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Biomedical subjects

A B Moser

Publications and source records attributed to A B Moser.

At least 37 records · Page 2Linked to original sources
PubMed1999

Metabolic control of peroxisome abundance.

Zellweger syndrome and related disorders represent a group of lethal, genetically heterogeneous diseases. These peroxisome biogenesis disorders (PBDs) are characterized by defective peroxisomal matrix protein import and comprise at least 10 complementation groups. The genes defective in seven of these groups and more than 90% of PBD patients are now known. Here we examine the distribution of peroxisomal membrane proteins in fibroblasts from PBD patients representing the seven complementation groups for which the mutant gene is known. Peroxisomes were detected in all PBD cells, indicating that the ability to form a minimal peroxisomal structure is not blocked in these mutants. We also observed that peroxisome abundance was reduced fivefold in PBD cells that are defective in the PEX1, PEX5, PEX12, PEX6, PEX10, and PEX2 genes. These cell lines all display a defect in the import of proteins with the type-1 peroxisomal targeting signal (PTS1). In contrast, peroxisome abundance was unaffected in cells that are mutated in PEX7 and are defective only in the import of proteins with the type-2 peroxisomal targeting signal. Interestingly, a fivefold reduction in peroxisome abundance was also observed for cells lacking either of two PTS1-targeted peroxisomal beta-oxidation enzymes, acyl-CoA oxidase and 2-enoyl-CoA hydratase/D-3-hydroxyacyl-CoA dehydrogenase. These results indicate that reduced peroxisome abundance in PBD cells may be caused by their inability to import these PTS1-containing enzymes. Furthermore, the fact that peroxisome abundance is influenced by peroxisomal 105-oxidation activities suggests that there may be metabolic control of peroxisome abundance.

Cells, Cultured↗
PubMed1998

Developmental delay and growth failure caused by a peroxisomal disorder, dihydroxyacetonephosphate acyltransferase (DHAP-AT) deficiency.

We describe a 6 1/2-year-old-girl presenting with a unique phenotype and dihydroxyacetonephosphate acyltransferase (DHAP-AT) deficiency (1.6% of control activity in cultured fibroblasts), a peroxisomal enzyme deficiency which was reported previously to cause rhizomelic chondroplasia punctata (RCDP). Her phenotype is less severe than that seen in classical RCDP, and is notable for short stature, microcataracts, normal limbs, mild hypotonia, and severe mental retardation. Epiphyseal stippling is present. This patient illustrates the variability of peroxisomal disorders whereby a specific defect in peroxisomal plasmalogen synthesis may lead to several phenotypes. Her case also suggests that children presenting with deficient growth, developmental delay, and epiphyseal stippling should be screened carefully for peroxisomal disorders, with measurement of plasmalogens in addition to very long chain fatty acids.

Acyltransferases↗
PubMed1998

Peroxisomal disease cell lines with cellular plasmalogen deficiency have impaired muscarinic cholinergic signal transduction activity and amyloid precursor protein secretion.

We tested whether alterations in membrane lipid composition associated with peroxisomal diseases affect muscarinic cholinergic signal transduction activity and amyloid precursor protein (APP) secretion in cultured human skin fibroblasts and Chinese hamster ovary (CHO) mutants. We found that in cell lines from patients with peroxisomal disorders where plasmalogen levels were low, the low-Km GTPase activity was not induced by carbachol, and APP secretion was reduced. This effect on signal transduction activity was not associated with decreased levels of the M1-muscarinic cholinergic receptor or its associated heterotrimeric G-protein. Specifically, this decrease was associated with a plasmalogen deficiency since a CHO cell line with only a deficit in plasmalogens was as severely affected as were generalized peroxisomal disorder cell lines. Thus, plasmalogens appear to be implicated in muscarinic cholinergic signal transduction and secretion of APP. These results provide new insights about the pathophysiology of peroxisomal diseases and may be relevant to Alzheimer's disease where reduced plasmalogen levels have been reported.

Amyloid beta-Protein Precursor↗
PubMed1998

Gene redundancy and pharmacological gene therapy: implications for X-linked adrenoleukodystrophy.

