The C-terminal module IV of connective tissue growth factor is a novel immune modulator of the Th17 response

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.

Type IV Collagen and SOX9 Are Molecular Targets of BET Inhibition in Experimental Glomerulosclerosis

Progressive glomerulonephritis (GN) is characterized by an excessive accumulation of extracellular (ECM) proteins, mainly type IV collagen (COLIV), in the glomerulus leading to glomerulosclerosis. The current therapeutic approach to GN is suboptimal. Epigenetic drugs could be novel therapeutic options for human disease. Among these drugs, bromodomain and extra-terminal domain (BET) inhibitors (iBETs) have shown beneficial effects in experimental kidney disease and fibrotic disorders. Sex-determining region Y-box 9 (SOX9) is a transcription factor involved in regulating proliferation, migration, and regeneration, but its role in kidney fibrosis is still unclear. We investigated whether iBETs could regulate ECM accumulation in experimental GN and evaluated the role of SOX9 in this process. For this purpose, we tested the iBET JQ1 in mice with anti-glomerular basement membrane nephritis induced by nephrotoxic serum (NTS). In NTS-injected mice, JQ1 treatment reduced glomerular ECM deposition, mainly by inhibiting glomerular COLIV accumulation and Col4a3 gene overexpression. Moreover, chromatin immunoprecipitation assays demonstrated that JQ1 inhibited the recruitment and binding of BRD4 to the Col4a3 promoter and reduced its transcription. Active SOX9 was found in the nuclei of glomerular cells of NTS-injured kidneys, mainly in COLIV-stained regions. JQ1 treatment blocked SOX9 nuclear translocation in injured kidneys. Moreover, in vitro JQ1 blocked TGF-β1-induced SOX9 activation and ECM production in cultured mesangial cells. Additionally, SOX9 gene silencing inhibited ECM production, including COLIV production. Our results demonstrated that JQ1 inhibited SOX9/COLIV, to reduce experimental glomerulosclerosis, supporting further research of iBET as a potential therapeutic option in progressive glomerulosclerosis.

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.

CCN2 Increases TGF-β Receptor Type II Expression in Vascular Smooth Muscle Cells: Essential Role of CCN2 in the TGF-β Pathway Regulation

The cellular communication network factor 2 (CCN2/CTGF) has been traditionally described as a mediator of the fibrotic responses induced by other factors including the transforming growth factor β (TGF-β). However, several studies have defined a direct role of CCN2 acting as a growth factor inducing oxidative and proinflammatory responses. The presence of CCN2 and TGF-β together in the cellular context has been described as a requisite to induce a persistent fibrotic response, but the precise mechanisms implicated in this relation are not described yet. Considering the main role of TGF-β receptors (TβR) in the TGF-β pathway activation, our aim was to investigate the effects of CCN2 in the regulation of TβRI and TβRII levels in vascular smooth muscle cells (VSMCs). While no differences were observed in TβRI levels, an increase in TβRII expression at both gene and protein level were found 48 h after stimulation with the C-terminal fragment of CCN2 (CCN2(IV)). Cell pretreatment with a TβRI inhibitor did not modify TβRII increment induced by CCN2(VI), demonstrating a TGF-β-independent response. Secondly, CCN2(IV) rapidly activated the SMAD pathway in VSMCs, this being crucial in the upregulation of TβRII since the preincubation with an SMAD3 inhibitor prevented it. Similarly, pretreatment with the epidermal growth factor receptor (EGFR) inhibitor erlotinib abolished TβRII upregulation, indicating the participation of this receptor in the observed responses. Our findings suggest a direct role of CCN2 maintaining the TGF-β pathway activation by increasing TβRII expression in an EGFR-SMAD dependent manner activation.

BMP6 increases CD68 expression by up-regulating CTGF expression in human granulosa-lutein cells

Bone morphogenetic protein 6 (BMP6) and connective tissue growth factor (CTGF) are critical growth factors required for normal follicular development and luteal function. Cluster of Differentiation 68 (CD68) is an intraovarian marker of macrophages that plays an important role in modulating the physiological regression of the corpus luteum. The aim of this study was to investigate the effect of BMP6 on the expression of CTGF and the subsequent increase in CD68 expression as well as its underlying mechanisms. Primary and immortalized (SVOG) human granulosa cells obtained from infertile women undergoing in vitro fertilization treatment were used as cell models to conduct the in vitro experiments. Our results showed that BMP6 treatment significantly increased the expression levels of CTGF and CD68. Using BMP type I receptor inhibitors (dorsomorphin, DMH-1 and SB431542), we demonstrated that both activin receptor-like kinase (ALK)2 and ALK3 are involved in BMP6-induced stimulatory effects on the expression of CTGF and CD68. Additionally, SMAD4-knock down reversed the BMP6-induced up-regulation of CTGF and CD68, indicating that the canonical SMAD signaling pathway is required for these effects. Moreover, CTGF-knock down abolished the BMP6-induced up-regulation of CD68 expression. These findings indicate that intrafollicular CTGF mediates BMP6-induced increases in CD68 expression through the ALK2/ALK3-mediated SMAD-dependent signaling pathway.

