Postischemic Cortex Research Articles

Glucocorticoid-induced TNF receptor-triggered T cells are key modulators for survival/death of neural stem/progenitor cells induced by ischemic stroke

Increasing evidences show that immune response affects the reparative mechanisms in injured brain. Recently, we have demonstrated that CD4+T cells serve as negative modulators in neurogenesis after stroke, but the mechanistic detail remains unclear. Glucocorticoid-induced tumor necrosis factor (TNF) receptor (GITR), a multifaceted regulator of immunity belonging to the TNF receptor superfamily, is expressed on activated CD4+T cells. Herein, we show, by using a murine model of cortical infarction, that GITR triggering on CD4+T cells increases poststroke inflammation and decreases the number of neural stem/progenitor cells induced by ischemia (iNSPCs). CD4+GITR+T cells were preferentially accumulated at the postischemic cortex, and mice treated with GITR-stimulating antibody augmented poststroke inflammatory responses with enhanced apoptosis of iNSPCs. In contrast, blocking the GITR–GITR ligand (GITRL) interaction by GITR–Fc fusion protein abrogated inflammation and suppressed apoptosis of iNSPCs. Moreover, GITR-stimulated T cells caused apoptosis of the iNSPCs, and administration of GITR-stimulated T cells to poststroke severe combined immunodeficient mice significantly reduced iNSPC number compared with that of non-stimulated T cells. These observations indicate that among the CD4+T cells, GITR+CD4+T cells are major deteriorating modulators of poststroke neurogenesis. This suggests that blockade of the GITR–GITRL interaction may be a novel immune-based therapy in stroke.

Bone Marrow Mononuclear Cells Promote Proliferation of Endogenous Neural Stem Cells Through Vascular Niches After Cerebral Infarction

Increasing evidence shows that administration of bone marrow mononuclear cells (BMMCs) is a potential treatment for various ischemic diseases, such as ischemic stroke. Although angiogenesis has been considered primarily responsible for the effect of BMMCs, their direct contribution to endothelial cells (ECs) by being a functional elements of vascular niches for neural stem/progenitor cells (NSPCs) has not been considered. Herein, we examine whether BMMCs affected the properties of ECs and NSPCs, and whether they promoted neurogenesis and functional recovery after stroke. We compared i.v. transplantations 1 x 10(6) BMMCs and phosphate-buffered saline in mice 2 days after cortical infarction. Systemically administered BMMCs preferentially accumulated at the postischemic cortex and peri-infarct area in brains; cell proliferation of ECs (angiogenesis) at these regions was significantly increased in BMMCs-treated mice compared with controls. We also found that endogenous NSPCs developed in close proximity to ECs in and around the poststroke cortex and that ECs were essential for proliferation of these ischemia-induced NSPCs. Furthermore, BMMCs enhanced proliferation of NSPCs as well as ECs. Proliferation of NSPCs was suppressed by additional treatment with endostatin (known to inhibit proliferation of ECs) following BMMCs transplantation. Subsequently, neurogenesis and functional recovery were also promoted in BMMCs-treated mice compared with controls. These results suggest that BMMCs can contribute to the proliferation of endogenous ischemia-induced NSPCs through vascular niche regulation, which includes regulation of endothelial proliferation. In addition, these results suggest that BMMCs transplantation has potential as a novel therapeutic option in stroke treatment.

Ischemic preconditioning-induced neuroprotection is associated with differential expression of IL-1β and IL-1 receptor antagonist in the ischemic cortex

Ischemic preconditioning (IP) is a phenomenon that organs develop a tolerance toward subsequent lethal ischemic insults. Among the factors that are involved in IP, IL-1β and its endogenous receptor antagonist IL-1ra have been identified as important players in the induction of IP. The present study investigated whether IP affects the levels of these two antagonistic proteins during tolerance and reperfusion periods after ischemic stroke. The IP 24 h prior to ischemic stroke resulted in neuroprotection in the cortex. IP-induced protection is accompanied by increased IL-1β gene and IL-1ra gene and protein levels during the tolerance period. In the post-ischemic cortex, IP resulted in the suppression of IL-1β mRNA and protein levels at 6 h without affecting IL-1ra expression and the up-regulation of IL-1ra protein at 24 h. These findings demonstrate that IP differentially regulates cortical IL-1β and IL-1ra expression before and after ischemic stroke and suggest that the shift toward an anti-inflammatory state in the post-ischemic cortex may contribute to IP-induced neuroprotection.

Transcription factor early growth response‐1 induction mediates inflammatory gene expression and brain damage following transient focal ischemia

Early growth response-1 (Egr1) is a sequence-specific transcription factor (TF) which is induced under hypoxic conditions. We presently report that transient middle cerebral artery occlusion (MCAO) leads to increased expression of Egr1 in the brains of adult mice and rats between 2 h and 5 days of reperfusion with a peak increase of 8-12-fold at 1 day. When subjected to transient MCAO and 3 days of reperfusion, Egr1-/- mice showed significantly smaller infarcts (by 44.9 +/- 8.4%, p < 0.05) and improved neurological function than Egr1+/+ littermates. Following transient MCAO, brains of Egr1-/- mice showed less water accumulation and decreased neutrophil infiltration (by 42 +/- 8%, p < 0.05) compared to Egr1+/+ mice. The number of activated microglia/macrophages were also significantly lower (OX42+ cells by 53 +/- 9%, p < 0.05 and ED1+ cells by 59 +/- 11%) in the post-ischemic cortex of Egr1-/- mice compared to Egr1+/+ mice. In addition, post-ischemic inflammatory gene expression was less pronounced in the brains of Egr1-/- mice compared to Egr1+/+ mice. Preventing cerebral Egr1 protein induction with small interference RNAs that target Egr1 decreased inflammatory gene expression and led to smaller infarcts (by 40.2 +/- 6.9%, p < 0.05) and reduced neurological deficits in rats subjected to transient MCAO. Conversely, transient MCAO following adenoviral-mediated Egr1 over-expression exacerbated the infarct volume (by 29 +/- 5.3%, p < 0.05) and worsened the neurological deficits in rats. These studies indicate Egr1 as a significant contributor of inflammation and neuronal damage after stroke.