As more functional redundancy in mammalian cells is discovered, enhanced expression of genes involved in alternative pathways may become an effective form of gene therapy. X-linked adrenoleukodystrophy (X-ALD) is a peroxisomal disorder with impaired very-long-chain fatty acid metabolism. The X-ALD gene encodes a peroxisomal membrane protein (ALDP) that is part of a small family of related peroxisomal membrane proteins. We show that 4-phenylbutyrate treatment of cells from both X-ALD patients and X-ALD knockout mice results in decreased levels of and increased beta-oxidation of very-long-chain fatty acids; increased expression of the peroxisomal protein ALDRP; and induction of peroxisome proliferation. We also demonstrate that ALDP and ALDRP are functionally related, by ALDRP cDNA complementation of X-ALD fibroblasts. Finally, we demonstrate the in vivo efficacy of dietary 4-phenylbutyrate treatment through its production of a substantial reduction of very-long-chain fatty acid levels in the brain and adrenal glands of X-ALD mice.

ATP Binding Cassette Transporter, Subfamily D↗
PubMed1998

Suppression of peroxisomal membrane protein defects by peroxisomal ATP binding cassette (ABC) proteins.

X-Linked adrenoleukodystrophy (X-ALD) is a neurodegenerative disorder characterized by reduced peroxisomal very long chain fatty acid (VLCFA) beta-oxidation. The X - ALD gene product (ALDP) is a peroxisomal transmembrane protein with an ATP binding cassette (ABC). ALDP and three other ABC proteins (PMP70, ALDR, P70R) localize to the peroxisomal membrane. The function of this family of peroxisomal membrane proteins is unknown. We used complementation studies to begin analysis of their role in VLCFA beta-oxidation and on the peroxisomal membrane. Expression of either ALDP or PMP70 restores VLCFA beta-oxidation in X-ALD fibroblasts, indicating overlapping functions. Their expression also restores peroxisome biogenesis in cells that are deficient in the peroxisomal membrane protein Pex2p. Thus it is likely that complex protein interactions are involved in the function and biogenesis of peroxisomal membranes that may contribute to disease heterogeneity.

ATP Binding Cassette Transporter, Subfamily D, Mem↗
PubMed1997

A mouse model for X-linked adrenoleukodystrophy.

X-linked adrenoleukodystrophy (X-ALD) is a peroxisomal disorder with impaired beta-oxidation of very long chain fatty acids (VLCFAs) and reduced function of peroxisomal very long chain fatty acyl-CoA synthetase (VLCS) that leads to severe and progressive neurological disability. The X-ALD gene, identified by positional cloning, encodes a peroxisomal membrane protein (adrenoleukodystrophy protein; ALDP) that belongs to the ATP binding cassette transporter protein superfamily. Mutational analyses and functional studies of the X-ALD gene confirm that it and not VLCS is the gene responsible for X-ALD. Its role in the beta-oxidation of VLCFAs and its effect on the function of VLCS are unclear. The complex pathology of X-ALD and the extreme variability of its clinical phenotypes are also unexplained. To facilitate understanding of X-ALD pathophysiology, we developed an X-ALD mouse model by gene targeting. The X-ALD mouse exhibits reduced beta-oxidation of VLCFAs, resulting in significantly elevated levels of saturated VLCFAs in total lipids from all tissues measured and in cholesterol esters from adrenal glands. Lipid cleft inclusions were observed in adrenocortical cells of X-ALD mice under the electron microscope. No neurological involvement has been detected in X-ALD mice up to 6 months. We conclude that X-ALD mice exhibit biochemical defects equivalent to those found in human X-ALD and thus provide an experimental system for testing therapeutic intervention.

Adrenoleukodystrophy↗
PubMed1996

Urinary bile acids and peroxisomal bifunctional enzyme deficiency.

The biosynthesis of normal bile acids involves beta-oxidation of the 8-carbon side-chain of cholesterol, in addition to numerous modifications of the sterol nucleus. Because beta-oxidation of the sterol side-chain has been localized to the peroxisome, bile acid analysis has been suggested to be useful in the diagnostic evaluation of individuals suspected of having peroxisomal disorders. Although data from subjects with generalized peroxisomal disorders support this, few data exist regarding the bile acids in individuals having single peroxisomal beta-oxidation enzyme disorders. In this study, we analyzed the urinary bile acids from 12 patients with peroxisomal bifunctional protein deficiency using continuous flow fast atom bombardment mass spectrometry. All 12 patients had abnormal spectra, although their ion profiles and rank order of intensity of ions varied considerably. Ten of 12 individuals had abnormal spectra with presence of taurine-conjugated tetrahydroxycholestenoates, allowing a definite diagnosis of a peroxisomal beta-oxidation defect and a presumptive diagnosis of bifunctional protein deficiency; the other two cases were nondiagnostically abnormal. The strengths and limitations of urinary bile acid analysis for the diagnosis of peroxisomal beta-oxidation disorders are discussed.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1996

Neuronal migration abnormality in peroxisomal bifunctional enzyme defect.

