Role of Cytoskeletal Components in Stress-Relaxation Behavior of Adherent Vascular Smooth Muscle Cells

Abstract

A number of recent studies have demonstrated the effectiveness of atomic force microscopy (AFM) for characterization of cellular stress-relaxation behavior. However, this technique's recent development creates considerable need for exploration of appropriate mechanical models for analysis of the resultant data and of the roles of various cytoskeletal components responsible for governing stress-relaxation behavior. The viscoelastic properties of vascular smooth muscle cells (VSMCs) are of particular interest due to their role in the development of vascular diseases, including atherosclerosis and restenosis. Various cytoskeletal agents, including cytochalasin D, jasplakinolide, paclitaxel, and nocodazole, were used to alter the cytoskeletal architecture of the VSMCs. Stress-relaxation experiments were performed on the VSMCs using AFM. The quasilinear viscoelastic (QLV) reduced-relaxation function, as well as a simple power-law model, and the standard linear solid (SLS) model, were fitted to the resultant stress-relaxation data. Actin depolymerization via cytochalasin D resulted in significant increases in both rate of relaxation and percentage of relaxation; actin stabilization via jasplakinolide did not affect stress-relaxation behavior. Microtubule depolymerization via nocodazole resulted in nonsignificant increases in rate and percentage of relaxation, while microtubule stabilization via paclitaxel caused significant decreases in both rate and percentage of relaxation. Both the QLV reduced-relaxation function and the power-law model provided excellent fits to the data (R(2)=0.98), while the SLS model was less adequate (R(2)=0.91). Data from the current study indicate the important role of not only actin, but also microtubules, in governing VSMC viscoelastic behavior. Excellent fits to the data show potential for future use of both the QLV reduced-relaxation function and power-law models in conjunction with AFM stress-relaxation experiments.

Measuring nanoscale viscoelastic parameters of cells directly from AFM force-displacement curves

“…For the SLS model E 0 is the instantaneous modulus [ E 0  =  E ( t  → 0)], E ∞ is the infinite (long-term, equilibrium) modulus [ E ∞  =  E ( t  → ∞)] and τ is the relaxation time of the material. For the PLR model one can find different representations in the literature from as simple as E ( t ) =  E 1 t −α ( E 1 is modulus at t  = 1 s) 39 . Here we used the following expression for the modified power law 71, 84 , which removes zero time singularity and allows more direct comparison with the SLS model:where E 0 and E ∞ have the same meaning as in SLS model, t ′ is a small time offset (here was set equal to the sampling time 5*10 −4  s), and α is the power law exponent.…”

Chemoenvironmental modulators of fluidity in the suspended biological cell

“…[6][7][8][9][10][11][12][13][14] Up to a threshold of nonlinearity corresponding to a strain rate of (1% s À1 , 15,16 whole cells are well described mechanically by two parameters: Fig. 1 Deformation regime map for biological cells around 1 s. Slanted darker regions denote findings of power-law rheology (log-log slope of fluidity a when load is fixed) by various techniques.…”

“…26 The crucial prediction of these models is a broad distribution of relaxation times that in cells is associated with the range of cytoskeletal length scales, including lament segment length and crosslink spacing, that precludes accurate representation of cell mechanics over a large frequency range by one or several spring-dashpot pairs. 6,9,10,12,17 Still lacking, however, is a direct understanding of the molecular origin of the magnitude of uidity and its modulation by various chemoenvironmental factors, especially when measured independently of stiffness. Therefore, the primary goal of the current work is to add experimental ndings that enable new models or extension of existing models to describe how uidity of suspended cells is modulated by temperature, cytoskeleton (dis)assembly, pH, and osmotic pressure.…”

Biomechanics of single chondrocytes under direct shear

“…In our study, sheared chondrocytes exhibit a reorganization of their actin filaments, which become localized on the trailing side of the cell, near its base. Moreover, it has been previously established that actin contributes significantly to cell stiffness parameters under compression or tension testing modalities (Trickey et al 2004;Leipzig et al 2006;Hemmer et al 2009). Thus, based on the results in this study, similar connections can be drawn between actin filaments and the spatial shear characteristics within a single cell.…”