Trypanosoma cruzi (T. cruzi) is an intracellular protozoan parasite and the etiological agent of Chagas disease, a chronic infectious illness that affects millions of people worldwide. Although the role of TLR and Nod1 in the control of T. cruzi infection is well-established, the involvement of inflammasomes remains to be elucidated. Herein, we demonstrate for the first time that T. cruzi infection induces IL-1β production in an NLRP3- and caspase-1-dependent manner. Cathepsin B appears to be required for NLRP3 activation in response to infection with T. cruzi, as pharmacological inhibition of cathepsin B abrogates IL-1β secretion. NLRP3−/− and caspase1−/− mice exhibited high numbers of T. cruzi parasites, with a magnitude of peak parasitemia comparable to MyD88−/− and iNOS−/− mice (which are susceptible models for T. cruzi infection), indicating the involvement of NLRP3 inflammasome in the control of the acute phase of T. cruzi infection. Although the inflammatory cytokines IL-6 and IFN-γ were found in spleen cells from NLRP3−/− and caspase1−/− mice infected with T. cruzi, these mice exhibited severe defects in nitric oxide (NO) production and an impairment in macrophage-mediated parasite killing. Interestingly, neutralization of IL-1β and IL-18, and IL-1R genetic deficiency demonstrate that these cytokines have a minor effect on NO secretion and the capacity of macrophages to control T. cruzi infection. In contrast, inhibition of caspase-1 with z-YVAD-fmk abrogated NO production by WT and MyD88−/− macrophages and rendered them as susceptible to T. cruzi infection as NLRP3−/− and caspase-1−/− macrophages. Taken together, our results demonstrate a role for the NLRP3 inflammasome in the control of T. cruzi infection and identify NLRP3-mediated, caspase-1-dependent and IL-1R-independent NO production as a novel effector mechanism for these innate receptors.

NAIP5/NLRC4 (neuronal apoptosis inhibitory protein 5/nucleotide oligomerization domain-like receptor family, caspase activation recruitment domain domain-containing 4) inflammasome activation by cytosolic flagellin results in caspase-1-mediated processing and secretion of IL-1β/IL-18 and pyroptosis, an inflammatory cell death pathway. Here, we found that although NLRC4, ASC, and caspase-1 are required for IL-1β secretion in response to cytosolic flagellin, cell death, nevertheless, occurs in the absence of these molecules. Cytosolic flagellin-induced inflammasome-independent cell death is accompanied by IL-1α secretion and is temporally correlated with the restriction of Salmonella Typhimurium infection. Despite displaying some apoptotic features, this peculiar form of cell death do not require caspase activation but is regulated by a lysosomal pathway, in which cathepsin B and cathepsin D play redundant roles. Moreover, cathepsin B contributes to NAIP5/NLRC4 inflammasome-induced pyroptosis and IL-1α and IL-1β production in response to cytosolic flagellin. Together, our data describe a pathway induced by cytosolic flagellin that induces a peculiar form of cell death and regulates inflammasome-mediated effector mechanisms of macrophages.

Autophagy and inflammasome activation are cell‐autonomous and cross‐regulated processes involved in host resistance against infections. Our group previously described that NLRP3 inflammasome is required for the control of Trypanosoma cruzi, the causative agent of Chagas disease. However, the involvement of autophagy in this process was unclear. Here, we demonstrated that T. cruzi was able to induce an increase in LC3‐II expression as well as autophagosome and autolysosome formation in peritoneal macrophages (PMs) from C57BL/6 wild‐type mice. Moreover, the pharmacologic inhibition of autophagic machinery impaired the ability of PMs to control T. cruzi replication. Importantly, NLRP3 was required for the induction of a regular autophagic flux in response to T. cruzi, an effect mediated by its participation in the autolysosomes formation. Together, these results indicate autophagy as an effector mechanism mediated by NLRP3 to control T. cruzi infection.

Trypanossoma cruzi (T. cruzi), the causative protozoan of Chagas disease (CD) invades many cell types, including central nervous system (CNS) cells triggering local lesions and neurological impact. Previous work from our group described NLRP3 inflammasomes as central effectors for the parasite control by macrophages. Recent evidences demonstrate that NLRP3 can be activated in CNS cells with controversial consequences to the control of infections and inflammatory pathologies. However, the relative contribution of NLRP3 in different cell types remains to be elucidated. In this article, we described an effector response mediated by NLRP3 that works on microglia but not on astrocytes to control T. cruzi infection. Despite T. cruzi ability to invade astrocytes and microglia, astrocytes were clearly more permissive to parasite replication. Moreover, the absence of NLRP3 renders microglia but not astrocytes more permissive to T. cruzi replication. In fact, microglia but not astrocytes were able to secrete NLRP3-dependent IL-1 and NO in response to T. cruzi. Importantly, the pharmacological inhibition of iNOS with aminoguanidine resulted in a significant increase in the numbers of amastigotes found in microglia from wild-type but not from NLRP3 −/− mice, indicating the importance of NLRP3-mediated NO secretion to the infection control by these cells. Taken together, our findings revealed that T. cruzi differentially activates NLRP3 inflammasomes in astrocytes and microglia and established a role for these platforms in the control of a protozoan infection by glial cells from CNS. K E Y W O R D S NLRP3, T. cruzi, astrocytes, microglia, nitric oxide associated molecular patterns (DAMPs) (revised by Kigerl et al. 3 ). Inflammasomes are cytosolic complexes composed by multiple proteins that assemble in cell cytoplasm after DAMPs or PAMPs stimulation. 4-6 The stimulation is sensed by cytosolic receptors such as 202 PACHECO ET AL.the NOD-leucin rich repeats (LRR)-containing receptors (NLRs), which oligomerize and start the formation of cytoplasmatic complexes resulting in the recruitment and activation of caspase-1. Active caspase-1 cleaves pro-IL-1 , pro-IL-18, leading to the secretion of mature IL-1 and IL-18. Caspase-1 and caspase-11 also cleave gasdermin-D (GsmD), the effector protein of an inflammatory process of cell death named pyroptosis. 7,8 In addition to the maturation and secretion of IL-1 and IL-18 and induction of pyroptosis, inflammasomes also activate other microbicidal responses (reviewed in refs. 9,10). In this sense, our group demonstrated that the induction of NO through NLRC4 11,12 and NLRP3 13 inflammasomes is involved in the clearance of pathogens by macrophages.The role of inflammasomes in neuroinflamation has been described in many situations from sterile spinal cord injury (SCI), Alzheimer Disease (AD), multiple sclerosis (MS), and others 14 to bacterial and viral infections such as Legionella pneumophila, 15 Brucella abortus, 16 Staphylococcus aureus,17,18 Zika virus, 19 and many others. For each cont...

