Mechanosensitivity Occurs along the Adhesome's Force Train and Affects Traction Stress

Can a bulky glycocalyx promote catch bonding in early integrin adhesion? Perhaps a bit

Many types of cancer cells overexpress bulky glycoproteins to form a thick glycocalyx layer. The glycocalyx physically separates the cell from its surroundings, but recent work has shown that the glycocalyx can paradoxically increase adhesion to soft tissues and therefore promote the metastasis of cancer cells. This surprising phenomenon occurs because the glycocalyx forces adhesion molecules (called integrins) on the cell's surface into clusters. These integrin clusters have cooperative effects that allow them to form stronger adhesions to surrounding tissues than would be possible with equivalent numbers of un-clustered integrins. These cooperative mechanisms have been intensely scrutinized in recent years. A more nuanced understanding of the biophysical underpinnings of glycocalyx-mediated adhesion could uncover therapeutic targets, deepen our general understanding of cancer metastasis, and elucidate general biophysical processes that extend far beyond the realm of cancer research. This work examines the hypothesis that the glycocalyx has the additional effect of increasing mechanical tension experienced by clustered integrins. Integrins function as mechanosensors that undergo catch bonding-meaning the application of moderate tension increases integrin bond lifetime relative to the lifetime of integrins experiencing low tension. In this work, a three-state chemomechanical catch bond model of integrin tension is used to investigate catch bonding in the presence of a bulky glycocalyx. A pseudo-steady-state approximation is applied, which relies on the assumption that integrin bond dynamics occur on a much faster timescale than the evolution of the full adhesion between the plasma membrane and the substrate. Force-dependent kinetic rate constants are used to calculate a steady-state distribution of integrin-ligand bonds for Gaussian-shaped adhesion geometries. The relationship between the energy of the system and adhesion geometry is then analyzed in the presence and absence of catch bonding in order to evaluate the extent to which catch bonding alters the energetics of adhesion formation. This modeling suggests that a bulky glycocalyx can lightly trigger catch bonding, increasing the bond lifetime of integrins at adhesion edges by up to 100%. The total number of integrin-ligand bonds within an adhesion is predicted to increase by up to ~ 60% for certain adhesion geometries. Catch bonding is predicted to decrease the activation energy of adhesion formation by ~ 1-4 kBT, which translates to a ~ 3-50 × increase in the kinetic rate of adhesion nucleation. This work reveals that integrin mechanics and clustering likely both contribute to glycocalyx-mediated metastasis.

Can a bulky glycocalyx promote catch bonding in early integrin adhesion? Perhaps a bit

Many types of cancer overexpress bulky glycoproteins to form a thick glycocalyx layer. The glycocalyx physically separates the cell from its surroundings, but recent work has shown that the glycocalyx can paradoxically increase adhesion to soft tissues and therefore promote the metastasis of cancer cells. This surprising phenomenon occurs because the glycocalyx forces adhesion molecules (called integrins) on the cell's surface into clusters. These integrin clusters have cooperative effects that allow them to form stronger adhesions to surrounding tissues than would be possible with equivalent numbers of un-clustered integrins. These cooperative mechanisms have been intensely scrutinized in recent years; a more nuanced understanding of the biophysical underpinnings of glycocalyx-mediated adhesion could uncover therapeutic targets, deepen our general understanding of cancer metastasis, and elucidate general biophysical processes that extend far beyond the realm of cancer research. This work examines the hypothesis that the glycocalyx has the additional effect of increasing mechanical tension experienced by clustered integrins. Integrins function as mechanosensors that undergo catch bonding - meaning the application of moderate tension increases integrin bond lifetime relative to the lifetime of integrins experiencing low tension. In this work, a three-state chemomechanical catch bond model of integrin tension is used to investigate catch bonding in the presence of a bulky glycocalyx. This modeling suggests that a bulky glycocalyx can lightly trigger catch bonding, increasing the bond lifetime of integrins at adhesion edges by up to 100%. The total number of integrin-ligand bonds within an adhesion is predicted to increase by up to ~60% for certain adhesion geometries. Catch bonding is predicted to decrease the activation energy of adhesion formation by ~1-4 k B T, which translates to a ~3-50× increase in the kinetic rate of adhesion nucleation. This work reveals that integrin mechanic and clustering likely both contribute to glycocalyx-mediated metastasis.

