TXNDC5 protects synovial fibroblasts of rheumatoid arthritis from the detrimental effects of endoplasmic reticulum stress.

TXNDC5 is an endoplasmic reticulum (ER)-resident chaperone that protects the endothelium from secondary effects of ER stress. Previous studies by the current authors identified TXNDC5 as a key pathological factor in promoting the inflammatory phenotype of fibroblast-like synoviocytes (FLSs) from rheumatoid arthritis (RA). However, its activity in RA FLSs under ER stress remains unclear. The current study found that TXNDC5 is responsive to ER stress in RA FLSs since its expression was induced by ER stress at both the endogenous and secretory level. A functional study indicated that silencing TXNDC5 reduced the viability of RA FLSs more markedly in the presence of ER stressors. In contrast, rhTXNDC5 attenuated a decrease in cell viability as a result of ER stress. Moreover, silencing TXNDC5 attenuated the induction of IL-6 and IL-8 from RA FLSs in response to ER stress. In addition, rhTXNDC5 induced a greater increase in VEGF production during ER stress. These findings confirm the pro-survival and pro-inflammation roles of TXNDC5 under ER stress in RA FLSs. TXNDC5 appears to act as a mediator linking ER stress and inflammation of RA.