Interstitial vascular rarefaction and reduced VEGF-A expression in human diabetic nephropathy

Reduction of renal interstitial fibrosis by targeting Tie2 in vascular endothelial cells

BACKGROUND

Tie2, a functional angiopoietin receptor, is expressed in vascular endothelial cells and plays an important role in angiogenesis and vascular stability. This study aimed to evaluate the effects of an agonistic Tie2 signal on renal interstitial fibrosis (RIF) and elucidate the underlying mechanisms.

METHODS

We established an in vivo mouse model of folic acid-induced nephropathy (FAN) and an in vitro model of lipopolysaccharide-stimulated endothelial cell injury, then an agonistic Tie2 monoclonal antibody (Tie2 mAb) was used to intervent these processes. The degree of tubulointerstitial lesions and related molecular mechanisms were determined by histological assessment, immunohistochemistry, western blotting, and qPCR.

RESULTS

Tie2 mAb attenuated RIF and reduced the level of fibroblast-specific protein 1 (FSP1). Further, it suppressed vascular cell adhesion molecule-1 (VCAM-1) and increased CD31 density in FAN. In the in vitro model, Tie2 mAb was found to decrease the expression of VCAM-1, Bax, and α-smooth muscle actin (α-SMA).

CONCLUSIONS

The present findings indicate that the agonistic Tie2 mAb exerted vascular protective effects and ameliorated RIF via inhibition of vascular inflammation, apoptosis, and fibrosis. Therefore, Tie2 may be a potential target for the treatment of this disease.

IMPACT

This is the first report to confirm that an agonistic Tie2 monoclonal antibody can reduce renal interstitial fibrosis in folic acid-induced nephropathy in mice. This mechanism possibly involves vascular protective effects brought about by inhibition of vascular inflammation, apoptosis and fibrosis. Our data show that Tie2 signal may be a novel, endothelium-specific target for the treatment of tubulointerstitial fibrosis.

Integrin β8 prevents pericyte-myofibroblast transition and renal fibrosis through inhibiting the TGF-β1/TGFBR1/Smad3 pathway in diabetic kidney disease

Diabetic kidney disease (DKD) is one of the leading causes to develop end-stage kidney disease worldwide. Pericytes are implicated in the development of tissue fibrosis. However, the underlying mechanisms of pericytes in DKD remain largely unknown. We isolated and cultured primary pericytes and rat mesangial cells (HBZY-1). Western blot and qRT-PCR analysis were used to explore the role and regulatory mechanism of Integrin β8/transforming growth factor beta 1 (TGF-β1) pathway. We also constructed pericyte-specific Integrin β8 knock-in mice as the research objects to determine the role of Integrin β8 in vivo. We discovered that reduced Integrin β8 expression was closely associated with pericyte transition in DKD. Overexpressed Integrin β8 in pericytes dramatically suppressed TGF-β1/TGF beta receptor 1 (TGFBR1)/Smad3 signaling pathway and protected glomerular endothelial cells (GECs) in vitro. In vivo, pericyte-specific Integrin β8 knock-in ameliorated pericyte transition, endothelium injury and renal fibrosis in STZ-induced diabetic mice. Mechanistically, Murine double minute 2 (MDM2) was found to increase the degradation of Integrin β8 and caused TGF-β1 release and activation. Knockdown MDM2 could partly reverse the decline of Integrin β8 and suppress pericytes transition. In conclusion, the present findings suggested that upregulated MDM2 expression contributes to the degradation of Integrin β8 and activation of TGF-β1/TGFBR1/Smad3 signaling pathway, which ultimately leads to pericyte transition during DKD progression. These results indicate MDM2/Integrin β8 might be considered as therapeutic targets for DKD.

Capillary rarefaction: a missing link in renal and cardiovascular disease?

Patients with chronic kidney disease (CKD) have an increased risk for cardiovascular morbidity and mortality. Capillary rarefaction may be both one of the causes as well as a consequence of CKD and cardiovascular disease. We reviewed the published literature on human biopsy studies and conclude that renal capillary rarefaction occurs independently of the cause of renal function decline. Moreover, glomerular hypertrophy may be an early sign of generalized endothelial dysfunction, while peritubular capillary loss occurs in advanced renal disease. Recent studies with non-invasive measurements show that capillary rarefaction is detected systemically (e.g., in the skin) in individuals with albuminuria, as sign of early CKD and/or generalized endothelial dysfunction. Decreased capillary density is found in omental fat, muscle and heart biopsies of patients with advanced CKD as well as in skin, fat, muscle, brain and heart biopsies of individuals with cardiovascular risk factors. No biopsy studies have yet been performed on capillary rarefaction in individuals with early CKD. At present it is unknown whether individuals with CKD and cardiovascular disease merely share the same risk factors for capillary rarefaction, or whether there is a causal relationship between rarefaction in renal and systemic capillaries. Further studies on renal and systemic capillary rarefaction, including their temporal relationship and underlying mechanisms are needed. This review stresses the importance of preserving and maintaining capillary integrity and homeostasis in the prevention and management of renal and cardiovascular disease.

Endothelial Glycocalyx of Peritubular Capillaries in Experimental Diabetic Nephropathy: A Target of ACE Inhibitor-Induced Kidney Microvascular Protection

Peritubular capillary rarefaction is a recurrent aspect of progressive nephropathies. We previously found that peritubular capillary density was reduced in BTBR ob/ob mice with type 2 diabetic nephropathy. In this model, we searched for abnormalities in the ultrastructure of peritubular capillaries, with a specific focus on the endothelial glycocalyx, and evaluated the impact of treatment with an angiotensin-converting enzyme inhibitor (ACEi). Mice were intracardially perfused with lanthanum to visualise the glycocalyx. Transmission electron microscopy analysis revealed endothelial cell abnormalities and basement membrane thickening in the peritubular capillaries of BTBR ob/ob mice compared to wild-type mice. Remodelling and focal loss of glycocalyx was observed in lanthanum-stained diabetic kidneys, associated with a reduction in glycocalyx components, including sialic acids, as detected through specific lectins. ACEi treatment preserved the endothelial glycocalyx and attenuated the ultrastructural abnormalities of peritubular capillaries. In diabetic mice, peritubular capillary damage was associated with an enhanced tubular expression of heparanase, which degrades heparan sulfate residues of the glycocalyx. Heparanase was also detected in renal interstitial macrophages that expressed tumor necrosis factor-α. All these abnormalities were mitigated by ACEi. Our findings suggest that, in experimental diabetic nephropathy, preserving the endothelial glycocalyx is important in order to protect peritubular capillaries from damage and loss.

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.

Significance of Diabetic Kidney Disease Biomarkers in Predicting Metabolic-Associated Fatty Liver Disease

Metabolic-associated fatty liver disease (MAFLD) and diabetic kidney disease (DKD) share various pathophysiological factors, and epidemiological evidence suggests that these two diseases are associated. Albuminuria and the estimated glomerular filtration rate, which are conventional biomarkers of DKD, are reportedly associated with the risk or severity of MAFLD. Recently, novel DKD biomarkers reflecting renal tubular injury have been introduced to complement conventional DKD markers. In this article, we looked at previous studies that showed an association between MAFLD and DKD, and also reviewed the significance of DKD biomarkers as predictive risk factors for MAFLD.

Enrichr-KG: bridging enrichment analysis across multiple libraries

Gene and protein set enrichment analysis is a critical step in the analysis of data collected from omics experiments. Enrichr is a popular gene set enrichment analysis web-server search engine that contains hundreds of thousands of annotated gene sets. While Enrichr has been useful in providing enrichment analysis with many gene set libraries from different categories, integrating enrichment results across libraries and domains of knowledge can further hypothesis generation. To this end, Enrichr-KG is a knowledge graph database and a web-server application that combines selected gene set libraries from Enrichr for integrative enrichment analysis and visualization. The enrichment results are presented as subgraphs made of nodes and links that connect genes to their enriched terms. In addition, users of Enrichr-KG can add gene-gene links, as well as predicted genes to the subgraphs. This graphical representation of cross-library results with enriched and predicted genes can illuminate hidden associations between genes and annotated enriched terms from across datasets and resources. Enrichr-KG currently serves 26 gene set libraries from different categories that include transcription, pathways, ontologies, diseases/drugs, and cell types. To demonstrate the utility of Enrichr-KG we provide several case studies. Enrichr-KG is freely available at: https://maayanlab.cloud/enrichr-kg.

