No abstract

Vascular endothelial growth factor (VEGF), an angiogenic factor produced in response to ischemic injury, promotes vascular permeability (VP). Evidence is provided that Src kinase regulates VEGF-mediated VP in the brain following stroke and that suppression of Src activity decreases VP thereby minimizing brain injury. Mice lacking pp60c-src are resistant to VEGF-induced VP and show decreased infarct volumes after stroke whereas mice deficient in pp59c-fyn, another Src family member, have normal VEGF-mediated VP and infarct size. Systemic application of a Src-inhibitor given up to six hours following stroke suppressed VP protecting wild-type mice from ischemia-induced brain damage without influencing VEGF expression. This was associated with reduced edema, improved cerebral perfusion and decreased infarct volume 24 hours after injury as measured by magnetic resonance imaging and histological analysis. Thus, Src represents a key intermediate and novel therapeutic target in the pathophysiology of cerebral ischemia where it appears to regulate neuronal damage by influencing VEGF-mediated VP.

In the adult rodent, stroke induces an increase in endogenous neural progenitor cell (NPC) proliferation in the subventricular zone (SVZ) and neuroblasts migrate towards the ischemic boundary. We investigated the role of stromal cell-derived factor 1a (SDF-1a) in mediating NPC migration after stroke. We found that cultured NPCs harvested from the normal adult SVZ, when they were overlaid onto stroke brain slices, exhibited significantly (Po0.01) increased migration (67.27 25.2 lm) compared with the migration on normal brain slices (29.5729.5 lm). Immunohistochemistry showed that CXCR 4, a receptor of SDF-1a, is expressed in the NPCs and migrating neuroblasts in stroke brain. Blocking SDF-1a by a neutralizing antibody against CXCR 4 significantly attenuated stroke-enhanced NPC migration. ELISA analysis revealed that SDF-1a levels significantly increased (Po0.01) in the stroke hemisphere (43.676.5 pg/mg) when compared with the normal brain (25.27 1.9 pg/mg). Blind-well chamber assays showed that SDF-1a enhanced NPC migration in a dosedependent manner with maximum migration at a dose of 500 ng/mL. In addition, SDF-1a induced directionally selective migration. These findings show that SDF-1a generated in the stroke hemisphere may guide NPC migration towards the ischemic boundary via binding to its receptor CXCR 4 in the NPC. Thus, our data indicate that SDF-1a/CXCR 4 is important for mediating specific migration of NPCs to the site of ischemic damaged neurons.

Because Berkeley sickle cell mice are used as an animal model for human sickle cell disease, we investigated the progression of the histopathology in these animals over 6 months and compared these findings to those published in humans with sickle cell disease. The murine study groups were composed of wild-type mixed C57Bl/6-SV129 (control) mice and sickle cell (SS) mice (␣ ؊/؊ , ␤ ؊/؊ , transgene ؉) of both sexes and between 1 and 6 months of age. SS mice were similar to humans with sickle cell disease in having erythrocytic sickling, vascular ectasia, intravascular hemolysis, exuberant hematopoiesis, cardiomegaly, glomerulosclerosis, visceral congestion, hemorrhages, multiorgan infarcts, pyknotic neurons, and progressive siderosis. Cerebral perfusion studies demonstrated increased blood-brain barrier permeability in SS mice. SS mice differed from humans with sickle cell disease in having splenomegaly, splenic hematopoiesis, more severe hepatic infarcts, less severe pulmonary manifestations, no significant vascular intimal hyperplasia, and only a trend toward vascular medial hypertrophy. Early retinal degeneration caused by a homozygous mutation (rd1) independent from that causing sickle hemoglobin was an incidental finding in some Berkeley mice. While our study reinforces the fundamental strength of this model, the notable differences warrant careful consideration when drawing parallels to human sickle cell disease. (Blood. 2006;107: 1651-1658)

The migratory behavior of neuroblasts after a stroke is poorly understood. Using time-lapse microscopy, we imaged migration of neuroblasts and cerebral vessels in living brain slices of adult doublecortin (DCX, a marker of neuroblasts) enhanced green fluorescent protein (eGFP) transgenic mice that were subjected to 7 days of stroke. Our results show that neuroblasts originating in the subventricular zone (SVZ) of adult mouse brain laterally migrated in chains or individually to reach the ischemic striatum. The chains were initially formed at the border between the SVZ and the striatum by neuroblasts in the SVZ and then extended to the striatum. The average speed of DCXeGFP-expressing cells within chains was 28.67±1.04 lm/h, which was significantly faster (P < 0.01) than the speed of the cells in the SVZ (17.98 ± 0.57 lm/h). Within the ischemic striatum, individual neuroblasts actively extended or retracted their processes, suggestive of probing the immediate microenvironment. The neuroblasts close to cerebral blood vessels exhibited multiple processes. Our data suggest that neuroblasts actively interact with the microenvironment to reach the ischemic striatum by multiple migratory routes.