Blocking CCN2 Reduces Progression of Sensorimotor Declines and Fibrosis in a Rat Model of Chronic Repetitive Overuse

Abstract

Fibrosis may be a key factor in sensorimotor dysfunction in patients with chronic overuse‐induced musculoskeletal disorders. Using a clinically relevant rodent model, in which performance of a high demand handle‐pulling task induces tissue fibrosis and sensorimotor declines, we pharmacologically blocked cellular communication network factor 2 (CCN2; connective tissue growth factor) with the goal of reducing the progression of these changes. Young adult, female Sprague–Dawley rats were shaped to learn to pull at high force levels (10 min/day, 5 weeks), before performing a high repetition high force (HRHF) task for 3 weeks (2 h/day, 3 days/week). HRHF rats were untreated, or treated in task weeks 2 and 3 with a monoclonal antibody that blocks CCN2 (FG‐3019), or a control immunoglobulin G (IgG). Control rats were untreated or received FG‐3019, IgG, or vehicle (saline) injections. Mean task reach rate and grasp force were higher in 3‐week HRHF + FG‐3019 rats, compared with untreated HRHF rats. Grip strength declined while forepaw mechanical sensitivity increased in untreated HRHF rats, compared with controls; changes improved by FG‐3019 treatment. The HRHF task increased collagen in multiple tissues (flexor digitorum muscles, nerves, and forepaw dermis), which was reduced with FG‐3019 treatment. FG‐3019 treatment also reduced HRHF‐induced increases in CCN2 and transforming growth factor β in muscles. In tendons, FG‐3019 reduced HRHF‐induced increases in CCN2, epitendon thickening, and cell proliferation. Our findings indicate that CCN2 is critical to the progression of chronic overuse‐induced multi‐tissue fibrosis and functional declines. FG‐3019 treatment may be a novel therapeutic strategy for overuse‐induced musculoskeletal disorders. © 2019 The Authors. Journal of Orthopaedic Research® published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 37:2004–2018, 2019

Blocking CTGF/CCN2 reduces established skeletal muscle fibrosis in a rat model of overuse injury

“…as the vehicle control. Effects of FG‐3019 and IgG in control rats have been reported (no negative side effects were observed) 19,35 …”

“…Rats were weighed twice per week, provided regular rat chow daily in addition to food reward pellets (banana and chocolate pellets, Bio‐Serv, Flemington, NJ), and allowed to gain weight over the course of the 30‐week experiment 19 . FRC rats received similar amounts of rat chow and food reward pellets as HRHF rats.…”

“…One animal in the HRHF‐Rest/IgG group died from unknown reasons in task week 12 (this group was originally n = 6; thereby reducing to final number to n = 5 for this group). Further rat care details are as previously described 19 …”

“…There is even evidence from studies examining fibrotic kidneys that fibroblasts collected from these fibrotic kidneys have undergone epigenetic alterations that render these cells chronically activated 16 . However, blocking CCN2 (cellular communication network factor 2; previously known as connective tissue growth factor, CTGF 17,18 ) signaling has shown promise for many fibrotic disorders, 19 as explained further below.…”

“…We recently found that CCN2 is critical to the early progression of chronic overuse‐induced muscle fibrosis and grip strength declines in rats that performed an operant reaching, grasping, and lever‐pulling task at high repetition high force (HRHF) levels for three weeks 19 . Systemic injections of the FG‐3019 agent reduced this early progression of musculotendinous fibrosis, and improved motor declines.…”