Mechanical loading in hypertension and other vascular diseases can lead to vascular remodeling which involves proliferation and apoptosis of vascular smooth muscle cells (VSMCs). The major hemodynamic force borne by VSMCs in physiological and pathophysiological conditions is the circumferential stress which results in mechanism strain.
Three specific aims are proposed to test our hypothesis that mechanical strain causes augmentation of both proliferation and apoptosis through mechanotransduction mechanisms in which integrins function as mechanotransducers to activate the mitogen-activated protein kinases (MAPKs) pathways.
In Specific Aim 1, we will determine the roles of the mechanical strain-activated MAPKs signaling pathways in modulating the VSMC proliferation and apoptosis. We propose that activation of the ERK (i.e., extracellular signal-regulated kinases) pathway is critical for mitotic events, whereas augmentation of the JNK (i.e., c-Jun N-terminal kinases) pathway is important for apoptotic responses. We will investigate whether the various negative mutants of signaling molecules in the ERK pathway can block the strain-induced VSMC proliferation, and whether mutants in the JNK pathway can abolish VSMC apoptosis.
In Specific Aim 2, we will use alphavbeta3 integrin as a model to study the functional roles of alphav and beta3 units in mechanical strain activation of ERK and JNK. Using monoclonal antibodies specific for integrins in their activation state, we will further test whether alphavbeta3 can be directly activated by mechanical strain.
In Specific Aim 3, we will delineate the signaling pathways linking integrins to MAPKs in response to mechanical strain. We propose that the action of mechanical strain on integrins/ECM complexes (e.g., alphavbeta3/vitronectin) triggers the association of integrins with Shc and Grb2. This event in conjunction with the increase in the kinase activities of FAK and c-Src, results in the activation of the MAPKs pathways. In all three Specific Aims, in vitro experiments will be conducted using a newly designed stretch device to apply uniform equi- biaxial strain to human aortic smooth muscle cells cultured on silicon elastic membrane. This interdisciplinary research will generate new insights into the molecular mechanism by which mechanical strain leads to accelerated mitosis and apoptosis of VSMCs and thus enhance our understanding of the pathophysiological basis of vascular remodeling resulting from alterations in mechanical strain.
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