The Notch pathway in podocytes plays a role in the development of glomerular disease

Identification of a novel nonsense mutation in α-galactosidase A that causes Fabry disease in a Chinese family

Fabry disease, a lysosomal storage disease, is an uncommon X-linked recessive genetic disorder stemming from abnormalities in the alpha-galactosidase gene (GLA) that codes human alpha-Galactosidase A (α-Gal A). To date, over 800 GLA mutations have been found to cause Fabry disease (FD). Continued enhancement of the GLA mutation spectrum will contribute to a deeper recognition and underlying mechanisms of FD. In this study, a 27-year-old male proband exhibited a typical phenotype of Fabry disease. Subsequently, family screening for Fabry disease was conducted, and high-throughput sequencing was employed to identify the mutated gene. The three-level structure of the mutated protein was analyzed, and its subcellular localization and enzymatic activity were determined. Apoptosis was assessed in GLA mutant cell lines to confirm the functional effects. As a result, a new mutation, c.777_778del (p. Gly261Leufs*3), in the GLA gene was identified. The mutation caused a frameshift during translation and the premature appearance of a termination codon, which led to a partial deletion of the domain in C-terminal region and altered the protein's tertiary structure. In vitro experiments revealed a significant reduction of the enzymatic activity in mutant cells. The expression was noticeably decreased at the mRNA and protein levels in mutant cell lines. Additionally, the subcellular localization of α-Gal A changed from a homogeneous distribution to punctate aggregation in the cytoplasm. GLA mutant cells exhibited significantly higher levels of apoptosis compared to wild-type cells.

Notch3 deletion regulates HIV-1 gene expression and systemic inflammation to ameliorate chronic kidney disease

Antiretroviral therapy (ART) has decreased HIV-1 associated morbidity. However, despite ART, immune cells remain latently infected and slowly release viral proteins, leading to chronic inflammation and HIV-1 associated comorbidities. New strategies are needed to target viral proteins and inflammation. We found activation of Notch3 in several renal cells of the HIV-1 mouse model (HIV-Tg26) and in patients with HIV associated Nephropathy. We hypothesized that targeting Notch3 activation constitutes an effective therapy for HIV-related chronic kidney diseases (HIV-CKD). We generated HIV-Tg26 mice with Notch3 knocked out (Tg-N3KO). Compared to HIV-Tg26 mice at 3 months, HIV-Tg-N3KO mice showed a marked reduction in renal injury, skin lesions and mortality rate. Bulk RNA sequencing revealed that N3KO not only reduced renal infiltrating cells but significantly reduced the expression of HIV genes. Moreover, Notch3 activated the HIV- promoter and induction of HIV-1 resulted in increased Notch3 activation indicating a feedback mechanism. Further, bone marrow derived macrophages (BMDMs) from HIV-Tg26 mice showed activation of Notch3 indicating systemic effects. Consistent with that, systemic levels of TNF-α, MCP-1 and other inflammatory chemokines and cytokines were reduced in Tg-N3KO mice. Thus, Notch3 inhibition/deletion has a dual therapeutic effect in HIV-CKD and may extend to other HIV-related pathologies.

Variants in tubule epithelial regulatory elements mediate most heritable differences in human kidney function

Kidney disease is highly heritable; however, the causal genetic variants, the cell types in which these variants function, and the molecular mechanisms underlying kidney disease remain largely unknown. To identify genetic loci affecting kidney function, we performed a GWAS using multiple kidney function biomarkers and identified 462 loci. To begin to investigate how these loci affect kidney function, we generated single-cell chromatin accessibility (scATAC-seq) maps of the human kidney and identified candidate cis-regulatory elements (cCREs) for kidney podocytes, tubule epithelial cells, and kidney endothelial, stromal, and immune cells. Kidney tubule epithelial cCREs explained 58% of kidney function SNP-heritability and kidney podocyte cCREs explained an additional 6.5% of SNP-heritability. In contrast, little kidney function heritability was explained by kidney endothelial, stromal, or immune cell-specific cCREs. Through functionally informed fine-mapping, we identified putative causal kidney function variants and their corresponding cCREs. Using kidney scATAC-seq data, we created a deep learning model (which we named ChromKid) to predict kidney cell type-specific chromatin accessibility from sequence. ChromKid and allele specific kidney scATAC-seq revealed that many fine-mapped kidney function variants locally change chromatin accessibility in tubule epithelial cells. Enhancer assays confirmed that fine-mapped kidney function variants alter tubule epithelial regulatory element function. To map the genes which these regulatory elements control, we used CRISPR interference (CRISPRi) to target these regulatory elements in tubule epithelial cells and assessed changes in gene expression. CRISPRi of enhancers harboring kidney function variants regulated NDRG1 and RBPMS expression. Thus, inherited differences in tubule epithelial NDRG1 and RBPMS expression may predispose to kidney disease in humans. We conclude that genetic variants affecting tubule epithelial regulatory element function account for most SNP-heritability of human kidney function. This work provides an experimental approach to identify the variants, regulatory elements, and genes involved in polygenic disease.

Characterizing Glomerular Barrier Dysfunction with Patient-Derived Serum in Glomerulus-on-a-Chip Models: Unveiling New Insights into Glomerulonephritis

Glomerulonephritis (GN) is characterized by podocyte injury or glomerular filtration dysfunction, which results in proteinuria and eventual loss of kidney function. Progress in studying the mechanism of GN, and developing an effective therapy, has been limited by the absence of suitable in vitro models that can closely recapitulate human physiological responses. We developed a microfluidic glomerulus-on-a-chip device that can recapitulate the physiological environment to construct a functional filtration barrier, with which we investigated biological changes in podocytes and dynamic alterations in the permeability of the glomerular filtration barrier (GFB) on a chip. We also evaluated the potential of GN-mimicking devices as a model for predicting responses to human GN. Glomerular endothelial cells and podocytes successfully formed intact monolayers on opposite sides of the membrane in our chip device. Permselectivity analysis confirmed that the chip was constituted by a functional GFB that could accurately perform differential clearance of albumin and dextran. Reduction in cell viability resulting from damage was observed in all serum-induced GN models. The expression of podocyte-specific marker WT1 was also decreased. Albumin permeability was increased in most models of serum-induced IgA nephropathy (IgAN) and membranous nephropathy (MN). However, sera from patients with minimal change disease (MCD) or lupus nephritis (LN) did not induce a loss of permeability. This glomerulus-on-a-chip system may provide a platform of glomerular cell culture for in vitro GFB in formation of a functional three-dimensional glomerular structure. Establishing a disease model of GN on a chip could accelerate our understanding of pathophysiological mechanisms of glomerulopathy.

Blockade of Notch1 Signaling Alleviated Podocyte Injury in Lupus Nephritis Via Inhibition of NLRP3 Inflammasome Activation

To explore the role of Notch1 pathway in the pathogenesis of podocyte injury, and to provide novel strategy for podocyte repair in lupus nephritis (LN). Bioinformatics analysis and immunofluorescence assay were applied to determine the expression and localization of Notch1 intracellular domain1 (NICD1) in kidneys of LN patients and MRL/lpr mice. The stable podocyte injury model in vitro was established by puromycin aminonucleoside (PAN) treatment. Expression of inflammasome activation related gene was detected by qPCR. The podocytes with PAN treatment were cultured with or without N-S-phenyl-glycine-t-butylester (DAPT), an inhibitor of Notch1 pathway. NICD1, Wilm'stumor1 (WT1), nucleotide-binding oligomerization domain-like receptors 3 (NLRP3), and absent in melanoma-like receptors 2 (AIM2) were detected by western blot. In vivo, MRL/lpr mice were administrated with DAPT or vehicle. The LN symptoms were assessed. The podocyte injury was evaluated, and the NLRP3 in podocytes of mice was detected. Notch1 pathway was overactivated in glomeruli of LN patients. NICD1 was colocalized with podocytes of LN patients and MRL/lpr mice. The inflammasome-related genes were significantly increased in podocytes with PAN treatment. NICD1 and NLRP3 were significantly decreased, while WT1 was significantly increased in injured podocytes treated with DAPT in vitro. In vivo, lupus-like symptoms were alleviated in DAPT treatment group. Notch1 pathway was inhibited in kidneys of mice treated with DAPT. The renal inflammation was reduced and the podocyte injury was mitigated in DAPT treatment group. The NLRP3 was decreased in podocytes of mice treated with DAPT. Notch1 pathway was overactivated in podocytes of LN patients and MRL/lpr mice. Blockade of Notch1 pathway reduced renal inflammation and alleviated podocyte injury via inhibition of NLRP3 inflammasome activation in LN.

