Role of Lipid Headgroups on Lateral Organization and Phase Transition Dynamics in Binary Mixture of Phospholipids and Cholesterol: What Can We Learn from Lipid Model Systems?

Biological membranes are highly complex structures comprising of a wide variety of phospholipids with differing headgroups, hydrocarbon chain lengths, and degrees of unsaturation, which distinguishably interact with cholesterol. The nature of lipid-cholesterol interactions, therefore, has been a long-standing interest not only to biochemists and biophysicists but also to clinicians, as it can provide important insight on physiologic and pathologic cellular pathways.

In this presentation, we describe the study performed to better understand the lateral interactions of two different types of phospholipids, i.e. 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) mixed with cholesterol in the membrane plane. The morphological heterogeneity originated from liquid-liquid immiscibility and corresponding phase transition behaviors were systematically studied in using a fluorescence microscopy coupled Langmuir trough as a function of composition and lateral pressure. To further evaluate the phase dynamics associated with monolayer compressibility, dilatational rheological responses of corresponding binary mixtures were also determined using the pendant drop tensiometer.

We anticipate that our results will provide a critical link as to how subtle changes in lipid compositions and surrounding conditions can alter membrane dynamics and structures, which, in turn, affect biological performance and functionality in cell membranes at large including myelin sheath of which defects and/or structural disruption can lead to neurodegenerative diseases such as Multiple Sclerosis.