No abstract

Because neurogenesis persists in the adult mammalian brain and can be regulated by physiological and pathological events, we investigated its possible involvement in the brain's response to focal cerebral ischemia. Ischemia was induced by occlusion of the middle cerebral artery in the rat for 90 min, and proliferating cells were labeled with 5-bromo-2 -deoxyuridine-5 -monophosphate (BrdUrd) over 2-day periods before sacrificing animals 1, 2 or 3 weeks after ischemia. Ischemia increased the incorporation of BrdUrd into cells in two neuroproliferative regions-the subgranular zone of the dentate gyrus and the rostral subventricular zone. Both effects were bilateral, but that in the subgranular zone was more prominent on the ischemic side. Cells labeled with BrdUrd coexpressed the immature neuronal markers doublecortin and proliferating cell nuclear antigen but did not express the more mature cell markers NeuN and Hu, suggesting that they were nascent neurons. These results support a role for ischemia-induced neurogenesis in what may be adaptive processes that contribute to recovery after stroke. D iseases of the brain have singularly adverse effects on the quality and duration of life. Unlike many other tissues, the mature brain has limited regenerative capacity, and its unusual degree of cellular specialization restricts the extent to which residual healthy tissue can assume the function of damaged brain. However, cerebral neurons are derived from precursor cells that persist in the adult brain (1-5), so stimulation of endogenous neural precursors in the adult brain could have therapeutic potential (6).Neurogenesis occurs in discrete regions of the adult brain, including the rostral subventricular zone (SVZ) of the lateral ventricles (7) and the subgranular zone (SGZ) of the dentate gyrus (DG) (8). Neurons that arise in the SVZ travel via the rostral migratory stream to the olfactory bulb (9) and also enter association neocortex (10), and new neurons leaving the SGZ migrate into the adjacent DG granule cell layer. Neurogenesis in these regions is subject to physiological regulation by glucocorticoids (11), sex hormones (12), growth factors (13-16), excitatory neurotransmission (17), learning (18), and stress (19) and can be modified pharmacologically (20).Pathological events can also stimulate neurogenesis in the adult brain. Mechanical injury to the DG granule cell layer in the rat increases proliferation of granule neuron precursors in the adjacent SGZ, as shown by enhanced incorporation of [ 3 H]thymidine and 5-bromo-2Ј-deoxyuridine-5Ј-monophosphate (BrdUrd), induction of proliferating cell nuclear antigen (PCNA), and coexpression of mature neuronal markers in [ 3 H]thymidinelabeled cells (21). Seizures also trigger neurogenesis in the SGZ, with BrdUrd-labeled cells expressing the neuronal markers TOAD-64, class III␤-tubulin, and microtubule-associated protein 2 (MAP-2) (22). Finally, apoptosis induced by oxidative stress in mouse corticothalamic neurons increases BrdUrd labeling in cells that go on to express ...

Neurogenesis, which persists in the adult mammalian brain, may provide a basis for neuronal replacement therapy in neurodegenerative diseases like Alzheimer's disease (AD). Neurogenesis is increased in certain acute neurological disorders, such as ischemia and epilepsy, but the effect of more chronic neurodegenerations is uncertain, and some animal models of AD show impaired neurogenesis. To determine how neurogenesis is affected in the brains of patients with AD, we investigated the expression of immature neuronal marker proteins that signal the birth of new neurons in the hippocampus of AD patients. Compared to controls, Alzheimer's brains showed increased expression of doublecortin, polysialylated nerve cell adhesion molecule, neurogenic differentiation factor and TUC-4. Expression of doublecortin and TUC-4 was associated with neurons in the neuroproliferative (subgranular) zone of the dentate gyrus, the physiological destination of these neurons (granule cell layer), and the CA1 region of Ammon's horn, which is the principal site of hippocampal pathology in AD. These findings suggest that neurogenesis is increased in AD hippocampus, where it may give rise to cells that replace neurons lost in the disease, and that stimulating hippocampal neurogenesis might provide a new treatment strategy.

Vascular endothelial growth factor (VEGF) is an angiogenic protein with therapeutic potential in ischemic disorders, including stroke. VEGF confers neuroprotection and promotes neurogenesis and cerebral angiogenesis, but the manner in which these effects may interact in the ischemic brain is poorly understood. We produced focal cerebral ischemia by middle cerebral artery occlusion for 90 minutes in the adult rat brain and measured infarct size, neurological function, BrdU labeling of neuroproliferative zones, and vWF-immunoreactive vascular profiles, without and with intracerebroventricular administration of VEGF on days 1-3 of reperfusion. VEGF reduced infarct size, improved neurological performance, enhanced the delayed survival of newborn neurons in the dentate gyrus and subventricular zone, and stimulated angiogenesis in the striatal ischemic penumbra, but not the dentate gyrus. We conclude that in the ischemic brain VEGF exerts an acute neuroprotective effect, as well as longer latency effects on survival of new neurons and on angiogenesis, and that these effects appear to operate independently. VEGF may, therefore, improve histological and functional outcome from stroke through multiple mechanisms.

