Podocyte detachment and reduced glomerular capillary endothelial fenestration in human type 1 diabetic nephropathy

Correlation of light and electron microscopic morphometric parameters of glomerular capillaries with serum creatinine and proteinuria

Waste products in the bloodstream are filtered by the glomerular capillaries in the kidneys and excreted into the urine. When making a differential diagnosis of kidney diseases, structural assessment of glomeruli using histological, ultrastructural, and immunological studies is crucial. This study assessed the microscopic and ultrastructural morphometric parameters of glomerular capillaries and examined their correlation with serum creatinine and proteinuria. A total of 60 kidney biopsy cases received by the transmission electron microscope (TEM) laboratory for diagnosis were included in the study. Toluidine blue stained 300 nm thick sections of TEM tissue blocks were scanned for glomerular morphometry by a whole slide imaging system, and the estimation of Bowman's capsule (BC) area, glomerular capillary lumen diameter (GCLD), glomerular capillary density (GCD), glomerular capillary surface area density (GCSA), and percentage of glomerular capillary lumen space (%GCLS) was performed with QuPath software. TEM images of 70 nm thick sections were used for the evaluation of endothelial fenestration diameter (EFD), glomerular basement membrane (GBM) thickness, and podocyte foot process (PFP) effacement. Proteinuria and serum creatinine showed positive correlations with GBM thickness and PFP effacement. Negative correlations of serum creatinine were observed with EFD, %GCLS, and GCSA. Hence, glomerular filtration is greatly affected by the total area of the glomerular capillary surface and structural changes of GBM. Reduction of glomerulus filtration due to foot process effacement and thickening of GBM results in damage to the filtration barrier leading to the leakage of plasma protein into urine.

IGFBP2 induces podocyte apoptosis promoted by mitochondrial damage via integrin α5/FAK in diabetic kidney disease

Podocyte apoptosis or loss is the pivotal pathological characteristic of diabetic kidney disease (DKD). Insulin-like growth factor-binding protein 2 (IGFBP2) have a proinflammatory and proapoptotic effect on diseases. Previous studies have shown that serum IGFBP2 level significantly increased in DKD patients, but the precise mechanisms remain unclear. Here, we found that IGFBP2 levels obviously increased under a diabetic state and high glucose stimuli. Deficiency of IGFBP2 attenuated the urine protein, renal pathological injury and glomeruli hypertrophy of DKD mice induced by STZ, and knockdown or deletion of IGFBP2 alleviated podocytes apoptosis induced by high concentration of glucose or in DKD mouse. Furthermore, IGFBP2 facilitated apoptosis, which was characterized by increase in inflammation and oxidative stress, by binding with integrin α5 (ITGA5) of podocytes, and then activating the phosphorylation of focal adhesion kinase (FAK)-mediated mitochondrial injury, including membrane potential decreasing, ROS production increasing. Moreover, ITGA5 knockdown or FAK inhibition attenuated the podocyte apoptosis caused by high glucose or IGFBP2 overexpression. Taken together, these findings unveiled the insight mechanism that IGFBP2 increased podocyte apoptosis by mitochondrial injury via ITGA5/FAK phosphorylation pathway in DKD progression, and provided the potential therapeutic strategies for diabetic kidney disease.

Association of podocyte ultrastructural changes with proteinuria and pathological classification in type 2 diabetic nephropathy

AIMS

Podocyte injury plays an essential role in the progression of diabetic nephropathy (DN). The associations between the ultrastructural changes of podocyte with proteinuria and the pathological classification of DN proposed by Renal Pathology Society (RPS) have not been clarified in patients with type 2 diabetic nephropathy (T2DN).

METHODS

We collected 110 patients with kidney biopsy-confirmed T2DN at Peking University First Hospital from 2017 to 2022. The morphometric analysis on the podocyte foot process width (FPW) and podocyte detachment (PD) as markers of podocyte injury was performed, and the correlations between the ultrastructural changes of podocytes with severity of proteinuria and the RPS pathological classification of DN were analyzed.

RESULTS

Mean FPW was significantly broader in the group of T2DN patients with nephrotic proteinuria (565.1 nm) than those with microalbuminuria (437.4 nm) or overt proteinuria (494.6 nm). The cut-off value of FPW (> 506 nm) could differentiate nephrotic proteinuria from non-nephrotic proteinuria with a sensitivity of 75.3% and a specificity of 75.8%. Percentage of PD was significantly higher in group of nephrotic proteinuria (3.2%) than that in microalbuminuria (0%) or overt proteinuria (0.2%). FPW and PD significantly correlated with proteinuria in T2DN (r = 0.473, p < 0.001 and r = 0.656, P < 0.001). FPW and PD correlated with RPS pathological classification of T2DN (r = 0.179, P = 0.014 and r = 0.250, P = 0.001). FPW value was increased significantly with more severe DN classification (P for trend =0.007). The percentage of PD tended to increase with more severe DN classification (P for trend = 0.017).

CONCLUSIONS

Podocyte injury, characterized by FPW broadening and PD, was associated with the severity of proteinuria and the pathological classification of DN.

Esm-1 mediates transcriptional polarization associated with diabetic kidney disease

Esm-1, endothelial cell-specific molecule-1, is a susceptibility gene for diabetic kidney disease (DKD) and is a secreted proteoglycan, with notable expression in kidney, which attenuates inflammation and albuminuria. However, little is known about Esm1 expression in mature tissues in the presence or absence of diabetes. We utilized publicly available single-cell RNA sequencing data to characterize Esm1 expression in 27,786 renal endothelial cells (RECs) obtained from three mouse and four human databases. We validated our findings using bulk transcriptome data from 20 healthy subjects and 41 patients with DKD and using RNAscope. In both mice and humans, Esm1 is expressed in a subset of all REC types and represents a minority of glomerular RECs. In patients, Esm1(+) cells exhibit conserved enrichment for blood vessel development genes. With diabetes, these cells are fewer in number and shift expression toward chemotaxis pathways. Esm1 correlates with a majority of genes within these pathways, delineating a glomerular transcriptional polarization reflected by the magnitude of Esm1 deficiency. Diabetes correlates with lower Esm1 expression and with changes in the functional characterization of Esm1(+) cells. Thus, Esm1 appears to be a marker for glomerular transcriptional polarization in DKD.NEW & NOTEWORTHY Esm-1 is primarily expressed in glomerular endothelium in humans. Cells expressing Esm1 exhibit a high degree of conservation in the enrichment of genes related to blood vessel development. In the context of diabetes, these cells are reduced in number and show a significant transcriptional shift toward the chemotaxis pathway. In diabetes, there is a transcriptional polarization in the glomerulus that is reflected by the degree of Esm1 deficiency.

Development of an automated estimation of foot process width using deep learning in kidney biopsies from patients with Fabry, minimal change, and diabetic kidney diseases

Podocyte injury plays a key role in pathogenesis of many kidney diseases with increased podocyte foot process width (FPW), an important measure of podocyte injury. Unfortunately, there is no consensus on the best way to estimate FPW and unbiased stereology, the current gold standard, is time consuming and not widely available. To address this, we developed an automated FPW estimation technique using deep learning. A U-Net architecture variant model was trained to semantically segment the podocyte-glomerular basement membrane interface and filtration slits. Additionally, we employed a post-processing computer vision approach to accurately estimate FPW. A custom segmentation utility was also created to manually classify these structures on digital electron microscopy (EM) images and to prepare a training dataset. The model was applied to EM images of kidney biopsies from 56 patients with Fabry disease, 15 with type 2 diabetes, 10 with minimal change disease, and 17 normal individuals. The results were compared with unbiased stereology measurements performed by expert technicians unaware of the clinical information. FPW measured by deep learning and by the expert technicians were highly correlated and not statistically different in any of the studied groups. A Bland-Altman plot confirmed interchangeability of the methods. FPW measurement time per biopsy was substantially reduced by deep learning. Thus, we have developed a novel validated deep learning model for FPW measurement on EM images. The model is accessible through a cloud-based application making calculation of this important biomarker more widely accessible for research and clinical applications.

The Role of α3β1 Integrin Modulation on Fabry Disease Podocyte Injury and Kidney Impairment

Podocyte dysfunction plays a crucial role in renal injury and is identified as a key contributor to proteinuria in Fabry disease (FD), primarily impacting glomerular filtration function (GFF). The α3β1 integrins are important for podocyte adhesion to the glomerular basement membrane, and disturbances in these integrins can lead to podocyte injury. Therefore, this study aimed to assess the effects of chloroquine (CQ) on podocytes, as this drug can be used to obtain an in vitro condition analogous to the FD. Murine podocytes were employed in our experiments. The results revealed a dose-dependent reduction in cell viability. CQ at a sub-lethal concentration (1.0 µg/mL) induced lysosomal accumulation significantly (p < 0.0001). Morphological changes were evident through scanning electron microscopy and immunofluorescence, highlighting alterations in F-actin and nucleus morphology. No significant changes were observed in the gene expression of α3β1 integrins via RT-qPCR. Protein expression of α3 integrin was evaluated with Western Blotting and immunofluorescence, demonstrating its lower detection in podocytes exposed to CQ. Our findings propose a novel in vitro model for exploring secondary Fabry nephropathy, indicating a modulation of α3β1 integrin and morphological alterations in podocytes under the influence of CQ.

