Mechanisms of mesothelial cell response to viral infections: HDAC1-3 inhibition blocks poly(I:C)-induced type I interferon response and modulates the mesenchymal/inflammatory phenotype

Infectious peritonitis is a leading cause of peritoneal functional impairment and a primary factor for therapy discontinuation in peritoneal dialysis (PD) patients. Although bacterial infections are a common cause of peritonitis episodes, emerging evidence suggests a role for viral pathogens. Toll-like receptors (TLRs) specifically recognize conserved pathogen-associated molecular patterns (PAMPs) from bacteria, viruses, and fungi, thereby orchestrating the ensuing inflammatory/immune responses. Among TLRs, TLR3 recognizes viral dsRNA and triggers antiviral response cascades upon activation. Epigenetic regulation, mediated by histone deacetylase (HDAC), has been demonstrated to control several cellular functions in response to various extracellular stimuli. Employing epigenetic target modulators, such as epidrugs, is a current therapeutic option in several cancers and holds promise in treating viral diseases. This study aims to elucidate the impact of TLR3 stimulation on the plasticity of human mesothelial cells (MCs) in PD patients and to investigate the effects of HDAC1-3 inhibition. Treatment of MCs from PD patients with the TLR3 agonist polyinosinic:polycytidylic acid (Poly(I:C)), led to the acquisition of a bona fide mesothelial-to-mesenchymal transition (MMT) characterized by the upregulation of mesenchymal genes and loss of epithelial-like features. Moreover, Poly(I:C) modulated the expression of several inflammatory cytokines and chemokines. A quantitative proteomic analysis of MCs treated with MS-275, an HDAC1-3 inhibitor, unveiled altered expression of several proteins, including inflammatory cytokines/chemokines and interferon-stimulated genes (ISGs). Treatment with MS-275 facilitated MMT reversal and inhibited the interferon signature, which was associated with reduced STAT1 phosphorylation. However, the modulation of inflammatory cytokine/chemokine production was not univocal, as IL-6 and CXCL8 were augmented while TNF-α and CXCL10 were decreased. Collectively, our findings underline the significance of viral infections in acquiring a mesenchymal-like phenotype by MCs and the potential consequences of virus-associated peritonitis episodes for PD patients. The observed promotion of MMT reversal and interferon response inhibition by an HDAC1-3 inhibitor, albeit without a general impact on inflammatory cytokine production, has translational implications deserving further analysis.

BET Protein Inhibitor JQ1 Ameliorates Experimental Peritoneal Damage by Inhibition of Inflammation and Oxidative Stress

Peritoneal dialysis (PD) is a current replacement therapy for end-stage kidney diseases (ESKDs). However, long-term exposure to PD fluids may lead to damage of the peritoneal membrane (PM) through mechanisms involving the activation of the inflammatory response and mesothelial-to-mesenchymal transition (MMT), leading to filtration failure. Peritoneal damage depends on a complex interaction among external stimuli, intrinsic properties of the PM, and subsequent activities of the local innate-adaptive immune system. Epigenetic drugs targeting bromodomain and extra-terminal domain (BET) proteins have shown beneficial effects on different experimental preclinical diseases, mainly by inhibiting proliferative and inflammatory responses. However the effect of BET inhibition on peritoneal damage has not been studied. To this aim, we have evaluated the effects of treatment with the BET inhibitor JQ1 in a mouse model of peritoneal damage induced by chlorhexidine gluconate (CHX). We found that JQ1 ameliorated the CHX-induced PM thickness and inflammatory cell infiltration. Moreover, JQ1 decreased gene overexpression of proinflammatory and profibrotic markers, together with an inhibition of the nuclear factor-κB (NF-κB) pathway. Additionally, JQ1 blocked the activation of nuclear factor erythroid 2-related factor 2 (NRF2) and restored changes in the mRNA expression levels of NADPH oxidases (NOX1 and NOX4) and NRF2/target antioxidant response genes. To corroborate the in vivo findings, we evaluated the effects of the BET inhibitor JQ1 on PD patients' effluent-derived primary mesothelial cells and on the MeT-5A cell line. JQ1 inhibited tumor necrosis factor-α (TNF-α)-induced proinflammatory gene upregulation and restored MMT phenotype changes, together with the downmodulation of oxidative stress. Taken together, these results suggest that BET inhibitors may be a potential therapeutic option to ameliorate peritoneal damage.

Regulated necrosis role in inflammation and repair in acute kidney injury

Acute kidney injury (AKI) frequently occurs in patients with chronic kidney disease (CKD) and in turn, may cause or accelerate CKD. Therapeutic options in AKI are limited and mostly relate to replacement of kidney function until the kidneys recover spontaneously. Furthermore, there is no treatment that prevents the AKI-to-CKD transition. Regulated necrosis has recently emerged as key player in kidney injury. Specifically, there is functional evidence for a role of necroptosis, ferroptosis or pyroptosis in AKI and the AKI-to-CKD progression. Regulated necrosis may be proinflammatory and immunogenic, triggering subsequent waves of regulated necrosis. In a paradigmatic murine nephrotoxic AKI model, a first wave of ferroptosis was followed by recruitment of inflammatory cytokines such as TWEAK that, in turn, triggered a secondary wave of necroptosis which led to persistent kidney injury and decreased kidney function. A correct understanding of the specific forms of regulated necrosis, their timing and intracellular molecular pathways may help design novel therapeutic strategies to prevent or treat AKI at different stages of the condition, thus improving patient survival and the AKI-to-CKD transition. We now review key regulated necrosis pathways and their role in AKI and the AKI-to-CKD transition both at the time of the initial insult and during the repair phase following AKI.

STING1 deficiency ameliorates immune-mediated crescentic glomerulonephritis in mice

Rapidly progressive/crescentic glomerulonephritis (RPGN/CGN) involves the formation of glomerular crescents by maladaptive differentiation of parietal epithelial cells that leads to rapid loss of renal function. The molecular mechanisms of crescent formation are poorly understood. Therefore, new insights into molecular mechanisms could identify alternative therapeutic targets for RPGN/CGN. Analysis of kidney biopsies from patients with RPGN revealed increased interstitial, glomerular, and tubular expression of STING1, an accessory protein of the c-GAS-dependent DNA-sensing pathway, which was also observed in murine nephrotoxic nephritis induced by an anti-GBM antibody. STING1 was expressed by key cell types involved in RPGN and crescent formation such as glomerular parietal epithelial cells, and tubular cells as well as by inflammation accessory cells. In functional in vivo studies, Sting1-/- mice with nephrotoxic nephritis had lower kidney cytokine expression, milder kidney infiltration by innate and adaptive immune cells, and decreased disease severity. Pharmacological STING1 inhibition mirrored these findings. Direct STING1 agonism in parietal and tubular cells activated the NF-κB-dependent cytokine response and the interferon-induced genes (ISGs) program. These responses were also triggered in a STING1-dependent manner by the pro-inflammatory cytokine TWEAK. These results identify STING1 activation as a pathological mechanism in RPGN/CGN and TWEAK as an activator of STING1. Pharmacological strategies targeting STING1, or upstream regulators may therefore be potential alternatives to treat RPGN. © 2023 The Pathological Society of Great Britain and Ireland.

Intravascular hemolysis triggers NAFLD characterized by a deregulation of lipid metabolism and lipophagy blockade

Intravascular hemolysis is a common feature of different clinical entities, including sickle cell disease and malaria. Chronic hemolytic disorders are associated with hepatic damage; however, it is unknown whether heme disturbs lipid metabolism and promotes liver steatosis, thereby favoring the progression to nonalcoholic fatty liver disease (NAFLD). Using an experimental model of acute intravascular hemolysis, we report here the presence of liver injury in association with microvesicular lipid droplet deposition. Hemolysis promoted serum hyperlipidemia and altered intrahepatic triglyceride fatty acid composition, with increments in oleic, palmitoleic, and palmitic acids. These findings were related to augmented expression of transporters involved in fatty acid uptake (CD36 and MSR1) and deregulation of LDL transport, as demonstrated by decreased levels of LDL receptor and increased PCSK9 expression. Hemolysis also upregulated hepatic enzymes associated with cholesterol biosynthesis (SREBP2, HMGC1, LCAT, SOAT1) and transcription factors regulating lipid metabolism (SREBP1). Increased LC3II/LC3I ratio and p62/SQSTM1 protein levels were reported in mice with intravascular hemolysis and hepatocytes stimulated with heme, indicating a blockade of lipophagy. In cultured hepatocytes, cell pretreatment with the autophagy inductor rapamycin diminished heme-mediated toxicity and accumulation of lipid droplets. In conclusion, intravascular hemolysis enhances liver damage by exacerbating lipid accumulation and blocking the lipophagy pathway, thereby promoting NAFLD. These new findings have a high translational potential as a novel NAFLD-promoting mechanism in individuals suffering from severe hemolysis episodes. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

B- and T-lymphocyte attenuator could be a new player in accelerated atherosclerosis associated with chronic kidney disease

BACKGROUND

In chronic kidney disease (CKD), cardiovascular morbi-mortality is higher than in general population. Atherosclerotic cardiovascular disease is accelerated in CKD, but specific CKD-related risk factors for atherosclerosis are unknown.

METHODS

CKD patients from the NEFRONA study were used. We performed mRNA array from blood of patients free from atheroma plaque at baseline, with (n=10) and without (n=10) de novo atherosclerotic plaque development 2 years later. Selected mRNA candidates were validated in a bigger sample (n=148). Validated candidates were investigated in vivo in an experimental model of CKD-accelerated atherosclerosis, and in vitro in murine macrophages.

