Induction of collagenase and stromelysin gene expression by mechanical injury in a vascular smooth muscle‐derived cell line

Abstract

We describe a novel system for studying the production of matrix metalloproteinases types I and Ill (collagenase and stromelysin) by a vascular smooth muscle cell line (Rb‐1 cells) in response to mechanical injury. Highly confluent Rb‐1 cells are disrupted by passing a plastic comb around the plate to clear a series of circumferential paths, which are bordered by two ridges of displaced cells. Over the next 24 hours, cells migrate into the cleared areas. Northern blot analysis demonstrates the accumulation of mRNAs for collagenase and stromelysin during this process, although they are undetectable prior to injury. Cotreatment with all‐trans‐retinoic acid (10⁻6 M) markedly decreases the level of mRNAs induced by injury, whereas dexamethasone (10⁻7 M) causes only a slight reduction. In situ hybridization studies for stromelysin mRNA and immunohistochemical staining for collagenase protein on plates of injured cells showed the highest levels of stromelysin mRNA in cells in the ridges left by the injury; lower levels were observed in some cells migrating into the clear region. The same pattern of expression was observed when cells were stained with antiserum to collagenase protein. Nuclear run‐on assays demonstrated increases in transcription of stromelysin and collagenase genes following injury. Transient transfection of cells with a vector containing the luciferase gene driven by a wild‐type promoter comprising 1.8 kb of the 5′ flanking region of the rabbit collagenase gene showed increased activity associated with injury. We conclude that: (1) mechanical injury is associated with induction of mRNAs for the metalloproteinases collagenase and stromelysin, (2) retinoic acid effectively antagonizes this responses, and (3) the increase in steady state mRNA levels is, at least in part, transcriptionally mediated. Thus our data suggest a role for mechanical forces in initiating the changes in gene expression in vascular smooth muscle cells following arterial injury in vivo.