Patterns of brain dysgenesis that resemble those in the Zellweger syndrome were demonstrated in a boy with an isolated defect of the peroxisomal bifunctional enzyme. There was bilateral centrosylvian pachygyria and polymicrogyria, diffuse hemispheric hypomyelination with heterotopic neurons, Purkinje cell heterotopias, and simplified convolutions of the dentate nucleus and inferior olive. This association of Zellweger syndrome-like brain dysgenesis with a defect of a single peroxisomal enzyme provides new opportunities for the study of pathogenetic mechanisms in peroxisomal disorders.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1996

Very long-chain fatty acids in diagnosis, pathogenesis, and therapy of peroxisomal disorders.

Abnormally high levels of very long-chain fatty acids (VLCFA) are a feature in nine of the fifteen peroxisomal disorders that have been identified so far. Saturated VLCFA accumulate in X-linked adrenoleukodystrophy, appear to disrupt membrane structure, and may play a role in the pathogenesis of a brain inflammatory response. Dietary therapy initiated when patients are still asymptomatic may be of clinical benefit.

Adrenoleukodystrophy↗
PubMed1995

Distinction between peroxisomal bifunctional enzyme and acyl-CoA oxidase deficiencies.

The clinical distinction between patients with a disorder of peroxisome assembly (e.g., Zellweger syndrome) and those with a defect in a peroxisomal fatty acid beta-oxidation enzyme can be difficult. We studied 29 patients suspected of belonging to the latter group. Using complementation analysis, 24 were found to be deficient in enoylcoenzyme A hydratase/3-hydroxyacylcoenzyme A dehydrogenase bifunctional enzyme and 5 were deficient in acyl-CoA oxidase. Elevated plasma very long-chain fatty acids (VLCFA), impaired fibroblast VLCFA beta-oxidation, decreased fibroblast phytanic acid oxidation, normal plasmalogen synthesis, normal plasma L-pipecolic acid level, and normal subcellular catalase distribution were characteristic findings in both disorders. The elevation in plasma VLCFA levels and impairment in fibroblast VLCFA beta-oxidation were more severe in bifunctional-deficient than in oxidase-deficient patients. The clinical course in bifunctional deficiency (profound hypotonia, neonatal seizures, dysmorphic features, age at death approximately 9 months) was more severe than in oxidase deficiency (moderate hypotonia without dysmorphic features, development of a leukodystrophy, age at death approximately 4 yr). Based on these findings, accurate early diagnosis of these deficiencies of peroxisomal beta-oxidation enzymes is possible.

Acyl-CoA Oxidase↗
PubMed1995

Sulfatide and sphingomyelin loading of living cells as tools for the study of ceramide turnover by lysosomal ceramidase--implications for the diagnosis of Farber disease.

The ceramide turnover by lysosomal ceramidase in intact, living cells was investigated by loading radiolabeled sulfatide or sphingomyelin in situ on skin fibroblasts and lymphoid cells. The cells originated from normal individuals and from patients with acid ceramidase deficiency (Farber disease). While fibroblasts from individuals with Farber disease exhibited some impairment in the degradation of the ceramide produced by sulfatide hydrolysis, lymphoid cells from individuals with Farber disease metabolized the ceramide as readily as did normal cells, suggesting the existence in lymphoid cells of a non-lysosomal degradation pathway for the sulfatide-derived ceramide. In contrast, sphingomyelin loading in the presence of serum showed a considerably decreased turnover of ceramide in both fibroblasts and lymphoid cells from individuals with Farber disease. Further methodologic variation led to the use of LDL-associated radioactive sphingomyelin; LDL-association promoted the targeting of exogenous sphingomyelin to lysosomes. As a result, an almost complete deficiency of ceramide degradation was found in cells from severely affected patients with Farber disease. Our data with this novel method show that sphingomyelin loading of intact living cells is a simple, alternative means for determining ceramide degradation by lysosomal ceramidase and for diagnosing Farber disease.