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

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

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.

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.

[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.

T helper 17 cells in the pathophysiology of acute and chronic kidney disease

Both acute and chronic kidney disease have a strong underlying inflammatory component. This review focuses primarily on T helper 17 (Th17) cells as mediators of inflammation and their potential to modulate acute and chronic kidney disease. We provide updated information on factors and signaling pathways that promote Th17 cell differentiation with specific reference to kidney disease. We highlight numerous clinical studies that have investigated Th17 cells in the setting of human kidney disease and provide updated summaries from various experimental animal models of kidney disease indicating an important role for Th17 cells in renal fibrosis and hypertension. We focus on the pleiotropic effects of Th17 cells in different renal cell types as potentially relevant to the pathogenesis of kidney disease. Finally, we highlight studies that present contrasting roles for Th17 cells in kidney disease progression.

Connective Tissue Growth Factor: From Molecular Understandings to Drug Discovery

Connective tissue growth factor (CTGF) is a key signaling and regulatory molecule involved in different biological processes, such as cell proliferation, angiogenesis, and wound healing, as well as multiple pathologies, such as tumor development and tissue fibrosis. Although the underlying mechanisms of CTGF remain incompletely understood, a commonly accepted theory is that the interactions between different protein domains in CTGF and other various regulatory proteins and ligands contribute to its variety of functions. Here, we highlight the structure of each domain of CTGF and its biology functions in physiological conditions. We further summarized main diseases that are deeply influenced by CTGF domains and the potential targets of these diseases. Finally, we address the advantages and disadvantages of current drugs targeting CTGF and provide the perspective for the drug discovery of the next generation of CTGF inhibitors based on aptamers.

IL-17A as a Potential Therapeutic Target for Patients on Peritoneal Dialysis

Chronic kidney disease (CKD) is a health problem reaching epidemic proportions. There is no cure for CKD, and patients may progress to end-stage renal disease (ESRD). Peritoneal dialysis (PD) is a current replacement therapy option for ESRD patients until renal transplantation can be achieved. One important problem in long-term PD patients is peritoneal membrane failure. The mechanisms involved in peritoneal damage include activation of the inflammatory and immune responses, associated with submesothelial immune infiltrates, angiogenesis, loss of the mesothelial layer due to cell death and mesothelial to mesenchymal transition, and collagen accumulation in the submesothelial compact zone. These processes lead to fibrosis and loss of peritoneal membrane function. Peritoneal inflammation and membrane failure are strongly associated with additional problems in PD patients, mainly with a very high risk of cardiovascular disease. Among the inflammatory mediators involved in peritoneal damage, cytokine IL-17A has recently been proposed as a potential therapeutic target for chronic inflammatory diseases, including CKD. Although IL-17A is the hallmark cytokine of Th17 immune cells, many other cells can also produce or secrete IL-17A. In the peritoneum of PD patients, IL-17A-secreting cells comprise Th17 cells, γδ T cells, mast cells, and neutrophils. Experimental studies demonstrated that IL-17A blockade ameliorated peritoneal damage caused by exposure to PD fluids. This article provides a comprehensive review of recent advances on the role of IL-17A in peritoneal membrane injury during PD and other PD-associated complications.

[The balance of proinflammatory cytokines and Treg cells in chronic glomerulonephritis]

Chronic glomerulonephritis (CGN) is a disease with a steadily progressing course, which is based on inflammation with the activation of immune cells. The severity of the inflammatory reaction in the kidney tissue is determined by the balance of locally pro-inflammatory factors and protective mechanisms, which include anti-inflammatory cytokines and T-regulatory lymphocytes (Treg). The study of processes that can modulate the severity of inflammation in the kidney is of particular interest for understanding the basic patterns of CGN progression.

AIM

To determine the clinical significance of the Th17, Th1, and Treg cytokines in urine to assess the activity and progression of chronic glomerulonephritis with nephrotic syndrome (NS).

MATERIALS AND METHODS

The study included 98 patients with CGN 37 women and 61 men. Patients were divided into two groups according to the degree of CGN activity. Group I consisted of 51 patients with NS. In 21 subjects, a decrease in GFR60 ml/min was revealed. Group II included 47 patients with proteinuria from 1 to 3 g/day without NS. GFR60 ml/min/1.73 m2 was observed in 26 patients. A kidney biopsy was performed in 65 patients and the hystological diagnosis was verified: 20 had mesangioproliferative GN, 16 had membranous nephropathy, 18 had focal segmental glomerulosclerosis, and 11 had membranoproliferative GN. The control group consisted of 15 healthy people. The levels of IL-6, IL-10, IL-17, tumor necrosis factor a (TNF-a) in the urine were determined using enzyme-linked immunosorbent assay. The number of FoxP3-positive cells in the inflammatory interstitial infiltrate of the cortical layer was determined in 39 patients (in a biopsy sample in a 1.5 mm2 area).

