Aquaporin-3 is involved in NLRP3-inflammasome activation contributing to the setting of inflammatory response.

Inflammasomes are large immune multiprotein complexes that tightly regulate the production of the pro-inflammatory cytokines, being dependent on cell regulatory volume mechanisms. Aquaporins (AQPs) are protein channels that facilitate the transport of water and glycerol (aquaglyceroporins) through membranes, essential for cell volume regulation. Although these membrane proteins are highly expressed in monocytes and macrophages, their role in the inflammatory process is still unclear. Here, we investigated the role of aquaglyceroporin AQP3 in NLRP3-inflammasome activation by complementary approaches based either on shRNA silencing or on AQP3 selective inhibition. The latter has been achieved using a reported potent gold-based inhibitor, Auphen. AQP3 inhibition or silencing partially blocked LPS-priming and decreased production of IL-6, proIL-1ß, and TNF-α, suggesting the possible involvement of AQP3 in macrophage priming by Toll-like receptor 4 engagement. Moreover, AQP3-dependent cell reswelling increased IL-1ß release through caspase-1 activation. NLRP3-inflammasome activation induced by reswelling, nigericin, and ATP was also blocked when AQP3 was inhibited or silenced. Altogether, these data point towards AQPs as potential players in the setting of the inflammatory response.

Caspase-1 deficiency in mice reduces intestinal triglyceride absorption and hepatic triglyceride secretion.

Caspase-1 is known to activate the proinflammatory cytokines IL-1ß and IL-18. Additionally, it can cleave other substrates, including proteins involved in metabolism. Recently, we showed that caspase-1 deficiency in mice strongly reduces high-fat diet-induced weight gain, at least partly caused by an increased energy production. Increased feces secretion by caspase-1-deficient mice suggests that lipid malabsorption possibly further reduces adipose tissue mass. In this study we investigated whether caspase-1 plays a role in triglyceride-(TG)-rich lipoprotein metabolism using caspase-1-deficient and wild-type mice. Caspase-1 deficiency reduced the postprandial TG response to an oral lipid load, whereas TG-derived fatty acid (FA) uptake by peripheral tissues was not affected, demonstrated by unaltered kinetics of [(3)H]TG-labeled very low-density lipoprotein (VLDL)-like emulsion particles. An oral gavage of [(3)H]TG-containing olive oil revealed that caspase-1 deficiency reduced TG absorption and subsequent uptake of TG-derived FA in liver, muscle, and adipose tissue. Similarly, despite an elevated hepatic TG content, caspase-1 deficiency reduced hepatic VLDL-TG production. Intestinal and hepatic gene expression analysis revealed that caspase-1 deficiency did not affect FA oxidation or FA uptake but rather reduced intracellular FA transport, thereby limiting lipid availability for the assembly and secretion of TG-rich lipoproteins. The current study reveals a novel function for caspase-1, or caspase-1-cleaved substrates, in controlling intestinal TG absorption and hepatic TG secretion.

Inflammatory role of ASC in antigen-induced arthritis is independent of caspase-1, NALP-3, and IPAF.

Because IL-1beta plays an important role in inflammation in human and murine arthritis, we investigated the contribution of the inflammasome components ASC, NALP-3, IPAF, and caspase-1 to inflammatory arthritis. We first studied the phenotype of ASC-deficient and wild-type mice during Ag-induced arthritis (AIA). ASC(-/-) mice showed reduced severity of AIA, decreased levels of synovial IL-1beta, and diminished serum amyloid A levels. In contrast, mice deficient in NALP-3, IPAF, or caspase-1 did not show any alteration of joint inflammation, thus indicating that ASC associated effects on AIA are independent of the classical NALP-3 or IPAF inflammasomes. Because ASC is a ubiquitous cytoplasmic protein that has been implicated in multiple cellular processes, we explored other pathways through which ASC may modulate inflammation. Ag-specific proliferation of lymph node and spleen cells from ASC-deficient mice was significantly decreased in vitro, as was the production of IFN-gamma, whereas IL-10 production was enhanced. TCR ligation by anti-CD3 Abs in the presence or absence of anti-CD28 Abs induced a reduction in T cell proliferation in ASC(-/-) T cells compared with wild-type ones. In vivo lymph node cell proliferation was also significantly decreased in ASC(-/-) mice, but no effects on apoptosis were observed either in vitro or in vivo in these mice. In conclusion, these results strongly suggest that ASC modulates joint inflammation in AIA through its effects on cell-mediated immune responses but not via its implication in inflammasome formation.

Crucial role for the Nalp3 inflammasome in the immunostimulatory properties of aluminium adjuvants.

Aluminium adjuvants, typically referred to as 'alum', are the most commonly used adjuvants in human and animal vaccines worldwide, yet the mechanism underlying the stimulation of the immune system by alum remains unknown. Toll-like receptors are critical in sensing infections and are therefore common targets of various adjuvants used in immunological studies. Although alum is known to induce the production of proinflammatory cytokines in vitro, it has been repeatedly demonstrated that alum does not require intact Toll-like receptor signalling to activate the immune system. Here we show that aluminium adjuvants activate an intracellular innate immune response system called the Nalp3 (also known as cryopyrin, CIAS1 or NLRP3) inflammasome. Production of the pro-inflammatory cytokines interleukin-1beta and interleukin-18 by macrophages in response to alum in vitro required intact inflammasome signalling. Furthermore, in vivo, mice deficient in Nalp3, ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain) or caspase-1 failed to mount a significant antibody response to an antigen administered with aluminium adjuvants, whereas the response to complete Freund's adjuvant remained intact. We identify the Nalp3 inflammasome as a crucial element in the adjuvant effect of aluminium adjuvants; in addition, we show that the innate inflammasome pathway can direct a humoral adaptive immune response. This is likely to affect how we design effective, but safe, adjuvants in the future.