(provided by Candidate): Children with the rare congenital disorders of glycosylation (CDG) have a mutation in one of the many genes required for N-linked protein glycosylation and of 38 distinct subtypes, 37 have no treatment options. Mutation of mannose-6-phosphate isomerase (MPI) causes the "gastrointestinal type" of CDG. It is not understood how defective synthesis of the lipid-linked oligosaccharide (LLO) in CDG patients results in multi-systemic abnormalities and few CDG animal models exist. zebrafish provide a powerful vertebrate system to study monogenic disorders with their high genetic conservation to humans, and morpholinos offer rapid and efficient gene knockdown. I used morpholino technology to establish mpi morphants with less than 15% residual Mpi enzyme activity. They develop defects in the head, eye, gut, liver, and body shape with increased cell death in affected tissues. MPI-CDG is the only CDG with a known treatment: oral mannose increases flux through hexokinase and a minor complementary metabolic pathway that produces mannose-6-phosphate and normalizes protein glycosylation, relieving most symptoms. Similarly, both the morphologic and cell death phenotype in mpi morphants are almost completely rescued by mannose supplementation. My preliminary data in a novel zebrafish model of MPI-CDG implicate activation of the tumor suppressor, p53, in CDG pathology. Our objective is to determine whether the well known tumor suppressor, p53, has a novel role in the mechanism of disease in MPI-CDG. Our central hypothesis is that p53 is responsible for disease in MPI-CDG and will determine the mechanism by which p53 affects either metabolic alterations in glycosylation or apoptosis.
Specific Aims : 1: Establish the relationship between p53 activation, mannose metabolism, and Mpi deficiency. 2: Determine whether MPI-CDG is a result of abnormal LLO or glycoprotein formation. 3: Determine the contribution of p53-mediated apoptosis to the mpi morphant phenotype. My long-term goal is to understand the molecular basis of CDG with a focus on the associated gastrointestinal disorders. The underlying genetic defect in CDG is simple and well understood. I will then apply this knowledge to more common causes of these same diseases in pediatric patients, as non-alcoholic fatty liver disease, fibrosis, and cirrhosis are all associated with defects in protein glycosylation.
Congenital disorders of glycosylation (CDG) are rare, multi-systemic diseases with high morbidity and mortality, and are an example of the consequences of abnormal protein glycosylation. On a broader level, common diseases such as fatty liver disease, fibrosis, and cirrhosis have also been associated with similar defects in protein glycosylation. Our research focuses on improving our understanding of how defects in protein glycosylation lead to disease with the goal to find new targets for therapy.