Negative Regulator Nlrc3-like Maintain the Balanced Innate Immune Response During Mycobacterial Infection in Zebrafish

Abstract

The NOD-like receptors (NLRs) have been shown to be involved in infection and autoinflammatory disease. Previously, we identified a zebrafish NLR, nlrc3-like, required for macrophage homeostasis in the brain under physiological conditions. Here, we found that a deficiency of nlrc3-like leads to decreased bacterial burden at a very early stage of Mycobacterium marinum infection, along with increased production of pro-inflammatory cytokines, such as il-1β and tnf-α. Interestingly, myeloid-lineage specific overexpression of nlrc3-like achieved the opposite effects, suggesting that the impact of nlrc3-like on the host anti-mycobacterial response is mainly due to its expression in the innate immune system. Fluorescence-activated cell sorting (FACS) and subsequent gene expression analysis demonstrated that inflammasome activation-related genes were upregulated in the infected macrophages of nlrc3-like deficient embryos. By disrupting asc, encoding apoptosis-associated speck-like protein containing a CARD, a key component for inflammasome activation, the bacterial burden increased in asc and nlrc3-like double deficient embryos compared with nlrc3-like single deficient embryos, implying the involvement of inflammasome activation in infection control. We also found extensive neutrophil infiltration in the nlrc3-like deficient larvae during infection, which was associated with comparable bacterial burden but increased tissue damage and death at a later stage that could be alleviated by administration of dexamethasone. Our findings uncovered an important role of nlrc3-like in the negative regulation of macrophage inflammasome activation and neutrophil infiltration during mycobacterial infection. This highlights the importance of a balanced innate immune response during mycobacterial infection and provides a potential molecular basis to explain how anti-inflammatory drugs can improve treatment outcomes in TB patients whose infection is accompanied by a hyperinflammatory response.

Emerging mechanisms and functions of inflammasome complexes in teleost fish

“…Loss of NLRC3-like function resulted in aberrant activation of inflammasome pathway in an ASC-dependent manner. All these data suggest that zebrafish NLRC3-like suppresses activities of inflammasomes by interfering the interactions between ASC and other inflammasome components ( 83 , 102 , 103 ). Interestingly, the analysis from genomes or transcriptomes suggest that the NLRC3 or NLRC3-like expansions exist in different species of fish ( 15 , 101 ).…”

“…Homologs of NLRC3 lacking CARD domain or containing other additional domain(s) are classified into NLRC3-like proteins ( 101 ).The interaction between NLRC3-like and ASC was confirmed in the goldfish and zebrafish ( 95 , 102 ). The deficiency of zebrafish NLRC3-like promoted ASC-mediated inflammasome activation and the early control of mycobacterial proliferation ( 103 ). Loss of NLRC3-like function resulted in aberrant activation of inflammasome pathway in an ASC-dependent manner.…”

Tibetan medicine salidroside improves host anti-mycobacterial response by boosting inflammatory cytokine production in zebrafish

“…Three-dpf zebrafish embryos were infected (∼250 CFU) via the duct of Cuvier by micro-injection unless otherwise indicated ( Niu et al, 2022 ).…”

“…It has been well documented that the host immune response has great impact on the outcome of TB infection ( Tobin et al, 2012 ; Roca and Ramakrishnan, 2013 ; Mayer-Barber et al, 2014 ; Boisson-Dupuis et al, 2015 ; Niu et al, 2022 ). Thus, developing novel anti-TB drugs from the perspective of immune regulation can provide an important supplement to traditional bactericidal treatment.…”