Non-enzymatic glycation and diabetic kidney disease

Chronic diabetes leads to various complications including diabetic kidney disease (DKD). DKD is a major microvascular complication and the leading cause of morbidity and mortality in diabetic patients. Varying degrees of proteinuria and reduced glomerular filtration rate are the cardinal clinical manifestations of DKD that eventually progress into end-stage renal disease. Histopathologically, DKD is characterized by renal hypertrophy, mesangial expansion, podocyte injury, glomerulosclerosis, and tubulointerstitial fibrosis, ultimately leading to renal replacement therapy. Amongst the many mechanisms, hyperglycemia contributes to the pathogenesis of DKD via a mechanism known as non-enzymatic glycation (NEG). NEG is the irreversible conjugation of reducing sugars onto a free amino group of proteins by a series of events, resulting in the formation of initial Schiff's base and an Amadori product and to a variety of advanced glycation end products (AGEs). AGEs interact with cognate receptors and evoke aberrant signaling cascades that execute adverse events such as oxidative stress, inflammation, phenotypic switch, complement activation, and cell death in different kidney cells. Elevated levels of AGEs and their receptors were associated with clinical and morphological manifestations of DKD. In this chapter, we discussed the mechanism of AGEs accumulation, AGEs-induced cellular and molecular events in the kidney and their impact on the pathogenesis of DKD. We have also reflected upon the possible options to curtail the AGEs accumulation and approaches to prevent AGEs mediated adverse renal outcomes.

ASH2L-mediated H3K4me3 drives diabetic nephropathy through HIPK2 and Notch1 pathway

Diabetic nephropathy (DN) is one of the complications of diabetes. Long-term hyperglycemia in the kidney results in renal insufficiency, and eventually leads to end-stage renal disease. Epigenetic factor ASH2L has long been identified as a transcriptional activator, and we previously indicated that ASH2L aggravated fibrosis and inflammation in high glucose-induced glomerular mesangial cells, but the pathophysiological relevance and the mechanism of ASH2L-mediated H3K4me3 in DN is not well understood. Here we demonstrated that ASH2L is upregulated in glomeruli isolated from db/db mice. Loss of ASH2L protected glomerular injury caused by hyperglycemia, as evidenced by reduced albuminuria, preserved structure, decreased glomerular extracellular matrix deposition, and lowered renal glomerular expression of proinflammatory and profibrotic markers in db/db mice. Furthermore, we demonstrated that enrichment of ASH2L-mediated H3K4me3 on the promoter regions of ADAM17 and HIPK2 triggered their transcription, leading to aberrant activation of Notch1 signaling pathway, thereby contributing to fibrosis and inflammation in DN. The findings of this study provide compelling evidence for targeting ASH2L as a potential therapeutic strategy to prevent or slow down the progression of DN.

Notch activation defines immune-suppressive subsets of ccRCCs with unfavorable benefits from immunotherapy over VEGFR/mTOR inhibitors

The evolutionarily conserved Notch pathway, involved in cancer stem cell capacity and cancer immunity, may predict the benefit from immune checkpoint inhibitors (ICIs) in clear cell renal cell carcinoma (ccRCC). In the TCGA dataset, mRNA expression of Notch pathway genes identified three clusters with different prognoses and molecular characteristics. Based on the differentially expressed Notch pathway genes between clusters, we constructed the Notch-score, correlated with Notch activation, angiogenesis, PI3K-AKT-mTOR activity, and sensitivities to VEGFR/mTOR inhibitors. A high Notch-score was linked with more "resting"/"anti-inflammatory" rather than "activated"/"pro-inflammatory" tumor-infiltrating immune cells, inactivated immune pathways, and scarce any benefits from ICI-based therapies over VEGFR/mTOR inhibitors in the JAVELIN Renal 101 (avelumab plus axitinib vs. sunitinib) and the CheckMate-009/010/025 trials (nivolumab vs. everolimus). For the Notch-activated ccRCCs, ICIs provide limited advantages and might not be strongly recommended, by which the cost-effectiveness of treatments in ccRCCs may be potentially improved.

To Explore the Putative Molecular Targets of Diabetic Nephropathy and their Inhibition Utilizing Potential Phytocompounds

BACKGROUND

This review critically addresses the putative molecular targets of Diabetic Nephropathy (DN) and screens effective phytocompounds that can be therapeutically beneficial, and highlights their mechanistic modalities of action.

INTRODUCTION

DN has become one of the most prevalent complications of clinical hyperglycemia, with individual-specific variations in the disease spectrum that leads to fatal consequences. Diverse etiologies involving oxidative and nitrosative stress, activation of polyol pathway, inflammasome formation, Extracellular Matrix (ECM) modifications, fibrosis, and change in dynamics of podocyte functional and mesangial cell proliferation adds up to the clinical complexity of DN. Current synthetic therapeutics lacks target-specific approach, and is associated with the development of inevitable residual toxicity and drug resistance. Phytocompounds provides a vast diversity of novel compounds that can become an alternative therapeutic approach to combat the DN.

METHODS

Relevant publications were searched and screened from research databases like GOOGLE SCHOLAR, PUBMED and SCISEARCH. Out of 4895 publications, the most relevant publications were selected and included in this article.

RESULT

This study critically reviews over 60 most promising phytochemical and provides with their molecular targets, that can be of pharmacological significance in context to current treatment and concomitant research in DN.

CONCLUSION

This review highlights those most promising phytocompounds that have the potential of becoming new safer naturally-sourced therapeutic candidates and demands further attention at clinical level.

Dysregulated coagulation system links to inflammation in diabetic kidney disease

Diabetic kidney disease (DKD) is a significant contributor to end-stage renal disease worldwide. Despite extensive research, the exact mechanisms responsible for its development remain incompletely understood. Notably, patients with diabetes and impaired kidney function exhibit a hypercoagulable state characterized by elevated levels of coagulation molecules in their plasma. Recent studies propose that coagulation molecules such as thrombin, fibrinogen, and platelets are interconnected with the complement system, giving rise to an inflammatory response that potentially accelerates the progression of DKD. Remarkably, investigations have shown that inhibiting the coagulation system may protect the kidneys in various animal models and clinical trials, suggesting that these systems could serve as promising therapeutic targets for DKD. This review aims to shed light on the underlying connections between coagulation and complement systems and their involvement in the advancement of DKD.

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

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

Polycystic kidneys: interaction of notch and renin

Polycystic kidney disease (PKD) is a developmental disorder, which either manifests in early childhood or later in life, depending on the genetic mutation one harbors. The mechanisms of cyst initiation are not well understood. Increasing literature is now suggesting that Notch signaling may play a critical role in PKD. Activation of Notch signaling is important during nephrogenesis and slows down after development. Deletion of various Notch molecules in the cap mesenchyme leads to formation of cysts and early death in mice. A new study by Belyea et al. has now found that cells of renin lineage may link Notch expression and cystic kidney disease. Here, we use our understanding of Notch signaling and PKD to speculate about the significance of these interactions.

Pericyte Loss in Diseases

Pericytes are specialized cells located in close proximity to endothelial cells within the microvasculature. They play a crucial role in regulating blood flow, stabilizing vessel walls, and maintaining the integrity of the blood-brain barrier. The loss of pericytes has been associated with the development and progression of various diseases, such as diabetes, Alzheimer's disease, sepsis, stroke, and traumatic brain injury. This review examines the detection of pericyte loss in different diseases, explores the methods employed to assess pericyte coverage, and elucidates the potential mechanisms contributing to pericyte loss in these pathological conditions. Additionally, current therapeutic strategies targeting pericytes are discussed, along with potential future interventions aimed at preserving pericyte function and promoting disease mitigation.

Notch1 signaling is limited in healthy mature kidneys in vivo

OBJECTIVE

A Delta-Notch signaling component, Notch1, is involved in the normal development and multiple disorders of the kidney. Although the increase in Notch1 signaling is crucial to these pathogeneses, the basal signaling level in 'healthy' mature kidneys is still unclear. To address this question, we used an artificial Notch1 receptor fused with Gal4/UAS components in addition to the Cre/loxP system and fluorescent proteins in mice. This transgenic reporter mouse system enabled labeling of past and ongoing Notch1 signaling with tdsRed or Cre recombinase, respectively.

RESULTS

We confirmed that our transgenic reporter mouse system mimicked the previously reported Notch1 signaling pattern. Using this successful system, we infrequently observed cells with ongoing Notch1 signaling only in Bowman's capsule and tubules. We consider that Notch1 activation in several lines of disease model mice was pathologically significant itself.

