Reversibility of structural and functional damage in a model of advanced diabetic nephropathy

Whole transcriptome mapping reveals the lncRNA regulatory network of TFP5 treatment in diabetic nephropathy

BACKGROUND

TFP5 is a Cdk5 inhibitor peptide, which could restore insulin production. However, the role of TFP5 in diabetic nephropathy (DN) is still unclear.

OBJECTIVE

This study aims to characterize the transcriptome profiles of mRNA and lncRNA in TFP5-treated DN mice to mine key lncRNAs associated with TFP5 efficacy.

METHODS

We evaluated the role of TFP5 in DN pathology and performed RNA sequencing in C57BL/6J control mice, C57BL/6J db/db model mice, and TFP5 treatment C57BL/6J db/db model mice. The differentially expressed lncRNAs (DElncRNAs) and mRNAs (DEmRNAs) were analyzed. WGCNA was used to screen hub-gene of TFP5 in treatment of DN.

RESULTS

Our results showed that TFP5 therapy ameliorated renal tubular injury in DN mice. In addition, compared with the control group, the expression profile of lncRNAs in the model group was significantly disordered, while TFP5 alleviated the abnormal expression of lncRNAs. A total of 67 DElncRNAs shared among the three groups, 39 DElncRNAs showed a trend of increasing in the DN group and decreasing after TFP treatment, while the remaining 28 showed the opposite trend. DElncRNAs were enriched in glycosphingolipid biosynthesis signaling pathways, NF-κB signaling pathways, and complement activation signaling pathways. There were 1028 up-regulated and 1117 down-regulated DEmRNAs in the model group compared to control group, and 123 up-regulated and 153 down-regulated DEmRNAs in the TFP5 group compared to the model group. The DEmRNAs were involved in PPAR and MAPK signaling pathway. We confirmed that MSTRG.28304.1 is a key DElncRNA for TFP5 treatment of DN. TFP5 ameliorated DN maybe by inhibiting MSTRG.28304.1 through regulating the insulin resistance and PPAR signaling pathway. The qRT-PCR results confirmed the reliability of the sequencing data through verifying the expression of ENSMUST00000211209, MSTRG.31814.5, MSTRG.28304.1, and MSTRG.45642.14.

CONCLUSION

Overall, the present study provides novel insights into molecular mechanisms of TFP5 treatment in DN.

Toxicological effects of microplastics in renal ischemia-reperfusion injury

The widespread presence of microplastics (MPs) in the environment poses a significant threat to biological survival and human health. However, our understanding of the toxic effects of MPs on the kidneys remains limited. This study aimed to investigate the underlying mechanism of the toxic effects of MPs on the kidneys using an ischemia-reperfusion (IR) mouse model. Four-week-old ICR mice were exposed to 0.5 μm MPs for 12 weeks prior to IR injury. The results showed that MPs exposure could aggravate the IR-induced damage to renal tubules and glomeruli. Although there were no significant changes in blood urea nitrogen and serum creatinine levels 7 days after IR, MPs treatment resulted in a slight increase in both parameters. In addition, the expression levels of inflammatory factors (MCP-1 and IL-6) at the mRNA level, as well as macrophage markers (CD68 and F4/80), were significantly higher in the MPs + IR group than in the Sham group after IR. Furthermore, MPs exposure exacerbated IR-induced renal fibrosis. Importantly, the expression of pyroptosis-related genes, including NLRP3, ASC, GSDMD, cleaved caspase-1, and IL-18, was significantly upregulated by MPs, indicating that MPs exacerbate pyroptosis in the context of renal IR. In conclusion, our findings suggest that MPs exposure can aggravate renal IR-induced pyroptosis by activating NLRP3-GSDMD signaling.

Podocytes from hypertensive and obese mice acquire an inflammatory, senescent, and aged phenotype

Patients with hypertension or obesity can develop glomerular dysfunction characterized by injury and depletion of podocytes. To better understand the molecular processes involved, young mice were treated with either deoxycorticosterone acetate (DOCA) or fed a high-fat diet (HFD) to induce hypertension or obesity, respectively. The transcriptional changes associated with these phenotypes were measured by unbiased bulk mRNA sequencing of isolated podocytes from experimental models and their respective controls. Key findings were validated by immunostaining. In addition to a decrease in canonical proteins and reduced podocyte number, podocytes from both hypertensive and obese mice exhibited a sterile inflammatory phenotype characterized by increases in NLR family pyrin domain containing 3 (NLRP3) inflammasome, protein cell death-1, and Toll-like receptor pathways. Finally, although the mice were young, podocytes in both models exhibited increased expression of senescence and aging genes, including genes consistent with a senescence-associated secretory phenotype. However, there were differences between the hypertension- and obesity-associated senescence phenotypes. Both show stress-induced podocyte senescence characterized by increased p21 and p53. Moreover, in hypertensive mice, this is superimposed upon age-associated podocyte senescence characterized by increased p16 and p19. These results suggest that senescence, aging, and inflammation are critical aspects of the podocyte phenotype in experimental hypertension and obesity in mice.NEW & NOTEWORTHY Hypertension and obesity can lead to glomerular dysfunction in patients, causing podocyte injury and depletion. Here, young mice given deoxycorticosterone acetate or a high-fat diet to induce hypertension or obesity, respectively. mRNA sequencing of isolated podocytes showed transcriptional changes consistent with senescence, a senescent-associated secretory phenotype, and aging, which was confirmed by immunostaining. Ongoing studies are determining the mechanistic roles of the accelerated aging podocyte phenotype in experimental hypertension and obesity.

Genetic Analysis of Obesity-Induced Diabetic Nephropathy in BTBR Mice

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease in the U.S. and has a significant impact on human suffering. Leptin-deficient BTBR (BTBRob/ob) mice develop hallmark features of obesity-induced DN, whereas leptin-deficient C57BL/6J (B6ob/ob) mice do not. To identify genetic loci that underlie this strain difference, we constructed an F2 intercross between BTBRob/ob and B6ob/ob mice. We isolated kidneys from 460 F2 mice and histologically scored them for percent mesangial matrix and glomerular volume (∼50 glomeruli per mouse), yielding ∼45,000 distinct measures in total. The same histological measurements were made in kidneys from B6 and BTBR mice, either lean or obese (Lepob/ob), at 4 and 10 weeks of age, allowing us to assess the contribution of strain, age, and obesity to glomerular pathology. All F2 mice were genotyped for ∼5,000 single nucleotide polymorphisms (SNPs), ∼2,000 of which were polymorphic between B6 and BTBR, enabling us to identify a quantitative trait locus (QTL) on chromosome 7, with a peak at ∼30 Mbp, for percent mesangial matrix, glomerular volume, and mesangial volume. The podocyte-specific gene nephrin (Nphs1) is physically located at the QTL and contains high-impact SNPs in BTBR, including several missense variants within the extracellular immunoglobulin-like domains.

ARTICLE HIGHLIGHTS

The crosstalk between glomerular endothelial cells and podocytes controls their responses to metabolic stimuli in diabetic nephropathy

In diabetic nephropathy (DN), glomerular endothelial cells (GECs) and podocytes undergo pathological alterations, which are influenced by metabolic changes characteristic of diabetes, including hyperglycaemia (HG) and elevated methylglyoxal (MGO) levels. However, it remains insufficiently understood what effects these metabolic factors have on GEC and podocytes and to what extent the interactions between the two cell types can modulate these effects. To address these questions, we established a co-culture system in which GECs and podocytes were grown together in close proximity, and assessed transcriptional changes in each cell type after exposure to HG and MGO. We found that HG and MGO had distinct effects on gene expression and that the effect of each treatment was markedly different between GECs and podocytes. HG treatment led to upregulation of "immediate early response" genes, particularly those of the EGR family, as well as genes involved in inflammatory responses (in GECs) or DNA replication/cell cycle (in podocytes). Interestingly, both HG and MGO led to downregulation of genes related to extracellular matrix organisation in podocytes. Crucially, the transcriptional responses of GECs and podocytes were dependent on their interaction with each other, as many of the prominently regulated genes in co-culture of the two cell types were not significantly changed when monocultures of the cells were exposed to the same stimuli. Finally, the changes in the expression of selected genes were validated in BTBR ob/ob mice, an established model of DN. This work highlights the molecular alterations in GECs and podocytes in response to the key diabetic metabolic triggers HG and MGO, as well as the central role of GEC-podocyte crosstalk in governing these responses.

