Defining the role of syndecan-4 in mechanotransduction using surface-modification approaches

Abstract

The ability of cells to respond to external mechanical stimulation is a complex and robust process involving a diversity of molecular interactions. Although mechanotransduction has been heavily studied, many questions remain regarding the link between physical stimulation and biochemical response. Of significant interest has been the contribution of the transmembrane proteins involved, and integrins in particular, because of their connectivity to both the extracellular matrix and the cytoskeleton. Here, we demonstrate the existence of a mechanically based initiation molecule, syndecan-4. We first demonstrate the ability of syndecan-4 molecules to support cell attachment and spreading without the direct extracellular binding of integrins. We also examine the distribution of focal adhesion-associated proteins through controlling surface interactions of beads with molecular specificity in binding to living cells. Furthermore, after adhering cells to elastomeric membranes via syndecan-4-specific attachments we mechanically strained the cells via our mechanical stimulation and polymer surface chemical modification approach. We found ERK phosphorylation similar to that shown for mechanotransductive response for integrin-based cell attachments through our elastomeric membrane-based approach and optical magnetic twisting cytometry for syndecan-4. Finally, through the use of cytoskeletal disruption agents, this mechanical signaling was shown to be actin cytoskeleton dependent. We believe that these results will be of interest to a wide range of fields, including mechanotransduction, syndecan biology, and cell-material interactions.T he biochemical response of cells to external mechanical stimulation has generated tremendous interest over the past decade. Of particular interest are the causative contributions of mechanotransductive transmembrane integrin molecules that link the extracellular matrix (ECM) to the cell interior and play a role in physiological response and molecular signaling within the cell. Recently, numerous exciting discoveries have evolved from these studies including the role of mechanotransduction in vascular physiology and atherogenesis, Src activation (Src phosphorylation/ activation under local mechanical stimulation), and the effect of matrix stiffness on stem cell differentiation (1-3). Mechanical stimulation has been shown to produce a wide range of cellular responses including the proteomic activation of the mitogenactivated protein kinase (MAPK) pathways in extracellular signalregulated kinases (ERKs), alterations of genomic expression profiles, and control of cell morphology, differentiation, and proliferation (4, 5). However, such research has focused primarily on the integrins as the mechanical signal initiator/transmembrane protein. Although other strain-sensitive proteins, such as mechanosensitive ion channels and protein kinase C, are known to be altered by mechanical stimulation, these responses are thought to occur downstream or be directly linked to the transmembrane proteininitiating...

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