The Yash Gandhi Foundation has awarded nearly half a million dollars in research grants to multiple academic institutions. With the funding of research from the Yash Gandhi Foundation, these institutions have been working in collaboration and conducting research to unravel the molecular basis of I-cell disease and develop new model systems (particularly in zebrafish) to identify how the loss of mannose 6-phosphate lysosomal targeting contributes to the development of disease symptoms. This information may lead to new therapies to treat Mucoliposis. YGF-funded researchers are interested in establishing partnerships with pharmaceutical companies to accelerate therapy.
The Yash Gandhi Foundation has been acknowleged in 8 different research publications. The published manuscripts are outlined below;
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1. Qian, Y., Van Meel, E., Flanagan-Steet, H., Yox, A., Steet, R., and Kornfeld, S. Analysis of Mucolipidosis II/III GNPTAB Missense Mutations Identifies Domains of UDP-GlcNAc:Lysosomal Enzyme GlcNAc-1-Phosphotransferase Involved in Catalytic Function and Lysosomal Enzyme Recognition. J. Biol. Chem., 290:3045-3056, 2015.
1. This paper investigated how individual missense mutations found in ML patients affect the function of the GlcNAc-1-phosphotransferase enzyme using both cell and zebrafish models, allowing conserved domains within the enzyme to be assigned a specific function in either catalysis (adding the M6P tag) or lysosomal enzyme recognition (selecting the enzymes that will be tagged).
2. Van Meel, E., Lee, W.S., Liu, L., Qian, Y., Doray, B., and Kornfeld, S. Multiple domains of GlcNAc-1-phosphotransferase mediate recognition of lysosomal enzymes. J. Biol. Chem., 291:8295-8304, 2016.
2. This work identifies new domains called Notch repeats within the GlcNAc-1-phosphotransferase enzyme that cooperate with the previously characterized DMAP domain to recognize the lysosomal enzymes that it modifies with mannose-6 phosphate. Different combinations of these domains is used to recognize different lysosomal enzymes, providing insight on how the GlcNAc-1-phosphotransferase enzyme is able to recognize a large number of structurally diverse lysosomal enzymes.
3. Van Meel, E., and Kornfeld, S. Mucolipidosis III GNPTG Missense Mutations Cause Misfolding of the gamma Subunit of GlcNAc-1-Phosphotransferase. Human Mutation, 37:623-626, 2016.
3. This work shows that certain missense mutations in GNPTG cause the gamma subunit expressed by this gene to misfold in the endoplasmic reticulum leading to its inability to function in a complex with the alpha/beta subunits of the GlcNAc-1-phosphotransferase enzyme.
4. Liu, L., Lee, W.S., Doray, B., and Kornfeld, S. Role of spacer-1 in the maturation and function of GlcNAc-1-phosphotransferase. FEBS Letters, 591:47-55, 2016.
4. A new role is described for a region of the GlcNAc-1-phosphotransferase enzyme, termed spacer-1, that lies between known conserved domains. Changes to the amino acid sequence in this region affect how the enzyme matures into its fully functional form.
5. Liu, L., Lee, W.S., Doray, B., and Kornfeld, S. Engineering of GlcNAc-1-PHosphotransferase for Production of Highly Phosphorylated Lysosomal Enzymes for Enzyme Replacement Therapy. Molecular Therapy: Methods & Clinical Development, 5:59-65, 2017.
5. This groundbreaking paper demonstrates that the function of the GlcNAc-1-phosphotransferase enzyme can actually be improved if certain regions of the amino acid sequence are removed. The resulting form of the enzyme is capable of adding more mannose-6-phosphate to many lysosomal hydrolases than the wild type version of the enzyme. This unexpected finding is important because it allows recombinant enzymes to be highly modified with mannose 6-phosphate, a discovery that may enhance enzyme replacement therapy for many lysosomal storage disorders.
6. Aarnio-Peterson M, Zhao P, Yu SH, Christian C, Flanagan-Steet H, Wells L, Steet R. Altered Met receptor phosphorylation and LRP1-mediated uptake in cells lacking carbohydrate-dependent lysosomal targeting. J Biol Chem 292:15094-15104, 2017.
6. This paper describes unexpected effects on receptor phosphorylation in cells lacking the alpha/beta subunits of the GlcNAc-1-phosphotransferase enzyme. The researchers show that the phosphorylation of the Met receptor is greatly increased in GNPTAB-/- cells and link this increase to reactive active oxygen species (ROS)-dependent loss of phosphatase activity. These findings demonstrate that increases in ROS caused by lysosomal storage can impact the action of cell surface receptors and increase their activity.
7. Flanagan-Steet H, Christian C, Lu PN, Aarnio-Peterson M, Sanman L, Archer-Hartmann S, Azadi P, Bogyo M, Steet RA. TGF-ß Regulates Cathepsin Activation during Normal and Pathogenic Development. Cell Reports 22:2964-2977, 2018.
7. This seminal paper describes a novel regulatory loop between the growth factor TGF-ß and the lysosomal protease, cathepsin K. Using innovative activity-based probes to track cathepsin activity, the authors show that TGF-ß signaling controls cathepsin K activity at the level of proenzyme processing. It does so by enhancing the expression of chondroitin-4-sulfate, a known activator and stabilizer of cathepsins. When the expression of the main enzyme that makes chondroitin-4-sulfate is inhibited, the proteolytic activation of cathepsin K is reduced, improving the phenotypes in MLII zebrafish. This work also highlights how disease-associated changes in chondroitin sulfate can impact pathogenesis in certain tissues.
8. Liu, L., Doray, B., and Kornfeld, S. Recycling of Golgi glycosyltransferases requires direct binding to coatomer. PNAS 2018;115 (36):8984-8989
8. This study began in 2014 with efforts to understand why mutations in the N-terminal cytoplasmic tail of Phosphotransferase detected in MLIII patients cause the enzyme to escape from the Golgi where it functions to generate the Man-6-P recognition marker on lysosomal enzymes to the endosomal lysosomal compartments where it is destroyed. This abnormal trafficking was described in a 2014 PNAS paper (van Meel, et al) that was also supported by the Yash Gandhi Foundation. The current paper greatly expands the original study and provides a biochemical explanation for why these mutations lead to the mislocalization
of the transferase. Further, the findings uncover a common pathway that is used by many other Golgi localized glycosyltransferases.