Inhibition of lethal inflammatory responses through the targeting of membrane-associated Toll-like receptor 4 signaling complexes with a Smad6-derived peptide

We have previously reported that Smad6, one of the inhibitory Smads of transforming growth factor-β (TGF-β)/bone morphogenetic protein (BMP) signaling, inhibits Toll-like receptor (TLR) 4 signaling by disrupting the Pellino-1-mediated TLR4 signaling complex. Here, we developed Smaducin-6, a novel membrane-tethered palmitic acid-conjugated Smad6-derived peptide composed of amino acids 422–441 of Smad6. Smaducin-6 interacted with Pellino-1, located in the inner membrane, thereby disrupting the formation of IRAK1-, RIP1-, IKKε-mediated TLR4 signaling complexes. Systemic administration of Smaducin-6 showed a significant therapeutic effect on mouse TLR4-mediated inflammatory disease models, cecal-ligation–puncture (CLP)-induced sepsis, and lipopolysaccharide-induced endotoxemia, by inhibiting pro-inflammatory cytokine production and apoptosis while enhancing neutrophil migration and bacterial clearance. Our findings provide clues to develop new peptide-based drugs to target Pellino-1 protein in TLR4 signaling pathway for the treatment of sepsis.