Anisotropic rheology and directional mechanotransduction in vascular endothelial cells

Abstract

Adherent cells remodel their cytoskeleton, including its directionality, in response to directional mechanical stimuli with consequent redistribution of intracellular forces and modulation of cell function. We analyzed the temporal and spatial changes in magnitude and directionality of the cytoplasmic creep compliance (⌫) in confluent cultures of bovine aortic endothelial cells subjected to continuous laminar flow shear stresses. We extended particle tracking microrheology to determine at each point in the cytoplasm the principal directions along which ⌫ is maximal and minimal. Under static condition, the cells have polygonal shapes without specific alignment. Although ⌫ of each cell exhibits directionality with varying principal directions, ⌫ averaged over the whole cell population is isotropic. After continuous laminar flow shear stresses, all cells gradually elongate and the directions of maximal and minimal ⌫ become, respectively, parallel and perpendicular to flow direction. This mechanical alignment is accompanied by a transition of the cytoplasm to be more fluid-like along the flow direction and more solid-like along the perpendicular direction; at the same time ⌫ increases at the downstream part of the cells. The resulting directional anisotropy and spatial inhomogeneity of cytoplasmic rheology may play an important role in mechanotransduction in adherent cells by providing a means to sense the direction of mechanical stimuli.anisotropy ͉ microrheology ͉ shear stress B lood vessels are exposed to flow-induced shear stresses, which are borne primarily by vascular endothelial cells (VECs) (1). VECs perform functions such as regulation of permeability, the production, secretion, and metabolism of biochemical substances, and modulation of vascular smooth muscle cell contractility. Sustained application (hours) of laminar shear stresses (LSS) to cultured VECs induces cell elongation and alignment along the flow direction (2). The actin stress fibers thicken and gradually align with flow (3), the focal adhesions relocate primarily to the upstream part of the cell (4), and cell-cell junctions are transiently disrupted (5). The structural reorganization of cytoskeleton leads to changes in subcellular microrheology that can play an important role in mechanosensing and signaling by redistributing the external forces among intracellular subdomains (6, 7). Existing evidence suggests that changes in subcellular microrheology, including directionality and polarity, could provide a mechanism for cells to sense external forces and their direction, modulate intracellular signaling, and regulate gene expression and cell turnover (8).The realization that mechanical polarity may modulate cell function has conferred special significance to measuring the spatiotemporal adaptation of rheological properties of VECs to shear stresses. Sato et al. (9) determined the viscous and elastic resistances to micropipette aspiration of VECs after 24 h of directional LSS and provided the first quantitative evidence of the adaptation of VE...

Endothelial Trauma From Mechanical Thrombectomy in Acute Stroke

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“…We have previously demonstrated that physiological blood flow and resultant shear stress are crucial for EC maintenance and remodeling after injury [13][14][15][16][17][18][19][20][21][22] and that locally disrupted blood flow contributes to inflammatory cascades. 23 Many of the proposed mechanisms of reperfusion injury after acute ischemic stroke also originate at the EC level.…”

Cytoplasmic dynein pushes the cytoskeletal meshwork forward during axonal elongation

“…Using this approach, we have shown that axonal stretching occurs during axonal elongation in vivo (Roossien et al, 2013), in cultured neurons from various species (Miller and Sheetz, 2006;O'Toole et al, 2008;Lamoureux et al, 2010a;Lamoureux et al, 2010b;Roossien et al, 2013) and in response to forces generated in or applied to the growth cone (O'Toole et al, 2008;Lamoureux et al, 2010a). Furthermore, in the field of nonneuronal cell biophysics, docked mitochondria are well-accepted fiducial markers for bulk subcellular deformation (Wang et al, 2001;Knight et al, 2006;Gilchrist et al, 2007;Wang et al, 2007;del Alamo et al, 2008;Bell et al, 2012;Silberberg and Pelling, 2013).…”

GEF-H1 controls focal adhesion signaling that regulates mesenchymal stem cell lineage commitment

“…The anisotropic orientation of stress fibers, together with the dynamic FAs, has been linked to the spatial organization of intracellular forces and changes in cell morphology, leading to the reinforcement of cell tension (Lee et al, 2013;Zemel et al, 2010a;Zemel et al, 2010b). The structural and mechanical polarization of the cytoskeleton has been observed in cells responding to diverse types of active mechanical stimuli (del Alamo et al, 2008;Hur et al, 2012;Kaunas et al, 2005). It is thus conceivable that the recruitment of NMIIB, through the DH domain of GEF-H1, to FAs contributes to a polarized distribution of stress fibers and FA formation, thereby generating an increase in intracellular tension and modulating cell shape.…”