Insight into the Molecular Mechanism of Diabetic Kidney Disease and the Role of Metformin in Its Pathogenesis

Diabetic kidney disease (DKD) is one of the leading causes of death among patients diagnosed with diabetes mellitus. Despite the growing knowledge about the pathogenesis of DKD, we still do not have effective direct pharmacotherapy. Accurate blood sugar control is essential in slowing down DKD. It seems that metformin has a positive impact on kidneys and this effect is not only mediated by its hypoglycemic action, but also by direct molecular regulation of pathways involved in DKD. The molecular mechanism of DKD is complex and we can distinguish polyol, hexosamine, PKC, and AGE pathways which play key roles in the development and progression of this disease. Each of these pathways is overactivated in a hyperglycemic environment and it seems that most of them may be regulated by metformin. In this article, we summarize the knowledge about DKD pathogenesis and the potential mechanism of the nephroprotective effect of metformin. Additionally, we describe the impact of metformin on glomerular endothelial cells and podocytes, which are harmed in DKD.

A2BAR Antagonism Decreases the Glomerular Expression and Secretion of Chemoattractants for Monocytes and the Pro-Fibrotic M2 Macrophages Polarization during Diabetic Nephropathy

Some chemoattractants and leukocytes such as M1 and M2 macrophages are known to be involved in the development of glomerulosclerosis during diabetic nephropathy (DN). In the course of diabetes, an altered and defective cellular metabolism leads to the increase in adenosine levels, and thus to changes in the polarity (M1/M2) of macrophages. MRS1754, a selective antagonist of the A2B adenosine receptor (A2BAR), attenuated glomerulosclerosis and decreased macrophage-myofibroblast transition in DN rats. Therefore, we aimed to investigate the effect of MRS1754 on the glomerular expression/secretion of chemoattractants, the intraglomerular infiltration of leukocytes, and macrophage polarity in DN rats. Kidneys/glomeruli of non-diabetic, DN, and MRS1754-treated DN rats were processed for transcriptomic analysis, immunohistopathology, ELISA, and in vitro macrophage migration assays. The transcriptomic analysis identified an upregulation of transcripts and pathways related to the immune system in the glomeruli of DN rats, which was attenuated using MRS1754. The antagonism of the A2BAR decreased glomerular expression/secretion of chemoattractants (CCL2, CCL3, CCL6, and CCL21), the infiltration of macrophages, and their polarization to M2 in DN rats. The in vitro macrophages migration induced by conditioned-medium of DN glomeruli was significantly decreased using neutralizing antibodies against CCL2, CCL3, and CCL21. We concluded that the pharmacological blockade of the A2BAR decreases the transcriptional expression of genes/pathways related to the immune response, protein expression/secretion of chemoattractants, as well as the infiltration of macrophages and their polarization toward the M2 phenotype in the glomeruli of DN rats, suggesting a new mechanism implicated in the antifibrotic effect of MRS1754.

Ang-(1-7) attenuates podocyte injury induced by high glucose in vitro

Objective

The incidence of diabetic nephropathy (DN) is gradually increasing worldwide. Podocyte injury, such as podocyte apoptosis and loss of the slit diaphragm (SD)-specific markers are early pathogenic features of DN.

Materials and methods

The cultured mouse podocytes were separated into a high glucose-treated (HG, 30mM) group to mimic DN in vitro, a low glucose-treated (LG, 5mM) group as a control and HG+ angiotensin-(1-7)(Ang-(1-7)) and HG+Ang-(1-7) + D-Ala7-Ang-(1-7) (A779, Ang-(1-7)/Mas receptor antagonist) experimental groups. The Cell Counting Kit-8 (CCK-8) method and flow cytometry was used to detect podocyte activity and podocyte apoptosis respectively. The expression of angiotensin type 1 receptor (AT1R), Mas receptor (MasR) and podocyte-specific markers were examined by q-PCR and Western blot, respectively.

Results

The results showed that the decrease in podocyte activity; the increase in podocyte apoptosis; the decreased mRNA and protein expression of nephrin, podocin, WT-1 and MasR; and the upregulated expression of AT1R induced by HG could be reversed by Ang-(1-7). However, these effects were blocked by A779. The possible mechanisms of the Ang-(1-7)-mediated effect depended on MasR. In addition, the protective effect of Ang-(1-7) on podocyte activity was dose-dependent and most obvious at 10 µM. A779 had the greatest antagonistic action against Ang-(1-7) at a concentration of 10 μM.

Conclusion

This study reveals that binding of Ang-(1-7) to its specific receptor MasR may counteract the effects of Ang II mediated by AT1R to significantly attenuate podocyte injury induced by high glucose. Ang-(1-7)/MasR targeting in podocytes may be a therapeutic approach to attenuate renal injury in DN.

Unraveling the Crosstalk between Lipids and NADPH Oxidases in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a serious complication of diabetes mellitus and a leading cause of end-stage renal disease. Abnormal lipid metabolism and intrarenal accumulation of lipids have been shown to be strongly correlated with the development and progression of diabetic kidney disease (DKD). Cholesterol, phospholipids, triglycerides, fatty acids, and sphingolipids are among the lipids that are altered in DKD, and their renal accumulation has been linked to the pathogenesis of the disease. In addition, NADPH oxidase-induced production of reactive oxygen species (ROS) plays a critical role in the development of DKD. Several types of lipids have been found to be tightly linked to NADPH oxidase-induced ROS production. This review aims to explore the interplay between lipids and NADPH oxidases in order to provide new insights into the pathogenesis of DKD and identify more effective targeted therapies for the disease.

Reduced methylation correlates with diabetic nephropathy risk in type 1 diabetes

Diabetic nephropathy (DN) is a polygenic disorder with few risk variants showing robust replication in large-scale genome-wide association studies. To understand the role of DNA methylation, it is important to have the prevailing genomic view to distinguish key sequence elements that influence gene expression. This is particularly challenging for DN because genome-wide methylation patterns are poorly defined. While methylation is known to alter gene expression, the importance of this causal relationship is obscured by array-based technologies since coverage outside promoter regions is low. To overcome these challenges, we performed methylation sequencing using leukocytes derived from participants of the Finnish Diabetic Nephropathy (FinnDiane) type 1 diabetes (T1D) study (n = 39) that was subsequently replicated in a larger validation cohort (n = 296). Gene body-related regions made up more than 60% of the methylation differences and emphasized the importance of methylation sequencing. We observed differentially methylated genes associated with DN in 3 independent T1D registries originating from Denmark (n = 445), Hong Kong (n = 107), and Thailand (n = 130). Reduced DNA methylation at CTCF and Pol2B sites was tightly connected with DN pathways that include insulin signaling, lipid metabolism, and fibrosis. To define the pathophysiological significance of these population findings, methylation indices were assessed in human renal cells such as podocytes and proximal convoluted tubule cells. The expression of core genes was associated with reduced methylation, elevated CTCF and Pol2B binding, and the activation of insulin-signaling phosphoproteins in hyperglycemic cells. These experimental observations also closely parallel methylation-mediated regulation in human macrophages and vascular endothelial cells.

Nephron deficit and low podocyte density increase risk of albuminuria and glomerulosclerosis in a model of diabetes

Podocytes are terminally differentiated epithelial cells in glomeruli. Podocyte injury and loss are features of many diseases leading to chronic kidney disease (CKD). The developmental origins of health and disease hypothesis propose an adverse intrauterine environment can lead to CKD later in life, especially when a second postnatal challenge is experienced. The aim of this study was to examine whether a suboptimal maternal environment would result in reduced podocyte endowment, increasing susceptibility to diabetes-induced renal injury. Female C57BL/6 mice were fed a low protein diet (LPD) to induce growth restriction or a normal protein diet (NPD) from 3 weeks before mating until weaning (postnatal Day 21, P21) when nephron and podocyte endowment were assessed in one male and one female offspring per litter. Littermates were administered streptozotocin or vehicle at 6 weeks of age. Urinary albumin excretion, glomerular size, and podometrics were assessed following 18 weeks of hyperglycemia. LPD offspring were growth restricted and had lower nephron and podocyte number at P21. However, by 24 weeks the podocyte deficit was no longer evident and despite low nephron endowment neither albuminuria nor glomerulosclerosis were observed. Podocyte number was unaffected by 18 weeks of hyperglycemia in NPD and LPD offspring. Diabetes increased glomerular volume reducing podocyte density, with more pronounced effects in LPD offspring. LPD and NPD diabetic offspring developed mild albuminuria with LPD demonstrating an earlier onset. LPD offspring also developed glomerular pathology. These findings indicate that growth-restricted LPD offspring with low nephron number and normalized podocyte endowment were more susceptible to alterations in glomerular volume and podocyte density leading to more rapid onset of albuminuria and renal injury than NPD offspring.

