Low-level laser irradiation treatment reduces CCL2 expression in rat rheumatoid synovia via a chemokine signaling pathway

Rheumatoid arthritis (RA) is an inflammatory joint disorder whose progression leads to the destruction of cartilage and bone. Although low-level laser irradiation (LLLI) is currently being evaluated for the treatment of RA, the molecular mechanisms underlying its effectiveness remain unclear. To investigate possible LLLI-mediated antiinflammatory effects, we utilized a collagen-induced arthritis (CIA) rat model and analyzed gene expression profiles in the synovial membranes of the knee joint. Total RNA was isolated from the synovial membrane tissue of the joints of untreated CIA rats or CIA rats treated with LLLI (830 nm Ga-Al-As diode), and gene expression profiles were analyzed by DNA microarray (41,000 rat genes), coupled with Ingenuity pathways analysis (IPA). DNA microarray analysis showed that CCL2 gene expression was increased in CIA tissue, and that LLLI treatment significantly decreased CIA-induced CCL2 mRNA levels. IPA revealed that chemokine signal pathways were involved in the activation of CCL2 production. These microarray data were further validated using real-time PCR and reverse transcription PCR. Immunohistochemistry confirmed that CCL2 production was decreased in CIA rats treated with LLLI. These findings suggest that decreased CCL2 expression may be one of the mechanisms involved in LLLI-mediated RA inflammation reduction.