#4392 TWEAK/FN14 SYSTEM IS INVOLVED IN RHABDOMYOLYSIS-INDUCED ACUTE KIDNEY INJURY

Abstract

Abstract Background and Aims Rhabdomyolysis is a pathological syndrome associated with massive and severe skeletal muscle injury. A common complication of rhabdomyolysis is acute kidney injury (AKI), a process that increases mortality of these patients. In rhabdomyolysis, myoglobin (Mb) is released from muscle cells and subsequently absorbed by the renal tubular epithelium causing a series of deleterious effects. TWEAK/Fn14 axis regulates renal inflammation and tubular cell death, pathogenic mechanisms involved in AKI. However, the role of this pathway in rhabdomyolysis-AKI has not been previously analyzed. In this study we analyzed the role of TWEAK/Fn14 axis in AKI associated with rhabdomyolysis and the AKI to chronic kidney disease (CKD) transition. Method We performed an experimental model of AKI associated to rhabdomyolysis by the intramuscular injection of 50% glycerol (10mg/Kg of weight) in Wild Type C57BL/6 (WT), TWEAK deficient (TWEAK -/-) and Fn14 deficient (Fn14 -/-) mice (male, 12 weeks old). In another set of experiments, C57BL/6 mice were intraperitoneally injected with anti-TWEAK mAb (10 mg/kg) or irrelevant isotype control IgG (10 mg/kg) every 48 hours. Blood and renal samples were taken 3 and 6 hours or 1, 3, 7 and 30 days after glycerol administration to perform gene expression studies by Real Time-PCR, immunohistochemistry analysis, protein expression studies by Western Blot and cell death assays (TUNEL). In vitro studies in murine tubular cells (MCTs) were also conducted to determine the effects of Mb on TWEAK/Fn14 expression, and the intracellular pathways involved in Mb-mediated regulation of TWEAK/Fn14 system. Results Fn14 renal expression was increased at earlier stages of rhabdomyolysis, correlating with decline of renal function. In MCTs cells, Mb induced Fn14 expression in a time- and dose-dependent manner, whereas TWEAK expression remained unchanged. The use of general antioxidants (N-Acetylcysteine) or Nrf2 inducers (curcumin or Sulforaphane) reduced Mb-mediated Fn14 upregulation in vivo and in cultured renal cells, whereas the opposite effect was observed with the HO-1 inhibitor tin protoporphyrin IX (SnPP). Furthermore, MAPK p38 and ERK1/2 inhibitors, such as SB203580 and PD98059 respectively, diminished Mb effects on Fn14 expression. Moreover, Mb enhanced pro-inflammatory effects of TWEAK in vitro. In the animal model, we observed that genetic TWEAK or Fn14 deficiency ameliorated rhabdomyolysis-related loss of renal function, reduced histological damage, tubular cell death, lipid peroxidation, and decreased the expression of inflammatory mediators (Ccl2, Tnf, Il6, Tlr4 and Ccl5), tubular injury markers (Havcr1 and Lcn2) and endothelial dysfunction (Edn1 and Icam1). TWEAK or Fn14 knockout mice also showed decreased long-term renal fibrosis (Collagen content and Fn1 expression) and inflammation (F4/80 macrophage infiltration and Ccl2 expression) 30 days after rhabdomyolysis induction. Treatment with a blocking anti-TWEAK monoclonal antibody reduced expression of Lcn2 and cell death at early stages of rhabdomyolysis and decreased long-term consequences, mainly fibrosis and inflammation. Conclusion Our data suggest that TWEAK/Fn14 axis is involved in AKI-rhabdomyolysis, as well as in the transition from AKI to CKD. TWEAK/Fn14 may be a potential therapeutic target to decrease harmful effects of rhabdomyolysis.