Globins are oxygen-binding heme proteins present in bacteria, protists, fungi, plants, and animals. Their functions have diverged widely in evolution, and include binding, transport, scavenging, detoxification, and sensing of gases like oxygen, nitric oxide, and carbon monoxide. Neuroglobin (Ngb) is a recently discovered monomeric globin with high affinity for oxygen and preferential localization to vertebrate brain. No function for Ngb is known, but its affinity for oxygen and its expression in cerebral neurons suggest a role in neuronal responses to hypoxia or ischemia. Here we report that Ngb expression is increased by neuronal hypoxia in vitro and focal cerebral ischemia in vivo, and that neuronal survival after hypoxia is reduced by inhibiting Ngb expression with an antisense oligodeoxynucleotide and enhanced by Ngb overexpression. Both induction of Ngb and its protective effect show specificity for hypoxia over other stressors. We conclude that hypoxiainducible Ngb expression helps promote neuronal survival from hypoxic-ischemic insults.T he fate of neurons undergoing hypoxic or ischemic injury is regulated by transcriptional and posttranscriptional events that contribute to competing cell-death and cell-survival programs (1, 2). Survival-promoting events include the transcriptional induction or posttranslational activation of neuroprotective proteins like erythropoietin (3), vascular endothelial growth factor (4), and heme oxygenase (5). In many cases, these are hypoxia-inducible proteins that help to counteract the adverse effects of hypoxia or ischemia by increasing anaerobic metabolism, tissue vascularity, or oxygen delivery (6). Another strategy for promoting the survival of metabolically active tissues like muscle or nerve may involve the tissue-specific expression of intracellular oxygen-binding proteins that can enhance oxygen extraction and intracellular diffusion, or neutralize reactive oxygen species. Examples include myoglobin, in the case of muscle (7), and invertebrate nerve myoglobins (8).Neuroglobin (Ngb) is a newly discovered vertebrate globin that is expressed most abundantly in neurons (9). Ngb was identified by searching murine and human expressed sequence tag databases for partial globin-like sequences, then cloned, and sequenced to reveal a 151-aa protein with a predicted molecular mass of Ϸ17 kDa, which exists as a monomer. Human and murine Ngbs show 94% sequence identity at the amino acid level but limited homology to other known globins. For example, there is Ͻ21% sequence identity with vertebrate myoglobins and Ͻ25% identity with vertebrate hemoglobins. The protein that most closely resembles Ngb (30% amino acid identity) is the intracellular nerve myoglobin of the polychaete annelid worm Aphrodite aculeata (8).Because Ngb is an oxygen-binding heme protein that is expressed preferentially in cerebral neurons, we investigated its possible involvement in neuronal responses to hypoxia or ischemia. The results indicate that Ngb is induced by neuronal hypoxia and cerebral ischemia and ...

Vascular endothelial growth factor (VEGF) is a hypoxia-inducible angiogenic peptide with recently identified neurotrophic effects. Because some neurotrophic factors can protect neurons from hypoxic or ischemic injury, we investigated the possibility that VEGF has similar neuroprotective properties. In HN33, an immortalized hippocampal neuronal cell line, VEGF reduced cell death associated with an in vitro model of cerebral ischemia: at a maximally effective concentration of 50 ng͞ml, VEGF approximately doubled the number of cells surviving after 24 h of hypoxia and glucose deprivation. To investigate the mechanism of neuroprotection by VEGF, the expression of known target receptors for VEGF was measured by Western blotting, which showed that HN33 cells expressed VEGFR-2 receptors and neuropilin-1, but not VEGFR-1 receptors. The neuropilin-1 ligand placenta growth factor-2 failed to reproduce the protective effect of VEGF, pointing to VEGFR-2 as the site of VEGF's neuroprotective action. Two phosphatidylinositol 3-kinase inhibitors, wortmannin and LY294002, reversed the neuroprotective effect of VEGF, implicating the phosphatidylinositol 3-kinase͞Akt signal transduction system in VEGF-mediated neuroprotection. VEGF also protected primary cultures of rat cerebral cortical neurons from hypoxia and glucose deprivation. We conclude that in addition to its known role as an angiogenic factor, VEGF may exert a direct neuroprotective effect in hypoxic-ischemic injury.

No abstract

Experimental stroke in rodents stimulates neurogenesis and migration of newborn neurons from their sites of origin into ischemic brain regions. We report that in patients with stroke, cells that express markers associated with newborn neurons are present in the ischemic penumbra surrounding cerebral cortical infarcts, where these cells are preferentially localized in the vicinity of blood vessels. These findings suggest that stroke-induced compensatory neurogenesis may occur in the human brain, where it could contribute to postischemic recovery and represent a target for stroke therapy.ischemia ͉ stem cells ͉ penumbra ͉ infarct ͉ vascular niche