|Di Huang, 3rd Year
Program: Molecular and Cellular Biology
Advisor: Scott Garman
Education: University of Alberta, Edmonton, AB, Canada, B.S. Molecular Genetics, 2010
Northwestern University, Biotechnology, 2012
The International Advocate for Glycoprotein Storage Diseases
D. Wang et al. Molecular Genetics and Metabolism 85 (2005) 181–189.3. E.J. Bonten et al. Biochimica et Biophysica Acta 1832 (2013) 1784–1792.
Sialidosis, a rare lysosomal storage disease, has an occurrence of approximately 1/250,000 live births in theUnited States. The patients suffer from involuntary muscle contractions, impaired vision and nightblindness, seizures to abnormal enlargement of liver and spleen, mental retardation, loss of muscle tissue,and difficulty in breathing. The onset of the symptoms ranges from birth to the second decade of patients’life depending on severity1. Unfortunately, there is no effective treatment for sialidosis. Currently, patientsare provided with supportive care and symptomatic relief. My research is focusing on the study of theenzyme, human lysosomal neuraminidase 1(NEU1), which causes sialidosis when defective. The lysosome is a cellular organelle that contains a collection of hydrolytic enzymes to break down thewaste materials and cell debris, such as glycoproteins and glycolipids. Deficiencies of lysosomal enzymescause the accumulation of the corresponding substrates in the lysosome and eventually lead to lysosomalstorage diseases. NEU1 is a lysosomal enzyme that cleaves the terminal sialic acid residues on theglycoproteins and glycolipids. Mutations in NEU1 can cause the misfolding of the enzyme, trigger itsdegradation by proteasome, create a deficiency in lysosome, and lead to sialidosis eventually. Researchersare actively seeking treatments for sialidosis. Enzyme replacement therapy has been attempted on asialidosis mouse model by injecting mice with a high dose of recombinant NEU1, and a severe immuneresponse was found after the treatment2. Gene therapy has also been tried but doesn’t show efficacy3. Sincethe protein structure of NEU1 is still unknown, it is difficult to design a small molecule as apharmacological chaperone. Based on the preliminary data in our lab, N–Acetylneuraminic acid (NANA) is suggested to be a potentialpharmacological chaperone for NEU1, which may help the folding of NEU1 in endoplasmic reticulum (ER),prevent its degradation and increase the amount of catalytically active NEU1 in the lysosome. I have beenworking on the effects of NANA on NEU1 in cellular experiments since I joined the lab in 2014. Ioverexpressed different NEU1 mutants in human embryonic kidney (HEK) 293T cells by transfecting thecells with plasmids containing the corresponding genes, and treated the cells with different concentrations ofNANA. At the end of the experiments, I harvested the cell lysates and measured the NEU1 expression levelusing western blot and its activity using a chromogenic substrate, X–NANA. Based on my current results, Ifound that both the expression level and the activity of NEU1 showed a dose–response relationship to theconcentration of NANA on the NEU1V217M mutant, which suggests that NANA could be used as a startingcompound for designing potential pharmacological chaperones for NEU1 to treat sialidosis. In the future, Iam planning to test the effects of NANA on other NEU1 mutants, establish a yeast expression system ofNEU1 in the lab, and study the structure of NEU1 and its interaction with other lysosomal enzymes. I amalso planning to collaborate with Professor Alessandra d’Azzo at St. Jude Children’s Research Hospital inMemphis for their sialidosis mouse model and Ultragenyx, a clinical–stage biopharmaceutical company,which is currently working on a secondary sialidosis in the future. With further study on NEU1, the knowledge gained from my research will benefit the academic field oflysosomal storage diseases, help us to understand more on the cause of sialidosis and to design potentialtreatments for patients.