Notch1 and Notch2 in Podocytes Play Differential Roles During Diabetic Nephropathy Development

Dang-Gui-Bu-Xue decoction improves wound healing in diabetic rats by the activation of Notch signaling

Diabetes serves as a severe chronic disease that severely affects the normal life of human beings. Diabetes causes the complication of diabetic wound dysfunction, which is characterized by sustained inflammation, altered angiogenesis, delayed epithelialization and abnormal secretion of protease. Dang-Gui-Bu-Xue decoction (DBD) is a Chinese traditional medicine that comprises Radix Astragali and Radix Angelicae sinensis and is widely applied in treatment of multiple diseases owing to its functions against inflammation, lipid peroxidation and oxidative stress. Nevertheless, the impact of DBD on diabetic wound healing remains elusive. In this study, we aimed to explore the function of DBD in the regulation of wound healing. We observed that the gavage administration of DBD reduced the wound area, inflammatory infiltration, inflammatory factor levesl, and enhanced granulation tissue formation, wound extracellular matrix (ECM) production, and CD31 accumulation in the diabetic rat wound model, and the co-treatment of gavage administration and the external administration of gauze containing DBD further improved the wound healing effect, while the combination of Notch signaling inhibitor DAPT ((N- [N- (3, 5-difluorophenacetyl)-l-alanyl]-s-phenylglycinet-butyl ester)) could attenuate the improvement. Regarding to the mechanism, the expression levels of Notch1, Delta-like canonical Notch ligand 4 (Dll4), Jagged1, and Hairy Enhancer of Split-1 (Hes1) were increased by DBD, while the treatment of DAPT impaired the effect in the rats. Furthermore, we found that the high glucose (HG)-inhibited viability and tube formation were induced by DBD in human umbilical vein endothelial cells (HUVECs), in which DAPT could reverse this effect. Therefore, we concluded that DBD contributed to wound healing by the activation of Notch signaling. Our finding provides new insight into the potential role of DBD in promoting diabetic wound healing.

Desmosterol-driven atypical macrophage polarization regulates podocyte dynamics in diabetic nephropathy

BACKGROUND

Diabetic nephropathy (DN) stands as a leading diabetes complication, with macrophages intricately involved in its evolution. While glucose metabolism's impact on macrophage activity is well-established, cholesterol metabolism's contributions remain less explored. Our study seeks to elucidate this association.

METHODS AND RESULTS

Methods and Results: Gene expression analysis of monocytes from the blood of both normal and diabetic patients was conducted using public databases, showing that cholesterol metabolism pathways, especially Bloch and Kandutsch-Russell, were more altered in diabetic monocytes/macrophages than glucose-responsive pathways. When bone marrow-derived macrophages (BMDMs) were subjected to desmosterol, they exhibited an unconventional polarization. These BMDMs displayed heightened levels of both M1-related pro-inflammatory cytokines and M2-linked anti-inflammatory factors. Further, in co-culture, desmosterol-conditioned BMDMs paralleled M2 macrophages in augmenting Ki-67 + podocyte populations while mimicking M1 macrophages in elevating TUNEL + apoptotic podocytes. Comparable outcomes on podocytes were obtained using conditioned media from the respective BMDMs.

CONCLUSIONS

Our data underscores the pivotal role of cholesterol metabolism, particularly via desmosterol, in steering macrophages toward an unconventional polarization marked by both inflammatory and regulatory traits. Such unique macrophage behavior concurrently impacts podocyte proliferation and apoptosis, shedding fresh light on DN pathogenesis and hinting at potential therapeutic interventions.

Notch1 and Notch2 Signaling Exclusively but Cooperatively Maintain Fetal Myogenic Progenitors

Myogenic progenitors (MPs) generate myocytes that fuse to form myofibers during skeletal muscle development while maintaining the progenitor pool, which is crucial for generating sufficient muscle. Notch signaling has been known to reserve a population of embryonic MPs during primary myogenesis by promoting cell cycle exit and suppressing premature differentiation. However, the roles of individual Notch receptors (Notch1-4) during embryonic/fetal myogenesis are still elusive. In this study, we found that Notch1 and Notch2, which exhibit the highest structural similarity among Notch receptors, maintain the MP population by distinct mechanisms: Notch1 induces cell cycle exit and Notch2 suppresses premature differentiation. Moreover, genetic and cell culture studies showed that Notch1 and Notch2 signaling in MPs are distinctively activated by interacting with Notch ligand-expressing myofibers and MP-lineage cells, respectively. These results suggest that through different activation modes, Notch1 and Notch2 distinctively and cooperatively maintain MP population during fetal myogenesis for proper muscle development.

Altered Expression of EMT-Related Factors Snail, Wnt4, and Notch2 in the Short-Term Streptozotocin-Induced Diabetic Rat Kidneys

Background: The aim of this study was to determine the expression of epithelial to mesenchymal transition (EMT)-related transcription factors Snail, Wnt4, and Notch2 with key roles in renal fibrosis, in different renal areas of diabetic rats: glomeruli (G), proximal and distal convoluted tubules (PCT; DCT). Methods: Male Sprague Dawley rats were instilled with 55 mg/kg streptozotocin (diabetes mellitus type I model, DM group) or citrate buffer (control group). Kidney samples were collected 2 weeks and 2 months after DM induction and processed for immunohistochemistry. Results: Diabetic animals showed higher Wnt4 kidney expression both 2 weeks and 2 months post-DM induction, while Snail expression significantly increased only 2 weeks after DM initiation (p < 0.0001). We determined significantly higher expression of examined EMT-related genes in different kidney regions in diabetic animals compared with controls. The most substantial differences were observed in tubular epithelial cells in the period of 2 weeks after induction, with higher Snail and Wnt4 expression in PCT and increased Snail and Notch2 expression in DCT of diabetic animals (p < 0.0001; p < 0.001). Conclusion: The obtained results point to the EMT-related factors Snail, Wnt4, and Notch2 as a potential contributor to diabetic nephropathy development and progression. Changes in their expression, especially in PCT and DCT, could serve as diagnostic biomarkers for the early stages of DM and might be a promising novel therapeutic target in this condition.

SGLT2 inhibitors attenuate nephrin loss and enhance TGF-β1 secretion in type 2 diabetes patients with albuminuria: a randomized clinical trial

To evaluate the effect of SGLT2 inhibitor (SGLT2i) on albuminuria, nephrin (NPH) and transforming-growth-factor-beta₁ (TGF-β1) levels in urine and low-grade inflammation in type 2 diabetes (T2D) patients. A randomized, blank-controlled clinical trial included 68 T2D patients and 10 controls. Based on the urinary albumin-to-creatinine ratio (UACR), 68 diabetic patients were stratified into three levels, UACR < 30 mg/g, UACR ≧ 30 mg/g to ≦ 300 mg/g and UACR ˃ 300 mg/g, who were randomized (1:1:1) to receive SGLT2i treatment for 12 weeks. The concentrations of NPH and TGF-β1 in urine were measured as indications of podocyte injury and renal fibrosis. Low-grade inflammation was assessed by the levels of IL-6, TNFα and hsCRP. After 12 weeks of SGLT2i treatment, the levels of UACR and NPH decreased, UTGF-β1 increased in the T2D with microalbuminuria and macroalbuminuria groups, NPH (1.12 [0.59, 1.29] vs. 0.71 [0.41, 1.07] µg/ml, P = 0.022) and (1.29 [0.99, 1.96] vs. 0.93 [0.57, 1.31] µg/ml, P = 0.002), UTGF-β1 (4.88 ± 1.31 vs. 7.27 ± 1.21 pg/ml, P  < 0.001) and (4.30 ± 1.34 vs. 6.78 ± 2.59 pg/ml, P  < 0.001), respectively. The changes in NPH were positively correlated with the UACR and negatively correlated with UTGF-β1 in T2D with albuminuria. SGLT2i alleviate nephrin loss and enhance TGF-β1 excretion in urine in T2DM with albuminuria. The anti-albuminuric effect of SGLT2i could be attributed to mitigating podocyte apoptosis and attenuating renal fibrosis.

