Surfactant processing in a simulated alveolar unit

Pulmonary surfactant is synthesized by alveolar type II cells and secreted by exocytosis into the alveolar lining fluid. It is a key determinant of alveolar stability and respiratory mechanics. These vital functions are mediated by its ability to create a surface active film, which drastically lowers the surface tension within the alveolar units. However, it is secreted as a particulate, viscoelastic material which does not readily disperse within an aqueous environment. This particulate nature of freshly released surfactant might be due to internal structural bonds and/or coherent thermodynamic forces, as it is composed of lipids and proteins in distinct structural arrangements. Naturally, at some point after cellular release, these aggregates (several m in diameter) must be transformed to provide material able of forming a surface active film, which is exceedingly thin throughout most parts of the air- exposed alveolar surface. However, the extracellular fate of native, freshly released surfactant, including all events and transformations taking place between exocytotic release and surfactant spreading at the air-liquid interface, are still poorly understood, hypothetical or even controversial. The studies described in this grant are therefore designated to address this issue in a specific way and with new methodological approaches. In particular, these studies will be performed with surfactant freshly released by alveolar type II cells in combination with a simulated alveolar unit (patent pending) comprising vital cells and an air-liquid interface. By applying new fluorescence imaging techniques in conjunction with several advanced microtechniques, we will conduct high-resolution and time-resolved analysis of the behavior of surfactant aggregates and their interaction with this interface. These investigations should provide new informations on the mechanisms responsible for the transformation of surfactant into functional units, which is of considerable scientific and medical interest.

Pulmonary surfactant is synthesized by alveolar type II cells and secreted by exocytosis into the alveolar lining fluid. It is a key determinant of alveolar stability and respiratory mechanics. These vital functions are mediated by its ability to create a surface active film, which drastically lowers the surface tension within the alveolar units. However, it is secreted as a particulate, viscoelastic material which does not readily disperse within an aqueous environment. This particulate nature of freshly released surfactant might be due to internal structural bonds and/or coherent thermodynamic forces, as it is composed of lipids and proteins in distinct structural arrangements. Naturally, at some point after cellular release, these aggregates (several m in diameter) must be transformed to provide material able of forming a surface active film, which is exceedingly thin throughout most parts of the air- exposed alveolar surface. However, the extracellular fate of native, freshly released surfactant, including all events and transformations taking place between exocytotic release and surfactant spreading at the air-liquid interface, are still poorly understood, hypothetical or even controversial. The studies described in this grant are therefore designated to address this issue in a specific way and with new methodological approaches. In particular, these studies will be performed with surfactant freshly released by alveolar type II cells in combination with a simulated alveolar unit (patent pending) comprising vital cells and an air-liquid interface. By applying new fluorescence imaging techniques in conjunction with several advanced microtechniques, we will conduct high-resolution and time-resolved analysis of the behavior of surfactant aggregates and their interaction with this interface. These investigations should provide new informations on the mechanisms responsible for the transformation of surfactant into functional units, which is of considerable scientific and medical interest.