On the effects of NLRP3 inflammasome on mice pancreatic β-cell damage induced by advanced glycation end products / 中华内分泌代谢杂志

Objective To explore the role of the pyrin domain-containing 3 ( NLRP3) inflammasome in advanced glycation end products ( AGEs )-induced mice pancreatic β-cell damage. Methods AGEs were administered intraperitoneally for 6 weeks in NLRP3 knockout mice or C57BL/6J mice. Intraperitoneal glucose tolerance test and insulin releasing test were performed. Pancreatic sections were stained with haematoxylin and eosin, or with F4/80 and NLRP3 antibodies. Insulin and pancreatic tissue monocyte chemotactic protein 1 ( MCP-1) as well as interleukin-1β( IL-1β) levels were measured with ELISA kits. Expression of MCP-1 protein was determined by western blot. MIN6 cells and mouse peritoneal macrophages cells were treated with AGEs and different interventions (antioxidant NAC, adenovirus NLRP3 shRNA or NLRP3 knockout). Reactive oxygen species production, NLRP3 mRNA expression, IL-1β secretion, caspase 1 activity, apoptosis and glucose stimulated insulin release were determined. Results Injection of AGEs induced an abnormal response to glucose, enhanced the insulitis score, and increased the levels of pancreatic tissue MCP-1 and IL-1β, as well as raised the expression of NLRP3 and F4/80 in pancreatic islet. Remarkably, co-localization of NLRP3 and macrophage marker F4/80 was observed in islet. The damages were improved in NLRP3 knockout mice. After incubation with AGEs, reactive oxygen species production and cell apoptosis was enhanced, NLRP3 inflammasome activated, with glucose-stimulated insulin release impaired in MIN6 cells. NAC treatment alliviated the above damages, but NLRP3 gene silencing had no effect on ROS level, apoptosis, and insulin secretion. Finally NAC treatment and NLRP3 gene knockout inhibited activation of NLRP3 inflammasome induced by AGEs in mouse peritoneal macrophages cells. Conclusion NLRP3 knockout ameliorates the islet β-cell damage induced by AGEs. These effects were associated with AGEs-induced islets macrophage infiltrating by up-regulation of MCP-1 expression, and AGEs-induced activation of NLRP3 inflammasome in macrophage through ROS pathway, which results in the release of active IL-1βand leads to the lesions of β-cell.

Pannexin-1 influences peritoneal cavity cell population but is not involved in NLRP3 inflammasome activation

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 deficient mice, we failed to find a correlation between Panx1 and NLRP3 inflammasome activation, although an interaction between these two proteins was evident. However, in thioglycollate induced peritonitis, Panx1 deficient mice showed much more phagocytes infiltration. Further analyses showed that mice deficient 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.

Cellular localization of NLRP3 inflammasome

Inflammasome is a large protein complex activated upon cellular stress or microbial infection, which triggers maturation of pro-inflammatory cytokines interleukin-1β and interleukin-18 through caspase-1 activation. Nod-like receptor family protein 3 (NLRP3) is the most characterized inflammasome 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 inflammasome with mitochondria and seven other organelles under adenosine triphosphate, nigericin or monosodium urate stimulation in mouse peritoneal macrophages using confocal microscopy approach. Our results revealed that the activated endogenous apoptosis-associated speck-like protein containing a CARD (ASC) pyroptosome forms in the cytoplasm 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 specific organelles.

Human pathogenic fungus Trichophyton schoenleinii activates the NLRP3 inflammasome

The fungus Trichophyton schoenleinii (T. schoenleinii) is the causative agent of Trichophytosis and Tinea favosa of the scalp in certain regions of Eurasia and Africa. Human innate immune system plays an important role in combating with various pathogens including fungi. The inflammasome is one of the most critical arms of host innate immunity, which is a protein complex controlling maturation of IL-1β. To clarify whether T. schoenleinii is able to activate the inflammasome, we analyzed human monocytic cell line THP-1 for IL-1β production upon infection with T. schoenleinii strain isolated from Tinea favosa patients, and rapid IL-1β secretion from THP-1 cells was observed. Moreover, applying competitive inhibitors and gene specific silencing with shRNA, we found that T. schoenleinii induced IL-1β secretion, ASC pyroptosome formation as well as caspase-1 activation were all dependent on NLRP3. Cathepsin B activity, ROS production and K⁺ efflux were required for the inflammasome activation by T. schoenleinii. Our data thus reveal that the NLRP3 inflammasome plays an important role in host defense against T. schoenleinii, and suggest that manipulating NLRP3 signaling can be a novel approach for control of diseases caused by T. schoenleinii infection.