RESULTS

mRNA array analysis showed 92 up-regulated and 67 down-regulated mRNAs in samples from CKD patients with de novo plaque development. The functional analysis pointed to a paramount role of the immune response. The validation in a bigger sample confirmed that B- and T-lymphocyte co-inhibitory molecule (BTLA) down-regulation was associated with de novo plaque presence after 2 years. However, BTLA down-regulation was not found to be associated with atherosclerotic progression in patients with plaque already present at baseline. In a model of CKD-accelerated atherosclerosis, mRNA and protein expression levels of BTLA were significantly decreased in blood samples and atheroma plaques. Plaques from animals with CKD were bigger, had more infiltration of inflammatory cells, higher expression of IL6 and IL17 and less presence of collagen than plaques from control animals. Incubation of macrophages with rat uremic serum decreased BTLA expression.

CONCLUSIONS

BTLA could be a potential biomarker or therapeutic target for atherosclerosis incidence in CKD patients.

CCN2 Activates RIPK3, NLRP3 Inflammasome, and NRF2/Oxidative Pathways Linked to Kidney Inflammation

Inflammation is a key characteristic of both acute and chronic kidney diseases. Preclinical data suggest the involvement of the NLRP3/Inflammasome, receptor-interacting protein kinase-3 (RIPK3), and NRF2/oxidative pathways in the regulation of kidney inflammation. Cellular communication network factor 2 (CCN2, also called CTGF in the past) is an established fibrotic biomarker and a well-known mediator of kidney damage. CCN2 was shown to be involved in kidney damage through the regulation of proinflammatory and profibrotic responses. However, to date, the potential role of the NLRP3/RIPK3/NRF2 pathways in CCN2 actions has not been evaluated. In experimental acute kidney injury induced with folic acid in mice, CCN2 deficiency diminished renal inflammatory cell infiltration (monocytes/macrophages and T lymphocytes) as well as the upregulation of proinflammatory genes and the activation of NLRP3/Inflammasome-related components and specific cytokine products, such as IL-1β. Moreover, the NRF2/oxidative pathway was deregulated. Systemic administration of CCN2 to C57BL/6 mice induced kidney immune cell infiltration and activated the NLRP3 pathway. RIPK3 deficiency diminished the CCN2-induced renal upregulation of proinflammatory mediators and prevented NLRP3 modulation. These data suggest that CCN2 plays a fundamental role in sterile inflammation and acute kidney injury by modulating the RIKP3/NLRP3/NRF2 inflammatory pathways.

BET Protein Inhibitor JQ1 Modulates Mitochondrial Dysfunction and Oxidative Stress Induced by Chronic Kidney Disease

Among the mechanisms involved in the progression of kidney disease, mitochondrial dysfunction has special relevance. Epigenetic drugs such as inhibitors of extra-terminal domain proteins (iBET) have shown beneficial effects in experimental kidney disease, mainly by inhibiting proliferative and inflammatory responses. The impact of iBET on mitochondrial damage was explored in in vitro studies in renal cells stimulated with TGF-β1 and in vivo in murine unilateral ureteral obstruction (UUO) model of progressive kidney damage. In vitro, JQ1 pretreatment prevented the TGF-β1-induced downregulation of components of the oxidative phosphorylation chain (OXPHOS), such as cytochrome C and CV-ATP5a in human proximal tubular cells. In addition, JQ1 also prevented the altered mitochondrial dynamics by avoiding the increase in the DRP-1 fission factor. In UUO model, renal gene expression levels of cytochrome C and CV-ATP5a as well as protein levels of cytochrome C were reduced These changes were prevented by JQ1 administration. In addition, JQ1 decreased protein levels of the DRP1 fission protein and increased the OPA-1 fusion protein, restoring mitochondrial dynamics. Mitochondria also participate in the maintenance of redox balance. JQ1 restored the gene expression of antioxidant proteins, such as Catalase and Heme oxygenase 1 in TGF-β1-stimulated human proximal tubular cells and in murine obstructed kidneys. Indeed, in tubular cells, JQ1 decreased ROS production induced by stimulation with TGF-β1, as evaluated by MitoSOXTM. iBETs, such as JQ1, improve mitochondrial dynamics, functionality, and oxidative stress in kidney disease.

Mitochondrial Dysfunction in the Cardio-Renal Axis

Cardiovascular disease (CVD) frequently complicates chronic kidney disease (CKD). The risk of all-cause mortality increases from 20% to 500% in patients who suffer both conditions; this is referred to as the so-called cardio-renal syndrome (CRS). Preclinical studies have described the key role of mitochondrial dysfunction in cardiovascular and renal diseases, suggesting that maintaining mitochondrial homeostasis is a promising therapeutic strategy for CRS. In this review, we explore the malfunction of mitochondrial homeostasis (mitochondrial biogenesis, dynamics, oxidative stress, and mitophagy) and how it contributes to the development and progression of the main vascular pathologies that could be affected by kidney injury and vice versa, and how this knowledge may guide the development of novel therapeutic strategies in CRS.

Novel Aspects of the Immune Response Involved in the Peritoneal Damage in Chronic Kidney Disease Patients under Dialysis

Chronic kidney disease (CKD) incidence is growing worldwide, with a significant percentage of CKD patients reaching end-stage renal disease (ESRD) and requiring kidney replacement therapies (KRT). Peritoneal dialysis (PD) is a convenient KRT presenting benefices as home therapy. In PD patients, the peritoneum is chronically exposed to PD fluids containing supraphysiologic concentrations of glucose or other osmotic agents, leading to the activation of cellular and molecular processes of damage, including inflammation and fibrosis. Importantly, peritonitis episodes enhance peritoneum inflammation status and accelerate peritoneal injury. Here, we review the role of immune cells in the damage of the peritoneal membrane (PM) by repeated exposure to PD fluids during KRT as well as by bacterial or viral infections. We also discuss the anti-inflammatory properties of current clinical treatments of CKD patients in KRT and their potential effect on preserving PM integrity. Finally, given the current importance of coronavirus disease 2019 (COVID-19) disease, we also analyze here the implications of this disease in CKD and KRT.

Vitamin D, Cellular Senescence and Chronic Kidney Diseases: What Is Missing in the Equation?

As life expectancy increases in many countries, the prevalence of age-related diseases also rises. Among these conditions, chronic kidney disease is predicted to become the second cause of death in some countries before the end of the century. An important problem with kidney diseases is the lack of biomarkers to detect early damage or to predict the progression to renal failure. In addition, current treatments only retard kidney disease progression, and better tools are needed. Preclinical research has shown the involvement of the activation of cellular senescence-related mechanisms in natural aging and kidney injury. Intensive research is searching for novel treatments for kidney diseases as well as for anti-aging therapies. In this sense, many experimental shreds of evidence support that treatment with vitamin D or its analogs can exert pleiotropic protective effects in kidney injury. Moreover, vitamin D deficiency has been described in patients with kidney diseases. Here, we review recent evidence about the relationship between vitamin D and kidney diseases, explaining the underlying mechanisms of the effect of vitamin D actions, with particular attention to the modulation of cellular senescence mechanisms.

Targeting inflammation to treat diabetic kidney disease: the road to 2030

Diabetic kidney disease (DKD) is one of the fastest growing causes of chronic kidney disease and associated morbidity and mortality. Preclinical research has demonstrated the involvement of inflammation in its pathogenesis and in the progression of kidney damage, supporting clinical trials designed to explore anti-inflammatory strategies. However, the recent success of sodium-glucose cotransporter-2 inhibitors and the nonsteroidal mineralocorticoid receptor antagonist finerenone has changed both guidelines and standard of care, rendering obsolete older studies directly targeting inflammatory mediators and the clinical development was discontinued for most anti-inflammatory drugs undergoing clinical trials for DKD in 2016. Given the contribution of inflammation to the pathogenesis of DKD, we review the impact on kidney inflammation of the current standard of care, therapies undergoing clinical trials, or repositioned drugs for DKD. Moreover, we review recent advances in the molecular regulation of inflammation in DKD and discuss potential novel therapeutic strategies with clinical relevance. Finally, we provide a road map for future research aimed at integrating the growing knowledge on inflammation and DKD into clinical practice to foster improvement of patient outcomes.

The CCN2 Polymorphism rs12526196 Is a Risk Factor for Ascending Thoracic Aortic Aneurysm

Cellular communication network factor 2 (CCN2/CTGF) has been traditionally described as a downstream mediator of other profibrotic factors including transforming growth factor (TGF)-β and angiotensin II. However, recent evidence from our group demonstrated the direct role of CCN2 in maintaining aortic wall homeostasis and acute and lethal aortic aneurysm development induced by angiotensin II in the absence of CCN2 in mice. In order to translate these findings to humans, we evaluated the potential association between three polymorphisms in the CCN2 gene and the presence of a thoracic aortic aneurysm (TAA). Patients with and without TAA retrospectively selected were genotyped for rs6918698, rs9402373 and rs12526196 polymorphisms related to the CCN2 gene. Multivariable logistic regression models were performed. In our population of 366 patients (69 with TAA), no associations were found between rs6918698 and rs9402373 and TAA. However, the presence of one C allele from rs12526196 was associated with TAA comparing with the TT genotype, independently of risk factors such as sex, age, hypertension, type of valvulopathy and the presence of a bicuspid aortic valve (OR = 3.17; 95% CI = 1.30-7.88; p = 0.011). In conclusion, we demonstrated an association between the C allele of rs12526196 in the CCN2 gene and the presence of TAA. This study extrapolates to humans the relevance of CCN2 in aortic aneurysm observed in mice and postulates, for the first time, a potential protective role to CCN2 in aortic aneurysm pathology. Our results encourage future research to explore new variants in the CCN2 gene that could be predisposed to TAA development.

