Mechanism of Anti-Inflammatory Activity of TLR4-Interacting SPA4 Peptide

The TLR4-interacting SPA4 peptide suppresses inflammation. We assessed the structural and physicochemical properties and binding of SPA4 peptide to TLR4–MD2. We also studied the changes at the whole transcriptome level, cell morphology, viability, secreted cytokines and chemokines, and cell influx in cell systems and mouse models challenged with LPS and treated with SPA4 peptide. Our results demonstrated that the SPA4 peptide did not alter the cell viability and size and only moderately affected the transcriptome of the cells. Computational docking and rendering suggested that the SPA4 peptide intercalates with LPS-induced TLR4–MD2 complex. Results with alanine mutations of D-2 amino acid and NYTXXXRG-12–19 motif of SPA4 peptide suggested their role in binding to TLR4 and in reducing the cytokine response against LPS stimulus. Furthermore, therapeutically administered SPA4 peptide significantly suppressed the secreted levels of cytokines and chemokines in cells and bronchoalveolar lavage fluids of LPS-challenged mice. The results suggest that the SPA4 peptide intercalates with LPS-induced TLR4 complex and signaling for the suppression of inflammation.