Provisional Matrix Citrullination Contributes to Enhanced Fibroblast Migration

Abstract

Activated fibroblasts—characterized by various altered behaviors including invasiveness, altered protein secretion profiles, and resistance to apoptosis—contribute to the development and exacerbation of numerous chronic human inflammatory diseases including cancer, rheumatoid arthritis, and interstitial lung disease. Citrullination, a post-translational protein modification known to occur extensively in inflammatory environments, alters the provisional extracellular matrix (ECM) and key arginine-containing cell-binding sites therein. We hypothesize that citrullination alters fibroblast interactions with provisional ECM such that adhesion is reduced and related downstream functions such as motility and contraction are also altered. Results have thus far indicated that provisional matrix citrullination does contribute, solely or in part, to several characteristics of activated fibroblasts. Adhesion assays, whereby human foreskin fibroblasts (HFFs) were allowed to attach to modified or normal provisional ECM and subsequently challenged with shear forces, suggest that citrullination significantly decreases fibroblast attachment and spreading. Blocking experiments have shown that these effects appear to be mediated, in part, by both RGD and αvβ3 integrin interactions. Despite this decreased adhesion, in vitro random migration and wound healing assays have paradoxically demonstrated the ability of citrullinated provisional ECM to significantly enhance fibroblast migration rates, indicating that adhesion differences alone do not fully explain differences in citrullination-mediated cell motility. This research will ultimately provide insight for understanding a fundamental pathway linking citrullination of provisional ECM proteins with fibroblast activation. It therefore constitutes an important step in the development of novel treatments to both prevent and ameliorate a panoply of human diseases, many of which currently have inadequate or nonexistent therapeutic solutions.