Clinical Relevance of Computationally Derived Attributes of Peritubular Capillaries from Kidney Biopsies

Key Points

Computational image analysis allows for the extraction of new information from whole-slide images with potential clinical relevance. Peritubular capillary (PTC) density is decreased in areas of interstitial fibrosis and tubular atrophy when measured in interstitial fractional space. PTC shape (aspect ratio) is associated with clinical outcome in glomerular diseases.

Background

The association between peritubular capillary (PTC) density and disease progression has been studied in a variety of kidney diseases using immunohistochemistry. However, other PTC attributes, such as PTC shape, have not been explored yet. The recent development of computer vision techniques provides the opportunity for the quantification of PTC attributes using conventional stains and whole-slide images.

Methods

To explore the relationship between PTC characteristics and clinical outcome, n =280 periodic acid–Schiff-stained kidney biopsies (88 minimal change disease, 109 focal segmental glomerulosclerosis, 46 membranous nephropathy, and 37 IgA nephropathy) from the Nephrotic Syndrome Study Network digital pathology repository were computationally analyzed. A previously validated deep learning model was applied to segment cortical PTCs. Average PTC aspect ratio (PTC major to minor axis ratio), size (PTC pixels per PTC segmentation), and density (PTC pixels per unit cortical area) were computed for each biopsy. Cox proportional hazards models were used to assess associations between these PTC parameters and outcome (40% eGFR decline or kidney failure). Cortical PTC characteristics and interstitial fractional space PTC density were compared between areas of interstitial fibrosis and tubular atrophy (IFTA) and areas without IFTA.

Results

When normalized PTC aspect ratio was below 0.6, a 0.1, increase in normalized PTC aspect ratio was significantly associated with disease progression, with a hazard ratio (95% confidence interval) of 1.28 (1.04 to 1.59) (P = 0.019), while PTC density and size were not significantly associated with outcome. Interstitial fractional space PTC density was lower in areas of IFTA compared with non-IFTA areas.

Conclusions

Computational image analysis enables quantification of the status of the kidney microvasculature and the discovery of a previously unrecognized PTC biomarker (aspect ratio) of clinical outcome.

Acute kidney injury in diabetes mellitus: Epidemiology, diagnostic, and therapeutic concepts

Acute kidney injury (AKI) and diabetes mellitus (DM) are public health problems that cause a high socioeconomic burden worldwide. In recent years, the landscape of AKI etiology has shifted: Emerging evidence has demonstrated that DM is an independent risk factor for the onset of AKI, while an alternative perspective considers AKI as a bona fide complication of DM. Therefore, it is necessary to systematically characterize the features of AKI in DM. In this review, we summarized the epidemiology of AKI in DM. While focusing on circulation- and tissue-specific microenvironment changes after DM, we described the active cellular and molecular mechanisms of increased kidney susceptibility to AKI under DM stress. We also reviewed the current diagnostic and therapeutic strategies for AKI in DM recommended in the clinic. Updated recognition of the epidemiology, pathophysiology, diagnosis, and medications of AKI in DM is believed to reveal a path to mitigate the frequency of AKI and DM comorbidity that will ultimately improve the quality of life in DM patients.

Suramin Affects the Renal VEGF-A/VEGFR Axis in Short-Term Streptozotocin-Induced Diabetes

Diabetic nephropathy (DN) accounts for approximately 50% of end-stage renal diseases. Vascular endothelial growth factor A (VEGF-A) is thought to be a critical mediator of vascular dysfunction in DN, but its role is unclear. The lack of pharmacological tools to modify renal concentrations further hinders the understanding of its role in DN. In this study, rats were evaluated after 3 weeks of streptozotocin-induced diabetes and two suramin treatments (10 mg/kg, ip). Vascular endothelial growth factor A expression was evaluated by western blot of glomeruli and immunofluorescence of the renal cortex. RT-PCR for receptors Vegfr1 mRNA and Vegfr2 mRNA quantitation was performed. The soluble adhesive molecules (sICAM-1, sVCAM-1) in blood were measured by ELISA and the vasoreactivity of interlobar arteries to acetylcholine was evaluated using wire myography. Suramin administration reduced the expression and intraglomerular localisation of VEGF-A. Increased VEGFR-2 expression in diabetes was reduced by suramin to non-diabetic levels. Diabetes reduced the sVCAM-1 concentrations. Suramin in diabetes restored acetylcholine relaxation properties to non-diabetic levels. In conclusion, suramin affects the renal VEGF-A/VEGF receptors axis and has a beneficial impact on endothelium-dependent relaxation of renal arteries. Thus, suramin may be used as a pharmacological agent to investigate the potential role of VEGF-A in the pathogenesis of renal vascular complications in short-term diabetes.

Renal Microcirculation Injury as the Main Cause of Ischemic Acute Kidney Injury Development

Acute kidney injury (AKI) can result from multiple factors. The main cause is reduced renal perfusion. Kidneys are susceptible to ischemia due to the anatomy of microcirculation that wraps around the renal tubules-peritubular capillary (PTC) network. Cortical and medullary superficial tubules have a large share in transport and require the supply of oxygen for ATP production, while it is the cortex that receives almost 100% of the blood flowing through the kidneys and the medulla only accounts for 5-10% of it. This difference makes the tubules present in the superficial layer of the medulla very susceptible to ischemia. Impaired blood flow causes damage to the endothelium, with an increase in its prothrombotic and pro-adhesive properties. This causes congestion in the microcirculation of the renal medulla. The next stage is the migration of pericytes with the disintegration of these vessels. The phenomenon of destruction of small vessels is called peritubular rarefaction, attributed as the main cause of further irreversible changes in the damaged kidney leading to the development of chronic kidney disease. In this article, we will present the characteristic structure of renal microcirculation, its regulation, and the mechanism of damage in acute ischemia, and we will try to find methods of prevention with particular emphasis on the inhibition of the renin-angiotensin-aldosterone system.

Paracrine Effects of Renal Proximal Tubular Epithelial Cells on Podocyte Injury under Hypoxic Conditions Are Mediated by Arginase-II and TGF-β1

Hypoxia is an important risk for renal disease. The mitochondrial enzyme arginase-II (Arg-II) is expressed and/or induced by hypoxia in proximal tubular epithelial cells (PTECs) and in podocytes, leading to cellular damage. Because PTECs are vulnerable to hypoxia and located in proximity to podocytes, we examined the role of Arg-II in the crosstalk of PTECs under hypoxic conditions with podocytes. A human PTEC cell line (HK2) and a human podocyte cell line (AB8/13) were cultured. Arg-ii gene was ablated by CRISPR/Case9 in both cell types. HK2 cells were exposed to normoxia (21% O₂) or hypoxia (1% O₂) for 48 h. Conditioned medium (CM) was collected and transferred to the podocytes. Podocyte injuries were then analyzed. Hypoxic (not normoxic) HK2-CM caused cytoskeletal derangement, cell apoptosis, and increased Arg-II levels in differentiated podocytes. These effects were absent when arg-ii in HK2 was ablated. The detrimental effects of the hypoxic HK2-CM were prevented by TGF-β1 type-I receptor blocker SB431542. Indeed, TGF-β1 levels in hypoxic HK2-CM (but not arg-ii^-/--HK2-CM) were increased. Furthermore, the detrimental effects of TGF-β1 on podocytes were prevented in arg-ii^-/--podocytes. This study demonstrates crosstalk between PTECs and podocytes through the Arg-II-TGF-β1 cascade, which may contribute to hypoxia-induced podocyte damage.

Title: Bioinformatic Identification of Genes Involved in Diabetic Nephropathy Fibrosis and their Clinical Relevance

Tubulointerstitial fibrosis is an important pathological feature of diabetic nephropathy that is associated with impaired renal function. However, the mechanism by which fibrosis occurs in diabetic nephropathy is unclear. Differentially expressed genes were identified from transcriptome profiles of renal tissue from diabetic patients and unilateral ureteral obstruction mice and intersected to obtain genes that may be involved in diabetic fibrosis. Biological function analysis and protein-protein interaction network analysis were performed. ROC curve and Pearson correlation analysis between hub genes were performed and glomerular filtration rate estimated. Finally, the RNA levels of hub genes were measured using real-time PCR. A total of 283 genes were identified as potentially involved in diabetic nephropathy fibrosis. TYROBP, CTSS, LCP2, LUM and TLR7 were identified as aberrantly expressed hub genes. Immune cell infiltration analysis demonstrated higher numbers of cytotoxic lymphocytes, B lineage cells, monocyte lineage cells, myeloid dendritic cells, neutrophils, and fibroblasts in the diabetic nephropathy group. The areas under ROC curves for TYROBP, CTSS, LCP2, LUM and TLR7 were 0.9167, 0.9583, 0.9917, 0.93333, and 0.9583, respectively (P < 0.001), and their correlation coefficients with estimated glomerular filtration rate were - 0.8332, - 0.752, - 0.7875, - 0.7567, and - 0.7136, respectively (P < 0.001). The RNA levels of TYROBP, CTSS, LUM and TLR7 were upregulated in high-glucose-treated human renal tubular epithelial cells (P < 0.005). Our study identified TYROBP, CTSS, LCP2, LUM and TLR7 as potentially involved in diabetic nephropathy fibrosis. Furthermore, TYROBP, CTSS, LUM and TLR7 may be associated with epithelial-mesenchymal transition of tubular epithelial cells.

