The Role of c-ABL in Mediating TIE2 Signaling and Formation of Venous Malformation - PROJECT SUMMARY/ABSTRACT Venous malformations (VMs) are vascular lesions with abnormally enlarged vessels that are disfiguring, painful, and have complications such as bleeding and thrombosis. Current therapeutic options are not universally effective, can require life-long treatment, and fail to produce full lesion regression, indicating that investigation of novel causative pathways is needed. VM is associated with mutation in the endothelial tyrosine kinase receptor TIE2, the most common of which is the p.L914F mutation. However, studies into the cellular mechanisms driving VM pathogenesis are hindered by the lack of an in vivo model of TIE2 mutation. In addition, our lab has recently shown that c-ABL, an intracellular tyrosine kinase, is activated in endothelial cells (EC) upon ligand stimulation of TIE2 or with expression of mutant TIE2 p.L914F. Furthermore, we have also observed that ABL inhibition mutually reduces TIE2 activation by an unknown mechanism. To address these questions, my proposal rests on a central hypothesis: increased c-ABL signaling downstream of hyperactive mutant TIE2 p.L914F in endothelial cells promotes formation of venous malformation through feed forward TIE2/c-ABL signaling. We will address this hypothesis through the following Specific Aims: 1) define the effects of c-ABL on TIE2 activation and signaling and 2) determine if c-ABL is required for formation of VM lesions in vivo. In this work, we will define how ABL signaling affects physiological and pathological TIE2 activation in endothelial cells utilizing in vitro functional assays and both loss of function and gain of function of c-ABL. We will also utilize our newly developed transgenic mouse model of TIE2 L914F-driven VM to investigate the cellular defects associated with VM pathogenesis. This model will then be used to investigate the role of c-ABL in VM formation in vivo and provide preclinical testing of ABL inhibition for the treatment of VM. The information obtained from this project will elucidate the relationship between TIE2 and c-ABL signaling in physiological and pathological vascular function and will establish the first genetic mouse model of mutant TIE2-driven VM, which will be essential for further study of the mechanisms of VM pathogenesis.
