Cell and tissues are subjected to different types of mechanical stress. Hypertension is a pathological state in which the increase in pressure induces enhanced mechanical forces within the vessel wall. One of the consequences of hypertension is the induction of inflammatory gene expression in the vasculature. Although inflammation may facilitate hypertension-related cardiovascular complications, the molecular pathways that result in hypertension-induced inflammation are incompletely described vascular smooth muscle cells (VSMCs), a main component of the vessel wall, respond to biomechanical forces initiated by hemodynamic changes and undergo phenotypic modulation. Indeed, this modulation results in reorientation of the cell body, which has been proposed as one mechanism to counteract the strain. Reactive oxygen species (ROS) play important roles as signaling molecules in all types of vascular cells. One main source of ROS in the vasculature is Nox4, which is found in focal adhesions (FAs), the sites of engagement of the cell to the extracellular substrate. We have shown that Slingshot 1L (SSH1L) phosphatase, which dephosphorylates and thus activates its substrate, the actin binding protein cofilin, plays a key role in the control of PDGF-induced lamellipodia formation and VSMC migration. Now, we have exciting preliminary data indicating that SSH1L-mediated cofilin activation is required for cell reorientation and, most significantly, for the regulation of inflammatory gene expression when VSMC are subjected to mechanical stress. We hypothesize that in response to mechanical stress, integrins activate the Nox4-based NADPH oxidase to produce H2O2 that induces SSH1IL-mediated cofilin activation within the FA, and that activated cofilin is required for cell reorientation and translocates to the nucleus where it regulates the transcription of inflammatory genes. During this grant period we aim to: 1. Identify the mechanism of mechanical stretch-induced SSH1L/cofilin activation and its role in cell reorientation in VSMC, 2. Define the mechanism of cofilin nuclear translocation and its role in regulating the gene expression and 3. Determine the role of the Nox4/cofilin pathway in attenuating hypertension-induced vascular inflammation in vivo. Experiments described in this application will increase our understanding about how cells sense mechanical stimuli and the consequences of such stimuli on cell phenotype, providing sufficient proof-of principle to support the identification of new therapeutic targets.
Vascular smooth muscle cells (VSMCs), a main component of the vessel wall are subjected to pulsatile strain. Hypertension, where cells are chronically subjected to increased strain, is a risk factor for cardiovascular diseases in part due to an increased inflammation in the vascular tissue. This project will investigate the role of the actin binding protein cofilin in mediating cell reorientation and inhibiting inflammatory gene expression in response to mechanical stress in VSMCs. Understanding the mechanism underlying the vessel adaptation to mechanical stimulus may lead to development of therapeutic treatments that target important events in disease initiation. !
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