Angiopoietin-2 inhibition attenuates kidney fibrosis by hindering chemokine C-C motif ligand 2 expression and apoptosis of endothelial cells

Angiopoietin-2 associates with poor prognosis in Moyamoya angiopathy

OBJECTIVE

Moyamoya angiopathy (MA) is a rare cerebrovascular disorder characterized by recurrent ischemic/hemorrhagic strokes due to progressive occlusion of the intracranial carotid arteries. The lack of reliable disease severity biomarkers led us to investigate molecular features of a Caucasian cohort of MA patients.

METHODS

The participants consisted of 30 MA patients and 40 controls. We measured cerebrospinal fluid (CSF) levels of angiogenic/inflammatory factors (ELISA). We then applied quantitative real-time PCR on cerebral artery specimens for expression analyses of angiogenic factors. By an immunoassay based on microfluidic technology, we examined the potential correlations between plasma protein expression and MA clinical progression. A RNA interference approach toward Ring Finger Protein 213 (RNF213) and a tube formation assay were applied in cellular model.

RESULTS

We detected a statistically significant (p < 0.000001) up-regulation of Angiopoietin-2 (Ang-2) in CSF and stenotic middle cerebral arteries (RQ >2) of MA patients compared to controls. A high Ang-2 plasma concentration (p = 0.018) was associated with unfavorable outcome in a subset of MA patients. ROC curve analyses indicated Ang-2 as diagnostic CSF biomarker (>3741 pg/mL) and prognostic plasma biomarker (>1162 pg/mL), to distinguish stable-from-progressive MA. Consistently, MA cellular model showed a significant up-regulation (RQ >2) of Ang-2 in RNF213 silenced condition.

INTERPRETATION

Our results pointed out Ang-2 as a reliable biomarker mirroring arterial steno-occlusion and vascular instability of MA in CSF and blood, providing a candidate factor for patient stratification. This pilot study may pave the way to the validation of a biomarker to identify progressive MA patients deserving a specific treatment path.

Preventive effects of vasohibin-2-targeting peptide vaccine for diabetic nephropathy

Diabetic nephropathy remains the leading cause of end-stage kidney disease in many countries, and additional therapeutic targets are needed to prevent its development and progression. Some angiogenic factors are involved in the pathogenesis of diabetic nephropathy. Vasohibin-2 (VASH2) is a novel proangiogenic factor, and our previous study showed that glomerular damage is inhibited in diabetic Vash2 homozygous knockout mice. Therefore, we established a VASH2-targeting peptide vaccine as a tool for anti-VASH2 therapy in diabetic nephropathy. In this study, the preventive effects of the VASH2-targeting peptide vaccine against glomerular injury were examined in a streptozotocin (STZ)-induced diabetic mouse model. The mice were subcutaneously injected with the vaccine at two doses 2 wk apart and then intraperitoneally injected with 50 mg/kg STZ for 5 consecutive days. Glomerular injury was evaluated 20 wk after the first vaccination. Treatment with the VASH2-targeting peptide vaccine successfully induced circulating anti-VASH2 antibody without inflammation in major organs. Although the vaccination did not affect blood glucose levels, it significantly prevented hyperglycemia-induced increases in urinary albumin excretion and glomerular volume. The vaccination did not affect increased VASH2 expression but significantly inhibited renal angiopoietin-2 (Angpt2) expression in the diabetic mice. Furthermore, it significantly prevented glomerular macrophage infiltration. The preventive effects of vaccination on glomerular injury were also confirmed in db/db mice. Taken together, the results of this study suggest that the VASH2-targeting peptide vaccine may prevent diabetic glomerular injury in mice by inhibiting Angpt2-mediated microinflammation.NEW & NOTEWORTHY This study demonstrated preventive effects of VASH2-targeting peptide vaccine therapy on albuminuria and glomerular microinflammation in STZ-induced diabetic mouse model by inhibiting renal Angpt2 expression. The vaccination was also effective in db/db mice. The results highlight the importance of VASH2 in the pathogenesis of early-stage diabetic nephropathy and the practicability of anti-VASH2 strategy as a vaccine therapy.