Histological Manifestations of Diabetic Kidney Disease and its Relationship with Insulin Resistance

Histological manifestations of diabetic kidney disease (DKD) include mesangiolysis, mesangial matrix expansion, mesangial cell proliferation, thickening of the glomerular basement membrane, podocyte loss, foot process effacement, and hyalinosis of the glomerular arterioles, interstitial fibrosis, and tubular atrophy. Glomerulomegaly is a typical finding. Histological features of DKD may occur in the absence of clinical manifestations, having been documented in patients with normal urinary albumin excretion and normal glomerular filtration rate. Furthermore, the histological picture progresses over time, while clinical data may remain normal. Conversely, histological lesions of DKD improve with metabolic normalization following effective pancreas transplantation. Insulin resistance has been associated with the clinical manifestations of DKD (nephromegaly, glomerular hyperfiltration, albuminuria, and kidney failure). Likewise, insulin resistance may underlie the histological manifestations of DKD. Morphological changes of DKD are absent in newly diagnosed type 1 diabetes patients (with no insulin resistance) but appear afterward when insulin resistance develops. In contrast, structural lesions of DKD are typically present before the clinical diagnosis of type 2 diabetes. Several heterogeneous conditions that share the occurrence of insulin resistance, such as aging, obesity, acromegaly, lipodystrophy, cystic fibrosis, insulin receptor dysfunction, and Alström syndrome, also share both clinical and structural manifestations of kidney disease, including glomerulomegaly and other features of DKD, focal segmental glomerulosclerosis, and C3 glomerulopathy, which might be ascribed to the reduction in the synthesis of factor H binding sites (such as heparan sulfate) that leads to uncontrolled complement activation. Alström syndrome patients show systemic interstitial fibrosis markedly similar to that present in diabetes.

FGF13-Sensitive Alteration of Parkin Safeguards Mitochondrial Homeostasis in Endothelium of Diabetic Nephropathy

Studies of diabetic glomerular injury have raised the possibility of developing useful early biomarkers and therapeutic approaches for the treatment of type 2 diabetic nephropathy (T2DN). In this study, we found that FGF13 expression is induced in glomerular endothelial cells (GECs) during T2DN progression. Endothelial-specific deletion of Fgf13 potentially alleviates T2DN damage, while Fgf13 overexpression has the opposite effect. Mechanistically, Fgf13 deficiency results in improved mitochondrial homeostasis and endothelial barrier integrity in T2DN. Moreover, FGF13-sensitive alteration of Parkin safeguards mitochondrial homeostasis in endothelium of T2DN through promotion of mitophagy and inhibition of apoptosis. Additionally, it is confirmed that the beneficial effects of Fgf13 deficiency on T2DN are abolished by endothelial-specific double deletion of Fgf13 and Prkn. The effects of Fgf13 deficiency on mitophagy and apoptosis through Parkin-dependent regulation may be distinct and separable events under diabetic conditions. These data show that the bifunctional role of Fgf13 deficiency in promoting mitophagy and inhibiting apoptosis through Parkin can shape mitochondrial homeostasis regulation in GECs and T2DN progression. As a potential therapeutic target for prevention and control of T2DN, a mechanistic understanding of the biofunction of FGF13 may also be relevant to the pathogenesis of other FGF13- and Parkin-associated 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.

Overexpression of Plasmalemmal Vesicle-Associated Protein-1 Reflects Glomerular Endothelial Injury in Cases of Proliferative Glomerulonephritis with Monoclonal IgG Deposits

Introduction

Proliferative glomerulonephritis with monoclonal IgG deposits (PGNMID) occasionally presents refractory nephrotic syndrome resulting in poor renal prognosis, but its etiology is not fully elucidated. Given that glomerular endothelial cell (GEC) stress or damage may lead to podocytopathy and subsequent proteinuria, as in thrombotic microangiopathy (TMA), diabetic kidney disease, and focal segmental glomerulosclerosis, we investigated the evidence of glomerular endothelial injury by evaluating the expression of plasmalemmal vesicle-associated protein-1 (PV-1), a component of caveolae in the cases of PGNMID.

Methods

We measured the immunofluorescent PV-1 intensities of 23 PGNMID cases and compared with those of primary membranoproliferative glomerulonephritis (MPGN) (n = 5) and IgA nephropathy (IgAN) (n = 54) cases. PV-1 localization was evaluated with Caveolin-1, and CD31 staining, and the ultrastructural analysis was performed using a low-vacuum scanning electron microscope (LVSEM). To check the association of podocyte injury, we also conducted 8-oxoguanine and Wilms tumor 1 (WT1) double stain. We then evaluated PV-1 expression in other glomerulitis and glomerulopathy such as lupus nephritis and minimal change disease.

Results

The intensity of glomerular PV-1 expression in PGNMID is significantly higher than that in the other glomerular diseases, although the intensity is not associated with clinical outcomes such as urinary protein levels or renal prognosis. Immunostaining and LVSEM analysis revealed that glomerular PV-1 expression is localized in GECs in PGNMID. 8-oxoguanine accumulation was detected in WT1-positive podocytes but not in PV-1-expressing GECs, suggesting GEC-derived podocyte injury in PGNMID.

Conclusion

PV-1 overexpression reflects glomerular endothelial injury, which could be associated with podocyte oxidative stress in PGNMID cases.

Diabetic Proteinuria Revisited: Updated Physiologic Perspectives

Albuminuria, a hallmark of diabetic nephropathy, reflects not only injury and dysfunction of the filtration apparatus, but is also affected by altered glomerular hemodynamics and hyperfiltration, as well as by the inability of renal tubular cells to fully retrieve filtered albumin. Albuminuria further plays a role in the progression of diabetic nephropathy, and the suppression of glomerular albumin leak is a key factor in its prevention. Although microalbuminuria is a classic manifestation of diabetic nephropathy, often progressing to macroalbuminuria or overt proteinuria over time, it does not always precede renal function loss in diabetes. The various components leading to diabetic albuminuria and their associations are herein reviewed, and the physiologic rationale and efficacy of therapeutic interventions that reduce glomerular hyperfiltration and proteinuria are discussed. With these perspectives, we propose that these measures should be initiated early, before microalbuminuria develops, as substantial renal injury may already be present in the absence of proteinuria. We further advocate that the inhibition of the renin–angiotensin axis or of sodium–glucose co-transport likely permits the administration of a normal recommended or even high-protein diet, highly desirable for sarcopenic diabetic patients.

Solasonine alleviates high glucose-induced podocyte injury through increasing Nrf2-medicated inhibition of NLRP3 activation

The worldwide high prevalence of diabetic nephropathy is one of the common causes of renal failure in diabetic patients. Hyperglycemia-caused podocyte injury is considered as a major contributor to diabetic kidney disease, accompanied by a chronic inflammatory condition. Pyroptosis, a characterized inflammatory form of programmed cell death, is believed to be involved in the pathogenesis of diabetic nephropathy. Solasonine (SS) is a natural alkaloid and received attention as a potential anticancer agent. However, its protective effect against hyperglycemia-caused podocyte injury remains to be determined. Our study found that SS alleviates cell apoptosis, and reduces pyroptosis and oxidative damage in high glucose (HG)-treated MPC5 podocytes. Pro-inflammatory cytokines, including interleukin (IL)-1β and IL-18, and caspase-1 activity were markedly suppressed by SS in HG-treated MPC5 podocytes. SS also reduced HG-induced oxidative damage in MPC5 podocytes. Nrf2 expression was activated by SS in vitro under a HG condition. In addition, Nrf2 silencing attenuated the protective effect of SS against apoptosis, pro-inflammatory cytokines release, caspase-1 activity, and oxidative damage in MPC5 podocytes under a HG condition. Taken together, our findings revealed for the first time that SS alleviated high glucose-induced podocyte apoptosis, pyroptosis, and oxidative damage via regulating the Nrf2/NLRP3 signaling pathway. Our results indicate that SS has the potential as a therapeutic agent for podocyte injury in diabetic nephropathy.

Urinary interleukin-9 in youth with type 1 diabetes mellitus

AIMS

Interleukin-9 (IL-9) attenuates podocyte injury in experimental kidney disease, but its role in diabetic nephropathy is unknown. We sought to relate urinary IL-9 levels to the release of podocyte-derived extracellular vesicles (EVs) in youth with type 1 diabetes. We related urinary IL-9 levels to clinical variables and studied interactions between urinary IL-9, vascular endothelial growth factor (VEGF), tumor necrosis factor alpha (TNFα) and interleukin-6 (IL-6) on urinary albumin/creatinine ratio (ACR) a functional measure of podocyte injury.