Trial registration This clinical trial was registered on 15/10/2019, in ClinicalTrials.gov, and the registry number is NCT04127084.

Revisiting the role of Notch in nephron segmentation confirms a role for proximal fate selection during mouse and human nephrogenesis

Notch signaling promotes maturation of nephron epithelia, but its proposed contribution to nephron segmentation into proximal and distal domains has been called into doubt. We leveraged single cell and bulk RNA-seq, quantitative immunofluorescent lineage/fate tracing, and genetically modified human induced pluripotent stem cells (iPSCs) to revisit this question in developing mouse kidneys and human kidney organoids. We confirmed that Notch signaling is needed for maturation of all nephron lineages, and thus mature lineage markers fail to detect a fate bias. By contrast, early markers identified a distal fate bias in cells lacking Notch2, and a concomitant increase in early proximal and podocyte fates in cells expressing hyperactive Notch1 was observed. Orthogonal support for a conserved role for Notch signaling in the distal/proximal axis segmentation is provided by the demonstration that nicastrin (NCSTN)-deficient human iPSC-derived organoids differentiate into TFA2B+ distal tubule and CDH1+ connecting segment progenitors, but not into HNF4A+ or LTL+ proximal progenitors.

MAD2B promotes podocyte injury through regulating Numb-dependent Notch 1 pathway in diabetic nephropathy

Rationale: Recent studies have demonstrated that the loss of podocyte is a critical event in diabetic nephropathy (DN). Previously, our group have found that the mitotic arrest deficient protein MAD2B was involved in high glucose (HG)-induced podocyte injury by regulating APC/C activity. However, the exact mechanism of MAD2B implicated in podocyte injury is still lacking. Methods: The experiments were conducted by using kidney tissues from streptozotocin (STZ) induced diabetic mice with or without podocyte-specific deletion of MAD2B and the cultured podocytes exposed to different treatments. Glomerular pathological injury was evaluated by periodic acid-Schiff staining and transmission electron microscopy. The endogenous interaction between MAD2B and Numb was discovered by yeast two-hybrid analysis and co-immunoprecipitation assay. The expressions of MAD2B, Numb and related pathway were detected by western blot, immunochemistry and immunofluorescence. Results: The present study revealed that MAD2B was upregulated in diabetic glomeruli and cultured podocytes under hyperglycemic conditions. Podocyte-specific deletion of MAD2B alleviated podocyte injury and renal function deterioration in mice of diabetic nephropathy. Afterwards, MAD2B was found to interact with Numb, which was downregulated in diabetic glomeruli and HG-stimulated cultured podocytes. Interestingly, MAD2B genetic deletion could partly reverse the decline of Numb in podocytes exposed to HG and in diabetic mice, and the expressions of Numb downstream molecules such as NICD and Hes-1 were decreased accordingly. In addition, overexpression of Numb ameliorated HG-induced podocyte injury. Conclusions: The present findings suggest that upregulated MAD2B expression contributes to Numb depletion and activation of Notch 1 signaling pathway, which ultimately leads to podocyte injury during DN progression.

Application of weighted gene co-expression network analysis to identify novel key genes in diabetic nephropathy

AIMS/INTRODUCTION

Diabetic nephropathy (DN) is among the leading causes of end-stage renal disease worldwide. DN pathogenesis remains largely unknown. Weighted gene co-expression network analysis is a powerful bioinformatic tool for identifying key genes in diseases.

MATERIALS AND METHODS

The datasets GSE30122, GSE104948, GSE37463 and GSE47185 containing 23 DN and 23 normal glomeruli samples were obtained from the National Center for Biotechnology Information Gene Expression Omnibus database. After data pre-processing, weighted gene co-expression network analysis was carried out to cluster significant modules. Then, Gene Set Enrichment Analysis-based Gene Ontology analysis and visualization of network were carried out to screen the key genes in the most significant modules. The connectivity map analysis was carried out to find the significant chemical compounds. Finally, some key genes were validated in in vivo and in vitro experiments.

RESULTS

A total of 454 upregulated and 392 downregulated genes were identified. A total of 16 modules were clustered, and the most significant modules (green, red and yellow modules) were determined. The green module was associated with extracellular matrix organization, the red module was associated with immunity reaction and the yellow module was associated with kidney development. We found several key genes in these three modules separately, and part of them were validated in vivo and in vitro successfully. We found the top 15 chemical compounds that could perturb the overall expression of key genes in DN.

CONCLUSION

Weighted gene co-expression network analysis was applied to DN expression profiling in combination with connectivity map analysis. Several novel key genes and chemical compounds were screened out, providing new molecular targets for DN.

The Role of PKM2 in Diabetic Microangiopathy

Diabetic microangiopathy is among the most common complications affecting patients with diabetes, and includes both diabetic retinopathy (DR) and diabetic nephropathy (DKD). Diabetic microangiopathy remains a persistent threat to the health and quality of life of affected patients. Mechanistically, the severity of DR and DKD is tied to mitochondrial and glucose metabolism abnormalities, with the activation of the glycolytic enzyme pyruvate kinase M2 (PKM2) contributing to mitochondrial and glomerular dysfunction, abnormal renal hemodynamics, and retinopathy. PKM2 can activate inflammatory bodies in macrophages to promote the release of inflammatory mediators, and serves as a key regulator of inflammatory factors, chemokines and adhesion molecules. As such, there is sufficient evidence that PKM2 can be used as a biomarker for the diagnosis of diabetes and diabetic microangiopathy. Here, we survey the mechanisms whereby PKM2 contributes to diabetes-related microvascular diseases, associated regulatory roles, post-translational modifications, and the potential utility of PKM2 as a therapeutic target. Through this literature review, we have determined that PKM2 offers promise as both a diagnostic marker and therapeutic target with direct relevance to research pertaining to diabetic microangiopathy.

Podocytopathy in Obesity: Challenges of Living Large

Renal injury resulting from obesity is a growing concern caused by the global obesity epidemic. We discuss the glomerular structure, obesity-related glomerular changes, and diagnostic pathologic criteria for obesity-related glomerulopathy. The three main hypothesized mechanisms of podocyte injury are mechanical stress on the podocytes, metabolic derangement, and genetic/molecular factors. Weight loss, renin-angiotensin-aldosterone system inhibitors, and improved insulin resistance may slow the progression. A more comprehensive understanding of obesity-related glomerulopathy will help in developing more effective therapies.

EP300/CBP is crucial for cAMP-PKA pathway to alleviate podocyte dedifferentiation via targeting Notch3 signaling

Podocyte injury is the hallmark of proteinuric glomerular diseases. Notch3 is neo-activated simultaneously in damaged podocytes and podocyte's progenitor cells of FSGS, indicating a unique role of Notch3. We previously showed that activation of cAMP-PKA pathway alleviated podocyte injury possibly via inhibiting Notch3 expression. However, the mechanisms are unknown. In the present study, Notch3 signaling was significantly activated in ADR-induced podocytes in vitro and in PAN nephrosis rats and patients with idiopathic FSGS in vivo, concomitantly with podocyte dedifferentiation. In cultured podocytes, pCPT-cAMP, a selective cAMP-PKA activator, dramatically blocked ADR-induced activation of Notch3 signaling as well as inhibition of cAMP-PKA pathway, thus alleviating the decreased cell viability and podocyte dedifferentiation. Bioinformatics analysis revealed EP300/CBP, a transcriptional co-activator, as a central hub for the crosstalk between these two signaling pathways. Additionally, CREB/KLF15 in cAMP-PKA pathway competed with RBP-J the major transcriptional factor of Notch3 signaling for binding to EP300/CBP. EP300/CBP siRNA significantly inhibited these two signaling transduction pathways and disrupted the interactions between the above major transcriptional factors. These data indicate a crucial role of EP300/CBP in regulating the crosstalk between cAMP-PKA pathway and Notch3 signaling and modulating the phenotypic change of podocytes, and enrich the reno-protective mechanisms of cAMP-PKA pathway.