The emerging role of regulated cell death in ischemia and reperfusion-induced acute kidney injury: current evidence and future perspectives

Renal ischemia‒reperfusion injury (IRI) is one of the main causes of acute kidney injury (AKI), which is a potentially life-threatening condition with a high mortality rate. IRI is a complex process involving multiple underlying mechanisms and pathways of cell injury and dysfunction. Additionally, various types of cell death have been linked to IRI, including necroptosis, apoptosis, pyroptosis, and ferroptosis. These processes operate differently and to varying degrees in different patients, but each plays a role in the various pathological conditions of AKI. Advances in understanding the underlying pathophysiology will lead to the development of new therapeutic approaches that hold promise for improving outcomes for patients with AKI. This review provides an overview of the recent research on the molecular mechanisms and pathways underlying IRI-AKI, with a focus on regulated cell death (RCD) forms such as necroptosis, pyroptosis, and ferroptosis. Overall, targeting RCD shows promise as a potential approach to treating IRI-AKI.

Update of pericytes function and their roles in kidney diseases

Studies have highlighted the significant involvement of kidney pericytes in renal fibrosis. Kidney pericytes, classified as interstitial mesenchymal cells, are extensively branched, collagen-producing cells that closely interact with endothelial cells. This article aims to provide an overview of the recent advancements in understanding the physiological functions of pericytes and their roles in kidney diseases. In a healthy kidney, pericytes have essential physiological function in angiogenesis, erythropoietin (EPO) production, and the regulation of renal blood flow. Nevertheless, pericyte-myofibroblast transition has been identified as the primary cause of disease progression in acute kidney injury (AKI)-to-chronic kidney disease (CKD) continuum. Our recent research has demonstrated that hypoxia-inducible factor-2α (HIF-2α) regulates erythropoietin production in pericytes. However, this production is repressed by EPO gene hypermethylation and HIF-2α downregulation which were induced by transforming growth factor-β1-activated DNA methyltransferase and activin receptor-like kinase-5 signaling pathway during renal fibrosis, respectively. Additionally, AKI induces epigenetic modifications in pericytes, rendering them more prone to extracellular matrix production, cell migration and proliferation, thereby contributing to subsequent capillary rarefaction and renal fibrosis. Further investigation into the specific functions and roles of different subpopulations of pericytes may contribute for the development of targeted therapies aimed at attenuating kidney disease and mitigating their adverse effects.

Targeted therapy in glomerular diseases

Targeted therapy has emerged as a more precise approach to treat glomerular diseases, focusing on specific molecular or cellular processes that contribute to disease development or progression. This approach complements or replaces traditional immunosuppressive therapy, optimizes supportive care, and provides a more personalized treatment strategy. In this review, we summarize the evolving understanding of pathogenic mechanisms in immune-mediated glomerular diseases and the developing targeted therapies based on these mechanisms. We begin by discussing pan-B-cell depletion, anti-CD20 rituximab, and targeting B-cell survival signaling through the BAFF/APRIL pathway. We also exam specific plasma cell depletion with anti-CD38 antibody. We then shift our focus to complement activation in glomerular diseases, which is involved in antibody-mediated glomerular diseases, such as IgA nephropathy, membranous nephropathy, ANCA-associated vasculitis, and lupus nephritis. Non-antibody-mediated complement activation occurs in glomerular diseases, including C3 glomerulopathy, complement-mediated atypical hemolytic uremic syndrome, and focal segmental glomerulosclerosis. We discuss specific inhibition of terminal, lectin, and alternative pathways in different glomerular diseases. Finally, we summarize current clinical trials targeting the final pathways of various glomerular diseases, including kidney fibrosis. We conclude that targeted therapy based on individualized pathogenesis should be the future of treating glomerular diseases.

Circulating Activin A, Kidney Fibrosis, and Adverse Events

BACKGROUND

Identification of reliable biomarkers to assess kidney fibrosis severity is necessary for patients with CKD. Activin A, a member of the TGF- β superfamily, has been suggested as a biomarker for kidney fibrosis. However, its precise utility in this regard remains to be established.

METHODS

We investigated the correlation between plasma activin A levels, kidney fibrosis severity, and the incidence of major adverse kidney events in patients who underwent native kidney biopsies at a tertiary medical center. We performed RNA sequencing and histological analyses on kidney biopsy specimens to assess activin A expression. In vitro experiments were also conducted to explore the potential attenuation of TGF- β -induced fibroblast activation through activin A inhibition.

