C3aR contributes to unilateral ureteral obstruction-induced renal interstitial fibrosis via the activation of the NLRP3 inflammasome

Balancing efficacy and safety of complement inhibitors

Complement inhibitors have been approved for several immune-mediated diseases and they are considered the next paradigm-shifting approach in the treatment of glomerulonephritis. The hierarchical organization of the complement system offers numerous molecular targets for therapeutic intervention. However, complement is an integral element of host defense and therefore complement inhibition can be associated with serious infectious complications. Here we give a closer look to the hierarchical complement system and how interfering with proximal versus distal or selective versus unselective molecular targets could determine efficacy and safety. Furthermore, we propose to consider the type of disease, immunological activity, and patient immunocompetence when stratifying patients, e.g., proximal/unselective targets for highly active and potentially fatal diseases while distal and selective targets may suit more chronic disease conditions with low or moderate disease activity requiring persistent complement blockade in patients with concomitant immunodeficiency. Certainly, there exists substantial promise for anti-complement therapeutics. However, balancing efficacy and safety will be key to establish powerful treatment effects with minimal adverse events, especially when complement blockade is continued over longer periods of time in chronic disorders.

Cichoric acid improves isoproterenol-induced myocardial fibrosis via inhibition of HK1/NLRP3 inflammasome-mediated signaling pathways by reducing oxidative stress, inflammation, and apoptosis

Cichoric acid (CA), a natural phenolic compound found in many plants, has been reported to have antioxidant, anti-inflammatory, hypoglycemic, and other effects. The aim of this study was to determine the potential role and underlying mechanisms of CA in isoproterenol (ISO)-induced myocardial fibrosis (MF). The MF model was induced by subcutaneous ISO injection in mice. Blood and heart tissue were collected for examination. Hematoxylin and eosin staining and Masson's trichrome staining were used to evaluate the histopathological changes and collagen deposition. The production of reactive oxygen species markers was observed by fluorescence microscopy, the degree of cardiomyocyte microstructure injury was observed by transmission electron microscope, and oxidative stress factors were detected by kit method, and the effect of CA on inflammatory factors was detected by ELISA. The expression levels of collagen proteins and signaling pathways were further investigated by western blotting. The results showed that CA inhibited the expression of ISO-induced proinflammatory factors (TNF-α, IL-1β, and IL-18) and proteins (HK1, NLRP3, caspase-1, cleaved-caspase-1, and ASC), and regulated the expression of apoptotic factors (caspase-3, cleaved-caspase-3, Bax, and Bcl-2). The results indicated that CA may regulate the HK1/NLRP3 inflammasome pathway by inhibiting HK1 expression and play a protective role in MF.

C3a/C3aR synergies with TGF-β to promote epithelial-mesenchymal transition of renal tubular epithelial cells via the activation of the NLRP3 inflammasome

BACKGROUND

Complement component 3a and its receptor (C3a/C3aR) and the nucleotide-binding oligomerization domain-like receptor protein-3 (NLRP3) inflammasome contribute to epithelial-mesenchymal transition (EMT). However, the relationship between C3a/C3aR and the NLRP3 inflammasome in EMT remains unclear. This study aimed to elucidate the roles of C3a/C3aR and the NLRP3 inflammasome involved in TGF-β-induced EMT.

METHOD

Mouse renal tubular epithelial cells (TCMK-1) were exposed to C3a and TGF-β for 48 h. C3aR antagonist, MCC950, an inhibitor of the NLRP3 inflammasome and PD98059, an inhibitor of ERK signaling, were respectively applied to pretreat the cells at 30 min before C3a and TGF-β administration.The cells were collected for western blot, immunofluorescence staining and ELISA. Unilateral ureteral obstruction (UUO) models were established using male C57BL/6 wild-type (WT) mice and age-matched C3aR-deficient mice. MCC950 was intraperitoneally injected in UUO mice. Kidney samples were collected for immunohistochemistry staining.

RESULTS

In vitro, C3a synergized with TGF-β to promote EMT and the activation of the NLRP3 inflammasome. Inhibition of C3aR attenuated EMT and the activation of the NLRP3 inflammasome. Inhibition of the NLRP3 inflammasome alleviated EMT but didn't affect the expression of C3aR. Inhibition of ERK signaling inhibited the activation of the NLRP3 inflammasome. In vivo, the expression of IL-1β was significantly higher in UUO mice compared to the sham-operated mice. C3aR deficiency and inhibition of the NLRP3 Inflammasome contributed to decreased IL-1β in UUO mice.

CONCLUSION

Our data revealed that C3a/C3aR synergies with TGF-β to activate the NLRP3 inflammasome to promote epithelial-mesenchymal transition of renal tubular epithelial cells through ERK signaling, and the way in which C3aR activates the inflammasome is to promote the assembly of the NLRP3 inflammasome.

