Measuring Cell Adhesion Forces with the Atomic Force Microscope at the Molecular Level

Abstract

In the past 25 years many techniques have been developed to characterize cell adhesion and to quantify adhesion forces. Atomic force microscopy (AFM) has been used to measure forces in the pico-newton range, an experimental technique known as force spectroscopy. We modified such an AFM to measure adhesion forces between live cells or between cells and surfaces. This strategy required functionalizing the surface of the sensors for immobilizing the cell. We used Dictyostelium discoideum cells which respond to starvation by surface expression of the adhesion molecule csA and consequent aggregation to measure the adhesion force of a single csA-csA bond. Relevant experimental parameters include the duration of contact between the interacting surfaces, the force against which this contact is maintained, the number and specificity of interacting adhesion molecules and the constituents of the medium in which the interaction occurs. This technology also permits the measurement of the viscoelastic properties of single cells or cell layers.

AFM as a tool to probe and manipulate cellular processes

“…A typical mechanical response is characterised by an initial contraction of the cell body (2) followed by small fluctuations in the amplitude of the signal (3) revealed how cells interact with various artificial and biological surfaces [14, 15, 18-21, 24, 25, 27, 29]. For example, Benoit et al described the interaction of cells with diverse artificially tailored surfaces with the goal of guiding the rational design of medical implants [17]. Similar experiments have revealed molecular mechanisms that might explain the divergences observed in the rolling behaviours of leukocytes over different selectin-decorated surfaces [9,22].…”

“…AFM experiments have also characterised specific cell signalling pathways affecting fibronectin-mediated adhesion in the gastrulation process in the early development of zebrafish embryos [26]. In addition, AFM has been employed to directly measure interaction forces between living cells [13,16,17,23,28,63]. In the Dictyostelium model of cell aggregation, two different types of adhesions have been observed depending on the developmental stage of the cells.…”

“…In the Dictyostelium model of cell aggregation, two different types of adhesions have been observed depending on the developmental stage of the cells. In this system, the relative contribution of csA adhesion proteins was assessed through genetic manipulations and variations of the composition of cellular environments [16,17]. Thie et al used AFM to examine the preferential interaction of human trophoblasts with uterine epithelium cells.…”

“…Moreover, the ability to attach functional biomolecules to the tip of the atomic force microscope has made it possible to characterise molecular recognition processes directly on the surfaces of living cells. This experimental approach has been widely applied to study cellular adhesion processes [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] and to map the distribution of membrane receptors, an application described in great details in several recent reviews [31][32][33][34].…”

“…AFM force experiments on living cells have also opened up new vistas in the investigation of the mechanical properties of individual cells and have demonstrated the importance of these mechanical properties to various physiological and physiopathological processes [17,19,[35][36][37][38][39][40]. This review will discuss some recent contributions of the AFM to cell physiology with a focus on the probing and nanomanipulation of structures in living cell.…”