Acid Ceramidase↗
PubMed1995

Neurodegenerative course in ceramidase deficiency (Farber disease) correlates with the residual lysosomal ceramide turnover in cultured living patient cells.

Farber's lipogranulomatosis is an inborn lipid storage disease characterized by tissue accumulation of ceramide due to deficient activity of lysosomal ceramidase. Symptoms include painful swelling of joints, subcutaneous nodules, a hoarse cry, hepatosplenomegaly and nervous system dysfunction of markedly variable degree. In most cases the neural dysfunction rather than the general dystrophy, seems to limit the duration of Farber disease. We examined whether the severity can be shown as a function of ceramide turnover by lysosomal ceramidase. The lysosomal degradation of sphingomyelin-derived ceramide was studied in situ in patient skin fibroblasts and lymphoid cells loaded with LDL-associated radioactive sphingomyelin. We could show for the first time a significant correlation between the ceramide accumulated in situ and the severity of Farber disease. Our method provides an alternative means for determining ceramide degradation by lysosomal ceramidase, but in intact cells. The relatively simple method is at least of the same diagnostic use for Farber disease as the in vitro assay of acid ceramidase using cell homogenates and may also have some prognostic use.

Acid Ceramidase↗
PubMed1995

Phenotype of patients with peroxisomal disorders subdivided into sixteen complementation groups.

OBJECTIVE: To use the technique of complementation analysis to help define genotype and classify patients with clinical manifestations consistent with those of the disorders of peroxisome assembly, namely the Zellweger syndrome (ZS), neonatal adrenoleukodystrophy (NALD), infantile Refsum disease (IRD), and rhizomelic chondrodysplasia punctata (RCDP). STUDY DESIGN: Clinical findings, peroxisomal function, and complementation groups were examined in 173 patients with the clinical manifestations of these disorders. RESULTS: In 37 patients (21%), peroxisome assembly was intact and isolated deficiencies of one of five peroxisomal enzymes involved in the beta-oxidation of fatty acids or plasmalogen biosynthesis were demonstrated. Ten complementation groups were identified among 93 patients (54%) with impaired peroxisome assembly and one of three phenotypes (ZS, NALD, or IRD) without correlation between complementation group and phenotype. Forty-three patients (25%) had impaired peroxisome assembly associated with the RCDP phenotype and belonged to a single complementation group. Of the 173 patients, 10 had unusually mild clinical manifestations, including survival to the fifth decade or deficits limited to congenital cataracts. CONCLUSIONS: At least 16 complementation groups, and hence genotypes, are associated with clinical manifestations of disorders of peroxisome assembly. The range of phenotype is wide, and some patients have mild involvement.

Acyltransferases↗
PubMed1995

Identification of three distinct peroxisomal protein import defects in patients with peroxisome biogenesis disorders.

Zellweger syndrome, neonatal adrenoleukodystrophy, infantile Refsum's disease, and classical rhizomelic chondrodysplasia punctata are lethal genetic disorders caused by defects in peroxisome biogenesis. We report here a characterization of the peroxisomal matrix protein import capabilities of fibroblasts from 62 of these peroxisome biogenesis disorder patients representing all ten known complementation groups. Using an immunofluorescence microscopy assay, we identified three distinct peroxisomal protein import defects among these patients. Type-1 cells have a specific inability to import proteins containing the PTS1 peroxisomal targeting signal, type-2 cells have a specific defect in import of proteins containing the PTS2 signal, and type-3 cells exhibit a loss of, or reduction in, the import of both PTS1 and PTS2 proteins. Considering that the common cellular phenotype of Zellweger syndrome, neonatal adrenoleukodystrophy and infantile Refsum's disease has been proposed to be a complete defect in peroxisomal matrix protein import, the observation that 85% (40/47) of the type-3 cell lines imported a low but detectable amount of both PTS1 and PTS2 proteins was surprising. Furthermore, different cell lines with the type-3 defect exhibited a broad spectrum of different phenotypes; some showed a complete absence of matrix protein import while others contained 50-100 matrix protein-containing peroxisomes per cell. We also noted certain relationships between the import phenotypes and clinical diagnoses: both type-1 cell lines were from neonatal adrenoleukodystrophy patients, all 13 type-2 cell lines were from classical rhizomelic chondrodysplasia punctata patients, and the type-3 import defect was found in the vast majority of Zellweger syndrome (22/22), neonatal adrenoleukodytrophy (17/19), and infantile Refsum's disease (7/7) patients. Our finding that all type-1 cell lines were from the second complementation group (CG2), all 13 type-2 cell lines were from CG11, and that cells from the eight remaining complementation groups only exhibit the type-3 defect indicates that mutations in particular genes give rise to the different types of peroxisomal protein import defects. This hypothesis is further supported by correlations between certain complementation groups and particular type-3 subphenotypes: all patient cell lines belonging to CG3 and CG10 showed a complete absence of peroxisomal matrix protein import while those from CG6, CG7, and CG8 imported some peroxisomal matrix proteins. However, the fact that cell lines from within particular complementation groups (CG1, CG4) could have different matrix protein import characteristics suggests that allelic heterogeneity also plays an important role in generating different import phenotypes in certain patients.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenoleukodystrophy↗
PubMed1995

