NLRP1 and NLRP3 inflammasomes mediate LPS/ATP-induced pyroptosis in knee osteoarthritis

Pyroptosis is triggered by inflammasomes after its activation by various inflammatory stimulations, including lipopolysaccharide (LPS) and improper pH. This may result in programmed death of the affected cell. It is well known that NLRP1 and NLRP3 inflammasomes mediate the production of various cytokines in inflammatory disorders; however, it is still unknown whether NLRP1 and NLRP3 inflammasomes can influence the LPS-induced pyroptosis in the progression of knee osteoarthritis (KOA). In the present study, the correlation between the NLRP inflammasomes and fibroblast-like synoviocytes (FLSs) pyroptosis was investigated in vivo and in vitro. Human synovial samples were collected from KOA patients and the expression of NLRP1 and NLRP3 inflammasomes was analyzed. Human FLS were isolated in vitro and stimulated with LPS. To determine whether NLRP1 and NLRP3 inflammasomes are involved in FLS pyroptosis, NLRP1 and NLRP3 small interfering RNAs (siRNAs) were used. The results showed that the expression of NLRPs and inflammasome-related proteins were upregulated and FLS stimulated with LPS+ATP resulted in cell pyroptosis. However, LPS+ATP-induced pyroptosis was attenuated by NLRP1 and NLRP3 siRNAs. The results of the present study indicate that LPS-induced FLS pyroptosis may be mediated by either NLRP1 or NLRP3 inflammsomes. Overall, based on the data obtained from patients and in vitro cells, the present finsings showed that NLRP1 and NLRP3 inflammasomes are highly involved in the FLS inflammation and pyroptosis. Furthermore, inhibition of NLRP1 and NLRP3 led to a remarkable reduction of pyroptosis-related cytokines. Thus, NLRP1 and NLRP3 inflammasomes may be important in the pathogenesis of OA and may represent a novel therapeutic target.