Notch1 participates in the activation of autophagy in the hippocampus of type I diabetic mice

Notch1 not only plays a key role in the development of the nervous system but also modulates synaptic plasticity and memory. However, the role of Notch1 in the brain of diabetes is still unclear. We hypothesize that Notch1 is involved in type I diabetes-induced cognitive dysfunction. In this study, adult male C57BL/6J mice carrying a heterozygous null mutation in the Notch1 gene (Notch1^+/-) and wild-type littermate controls were used in this experiment. They were subjected to streptozocin (55 mg/kg, i.p.) for consecutive five days. After 12 weeks, the cognitive function of all mice was detected by novel object recognition (NOR) test and electrophysiological recording. Our results demonstrated that the levels of Notch1 mRNA and Notch1 receptor were increased in the hippocampus of the wild-type diabetic mice at 12 weeks. It suggested that the Notch1 signal pathway was activated. Compared with the wild-type diabetic mice, the discrimination index and the long-term potentiation was further decreased in the Notch1^+/- diabetic group, the impairment of neuronal ultrastructure was exacerbated in the hippocampus of the Notch1^+/- diabetic mice, and the number of synapses and autophagic vacuoles were significantly reduced in the Notch1^+/- diabetic group. Moreover, some postsynaptic associated protein expressions were down-regulated, as well as the Beclin1 expression and the ratio of LC3II/LC3I were reduced in the hippocampus of the Notch1^+/- diabetic mice. Interestingly, the phosphorylation of mTOR, Akt, and ERK1/2 were all inhibited in the Notch1^+/- diabetic group. Taken together, these results suggest that Notch1 deficiency deteriorates the synaptic plasticity and inhibits the activation of autophagy partly via the mTOR-independent signal pathway in the hippocampus of type I diabetic mice.

A Homozygous Dab1-/- Is a Potential Novel Cause of Autosomal Recessive Congenital Anomalies of the Mice Kidney and Urinary Tract

This study aimed to explore morphology changes in the kidneys of Dab1^−/− (yotari) mice, as well as expression patterns of reelin, NOTCH2, LC3B, and cleaved caspase3 (CASP3) proteins, as potential determinants of normal kidney formation and function. We assumed that Dab1 functional inactivation may cause disorder in a wide spectrum of congenital anomalies of the kidney and urinary tract (CAKUT). Animals were sacrificed at postnatal days P4, P11, and P14. Paraffin-embedded kidney tissues were sectioned and analyzed by immunohistochemistry using specific antibodies. Kidney specimens were examined by bright-field, fluorescence, and electron microscopy. Data were analyzed by two-way ANOVA and t-tests. We noticed that yotari kidneys were smaller in size with a reduced diameter of nephron segments and thinner cortex. TEM microphotographs revealed foot process effacement in the glomeruli (G) of yotari mice, whereas aberrations in the structure of proximal convoluted tubules (PCT) and distal convoluted tubules (DCT) were not observed. A significant increase in reelin expression, NOTCH2, LC3B and cleaved CASP3 proteins was observed in the glomeruli of yotari mice. Renal hypoplasia in conjunction with foot process effacement and elevation in the expression of examined proteins in the glomeruli revealed CAKUT phenotype and loss of functional kidney tissue of yotari.

The Role of Glomerular Epithelial Injury in Kidney Function Decline in Patients With Diabetic Kidney Disease in the TRIDENT Cohort

Introduction

Although diabetic kidney disease (DKD) is responsible for more than half of all chronic and end-stage kidney disease (ESKD), the association of light (LM) and electron microscopic (EM) structural changes with clinical parameters and prognosis in DKD is incompletely understood.

Methods

This is an interim analysis of 62 patients diagnosed with biopsy-confirmed DKD from the multicenter TRIDENT (Transformative Research in Diabetic Nephropathy) study. Twelve LM and 8 EM descriptors, representing changes in glomeruli, tubulointerstitium, and vasculature were analyzed for their relationship with clinical measures of renal function. Patients were followed every 6 months.

Results

Multivariable linear regression analysis revealed that estimated glomerular filtration rate (eGFR) upon enrollment correlated the best with interstitial fibrosis. On the other hand, the rate of kidney function decline (eGFR slope) correlated the most with glomerular lesions including global glomerulosclerosis and mesangiolysis. Unbiased clustering analysis based on histopathologic data identified 3 subgroups. The first cluster, encompassing subjects with the mildest histologic lesions, had the most preserved kidney function. The second and third clusters had similar degrees of kidney dysfunction and structural damage, but differed in the degree of glomerular epithelial cell and podocyte injury (podocytopathy DKD subtype). Cox proportional hazard analysis showed that subjects in cluster 2 had the highest risk to reach ESKD (hazard ratio: 17.89; 95% confidence interval: 2.13–149.79). Glomerular epithelial hyperplasia and interstitial fibrosis were significant predictors of ESKD in the multivariate model.

Conclusion

The study highlights the association between fibrosis and kidney function and identifies the role of glomerular epithelial changes and kidney function decline.

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.

Podocytopathies

Podocytopathies are kidney diseases in which direct or indirect podocyte injury drives proteinuria or nephrotic syndrome. In children and young adults, genetic variants in >50 podocyte-expressed genes, syndromal non-podocyte-specific genes and phenocopies with other underlying genetic abnormalities cause podocytopathies associated with steroid-resistant nephrotic syndrome or severe proteinuria. A variety of genetic variants likely contribute to disease development. Among genes with non-Mendelian inheritance, variants in APOL1 have the largest effect size. In addition to genetic variants, environmental triggers such as immune-related, infection-related, toxic and haemodynamic factors and obesity are also important causes of podocyte injury and frequently combine to cause various degrees of proteinuria in children and adults. Typical manifestations on kidney biopsy are minimal change lesions and focal segmental glomerulosclerosis lesions. Standard treatment for primary podocytopathies manifesting with focal segmental glomerulosclerosis lesions includes glucocorticoids and other immunosuppressive drugs; individuals not responding with a resolution of proteinuria have a poor renal prognosis. Renin-angiotensin system antagonists help to control proteinuria and slow the progression of fibrosis. Symptomatic management may include the use of diuretics, statins, infection prophylaxis and anticoagulation. This Primer discusses a shift in paradigm from patient stratification based on kidney biopsy findings towards personalized management based on clinical, morphological and genetic data as well as pathophysiological understanding.

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.