METHODS

We performed an analysis of urine samples and clinical data from a cohort of youth with type 1 diabetes (n = 53). Cytokines were measured using a Luminex platform (Eve Technologies), and nanoscale flow cytometry was employed to quantify urinary podocyte-derived EVs. All urinary measures were normalized to urinary creatinine.

RESULTS

Mean age was 14.7 ± 1.6 years, and the mean time from diagnosis was 6.7 ± 2.9 years. Mean HbA1c was 70.3 ± 13.9 mmol/mol, mean ACR was 1.3 ± 1.9 mg/mmol, and mean eGFR was 140.3 ± 32.6 ml/min/1.73 m². IL-9 was inversely related to podocyte EVs (r = - 0.56, p = 0.003). IL-9 was also inversely related to blood glucose, HbA1C and eGFR (r = - 0.44, p = 0.002; r = - 0.41, p = 0.003; r = - 0.49, p < 0.001, respectively) and positively correlated with systolic BP (r = 0.30, p = 0.04). There was a significant interaction between IL-9, EVs and ACR (p = 0.0143), and the relationship between IL-9 and ACR depended on VEGF (p = 0.0083), TNFα (p = 0.0231) and IL-6 levels (p = 0.0178).

CONCLUSIONS

IL-9 is associated with podocyte injury in early type 1 diabetes, and there are complex interactions between urinary IL-9, inflammatory cytokines and ACR.

Reduced Glomerular Filtration in Diabetes Is Attributable to Loss of Density and Increased Resistance of Glomerular Endothelial Cell Fenestrations

BACKGROUND

Glomerular endothelial cell (GEnC) fenestrations are recognized as an essential component of the glomerular filtration barrier, yet little is known about how they are regulated and their role in disease.

METHODS

We comprehensively characterized GEnC fenestral and functional renal filtration changes including measurement of glomerular Kf and GFR in diabetic mice (BTBR ob-/ob- ). We also examined and compared human samples. We evaluated Eps homology domain protein-3 (EHD3) and its association with GEnC fenestrations in diabetes in disease samples and further explored its role as a potential regulator of fenestrations in an in vitro model of fenestration formation using b.End5 cells.

RESULTS

Loss of GEnC fenestration density was associated with decreased filtration function in diabetic nephropathy. We identified increased diaphragmed fenestrations in diabetes, which are posited to increase resistance to filtration and further contribute to decreased GFR. We identified decreased glomerular EHD3 expression in diabetes, which was significantly correlated with decreased fenestration density. Reduced fenestrations in EHD3 knockdown b.End5 cells in vitro further suggested a mechanistic role for EHD3 in fenestration formation.

CONCLUSIONS

This study demonstrates the critical role of GEnC fenestrations in renal filtration function and suggests EHD3 may be a key regulator, loss of which may contribute to declining glomerular filtration function through aberrant GEnC fenestration regulation. This points to EHD3 as a novel therapeutic target to restore filtration function in disease.

Myeloid-derived Growth Factor Deficiency Exacerbates Mitotic Catastrophe of Podocytes in Glomerular Disease

Podocytes are unique, highly specialized, terminally differentiated cells, which are restricted in a post-mitotic state with limited ability to repair or regenerate. Re-entering mitotic phase causes podocyte mitotic catastrophe, thereby leading to podocyte death and glomerular injury. Myeloid-derived growth factor (MYDGF) is a novel secreted protein and plays an important role on the regulation of cardiovascular function. However, whether MYDGF is expressed in kidney parenchymal cells and whether it has biological functions in the kidney remain unknown. Here, we found that MYDGF was expressed in kidney parenchymal cells and was significantly reduced in podocytes from mice with models of focal segmental glomerulosclerosis and diabetic kidney disease. Podocyte-specific deletion of MYDGF in mice exacerbated podocyte injury and proteinuria in both disease models. Functionally, MYDGF protected podocytes against mitotic catastrophe by reducing accumulation of podocytes in S phase, a portion of the cell cycle in which DNA is replicated. Mechanistically, MYDGF regulates the expression of the transcription factor RUNX2 which mediates part of MYDGF effects. Importantly, a significant reduction of MYDGF was found in glomeruli from patients with glomerular disease due to focal segmental glomerulosclerosis and diabetic kidney disease and the level of MYDGF was correlated with glomerular filtration rate, serum creatinine and podocyte loss. Thus, our studies indicate that MYDGF may be an attractive therapeutic target for glomerular disease.

Ginsenoside Rb1 alleviates diabetic kidney podocyte injury by inhibiting aldose reductase activity

Panax notoginseng, a traditional Chinese medicine, exerts beneficial effect on diabetic kidney disease (DKD), but its mechanism is not well clarified. In this study we investigated the effects of ginsenoside Rb1 (Rb1), the main active ingredients of Panax notoginseng, in alleviating podocyte injury in diabetic nephropathy and the underlying mechanisms. In cultured mouse podocyte cells, Rb1 (10 μM) significantly inhibited high glucose-induced cell apoptosis and mitochondrial injury. Furthermore, Rb1 treatment reversed high glucose-induced increases in Cyto c, Caspase 9 and mitochondrial regulatory protein NOX4, but did not affect the upregulated expression of aldose reductase (AR). Molecular docking analysis revealed that Rb1 could combine with AR and inhibited its activity. We compared the effects of Rb1 with eparestat, a known aldose reductase inhibitor, in high glucose-treated podocytes, and found that both alleviated high glucose-induced cell apoptosis and mitochondrial damage, and Rb1 was more effective in inhibiting apoptosis. In AR-overexpressing podocytes, Rb1 (10 μM) inhibited AR-mediated ROS overproduction and protected against high glucose-induced mitochondrial injury. In streptozotocin-induced DKD mice, administration of Rb1 (40 mg·kg^-1·d^-1, ig, for 7 weeks) significantly mitigated diabetic-induced glomerular injuries, such as glomerular hypertrophy and mesangial matrix expansion, and reduced the expression of apoptotic proteins. Collectively, Rb1 combines with AR to alleviate high glucose-induced podocyte apoptosis and mitochondrial damage, and effectively mitigates the progression of diabetic kidney disease.

Role of the adaptive immune system in diabetic kidney disease

Diabetic kidney disease (DKD) is a highly prevalent complication of diabetes and the leading cause of end-stage kidney disease. Inflammation is recognized as an important driver of progression of DKD. Activation of the immune response promotes a pro-inflammatory milieu and subsequently renal fibrosis, and a progressive loss of renal function. Although the role of the innate immune system in diabetic renal disease has been well characterized, the potential contribution of the adaptive immune system remains poorly defined. Emerging evidence in experimental models of DKD indicates an increase in the number of T cells in the circulation and in the kidney cortex, that in turn triggers secretion of inflammatory mediators such as interferon-γ and tumor necrosis factor-α, and activation of cells in innate immune response. In human studies, the number of T cells residing in the interstitial region of the kidney correlates with the degree of albuminuria in people with type 2 diabetes. Here, we review the role of the adaptive immune system, and associated cytokines, in the development of DKD. Furthermore, the potential therapeutic benefits of targeting the adaptive immune system as a means of preventing the progression of DKD are discussed.

The Glomerular Endothelium Restricts Albumin Filtration

Inflammatory activation and/or dysfunction of the glomerular endothelium triggers proteinuria in many systemic and localized vascular disorders. Among them are the thrombotic microangiopathies, many forms of glomerulonephritis, and acute inflammatory episodes like sepsis and COVID-19 illness. Another example is the chronic endothelial dysfunction that develops in cardiovascular disease and in metabolic disorders like diabetes. While the glomerular endothelium is a porous sieve that filters prodigious amounts of water and small solutes, it also bars the bulk of albumin and large plasma proteins from passing into the glomerular filtrate. This endothelial barrier function is ascribed predominantly to the endothelial glycocalyx with its endothelial surface layer, that together form a relatively thick, mucinous coat composed of glycosaminoglycans, proteoglycans, glycolipids, sialomucins and other glycoproteins, as well as secreted and circulating proteins. The glycocalyx/endothelial surface layer not only covers the glomerular endothelium; it extends into the endothelial fenestrae. Some glycocalyx components span or are attached to the apical endothelial cell plasma membrane and form the formal glycocalyx. Other components, including small proteoglycans and circulating proteins like albumin and orosomucoid, form the endothelial surface layer and are bound to the glycocalyx due to weak intermolecular interactions. Indeed, bound plasma albumin is a major constituent of the endothelial surface layer and contributes to its barrier function. A role for glomerular endothelial cells in the barrier of the glomerular capillary wall to protein filtration has been demonstrated by many elegant studies. However, it can only be fully understood in the context of other components, including the glomerular basement membrane, the podocytes and reabsorption of proteins by tubule epithelial cells. Discovery of the precise mechanisms that lead to glycocalyx/endothelial surface layer disruption within glomerular capillaries will hopefully lead to pharmacological interventions that specifically target this important structure.

