NOTCH SIGNALLING IN VASCULAR SMOOTH MUSCLE CELL SURVIVAL

Vascular smooth muscle cells (VSMCs), in the fibrous cap of atherosclerotic plaques, play an essential role in maintaining plaque stability. Apoptosis of VSMCs leads to plaque rupture resulting in myocardial infarction and sudden death. A number of signalling pathways contribute to the regulation of VSMC growth and survival, and Notch signalling is a critical pathway in this process. We have previously reported the anti-apoptotic role of Notch signalling by stable transfection of Notch3 in Human Embryonic Kidney (HEK) 293 cells. VSMCs were used to explore the molecular mechanisms of Notch signalling in VSMC survival. Endogenous Notch signalling was stimulated in vitro by immobilised Notch ligand Jagged1/FC chimera in a WKY rat smooth muscle cell line; exogenous Notch signalling was introduced by stable transfection of Notch3 or the constitutive active form of Notch3 (N3IC) in these cells. Western blotting of cells following either Jagged1 stimulation or overexpression of Notch3 or N3IC showed up-regulations of total Akt and phosphorilated-Akt, a key component of the cell survival pathway. The activation of Akt, induced by Jagged1, is associated with decreased expression of PTEN, a negative regulator of the Akt pathway. Activation of the Akt pathway contributes, at least in part, to Notch signalling-mediated VSMC survival. A possible mechanism is via suppression of PTEN expression. Further studies aim at elucidating the signalling network that relates to VSMC survival by the role of Notch receptors.