Cellular communication network 2 (connective tissue growth factor) aggravates acute DNA damage and subsequent DNA damage response-senescence-fibrosis following kidney ischemia reperfusion injury

Chronic allograft dysfunction with progressive fibrosis of unknown cause remains a major issue after kidney transplantation, characterized by ischemia-reperfusion injury (IRI). One hypothesis to account for this is that spontaneous progressive tubulointerstitial fibrosis following IRI is driven by cellular senescence evolving from a prolonged, unresolved DNA damage response (DDR). Since cellular communication network factor 2 ((CCN2), formerly called connective tissue growth factor), an established mediator of kidney fibrosis, is also involved in senescence-associated pathways, we investigated the relation between CCN2 and cellular senescence following kidney transplantation. Tubular CCN2 overexpression was found to be associated with DDR, loss of kidney function and tubulointerstitial fibrosis in both the early and the late phase in human kidney allograft biopsies. Consistently, CCN2 deficient mice developed reduced senescence and tubulointerstitial fibrosis in the late phase; six weeks after experimental IRI. Moreover, tubular DDR markers and plasma urea were less elevated in CCN2 knockout than in wild-type mice. Finally, CCN2 administration or overexpression in epithelial cells induced upregulation of tubular senescence-associated genes including p21, while silencing of CCN2 alleviated DDR induced by anoxia-reoxygenation injury in cultured proximal tubule epithelial cells. Thus, our observations indicate that inhibition of CCN2 can mitigate IRI-induced acute kidney injury, DNA damage, and the subsequent DDR-senescence-fibrosis sequence. Hence, targeting CCN2 might help to protect the kidney from transplantation-associated post-IRI chronic kidney dysfunction.

Poster No. 117 rs12526196 polymorphism in CCN2 gene is an independent risk factor for ascending thoracic aortic aneurysm

Background

The Cellular Communication Network Factor-2 (CCN2/CTGF) has been traditionally described as a downstream mediator of other profibrotic factors including transforming growth factor (TGF)-ß and Angiotensin II. However, recent evidence from our group demonstrated the direct role of CCN2 in maintaining aortic wall homeostasis and, in addition, the development of acute and lethal aortic aneurysm induced by Angiotensin II in absence of CCN2 in mice. In order to translate these findings to humans, we evaluated the potential association between three polymorphisms in the CCN2 gene and the presence of thoracic aortic aneurysm (TAA).

Material and methods

69 patients with TAA and 297 controls were genotyped for rs6918698, rs9402373 and rs12526196 polymorphisms related to CCN2 gene.Multivariable logistic regression models were performed.

Results and conclusions

While no associations were found between rs6918698 and rs9402373 with TAA development, patients carrying the C allele from rs12526196 polymorphism have a higher probability of suffering TAA compared to patients with TT genotype, independently of other risk factors such as sex, age, hypertension, type of valvulopathy and presence of bicuspid aortic valve (OR = 3.17; 95% CI = 1.30–7.88;P = 0.011). This study extrapolates to humans the relevance of CCN2 in aortic aneurysm observed in mice and postulate, for the first time, a protective role to CCN2 in aortic aneurysm pathology. Our results encourage future research to explore new variants, polymorphisms or mutations, in the CCN2 gene that could be predisposing to TAA development.

Funding

Research funded by ISCIII (PI20/000140, PI18/00694, PI19/00184, PI20/00639); RICORS2040-KIDNEY-DISEASE (RD21/0005/0002, RD21/0005/0017); Sara-Borrell-CD20/00042; Miguel-Servet-CP18/00106; Sociedad Española de Nefrología.

Antifibrotic Agents for the Management of CKD: A Review

Kidney fibrosis is a hallmark of chronic kidney disease (CKD) and a potential therapeutic target. However, there are conceptual and practical challenges to directly targeting kidney fibrosis. Whether fibrosis is mainly a cause or a consequence of CKD progression has been disputed. It is unclear whether specifically targeting fibrosis is feasible in clinical practice because most drugs that decrease fibrosis in preclinical models target additional and often multiple pathogenic pathways (eg, renin-angiotensin-aldosterone system blockade). Moreover, tools to assess whole-kidney fibrosis in routine clinical practice are lacking. Pirfenidone, a drug used for idiopathic pulmonary fibrosis, is undergoing a phase 2 trial for kidney fibrosis. Other drugs in use or being tested for idiopathic pulmonary fibrosis (eg, nintedanib, PRM-151, epigallocatechin gallate) are also potential candidates to treat kidney fibrosis. Novel therapeutic approaches may include antagomirs (eg, lademirsen) or drugs targeting interleukin 11 or NKD2 (WNT signaling pathway inhibitor). Reversing the dysfunctional tubular cell metabolism that leads to kidney fibrosis offers additional therapeutic opportunities. However, any future drug targeting fibrosis of the kidneys should demonstrate added benefit to a standard of care that combines renin-angiotensin system with mineralocorticoid receptor (eg, finerenone) blockade or with sodium/glucose cotransporter 2 inhibitors.

FC089: The Absence of Sting Prevents Peritoneal Damage in a Murine Model of Peritoneal Fibrosis

BACKGROUND AND AIMS

Peritoneal dialysis (PD) is the current replacement therapy for end-stage renal disease (ESRD) patients until renal transplantation can be achieved. However, chronic exposure to non-physiological PD fluids (PDF) and occasional infection episodes may lead to peritoneal damage and membrane transport failure. Chronic inflammation, together with mesothelial-to-mesenchymal transition (MMT) and submesothelial fibrosis, is a hallmark of PDF-associated peritoneal damage whose intrinsic mechanisms are still expected to be disclosed [1–2]. Activation of the innate immunity is the cornerstone for infectious agents’ elimination, also enrolled in response to damage-associated molecular patterns (DAMPs) released from stressed or injured host cells. Leakage of DNA from stressed mitochondria and damaged genomic DNA may act as DAMPs that are recognized by cytosolic double-strand DNA sensors, like the stimulator of interferon gene (STING), to mount an inflammatory response [3]. Excessive activation of STING is involved in autoinflammatory, autoimmune, and increasingly related to several chronic inflammatory conditions [4]. Thus, this study aimed to investigate the role of STING in experimental peritoneal damage.

METHOD

We induced peritoneal fibrosis in wild-type and STING-KO mice by intraperitoneal administration of 0.1% chlorhexidine gluconate (CHX) daily for 4 weeks. No treated WT and STING-KO mice were used as control. Then, mice were euthanized, and peritoneal tissue and peritoneal lavage fluids were recollected for the following experiments. STING mRNA (Tmem173) and protein levels in control and CHX-treated wild-type were measured by RT-qPCR, western blot and immunohistochemistry. Peritoneal levels of the STING downstream proteins TBK1 and IRF3 and their phosphorylated isoforms were assayed by western blot. Peritoneal membrane thickness was measured in formalin-fixed paraffin-embedded tissues stained with Masson's trichrome stain. Fibronectin protein levels were evaluated by western blot and MMT, fibrosis, and inflammation markers were determined by RT-qPCR. Inflammatory cells present in peritoneal effluents were assayed by flow cytometry.

RESULTS

We found that in the peritoneum of CHX-treated wild-type mice both Tmem173 expression and STING protein levels were increased. Interestingly, STING-positive cells were located in areas of peritoneal thickness and immune infiltration. Moreover, the protein levels of IRF3, p-IRF3, TBK1 and p-TBK1 were increased, indicating that the STING pathway is activated in experimental peritoneal damage. In STING-KO mice, CHX-induced peritoneal damage was prevented. STING-KO mice under CHX treatment showed decreased peritoneal membrane thickness and attenuated CHX-induced expression of fibrosis and MMT markers, such as Tgb1, Snai1, Cdh2, Col1a1, Fn1 and fibronectin protein when compared with CHX-treated WT mice. The absence of STING also prevented the gene expression of cytokines (Il1b, Il6 and Ifng) and chemokines (Ccl5, Ccl2 and Ccl19) and macrophages infiltration into the peritoneum. Inflammatory cell recruitment into the peritoneal cavity was also decreased in STING-KO mice, including CD3+CD4+ lymphocytes and CD11b+F4/80+ macrophages.

CONCLUSION

In summary, STING absence prevents peritoneal membrane thickness, fibrosis, and inflammation induced by CHX in a mice model. These results suggest that STING plays a key role in peritoneal membrane injury. Therefore, STING may become a new potential therapeutic target in PD-associated peritoneal damage.