SPARC-YAP/TAZ inhibition prevents the fibroblasts-myofibroblast transformation

BACKGROUND

Fibrotic scar is a severe side effect of trabeculectomy, resulting in unsatisfactory outcomes for glaucoma surgery. Accumulating evidence showed human Tenon's fibroblasts (HTFs) play an important role in fibrosis formation. We previously reported that the aqueous level of secreted protein acidic and rich in cysteine (SPARC) was higher in the patients with primary angle closure glaucoma, which was associated with the failure of trabeculectomy. In this study, the potential effect and mechanism of SPARC in promoting fibrosis were explored by using HTFs.

METHODS

HTFs were employed in this study and examined under a phase-contrast microscope. Cell viability was determined by CCK-8. The expressions of SPARC-YAP/TAZ signaling and the fibrosis-related markers were examined with reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR), Western blot, and immunofluorescence, subcellular fractionation was conducted to further determined the variation of YAP and phosphorylated YAP. The differential gene expressions were analyzed with RNA sequencing (RNAseq), followed by Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses.

RESULTS

Exogenous SPARC induced HTFs-myofibroblast transformation, as evidenced by the increased expression of α-SMA, collagen I and fibronectin in both protein and mRNA levels. SPARC knockdown decreased the expressions of the above genes in TGF-β2-treated HTFs. KEGG analysis showed that the Hippo signaling pathway was mostly enriched. SPARC treatment increased the expressions of YAP, TAZ, CTGF and CYR61 as well as enhanced YAP translocation from cytoplasm to nucleus, and decreased the phosphorylation of YAP and LAST1/2, which was reversed by SPARC knockdown. Knockdown of YAP1 decreased the fibrosis-related markers, such as α-SMA, collagen I and Fibronectin, in SPARC-treated HTFs.

CONCLUSIONS

SPARC induced HTFs-myofibroblast transformation via activating YAP/TAZ signaling. Targeting SPARC-YAP/TAZ axis in HTFs might provide a novel strategy for inhibiting fibrosis formation after trabeculectomy.

An MRTF-A-ZEB1-IRF9 axis contributes to fibroblast-myofibroblast transition and renal fibrosis

Myofibroblasts, characterized by the expression of the matricellular protein periostin (Postn), mediate the profibrogenic response during tissue repair and remodeling. Previous studies have demonstrated that systemic deficiency in myocardin-related transcription factor A (MRTF-A) attenuates renal fibrosis in mice. In the present study, we investigated the myofibroblast-specific role of MRTF-A in renal fibrosis and the underlying mechanism. We report that myofibroblast-specific deletion of MRTF-A, achieved through crossbreeding Mrtfa-flox mice with Postn-Cre^ERT2 mice, led to amelioration of renal fibrosis. RNA-seq identified zinc finger E-Box binding homeobox 1 (Zeb1) as a downstream target of MRTF-A in renal fibroblasts. MRTF-A interacts with TEA domain transcription factor 1 (TEAD1) to bind to the Zeb1 promoter and activate Zeb1 transcription. Zeb1 knockdown retarded the fibroblast-myofibroblast transition (FMyT) in vitro and dampened renal fibrosis in mice. Transcriptomic assays showed that Zeb1 might contribute to FMyT by repressing the transcription of interferon regulatory factor 9 (IRF9). IRF9 knockdown overcame the effect of Zeb1 depletion and promoted FMyT, whereas IRF9 overexpression antagonized TGF-β-induced FMyT. In conclusion, our data unveil a novel MRTF-A-Zeb1-IRF9 axis that can potentially contribute to fibroblast-myofibroblast transition and renal fibrosis. Screening for small-molecule compounds that target this axis may yield therapeutic options for the mollification of renal fibrosis.

Aristolocholic acid I promotes renal tubular epithelial fibrosis by upregulating matrix metalloproteinase-9 expression via activating the C3a/C3aR axis of macrophages

Aristolochic acid I (AAI) can cause nephrotoxicity and is characterized by interstitial fibrosis. The C3a/C3aR axis of macrophages and matrix metalloproteinase-9 (MMP-9) play important roles in fibrosis, but whether they are involved in AAI-induced renal interstitial fibrosis and are related remains to be elucidated. In this study, we investigated whether C3a/C3aR axis of macrophages promotes renal interstitial fibrosis by regulating MMP-9 in aristolochic acid nephropathy (AAN). Intraperitoneal injection of AAI for 28 days successfully induced AAN in C57bl/6 mice. The content of C3a in the kidney of AAN mice was increased, and there was a significant distribution of macrophages in the renal tubules. The same results were observed in the in vitro experiment. We also explored the role and mechanism of macrophages after AAI administration in the epithelial-mesenchymal transformation (EMT) of renal tubular epithelial cells (RTECs) and found that AAI could activate the C3a/C3aR axis of macrophages to upregulate p65 expression in macrophages. p65 upregulated MMP-9 expression in macrophages not only directly but also by promoting the secretion if interleukin-6 by macrophages and then activating STAT3 in RTECs. The upregulation of MMP-9 expression could promote the EMT of RTECs. Taken together, our study demonstrated that the AAI-activated the C3a/C3aR axis of macrophages, which induced MMP-9 production, was one of the causes of renal interstitial fibrosis. Therefore, targeting the C3a/C3aR axis of macrophages is an effective therapeutic strategy for the prevention and treatment of renal interstitial fibrosis in AAN.