bims-meglyc 2023-12-17 papers

Issue of 2023‒12‒17
three papers selected by
Silvia Radenkovic

Front Genet. 2023 ;14 1264237

Expanding the phenotype and metabolic basis of ATP6AP2-congenital disorder of glycosylation in a Chinese patient with a novel variant c.185G>A (p.Gly62Glu).

Yuan Fang, Yi-Zhen Wang, Lian Chen, Xin-Bao Xie.

Background: A rare X-linked hereditary condition known as ATP6AP2-congenital disorder of glycosylation (ATP6AP2-CDG) is caused by pathogenic variants in ATP6AP2, resulting in autophagic misregulation with reduced siganling of mammalian target of rapamycin (mTOR) that clinically presents with aberrant protein glycosylation, hepatosteatosis, immunodeficiency, cutis laxa, and psychomotor dysfunction. To date, only two missense mutations have been reported in three patients from two unrelated families. Methods: In order to extend the profiles of phenotype and genotype associated with ATP6AP2-CDG, we assessed the clinical history, whole exome sequencing (WES), and liver histology as well as immunohistochemistry in a Chinese patient, and performed quantitative real-time polymerase chain reaction (qRT-PCR), Western blotting and untargeted metabolomics in genetic exogenously constructed cells. Results: The 11-month-old Chinese boy presented with recurrent jaundice, cutis laxa, cirrhosis, growth retardation, coagulopathy, anemia, and cardiomegaly, and underwent liver transplantation. A novel mutation, c.185G>A (p.Gly62Glu), was identified in exon 3 of ATP6AP2. The expression of ATP6AP2 was observed to remain unchanged in the liver sample of the patient as well as in HEK293T cells harboring the p.Gly62Glu. This missense mutation was found to dysregulate autophagy and mTOR signaling. Moreover, metabolomics analysis revealed that the exogenously introduced Gly62Glu mutant resulted in the downregulation of numerous metabolites involved in lipid metabolism pathway. Conclusion: This study may enable a more detailed exploration of its precise pathogenesis and potential therapeutic interventions.

Keywords: ATP6AP2; X-linked; cirrhosis; congenital disorders of glycosylation; hereditary

DOI: https://doi.org/10.3389/fgene.2023.1264237

Exp Physiol. 2023 Dec 14.

Targeted genetic therapies for inherited disorders that affect both cardiac and skeletal muscle.

Yiangos Psaras, Christopher N Toepfer.

Skeletal myopathies and ataxias with secondary cardiac involvement are complex, progressive and debilitating conditions. As life expectancy increases across these conditions, cardiac involvement often becomes more prominent. This highlights the need for targeted therapies that address these evolving cardiac pathologies. Musculopathies by and large lack cures that directly target the genetic basis of the diseases; however, as our understanding of the genetic causes of these conditions has evolved, it has become tractable to develop targeted therapies using biologics, to design precision approaches to target the primary genetic causes of these varied diseases. Using the examples of Duchenne muscular dystrophy, Friedreich ataxia and Pompe disease, we discuss how the genetic causes of such diseases derail diverse homeostatic, energetic and signalling pathways, which span multiple cellular systems in varied tissues across the body. We outline existing therapeutics and treatments in the context of emerging novel genetic approaches. We discuss the hurdles that the field must overcome to deliver targeted therapies across the many tissue types affected in primary myopathies. NEW FINDINGS: What is the topic of this review? Overlapping disease pathomechanisms and therapeutic opportunities in neuromuscular, skeletal and cardiac muscle diseases in the context of novel genetic therapies. What advances does it highlight? This review outlines the diverse genetic changes that drive pathomechanism across a set of neuromuscular conditions and highlight the emerging targeted biological therapies that are being developed to treat these conditions, with additional discussion of the hurdles to actualising genetically targeted precision medicine.

Keywords: Duchenne muscular dystrophy; Friedreich's ataxia; Pompe disease; gene therapy; skeletal and cardiac muscle disease; therapeutics

DOI: https://doi.org/10.1113/EP090436

Front Biosci (Landmark Ed). 2023 Nov 24. 28(11): 300

Evaluation of N-Acetylmannosamine Administration to Restore Sialylation in GNE-Deficient Human Embryonal Kidney Cells.

Emilia Peters, Philipp Selke, Kaya Bork, Rüdiger Horstkorte, Astrid Gesper.

BACKGROUND: A key mechanism in the neuromuscular disease GNE myopathy (GNEM) is believed to be that point mutations in the GNE gene impair sialic acid synthesis - maybe due to UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE) activity restrictions - and resulting in muscle tissue loss. N-acetylmannosamine (ManNAc) is the first product of the bifunctional GNE enzyme and can therefore be regarded as a precursor of sialic acids. This study investigates whether this is also a suitable substance for restoring the sialic acid content in GNE-deficient cells.METHODS: A HEK-293 GNE-knockout cell line was generated using CRISPR-Cas9 and analyzed for its ability to synthesize sialic acids. The cells were then supplemented with ManNAc to compensate for possible GNE inactivity and thereby restore sialic acid synthesis. Sialic acid levels were monitored by immunoblot and high performance liquid chromatography (HPLC).
RESULTS: The HEK-293 GNE-knockout cells showed almost no polysialylation signal (immunoblot) and a reduced overall (-71%) N-acetylneuraminic acid (Neu5Ac) level (HPLC) relative to total protein and normalized to wild type level. Supplementation of GNE-deficient HEK-293 cells with 2 mM ManNAc can restore polysialylation and free intracellular sialic acid levels to wild type levels. The addition of 1 mM ManNAc is sufficient to restore the membrane-bound sialic acid level.
CONCLUSIONS: Although the mechanism behind this needs further investigation and although it remains unclear why adding ManNAc to GNE-deficient cells is sufficient to elevate polysialylation back to wild type levels - since this substance is also converted by the GNE, all of this might yet prove helpful in the development of an appropriate therapy for GNEM.

Keywords: GNE; GNE myopathy; ManNAc; glycobiology; glycosylation; posttranslational modification; sialic acids

DOI: https://doi.org/10.31083/j.fbl2811300