ADAM10 and ADAM17, Major Regulators of Chronic Kidney Disease Induced Atherosclerosis?

Chronic kidney disease (CKD) is a major health problem, affecting millions of people worldwide, in particular hypertensive and diabetic patients. CKD patients suffer from significantly increased cardiovascular disease (CVD) morbidity and mortality, mainly due to accelerated atherosclerosis development. Indeed, CKD not only affects the kidneys, in which injury and maladaptive repair processes lead to local inflammation and fibrosis, but also causes systemic inflammation and altered mineral bone metabolism leading to vascular dysfunction, calcification, and thus, accelerated atherosclerosis. Although CKD and CVD individually have been extensively studied, relatively little research has studied the link between both diseases. This narrative review focuses on the role of a disintegrin and metalloproteases (ADAM) 10 and ADAM17 in CKD and CVD and will for the first time shed light on their role in CKD-induced CVD. By cleaving cell surface molecules, these enzymes regulate not only cellular sensitivity to their micro-environment (in case of receptor cleavage), but also release soluble ectodomains that can exert agonistic or antagonistic functions, both locally and systemically. Although the cell-specific roles of ADAM10 and ADAM17 in CVD, and to a lesser extent in CKD, have been explored, their impact on CKD-induced CVD is likely, yet remains to be elucidated.

Cell Cycle and Senescence Regulation by Podocyte Histone Deacetylase 1 and 2

SIGNIFICANCE STATEMENT

The loss of integrity of the glomerular filtration barrier results in proteinuria that is often attributed to podocyte loss. Yet how damaged podocytes are lost remains unknown. Germline loss of murine podocyte-associated Hdac1 and Hdac2 ( Hdac1/2 ) results in proteinuria and collapsing glomerulopathy due to sustained double-stranded DNA damage. Hdac1/2 deletion induces loss of podocyte quiescence, cell cycle entry, arrest in G1, and podocyte senescence, observed both in vivo and in vitro . Through the senescence secretory associated phenotype, podocytes secrete proteins that contribute to their detachment. These results solidify the role of HDACs in cell cycle regulation and senescence, providing important clues in our understanding of how podocytes are lost following injury.

BACKGROUND

Intact expression of podocyte histone deacetylases (HDAC) during development is essential for maintaining a normal glomerular filtration barrier because of its role in modulating DNA damage and preventing premature senescence.

METHODS

Germline podocyte-specific Hdac1 and 2 ( Hdac1 / 2 ) double-knockout mice were generated to examine the importance of these enzymes during development.

RESULTS

Podocyte-specific loss of Hdac1 / 2 in mice resulted in severe proteinuria, kidney failure, and collapsing glomerulopathy. Hdac1 / 2 -deprived podocytes exhibited classic characteristics of senescence, such as senescence-associated β-galactosidase activity and lipofuscin aggregates. In addition, DNA damage, likely caused by epigenetic alterations such as open chromatin conformation, not only resulted in podocyte cell-cycle entry as shown in vivo by Ki67 expression and by FUCCI-2aR mice, but also in p21-mediated cell-cycle arrest. Through the senescence secretory associated phenotype, the damaged podocytes secreted proinflammatory cytokines, growth factors, and matrix metalloproteinases, resulting in subsequent podocyte detachment and loss, evidenced by senescent podocytes in urine.

CONCLUSIONS

Hdac1 / 2 plays an essential role during development. Loss of these genes in double knockout mice leads to sustained DNA damage and podocyte senescence and loss.

Molecular pathways that drive diabetic kidney disease

Kidney disease is a major driver of mortality among patients with diabetes and diabetic kidney disease (DKD) is responsible for close to half of all chronic kidney disease cases. DKD usually develops in a genetically susceptible individual as a result of poor metabolic (glycemic) control. Molecular and genetic studies indicate the key role of podocytes and endothelial cells in driving albuminuria and early kidney disease in diabetes. Proximal tubule changes show a strong association with the glomerular filtration rate. Hyperglycemia represents a key cellular stress in the kidney by altering cellular metabolism in endothelial cells and podocytes and by imposing an excess workload requiring energy and oxygen for proximal tubule cells. Changes in metabolism induce early adaptive cellular hypertrophy and reorganization of the actin cytoskeleton. Later, mitochondrial defects contribute to increased oxidative stress and activation of inflammatory pathways, causing progressive kidney function decline and fibrosis. Blockade of the renin-angiotensin system or the sodium-glucose cotransporter is associated with cellular protection and slowing kidney function decline. Newly identified molecular pathways could provide the basis for the development of much-needed novel therapeutics.

Notch Signaling in Acute Inflammation and Sepsis

Notch signaling, a highly conserved pathway in mammals, is crucial for differentiation and homeostasis of immune cells. Besides, this pathway is also directly involved in the transmission of immune signals. Notch signaling per se does not have a clear pro- or anti-inflammatory effect, but rather its impact is highly dependent on the immune cell type and the cellular environment, modulating several inflammatory conditions including sepsis, and therefore significantly impacts the course of disease. In this review, we will discuss the contribution of Notch signaling on the clinical picture of systemic inflammatory diseases, especially sepsis. Specifically, we will review its role during immune cell development and its contribution to the modulation of organ-specific immune responses. Finally, we will evaluate to what extent manipulation of the Notch signaling pathway could be a future therapeutic strategy.

Epigenetic regulation of Neuregulin 1 promotes breast cancer progression associated to hyperglycemia

Hyperglycemia is a risk factor for breast cancer-related morbidity and mortality. Hyperglycemia induces Neuregulin 1 (Nrg1) overexpression in breast cancer, which subsequently promotes tumor progression. However, molecular mechanisms underlying hyperglycemia-induced Nrg1 overexpression remain poorly understood. Here, we show that hyperglycemia causes active histone modifications at the Nrg1 enhancer, forming enhanceosome complexes where recombination signal binding protein for immunoglobulin kappa J region (RBPJ), E1A binding protein p300 (P300), and SET domain containing 1 A (SETD1A) are recruited to upregulate Nrg1 expression. Deletions in RBPJ-binding sites causes hyperglycemia-controlled Nrg1 levels to be downregulated, resulting in decreased tumor growth in vitro and in vivo. Mice with modest-temporary hyperglycemia, induced by low-dose short-exposure streptozotocin, display accelerated tumor growth and lapatinib resistance, whereas combining lapatinib with N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S42 phenylglycine t-butyl ester (DAPT) ameliorates tumor growth under these modest hyperglycemic conditions by inhibiting NOTCH and EGFR superfamilies. NOTCH activity is correlated with NRG1 levels, and high NRG1 levels predicts poor outcomes, particularly in HER2-positive breast cancer patients. Our findings highlight the hyperglycemia-linked epigenetic modulation of NRG1 as a potential therapeutic strategy for treating breast cancer patients with diabetes.

Notch Blockade Specifically in Bone Marrow-Derived FSP-1-Positive Cells Ameliorates Renal Fibrosis

BACKGROUND

The infiltration of inflammatory cells during a kidney injury stimulates myofibroblast activation leading to kidney fibrosis. Fibroblast-specific protein 1 (FSP-1) positive cells have been reported as either myofibroblasts or monocytes during tissue fibrosis. The functions of FSP-1⁺ cells that are associated with the development of renal fibrosis and the signaling pathways that regulate FSP-1⁺ cell activation have not been well defined.

METHODS

In mice with unilateral ureteral obstruction (UUO), we characterized FSP-1⁺ cells and determined the role of the Notch signaling pathway in the activation of bone marrow-derived FSP-1⁺ cells during kidney fibrosis.

RESULTS

In kidneys from mice with UUO, the FSP-1⁺ cells accumulated significantly in the tubulointerstitial area. By using immunostaining and FSP-1 reporter mice, we found that FSP-1 was co-stained with inflammatory cell markers, but not myofibroblast markers. Results from mice with bone marrow transplantations showed that FSP-1⁺ cells in obstructed kidneys represent a bone marrow-derived population of inflammatory cells. In cultured FSP-1⁺ cells, the inhibition of Notch signaling suppressed the activation and cytokine secretion of FSP-1⁺ cells that were induced by LPS but not by IL-4. The specific KO or blockade of Notch signaling in bone marrow-derived FSP-1⁺ cells suppressed UUO-induced ECM deposition, the infiltration of FSP-1⁺ inflammatory cells, and cytokine production. These responses ameliorated myofibroblast accumulation and renal fibrosis in obstructed kidneys.

