Browsing by Author "Sun, Ramon C."

Now showing 1 - 4 of 4
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    Accurate and sensitive quantitation of glucose and glucose phosphates derived from storage carbohydrates by mass spectrometry
    (Elsevier, 2020-02-15) Young, Lyndsay E.A.; Brizzee, Corey O.; Macedo, Jessica K. A.; Murphy, Robert D.; Contreras, Christopher J.; DePaoli-Roach, Anna A.; Roach, Peter J.; Gentry, Matthew S.; Sun, Ramon C.; Biochemistry and Molecular Biology, School of Medicine
    The addition of phosphate groups into glycogen modulates its branching pattern and solubility which all impact its accessibility to glycogen interacting enzymes. As glycogen architecture modulates its metabolism, it is essential to accurately evaluate and quantify its phosphate content. Simultaneous direct quantitation of glucose and its phosphate esters requires an assay with high sensitivity and a robust dynamic range. Herein, we describe a highly-sensitive method for the accurate detection of both glycogen-derived glucose and glucose-phosphate esters utilizing gas-chromatography coupled mass spectrometry. Using this method, we observed higher glycogen levels in the liver compared to skeletal muscle, but skeletal muscle contained many more phosphate esters. Importantly, this method can detect femtomole levels of glucose and glucose phosphate esters within an extremely robust dynamic range with excellent accuracy and reproducibility. The method can also be easily adapted for the quantification of plant starch, amylopectin or other biopolymers.
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    Brain glycogen serves as a critical glucosamine cache required for protein glycosylation
    (Elsevier, 2021) Sun, Ramon C.; Young, Lyndsay E.A.; Bruntz, Ronald C.; Markussen, Kia H.; Zhou, Zhengqiu; Conroy, Lindsey R.; Hawkinson, Tara R.; Clarke, Harrison A.; Stanback, Alexandra E.; Macedo, Jessica K.A.; Emanuelle, Shane; Brewer, M. Kathryn; Rondon, Alberto L.; Mestas, Annette; Sanders, William C.; Mahalingan, Krishna K.; Tang, Buyun; Chikwana, Vimbai M.; Segvich, Dyann M.; Contreras, Christopher J.; Allenger, Elizabeth J.; Brainson, Christine F.; Johnson, Lance A.; Taylor, Richard E.; Armstrong, Dustin D.; Shaffer, Robert; Waechter, Charles J.; Vander Kooi, Craig W.; DePaoli-Roach, Anna A.; Roach, Peter J.; Hurley, Thomas D.; Drake, Richard R.; Gentry, Matthew S.; Biochemistry and Molecular Biology, School of Medicine
    Glycosylation defects are a hallmark of many nervous system diseases. However, the molecular and metabolic basis for this pathology is not fully understood. In this study, we found that N-linked protein glycosylation in the brain is metabolically channeled to glucosamine metabolism through glycogenolysis. We discovered that glucosamine is an abundant constituent of brain glycogen, which functions as a glucosamine reservoir for multiple glycoconjugates. We demonstrated the enzymatic incorporation of glucosamine into glycogen by glycogen synthase, and the release by glycogen phosphorylase by biochemical and structural methodologies, in primary astrocytes, and in vivo by isotopic tracing and mass spectrometry. Using two mouse models of glycogen storage diseases, we showed that disruption of brain glycogen metabolism causes global decreases in free pools of UDP-N-acetylglucosamine and N-linked protein glycosylation. These findings revealed fundamental biological roles of brain glycogen in protein glycosylation with direct relevance to multiple human diseases of the central nervous system.
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    Small-molecule inhibition of glycogen synthase 1 for the treatment of Pompe disease and other glycogen storage disorders
    (American Association for the Advancement of Science, 2024) Ullman, Julie C.; Mellem, Kevin T.; Xi, Yannan; Ramanan, Vyas; Merritt, Hanne; Choy, Rebeca; Gujral, Tarunmeet; Young, Lyndsay E. A.; Blake, Kerrigan; Tep, Samnang; Homburger, Julian R.; O'Regan, Adam; Ganesh, Sandya; Wong, Perryn; Satterfield, Terrence F.; Lin, Baiwei; Situ, Eva; Yu, Cecile; Espanol, Bryan; Sarwaikar, Richa; Fastman, Nathan; Tzitzilonis, Christos; Lee, Patrick; Reiton, Daniel; Morton, Vivian; Santiago, Pam; Won, Walter; Powers, Hannah; Cummings, Beryl B.; Hoek, Maarten; Graham, Robert R.; Chandriani, Sanjay J.; Bainer, Russell; DePaoli-Roach, Anna A.; Roach, Peter J.; Hurley, Thomas D.; Sun, Ramon C.; Gentry, Matthew S.; Sinz, Christopher; Dick, Ryan A.; Noonberg, Sarah B.; Beattie, David T.; Morgans, David J., Jr.; Green, Eric M.; Biochemistry and Molecular Biology, School of Medicine
    Glycogen synthase 1 (GYS1), the rate-limiting enzyme in muscle glycogen synthesis, plays a central role in energy homeostasis and has been proposed as a therapeutic target in multiple glycogen storage diseases. Despite decades of investigation, there are no known potent, selective small-molecule inhibitors of this enzyme. Here, we report the preclinical characterization of MZ-101, a small molecule that potently inhibits GYS1 in vitro and in vivo without inhibiting GYS2, a related isoform essential for synthesizing liver glycogen. Chronic treatment with MZ-101 depleted muscle glycogen and was well tolerated in mice. Pompe disease, a glycogen storage disease caused by mutations in acid α glucosidase (GAA), results in pathological accumulation of glycogen and consequent autophagolysosomal abnormalities, metabolic dysregulation, and muscle atrophy. Enzyme replacement therapy (ERT) with recombinant GAA is the only approved treatment for Pompe disease, but it requires frequent infusions, and efficacy is limited by suboptimal skeletal muscle distribution. In a mouse model of Pompe disease, chronic oral administration of MZ-101 alone reduced glycogen buildup in skeletal muscle with comparable efficacy to ERT. In addition, treatment with MZ-101 in combination with ERT had an additive effect and could normalize muscle glycogen concentrations. Biochemical, metabolomic, and transcriptomic analyses of muscle tissue demonstrated that lowering of glycogen concentrations with MZ-101, alone or in combination with ERT, corrected the cellular pathology in this mouse model. These data suggest that substrate reduction therapy with GYS1 inhibition may be a promising therapeutic approach for Pompe disease and other glycogen storage diseases.
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    Targeting Pathogenic Lafora Bodies in Lafora Disease Using an Antibody-Enzyme Fusion
    (Elsevier, 2019-07-25) Brewer, M. Kathryn; Uittenbogaard, Annette; Austin, Grant L.; Segvich, Dyann M.; DePaoli-Roach, Anna; Roach, Peter J.; McCarthy, John J.; Simmons, Zoe R.; Brandon, Jason A.; Zhou, Zhengqiu; Zeller, Jill; Young, Lyndsay E. A.; Sun, Ramon C.; Pauly, James R.; Aziz, Nadine M.; Hodges, Bradley L.; McKnight, Tracy R.; Armstrong, Dustin D.; Gentry, Matthew S.; Biochemistry and Molecular Biology, School of Medicine