RNF213: Molecular Functions and Moyamoya Disease

About This Grant

ABSTRACT Moyamoya disease (MMD), a progressive vasculopathy leading to narrowing and ultimate occlusion of the intracranial internal carotid arteries, is an important cause of childhood stroke. Our lack of knowledge of the etiopathogenesis of MMD hampers the development of preventive and therapeutic strategies. MMD can be genetically triggered and is highly genetically heterogeneous. The gene most commonly associated with MMD is RNF213, due to a founder variant in Asian individuals that confers a low penetrant risk of disease. We identified de novo RNF213 rare variants in a limited region of the protein that lead to early onset, severe, and progressive MMD in infants and toddlers. However, the function of the RNF213 protein and its role in MMD pathogenesis is poorly understood. Our prior work supports the hypothesis that incomplete differentiation of smooth muscle cells (SMCs) from neural crest progenitor cells (NCPCs) leads to increased migration into the lumen and proliferation that fills the occlusive lesion. We identified that decreased oxidative phosphorylation is a consequence of incomplete differentiation and that treatments to increase mitochondrial respiration can rescue the differentiation defect in vitro and prevent MMD-like lesions in vivo in a mouse model. Our goals in this study are to assess whether a highly penetrant RNF213 pathogenic variant, p.F4120L, conforms to this hypothesis and to identify specific molecular mechanisms linking RNF213 to SMC phenotype. The best evidence for RNF213 function comes from a study using mCherry- tagged RNF213, which showed localization of the protein to intracellular lipid droplets (LDs). RNF213 prevents localization of the lipolysis enzyme ATGL to LDs and thus regulates LD turnover. NCPCs have highly variable numbers of LDs, and increasing LDs by lipid loading affects both cell fate and cellular metabolism. We therefore hypothesize that RNF213 in NCPCs is required to modulate LDs to permit SMC differentiation and that the RNF213 p.F4120L variant increases lipolysis of LDs, preventing complete SMC differentiation and leading to increased proliferation and migration and thus occlusive lesion formation. We will test this hypothesis in two specific aims by using (1) an in vitro system of genetically edited induced pluripotent stem cells differentiated to NCPCs then SMCs and (2) a novel Rnf213F4120L/+ knock-in mouse model. Completion of these aims will yield novel and critical insights into MMD pathogenesis, RNF213 function, and the role of LDs in SMC differentiation. We will generate resources that will be made freely available to the research community with the goal to accelerate discovery and testing of potential therapeutic options to prevent, diagnose, and treat MMD.