A regenerative response of endogenous neural stem cells to perinatal hypoxic/ischemic brain damage

Hypoxic/ischemic (H/I) insults are the leading cause of neurologic injury during the perinatal period, affecting 2-4 per 1000 term births as well as a high percentage of premature infants. The ensuing sequelae are devastating and include cerebral palsy, epilepsy and cognitive deficits. Despite astounding advances in perinatal care, the incidence of cerebral palsy has changed little over the last 50 years. This demands that we pursue alternative therapeutic strategies that will reduce the significant morbidity associated with perinatal H/I encephalopathy.; The revelation that the brain retains populations of neural stem cells throughout life offers the promise of endogenous regeneration following brain injury. Already extensive data have demonstrated that new neurons are born after cerebral ischemia and migrate to sites of injury. The existence of multipotential, self-renewing neural stem and progenitors, however, suggests that this response could be much more significant. This thesis offers data indicative of a mobilization of this population following perinatal H/I.; Using a clonal assay to quantify neural stem and progenitors (NSPs), we demonstrated almost a doubling in the numbers of NSPs following perinatal H/I. This was accompanied by the generation of larger neurospheres and increased symmetric proliferative divisions in vitro upon EGF and FGF-2 stimulation. Furthermore, a higher proportion of the clonal neurospheres retained the capacity to generate all 3 neural cell types upon differentiation. These effects were preceded by an upregulation of genes important in the regulation of NSP maintenance and proliferation, including notably the EGF receptor and Notch1.; Further investigation demonstrated that the larger size of neurospheres following perinatal H/I was due to increased proliferation, specifically in response to EGF stimulation. These effects as well as the induction of Notch1, were dependent upon signals from mature cells as demonstrated by an in vitro paradigm of H/I injury. Other components of the Notch signaling cascade were also induced specifically within the NSP niche of the subventricular zone (SVZ). Pharmacological inhibition of this pathway using a well-characterized inhibitor of gamma-secretase that prevents release of the intracellular mediator, the Notch intracellular domain (NICD) effectively reduced both the increase in numbers of NSPs as well as the increase in tripotency of the neurospheres.; These data provide evidence of a mobilization of the NSP population in response to perinatal H/I. A better understanding of the molecular mechanisms underlying these results will identify therapeutic targets for enhancing this response. It is no longer acceptable to settle for just managing neurologic injuries such as perinatal H/I encephalopathy; we must pursue strategies to repair the brain after such damage. This thesis demonstrates the basis for endogenous regeneration of the CNS following brain injury and describes several potential molecules that may be used to manipulate this response.