Gremlin regulates renal inflammation via the vascular endothelial growth factor receptor 2 pathway

Inflammation is a main feature of progressive kidney disease. Gremlin binds to bone morphogenetic proteins (BMPs), acting as an antagonist and regulating nephrogenesis and fibrosis among other processes. Gremlin also binds to vascular endothelial growth factor receptor‐2 (VEGFR2) in endothelial cells to induce angiogenesis. In renal cells, gremlin regulates proliferation and fibrosis, but there are no data about inflammatory‐related events. We have investigated the direct effects of gremlin in the kidney, evaluating whether VEGFR2 is a functional gremlin receptor. Administration of recombinant gremlin to murine kidneys induced rapid and sustained activation of VEGFR2 signalling, located in proximal tubular epithelial cells. Gremlin bound to VEGFR2 in these cells in vitro, activating this signalling pathway independently of its action as an antagonist of BMPs. In vivo, gremlin caused early renal damage, characterized by activation of the nuclear factor (NF)‐κB pathway linked to up‐regulation of pro‐inflammatory factors and infiltration of immune inflammatory cells. VEGFR2 blockade diminished gremlin‐induced renal inflammatory responses. The link between gremlin/VEGFR2 and NF‐κB/inflammation was confirmed in vitro. Gremlin overexpression was associated with VEGFR2 activation in human renal disease and in the unilateral ureteral obstruction experimental model, where VEGFR2 kinase inhibition diminished renal inflammation. Our data show that a gremlin/VEGFR2 axis participates in renal inflammation and could be a novel target for kidney disease. Copyright © 2015 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Connective tissue growth factor and cardiac fibrosis

Cardiac fibrosis is a major pathogenic factor in a variety of cardiovascular diseases and refers to an excessive deposition of extracellular matrix components in the heart, which leads to cardiac dysfunction and eventually overt heart failure. Evidence is accumulating for a crucial role of connective tissue growth factor (CTGF) in fibrotic processes in several tissues including the heart. CTGF orchestrates the actions of important local factors evoking cardiac fibrosis. The central role of CTGF as a matricellular protein modulating the fibrotic process in cardiac remodelling makes it a possible biomarker for cardiac fibrosis and a potential candidate for therapeutic intervention to mitigate fibrosis in the heart.     

DC‐SIGN reacts with TLR‐4 and regulates inflammatory cytokine expression via NF‐κB activation in renal tubular epithelial cells during acute renal injury

In the pathological process of acute kidney injury (AKI), innate immune receptors are essential in inflammatory response modulation; however, the precise molecular mechanisms are still unclear. Our study sought to demonstrate the inflammatory response mechanisms in renal tubular epithelial cells via Toll‐like receptor‐4 (TLR‐4) and dendritic cell‐specific intercellular adhesion molecule 3‐grabbing non‐integrin 1 (DC‐SIGN) signalling. We found that DC‐SIGN exhibited strong expression in renal tubular epithelial cells of human acute renal injury tissues. DC‐SIGN protein expression was increased significantly when renal tubular epithelial cells were exposed to lipopolysaccharide (LPS) for a short period. Furthermore, DC‐SIGN was involved in the activation of p65 by TLR‐4, which excluded p38 and c‐Jun N‐terminal kinases (JNK). Interleukin (IL)‐6 and tumour necrosis factor (TNF)‐α expression was decreased after DC‐SIGN knock‐down, and LPS induced endogenous interactions and plasma membrane co‐expression between TLR‐4 and DC‐SIGN. These results show that DC‐SIGN and TLR‐4 interactions regulate inflammatory responses in renal tubular epithelial cells and participate in AKI pathogenesis.     

TWEAK transactivation of the epidermal growth factor receptor mediates renal inflammation

