Abstract
Interaction between surfactant protein-A (SP-A) and toll-like receptor (TLR)4 plays a critical role in host defense. In this work, we studied the host defense function of SPA4 peptide (amino acids GDFRYSDGTPVNYTNWYRGE), derived from the TLR4-interacting region of SP-A, against Pseudomonas aeruginosa. We determined the binding of SPA4 peptide to live bacteria, and its direct antibacterial activity against P. aeruginosa. Pro-phagocytic and anti-inflammatory effects were investigated in JAWS II dendritic cells and primary alveolar macrophages. The biological relevance of SPA4 peptide was evaluated in a mouse model of acute lung infection induced by intratracheal challenge with P. aeruginosa. Our results demonstrate that the SPA4 peptide does not interact with or kill P. aeruginosa when cultured outside the host. The SPA4 peptide treatment induces the uptake and localization of bacteria in the phagolysosomes of immune cells. At the same time, the secreted amounts of TNF-α are significantly reduced in cell-free supernatants of SPA4 peptide-treated cells. In cells overexpressing TLR4, the TLR4-induced phagocytic response is maintained, but the levels of TLR4-stimulated TNF-α are reduced. Furthermore, our results demonstrate that the therapeutic administration of SPA4 peptide reduces bacterial burden, inflammatory cytokines and chemokines, intracellular signaling, and lactate levels, and alleviates lung edema and tissue damage in P. aeruginosa-infected mice. Together, our results suggest that the treatment with SPA4 peptide can help control the bacterial burden, inflammation, and tissue injury in a P. aeruginosa lung infection model.
Highlights
Antimicrobial resistance and the acquisition of new virulence traits have contributed to a worldwide increase in the incidence of infections and associated morbidity and mortality.[1,2,3] new therapeutic approaches are urgently needed to control difficult-to-treat infections
We examined whether SPA4 peptide affects the Toll-like receptor 4 (TLR4)-induced phagocytic and inflammatory response against Pseudomonas aeruginosa, an LPS-expressing Gramnegative bacteria, and evaluated its biological affects in vitro and in a mouse model of P. aeruginosa-induced lung infection and inflammation
We solved the structure of the SPA4 peptide by nuclear magnetic resonance spectroscopy, and studied the physicochemical features, which demonstrated its structural adaptability for binding to TLR4.[39]
Summary
Antimicrobial resistance and the acquisition of new virulence traits have contributed to a worldwide increase in the incidence of infections and associated morbidity and mortality.[1,2,3] new therapeutic approaches are urgently needed to control difficult-to-treat infections. SP-A utilizes different mechanisms and facilitates clearance of respiratory pathogens. It reduces microbial growth by increasing the membrane permeability of Gram-negative bacteria,[4,5,6,7] and fungal pathogen, [8] and stimulates the pathogen recognition, clearance, and immune responses of phagocytes through its interaction with calreticulin/CD91, signal regulatory protein (SIRP)α, Toll-like receptors (TLRs), and SP-R210.[4, 9, 10] Secreted levels of SP-A are, reduced during lung infection and inflammatory conditions.[11, 12] Replenishing SP-A in such scenarios could aid in the elimination of pathogens. Despite an understanding of the host defense role, the use of SP-A for therapeutic purposes has been difficult due to its large size, amenability to degradation, and undesirable pro-inflammatory effects of the N-terminal region of SP-A, through its binding to calreticulin/CD91.[13]
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