POFUT1 is dispensable for structure, function and survival of mouse podocytes

Pofut1 gene encodes a O-fucosyltransferase that adds fucose to the serine/threonine residue in the sequence of C²XXXX(S/T)C³ of EGF-like domain in a protein. O-fucosylation has been shown to be required for some EGF-like domain-containing proteins to function, e.g., Notch1, and POFUT1 deficiency could affect cellular function and cause diseases. Pofut1 is ubiquitously expressed, but its essentiality for most cell types is not known. In the present study, we examined the consequence of Pofut1 gene abrogation in mouse podocytes using Cre-loxP system, and found that the conditional knockout mice were indistinguishable from wild-type controls in urinary protein level, glomerular morphology, podocyte foot process ultrastructure, podocyte marker expression and podocyte numbers. These results indicated that POFUT1 is not essential for podocyte structure, function and survival in mice. To understand why POFUT1 is dispensable for podocytes, we searched mouse podocyte essential gene candidates (as determined by single-cell RNA-seq) and found only two POFUT1 substrates, NOTCH2 and tPA. It has been shown that abrogation of these genes does not cause podocyte injury, explaining dispensability of POFUT1 for mouse podocytes and demonstrating a feasibility to predict POFUT1 essentiality for a given cell type. At present, most mouse cell types have been subject to single-cell RNA-seq, making essential gene prediction and thus POFUT1 requirement prediction possible for the cell types.

The Role of Podocytes and Podocyte-Associated Biomarkers in Diagnosis and Treatment of Diabetic Kidney Disease

Diabetic kidney disease (DKD) is an important public health problem. Podocyte injury is a central event in the mechanism of DKD development. Podocytes are terminally differentiated, highly specialized glomerular visceral epithelial cells critical for the maintenance of the glomerular filtration barrier. Although potential mechanisms by which diabetic milieu contributes to irreversible loss of podocytes have been described, identification of markers that prognosticate either the development of DKD or the progression to end-stage kidney disease (ESKD) have only recently made it to the forefront. Currently, the most common marker of early DKD is microalbuminuria; however, this marker has significant limitations: not all diabetic patients with microalbuminuria will progress to ESKD and as many as 30% of patients with DKD have normal urine albumin levels. Several novel biomarkers indicating glomerular or tubular damage precede microalbuminuria, suggesting that the latter develops when significant kidney injury has already occurred. Because podocyte injury plays a key role in DKD pathogenesis, identification of markers of early podocyte injury or loss may play an important role in the early diagnosis of DKD. Such biomarkers in the urine include podocyte-released microparticles as well as expression of podocyte-specific markers. Here, we review the mechanisms by which podocyte injury contributes to DKD as well as key markers that have been recently implicated in the development and/or progression of DKD and might serve to identify individuals that require earlier preventative care and treatment in order to slow the progression to ESKD.

Transforming Growth Factor-Beta1 in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD) worldwide. Renin-angiotensin-aldosterone system (RAAS) inhibitors and sodium-glucose co-transporter 2 (SGLT2) inhibitors have shown efficacy in reducing the risk of ESRD. However, patients vary in their response to RAAS blockades, and the pharmacodynamic responses to SGLT2 inhibitors decline with increasing severity of renal impairment. Thus, effective therapy for DKD is yet unmet. Transforming growth factor-β1 (TGF-β1), expressed by nearly all kidney cell types and infiltrating leukocytes and macrophages, is a pleiotropic cytokine involved in angiogenesis, immunomodulation, and extracellular matrix (ECM) formation. An overactive TGF-β1 signaling pathway has been implicated as a critical profibrotic factor in the progression of chronic kidney disease in human DKD. In animal studies, TGF-β1 neutralizing antibodies and TGF-β1 signaling inhibitors were effective in ameliorating renal fibrosis in DKD. Conversely, a clinical study of TGF-β1 neutralizing antibodies failed to demonstrate renal efficacy in DKD. However, overexpression of latent TGF-β1 led to anti-inflammatory and anti-fibrosis effects in non-DKD. This evidence implied that complete blocking of TGF-β1 signaling abolished its multiple physiological functions, which are highly associated with undesirable adverse events. Ideal strategies for DKD therapy would be either specific and selective inhibition of the profibrotic-related TGF-β1 pathway or blocking conversion of latent TGF-β1 to active TGF-β1.

Panax Notoginseng Ameliorates Podocyte EMT by Targeting the Wnt/β-Catenin Signaling Pathway in STZ-Induced Diabetic Rats

Introduction

Epithelial–mesenchymal transition (EMT) may contribute to podocyte dysfunction in diabetic nephropathy (DN). Aiming to identify novel therapeutic options, we investigated the protective effects of Panax notoginseng (PN) on podocyte EMT in diabetic rats and explored its mechanisms.

Methods

Diabetes was induced in rats with streptozotocin (STZ) by intraperitoneal injection at 55 mg/kg. Diabetic rats were randomly divided into three groups, namely, diabetic rats, diabetic rats treated with beraprost sodium (BPS) at 0.6 mg/kg/d or PN at 0.4 g/kg/d p.o., for 12 weeks. Urinary albumin/creatinine ratio (ACR), biochemical parameters, renal histopathology, and podocyte morphological changes were evaluated. Protein expression of EMT markers (desmin, α-SMA, and nephrin) as well as components of the Wnt/β-catenin pathway (wnt1, β-catenin, and snail) was detected by immunohistochemistry and Western blot, respectively.

Results

In diabetic rats, severe hyperglycemia and albuminuria were detected. Moreover, mesangial expansion and podocyte foot process effacement were found markedly increased in diabetic kidneys. Increased protein expression of wnt1, β-catenin, snail, desmin, and α-SMA, as well as decreased protein expression of nephrin was detected in diabetic kidneys. All these abnormalities found in DN rats were partially restored by PN treatment.

Conclusion

PN ameliorated albuminuria and podocyte EMT in diabetic rats partly through inhibiting Wnt/β-catenin signaling pathway. These findings provide experimental arguments for a novel therapeutic option in DN.

EGCG targeting Notch to attenuate renal fibrosisviainhibition of TGFβ/Smad3 signaling pathway activation in streptozotocin-induced diabetic mice

EGCG may improve renal fibrosis by targeting Notchviainhibition of the TGFβ/Smad3 pathway in diabetic mice.

Alteration of thyroid hormone signaling triggers the diabetes-induced pathological growth, remodeling, and dedifferentiation of podocytes

Thyroid hormone (TH) signaling is a universal regulator of metabolism, growth, and development. Here, we show that TH-TH receptor (TH-TR) axis alterations are critically involved in diabetic nephropathy-associated (DN-associated) podocyte pathology, and we identify TRα1 as a key regulator of the pathogenesis of DN. In ZSF1 diabetic rats, T3 levels progressively decreased during DN, and this was inversely correlated with metabolic and renal disease worsening. These phenomena were associated with the reexpression of the fetal isoform TRα1 in podocytes and parietal cells of both rats and patients with DN and with the increased glomerular expression of the TH-inactivating enzyme deiodinase 3 (DIO3). In diabetic rats, TRα1-positive cells also reexpressed several fetal mesenchymal and damage-related podocyte markers, while glomerular and podocyte hypertrophy was evident. In vitro, exposing human podocytes to diabetes milieu typical components markedly increased TRα1 and DIO3 expression and induced cytoskeleton rearrangements, adult podocyte marker downregulation and fetal kidney marker upregulation, the maladaptive cell cycle induction/arrest, and TRα1-ERK1/2-mediated hypertrophy. Strikingly, T3 treatment reduced TRα1 and DIO3 expression and completely reversed all these alterations. Our data show that diabetic stress induces the TH-TRα1 axis to adopt a fetal ligand/receptor relationship pattern that triggers the recapitulation of the fetal podocyte phenotype and subsequent pathological alterations.