TWEAK, a member of the TNF superfamily, binds to the Fn14 receptor, eliciting biological responses. EGFR signalling is involved in experimental renal injury. Our aim was to investigate the relationship between TWEAK and EGFR in the kidney. Systemic TWEAK administration into C57BL/6 mice increased renal EGFR phosphorylation, mainly in tubular epithelial cells. In vitro, in these cells TWEAK phosphorylated EGFR via Fn14 binding, ADAM17 activation and subsequent release of the EGFR ligands HB‐EGF and TGFα. In vivo the EGFR kinase inhibitor Erlotinib inhibited TWEAK‐induced renal EGFR activation and downstream signalling, including ERK activation, up‐regulation of proinflammatory factors and inflammatory cell infiltration. Moreover, the ADAM17 inhibitor WTACE‐2 also prevented those TWEAK‐induced renal effects. In vitro TWEAK induction of proinflammatory factors was prevented by EGFR, ERK or ADAM17 inhibition. In contrast, EGFR transactivation did not modify TWEAK‐mediated NF‐κB activation. Our data suggest that TWEAK transactivates EGFR in the kidney, leading to modulation of downstream effects, including ERK activation and inflammation, and suggest that inhibition of EGFR signalling could be a novel therapeutic tool for renal inflammation. Copyright © 2013 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

B cell activation regulates exosomal HLA production

Exosomes are nanovesicles produced constitutively and inducibly by several types of cells. They are generated as intraluminal vesicles of multivesicular bodies and express MHC and several endosomal/lysosomal proteins. In spite of their potential role in cellular immunity, the regulatory mechanisms of exosome production are largely unknown. In this study, we have established a novel ELISA system to quantify exosomal HLA using a combination of anti-HLA class I and anti-HLA-DR mAb. We found that exosomal HLA production of B cells was enhanced by contact with CD4(+) T cells. Neutralizing anti-CD154 (CD40L) mAb inhibited this effect, and a soluble CD40L significantly increased production of exosomal HLA in B cells. In addition, B cell stimulation via BCR and TLR9 enhanced their production while IL-4 stimulation alone failed to do so. Strikingly, an inhibitor of the classical NF-kappaB pathway drastically inhibited exosomal HLA production in stimulated B cells, indicating that the classical NF-kappaB pathway is critical for exosomal HLA production in B cells. Together, these findings suggest a pivotal role of B cell activation in exosomal HLA production in vivo.     

Bacteroides fragilis enterotoxin induces cyclooxygenase-2 and fluid secretion in intestinal epithelial cells through NF-kappaB activation

Bacteroides fragilis produces an approximately 20-kDa heat-labile toxin (B. fragilis enterotoxin, BFT) which is known to be associated with diarrhea. To determine whether cyclooxygenase (COX)-2, via NF-kappaB activation, can contribute to BFT-induced diarrhea, the relationship between COX-2 expression and fluid secretion in BFT-stimulated human intestinal epithelial cells was examined. BFT stimulation increased the expression of COX-2, but not COX-1, in human intestinal epithelial cells. Suppression of the NF-kappaB signal significantly decreased COX-2 expression in response to BFT stimulation. Prostaglandin E2 (PGE2) levels were increased in parallel with COX-2 expression, and, conversely, PGE2 production was significantly inhibited when COX-2 or NF-kappaB activities were suppressed using COX-2 small interfering RNA (siRNA), p65 NF-kappaB subunit siRNA, or a retrovirus encoding the IkappaBalpha superrepressor. In addition, a selective COX-2 inhibitor, NS-398, significantly inhibited the increased cAMP level induced by BFT stimulation. Furthermore, a selective COX-2 inhibitor prevented BFT-induced PGE2 production and ileal fluid secretion in a mouse ileal loop model. These results suggest that the secretory response to BFT stimulation may be mediated by the production of PGE2, through NF-kappaB activation and the up-regulation of COX-2 in intestinal epithelial cells.     

BMP-7 attenuates liver fibrosis via regulation of epidermal growth factor receptor

The aim of this study was to elucidate the effect of bone morphogenetic protein-7 (BMP-7) on liver fibrosis induced by carbon tetrachloride (CCl4) in vivo and on the hepatic stellate cells (HSC) activation in vitro. In vivo, thirty male ICR mice were randomly allocated to three groups, the control group (n = 6), the CCl4 group (n = 18) and the BMP-7+CCl4 group (n = 6). The model of liver fibrosis was induced by intraperitoneal injection with CCl4 three times per week lasting for 12 weeks in CCl4 group and the BMP-7+CCl4 group. After 8 weeks injection with CCl4, mice were intraperitoneal injected with human recombinant BMP-7 in BMP-7+CCl4 group. Meanwhile, mice in the CCl4 group were only intraperitoneal injection with equal amount of saline. The degree of liver fibrosis was assessed by HE and Masson’s staining. PCR and western blot were used to detect mRNA and protein levels. In BMP-7+CCl4 group, serum levels of alanine aminotransferase (ALT) and aminotransferase (AST) were decreased and serum albumin (Alb) was increased. Meanwhile, the expressions of transforming growth factor-β1 (TGF-β1) and α-smooth muscle actin (α-SMA) were down-regulated by BMP-7 intervention as compared to the CCl4 group (P < 0.05). Furthermore, BMP-7 also suppressed the expression of epidermal growth factor receptor (EGFR) and phosphorylated-epidermal growth factor receptor (pEGFR). HE and Masson stain showed that liver damage was alleviated in BMP-7+CCl4 group. In vitro study, expression of EGFR, TGF-β1 and α-SMA were down regulated by BMP-7 dose-dependently, indicating it might effect on suppression of HSC activation. Therefore, our data indicate BMP-7 was capable of inhibiting liver fibrosis and suppressing HSCs activation, and these effects might rely on its crosstalk with EGFR and TGF-β1. We suggest that BMP-7 may be a potential reagentfor the prevention and treatment of liver fibrosis.     

