Age-associated reduction in angiogenic capacity associates with impaired functions of neuropeptide Y

Abstract

Impaired angiogenesis is associated with aging and several age-related pathologies, including ischemic vascular disease and delayed wound healing. However, such a reduction in angiogenic capacity could also inform therapeutic applications aiming at inhibiting tumor vascularization. Neuropeptide Y (NPY) and its Y receptors (Rs) - Y2R and Y5R - have been implicated in angiogenic responses associated with cardiovascular disease and cancer. Yet, changes in the NPY system associated with aging are not clear. Therefore, we sought to determine whether alterations in the NPY system are involved in age-associated impairment of angiogenesis. We hypothesized that NPY-mediated angiogenesis is diminished with age due to downregulation of the peptide, its receptors, and converting enzyme - cleaving full-length NPY to a Y2R agonist, as well as downstream signaling pathways. To test our hypothesis, the angiogenic profiles of human microvascular endothelial cells (HMVECs) from 24- and 90-year-old subjects were assessed via proliferation and mRNA expression. This analysis included dose-response and cross-inhibition assays with NPY, fibroblast growth factor 2 (FGF2), and vascular endothelial growth factor (VEGF) systems. Also, basal plasma levels of NPY were compared in old (24 months) and young (3 months) Balb/c mice. Further, NPY-mediated aortic sprouting was assessed in Y2R knockout (KO) mice. Angiogenic stimulation via NPY, FGF, and VEGF was observed in HMVECs from both age groups, with lower basal proliferation levels and less responsiveness to all three factors in aged HMVECs (p<0.05). While qRT-PCR analysis revealed no differences in basal expression of the NPY system, Y2R and DPPIV were induced by NPY in young HMVECs only. These results suggest that the decreased responsiveness of aged HMVECs to NPY stimulation is caused by impairment of NPY receptor function and/or signaling pathways. NPY stimulation increased mRNA expression of FGF2, FGFR1 and 2, and VEGFR2 in young HMVECs only. Further, anti-FGF2 neutralizing antibody and VEGFR2/Fc chimera, which is a potent VEGF antagonist, blocked the mitogenic effect of NPY in HMVECs from both age groups; while NPY receptor antagonists had no effect on HMVEC proliferation stimulated by FGF2 and VEGF (p<0.05). Moreover, despite completely impaired NPY-induced sprouting of Y2KO aortic rings, the response to FGF2 and VEGF remained intact. These data indicate that the FGF2 and VEGF pathways mediate angiogenic activities of NPY. In summary, our results show age-associated impairment of NPY-induced angiogenesis is due to a diminished mitogenic response of endothelium to the peptide via loss of induction of its angiogenic Y2R and DPPIV. This is also associated with reduced stimulation of downstream FGF2 and VEGF signaling. Future studies will determine if impaired angiogenesis in aging can be rescued with stimulation of the NPY angiogenic system and how these manipulations can improve revascularization of ischemic tissue. NIH R03 AG-20795 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.