Optimizing diabetic kidney disease animal models: Insights from a meta-analytic approach

Diabetic kidney disease (DKD) is a prevalent complication of diabetes, often leading to end-stage renal disease. Animal models have been widely used to study the pathogenesis of DKD and evaluate potential therapies. However, current animal models often fail to fully capture the pathological characteristics of renal injury observed in clinical patients with DKD. Additionally, modeling DKD is often a time-consuming, costly, and labor-intensive process. The current review aims to summarize modeling strategies in the establishment of DKD animal models by utilizing meta-analysis related methods and to aid in the optimization of these models for future research. A total of 1215 articles were retrieved with the keywords of "diabetic kidney disease" and "animal experiment" in the past 10 years. Following screening, 84 articles were selected for inclusion in the meta-analysis. Review manager 5.4.1 was employed to analyze the changes in blood glucose, glycosylated hemoglobin, total cholesterol, triglyceride, serum creatinine, blood urea nitrogen, and urinary albumin excretion rate in each model. Renal lesions shown in different models that were not suitable to be included in the meta-analysis were also extensively discussed. The above analysis suggested that combining various stimuli or introducing additional renal injuries to current models would be a promising avenue to overcome existing challenges and limitations. In conclusion, our review article provides an in-depth analysis of the limitations in current DKD animal models and proposes strategies for improving the accuracy and reliability of these models that will inspire future research efforts in the DKD research field.

Rodent models to study type 1 and type 2 diabetes induced human diabetic nephropathy

INTRODUCTION

Diabetic nephropathy (DN), an outcome of prolonged diabetes, has affected millions of people worldwide and every year the incidence and prevalence increase substantially. The symptoms may start with mild manifestations of the disease such as increased albuminuria, serum creatinine levels, thickening of glomerular basement membrane, expansion of mesangial matrix to severe pathological symptoms such as glomerular lesions and tubulointerstitial fibrosis which may further proceed to cardiovascular dysfunction or end-stage renal disease.

PERSPECTIVE

Numerous therapeutic interventions are being explored for the management of DN, however, these interventions do not completely halt the progression of this disease and hence animal models are being explored to identify critical genetic and molecular parameters which could help in tackling the disease. Rodent models which mostly include mice and rats are commonly used experimental animals which provide a wide range of advantages in understanding the onset and progression of disease in humans and also their response to a wide range of interventions helps in the development of effective therapeutics. Rodent models of type 1 and type 2 diabetes induced DN have been developed utilizing different platforms and interventions during the last few decades some of which mimic various stages of diabetes ranging from early to later stages. However, a rodent model which replicates all the features of human DN is still lacking. This review tries to evaluate the rodent models that are currently available and understand their features and limitations which may help in further development of more robust models of human DN.

CONCLUSION

Using these rodent models can help to understand different aspects of human DN although further research is required to develop more robust models utilizing diverse genetic platforms which may, in turn, assist in developing effective interventions to target the disease at different levels.

What the BTBR/J mouse has taught us about diabetes and diabetic complications

Human and mouse genetics have delivered numerous diabetogenic loci, but it is mainly through the use of animal models that the pathophysiological basis for their contribution to diabetes has been investigated. More than 20 years ago, we serendipidously identified a mouse strain that could serve as a model of obesity-prone type 2 diabetes, the BTBR (Black and Tan Brachyury) mouse (BTBR T+ Itpr3tf/J, 2018) carrying the Lepob mutation. We went on to discover that the BTBR-Lepob mouse is an excellent model of diabetic nephropathy and is now widely used by nephrologists in academia and the pharmaceutical industry. In this review, we describe the motivation for developing this animal model, the many genes identified and the insights about diabetes and diabetes complications derived from >100 studies conducted in this remarkable animal model.

Diabetic Kidney Disease: An Update

Diabetes is a major public health challenge and diabetic kidney disease (DKD), a broader diagnostic term than diabetic nephropathy, is the leading cause of chronic kidney disease and end-stage kidney disease in the United States and worldwide. A better understanding of the underlying pathophysiological mechanisms of DKD, and recent clinical trials testing new therapeutic interventions, have shown promising results to curb this epidemic. Given the global health burden of DKD, it is extremely important to prioritize prevention, early recognition, referral, and aggressive management of DKD in the primary care setting.

Expression of leptin receptor in renal tubules is sparse but implicated in leptin-dependent kidney gene expression and function

Leptin regulates energy balance via leptin receptors expressed in central and peripheral tissues, but little is known about leptin-sensitive kidney genes and the role of the tubular leptin receptor (Lepr) in response to a high-fat diet (HFD). Quantitative RT-PCR analysis of Lepr splice variants A, B, and C revealed a ratio of ∼100:10:1 in the mouse kidney cortex and medulla, with medullary levels being ∼10 times higher. Leptin replacement in ob/ob mice for 6 days reduced hyperphagia, hyperglycemia, and albuminuria, associated with normalization of kidney mRNA expression of molecular markers of glycolysis, gluconeogenesis, amino acid synthesis, and megalin. Normalization of leptin for 7 h in ob/ob mice did not normalize hyperglycemia or albuminuria. Tubular knockdown of Lepr [Pax8-Lepr knockout (KO)] and in situ hybridization revealed a minor fraction of Lepr mRNA in tubular cells compared with endothelial cells. Nevertheless, Pax8-Lepr KO mice had lower kidney weight. Moreover, while HFD-induced hyperleptinemia, increases in kidney weight and glomerular filtration rate, and a modest blood pressure lowering effect were similar compared with controls, they showed a blunted rise in albuminuria. Use of Pax8-Lepr KO and leptin replacement in ob/ob mice identified acetoacetyl-CoA synthetase and gremlin 1 as tubular Lepr-sensitive genes that are increased and reduced by leptin, respectively. In conclusion, leptin deficiency may increase albuminuria via systemic metabolic effects that impinge on kidney megalin expression, whereas hyperleptinemia may induce albuminuria by direct tubular Lepr effects. Implications of Lepr variants and the novel tubular Lepr/acetoacetyl-CoA synthetase/gremlin 1 axis remain to be determined.NEW & NOTEWORTHY This study provides new insights into kidney gene expression of leptin receptor splice variants, leptin-sensitive kidney gene expression, and the role of the leptin receptor in renal tubular cells for the response to diet-induced hyperleptinemia and obesity including albuminuria.

Pharmacologic blockade of the natriuretic peptide clearance receptor promotes weight loss and enhances insulin sensitivity in type 2 diabetes

While natriuretic peptides (NPs) are primarily known for their renal and cardiovascular actions, NPs stimulate lipolysis in adipocytes and induce a thermogenic program in white adipose tissue (WAT) that resembles brown fat. The biologic effects of NPs are negatively regulated by the NP clearance receptor (NPRC), which binds and degrades NPs. Knockout (KO) of NPRC protects against diet induced obesity and improves insulin sensitivity in obese mice. To determine if pharmacologic blockade of NPRC enhanced the beneficial metabolic actions of NPs in type 2 diabetes, we blocked NP clearance in a mouse model of type 2 diabetes using the specific NPRC ligand ANP(4-23). We found that treatment with ANP(4-23) caused a significant decrease in body weight by increasing energy expenditure and reducing fat mass without a change in lean body mass. The decrease in fat mass was associated with a significant improvement in insulin sensitivity and reduced serum insulin levels. These beneficial effects were accompanied by a decrease in infiltrating macrophages in adipose tissue, and reduced expression of inflammatory markers in both serum and WAT. These data suggest that inhibiting NP clearance may be an effective pharmacologic approach to promote weight loss and enhance insulin sensitivity in type 2 diabetes. Optimizing the therapeutic approach may lead to useful therapies for obesity and type 2 diabetes.

Parietal Epithelial Cell Behavior and Its Modulation by microRNA-193a

Glomerular parietal epithelial cells (PECs) have been increasingly recognized to have crucial functions. Lineage tracking in animal models showed the expression of a podocyte phenotype by PECs during normal glomerular growth and after acute podocyte injury, suggesting a reparative role of PECs. Conversely, activated PECs are speculated to be pathogenic and comprise extracapillary proliferation in focal segmental glomerulosclerosis (FSGS) and crescentic glomerulonephritis (CrescGN). The reparative and pathogenic roles of PECs seem to represent two sides of PEC behavior directed by the local milieu and mediators. Recent studies suggest microRNA-193a (miR193a) is involved in the pathogenesis of FSGS and CrescGN. In a mouse model of primary FSGS, the induction of miR193a caused the downregulation of Wilms' tumor protein, leading to the dedifferentiation of podocytes. On the other hand, the inhibition of miR193a resulted in reduced crescent lesions in a mouse model of CrescGN. Interestingly, in vitro studies report that the downregulation of miR193a induces trans-differentiation of PECs into a podocyte phenotype. This narrative review highlights the critical role of PEC behavior in health and during disease and its modulation by miR193a.

