Receptor-Independent Interaction of Bacterial Lipopolysaccharide with Lipid and Lymphocyte Membranes; the Role of Cholesterol

Abstract

Lipopolysaccharide (LPS) is a major constituent of bacterial outer membranes where it makes up the bulk of the outer leaflet and plays a key role as determinant of bacterial interactions with the host. Membrane-free LPS is known to activate T-lymphocytes through interactions with Toll-like receptor 4 via multiprotein complexes. In the present study, we investigate the role of cholesterol and membrane heterogeneities as facilitators of receptor-independent LPS binding and insertion, which underpin bacterial interactions with the host in symbiosis, pathogenesis and cell invasion. We use fluorescence spectroscopy to investigate the interactions of membrane-free LPS from intestinal Gram-negative organisms with cholesterol-containing model membranes and with T-lymphocytes. LPS preparations from Klebsiella pneumoniae and Salmonella enterica were found to bind preferentially to mixed lipid membranes by comparison to pure PC bilayers. The same was observed for LPS from the symbiote Escherichia coli but with an order of magnitude higher dissociation constant. Insertion of LPS into model membranes confirmed the preference for sphimgomyelin/cholesterol-containing systems. LPS insertion into Jurkat T-lymphocyte membranes reveals that they have a significantly greater LPS-binding capacity by comparison to methyl-β-cyclodextrin cholesterol-depleted lymphocyte membranes, albeit at slightly lower binding rates.

Introductory Chapter: Obesity—“OMICS” and Endocrinology

“…Sirt1 and its posttranscriptional impact on p53 [42,43] is heavily involved in the differentiation of adipocytes, as well as lipid metabolism in general [44][45][46][47][48], with their implications for abnormal Sirt1 deacetylation of p53, linked to lipid metabolism with its characteristic transformation of adipocytes and ensuing liver disease. Interestingly, both Sirt1 and p53 knockout mice develop NAFLD [49][50][51][52], which alludes to a close connections between adipocyte phenotype "switch" involving Sirt 1 and/or p53 impact on mitochondrial functioning [53][54][55][56].…”

“…Hence, the p53-mediated downregulation of PXR activity [55,56] is not dependent of the Sirt1/PXR-mediated reactions [57][58][59][60]. Therefore, the untoward p53/PXR interactions, which lead to NAFLD, are coupled to an altered expression of miRNA species related to the turnover of xenobiotics [61][62][63].…”

Magnesium Therapy Prevents Senescence with the Reversal of Diabetes and Alzheimer’s Disease

“…LPS may influence membrane cholesterol by binding to cell membranes and lipoproteins and its packing in the membrane allows the increased interaction or displacement of the Aβ peptide. LPS can rapidly insert into cell membranes with a preference for insertion and partition into cholesterol/sphingomyelin domains in cell membranes [159]- [161]. Lipid rafts containing sphingomyelin and cholesterol form microdomains in cell membranes for the recruitment of lipid modified proteins such as Aβ oligomers with the binding of these hydrophobic proteins to membranes.…”

LPS Regulates Apolipoprotein E and A<i>β</i> Interactionswith Effects on Acute Phase Proteins and Amyloidosis

“…LPS has been shown to effect hepatic genomic stability [32] with effects on reverse cholesterol transport in macrophages [4] and with macrophage activation [33]. LPS can rapidly insert into cell membranes with a preference for insertion and partition into cholesterol/ sphingomyelin domains in cell membranes [34]- [36]. Cholesterol is an essential membrane component and in association with phospholipids, glycosphingolipids such as ceramide or gangliosides, glycerophospholipids (plasmalogen) and sterols make up the membrane bilayers in cells.…”