Serogroup-specific interactions of lipopolysaccharides with supported lipid bilayer assemblies

Lipopolysaccharide (LPS) is an amphiphilic lipoglycan that is the primary component of the outer membrane of Gramnegative bacteria. Classified as a pathogen associated molecular pattern (PAMPs), LPS is an essential biomarker for identifying pathogen serogroups. Structurally, LPS is comprised of a hydrophobic lipophilic domain that partitions into the outer membrane of Gram-negative bacteria. Previous work by our team explored biophysical interactions of LPS in supported lipid bilayer assemblies (sLBAs), and demonstrated LPS-induced hole formation in DOPC lipid bilayers. Here, we have incorporated cholesterol and sphingomyelin into sLBAs to evaluate the interaction of LPS in a more physiologically relevant system. The goal of this work was to determine whether increasing membrane complexity of sLBAs, and changing physiological parameters such as temperature, affects LPS-induced hole formation. Integrating cholesterol and sphingomyelin into sLBAs decreased LPS-induced hole formation at lower concentrations of LPS, and bacterial serotype contributed to differences in hole formation as a response to changes in temperature. We also investigated the possibility of LPS-induced hole formation in cellular systems using the cytokine response in both TLR4 (+)/(-) murine macrophages. LPS was presented to each cell line in murine serum, delipidated serum, and buffer (i.e. no serum), and the resulting cytokine levels were measured. Results indicate that the method of LPS presentation directly affects cellular cytokine expression. The two model systems presented in this study provide preliminary insight into the interactions of LPS in the host, and suggest the significance of amphiphile-carrier interactions in regulating host-pathogen biology during infection.