Kidney microRNA Expression Pattern in Type 2 Diabetic Nephropathy in BTBR Ob/Ob Mice

Diabetic nephropathy (DN) is the main leading cause of chronic kidney disease worldwide. Although remarkable therapeutic advances have been made during the last few years, there still exists a high residual risk of disease progression to end-stage renal failure. To further understand the pathogenesis of tissue injury in this disease, by means of the Next-Generation Sequencing, we have studied the microRNA (miRNA) differential expression pattern in kidneys of Black and Tan Brachyury (BTBR) ob/ob (leptin deficiency mutation) mouse. This experimental model of type 2 diabetes and obesity recapitulates the key histopathological features described in advanced human DN and therefore can provide potential useful translational information. The miRNA-seq analysis, performed in the renal cortex of 22-week-old BTBR ob/ob mice, pointed out a set of 99 miRNAs significantly increased compared to non-diabetic, non-obese control mice of the same age, whereas no miRNAs were significantly decreased. Among them, miR-802, miR-34a, miR-132, miR-101a, and mir-379 were the most upregulated ones in diabetic kidneys. The in silico prediction of potential targets for the 99 miRNAs highlighted inflammatory and immune processes, as the most relevant pathways, emphasizing the importance of inflammation in the pathogenesis of kidney damage associated to diabetes. Other identified top canonical pathways were adipogenesis (related with ectopic fatty accumulation), necroptosis (an inflammatory and regulated form of cell death), and epithelial-to-mesenchymal transition, the latter supporting the importance of tubular cell phenotype changes in the pathogenesis of DN. These findings could facilitate a better understanding of this complex disease and potentially open new avenues for the design of novel therapeutic approaches to DN.

CCN2 Binds to Tubular Epithelial Cells in the Kidney

Cellular communication network-2 (CCN2), also called connective tissue growth factor (CTGF), is considered a fibrotic biomarker and has been suggested as a potential therapeutic target for kidney pathologies. CCN2 is a matricellular protein with four distinct structural modules that can exert a dual function as a matricellular protein and as a growth factor. Previous experiments using surface plasmon resonance and cultured renal cells have demonstrated that the C-terminal module of CCN2 (CCN2(IV)) interacts with the epidermal growth factor receptor (EGFR). Moreover, CCN2(IV) activates proinflammatory and profibrotic responses in the mouse kidney. The aim of this paper was to locate the in vivo cellular CCN2/EGFR binding sites in the kidney. To this aim, the C-terminal module CCN2(IV) was labeled with a fluorophore (Cy5), and two different administration routes were employed. Both intraperitoneal and direct intra-renal injection of Cy5-CCN2(IV) in mice demonstrated that CCN2(IV) preferentially binds to the tubular epithelial cells, while no signal was detected in glomeruli. Moreover, co-localization of Cy5-CCN2(IV) binding and activated EGFR was found in tubules. In cultured tubular epithelial cells, live-cell confocal microscopy experiments showed that EGFR gene silencing blocked Cy5-CCN2(IV) binding to tubuloepithelial cells. These data clearly show the existence of CCN2/EGFR binding sites in the kidney, mainly in tubular epithelial cells. In conclusion, these studies show that circulating CCN2(IV) can directly bind and activate tubular cells, supporting the role of CCN2 as a growth factor involved in kidney damage progression.

Bone Marrow-Derived RIPK3 Mediates Kidney Inflammation in Acute Kidney Injury

BACKGROUND

Receptor-interacting protein kinase 3 (RIPK3), a component of necroptosis pathways, may have an independent role in inflammation. It has been unclear which RIPK3-expressing cells are responsible for the anti-inflammatory effect of overall Ripk3 deficiency and whether Ripk3 deficiency protects against kidney inflammation occurring in the absence of tubular cell death.

METHODS

We used chimeric mice with bone marrow from wild-type and Ripk3-knockout mice to explore RIPK3's contribution to kidney inflammation in the presence of folic acid-induced acute kidney injury AKI (FA-AKI) or absence of AKI and kidney cell death (as seen in systemic administration of the cytokine TNF-like weak inducer of apoptosis [TWEAK]).

RESULTS

Tubular and interstitial cell RIPK3 expressions were increased in murine AKI. Ripk3 deficiency decreased NF-κB activation and kidney inflammation in FA-AKI but did not prevent kidney failure. In the chimeric mice, RIPK3-expressing bone marrow-derived cells were required for early inflammation in FA-AKI. The NLRP3 inflammasome was not involved in RIPK3's proinflammatory effect. Systemic TWEAK administration induced kidney inflammation in wild-type but not Ripk3-deficient mice. In cell cultures, TWEAK increased RIPK3 expression in bone marrow-derived macrophages and tubular cells. RIPK3 mediated TWEAK-induced NF-κB activation and inflammatory responses in bone marrow-derived macrophages and dendritic cells and in Jurkat T cells; however, in tubular cells, RIPK3 mediated only TWEAK-induced Il-6 expression. Furthermore, conditioned media from TWEAK-exposed wild-type macrophages, but not from Ripk3-deficient macrophages, promoted proinflammatory responses in cultured tubular cells.

CONCLUSIONS

RIPK3 mediates kidney inflammation independently from tubular cell death. Specific targeting of bone marrow-derived RIPK3 may limit kidney inflammation without the potential adverse effects of systemic RIPK3 targeting.

Oxidative Stress and Cellular Senescence Are Involved in the Aging Kidney

Chronic kidney disease (CKD) can be considered as a clinical model for premature aging. However, non-invasive biomarkers to detect early kidney damage and the onset of a senescent phenotype are lacking. Most of the preclinical senescence studies in aging have been done in very old mice. Furthermore, the precise characterization and over-time development of age-related senescence in the kidney remain unclear. To address these limitations, the age-related activation of cellular senescence-associated mechanisms and their correlation with early structural changes in the kidney were investigated in 3- to 18-month-old C57BL6 mice. Inflammatory cell infiltration was observed by 12 months, whereas tubular damage and collagen accumulation occurred later. Early activation of cellular-senescence-associated mechanisms was found in 12-month-old mice, characterized by activation of the DNA-damage-response (DDR), mainly in tubular cells; activation of the antioxidant NRF2 pathway; and klotho downregulation. However, induction of tubular-cell-cycle-arrest (CCA) and overexpression of renal senescent-associated secretory phenotype (SASP) components was only found in 18-month-old mice. In aging mice, both inflammation and oxidative stress (marked by elevated lipid peroxidation and NRF2 inactivation) remained increased. These findings support the hypothesis that prolonged DDR and CCA, loss of nephroprotective factors (klotho), and dysfunctional redox regulatory mechanisms (NRF2/antioxidant defense) can be early drivers of age-related kidney-damage progression.

Studying the NOTCH Signaling Pathway Activation in Kidney Biopsies

The NOTCH signaling pathway is an evolutionarily conserved family of transmembrane receptors, ligands, and transcription factors. The NOTCH signaling is activated in many biological processes including nephrogenesis, tubulogenesis, and glomerulogenesis, as well as during pathological situations. Activation of Notch signaling is characterized by successive proteolytic cleavages triggered by the interaction between membrane-bound Notch receptors and ligands expressed on neighboring cells. In chronic kidney diseases, activation of the canonical NOTCH signaling pathway has been described. The following protocols will allow the direct assessment of Jagged-1/NOTCH signaling activation in biopsies of patients with chronic kidney diseases and in murine experimental models of renal damage.

CCN2 (Cellular Communication Network Factor 2) Deletion Alters Vascular Integrity and Function Predisposing to Aneurysm Formation

Background:

CCN2 (cellular communication network factor 2) is a matricellular protein involved in cell communication and microenvironmental signaling responses. CCN2 is known to be overexpressed in several cardiovascular diseases, but its role is not completely understood.

Methods:

Here, CCN2 involvement in aortic wall homeostasis and response to vascular injury was investigated in inducible Ccn2 -deficient mice, with induction of vascular damage by infusion of Ang II (angiotensin II; 15 days), which is known to upregulate CCN2 expression in the aorta.

Results:

Ang II infusion in CCN2-silenced mice lead to 60% mortality within 10 days due to rapid development and rupture of aortic aneurysms, as evidenced by magnetic resonance imaging, echography, and histological examination. Ccn2 deletion decreased systolic blood pressure and caused aortic structural and functional changes, including elastin layer disruption, smooth muscle cell alterations, augmented distensibility, and increased metalloproteinase activity, which were aggravated by Ang II administration. Gene ontology analysis of RNA sequencing data identified aldosterone biosynthesis as one of the most enriched terms in CCN2-deficient aortas. Consistently, treatment with the mineralocorticoid receptor antagonist spironolactone before and during Ang II infusion reduced aneurysm formation and mortality, underscoring the importance of the aldosterone pathway in Ang II–induced aorta pathology.

Conclusions:

CCN2 is critically involved in the functional and structural homeostasis of the aorta and in maintenance of its integrity under Ang II–induced stress, at least, in part, by disruption of the aldosterone pathway. Thus, this study opens new avenues to future studies in disorders associated to vascular pathologies.

Role of Macrophages and Related Cytokines in Kidney Disease

Inflammation is a key characteristic of kidney disease, but this immune response is two-faced. In the acute phase of kidney injury, there is an activation of the immune cells to fight against the insult, contributing to kidney repair and regeneration. However, in chronic kidney diseases (CKD), immune cells that infiltrate the kidney play a deleterious role, actively participating in disease progression, and contributing to nephron loss and fibrosis. Importantly, CKD is a chronic inflammatory disease. In early CKD stages, patients present sub-clinical inflammation, activation of immune circulating cells and therefore, anti-inflammatory strategies have been proposed as a common therapeutic target for renal diseases. Recent studies have highlighted the plasticity of immune cells and the complexity of their functions. Among immune cells, monocytes/macrophages play an important role in all steps of kidney injury. However, the phenotype characterization between human and mice immune cells showed different markers; therefore the extrapolation of experimental studies in mice could not reflect human renal diseases. Here we will review the current information about the characteristics of different macrophage phenotypes, mainly focused on macrophage-related cytokines, with special attention to the chemokine CCL18, and its murine functional homolog CCL8, and the macrophage marker CD163, and their role in kidney pathology.

