http://www.sciencedirect.com/science/article/pii/S0969996113001484
Abstract
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protein activated by cAMP-1 (Epac1) plays an important role in cell
proliferation, cell survival and neuronal signaling, and activation of
Epac1 in endothelial progenitor cells increases their homing to ischemic
muscles and promotes neovascularization in a model of hind limb
ischemia. Moreover, upregulation of Epac1 occurs during organ
development and in diseases such as myocardial hypertrophy, diabetes,
and Alzheimer's disease. We report here that hypoxia upregulated Epac1
through HIF-1α induction in the CD34-immunosorted human umbilical cord
blood hematopoietic stem cells (hUCB34). Importantly, implantation of hUCB34 subjected to hypoxia-preconditioning (HP-hUCB34) improved stroke outcome, more than did implantation of untreated hUCB34,
in rodents subjected to cerebral ischemia, and this required
Epac1-to-matrix metalloprotease (MMP) signaling. This improved
therapeutic efficacy correlated with better engraftment and
differentiation of these cells in the ischemic host brain. In addition,
more than did implantation of untreated HP-hUCB34, implantation of HP-hUCB34
improved cerebral blood flow into the ischemic brain via induction of
angiogenesis, facilitated proliferation/recruitment of endogenous neural
progenitor cells in the ischemic brain, and promoted neurite outgrowth
following cerebral ischemia. Consistent with our proposed role of
Epac1-to-MMP signaling in hypoxia-preconditioning, the above mentioned
effects of implanting HP-hUCB34 could be abolished by
pharmacological inhibition and genetic disruption/deletion of Epac1 or
MMPs. We have discovered a HIF-1α-to-Epac1-to-MMP signaling pathway that
is required for the improved therapeutic efficacy resulting from
hypoxia preconditioning of hUCB34 in vitro prior to their implantation into the host brain in vivo.
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