CONCLUSION

Our study reveals that most FSP-1⁺ cells in obstructed kidneys are activated macrophages that are derived from bone marrow and that Notch signaling activates the production of M1 cytokines in FSP-1⁺ monocytes/macrophages, which is important for renal inflammation and fibrosis.

Abietic acid ameliorates nephropathy progression via mitigating renal oxidative stress, inflammation, fibrosis and apoptosis in high fat diet and low dose streptozotocin-induced diabetic rats

BACKGROUND

Abietic acid (AA) has been reported to exhibit anti-inflammatory activity, however its protective effect against inflammation and its trigger factor i.e., oxidative stress and the related sequelae i.e., apoptosis and fibrosis in the kidney in diabetes mellitus (DM) is unknown.

PURPOSE

To identify the ability of AA to mitigate the inflammatory and inflammation-related insults to the kidney in DM.

METHODS & STUDY DESIGN

Adult male rats were induced type-2 DM by feeding with a high-fat diet for twelve weeks followed by injection with a single dose of streptozotocin (STZ) (30 mg/kg/bw) intraperitoneally at twelve weeks. Following DM confirmation, AA (10 and 20 mg/kg/day) was given orally for another four weeks. Then the fasting blood glucose (FBG) and renal profile were determined and oral glucose tolerance test (OGTT) and insulin tolerance test (ITT) tests were performed. A day after the last treatment, rats were sacrificed and kidneys were harvested and subjected for histopathological and molecular biological analysis.

RESULTS

AA treatment was found to reduce the FBG, serum urea and creatinine levels (p < 0.05) while improving the OGTT and ITT (p < 0.05) in diabetic rats. Besides, AA treatment also mitigated kidney histopathological changes, reduces kidney oxidative stress as reflected by reduced levels of RAGE and Keap1 but increased levels of kidney antioxidants Nrf2, SOD, CAT, GPX, HO-1 & NQO-1 (p < 0.05). Additionally, AA treatment also decreases kidney inflammation (NF-kB p65, IL-1β, IL-6, TNF-α and iNOS) and fibrosis (TGF-β1 and GSK-3β) (p < 0/05). Kidney apoptosis decreased as reflected by decreased levels of Bax, caspase-3 and caspase-9 while its anti-apoptosis Bcl-2 protein levels increased (p < 0.05).

CONCLUSION

AA helps to mitigate nephropathy development in DM via counteracting oxidative stress, inflammation and apoptosis.

Podocytes are lost from glomeruli before completing apoptosis

Although apoptosis of podocytes has been widely reported in in vitro studies, it has been less frequently and less definitively documented in in vivo situations. To investigate this discrepancy, we analyzed the dying process of podocytes in vitro and in vivo using LMB2, a human (h)CD25-directed immunotoxin. LMB2 induced cell death within 2 days in 56.8 ± 13.6% of cultured podocytes expressing hCD25 in a caspase-3, Bak1, and Bax-dependent manner. LMB2 induced typical apoptotic features, including TUNEL staining and fragmented nuclei without lactate dehydrogenase leakage. In vivo, LMB2 effectively eliminated hCD25-expressing podocytes in NEP25 mice. Podocytes injured by LMB2 were occasionally stained for cleaved caspase-3 and cleaved lamin A but never for TUNEL. Urinary sediment contained TUNEL-positive podocytes. To examine the effect of glomerular filtration, we performed unilateral ureteral obstruction in NEP25 mice treated with LMB2 1 day before euthanasia. In the obstructed kidney, glomeruli contained significantly more cleaved lamin A-positive podocytes than those in the contralateral kidney (50.1 ± 5.4% vs. 29.3 ± 4.1%, P < 0.001). To further examine the dying process without glomerular filtration, we treated kidney organoids generated from nephron progenitor cells of NEP25 mice with LMB2. Podocytes showed TUNEL staining and nuclear fragmentation. These results indicate that on activation of apoptotic caspases, podocytes are detached and lost in the urine before nuclear fragmentation and that the physical force of glomerular filtration facilitates detachment. This phenomenon may be the reason why definitive apoptosis is not observed in podocytes in vivo.NEW & NOTEWORTHY This report clarifies why morphologically definitive apoptosis is not observed in podocytes in vivo. When caspase-3 is activated in podocytes, these cells are immediately detached from the glomerulus and lost in the urine before DNA fragmentation occurs. Detachment is facilitated by glomerular filtration. This phenomenon explains why podocytes in vivo rarely show TUNEL staining and never apoptotic bodies.

Emerging role of tumor suppressor p53 in acute and chronic kidney diseases

p53 is a major regulator of cell cycle arrest, apoptosis, and senescence. While involvement of p53 in tumorigenesis is well established, recent studies implicate p53 in the initiation and progression of several renal diseases, which is the focus of this review. Ischemic-, aristolochic acid (AA) -, diabetic-, HIV-associated-, obstructive- and podocyte-induced nephropathies are accompanied by activation and/or elevated expression of p53. Studies utilizing chemical or renal-specific inhibition of p53 in mice confirm the pathogenic role of this transcription factor in acute kidney injury and chronic kidney disease. TGF-β1, NOX, ATM/ATR kinases, Cyclin G, HIPK, MDM2 and certain micro-RNAs are important determinants of renal p53 function in response to trauma. AA, cisplatin or TGF-β1-mediated ROS generation via NOXs promotes p53 phosphorylation and subsequent tubular dysfunction. p53-SMAD3 transcriptional cooperation downstream of TGF-β1 orchestrates induction of fibrotic factors, extracellular matrix accumulation and pathogenic renal cell communication. TGF-β1-induced micro-RNAs (such as mir-192) could facilitate p53 activation, leading to renal hypertrophy and matrix expansion in response to diabetic insults while AA-mediated mir-192 induction regulates p53 dependent epithelial G2/M arrest. The widespread involvement of p53 in tubular maladaptive repair, interstitial fibrosis, and podocyte injury indicate that p53 clinical targeting may hold promise as a novel therapeutic strategy for halting progression of certain acute and chronic renal diseases, which affect hundreds of million people worldwide.

Differences in Immunohistochemical and Ultrastructural Features between Podocytes and Parietal Epithelial Cells (PECs) Are Observed in Developing, Healthy Postnatal, and Pathologically Changed Human Kidneys

During human kidney development, cells of the proximal nephron gradually differentiate into podocytes and parietal epithelial cells (PECs). Podocytes are terminally differentiated cells that play a key role in both normal and pathological kidney function. Therefore, the potential of podocytes to regenerate or be replaced by other cell populations (PECs) is of great interest for the possible treatment of kidney diseases. In the present study, we analyzed the proliferation and differentiation capabilities of podocytes and PECs, changes in the expression pattern of nestin, and several early proteins including WNT4, Notch2, and Snail, as well as Ki-67, in tissues of developing, postnatal, and pathologically changed human kidneys by using immunohistochemistry and electron microscopy. Developing PECs showed a higher proliferation rate than podocytes, whereas nestin expression characterized only podocytes and pathologically changed kidneys. In the developing kidneys, WNT4 and Notch2 expression increased moderately in podocytes and strongly in PECs, whereas Snail increased only in PECs in the later fetal period. During human kidney development, WNT4, Notch2, and Snail are involved in early nephrogenesis control. In kidneys affected by congenital nephrotic syndrome of the Finnish type (CNF) and focal segmental glomerulosclerosis (FSGS), WNT4 decreased in both cell populations, whereas Notch2 decreased in FSGS. In contrast, Snail increased both in CNF and FSGS, whereas Notch2 increased only in CNF. Electron microscopy revealed cytoplasmic processes spanning the urinary space between the podocytes and PECs in developing and healthy postnatal kidneys, whereas the CNF and FSGS kidneys were characterized by numerous cellular bridges containing cells with strong expression of nestin and all analyzed proteins. Our results indicate that the mechanisms of gene control in nephrogenesis are reactivated under pathological conditions. These mechanisms could have a role in restoring glomerular integrity by potentially inducing the regeneration of podocytes from PECs.

Precision Nephrology in Patients with Diabetes and Chronic Kidney Disease

Diabetes is the leading cause of kidney failure and specifically, diabetic kidney disease (DKD) occurs in up to 30% of all diabetic patients. Kidney disease attributed to diabetes is a major contributor to the global burden of the disease in terms of clinical and socio-economic impact, not only because of the risk of progression to End-Stage Kidney Disease (ESKD), but also because of the associated increase in cardiovascular (CV) risk. Despite the introduction of novel treatments that allow us to reduce the risk of future outcomes, a striking residual cardiorenal risk has been reported. This risk is explained by both the heterogeneity of DKD and the individual variability in response to nephroprotective treatments. Strategies that have been proposed to improve DKD patient care are to develop novel biomarkers that classify with greater accuracy patients with respect to their future risk (prognostic) and biomarkers that are able to predict the response to nephroprotective treatment (predictive). In this review, we summarize the principal prognostic biomarkers of type 1 and type 2 diabetes and the novel markers that help clinicians to individualize treatments and the basis of the characteristics that predict an optimal response.

