Bile acid analysis in human disorders of bile acid biosynthesis

Bile acids facilitate the absorption of lipids in the gut, but are also needed to maintain cholesterol homeostasis, induce bile flow, excrete toxic substances and regulate energy metabolism by acting as signaling molecules. Bile acid biosynthesis is a complex process distributed across many cellular organelles and requires at least 17 enzymes in addition to different metabolite transport proteins to synthesize the two primary bile acids, cholic acid and chenodeoxycholic acid. Disorders of bile acid synthesis can present from the neonatal period to adulthood and have very diverse clinical symptoms ranging from cholestatic liver disease to neuropsychiatric symptoms and spastic paraplegias. This review describes the different bile acid synthesis pathways followed by a summary of the current knowledge on hereditary disorders of human bile acid biosynthesis with a special focus on diagnostic bile acid profiling using mass spectrometry.

Reinvestigation of peroxisomal 3-ketoacyl-CoA thiolase deficiency: identification of the true defect at the level of d-bifunctional protein

In this report, we reinvestigate the only patient ever reported with a deficiency of peroxisomal 3-ketoacyl-CoA thiolase (THIO). At the time when they were described, the abnormalities in this patient, which included accumulation of very-long-chain fatty acids and the bile-acid intermediate trihydroxycholestanoic acid, were believed to be the logical consequence of a deficiency of the peroxisomal beta-oxidation enzyme THIO. In light of the current knowledge of the peroxisomal beta-oxidation system, however, the reported biochemical aberrations can no longer be explained by a deficiency of this thiolase. In this study, we show that the true defect in this patient is at the level of d-bifunctional protein (DBP). Immunoblot analysis revealed the absence of DBP in postmortem brain of the patient, whereas THIO was normally present. In addition, we found that the patient had a homozygous deletion of part of exon 3 and intron 3 of the DBP gene, resulting in skipping of exon 3 at the cDNA level. Our findings imply that the group of single-peroxisomal beta-oxidation-enzyme deficiencies is limited to straight-chain acyl-CoA oxidase, DBP, and alpha-methylacyl-CoA racemase deficiency and that there is no longer evidence for the existence of THIO deficiency as a distinct clinical entity.

The neuronal migration defect in mice with Zellweger syndrome (Pex5 knockout) is not caused by the inactivity of peroxisomal beta-oxidation

The purpose of this study was to investigate whether deficient peroxisomal beta-oxidation is causally involved in the neuronal migration defect observed in Pex5 knockout mice. These mice are models for Zellweger syndrome, a peroxisome biogenesis disorder. Neocortical development was evaluated in mice carrying a partial or complete defect of peroxisomal beta-oxidation at the level of the second enzyme of the pathway, namely, the hydratase-dehydrogenase multifunctional/bifunctional enzymes MFP1/L-PBE and MFP2/D-PBE. In contrast to patients with multifunctional protein 2 deficiency who present with neocortical dysgenesis, impairment of neuronal migration was not observed in the single MFP2 or in the double MFP1/MFP2 knockout mice. At birth, the double knockout pups displayed variable growth retardation and about one half of them were severely hypotonic, whereas the single MFP2 knockout animals were all normal in the perinatal period. These results indicate that in the mouse, defective peroxisomal beta-oxidation does not cause neuronal migration defects by itself. This does not exclude that the inactivity of this metabolic pathway contributes to the brain pathology in mice and patients with complete absence of functional peroxisomes.

Disorders of peroxisome biogenesis due to mutations in PEX1: phenotypes and PEX1 protein levels

Zellweger syndrome (ZS), neonatal adrenoleukodystrophy (NALD), and infantile Refsum disease (IRD) are clinically overlapping syndromes, collectively called "peroxisome biogenesis disorders" (PBDs), with clinical features being most severe in ZS and least pronounced in IRD. Inheritance of these disorders is autosomal recessive. The peroxisome biogenesis disorders are genetically heterogeneous, having at least 12 different complementation groups (CGs). The gene affected in CG1 is PEX1. Approximately 65% of the patients with PBD harbor mutations in PEX1. In the present study, we used SSCP analysis to evaluate a series of patients belonging to CG1 for mutations in PEX1 and studied phenotype-genotype correlations. A complete lack of PEX1 protein was found to be associated with severe ZS; however, residual amounts of PEX1 protein were found in patients with the milder phenotypes, NALD and IRD. The majority of these latter patients carried at least one copy of the common G843D allele. When patient fibroblasts harboring this allele were grown at 30 degrees C, a two- to threefold increase in PEX1 protein levels was observed, associated with a recovery of peroxisomal function. This suggests that the G843D missense mutation results in a misfolded protein, which is more stable at lower temperatures. We conclude that the search for the factors and/or mechanisms that determine the stability of mutant PEX1 protein by high-throughput procedures will be a first step in the development of therapeutic strategies for patients with mild PBDs.

Peroxisomal deficiencies are associated with altered activity of endothelial NOS in human fibroblasts

As shown recently, in human skin fibroblasts both a constitutively expressed and the inducible nitric oxide synthase (NOS) isoform are present. To identify the NOS isoforms expressed under standard conditions in healthy human skin fibroblasts and fibroblasts with peroxisomal deficiencies (cell lines from patients suffering from X-chromosome linked Adrenoleukodystrophy (X-ALD) and the Zellweger Syndrome), we cultivated the cells in Dulbecco's modified Eagle's medium without inflammatory mediators. Our experiments clearly showed that human fibroblasts with and without peroxisomal deficiencies only contain the constitutively expressed endothelial nitric oxide synthase (eNOS) isoform and that the eNOS is tyrosine-phosphorylated. The inducible isoform (iNOS) could not be detected under standard conditions. Healthy human skin fibroblasts show a higher specific NOS activity than X-ALD and Zellweger cells (2.25 to 1.68 and 1.17 pmol L-citrulline/min/mg total cellular protein), although the content of eNOS protein does not differ significantly in these cell lines. However the tyrosine-phosphorylated portion of eNOS is significantly lower in X-ALD and Zellweger cells.

