Abstract 5598: Notch Signaling in Intrinsic Stem Cell is a Prerequisite for Therapeutic Angiogenesis

Abstract

Cell transplantation became a prevalent method to induce therapeutic angiogenesis for patients with ischemic burden. However, its mechanism has been a matter of debate. We previously reported that therapeutic limb angiogenesis by peripheral blood mononuclear cells (PBMNC) transplantation was accomplished through enhancement of muscle regeneration process, which essentially coincides with massive production of angiogenic growth factors. Here, we show that Notch signaling in skeletal myoblasts is critical to initiate this therapeutic process. PBMNC instantly induced robust proliferation of interstitial cells in ischemic tissue. In sections, majority of these cells stained double-positive for myoblast markers and activated Notch-1 receptor. Production of cytokines and myogenic growth factors by host tissue, and subsequent recruitment of activated macrophages, were also observed as acute effects after PBMNC transplantation, and was shown to be crucial for adequate muscle regeneration and angiogenesis in the later phase. Such beneficial effects by PBMNC were abolished in myoblast null Pax7 knockout mice, indicating a critical role of intrinsic stem cells in therapeutic angiogenesis. Importantly, treatment of wild type ischemic host with a Notch inhibitor markedly reduced the ratio of myoblasts among the proliferating interstitial cells, resulting in severe impairment of both acute and late-phase effects by PBMNC transplantation. Notch-1 conditional knockout mice showed similar results after PBMNC transplantation, further confirming the importance of host Notch signaling. Interestingly, deletion of a Notch ligand Jagged-1 from the donor PBMNC resulted in marked attenuation of muscle regeneration and neovascularization. Conversely, over expression of Jagged-1 in the implanted cells significantly increased the efficacy of this treatment. Taken together, we conclude that activation of Notch signaling in myoblasts is crucial for tissue regeneration by cell therapy. Additionally, we provide a model showing that activation of intrinsic stem cells, through exogenous introduction of Notch ligands, could be a novel strategy to enhance tissue regeneration in a therapeutic context.