Growth hormone induces Notch1 signaling in podocytes and contributes to proteinuria in diabetic nephropathy

Growth hormone (GH) plays a significant role in normal renal function and overactive GH signaling has been implicated in proteinuria in diabetes and acromegaly. Previous results have shown that the glomerular podocytes, which play an essential role in renal filtration, express the GH receptor, suggesting the direct action of GH on these cells. However, the exact mechanism and the downstream pathways by which excess GH leads to diabetic nephropathy is not established. In the present article, using immortalized human podocytes in vitro and a mouse model in vivo, we show that excess GH activates Notch1 signaling in a γ-secretase-dependent manner. Pharmacological inhibition of Notch1 by γ-secretase inhibitor DAPT (N-[N-(3,5-Difluorophenacetyl)-l-alanyl]-S-phenyl glycine t-butylester) abrogates GH-induced epithelial to mesenchymal transition (EMT) and is associated with a reduction in podocyte loss. More importantly, our results show that DAPT treatment blocks cytokine release and prevents glomerular fibrosis, all of which are induced by excess GH. Furthermore, DAPT prevented glomerular basement membrane thickening and proteinuria induced by excess GH. Finally, using kidney biopsy sections from people with diabetic nephropathy, we show that Notch signaling is indeed up-regulated in such settings. All these results confirm that excess GH induces Notch1 signaling in podocytes, which contributes to proteinuria through EMT as well as renal fibrosis. Our studies highlight the potential application of γ-secretase inhibitors as a therapeutic target in people with diabetic nephropathy.

DNMT1 in Six2 Progenitor Cells Is Essential for Transposable Element Silencing and Kidney Development

BACKGROUND

Cytosine methylation of regulatory regions, such as promoters and enhancers, plays a key role in regulating gene expression, however, its role in kidney development has not been analyzed.

METHODS

To identify functionally important epigenome-modifying enzymes and genome regions where methylation modifications are functionally important for kidney development, we performed genome-wide methylation analysis, expression profiling, and systematic genetic targeting of DNA methyltransferases (Dnmt1, Dnmt3a, and Dnmt3b) and Ten-eleven translocation methylcytosine hydroxylases (Tet2) in nephron progenitor cells (Six2Cre) in mice.

RESULTS

Genome-wide methylome analysis indicated dynamic changes on promoters and enhancers during development. Six2CreDnmt3af/f, Six2CreDnmt3bf/f, and Six2CreTet2f/f mice showed no significant structural or functional renal abnormalities. In contrast, Six2CreDnmt1f/f mice died within 24 hours of birth, from a severe kidney developmental defect. Genome-wide methylation analysis indicated a marked loss of methylation of transposable elements. RNA sequencing detected endogenous retroviral transcripts. Expression of intracellular viral sensing pathways (RIG-I), early embryonic, nonrenal lineage genes and increased cell death contributed to the phenotype development. In podocytes, loss of Dnmt1, Dnmt3a, Dnmt3b, or Tet2 did not lead to functional or structural differences at baseline or after toxic injury.

CONCLUSIONS

Genome-wide cytosine methylation and gene expression profiling showed that by silencing embryonic, nonrenal lineage genes and transposable elements, DNMT1-mediated cytosine methylation is essential for kidney development.

Triggering of a Dll4-Notch1 loop impairs wound healing in diabetes

Diabetic foot ulcerations (DFUs) represent a major medical, social, and economic problem. Therapeutic options are restricted due to a poor understanding of the pathogenic mechanisms. The Notch pathway plays a pivotal role in cell differentiation, proliferation, and angiogenesis, processes that are profoundly disturbed in diabetic wounds. Notch signaling is activated upon interactions between membrane-bound Notch receptors (Notch 1-4) and ligands (Jagged 1-2 and Delta-like 1, 3, 4), resulting in cell-context-dependent outputs. Here, we report that Notch1 signaling is activated by hyperglycemia in diabetic skin and specifically impairs wound healing in diabetes. Local inhibition of Notch1 signaling in experimental wounds markedly improves healing exclusively in diabetic, but not in nondiabetic, animals. Mechanistically, high glucose levels activate a specific positive Delta-like 4 (Dll4)-Notch1 feedback loop. Using loss-of-function genetic approaches, we demonstrate that Notch1 inactivation in keratinocytes is sufficient to cancel the repressive effects of the Dll4-Notch1 loop on wound healing in diabetes, thus making Notch1 signaling an attractive locally therapeutic target for the treatment of DFUs.

Identification of six cardiovascular risk biomarkers in the young population: A promising tool for early prevention

BACKGROUND AND AIMS

The predictive value of traditional CV risk calculators is limited. Novel indicators of CVD progression are needed particularly in the young population. The main aim of this study was the identification of a molecular profile with added value to classical CV risk estimation.

METHODS

Eighty-one subjects (30-50 years) were classified in 3 groups according to their CV risk: healthy subjects; individuals with CV risk factors; and those who had suffered a previous CV event. The urine proteome was quantitatively analyzed and significantly altered proteins were identified between patients' groups, either related to CV risk or established organ damage. Target-MS and ELISA were used for confirmation in independent patients' cohorts. Systems Biology Analysis (SBA) was carried out to identify functional categories behind CVD.

RESULTS

4309 proteins were identified, 75 of them differentially expressed. ADX, ECP, FETUB, GDF15, GUAD and NOTCH1 compose a fingerprint positively correlating with lifetime risk estimate (LTR QRISK). Best performance ROC curve was obtained when ECP, GDF15 and GUAD were combined (AUC = 0.96). SBA revealed oxidative stress response, dilated cardiomyopathy, signaling by Wnt and proteasome, as main functional processes related to CV risk.

CONCLUSIONS

A novel urinary protein signature is shown, which correlates with CV risk estimation in young individuals. Pending further confirmation, this six-protein-panel could help in CV risk assessment.

Jagged1/Notch2 controls kidney fibrosis via Tfam-mediated metabolic reprogramming

While Notch signaling has been proposed to play a key role in fibrosis, the direct molecular pathways targeted by Notch signaling and the precise ligand and receptor pair that are responsible for kidney disease remain poorly defined. In this study, we found that JAG1 and NOTCH2 showed the strongest correlation with the degree of interstitial fibrosis in a genome-wide expression analysis of a large cohort of human kidney samples. Transcript analysis of mouse kidney disease models, including folic-acid (FA)-induced nephropathy, unilateral ureteral obstruction (UUO), or apolipoprotein L1 (APOL1)-associated kidney disease, indicated that Jag1 and Notch2 levels were higher in all analyzed kidney fibrosis models. Mice with tubule-specific deletion of Jag1 or Notch2 (Kspcre/Jag1flox/flox and Kspcre/Notch2flox/flox) had no kidney-specific alterations at baseline but showed protection from FA-induced kidney fibrosis. Tubule-specific genetic deletion of Notch1 and global knockout of Notch3 had no effect on fibrosis. In vitro chromatin immunoprecipitation experiments and genome-wide expression studies identified the mitochondrial transcription factor A (Tfam) as a direct Notch target. Re-expression of Tfam in tubule cells prevented Notch-induced metabolic and profibrotic reprogramming. Tubule-specific deletion of Tfam resulted in fibrosis. In summary, Jag1 and Notch2 play a key role in kidney fibrosis development by regulating Tfam expression and metabolic reprogramming.

Presenilin gene function and Notch signaling feedback regulation in the developing mouse lens

Presenilins (Psen1 and Psen2 in mice) are polytopic transmembrane proteins that act in the γ-secretase complex to make intra-membrane cleavages of their substrates, including the well-studied Notch receptors. Such processing releases the Notch intracellular domain, allowing it to physically relocate from the cell membrane to the nucleus where it acts in a transcriptional activating complex to regulate downstream genes in the signal-receiving cell. Previous studies of Notch pathway mutants for Jagged1, Notch2, and Rbpj demonstrated that canonical signaling is a necessary component of normal mouse lens development. However, the central role of Psens within the γ-secretase complex has never been explored in any developing eye tissue or cell type. By directly comparing Psen single and double mutant phenotypes during mouse lens development, we found a stronger requirement for Psen1, although both genes are needed for progenitor cell growth and to prevent apoptosis. We also uncovered a novel genetic interaction between Psen1 and Jagged1. By quantifying protein and mRNA levels of key Notch pathway genes in Psen1/2 or Jagged1 mutant lenses, we identified multiple points in the overall signaling cascade where feedback regulation can occur. Our data are consistent with the loss of particular genes indirectly influencing the transcription level of another. However, we conclude that regulating Notch2 protein levels is particularly important during normal signaling, supporting the importance of post-translational regulatory mechanisms in this tissue.