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.

SARS-CoV-2 Employ BSG/CD147 and ACE2 Receptors to Directly Infect Human Induced Pluripotent Stem Cell-Derived Kidney Podocytes

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes the Coronavirus disease 2019 (COVID-19), which has resulted in over 5.9 million deaths worldwide. While cells in the respiratory system are the initial target of SARS-CoV-2, there is mounting evidence that COVID-19 is a multi-organ disease. Still, the direct affinity of SARS-CoV-2 for cells in other organs such as the kidneys, which are often targeted in severe COVID-19, remains poorly understood. We employed a human induced pluripotent stem (iPS) cell-derived model to investigate the affinity of SARS-CoV-2 for kidney glomerular podocytes, and examined the expression of host factors for binding and processing of the virus. We studied cellular uptake of the live SARS-CoV-2 virus as well as a pseudotyped virus. Infection of podocytes with live SARS-CoV-2 or spike-pseudotyped lentiviral particles revealed cellular uptake even at low multiplicity of infection (MOI) of 0.01. We found that direct infection of human iPS cell-derived podocytes by SARS-CoV-2 virus can cause cell death and podocyte foot process retraction, a hallmark of podocytopathies and progressive glomerular diseases including collapsing glomerulopathy observed in patients with severe COVID-19 disease. We identified BSG/CD147 and ACE2 receptors as key mediators of spike binding activity in human iPS cell-derived podocytes. These results show that SARS-CoV-2 can infect kidney glomerular podocytes in vitro via multiple binding interactions and partners, which may underlie the high affinity of SARS-CoV-2 for kidney tissues. This stem cell-derived model is potentially useful for kidney-specific antiviral drug screening and mechanistic studies of COVID-19 organotropism.

Construction and validation of a prognostic model for kidney renal clear cell carcinoma based on podocyte-associated genes

Background

As the most common renal malignancy, kidney renal clear cell carcinoma (KIRC) has a high prevalence and death rate as well as a poor response to treatment. Developing an efficient prognostic model is essential for accurately predicting the outcome and therapeutic benefit of KIRC patients.

Methods

Gene expression profiles of podocyte‐associated genes (PAGs) were obtained from The Cancer Genome Atlas and GEO datasets. Cox regression and Lasso regression analyses were then used for filtering prognosis‐associated PAGs. Risk score (RS) was computed from these genetic characteristics. Kaplan–Meier analysis and receiver operating characteristic (ROC) curves were applied for ascertaining the prognostic value. Stratified analysis was used to sufficiently validate model performance. Concordance index was used to compare the predictive ability of different models. Immuno‐infiltration analysis and immunophenoscore were utilized for the prediction of patient reaction to immune checkpoint inhibitors (ICIs).

Results

WT1, ANLN, CUBN, OSGEP, and RHOA were significantly associated with KIRC prognosis. Prognostic analysis indicated that high‐RS patients have a significantly poorer outcome. Cox regression analysis demonstrated a potential for RS to be an independent prognostic factor. Pathway enrichment results indicated a lower enrichment of cancer‐related biological pathways in the low‐RS subgroup. Immune infiltration analysis and IPS demonstrated greater responsiveness to ICIs in the high RS group.

Conclusions

This podocyte‐associated KIRC prognostic model can effectively predict KIRC prognosis and immunotherapy response, which may help to provide clinicians with more effective treatment strategies.

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.

Molecular mechanisms of developmental pathways in neurological disorders: a pharmacological and therapeutic review

Developmental signalling pathways such as Wnt/β-catenin, Notch and Sonic hedgehog play a central role in nearly all the stages of neuronal development. The term 'embryonic' might appear to be a misnomer to several people because these pathways are functional during the early stages of embryonic development and adulthood, albeit to a certain degree. Therefore, any aberration in these pathways or their associated components may contribute towards a detrimental outcome in the form of neurological disorders such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and stroke. In the last decade, researchers have extensively studied these pathways to decipher disease-related interactions, which can be used as therapeutic targets to improve outcomes in patients with neurological abnormalities. However, a lot remains to be understood in this domain. Nevertheless, there is strong evidence supporting the fact that embryonic signalling is indeed a crucial mechanism as is manifested by its role in driving memory loss, motor impairments and many other processes after brain trauma. In this review, we explore the key roles of three embryonic pathways in modulating a range of homeostatic processes such as maintaining blood-brain barrier integrity, mitochondrial dynamics and neuroinflammation. In addition, we extensively investigated the effect of these pathways in driving the pathophysiology of a range of disorders such as Alzheimer's, Parkinson's and diabetic neuropathy. The concluding section of the review is dedicated to neurotherapeutics, wherein we identify and list a range of biological molecules and compounds that have shown enormous potential in improving prognosis in patients with these disorders.

Glucocorticoids Inhibit EGFR Signaling Activation in Podocytes in Anti-GBM Crescentic Glomerulonephritis

Glucocorticoids are commonly used to treat anti-GBM crescentic glomerulonephritis, however, the mechanism underlying its therapeutic effectiveness is not completely understood. Since podocyte EGFR/STAT3 signaling is known to mediate the development of anti-GBM glomerulonephritis, we investigated the effect of glucocorticoids on EGFR/STAT3 signaling in podocytes. We found that the levels of phosphorylated (activated) EGFR and STAT3 in podocytes were markedly elevated in anti-GBM patients without glucocorticoids treatment, but were normalized in patients with glucocorticoids treatment. In a rat model of anti-GBM glomerulonephritis, glucocorticoids treatment significantly attenuated the proteinuria, crescent formation, parietal epithelial cell (PEC) activation and proliferation, accompanied by elimination of podocyte EGFR/STAT3 signaling activation. In cultured podocytes, glucocorticoids were found to inhibit HB-EGF-induced EGFR and STAT3 activation. The conditioned medium from podocytes treated with HB-EGF in the absence but not presence of glucocorticoids was capable of activating Notch signaling (which is known to be involved in PEC proliferation and crescent formation) and enhancing proliferative activity in primary PECs, suggesting that glucocorticoids prevent podocytes from producing secreted factors that cause PEC proliferation and crescent formation. Furthermore, we found that glucocorticoids can downregulate the expression of EGFR ligands, EGF and HB-EGF, while upregulate the expression of EGFR inhibitor, Gene 33, explaining how glucocorticoids suppress EGFR signaling. Taken together, glucocorticoids exert therapeutic effect on anti-GBM crescentic glomerulonephritis through inhibiting podocyte EGFR/STAT3 signaling and the downstream pathway that leads to PEC proliferation and crescent formation.

The mechanism of HMGB1 secretion and release

High mobility group box 1 (HMGB1) is a nonhistone nuclear protein that has multiple functions according to its subcellular location. In the nucleus, HMGB1 is a DNA chaperone that maintains the structure and function of chromosomes. In the cytoplasm, HMGB1 can promote autophagy by binding to BECN1 protein. After its active secretion or passive release, extracellular HMGB1 usually acts as a damage-associated molecular pattern (DAMP) molecule, regulating inflammation and immune responses through different receptors or direct uptake. The secretion and release of HMGB1 is fine-tuned by a variety of factors, including its posttranslational modification (e.g., acetylation, ADP-ribosylation, phosphorylation, and methylation) and the molecular machinery of cell death (e.g., apoptosis, pyroptosis, necroptosis, alkaliptosis, and ferroptosis). In this minireview, we introduce the basic structure and function of HMGB1 and focus on the regulatory mechanism of HMGB1 secretion and release. Understanding these topics may help us develop new HMGB1-targeted drugs for various conditions, especially inflammatory diseases and tissue damage.

