bims-glecem 2022-10-23 papers

Issue of 2022‒10‒23
six papers selected by
Dipsikha Biswas, Københavns Universitet

Diabetes. 2022 Nov 01. 71(11): 2237-2250

Insulin Sensitization Following a Single Exercise Bout Is Uncoupled to Glycogen in Human Skeletal Muscle: A Meta-analysis of 13 Single-Center Human Studies.

Exercise profoundly influences glycemic control by enhancing muscle insulin sensitivity, thus promoting glucometabolic health. While prior glycogen breakdown so far has been deemed integral for muscle insulin sensitivity to be potentiated by exercise, the mechanisms underlying this phenomenon remain enigmatic. We have combined original data from 13 of our studies that investigated insulin action in skeletal muscle either under rested conditions or following a bout of one-legged knee extensor exercise in healthy young male individuals (n = 106). Insulin-stimulated glucose uptake was potentiated and occurred substantially faster in the prior contracted muscles. In this otherwise homogenous group of individuals, a remarkable biological diversity in the glucometabolic responses to insulin is apparent both in skeletal muscle and at the whole-body level. In contrast to the prevailing concept, our analyses reveal that insulin-stimulated muscle glucose uptake and the potentiation thereof by exercise are not associated with muscle glycogen synthase activity, muscle glycogen content, or degree of glycogen utilization during the preceding exercise bout. Our data further suggest that the phenomenon of improved insulin sensitivity in prior contracted muscle is not regulated in a homeostatic feedback manner from glycogen. Instead, we put forward the idea that this phenomenon is regulated by cellular allostatic mechanisms that elevate the muscle glycogen storage set point and enhance insulin sensitivity to promote the uptake of glucose toward faster glycogen resynthesis without development of glucose overload/toxicity or feedback inhibition.

DOI: https://doi.org/10.2337/db22-0015

Nat Commun. 2022 Oct 19. 13(1): 6199

Molecular architecture of the glycogen- committed PP1/PTG holoenzyme.

Marta Stefania Semrau, Gabriele Giachin, Sonia Covaceuszach, Alberto Cassetta, Nicola Demitri, Paola Storici, Graziano Lolli.

The delicate alternation between glycogen synthesis and degradation is governed by the interplay between key regulatory enzymes altering the activity of glycogen synthase and phosphorylase. Among these, the PP1 phosphatase promotes glycogenesis while inhibiting glycogenolysis. PP1 is, however, a master regulator of a variety of cellular processes, being conveniently directed to each of them by scaffolding subunits. PTG, Protein Targeting to Glycogen, addresses PP1 action to glycogen granules. In Lafora disease, the most aggressive pediatric epilepsy, genetic alterations leading to PTG accumulation cause the deposition of insoluble polyglucosans in neurons. Here, we report the crystallographic structure of the ternary complex PP1/PTG/carbohydrate. We further refine the mechanism of the PTG-mediated PP1 recruitment to glycogen by identifying i) an unusual combination of recruitment sites, ii) their contributions to the overall binding affinity, and iii) the conformational heterogeneity of this complex by in solution SAXS analyses.

DOI: https://doi.org/10.1038/s41467-022-33693-z

Clin Case Rep. 2022 Oct;10(10): e06480

Choice of diagnostic method for liver-type glycogen storage disease.

Toshihiko Kakiuchi, Yumeng Zhang.

Liver biopsy is a highly invasive in nature, and measurement of enzyme activity in blood cells and the Fernandez test are less certain for the diagnosis of glycogen storage disease (GSD). Therefore, genetic testing, which can also identify typing, should be prioritized for the diagnosis of GSD.

Keywords: biopsy; enzymology; genetic testing; glycogen storage disease type VI

DOI: https://doi.org/10.1002/ccr3.6480

JCI Insight. 2022 Oct 20. pii: e152970. [Epub ahead of print]

Suppression of Pullulanase-induced cytotoxic T cell response with a dual promoter in GSD IIIa mice.

Jeong-A Lim, Priya S Kishnani, Baodong Sun.

Deficiency of glycogen debranching enzyme in glycogen storage disease type III (GSD III) results in excessive glycogen accumulation in multiple tissues, primarily the liver, heart, and skeletal muscle. We recently reported that an adeno-associated virus (AAV) vector expressing a bacterial debranching enzyme (Pullulanase) driven by the ubiquitous CMV enhancer/chicken β-actin (CB) promoter cleared glycogen in major affected tissues of infant GSD IIIa mice. In this study, we developed a novel dual promoter consisting of a liver-specific promoter (LSP) and the CB promoter for gene therapy in adult GSD IIIa mice. Ten-week treatment with an AAV vector containing the LSP-CB dual promoter in adult GSD IIIa mice significantly increased Pullulanase expression and reduced glycogen contents in the liver (-60%), heart (-76%), and skeletal muscle (-63%), accompanied by the reversal of liver fibrosis, improved muscle function, and significant decrease in plasma biomarkers alanine aminotransferase, aspartate aminotransferase, and creatine kinase. Compared to the CB promoter, the dual promoter effectively decreased Pullulanase-induced cytotoxic T lymphocyte responses and enabled persistent therapeutic gene expression in adult GSD IIIa mice. Future studies are needed to determine the long-term durability of the dual promoter mediated expression of Pullulanase in adult GSD IIIa mice and in large animal models.

