Histamine effects on endothelial cell fibronectin interaction studied by atomic force microscopy

Atomic force-multi-optical imaging integrated microscope for monitoring molecular dynamics in live cells

A novel hybrid imaging system is constructed integrating atomic force microscopy (AFM) with a combination of optical imaging techniques that offer high spatial resolution. The main application of this instrument (the NanoFluor microscope) is the study of mechanotransduction with an emphasis on extracellular matrix-integrin-cytoskeletal interactions and their role in the cellular responses to changes in external chemical and mechanical factors. The AFM allows the quantitative assessment of cytoskeletal changes, binding probability, adhesion forces, and micromechanical properties of the cells, while the optical imaging applications allow thin sectioning of the cell body at the coverslip-cell interface, permitting the study of focal adhesions using total internal reflection fluorescence (TIRF) and internal reflection microscopy (IRM). Combined AFM-optical imaging experiments show that mechanical stimulation at the apical surface of cells induces a force-generating cytoskeletal response, resulting in focal contact reorganization on the basal surface that can be monitored in real time. The NanoFluor system is also equipped with a novel mechanically aligned dual camera acquisition system for synthesized Forster resonance energy transfer (FRET). The integrated NanoFluor microscope system is described, including its characteristics, applications, and limitations.

Endothelial focal adhesions and barrier function

Focal adhesions composed of integrins provide an important structural basis for anchoring the endothelial lining to its surrounding matrices in the vascular wall. Complex molecular reactions occur at the endothelial cell-matrix contact sites in response to physical and chemical stress present in the circulatory system. Recent experimental evidence points to the importance of focal adhesions in the regulation of microvascular barrier function. On one hand, the adhesive interaction between integrins and their extracellular ligands is essential to the maintenance of endothelial barrier properties, and interruption of integrin-matrix binding leads to leaky microvessels. On the other hand, focal adhesion assembly and activation serve as important signalling events in modulating endothelial permeability under stimulatory conditions in the presence of angiogenic factors, inflammatory mediators, or physical forces. The focal responses show distinctive patterns with different temporal characteristics, whereas focal adhesion kinase (FAK) plays a central role in initiating and integrating various signalling pathways that ultimately affect the barrier function. The molecular basis of focal adhesion-dependent microvascular permeability is currently under investigation, and advances in the technologies of computerized quantitative microscopy and intact microvessel imaging should aid the establishment of a functional significance for focal adhesions in the physiological regulation of microvascular permeability.