms.

AIM

To identify the risk factors and biomarkers of albuminuric and non-albuminuric patterns of CKD in patients with T2D.

METHODS

Three hundred sixty patients with T2D duration ≥ 10 years were included in this observational cross-sectional study. The associations of a panel of demographic and clinical characteristics, complications, comorbidities, and metabolic and hematology parameters with albuminuric and non-albuminuric CKD patterns were analyzed. The urinary excretion of nephrin and podocin, two podocyte-specific markers, and WAP-four-disulfide core domain protein 2 (WFDC-2), a marker of tubulointerstitial fibrosis, was determined by ELISA in comparison with healthy controls.

RESULTS

Non-albuminuric CKD was associated with age ≥ 65 years (P = 0.0001), female sex (P = 0.04), diabetes duration ≥ 15 years (P = 0.0009), and the use of diuretics (P = 0.0005). Male sex (P = 0.01), smoking (P = 0.01), waist-to-hip ratio >1.0 (P = 0.01) and hemoglobin A1c (HbA1c) > 8.0% (P = 0.005) were risk factors for elevated albuminuria not accompanied by a decrease in estimated glomerular filtration rate (eGFR). Duration of diabetes ≥ 15 years and the use of calcium channel blockers were risk factors for albuminuria with decreased eGFR (both P = 0.01). In multivariate logistic regression analysis, age, HbA1c, female sex and diuretics were significant predictors for reduced eGFR, while waist-to-hip ratio, HbA1c and male sex were associated with elevated urinary albumin-to-creatinine ratio (UACR). Excretion of nephrin and podocin was increased in patients with albuminuria, regardless of decline in renal function (P < 0.001), correlating positively with UACR. The urinary excretion of WFDC-2 was markedly higher in men than in women (P < 0.000001). Men with T2D demonstrated increased WFDC-2 levels independently of the CKD pattern (all P < 0.05). In T2D women, WFDC-2 excretion was increased in those with reduced renal function (P ≤ 0.01), correlating negatively with eGFR.

CONCLUSION

The data provide further evidence that albuminuric and non-albuminuric CKD phenotypes correspond to different pathways of diabetic kidney disease progression.

Podocyturia: why it may have added value in rare diseases

Fabry disease is an inherited lysosomal disease in which defects in the GLA gene lead to α-galactosidase-A deficiency, and accumulation of glycosphingolipids, including lyso-Gb3, a podocyte stressor. Therapy is available as enzyme replacement therapy and, for some patients, the chaperone migalastat. A key decision is when to start therapy, given its costs and potential impact on some aspects of quality of life. The decision is especially difficult in otherwise asymptomatic patients. A delayed start of therapy may allow kidney injury to progress subclinically up to the development of irreversible lesions. Non-invasive tools to monitor subclinical kidney injury are needed. One such tool may be assessment of podocyturia. In this issue of CKJ, [Trimarchi H, Canzonieri R, Costales-Collaguazo C et al. Early decrease in the podocalyxin to synaptopodin ratio in urinary Fabry podocytes. Clin Kidney J 2019; doi.org/10.1093/ckj/sfy053] report on podocyturia assessment in Fabry nephropathy. Specifically, they report that podocalyxin may be lost from detached urinary podocytes.

Deregulated profiles of urinary microRNAs may explain podocyte injury and proximal tubule dysfunction in normoalbuminuric patients with type 2 diabetes mellitus

