PROK2 and rheumatoid arthritis: In light of the fact that angiogenesis plays an important role in the pathogenesis of rheumatoid arthritis [13, 14], we previously investigated PK2 expression in mice with collagen-induced arthritis (CIA), the animal model of rheumatoid arthritis, and reported that PK2 gene expression was significantly elevated in the joints of CIA mice and correlated with the severity of the arthritis [15].