title: Pulmonary surfactant protein SP-C counteracts the deleterious effects of cholesterol on the activity of surfactant films under physiologically relevant compression-expansion dynamics.
abstract: The presence of cholesterol is critical in defining a dynamic lateral structure in pulmonary surfactant membranes. However, an excess of cholesterol has been associated with impaired surface activity of surfactant. It has also been reported that surfactant protein SP-C interacts with cholesterol in lipid/protein interfacial films. In this study, we analyzed the effect of SP-C on the thermodynamic properties of phospholipid membranes containing cholesterol, and the ability of lipid/protein complexes containing cholesterol to form and respread interfacial films capable of producing very low surface tensions upon repetitive compression-expansion cycling. SP-C modulates the effect of cholesterol to reduce the enthalpy associated with the gel-to-liquid-crystalline melting transition in dipalmitoylphosphatidylcholine (DPPC) bilayers, as analyzed by differential scanning calorimetry. The presence of SP-C affects more subtly the effects of cholesterol on the thermotropic properties of ternary membranes, mimicking more closely the lipid composition of native surfactant, where SP-C facilitates the miscibility of the sterol. Incorporation of 1% or 2% SP-C (protein/phospholipid by weight) promotes almost instantaneous adsorption of suspensions of DPPC/palmitoyloleoylphospatidylcholine (POPC)/palmitoyloleoyl-phosphatidylglycerol (POPG) (50:25:15, w/w/w) into the air-liquid interface of a captive bubble, in both the absence and presence of cholesterol. However, cholesterol impairs the ability of SP-C-containing films to achieve very low surface tensions in bubbles subjected to compression-expansion cycling. Cholesterol also substantially impairs the ability of DPPC/POPC/POPG films containing 1% surfactant protein SP-B to mimic the interfacial behavior of native surfactant films, which are characterized by very low minimum surface tensions with only limited area change during compression and practically no compression-expansion hysteresis. However, the simultaneous presence of 2% SP-C practically restores the compression-expansion dynamics of cholesterol- and SP-B-containing films to the efficient behavior shown in the absence of cholesterol. This suggests that cooperation between the two proteins is required for lipid-protein films containing cholesterol to achieve optimal performance under physiologically relevant compression-expansion dynamics.
authors.affiliation: Laboratoire de Chimie Physique des Macromolécules aux Interfaces, CP206/2, Université Libre de Bruxelles, Brussels, Belgium.
authors.forename: Leticia
authors.initials: L
authors.lastname: Gómez-Gil
authors.forename: David
authors.initials: D
authors.lastname: Schürch
authors.forename: Erik
authors.initials: E
authors.lastname: Goormaghtigh
authors.forename: Jesús
authors.initials: J
authors.lastname: Pérez-Gil
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D000388:Air; D000818:Animals; D002152:Calorimetry, Differential Scanning; D002784:Cholesterol / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D044367:Phase Transition; D010713:Phosphatidylcholines / Q000737:chemistry*; D010715:Phosphatidylglycerols / Q000737:chemistry*; D037701:Pulmonary Surfactant-Associated Protein B / Q000737:chemistry; D037721:Pulmonary Surfactant-Associated Protein C / Q000737:chemistry*; D013500:Surface Tension; D013552:Swine; D013816:Thermodynamics; D013997:Time Factors
chemical_list: D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010715:Phosphatidylglycerols; D037701:Pulmonary Surfactant-Associated Protein B; D037721:Pulmonary Surfactant-Associated Protein C; D015060:1,2-Dipalmitoylphosphatidylcholine; C060037:1-palmitoyl-2-oleoylglycero-3-phosphoglycerol; D002784:Cholesterol; C028694:1-palmitoyl-2-oleoylphosphatidylcholine