RESULTS

A total of 339 patients with biopsy-confirmed kidney diseases were enrolled. Baseline eGFR was 36 ml/min per 1.73 m 2 , and the urine protein/creatinine ratio was 2.9 mg/mg. Multivariable logistic regression analysis revealed a significant association between plasma activin A levels and the extent of tubulointerstitial fibrosis. Our RNA sequencing data demonstrated a positive correlation between kidney INHBA expression and plasma activin A levels. Furthermore, the histological analysis showed that myofibroblasts were the primary activin A-positive interstitial cells in diseased kidneys. During a median follow-up of 22 months, 113 participants experienced major adverse kidney events. Cox proportional hazards analysis initially found a positive association between plasma activin A levels and kidney event risk, but it became insignificant after adjusting for confounders. In cultured fibroblasts, knockdown of activin A significantly attenuated TGF- β -induced fibroblast-myofibroblast conversion.

CONCLUSIONS

Plasma activin A levels correlate with kidney fibrosis severity and adverse outcomes in various kidney disorders.

Mechanisms of kidney fibrosis and routes towards therapy

Kidney fibrosis is the final common pathway of virtually all chronic kidney diseases (CKDs) and is therefore considered to be a promising therapeutic target for these conditions. However, despite great progress in recent years, no targeted antifibrotic therapies for the kidney have been approved, likely because the complex mechanisms that initiate and drive fibrosis are not yet completely understood. Recent single-cell genomic approaches have allowed novel insights into kidney fibrosis mechanisms in mouse and human, particularly the heterogeneity and differentiation processes of myofibroblasts, the role of injured epithelial cells and immune cells, and their crosstalk mechanisms. In this review we summarize the key mechanisms that drive kidney fibrosis, including recent advances in understanding the mechanisms, as well as potential routes for developing novel targeted antifibrotic therapeutics.

Role of MCP-1/CCR2 axis in renal fibrosis: Mechanisms and therapeutic targeting

Renal fibrosis is a common pathological manifestation in various chronic kidney diseases. Inflammation plays a central role in renal fibrosis development. Owing to their significant participation in inflammation and autoimmunity, chemokines have always been the hot spot and focus of scientific research and clinical intervention. Among the chemokines, monocyte chemoattractant protein-1 (MCP-1), also known as C-C motif chemokine ligand 2, together with its main receptor C-C chemokine receptor type 2 (CCR2) are important chemokines in renal fibrosis. The MCP-1/CCR2 axis is activated when MCP-1 binds to CCR2. Activation of MCP-1/CCR2 axis can induce chemotaxis and activation of inflammatory cells, and initiate a series of signaling cascades in renal fibrosis. It mediates and promotes renal fibrosis by recruiting monocyte, promoting the activation and transdifferentiation of macrophages. This review summarizes the complex physical processes of MCP-1/CCR2 axis in renal fibrosis and addresses its general mechanism in renal fibrosis by using specific examples, together with the progress of targeting MCP-1/CCR2 in renal fibrosis with a view to providing a new direction for renal fibrosis treatment.

Sirt3 deficiency promotes endothelial dysfunction and aggravates renal injury

Sirtuin 3 (SIRT3), the main deacetylase of mitochondria, modulates the acetylation levels of substrates governing metabolism and oxidative stress. In the kidney, we showed that SIRT3 affects the proper functioning of high energy-demanding cells, such as tubular cells and podocytes. Less is known about the role of SIRT3 in regulating endothelial cell function and its impact on the progression of kidney disease. Here, we found that whole body Sirt3-deficient mice exhibited reduced renal capillary density, reflecting endothelial dysfunction, and VEGFA expression compared to wild-type mice. This was paralleled by activation of hypoxia signaling, upregulation of HIF-1α and Angiopietin-2, and oxidative stress increase. These alterations did not result in kidney disease. However, when Sirt3-deficient mice were exposed to the nephrotoxic stimulus Adriamycin (ADR) they developed aggravated endothelial rarefaction, altered VEGFA signaling, and higher oxidative stress compared to wild-type mice receiving ADR. As a result, ADR-treated Sirt3-deficient mice experienced a more severe injury with exacerbated albuminuria, podocyte loss and fibrotic lesions. These data suggest that SIRT3 is a crucial regulator of renal vascular homeostasis and its dysregulation is a predisposing factor for kidney disease. By extension, our findings indicate SIRT3 as a pharmacologic target in progressive renal disease whose treatments are still imperfect.

