(464f) Unraveling the Role of Total Cerebroside in Modulating the Biomechanical and Thermodynamic Properties of Myelin Monolayers

The myelin sheath, a multilamellar plasma membrane surrounding nerve axons, functions as an electrical insulator, facilitating the rapid propagation of action potentials along the axon. Synthesized by oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system, myelin sheath is essential for efficient signal transduction. Perturbations in its integrity can result in various neurodegenerative pathologies. The myelin membrane is a complex combination of lipids and proteins, with a lipid-to-protein ratio of approximately 3:1 to 4:1 in its dehydrated state. Although previous studies have employed model lipid bilayers and monolayers to investigate interactions with essential myelin proteins such as myelin basic protein (MBP) and proteolipid protein (PLP), the impact of lipid composition, particularly cerebrosides, on the thermodynamics and rheological properties of membrane formation remains elusive. In this study, we elucidate the influence of total cerebrosides (TCERs, hydroxylated as well as non-hydroxylated ones) on the biophysical properties of extracellular myelin membranes. Employing a Langmuir-trough apparatus at physiologically relevant temperature of 37°C, we performed surface pressure-area isotherm measurements and dilational rheology experiments, coupled with simultaneous fluorescence imaging for structural and thermodynamic characterization. Our findings demonstrate that TCER shows a condensing effect, resulting in a more densely packed monolayer conformation. This condensation is attributed to the hydrogen bonding interactions between the galactose headgroups of cerebrosides, as well as the van der Waals forces between their long, saturated acyl chains. From isotherm data, we further calculated differences in the Gibbs free energy of mixing between the four monolayers to show differences in intermolecular interactions and miscibility. In addition, the dilational rheology measurements revealed an increase in the viscoelastic moduli with increasing TCER concentration, indicating enhanced membrane stability and resistance to deformation. The subtle changes in biophysical properties induced by trace amounts of TCER may have profound implications for the structural integrity and function of myelin membranes. We anticipate that these findings will provide valuable insights into the critical role of lipid composition in maintaining the stability of the myelin sheath and the potential consequences of lipid dysregulation in demyelinating disorders.