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Endothelial MAP2K1 Mutation Causes Abnormal Vascular Development In Inducible Mouse Strain
Christopher L. Sudduth, MD, Patrick J. Smits, PhD, Matthew P. Vivero, MD, Yu Sheng Cheng, BS, Arin K. Greene, MD.
Boston Children's Hospital, Harvard Medical School, Boston, MA, USA.

PURPOSE:Arteriovenous malformation (AVM) is defined by abnormal connections between arteries and veins instead of a normal capillary bed. Extracranial AVM is caused by an activating MAP2K1 mutation in endothelial cells. The downstream events and underlying mechanism that result in AVM are not known. The purpose of this study was to describe how the MAP2K1 mutation alters endothelial cell function.
METHODS: ROSA-GT-Map2k1-K57N+/- mice were crossed with Tg(Cdh5-CreER+/-; ROSA-GT-mTmG+/+) mice to produce offspring that would express mutant Map2k1 mRNA in endothelial cells after administration of tamoxifen. 9-day-old mouse brains were dissected and examined for phenotypic changes. Cerebral endothelial cells were isolated using anti-CD31 magnetic Dynabeads (Invitrogen). ddPCR was performed to calculate recombination frequency of the mutant allele. Bulk RNA sequencing was performed, and gene expression was compared using DESeq2. Genes with an adjusted p-value < 0.05 and absolute log2 fold change > 1 were called as differentially expressed genes. Significantly differentially expressed genes were clustered by their gene ontology.
RESULTS: Mutant mouse brains had abnormal vascular development with diffuse punctate vascular lesions. Confocal imaging identified vascular sacculations. The control mouse brain had normal vascular development and lacked these lesions. Mutant allele recombination frequency was 27% in the mutants and 0.1% in the control. Map2k1 expression was higher in mutant endothelial cells (log2FoldChange 2.18). 581 genes were significantly differentially expressed. The gene ontology pathways impacted most were (1) positive regulation of cell migration (GO:0030335) and (2) cell adhesion (GO:0007155).
CONCLUSION:
Expression of mutant Map2k1 in mouse endothelial cells results in abnormal cerebral vascular development. The transcriptome of these mutant cells shows significant changes in pathways affecting cell migration and cell adhesion. This inducible mouse strain is a promising animal model to study how the endothelial MAP2K1 mutation causes AVM and to test pharmacotherapy (MEK inhibitors) to treat AVM.


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