SIRT1 and rheumatoid arthritis: Notably, the expression level of IL-38 is abnormal in rheumatoid arthritis (RA) patients, and IL-38 can restrain inflammatory responses in collagen-induced arthritis (CIA) mice via Sirtuin1/Hypoxia-inducible factor-1α (SIRT1/HIF-1α) signaling pathway (Xu et al., 2018; Pei et al., 2020).