Anti‐Inflammatory and Neuroprotective Effects of Triptolide via the NF‐κB Signaling Pathway in a Rat MCAO Model

Stroke is the leading cause of neurological disability in humans. Middle cerebral artery occlusion (MCAO) followed by reperfusion is widely accepted to mimic stroke in basic medical research. Triptolide is one of the major active components of the traditional Chinese herb Tripterygium wilfordii Hook F, and has been reported to have potent anti‐inflammatory and immunosuppressive properties. Since its preclinical effects on stroke were still unclear, we decided to study the effects of Triptolide on focal cerebral ischemia/reperfusion injury in this study. The results showed that Triptolide treatment significantly attenuates brain infarction volume, water content, neurological deficits, and neuronal cell death rate, which were increased in the MCAO model rats. Immunohistochemistry was used to analyze the expression of glial fibrillary acidic protein (GFAP), Cyclooxygenase‐2 (COX‐2), inducible nitric oxide (iNOS), and NF‐κB in the ischemic brains. The administration of Triptolide showed down‐regulation of the iNOS, COX‐2, GFAP, and NF‐κB expression in MCAO rats. It also increased the expression of bcl‐2, and suppressed levels of bax and caspase‐3 compared with the MCAO group. Our findings revealed that Triptolide exerts its neuroprotective effects against inflammation with the involvement of inhibition of NF‐κB activation. Anat Rec, 299:256–266, 2016. © 2015 Wiley Periodicals, Inc.     

Switching on the Aire conditioner

Aire has been cloned as the gene responsible for a hereditary type of organ‐specific autoimmune disease. Aire controls the expression of a wide array of tissue‐restricted Ags by medullary thymic epithelial cells (mTECs), thereby leading to clonal deletion and Treg‐cell production, and ultimately to the establishment of self‐tolerance. However, relatively little is known about the mechanism responsible for the control of Aire expression itself. In this issue of the European Journal of Immunology, Haljasorg et al. [Eur. J. Immunol. 2015. 45: 3246–3256] have reported the presence of an enhancer element for Aire that binds with NF‐κB components downstream of the TNF receptor family member, RANK (receptor activator of NF‐κB). The results suggest that RANK has a dual mode of action in Aire expression: one involving the promotion of mTEC differentiation and the other involving activation of the molecular switch for Aire within mature mTECs.     

Human mesenchymal stromal cells modulate T‐cell responses through TNF‐α‐mediated activation of NF‐κB

Although mesenchymal stromal cells (MSCs) possess the capacity to modulate immune responses, little is known about the mechanisms that underpin these processes. In this study, we show that immunosupression is mediated by activation of nuclear factor kappa B (NF‐κB) in human MSCs. This pathway is activated by TNF‐α that is generated following TCR stimulation of T cells. Inhibition of NF‐κB through silencing of IκB kinase β or the TNF‐α receptor abolishes the immunosuppressive capacity of MSCs. Our data also indicate that MSC‐associated NF‐κB activation primarily leads to inhibition of T‐cell proliferation with little effect on expression of the activation markers CD69 and CD25. Thus, our data support the hypothesis that the TNF‐α/NF‐κB signalling pathway is required for the initial priming of immunosuppressive function in human MSCs. Interestingly, drugs that interfere with NF‐κB activation significantly antagonise the immunoregulatory effect of MSCs, which could have important implications for immunosuppression regimens in the clinic.