Combined multiomics analysis reveals the mechanism of CENPF overexpression-mediated immune dysfunction in diffuse large B-cell lymphoma in vitro

Diffuse large B-cell lymphoma (DLBCL) is one of the most common aggressive B-cell lymphomas with significant heterogeneity. More than half of patients are cured, but 40%-45% still face relapse or develop drug resistance, and the mechanism is not yet known. In this study, Centrimeric protein F (CENPF) overexpression was found in several DLBCL patients with relapsed or refractory disease compared to patients with complete remission. Thus, the human DLBCL cell line SU-DHL-4 was chosen for this study, and CENPF was upregulated in that cell line by using an adenovirus in vitro. Mass spectrometry-based quantitative proteome analysis was first performed, and the results showed that the expression levels of various proteins were increased when CENPF was upregulated, and these proteins are mainly involved in cellular processes, biological regulation, immune system processes and transcriptional regulator activity. Bioinformatics data analysis revealed that the main enriched proteins, including UBE2A, UBE2C, UBE2S, TRIP12, HERC2, PIRH2, and PIAS, were involved in various ubiquitin-related kinase activities and ubiquitination processes. Thus, ubiquitinome analysis was further performed, and the results demonstrated that proteins in many immune-related cellular pathways, such as natural killer cell-mediated cytotoxicity, the T-cell receptor signaling pathway and the B-cell receptor signaling pathway, were significantly deubiquitinated after CENPF was upregulated in DLBCL cells. Furthermore, TIMER2.0 was also used to reveal the association between CENPF and immune infiltration in DLBCL. The results showed that CENPF expression was positively correlated with CD8⁺ T cells, NK cells and B lymphocytes in DLBCL samples but negatively correlated with regulatory T cells. Aberrant activation of CENPF may induce immune dysregulation in DLBCL cells by mediating protein deubiquitination in various immune signaling pathways, which leads to tumor escape of DLBCL, but further experimental validation is still needed.

Cellular phenotypic transitions in diabetic nephropathy: An update

Diabetic nephropathy (DN) is a major cause of morbidity and mortality in diabetes and is the most common cause of end stage renal disease (ESRD). Renal fibrosis is the final pathological change in DN. It is widely believed that cellular phenotypic switching is the cause of renal fibrosis in diabetic nephropathy. Several types of kidney cells undergo activation and differentiation and become reprogrammed to express markers of mesenchymal cells or podocyte-like cells. However, the development of targeted therapy for DN has not yet been identified. Here, we discussed the pathophysiologic changes of DN and delineated the possible origins that contribute to myofibroblasts and podocytes through phenotypic transitions. We also highlight the molecular signaling pathways involved in the phenotypic transition, which would provide valuable information for the activation of phenotypic switching and designing effective therapies for DN.

Lack of renoprotective effects of targeting the endothelin A receptor and (or) sodium glucose transporter 2 in a mouse model of Type 2 diabetic kidney disease

Two recent clinical trials, using sodium glucose cotransporter (SGLT2) or endothelin-A receptor (ET-A) blocker, reported the first efficacious treatments in 18 years to slow progression of diabetic kidney disease (DKD). We hypothesized that combined inhibition of SGLT2 and ET-A receptor may confer greater protection against renal injury than either agent alone. Uninephrectomized male db/db mice were randomized to four groups: vehicle, SGLT2 inhibitor (dapagliflozin (dapa), 1 mg/kg/day), ET-A blocker (atrasentan (atra), 5 mg/kg/day), or dual treatment from 10 weeks until 22 weeks of age. At 10 weeks of age, no differences were observed in body weight, blood glucose or urinary albumin excretion among the four groups. At 16 and 22 weeks of age, body weight was lower and blood glucose levels higher in the vehicle and atra groups compared with dapa- and dual-treated groups. No notable differences were observed among the four groups in urinary albumin excretion at weeks 16 and 22. Histological analysis showed mild glomerulosclerosis and tubular injury (<5%) in all four groups with reduced glomerulosclerosis in the dual treatment group compared with vehicle. Individual or combined treatment with an SGLT2 inhibitor and (or) an ET-A antagonist did not confer renoprotective effects in this model.

Podocyte-Related Mechanisms Underlying Survival Benefit of Long-Term Angiotensin Receptor Blocker

We previously found that short-term treatment (week 8 to 12 after injury) with high-dose angiotensin receptor blocker (ARB) induced the regression of existing glomerulosclerosis in 5/6 nephrectomy rats. We therefore assessed the effects of long-term intervention with ARB vs. nonspecific antihypertensives in this study. Adult rats underwent 5/6 nephrectomy and renal biopsy 8 weeks later. The rats were then divided into three groups with equivalent renal function and glomerular sclerosis and treated with high-dose losartan (ARB), nonspecific antihypertensive triple-therapy (TRX), or left untreated (Control) until week 30. We found that blood pressure, serum creatinine levels, and glomerulosclerosis were lower at sacrifice in ARB and TRX vs. Control. Only ARB reduced proteinuria and maintained the density of WT-1-positive podocytes. Glomerular tufts showed more double-positive cells for CD44, a marker of activated parietal epithelial cells, and synaptopodin after ARB vs. TRX or Control. ARB treatment reduced aldosterone levels. ARB-treated rats had significantly improved survival when compared with TRX or Control. We conclude that both long-term ARB and triple-therapy ameliorate progression, but do not sustain the regression of glomerulosclerosis. ARB resulted in the superior preservation of podocyte integrity and decreased proteinuria and aldosterone, linked to increased survival in the uremic environment.

FGF21-FGFR4 signaling in cardiac myocytes promotes concentric cardiac hypertrophy in mouse models of diabetes

Fibroblast growth factor (FGF) 21, a hormone that increases insulin sensitivity, has shown promise as a therapeutic agent to improve metabolic dysregulation. Here we report that FGF21 directly targets cardiac myocytes by binding β-klotho and FGF receptor (FGFR) 4. In combination with high glucose, FGF21 induces cardiac myocyte growth in width mediated by extracellular signal-regulated kinase 1/2 (ERK1/2) signaling. While short-term FGF21 elevation can be cardio-protective, we find that in type 2 diabetes (T2D) in mice, where serum FGF21 levels are elevated, FGFR4 activation induces concentric cardiac hypertrophy. As T2D patients are at risk for heart failure with preserved ejection fraction (HFpEF), we propose that induction of concentric hypertrophy by elevated FGF21-FGFR4 signaling may constitute a novel mechanism promoting T2D-associated HFpEF such that FGFR4 blockade might serve as a cardio-protective therapy in T2D. In addition, potential adverse cardiac effects of FGF21 mimetics currently in clinical trials should be investigated.

Mechanisms of podocyte injury and implications for diabetic nephropathy

Albuminuria is the hallmark of both primary and secondary proteinuric glomerulopathies, including focal segmental glomerulosclerosis (FSGS), obesity-related nephropathy, and diabetic nephropathy (DN). Moreover, albuminuria is an important feature of all chronic kidney diseases (CKDs). Podocytes play a key role in maintaining the permselectivity of the glomerular filtration barrier (GFB) and injury of the podocyte, leading to foot process (FP) effacement and podocyte loss, the unifying underlying mechanism of proteinuric glomerulopathies. The metabolic insult of hyperglycemia is of paramount importance in the pathogenesis of DN, while insults leading to podocyte damage are poorly defined in other proteinuric glomerulopathies. However, shared mechanisms of podocyte damage have been identified. Herein, we will review the role of haemodynamic and oxidative stress, inflammation, lipotoxicity, endocannabinoid (EC) hypertone, and both mitochondrial and autophagic dysfunction in the pathogenesis of the podocyte damage, focussing particularly on their role in the pathogenesis of DN. Gaining a better insight into the mechanisms of podocyte injury may provide novel targets for treatment. Moreover, novel strategies for boosting podocyte repair may open the way to podocyte regenerative medicine.

The Role of Parietal Epithelial Cells in the Pathogenesis of Podocytopathy

Podocytopathy is the most common feature of glomerular disorder characterized by podocyte injury- or dysfunction-induced excessive proteinuria, which ultimately develops into glomerulosclerosis and results in persistent loss of renal function. Due to the lack of self-renewal ability of podocytes, mild podocyte depletion triggers replacement and repair processes mostly driven by stem cells or resident parietal epithelial cells (PECs). In contrast, when podocyte recovery fails, activated PECs contribute to the establishment of glomerular lesions. Increasing evidence suggests that PECs, more than just bystanders, have a crucial role in various podocytopathies, including minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, diabetic nephropathy, IgA nephropathy, and lupus podocytopathy. In this review, we attempt to dissect the diverse role of PECs in the pathogenesis of podocytopathy based on currently available information.

Microencapsulated islet transplantation alleviates podocyte injury in diabetic nephropathy via inhibiting Notch-1 signaling

OBJECTIVE

Podocyte injury has a critical role in the pathogenesis of diabetic nephropathy (DN). Microencapsulated islet transplantation (MIT) is identified as an effective method for improving the clinical condition of DN. This study aimed to explore the role and mechanism of MIT in alleviating podocyte injury in DN.