Tuberculosis (TB), caused by the bacterium Mycobacterium tuberculosis, and malaria, caused by parasites from the Plasmodium genus, are two of the major causes of death due to infectious diseases in the world. Both diseases are treatable with drugs that have microbicidal properties against each of the etiologic agents. However, problems related to treatment compliance by patients and emergence of drug resistant microorganisms have been a major problem for combating TB and malaria. This factor is further complicated by the absence of highly effective vaccines that can prevent the infection with either M. tuberculosis or Plasmodium. However, certain host biological processes have been found to play a role in the promotion of infection or in the pathogenesis of each disease. These processes can be targeted by host-directed therapies (HDTs), which can be administered in conjunction with the standard drug treatments for each pathogen, aiming to accelerate their elimination or to minimize detrimental side effects resulting from exacerbated inflammation. In this review we discuss potential new targets for the development of HDTs revealed by recent advances in the knowledge of host-pathogen interaction biology, and present an overview of strategies that have been tested in vivo, either in experimental models or in patients.

Chagas disease is a life-threatening disorder caused by the protozoan parasite Trypanosoma cruzi. Parasite-specific antibodies, CD8+ T cells, as well as IFN-γ and nitric oxide (NO) are key elements of the adaptive and innate immunity against the extracellular and intracellular forms of the parasite. Bim is a potent pro-apoptotic member of the Bcl-2 family implicated in different aspects of the immune regulation, such as negative selection of self-reactive thymocytes and elimination of antigen-specific T cells at the end of an immune response. Interestingly, the role of Bim during infections remains largely unidentified. To explore the role of Bim in Chagas disease, we infected WT, Bim+/−, Bim−/− mice with trypomastigotes forms of the Y strain of T. cruzi. Strikingly, our data revealed that Bim−/− mice exhibit a delay in the development of parasitemia followed by a deficiency in the control of parasite load in the bloodstream and a decreased survival compared to WT and Bim+/− mice. At the peak of parasitemia, peritoneal macrophages of Bim−/− mice exhibit decreased NO production, which correlated with a decrease in the pro-inflammatory Small Peritoneal Macrophage (SPM) subset. A similar reduction in NO secretion, as well as in the pro-inflammatory cytokines IFN-γ and IL-6, was also observed in Bim−/− splenocytes. Moreover, an impaired anti-T. cruzi CD8+ T-cell response was found in Bim−/− mice at this time point. Taken together, our results suggest that these alterations may contribute to the establishment of a delayed yet enlarged parasitic load observed at day 9 after infection of Bim−/− mice and place Bim as an important protein in the control of T. cruzi infections.

Endoplasmic reticulum (ER) stress plays a major role in several inflammatory disorders. ER stress induces the unfolded protein response (UPR), a conserved response broadly associated with innate immunity and cell metabolic function in various scenarios. Brucella abortus, an intracellular pathogen, triggers the UPR via Stimulator of interferon genes (STING), an important regulator of macrophage metabolism during B. abortus infection. However, whether ER stress pathways underlie macrophage metabolic function during B. abortus infection remains to be elucidated. Here, we showed that the UPR sensor inositol-requiring enzyme 1α (IRE1α) is as an important component regulating macrophage immunometabolic function. In B. abortus infection, IRE1α supports the macrophage inflammatory profile, favoring M1-like macrophages. IRE1α drives the macrophage metabolic reprogramming in infected macrophages, contributing to the reduced oxidative phosphorylation and increased glycolysis. This metabolic reprogramming is probably associated with the IRE1α-dependent expression and stabilization of hypoxia-inducible factor-1 alpha (HIF-1α), an important molecule involved in cell metabolism that sustains the inflammatory profile in B. abortus-infected macrophages. Accordingly, we demonstrated that IRE1α favors the generation of mitochondrial reactive oxygen species (mROS) which has been described as an HIF-1α stabilizing factor. Furthermore, in infected macrophages, IRE1α drives the production of nitric oxide and the release of IL-1β. Collectively, these data unravel a key mechanism linking the UPR and the immunometabolic regulation of macrophages in Brucella infection and highlight IRE1α as a central pathway regulating macrophage metabolic function during infectious diseases.

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