58 research outputs found
Hypoglycosylation of alpha-dystroglycan in patients with hereditary IBM due to GNE mutations
Hereditary inclusion body myopathy (HIBM) is an adult onset
neuromuscular disorder associated with mutations in the gene
UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase (GNE),
whose product is the rate limiting bi-functional enzyme catalyzing the
first two steps of sialic acid biosynthesis. Loss of GNE activity in
HIBM is thought to impair sialic acid production and interfere with
proper sialylation of glycoconjugates, but it remains unclear how such a
defect would lead to muscle destruction and muscle weakness.
Hypoglycosylation of alpha-dystroglycan, a central protein of the
skeletal muscle dystrophin-glycoprotein complex, results in disturbed
interactions with extracellular matrix proteins. This has recently been
identified as the pathomechanism involved in several congenital muscular
dystrophies. We examined the glycosylation status of alpha-dystroglycan
in muscle biopsies of four HIBM patients of non-Iranian Jewish origin
(one American, two Indians, and one Greek). Two of these patients carry
novel compound heterozygous GNE mutations on exon 2 and exon 9. All four
muscle biopsies showed absent or markedly reduced immunolabeling with
two different antibodies (VIA4 and IIH6) to glycosylated epitopes of
alpha-dystroglycan. Normal labeling was found using antibodies to the
core alpha-dystroglycan protein, beta-dystroglycan, and laminin alpha-2.
These findings resemble those found for other congenital muscular
dystrophies, suggesting that HIBM may be a “dystroglycanopathy,” and
providing an explanation for the muscle weakness of patients with GNE
mutations. Published by Elsevier Inc
Allele-specific silencing of the dominant disease allele in sialuria by RNA interference
Dominant disease alleles are attractive therapeutic targets for allele-specific gene silencing by small interfering RNA (siRNA). Sialuria is a dominant disorder caused by missense mutations in the allosteric site of GNE, coding for the rate-limiting enzyme of sialic acid biosynthesis, UDP-GlcNAc 2-epimerase/ManNAc kinase. The resultant loss of feedback inhibition of GNE-epimerase activity by CMP-sialic acid causes excessive production of free sialic acid. For this study we employed synthetic siRNAs specifically targeting the dominant GNE mutation c.797G>A (p.R266Q) in sialuria fibroblasts. We demonstrated successful siRNA-mediated down-regulation of the mutant allele by allele-specific real-time PCR. Importantly, mutant allele-specific silencing resulted in a significant decrease of free sialic acid, to within the normal range. Feedback inhibition of GNE-epimerase activity by CMP-sialic acid recovered after silencing demonstrating specificity of this effect. These findings indicate that allele-specific silencing of a mutated allele is a viable therapeutic strategy for autosomal dominant diseases, including sialuria.—Klootwijk, R. D., Savelkoul, P. J. M., Ciccone, C., Manoli, I., Caplen, N. J., Krasnewich, D. M., Gahl, W. A., Huizing, M. Allele-specific silencing of the dominant disease allele in sialuria by RNA interference
Familial dementia caused by polymerization of mutant neuroserpin
Aberrant protein processing with tissue deposition is associated with many common neurodegenerative disorders1, 2; however, the complex interplay of genetic and environmental factors has made it difficult to decipher the sequence of events linking protein aggregation with clinical disease3. Substantial progress has been made toward understanding the pathophysiology of prototypical conformational diseases and protein polymerization in the superfamily of serine proteinase inhibitors (serpins)4, 5. Here we describe a new disease, familial encephalopathy with neuroserpin inclusion bodies, characterized clinically as an autosomal dominantly inherited dementia, histologically by unique neuronal inclusion bodies and biochemically by polymers of the neuron-specific serpin, neuroserpin6, 7. We report the cosegregation of point mutations in the neuroserpin gene (PI12) with the disease in two families. The significance of one mutation, S49P, is evident from its homology to a previously described serpin mutation8, whereas that of the other, S52R, is predicted by modelling of the serpin template. Our findings provide a molecular mechanism for a familial dementia and imply that inhibitors of protein polymerization may be effective therapies for this disorder and perhaps for other more common neurodegenerative diseases
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