METHODS

A mouse model of DN was constructed using streptozotocin (STZ). Mice were divided into 3 groups: the untreated diabetic nephropathy group (DN group), the microencapsulated islet transplantation-treated group (MIT group) and the control group. The mice were raised for 6 weeks posterior to islet transplantation to identify the role of MIT. Renal function and structure of glomerular filtration barrier were assessed by urine analysis, histopathological examination, and transmission electron microscopy. The expression levels of several proteins including Caspase-3, Bcl2/Bax, β-galactosidase, Ki-67, synaptopodin, WT-1, Jagged-1, Notch-1, and Hes-1 in renal tissues were identified via immunohistochemistry (IHC), immunofluorescence (IF), and western blotting techniques.

RESULTS

Compared with the DN group, the MIT group presented decreased levels of blood glucose, urinary albumin/creatinine, urea nitrogen, and serum creatinine while their body weight gradually increased. Glomerular injury in the MIT group was significantly better than that in the DN group. The MIT group indicated significantly decreased expression of Caspase-3, β-galactosidase, Bax/Bcl-2, and Ki-67 when compared with DN group, while the proportion of synaptopodin- and WT-1-positive cells was significantly increased (P < 0.05). The protein expression of Jagged-1, Notch-1, and Hes-1 in the glomerulus of the MIT group was significantly lower than that in the DN group (P < 0.05).

CONCLUSION

MIT alleviates podocyte injury induced by DN by inhibiting Notch-1 signaling. The identification of signaling pathways influencing podocyte restoration can help evaluate personalized medicine efficacy for patients treated with islet transplantation.

Imaging the Kidney with an Unconventional Scanning Electron Microscopy Technique: Analysis of the Subpodocyte Space in Diabetic Mice

Transmission electron microscopy (TEM) remains the gold standard for renal histopathological diagnoses, given its higher resolving power, compared with light microscopy. However, it imposes several limitations on pathologists, including longer sample preparation time and a small observation area. To overcome these, we introduced a scanning electron microscopy (SEM) technique for imaging resin-embedded semi-thin sections of renal tissue. We developed a rapid tissue preparation protocol for experimental models and human biopsies which, alongside SEM digital imaging acquisition of secondary electrons (SE–SEM), enables fast electron microscopy examination, with a resolution similar to that achieved by TEM. We used this unconventional SEM imaging approach to investigate the subpodocyte space (SPS) in BTBR ob/ob mice with type 2 diabetes. Analysis of semi-thin sections with secondary electrons revealed that the SPS had expanded in volume and covered large areas of the glomerular basement membrane, forming wide spaces between the podocyte body and the underlying filtering membrane. Our results show that SE–SEM is a valuable tool for imaging the kidney at the ultrastructural level, filling the magnification gap between light microscopy and TEM, and reveal that in diabetic mice, the SPS is larger than in normal controls, which is associated with podocyte damage and impaired kidney function.

Empagliflozin protects glomerular endothelial cell architecture in experimental diabetes through the VEGF-A/caveolin-1/PV-1 signaling pathway

In addition to having blood glucose-lowering effects, inhibitors of sodium glucose cotransporter 2 (SGLT2) afford renoprotection in diabetes. We sought to investigate which components of the glomerular filtration barrier could be involved in the antiproteinuric and renoprotective effects of SGLT2 inhibition in diabetes. BTBR ob/ob mice that develop a type 2 diabetic nephropathy received a standard diet with or without empagliflozin for 10 weeks, starting at 8 weeks of age, when animals had developed albuminuria. Empagliflozin caused marked decreases in blood glucose levels and albuminuria but did not correct glomerular hyperfiltration. The protective effect of empagliflozin against albuminuria was not due to a reduction in podocyte damage since empagliflozin did not affect the larger podocyte filtration slit pore size nor the defective expression of nephrin and nestin. Empagliflozin did not reduce the thickening of the GBM. In BTBR ob/ob mice, the most profound abnormality seen using electron microscopy was in the endothelial aspect of the glomerular capillary, with significant loss of endothelial fenestrations. Remarkably, empagliflozin ameliorated the subverted microvascular endothelial ultrastructure. Caveolae and bridging diaphragms between adjacent endothelial fenestrae were seen in diabetic mice and associated with increased expression of caveolin-1 and the appearance of PV-1. These endothelial abnormalities were limited by the SGLT2 inhibitor. While no expression of SGLT2 was found in glomerular endothelial cells, SGLT2 was expressed in the podocytes of diabetic mice. VEGF-A which is a known stimulus for endothelial caveolin-1 and PV-1 was increased in podocytes of BTBR ob/ob mice and normalized by SGLT2 inhibitor treatment. Thus, empagliflozin's protective effect on the glomerular endothelium of diabetic mice could be due to a limitation of the paracrine signaling of podocyte-derived VEGF-A that resulted in a reduction of the abnormal endothelial caveolin-1 and PV-1, with the consequent preservation of glomerular endothelial function and permeability. This article is protected by copyright. All rights reserved.

Long-standing donor diabetes and pathologic findings are associated with shorter allograft survival in recipients of kidney transplants from diabetic donors

Approximately 6% of deceased kidney donors (DKDs) are diabetic; their kidneys may be associated with worse allograft survival, but published studies suggest that recipient diabetes status has a greater impact on mortality and survival. Since biopsy findings are the most common reason for organ discard, we sought to understand histologic and clinical factors that influence graft survival in patients who receive a kidney from a diabetic DKD. We retrospectively reviewed our institutional experience from 2005 to 2019, and re-evaluated pre-implantation and earliest post-transplant biopsies. Histologic findings were compared against a control cohort of non-diabetic DKD. Of 829 adult DKD transplants, 37 (4.5%) came from diabetic donors. There was no significant difference in diabetic vs. non-diabetic DKD graft survival for all-comers; however, when stratified by duration of donor diabetes, donor diabetes ≥6 years was associated with graft failure. In 25 patients with post-transplant biopsies available, diabetic DKD allografts had significantly greater non-glomerular chronic injury than non-diabetic DKD allografts. Moderate arteriolar hyalinosis (in 24%), moderate tubular atrophy and interstitial fibrosis (IFTA, in 36%), and diabetic glomerulopathy (in 24%) on early post-transplant biopsy were associated with allograft failure. Pre-implantation frozen section discrepancies were more common in long-standing donor diabetes, and arteriolar hyalinosis and IFTA scores on frozen accurately prognosticated graft loss. There was no morphologic improvement in lesions of diabetic nephropathy on short-term follow-up. In conclusion, donor diabetes ≥6 years, and histologic findings on frozen section and early post-transplant biopsy are associated with diabetic DKD allograft loss.

Pathologic Diabetic Nephropathy in Autopsied Diabetic Cases With Normoalbuminuria From a Japanese Community-Based Study

Introduction

Albuminuria is a clinical hallmark of diabetic nephropathy (DN). Nevertheless, it is controversial whether pathologic DN lesions exist in individuals with diabetes with normoalbuminuria. We investigated the association between albuminuria levels and the frequency of DN lesions in autopsied diabetic cases from a Japanese community.

Methods

A total of 106 autopsied cases with diabetes mellitus (mean age = 76 years, 43.4% male) who died within 6 years after their last health examination were included in the study. Urinary albumin-creatinine ratio (UACR) levels were divided into the following 3 groups: <30.0, 30.0 to 299.9, and ≥300.0 mg/g. The kidney specimens were evaluated with light microscopy. Glomerular DN lesions were categorized into class 0 to I, IIa, IIb, and III glomerular DN lesions according to the criteria of the Renal Pathology Society. A Cochran-Armitage test was used to evaluate the association between the UACR levels and the presence of class IIa or higher glomerular DN lesions.

Results

The frequency of class IIa or higher glomerular DN lesions was 63.2% (IIa, 36.8%; IIb, 3.8%; and III, 22.6%) among overall cases. The frequencies increased significantly with higher UACR levels (P for trend = 0.02). The frequency of class IIa or higher glomerular DN lesions was 51.2%, even in individuals with UACR < 30 mg/g.

Conclusion

This study revealed a positive association of the UACR levels with the presence of class IIa or higher glomerular DN lesions, which were also frequently found even in the normal range of UACR levels, among autopsied diabetic cases from a Japanese community.

Regression of diabetic nephropathy by treatment with empagliflozin in BTBR ob/ob mice

BACKGROUND

The SGLT2 inhibitor empagliflozin lowers blood glucose via reduced tubular reabsorption of filtered glucose and is an important new therapy for diabetic nephropathy (DN). This study tested whether treatment with empagliflozin would ameliorate proteinuria and the pathologic alterations of DN including podocyte number and integrity in the leptin deficient BTBR ob/ob mouse model of DN.

