Expression of inflammasome proteins and inflammasome activation occurs in human, but not in murine keratinocytes

Inflammasomes are multimeric protein complexes that assemble upon sensing of a variety of stress factors. Their formation results in caspase-1-mediated activation and secretion of the pro-inflammatory cytokines pro-interleukin(IL)-1β and -18, which induce an inflammatory response. Inflammation is supported by a lytic form of cell death, termed pyroptosis. Innate immune cells, such as macrophages or dendritic cells, express and activate inflammasomes. However, it has also been demonstrated that human primary keratinocytes activate different types of inflammasomes in vitro, for example, upon UVB irradiation or viral infection. Keratinocytes are the main cell type of the epidermis, the outermost layer of the body, and form a protective barrier consisting of a stratified multi-layered epithelium. In human, gain-of-function mutations of the NLRP1 gene cause syndromes mediated by inflammasome activation in keratinocytes that are characterised by skin inflammation and skin cancer susceptibility. Here we demonstrate that murine keratinocytes do not activate inflammasomes in response to stimuli, which induce IL-1β and -18 secretion by human keratinocytes. Whereas murine keratinocytes produced caspase-1 and proIL-18, expression of the inflammasome proteins Nlrp1, Nlrp3, Aim2, Asc, and proIL-1β was, compared to human keratinocytes or murine dendritic cells, very low or even undetectable. Priming of murine keratinocytes with cytokines commonly used for induction of proIL-1β and inflammasome protein expression did not rescue inflammasome activation. Nevertheless, UVB-induced inflammation and neutrophil recruitment in murine skin was dependent on IL-1β and caspase-1. However, also under these conditions, we did not detect expression of proIL-1β by keratinocytes in murine skin, but by immune cells. These results demonstrate a higher immunological competence of human compared to murine keratinocytes, which is reflected by stress-induced IL-1β secretion that is mediated by inflammasomes. Therefore, keratinocytes in human skin can exert immune functions, which are carried out by professional immune cells in murine skin

Polymorphisms and expression of inflammasome genes are associated with the development and severity of rheumatoid arthritis in Brazilian patients

OBJECTIVE: In the present study, we analyzed the possible association of inflammasome gene variants and expression to rheumatoid arthritis (RA)'s development and severity in the Brazilian population. MATERIALS AND METHODS: Thirteen single nucleotide polymorphisms within six inflammasome genes (NLRP1, NLRP3, NLRC4, AIM2, CARD8, CASP1) as well as IL1B and IL18 genes in two different Brazilian populations (from Northeast and Southeast Brazil) were analyzed. We also evaluated inflammasome gene expression profile in resting and LPS\u2009+\u2009ATP-treated monocytes from RA patients and healthy individuals. For genetic association study, 218 patients and 307 healthy controls were genotyped. For gene expression study, inflammasome genes mRNA levels of 12 patients and ten healthy individuals were assessed by qPCR. RESULTS: Our results showed that rs10754558 NLRP3 and rs2043211 CARD8 polymorphisms are associated with RA development (p value\u2009=\u20090.044, OR\u2009=\u20091.77, statistical power\u2009=\u20090.999) and severity measured by Health Assessment Questionnaire (HAQ) (p value\u2009=\u20090.03), respectively. Gene expression analyses showed that RA patients display activation of CASP1, IL1B and IL1R genes independently of LPS + ATP activation. In LPS\u2009+\u2009ATP-treated monocytes, NLRP3 and NLRC4 expressions were also significantly higher in patients compared with controls. CONCLUSIONS: The first reported results in Brazilian populations support the role of inflammasome in the development of RA