Comprehensive analyses of the microRNA-messenger RNA-transcription factor regulatory network in mouse and human renal fibrosis

Objective: The aim of this study was to construct a microRNA (miRNA)-messenger RNA (mRNA)-transcription factor (TF) regulatory network and explore underlying molecular mechanisms, effective biomarkers, and drugs in renal fibrosis (RF). Methods: A total of six datasets were downloaded from Gene Expression Omnibus. "Limma" and "DESeq2" packages in R software and GEO2R were applied to identify the differentially expressed miRNAs and mRNAs (DEmiRNAs and DEmRNAs, respectively). The determination and verification of DEmiRNAs and DEmRNAs were performed through the integrated analysis of datasets from five mouse 7 days of unilateral ureteral obstruction datasets and one human chronic kidney disease dataset and the Human Protein Atlas (http://www.proteinatlas.org). Target mRNAs of DEmiRNAs and TFs were predicted by prediction databases and the iRegulon plugin in Cytoscape, respectively. A protein-protein interaction network was constructed using STRING, Cytoscape v3.9.1, and CytoNCA. Functional enrichment analysis was performed by DIANA-miRPath v3.0 and R package "clusterProfiler." A miRNA-mRNA-TF network was established using Cytoscape. Receiver operating characteristic (ROC) curve analysis was used to examine the diagnostic value of the key hub genes. Finally, the Comparative Toxicogenomics Database and Drug-Gene Interaction database were applied to identify potential drugs. Results: Here, 4 DEmiRNAs and 11 hub genes were determined and confirmed in five mouse datasets, of which Bckdha and Vegfa were further verified in one human dataset and HPA, respectively. Moreover, Bckdha and Vegfa were also predicted by miR-125a-3p and miR-199a-5p, respectively, in humans as in mice. The sequences of miR-125a-3p and miR-199a-5p in mice were identical to those in humans. A total of 6 TFs were predicted to regulate Bckdha and Vegfa across mice and humans; then, a miRNA-mRNA-TF regulatory network was built. Subsequently, ROC curve analysis showed that the area under the curve value of Vegfa was 0.825 (p = 0.002). Finally, enalapril was identified to target Vegfa for RF therapy. Conclusion: Pax2, Pax5, Sp1, Sp2, Sp3, and Sp4 together with Bckdha-dependent miR-125a-3p/Vegfa-dependent miR-199a-5p formed a co-regulatory network enabling Bckdha/Vegfa to be tightly controlled in the underlying pathogenesis of RF across mice and humans. Vegfa could act as a potential novel diagnostic marker and might be targeted by enalapril for RF therapy.

Pro- and anti-fibrotic effects of vascular endothelial growth factor in chronic kidney diseases

Renal fibrosis is the inevitable common end-point of all progressive chronic kidney diseases. The underlying mechanisms of renal fibrosis are complex, and currently there is no effective therapy against renal fibrosis. Renal microvascular rarefaction contributes to the progression of renal fibrosis; however, an imbalance between proangiogenic and antiangiogenic factors leads to the loss of renal microvasculature. Vascular endothelial growth factor (VEGF) is the most important pro-angiogenic factor. Recent studies have unraveled the involvement of VEGF in the regulation of renal microvascular rarefaction and fibrosis via various mechanisms; however, it is not clear whether it has anti-fibrotic or pro-fibrotic effect. This paper reviews the available evidence pertaining to the function of VEGF in the fibrotic process and explores the associated underlying mechanisms. Our synthesis will help identify the future research priorities for developing specialized treatments for alleviating or preventing renal fibrosis. Abbreviation: VEGF: vascular endothelial growth factor; CKD: chronic kidney disease; ESKD: end-stage kidney disease; ER: endoplasmic reticulum; VEGFR: vascular endothelial growth factor receptor; AKI: acute kidney injury; EMT: epithelial-to-mesenchymal transition; HIF: hypoxia-inducible factor; α-SMA: α smooth muscle actin; UUO: unilateral ureteral obstruction; TGF-β: transforming growth factor-β; PMT: pericyte-myofibroblast transition; NO: nitric oxide; NOS: nitric oxide synthase; nNOS: neuronal nitric oxide synthase; iNOS: inducible nitric oxide synthase; eNOS: endothelial nitric oxide synthase; sGC: soluble guanylate cyclase; PKG: soluble guanylate cyclase dependent protein kinases; UP R: unfolded protein response

The SARS-CoV-2 receptor ACE2 is expressed in mouse pericytes but not endothelial cells: Implications for COVID-19 vascular research

Humanized mouse models and mouse-adapted SARS-CoV-2 virus are increasingly used to study COVID-19 pathogenesis, so it is important to learn where the SARS-CoV-2 receptor ACE2 is expressed. Here we mapped ACE2 expression during mouse postnatal development and in adulthood. Pericytes in the CNS, heart, and pancreas express ACE2 strongly, as do perineurial and adrenal fibroblasts, whereas endothelial cells do not at any location analyzed. In a number of other organs, pericytes do not express ACE2, including in the lung where ACE2 instead is expressed in bronchial epithelium and alveolar type II cells. The onset of ACE2 expression is organ specific: in bronchial epithelium already at birth, in brain pericytes before, and in heart pericytes after postnatal day 10.5. Establishing the vascular localization of ACE2 expression is central to correctly interpret data from modeling COVID-19 in the mouse and may shed light on the cause of vascular COVID-19 complications.

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Detailed Ace2/ACE2 expression patterns are reported for multiple mouse organs

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Vascular Ace2/ACE2 expression occurs in pericytes but not endothelial cells

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Ace2/ACE2 expression is organotypic and developmentally regulated

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Ace2/ACE2 expression in pericytes may suggest their involvement in COVID-19

Podocyte VEGF-A Knockdown Induces Diffuse Glomerulosclerosis in Diabetic and in eNOS Knockout Mice

Vascular endothelial growth factor-a (VEGF-A) and nitric oxide (NO) are essential for glomerular filtration barrier homeostasis, and are dysregulated in diabetic kidney disease (DKD). While NO availability is consistently low in diabetes, both high and low VEGF-A have been reported in patients with DKD. Here we examined the effect of inducible podocyte VEGF-A knockdown (VEGF^KD) in diabetic mice and in endothelial nitric oxide synthase knockout mice (eNOS^−/−). Diabetes was induced with streptozotocin using the Animal Models of Diabetic Complications Consortium (AMDCC) protocol. Induction of podocyte VEGF^KD led to diffuse glomerulosclerosis, foot process effacement, and GBM thickening in both diabetic mice with intact eNOS and in non-diabetic eNOS^−/−:VEGF^KD mice. VEGF^KD diabetic mice developed mild proteinuria and maintained normal glomerular filtration rate (GFR), associated with extremely high NO and thiol urinary excretion. In eNOS^−/−:VEGF^KD (+dox) mice severe diffuse glomerulosclerosis was associated with microaneurisms, arteriolar hyalinosis, massive proteinuria, and renal failure. Collectively, data indicate that combined podocyte VEGF-A and eNOS deficiency result in diffuse glomerulosclerosis in mice; compensatory NO and thiol generation prevents severe proteinuria and GFR loss in VEGF^KD diabetic mice with intact eNOS, whereas VEGF^KD induction in eNOS^−/−:VEGF^KD mice causes massive proteinuria and renal failure mimicking DKD in the absence of diabetes. Mechanistically, we identify VEGF^KD-induced abnormal S-nitrosylation of specific proteins, including β3-integrin, laminin, and S-nitrosoglutathione reductase (GSNOR), as targetable molecular mechanisms involved in the development of advanced diffuse glomerulosclerosis and renal failure.