METHODS

Study cohorts included wild type BTBR mice, untreated diabetic BTBR ob/ob mice, and mice treated with empagliflozin for six weeks after development of established DN at 18 weeks of age.

RESULTS

Hyperglycemia, proteinuria, serum creatinine, accumulation of mesangial matrix and the extent of mesangiolysis were reversed with empagliflozin treatment. Treatment with empagliflozin resulted in increased podocyte number and podocyte density, improvement in the degree of podocyte foot process effacement and parietal epithelial cell activation. SGLT2 inhibition reduced renal oxidative stress, measured by urinary excretion of markers of RNA/DNA damage and in situ demonstration of decreased carbonyl oxidation. There was no discernable difference in accumulations of advanced glycation endproducts by immunohistochemistry.

CONCLUSION

The structural improvements seen in BTBR ob/ob mice treated with empagliflozin provide insight into potential long term benefits for humans with DN, for whom there is no comparable biopsy information to identify structural changes effected by SGLT2 inhibition. The findings suggest SGLT2 inhibition may ameliorate diabetic nephropathy through glucose lowering-dependent and -independent mechanisms that lead to podocyte restoration and delay or reversal of the disease progress.

The recruitment mechanisms and potential therapeutic targets of podocytes from parietal epithelial cells

Podocytes are differentiated postmitotic cells which cannot be replaced after podocyte injury. The mechanism of podocyte repopulation after injury has aroused wide concern. Parietal epithelial cells (PECs) are heterogeneous and only a specific subpopulation of PECs has the capacity to replace podocytes. Major progress has been achieved in recent years regarding the role and function of a subset of PECs which could transdifferentiate toward podocytes. Additionally, several factors, such as Notch, Wnt/ß-catenin, Wilms’ tumor-1, miR-193a and growth arrest-specific protein 1, have been shown to be involved in these processes. Finally, PECs serve as a potential therapeutic target in the conditions of podocyte loss. In this review, we discuss the latest observations and concepts about the recruitment of podocytes from PECs in glomerular diseases as well as newly identified mechanisms and the most recent treatments for this process.

Parietal epithelial cell dysfunction in crescentic glomerulonephritis

Crescentic glomerulonephritis represents a group of kidney diseases characterized by rapid loss of kidney function and the formation of glomerular crescents. While the role of the immune system has been extensively studied in relation to the development of crescents, recent findings show that parietal epithelial cells play a key role in the pathophysiology of crescent formation, even in the absence of immune modulation. This review highlights our current understanding of parietal epithelial cell biology and the reported physiological and pathological roles that these cells play in glomerular lesion formation, especially in the context of crescentic glomerulonephritis.

Reversal of hypertriglyceridemia in diabetic BTBR ob/ob mice does not prevent nephropathy

The etiology of diabetic nephropathy in type 2 diabetes is multifactorial. Sustained hyperglycemia is a major contributor, but additional contributions come from the hypertension, obesity, and hyperlipidemia that are also commonly present in patients with type 2 diabetes and nephropathy. The leptin deficient BTBR ob/ob mouse is a model of type 2 diabetic nephropathy in which hyperglycemia, obesity, and hyperlipidemia, but not hypertension, are present. We have shown that reversal of the constellation of these metabolic abnormalities with leptin replacement can reverse the morphologic and functional manifestations of diabetic nephropathy. Here we tested the hypothesis that reversal specifically of the hypertriglyceridemia, using an antisense oligonucleotide directed against ApoC-III, an apolipoprotein that regulates the interactions of VLDL (very low density lipoproteins) with the LDL receptor, is sufficient to ameliorate the nephropathy of Type 2 diabetes. Antisense treatment resulted in reduction of circulating ApoC-III protein levels and resulted in substantial lowering of triglycerides to near-normal levels in diabetic mice versus controls. Antisense treatment did not ameliorate proteinuria or pathologic manifestations of diabetic nephropathy, including podocyte loss. These studies indicate that pathologic manifestations of diabetic nephropathy are unlikely to be reduced by lipid-lowering therapeutics alone, but does not preclude a role for such interventions to be used in conjunction with other therapeutics commonly employed in the treatment of diabetes and its complications.

Losartan Protects Podocytes against High Glucose-induced Injury by Inhibiting B7-1 Expression

The role of B7-1 in podocyte injury has received increasing attention. The aim of this study was to investigate whether losartan protects podocytes of patients with diabetic kidney disease (DKD) by regulating B7-1 and the underlying mechanisms. Rats with streptozotocin-induced DKD were treated with losartan for 8 weeks. Biochemical changes in blood and urine were analyzed. Kidneys were isolated for electron microscopy, immunofluorescence, real-time quantitative PCR (RT-PCR), and Western blot analysis. Immortalized mouse podocyte cells were cultured in normal or high glucose medium in the presence or absence of losartan for 48 h, and then the cells were collected for immunofluorescence, PCR, Western blotting and monolayer permeability detection. The phosphatidylinositol 3-kinase (PI3K) 110α subunit and angiotensin II type 1 receptor (AT1R) plasmids were transfected into podocytes, respectively, and then Western blotting was performed to assess the expression of B7-1 protein. The results showed that losartan ameliorated podocyte structure and function in the rat model of DKD, and reduced the expression of B7-1 protein. Overexpression of PI3K 110α subunit in podocytes attenuated the inhibitory effect of losartan on B7-1 expression in high glucose-stimulated podocytes. The expression of B7-1 was significantly increased by overexpression of AT1R and significantly reduced by blocking PI3K 110α subunit. We conclude that losartan protects podocytes against high glucose-induced injury by inhibiting AT1R-mediated B7-1 expression. This effect is dependent on the AT1R-PI3K 110α subunit pathway.

Caspase-11/4 and gasdermin D-mediated pyroptosis contributes to podocyte injury in mouse diabetic nephropathy

Diabetic nephropathy (DN) is characterized by sterile inflammation with continuous injury and loss of renal inherent parenchyma cells. Podocyte is an essential early injury target in DN. The injury and loss of podocytes are closely associated with proteinuria, the early symptom of renal injury in DN. However, the exact mechanism for podocyte injury and death in DN remains ambiguous. In this study we investigated whether pyroptosis, a newly discovered cell death pathway was involved in DN. Diabetic mice were generated by high-fat diet/STZ injections. We showed that the expression levels of caspase-11 and cleavage of gasdermin D (GSDMD-N) in podocytes were significantly elevated, accompanied by reduced expression of podocyte makers nephrin and podocin, loss and fusion in podocyte foot processes, increased inflammatory cytokines NF-κB, IL-1β, and IL-18, macrophage infiltration, glomerular matrix expansion and increased urinary albumin to creatinine ratio (UACR). All these changes in diabetic mice were blunted by knockout of caspase-11 or GSDMD. Cultured human and mouse podocytes were treated with high glucose (30 mM), which significantly increased the expression levels of caspase-11 or caspase-4 (the homolog of caspase-11 in human), GSDMD-N, NF-κB, IL-1β, and IL-18, and decreased the expression of nephrin and podocin. Either caspase-4 or GSDMD knockdown by siRNA significantly blunted these changes. In summary, our results demonstrate that caspase-11/4 and GSDMD-mediated pyroptosis is activated and involved in podocyte loss under hyperglycemia condition and the development of DN.

Combined Melatonin and Extracorporeal Shock Wave Therapy Enhances Podocyte Protection and Ameliorates Kidney Function in a Diabetic Nephropathy Rat Model

(1) Background: Diabetic nephropathy (DN) is common complication of diabetes. Current therapy for DN does not include promotion of podocyte protection. Therefore, we investigated the therapeutic effect of melatonin (Mel) combined extracorporeal shock wave (SW) therapy on a DN rat model. (2) Methods: The DN rats were treated with Mel (5 mg/kg) twice a week for 6 weeks and SW treatment once a week (0.13 mJ/mm²) for 6 weeks. We assessed urine microalbumin, albumin to creatinine ratio (ACR), glomerular hypertrophy, glomerular fibrosis, podocyte markers (Wilm’s tumor protein-1, synaptopodin and nephrin), cell proliferation, cell survival, cell apoptosis, renal inflammation and renal oxidative stress. (3) Results: The Mel combined SW therapy regimen significantly reduced urine microalbumin excretion (3.3 ± 0.5 mg/dL, p < 0.001), ACR (65.2 ± 8.3 mg/g, p < 0.001), glomerular hypertrophy (3.1 ± 0.1 × 10⁶ μm³, p < 0.01) and glomerular fibrosis (0.9 ± 0.4 relative mRNA fold, p < 0.05). Moreover, the Mel combined SW therapy regimen significantly increased podocyte number (44.1 ± 5.0% area of synaptopodin, p < 0.001) in the Mel combined SW group. This is likely primarily because Mel combined with SW therapy significantly reduced renal inflammation (753 ± 46 pg/mg, p < 0.01), renal oxidative stress (0.6 ± 0.04 relative density, p < 0.05), and apoptosis (0.3 ± 0.03 relative density, p < 0.001), and also significantly increased cell proliferation (2.0 ± 0.2% area proliferating cell nuclear antigen (PCNA), p < 0.01), cell survival, and nephrin level (4.2 ± 0.4 ng/mL, p < 0.001). (4) Conclusions: Mel combined SW therapy enhances podocyte protection and ameliorates kidney function in a DN rat model. Mel combined SW therapy may serve as a novel noninvasive and effective treatment of DN.