RESULTS

In group of patients with CGN, there was an increase in the levels of Th17, Th1, and Treg cytokines in urine TNF-a and IL-10 compared with healthy individuals. An increase in the levels of IL-6 in the urine of patients with high clinical activity of CGN (with NS and renal dysfunction) was more pronounced than in patients with NS and normal renal function. There was a decrease in the number of Treg cells in the interstitium of the kidney and a decrease in the production of anti-inflammatory IL-10 in CGN patients with NS, compared with patients without NS. The most pronounced changes in the cytokine profile were observed in patients with FSGS with an increase in pro-inflammatory cytokines and a decrease in Treg in the kidney tissue/anti-inflammatory IL-10 in the urine.

CONCLUSION

An imbalance of cytokines characterized by an increased levels of pro-inflammatory IL-17, IL-6, TNF-a, and a reduced levels of anti-inflammatory IL-10 and T-regulatory cells in the kidney tissue is noted in patients with NS, especially with FSGS. Imbalance of cytokines reflects the high activity of CGN and the risk of the progression of the disease.

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.

Targeting the progression of chronic kidney disease

Chronic kidney disease (CKD) is a devastating condition that is reaching epidemic levels owing to the increasing prevalence of diabetes mellitus, hypertension and obesity, as well as ageing of the population. Regardless of the underlying aetiology, CKD is slowly progressive and leads to irreversible nephron loss, end-stage renal disease and/or premature death. Factors that contribute to CKD progression include parenchymal cell loss, chronic inflammation, fibrosis and reduced regenerative capacity of the kidney. Current therapies have limited effectiveness and only delay disease progression, underscoring the need to develop novel therapeutic approaches to either stop or reverse progression. Preclinical studies have identified several approaches that reduce fibrosis in experimental models, including targeting cytokines, transcription factors, developmental and signalling pathways and epigenetic modulators, particularly microRNAs. Some of these nephroprotective strategies are now being tested in clinical trials. Lessons learned from the failure of clinical studies of transforming growth factor β1 (TGFβ1) blockade underscore the need for alternative approaches to CKD therapy, as strategies that target a single pathogenic process may result in unexpected negative effects on simultaneously occurring processes. Additional promising avenues include preventing tubular cell injury and anti-fibrotic therapies that target activated myofibroblasts, the main collagen-producing cells.

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.

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.

Interleukin-17A blockade reduces albuminuria and kidney injury in an accelerated model of diabetic nephropathy

Diabetic nephropathy (DN) is one of the most common complications of diabetes, and currently the first end-stage renal disease worldwide. New strategies to treat DN using agents that target inflammatory pathways have attracted special interest. Recent pieces of evidences suggest a promising effect of IL-17A, the Th17 effector cytokine. Among experimental DN models, mouse strain BTBR ob/ob (leptin deficiency mutation) develops histological features similar to human DN, which means an opportunity to study mechanisms and novel therapies aimed at DN regression. We found that BTBR ob/ob mice presented renal activation of the factors controlling Th17 differentiation. The presence of IL-17A-expressing cells, mainly CD4⁺ and γδ lymphocytes, was associated with upregulation of proinflammatory factors, macrophage infiltration and the beginning of renal damage. To study IL-17A involvement in experimental DN pathogenesis, treatment with an IL-17A neutralizing antibody was carried out starting when the renal damage had already appeared. IL-17A blockade ameliorated renal dysfunction and disease progression in BTBR ob/ob mice. These beneficial effects correlated to podocyte number restoration and inhibition of NF-κB/proinflammatory factors linked to a decrease in renal inflammatory-cell infiltration. These data demonstrate that IL-17A takes part in diabetes-mediated renal damage and could be a promising therapeutic target to improve DN.