A nuclear protein that gets released after cell death or is actively secreted by immune cells offers a promising therapeutic target for treating diseases linked to excessive inflammation. Daolin Tang from the University of Texas Southwestern Medical Center in Dallas, USA, and colleagues review how cellular stresses can trigger the accumulation of HMGB1, a type of alarm signal protein that promotes the recruitment and activation of inflammation-promoting immune cells. The researchers discuss various mechanisms that drive both passive and active release of HMGB1 into the space around cells. These processes, which include enzymatic modifications of the HMGB1 protein, cell–cell interactions and molecular pathways of cell death, could be targeted by drugs to lessen tissue damage and inflammatory disease caused by HMGB1-induced immune responses

Epigenetic Modulation of Gremlin-1/NOTCH Pathway in Experimental Crescentic Immune-Mediated Glomerulonephritis

Crescentic glomerulonephritis is a devastating autoimmune disease that without early and properly treatment may rapidly progress to end-stage renal disease and death. Current immunosuppressive treatment provides limited efficacy and an important burden of adverse events. Epigenetic drugs are a source of novel therapeutic tools. Among them, bromodomain and extraterminal domain (BET) inhibitors (iBETs) block the interaction between bromodomains and acetylated proteins, including histones and transcription factors. iBETs have demonstrated protective effects on malignancy, inflammatory disorders and experimental kidney disease. Recently, Gremlin-1 was proposed as a urinary biomarker of disease progression in human anti-neutrophil cytoplasmic antibody (ANCA)-associated crescentic glomerulonephritis. We have now evaluated whether iBETs could regulate Gremlin-1 in experimental anti-glomerular basement membrane nephritis induced by nephrotoxic serum (NTS) in mice, a model resembling human crescentic glomerulonephritis. In NTS-injected mice, the iBET JQ1 inhibited renal Gremlin-1 overexpression and diminished glomerular damage, restoring podocyte numbers. Chromatin immunoprecipitation assay demonstrated BRD4 enrichment of the Grem-1 gene promoter in injured kidneys, consistent with Gremlin-1 epigenetic regulation. Moreover, JQ1 blocked BRD4 binding and inhibited Grem-1 gene transcription. The beneficial effect of iBETs was also mediated by modulation of NOTCH pathway. JQ1 inhibited the gene expression of the NOTCH effectors Hes-1 and Hey-1 in NTS-injured kidneys. Our results further support the role for epigenetic drugs, such as iBETs, in the treatment of rapidly progressive crescentic glomerulonephritis.

METTL3-mediated m6A modification of TIMP2 mRNA promotes podocyte injury in diabetic nephropathy

Epigenetic changes are present in many physiological and pathological processes. The N⁶-methyladenosine (m6A) modification is the most common modification in eukaryotic mRNA. However, the role of m6A modification in diabetic nephropathy (DN) remains elusive. Here, we found that m6A modification was significantly upregulated in the kidney of type 1 and type 2 diabetic mice, which was caused by elevated levels of METTL3. Moreover, METTL3 is increased in podocyte of renal biopsy from patients with DN, which is related to renal damage. METTL3 knockout significantly reduced the inflammation and apoptosis in high glucose (HG)-stimulated podocytes, while its overexpression significantly aggravated these responses in vitro. Podocyte-conditional knockout METTL3 significantly alleviated podocyte injury and albuminuria in streptozotocin (STZ)-induced diabetic mice. Therapeutically, silencing METTL3 with adeno-associated virus serotype-9 (AAV9)-shMETTL3 in vivo mitigated albuminuria and histopathological injury in STZ-induced diabetic mice and db/db mice. Mechanistically, METTL3 modulated Notch signaling via the m6A modification of TIMP2 in an insulin-like growth factor 2 mRNA binding protein 2 (IGF2BP2)-dependent manner and exerted pro-inflammatory and pro-apoptotic effects. In summary, this study suggested that METTL3-mediated m6A modification is an important mechanism of podocyte injury in DN. Targeting m6A through the writer enzyme METTL3 is a potential approach for the treatment of DN.

Integrated analysis of potential gene crosstalk between non-alcoholic fatty liver disease and diabetic nephropathy

BACKGROUND

Growing evidence indicates that non-alcoholic fatty liver disease (NAFLD) is related to the occurrence and development of diabetic nephropathy (DN). This bioinformatics study aimed to explore optimal crosstalk genes and related pathways between NAFLD and DN.

METHODS

Gene expression profiles were downloaded from Gene Expression Omnibus. CIBERSORT algorithm was employed to analyze the similarity of infiltrating immunocytes between the two diseases. Protein-protein interaction (PPI) co-expression network and functional enrichment analysis were conducted based on the identification of common differentially expressed genes (DEGs). Least absolute shrinkage and selection operator (LASSO) regression and Boruta algorithm were implemented to initially screen crosstalk genes. Machine learning models, including support vector machine, random forest model, and generalized linear model, were utilized to further identify the optimal crosstalk genes between DN and NAFLD. An integrated network containing crosstalk genes, transcription factors, and associated pathways was developed.

RESULTS

Four gene expression datasets, including GSE66676 and GSE48452 for NAFLD and GSE30122 and GSE1009 for DN, were involved in this study. There were 80 common DEGs between the two diseases in total. The PPI network built with the 80 common genes included 77 nodes and 83 edges. Ten optimal crosstalk genes were selected by LASSO regression and Boruta algorithm, including CD36, WIPI1, CBX7, FCN1, SLC35D2, CP, ZDHHC3, PTPN3, LPL, and SPP1. Among these genes, LPL and SPP1 were the most significant according to NAFLD-transcription factor network. Five hundred twenty-nine nodes and 1,113 edges comprised the PPI network of activated pathway-gene. In addition, 14 common pathways of these two diseases were recognized using Gene Ontology (GO) analysis; among them, regulation of the lipid metabolic process is closely related to both two diseases.

CONCLUSIONS

This study offers hints that NAFLD and DN have a common pathogenesis, and LPL and SPP1 are the most relevant crosstalk genes. Based on the common pathways and optimal crosstalk genes, our proposal carried out further research to disclose the etiology and pathology between the two diseases.

Role of YB-1 Protein in Inflammation

This review discusses the role of the multifunctional DNA/RNA-binding protein YB-1 in inflammation. YB-1 performs multiple functions in the cell depending on its location: it acts as transcriptional factor for many genes in the nucleus, regulates translation and stability of mRNA in the cytoplasm, and becomes a paracrine factor when secreted from the cells. The review presents the data on the YB-1-mediated regulation of inflammation-associated genes, as well as results of studies on the YB-1 role in animal model of various inflammatory diseases, such as glomerulonephritis, tubulointerstitial fibrosis, and bacterial sepsis, and on the YB-1 expression in different human diseases associated with inflammatory processes in kidney, liver, and endometrium. The last section of the review presents several approaches to the regulation of YB-1 with small molecules in the treatment of inflammatory diseases.

Roles of SIRT6 in kidney disease: a novel therapeutic target

SIRT6 is an NAD+ dependent deacetylase that belongs to the mammalian sirtuin family. SIRT6 is mainly located in the nucleus and regulates chromatin remodeling, genome stability, and gene transcription. SIRT6 extensively participates in various physiological activities such as DNA repair, energy metabolism, oxidative stress, inflammation, and fibrosis. In recent years, the role of epigenetics such as acetylation modification in renal disease has gradually received widespread attention. SIRT6 reduces oxidative stress, inflammation, and renal fibrosis, which is of great importance in maintaining cellular homeostasis and delaying the chronic progression of kidney disease. Here, we review the structure and biological function of SIRT6 and summarize the regulatory mechanisms of SIRT6 in kidney disease. Moreover, the role of SIRT6 as a potential therapeutic target for the progression of kidney disease will be discussed. SIRT6 plays an important role in kidney disease. SIRT6 regulates mitochondrial dynamics and mitochondrial biogenesis, induces G2/M cycle arrest, and plays an antioxidant role in nephrotoxicity, IR, obstructive nephropathy, and sepsis-induced AKI. SIRT6 prevents and delays progressive CKD induced by hyperglycemia, kidney senescence, hypertension, and lipid accumulation by regulating mitochondrial biogenesis, and has antioxidant, anti-inflammatory, and antifibrosis effects. Additionally, hypoxia, inflammation, and fibrosis are the main mechanisms of the AKI-to-CKD transition. SIRT6 plays a critical role in the AKI-to-CKD transition and kidney repair through anti-inflammatory, antifibrotic, and mitochondrial quality control mechanisms. AKI Acute kidney injury, CKD Chronic kidney disease.

