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.

ABSTRACT   INTRODUCTION   MATERIALS AND METHODS    Animals    Induction of RA    Assessment of Arthritis    Tissue Collection    Analysis of Gene Expression    Statistical Analysis   RESULTS    Changes in Body Weight in Collagen-Induced RA Animals    Disease Development from Initial Immunization   DISCUSSION   REFERENCES

• Yunkyung Hong(Department Rehabilitation Science in Interdisciplinary PhD Program, Inje University, These authors contributed equally.)
• Joo-Heon Kim(Institute of Animal Medicine, College of Veterinary Medicine, Gyeongsang National University, These authors contributed equally.)
• Palaksha Kanive Javaregowda(Cardiovascular & Metabolic Disease Center, College of Biomedical Science & Engineering)
• Sang-Kil Lee(Cardiovascular & Metabolic Disease Center, College of Biomedical Science & Engineering)
• Sang-Rae Lee(National Primate Research Center, Korea Research Institute of Biotechnology)
• Kyu-Tae Chang(National Primate Research Center, Korea Research Institute of Biotechnology) Corresponding author
• Yonggeun Hong(Department Rehabilitation Science in Interdisciplinary PhD Program, Inje University, Cardiovascular & Metabolic Disease Center, College of Biomedical Science & Engineering, National Primate Research Center, Korea Research Institute of Biotechnology) Corresponding author