Role of Epidermal Growth Factor Receptor (EGFR) and Its Ligands in Kidney Inflammation and Damage

Chronic kidney disease (CKD) is characterized by persistent inflammation and progressive fibrosis, ultimately leading to end-stage renal disease. Although many studies have investigated the factors involved in the progressive deterioration of renal function, current therapeutic strategies only delay disease progression, leaving an unmet need for effective therapeutic interventions that target the cause behind the inflammatory process and could slow down or reverse the development and progression of CKD. Epidermal growth factor receptor (EGFR) (ERBB1), a membrane tyrosine kinase receptor expressed in the kidney, is activated after renal damage, and preclinical studies have evidenced its potential as a therapeutic target in CKD therapy. To date, seven official EGFR ligands have been described, including epidermal growth factor (EGF) (canonical ligand), transforming growth factor-α, heparin-binding epidermal growth factor, amphiregulin, betacellulin, epiregulin, and epigen. Recently, the connective tissue growth factor (CTGF/CCN2) has been described as a novel EGFR ligand. The direct activation of EGFR by its ligands can exert different cellular responses, depending on the specific ligand, tissue, and pathological condition. Among all EGFR ligands, CTGF/CCN2 is of special relevance in CKD. This growth factor, by binding to EGFR and downstream signaling pathway activation, regulates renal inflammation, cell growth, and fibrosis. EGFR can also be “transactivated” by extracellular stimuli, including several key factors involved in renal disease, such as angiotensin II, transforming growth factor beta (TGFB), and other cytokines, including members of the tumor necrosis factor superfamily, showing another important mechanism involved in renal pathology. The aim of this review is to summarize the contribution of EGFR pathway activation in experimental kidney damage, with special attention to the regulation of the inflammatory response and the role of some EGFR ligands in this process. Better insights in EGFR signaling in renal disease could improve our current knowledge of renal pathology contributing to therapeutic strategies for CKD development and progression.

Epigenetic Modification Mechanisms Involved in Inflammation and Fibrosis in Renal Pathology

The growing incidence of obesity, hypertension, and diabetes, coupled with the aging of the population, is increasing the prevalence of renal diseases in our society. Chronic kidney disease (CKD) is characterized by persistent inflammation, fibrosis, and loss of renal function leading to end-stage renal disease. Nowadays, CKD treatment has limited effectiveness underscoring the importance of the development of innovative therapeutic options. Recent studies have identified how epigenetic modifications participate in the susceptibility to CKD and have explained how the environment interacts with the renal cell epigenome to contribute to renal damage. Epigenetic mechanisms regulate critical processes involved in gene regulation and downstream cellular responses. The most relevant epigenetic modifications that play a critical role in renal damage include DNA methylation, histone modifications, and changes in miRNA levels. Importantly, these epigenetic modifications are reversible and, therefore, a source of potential therapeutic targets. Here, we will explain how epigenetic mechanisms may regulate essential processes involved in renal pathology and highlight some possible epigenetic therapeutic strategies for CKD treatment.

New Functions of Classical Compounds against Orofacial Inflammatory Lesions

Anti-inflammatory agents have been widely used to ameliorate severe inflammatory symptoms of a number of diseases, and such therapeutics are particularly useful for diseases with intolerable pain without significant mortality. A typical example of this is a disease known as stomatitis; although stomatitis itself is not a life-threatening disease, it severely impairs the individual’s quality of life, and thus a standard therapeutic strategy for it has already been established. The topical application of a bioactive agent is quite easy, and a strong anti-inflammatory agent can be used without significant adverse effects. In contrast, natural products with relatively mild bioactivity are used for systemic intervention. However, new aspects of classical drugs used in these established therapeutic methods have recently been discovered, which is expanding the utility of these compounds to other oral diseases such as osteoarthritis of temporomandibular joints (TMJ-OA). In this review article, after summarizing the general concept and pathobiology of stomatitis, its established therapeutics are explained. Thereafter, recent advances in the research into related compounds, which is uncovering new biological functions of the agents used therein, are introduced. Indeed, regenerative therapeutics for TMJ-OA may be developed with the classical compounds currently being used.

CTGF in kidney fibrosis and glomerulonephritis

Background

Glomerulonephritis, which causes inflammation in glomeruli, is a common cause of end-stage renal failure. Severe and prolonged inflammation can damage glomeruli and lead to kidney fibrosis. Connective tissue growth factor (CTGF) is a member of the CCN matricellular protein family, consisting of four domains, that regulates the signaling of other growth factors and promotes kidney fibrosis.

Main body of the abstract

CTGF can simultaneously interact with several factors with its four domains. The microenvironment differs depending on the types of cells and tissues and differentiation stages of these cells. The diverse biological actions of CTGF on various types of cells and tissues depend on this difference in microenvironment. In the kidney, CTGF is expressed at low levels in normal condition and its expression is upregulated by kidney fibrosis. CTGF expression is known to be upregulated in the extra-capillary and mesangial lesions of glomerulonephritis in human kidney biopsy samples. In addition to involvement in fibrosis, CTGF modulates the expression of inflammatory mediators, including cytokines and chemokines, through distinct signaling pathways, in various cell systems. In anti-glomerular basement membrane (GBM) glomerulonephritis, systemic CTGF knockout (Rosa-CTGF cKO) mice exhibit 50% reduction of proteinuria and decreased crescent formation and mesangial expansion compared with control mice. In addition to fibrotic markers, the glomerular mRNA expression of Ccl2 is increased in the control mice with anti-GBM glomerulonephritis, and this increase is reduced in Rosa-CTGF cKO mice with nephritis. Accumulation of MAC2-positive cells in glomeruli is also reduced in Rosa-CTGF cKO mice. These results suggest that CTGF may be required for the upregulation of Ccl2 expression not only in anti-GBM glomerulonephritis but also in other types of glomerulonephritis, such as IgA nephropathy; CTGF expression and accumulation of macrophages in the mesangial area have been documented in these glomerular diseases. CTGF induces the expression of inflammatory mediators and promotes cell adhesion.

