MicroRNA negatively regulates NF-κB-mediated immune responses by targeting NOD1 in the teleost fish Miichthys miiuy.

Inflammation is a self-protection mechanism that can be triggered when innate immune cells detect infection. Eradication of pathogen infection requires appropriate immune and inflammatory responses, but excessive inflammatory responses can cause uncontrolled inflammation, autoimmune diseases, or pathogen dissemination. Mounting evidence has shown that microRNAs (miRNAs) in mammals act as important and versatile regulators of innate immunity and inflammation. However, miRNA-mediated regulation networks are largely unknown in inflammatory responses in lower vertebrates. Here miR-144 and miR-217 are identified as negative regulators in teleost inflammatory responses. We find that Vibrio harveyi and lipopolysaccharide (LPS) treatment significantly upregulate the expression of fish miR-144 and miR-217. Upregulated miR-144 and miR-217 suppress LPS-induced inflammatory cytokine expression by targeting nucleotide-binding oligomerization domain-containing protein 1 (NOD1), thereby avoiding excessive inflammatory responses. In addition, miR-144 and miR-217 regulate inflammatory responses through NOD1-induced nuclear factor kappa (NF-kB) signaling pathways. These findings demonstrate that miR-144 and miR-217 play regulatory roles in inflammatory responses by modulating the NOD1-induced NF-κB signaling pathway.