MicroRNAs and their delivery in diabetic fibrosis

The global prevalence of diabetes mellitus was estimated to be 463 million people in 2019 and is predicted to rise to 700 million by 2045. The associated financial and societal costs of this burgeoning epidemic demand an understanding of the pathology of this disease, and its complications, that will inform treatment to enable improved patient outcomes. Nearly two decades after the sequencing of the human genome, the significance of noncoding RNA expression is still being assessed. The family of functional noncoding RNAs known as microRNAs regulates the expression of most genes encoded by the human genome. Altered microRNA expression profiles have been observed both in diabetes and in diabetic complications. These transcripts therefore have significant potential and novelty as targets for therapy, therapeutic agents and biomarkers.

The role of microRNA-155 in glomerular endothelial cell injury induced by high glucose

Objective

To investigate the role of microRNA-155-5p on apoptosis and inflammatory response in human renal glomerular endothelial cells (HRGEC) cultured with high glucose.

Methods

The primary HRGEC were mainly studied, light microscopy was used to detect changes in cell morphology. Quantitative Real Time-Polymerase Chain Reaction, Western Blot, immunofluorescence were aimed to observe the mRNA and protein expression levels of target gene ETS-1, downstream factors VCAM-1, MCP-1 and cleaved caspase-3 in each group after high glucose treatment as well as transfection with miR-155 mimics or inhibitor.

Results

The expression of inflammatory factors and apoptosis of HRGEC cells increased under high glucose treatment. Compared with normal-glucose treatment, the expression of microRNA-155 markedly increased in HRGECs treated with high-glucose, as well as the mRNA and protein levels of ETS-1, VCAM-1, MCP-1 and cleaved caspase-3. Overexpression of microRNA-155 remarkably downregulated mRNA and protein levels of ETS-1, VCAM-1, MCP-1 and cleaved caspase-3, whereas miRNA-155 knockdown upregulated their levels. In addition, HRGEC cells were transfected with miR-155 mimics and ETS-1 siRNA with high glucose stimulation. The expression of ETS-1 was positively correlated with the expression of downstream factors VCAM-1 and MCP-1. These results suggest that ETS-1 can mediate endothelial cell inflammation by regulating VCAM-1 and MCP-1.

Conclusion

MiR-155 can negatively regulate the expression of target gene ETS-1 and its downstream factors VCAM-1, MCP-1 and cleaved caspase-3, thus mediating the inflammatory response and apoptosis of HRGEC.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11033-021-07106-1.

Variable expression of eighteen common housekeeping genes in human non-cancerous kidney biopsies

Housekeeping, or reference genes (RGs) are, by definition, loci with stable expression profiles that are widely used as internal controls to normalize mRNA levels. However, due to specific events, such as pathological changes, or technical procedures, their expression might be altered, failing to fulfil critical normalization pre-requisites. To identify RG genes suitable as internal controls in human non-cancerous kidney tissue, we selected 18 RG candidates based on previous data and screen them in 30 expression datasets (>800 patients), including our own, publicly available or provided by independent groups. Datasets included specimens from patients with hypertensive and diabetic nephropathy, Fabry disease, focal segmental glomerulosclerosis, IgA nephropathy, membranous nephropathy, and minimal change disease. We examined both microdissected and whole section-based datasets. Expression variability of 4 candidate genes (YWHAZ, SLC4A1AP, RPS13 and ACTB) was further examined by qPCR in biopsies from patients with hypertensive nephropathy (n = 11) and healthy controls (n = 5). Only YWHAZ gene expression remained stable in all datasets whereas SLC4A1AP was stable in all but one Fabry dataset. All other RGs were differentially expressed in at least 2 datasets, and in 4.5 datasets on average. No differences in YWHAZ, SLC4A1AP, RPS13 and ACTB gene expression between hypertensive and control biopsies were detected by qPCR. Although RGs suitable to all techniques and tissues are unlikely to exist, our data suggest that in non-cancerous kidney biopsies expression of YWHAZ and SLC4AIAP genes is stable and suitable for normalization purposes.

Hypoxia-Inducible Factor Stabilizers in End Stage Kidney Disease: "Can the Promise Be Kept?"

Anemia is a common complication of chronic kidney disease (CKD). The prevalence of anemia in CKD strongly increases as the estimated Glomerular Filtration Rate (eGFR) decreases. The pathophysiology of anemia in CKD is complex. The main causes are erythropoietin (EPO) deficiency and functional iron deficiency (FID). The administration of injectable preparations of recombinant erythropoiesis-stimulating agents (ESAs), especially epoetin and darbepoetin, coupled with oral or intravenous(iv) iron supplementation, is the current treatment for anemia in CKD for both dialysis and non-dialysis patients. This approach reduces patients’ dependence on transfusion, ensuring the achievement of optimal hemoglobin target levels. However, there is still no evidence that treating anemia with ESAs can significantly reduce the risk of cardiovascular events. Meanwhile, iv iron supplementation causes an increased risk of allergic reactions, gastrointestinal side effects, infection, and cardiovascular events. Currently, there are no studies defining the best strategy for using ESAs to minimize possible risks. One class of agents under evaluation, known as prolyl hydroxylase inhibitors (PHIs), acts to stabilize hypoxia-inducible factor (HIF) by inhibiting prolyl hydroxylase (PH) enzymes. Several randomized controlled trials showed that HIF-PHIs are almost comparable to ESAs. In the era of personalized medicine, it is possible to envisage and investigate specific contexts of the application of HIF stabilizers based on the individual risk profile and mechanism of action.

Novel Protein Therapeutics Created Using the Elastin-Like Polypeptide Platform

Elastin-like polypeptides (ELPs) are bioengineered proteins that have a unique physical property, a thermally triggered inverse phase transition, that can be exploited for drug delivery. ELP-fusion proteins can be used as soluble biologics, thermally targeted drug carriers, self-assembling nanoparticles, and slow-release drug depots. Because of their unique physical characteristics and versatility for delivery of nearly any type of therapeutic, ELP-based drug delivery systems represent a promising platform for biologics development.

Glomerular Kidney Diseases in the Single-Cell Era

Recent advances in single-cell technology have enabled investigation of genomic profiles and molecular crosstalk among individual cells obtained from tissues and biofluids at unprecedented resolution. Glomerular diseases, either primary or secondary to systemic diseases, often manifest elements of inflammation and of innate and adaptive immune responses. Application of single-cell methods have revealed cellular signatures of inflammation, cellular injury, and fibrosis. From these signatures, potential therapeutic targets can be inferred and in theory, this approach might facilitate identification of precision therapeutics for these diseases. Single-cell analyses of urine samples and skin lesions from patients with lupus nephritis and of urine samples from patients with diabetic nephropathy and focal segmental glomerulosclerosis have presented potential novel approaches for the diagnosis and monitoring of disease activity. These single-cell approaches, in contrast to kidney biopsy, are non-invasive and could be repeated multiple times as needed.

Novel insights into the disease transcriptome of human diabetic glomeruli and tubulointerstitium

BACKGROUND

Diabetic nephropathy (DN) is the most common cause of end-stage renal disease, affecting ∼30% of the rapidly growing diabetic population, and strongly associated with cardiovascular risk. Despite this, the molecular mechanisms of disease remain unknown.

METHODS

RNA sequencing (RNAseq) was performed on paired, micro-dissected glomerular and tubulointerstitial tissue from patients diagnosed with DN [n = 19, 15 males, median (range) age: 61 (30-85) years, chronic kidney disease stages 1-4] and living kidney donors [n = 20, 12 males, median (range) age: 56 (30-70) years].

RESULTS

Principal component analysis showed a clear separation between glomeruli and tubulointerstitium transcriptomes. Differential expression analysis identified 1550 and 4530 differentially expressed genes, respectively (adjusted P < 0.01). Gene ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses highlighted activation of inflammation and extracellular matrix (ECM) organization pathways in glomeruli, and immune and apoptosis pathways in tubulointerstitium of DN patients. Specific gene modules were associated with renal function in weighted gene co-expression network analysis. Increased messengerRNA (mRNA) expression of renal damage markers lipocalin 2 (LCN) and hepatitis A virus cellular receptor1 (HAVCR1) in the tubulointerstitial fraction was observed alongside higher urinary concentrations of the corresponding proteins neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1) in DN patients.

CONCLUSIONS

Here we present the first RNAseq experiment performed on paired glomerular and tubulointerstitial samples from DN patients. We show that prominent disease-specific changes occur in both compartments, including relevant cellular processes such as reorganization of ECM and inflammation (glomeruli) as well as apoptosis (tubulointerstitium). The results emphasize the potential of utilizing high-throughput transcriptomics to decipher disease pathways and treatment targets in this high-risk patient population.