Short conclusion

CTGF plays an important role in the development of glomerulonephritis by inducing the inflammatory process. CTGF is a potentiate target for the treatment of glomerulonephritis.

Matrix Metalloproteinases and Tissue Inhibitor of Metalloproteinases in Inflammation and Fibrosis of Skeletal Muscles

In skeletal muscles, levels and activity of Matrix MetalloProteinases (MMPs) and Tissue Inhibitors of MetalloProteinases (TIMPs) have been involved in myoblast migration, fusion and various physiological and pathological remodeling situations including neuromuscular diseases. This has opened perspectives for the use of MMPs' overexpression to improve the efficiency of cell therapy in muscular dystrophies and resolve fibrosis. Alternatively, inhibition of individual MMPs in animal models of muscular dystrophies has provided evidence of beneficial, dual or adverse effects on muscle morphology or function. We review here the role played by MMPs/TIMPs in skeletal muscle inflammation and fibrosis, two major hurdles that limit the success of cell and gene therapy. We report and analyze the consequences of genetic or pharmacological modulation of MMP levels on the inflammation of skeletal muscles and their repair in light of experimental findings. We further discuss how the interplay between MMPs/TIMPs levels, cytokines/chemokines, growth factors and permanent low-grade inflammation favor cellular and molecular modifications resulting in fibrosis.

Connective tissue growth factor induces renal fibrosis via epidermal growth factor receptor activation

Connective tissue growth factor (CCN2/CTGF) is a matricellular protein that is overexpressed in progressive human renal diseases, mainly in fibrotic areas. In vitro studies have demonstrated that CCN2 regulates the production of extracellular matrix (ECM) proteins and epithelial-mesenchymal transition (EMT), and could therefore contribute to renal fibrosis. CCN2 blockade ameliorates experimental renal damage, including diminution of ECM accumulation. We have reported that CCN2 and its C-terminal degradation product CCN2(IV) bind to epidermal growth factor receptor (EGFR) to modulate renal inflammation. However, the receptor involved in CCN2 profibrotic actions has not been described so far. Using a murine model of systemic administration of CCN2(IV), we have unveiled a fibrotic response in the kidney that was diminished by EGFR blockade. Additionally, in conditional CCN2 knockout mice, renal fibrosis elicited by folic acid-induced renal damage was prevented, and this was linked to inhibition of EGFR pathway activation. Our in vitro studies demonstrated a direct effect of CCN2 via the EGFR pathway on ECM production by fibroblasts and the induction of EMT in tubular epithelial cells. Our studies clearly show that the EGFR regulates CCN2 fibrotic signalling in the kidney, and suggest that EGFR pathway blockade could be a potential therapeutic option to block CCN2-mediated profibrotic effects in renal diseases. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Atrasentan for the treatment of diabetic nephropathy

INTRODUCTION

Endothelin-1 (ET-1) is the most potent vasoconstrictor, and is involved in the renal regulation of salt and water homeostasis. When produced in excess in the kidney, ET-1 promotes proteinuria and tubulointerstitial injury. There is great interest in the clinical use of endothelin receptor antagonists (ERAs) in chronic kidney disease (CKD), mainly in diabetic nephropathy (DN). Areas covered: Physiopathological actions of ET-1 on the kidney. Both dual ETAR/ET_BR (bosentan) or ET_AR specific endothelin antagonists (avosentan and atrasentan, among others), which have progressed to early clinical development, with particular emphasis on atrasentan. Expert opinion: Different phase I and II clinical trials with ERAs in DN, mostly with atrasentan, have shown that these drugs have a marked anti-proteinuric effect on residual proteinuria when administered as add-on therapy in addition to ACEi or ARAII treatment. In the past few years, a series of randomized controlled trials investigating new approaches to DN have provided negative or inconclusive data, or even were terminated due to safety concerns or lack of efficacy. Therefore, we eagerly but cautiously await the results of the ongoing SONAR trial with atrasentan in more than 4,000 patients including assessment of renal and cardiovascular hard-end points (estimated primary completion date, July 2018).