High glucose dialysate-induced peritoneal fibrosis: Pathophysiology, underlying mechanisms and potential therapeutic strategies

Peritoneal dialysis is an efficient renal replacement therapy for patients with end-stage kidney disease. However, continuous exposure of the peritoneal membrane to dialysate frequently leads to peritoneal fibrosis, which alters the function of the peritoneal membrane and results in withdrawal from peritoneal dialysis in patients. Among others, high glucose dialysate is considered as a predisposing factor for peritoneal fibrosis in patients on peritoneal dialysis. Glucose-induced inflammation, metabolism disturbance, activation of the renin-angiotensin-aldosterone system, angiogenesis and noninflammation-induced reactive oxygen species are implicated in the pathogenesis of high glucose dialysate-induced peritoneal fibrosis. Specifically, high glucose causes chronic inflammation and recurrent peritonitis, which could cause migration and polarization of inflammatory cells, as well as release of cytokines and fibrosis. High glucose also interferes with lipid metabolism and glycolysis by activating the sterol-regulatory element-binding protein-2/cleavage-activating protein pathway and increasing hypoxia inducible factor-1α expression, leading to angiogenesis and peritoneal fibrosis. Activation of the renin-angiotensin-aldosterone system and Ras-mitogen activated protein kinase signaling pathway is another contributing factor in high glucose dialysate-induced fibrosis. Ultimately, activation of the transforming growth factor-β1/Smad pathway is involved in mesothelial-mesenchymal transition or epithelial-mesenchymal transition, which leads to the development of fibrosis. Although possible intervention strategies for peritoneal dialysate-induced fibrosis by targeting the transforming growth factor-β1/Smad pathway have occasionally been proposed, lack of laboratory evidence renders clinical decision-making difficult. We therefore aim to revisit the upstream pathways of transforming growth factor-beta1/Smad and propose potential therapeutic targets for high glucose-induced peritoneal fibrosis.

TSLP/TSLPR promotes renal fibrosis by activating STAT3 in renal fibroblasts

Previous studies have demonstrated the importance of TSLP-TSLPR in inflammatory, allergic, and fibrotic diseases. However, their exact molecular mechanism in regulating renal fibrosis has not been fully explored yet. The current study identified the high expression levels of TSLP and TSLPR in human and mouse hydronephrotic tissues. In addition, immunofluorescence staining showed that TSLP was highly expressed in renal tubular cells, while TSLPR was mainly co-localized with α-SMA, a marker of fibroblasts. Knocking out TSLPR in the UUO model could alleviate the severity of renal fibrosis. Most importantly, the application of antibody blockade of TSLP reduced the fibrotic level in the UUO model. The functional analysis revealed that the hypoxic exposure could induce the overexpression of TSLP in renal tubular cells via HIF-1α. The tubular cell-derived TSLP could bind to the TSLPR of fibroblasts in a paracrine manner to activate them. Specifically, the HIF-1α/TSLP/TSLPR-axis could activate fibroblasts through the STAT3 signaling pathway. This study revealed a mechanistic interaction of HIF-1α/TSLP/TSLPR and STAT3 signaling pathways in the activation and proliferation of human and murine kidney fibroblasts; these pathways might be exploited as a therapeutic target in renal fibrosis.

High Plasma Angiopoietin-2 Levels Predict the Need to Initiate Dialysis within Two Years in Patients with Chronic Kidney Disease

Volume status, congestion, endothelial activation, and injury all play roles in glomerular filtration rate (GFR) decline. In this study, we aimed to determine whether the plasma endothelial and overhydration markers could serve as independent predictors for dialysis initiation in patients with chronic kidney disease (CKD) 3b-5 (GFR < 45 mL/min/1.72 m²) and preserved ejection fraction. A prospective, observational study in a single academic center was conducted from March 2019 to March 2022. Plasma levels of angiopoietin (Ang)-2, Vascular Endothelial Growth Factor-C (VEGF-C), Vascular Cell Adhesion Molecule-1 (VCAM-1), Copeptin (CPP), beta-trace protein (BTP), brain natriuretic peptide (BNP), and cardiac troponin I (cTnI) were all measured. Lung ultrasound (US) B-lines, bioimpedance, and echocardiography with global longitudinal strain (GLS) were recorded. The study outcome was the initiation of chronic dialysis (renal replacement therapy) during 24 months of follow-up. A total of 105 consecutive patients with a mean eGFR of 21.3 mL/min/1.73 m were recruited and finally analyzed. A positive correlation between Ang-2 and VCAM-1 and BTP was observed. Ang-2 correlated positively with BNP, cTnI, sCr, E/e', and the extracellular water (ECW)/intracellular water (ICW) ratio (ECW/ICW). After 24 months, a deterioration in renal function was observed in 47 patients (58%). In multivariate regression analysis, both VCAM-1 and Ang-2 showed independent influences on risk of renal replacement therapy initiation. In a Kaplan-Meier analysis, 72% of patients with Ang-2 concentrations below the median (3.15 ng/mL) survived without dialysis for two years. Such an impact was not observed for GFR, VCAM, CCP, VEGF-C, or BTP. Endothelial activation, quantified by plasma levels of Ang-2, may play a key role in GFR decline and the need for dialysis initiation in patients with CKD 3b, 4, and 5.