Suppression of microRNA-495 alleviates high-glucose-induced retinal ganglion cell apoptosis by regulating Notch/PTEN/Akt signaling

High glucose (HG)-induced apoptosis of retinal ganglion cells (RGCs) contributes to the pathogenesis of diabetic retinopathy, which is one of the most common and severe complications of diabetes mellitus. Accumulating evidence has documented that microRNAs (miRNAs) play an important role in the pathogenesis of diabetic retinopathy. However, the role of miRNAs in regulating HG-induced apoptosis of RGCs remains largely unknown. Various studies have suggested that miR-495 is an important regulator of cell apoptosis and survival. In this study, we aimed to investigate whether miR-495 is involved in regulating HG-induced apoptosis of RGCs and reveal its possible relevance in diabetic retinopathy. We found that miR-495 was significantly upregulated in HG-treated RGCs. Downregulation of miR-495 protected RGCs against HG-induced apoptosis, whereas overexpression of miR-495 had the opposite effect. Notably, Notch1 was identified as a target gene of miR-495, as miR-495 negatively regulated Notch1 expression and the Notch signaling pathway. Moreover, downregulation of miR-495 inhibited PTEN expression while promoting Akt activation. However, knockdown of Notch1 significantly abolished the protective effect of miR-495 inhibition against HG-induced apoptosis. Overall, our study suggests that downregulation of miR-495 alleviates HG-induced apoptosis of RGCs by targeting Notch1 to regulate PTEN/Akt signaling, which provides novel insights into understanding the pathogenesis of HG-induced apoptosis of RGCs.

Single-cell transcriptomics of the mouse kidney reveals potential cellular targets of kidney disease

Our understanding of kidney disease pathogenesis is limited by an incomplete molecular characterization of the cell types responsible for the organ's multiple homeostatic functions. To help fill this knowledge gap, we characterized 57,979 cells from healthy mouse kidneys by using unbiased single-cell RNA sequencing. On the basis of gene expression patterns, we infer that inherited kidney diseases that arise from distinct genetic mutations but share the same phenotypic manifestation originate from the same differentiated cell type. We also found that the collecting duct in kidneys of adult mice generates a spectrum of cell types through a newly identified transitional cell. Computational cell trajectory analysis and in vivo lineage tracing revealed that intercalated cells and principal cells undergo transitions mediated by the Notch signaling pathway. In mouse and human kidney disease, these transitions were shifted toward a principal cell fate and were associated with metabolic acidosis.

Activation of podocyte Notch mediates early Wt1 glomerulopathy

The Wilms' tumor suppressor gene, WT1, encodes a zinc finger protein that regulates podocyte development and is highly expressed in mature podocytes. Mutations in the WT1 gene are associated with the development of renal failure due to the formation of scar tissue within glomeruli, the mechanisms of which are poorly understood. Here, we used a tamoxifen-based CRE-LoxP system to induce deletion of Wt1 in adult mice to investigate the mechanisms underlying evolution of glomerulosclerosis. Podocyte apoptosis was evident as early as the fourth day post-induction and increased during disease progression, supporting a role for Wt1 in mature podocyte survival. Podocyte Notch activation was evident at disease onset with upregulation of Notch1 and its transcriptional targets, including Nrarp. There was repression of podocyte FoxC2 and upregulation of Hey2 supporting a role for a Wt1/FoxC2/Notch transcriptional network in mature podocyte injury. The expression of cleaved Notch1 and HES1 proteins in podocytes of mutant mice was confirmed in early disease. Furthermore, induction of podocyte HES1 expression was associated with upregulation of genes implicated in epithelial mesenchymal transition, thereby suggesting that HES1 mediates podocyte EMT. Lastly, early pharmacological inhibition of Notch signaling ameliorated glomerular scarring and albuminuria. Thus, loss of Wt1 in mature podocytes modulates podocyte Notch activation, which could mediate early events in WT1-related glomerulosclerosis.

High glucose induces podocyte epithelial‑to‑mesenchymal transition by demethylation‑mediated enhancement of MMP9 expression

Abnormal expression of matrix metalloproteinase 9 (MMP9) is correlated with podocyte epithelial-to-mesenchymal transition (EMT) in diabetic nephropathy (DN). However, the mechanisms underlying this process are not well defined. Site-specific demethylation may sustain high expression levels of target genes. In the present study, in order to investigate the association between DNA demethylation of MMP9 promoter and podocyte EMT in DN, human podocytes were cultured in high-glucose (HG) medium and a rat model of DN was established by intraperitoneal injection of streptozotocin (STZ) to determine whether site-specific demethylation of the MMP9 promoter was involved in regulating podocyte EMT in DN. The MTT assay was used to assess the effects of HG culture on the growth of podocytes, and the demethylation status of the MMP9 promoter was assessed by bisulfite sequencing polymerase chain reaction. mRNA and protein expression levels of MMP9, α-smooth muscle actin (α-SMA), podocalyxin and fibronectin-1 in podocytes were assessed by reverse transcription-quantitative PCR (RT-qPCR) and western blot analyses. The results demonstrated that HG treatment up regulated the expression of MMP9, α-SMA and fibronectin-1, but down regulated the expression of podocalyxin in podocytes. The MMP9 promoter region was revealed to contain a variety of demethylated CpG sites, and HG treatment reduced the rate of MMP9 promotermethylation, which, in turn, enhanced its promoter activity. In summary, these data suggested that demethylation of the MMP9 promoter may serve an important role in podocyte EMT in DN. The demethylation status of the MMP9 promoter maybe used as an important prognostic marker of DN in clinic.

Cell-Based High Content Analysis of Cell Proliferation and Apoptosis

High content imaging-based cell cycle analysis allows multiplexing of various parameters including DNA content, DNA synthesis, cell proliferation, and other cell cycle markers such as phosho-histone H3. 5'-Ethynyl-2'-deoxyuridine (EdU) incorporation is a thymidine analog that provides a sensitive method for the detection of DNA synthesis in proliferating cells that is a more convenient method than the traditional BrdU detection by antibody. Caspase 3 is activated in programmed cell death induced by both intrinsic (mitochondrial) and extrinsic factors (death ligand). Cell cycle and apoptosis are common parameters studied in the phenotypic analysis of compound toxicity and anti-cancer drugs. In this chapter, we describe methods for the detection of s-phase cell cycle progression by EdU incorporation, and caspase 3 activation using the CellEvent caspase 3/7 detection reagent.