Crucial Role of Mesangial Cell-derived Connective Tissue Growth Factor in a Mouse Model of Anti-Glomerular Basement Membrane Glomerulonephritis

Connective tissue growth factor (CTGF) coordinates the signaling of growth factors and promotes fibrosis. Neonatal death of systemic CTGF knockout (KO) mice has hampered analysis of CTGF in adult renal diseases. We established 3 types of CTGF conditional KO (cKO) mice to investigate a role and source of CTGF in anti-glomerular basement membrane (GBM) glomerulonephritis. Tamoxifen-inducible systemic CTGF (Rosa-CTGF) cKO mice exhibited reduced proteinuria with ameliorated crescent formation and mesangial expansion in anti-GBM nephritis after induction. Although CTGF is expressed by podocytes at basal levels, podocyte-specific CTGF (pod-CTGF) cKO mice showed no improvement in renal injury. In contrast, PDGFRα promoter-driven CTGF (Pdgfra-CTGF) cKO mice, which predominantly lack CTGF expression by mesangial cells, exhibited reduced proteinuria with ameliorated histological changes. Glomerular macrophage accumulation, expression of Adgre1 and Ccl2, and ratio of M1/M2 macrophages were all reduced both in Rosa-CTGF cKO and Pdgfra-CTGF cKO mice, but not in pod-CTGF cKO mice. TGF-β1-stimulated Ccl2 upregulation in mesangial cells and macrophage adhesion to activated mesangial cells were decreased by reduction of CTGF. These results reveal a novel mechanism of macrophage migration into glomeruli with nephritis mediated by CTGF derived from mesangial cells, implicating the therapeutic potential of CTGF inhibition in glomerulonephritis.

Inhibition of Bromodomain and Extraterminal Domain Family Proteins Ameliorates Experimental Renal Damage

Renal inflammation has a key role in the onset and progression of immune- and nonimmune-mediated renal diseases. Therefore, the search for novel anti-inflammatory pharmacologic targets is of great interest in renal pathology. JQ1, a small molecule inhibitor of bromodomain and extraterminal (BET) proteins, was previously found to preserve renal function in experimental polycystic kidney disease. We report here that JQ1-induced BET inhibition modulated the in vitro expression of genes involved in several biologic processes, including inflammation and immune responses. Gene silencing of BRD4, an important BET protein, and chromatin immunoprecipitation assays showed that JQ1 alters the direct association of BRD4 with acetylated histone-packaged promoters and reduces the transcription of proinflammatory genes (IL-6, CCL-2, and CCL-5). In vivo, JQ1 abrogated experimental renal inflammation in murine models of unilateral ureteral obstruction, antimembrane basal GN, and infusion of Angiotensin II. Notably, JQ1 downregulated the expression of several genes controlled by the NF-κB pathway, a key inflammatory signaling pathway. The RelA NF-κB subunit is activated by acetylation of lysine 310. In damaged kidneys and cytokine-stimulated renal cells, JQ1 reduced the nuclear levels of RelA NF-κB. Additionally, JQ1 dampened the activation of the Th17 immune response in experimental renal damage. Our results show that inhibition of BET proteins reduces renal inflammation by several mechanisms: chromatin remodeling in promoter regions of specific genes, blockade of NF-κB pathway activation, and modulation of the Th17 immune response. These results suggest that inhibitors of BET proteins could have important therapeutic applications in inflammatory renal diseases.

TGF-Beta Blockade Increases Renal Inflammation Caused by the C-Terminal Module of the CCN2

The CCN family member 2 (CCN2, also known as connective tissue growth factor) may behave as a risk biomarker and a potential therapeutic target for renal disease. CCN2 participates in the regulation of inflammation and fibrosis. TGF-β is considered the main fibrogenic cytokine; however, in some pathological settings TGF-β also has anti-inflammatory properties. CCN2 has been proposed as a downstream profibrotic mediator of TGF-β, but data on TGF-β role in CCN2 actions are scarce. Our aim was to evaluate the effect of TGF-β blockade in CCN2-mediated experimental renal damage. Systemic administration of the C-terminal module of CCN2 to mice caused sustained renal inflammation. In these mice, TGF-β blockade, using an anti-TGF-β neutralizing antibody, significantly increased renal expression of the NGAL (a kidney injury biomarker), kidney infiltration by monocytes/macrophages, and upregulation of MCP-1 expression. The anti-inflammatory effect of TGF-β seems to be mediated by a dysregulation of the systemic Treg immune response, shown by decreased levels of circulating CD4⁺/Foxp3⁺Treg cells. Our experimental data support the idea that TGF-β exerts anti-inflammatory actions in the kidney and suggest that it is not an optimal therapeutic target.