Heart failure in diabetes

Heart failure and cardiovascular disorders represent the leading cause of death in diabetic patients. Here we present a systematic review of the main mechanisms underlying the development of diabetic cardiomyopathy. We also provide an excursus on the relative contribution of cardiomyocytes, fibroblasts, endothelial and smooth muscle cells to the pathophysiology of heart failure in diabetes. After having described the preclinical tools currently available to dissect the mechanisms of this complex disease, we conclude with a section on the most recent updates of the literature on clinical management.

Trajectories of kidney function in diabetes: a clinicopathological update

Diabetic nephropathy has been traditionally diagnosed based on persistently high albuminuria and a subsequent decline in glomerular filtration rate (GFR), which is widely recognized as the classical phenotype of diabetic kidney disease (DKD). Several studies have emphasized that trajectories of kidney function in patients with diabetes (specifically, changes in GFR and albuminuria over time) can differ from this classical DKD phenotype. Three alternative DKD phenotypes have been reported to date and are characterized by albuminuria regression, a rapid decline in GFR, or non-proteinuric or non-albuminuric DKD. Although kidney biopsies are not typically required for the diagnosis of DKD, a few studies of biopsy samples from patients with DKD have demonstrated that changes in kidney function associate with specific histopathological findings in diabetes. In addition, various clinical and biochemical parameters are related to trajectories of GFR and albuminuria. Collectively, pathological and clinical characteristics can be used to predict trajectories of GFR and albuminuria in diabetes. Furthermore, cohort studies have suggested that the risks of kidney and cardiovascular outcomes might vary among different phenotypes of DKD. A broader understanding of the clinical course of DKD is therefore crucial to improve risk stratification and enable early interventions that prevent adverse outcomes.

Podocyte Foot Process Effacement Precedes Albuminuria and Glomerular Hypertrophy in CD2-Associated Protein Deficient Mice

Background: Podocyte foot process effacement is a key histologic finding in proteinuric kidney disease. We previously showed that 3-week old CD2AP-deficient mice have significant proteinuria, glomerular hypertrophy and mesangial expansion. The goal of this study is to use morphometry to establish the temporal sequence of podocyte foot process effacement, glomerular volume expansion and albuminuria in Cd2ap^−/− mice by measuring these parameters at the 2-week time point.

Methods: Wild-type mice age 14 ± 1 days with the Cd2ap gene (WT, N = 5) and mice deficient for Cd2ap (Cd2ap KO, N = 5) were generated. Kidneys were harvested and fixed in 2.5% glutaraldehyde and processed for examination by light and electron microscopy. An average of 415.2 (range 268–716) grid points were counted for all the glomeruli, and quantification of glomerular volume from each kidney. Urine was collected the day prior to sacrifice for urine albumin-to-creatinine ratio (ACR) measurements.

Results: There was no difference in albuminuria [median (range) mg/g] between WT [212.2 (177.6–388.4) mg/g] vs. Cd2ap KO mice [203.3 (164.7–910.2) mg/g], P = 0.89; or glomerular volume 68,307[10,931] vs. 66,844[13,022] μm³, p = 0.92. The volume densities of glomerular components of the podocyte, capillary lumen and mesangium were not different for the two groups, P = 0.14, 0.14 and 0.17 respectively. However, foot process width was increased in Cd2ap KO 1128[286] vs. WT [374 ± 42] nm, P = 0.02.

Conclusion: Here we show that while 2-week old WT and Cd2ap KO mice have similar levels of albuminuria, glomerular and mesangial volume, Cd2ap KO mice have more extensive podocyte foot process effacement. The data suggests that podocyte injury is the initiating event leading to mesangial expansion and albuminuria in this model.

Single Cell Transcriptome Helps Better Understanding Crosstalk in Diabetic Kidney Disease

Years of research revealed that crosstalk extensively existed among kidney cells, cell factors and metabolites and played an important role in the development of diabetic kidney disease (DKD). In the last few years, single-cell RNA sequencing (scRNA-seq) technology provided new insight into cellular heterogeneity and genetic susceptibility regarding DKD at cell-specific level. The studies based on scRNA-seq enable a much deeper understanding of cell-specific processes such as interaction between cells. In this paper, we aim to review recent progress in single cell transcriptomic analyses of DKD, particularly highlighting on intra- or extra-glomerular cell crosstalk, cellular targets and potential therapeutic strategies for DKD.

The AGE receptor, OST48 drives podocyte foot process effacement and basement membrane expansion (alters structural composition)

AIMS

The accumulation of advanced glycation end products is implicated in the development and progression of diabetic kidney disease. No study has examined whether stimulating advanced glycation clearance via receptor manipulation is reno-protective in diabetes. Podocytes, which are early contributors to diabetic kidney disease and could be a target for reno-protection.

MATERIALS AND METHODS

To examine the effects of increased podocyte oligosaccharyltransferase-48 on kidney function, glomerular sclerosis, tubulointerstitial fibrosis and proteome (PXD011434), we generated a mouse with increased oligosaccharyltransferase-48kDa subunit abundance in podocytes driven by the podocin promoter.

RESULTS

Despite increased urinary clearance of advanced glycation end products, we observed a decline in renal function, significant glomerular damage including glomerulosclerosis, collagen IV deposition, glomerular basement membrane thickening and foot process effacement and tubulointerstitial fibrosis. Analysis of isolated glomeruli identified enrichment in proteins associated with collagen deposition, endoplasmic reticulum stress and oxidative stress. Ultra-resolution microscopy of podocytes revealed denudation of foot processes where there was co-localization of oligosaccharyltransferase-48kDa subunit and advanced glycation end-products.

CONCLUSIONS

These studies indicate that increased podocyte expression of oligosaccharyltransferase-48 kDa subunit results in glomerular endoplasmic reticulum stress and a decline in kidney function.

IGFBP-1 expression is reduced in human type 2 diabetic glomeruli and modulates β1-integrin/FAK signalling in human podocytes

AIMS/HYPOTHESIS

Podocyte loss or injury is one of the earliest features observed in the pathogenesis of diabetic kidney disease (DKD), which is the leading cause of end-stage renal failure worldwide. Dysfunction in the IGF axis, including in IGF binding proteins (IGFBPs), is associated with DKD, particularly in the early stages of disease progression. The aim of this study was to investigate the potential roles of IGFBPs in the development of type 2 DKD, focusing on podocytes.

METHODS

IGFBP expression was analysed in the Pima DKD cohort, alongside data from the Nephroseq database, and in ex vivo human glomeruli. Conditionally immortalised human podocytes and glomerular endothelial cells were studied in vitro, where IGFBP-1 expression was analysed using quantitative PCR and ELISAs. Cell responses to IGFBPs were investigated using migration, cell survival and adhesion assays; electrical cell-substrate impedance sensing; western blotting; and high-content automated imaging.

RESULTS

Data from the Pima DKD cohort and from the Nephroseq database demonstrated a significant reduction in glomerular IGFBP-1 in the early stages of human type 2 DKD. In the glomerulus, IGFBP-1 was predominantly expressed in podocytes and controlled by phosphoinositide 3-kinase (PI3K)-forkhead box O1 (FoxO1) activity. In vitro, IGFBP-1 signalled to podocytes via β1-integrins, resulting in increased phosphorylation of focal-adhesion kinase (FAK), increasing podocyte motility, adhesion, electrical resistance across the adhesive cell layer and cell viability.

CONCLUSIONS/INTERPRETATION

This work identifies a novel role for IGFBP-1 in the regulation of podocyte function and that the glomerular expression of IGFBP-1 is reduced in the early stages of type 2 DKD, via reduced FoxO1 activity. Thus, we hypothesise that strategies to maintain glomerular IGFBP-1 levels may be beneficial in maintaining podocyte function early in DKD.