Shifts in podocyte histone H3K27me3 regulate mouse and human glomerular disease

Histone protein modifications control fate determination during normal development and dedifferentiation during disease. Here, we set out to determine the extent to which dynamic changes to histones affect the differentiated phenotype of ordinarily quiescent adult glomerular podocytes. To do this, we examined the consequences of shifting the balance of the repressive histone H3 lysine 27 trimethylation (H3K27me3) mark in podocytes. Adriamycin nephrotoxicity and subtotal nephrectomy (SNx) studies indicated that deletion of the histone methylating enzyme EZH2 from podocytes decreased H3K27me3 levels and sensitized mice to glomerular disease. H3K27me3 was enriched at the promoter region of the Notch ligand Jag1 in podocytes, and derepression of Jag1 by EZH2 inhibition or knockdown facilitated podocyte dedifferentiation. Conversely, inhibition of the Jumonji C domain-containing demethylases Jmjd3 and UTX increased the H3K27me3 content of podocytes and attenuated glomerular disease in adriamycin nephrotoxicity, SNx, and diabetes. Podocytes in glomeruli from humans with focal segmental glomerulosclerosis or diabetic nephropathy exhibited diminished H3K27me3 and heightened UTX content. Analogous to human disease, inhibition of Jmjd3 and UTX abated nephropathy progression in mice with established glomerular injury and reduced H3K27me3 levels. Together, these findings indicate that ostensibly stable chromatin modifications can be dynamically regulated in quiescent cells and that epigenetic reprogramming can improve outcomes in glomerular disease by repressing the reactivation of developmental pathways.

Triptolide prevents extracellular matrix accumulation in experimental diabetic kidney disease by targeting microRNA-137/Notch1 pathway

MicroRNAs (miRNAs) are involved in multiple biological functions via suppressing target genes. Triptolide is a monomeric compound isolated from a traditional Chinese herb, which exerts protective roles in many kinds of glomerular diseases. However, our understanding of the triptolide effect on miRNAome is still limited. In this study, we found that triptolide significantly decreased albuminuria and improved glomerulosclerosis in rats with diabetic kidney disease (DKD). And triptolide also inhibited extracellular matrix (ECM) protein accumulation and the notch1 pathway activation under diabetic conditions. MiR-137 was significantly decreased in the HG (high glucose)-treated HRMCs and in the kidney tissues of the diabetic rats, but was upregulated by triptolide. In addition, overexpression of miR-137 exerted similar effects to those of triptolide, while miR-137 inhibition aggravated ECM protein accumulation. Luciferase reporter assay results demonstrated that miR-137 directly targets Notch1. Furthermore, the miR-137-dependent effects were due to Notch1 suppression that in turn inhibited ECM protein expression, key mediators of glomerulosclerosis. Finally, downregulation of miR-137 reversed the ECM inhibition role of triptolide in HG cultured HRMCs. Taken together, these findings indicate that triptolide is a potential therapeutic option for DKD and that miR-137/Notch1 pathway play roles in the anti-glomerulosclerosis mechanism of triptolide.

MDM2 Contributes to High Glucose-Induced Glomerular Mesangial Cell Proliferation and Extracellular Matrix Accumulation via Notch1

Murine double minute 2 (MDM2) is an E3-ubiquitin ligase critical for various biological functions. Previous data have revealed an indispensable role of MDM2 in kidney homeostasis. However, its role in glomerular mesangial cell (GMC) proliferation and extracellular matrix (ECM) accumulation during hyperglycemia condition remains unclear. In our present study, we found that MDM2 protein level was significantly upregulated in high glucose-treated GMCs, while knocking down MDM2 by siRNA could attenuate high glucose-induced ECM accumulation and GMCs proliferation. Unexpectedly, Nutlin-3a, a MDM2-p53 interaction blocker, had no benefit in protecting diabetic mice from renal impairment in vivo and in alleviating high glucose-induced ECM accumulation in vitro. Intriguingly, we found that Notch1 signaling activation was obviously attenuated by MDM2 depletion in GMCs with high glucose exposure. However, Numb, a substrate of MDM2 which suppresses Notch1 signaling, was found not to be involved in the MDM2 and Notch1 association. Moreover, our findings demonstrated that MDM2 interacted with Notch1 intracellular domain (NICD1) independent of Numb and regulated the ubiquitination status of NICD1. Collectively, our data propose a pivotal role of MDM2 in high glucose-induced GMC proliferation and ECM accumulation, via modulating the activation of Notch1 signaling pathway in an ubiquitination-dependent way.

Notch1 maintains dormancy of olfactory horizontal basal cells, a reserve neural stem cell

The remarkable capacity of the adult olfactory epithelium (OE) to regenerate fully both neurosensory and nonneuronal cell types after severe epithelial injury depends on life-long persistence of two stem cell populations: the horizontal basal cells (HBCs), which are quiescent and held in reserve, and mitotically active globose basal cells. It has recently been demonstrated that down-regulation of the ΔN form of the transcription factor p63 is both necessary and sufficient to release HBCs from dormancy. However, the mechanisms by which p63 is down-regulated after acute OE injury remain unknown. To identify the cellular source of potential signaling mechanisms, we assessed HBC activation after neuron-only and sustentacular cell death. We found that ablation of sustentacular cells is sufficient for HBC activation to multipotency. By expression analysis, next-generation sequencing, and immunohistochemical examination, down-regulation of Notch pathway signaling is coincident with HBC activation. Therefore, using HBC-specific conditional knockout of Notch receptors and overexpression of N1ICD, we show that Notch signaling maintains p63 levels and HBC dormancy, in contrast to its suppression of p63 expression in other tissues. Additionally, Notch1, but not Notch2, is required to maintain HBC dormancy after selective neuronal degeneration. Taken together, our data indicate that the activation of HBCs observed after tissue injury or sustentacular cell ablation is caused by the reduction/elimination of Notch signaling on HBCs; elimination of Jagged1 expressed by sustentacular cells may be the ligand responsible.

The effect of Astragalus polysaccharides on attenuation of diabetic cardiomyopathy through inhibiting the extrinsic and intrinsic apoptotic pathways in high glucose -stimulated H9C2 cells

Background

Apoptosis plays a critical role in the progression of diabetic cardiomyopathy (DC). Astragalus polysaccharides (APS), an extract of astragalus membranaceus (AM), is an effective cardioprotectant. Currently, little is known about the detailed mechanisms underlying cardioprotective effects of APS. The aims of this study were to investigate the potential effects and mechanisms of APS on apoptosis employing a model of high glucose induction of apoptosis in H9C2 cells.

Methods

A model of high glucose induction of H9C2 cell apoptosis was adopted in this research. The cell viabilities were analyzed by MTT assay, and the apoptotic response was quantified by flow cytometry. The expression levels of the apoptosis related proteins were determined by Real-time PCR and western blotting.

Results

Incubation of H9C2 cells with various concentrations of glucose (i.e., 5.5, 12.5, 25, 33 and 44 mmol/L) for 24 h revealed that cell viability was reduced by high glucose dose-dependently. Pretreatment of cells with APS could inhibit high glucose-induced H9C2 cell apoptosis by decreasing the expressions of caspases and the release of cytochrome C from mitochondria to cytoplasm. Further experiments also showed that APS could modulate the ratio of Bcl-2 to Bax in mitochondria.

Conclusions

APS decreases high glucose-induced H9C2 cell apoptosis by inhibiting the expression of pro-apoptotic proteins of both the extrinsic and intrinsic pathways and modulating the ratio of Bcl-2 to Bax in mitochondria.

Pyruvate kinase M2 activation may protect against the progression of diabetic glomerular pathology and mitochondrial dysfunction

Diabetic nephropathy (DN) is a major cause of end-stage renal disease, and therapeutic options for preventing its progression are limited. To identify novel therapeutic strategies, we studied protective factors for DN using proteomics on glomeruli from individuals with extreme duration of diabetes (ł50 years) without DN and those with histologic signs of DN. Enzymes in the glycolytic, sorbitol, methylglyoxal and mitochondrial pathways were elevated in individuals without DN. In particular, pyruvate kinase M2 (PKM2) expression and activity were upregulated. Mechanistically, we showed that hyperglycemia and diabetes decreased PKM2 tetramer formation and activity by sulfenylation in mouse glomeruli and cultured podocytes. Pkm-knockdown immortalized mouse podocytes had higher levels of toxic glucose metabolites, mitochondrial dysfunction and apoptosis. Podocyte-specific Pkm2-knockout (KO) mice with diabetes developed worse albuminuria and glomerular pathology. Conversely, we found that pharmacological activation of PKM2 by a small-molecule PKM2 activator, TEPP-46, reversed hyperglycemia-induced elevation in toxic glucose metabolites and mitochondrial dysfunction, partially by increasing glycolytic flux and PGC-1α mRNA in cultured podocytes. In intervention studies using DBA2/J and Nos3 (eNos) KO mouse models of diabetes, TEPP-46 treatment reversed metabolic abnormalities, mitochondrial dysfunction and kidney pathology. Thus, PKM2 activation may protect against DN by increasing glucose metabolic flux, inhibiting the production of toxic glucose metabolites and inducing mitochondrial biogenesis to restore mitochondrial function.