Therapeutic Potential of Mesenchymal Stem Cells in a Pre-Clinical Model of Diabetic Kidney Disease and Obesity

Diabetic kidney disease (DKD) is a worldwide microvascular complication of type 2 diabetes mellitus (T2DM). From several pathological mechanisms involved in T2DM-DKD, we focused on mitochondria damage induced by hyperglycemia-driven reactive species oxygen (ROS) accumulation and verified whether mesenchymal stem cells (MSCs) anti-oxidative, anti-apoptotic, autophagy modulation, and pro-mitochondria homeostasis therapeutic potential curtailed T2DM-DKD progression. For that purpose, we grew immortalized glomerular mesangial cells (GMCs) in hyper glucose media containing hydrogen peroxide. MSCs prevented these cells from apoptosis-induced cell death, ROS accumulation, and mitochondria membrane potential impairment. Additionally, MSCs recovered GMCs' biogenesis and mitophagy-related gene expression that were downregulated by stress media. In BTBRob/ob mice, a robust model of T2DM-DKD and obesity, MSC therapy (1 × 106 cells, two doses 4-weeks apart, intra-peritoneal route) led to functional and structural kidney improvement in a time-dependent manner. Therefore, MSC-treated animals exhibited lower levels of urinary albumin-to-creatinine ratio, less mesangial expansion, higher number of podocytes, up-regulation of mitochondria-related survival genes, a decrease in autophagy hyper-activation, and a potential decrease in cleaved-caspase 3 expression. Collectively, these novel findings have important implications for the advancement of cell therapy and provide insights into cellular and molecular mechanisms of MSC-based therapy in T2DM-DKD setting.

Parietal epithelial cells role in repair versus scarring after glomerular injury

PURPOSE OF REVIEW

The recent years have been marked by the publication of several articles highlighting the pathophysiological role of glomerular parietal epithelial cells (PEC) and refining their phenotypic heterogeneity.

RECENT FINDINGS

The present review synthetizes recent findings on (i) the potential regenerative role of PEC in glomerular diseases, and (ii) the mechanisms and signaling of leading to PEC pathogenic involvement in crescentic glomerulonephritis (CGN) and focal segmental glomerulosclerosis (FSGS).

SUMMARY

The debate is still open regarding the podocyte regenerative properties of PEC in glomerular disease, whereas the pathogenic involvement of PEC activation in glomerular disease is increasingly admitted. Recent highlights on the podocyte regenerative role of PEC, on one hand, and on their pathological function, on the other hand, for sure will feed the debate in the kidney community for the next years. Nevertheless, from a therapeutic perspective, the two options, boosting cellular regeneration and blocking PECs pathogenicity, should not be seen as antagonistic but, rather, complementary.

Molecular Mechanisms of Renal Progenitor Regulation: How Many Pieces in the Puzzle?

Kidneys of mice, rats and humans possess progenitors that maintain daily homeostasis and take part in endogenous regenerative processes following injury, owing to their capacity to proliferate and differentiate. In the glomerular and tubular compartments of the nephron, consistent studies demonstrated that well-characterized, distinct populations of progenitor cells, localized in the parietal epithelium of Bowman capsule and scattered in the proximal and distal tubules, could generate segment-specific cells in physiological conditions and following tissue injury. However, defective or abnormal regenerative responses of these progenitors can contribute to pathologic conditions. The molecular characteristics of renal progenitors have been extensively studied, revealing that numerous classical and evolutionarily conserved pathways, such as Notch or Wnt/β-catenin, play a major role in cell regulation. Others, such as retinoic acid, renin-angiotensin-aldosterone system, TLR2 (Toll-like receptor 2) and leptin, are also important in this process. In this review, we summarize the plethora of molecular mechanisms directing renal progenitor responses during homeostasis and following kidney injury. Finally, we will explore how single-cell RNA sequencing could bring the characterization of renal progenitors to the next level, while knowing their molecular signature is gaining relevance in the clinic.

Mesenchymal Stem Cell Therapy for Diabetic Kidney Disease: A Review of the Studies Using Syngeneic, Autologous, Allogeneic, and Xenogeneic Cells

Diabetic kidney disease (DKD) is a microvascular complication of diabetes mellitus (DM) and comprises multifactorial pathophysiologic mechanisms. Despite current treatment, around 30-40% of individuals with type 1 and type 2 DM (DM1 and DM2) have progressive DKD, which is the most common cause of end-stage chronic kidney disease worldwide. Mesenchymal stem cell- (MSC-) based therapy has important biological and therapeutic implications for curtailing DKD progression. As a chronic disease, DM may impair MSC microenvironment, but there is compelling evidence that MSC derived from DM1 individuals maintain their cardinal properties, such as potency, secretion of trophic factors, and modulation of immune cells, so that both autologous and allogeneic MSCs are safe and effective. Conversely, MSCs derived from DM2 individuals are usually dysfunctional, exhibiting higher rates of senescence and apoptosis and a decrease in clonogenicity, proliferation, and angiogenesis potential. Therefore, more studies in humans are needed to reach a conclusion if autologous MSCs from DM2 individuals are effective for treatment of DM-related complications. Importantly, the bench to bedside pathway has been constructed in the last decade for assessing the therapeutic potential of MSCs in the DM setting. Laboratory research set the basis for establishing further translation research including preclinical development and proof of concept in model systems. Phase I clinical trials have evaluated the safety profile of MSC-based therapy in humans, and phase II clinical trials (proof of concept in trial participants) still need to answer important questions for treating DKD, yet metabolic control has already been documented. Therefore, randomized and controlled trials considering the source, optimal cell number, and route of delivery in DM patients are further required to advance MSC-based therapy. Future directions include strategies to reduce MSC heterogeneity, standardized protocols for isolation and expansion of those cells, and the development of well-designed large-scale trials to show significant efficacy during a long follow-up, mainly in individuals with DKD.

Anti-inflammatory, antioxidant and renoprotective effects of SOCS1 mimetic peptide in the BTBR ob/ob mouse model of type 2 diabetes

INTRODUCTION

Diabetic nephropathy (DN) is the leading cause of chronic kidney disease worldwide. The Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway participates in the development and progression of DN. Among the different mechanisms involved in JAK/STAT negative regulation, the family of suppressor of cytokine signaling (SOCS) proteins has been proposed as a new target for DN. Our aim was to evaluate the effect of SOCS1 mimetic peptide in a mouse model of obesity and type 2 diabetes (T2D) with progressive DN.

RESEARCH DESIGN AND METHODS

Six-week-old BTBR (black and tan brachyuric) mice with the ob/ob (obese/obese) leptin-deficiency mutation were treated for 7 weeks with two different doses of active SOCS1 peptide (MiS1 2 and 4 µg/g body weight), using inactive mutant peptide (Mut 4 µg) and vehicle as control groups. At the end of the study, the animals were sacrificed to obtain blood, urine and kidney tissue for further analysis.

RESULTS

Treatment of diabetic mice with active peptide significantly decreased urine albumin to creatinine ratio by up to 50%, reduced renal weight, glomerular and tubulointerstitial damage, and restored podocyte numbers. Kidneys from treated mice exhibited lower inflammatory infiltrate, proinflammatory gene expression and STAT activation. Concomitantly, active peptide administration modulated redox balance markers and reduced lipid peroxidation and cholesterol transporter gene expression in diabetic kidneys.

CONCLUSION

Targeting SOCS proteins by mimetic peptides to control JAK/STAT signaling pathway ameliorates albuminuria, morphological renal lesions, inflammation, oxidative stress and lipotoxicity, and could be a therapeutic approach to T2D kidney disease.