Characterization of fibroblast cytoplasmic proteins that bind to the 3' UTR of human catalase mRNA

The excessive expression of catalase protein and its activity in cultured skin fibroblast from Zellweger Syndrome (ZS), a disorder of peroxisomal biogenesis, was found to be regulated at the translational level (J. Neurochem. 67: 2373-2378, 1996). Overall there is a considerable increase in the association of catalase mRNA with polysomes in ZS cell lines as compared to control indicating translational upregulation. To investigate the possibility that RNA-protein interactions are involved in the mediation of this increase in translation, the interaction between 3' untranslated region of human catalase mRNA and human fibroblast cytoplasmic proteins were investigated by RNA gel shift assay technique. Competition experiments demonstrated that all the 600 bases of 3' UTR (of human catalase gene) was required for efficient binding. Catalase RNA- protein interaction was sensitive to the altered redox state in these in vitro assays and this RNA-protein interaction could be enhanced by the addition of beta-mercaptoethanol in cytoplasm from control fibroblast but not in cytoplasm from ZS fibroblast. UV cross linked RNA-protein complexes on SDS polyacrylamide gel electrophoresis revealed the presence of at least four protein bands with approximate molecular masses of 38 kDa, 50 kDa, 66 kDa and 80 kDa. The potential role of these mRNA binding proteins in the regulation of catalase gene expression is discussed.

Developmental and pathological expression of peroxisomal enzymes: their relationship of D-bifunctional protein deficiency and Zellweger syndrome

We present the developmental changes of peroxisomal enzymes, catalase, L-bifunctional protein (L-BF) and D-bifunctional protein (D-BF), in the normal brains, and patients with D-BF deficiency, a new peroxisomal disease. D-BF immunoreactivity was observed in controls as early as 13 gestational weeks (GW) and increased with maturation. The adult pattern with fine granule staining of somata and dendrites became apparent in adolescence. L-BF appeared at 20 GW in the cerebral cortex and Purkinje cells and positive glia appeared early in the white matter at 17 GW, and then increased with age. Catalase-positive neurons were identified in the same manner as L-BF, D-BF deficiency in both fetus and infant showed markedly diminished enzyme immunoreactivity. Patients demonstrate reduced D-BF expression. Zellweger syndrome shows decreased expression for the three proteins. This study shows that the peroxisomal enzymes may be closely related to neuronal maturation and gliogenesis in human brain and to disturbance of neuronal migration as seen in Zellweger syndrome significant. D-BF deficiency may exhibit a range of symptoms during the neonatal and early infantile periods some of which may be similar to Zellweger syndrome.

Unique multifunctional HSD17B4 gene product: 17beta-hydroxysteroid dehydrogenase 4 and D-3-hydroxyacyl-coenzyme A dehydrogenase/hydratase involved in Zellweger syndrome

Six types of human 17beta-hydroxysteroid dehydrogenases catalyzing the conversion of estrogens and androgens at position C17 have been identified so far. The peroxisomal 17beta-hydroxysteroid dehydrogenase type 4 (17beta-HSD 4, gene name HSD17B4) catalyzes the oxidation of estradiol with high preference over the reduction of estrone. The highest levels of 17beta-HSD 4 mRNA transcription and specific activity are found in liver and kidney followed by ovary and testes. A 3 kb mRNA codes for an 80 kDa (737 amino acids) protein featuring domains which are not present in the other 17beta-HSDs. The N-terminal domain of 17beta-HSD 4 reveals only 25% amino acid similarity with the other types of 17beta-HSDs. The 80 kDa protein is N-terminally cleaved to a 32 kDa enzymatically active fragment. Both the 80 kDa and the N-terminal 32 kDa (amino acids 1-323) protein are able to perform the dehydrogenase reaction not only with steroids at the C17 position but also with D-3-hydroxyacyl-coenzyme A (CoA). The enzyme is not active with L-stereoisomers. The central part of the 80 kDa protein (amino acids 324-596) catalyzes the 2-enoyl-acyl-CoA hydratase reaction with high efficiency. The C-terminal part of the 80 kDa protein (amino acids 597-737) facilitates the transfer of 7-dehydrocholesterol and phosphatidylcholine between membranes in vitro. The HSD17B4 gene is stimulated by progesterone, and ligands of PPARalpha (peroxisomal proliferator activated receptor alpha) such as clofibrate, and is down-regulated by phorbol esters. Mutations in the HSD17B4 lead to a fatal form of Zellweger syndrome.

3-Hydroxy-3-methylglutaryl coenzyme A lyase: targeting and processing in peroxisomes and mitochondria

3-Hydroxy-3-methylglutaryl coenzyme A lyase (HL, E.C. 4.1.3.4) has a unique dual localization in both mitochondria and peroxisomes. Mitochondrial HL ( approximately 31.0 kDa) catalyzes the last step of ketogenesis; the function of peroxisomal HL ( approximately 33.5 kDa) is unknown. On density gradient fractionation, normal human lymphoblasts contain both peroxisomal and mitochondrial HL whereas in lymphoblasts from a patient with Zellweger syndrome, in which functional peroxisomes are absent, only the mitochondrial HL isoform was present. To study the kinetics of the dual targeting of HL, we performed pulse-chase experiments in normal and Zellweger cells. Pulse-chase studies revealed a biphasic curve for processing of the HL precursor. The first phase, with a calculated half-life of approximately 3 h in both normal and Zellweger fibroblasts and lymphoblasts and in HepG2 cells, presumably reflects mitochondrial import and processing of the precursor; the second (t1/2, 12-19 h) is present only in normal cells and presumably represents the half-life of peroxisomal HL. The half-life of mature mitochondrial HL was 14 to 19 h in both normal and Zellweger cells. Studies of the HMG-CoA lyase precursor in isolated rat mitochondria showed a rate of processing approximately 2.6-fold lower than that of the ornithine transcarbamylase precursor.