TIMP3 involvement and potentiality in the diagnosis, prognosis and treatment of diabetic nephropathy

Diabetic kidney disease, one of the most severe complications associated with diabetes, is characterized by albuminuria, glomerulosclerosis and progressive loss of renal function. Loss of TIMP3, an Extracellular matrix-bound protein, is a hallmark of diabetic nephropathy in human and mouse models, suggesting its pivotal role in renal diseases associated to diabetes. There is currently no specific therapy for diabetic nephropathy, and the ability to restore high TIMP3 activity specifically in the kidney may represent a potential therapeutic strategy for the amelioration of renal injury under conditions in which its reduction is directly related to the disease. Increasing evidence shows that diabetic nephropathy is also regulated by epigenetic mechanisms, including noncoding RNA. This review recapitulates the pathological, diagnostic and therapeutic potential roles of TIMP3 and the noncoding RNA (microRNA, long noncoding RNA) related to its expression, in the progression of diabetic nephropathy.

BSG/CD147 and ACE2 receptors facilitate SARS-CoV-2 infection of human iPS cell-derived kidney podocytes

BACKGROUND

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes the Coronavirus disease 2019 (COVID-19), which was declared a pandemic by the World Health Organization (WHO) in March 2020. The disease has caused more than 5.1 million deaths worldwide. While cells in the respiratory system are frequently the initial target for SARS-CoV-2, clinical studies suggest that COVID-19 can become a multi-organ disease in the most severe cases. Still, the direct affinity of SARS-CoV-2 for cells in other organs such as the kidneys, which are often affected in severe COVID-19, remains poorly understood.

METHOD

In this study, we employed a human induced pluripotent stem (iPS) cell-derived model to investigate the affinity of SARS-CoV-2 for kidney glomerular podocytes. We studied uptake of the live SARS-CoV-2 virus as well as pseudotyped viral particles by human iPS cell derived podocytes using qPCR, western blot, and immunofluorescence. Global gene expression and qPCR analyses revealed that human iPS cell-derived podocytes express many host factor genes (including ACE2, BSG/CD147, PLS3, ACTR3, DOCK7, TMPRSS2, CTSL CD209, and CD33) associated with SARS-CoV-2 binding and viral processing.

RESULT

Infection of podocytes with live SARS-CoV-2 or spike-pseudotyped lentiviral particles revealed viral uptake by the cells at low Multiplicity of Infection (MOI of 0.01) as confirmed by RNA quantification and immunofluorescence studies. Our results also indicate that direct infection of human iPS cell-derived podocytes by SARS-CoV-2 virus can cause cell death and podocyte foot process retraction, a hallmark of podocytopathies and progressive glomerular diseases including collapsing glomerulopathy observed in patients with severe COVID-19 disease. Additionally, antibody blocking experiments identified BSG/CD147 and ACE2 receptors as key mediators of spike binding activity in human iPS cell-derived podocytes.

CONCLUSION

These results show that SARS-CoV-2 can infect kidney glomerular podocytes in vitro . These results also show that the uptake of SARS-CoV-2 by kidney podocytes occurs via multiple binding interactions and partners, which may underlie the high affinity of SARS-CoV-2 for kidney tissues. This stem cell-derived model is potentially useful for kidney-specific antiviral drug screening and mechanistic studies of COVID-19 organotropism.

SIGNIFICANT STATEMENT

Many patients with COVID19 disease exhibit multiorgan complications, suggesting that SARS-CoV-2 infection can extend beyond the respiratory system. Acute kidney injury is a common COVID-19 complication contributing to increased morbidity and mortality. Still, SARS-Cov-2 affinity for specialized kidney cells remain less clear. By leveraging our protocol for stem cell differentiation, we show that SARS-CoV-2 can directly infect kidney glomerular podocytes by using multiple Spike-binding proteins including ACE2 and BSG/CD147. Our results also indicate that infection by SARS-CoV-2 virus can cause podocyte cell death and foot process effacement, a hallmark of podocytopathies including collapsing glomerulopathy observed in patients with severe COVID-19 disease. This stem cell-derived model is potentially useful for kidney-specific antiviral drug screening and mechanistic studies of COVID-19 organotropism.

Recent Advances in Diabetic Kidney Diseases: From Kidney Injury to Kidney Fibrosis

Diabetic kidney disease (DKD) is the leading cause of chronic kidney disease and end-stage renal disease. The natural history of DKD includes glomerular hyperfiltration, progressive albuminuria, declining estimated glomerular filtration rate, and, ultimately, kidney failure. It is known that DKD is associated with metabolic changes caused by hyperglycemia, resulting in glomerular hypertrophy, glomerulosclerosis, and tubulointerstitial inflammation and fibrosis. Hyperglycemia is also known to cause programmed epigenetic modification. However, the detailed mechanisms involved in the onset and progression of DKD remain elusive. In this review, we discuss recent advances regarding the pathogenic mechanisms involved in DKD.

Ectodomain shedding by ADAM proteases as a central regulator in kidney physiology and disease

Besides its involvement in blood and bone physiology, the kidney's main function is to filter substances and thereby regulate the electrolyte composition of body fluids, acid-base balance and toxin removal. Depending on underlying conditions, the nephron must undergo remodeling and cellular adaptations. The proteolytic removal of cell surface proteins via ectodomain shedding by A Disintegrin and Metalloproteases (ADAMs) is of importance for the regulation of cell-cell and cell-matrix adhesion of renal cells. ADAM10 controls glomerular and tubule development in a Notch1 signaling-dependent manner and regulates brush border composition. ADAM17 regulates the renin angiotensin system and is together with ADAM10 involved in calcium phosphate homeostasis. In kidney disease ADAMs, especially ADAM17 contribute to inflammation through their involvement in IL-6 trans-signaling, Notch-, epithelial growth factor receptor-, and tumor necrosis factor α signaling. ADAMs are interesting drug targets to reduce the inflammatory burden, defective cell adhesion and impaired signaling pathways in kidney diseases.

ADAMs family in kidney physiology and pathology

A disintegrin and metalloproteinases (ADAMs) family are proteolytic transmembrane proteases that modulate diverse cell functions and coordinate intercellular communication. ADAMs are responsible for regulating cell proliferation, differentiation, migration, and organ morphogenesis in kidney development. Abnormally activated ADAMs drive inflammation and fibrosis in response to kidney diseases such as acute kidney injury, diabetic kidney disease, polycystic kidney disease, and chronic allograft nephropathy. ADAM10 and ADAM17, known as the most characterized members of ADAMs, are extensively investigated in kidney diseases. Notably, ADAM proteases have the potential to be targets for developing novel treatment approaches in kidney diseases.

Autophagy Dysregulation in Diabetic Kidney Disease: From Pathophysiology to Pharmacological Interventions

Diabetic kidney disease (DKD) is a frequent, potentially devastating complication of diabetes mellitus. Several factors are involved in its pathophysiology. At a cellular level, diabetic kidney disease is associated with many structural and functional alterations. Autophagy is a cellular mechanism that transports intracytoplasmic components to lysosomes to preserve cellular function and homeostasis. Autophagy integrity is essential for cell homeostasis, its alteration can drive to cell damage or death. Diabetic kidney disease is associated with profound autophagy dysregulation. Autophagy rate and flux alterations were described in several models of diabetic kidney disease. Some of them are closely linked with disease progression and severity. Some antidiabetic agents have shown significant effects on autophagy. A few of them have also demonstrated to modify disease progression and improved outcomes in affected patients. Other drugs also target autophagy and are being explored for clinical use in patients with diabetic kidney disease. The modulation of autophagy could be relevant for the pharmacological treatment and prevention of this disease in the future. Therefore, this is an evolving area that requires further experimental and clinical research. Here we discuss the relationship between autophagy and Diabetic kidney disease and the potential value of autophagy modulation as a target for pharmacological intervention.

Interplay between extracellular matrix components and cellular and molecular mechanisms in kidney fibrosis

Chronic kidney disease (CKD) is characterized by pathological accumulation of extracellular matrix (ECM) proteins in renal structures. Tubulointerstitial fibrosis is observed in glomerular diseases as well as in the regeneration failure of acute kidney injury (AKI). Therefore, finding antifibrotic therapies comprises an intensive research field in Nephrology. Nowadays, ECM is not only considered as a cellular scaffold, but also exerts important cellular functions. In this review, we describe the cellular and molecular mechanisms involved in kidney fibrosis, paying particular attention to ECM components, profibrotic factors and cell-matrix interactions. In response to kidney damage, activation of glomerular and/or tubular cells may induce aberrant phenotypes characterized by overproduction of proinflammatory and profibrotic factors, and thus contribute to CKD progression. Among ECM components, matricellular proteins can regulate cell-ECM interactions, as well as cellular phenotype changes. Regarding kidney fibrosis, one of the most studied matricellular proteins is cellular communication network-2 (CCN2), also called connective tissue growth factor (CTGF), currently considered as a fibrotic marker and a potential therapeutic target. Integrins connect the ECM proteins to the actin cytoskeleton and several downstream signaling pathways that enable cells to respond to external stimuli in a coordinated manner and maintain optimal tissue stiffness. In kidney fibrosis, there is an increase in ECM deposition, lower ECM degradation and ECM proteins cross-linking, leading to an alteration in the tissue mechanical properties and their responses to injurious stimuli. A better understanding of these complex cellular and molecular events could help us to improve the antifibrotic therapies for CKD.