Acute Kidney Injury is Aggravated in Aged Mice by the Exacerbation of Proinflammatory Processes

Acute kidney injury (AKI) is more frequent in elderly patients. Mechanisms contributing to AKI (tubular cell death, inflammatory cell infiltration, impaired mitochondrial function, and prolonged cell-cycle arrest) have been linked to cellular senescence, a process implicated in regeneration failure and progression to fibrosis. However, the molecular and pathological basis of the age-related increase in AKI incidence is not completely understood. To explore these mechanisms, experimental AKI was induced by folic acid (FA) administration in young (3-months-old) and old (1-year-old) mice, and kidneys were evaluated in the early phase of AKI, at 48 h. Tubular damage score, KIM-1 expression, the recruitment of infiltrating immune cells (mainly neutrophils and macrophages) and proinflammatory gene expression were higher in AKI kidneys of old than of young mice. Tubular cell death in FA-AKI involves several pathways, such as regulated necrosis and apoptosis. Ferroptosis and necroptosis cell-death pathways were upregulated in old AKI kidneys. In contrast, caspase-3 activation was only found in young but not in old mice. Moreover, the antiapoptotic factor BCL-xL was significantly overexpressed in old, injured kidneys, suggesting an age-related apoptosis suppression. AKI kidneys displayed evidence of cellular senescence, such as increased levels of cyclin dependent kinase inhibitors p16ink4a and p21cip1, and of the DNA damage response marker γH2AX. Furthermore, p21cip1 mRNA expression and nuclear staining for p21cip1 and γH2AX were higher in old than in young FA-AKI mice, as well as the expression of senescence-associated secretory phenotype (SASP) components (Il-6, Tgfb1, Ctgf, and Serpine1). Interestingly, some infiltrating immune cells were p21 or γH2AX positive, suggesting that molecular senescence in the immune cells (“immunosenescence”) are involved in the increased severity of AKI in old mice. In contrast, expression of renal protective factors was dramatically downregulated in old AKI mice, including the antiaging factor Klotho and the mitochondrial biogenesis driver PGC-1α. In conclusion, aging resulted in more severe AKI after the exposure to toxic compounds. This increased toxicity may be related to magnification of proinflammatory-related pathways in older mice, including a switch to a proinflammatory cell death (necroptosis) instead of apoptosis, and overactivation of cellular senescence of resident renal cells and infiltrating inflammatory cells.

Deletion of delta-like 1 homologue accelerates renal inflammation by modulating the Th17 immune response

Preclinical studies have demonstrated that activation of the NOTCH pathway plays a key role in the pathogenesis of kidney damage. There is currently no information on the role of the Delta-like homologue 1 (DLK1), a NOTCH inhibitor, in the regulation of renal damage. Here, we investigated the contribution of DLK1 to experimental renal damage and the underlying molecular mechanisms. Using a Dlk1-null mouse model in the experimental renal damage of unilateral ureteral obstruction, we found activation of NOTCH, as shown by increased nuclear translocation of the NOTCH1 intracellular domain, and upregulation of Dlk2/hey-1 expression compared to wild-type (WT) littermates. NOTCH1 over-activation in Dlk1-null injured kidneys was associated with a higher inflammatory response, characterized by infiltration of inflammatory cells, mainly CD4/IL17A + lymphocytes, and activation of the Th17 immune response. Furthermore, pharmacological NOTCH blockade inhibited the transcription factors controlling Th17 differentiation and gene expression of the Th17 effector cytokine IL-17A and other related-inflammatory factors, linked to a diminution of inflammation in the injured kidneys. We propose that the non-canonical NOTCH ligand DLK1 acts as a NOTCH antagonist in renal injury regulating the Th17-mediated inflammatory response.

Renin-angiotensin system and inflammation update

The most classical view of the renin-angiotensin system (RAS) emphasizes its role as an endocrine regulator of sodium balance and blood pressure. However, it has long become clear that the RAS has pleiotropic actions that contribute to organ damage, including modulation of inflammation. Angiotensin II (Ang II) activates angiotensin type 1 receptors (AT1R) to promote an inflammatory response and organ damage. This represents the pathophysiological basis for the successful use of RAS blockers to prevent and treat kidney and heart disease. However, other RAS components could have a built-in capacity to brake proinflammatory responses. Angiotensin type 2 receptor (AT2R) activation can oppose AT1R actions, such as vasodilatation, but its involvement in modulation of inflammation has not been conclusively proven. Angiotensin-converting enzyme 2 (ACE2) can process Ang II to generate angiotensin-(1-7) (Ang-(1-7)), that activates the Mas receptor to exert predominantly anti-inflammatory responses depending on the context. We now review recent advances in the understanding of the interaction of the RAS with inflammation. Specific topics in which novel information became available recently include intracellular angiotensin receptors; AT1R posttranslational modifications by tissue transglutaminase (TG2) and anti-AT1R autoimmunity; RAS modulation of lymphoid vessels and T lymphocyte responses, especially of Th17 and Treg responses; interactions with toll-like receptors (TLRs), programmed necrosis, and regulation of epigenetic modulators (e.g. microRNAs and bromodomain and extraterminal domain (BET) proteins). We additionally discuss an often overlooked effect of the RAS on inflammation which is the downregulation of anti-inflammatory factors such as klotho, peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α), transient receptor potential ankyrin 1 (TRPA1), SNF-related serine/threonine-protein kinase (SNRK), serine/threonine-protein phosphatase 6 catalytic subunit (Ppp6C) and n-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP). Both transcription factors, such as nuclear factor κB (NF-κB), and epigenetic regulators, such as miRNAs are involved in downmodulation of anti-inflammatory responses. A detailed analysis of pathways and targets for downmodulation of anti-inflammatory responses constitutes a novel frontier in RAS research.

MO338INCREASED INFLAMMATORY RESPONSE IS A HALLMARK OF AGE-RELATED AGGRAVATION OF EXPERIMENTAL AKI

Background and Aims

Acute kidney injury (AKI) is associated with elevated mortality and morbidity presenting higher frequency in aged patients. Different mechanisms are activated in AKI, including tubular epithelial cell death (apoptosis and regulated necrosis), inflammatory cell infiltration, impaired mitochondrial function, and prolonged cell-cycle arrest (or cellular senescence). There is a strong connection between pathways activated in AKI and development of cellular senescence, a process implicated in regeneration failure and progression to fibrosis. However, the molecular mechanisms in ageing-associated mortality are not completely understood. Our aim was to investigate age-related molecular mechanisms of AKI.

Method

Experimental nephropathy by folic acid administration (FA, 125mg/kg) was induced in young (3 months) and old (12 months) mice. Renal lesions and mechanisms were evaluated at 48 hours (AKI acute phase).

Results

AKI mortality was higher in old (50 %) than in young (15%) mice 4 days after FA injection (pilot study). Tubular damage score (PAS evaluation) and KIM-1 tubular expression (renal damage biomarker) were also higher in old than in young FA-injected mice after 48h. The number of infiltrating immune cells (mainly neutrophils and macrophages) and gene expression levels of proinflammatory genes (Lcn-2 and ccl2) were significantly higher in FA kidneys of old as compared to young mice. Regulated necrosis (necroptosis), contrary to apoptosis, induces an inflammatory response and necroinflammation, being macrophages the key effector immune cells of this cell death pathway. Among some of the key necroptosis mediators, MLKL and RIPK3 were higher in old FA kidneys. These data could indicate a magnification of the inflammatory response to AKI in older mice. In contrast, expression of protective factors was dramatically downregulated in old FA mice, including the mitochondrial biogenesis driver PGC-1α, and the antiaging factor Klotho. Cellular senescence was induced in FA kidneys, as indicated by increased levels of cyclin-dependent kinase inhibitors p16ink4a and p21cip1, and of the DNA Damage Response marker yH2AX. Importantly, p21 mRNA expression and nuclear staining for p21 and yH2AX were increased in FA kidneys, and the fold increase was significantly higher in old than in young mice. Also, the expression of senescence-associated secretory phenotype (SASP) components (Tgfb1, Il-6, and Serpine-1) was significantly higher in old FA mouse kidneys. Interestingly, also some infiltrating immune cells were p21/yH2AX positive, suggesting molecular senescence in the immune cells (“immunesenescence”) and inflammation in the ageing kidney (“inflammaging”) are involved in the aggravated AKI response to FA in old mice.

Conclusion

Our data indicate that in advanced age, exposure to toxic compounds results in a more severe AKI response that might relate to an early inflammatory response characterize by more extensive necroptosis and activation of pathways related to cellular senescence of resident kidney cells and infiltrating inflammatory cells.