Non-Albumin Proteinuria (NAP) as a Complementary Marker for Diabetic Kidney Disease (DKD)

Diabetic kidney disease (DKD) is one of the most common forms of chronic kidney disease. Its pathogenic mechanism is complex, and it can affect entire structures of the kidney. However, conventional approaches to early stage DKD have focused on changes to the glomerulus. Current standard screening tools for DKD, albuminuria, and estimated glomerular filtration rate are insufficient to reflect early tubular injury. Therefore, many tubular biomarkers have been suggested. Non-albumin proteinuria (NAP) contains a wide range of tubular biomarkers and is convenient to measure. We reviewed the clinical meanings of NAP and its significance as a marker for early stage DKD.

Acute Kidney Injury, Microvascular Rarefaction, and Estimated Glomerular Filtration Rate in Kidney Transplant Recipients

BACKGROUND AND OBJECTIVES

Animal studies suggest that microvascular rarefaction is a key factor in the acute kidney disease to CKD transition. Hence, delayed graft function appears as a unique human model of AKI to further explore the role of microvascular rarefaction in kidney transplant recipients. Here, we assessed whether delayed graft function is associated with peritubular capillary loss and evaluated the association between this loss and long-term kidney graft function.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This observational, retrospective cohort study included 61 participants who experienced delayed graft function and 130 who had immediate graft function. We used linear regression models to evaluate associations between delayed graft function and peritubular capillary density expressed as the percentage of efficient cortical area occupied by peritubular capillaries in pre- and post-transplant graft biopsies. eGFRs 1 and 3 years post-transplant were secondary outcomes.

RESULTS

Post-transplant biopsies were performed at a median of 113 days (interquartile range, 101-128) after transplantation. Peritubular capillary density went from 15.4% to 11.5% in patients with delayed graft function (median change, -3.7%; interquartile range, -6.6% to -0.8%) and from 19.7% to 15.1% in those with immediate graft function (median change, -4.5%; interquartile range, -8.0% to -0.8%). Although the unadjusted change in peritubular capillary density was similar between patients with and without delayed graft function, delayed graft function was associated with more peritubular capillary loss in the multivariable analysis (adjusted difference in change, -2.9%; 95% confidence interval, -4.0 to -1.8). Pretransplant peritubular capillary density and change in peritubular capillary density were associated with eGFR 1 and 3 years post-transplantation.

CONCLUSIONS

Perioperative AKI is associated with lower density in peritubular capillaries before transplantation and with loss of peritubular capillaries following transplantation. Lower peritubular capillary density is linked to lower long-term eGFR.

Heme Oxygenase 1: A Defensive Mediator in Kidney Diseases

The incidence of kidney disease is rising, constituting a significant burden on the healthcare system and making identification of new therapeutic targets increasingly urgent. The heme oxygenase (HO) system performs an important function in the regulation of oxidative stress and inflammation and, via these mechanisms, is thought to play a role in the prevention of non-specific injuries following acute renal failure or resulting from chronic kidney disease. The expression of HO-1 is strongly inducible by a wide range of stimuli in the kidney, consequent to the kidney's filtration role which means HO-1 is exposed to a wide range of endogenous and exogenous molecules, and it has been shown to be protective in a variety of nephropathological animal models. Interestingly, the positive effect of HO-1 occurs in both hemolysis- and rhabdomyolysis-dominated diseases, where the kidney is extensively exposed to heme (a major HO-1 inducer), as well as in non-heme-dependent diseases such as hypertension, diabetic nephropathy or progression to end-stage renal disease. This highlights the complexity of HO-1's functions, which is also illustrated by the fact that, despite the abundance of preclinical data, no drug targeting HO-1 has so far been translated into clinical use. The objective of this review is to assess current knowledge relating HO-1's role in the kidney and its potential interest as a nephroprotection agent. The potential therapeutic openings will be presented, in particular through the identification of clinical trials targeting this enzyme or its products.

Association Between Urinary Epidermal Growth Factor and Renal Prognosis in Lupus Nephritis

OBJECTIVE

To evaluate the role of urinary epidermal growth factor (EGF) as a biomarker of chronic kidney damage in lupus nephritis (LN).

METHODS

A proteomics approach was used to identify urinary EGF as a biomarker of interest in a discovery cohort of patients with LN. The expression of urinary EGF was characterized in 2 large multiethnic LN cohorts, and the association between urinary EGF levels at the time of flare and kidney outcomes was evaluated in a subset of 120 patients with long-term follow-up data. For longitudinal studies, the expression of urinary EGF over time was determined in 2 longitudinal cohorts of patients with LN from whom serial urine samples were collected.

RESULTS

Discovery analysis showed the urinary EGF levels as being low in patients with active LN (median peptide count 8.4, interquartile range [IQR] 2.8-12.3 in patients with active LN versus median 48.0, IQR 45.3-64.6 in healthy controls). The peptide sequence was consistent with that of proEGF, and this was confirmed by immunoblotting. The discovery findings were verified by enzyme-linked immunosorbent assay. Patients with active LN had a significantly lower level of urinary EGF compared to that in patients with active nonrenal systemic lupus erythematosus (SLE), patients with inactive SLE, and healthy kidney donors (each P < 0.05). The urinary EGF level was inversely correlated with the chronicity index of histologic features assessed in kidney biopsy tissue (Spearman's r = -0.67, P < 0.001). Multivariate survival analysis showed that the urinary EGF level was associated with time to doubling of the serum creatinine level (DSCr), a marker of future end-stage kidney disease (ESKD) (hazard ratio 0.88, 95% confidence interval 0.77-0.99, P = 0.045). Patients whose LN symptoms progressed to DSCr and those who experienced progression to ESKD had a lower urinary EGF level at the time of flare, and urinary EGF levels decreased over the 12 months following flare. All patients who experienced progression to ESKD were identified based on a urinary EGF cutoff level of <5.3 ng/mg.

CONCLUSION

Urinary EGF levels are correlated with histologic kidney damage in patients with LN. Low urinary EGF levels at the time of flare and decreasing urinary EGF levels over time are associated with adverse long-term kidney outcomes.

Acute Kidney Injury in Pediatric Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a common complication of type 1 and 2 diabetes and often presents during adolescence and young adulthood. Given the growing incidence of both type 1 and type 2 diabetes in children and adolescents, DKD represents a significant public health problem. Acute kidney injury (AKI) in youth with diabetes is strongly associated with risk of DKD development. This review will summarize the epidemiology and pathophysiology of AKI in children with diabetes, the relationship between AKI and DKD, and the potential therapeutic interventions. Finally, we will appraise the impact of the recent COVID-19 infection pandemic on AKI in children with diabetes.

Peritubular Capillary Rarefaction: An Underappreciated Regulator of CKD Progression

Peritubular capillary (PTC) rarefaction is commonly detected in chronic kidney disease (CKD) such as hypertensive nephrosclerosis and diabetic nephropathy. Moreover, PTC rarefaction prominently correlates with impaired kidney function and predicts the future development of end-stage renal disease in patients with CKD. However, it is still underappreciated that PTC rarefaction is a pivotal regulator of CKD progression, primarily because the molecular mechanisms of PTC rarefaction have not been well-elucidated. In addition to the established mechanisms (reduced proangiogenic factors and increased anti-angiogenic factors), recent studies discovered significant contribution of the following elements to PTC loss: (1) prompt susceptibility of PTC to injury, (2) impaired proliferation of PTC, (3) apoptosis/senescence of PTC, and (4) pericyte detachment from PTC. Mainly based on the recent and novel findings in basic research and clinical study, this review describes the roles of the above-mentioned elements in PTC loss and focuses on the major factors regulating PTC angiogenesis, the assessment of PTC rarefaction and its surrogate markers, and an overview of the possible therapeutic agents to mitigate PTC rarefaction during CKD progression. PTC rarefaction is not only a prominent histological characteristic of CKD but also a central driving force of CKD progression.