Parietal epithelial cell differentiation to a podocyte fate in the aged mouse kidney

Healthy aging is typified by a progressive and absolute loss of podocytes over the lifespan of animals and humans. To test the hypothesis that a subset of glomerular parietal epithelial cell (PEC) progenitors transition to a podocyte fate with aging, dual reporter PEC-rtTA|LC1|tdTomato|Nphs1-FLPo|FRT-EGFP mice were generated. PECs were inducibly labeled with a tdTomato reporter, and podocytes were constitutively labeled with an EGFP reporter. With advancing age (14 and 24 months) glomeruli in the juxta-medullary cortex (JMC) were more severely injured than those in the outer cortex (OC). In aged mice (24m), injured glomeruli with lower podocyte number (41% decrease), showed more PEC migration and differentiation to a podocyte fate than mildly injured or healthy glomeruli. PECs differentiated to a podocyte fate had ultrastructural features of podocytes and co-expressed the podocyte markers podocin, nephrin, p57 and VEGF164, but not markers of mesangial (Perlecan) or endothelial (ERG) cells. PECs differentiated to a podocyte fate did not express CD44, a marker of PEC activation. Taken together, we demonstrate that a subpopulation of PECs differentiate to a podocyte fate predominantly in injured glomeruli in mice of advanced age.

MicroRNAs in Podocyte Injury in Diabetic Nephropathy

Diabetic nephropathy is one of the major complications of diabetes mellitus and is the leading cause of end-stage renal disease worldwide. Podocyte injury contributes to the development of diabetic nephropathy. However, the molecules that regulate podocyte injury in diabetic nephropathy have not been fully clarified. MicroRNAs (miRNAs) are small non-coding RNAs that can inhibit the translation of target messenger RNAs. Previous reports have described alteration of the expression levels of many miRNAs in cultured podocyte cells stimulated with a high glucose concentration and podocytes in rodent models of diabetic nephropathy. The associations between podocyte injury and miRNA expression levels in blood, urine, and kidney in patients with diabetic nephropathy have also been reported. Moreover, modulation of the expression of several miRNAs has been shown to have protective effects against podocyte injury in diabetic nephropathy in cultured podocyte cells in vitro and in rodent models of diabetic nephropathy in vivo. Therefore, this review focuses on miRNAs in podocyte injury in diabetic nephropathy, with regard to their potential as biomarkers and miRNA modulation as a therapeutic option.

Drug Testing for Residual Progression of Diabetic Kidney Disease in Mice Beyond Therapy with Metformin, Ramipril, and Empagliflozin

BACKGROUND

Progression of CKD in type 2 diabetes, despite dual inhibition of sodium-glucose transporter-2 and the renin-angiotensin system, remains a concern. Bromoindirubin-3'-oxime (BIO), previously reported to promote podocyte survival and regeneration, is a candidate additional drug to elicit renoprotective effects beyond therapy with metformin, ramipril, and empagliflozin (MRE). Evaluating a drug with standard therapeutics more closely mimics the clinical setting than evaluating the drug alone.

METHODS

Uninephrectomized BKS-Lepr-/- (db/db) mice treated with or without MRE served as a model of progressive CKD in type 2 diabetes. Mice on or off MRE were randomized to only 4 weeks of add-on BIO or vehicle. The primary end point was slope of GFR (ΔGFR).

RESULTS

Four weeks of MRE treatment alone did not affect ΔGFR, but significantly attenuated hyperglycemia, albuminuria, and glomerulosclerosis and increased podocyte filtration slit density, as assessed by STED super-resolution microscopy upon tissue clearing. BIO alone improved albuminuria, podocyte density in superficial and juxtamedullary nephrons, and podocyte filtration slit density. MRE+BIO combination therapy had additive protective effects on ΔGFR, glomerulosclerosis, podocyte density in juxtamedullary nephrons, and filtration slit density.

CONCLUSIONS

Add-on treatment with BIO for only 4 weeks attenuates progression of CKD beyond MRE therapy in mice with type 2 diabetes. Additional drug combinations may help to further delay ESKD in type 2 diabetes.

Targeting NF-κB by the Cell-Permeable NEMO-Binding Domain Peptide Improves Albuminuria and Renal Lesions in an Experimental Model of Type 2 Diabetic Nephropathy

Diabetic nephropathy (DN) is a multifactorial disease characterized by hyperglycemia and close interaction of hemodynamic, metabolic and inflammatory factors. Nuclear factor-κB (NF-κB) is a principal matchmaker linking hyperglycemia and inflammation. The present work investigates the cell-permeable peptide containing the inhibitor of kappa B kinase γ (IKKγ)/NF-κB essential modulator (NEMO)-binding domain (NBD) as therapeutic option to modulate inflammation in a preclinical model of type 2 diabetes (T2D) with DN. Black and tan, brachyuric obese/obese mice were randomized into 4 interventions groups: Active NBD peptide (10 and 6 µg/g body weight); Inactive mutant peptide (10 µg/g); and vehicle control. In vivo/ex vivo fluorescence imaging revealed efficient delivery of NBD peptide, systemic biodistribution and selective renal metabolization. In vivo administration of active NBD peptide improved albuminuria (>40% reduction on average) and kidney damage, decreased podocyte loss and basement membrane thickness, and modulated the expression of proinflammatory and oxidative stress markers. In vitro, NBD blocked IKK-mediated NF-κB induction and target gene expression in mesangial cells exposed to diabetic-like milieu. These results constitute the first nephroprotective effect of NBD peptide in a T2D mouse model that recapitulates the kidney lesions observed in DN patients. Targeting IKK-dependent NF-κB activation could be a therapeutic strategy to combat kidney inflammation in DN.

Podocyte and endothelial-specific elimination of BAMBI identifies differential transforming growth factor-β pathways contributing to diabetic glomerulopathy

Transforming growth factor-β (TGF-β) is a central mediator of diabetic nephropathy. The effect of TGF-β, mediated by the type I TGF-β receptor, ALK5, and subsequent Smad2/3 activation results in podocyte apoptosis and loss. Previously, we demonstrated that the genetic deletion of the BMP and Activin Membrane-Bound Inhibitor (BAMBI), a negative modulator TGF-β signaling, accelerates diabetic nephropathy in mice. This was associated with heightened ALK1-mediated activation of Smad1/5 in the glomerular endothelial cells (ECs). Therefore, to evaluate the glomerular cell-specific effects of TGF-β in diabetic nephropathy we examined the effects of the podocyte- or EC-specific loss of Bambi (Pod-Bambi-/- or EC-Bambi-/-) in streptozotocin-induced diabetic mice with endothelial nitric oxide synthase deficiency. Interestingly, although hyperglycemia and body weight loss were similar in all groups of diabetic mice, significant hypertension was present only in the diabetic EC-Bambi-/- mice. While the podocyte or EC-specific loss of BAMBI both accelerated the progression of diabetic nephropathy, the worsened podocyte injury and loss observed in the diabetic Pod-Bambi-/- mice were associated with enhanced Smad3 activation. Increased Smad1/5 activation and EC proliferation were apparent only in the glomeruli of diabetic EC-Bambi-/- mice. The enhanced Smad1/5 activation in diabetic EC-Bambi-/- mice was associated with increased glomerular expression of plasmalemma vesicle-associated protein, pointing to the involvement of immature or dedifferentiated glomerular ECs in diabetic nephropathy. Notably, diabetic EC-Bambi-/- mice displayed podocyte injury and loss that were comparable to diabetic Pod-Bambi-/- mice. Thus, our results highlight the glomerular cell-specific contribution of TGF-β signaling and the intricate cross-talk between injured glomerular cells in the progression of diabetic nephropathy.

Beneficial effect on podocyte number in experimental diabetic nephropathy resulting from combined atrasentan and RAAS inhibition therapy

Podocyte loss and proteinuria are both key features of human diabetic nephropathy (DN). The leptin-deficient BTBR mouse strain with the ob/ob mutation develops progressive weight gain, type 2 diabetes, and diabetic nephropathy that has many features of advanced human DN, including increased mesangial matrix, mesangiolysis, podocyte loss, and proteinuria. Selective antagonism of the endothelin-1 type A receptor (ET_AR) by atrasentan treatment in combination with renin-angiotensin-aldosterone system inhibition with losartan has been shown to have the therapeutic benefit of lowering proteinuria in patients with DN, but the underlying mechanism for this benefit is not well understood. Using a similar therapeutic approach in diabetic BTBR ob/ob mice, this treatment regimen significantly increased glomerular podocyte number compared with diabetic BTBR ob/ob controls and suggested that parietal epithelial cells were a source for podocyte restoration. Atrasentan treatment alone also increased podocyte number but to a lesser degree. Mice treated with atrasentan demonstrated a reduction in proteinuria, matching the functional improvement reported in humans. This is a first demonstration that treatment with the highly selective ET_AR antagonist atrasentan can lead to restoration of the diminished podocyte number characteristic of DN in humans and thereby underlies the reduction in proteinuria in patients with diabetes undergoing similar treatment. The benefit of ET_AR antagonism in DN extended to a decrease in mesangial matrix as measured by a reduction in accumulations of collagen type IV in both the atrasentan and atrasentan + losartan-treated groups compared with untreated controls.