Keywords: Gene therapy; Genetic diseases; Genetics; Glucose metabolism; Therapeutics

DOI: https://doi.org/10.1172/jci.insight.152970

Front Genet. 2022 ;13 1001154

Development of a clinically validated in vitro functional assay to assess pathogenicity of novel GAA variants in patients with Pompe disease identified via newborn screening.

Shelly Goomber, Erin Huggins, Catherine W Rehder, Jennifer L Cohen, Deeksha S Bali, Priya S Kishnani.

Purpose: The addition of Pompe disease (Glycogen Storage Disease Type II) to the Recommended Uniform Screening Panel in the United States has led to an increase in the number of variants of uncertain significance (VUS) and novel variants identified in the GAA gene. This presents a diagnostic challenge, especially in the setting of late-onset Pompe disease when symptoms are rarely apparent at birth. There is an unmet need for validated functional studies to aid in classification of GAA variants. Methods: We developed an in vitro mammalian cell expression and functional analysis system based on guidelines established by the Clinical Genome Resource (ClinGen) Sequence Variant Interpretation Working Group for PS3/BS3. We validated the assay with 12 control variants and subsequently analyzed eight VUS or novel variants in GAA identified in patients with a positive newborn screen for Pompe disease without phenotypic evidence of infantile-onset disease. Results: The control variants were analyzed in our expression system and an activity range was established. The pathogenic controls had GAA activity between 0% and 11% of normal. The benign or likely benign controls had an activity range of 54%-100%. The pseudodeficiency variant had activity of 17%. These ranges were then applied to the variants selected for functional studies. Using the threshold of <11%, we were able to apply PS3_ supporting to classify two variants as likely pathogenic (c.316C > T and c.1103G > A) and provide further evidence to support the classification of likely pathogenic for two variants (c.1721T > C and c.1048G > A). One variant (c.1123C > T) was able to be reclassified based on other supporting evidence. We were unable to reclassify three variants (c.664G > A, c.2450A > G, and c.1378G > A) due to insufficient or conflicting evidence. Conclusion: We investigated eight GAA variants as proof of concept using our validated and reproducible in vitro expression and functional analysis system. While additional work is needed to further refine our system with additional controls and different variant types in order to apply the PS3/BS3 criteria at a higher level, this tool can be utilized for variant classification to meet the growing need for novel GAA variant classification in the era of newborn screening for Pompe disease.

Keywords: functional studies; glycogen storage disease type 2; in vitro assay; lysosomal storage disease (LSD); newborn screening; pompe disease; variant classification

DOI: https://doi.org/10.3389/fgene.2022.1001154

Front Pediatr. 2022 ;10 944178

Infantile-onset Pompe disease complicated by sickle cell anemia: Case report and management considerations.

Rodrigo Tzovenos Starosta, Ying-Chen Claire Hou, Katelyn Leestma, Prapti Singh, Luke Viehl, Linda Manwaring, Jorge Luis Granadillo, Molly C Schroeder, Jamie N Colombo, Halana Whitehead, Patricia Irene Dickson, Monica L Hulbert, Hoanh Thi Nguyen.

Infantile-onset Pompe disease (IOPD) is a rare, severe disorder of lysosomal storage of glycogen that leads to progressive cardiac and skeletal myopathy. IOPD is a fatal disease in childhood unless treated with enzyme replacement therapy (ERT) from an early age. Sickle cell anemia (SCA) is a relatively common hemoglobinopathy caused by a specific variant in the hemoglobin beta-chain. Here we report a case of a male newborn of African ancestry diagnosed and treated for IOPD and SCA. Molecular testing confirmed two GAA variants, NM_000152.5: c.842G>C, p.(Arg281Pro) and NM_000152.5: c.2560C>T, p.(Arg854*) in trans, and homozygosity for the HBB variant causative of SCA, consistent with his diagnosis. An acute neonatal presentation of hypotonia and cardiomyopathy required ERT with alglucosidase alfa infusions preceded by immune tolerance induction (ITI), as well as chronic red blood cell transfusions and penicillin V potassium prophylaxis for treatment of IOPD and SCA. Clinical course was further complicated by multiple respiratory infections. We review the current guidelines and interventions taken to optimize his care and the pitfalls of those guidelines when treating patients with concomitant conditions. To the best of our knowledge, no other case reports of the concomitance of these two disorders was found. This report emphasizes the importance of newborn screening, early intervention, and treatment considerations for this complex patient presentation of IOPD and SCA.

Keywords: alpha-glucosidase; enzyme replacement therapy; glycogen storage disorder type II; immune tolerance induction; methotrexate; newborn screening; sickle cell anemia

DOI: https://doi.org/10.3389/fped.2022.944178