Pneumococcal protein PspA facilitates Streptococcus Pneumoniae‐induced pyrotosis

Abstract

Pyroptosis is a process in which a programmed cell death occurs via caspase‐1‐dependent mechanism which is triggered by various pathological stimuli. Streptococcus pneumoniae is gram‐negative bacteria that bring about a variety of serious diseases. D39 is serotype 2 strain of Streptococcus pneumoniae and virulent. D39 is widely used to study pathogenesis of Streptococcus pneumoniae. Nevertheless, proteins which are involved in Streptococcus Pneumoniae‐induced pyroptosis are not revealed yet. The cleavage of procaspase‐1 into the active form of caspase‐1 was reduced in PspA mutant‐infected BV2 cells, compared with D39‐infected BV2 cells. Western blot analysis demonstrated that the expression of IL‐18 was decreased in PspA mutant‐infected BV2 cells, compared with D39‐infected BV2 cells. When BV2 cells were treated with various doses of PspA recombinant protein alone, no significant change in cell proliferation was observed, comparing with uninfected cells. On the other hand, the cell proliferation of BV2 cells treated with both PspA recombinant protein and 1:10 of MOI of D39 was gradually decreased with time and this change is not statistically important when comparing with D39 only‐infected cells. This suggests that PspA is unable to act as a pyroptosis‐inducing factor. Immunoblotting analysis indicated that the expression of NLRP3 was increased in the presence of D39 or PspAmutants, compared with uninfected BV2 cells. Western blot analysis also demonstrated that the expression of NLRP3 was increased in D39‐infected after 30 min of infection, whereas an increased expression of NLRP3 in PspA mutant‐infected BV2 cells was exhibited but later than 30 min of infection. Taken together, these results suggest that pneumococcal PspA facilitates pyroptosis via NLRP3 expression in BV2 cells.