Targeting the RNA-Binding Protein QKI in Myeloid Cells Ameliorates Macrophage-Induced Renal Interstitial Fibrosis

In the pathophysiologic setting of acute and chronic kidney injury, the excessive activation and recruitment of blood-borne monocytes prompts their differentiation into inflammatory macrophages, a process that leads to progressive glomerulosclerosis and interstitial fibrosis. Importantly, this differentiation of monocytes into macrophages requires the meticulous coordination of gene expression at both the transcriptional and post-transcriptional level. The transcriptomes of these cells are ultimately determined by RNA-binding proteins such as QUAKING (QKI), that define their pre-mRNA splicing and mRNA transcript patterns. Using two mouse models, namely (1) quaking viable mice (qk^v) and (2) the conditional deletion in the myeloid cell lineage using the lysozyme 2-Cre (QKI^{FL/FL;LysM-Cre} mice), we demonstrate that the abrogation of QKI expression in the myeloid cell lineage reduces macrophage infiltration following kidney injury induced by unilateral urethral obstruction (UUO). The qk^v and QKI^{FL/FL;LysM-Cre} mice both showed significant diminished interstitial collagen deposition and fibrosis in the UUO-damaged kidney, as compared to wild-type littermates. We show that macrophages isolated from QKI^{FL/FL;LysM-Cre} mice are associated with defects in pre-mRNA splicing. Our findings demonstrate that reduced expression of the alternative splice regulator QKI in the cells of myeloid lineage attenuates renal interstitial fibrosis, suggesting that inhibition of this splice regulator may be of therapeutic value for certain kidney diseases.

Could IL-17A Be a Novel Therapeutic Target in Diabetic Nephropathy?

Chronic kidney disease has become a major medical issue in recent years due to its high prevalence worldwide, its association with premature mortality, and its social and economic implications. A number of patients gradually progress to end-stage renal disease (ESRD), requiring then dialysis and kidney transplantation. Currently, approximately 40% of patients with diabetes develop kidney disease, making it the most prevalent cause of ESRD. Thus, more effective therapies for diabetic nephropathy are needed. In preclinical studies of diabetes, anti-inflammatory therapeutic strategies have been used to protect the kidneys. Recent evidence supports that immune cells play an active role in the pathogenesis of diabetic nephropathy. Th17 immune cells and their effector cytokine IL-17A have recently emerged as promising targets in several clinical conditions, including renal diseases. Here, we review current knowledge regarding the involvement of Th17/IL-17A in the genesis of diabetic renal injury, as well as the rationale behind targeting IL-17A as an additional therapy in patients with diabetic nephropathy.

Excessive cholecalciferol supplementation increases kidney dysfunction associated with intrarenal artery calcification in obese insulin-resistant mice

Diabetes mellitus accelerates vascular calcification (VC) and increases the risk of end-stage renal disease (ESRD). Nevertheless, the impact of VC in renal disease progression in type 2 diabetes mellitus (T2DM) is poorly understood. We addressed the effect of VC and mechanisms involved in renal dysfunction in a murine model of insulin resistance and obesity (ob/ob), comparing with their healthy littermates (C57BL/6). We analyzed VC and renal function in both mouse strains after challenging them with Vitamin D₃ (VitD₃). Although VitD₃ similarly increased serum calcium and induced bone disease in both strains, 24-hour urine volume and creatinine pronouncedly decreased only in ob/ob mice. Moreover, ob/ob increased urinary albumin/creatinine ratio (ACR), indicating kidney dysfunction. In parallel, ob/ob developed extensive intrarenal VC after VitD₃. Coincidently with increased intrarenal vascular mineralization, our results demonstrated that Bone Morphogenetic Protein-2 (BMP-2) was highly expressed in these arteries exclusively in ob/ob. These data depict a greater susceptibility of ob/ob mice to develop renal disease after VitD₃ in comparison to paired C57BL/6. In conclusion, this study unfolds novel mechanisms of progressive renal dysfunction in diabetes mellitus (DM) after VitD₃in vivo associated with increased intrarenal VC and highlights possible harmful effects of long-term supplementation of VitD₃ in this population.

Differential expression of parietal epithelial cell and podocyte extracellular matrix proteins in focal segmental glomerulosclerosis and diabetic nephropathy

In healthy glomeruli, parietal epithelial cell (PEC)-derived extracellular matrix (ECM) proteins include laminin-β1, perlecan, and collagen type IV-α2 and podocyte-specific ECM proteins include laminin-β2, agrin, and collagen type IV-α4. This study aimed to define individual ECM protein isoform expression by PECs in both experimental and human focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy (DN) and to determine if changes were CD44 dependent. In experimental FSGS induced with a cytotoxic podocyte antibody and in the BTBR ob/ob mouse model of DN, PEC-derived protein staining was significantly increased in PECs. Dual staining also showed de novo expression of the podocyte-specific ECM proteins laminin-β2 and agrin in PECs. Similar findings were observed in biopsies from patients with FSGS and DN. Increases in individual ECM proteins colocalized with CD44 in PECs in disease. To determine the role of CD44, FSGS was induced in CD44-/- and CD44+/+ mice. PEC staining for perlecan, collagen type IV-α2, laminin-β2, and agrin were significantly lower in diseased CD44-/- mice compared with diseased CD44+/+ mice. These results show that in experimental and human FSGS and DN, PECs typically in an activated state, produce both PEC-derived and podocyte-specific ECM protein isoforms, and that the majority of these changes were dependent on CD44.

Histological Examination of the Diabetic Kidney

The increasing prevalence of diabetes worldwide has led to a concomitant rise in diabetic kidney disease (DKD) as a major cause of end-stage renal disease. Glomerular lesions constitute the most striking and consistent features identified in biopsies from patients with DKD, although tubulointerstitial injury has an important and often under-recognized role in the progression to overt nephropathy. In advanced stages of the disease, podocyte detachment is a pivotal event in the loss of glomerular filtration barrier integrity and may explain, at least in part, the inability of current therapies to halt renal function decline. This chapter details the systematic method that can be used to study renal tissue samples from diabetic patients, and the specific role of different imaging techniques, such as light microscopy, immunofluorescence microscopy, and transmission and scanning electron microscopy in detecting histologic lesions specific to DKD.

tRNA-derived fragments (tRFs) contribute to podocyte differentiation

Loss of glomerular podocytes is the crucial event in the progression of chronic kidney disease (CKD). tRNA-derived fragments (tRFs), a newfangled branch of small non-coding RNA (sncRNA), recently reported to play a vital part in several diseases. In present study, we aimed to detect and reveal the role of tRFs in podocyte differentiation. The expression levels of tRFs between undifferentiated and differentiated podocytes were sequenced by illumina nextseq 500, and further verified by quantitative RT-PCR. 69 upregulated and 70 downregulated tRFs in total were singled out (Fold change > 2, P < 0.05). Gene ontology (GO) analysis indicated they are involved in the biological processes of transcription, DNA-templated, positive regulation of transcription from RNA polymerase II promoter, angiogenesis, cell adhesion. Besides, KEGG analysis suggested that these differentially tRFs are associated with PI3K-Akt signaling pathway, Rap1 signaling pathway, Ras signaling pathway, MAPK signaling pathway, and Wnt signaling pathway. Therefore, the differentially tRFs might regulate the differentiation of podocyte and the process of CKD. The functions and mechanisms of tRFs in podocytes are needed to be further explored.

Altered expression of glucose metabolism associated genes in a tacrolimus‑induced post‑transplantation diabetes mellitus in rat model

Post‑transplantation diabetes mellitus (PTDM) is a known side effect in transplant recipients administered with immunosuppressant drugs, such as tacrolimus (Tac). Although injury of islet cells is considered a major reason for Tac‑induced PTDM, the involvement of insulin resistance in PTDM remains unknown. In the present study, expression levels of adipocytokines, glucose metabolism associated genes and peroxisome proliferator‑activated receptor (PPAR)‑γ in adipose, muscular and liver tissues from a rat model induced with Tac (1 mg/kg/day) were examined. Rats developed hyperglycemia and glucose intolerance after 10 days of Tac administration. A subgroup of diabetic rats was further treated with rosiglitazone (4 mg/kg), a PPAR‑γ activator. Adipose, muscle and liver tissues were obtained on day 15 after induction and the results demonstrated that expression levels of adipocytokines, PPAR‑γ and proteins in the insulin associated signaling pathway varied in the different groups. Rosiglitazone administration significantly improved hyperglycemia, glucose intolerance and expression levels of proteins associated with insulin signaling, as well as adipocytokines expression. The results of this study demonstrated that adipocytokines and PPAR‑γ signaling may serve important roles in the pathogenesis of Tac‑induced PTDM, which may provide a promising application in the treatment of PTDM in the future.