T Helper 17/Regulatory T Cell Balance and Experimental Models of Peritoneal Dialysis-Induced Damage

Fibrosis is a general complication in many diseases. It is the main complication during peritoneal dialysis (PD) treatment, a therapy for renal failure disease. Local inflammation and mesothelial to mesenchymal transition (MMT) are well known key phenomena in peritoneal damage during PD. New data suggest that, in the peritoneal cavity, inflammatory changes may be regulated at least in part by a delicate balance between T helper 17 and regulatory T cells. This paper briefly reviews the implication of the Th17/Treg-axis in fibrotic diseases. Moreover, it compares current evidences described in PD animal experimental models, indicating a loss of Th17/Treg balance (Th17 predominance) leading to peritoneal damage during PD. In addition, considering the new clinical and animal experimental data, new therapeutic strategies to reduce the Th17 response and increase the regulatory T response are proposed. Thus, future goals should be to develop new clinical biomarkers to reverse this immune misbalance and reduce peritoneal fibrosis in PD.

Designing drugs that combat kidney damage

INTRODUCTION

Kidney disease remains one of the last worldwide frontiers in the field of non-communicable human disease. From 1990 to 2013, chronic kidney disease (CKD) was the top non-communicable cause of death with a greatest increase in global years of life lost while mortality of acute kidney injury (AKI) still hovers around 50%. This reflects the paucity (for CKD) or lack of (for AKI) therapeutic approaches beyond replacing renal function. Understanding what the barriers are and what potential pathways may facilitate the design of new drugs to combat kidney disease is a key public health priority.

AREAS COVERED

The authors discuss the hurdles and opportunities for future drug development for kidney disease in light of experience accumulated with drugs that made it to clinical trials.

EXPERT OPINION

Inflammation, cell death and fibrosis are key therapeutic targets to combat kidney damage. While the specific targeting of drugs to kidney cells would be desirable, the technology is only working at the preclinical stage and with mixed success. Nanomedicines hold promise in this respect. Most drugs undergoing clinical trials for kidney disease have been repurposed from other indications. Currently, the chemokine receptor inhibitor CCX140 holds promise for CKD and the p53 inhibitor QPI-1002 for AKI.

Association between the IL17RA rs4819554 polymorphism and reduced renal filtration rate in the Spanish RENASTUR cohort

DNA variants at the genes that encode components of the IL17-pathway may contribute to the risk of impaired renal function/chronic kidney disease. Our aim was to determine whether common IL17RA single nucleotide polymorphisms (SNPs) were associated with a reduced estimated glomerular filtration rate (eGFR) in a cohort of healthy elderly individuals (n=650). We found a significantly higher frequency of SNP rs4819554 AA homozygotes among individuals with eGFR<60 ml/min/1.73 m(2) (n=90) (p=0.005, OR=2.11; 1.26-3.54), an effect that was independent of the presence of type 2 diabetes. Allele rs4819554 A had been associated to the risk of developing end stage renal disease, and was also linked to an increased expression of the IL17RA protein and higher levels of Th17 cell subsets. A scenario in which the pro-inflammatory role of the IL17-pathway contributes to kidney damage might explain the association between Il17RA polymorphisms and an impaired renal function.

The C-terminal module IV of connective tissue growth factor, through EGFR/Nox1 signaling, activates the NF-κB pathway and proinflammatory factors in vascular smooth muscle cells

AIMS

Connective tissue growth factor (CTGF/CCN2) is a developmental gene upregulated in pathological conditions, including cardiovascular diseases, whose product is a matricellular protein that can be degraded to biologically active fragments. Among them, the C-terminal module IV [CCN2(IV)] regulates many cellular functions, but there are no data about redox process. Therefore, we investigated whether CCN2(IV) through redox signaling regulates vascular responses.

RESULTS

CCN2(IV) increased superoxide anion (O2(•-)) production in murine aorta (ex vivo and in vivo) and in cultured vascular smooth muscle cells (VSMCs). In isolated murine aorta, CCN2(IV), via O2(•-), increased phenylephrine-induced vascular contraction. CCN2(IV) in vivo regulated several redox-related processes in mice aorta, including increased nonphagocytic NAD(P)H oxidases (Nox)1 activity, protein nitrosylation, endothelial dysfunction, and activation of the nuclear factor-κB (NF-κB) pathway and its related proinflammatory factors. The role of Nox1 in CCN2(IV)-mediated vascular responses in vivo was investigated by gene silencing. The administration of a Nox1 morpholino diminished aortic O2(•-) production, endothelial dysfunction, NF-κB activation, and overexpression of proinflammatory genes in CCN2(IV)-injected mice. The link CCN2(IV)/Nox1/NF-κB/inflammation was confirmed in cultured VSMCs. Epidermal growth factor receptor (EGFR) is a known CCN2 receptor. In VSMCs, CCN2(IV) activates EGFR signaling. Moreover, EGFR kinase inhibition blocked vascular responses in CCN2(IV)-injected mice.

