| Neuropeptide Y (NPY) is a sympathetic neurotransmitter that potently modulates vasoconstriction, vascular smooth muscle cell (VSMC) proliferation, and neointima formation. Cold stress elevates platelet-poor and platelet-rich plasma NPY levels, which is associated with increased neointima following angioplasty. Factors governing the elevation of NPY in platelets following cold stress, as well as the role of platelet NPY in vascular remodeling, have yet to be explored. This thesis, therefore, investigates the mechanism of NPY elevation in platelets following stress and the effect of platelet NPY on neointimal formation.; NPY stimulated [3H]thymidine uptake in primary murine VSMCs. Y1 antagonist reduced proliferation, whereas Y5 antagonist had no effect. 14 days post-angioplasty, Npy+/+ mice developed increased neointima compared to Npy-/- mice. Y1 receptor antagonist significantly reduced neointima formation in Npy+/+ mice.; In response to cold stress platelet NPY levels initially decreased, but by day 7 were significantly elevated. In contrast, platelet-poor plasma NPY was elevated by day 3 and remained throughout the stress period. Stress increased megakaryocyte NPY mRNA, megakaryocyte turnover, and platelet GPIIbIIIa surface expression. Angioplasty with cold stress increased neointima formation relative to non-stressed controls. Chemical sympathectomy (6-hydroxydopamine) decreased neointima as well as the proliferation of megakaryocytes.; To determine the role of platelet NPY in neointimal formation, platelet transfer experiments were performed. Platelets transferred from Npy +/+ mice into Npy-/- mice induced greater neointima relative to Npy -/- mice receiving platelets from Npy -/- mice. Conversely, platelets from Npy -/- mice transferred into Npy +/+ mice stimulated less neointimal formation than platelets from Npy+/+ mice.; Immunohistochemical staining for synapsin, tyrosine hydroxylase (TH), and NPY associated sympathetic nerves with megakaryocytes. Co-culture of sympathetically-derived (TH+INPY+) SKNBE cells with hematopoietic cells increased megakaryocyte cell number compared to hematopoietic cells cultured alone.; These studies are the first to demonstrate that platelet NPY significantly accelerates neointimal formation. In addition, we present a novel sympathetic nerve bone marrow association that could increase the exposure of vessels to platelet NPY, and subsequent amplification of neointima. Thus, platelet expression of NPY or its induction through stress could be a novel risk factor for restenosis and/or atherosclerosis. |
