Defect in Vitamin B
            <sub>12</sub>
            Release from Lysosomes: Newly Described Inborn Error of Vitamin B
            <sub>12</sub>
            Metabolism

Rosenblatt, David S.; Hosack, Angela; Matiaszuk, Nora; Cooper, Bernard A.; Laframboise, Rachel

doi:10.1126/science.4001945

Cited by 133 publications

(59 citation statements)

References 12 publications

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“…This life-threatening condition is caused by defects in the LMBRD1 gene that encodes LMBD1 (Rutsch et al, 2009). The defect in lysosomal Cbl release was discovered 25 years ago, well before the likely transporter involved was characterised (Rosenblatt et al, 1985).…”

Section: Discussionmentioning

confidence: 99%

“…These pioneering studies also showed that chloroquine, a compound that increases lysosomal pH above its physiological level of ~ 4.5 thereby inhibiting lysosomal protease activity, prevents the release of Cbl from TCII and blocks the transport of lysosomal [ 57 Co]Cbl to both MS and MMCM (Rosenblatt et al, 1985). We have recently hypothesized that in addition to LMBRD1 mutations and drug-mediated alterations of lysosomal function that may trap Cbl in the lysosome, additional pathophysiological perturbations in lysosome function could also represent a "roadblock" for Cbl transit through the lysosomal compartment (Zhao et al, 2011).…”

Section: Discussionmentioning

confidence: 99%

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Analysis of subcellular [57Co] cobalamin distribution in SH-SY5Y neurons and brain tissue

Zhao¹,

Ruberu²,

Li³

et al. 2013

Journal of Neuroscience Methods

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Cobalamin (Cbl) utilization as a cofactor for methionine synthase and methylmalonyl-CoA mutase is dependent on the transport of Cbl through lysosomes and its subsequent delivery to the cytosol and mitochondria. We speculated that neuropathological conditions that impair lysosomal function (e.g., agerelated lipofuscinosis and specific neurodegenerative diseases) might impair lysosomal Cbl transport. To address this question, an appropriate method to quantify intracellular Cbl transport in neuronal cell types and brain tissue is required. Thus, we developed methods to measure [ 57 Co] Cbl levels in lysosomes, mitochondria and cytosol obtained from in vitro and in vivo sources. Human SH-SY5Y neurons or HT1080 fibroblasts were labeled with [ 57 Co] Cbl and homogenized using a ball-bearing homogenizer, and the lysates were separated into 10 fractions using ultracentrifugation in an OptiPrep density gradient. Lysosomes were recovered from the top of the gradient (fractions 1-5), which were clearly separated from mitochondria (fractions 7-9) on the basis of the expression of the marker proteins, LAMP2 and VDAC1. The isolated lysosomes were intact based on their colocalization with acid phosphatase activity. The lysosomal and mitochondrial fractions were free of the cytosolic markers beta-actin and methionine synthase. The relative distribution of [ 57 Co] Cbl in both neurons and fibroblasts was as follows: 6% in the lysosomes, 14% in the mitochondria and 80% in the cytosol. This technique was also used to fractionate organelles from mouse brain, where marker proteins were detected in the gradient at positions similar to those observed for the cell lines, and the relative distribution of [ 57 Co] Cbl was as follows: 12% in the lysosomes, 15% in the mitochondria and 73% in the cytosol. These methods provide a useful tool for the investigation of intracellular Cbl trafficking in a neurobiological setting. fractions using ultracentrifugation on an OptiPrep density gradient. Lysosomes were recovered at the top of the gradient (fractions 1 to 5) and were clearly separated from mitochondria (fractions 7 to 9) based on marker proteins LAMP2 and VDAC1, respectively.The isolated lysosomes were intact based on colocalisation with acid phosphatase activity.The lysosomal and mitochondrial fractions were free of cytosolic markers beta-actin and methionine synthase.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Analysis of subcellular [57Co] cobalamin distribution in SH-SY5Y neurons and brain tissue

Zhao¹,

Ruberu²,

Li³

et al. 2013

Journal of Neuroscience Methods

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“…These include the cblA and cblB mutations, in which the synthesis of AdoCbl alone is impaired and patients present with cobalamin-responsive methylmalonic aciduria, and the cblC and cblD mutations, in which synthesis of both cobalamin coenzyme derivatives is impaired and patients present with combined methylmalonic aciduria and homocystinuria (3,4). Recently a patient has been described with a mutation, designated cblF, that affects translocation of free cobalamin from the lysosome to the cytoplasm (5,6).…”

Section: Introductionmentioning

confidence: 99%

Genetic heterogeneity among patients with methylcobalamin deficiency. Definition of two complementation groups, cblE and cblG.