Endoglin Promotes Myofibroblast Differentiation and Extracellular Matrix Production in Diabetic Nephropathy

Diabetic nephropathy (DN) is a complication of diabetes mellitus that can lead to proteinuria and a progressive decline in renal function. Endoglin, a co-receptor of TGF-β, is known primarily for regulating endothelial cell function; however, endoglin is also associated with hepatic, cardiac, and intestinal fibrosis. This study investigates whether endoglin contributes to the development of interstitial fibrosis in DN. Kidney autopsy material from 80 diabetic patients was stained for endoglin and Sirius Red and scored semi-quantitatively. Interstitial endoglin expression was increased in samples with DN and was correlated with Sirius Red staining (p < 0.001). Endoglin expression was also correlated with reduced eGFR (p = 0.001), increased creatinine (p < 0.01), increased systolic blood pressure (p < 0.05), hypertension (p < 0.05), and higher IFTA scores (p < 0.001). Biopsy samples from DN patients were also co-immunostained for endoglin together with CD31, CD68, vimentin, or α-SMA Endoglin co-localized with both the endothelial marker CD31 and the myofibroblast marker α-SMA. Finally, we used shRNA to knockdown endoglin expression in a human kidney fibroblast cell line. We found that TGF-β1 stimulation upregulated SERPINE1, CTGF, and ACTA2 mRNA and α-SMA protein, and that these effects were significantly reduced in fibroblasts after endoglin knockdown. Taken together, these data suggest that endoglin plays a role in the pathogenesis of interstitial fibrosis in DN.

Investigation of hub genes involved in diabetic nephropathy using biological informatics methods

Background

The aim of this study was to find genes with significantly aberrant expression in diabetic nephropathy (DN) and determine their underlying mechanisms.

Methods

GSE30528 and GSE1009 were obtained by querying the Gene Expression Omnibus (GEO) database. The difference in target gene expression between normal renal tissues and kidney tissues in patients with DN was screened by using the GEO2R tool. Using the Database for Annotation, Visualization, and Integrated Discovery (DAVID) database, differentially expressed genes (DEGs) were analysed by Gene Ontology (GO) annotation and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment. Then, the protein-protein interactions (PPIs) of DEGs were analyzed by Cytoscape with the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) database, and the hub genes in this PPI network were recognized by centrality analysis.

Results

There were 110 genes with significant expression differences between normal and DN tissues. The differences in gene expression involved many functions and expression pathways, such as the formation of the extracellular matrix and the construction of the extracellular domain. The correlation analysis and subgroup analysis of 14 hub genes and the clinical characteristics of DN showed that CTGF, ALB, PDPN, FLT1, IGF1, WT1, GJA1, IGFBP2, FGF9, BMP2, FGF1, BMP7, VEGFA, and TGFBR3 may be involved in the progression of DN.

Conclusions

We confirmed the differentially expressed hub genes and other genes which may be the novel biomarker and target candidates in DN.

Role of Renal Hypoxia in the Progression From Acute Kidney Injury to Chronic Kidney Disease

Over the past 20 years, there has been an increased appreciation of the long-term sequelae of acute kidney injury (AKI) and the potential development of chronic kidney disease (CKD). Several pathophysiologic features have been proposed to mediate AKI to CKD progression including maladaptive alterations in tubular, interstitial, inflammatory, and vascular cells. These alterations likely interact to culminate in the progression to CKD. In this article we focus primarily on evidence of vascular rarefaction secondary to AKI, and the potential mechanisms by which rarefaction occurs in relation to other alterations in tubular and interstitial compartments. We further focus on the potential that rarefaction contributes to renal hypoxia. Consideration of the role of hypoxia in AKI to CKD transition focuses on experimental evidence of persistent renal hypoxia after AKI and experimental maneuvers to evaluate the influence of hypoxia, per se, in progressive disease. Finally, consideration of methods to evaluate hypoxia in patients is provided with the suggestion that noninvasive measurement of renal hypoxia may provide insight into progression in post-AKI patients.

Hypoxia in chronic kidney disease: towards a paradigm shift?

Chronic kidney disease (CKD) is defined as an alteration of kidney structure and/or function lasting for >3 months [1]. CKD affects 10% of the general adult population and is responsible for large healthcare costs [2]. Since the end of the last century, the role of hypoxia in CKD progression has controversially been discussed. To date, there is evidence of the presence of hypoxia in late-stage renal disease, but we lack time-course evidence, stage correlation and also spatial co-localization with fibrotic lesions to ensure its causative role. The classical view of hypoxia in CKD progression is that it is caused by peritubular capillary alterations, renal anaemia and increased oxygen consumption regardless of the primary injury. In this classical view, hypoxia is assumed to further induce pro-fibrotic and pro-inflammatory responses, as well as oxidative stress, leading to CKD worsening as part of a vicious circle. However, recent investigations tend to question this paradigm, and both the presence of hypoxia and its role in CKD progression are still not clearly demonstrated. Hypoxia-inducible factor (HIF) is the main transcriptional regulator of the hypoxia response. Genetic HIF modulation leads to variable effects on CKD progression in different murine models. In contrast, pharmacological modulation of the HIF pathway [i.e. by HIF hydroxylase inhibitors (HIs)] appears to be generally protective against fibrosis progression experimentally. We here review the existing literature on the role of hypoxia, the HIF pathway and HIF HIs in CKD progression and summarize the evidence that supports or rejects the hypoxia hypothesis, respectively.

Astragaloside IV acts through multi-scale mechanisms to effectively reduce diabetic nephropathy

Diabetic nephropathy (DN), a common complication of diabetes mellitus, is the main cause of end-stage nephropathy, and thus developing novel strategies for reversing DN remains urgent. Astragaloside IV (AS-IV), a glycoside extracted from the Astragalus membranaceus (Fisch.) Bunge, is a widely used Traditional Chinese Medicine (TCM) in China and presents diverse pharmacological properties including the protective effect on DN. However, the rudimentary mechanism of AS-IV in remedying DN remains indeterminate. Currently, we systematically explore the pharmacological mechanism of action of AS-IV for treating DN. Firstly, AS-IV was evaluated by ADME assessment, and 26 targets were screened out through target prediction. Then, we decipher the protein-protein interaction (PPI), Gene Ontology (GO) enrichment analysis, disease and pathway network analysis to obtain the specific molecular biological process and pharmacological activity of AS-IV in the treatment of DN. Meanwhile, both in vivo and in vitro experiments confirmed that AS-IV has anti-oxidative stress, anti-inflammatory, anti-epithelial-mesenchymal transition (EMT) effects, and can inhibit the Wnt/β-catenin signaling pathway, ultimately ameliorating the renal injury caused by high glucose. Additionally, we also applied molecular docking and molecular dynamics simulation to predict the specific binding sites and binding capacity of AS-IV and related targets. Overall, the comprehensive system pharmacology method and experiment validations provide an accurate explanation for the molecular mechanism of AS-IV in the treatment of DN. Moreover, it is expected to provide a brand new strategy for exploring the effective components of TCM.

The incidence, risk factors, and long-term outcomes of acute kidney injury in hospitalized diabetic ketoacidosis patients

Background

Emerging evidence has demonstrated that acute kidney injury (AKI) is an important risk factor associated with increased morbidity and mortality in diabetic ketoacidosis (DKA) patients. The current study aimed to investigate the incidence rate, risk factors, long-term renal outcomes, and mortality in DKA patients with AKI.

Methods

A total of 179 patients diagnosed with DKA at Sun Yat-sen Memorial Hospital from January 2012 to January 2018 were included in the analysis. AKI was diagnosed according to the 2012 KDIGO criteria. Risk factors, long-term renal outcomes, and mortality were analyzed by logistic regression and Cox proportional hazards models.

Results

Among 179 DKA patients, 98 patients (54.75%) were diagnosed as AKI. Aging; increased blood glucose, serum uric acid and white blood cells; decreased serum pH and albumin; coma; and preexisting chronic kidney disease (CKD) were risk factors of AKI in patients with DKA. During follow-up, DKA patients with AKI showed more than a two-fold decline in eGFR within 1 year after discharge from the hospital when compared with non-AKI DKA patients. Furthermore, AKI was also an independent risk factor for poor long-term renal outcomes and mortality in DKA patients.

Conclusions

Multiple risk factors contribute to the development of AKI in DKA patients. AKI and advanced AKI stage are associated with rapid progressive CKD and long-term mortality in patients with DKA.

Pathogenesis of Fabry nephropathy: The pathways leading to fibrosis

BACKGROUND

Kidney is one of the main target organs in Fabry disease, a lysosomal X-linked genetic disorder. Renal involvement is characterized by proteinuria and progressive chronic kidney disease leading to end-stage renal disease. Pathogenic mechanisms in the progression of renal damage in Fabry disease are not thoroughly known yet. The lysosomal Gb3 deposition is the first step of complex pathological pathways resulting in renal sclerosis/fibrosis. Our hypothesis is that Fabry disease associated cellular alterations in tubular cells induce the production of TGF-β1, which mediate transdifferentiation of renal cells into myofibroblasts resulting in fibrosis of renal tissue.

