Fn14 Deficiency Ameliorates Anti-dsDNA IgG-Induced Glomerular Damage in SCID Mice

Emerging role of TWEAK-Fn14 axis in lupus, a disease related to autoimmunity and fibrosis

Systemic lupus erythematosus (SLE) is a chronic autoimmune disorder. Lupus nephritis (LN) is one of the severe clinical implications in SLE, and this was relates to fibrosis in the kidney. As an important marker in the tumor necrosis factor (TNF) superfamily, TNF-like weak inducer of apoptosis (TWEAK) has been given much attention with respect to its role in regulating pro-inflammatory immune response. Fibroblast growth factor-inducible 14 (Fn14), the sole receptor for TWEAK, has been found expressed in different immune and non-immune cells. TWEAK binds to Fn14, and then regulates inflammatory components production via downstream signaling pathways. To date, dysregulated expression of TWEAK, Fn14 has been reported in SLE, LN patients, and in vivo, in vitro studies have discussed the significant role of TWEAK-Fn14 axis in SLE, LN pathogenesis, partly through mediating the fibrosis process. In this review, we will discuss the association of TWEAK-Fn14 axis in lupus. Understanding the relationship will better realize the potential for making TWEAK-Fn14 as a marker for the diseases, and will help to give many clues for targeting them in treatment of lupus in the future.

Interruption of neutrophil extracellular traps formation dictates host defense and tubular HOXA5 stability to augment efficacy of anti-Fn14 therapy against septic AKI

The immunosuppressive, inflammatory microenvironment orchestrated by neutrophil extracellular traps (NETs) plays a principal role in pathogenesis of sepsis. Fibroblast growth factor-inducible molecule 14 (Fn14) has been established as a potential target for septic acute kidney injury (AKI), making further therapeutic benefits from combined NETs and Fn14 blockade possible. Methods: The concurrence of NETs and Fn14 in mice and patients with septic AKI were assessed by immunofluorescence, immunohistochemistry, enzyme-linked immunosorbent assay (ELISA) and in silico studies. Survival, histopathological and biochemical analyses of wild-type and PAD4-deficient CMV-Cre; PAD4 fl/fl mice with septic AKI were applied to evaluate the efficacy of either pharmacological or genetic NETs interruption in combination with Fn14 blockade. Molecular mechanisms underlying such effects were determined by CRISPR technology, fluorescence-activated cell sorter analysis (FACS), cycloheximide (CHX) pulse-chase, luciferase reporter and chromatin immunoprecipitation (ChIP) assay. Results: NETs formation is concurred with Fn14 upregulation in murine AKI models of abdominal, endotoxemic, multidrug-resistant sepsis as well as in serum samples of patients with septic AKI. Pharmacological or genetic interruption of NETs formation synergizes with ITEM-2, a monoclonal antibody (mAb) of Fn14, to prolong mice survival and provide renal protection against abdominal sepsis, the effects that could be abrogated by elimination of macrophages. Interrupting NETs formation predominantly perpetuates infiltration and survival of efferocytic growth arrest-specific protein 6+ (GAS6+) macrophages in combination with ITEM-2 therapy and enhances transcription of tubular cell-intrinsic Fn14 in a DNA methyltransferase 3a (DNMT3a)-independent manner through dismantling the proteasomes-mediated turnover of homeobox protein Hox-A5 (HOXA5) upon abdominal sepsis challenge or LPS stimuli. Pharmacological NETs interruption potentiates the anti-septic AKI efficacy of ITEM-2 in murine models of endotoxemic and multidrug-resistant sepsis. Conclusion: Our preclinical data propose that interrupting NETs formation in combination with Fn14 mAb might be a feasible therapeutic strategy for septic AKI.

MicroRNA-19a Targets Fibroblast Growth Factor-Inducible Molecule 14 and Prevents Tubular Damage in Septic AKI

Fibroblast growth factor-inducible molecule 14 (Fn14) plays a principal role in triggering tubular damage during septic acute kidney injury (AKI). Here, we explore the mechanism underlying Fn14 deregulation in septic AKI. We identify Fn14 as a bona fide target of miR-19a, which directly binds to 3′ UTR of Fn14 for repression independent of cylindromatosis (CYLD), the deubiquitinase (DUB) downstream of miR-19a, and thereby antagonizes the LPS-induced tubular cell apoptosis. Genetic ablation of Fn14, but not of CYLD, abolishes the ability of miR-19a to antagonize the tubular apoptosis by lipopolysaccharide (LPS). In mice, systemic delivery of miR-19a confers protection against septic AKI. Our findings implicate that miR-19a may serve as a promising therapeutic candidate in the prevention of septic AKI.

Fibroblast growth factor inducible 14 signaling facilitates anti-dsDNA IgG penetration into mesangial cells

Anti-double-stranded DNA (dsDNA) antibodies induce renal damage in patients with systemic lupus erythematosus by triggering fibrotic processes in kidney cells. However, the precise mechanism underlying penetration of anti-dsDNA immunoglubolin G (IgG) into cells remains unclear. This study was designed to investigate the effect of tumor necrosis factor-like weak inducer of apoptosis (TWEAK)/fibroblast growth factor inducible 14 (Fn14) signaling on anti-dsDNA IgG penetration into cells. Mesangial cells were cultured in vitro, and stimulated with TWEAK and anti-dsDNA IgG. The results revealed that TWEAK dose-dependently enhanced cellular internalization of anti-dsDNA IgG and the expression of high-mobility group box 1 (HMGB1). In addition, TWEAK and anti-dsDNA IgG synthetically downregulate suppressor of cytokine signaling 1, and induce the expression of various fibrotic factors. Furthermore, inhibition of HMGB1 attenuates the enhancement effect of TWEAK on anti-dsDNA IgG internalization. The TWEAK upregulation of HMGB1 involves the nuclear factor-κB and phosphatidylinositide 3-kinase/protein kinase B pathways. Therefore, TWEAK/Fn14 signaling contributes to the penetration of anti-dsDNA IgG and relevant fibrotic processes in mesangial cells.