Differential deficiency of mevalonate kinase and phosphomevalonate kinase in patients with distinct defects in peroxisome biogenesis: evidence for a major role of peroxisomes in cholesterol biosynthesis

Peroxisomes catalyze a number of essential metabolic functions especially related to lipid metabolism. There is increasing evidence suggesting that peroxisomes are also involved in the synthesis of isoprenoids via the mevalonate pathway at least in rat liver. In order to obtain independent evidence for a role of peroxisomes in isoprenoid synthesis in man, we have measured the activity of two key enzymes of the mevalonate pathway in patients suffering from certain defined defects in peroxisome biogenesis. We now report that mevalonate kinase is not only deficient in livers from Zellweger patients in which peroxisome biogenesis is defective, but also in livers from rhizomelic chondrodysplasia punctata (RCDP) Type 1 patients. In the latter group of patients there is a selective defect in peroxisome biogenesis due to a genetic defect in the PTS2-receptor, a mobile receptor-protein guiding peroxisomal proteins with a certain peroxisomal targeting signal (PTS2) to the peroxisome. Phosphomevalonate kinase was found to be strongly deficient in Zellweger patients thus suggesting that this enzyme is also peroxisomal. Taken together, our data indicate that in human liver mevalonate kinase and phosphomevalonate kinase are truly peroxisomal enzymes which strongly suggests that peroxisomes play a major role in cholesterol biosynthesis.

Phytanic acid and pristanic acid are oxidized by sequential peroxisomal and mitochondrial reactions in cultured fibroblasts

The relationship between peroxisomal and mitochondrial oxidation of the methyl branched fatty acids, phytanic acid and pristanic acid, was studied in normal and mutant human skin fibroblasts with established enzyme deficiencies. Tandem mass spectrometry was used for analysis of the acylcarnitine intermediates. In normal cells, 4,8-dimethylnonanoylcarnitine (C11:0) and 2,6-dimethylheptanoylcarnitine (C9:0) accumulated after incubation with either phytanic acid or pristanic acid. These intermediates were not observed when peroxisome-deficient cells from Zellweger patients were incubated with the same compounds, pointing to the involvement of peroxisomes in the formation of these acylcarnitine intermediates. Similar experiments with fibroblasts deficient in carnitine palmitoyltransferase I, carnitine-acylcarnitine translocase or carnitine palmitoyltransferase II revealed that mitochondrial carnitine palmitoyltransferase I is not required for the oxidation of phytanic acid or pristanic acid, whereas both carnitine-acylcarnitine translocase and carnitine palmitoyltransferase II are necessary. These studies demonstrate that both phytanic acid and pristanic acid are initially oxidized in peroxisomes to 4,8-dimethylnonanoyl-CoA, which is converted to the corresponding acylcarnitine (presumably by peroxisomal carnitine octanoyltransferase), and exported to the mitochondrion. After transport across the mitochondrial membrane and transfer of the acylgroup to coenzyme A, further oxidation to 2,6-dimethylheptanoyl-CoA occurs.

Molecular basis of Zellweger syndrome, beta-ketothiolase deficiency and mucopolysaccharidoses

1. A human peroxisome assembly factor-1 (PAF-1) complementary DNA has been cloned that restores the morphological and biochemical abnormalities (including defective peroxisome assembly) in fibroblasts from a patient with group F Zellweger syndrome. The cause of the syndrome in this patient was a point mutation that resulted in the premature termination of PAF-1. The homozygous patient apparently inherited the mutation from her parents, each of whom was heterozygous for that mutation. Furthermore, we cloned and characterized the rat and human cDNAs for peroxisome-assembly factor-2 (PAF-2), which restores peroxisomes of the complementary group C Zellweger cells, by functional complementation, and identified two pathogenic mutations in the PAF-2 gene in two patients. 2. Seventeen mutations have been identified in 13 mitochondrial acetoacetyl-CoA thiolase-deficient patients. 3. We purified N-acetylgalactosamine-6-sulfate (GalNAc6S) sulfatase and cloned the full-length cDNA of human N-acetylgalactosamine-6-sulfate sulfatase (GALNS). The gene encoding GalNAc6S sulfatase has been localized by fluorescence in situ hybridization to chromosome 16q24, and the entire genomic gene structure has been characterized. About 40 different GALNS gene mutations have been identified in the patients with mucopolysaccharidosis IV A.

Phytanoyl-CoA hydroxylase is present in human liver, located in peroxisomes, and deficient in Zellweger syndrome: direct, unequivocal evidence for the new, revised pathway of phytanic acid alpha-oxidation in humans

Phytanic acid (3,7,11,15-tetramethylhexadecanoic acid) is a branched-chain fatty acid which accumulates in a number of inherited diseases in human. Because beta-oxidation is blocked by the methyl group at C-3, phytanic acid first undergoes decarboxylation via an alpha-oxidation mechanism. The structure and subcellular localization of the phytanic acid alpha-oxidation pathway have remained enigmatic through the years, although they have generally been assumed to involve phytanic acid and not its CoA-ester. This view has recently been challenged by the findings that in rat liver phytanic acid first has to be activated to its CoA-ester before alpha-oxidation and by the discovery of a new enzyme, phytanoyl-CoA hydroxylase, which converts phytanoyl-CoA to 2-hydroxyphytanoyl-CoA. We now show that this newly discovered enzyme is also present in human liver. Furthermore, we show that this enzyme is located in peroxisomes and deficient in liver from Zellweger patients who lack morphologically distinguishable peroxisomes, which provides an explanation for the long-known deficient oxidation of phytanic acid in these patients. These results suggest that phytanic acid alpha-oxidation is peroxisomal and that it utilizes the coenzyme A derivative as substrate, thus giving further support in favour of the new, revised pathway of phytanic acid alpha-oxidation.

