Nerve Growth Factor and Human Umbilical Cord Blood-Derived Cells Confer Neurovascular Protection in Ischemia

Abstract

Human umbilical cord blood (HUCB), a valuable source for cell therapy of hematologic diseases, was recently found to confer neuroprotection in animal models of brain injury. To explore the neuroprotective properties of HUCB in an ischemic environment, we studied a unique sub-population of collagen-adherent cells. In the presence of nerve growth factor (NGF) and interferon-gamma, these cells differentiate in vitro into a neuronal phenotype (termed HUCBNPs). Using a closed-head injury brain trauma model, we recently demonstrated neuroprotective effects of HUCB upon their local injection into the brain. Our in-vitro studies indicated that upon co-culture with ischemia exposed PC12 cells, HUCBNP conferred about 30% neuroprotection, as assessed by decreased lactate dehydrogenase (LDH) release and inhibition of caspase-3 activity. HUCBNP decreased by 95% the level of free radicals in the insulted-PC12 cells, which was in correlation with the appearance of antioxidants and NGF in the medium. HUCBNP-induced neuroprotection also correlated with changes in NGF mRNA expression levels, a process which was blocked by K252a, an antagonist of the NGF-neurotrophin receptor TrkA. To further extend the possible contribution of NGF-mediated protective role, we investigated its neuroprotective mechanisms using PC12 cells and brain capillary endothelial cells exposed to ischemic insult. Pretreatment of the cultures with NGF conferred neuroprotection in a dose- and time-dependent fashion. Time course experiments indicated marked activation of mitogen activated protein kinasas (MAPKs) during the ischemic insult, while treatment of the cultures with NGF inhibited them to different degrees. It appears that both neuronal and endothelial compartments may be protected by NGF under ischemic conditions. Therefore, in future neuroprotection studies, we propose to address additional components of the neurovascular unit such as astrocytes and pericytes in mono-, co- and multi-culture setups. In conclusion, our findings indicate that HUCBNP-induced neuroprotection involves antioxidant(s) and NGF, which by paracrine and/or autocrine route, affects all components of the neurovascular unit.