Mechanosensitive channel Piezo1 is required for pulmonary artery smooth muscle cell proliferation

Concentric pulmonary vascular wall thickening due partially to increased pulmonary artery (PA) smooth muscle cell (PASMC) proliferation contributes to elevating pulmonary vascular resistance (PVR) in patients with pulmonary hypertension (PH). Although pulmonary vasoconstriction may be an early contributor to increasing PVR, the transition of contractile PASMCs to proliferative PASMCs may play an important role in the development and progression of pulmonary vascular remodeling in PH. A rise in cytosolic Ca2+ concentration ([Ca2+]cyt) is a trigger for PASMC contraction and proliferation. Here, we report that upregulation of Piezo1, a mechanosensitive cation channel, is involved in the contractile-to-proliferative phenotypic transition of PASMCs and potential development of pulmonary vascular remodeling. By comparing freshly isolated PA (contractile PASMCs) and primary cultured PASMCs (from the same rat) in a growth medium (proliferative PASMCs), we found that Piezo1, Notch2/3, and CaSR protein levels were significantly higher in proliferative PASMCs than in contractile PASMCs. Upregulated Piezo1 was associated with an increase in expression of PCNA, a marker for cell proliferation, whereas downregulation (with siRNA) or inhibition (with GsMTx4) of Piezo1 attenuated PASMC proliferation. Furthermore, Piezo1 in the remodeled PA from rats with experimental PH was upregulated compared with PA from control rats. These data indicate that PASMC contractile-to-proliferative phenotypic transition is associated with the transition or adaptation of membrane channels and receptors. Upregulated Piezo1 may play a critical role in PASMC phenotypic transition and PASMC proliferation. Upregulation of Piezo1 in proliferative PASMCs may likely be required to provide sufficient Ca2+ to assure nuclear/cell division and PASMC proliferation, contributing to the development and progression of pulmonary vascular remodeling in PH.

Red Blood Cells: Tethering, Vesiculation, and Disease in Micro-Vascular Flow

The red blood cell has become implicated in the progression of a range of diseases; mechanisms by which red cells are involved appear to include the transport of inflammatory species via red cell-derived vesicles. We review this role of RBCs in diseases such as diabetes mellitus, sickle cell anemia, polycythemia vera, central retinal vein occlusion, Gaucher disease, atherosclerosis, and myeloproliferative neoplasms. We propose a possibly unifying, and novel, paradigm for the inducement of RBC vesiculation during vascular flow of red cells adhered to the vascular endothelium as well as to the red pulp of the spleen. Indeed, we review the evidence for this hypothesis that links physiological conditions favoring both vesiculation and enhanced RBC adhesion and demonstrate the veracity of this hypothesis by way of a specific example occurring in splenic flow which we argue has various renderings in a wide range of vascular flows, in particular microvascular flows. We provide a mechanistic basis for membrane loss and the formation of lysed red blood cells in the spleen that may mediate their turnover. Our detailed explanation for this example also makes clear what features of red cell deformability are involved in the vesiculation process and hence require quantification and a new form of quantitative indexing.

Recent Advances and Prospects in the Research of Nascent Adhesions

Nascent adhesions are submicron transient structures promoting the early adhesion of cells to the extracellular matrix. Nascent adhesions typically consist of several tens of integrins, and serve as platforms for the recruitment and activation of proteins to build mature focal adhesions. They are also associated with early stage signaling and the mechanoresponse. Despite their crucial role in sampling the local extracellular matrix, very little is known about the mechanism of their formation. Consequently, there is a strong scientific activity focused on elucidating the physical and biochemical foundation of their development and function. Precisely the results of this effort will be summarized in this article.

Tethering, evagination, and vesiculation via cell-cell interactions in microvascular flow

Vesiculation is a ubiquitous process undergone by most cell types and serves a variety of vital cell functions; vesiculation from erythrocytes, in particular, is a well-known example and constitutes a self-protection mechanism against premature clearance, inter alia. Herein, we explore a paradigm that red blood cell derived vesicles may form within the microvascular, in intense shear flow, where cells become adhered to either other cells or the extracellular matrix, by forming tethers or an evagination. Adherence may be enhanced, or caused, by diseased states or chemical anomalies as are discussed herein. The mechanisms for such processes are detailed via numerical simulations that are patterned directly from video-recorded cell microflow within the splenic venous sinus (MacDonald et al. 1987), as included, e.g., as Supplementary Material. The mechanisms uncovered highlight the necessity of accounting for remodeling of the erythrocyte's membrane skeleton and, specifically, for the time scales associated with that process that is an integral part of cell deformation. In this way, the analysis provides pointed, and vital, insights into the notion of what the, often used phrase, cell deformability actually entails in a more holistic manner. The analysis also details what data are required to make further quantitative descriptions possible and suggests experimental pathways for acquiring such.