Interleukin-17A: Potential mediator and therapeutic target in hypertension

Interleukin-17A (IL-17A) is a proinflammatory cytokine produced by cells of the immune system, predominantly Th17 and γδ lymphocytes. In this paper, we review the role of IL-17A in the pathogenesis of hypertension and in target organ damage. Preclinical studies in mice have shown that systemic adminstration of IL-17A increases blood pressure, probably by acting on multiple levels. Furthermore, IL-17A plasma concentrations are already elevated in patients with mild or moderate hypertension. Many studies in hypertensive mice models have detected IL-17A-producing cells in target organs such as the heart, vessels and kidneys. Patients with hypertensive nephrosclerosis show kidney infiltration by Th17 lymphocytes and γδ lymphocytes that express IL-17A. In addition, in experimental models of hypertension, the blockade of IL-17A by genetic strategies or using neutralizing antibodies, disminished blood pressure, probablyby acting on the small mesenteric arteries as well as in the regulation of tubule sodium transport. Moreover, IL-17A inhibition reduces end-organs damage. As a whole, the data presented in this review suggest that IL-17A participates in the regulation of blood pressure and in the genesis and maintenance of arterial hypertension, and may constitute a therapeutic target of hypertension-related pathologies in the future.

The receptor activator of nuclear factor κΒ ligand receptor leucine-rich repeat-containing G-protein-coupled receptor 4 contributes to parathyroid hormone-induced vascular calcification

BACKGROUND

In chronic kidney disease, serum phosphorus (P) elevations stimulate parathyroid hormone (PTH) production, causing severe alterations in the bone-vasculature axis. PTH is the main regulator of the receptor activator of nuclear factor κB (RANK)/RANK ligand (RANKL)/osteoprotegerin (OPG) system, which is essential for bone maintenance and also plays an important role in vascular smooth muscle cell (VSMC) calcification. The discovery of a new RANKL receptor, leucine-rich repeat-containing G-protein-coupled receptor 4 (LGR4), which is important for osteoblast differentiation but with an unknown role in vascular calcification (VC), led us to examine the contribution of LGR4 in high P/high PTH-driven VC.

METHODS

In vivo studies were conducted in subtotally nephrectomized rats fed a normal or high P diet, with and without parathyroidectomy (PTX). PTX rats were supplemented with PTH(1-34) to achieve physiological serum PTH levels. In vitro studies were performed in rat aortic VSMCs cultured in control medium, calcifying medium (CM) or CM plus 10-7 versus 10-9 M PTH.

RESULTS

Rats fed a high P diet had a significantly increased aortic calcium (Ca) content. Similarly, Ca deposition was higher in VSMCs exposed to CM. Both conditions were associated with increased RANKL and LGR4 and decreased OPG aorta expression and were exacerbated by high PTH. Silencing of LGR4 or parathyroid hormone receptor 1 (PTH1R) attenuated the high PTH-driven increases in Ca deposition. Furthermore, PTH1R silencing and pharmacological inhibition of protein kinase A (PKA), but not protein kinase C, prevented the increases in RANKL and LGR4 and decreased OPG. Treatment with PKA agonist corroborated that LGR4 regulation is a PTH/PKA-driven process.

CONCLUSIONS

High PTH increases LGR4 and RANKL and decreases OPG expression in the aorta, thereby favouring VC. The hormone's direct pro-calcifying actions involve PTH1R binding and PKA activation.

[Interleukin-17A: Possible mediator and therapeutic target in hypertension]

Interleukin-17A (IL-17A) is a proinflammatory cytokine produced by cells of the immune system, predominantly Th17 lymphocytes and γδ lymphocytes. In this paper, we review the role of IL-17A in the pathogenesis of hypertension and target organ damage. Studies in mice have shown that IL-17A increases blood pressure, probably by acting on multiple levels. Furthermore, IL-17A plasma concentrations are already elevated in patients with mild or moderate hypertension. Preclinical studies on arterial hypertension have detected IL-17A-producing cells in target organs such as the heart, vessels and kidneys. Patients with hypertensive nephrosclerosis show kidney infiltration by Th17 lymphocytes and γδ lymphocytes that express IL-17A. In addition, in experimental models of hypertension, blocking IL-17A by genetic strategies, or using neutralising antibodies, lowers blood pressure by acting on the vascular wall and tubule sodium transport and reduces damage to target organs. As a whole, the data presented in this review suggest that IL-17A participates in the regulation of blood pressure and in the genesis and maintenance of arterial hypertension, and may constitute a therapeutic target in the future.

Renal tubule Cpt1a overexpression protects from kidney fibrosis by restoring mitochondrial homeostasis

Chronic kidney disease (CKD) remains a major epidemiological, clinical, and biomedical challenge. During CKD, renal tubular epithelial cells (TECs) present a persistent inflammatory and profibrotic response. Fatty acid oxidation (FAO), the main source of energy for TECs, is reduced in kidney fibrosis and contributes to its pathogenesis. To determine whether gain of function in FAO (FAO-GOF) could protect from fibrosis, we generated a conditional transgenic mouse model with overexpression of the fatty acid shuttling enzyme carnitine palmitoyl-transferase 1A (CPT1A) in TECs. Cpt1a-knockin (CPT1A-KI) mice subjected to 3 models of renal fibrosis (unilateral ureteral obstruction, folic acid nephropathy [FAN], and adenine-induced nephrotoxicity) exhibited decreased expression of fibrotic markers, a blunted proinflammatory response, and reduced epithelial cell damage and macrophage influx. Protection from fibrosis was also observed when Cpt1a overexpression was induced after FAN. FAO-GOF restored oxidative metabolism and mitochondrial number and enhanced bioenergetics, increasing palmitate oxidation and ATP levels, changes that were also recapitulated in TECs exposed to profibrotic stimuli. Studies in patients showed decreased CPT1 levels and increased accumulation of short- and middle-chain acylcarnitines, reflecting impaired FAO in human CKD. We propose that strategies based on FAO-GOF may constitute powerful alternatives to combat fibrosis inherent to CKD.

Wilms Tumor 1b Expression Defines a Pro-regenerative Macrophage Subtype and Is Required for Organ Regeneration in the Zebrafish

Organ regeneration is preceded by the recruitment of innate immune cells, which play an active role during repair and regrowth. Here, we studied macrophage subtypes during organ regeneration in the zebrafish, an animal model with a high regenerative capacity. We identified a macrophage subpopulation expressing Wilms tumor 1b (wt1b), which accumulates within regenerating tissues. This wt1b⁺ macrophage population exhibited an overall pro-regenerative gene expression profile and different migratory behavior compared to the remainder of the macrophages. Functional studies showed that wt1b regulates macrophage migration and retention at the injury area. Furthermore, wt1b-null mutant zebrafish presented signs of impaired macrophage differentiation, delayed fin growth upon caudal fin amputation, and reduced cardiomyocyte proliferation following cardiac injury that correlated with altered macrophage recruitment to the regenerating areas. We describe a pro-regenerative macrophage subtype in the zebrafish and a role for wt1b in organ regeneration.

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Wt1b⁺ macrophages reveal a pro-regenerative gene expression prolife

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Wt1b controls migration behavior of macrophages during fin and heart regeneration

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Wt1b regulates differentiation of macrophages in the kidney marrow

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wt1b mutants reveal impaired fin and heart regeneration

TRAF3 Modulation: Novel Mechanism for the Anti-inflammatory Effects of the Vitamin D Receptor Agonist Paricalcitol in Renal Disease

BACKGROUND

CKD leads to vitamin D deficiency. Treatment with vitamin D receptor agonists (VDRAs) may have nephroprotective and anti-inflammatory actions, but their mechanisms of action are poorly understood.

METHODS

Modulation of the noncanonical NF-κB2 pathway and its component TNF receptor-associated factor 3 (TRAF3) by the VDRA paricalcitol was studied in PBMCs from patients with ESKD, cytokine-stimulated cells, and preclinical kidney injury models.

RESULTS

In PBMCs isolated from patients with ESKD, TRAF3 protein levels were lower than in healthy controls. This finding was associated with evidence of noncanonical NF-κB2 activation and a proinflammatory state. However, PBMCs from patients with ESKD treated with paricalcitol did not exhibit these features. Experiments in cultured cells confirmed the link between TRAF3 and NF-κB2/inflammation. Decreased TRAF3 ubiquitination in K48-linked chains and cIAP1-TRAF3 interaction mediated the mechanisms of paricalcitol action.TRAF3 overexpression by CRISPR/Cas9 technology mimicked VDRA's effects. In a preclinical model of kidney injury, paricalcitol inhibited renal NF-κB2 activation and decreased renal inflammation. In VDR knockout mice with renal injury, paricalcitol prevented TRAF3 downregulation and NF-κB2-dependent gene upregulation, suggesting a VDR-independent anti-inflammatory effect of paricalcitol.

CONCLUSIONS

These data suggest the anti-inflammatory actions of paricalcitol depend on TRAF3 modulation and subsequent inhibition of the noncanonical NF-κB2 pathway, identifying a novel mechanism for VDRA's effects. Circulating TRAF3 levels could be a biomarker of renal damage associated with the inflammatory state.

P0087TRAF3 MODULATION: A NOVEL MECHANISM OF THE ANTI-INFLAMMATORY EFFECTS OF VITAMIN D RECEPTOR AGONIST PARICALCITOL IN RENAL DISEASE

Background and Aims

Tumor necrosis factor receptor-associated factors (TRAFs) are critical signaling adaptors downstream of pro-inflammatory receptors, involved in canonical and non-canonical nuclear factor-κB (NF-κB) activation. Vitamin D receptor agonists (VDRAs) exert beneficial effects in renal disease and possess anti-inflammatory properties, but the underlying mechanism remains unknown. Our aim was to investigate TRAF3 involvement on renal disease and its potential modulation by VDRAs.