Molecular characterization of the human peroxisomal branched-chain acyl-CoA oxidase: cDNA cloning, chromosomal assignment, tissue distribution, and evidence for the absence of the protein in Zellweger syndrome

Peroxisomes in human liver contain two distinct acyl-CoA oxidases with different substrate specificities: (i) palmitoyl-CoA oxidase, oxidizing very long straight-chain fatty acids and eicosanoids, and (ii) a branched-chain acyl-CoA oxidase (hBRCACox), involved in the degradation of long branched fatty acids and bile acid intermediates. The accumulation of branched fatty acids and bile acid intermediates leads to severe mental retardation and death of the diseased children. In this study, we report the molecular characterization of the hBRCACox, a prerequisite for studying mutations in patients with a single enzyme deficiency. The composite cDNA sequence of hBRCACox, derived from overlapping clones isolated via immunoscreening and hybridization of human liver cDNA expression libraries, consisted of 2225 bases and contained an open reading frame of 2046 bases, encoding a protein of 681 amino acids with a calculated molecular mass of 76,739 Da. The C-terminal tripeptide of the protein is SKL, a known peroxisome targeting signal. Sequence comparison with the other acyl-CoA oxidases and evolutionary analysis revealed that, despite its broader substrate specificity, the hBRCACox is the human homolog of rat trihydroxycoprostanoyl-CoA oxidase (rTHCCox) and that separate gene duplication events led to the occurrence in mammals of acyl-CoA oxidases with different substrate specificities. Northern blot analysis demonstrated that--in contrast to the rTHCCox gene--the hBRCACox gene is transcribed also in extrahepatic tissues such as heart, kidney, skeletal muscle, and pancreas. The highest levels of the 2.6-kb mRNA were found in heart, followed by liver. The enzyme is encoded by a single-copy gene, which was assigned to chromosome 3p14.3 by fluorescent in situ hybridization. It was absent from livers of Zellweger patients as shown by immunoblot analysis and immunocytochemistry.

Protein kinase C activity, phosphate uptake and endogenous substrate phosphorylation are altered in Zellweger syndrome

Protein kinase C (PKC) is a key enzyme in lipid-mediated signal transduction. Regulation of PKC activation is dependent upon the phospholipid constituents of cellular membranes. PKC is also activated by very long-chain and long-chain cis-unsaturated fatty acids. The present study was undertaken as a first step towards elucidating a possible role for PKC in the pathogenesis of Zellweger syndrome, in which there are both perturbation of plasma membrane phospholipids and accumulation of very long-chain fatty acids. PKC activity, phosphate uptake and endogenous substrate phosphorylation were examined in intact human skin fibroblasts from Zellweger patients. PKC catalytic activity was increased in the membranous fraction of Zellweger cells compared with control cells, with no apparent translocation of the enzyme from the cytosolic to the membranous compartment. Phosphate uptake was increased in both cytosolic and membranous fractions 2.5-fold and 4.5-fold, respectively. Several proteins were extensively phosphorylated in Zellweger cells compared with control cells. These findings indicate that PKC activity is perturbed in Zellweger cells, but the exact role of PKC in altered phosphate uptake and protein phosphorylation and its relevance to the pathogenesis of Zellweger syndrome require further study.

Epoxide hydrolase in human and rat peroxisomes: implication for disorders of peroxisomal biogenesis

To understand the basis of excretion of excessive amounts of epoxydicarboxylic fatty acids (EDFA) in urine of patients with disorders of peroxisomal biogenesis (Pitt, J. J., and A. Poulos. 1993. Clin. Chim. Acta. 223: 23-29), the activity of epoxide hydrolase (EH) was measured in cultured skin fibroblasts from control subjects and patients with peroxisomal disorders. EH activity was approximately 40% lower in fibroblasts that lack intact peroxisomes (Zellweger syndrome), whereas the activity in other peroxisomal disorders (X-adrenoleukodystrophy and rhizomelic chondrodysplasia punctata) with intact peroxisomes was similar to control. To identify the specific enzyme/organelle that represents the decrease in EH activity in Zellweger cells, we have analyzed this activity in different subcellular organelles from control and Zellweger skin fibroblasts. EH activity was enriched in peroxisomes from control fibroblast. EH activity in isolated mitochondria, microsomes, or cytosol from Zellweger fibroblast was similar to that of control fibroblast. These observations indicate that deficient activity of EH in cells from Zellweger patients is due to lack of peroxisomal EH activity. The peroxisomal EH is differentially induced to a higher degree by ciprofibrate, a hypolipidemic agent and peroxisome proliferator, than EH activity in other organelles and cytoplasm. The high specific activity of EH in peroxisomes and differential induction of EH activity in peroxisomes as compared to other organelles, and the excretion of EDFA in patients who lack peroxisomes suggests that peroxisomal EH may be responsible for the detoxification of EDFA, and that this enzyme in peroxisomes may be a different protein than the EH found in other organelles.

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.

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.

