Background Rheumatoid arthritis is an autoimmune inflammatory disease associated with systemic complications like fatigue and muscle wasting. Muscle wasting could be related to the activation of the ubiquitin-proteasome system.
Objectives To evaluate muscle loss and involvement of the proteasome in collagen-induced arthritis (CIA), with or without treatment with methotrexate or a TNF inhibitor (etanercept).
Methods Male DBA1/J mice were divided into 4 groups (n=8 each): CIA (saline); ETN (etanercept, 5.5 mg/kg) and MTX (methotrexate, 35 mg/kg), treated twice a week for 6 weeks, and a healthy control group (CO). Treatments started one week after booster injection. Clinical score, hind paw oedema, and body weight were analysed during the experimental period. Gastrocnemius muscles (GA) were weighted after death and used to quantify proteasome activity, protein levels and mRNA expression of its subunits by Western blot and rtPCR. Significance was considered when p≤0.05.
Results Treatments slowed disease development, observed through smaller clinical score and hindpaw edema in ETN and MTX. ETN presented higher body weight (21±1.0g) compared to MTX (19±1.3) at weeks 5 and 7. GA weight was heavier in ETN (105±12g) than CIA and MTX (80±10 and 79±10g, respectively), a result also observed after normalization of muscle with body weight. Of note, the catalytic properties of 26S proteasome showed an increase of caspase-like activity in CIA and MTX groups (150 and 200% of activity, respectively). Furthermore, muscles of MTX treated animals showed higher protein levels for proteasomal subunits PSMB8 and PSMB9 and increased gene expression for Psmb5, Psmb8 and Psmb9. In contrast, expression of Psmb6 was decreased and of Psmb9 was enhanced in CIA.
Conclusions Although both drugs improved the disease score, ETN presented a stronger anti-arthritic effect and was the only treatment able to partially prevent muscle wasting. In contrast to ETN, MTX treatment did not prevent muscle loss due to CIA accompanied by persistent up-regulation of proteasome expression and activity.
Acknowledgement Financial support: CAPES, CNPq, FIPE-HCPA.
Disclosure of Interest None declared