Popis: |
Cells and tissues are subjected to various types of mechanical cues such as stretch. These forces play a significant role in regulating cell functions. The lung is an organ where cells experience cyclic stretch by breathing. There are two types of cells in the lung. The squamous ATI cells contribute to the majority of the alveolar surface and undergo the mechanical stretch, and the cuboidal ATII cells are secreting surfactant proteins to reduce the surface tension of the alveolus. ATI cells have plenty invaginations in their plasma membrane known as caveolae, which are associated with stress fibers that contribute to cell contractile force generation, and are believed to have a mechanosensing role. Measurement of contractile forces is one of the main topics of interest in research in understanding the sub-cellular pathways. These forces, however, are not directly measurable and are calculated by Traction force microscopy (TFM). In this work, TFM was applied on an elastic substrate to study the alveolar traction forces under uniaxial stretch. The elastic substrate was made as a thin membrane consisting of two different layers of biocompatible polydimethylsiloxane (PDMS) polymer. The bottom layer was made of a stiffer type of PDMS providing support for the top layer that was made of an ultra-soft PDMS gel. In TFM, the traction forces are calculated by measuring the deformation of the soft gel caused by the cells. Fluorescent beads added on top of the gel help measure the substrate deformation. Deformation measurement and conversion to traction forces were done by Matlab codes. In this work, alveolar epithelial lentivirus immortalized (hAELVi) cells, an ATI-like cell line, were used to investigate the effect of stretch on the traction forces. Mutant hAELVi cells were also used to study caveolae's contribution to cell forces. The results indicated that ATI cells produced less traction force than the caveolae deficient cells. Normal alveolar cells responded to the stretch of 50\% strain magnitude by increasing their traction force, while the mutant cells responded to the stretch by reducing their traction force. Comparison between cell responses to slow and fast stretch indicate that the mechanical response of alveolar cells to stretch depends on both their physical properties in the beginning, and later responses depend on the signaling pathways triggered by the stretch. |