Evidence that the bradykinin-induced activation of phospholipase D and of the mitogen-activated protein kinase cascade involve different protein kinase C isoforms

The effect of alkylglycerol supplementation on protein kinase C (PKC)-mediated signaling events has been studied in fibroblasts from Zellweger patients (SF 3271 cells). Western blotting analysis established that Zellweger fibroblasts express PKC alpha, epsilon, and zeta. Incubation with bradykinin induced a rapid transient translocation of PKC alpha and a more sustained translocation of PKC epsilon to the particulate fraction; translocation of PKC zeta was unaffected. Bradykinin-induced translocation and activation of PKC alpha, but not translocation of PKC epsilon, was blocked in SF 3271 cells which had been incubated with 1-O-hexadecylglycerol (1-O-HDG; 20 micrograms/ml) for 24 h and then incubated in the absence of 1-O-HDG and serum for a further 24 h. Supplementation with 1-O-HDG increased the mass of ether-linked phospholipid. Bradykinin initiated a transient increase in cytosolic Ca2+ concentration in both control and 1-O-HDG supplemented cells, indicating that the initial receptor linked events were not affected by 1-O-HDG supplementation. Bradykinin also caused a rapid activation of phospholipase D (PLD), measured by phosphatidylbutanol accumulation, and mitogen-activated protein kinase (MAPK) determined by myelin basic protein phosphorylation of Mono Q fractions. Both events were blocked by preincubation of the cells with 12-O-tetradecanoylphorbol-13-acetate for 24 h to deplete PKC protein. 1-O-HDG supplementation prevented the bradykinin-induced activation of PLD, but had no effect on the stimulation of MAPK activity. These results establish that modulation of the ether lipid composition of membranes can alter PKC isozyme translocation and indicate that a PKC isozyme other than PKC alpha, most likely PKC epsilon, is involved in MAPK activation.

2-Hydroxyphytanic acid oxidase activity in rat and human liver and its deficiency in the Zellweger syndrome

Phytanic acid is a saturated, branched-chain fatty acid which as a consequence of the presence of a methyl group at the 3-position cannot be degraded by beta-oxidation. Instead, phytanic acid first undergoes alpha-oxidation to yield pristanic acid which can be degraded by beta-oxidation. The structure of the alpha-oxidation pathway and its subcellular localization has remained an enigma although there is convincing evidence that 2-hydroxyphytanic acid is an obligatory intermediate. We have now studied the degradation of 2-hydroxyphytanic acid in both rat and human liver. The results show that 2-hydroxyphytanic acid is converted to 2-ketophytanic acid in homogenates of rat as well as human liver. Detailed studies in rat liver showed that the enzyme involved is localized in peroxisomes accepting molecular oxygen as second substrate and producing H2O2. 2-Ketophytanic acid formation from 2-hydroxyphytanic acid was found to be strongly deficient in liver samples from Zellweger patients which lack morphologically distinguishable peroxisomes. The latter results not only provide an explanation for the elevated levels of 2-hydroxyphytanic acid in Zellweger patients but also suggest that the subcellular localization of 2-hydroxyphytanic acid dehydrogenation is identical in rat and man, i.e., in peroxisomes.

Farnesyl-diphosphate synthase is localized in peroxisomes

In this study, we have investigated the subcellular localization of farnesyl-diphosphate synthase (FPP synthase). FPP synthase produces FPP, which is utilized in the synthesis of squalene, cholesterol, farnesylated and geranylgeranylated proteins, dolichols, coenzyme Q, and the isoprenoid moiety of heme a. This enzyme is found in the 100,000 x g supernatant fraction of cells or tissues and has been considered to be a cytoplasmic protein. In this study, analysis of FPP synthase activity and protein in fractionated rat liver together with immunofluorescent and immunoelectron microscopy studies demonstrated unequivocally that FPP synthase is largely localized in peroxisomes. These data, in combination with the previous observation that mevalonate kinase is predominantly localized in peroxisomes, suggest that peroxisomes are the major site of synthesis of FPP from mevalonate. We also demonstrate that in liver tissue obtained from patients with peroxisomal deficiency diseases (Zellweger syndrome and neonatal adrenoleukodystrophy), the activities of five enzymes involved in isoprenoid synthesis, namely mevalonate kinase, phosphomevalonate kinase, mevalonate-diphosphate decarboxylase, isopentenyl-diphosphate isomerase, and FPP synthase, are significantly reduced, consistent with a peroxisomal localization of these enzymes.

Sphinganine 1-phosphate metabolism in cultured skin fibroblasts: evidence for the existence of a sphingosine phosphatase

On addition of [4,5-3H]sphinganine 1-phosphate to human fibroblast monolayers, the label was efficiently removed from the culture medium. In contrast with the reported stability of phosphorylated sphingenine in 3T3 cells [Desai, Zhang, Olivera, Mattie and Spiegel (1992). J. Biol. Chem. 267, 23122-23128] and B16 melanoma cells [Sadahira, Ruan, Hakomuri and Igarashi (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 9686-9690], sphinganine 1-phosphate appeared to be subjected to a fast and extensive metabolism in fibroblasts, the major pathways being cleavage and dephosphorylation. The first of these pathways, catalysed by sphingosine-phosphate lyase, resulted in the formation of labelled palmitaldehyde, which was recovered, mainly after oxidation, in glycerophospholipids in an ester bond. A smaller part of the palmitaldehyde was reduced and incorporated in alk(en)ylphospholipids. Dephosphorylation of spinganine 1-phosphate, a hitherto overlooked pathway catalysed by an unknown phosphatase(s), gave rise to sphinganine, which was converted by N-acylation into ceramide and then incorporated in spingomyelin and glycosphingolipids.

