Cellular origins and molecular mechanisms of arthrofibrosis

University Of Southern California, Los Angeles CA

Investigators

Abstract

ABSTRACT Arthrofibrosis is a debilitating fibrotic joint disorder, which causes excessive scar tissue formation within the joint and surrounding soft tissues after injury and/or surgery leading to painful restriction of joint flexion and extension that persists despite rehabilitation. Damage to the joint resulting in chronic inflammation activates proliferation and differentiation of progenitor cells, also known as fibro-adipogenic progenitors, into highly specialized pro- fibrotic cells that deposit excessive amounts of disorganized collagen causing contraction. Estimated rates of arthrofibrosis induced by knee surgery, such as anterior cruciate ligament reconstruction or total knee arthroplasty, affects a significant number of suffering patients with prevalence ranging from 12%-35%. Unfortunately, there is a significant gap in knowledge of the molecular and cellular biology and pathophysiology of arthrofibrosis, which limits mechanism-based therapies. Thus, to date, there is no available non-surgical, non- invasive treatments to prevent or cure arthrofibrosis and management only includes treating the symptoms and not the underlying cause. Pathogenesis of organ fibrosis is mediated by the aberrant activity of pro-inflammatory, pro-fibrotic cytokines, including IL-6 family that signal through gp130 transmembrane protein. Alas, specific cellular and molecular mechanisms that trigger fibrotic processes and responses downstream of gp130 remain elusive. Our previously published data demonstrates that manipulation of gp130 signaling upstream prevents fibrosis development after joint injury rats in vivo. In our recent study, we have identified a signaling residue within gp130 receptor that is responsible for triggering inflammatory and fibrotic responses in the joint and other tissues in vitro and in vivo. The study also suggests that fibrotic outcomes are induced by a gp130-mediated arginine metabolism and hence, the current grant application is designed to investigate the significance of this circuit in arthrofibrosis. To illuminate on this mechanism in depth, we will employ several new genetic mouse lines to ablate central players in arginase metabolism including Arg2, Odc1 genes in fibrogenic cells in a murine model of arthrofibrosis. First, we will investigate whether polyamine production by ARG2/ODC1 enzymes, which catalyze abnormal ECM synthesis upon tissue injury, can promote knee arthrofibrosis after post-traumatic joint injury in vivo. In parallel, we will employ our generated CRISPR/Cas9 mutant mouse with a point mutation in gp130 intracellular domain to test whether local delivery of polyamines to the knee will lead to arthrofibrosis in the injured mice. Furthermore, we will assess the contribution of different progenitor populations to arthrofibrosis in mice, and lastly, will elucidate whether the mechanism of gp130-induced fibrosis is conserved in human fibroprogenitors. The experiments in this proposal are designed to define the role of the arginine metabolism downstream of gp130 and determine whether genetic modulation of this mechanism can prevent or halt fibrosis progression in vivo after injury.