From Diabetic Nephropathy to End-Stage Renal Disease: The Effect of Chemokines on the Immune System

Background

Diabetic nephropathy (DN) is a major cause of end-stage renal disease (ESRD), and there is growing evidence to support the role of immunity in the progression of DN to ESRD. Chemokines and chemokine receptors (CCRs) can recruit immune cells to sites of inflammation or injury. Currently, no studies have reported the effect of CCRs on the immune environment during the progression of DN to ESRD.

Methods

Differentially expressed genes (DEGs) from the GEO database were identified in DN patients versus ESRD patients. GO and KEGG enrichment analyses were performed using DEGs. A protein-protein interaction (PPI) network was constructed to identify hub CCRs. Differentially expressed immune cells were screened by immune infiltration analysis, and the correlation between immune cells and hub CCRs was also calculated.

Result

In this study, a total of 181 DEGs were identified. Enrichment analysis showed that chemokines, cytokines, and inflammation-related pathways were significantly enriched. Combining the PPI network and CCRs, four hub CCRs (CXCL2, CXCL8, CXCL10, and CCL20) were identified. These hub CCRs showed an upregulation trend in DN patients and a downregulation trend in ESRD patients. Immune infiltration analysis identified a variety of immune cells that underwent significant changes during disease progression. Among them, CD56bright natural killer cell, effector memory CD8 T cell, memory B cell, monocyte, regulatory T cell, and T follicular helper cell were significantly associated with all hub CCR correlation.

Conclusion

The effect of CCRs on the immune environment may contribute to the progression of DN to ESRD.

Kidney fibrosis: from mechanisms to therapeutic medicines

Chronic kidney disease (CKD) is estimated to affect 10-14% of global population. Kidney fibrosis, characterized by excessive extracellular matrix deposition leading to scarring, is a hallmark manifestation in different progressive CKD; However, at present no antifibrotic therapies against CKD exist. Kidney fibrosis is identified by tubule atrophy, interstitial chronic inflammation and fibrogenesis, glomerulosclerosis, and vascular rarefaction. Fibrotic niche, where organ fibrosis initiates, is a complex interplay between injured parenchyma (like tubular cells) and multiple non-parenchymal cell lineages (immune and mesenchymal cells) located spatially within scarring areas. Although the mechanisms of kidney fibrosis are complicated due to the kinds of cells involved, with the help of single-cell technology, many key questions have been explored, such as what kind of renal tubules are profibrotic, where myofibroblasts originate, which immune cells are involved, and how cells communicate with each other. In addition, genetics and epigenetics are deeper mechanisms that regulate kidney fibrosis. And the reversible nature of epigenetic changes including DNA methylation, RNA interference, and chromatin remodeling, gives an opportunity to stop or reverse kidney fibrosis by therapeutic strategies. More marketed (e.g., RAS blockage, SGLT2 inhibitors) have been developed to delay CKD progression in recent years. Furthermore, a better understanding of renal fibrosis is also favored to discover biomarkers of fibrotic injury. In the review, we update recent advances in the mechanism of renal fibrosis and summarize novel biomarkers and antifibrotic treatment for CKD.

Targeting angiopoietin-2 as a novel treatment option for kidney fibrosis

Kidney fibrosis is a hallmark of chronic kidney disease yet is poorly treated. Chang et al. determined that plasma and kidney levels of the vascular growth factor, angiopoietin-2, were elevated in patients with chronic kidney disease and mice with kidney disease. Angiopoietin-2 inhibited the renoprotective effects of angiopoietin-1 and promoted CC chemokine ligand 2-mediated kidney damage, endothelial cell apoptosis, vascular rarefaction, inflammation, fibrosis, and kidney dysfunction. Hence, therapeutically inhibiting angiopoietin-2 may represent a novel means of treating these chronic kidney disease-associated pathologies.