Molecular cloning and functional expression of a human peroxisomal acyl-coenzyme A oxidase

cDNA encoding the human peroxisomal acyl-coenzyme A oxidase (AOX) was cloned and sequenced. The longest cDNA insert isolated has 3083 bases and encodes the entire protein of 661-amino acids, including the carboxyl-terminal sequence (Ser-Lys-Leu) known as a minimal peroxisome-targeting signal. At the amino acid level, the significantly high homology (89%) to rat AOX was found. In the cDNA-expression experiment, significant amount of AOX was accumulated in human skin fibroblast and the expressed AOX was catalytically active, while only a limited amount was found in Zellweger syndrome patient's fibroblast not having normal peroxisomes.

Mevalonate kinase is predominantly localized in peroxisomes and is defective in patients with peroxisome deficiency disorders

We reported recently that mevalonate kinase (EC 2.7.1.36; ATP:mevalonate 5-phosphotransferase) that was isolated from rat liver and believed to be a cytosolic protein was localized in rat liver peroxisomes. In addition, we found that the mevalonate kinase monoclonal antibody used in the study also reacted with several other proteins present in the mitochondrial and cytosolic fractions. These findings raised the prospect of the presence of several isoenzymes of mevalonate kinase localized in different compartments of the cell. In the current study we produced four new polyclonal antibodies against different epitopes of mevalonate kinase to investigate the subcellular localization of the protein by several different approaches: (i) by analytical subcellular fractionation and immunoblotting of mevalonate kinase in the isolated subcellular fractions with the monospecific antibodies; (ii) by immunocryoelectron microscopy techniques; and (iii) by expressing the cDNA encoding mevalonate kinase in mammalian cells. The data obtained demonstrate that there is only one mevalonate kinase protein that is predominantly localized in peroxisomes. We also illustrate that the protein is targeted to and imported into peroxisomes. In addition, we show that in cells and tissues obtained from patients with peroxisomal deficiency diseases mevalonate kinase protein and its activity are severely reduced.

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.

Topology of catalase assembly in human skin fibroblasts

The biogenesis, assembly and import of the peroxisomal enzyme catalase was studied in human skin fibroblasts from control persons and from patients with the Zellweger syndrome. For this purpose, two monoclonal antibodies were generated which are able to discriminate between the monomeric or dimeric form and the tetrameric, enzymically active conformation of the enzyme. Metabolic labelling studies showed that catalase is assembled to the tetrameric conformation within one hour after its synthesis, while it is still in the cytosol of the cell. Subsequently, the enzyme becomes particle-bound in the control cells, a process that is retarded by addition of the catalase inhibitor 3-amino-1,2,4-triazole. However, the tetramer remains in the cytosol in cells from Zellweger patients. It is concluded that newly synthesized catalase can be assembled to a tetramer in the cytosol in human skin fibroblasts. Unfolding of this tetramer prior to import into peroxisomes is indicated.

A case of pseudo-Zellweger syndrome with a possible bifunctional enzyme deficiency but detectable enzyme protein. Comparison of two cases of Zellweger syndrome

Three infants with peroxisomal disorders were investigated clinicobiochemically and neuroradiologically. Two had classical Zellweger syndrome, and cranial CT scans showed typical disproportionate enlargement of the occipital horns of the lateral ventricles (colpocephaly) with marked hypodensity of the white matter. In one female infant, although the clinical findings were similar to those in Zellweger syndrome, some findings, such as elevated transaminase levels, liver fibrosis, the absence of renal cortical cysts and colpocephaly, were negative or milder. Biochemical analyses revealed increased very long-chain fatty acids, dicarboxylic aciduria and impaired beta-oxidation of lignoceric acid. However, peroxisomes were abundantly present in hepatocytes and cultured fibroblasts, and all peroxisomal beta-oxidation enzyme proteins were detected on immunoblot analysis. A cell fusion study suggested that the enzyme responsible for this case of 'pseudo-Zellweger syndrome' is bifunctional.

Purification of peroxisomes and subcellular distribution of enzyme activities for activation and oxidation of very-long-chain fatty acids in rat brain

Brain contains high amounts of very-long-chain (VLC) fatty acids (> C22). Since mitochondria from liver and skin fibroblasts lack lignoceroyl-CoA ligase, in liver and skin fibroblasts fatty acids are exclusively oxidized in peroxisomes. Findings by Poulos and associates [9] suggested that contrary to liver and cultured skin fibroblasts brain mitochondria contain lignoceroyl-CoA ligase and can oxidize lignoceric acid. The present study was undertaken to develop a procedure for the isolation of subcellular organelles of higher purity from brain and to get a better understanding of the subcellular localization of the oxidation of VLC fatty acids in brain. The enzyme activities for activation and oxidation of palmitic and lignoceric acids were determined in peroxisomes, mitochondria, microsomes and a myelin fraction from rat brain and peroxisomes, mitochondria and microsomes purified from rat liver. Like in liver, brain lignoceroyl-CoA ligase activity in microsomes and peroxisomes was approx. 9 times higher than in mitochondria. In addition to palmitoyl-CoA ligase the antibodies against palmitoyl-CoA ligase inhibited the residual mitochondrial lignoceroyl-CoA ligase activity, meaning that lignoceroyl-CoA ligase activity in mitochondria was derived from palmitoyl-CoA ligase. Accordingly, in peroxisomes lignoceric acid was oxidized at 7 times higher rate than in mitochondria. Mitochondria were able to oxidize lignoceric acid efficiently when supplemented with lignoceroyl-CoA ligase activity from microsomes or myelin. These results show that in brain lignoceric acid is oxidized in peroxisomes and that lignoceroyl-CoA ligase activity is localized in peroxisomes and microsomes, but not in mitochondria. Peroxisomes and microsomes contain both lignoceroyl-CoA and palmitoyl-CoA ligases. Similar to peroxisomes and microsomes, the antibodies against palmitoyl-CoA ligase inhibited only the palmitoyl-CoA ligase activity in myelin but not the lignoceroyl-CoA ligase activity. These results suggest that in addition to palmitoyl-CoA ligase, myelin also contains lignoceroyl-CoA ligase.