A systematic review and meta-analysis of cell-based interventions in experimental diabetic kidney disease

Regenerative, cell‐based therapy is a promising treatment option for diabetic kidney disease (DKD), which has no cure. To prepare for clinical translation, this systematic review and meta‐analysis summarized the effect of cell‐based interventions in DKD animal models and treatment‐related factors modifying outcomes. Electronic databases were searched for original investigations applying cell‐based therapy in diabetic animals with kidney endpoints (January 1998‐May 2019). Weighted or standardized mean differences were estimated for kidney outcomes and pooled using random‐effects models. Subgroup analyses tested treatment‐related factor effects for outcomes (creatinine, urea, urine protein, fibrosis, and inflammation). In 40 studies (992 diabetic rodents), therapy included mesenchymal stem/stromal cells (MSC; 61%), umbilical cord/amniotic fluid cells (UC/AF; 15%), non‐MSC (15%), and cell‐derived products (13%). Tissue sources included bone marrow (BM; 65%), UC/AF (15%), adipose (9%), and others (11%). Cell‐based therapy significantly improved kidney function while reducing injury markers (proteinuria, histology, fibrosis, inflammation, apoptosis, epithelial‐mesenchymal‐transition, oxidative stress). Preconditioning, xenotransplantation, and disease‐source approaches were effective. MSC and UC/AF cells had greater effect on kidney function while cell products improved fibrosis. BM and UC/AF tissue sources more effectively improved kidney function and proteinuria vs adipose or other tissues. Cell dose, frequency, and administration route also imparted different benefits. In conclusion, cell‐based interventions in diabetic animals improved kidney function and reduced injury with treatment‐related factors modifying these effects. These findings may aid in development of optimal repair strategies through selective use of cells/products, tissue sources, and dose administrations to allow for successful adaptation of this novel therapeutic in human DKD.

Excessively Enlarged Mitochondria in the Kidneys of Diabetic Nephropathy

Diabetic nephropathy (DN) is the most serious complication of diabetes and a leading cause of kidney failure and mortality in patients with diabetes. However, the exact pathogenic mechanisms involved are poorly understood. Impaired mitochondrial function and accumulation of damaged mitochondria due to increased imbalance in mitochondrial dynamics are known to be involved in the development and progression of DN. Accumulating evidence suggests that aberrant mitochondrial fission is involved in the progression of DN. Conversely, studies linking excessively enlarged mitochondria to DN pathogenesis are emerging. In this review, we summarize the current concepts of imbalanced mitochondrial dynamics and their molecular aspects in various experimental models of DN. We discuss the recent evidence of enlarged mitochondria in the kidneys of DN and examine the possibility of a therapeutic application targeting mitochondrial dynamics in DN.

β-LAPachone is renoprotective in streptozotocin-induced diabetic mice via regulating the PI3K/Akt/mTOR signaling pathway

OBJECTIVES

β-LAPachone (B-LAP) is a natural product with established anti-inflammatory properties. In this study, we investigated the protective potential of B-LAP against diabetic nephropathy in streptozotocin (STZ) induced diabetic mice.

MATERIALS AND METHODS

Diabetes induction in mice was carried out by a single intraperitoneal injection of STZ. 2.5 mg/kg/day and 5 mg/kg/day doses of B-LAP were administered orally for twelve weeks and renal histoarchitecture, caspase-3, tumor necrosis factor-alpha (TNF-α), malondialdehyde (MDA), glutathione peroxidase (GPX), as well as urinary nephrin and neutrophil gelatinase-associated lipocalin (NGAL) were evaluated. Additionally, kidney levels of PI3K, phosphorylated (p)-Akt, p-mTOR, p-CREB, and SIRT1 were assessed in the present investigation.

RESULTS

5 mg/kg B-LAP significantly decreased urinary excretions of nephrin and NGAL. It also mitigated renal TNF-α and MDA levels and simultaneously improved GPX activities. 5 mg/kg B-LAP improved renal function in diabetic mice as indicated by elevated values of creatinine clearance. While B-LAP elevated renal levels of SIRT1, it alleviated PI3K, p-Akt, p-mTOR, and p-CREB levels in the kidneys of diabetic mice.

CONCLUSION

Collectively, these findings suggest B-LAP as a potential renoprotective agent in STZ-induced diabetic mice probably via modulating the PI3K/Akt/mTOR pathway.

Transforming growth factor-β1-induced podocyte injury is associated with increased microRNA-155 expression, enhanced inflammatory responses and MAPK pathway activation

MicroRNA-155 (miR-155) is associated with various diseases. However, the potential role of miR-155 in early glomerular disease (EGD) remains elusive. In the present study, the clinical significance of urinary miR-155 expression was explored in patients with EGD using receiver operating characteristic curve analysis. Conditionally immortalized mouse podocytes were cultured in vitro and treated with transforming growth factor-β1 (TGF-β1) at different concentrations and durations. The gene expression levels of mRNAs and miR-155 were detected using reverse transcription-quantitative PCR. Synaptopodin, CD2-associated protein (CD2AP), p38, and extracellular signal-regulated kinase (Erk) 1/2 expressions were detected using western blotting. Cell supernatants were collected for assaying tumor necrosis factor (TNF)-α and interleukin (IL)-6 concentrations using enzyme-linked immunosorbent assay. The Pearson correlation analysis was used to analyze the correlation between miR-155 levels and TNF-α or IL-6. It was found that miR-155 levels in urine have high sensitivity and specificity in the diagnosis of EGD. Time- and dose-dependent TGF-β1 treatments downregulated synaptopodin and CD2AP expression levels, and activated the p38 and Erk 1/2 pathway. However, these effects were attenuated by p38 and Erk 1/2 phosphorylation inhibitors. Additionally, TNF-α and IL-6 secretions were elevated, and their concentrations were positively correlated with the expression of miR-155 during podocyte injury. Thus, the present study indicated that miR-155 is a potential biomarker for the diagnosis of EGD, and its expression is associated with the release of pro-inflammatory cytokines and activation of mitogen-activated protein kinase (MAPK) pathway in TGF-β1-induced podocyte injury. The present study suggests that the TGF-β1/miR-155/MAPK axis is a novel target in the mechanism of EGD.

Single-cell RNA sequencing reveals the mesangial identity and species diversity of glomerular cell transcriptomes

Molecular characterization of the individual cell types in human kidney as well as model organisms are critical in defining organ function and understanding translational aspects of biomedical research. Previous studies have uncovered gene expression profiles of several kidney glomerular cell types, however, important cells, including mesangial (MCs) and glomerular parietal epithelial cells (PECs), are missing or incompletely described, and a systematic comparison between mouse and human kidney is lacking. To this end, we use Smart-seq2 to profile 4332 individual glomerulus-associated cells isolated from human living donor renal biopsies and mouse kidney. The analysis reveals genetic programs for all four glomerular cell types (podocytes, glomerular endothelial cells, MCs and PECs) as well as rare glomerulus-associated macula densa cells. Importantly, we detect heterogeneity in glomerulus-associated Pdgfrb-expressing cells, including bona fide intraglomerular MCs with the functionally active phagocytic molecular machinery, as well as a unique mural cell type located in the central stalk region of the glomerulus tuft. Furthermore, we observe remarkable species differences in the individual gene expression profiles of defined glomerular cell types that highlight translational challenges in the field and provide a guide to design translational studies.

The molecular identity of renal glomerular cells is poorly characterized and rodent glomerulopathy models translate poorly to humans. Here, the authors show molecular signatures of glomerulus-associated cells using single cell RNA sequencing and highlight differences between mouse and human cells.

Glomerular Endothelial Cell Crosstalk With Podocytes in Diabetic Kidney Disease

Diabetes is the main cause of renal failure worldwide. Complications of the kidney micro-and macro-circulation are common in diabetic patients, leading to proteinuria and can progress to end-stage renal disease. Across the complex interplays aggravating diabetes kidney disease progression, lesions of the glomerular filtration barrier appear crucial. Among its components, glomerular endothelial cells are known to be central safeguards of plasma filtration. An array of evidence has recently pinpointed its intricate relations with podocytes, highly specialized pericytes surrounding glomerular capillaries. During diabetic nephropathy, endothelial cells and podocytes are stressed and damaged. Besides, each can communicate with the other, directly affecting the progression of glomerular injury. Here, we review recent studies showing how in vitro and in vivo studies help to understand pathological endothelial cells-podocytes crosstalk in diabetic kidney disease.

Urinary podocyte-derived microparticles in youth with type 1 and type 2 diabetes

AIMS/HYPOTHESIS

The release of podocyte-derived microparticles into the urine may reflect early kidney injury in diabetes. We measured the urinary excretion of podocyte-derived microparticles in youth with type 1 and type 2 diabetes, and related the values to blood pressure, renal function and blood glucose levels.

METHODS

Cross-sectional, exploratory analysis of urine samples and clinical data from youth with type 1 (n = 53) and type 2 (n = 50) diabetes was carried out. Urinary podocyte-derived microparticle numbers, measured by flow cytometry, were assessed in relation to measures of blood glucose levels and renal function.

