Serum Amyloid A Induces NLRP-3-Mediated IL-1β Secretion in Neutrophils

Abstract

Background/AimsSerum amyloid A (SAA) is an acute phase reactant with significant immunological activities, including effects on cytokine synthesis and neutrophil chemotaxis. Neutrophils can also release cytokines with proinflammatory properties. IL-1β is a key proinflammatory cytokine, the secretion of which is controlled by inflammasome. We investigated the proinflammatory effects of SAA in vitro in relation to the NLRP3 inflammasome in neutrophils.Methodology/Principal FindingsHuman neutrophils isolated form healthy subjects were stimulated with serum amyloid A (SAA). The cellular supernatants were analyzed by western blot using anti-IL-1β or anti-caspase-1 antibodies. IL-1β or Nod-like receptor family, pyrin domain containing 3 (NLRP3) mRNA expressions were analyzed by real-time PCR or reverse transcription-PCR (RT-PCR) method. SAA stimulation induced pro-IL-1β mRNA expression in neutrophils. Furthermore, SAA engaged the caspase-1-activating inflammasome, resulting in the production of active IL-1β. SAA-induced pro-IL-1β expression was marginally suppressed by the Syk specific inhibitor, R406, and SAA-induced pro-IL-1β processing in neutrophils was prevented by R406. Furthermore, SAA-induced NLRP3 mRNA expression was completely blocked by R406. Analysis of intracellular signaling revealed that SAA stimulation activated the tyrosine kinase Syk and mitogen-activated protein kinase (MAPK).Conclusions/SignificanceThese results demonstrate that the innate neutrophil immune response against SAA involves a two-step activation process: an initial signal promoting expression of pro-IL-1β and a second signal involving Syk-dependent activation of the NLRP3 inflammasome and caspase-1, allowing processing of pro-IL-1β and secretion of mature IL-1β.

Mycobacterium tuberculosisstimulates IL-1β production by macrophages in an ESAT-6 dependent manner with the involvement of serum amyloid A3

“…Infection of H37Rv but not its esat-6 deletion mutant induced elevated expression of SAA3 in macrophages and mouse lungs both at mRNA and protein levels and silencing SAA3 in macrophages resulted in reduced IL-1β but not IL-6 production upon Mtb infection, supporting a role for SAA3 in Mtb- induced IL-1β production in tuberculosis infection. This is consistent with the previous reports showing the potential role of SAA3 activated NLRP3 in mature IL-1β production by macrophages in chronic allergic diseases (32) and SAA3 induces transcription and maturation of IL-1β in macrophages (14) and neutrophils (37). This study further extends the role of SAA3 in Mtb -induced IL-1β production, thus suggesting a potential role of SAA3 in both the immune responses against and the pathology of tuberculosis infection at least in part by regulation of IL-1β production by macrophages.…”

High-density lipoprotein inhibits serum amyloid A–mediated reactive oxygen species generation and NLRP3 inflammasome activation

“…Other groups have reported that SAA stimulates dendritic cells, macrophages, and neutrophils to secrete IL-1β by activating the NLRP3 inflammasome (8)(9)(10). However, these studies utilized a recombinant SAA protein that has 2 amino acid substitutions (at positions 61 and 72) when compared to native SAA1, and recent evidence suggests that this recombinant form of SAA may exert activities not shared by mouse or human SAA (46,47).…”

“…SAA stimulates secretion of IL-1β in human and mouse macrophages, dendritic cells and neutrophils (8)(9)(10). SAA represents a family of proteins with 103-104 amino acids that share high sequence homology that presumably arose from gene duplication.…”

Serum amyloid A induces interleukin-1β secretion from keratinocytes via the NACHT, LRR and PYD domains-containing protein 3 inflammasome

“…Recent evidence has indicated that SAA possesses a number of cytokine‐like properties. It has been reported that SAA stimulates the release of mature IL‐1β from neutrophils, mast cells, macrophages and fibroblasts . However, whether or not SAA can induce IL‐1β production in keratinocytes remains to be investigated.…”