Persistent Production of Neurons from Adult Brain Stem Cells During Recovery after Stroke
¨ ´ PAR THORED,a,c ANDREAS ARVIDSSON,a,c EMANUELE CACCI,b,c HENRIK AHLENIUS,b,c THERESE KALLUR,b,c b,c a,c b,c a,c VLADIMER DARSALIA, CHRISTINE T. EKDAHL, ZAAL KOKAIA, OLLE LINDVALL Laboratory of Neurogenesis and Cell Therapy, Section of Restorative Neurology, WallenbergNeuroscience Center, University Hospital, Lund, Sweden; bLaboratory of Neural Stem Cell Biology, Section of Restorative Neurology, Stem Cell Institute, University Hospital, Lund, Sweden; cLund Strategic Research Center for Stem Cell Biology and Cell Therapy, Lund, Sweden
Key Words. Stem cells • Neurogenesis • Striatum • Stroke
Neural stem cells in the subventricular zone of adultrodents produce new striatal neurons that may replace those that have died after stroke; however, the neurogenic response has been considered acute and transient, yielding only small numbers of neurons. In contrast, we show herein that striatal neuroblasts are generated without decline at least for 4 months after stroke in adult rats. Neuroblasts formed early or late after stroke either differentiateinto mature neurons, which survive for several months, or die through caspasemediated apoptosis. The directed migration of the new neurons toward the ischemic damage is regulated by stromal cell-derived factor-1 and its receptor CXCR4. These results show that endogenous neural stem cells continuously supply the injured adult brain with new neurons, which suggests novel self-repair strategies toimprove recovery after stroke. STEM CELLS 2006;24:739 –747
Stroke is a leading cause of chronic disability in humans for which effective treatment is lacking. Recent experimental findings raise the possibility that functional improvement after stroke may be induced through neuronal replacement by endogenous neural stem cells (NSCs) in the subventricular zone (SVZ). Ischemic strokecaused by middle cerebral artery occlusion (MCAO) triggers increased cell proliferation in the rat SVZ [1–3]. The newly formed neuroblasts migrate into the damaged striatum [4 –7], a region where neurogenesis does not occur in the intact brain. After maturation, a substantial portion of the new neurons express markers characteristic of those mature neurons that have died, that is, striatalprojection neurons [4, 5]. However, this potential self-repair mechanism is thought to operate only acutely after stroke, with the number of generated neurons being small and their existence transitory . We show herein that stroke-induced neurogenesis is extensive and long-lasting, with continuous production of mature striatal neurons for several months after the insult. We also find that stromalcell– derived factor-1 (SDF-1 )/ CXCR4 signaling regulates the directed migration of new neurons to the injured area.
MATERIALS AND METHODS Induction of Stroke and 5-Bromo-2 -Deoxyuridine Labeling
Under halothane anesthesia, the middle cerebral artery of artificially ventilated male Wistar rats was occluded with a filament inserted through the common carotid artery [9, 10]. After 30 minutes or2 hours, the filament was withdrawn. For sham surgery, the filament was advanced a few millimeters inside the internal carotid artery. Physiological parameters were kept within a predetermined range. Intraperitoneal injections of 5-bromo-2 -deoxyuridine (BrdU; 50 mg/kg, Sigma-Aldrich, St. Louis, http://www.sigmaaldrich.com) were given twice daily during weeks 1–2, 5– 6, or 7– 8 after surgery. Inone experiment, three BrdU injections with 2-hour intervals were given 4 days or 6 weeks after MCAO, and the animals were killed 2 hours thereafter.
Caspase Inhibitor and CXCR4 Antagonist Treatments
Daily intraventricular infusions of a caspase inhibitor cocktail, comprising equal portions of a multicaspase, a caspase 3, and a caspase 9 inhibitor, were given over 12 days, starting on day 3...