OBJECTIVES

The aim of this work is to study the mechanisms leading to fibrosis in kidney from human Fabry patients.

METHODS

Fifteen renal biopsies from naïve Fabry patients were included. Histological and immunohistochemical analysis was carried out.

RESULTS

Positive staining for TGF-β1 was found in tubular epithelial cells in biopsies from Fabry patients. Apoptosis was determined by active caspase 3 staining in tubular and mesangial glomerular cells. Due to TGF-β1 is the main profibrotic cytokine and induces accumulation of myofibroblasts, we performed a study for its marker α-smooth muscle actin (α-SMA). This study revealed expression of α-SMA on pericytes surrounding peritubular capillaries, smooth muscle cells of blood vessels, mesangial cells and periglomerular zone. TGF-β1 is produced mainly by tubular cells in Fabry kidney biopsies probably inducing cellular trans-differentiation of renal cells into myofibroblasts. A positive staining for a marker of myofibroblasts was present, affirming the presence of those profibrotic cells.

CONCLUSIONS

These results show for the first time that TGF-β1 is expressed in human renal tissue from Fabry patients, and that this profibrotic cytokine is mainly produced by proximal tubular cells. In addition both, peritubular interstitium and glomeruli, presented cells positive for myofibroblasts markers.

Inhibition of lysyl oxidase ameliorates renal injury by inhibiting CD44-mediated pericyte detachment and loss of peritubular capillaries

Renal fibrosis is a common pathological manifestation of almost all forms of kidney disease irrespective of the etiological cause. Microvascular rarefaction represents itself as an important phenomenon associated with renal fibrosis and shows strong correlation with decline in renal functions. Lysyl oxidase (LOX) catalyzes crosslinking of extracellular matrix (ECM) proteins including collagens, plays an important role in stabilization of degradation resistant matrix. Since, there seems to be a causal link between deposition of excessive ECM and microvascular rarefaction, we investigated the effects of reduction in renal fibrosis on microvascular rarefaction in acute as well as end stage kidney. We used a well-established unilateral ureteral obstruction (UUO)-induced renal fibrosis model to produce renal fibrosis in animals. We treated animals with a LOX inhibitor, β-aminopropionitrile (BAPN, 100 mg/kg, i.p.) and investigated effects on renal fibrosis and microvascular rarefaction. We observed that LOX inhibition was associated with reduction in collagen deposition in UUO-induced renal fibrosis animal model. Further, ECM normalization by LOX inhibition decreased the loss of peritubular capillaries (PTCs) in fibrotic kidney in acute study while the LOX inhibition failed to inhibit PTCs loss in end stage kidney. The results of present study suggested that inhibition of LOX reduces collagen deposition and renal fibrosis. Further, the reduction in fibrosis fails to protect from PTCs loss in chronic study suggesting the absence of strong link between reduction in fibrosis and improvement in PTCs in an end stage kidney.

Comparison of Kidney Transcriptomic Profiles of Early and Advanced Diabetic Nephropathy Reveals Potential New Mechanisms for Disease Progression

To identify the factors mediating the progression of diabetic nephropathy (DN), we performed RNA sequencing of kidney biopsy samples from patients with early DN, advanced DN, and normal kidney tissue from nephrectomy samples. A set of genes that were upregulated at early but downregulated in late DN were shown to be largely renoprotective, which included genes in the retinoic acid pathway and glucagon-like peptide 1 receptor. Another group of genes that were downregulated at early but highly upregulated in advanced DN consisted mostly of genes associated with kidney disease pathogenesis, such as those related to immune response and fibrosis. Correlation with estimated glomerular filtration rate (eGFR) identified genes in the pathways of iron transport and cell differentiation to be positively associated with eGFR, while those in the immune response and fibrosis pathways were negatively associated. Correlation with various histopathological features also identified the association with the distinct gene ontological pathways. Deconvolution analysis of the RNA sequencing data set indicated a significant increase in monocytes, fibroblasts, and myofibroblasts in advanced DN kidneys. Our study thus provides potential molecular mechanisms for DN progression and association of differential gene expression with the functional and structural changes observed in patients with early and advanced DN.

Endothelium-mediated contributions to fibrosis

Fibrosis, characterized by abnormal and excessive deposition of extracellular matrix, results in compromised tissue and organ structure. This can lead to reduced organ function and eventual failure. Although activated fibroblasts, called myofibroblasts, are considered the central players in fibrosis, the contribution of endothelial cells to the inception and progression of fibrosis has become increasingly recognized. Endothelial cells can contribute to fibrosis by acting as a source of myofibroblasts via endothelial-mesenchymal transition (EndoMT), or by becoming senescent, by secretion of profibrotic mediators and pro-inflammatory cytokines, chemokines and exosomes, promoting the recruitment of immune cells, and by participating in vascular rarefaction and decreased angiogenesis. In this review, we provide an overview of the different aspects of fibrosis in which endothelial cells have been implicated.

Interstitial HIF1A induces an estimated glomerular filtration rate decline through potentiating renal fibrosis in diabetic nephropathy

AIMS

This study aimed to identify interstitial molecules that were responsible for the deterioration of the esiantimated glomerular filtration rate (eGFR) in diabetic nephropathy (DN).

MATERIALS AND METHODS

Weighted gene co-expression network analysis (WGCNA) was used to link the tubulointerstitial gene expression profile of DN to eGFR values. The relationship of eGFR with each sub-domain regulator in the network was analyzed with the linear regression model. Gene sets enrichment analysis (GSEA) was applied to detect the molecular changes mostly relating to the essential regulators.

KEY FINDINGS

Four co-expression modules were found strongly correlating with eGFR values. Genes from these modules were over-represented in fibrosis-related biological processes (extracellular matrix (ECM) organization and cell adhesion) and pathways (integrin signaling and ECM-receptor interaction). Of sub-domains in the gene interaction network, the expression of hypoxia-inducible factor 1A (HIF1A) was most negatively correlated with eGFR (R² = 0.417, P = 0.026). The positive correlations between HIF1A and its target genes were found, indicating an enhanced transcriptional activity of HIF1A. We also found that HIF1A positively correlated with CCAAT enhancer binding protein delta (CEBPD) (r = 0.731, P = 0.011), an activator of HIF1A transcription. Moreover, GSEA showed that samples with high HIF1A expression were enriched with fibrosis associated signaling, like ECM-receptor interaction and cell adhesion. Intriguingly, vascular epithelial growth factor A (VEGFA) expression decreased while HIF1A increased (R² = 0.733, P = 0.001), suggesting VEGFA loss may exacerbate hypoxia and stimulate HIF1A induction.

SIGNIFICANCE

The present study suggested that interstitial HIF1A may be involved in renal interstitial fibrosis in DN.

Mechanism and Consequences of The Impaired Hif-1α Response to Hypoxia in Human Proximal Tubular HK-2 Cells Exposed to High Glucose

Renal hypoxia and loss of proximal tubular cells (PTC) are relevant in diabetic nephropathy. Hypoxia inhibits hypoxia-inducible factor-1α (HIF-1α) degradation, which leads to cellular adaptive responses through HIF-1-dependent activation of gene hypoxia-responsive elements (HRE). However, the diabetic microenvironment represses the HIF-1/HRE response in PTC. Here we studied the mechanism and consequences of impaired HIF-1α regulation in human proximal tubular HK-2 cells incubated in hyperglycemia. Inhibition at different levels of the canonical pathway of HIF-1α degradation did not activate the HIF-1/HRE response under hyperglycemia, except when proteasome was inhibited. Further studies suggested that hyperglycemia disrupts the interaction of HIF-1α with Hsp90, a known cause of proteasomal degradation of HIF-1α. Impaired HIF-1α regulation in cells exposed to hyperglycemic, hypoxic diabetic-like milieu led to diminished production of vascular endothelial growth factor-A and inhibition of cell migration (responses respectively involved in tubular protection and repair). These effects, as well as impaired HIF-1α regulation, were reproduced in normoglycemia in HK-2 cells incubated with microparticles released by HK-2 cells exposed to diabetic-like milieu. In summary, these results highlight the role of proteasome-dependent mechanisms of HIF-1α degradation on diabetes-induced HK-2 cells dysfunction and suggest that cell-derived microparticles may mediate negative effects of the diabetic milieu on PTC.

