Abstract W P218: Interleukin 21 receptor: A Major Modulator of Infarct Volume

Abstract

Using the permanent middle cerebral artery occlusion (MCAO) model of stroke, we have demonstrated that different inbred mouse strains show profound differences in infarct volume, indicating that infarction is under strong genetic control. To identify natural genetic determinants modulating infarction, we employed quantitative trait locus (QTL) linkage analysis and a genome-wide association study of cerebral infarct volume. We identified a locus on distal chromosome 7 that contributes over 50% of the variation in infarct volume, as well as other loci of smaller effect. Using interval-specific ancestral haplotype analysis, we fine-mapped the chromosome 7 locus to only 12 candidate genes. To identify the gene(s) underlying this locus, we determined the strain-specific transcript levels of all 12 genes in relevant tissues that included P1 and adult brain cortex, and embryonic macrophages, the latter due to their importance in the development of the cerebrovascular system. One gene, interleukin 21 receptor (Il21r), showed a 7-fold expression difference between strains and harbors a coding SNP difference that segregates with infarct volume. To determine whether Il21r is a major modulator of infarction, we examined Il21r in mice for their cerebrovascular anatomy as well as the cerebral infarct volume after MCAO. While Il21r-/- mice show a moderate reduction in collateral vessel connections compared to wild-type littermate mice cerebral infarct volume in Il21r-/- mice is increased 3-fold. This suggests that Il21r has effects on both cerebrovascular anatomy and innate neuroprotection. To examine the latter, we performed an ex vivo study of brain slices under in vitro oxygen deprivation. In this system devoid of any potential circulatory effects, but retaining appropriate tissue architecture, Il21r-/- brain slices showed an increase in oxygen-deprivation induced cell death, showing that Il21r is also involved in cerebrovascular-independent neuroprotection. Biochemical studies of the brain slices show that Il21R regulates ischemia-induced apoptosis. The identification of Il21R as a cerebrovascular-independent modulator of infarct volume provides a fundamental advance in the understanding of genetic modulation of ischemic stroke.