Objectives

Recent studies indicate that glucose metabolism is altered in rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS). Hexokinases (HKs) catalyse the first step in glucose metabolism, and HK2 constitutes the principal HK inducible isoform. We hypothesise that HK2 contributes to the synovial lining hypertrophy and plays a critical role in bone and cartilage damage.

Methods

HK1 and HK2 expression were determined in RA and osteoarthritis (OA) synovial tissue by immunohistochemistry. RA FLS were transfected with either HK1 or HK2 siRNA, or infected with either adenovirus (ad)-GFP, ad-HK1 or ad-HK2. FLS migration and invasion were assessed. To study the role of HK2 in vivo, 10⁸ particles of ad-HK2 or ad-GFP were injected into the knee of wild-type mice. K/BxN serum transfer arthritis was induced in HK2^F/F mice harbouring Col1a1-Cre (HK2^Col1), to delete HK2 in non-haematopoietic cells.

Results

HK2 is particular of RA histopathology (9/9 RA; 1/8 OA) and colocalises with FLS markers. Silencing HK2 in RA FLS resulted in a less invasive and migratory phenotype. Consistently, overexpression of HK2 resulted in an increased ability to migrate and invade. It also increased extracellular lactate production. Intra-articular injection of ad-HK2 in normal knees dramatically increased synovial lining thickness, FLS activation and proliferation. HK2 was highly expressed in the synovial lining after K/BxN serum transfer arthritis. HK2^Col1 mice significantly showed decreased arthritis severity, bone and cartilage damage.

Conclusion

HK2 is specifically expressed in RA synovial lining and regulates FLS aggressive functions. HK2 might be an attractive selective metabolic target safer than global glycolysis for RA treatment.