Natriuretic peptide receptor guanylyl cyclase-A pathway counteracts glomerular injury evoked by aldosterone through p38 mitogen-activated protein kinase inhibition

Guanylyl cyclase-A (GC-A) signaling, a natriuretic peptide receptor, exerts renoprotective effects by stimulating natriuresis and reducing blood pressure. Previously we demonstrated massive albuminuria with hypertension in uninephrectomized, aldosterone-infused, and high salt-fed (ALDO) systemic GC-A KO mice with enhanced phosphorylation of p38 mitogen-activated protein kinase (MAPK) in podocytes. In the present study, we examined the interaction between p38 MAPK and GC-A signaling. The administration of FR167653, p38 MAPK inhibitor, reduced systolic blood pressure (SBP), urinary albumin excretion, segmental sclerosis, podocyte injury, and apoptosis. To further investigate the local action of natriuretic peptide and p38 MAPK in podocytes, we generated podocyte-specific (pod) GC-A conditional KO (cKO) mice. ALDO pod GC-A cKO mice demonstrated increased urinary albumin excretion with marked mesangial expansion, podocyte injury and apoptosis, but without blood pressure elevation. FR167653 also suppressed urinary albumin excretion without reducing SBP. Finally, we revealed that atrial natriuretic peptide increased phosphorylation of MAPK phosphatase-1 (MKP-1) concomitant with inhibited phosphorylation of p38 MAPK in response to MAPK kinase 3 activation, thereby resulting in decreased mRNA expression of the apoptosis-related gene, Bax, and Bax/Bcl2 ratio in cultured podocytes. These results indicate that natriuretic peptide exerts a renoprotective effect via inhibiting phosphorylation of p38 MAPK in podocytes.

Stabilization of endogenous Nrf2 by minocycline protects against Nlrp3-inflammasome induced diabetic nephropathy

While a plethora of studies support a therapeutic benefit of Nrf2 activation and ROS inhibition in diabetic nephropathy (dNP), the Nrf2 activator bardoxolone failed in clinical studies in type 2 diabetic patients due to cardiovascular side effects. Hence, alternative approaches to target Nrf2 are required. Intriguingly, the tetracycline antibiotic minocycline, which has been in clinical use for decades, has been shown to convey anti-inflammatory effects in diabetic patients and nephroprotection in rodent models of dNP. However, the mechanism underlying the nephroprotection remains unknown. Here we show that minocycline protects against dNP in mouse models of type 1 and type 2 diabetes, while caspase -3,-6,-7,-8 and -10 inhibition is insufficient, indicating a function of minocycline independent of apoptosis inhibition. Minocycline stabilizes endogenous Nrf2 in kidneys of db/db mice, thus dampening ROS-induced inflammasome activation in the kidney. Indeed, minocycline exerts antioxidant effects in vitro and in vivo, reducing glomerular markers of oxidative stress. Minocycline reduces ubiquitination of the redox-sensitive transcription factor Nrf2 and increases its protein levels. Accordingly, minocycline mediated Nlrp3 inflammasome inhibition and amelioration of dNP are abolished in diabetic Nrf2^−/− mice. Taken together, we uncover a new function of minocycline, which stabilizes the redox-sensitive transcription factor Nrf2, thus protecting from dNP.

Notch signaling in cerebrovascular diseases (Review)

The Notch signaling pathway is a crucial regulator of numerous fundamental cellular processes. Increasing evidence suggests that Notch signaling is involved in inflammation and oxidative stress, and thus in the progress of cerebrovascular diseases. In addition, Notch signaling in cerebrovascular diseases is associated with apoptosis, angiogenesis and the function of blood-brain barrier. Despite the contradictory results obtained to date as to whether Notch signaling is harmful or beneficial, the regulation of Notch signaling may provide a novel strategy for the treatment of cerebrovascular diseases.

Challenging the dogma of mitochondrial reactive oxygen species overproduction in diabetic kidney disease

The paradigm that high glucose drives overproduction of superoxide from mitochondria as a unifying theory to explain end organ damage in diabetes complications has been tightly held for more than a decade. With the recent development of techniques and probes to measure the production of distinct reactive oxygen species (ROS) in vivo, this widely held dogma is now being challenged with the emerging view that specific ROS moieties are essential for the function of specific intracellular signaling pathways and represent normal mitochondrial function. This review will provide a balanced overview of the dual nature of ROS, detailing current evidence for ROS overproduction in diabetic kidney disease, with a focus on cell types and sources of ROS. The technical aspects of measurement of mitochondrial ROS, both in isolated mitochondria and emerging in vivo methods will be discussed. The counterargument, that mitochondrial ROS production is reduced in diabetic complications, is consistent with a growing recognition that stimulation of mitochondrial biogenesis and oxidative phosphorylation activity reduces inflammation and fibrosis. It is clear that there is an urgent need to fully characterize ROS production paying particular attention to spatiotemporal aspects and to factor in the relevance of ROS in the regulation of cellular signaling in the pathogenesis of diabetic kidney disease. With improved tools and real-time imaging capacity, a greater understanding of the complex role of ROS will be able to guide novel therapeutic regimens.

Developmental signalling pathways in renal fibrosis: the roles of Notch, Wnt and Hedgehog

Kidney fibrosis is a common histological manifestation of functional decline in the kidney. Fibrosis is a reactive process that develops in response to excessive epithelial injury and inflammation, leading to myofibroblast activation and an accumulation of extracellular matrix. Here, we describe how three key developmental signalling pathways - Notch, Wnt and Hedgehog (Hh) - are reactivated in response to kidney injury and contribute to the fibrotic response. Although transient activation of these pathways is needed for repair of injured tissue, their sustained activation is thought to promote fibrosis. Excessive Wnt and Notch expression prohibit epithelial differentiation, whereas increased Wnt and Hh expression induce fibroblast proliferation and myofibroblastic transdifferentiation. Notch, Wnt and Hh are fundamentally different signalling pathways, but their choreographed activation seems to be just as important for fibrosis as it is for embryonic kidney development. Decreasing the activity of Notch, Wnt or Hh signalling could potentially provide a new therapeutic strategy to ameliorate the development of fibrosis in chronic kidney disease.

Podocytes: the Weakest Link in Diabetic Kidney Disease?

Diabetes is increasing in prevalence and is the leading cause of end-stage renal disease in the United States. Diabetic kidney disease is considered a proteinuric glomerular disease. Although the glomerulus is composed of various cell types, research suggests that podocytes are critical to overall glomerular health. Podocyte injury has been identified as a pivotal event resulting in proteinuric kidney disease, glomerulosclerosis, and loss of renal function. Thus, understanding the signaling mechanisms that trigger podocyte injury in diabetic kidney disease might allow for the development of targeted therapeutics to prevent or ameliorate progression to end-stage renal failure. This review focuses on the role of podocytes in diabetic kidney disease.