Fibrillin-1 is a novel ligand of the epidermal growth factor receptor promoting mesangial cell activation and glomerulosclerosis.

Abstract

INTRODUCTION: Podocyte injury and mesangial activation are hallmarks of a wide variety of glomerular diseases. Although podocyte damage is thought to be an early event that causes subsequent mesangial activation, the mechanism connecting these two events remains poorly understood. Since the protein fibrillin-1 (FBN1) may be involved in glomerular injury in several kidney diseases, we tested whether FBN1 expression in injured podocytes trigger mesangial cell activation and proliferation. METHODS: FBN1 expression was assessed in various models of glomerular diseases. Mice with podocyte-specific knockout of FBN1 were generated to evaluate the role of FBN1 in glomerular disease. The interaction between FBN1 and epidermal growth factor receptor (EGFR) was studied by molecular docking, cellular thermal shift assay, and co-immunoprecipitation. RESULTS: Podocyte FBN1 was upregulated in various animal models of glomerular diseases and in patients with proteinuric kidney disorders. FBN1 stimulated mesangial cell activation and proliferation both in vitro and in glomerular mini-organ cultures. Overexpression of FBN1 promoted mesangial cell activation and aggravated glomerulosclerosis in Adriamycin (ADR) nephropathy. Conversely, podocyte-specific knockout of the FBN1 gene attenuated mesangial activation and glomerulosclerosis in mice with ADR nephropathy or streptozotocin-induced diabetes. RNA sequencing, molecular docking simulation and protein interactions analyses demonstrated that FBN1 could directly bind to EGFR in mesangial cells, which resulted in a sequential phosphorylation of EGFR, phosphoinositide 3-kinase (PI3K) and AKT kinase. Compared to EGF, FBN1 triggered a sustained activation of EGFR, PI3K and AKT in comparable doses, but not extracellular signal-regulated kinase-1 and -2. Pharmacologic inhibition of EGFR, PI3K or AKT abolished FBN1-induced mesangial cell activation in vitro. Furthermore, inhibition of EGFR activation by erlotinib ameliorated FBN1-induced mesangial activation and glomerulosclerosis in vivo. CONCLUSIONS: These findings illustrate that extracellular matrix protein FBN1 is a previously unrecognized ligand for EGFR and induces a sustained activation of EGFR/PI3K/AKT signaling, which leads to mesangial cell activation and glomerulosclerosis.