Method

Studies were done in isolated peripheral blood mononuclear cells (PBMCs) from end-stage renal disease (ESRD) on haemodialysis (treated or not with VDRAs) patients, healthy donors or cultured renal cells. Preclinical models of renal damage were: unilateral ureteral obstruction (UUO), acute renal damage induced by Folic acid (FA) administration and TWEAK-induced renal inflammation. The effect of VDRA (paricalcitol) was tested in vitro and in vivo.

Results

In PBMCs isolated from ESRD, TRAF3 protein levels were downregulated compared to healthy controls, associated to activation of non-canonical NF-κB2 (downregulation of RelB or p52/NF-κB2 protein levels) and altered pro-inflammatory cytokine profile. Interestingly, treatment of those patients with the VDRA paricalcitol restored all the described features. In vitro experiments in PBMCs and tubular epithelial cells exposed to inflammatory stimuli showed that paricalcitol prevented TRAF3 downregulation, NF-κB2 activation and proinflammatory genes upregulation. Moreover, immunoprecipitation studies showed that paricalcitol diminished TRAF3 ubiquitination in the K48-linked chains and CIAP1-TRAF3 interaction. TRAF3 overexpression by CRIPS/cas9 technology mimics VDRAs effects. In preclinical models of renal damage paricalcitol inhibited renal NF-κB2 activation, reducing p52 and RelB nuclear accumulation and transcriptional activity associated to lower renal inflammation. In TWEAK-induced renal injury in VDR knockout mice, paricalcitol prevented TRAF3 downregulation and NF-κB2-dependent gene upregulation, suggesting a VDR-independent anti-inflammatory effect of paricalcitol.

Conclusion

The present studies identify TRAF3 downregulation as a key feature promoting inflammation in CKD identifying non-canonical NF-κB activation as a key driver of inflammation in this context. The fact that the VDR is not required for paricalcitol actions suggests novel-signaling pathways involved in the anti-inflammatory effect of paricalcitol. This may allow the design of drugs that restore TRAF3 levels but are devoid of VDR-dependent effects on mineral bone metabolism, which may limit the use of VDRAs as anti-inflammatory agents.

Protective role of renal proximal tubular alpha-synuclein in the pathogenesis of kidney fibrosis

Kidney fibrosis is a highly deleterious process and a final manifestation of chronic kidney disease. Alpha-(α)-synuclein (SNCA) is an actin-binding neuronal protein with various functions within the brain; however, its role in other tissues is unknown. Here, we describe the expression of SNCA in renal epithelial cells and demonstrate its decrease in renal tubules of murine and human fibrotic kidneys, as well as its downregulation in renal proximal tubular epithelial cells (RPTECs) after TGF-β1 treatment. shRNA-mediated knockdown of SNCA in RPTECs results in de novo expression of vimentin and α-SMA, while SNCA overexpression represses TGF-β1-induced mesenchymal markers. Conditional gene silencing of SNCA in RPTECs leads to an exacerbated tubulointerstitial fibrosis (TIF) in two unrelated in vivo fibrotic models, which is associated with an increased activation of MAPK-p38 and PI3K-Akt pathways. Our study provides an evidence that disruption of SNCA signaling in RPTECs contributes to the pathogenesis of renal TIF by facilitating partial epithelial-to-mesenchymal transition and extracellular matrix accumulation.

The Contribution of Histone Crotonylation to Tissue Health and Disease: Focus on Kidney Health

Acute kidney injury (AKI) and chronic kidney disease (CKD) are the most severe consequences of kidney injury. They are interconnected syndromes as CKD predisposes to AKI and AKI may accelerate CKD progression. Despite their growing impact on the global burden of disease, there is no satisfactory treatment for AKI and current therapeutic approaches to CKD remain suboptimal. Recent research has focused on the therapeutic target potential of epigenetic regulation of gene expression, including non-coding RNAs and the covalent modifications of histones and DNA. Indeed, several drugs targeting histone modifications are in clinical use or undergoing clinical trials. Acyl-lysine histone modifications (e.g. methylation, acetylation, and crotonylation) have modulated experimental kidney injury. Most recently, increased histone lysine crotonylation (Kcr) was observed during experimental AKI and could be reproduced in cultured tubular cells exposed to inflammatory stress triggered by the cytokine TWEAK. The degree of kidney histone crotonylation was modulated by crotonate availability and crotonate supplementation protected from nephrotoxic AKI. We now review the functional relevance of histone crotonylation in kidney disease and other pathophysiological contexts, as well as the implications for the development of novel therapeutic approaches. These studies provide insights into the overall role of histone crotonylation in health and disease.

The Role of PGC-1α and Mitochondrial Biogenesis in Kidney Diseases

Chronic kidney disease (CKD) is one of the fastest growing causes of death worldwide, emphasizing the need to develop novel therapeutic approaches. CKD predisposes to acute kidney injury (AKI) and AKI favors CKD progression. Mitochondrial derangements are common features of both AKI and CKD and mitochondria-targeting therapies are under study as nephroprotective agents. PGC-1α is a master regulator of mitochondrial biogenesis and an attractive therapeutic target. Low PGC-1α levels and decreased transcription of its gene targets have been observed in both preclinical AKI (nephrotoxic, endotoxemia, and ischemia-reperfusion) and in experimental and human CKD, most notably diabetic nephropathy. In mice, PGC-1α deficiency was associated with subclinical CKD and predisposition to AKI while PGC-1α overexpression in tubular cells protected from AKI of diverse causes. Several therapeutic strategies may increase kidney PGC-1α activity and have been successfully tested in animal models. These include AMP-activated protein kinase (AMPK) activators, phosphodiesterase (PDE) inhibitors, and anti-TWEAK antibodies. In conclusion, low PGC-1α activity appears to be a common feature of AKI and CKD and recent characterization of nephroprotective approaches that increase PGC-1α activity may pave the way for nephroprotective strategies potentially effective in both AKI and CKD.

Molecular pathways driving omeprazole nephrotoxicity

Omeprazole, a proton pump inhibitor used to treat peptic ulcer and gastroesophageal reflux disease, has been associated to chronic kidney disease and acute interstitial nephritis. However, whether omeprazole is toxic to renal cells is unknown. Omeprazole has a lethal effect over some cancer cells, and cell death is a key process in kidney disease. Thus, we evaluated the potential lethal effect of omeprazole over tubular cells. Omeprazole induced dose-dependent cell death in human and murine proximal tubular cell lines and in human primary proximal tubular cell cultures. Increased cell death was observed at the high concentrations used in cancer cell studies and also at lower concentrations similar to those in peptic ulcer patient serum. Cell death induced by omeprazole had features of necrosis such as annexin V/7-AAD staining, LDH release, vacuolization and irregular chromatin condensation. Weak activation of caspase-3 was observed but inhibitors of caspases (zVAD), necroptosis (Necrostatin-1) or ferroptosis (Ferrostatin-1) did not prevent omeprazole-induced death. However, omeprazole promoted a strong oxidative stress response affecting mitochondria and lysosomes and the antioxidant N-acetyl-cysteine reduced oxidative stress and cell death. By contrast, iron overload increased cell death. An adaptive increase in the antiapoptotic protein BclxL failed to protect cells. In mice, parenteral omeprazole increased tubular cell death and the expression of NGAL and HO-1, markers of renal injury and oxidative stress, respectively. In conclusion, omeprazole nephrotoxicity may be related to induction of oxidative stress and renal tubular cell death.

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

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

Molecular Regulation of Notch Signaling by Gremlin

Gremlin is a member of the TGF-β superfamily that can act as a BMP antagonist, and recently, has been described as a ligand of the vascular endothelial growth factor receptor 2 (VEGFR2). Gremlin shares properties with the Notch signaling pathway. Both participate in embryonic development and are reactivated in pathological conditions. Gremlin is emerging as a potential therapeutic target and biomarker of renal diseases. Here we review the role of the Gremlin-VEGFR2 axis in renal damage and downstream signaling mechanisms, such as Notch pathway.

MiR-9-5p protects from kidney fibrosis by metabolic reprogramming

MicroRNAs (miRNAs) regulate gene expression posttranscriptionally and control biological processes (BPs), including fibrogenesis. Kidney fibrosis remains a clinical challenge and miRNAs may represent a valid therapeutic avenue. We show that miR-9-5p protected from renal fibrosis in the mouse model of unilateral ureteral obstruction (UUO). This was reflected in reduced expression of pro-fibrotic markers, decreased number of infiltrating monocytes/macrophages, and diminished tubular epithelial cell injury and transforming growth factor-beta 1 (TGF-β1)-dependent de-differentiation in human kidney proximal tubular (HKC-8) cells. RNA-sequencing (RNA-Seq) studies in the UUO model revealed that treatment with miR-9-5p prevented the downregulation of genes related to key metabolic pathways, including mitochondrial function, oxidative phosphorylation (OXPHOS), fatty acid oxidation (FAO), and glycolysis. Studies in human tubular epithelial cells demonstrated that miR-9-5p impeded TGF-β1-induced bioenergetics derangement. The expression of the FAO-related axis peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α)-peroxisome proliferator-activated receptor alpha (PPARα) was reduced by UUO, although preserved by the administration of miR-9-5p. We found that in mice null for the mitochondrial master regulator PGC-1α, miR-9-5p was unable to promote a protective effect in the UUO model. We propose that miR-9-5p elicits a protective response to chronic kidney injury and renal fibrosis by inducing reprogramming of the metabolic derangement and mitochondrial dysfunction affecting tubular epithelial cells.