Watkins¹,

Rosenblatt²

1988

J. Clin. Invest.

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A number of patients with megaloblastic anemia and homocystinuria associated with low levels of methylcobalamin synthesis in cultured cells have been recognized. Methionine biosynthesis by intact cells, as determined by incorporation of label from 5-I14Clmethyl-tetrahydrofolate into acid-precipitable material, was deficient in cultured skin fibroblasts that were derived from all of these patients. In one group of patients, activity of the methylcobalamin-dependent enzyme, methionine synthase, in cell extracts was within the normal range when the enzyme was assayed under standard conditions. In a second group of patients, methionine synthase activity was decreased under the same assay conditions. Genetic complementation analysis demonstrated the existence of two complementation classes that corresponded to these two groups of patients. The designation cblE has previously been proposed for the mutation in a patient with methylcobalamin deficiency and normal methionine synthase activity. We propose the designation cblG for the mutation in those patients with methylcobalamin deficiency and decreased synthase activity. The results of these studies suggest that the products of at least two loci are required for cobalamin-dependent methionine biosynthesis in mammalian cells.

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“…There is relatively little synthesis of AdoCbl or MeCbl and decreased function of both methylmalonyl-CoA mutase and methionine synthase. 8,9 CLINICAL REPORT The proband, the product of an unremarkable pregnancy, was a full-term female infant with a birth weight of 3175 g. There was no family history of metabolic disease or consanguinity. Her parents were of mixed white European descent, and she has a healthy older sister.…”

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confidence: 99%

A Patient With an Inborn Error of Vitamin B12 Metabolism (cblF) Detected by Newborn Screening

et al. 2013

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A neonate, who was found to have an elevated C3/C2 ratio and minimally elevated propionylcarnitine on newborn screening, was subsequently identified as having the rare cblF inborn error of vitamin B 12 (cobalamin) metabolism. This disorder is characterized by the retention of unmetabolized cobalamin in lysosomes such that it is not readily available for cellular metabolism. Although cultured fibroblasts from the patient did not show the expected functional abnormalities of the cobalamin-dependent enzymes, methylmalonyl-CoA mutase and methionine synthase, they did show reduced synthesis of the active cobalamin cofactors adenosylcobalamin and methylcobalamin. Mutation analysis of LMBRD1 established that the patient had the cblF disorder. Treatment was initiated promptly, and the patient showed a robust response to regular injections of cyanocobalamin, and she was later switched to hydroxocobalamin. Currently, at 3 years of age, the child is clinically well, with appropriate development. Adjusted newborn screening cutoffs in Ontario allowed detection of a deficiency that might not have otherwise been identified, allowing early treatment and perhaps preventing the adverse sequelae seen in some untreated patients. Pediatrics 2013;132:e257-e261 AUTHORS:

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Defect in Vitamin B ₁₂ Release from Lysosomes: Newly Described Inborn Error of Vitamin B ₁₂ Metabolism

Cited by 133 publications

References 12 publications

Analysis of subcellular [57Co] cobalamin distribution in SH-SY5Y neurons and brain tissue

Analysis of subcellular [57Co] cobalamin distribution in SH-SY5Y neurons and brain tissue

Genetic heterogeneity among patients with methylcobalamin deficiency. Definition of two complementation groups, cblE and cblG.

A Patient With an Inborn Error of Vitamin B12 Metabolism (cblF) Detected by Newborn Screening

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Defect in Vitamin B 12 Release from Lysosomes: Newly Described Inborn Error of Vitamin B 12 Metabolism

Cited by 133 publications

References 12 publications

Analysis of subcellular [57Co] cobalamin distribution in SH-SY5Y neurons and brain tissue

Analysis of subcellular [57Co] cobalamin distribution in SH-SY5Y neurons and brain tissue

Genetic heterogeneity among patients with methylcobalamin deficiency. Definition of two complementation groups, cblE and cblG.

A Patient With an Inborn Error of Vitamin B12 Metabolism (cblF) Detected by Newborn Screening

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Defect in Vitamin B ₁₂ Release from Lysosomes: Newly Described Inborn Error of Vitamin B ₁₂ Metabolism