Herniation of the tuft with outgrowth of vessels through the glomerular entrance in diabetic nephropathy damages the juxtaglomerular apparatus

As shown in our previous paper (Kriz W, Löwen J, Federico G, van den Born J, Gröne E, Gröne HJ. Am J Physiol Renal Physiol 312: F1101-F1111, 2017), mesangial matrix expansion in diabetic nephropathy (DN) results for a major part from the accumulation of worn-out undegraded glomerular basement membrane material. Here, based on the reevaluation of >900 biopsies of DN, we show that this process continues with the progression of the disease finally leading to the herniation of the matrix-overloaded tuft through the glomerular entrance to the outside. This leads to severe changes in the glomerular surroundings, including a dissociation of the juxtaglomerular apparatus with displacement of the macula densa. The herniation is associated with a prominent outgrowth of glomerular vessels from the tuft. Mostly, these aberrant vessels are an abnormal type of arteriole with frequent intramural insudations of plasma. They spread into glomerular surroundings extending in intertubular and periglomerular spaces. Their formation is associated with elevated mRNA levels of vascular endothelial growth factor-A, angiopoietins 1 and 2, and the corresponding receptors. Functionally, these processes seem to compromise tubuloglomerular feedback-related functions and may be one factor why Na⁺-glucose cotransporter-2 inhibitors are not effective in advanced stages of DN.

Mesangial Cells and Renal Fibrosis

The main cellular constituents in glomerular mesangium are mesangial cells, which account for approximately 30-40% of the total cells in the glomerulus. Together with the mesangial matrix, mesangial cells form the glomerular basement membrane (GBM) in the glomerulus, whose main function is to perform the filtration. Under the pathologic conditions, mesangial cells are activated, leading to hyperproliferation and excess extracellular matrix (ECM). Moreover, mesangial cells also secrete several kinds of inflammatory cytokines, adhesion molecules, chemokines, and enzymes, all of which participate in the process of renal glomerular fibrosis. During the past years, researchers have revealed the roles of mesangial cells and the associated signal pathways involved in renal fibrosis. In this section, we will discuss how mesangial cells are activated and its contributions to renal fibrosis, as well as the molecular mechanisms and novel anti-fibrotic agents. Full understanding of the contributions of mesangial cells to renal fibrosis will benefit the clinical drug developing.

The determinants, biomarkers, and consequences of microvascular injury in kidney transplant recipients

Independent of the initial cause of kidney disease, microvascular injury to the peritubular capillary network appears to play a central role in the development of interstitial fibrosis in both native and transplanted kidney disease. This association is explained by mechanisms such as the upregulation of profibrotic genes and epigenetic changes induced by hypoxia, capillary leakage, endothelial and pericyte transition to interstitial fibroblasts, as well as modifications in the secretome of endothelial cells. Alloimmune injury due to antibody-mediated rejection and ischemia-reperfusion injury are the two main etiologies of microvascular damage in kidney transplant recipients. The presence of circulating donor-specific anti-human leukocyte antigen (HLA) antibodies, histological findings, such as diffuse C4d staining in peritubular capillaries, and the extent and severity of peritubular capillaritis, are commonly used clinically to provide both diagnostic and prognostic information. Complement-dependent assays, circulating non-HLA antibodies, or evaluation of the microvasculature with novel imaging techniques are the subject of ongoing studies.

Abnormal Expression of miR-21 in Kidney Tissue of Dogs With X-Linked Hereditary Nephropathy: A Canine Model of Chronic Kidney Disease

MicroRNAs (miRNAs) are a group of small noncoding RNAs that act as regulators of posttranslational gene/protein expression and are known to play a key role in physiological and pathological processes. The objective of our study was to compare expression of miR-21 in renal tissue from dogs affected with chronic kidney disease (CKD) caused by X-linked hereditary nephropathy (XLHN), a disease equivalent to human Alport syndrome, to that from unaffected dogs. Additionally, we sought to characterize changes in relative mRNA expression of various genes associated with miR-21 function. miRNA was isolated from kidney tissue collected from both affected dogs and unaffected, age-matched littermates at defined milestones of disease progression, including end-stage renal disease (ESRD). Additionally, autopsy samples from affected dogs at ESRD and corresponding unaffected dogs were evaluated. Samples were scored based on histological changes, and relative expression of miR-21 and kidney disease-related genes was determined using quantitative real-time polymerase chain reaction. In affected dogs, significant upregulation of kidney miR-21 was first detected at the milestone corresponding with increased serum creatinine. Furthermore, miR-21 expression correlated significantly with urine protein: urine creatinine ratio, serum creatinine concentration, glomerular filtration rate, and histologic lesions (glomerular damage, tubular damage, chronic inflammation, and fibrosis). At end-stage disease, COL1A1, TGFB1 and its receptor, TGFB2, and Serpine1 were upregulated, while PPARA, PPARGC1A, ACADM, SOD1, and EGF were downregulated. In conclusion, miR-21 is abnormally upregulated in the kidneys of dogs with CKD caused by XLHN, which may play an important pathologic role in the progression of disease by dysregulating multiple pathways.

Endoglin Mediates Vascular Endothelial Growth Factor-A-Induced Endothelial Cell Activation by Regulating Akt Signaling

In diabetic nephropathy, differential expression of growth factors leads to vascular changes, including endothelial cell activation, monocyte infiltration, and inflammation. Endoglin plays an important role in endothelial function and is also associated with inflammation. In the kidney, vascular endoglin expression is increased in animal models of renal injury, where it contributes to disease severity, possibly by promoting endothelial cell activation and inflammation. Herein, we investigated whether endoglin expression is associated with diabetic nephropathy. In addition, we examined whether reducing endothelial endoglin expression in vitro affects endothelial cell activation and monocyte adhesion and, if so, which intracellular pathways are involved. Finally, we analyzed whether glomerular endoglin expression is correlated with endothelial cell activation in patients with diabetic nephropathy. Endoglin levels were significantly increased in mice with type 1 diabetes compared with control mice. Reducing endoglin expression in cultured endothelial cells significantly impaired the vascular endothelial growth factor-A-induced up-regulation of activation markers and monocyte adhesion. This was mediated by increased phosphorylation of Akt, thereby inhibiting activating transcription factor 2 phosphorylation, which regulates vascular cell adhesion molecule-1 (VCAM1) gene transcription in these cells. Last, endoglin colocalized with VCAM-1 in the glomeruli of diabetic patients, glomerular VCAM-1 expression was significantly increased in these patients, and this increase in VCAM-1 expression was correlated with increased glomerular endoglin expression. Thus, targeting endoglin function may have therapeutic value in patients at risk for diabetic nephropathy.

The association of angiogenic factors and chronic kidney disease

BACKGROUND

There are limited data on the associations of circulating angiogenic factors with chronic kidney disease (CKD). We investigate the associations of circulating vascular endothelial growth factor (VEGF)-A, angiopoietin-1, angiopoietin-1/VEGF-A ratio, VEGF receptor 1 (VEGFR-1), VEGFR-2, and pentraxin-3 with CKD.

METHODS

We recruited 201 patients with CKD and 201 community controls without CKD from the greater New Orleans area. CKD was defined as estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m² or presence of albuminuria. Multivariable quantile and logistic regression models were used to examine the relationship between angiogenesis-related factors and CKD adjusting for confounding factors.

RESULTS

After adjusting for covariables including traditional cardiovascular disease (CVD) risk factors, C-reactive protein, and history of CVD, the medians (interquartile range) were 133.08 (90.39, 204.15) in patients with CKD vs. 114.17 (72.45, 170.32) pg/mL in controls without CKD (p = 0.002 for group difference) for VEGF-A; 3951.2 (2471.9, 6656.6) vs. 4270.5 (2763.7, 6537.2) pg/mL (p = 0.70) for angiopoietin-1; 25.87 (18.09, 47.90) vs. 36.55 (25.71, 61.10) (p = 0.0001) for angiopoietin-1/VEGF-A ratio; 147.81 (122.94, 168.79) vs. 144.16 (123.74, 168.05) ng/mL (p = 0.25) for VEGFR-1; 26.20 (22.67, 29.92) vs. 26.28 (23.10, 29.69) ng/mL (p = 0.31) for VEGFR-2; and 1.01 (0.79, 1.49)vs. 0.89 (0.58, 1.18) ng/mL (p = 0.01) for pentraxin-3, respectively. In addition, an elevated VEGF-A level and decreased angiopoietin-1/VEGF-A ratio were associated with increased odds of CKD.

CONCLUSIONS

These data indicate that plasma VEGF-A and pentraxin-3 levels were increased and the angiopoietin-1/VEGF-A ratio was decreased in patients with CKD. Future prospective studies are warranted to examine whether angiogenic factors play a role in progression of CKD.