S9B-03 SESSION 9B: FACE RESEARCH - PART II SOMATIC ARTERIOVENOUS MALFORMATION MAP2K1 MUTATION CAUSES CARTILAGE OVERGROWTH BY A CELL NON-AUTONOMOUS MECHANISM

Abstract

Introduction: Arteriovenous malformation (AVM) is a fast-flow, congenital vascular anomaly that is locally destructive and characterized by abnormal connections between arteries and veins. We previously reported that AVMs contain somatic mutations in MAP2K1 which are enriched in blood vessels. Overtime AVMs enlarge to cause significant morbidity. The purpose of this study was to determine if tissue overgrowth associated with AVM was caused by direct or indirect effects of a MAP2K1 mutation (i.e., cell-autonomous or cell-non autonomous). Methods: AVMs affecting the auricle cause overgrowth of the cartilage and overlying soft-tissue resulting in a prominent ear. Because cartilage is a unique tissue that does not contain vasculature, we used this clinical scenario to gain insight into the pathophysiology of how MAP2K1 mutations cause AVM enlargement. We obtained cartilage and its overlying skin/subcutis during a clinically-indicated otoplasty procedure to improve the appearance of the patient with an AVM of the ear. The cartilage was separated from the overlying skin/subcutis grossly and the skin/subcutis was tested with droplet digital PCR (ddPCR) for MAP2K1 mutation (p.K57N). Because MAP2K1 mutations are known to be enriched in endothelial cells (ECs), cartilage was subjected to laser capture microdissection (LCM) to ensure that cartilage being tested for MAP2K1 mutations was not contaminated by microscopic tissue containing blood vessels. LCM was performed on frozen section slides and genomic DNA was extracted from cartilage and adjacent connective tissue and measured for the abundance of mutant MAP2K1 alleles. Results: Skin/subcutaneous tissue from the ear AVM contained a mutation in MAP2K1 (p.K57N); the whole tissue mutant allele frequency was 3.1%. Staining with hematoxylin, eosin, and alcian blue delineated cartilage from the surrounding vessel-rich connective tissue. MAP2K1 (p.K57N) mutations were found in microscopic connective tissue adjacent to the cartilage (mutant allele frequency: 7.5%). MAP2K1 mutations were not identified in the cartilage. Conclusion:MAP2K1 mutations in AVMs are not found in cartilage and thus, the likely mechanism of cartilage overgrowth is paracrine signaling from adjacent mutant blood vessels (i.e., cell-non autonomous). MAP2K1 inhibitors might inhibit secondary overgrowth of tissues in AVM adjacent to blood vessels containing MAP2K1 mutations.