Design and optimization strategies for the development of new drugs that treat chronic kidney disease

Introduction: Chronic kidney disease (CKD) is characterized by increased risks of progression to end-stage kidney disease requiring dialysis and cardiovascular mortality, predicted to be among the five top causes of death by 2040. Only the design and optimization of novel strategies to develop new drugs to treat CKD will contain this trend. Current therapy for CKD includes nonspecific therapy targeting proteinuria and/or hypertension and cause-specific therapies for diabetic kidney disease, autosomal dominant polycystic kidney disease, glomerulonephritides, Fabry nephropathy, hemolytic uremic syndrome and others.Areas covered: Herein, the authors review the literature on new drugs under development for CKD as well as novel design and development strategies.Expert opinion: New therapies for CKD have become a healthcare priority. Emerging therapies undergoing clinical trials are testing expanded renin-angiotensin system blockade with double angiotensin receptor/endothelin receptor blockers, SGLT2 inhibition, and targeting inflammation, the immune response, fibrosis and the Nrf2 transcription factor. Emerging therapeutic targets include cell senescence, complement activation, Klotho expression preservation and microbiota. Novel approaches include novel model systems that can be personalized (e.g. organoids), unbiased systems biology-based identification of new therapeutic targets, drug databases that speed up drug identification and repurposing, nanomedicines that improve drug delivery and RNA targeting to expand the number of targetable proteins.

Bromodomain and Extraterminal Proteins as Novel Epigenetic Targets for Renal Diseases

Epigenetic mechanisms, especially DNA methylation and histone modifications, are dynamic processes that regulate the gene expression transcriptional program in normal and diseased states. The bromodomain and extraterminal (BET) protein family (BRD2, BRD3, BRD4, and BRDT) are epigenetic readers that, via bromodomains, regulate gene transcription by binding to acetylated lysine residues on histones and master transcriptional factors. Experimental data have demonstrated the involvement of some BET proteins in many pathological conditions, including tumor development, infections, autoimmunity, and inflammation. Selective bromodomain inhibitors are epigenetic drugs that block the interaction between BET proteins and acetylated proteins, thus exerting beneficial effects. Recent data have described the beneficial effect of BET inhibition on experimental renal diseases. Emerging evidence underscores the importance of environmental modifications in the origin of pathological features in chronic kidney diseases (CKD). Several cellular processes such as oxidation, metabolic disorders, cytokines, inflammation, or accumulated uremic toxins may induce epigenetic modifications that regulate key processes involved in renal damage and in other pathological conditions observed in CKD patients. Here, we review how targeting bromodomains in BET proteins may regulate essential processes involved in renal diseases and in associated complications found in CKD patients, such as cardiovascular damage, highlighting the potential of epigenetic therapeutic strategies against BET proteins for CKD treatment and associated risks.

Targeting epigenetic DNA and histone modifications to treat kidney disease

Epigenetics refers to heritable changes in gene expression patterns not caused by an altered nucleotide sequence, and includes non-coding RNAs and covalent modifications of DNA and histones. This review focuses on functional evidence for the involvement of DNA and histone epigenetic modifications in the pathogenesis of kidney disease and the potential therapeutic implications. There is evidence of activation of epigenetic regulatory mechanisms in acute kidney injury (AKI), chronic kidney disease (CKD) and the AKI-to-CKD transition of diverse aetiologies, including ischaemia-reperfusion injury, nephrotoxicity, ureteral obstruction, diabetes, glomerulonephritis and polycystic kidney disease. A beneficial in vivo effect over preclinical kidney injury has been reported for drugs that decrease DNA methylation by either inhibiting DNA methylation (e.g. 5-azacytidine and decitabine) or activating DNA demethylation (e.g. hydralazine), decrease histone methylation by inhibiting histone methyltransferases, increase histone acetylation by inhibiting histone deacetylases (HDACs, e.g. valproic acid, vorinostat, entinostat), increase histone crotonylation (crotonate) or interfere with histone modification readers [e.g. inhibits of bromodomain and extra-terminal proteins (BET)]. Most preclinical studies addressed CKD or the AKI-to-CKD transition. Crotonate administration protected from nephrotoxic AKI, but evidence is conflicting on DNA methylation inhibitors for preclinical AKI. Several drugs targeting epigenetic regulators are in clinical development or use, most of them for malignancy. The BET inhibitor apabetalone is in Phase 3 trials for atherosclerosis, kidney function being a secondary endpoint, but nephrotoxicity was reported for DNA and HDAC inhibitors. While research into epigenetic modulators may provide novel therapies for kidney disease, caution should be exercised based on the clinical nephrotoxicity of some drugs.

Interleukin 17A Participates in Renal Inflammation Associated to Experimental and Human Hypertension

Hypertension is now considered as an inflammatory disease, and the kidney is a key end-organ target. Experimental and clinical studies suggest that interleukin 17A (IL-17A) is a promising therapeutic target in immune and chronic inflammatory diseases, including hypertension and kidney disease. Elevated circulating IL-17A levels have been observed in hypertensive patients. Our aim was to investigate whether chronically elevated circulating IL-17A levels could contribute to kidney damage, using a murine model of systemic IL-17A administration. Blood pressure increased after 14 days of IL-17A infusion in mice when compared with that in control mice, and this was associated to kidney infiltration by inflammatory cells, including CD3⁺ and CD4⁺ lymphocytes and neutrophils. Moreover, proinflammatory factors and inflammatory-related intracellular mechanisms were upregulated in kidneys from IL-17A-infused mice. In line with these findings, in the model of angiotensin II infusion in mice, IL-17A blockade, using an anti-IL17A neutralizing antibody, reduced kidney inflammatory cell infiltrates and chemokine overexpression. In kidney biopsies from patients with hypertensive nephrosclerosis, IL-17A positive cells, mainly Th17 and γδ T lymphocytes, were found. Overall, the results support a pathogenic role of IL-17A in hypertensive kidney disease-associated inflammation. Therapeutic approaches targeting this cytokine should be explored to prevent hypertension-induced kidney injury.

Gremlin and renal diseases: ready to jump the fence to clinical utility?

The current therapeutic strategy for the treatment of chronic kidney diseases only ameliorates disease progression. During renal injury, developmental genes are re-expressed and could be potential therapeutic targets. Among those genes reactivated in the adult damaged kidney, Gremlin is of particular relevance since recent data suggest that it could be a mediator of diabetic nephropathy and other progressive renal diseases. Earlier studies have shown that Gremlin is upregulated in trans-differentiated renal proximal tubular cells and in several chronic kidney diseases associated with fibrosis. However, not much was known about the mechanisms by which Gremlin acts in renal pathophysiology. The role of Gremlin as a bone morphogenetic protein antagonist has clearly been demonstrated in organogenesis and in fibrotic-related disorders. Gremlin binds to vascular endothelial growth factor receptor 2 (VEGFR2) in endothelial and tubular epithelial cells. Activation of the Gremlin-VEGFR2 axis was found in several human nephropathies. We have recently described that Gremlin activates the VEGFR2 signaling pathway in the kidney, eliciting a downstream mechanism linked to renal inflammatory response. Gremlin deletion improves experimental renal damage, diminishing fibrosis. Overall, the available data identify the Gremlin-VEGFR2 axis as a novel therapeutic target for kidney inflammation and fibrosis and provide a rationale for unveiling new concepts to investigate in several clinical conditions.

Gremlin, A Potential Urinary Biomarker of Anca-Associated Crescentic Glomerulonephritis

Gremlin renal overexpression has been reported in diabetic nephropathy, pauci-immune crescentic glomerulonephritis and chronic allograft nephropathy and has been implicated in the pathophysiology of the progression of renal damage. However, it is unknown whether urinary Gremlin can be associated with renal functional status, renal biopsy findings and outcome. To examine these associations we studied 20 patients with ANCA+ renal vasculitis and very high urinary Gremlin (354 ± 76 ug/gCr), 86 patients with other glomerular diseases and moderately elevated urinary Gremlin (83 ± 14 ug/gCr) and 11 healthy controls (urinary Gremlin 11.3 ± 2.4 ug/gCr). Urinary Gremlin was significantly correlated with renal expression of Gremlin (r = 0.64, p = 0.013) observed in cellular glomerular crescents, tubular epithelial cells and interstitial inflammatory cells. Moreover, urinary Gremlin levels were correlated with the number of glomerular crescents (r = 0.53; p < 0.001), renal CD68 positive cells (r = 0.71; p < 0.005), tubulointerstitial fibrosis (r = 0.50; p < 0.05), and serum creatinine levels (r = 0.60; p < 0.001). Interestingly, Gremlin expression was colocalized with CD68, CD163 (monocyte/macrophage markers) and CCL18 positive cells. ROC curve analysis showed that the cutoff value of urinary Gremlin in glomerular diseases as 43 ug/gCr with 72% of sensitivity and 100% of specificity [AUC: 0.96 (CI 95% 0.92–0.99] (p < 0.001). For ANCA+ renal vasculitis the value of urinary Gremlin of 241 ug/gCr had 55% of sensitivity and 100% of specificity [AUC: 0.81 (CI 95% 0.68–0.94) (p < 0.001]. Based on these results we propose that urinary Gremlin represents a non-invasive biomarker in ANCA+ renal vasculitis, and suggest a role of Gremlin in the formation of crescents.