Clinical arthritis is typically divided into rheumatoid arthritis (RA) and osteoarthritis (OA). Arthritis-induced muscle weakness is a major problem in aged people, leading to a disturbance of balance during the gait cycle and frequent falls. The purposes of the present study were to confirm fiber type-dependent expression of muscle atrophy markers induced by arthritis and to identify the relationship between clinical signs and expression of muscle atrophy markers. Mice were divided into four experimental groups as follows: (1) negative control (normal), (2) positive control (CFA+acetic acid), (3) RA group (CFA+acetic acid+type Ⅱ collagen), and (4) aging-induced OA group. DBA/1J mice (8 weeks of age) were injected with collagen (50 μg/kg), and physiological (body weight) and pathological (arthritis score and paw thickness) parameters were measured once per week. The gastrocnemius muscle from animals in each group was removed, and the expression of muscle atrophy markers (MAFbx and MuRF1) and myosin heavy chain isoforms were analyzed by reverse transcription-polymerase chain reaction. No significant change in body weight occurred between control groups and collagen-induced RA mice at week 10. However, bovine type Ⅱ collagen induced a dramatic increase in clinical score or paw thickness at week 10 (p<0.01). Concomitantly, the expression of the muscle atrophy marker MAFbx was upregulated in the RA and OA groups (p<0.01). A dramatic reduction in myosin heavy chain (MHC)-Iβ was seen in the gastrocnemius muscles from RA and OA mice, while only a slight decrease in MHC-Ⅱb was seen. These results suggest that muscle atrophy gene expression occurred in a fiber type-specific manner in both RA- and OA-induced mice. The present study suggests evidence regarding why different therapeutic interventions are required between RA and OA.

Arthritis is a common disease in aged people, and is clinically divided into rheumatoid arthritis (RA) and osteoarthritis (OA). Although common symptoms such as pain are present, the underlying pathological mechanisms are slightly different. Therefore, the objectives of the present study were to compare joint damage induced by RA and OA by analyzing the major morphological and molecular differences, and to propose a suitable therapeutic intervention based on the pathophysiological conditions of bones and joints. For the RA animal model, 8-week-old DBA1/J mice were immunized with bovine type II collagen emulsified in complete Freund’s adjuvant (CFA). Normal C57BL/6 mice (over 2 years of age) were used for OA. The clinical arthritis score was calculated using a subjective scoring system, and paw thicknesses were measured using calipers. The serum TNFα level was analyzed using an ELISA kit. Micro- CT was used to identify pathological characteristics and morphological changes. In collagen-induced RA mice, there were increased ankle joint volumes and clinical scores (p<0.01). The concentration of TNFα was significantly increased from 3 to 7 weeks after immunization. Micro-CT images showed trabecular bone destruction, pannus formation, and subchondral region destruction in RA mice. OA among aged mice showed narrowed joint spaces and breakdown of articular cartilage. This study suggests that a careful therapeutic intervention between RA and OA is required, and it should be based on morphological alteration of bone and joint.