Isoforms of protein kinase C in postsynaptic densities after cerebral ischemia

Relatively mild ischemic insult can lead to delayed neuronal cell death in vulnerable brain regions. We provide evidence that the protein composition of the postsynaptic densities (PSD) undergoes rapid modification after 15 min postdecapitative as well as 5 min transient global ischemia. We observed a significant increase in cPKC and nPKC protein content in the postischemic PSD. Of the calcium-regulated PKC isoforms, the α and β subtypes increase in PSD over ten times above the control values whereas γPKC, an isoform most abundant in the native PSD structure, shows relatively smaller changes under ischemic conditions. For the first time, the PSD membrane translocation of Ca 2+-independent isoforms δ and ε is shown. The yield of the PSD protein preparation from the postischemic cortex was two times higher compared with control. This correlated with an abundant increase in electron density and changes in ultrastructure of PSD isolated from postischemic cortex. Also sections from CA1 gerbils hippocampus after transient ischemia showed persistent enlargement of postsynaptic densities up to 24 h of reperfusion. This was accompanied by elevation of the PSD/cytoskeleton-associated α, β PKC immunoreactivity and other changes in neuronal and glial cell morphology typical of the early postischemic degeneration. Sustained changes in PKC composition and organization of postsynaptic membranes during and after ischemia may cause persistent alteration in synaptic transmission and subsequently contribute to delayed neuronal injury.

Neural progenitor cells proliferate and differentiate when transplanted into ischemic brain or retina.

57 The adult mammalian brain contains neural stem and progenitor cells (NPCs) that can proliferate, self-renew, and generate all of the cellular elements of the mature brain, including neurons. The ability of NPCs to respond in vivo to injury-induced signals that can direct their differentiation towards multiple distinct neural lineages suggest that these undifferentiated progenitors offer a dynamic and versatile source of cells for neural regeneration following CNS injury. The purpose of this study was to determine if NPCs obtained from rat embryonic cortex would proliferate and differentiate into mature neurons and glia when transplanted in vivo into rat brain or retina subjected to ischemia. Primary undifferentiated progenitor cell clones from embryonic day 14.5 rat cortex were labeled with the cell membrane marker, PKH-26. Donor cells were transplanted into the cerebral cortex (CC), subventricular zone (SVZ) and vitreous cavity (VC) of the eye. In the ischemic animals as well as the control animals, some of the donor cells proliferated and differentiated into oligodendrocytes (CNPase) and astrocytes (GFAP) as early as 7 days following transplantation. By contrast, by 21 increasing to 45 days, most donor cells in CC and SVZ exhibited a neuronal phenotype (NeuN, MAP-2). However, transplantation into the SVZ was highly effective in generating new neurons in ischemic brain whereas direct transplantation into post-ischemic cortex was significantly less effective. Interestingly, donor cells transplanted in VC acquired a neuronal phenotype compatible with those seen in CC. Our data suggest the exogenous NPCs can differentiate into neurons and glia and that local environmental factors differentially regulate the profile of progenitor cell regenerative responses to CNS injury.

Neural progenitor cells proliferate and differentiate when transplanted into ischemic brain or retina.

57 The adult mammalian brain contains neural stem and progenitor cells (NPCs) that can proliferate, self-renew, and generate all of the cellular elements of the mature brain, including neurons. The ability of NPCs to respond in vivo to injury-induced signals that can direct their differentiation towards multiple distinct neural lineages suggest that these undifferentiated progenitors offer a dynamic and versatile source of cells for neural regeneration following CNS injury. The purpose of this study was to determine if NPCs obtained from rat embryonic cortex would proliferate and differentiate into mature neurons and glia when transplanted in vivo into rat brain or retina subjected to ischemia. Primary undifferentiated progenitor cell clones from embryonic day 14.5 rat cortex were labeled with the cell membrane marker, PKH-26. Donor cells were transplanted into the cerebral cortex (CC), subventricular zone (SVZ) and vitreous cavity (VC) of the eye. In the ischemic animals as well as the control animals, some of the donor cells proliferated and differentiated into oligodendrocytes (CNPase) and astrocytes (GFAP) as early as 7 days following transplantation. By contrast, by 21 increasing to 45 days, most donor cells in CC and SVZ exhibited a neuronal phenotype (NeuN, MAP-2). However, transplantation into the SVZ was highly effective in generating new neurons in ischemic brain whereas direct transplantation into post-ischemic cortex was significantly less effective. Interestingly, donor cells transplanted in VC acquired a neuronal phenotype compatible with those seen in CC. Our data suggest the exogenous NPCs can differentiate into neurons and glia and that local environmental factors differentially regulate the profile of progenitor cell regenerative responses to CNS injury.