Abstract
Regulatory Nod-like receptors (NLRs) are a subgroup of the cytosolic NLR family of pathogen recognition receptors (PRRs). These receptors can tune the innate immune responses triggered by the activation of other PRRs by either augmenting or attenuating the activated pro-inflammatory signaling cascades. Nod-like receptor X1 (NLRX1) is the only known mitochondria-associated negative regulatory NLR. NLRX1 attenuates several inflammatory pathways and modulates cellular processes such as autophagy and mitochondrial function following infection or injury. Using both in vitro expression and in vivo experimental models, NLRX1 is extensively described in the context of anti-viral signaling and host-defense against invading pathogens. More recently, NLRX1 has also gained interest in the field of cancer and metabolism where NLRX1 functions to attenuate overzealous inflammation in various inflammatory and autoimmune diseases. However, the exact function of this novel receptor is still under debate and many, often contradictory, mechanisms of action together with cellular localizations have been proposed. Thus, a better understanding of the underlying mechanism is crucial for future research and development of novel therapeutical approaches. Here, we summarize the current findings on NLRX1 and discuss its role in both infectious and inflammatory context.
Highlights
To respond to infection, innate immune cells of the host express multiple pathogen recognition receptors (PRRs) that recognize different danger- and pathogen associated molecular patterns (DAMPs and PAMPs) and induce the expression of key proinflammatory pathways
More evidence is required to explain the interaction with cytosolic proteins such as TRAF6 or stimulator of interferon genes (STING), or mitochondrial outer membrane proteins such as mitochondrial antiviral signalling protein (MAVS)
It is possible that the function of Nod-like receptor X1 (NLRX1) is highly dependent on the cellular environment and an altered metabolic state could explain some of the differences observed in the different infectious and cancer models
Summary
Innate immune cells of the host express multiple pathogen recognition receptors (PRRs) that recognize different danger- and pathogen associated molecular patterns (DAMPs and PAMPs) and induce the expression of key proinflammatory pathways. Moore et al (2008) propose that NLRX1 negatively regulates mitochondrial antiviral signalling protein (MAVS)-mediated type I IFN signaling by directly interacting with MAVS through its LRR domain at the MOM.
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