RESULTS

Podocyte-derived microparticle excretion (MPE) normalised to urinary creatinine (MP/UCr) was higher in type 1 vs type 2 diabetes (median [IQR] MP/UCr: 7.88 [8.97] vs 1.84 [8.62]; p < 0.0001), despite the type 2 diabetes group having higher blood pressure (systolic blood pressure, median [range]: 124 [110-154] vs 114 [94-143] mmHg) and higher proportions of microalbuminuria (44.0% vs 13.2%), but shorter time since diabetes diagnosis (median [range]: 1.2 [0.0-7.0] vs 6.4 [2.0-13.9] years), than the type 1 diabetes cohort. MPE in youth with type 1 diabetes was associated with blood glucose (p = 0.01) and eGFR (p = 0.03) but not HbA_1c, systolic or diastolic blood pressure or urine albumin/creatinine ratio. After adjustment for age at baseline, duration of diabetes, sex and BMI, the association with eGFR remained significant (p = 0.04). No associations were found between MPE and these clinical variables in youth with type 2 diabetes.

CONCLUSIONS/INTERPRETATION

Significant associations between podocyte MPE, blood glucose levels and eGFR were observed in youth with type 1 diabetes but not in those with type 2 diabetes, notwithstanding increased renal pathology in the type 2 diabetes cohort. These findings suggest that podocyte injury differs in the two diabetes cohorts. Graphical abstract.

Diabetic Nephropathy: Novel Molecular Mechanisms and Therapeutic Targets

Diabetic nephropathy (DN) is one of the major microvascular complications of diabetes mellitus and the leading cause of end-stage kidney disease. The standard treatments for diabetic patients are glucose and blood pressure control, lipid lowering, and renin-angiotensin system blockade; however, these therapeutic approaches can provide only partial renoprotection if started late in the course of the disease. One major limitation in developing efficient therapies for DN is the complex pathobiology of the diabetic kidney, which undergoes a set of profound structural, metabolic and functional changes. Despite these difficulties, experimental models of diabetes have revealed promising therapeutic targets by identifying pathways that modulate key functions of podocytes and glomerular endothelial cells. In this review we will describe recent advances in the field, analyze key molecular pathways that contribute to the pathogenesis of the disease, and discuss how they could be modulated to prevent or reverse DN.

Molecular Mechanisms in Early Diabetic Kidney Disease: Glomerular Endothelial Cell Dysfunction

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD), with prevalence increasing at an alarming rate worldwide and today, there are no known cures. The pathogenesis of DKD is complex, influenced by genetics and the environment. However, the underlying molecular mechanisms that contribute to DKD risk in about one-third of diabetics are still poorly understood. The early stage of DKD is characterized by glomerular hyperfiltration, hypertrophy, podocyte injury and depletion. Recent evidence of glomerular endothelial cell injury at the early stage of DKD has been suggested to be critical in the pathological process and has highlighted the importance of glomerular intercellular crosstalk. A potential mechanism may include reactive oxygen species (ROS), which play a direct role in diabetes and its complications. In this review, we discuss different cellular sources of ROS in diabetes and a new emerging paradigm of endothelial cell dysfunction as a key event in the pathogenesis of DKD.

Role of Sphingolipid Signaling in Glomerular Diseases: Focus on DKD and FSGS

Sphingolipids are well-recognized as major players in the pathogenesis of many human diseases, including chronic kidney disease. The kidney is a very sensitive organ to alterations in sphingolipid metabolism. The critical issues to be addressed in this review relate to the role of sphingolipids and enzymes involved in sphingolipid metabolism in the pathogenesis of glomerular diseases with a special focus on podocytes, a key cellular component of the glomerular filtration barrier. Among several sphingolipids, we will highlight the role of ceramide, sphingosine, sphingosine-1-phosphate and ceramide-1-phosphate. Additionally, we will summarize the current knowledge with regard to the use of sphingolipids as therapeutic agents for the treatment of podocyte injury in kidney disease.

Multifunctional Natural Polymer Nanoparticles as Antifibrotic Gene Carriers for CKD Therapy

BACKGROUND

Progressive fibrosis is the underlying pathophysiological process of CKD, and targeted prevention or reversal of the profibrotic cell phenotype is an important goal in developing therapeutics for CKD. Nanoparticles offer new ways to deliver antifibrotic therapies to damaged tissues and resident cells to limit manifestation of the profibrotic phenotype.

METHODS

We focused on delivering plasmid DNA expressing bone morphogenetic protein 7 (BMP7) or hepatocyte growth factor (HGF)-NK1 (HGF/NK1) by encapsulation within chitosan nanoparticles coated with hyaluronan, to safely administer multifunctional nanoparticles containing the plasmid DNA to the kidneys for localized and sustained expression of antifibrotic factors. We characterized and evaluated nanoparticles in vitro for biocompatibility and antifibrotic function. To assess antifibrotic activity in vivo, we used noninvasive delivery to unilateral ureteral obstruction mouse models of CKD.

RESULTS

Synthesis of hyaluronan-coated chitosan nanoparticles containing plasmid DNA expressing either BMP7 or NGF/NKI resulted in consistently sized nanoparticles, which-following endocytosis driven by CD44⁺ cells-promoted cellular growth and inhibited fibrotic gene expression in vitro. Intravenous tail injection of these nanoparticles resulted in approximately 40%-45% of gene uptake in kidneys in vivo. The nanoparticles attenuated the development of fibrosis and rescued renal function in unilateral ureteral obstruction mouse models of CKD. Gene delivery of BMP7 reversed the progression of fibrosis and regenerated tubules, whereas delivery of HGF/NK1 halted CKD progression by eliminating collagen fiber deposition.

CONCLUSIONS

Nanoparticle delivery of HGF/NK1 conveyed potent antifibrotic and proregenerative effects. Overall, this research provided the proof of concept on which to base future investigations for enhanced targeting and transfection of therapeutic genes to kidney tissues, and an avenue toward treatment of CKD.

A role for NPY-NPY2R signaling in albuminuric kidney disease

Neuropeptide Y (NPY) is implicated in many pathological conditions including obesity, diabetes, and insulin resistance. However, a pathogenic role of NPY in kidney disease has not been described. We found that NPY is produced by the podocyte in the glomerulus, and this production decreases in renal disease, in contrast to an increase in circulating NPY levels. In the glomerulus, NPY signals via the NPY receptor 2 (NPY2R) and modulates PI3K, MAPK, and NFAT signaling, along with RNA processing and cell migration and, if prolonged, predicted nephrotoxicity. The pharmacological inhibition of NPY-NPY2R signaling also protected against albuminuria and kidney disease in a mouse model of glomerulosclerosis, suggesting that inhibiting this pathway may be therapeutically beneficial in the prevention of kidney disease.

Albuminuria is an independent risk factor for the progression to end-stage kidney failure, cardiovascular morbidity, and premature death. As such, discovering signaling pathways that modulate albuminuria is desirable. Here, we studied the transcriptomes of podocytes, key cells in the prevention of albuminuria, under diabetic conditions. We found that Neuropeptide Y (NPY) was significantly down-regulated in insulin-resistant vs. insulin-sensitive mouse podocytes and in human glomeruli of patients with early and late-stage diabetic nephropathy, as well as other nondiabetic glomerular diseases. This contrasts with the increased plasma and urinary levels of NPY that are observed in such conditions. Studying NPY-knockout mice, we found that NPY deficiency in vivo surprisingly reduced the level of albuminuria and podocyte injury in models of both diabetic and nondiabetic kidney disease. In vitro, podocyte NPY signaling occurred via the NPY2 receptor (NPY2R), stimulating PI3K, MAPK, and NFAT activation. Additional unbiased proteomic analysis revealed that glomerular NPY-NPY2R signaling predicted nephrotoxicity, modulated RNA processing, and inhibited cell migration. Furthermore, pharmacologically inhibiting the NPY2R in vivo significantly reduced albuminuria in adriamycin-treated glomerulosclerotic mice. Our findings suggest a pathogenic role of excessive NPY-NPY2R signaling in the glomerulus and that inhibiting NPY-NPY2R signaling in albuminuric kidney disease has therapeutic potential.

Loss of Roundabout Guidance Receptor 2 (Robo2) in Podocytes Protects Adult Mice from Glomerular Injury by Maintaining Podocyte Foot Process Structure

Roundabout guidance receptor 2 (ROBO2) plays an important role during early kidney development. ROBO2 is expressed in podocytes, inhibits nephrin-induced actin polymerization, down-regulates nonmuscle myosin IIA activity, and destabilizes kidney podocyte adhesion. However, the role of ROBO2 during kidney injury, particularly in mature podocytes, is not known. Herein, we report that loss of ROBO2 in podocytes [Robo2 conditional knockout (cKO) mouse] is protective from glomerular injuries. Ultrastructural analysis reveals that Robo2 cKO mice display less foot process effacement and better-preserved slit-diaphragm density compared with wild-type littermates injured by either protamine sulfate or nephrotoxic serum (NTS). The Robo2 cKO mice also develop less proteinuria after NTS injury. Further studies reveal that ROBO2 expression in podocytes is up-regulated after glomerular injury because its expression levels are higher in the glomeruli of NTS injured mice and passive Heymann membranous nephropathy rats. Moreover, the amount of ROBO2 in the glomeruli is also elevated in patients with membranous nephropathy. Finally, overexpression of ROBO2 in cultured mouse podocytes compromises cell adhesion. Taken together, these findings suggest that kidney injury increases glomerular ROBO2 expression that might compromise podocyte adhesion and, thus, loss of Robo2 in podocytes could protect from glomerular injury by enhancing podocyte adhesion that helps maintain foot process structure. Our findings also suggest that ROBO2 is a therapeutic target for podocyte injury and podocytopathy.

