AFM Force Relaxation Curve Reveals That the Decrease of Membrane Tension Is the Essential Reason for the Softening of Cancer Cells

Abstract

Differences in stiffness constitute an extremely important aspect of the mechanical differences between cancer cells and normal cells, and atomic force microscopy (AFM) is the most commonly used tool to characterize the difference in stiffness. However, the process of mechanical characterization using AFM has been controversial and the influence of the membrane tension on AFM measurement results was often ignored. Here, a physical model involving a simultaneous consideration of the effects of the cell membrane, cytoskeleton network and cytosol was proposed. We carried out a theoretical analysis of AFM force relaxation curves, and as a result solved many of the remaining controversial issues regarding AFM-based mechanical characterization of cells, and provided a quantitative solution for the membrane tension measured using AFM indentation experiments for the first time. From the results of experiments on cells with different adherent shapes and different pairs of normal cells and cancer cells, we found additional force provided by membrane tension to be the main component of the force applied to the AFM probe, with decreased cell membrane tension being the essential reason for the greater softness of cancer cells than of normal cells. Hence, regulating membrane tension may become an important method for regulating the behavior of cancer cells.

Elastic moduli of normal and cancer cell membranes revealed by molecular dynamics simulations

“…68 Very recently, Ren et al developed a physical model to analyze the AFM force relaxation curves, and showed that the softening of cancer cells is mostly due to the decrease of the membrane surface tension. 69 In a traditional AFM experiment, the membrane tension, σ , is estimated by measuring the force required to pull a membrane tether with radius of R 0 from the bilayer membrane. It has been shown that σ is approximately related to the membrane bending modulus K c as σ = K c /2 R 0 2 .…”

Fibronectin: Molecular Structure, Fibrillar Structure and Mechanochemical Signaling

“…On a mesocellular level, microcontact printing, microfluidics and microfabrication have been combined to study the role of FN fibrils in transmitting forces, using either cell-derived fibrils [ 22 , 47 ] or artificially derived fibers [ 64 , 109 ], but these studies do not specifically investigate FN fibril mechanics. In the interest of measuring cell-substrate forces, some techniques such as AFM [ 117 ], (astigmatic) traction force microscopy [ 111 ], elastic resonator interference stress microscopy [ 118 ], or hex dot microcontact printing [ 119 ] tend not to focus directly on ECM response to deformation, where often FN, if involved, may only be considered for facilitating substrate attachment or is subjected to the survey only at the molecular or domain constitution [ 110 ].…”

Fibronectin: Molecular Structure, Fibrillar Structure, and Mechanochemical Signaling

“…On a mesocellular level, microcontact printing, microfluidics and microfabrication have been combined to study the role of FN fibrils in transmitting forces, using either cell-derived fibrils [19,45] or artificially derived fibers [65,96], but these studies do not specifically investigate FN fibril mechanics. In the interest of measuring cell-substrate forces, some techniques such as atomic force microscopy (AFM) [103], (astigmatic) traction force microscopy [104], elastic resonator interference stress microscopy (ERISM) [105], or hex dot microcontact printing [106] tend not to focus directly on ECM response to deformation, where often FN, if involved, may only be considered for facilitating substrate attachment or is subjected to the survey only at the molecular or domain constitution [97].…”