MicroRNAs (miRNAs) are short non-coding RNA species that are important post-transcriptional regulators of gene expression. The aim of the study was to establish a potential explanation of podocyte damage and proximal tubule (PT) dysfunction induced by deregulated miRNAs expression in the course of type 2 diabetes mellitus (DM). A total of 68 patients with type 2 DM and 11 healthy subjects were enrolled in a cross-sectional study and assessed concerning urinary albumin:creatinine ratio (UACR), urinary N-acetyl-β-D-glucosamininidase (NAG), urinary kidney injury molecule-1, urinary nephrin, podocalyxin, synaptopodin, estimated glomerular filtration rate (eGFR), urinary miRNA21, miRNA124, and miRNA192. In univariable regression analysis, miRNA21, miRNA124, and miRNA192 correlated with urinary nephrin, synaptopodin, podocalyxin, NAG, KIM-1, UACR, and eGFR. Multivariable regression analysis yielded models in which miRNA192 correlated with synaptopodin, uNAG, and eGFR (R²=0.902; P<0.0001), miRNA124 correlated with synaptopodin, uNAG, UACR, and eGFR (R²=0.881; P<0.0001), whereas miRNA21 correlated with podocalyxin, uNAG, UACR, and eGFR (R²=0.882; P<0.0001). Urinary miRNA192 expression was downregulated, while urinary miRNA21 and miRNA124 expressions were upregulated. In patients with type 2 DM, there is an association between podocyte injury and PT dysfunction, and miRNA excretion, even in the normoalbuminuria stage. This observation documents a potential role of the urinary profiles of miRNA21, miRNA124, and miRNA192 in early DN. Despite their variability across the segments of the nephron, urinary miRNAs may be considered as a reliable tool for the identification of novel biomarkers in order to characterize the genetic pattern of podocyte damage and PT dysfunction in early DN of type 2 DM.

Podocytes from the diagnostic and therapeutic point of view

The central role of podocytes in glomerular diseases makes this cell type an interesting diagnostic tool as well as a therapeutic target. In this review, we discuss the current literature on the use of podocytes and podocyte-specific markers as non-invasive diagnostic tools in different glomerulopathies. Furthermore, we highlight the direct effects of drugs currently used to treat primary glomerular diseases and describe their direct cellular effects on podocytes. A new therapeutic potential is seen in drugs targeting the podocytic actin cytoskeleton which is essential for podocyte foot process structure and function. Incubation of cultured human podocyte cell lines with sera from patients with active glomerular diseases is currently also used to identify novel circulating factors with pathophysiological relevance for the glomerular filtration barrier. In addition, treatment of detached urinary podocytes from patients with substances that restore their cytoskeleton might serve as a novel personalized tool to estimate their potential for podocyte recovery ex vivo.

Urinary podocyte-associated mRNA levels correlate with proximal tubule dysfunction in early diabetic nephropathy of type 2 diabetes mellitus

AIM

The study assessed mRNA expression of podocyte-associated molecules in urinary sediments of patients with type 2 diabetes mellitus (DM) in relation to urinary podocytes, biomarkers of podocyte injury and of proximal tubule (PT) dysfunction.

METHODS

A total of 76 patients with type 2 DM and 20 healthy subjects were enrolled in a cross-sectional study, and assessed concerning urinary podocytes, urinary mRNA of podocyte-associated genes, urinary biomarkers of podocyte damage and of PT dysfunction.

RESULTS

We found significant differences between urinary mRNA of podocyte-associated molecules in relation with albuminuria stage. In multivariable regression analysis, urinary mRNA of nephrin, podocin, alpha-actinin-4, CD2-associated protein, glomerular epithelial protein 1 (GLEPP1), ADAM 10, and NFκB correlated directly with urinary podocytes, albuminuria, urinary alpha₁-microglobulin, urinary kidney-injury molecule-1, nephrinuria, urinary vascular endothelial growth factor, urinary advanced glycation end-products (AGE), and indirectly with eGFR (p < 0.0001, R² = 0.808; p < 0.0001, R² = 0.825; p < 0.0001, R² = 0.805; p < 0.0001, R² = 0.663; p < 0.0001, R² = 0.726; p < 0.0001, R² = 0.720; p < 0.0001, R² = 0.724).

CONCLUSIONS

In patients with type 2 DM there is an association between urinary mRNA of podocyte-associated molecules, biomarkers of podocyte damage, and of PT dysfunction. GLEPP1, ADAM10, and NFκB may be considered additional candidate molecules indicative of early diabetic nephropathy. AGE could be involved in this association.