Glomerular endothelial derived vesicles mediate podocyte dysfunction: A potential role for miRNA

MicroRNAs (miRNA) are shown to be involved in the progression of several types of kidney diseases. Podocytes maintain the integrity of the glomerular basement membrane. Extracellular vesicles (EV) are important in cell-to-cell communication as they can transfer cellular content between cells, including miRNA. However, little is known about how extracellular signals from the glomerular microenvironment regulate podocyte activity. Using a non-contact transwell system, communication between glomerular endothelial cells (GEnC) and podocytes was characterised in-vitro. Identification of transferred EV-miRNAs from GEnC to podocytes was performed using fluorescence cell tracking and miRNA mimetics. To represent kidney disease, podocyte molecular profiling and functions were analysed after EV treatments derived from steady state or activated GEnC. Our data shows activation of GEnC alters EV-miRNA loading, but activation was not found to alter EV secretion. EV delivery of miRNA to recipient podocytes altered cellular miRNA abundance and effector functions in podocytes, including decreased secretion of VEGF and increased mitochondrial stress which lead to altered cellular metabolism and cytoskeletal rearrangement. Finally, results support our hypothesis that miRNA-200c-3p is transfered by EVs from GEnC to podocytes in response to activation, ultimately leading to podocyte dysfunction.

The imidazopyridine derivative X22 prevents diabetic kidney dysfunction through inactivating NF-κB signaling

Diabetic kidney disease (DKD) is considered a chronic inflammatory renal disease induced by hyperglycemia. Therefore, even meticulous control of blood glucose levels cannot prevent the progression of DKD efficiently. Management of the inflammatory response could be one of the most promising strategies for treatment. We previously validated an imidazopyridine derivative (X22) as an active compound in suppressing lipopolysaccharide-induced inflammation. However, its potential for protection against DKD has not been exanimated. In the present study, streptozotocin-induced type 1 diabetic mice were used to study the effect of X22 on DKD associated inflammation and fibrosis by Q-PCR and immunoblotting assays. The results showed that X22 significantly inhibited the production of inflammatory cytokines (IL-6, TNF-α) and fibrosis biomarkers. At the same time, kidney function was dramatically improved. To elucidate the mechanism of action of X22, we examined its effects on the NRK-52E cell line. Strikingly, X22 restored the protein level of IKB-α and blocked the nuclear translocation of P65. Collectively, the data indicate that X22 can attenuate diabetic kidney dysfunction and inflammatory injury and may represent a potential agent for the treatment of DKD. It could be a potential agent for use in the treatment of DKD.

Accumulation of Globotriaosylceramide in Podocytes in Fabry Nephropathy Is Associated with Progressive Podocyte Loss

BACKGROUND

In males with classic Fabry disease, the processes leading to the frequent outcome of ESKD are poorly understood. Defects in the gene encoding α-galactosidase A lead to accumulation of globotriaosylceramide (GL3) in various cell types. In the glomerular podocytes, accumulation of GL3 progresses with age. Of concern, podocytes are relatively resistant to enzyme replacement therapy and are poorly replicating, with little ability to compensate for cell loss.

METHODS

In this study of 55 males (mean age 27 years) with classic Fabry disease genotype and/or phenotype, we performed unbiased quantitative morphometric electron microscopic studies of biopsied kidney samples from patients and seven living transplant donors (to serve as controls). We extracted clinical information from medical records and clinical trial databases.

RESULTS

Podocyte GL3 volume fraction (proportion of podocyte cytoplasm occupied by GL3) increased with age up to about age 27, suggesting that increasing podocyte GL3 volume fraction beyond a threshold may compromise survival of these cells. GL3 accumulation was associated with podocyte injury and loss, as evidenced by increased foot process width (a generally accepted structural marker of podocyte stress and injury) and with decreased podocyte number density per glomerular volume. Worsening podocyte structural parameters (increasing podocyte GL3 volume fraction and foot process width) was also associated with increasing urinary protein excretion-a strong prognosticator of adverse renal outcomes in Fabry disease-as well as with decreasing GFR.

CONCLUSIONS

Given the known association between podocyte loss and irreversible FSGS and global glomerulosclerosis, this study points to an important role for podocyte injury and loss in the progression of Fabry nephropathy and indicates a need for therapeutic intervention before critical podocyte loss occurs.

Long-term case study of a Wuzhishan miniature pig with diabetes

BACKGROUND

Miniature pigs are attractive animal models for exploring diabetes because they are similar to humans in terms of physiological structure and metabolism. However, little is known about the complications of diabetes in pigs.

METHODS

In this study, a 28-month observation of a Wuzhishan miniature pig with streptozotocin (STZ)-induced (120 mg/kg) diabetes was conducted, to investigate diabetes-related complications and the possibility of self-recovery in miniature pigs. Blood glucose, serum and urinary biochemistry was measured, and histopathologic examinations of eyes, kidney and pancreas were made.

RESULTS

During the observation, diabetic complications of eyes and kidney were observed. The eye complications included bilateral cataracts in the 15th month and degeneration of inner retina and microaneurysm in the 28th month. Kidney complications included glomerular mesangial expansion, focal segmental glomerular sclerosis, and renal tubular epithelial degeneration, but no proteinuria was observed. By 28 months after the application of STZ, with no treatment given, blood glucose had recovered and the number of pancreatic islet beta-cells had increased significantly.

CONCLUSIONS

We showed that the STZ-induced diabetes model in miniature pigs could accurately mimic the pathological changes of human diabetes, and that pancreatic islet beta-cell regeneration did occur in an adult miniature pig, providing a new means for exploring diabetic complications and pancreatic islet beta-cell regeneration.

Ultrastructural Characterization of Proteinuric Patients Predicts Clinical Outcomes

BACKGROUND

The analysis and reporting of glomerular features ascertained by electron microscopy are limited to few parameters with minimal predictive value, despite some contributions to disease diagnoses.

METHODS

We investigated the prognostic value of 12 electron microscopy histologic and ultrastructural changes (descriptors) from the Nephrotic Syndrome Study Network (NEPTUNE) Digital Pathology Scoring System. Study pathologists scored 12 descriptors in NEPTUNE renal biopsies from 242 patients with minimal change disease or FSGS, with duplicate readings to evaluate reproducibility. We performed consensus clustering of patients to identify unique electron microscopy profiles. For both individual descriptors and clusters, we used Cox regression models to assess associations with time from biopsy to proteinuria remission and time to a composite progression outcome (≥40% decline in eGFR, with eGFR<60 ml/min per 1.73 m², or ESKD), and linear mixed models for longitudinal eGFR measures.

RESULTS

Intrarater and interrater reproducibility was >0.60 for 12 out of 12 and seven out of 12 descriptors, respectively. Individual podocyte descriptors such as effacement and microvillous transformation were associated with complete remission, whereas endothelial cell and glomerular basement membrane abnormalities were associated with progression. We identified six descriptor-based clusters with distinct electron microscopy profiles and clinical outcomes. Patients in a cluster with more prominent foot process effacement and microvillous transformation had the highest rates of complete proteinuria remission, whereas patients in clusters with extensive loss of primary processes and endothelial cell damage had the highest rates of the composite progression outcome.

CONCLUSIONS

Systematic analysis of electron microscopic findings reveals clusters of findings associated with either proteinuria remission or disease progression.

The Pathological Relevance of Increased Endothelial Glycocalyx Permeability

The endothelial glycocalyx is a vital regulator of vascular permeability. Damage to this delicate layer can result in increased protein and water transit. The clinical importance of albuminuria as a predictor of kidney disease progression and vascular disease has driven research in this area. This review outlines how research to date has attempted to measure the contribution of the endothelial glycocalyx to vessel wall permeability. We discuss the evidence for the role of the endothelial glycocalyx in regulating permeability in discrete areas of the vasculature and highlight the inherent limitations of the data that have been produced to date. In particular, this review emphasizes the difficulties in interpreting urinary albumin levels in early disease models. In addition, the research that supports the view that glycocalyx damage is a key pathologic step in a diverse array of clinical conditions, including diabetic complications, sepsis, preeclampsia, and atherosclerosis, is summarized. Finally, novel methods are discussed, including an ex vivo glomerular permeability assay that enhances the understanding of permeability changes in disease.