Altered expression of ALDP in X-linked adrenoleukodystrophy.

X-linked adrenoleukodystrophy (ALD) is a neurodegenerative disorder with variable phenotypic expression that is characterized by elevated plasma and tissue levels of very long-chain fatty acids. However, the product of the gene defective in ALD (ALDP) is a membrane transporter of the ATP-binding cassette family of proteins and is not related to enzymes known to activate or oxidize fatty acids. We generated an antibody that specifically recognizes the C-terminal 18 amino acids of ALDP and can detect ALDP by indirect immunofluorescence. To better understand the mechanism by which mutations in ALDP lead to disease, we used this antibody to examine the subcellular distribution and relative abundance of ALDP in skin fibroblasts from normal individuals and ALD patients. Punctate immunoreactive material typical of fibroblast peroxisomes was observed in cells from seven normal controls and eight non-ALD patients. Of 35 ALD patients tested, 17 had the childhood-onset cerebral form of the disease, 13 had the milder adult phenotype adrenomyeloneuropathy, 3 had adrenal insufficiency only, and 2 were affected fetuses. More than two-thirds (69%) of all patients studied showed no punctate immunoreactive material. There was no correlation between the immunofluorescence pattern and clinical phenotype. We determined the mutation in the ALD gene in 15 of these patients. Patients with either a deletion or frameshift mutation lacked ALDP immunoreactivity, as expected. Four of 11 patients with missense mutations were also immunonegative, indicating that these mutations affected the stability or localization of ALDP. In the seven immunopositive patients with missense mutations, correlation of the location and nature of the amino acid substitution may provide new insights into the function of this peroxisomal membrane protein. Furthermore, the study of female relatives of immunonegative ALD probands may aid in the assessment of heterozygote status.

ATP Binding Cassette Transporter, Subfamily D, Mem↗
PubMed1994

Cytosolic compartmentalization of hepatic alanine:glyoxylate aminotransferase in patients with aberrant peroxisomal biogenesis and its effect on oxalate metabolism.

Two patients with atypical manifestations of aberrant peroxisomal biogenesis are described. Contrary to previous studies, which had shown that Zellweger syndrome patients usually have normal levels of urinary oxalate excretion, the patients in the present study had evidence of abnormal oxalate metabolism in the form of hyperoxaluria and, in one of the patients, calcium oxalate urolithiasis. Activity of the liver-specific peroxisomal enzyme alanine:-glyoxylate aminotransferase (AGT), which is a major determinant of the level of endogenous oxalate synthesis in humans, was normal in one patient and markedly supranormal in the other. Using the technique of post-embedding protein A-colloidal gold immunoelectron microscopy, AGT was found to be mainly cytosolic in the livers of both patients, with significant amounts also localized in the nuclei. In a small minority of the hepatocytes of one patient, who was homozygous for the more common (major) AGT allele, large numbers of unidentified fibrillar arrays were found in the cytosol, which labelled heavily for immunoreactive AGT. The background cytosolic AGT labelling was markedly reduced in such cells when compared to the majority of cells that did not contain fibrils. In the other patient, who was heterozygous for the major and minor AGT alleles, there appeared to be low levels of mitochondrial AGT labelling. In the light of these data, the possible metabolic function of cytosolic AGT in the livers of panperoxisomal disease patients is discussed.

Alanine Transaminase↗