Inhibition of p53/miR-34a/SIRT1 axis ameliorates podocyte injury in diabetic nephropathy

Podocyte injury is associated with albuminuria and the progression of diabetic nephropathy (DN). MiR-34a, a p53-regulated miRNA, directly targets SIRT1 and contributed to DN progression. MiR-34a represses SIRT1 to activate p53 and establish a positive feedback loop. However, whether p53/miR-34a/SIRT1 signaling is activated in podocytes and contributes to DN pathogenesis remains elusive. In this study, we observed that serum miR-34a level was positively correlated with podocyte injury in DN patients. The expression of acetylated p53 and miR-34a was upregulated, SIRT1was downregulated in glomeruli from patients with DN and STZ induced diabetic mice, as well as in human podocytes treated with advanced glycation end (AGE). MiR-34a antagonism in vitro and vivo in STZ induced diabetic mice developed alleviated glomerulus injury as reflected by attenuated albuminuria, reduced podocyte loss and restored autophagic flux. In human podocyte, inhibition of AGE formation by pyridoxamine prevented miR-34a dependent repression of SIRT1, p53 acetylation and activate podocyte autophagy in a dose-dependent manner. MiR-34a overexpression increases acetylation of p53 by translational repression of SIRT1. SIRT1 overexpression also impacts AGE induced apoptosis through deacetylating p53, whereas silencing of SIRT1 by EX527 attenuated the cytoprotective functions of miR-34a knockdown. Moreover, blockade of p53 acetylation significantly rescued miR-34a-induced apoptosis through SIRT1 restoration. Collectively, we demonstrate that by activation of p53, AGE induced the transcription of miR-34a, miR-34a in turn repressed SIRT1 to activate p53, resulting in a positive-feedback loop and contributing to podocyte injury. Targeting modulation of p53/miR-34a/SIRT1 feedback by miR-34a knockdown or overexpression of SIRT1 could rescue podocyte injury during DN.

ADAM10-Mediated Ectodomain Shedding Is an Essential Driver of Podocyte Damage

BACKGROUND

Podocytes embrace the glomerular capillaries with foot processes, which are interconnected by a specialized adherens junction to ultimately form the filtration barrier. Altered adhesion and loss are common features of podocyte injury, which could be mediated by shedding of cell-adhesion molecules through the regulated activity of cell surface-expressed proteases. A Disintegrin and Metalloproteinase 10 (ADAM10) is such a protease known to mediate ectodomain shedding of adhesion molecules, among others. Here we evaluate the involvement of ADAM10 in the process of antibody-induced podocyte injury.

METHODS

Membrane proteomics, immunoblotting, high-resolution microscopy, and immunogold electron microscopy were used to analyze human and murine podocyte ADAM10 expression in health and kidney injury. The functionality of ADAM10 ectodomain shedding for podocyte development and injury was analyzed, in vitro and in vivo, in the anti-podocyte nephritis (APN) model in podocyte-specific, ADAM10-deficient mice.

RESULTS

ADAM10 is selectively localized at foot processes of murine podocytes and its expression is dispensable for podocyte development. Podocyte ADAM10 expression is induced in the setting of antibody-mediated injury in humans and mice. Podocyte ADAM10 deficiency attenuates the clinical course of APN and preserves the morphologic integrity of podocytes, despite subepithelial immune-deposit formation. Functionally, ADAM10-related ectodomain shedding results in cleavage of the cell-adhesion proteins N- and P-cadherin, thus decreasing their injury-related surface levels. This favors podocyte loss and the activation of downstream signaling events through the Wnt signaling pathway in an ADAM10-dependent manner.

CONCLUSIONS

ADAM10-mediated ectodomain shedding of injury-related cadherins drives podocyte injury.

Podocyte apoptosis in diabetic nephropathy by BASP1 activation of the p53 pathway via WT1

AIMS

Diabetic nephropathy (DN) is a leading cause of end-stage renal disease. BASP1 (brain acid-soluble protein) is up-regulated in podocyte-specific protein phosphatase 2A knockout mice (Pod-PP2A-KO) that develop kidney dysfunction. Here, we explore the role of BASP1 for podocytes in DN.

METHODS

BASP1 was assessed in kidneys from DN patients and DN mouse models, podocyte specific BASP1 knockout mice (Pod-BASP1-KO mice) were generated and studied in vivo. Furthermore, podocyte injury and apoptosis were measured after BASP1 knockdown and overexpression in a mouse podocyte cell line (MPC5). Potential signalling pathways involved in podocyte apoptosis were detected.

RESULTS

BASP1 expression was up-regulated in DN patients compared to normal controls. BASP1 specific deletion in podocytes protected against podocyte injury by reducing the loss of expression of slit diaphragm molecules and foot process effacement in the DN model. BASP1 promoted actin cytoskeleton rearrangements and apoptosis in the MPC5 podocyte line. Molecules involved in the p53 pathway were down-regulated in BASP1 knockdown podocytes treated with high glucose compared to controls. BASP1 promoted podocyte apoptosis and P53 pathway activation through co-repression with Wilms' tumour 1 transcription factor (WT1).

CONCLUSION

BASP1 activates the p53 pathway through modulation of WT1 to induce podocyte apoptosis in diabetic nephropathy.

Growth hormone induces mitotic catastrophe of glomerular podocytes and contributes to proteinuria

Glomerular podocytes are integral members of the glomerular filtration barrier in the kidney and are crucial for glomerular permselectivity. These highly differentiated cells are vulnerable to an array of noxious stimuli that prevail in several glomerular diseases. Elevated circulating growth hormone (GH) levels are associated with podocyte injury and proteinuria in diabetes. However, the precise mechanism(s) by which excess GH elicits podocytopathy remains to be elucidated. Previous studies have shown that podocytes express GH receptor (GHR) and induce Notch signaling when exposed to GH. In the present study, we demonstrated that GH induces TGF-β1 signaling and provokes cell cycle reentry of otherwise quiescent podocytes. Though differentiated podocytes reenter the cell cycle in response to GH and TGF-β1, they cannot accomplish cytokinesis, despite karyokinesis. Owing to this aberrant cell cycle event, GH- or TGF-β1-treated cells remain binucleated and undergo mitotic catastrophe. Importantly, inhibition of JAK2, TGFBR1 (TGF-β receptor 1), or Notch prevented cell cycle reentry of podocytes and protected them from mitotic catastrophe associated with cell death. Inhibition of Notch activation prevents GH-dependent podocyte injury and proteinuria. Similarly, attenuation of GHR expression abated Notch activation in podocytes. Kidney biopsy sections from patients with diabetic nephropathy (DN) show activation of Notch signaling and binucleated podocytes. These data indicate that excess GH induced TGF-β1-dependent Notch1 signaling contributes to the mitotic catastrophe of podocytes. This study highlights the role of aberrant GH signaling in podocytopathy and the potential application of TGF-β1 or Notch inhibitors, as a therapeutic agent for DN.

Unraveling the epigenetic landscape of glomerular cells in kidney disease

Chronic kidney disease (CKD) is a major public health concern and its prevalence and incidence are rising quickly. It is a non-communicable disease primarily caused by diabetes and/or hypertension and is associated with high morbidity and mortality. Despite decades of research efforts, the pathogenesis of CKD remains a puzzle with missing pieces. Understanding the cellular and molecular mechanisms that govern the loss of kidney function is crucial. Abrupt regulation of gene expression in kidney cells is apparent in CKD and shown to be responsible for disease onset and progression. Gene expression regulation extends beyond DNA sequence and involves epigenetic mechanisms including changes in DNA methylation and post-translational modifications of histones, driven by the activity of specific enzymes. Recent advances demonstrate the essential participation of epigenetics in kidney (patho)physiology, as its actions regulate both the integrity of cells but also triggers deleterious signaling pathways. Here, we review the known epigenetic processes regulating the complex filtration unit of the kidney, the glomeruli. The review will elaborate on novel insights into how epigenetics contributes to cell injury in the CKD setting majorly focusing on kidney glomerular cells: the glomerular endothelial cells, the mesangial cells, and the specialized and terminally differentiated podocyte cells.