Compositional Effects on Phase Transition Behaviors of Myelin Monolayers

The myelin sheath is a multilamellar membrane surrounding the axon of the nervous system to form few tens of microns in diameter and its role is known to enhance the efficiency of electrochemical nervous signal by insulating the axon. Multiple sclerosis (MS) is an autoimmune disease of the central nervous system without fully known pathogenesis or cure. During MS the myelin sheath that insulates the axon deteriorates which leads to physical and cognitive disabilities. With so many people affected by MS it is unfortunate that the structure, composition, and interactions of healthy myelin are not fully understood. This research aims to understand how myelin lipid compositions affect the stability of the myelin sheath. In this research different mole ratios of cholesterol (CHOL) and phosphatidylethanolamine (PE) were used in isotherm experiments that measured lateral surface tension and the phase transition behaviors. The tool employed to accomplish this research goal was a Nima Langmuir Trough, a piece of lab equipment that measures the interfacial properties of monolayers of amphiphilic molecules. Computer software uses the Line Tension Equation to compute the lateral surface tension and generates a graph. A MOPS buffer solution of morpholinepropanesulfonic acid (MOPS), calcium chloride, and sodium chloride at pH 7.2 was used to mimic the physiological environment of the lipid mixtures. Binary lipid mixture ratios included (CHOL:PE): 1:0, 0.85:0.15, 0:75:0.25, 0.65:0.35, 0.50:0.50, 0.35:0.65, 0.25:0.75, 0.85:0.15, 0:1. Results show that samples with more prominent amounts of PE are more lipid-expanded than those samples with more CHOL. Upcoming experiments will include more realistic myelin compositions.