Background: Mitochondrial dysfunction is considered crucial for triggering NLRP3 inflammasome activation. Results: Rotenone-induced impairment of mitochondrial electron transport chain promotes NLRP3 inflammasome activation exclusively with ATP but not with other NLRP3-activating stimulators. Conclusion: High-grade mROS and hyperpolarization are essential for NLRP3 inflammasome activation upon rotenoneinduced mitochondrial dysfunction. Significance: Mitochondrial impairment may selectively prime NLRP3 inflammasome activation, leading to many degenerative diseases.

Advanced glycation end products (AGEs) are adducts formed on proteins by glycation with reducing sugars, such as glucose, and tend to form and accumulate under hyperglycemic conditions. AGE accumulation alters protein function and has been implicated in the pathogenesis of many degenerative diseases such as diabetic complications. AGEs have also been shown to promote the production of pro-inflammatory cytokines, but the roles of AGEs in inflammasome signaling have not been explored in detail. Here, we present evidence that AGEs attenuate activation of the NLRP3 inflammasome in bone marrow-derived macrophages (BMDMs) as determined by caspase-1 processing and interleukin-1β production. AGEs also dampened the assembly of the NLRP3 inflammasome, but did not affect the NLRC4 or AIM2 inflammasome activation. Moreover, our data indicated that AGE treatment inhibited Toll-like receptor (TLR)-dependent production of pro-inflammatory cytokines in BMDMs. This immunosuppressive effect of AGE was not associated with a receptor for AGEs (RAGE)-mediated signaling. Instead, AGE treatment markedly suppressed lipopolysaccharide-induced M1 polarization of macrophages. Furthermore, AGEs significantly dampened innate immune responses including NLRP3 inflammasome activation and type-I interferon production in macrophages upon influenza virus infection. These observations collectively suggest that AGEs could impair host NLRP3 inflammasome-mediated innate immune defenses against RNA virus infection leading to an increased susceptibility to infection.

BackgroundInflammation may play a significant role in the pathogenesis of depression, although the molecular target for the treatment of inflammation-mediated depressive symptoms remains to be elucidated. Recent studies have implicated the NLRP3 inflammasome in various psychiatric disorders, including depression. However, the underlying mechanism by which NLRP3 inflammasome activation mediates the progression of depressive-like behaviors remains poorly understood.MethodsWe examined whether NLRP3 deficiency influenced depressive-like behaviors and cerebral inflammation following systemic administration of lipopolysaccharide in mice. To further assess the contribution of the NLRP3 inflammasome to the progression of depression, we evaluated the effects of NLRP3 signaling on levels of indoleamine 2,3-dioxygenase.Results Nlrp3-deficient mice exhibited significant attenuation of depressive-like behaviors and cerebral caspase-1 activation in a lipopolysaccharide-induced model of depression. Treatment with the antidepressant amitriptyline failed to block NLRP3-dependent activation of caspase-1, but inhibited lipopolysaccharide-promoted production of interleukin-1β mRNA via suppressing NF-κB signaling in mouse mixed glial cultures. Interestingly, lipopolysaccharide administration produced NLRP3-dependent increases in indoleamine 2,3-dioxygenase expression and activity of mouse brain. Furthermore, inflammasome-activating stimulations, but not treatment with the inflammasome product interleukin-1β, triggered indoleamine 2,3-dioxygenase mRNA induction in mixed glial cells.ConclusionsOur data indicate that the NLRP3 inflammasome is significantly implicated in the progression of systemic inflammation-induced depression. NLRP3-dependent caspase-1 activation produced significant increases in indoleamine 2,3-dioxygenase levels, which may play a significant role in lipopolysaccharide-induced depression. Collectively, our findings suggest that indoleamine 2,3-dioxygenase is a potential downstream mediator of the NLRP3 inflammasome in inflammation-mediated depressive-like behaviors.

Aberrant inflammasome activation contributes to various chronic inflammatory diseases; however, pyroptosis of inflammasome-active cells promptly terminates local inflammasome response. Molecular mechanisms underlying prolonged inflammasome signaling thus require further elucidation. Here, we report that neutrophil-specific resistance to pyroptosis and NLRP3 desensitization can facilitate sustained inflammasome response and interleukin-1β secretion. Unlike macrophages, inflammasome-activated neutrophils did not undergo pyroptosis, indicated by using in vitro cell-based assay and in vivo mouse model. Intriguingly, danger-associated molecular patterns (DAMP)-rich milieu in the inflammatory region significantly abrogated NLRP3-activating potential of macrophages, but not of neutrophils. This macrophage-specific NLRP3 desensitization was associated with DAMP-induced mitochondrial depolarization that was not observed in neutrophils due to a lack of SARM1 expression. Indeed, valinomycin-induced compulsory mitochondrial depolarization in neutrophils restored inflammasome-dependent cell death and ATP-induced NLRP3 desensitization in neutrophils. Alongside prolonged inflammasome-activating potential, neutrophils predominantly secreted interleukin-1β rather than other proinflammatory cytokines upon NLRP3 stimulation. Furthermore, inflammasome-activated neutrophils did not trigger efferocytosis-mediated M2 macrophage polarization essential for the initiation of inflammation resolution. Taken together, our results indicate that neutrophils can prolong inflammasome response via mitochondria-dependent resistance to NLRP3 desensitization and function as major interleukin-1β-secreting cells in DAMP-rich inflammatory region.

Paclitaxel is a chemotherapeutic drug commonly used to treat different types of cancer. In addition to its antitumor effect, paclitaxel is also known to promote Toll-like receptor (TLR) 4-dependent inflammatory responses, which may lower its chemotherapeutic efficacy. However, it remains unclear whether paclitaxel is able to affect inflammasome signaling in myeloid or cancer cells. Therefore, we examined the potential effect of paclitaxel on the activation of an inflammasome complex by examining caspase-1 activation and interleukin (IL)-1β secretion in bone marrow-derived macrophages (BMDMs). The results showed that treatment with paclitaxel alone or following LPS priming failed to trigger the secretion of active caspase-1 and IL-1β from BMDMs. However, paclitaxel could induce robust activation of caspase-1 in BMDMs in the presence of NLRP3 inflammasome-activating signal 2, such as ATP or nigericin. This paclitaxel/ATP-mediated inflammasome activation was completely abrogated in Nlrp3 -deficient macrophages. Mechanistically, paclitaxel treatment induced robust activation of the TLR4 signaling cascade, including phosphorylation of IκB and JNK and upregulation of proinflammatory cytokine mRNA levels in a TLR4-dependent manner. In contrast, paclitaxel treatment alone did not induce mitochondrial damages such as the loss of the mitochondrial membrane potential and production of mitochondrial ROS. These findings suggest that paclitaxel can drive the priming of signal-mediated events for NLRP3 activation but not a second signal-triggered phenomenon such as mitochondrial damage. This suggestion was supported by the observations that paclitaxel treatment caused robust IL-1β production in macrophages in the presence of cell-free medium derived from growth of injured cells and also in the spleen of mice. Collectively, our data strongly indicate that paclitaxel is able to facilitate the activation of NLRP3 inflammasome signaling in a certain physiological environment.