INNOVATION AND CONCLUSION

CCN2(IV) is a novel prooxidant factor that in VSMCs induces O2(•-) production via EGFR/Nox1 activation. Our in vivo data demonstrate that CCN2(IV) through EGFR/Nox1 signaling pathway induces endothelial dysfunction and activation of the NF-κB inflammatory pathway. Therefore, CCN2(IV) could be considered a potential therapeutic target for redox-related cardiovascular diseases.

Potential Renoprotective Agents through Inhibiting CTGF/CCN2 in Diabetic Nephropathy

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease (ESRD). The development and progression of DN might involve multiple factors. Connective tissue growth factor (CCN2, originally known as CTGF) is the one which plays a pivotal role. Therefore, increasing attention is being paid to CCN2 as a potential therapeutic target for DN. Up to date, there are also many drugs or agents which have been shown for their protective effects against DN via different mechanisms. In this review, we only focus on the potential renoprotective therapeutic agents which can specifically abolish CCN2 expression or nonspecifically inhibit CCN2 expression for retarding the development and progression of DN.

Cellular and molecular actions of CCN2/CTGF and its role under physiological and pathological conditions

CCN family protein 2 (CCN2), also widely known as connective tissue growth factor (CTGF), is one of the founding members of the CCN family of matricellular proteins. Extensive investigation on CCN2 over decades has revealed the novel molecular action and functional properties of this unique signalling modulator. By its interaction with multiple molecular counterparts, CCN2 yields highly diverse and context-dependent biological outcomes in a variety of microenvironments. Nowadays, CCN2 is recognized to conduct the harmonized development of relevant tissues, such as cartilage and bone, in the skeletal system, by manipulating extracellular signalling molecules involved therein by acting as a hub through a web. However, on the other hand, CCN2 occasionally plays profound roles in major human biological disorders, including fibrosis and malignancies in major organs and tissues, by modulating the actions of key molecules involved in these clinical entities. In this review, the physiological and pathological roles of this unique protein are comprehensively summarized from a molecular network-based viewpoint of CCN2 functionalities.

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and kidney disease

PURPOSE OF REVIEW

The tumor necrosis factor-like weak inducer of apoptosis (TWEAK) cytokine has been linked to kidney injury by functional studies in experimental animals, and has biomarker potential in kidney disease.

RECENT FINDINGS

TWEAK was known to promote tubular cell injury and kidney inflammation. Recent studies have expanded these observations, identifying additional targets of TWEAK relevant to kidney injury. Thus, TWEAK upregulates the chemokine and cholesterol scavenger receptor CXCL16 and downregulates the antiaging and antifibrotic molecule Klotho in tubular cells. Furthermore, fibrogenic TWEAK actions on renal fibroblasts were described. TWEAK or factor-inducible molecule 14 targeting decreased the kidney fibrosis resulting from immune and nonimmune kidney injury induced by transient tubular or glomerular insults or by persistent urinary tract obstruction. TWEAK might also contribute to the link between chronic kidney disease and kidney cancer, as suggested by its role in other genitourinary cancers. Progress has also been made in TWEAK targeting. A phase I clinical trial showed that TWEAK targeting is well tolerated in humans, and an ongoing trial is exploring efficacy in lupus nephritis. Nanomolecules and inhibitors of epidermal growth factor receptor pathway may also protect from the adverse effects of TWEAK in the kidney.

SUMMARY

These findings suggest that TWEAK targeting has clinical potential in kidney injury of immune and nonimmune origin.

IL-17A is a novel player in dialysis-induced peritoneal damage

The classical view of the immune system has changed by the discovery of novel T-helper (Th) subsets, including Th17 (IL-17A-producing cells). IL-17A participates in immune-mediated glomerulonephritis and more recently in inflammatory pathologies, including experimental renal injury. Peritoneal dialysis patients present chronic inflammation and Th1/Th2 imbalance, but the role of the Th17 response in peritoneal membrane damage has not been investigated. In peritoneal biopsies from dialyzed patients, IL-17A immunostaining was found mainly in inflammatory areas and was absent in the healthy peritoneum. IL-17A-expressing cells included lymphocytes (CD4+ and γδ), neutrophils, and mast cells. Elevated IL-17A effluent concentrations were found in long-term peritoneal dialysis patients. Studies in mice showed that repeated exposure to recombinant IL-17A caused peritoneal inflammation and fibrosis. Moreover, chronic exposure to dialysis fluids resulted in a peritoneal Th17 response, including elevated IL-17A gene and protein production, submesothelial cell infiltration of IL-17A-expressing cells, and upregulation of Th17 differentiation factors and cytokines. IL-17A neutralization diminished experimental peritoneal inflammation and fibrosis caused by chronic exposure to dialysis fluids in mice. Thus, IL-17A is a key player of peritoneum damage and it may be a good candidate for therapeutic intervention in peritoneal dialysis patients.