Cyclooxygenase pathway in dermal fibroblasts from patients with metabolic disorders of peroxisomal origin

Cyclooxygenase metabolism was studied in fibroblasts from patients with metabolic disorders of peroxisomal origin (adrenomyeloneuropathy, X-linked adrenoleukodystrophy, cerebrohepatorenal syndrome of Zellweger and rhizomelic chondrodysplasia punctata). In response to arachidonic acid (6.25-100 microM) or calcium ionophore A23187 (2.5-20 microM) prostaglandin E2 and 6-keto-prostaglandin F1 alpha are the main cyclooxygenase metabolites formed. No formation of thromboxane B2 or 2,3-dinor-thromboxane B2 was found. Apparently due to the heterogeneous nature of peroxisomal disorders no uniform pattern of cyclooxygenase metabolism and eicosanoid concentrations in cell lines from patients with peroxisomal defects was found.

The CoA esters of 2-methyl-branched chain fatty acids and of the bile acid intermediates di- and trihydroxycoprostanic acids are oxidized by one single peroxisomal branched chain acyl-CoA oxidase in human liver and kidney

Rat liver peroxisomes contain three acyl-CoA oxidases: palmitoyl-CoA oxidase, which oxidizes the CoA esters of straight chain fatty acids and prostaglandins; pristanoyl-CoA oxidase, which oxidizes the CoA esters of 2-methyl-branched fatty acids (e.g. pristanic acid); and trihydroxycoprostanoyl-CoA oxidase, which oxidizes the CoA esters of the bile acid intermediates di- and trihydroxycoprostanic acids (Van Veldhoven, P. P., Vanhove, G., Asselberghs, S., Eyssen, H. J., and Mannaerts, G. P. (1992) J. Biol. Chem. 267, 20065-20074). In the present report we demonstrate that human liver peroxisomes contain only two acyl-CoA oxidases: palmitoyl-CoA oxidase, which oxidizes the CoA esters of straight chain fatty acids and prostaglandins, and a novel branched chain acyl-CoA oxidase, which oxidizes the CoA esters of 2-methyl-branched fatty acids as well as those of the bile acid intermediates (which also possess a 2-methyl substitution in their side chains). The branched chain acyl-CoA oxidase was purified to near homogeneity by means of column chromatography. It appeared to be a 70-kDa monomeric protein that did not cross-react with antisera raised against rat palmitoyl-CoA oxidase and pristanoyl-CoA oxidase. No indication was found for the presence of a separate trihydroxycoprostanoyl-CoA oxidase in human liver. The branched chain acyl-CoA oxidase was present also in human kidney, suggesting that it is expressed in other extrahepatic tissues as well. Our results explain a number of clinical-chemical observations made in certain cases of peroxisomal beta-oxidation disorders.

Complementation analysis of patients with intact peroxisomes and impaired peroxisomal beta-oxidation

Complementation analysis, using peroxisomal beta-oxidation of very long chain fatty acids (VLCFA) as the criterion for complementation, is useful in the study of patients who are suspected of having a single enzyme defect in the peroxisomal beta-oxidation pathway. Laboratory findings for these patients include elevated plasma VLCFA and impaired VLCFA oxidation in fibroblasts. Some of these patients have slightly abnormal phytanic acid oxidation in fibroblasts. In addition, elevated levels of bile acid intermediates have been reported in some cases. Plasmalogen synthesis, pipecolic acid levels, and subcellular distribution of catalase are normal. Using complementation analysis, we show that six patients, who were suspected of having a single enzyme defect in the peroxisomal beta-oxidation pathway, are deficient in peroxisomal bifunctional enzyme [enoyl-CoA hydratase (EC 4.2.1.17)/3-hydroxyacyl-CoA dehydrogenase (EC 1.1.1.35)] activity. This group of six patients, deficient in bifunctional enzyme activity, may be subdivided into two complementation groups. It would appear that patients in each of these two groups are deficient in only one of the bifunctional enzyme activities.

Histochemistry of peroxisomal enzyme activities: a tool in the diagnosis of Zellweger syndrome

The localization of the activity of the peroxisomal enzymes D-amino acid oxidase and hydroxyacid oxidase was studied at the light-microscopical level in livers and kidneys of control subjects and patients with Zellweger syndrome, an inherited disease characterized by a lack of intact peroxisomes. D-Amino acid oxidase and hydroxyacid oxidase activities were demonstrated in unfixed cryostat sections with the cerium-diaminobenzidine-cobalt-hydrogen peroxide procedure, in which cerium ions capture hydrogen peroxide, the product of both enzymes. In a second step reaction decomposition of cerium perhydroxide gives rise to a diaminobenzidine polymer complexed with cobalt ions. D-Amino acid oxidase and hydroxyacid oxidase activities were found in peroxisomes of liver parenchymal cells, and only D-amino acid oxidase in peroxisomes of proximal tubular cells of kidneys of control humans. The activities of these enzymes were not detectable in livers and kidneys of Zellweger patients. It is concluded that the cerium-diaminobenzidine-cobalt-hydrogen peroxide procedure enables the demonstration of peroxisomal enzyme activities in human tissues at the light-microscopical level and is an important tool in detecting patients with Zellweger syndrome.

