SIGNAL 1 ALONE IS ENOUGH TO ACTIVATE THE NLRP3 INFLAMMAOSME IN HUMAN CELLS According to our current understanding,the NLR family,pyrin domain containing 3(NLRP3)infl ammasome activation is generally a two-step process.The fi rst step is priming,in which pathogen associated molecular patterns(PAMPs)such as LPS or pro-inflammatory cytokines such as tumor necrosis factor-α(TNF-α)induced NF-κB activation provides synthesis of pro-IL-1βand NLRP3 proteins.This priming step is considered as signal 1,which makes the cell ready for a second strike to assemble the infl ammasome.Then danger signals such as ATP and MSU provide the signal 2 that promotes formation of the NLRP3 infl ammasome and activates caspase-1.Both of these 2 steps are required in mouse macrophages for the NLRP3 inflammasome activation(Dinarello,2007).
Pannexin-1(Panx1)forms nonselective large channel in cell plasma membrane and has been shown to be associated with NLRP3 inflammasome activation,ATP release and phagocytes recruitment.In the current study,by manipulation of Panx1 expression in human myeloid cells and application of Panx1 defi cient mice,we failed to fi nd a correlation between Panx1 and NLRP3 infl ammasome activation,although an interaction between these two proteins was evident.However,in thioglycollate induced peritonitis,Panx1 defi cient mice showed much more phagocytes infiltration.Further analyses showed that mice defi cient for Panx1 exhibited enlarged F4/80^(low)Gr1-Ly6C-cell population in the peritonea.Our study thus reveals an important role for Panx1 in regulation of peritoneal cell population and peritonitis development.
Infl ammasome is a large protein complex activated upon cellular stress or microbial infection,which triggers maturation of pro-inflammatory cytokines interleukin-1βand interleukin-18 through caspase-1 activation.Nod-like receptor family protein 3(NLRP3)is the most character-ized infl ammasome activated by various stimuli.However,the mechanism of its activation is unclear and its exact cellular localization is still unknown.We examined the potential co-localization of NLRP3 infl ammasome with mi-tochondria and seven other organelles under adenosine triphosphate,nigericin or monosodium urate stimulation in mouse peritoneal macrophages using confocal micros-copy approach.Our results revealed that the activated endogenous apoptosis-associated speck-like protein containing a CARD(ASC)pyroptosome forms in the cyto-plasm and co-localizes with NLRP3 and caspase-1,but not with any of the organelles screened.This study indicates that the ASC pyroptosome universally localizes within the cytoplasm rather than with any specifi c organelles.
Yan WangChen YangKairui MaoShuzhen ChenGuangxun MengBing Sun
