Browsing by Subject "Pompe disease"

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    The effects of laforin, malin, Stbd1, and Ptg deficiencies on heart glycogen levels in Pompe disease mouse models
    (2015-08) Conway, Betsy Ann; Roach, Peter J.; DePaoli-Roach, Anna; Hurley, Thomas
    Pompe disease (PD) is a rare metabolic myopathy characterized by loss of acid alpha-glucosidase (GAA), the enzyme responsible for breaking down glycogen to glucose within the lysosomes. PD cells accumulate massive quantities of glycogen within their lysosomes, and as such, PD is classified as a “lysosomal storage disease” (LSD). GAA-deficient cells also exhibit accumulation of autophagic debris. Symptoms of severe infantile PD include extreme muscle weakness, hypotonia, and hypertrophic cardiomyopathy, resulting in death before one year of age. Certain LSDs are currently being successfully treated with enzyme replacement therapy (ERT), which involves intravenous infusion of a recombinant enzyme to counteract the endogenous deficiency. ERT has been less successful in PD, however, due to ineffective delivery of the recombinant enzyme. Alternatively, specific genes deletion may reduce lysosomal glycogen load, and could thus be targeted in PD therapy development. Absence of malin (EPM2B) or laforin (EPM2A) has been proposed to impair autophagy, which could reduce lysosomal glycogen levels. Additionally, deficiency of Stbd1 has been postulated to disable lysosomal glycogen import. Furthermore, Ptg deficiency was previously reported to abrogate Lafora body formation and correct neurological abnormalities in Lafora disease mouse models and could have similar effects on PD pathologies. The goal of this study was to characterize the effects of homozygous disruption of Epm2a, Epm2b, Stbd1, and Ptg loci on total glycogen levels in PD mouse model heart tissue, as in severe infantile PD, it is accumulation of glycogen in the heart that results in fatal hypertrophic cardiomyopathy. Gaa-/- mice were intercrossed with Epm2a-/-, Epm2b-/-, Stbd1-/-, and Ptg-/- mice to generate wildtype (WT), single knockout, and double knockout mice. The results indicated that Gaa-/- hearts accumulated up to 100-fold more glycogen than the WT. These mice also displayed cardiac hypertrophy. However, deficiency of Epm2a, Epm2b, Stbd1, or PTG in the Gaa-/- background did not reveal changes of statistical significance in either heart glycogen or cardiac hypertrophy. Nevertheless, since total glycogen was measured, these deficiencies should not be discarded in future discussions of PD therapy, as increasing sample sizes and/or distinguishing cytosolic from lysosomal glycogen content may yet reveal differences of greater significance.
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    Novel method for detection of glycogen in cells
    (Oxford University Press, 2017-05-01) Skurat, Alexander V.; Segvich, Dyann M.; DePaoli-Roach, Anna A.; Roach, Peter J.; Biochemistry and Molecular Biology, School of Medicine
    Glycogen, a branched polymer of glucose, functions as an energy reserve in many living organisms. Abnormalities in glycogen metabolism, usually excessive accumulation, can be caused genetically, most often through mutation of the enzymes directly involved in synthesis and degradation of the polymer leading to a variety of glycogen storage diseases (GSDs). Microscopic visualization of glycogen deposits in cells and tissues is important for the study of normal glycogen metabolism as well as diagnosis of GSDs. Here, we describe a method for the detection of glycogen using a renewable, recombinant protein which contains the carbohydrate-binding module (CBM) from starch-binding domain containing protein 1 (Stbd1). We generated a fusion protein containing g lutathione S-transferase, a cM c eptitope and the tbd1 BM (GYSC) for use as a glycogen-binding probe, which can be detected with secondary antibodies against glutathione S-transferase or cMyc. By enzyme-linked immunosorbent assay, we demonstrate that GYSC binds glycogen and two other polymers of glucose, amylopectin and amylose. Immunofluorescence staining of cultured cells indicate a GYSC-specific signal that is co-localized with signals obtained with anti-glycogen or anti-glycogen synthase antibodies. GYSC-positive staining inside of lysosomes is observed in individual muscle fibers isolated from mice deficient in lysosomal enzyme acid alpha-glucosidase, a well-characterized model of GSD II (Pompe disease). Co-localized GYSC and glycogen signals are also found in muscle fibers isolated from mice deficient in malin, a model for Lafora disease. These data indicate that GYSC is a novel probe that can be used to study glycogen metabolism under normal and pathological conditions.
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    Oral tolerance to prevent anti-drug antibody formation in protein replacement therapies
    (Elsevier, 2022-12) Rana, Jyoti; Muñoz, Maite Melero; Biswas , Moanaro; Pediatrics, School of Medicine
    Protein based therapeutics have successfully improved the quality of life for patients of monogenic disorders like hemophilia, Pompe and Fabry disease. However, a significant proportion of patients develop immune responses towards intravenously infused therapeutic protein, which can complicate or neutralize treatment and compromise patient safety. Strategies aimed at circumventing immune responses following therapeutic protein infusion can greatly improve therapeutic efficacy. In recent years, antigen-based oral tolerance induction has shown promising results in the prevention and treatment of autoimmune diseases, food allergies and can prevent anti-drug antibody formation to protein replacement therapies. Oral tolerance exploits regulatory mechanisms that are initiated in the gut associated lymphoid tissue (GALT) to promote active suppression of orally ingested antigen. In this review, we outline general perceptions and current knowledge about the mechanisms of oral tolerance, including tissue specific sites of tolerance induction and the cells involved, with emphasis on antigen presenting cells and regulatory T cells. We define several factors, such as cytokines and metabolites that impact the stability and expansion potential of these immune modulatory cells. We highlight preclinical studies that have been performed to induce oral tolerance to therapeutic proteins or enzymes for single gene disorders, such as hemophilia or Pompe disease. These studies mainly utilize a transgenic plant-based system for oral delivery of antigen in conjugation with fusion protein technology that favors the prevention of antigen degradation in the stomach while enhancing uptake in the small intestine by antigen presenting cells and regulatory T cell induction, thereby promoting antigen specific systemic tolerance.
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    The structural mechanism of human glycogen synthesis by the GYS1-GYG1 complex
    (Elsevier, 2022) Fastman, Nathan M.; Liu, Yuxi; Ramanan, Vyas; Merritt, Hanne; Ambing, Eileen; DePaoli-Roach, Anna A.; Roach, Peter J.; Hurley, Thomas D.; Mellem, Kevin T.; Ullman, Julie C.; Green, Eric; Morgans, David, Jr.; Tzitzilonis, Christos; Biochemistry and Molecular Biology, School of Medicine
    Glycogen is the primary energy reserve in mammals, and dysregulation of glycogen metabolism can result in glycogen storage diseases (GSDs). In muscle, glycogen synthesis is initiated by the enzymes glycogenin-1 (GYG1), which seeds the molecule by autoglucosylation, and glycogen synthase-1 (GYS1), which extends the glycogen chain. Although both enzymes are required for proper glycogen production, the nature of their interaction has been enigmatic. Here, we present the human GYS1:GYG1 complex in multiple conformations representing different functional states. We observe an asymmetric conformation of GYS1 that exposes an interface for close GYG1 association, and propose this state facilitates handoff of the GYG1-associated glycogen chain to a GYS1 subunit for elongation. Full activation of GYS1 widens the GYG1-binding groove, enabling GYG1 release concomitant with glycogen chain growth. This structural mechanism connecting chain nucleation and extension explains the apparent stepwise nature of glycogen synthesis and suggests distinct states to target for GSD-modifying therapeutics.