Abstract 998: Increased Infarct Size and Decreased Vascular Leakage Following Transient Focal Cerebral Ischemia in Mice With Inhibition of Endothelial and Leukocyte NF-kB
Background: Cerebral ischemia induces an inflammatory response with NFkB as a central regulator. However, it is not known whether the signaling pathways mediated by NF-kB in vascular wall cells and/or circulating leukocytes contribute to cerebral infarct size and vascular leakage following cerebral ischemia.
Methods: Mice deficient in endothelial-specific NFkB (ecNFkB−/−) were established by crossing mice with loxP-flanked IkBasr (inhibitor of NF-kB) alleles with transgenic mice expressing a Cre-fusion protein under control of the endothelial-specific Tie2 promoter. The level of NFkB activation in endothelial cells (ECs) from ecNFkB−/−mice was decreased by 30 – 40% compared to controls. Transient cerebral ischemia was produced by left middle cerebral artery occlusion (MCAO) for 2 hours, followed by reperfusion. After 24 hours, cerebral infarct areas were quantified using TTC-stained sections. Neurological deficit score (NDS) was measured using the Bederson score. Quantitative measurements of changes in blood-brain barrier integrity (i.e., leakage size) were assessed using Evans-blue staining. Because Tie2 is also expressed in hematopoetic stem cells, bone marrow transplantation (BMT) using WT BM (donor) into irradiated recipient mice (WT or ecNFkB−/− mice) was performed in order to distinguish the effect of NF-kB in ECs cells versus leukocytes.
Results: Compared to controls, ecNFkB−/− mice exhibited increased infarct size (72 ± 20 vs. 51 ± 13; P=0.003) and higher NDS (2.6 ± 0.6 vs. 1.9 ± 0.9; P=0.02) following MCAO. However, vascular leakage was smaller in ecNFkB−/− mice compared to controls (Evans Blue [ng/hemisphere]: 2840 ± 245 vs. 7960 ± 480; P=0.013). After BMT, infarct size tended to be larger in ecNFkB−/− mice compared to that of controls (67 ± 31 vs. 46 ± 28). In contrast, vascular leakage in recipient ecNFkB−/−mice receiving WT BMT was similar compared to that of controls receiving WT BMT.
Conclusion: These findings indicate that endothelial NF-kB may protect against cerebrovascular injury while leukocyte NF-kB worsens vascular leakage. These results suggest that modulation of NF-kB may have protective or detrimental effects following cerebral ischemia depending upon the cell type in which NF-kB is being modulated.