Functional characterization of GNE mutations prevalent in Asian subjects with GNE myopathy, an ultra-rare neuromuscular disorder

Sharma, Shweta; Chanana, Pratibha; Bharadwaj, Ravi; Bhattacharya, Sudha; Arya, Ranjana

doi:10.1016/j.biochi.2022.03.014

Cited by 6 publications

(1 citation statement)

References 57 publications

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“…Only the individual domains of the GNE were examined in this study because the purification of the GNE as whole is still quite challenging. One critical point seems to be the removal of chaperone proteins [ 145 ]. Furthermore, our approach enables us to better estimate the individual effects of glycation of the two domains of the GNE.…”

Section: Discussion and Outlookmentioning

confidence: 99%

Glycation Interferes with the Activity of the Bi-Functional UDP-N-Acetylglucosamine 2-Epimerase/N-Acetyl-mannosamine Kinase (GNE)

et al. 2023

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Mutations in the gene coding for the bi-functional UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE), the key enzyme of the sialic acid biosynthesis, are responsible for autosomal-recessive GNE myopathy (GNEM). GNEM is an adult-onset disease with a yet unknown exact pathophysiology. Since the protein appears to work adequately for a certain period of time even though the mutation is already present, other effects appear to influence the onset and progression of the disease. In this study, we want to investigate whether the late onset of GNEM is based on an age-related effect, e.g., the accumulation of post-translational modifications (PTMs). Furthermore, we also want to investigate what effect on the enzyme activity such an accumulation would have. We will particularly focus on glycation, which is a PTM through non-enzymatic reactions between the carbonyl groups (e.g., of methylglyoxal (MGO) or glyoxal (GO)) with amino groups of proteins or other biomolecules. It is already known that the levels of both MGO and GO increase with age. For our investigations, we express each domain of the GNE separately, treat them with one of the glycation agents, and determine their activity. We demonstrate that the enzymatic activity of the N-acetylmannosamine kinase (GNE-kinase domain) decreases dramatically after glycation with MGO or GO—with a remaining activity of 13% ± 5% (5 mM MGO) and 22% ± 4% (5 mM GO). Whereas the activity of the UDP-N-acetylglucosamine 2-epimerase (GNE-epimerase domain) is only slightly reduced after glycation—with a remaining activity of 60% ± 8% (5 mM MGO) and 63% ± 5% (5 mM GO).

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Section: Discussion and Outlookmentioning

confidence: 99%

Glycation Interferes with the Activity of the Bi-Functional UDP-N-Acetylglucosamine 2-Epimerase/N-Acetyl-mannosamine Kinase (GNE)

et al. 2023

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Calcium level and autophagy defect in GNE mutants of rare neuromuscular disorder

Sharma,

Mashangva,

Oswalia

et al. 2024

Cell Biology International

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Rare genetic disorders are low in prevalence and hence there is little or no attention paid to them in the mainstream medical industry. One of the ultra‐rare neuromuscular disorders, GNE myopathy is caused due to biallelic mutations in the bifunctional enzyme, GNE (UDP N‐acetylglucosamine‐2‐epimerase/N‐acetylmannosamine kinase). It catalyses the rate‐limiting step in sialic acid biosynthesis. There are no effective treatments for GNE myopathy as the pathomechanism is poorly understood. Pathologically, the disease is characterized by the formation of rimmed vacuoles that contain aggregates of β‐amyloid, tau, presenilin etc proteins in muscle biopsy samples. Accumulation of aggregated proteins in the cells may occur due to the failure of the regulated autophagy phenomenon. In the present study, we aim to understand the effect of GNE mutations on autophagy. The cytosolic calcium levels in GNE mutant cells were found to be altered in a GNE mutation‐specific manner. The chaperone levels, such as HSP70 and PDI, as well as autophagic markers (LC3II/I ratios) were altered in the GNE mutant cells. Treatment with BAPTA‐AM, calcium chelator, significantly restored cytosolic calcium levels in some GNE mutant cells as well as autophagic marker levels and autophagic punctae formation. The effect on the calcium signalling cascade involving CaMKKβ/AMPK/mTOR was studied in the GNE mutant cells. Our study provides insights into the role of calcium in autophagic vacuole formation in the cells with GNE mutations that will have significance towards understanding the pathomechanism of GNE Myopathy and drug target identification for the rare disease.

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Understanding pathophysiology of GNE myopathy and current progress towards drug development

Mashangva,

Singh,

Oswalia

et al. 2024

J Biosci

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Functional characterization of GNE mutations prevalent in Asian subjects with GNE myopathy, an ultra-rare neuromuscular disorder

Cited by 6 publications

References 57 publications

Glycation Interferes with the Activity of the Bi-Functional UDP-N-Acetylglucosamine 2-Epimerase/N-Acetyl-mannosamine Kinase (GNE)

Glycation Interferes with the Activity of the Bi-Functional UDP-N-Acetylglucosamine 2-Epimerase/N-Acetyl-mannosamine Kinase (GNE)

Calcium level and autophagy defect in GNE mutants of rare neuromuscular disorder

Understanding pathophysiology of GNE myopathy and current progress towards drug development

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