Pinchiaroli Julie, Saldanha Renita, Patteson Alison E, Robertson-Anderson Rae M, Gurmessa Bekele J
bioRxiv. 2024 Jun 9:2024.06.07.597906. doi: 10.1101/2024.06.07.597906.
The mechanical properties of the mammalian cell regulate many cellular functions and are largely dictated by the cytoskeleton, a composite network of protein filaments, including actin, microtubules, and intermediate filaments. Interactions between these distinct filaments give rise to emergent mechanical properties that are difficult to generate synthetically, and recent studies have made great strides in advancing our understanding of the mechanical interplay between actin and microtubule filaments. While intermediate filaments play critical roles in the stress response of cells, their effect on the rheological properties of the composite cytoskeleton remains poorly understood. Here, we use optical tweezers microrheology to measure the linear viscoelastic properties and nonlinear stress response of composites of actin and vimentin with varying molar ratios of actin to vimentin. We reveal a surprising, nearly opposite effect of actin-vimentin network mechanics compared to single-component networks in the linear versus nonlinear regimes. Namely, the linear elastic plateau modulus and zero-shear viscosity are markedly reduced in composites compared to single-component networks of actin or vimentin, whereas the initial response force and stiffness are maximized in composites versus single-component networks in the nonlinear regime. While these emergent trends are indicative of distinct interactions between actin and vimentin, nonlinear stiffening and longtime stress response appear to both be dictated primarily by actin, at odds with previous bulk rheology studies. We demonstrate that these complex, scale-dependent effects arise from the varied contributions of network density, filament stiffness, non-specific interactions, and poroelasticity to the mechanical response at different spatiotemporal scales. Cells may harness this complex behavior to facilitate distinct stress responses at different scales and in response to different stimuli to allow for their hallmark multifunctionality.
哺乳动物细胞的力学特性调节着许多细胞功能，并且在很大程度上由细胞骨架决定，细胞骨架是一个由蛋白质细丝组成的复合网络，包括肌动蛋白、微管和中间丝。这些不同细丝之间的相互作用产生了难以通过合成方式产生的新兴力学特性，并且最近的研究在推进我们对肌动蛋白和微管细丝之间力学相互作用的理解方面取得了很大进展。虽然中间丝在细胞的应激反应中发挥着关键作用，但它们对复合细胞骨架流变学特性的影响仍然知之甚少。在这里，我们使用光镊微流变学来测量肌动蛋白和波形蛋白复合材料在肌动蛋白与波形蛋白摩尔比不同时的线性粘弹性特性和非线性应力响应。我们揭示了在线性与非线性区域中，与单组分网络相比，肌动蛋白 - 波形蛋白网络力学具有惊人的、几乎相反的效果。具体而言，与肌动蛋白或波形蛋白的单组分网络相比，复合材料中的线性弹性平台模量和零剪切粘度显著降低，而在非线性区域中，复合材料相对于单组分网络的初始响应力和刚度则达到最大值。虽然这些新兴趋势表明肌动蛋白和波形蛋白之间存在不同的相互作用，但非线性硬化和长时间应力响应似乎都主要由肌动蛋白决定，这与之前的宏观流变学研究不一致。我们证明，这些复杂的、与尺度相关的效应源于网络密度、细丝刚度、非特异性相互作用和孔隙弹性在不同时空尺度下对力学响应的不同贡献。细胞可能利用这种复杂行为来促进在不同尺度下以及对不同刺激做出不同的应激反应，从而实现其标志性的多功能性。
