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

Tissue fibrosis is a hallmark of overuse musculoskeletal injuries and contributes to functional declines. We tested whether inhibition of CCN2 (cellular communication network factor 2, previously known as connective tissue growth factor, CTGF) using a specific antibody (termed FG-3019 or pamrevlumab) reduces established overuse-induced muscle fibrosis in a clinically relevant rodent model of upper extremity overuse injury. Young adult rats performed a high repetition high force (HRHF) reaching and lever-pulling task for 18 weeks, after first being shaped for 6 weeks to learn this operant task. Rats were then euthanized (HRHF-Untreated), or rested and treated for 6 weeks with FG-3019 (HRHF-Rest/FG-3019) or a human IgG as a vehicle control (HRHF-Rest/IgG). HRHF-Untreated and HRHF-Rest/IgG rats had higher muscle levels of several fibrosis-related proteins (TGF beta 1, CCN2, collagen types I and III, and FGF2), and higher muscle numbers of alpha SMA and pERK immunopositive cells, compared to control rats. Each of these fibrogenic changes was restored to control levels by the blocking of CCN2 signaling in HRHF-Rest/FG-3019 rats, as were HRHF task-induced increases in serum CCN2 and pro-collagen I intact N-terminal protein. Levels of cleaved CCN3, an antifibrotic protein, were lowered in HRHF-Untreated and HRHF-Rest/IgG rats, compared to control rats, yet elevated back to control levels in HRHF-Rest/FG-3019 rats. Significant grip strength declines observed in HRHF-Untreated and HRHF-Rest/IgG rats, were restored to control levels in HRHF-Rest/FG-3019 rats. These results are highly encouraging for use of FG-3019 for therapeutic treatment of persistent skeletal muscle fibrosis, such as those induced with chronic overuse.