Peroxisomal beta-oxidation of polyunsaturated long chain fatty acids in human fibroblasts. The polyunsaturated and the saturated long chain fatty acids are retroconverted by the same acyl-CoA oxidase

The metabolism of the C22 unsaturated fatty acids erucic acid (22:1(n-9)), adrenic acid (22:4(n-6)), docosapentaenoic acid (22:5(n-3)) and docosahexaenoic acid (22:6(n-3)) was studied in cultured fibroblasts from patients with acyl-CoA oxidase deficiency, the Zellweger syndrome, X-linked adrenoleukodystrophy (X-ALD) and normal controls. [3-14C] 22:4 (n-6) and [3-14C] 22:5 (n-3) were shortened (retroconverted) to [1-14C] 20:4 (n-6) and [1-14C] 20:5 (n-3), respectively, in normal and X-ALD fibroblasts. In Zellweger and acyl-CoA oxidase deficient fibroblasts these reactions were deficient. Since the retroconversion is normal in X-ALD fibroblasts peroxisomal very long chain (lignoceryl) CoA ligase is probably not required for the activation of C22 unsaturated fatty acids. The present work with fibroblasts from patients with a specific acyl-CoA oxidase deficiency, previously shown to have a deficient peroxisomal clofibrate-inducible acyl-CoA oxidase, and which accumulate 24:0 and 26:0 fatty acids, supports the view that this enzyme is responsible for the chain-shortening of docosahexaenoic acid (22:6(n-3)), erucic acid (22:1(n-9)), docosapentaenoic acid (22:5(n-3)), and adrenic acid (22:4(n-6)) as well.

Low-density particles (W-particles) containing catalase in Zellweger syndrome and normal fibroblasts

By both histological and biochemical criteria, peroxisomes in patients with Zellweger syndrome appear to be absent or severely deficient. By using 15-30% (wt/vol) Nycodenz/sucrose gradients to study the subcellular localization of extraperoxisomal catalase activity, a commonly used marker for mature peroxisomes, we detected a single peak of activity in Zellweger syndrome fibroblasts at an equilibrium density of 1.13 g/cm3, lower than the expected 1.17 g/cm3 of mature peroxisomes. Upon recentrifugation in either the original gradient or one with a higher salt concentration, essentially all catalase activity was recovered in fractions of the original densities. The activity of the catalase peak was further analyzed by a digitonin titration and filtration assay in combination with Triton X-100 treatment. The catalase activity passed through 0.1-microns and 0.22-microns but was retained on 0.025-microns membrane filters (mean pore size). After treatment with Triton X-100 nearly all catalase activity passed through the filters. The results from fractionations data, digitonin latency measurement, and the detergent effect on the filtration behavior suggest that catalase is not free in the cytosol of Zellweger syndrome fibroblasts as commonly thought but in particles (W-particles). Similar low-density catalase-containing particles, distinct from peroxisomes, are also found in normal fibroblasts. We found that L-alpha-hydroxyacid oxidase, another peroxisomal matrix enzyme, is also present in W-particles derived from normal and Zellweger syndrome fibroblasts. We speculate that the low-density catalase-containing W-particle may represent an immature or incomplete form of peroxisome distinct from previously described "peroxisomal ghosts" in Zellweger syndrome fibroblasts.

Phenotypic heterogeneity in cultured skin fibroblasts from patients with disorders of peroxisome biogenesis belonging to the same complementation group

We have studied fibroblast cell lines derived from a control subject (cell line 85AD5035F) and three patients clinically described as having the Zellweger syndrome (cell line W78/515), the infantile form of Refsum disease (cell line BOV84AD) and hyperpipecolic acidaemia (cell line GM3605), respectively. The mutant cell lines belonged to the same complementation group. The fibroblasts were cultured under identical conditions and were harvested at different time intervals after reaching confluence. Several peroxisomal parameters were determined. In agreement with previous reports, a lowered enzymic activity of acyl-CoA: dihydroxyacetonephosphate acyltransferase and a decrease in latent catalase clearly distinguished the patient cell lines from the control cell line. However, the cell lines exhibited a phenotypic heterogeneity. This was most strikingly encountered when cells were processed for indirect immunofluorescence microscopy and stained with anti-(catalase). The control cells exhibited a punctate fluorescence, which is indicative of the presence of catalase in peroxisomes. In the mutant cell line W78/515 a diffuse fluorescence was observed, indicative of the presence of catalase in the cytosol. In the other two mutant cell lines a punctate fluorescence was observed in some of the cells. Moreover, clear differences in the extent of proteolytic processing of acyl-CoA oxidase were detected. The mutant cell line BOV84AD displayed a control-like pattern with all molecular forms of acyl-CoA oxidase (72, 52 and 20 kDa) present, whereas in the W78/515 cell line only the 72 kDa component could be visualised. The GM3605 cell line was intermediate in this respect.

Cu,Zn superoxide dismutase is a peroxisomal enzyme in human fibroblasts and hepatoma cells

The intracellular localization of Cu,Zn superoxide dismutase (superoxide:superoxide oxidoreductase, EC 1.15.1.1) has been examined by immunofluorescence using four monoclonal anti-Cu,Zn superoxide dismutase antibodies raised against a recombinant human Cu,Zn superoxide dismutase derivative produced and purified from Escherichia coli. Colocalization with catalase, a peroxisomal matrix enzyme, was used to demonstrate the peroxisomal localization of Cu,Zn superoxide dismutase in human fibroblasts and hepatoma cells. In the fibroblasts of Zellweger syndrome patients, the enzyme is not transported to the peroxisomal ghosts but, like catalase, remains in the cytoplasm. In addition, immunocryoelectron microscopy of yeast cells expressing human Cu,Zn superoxide dismutase showed that the enzyme is translocated to the peroxisomes.

Zellweger syndrome: a histochemical diagnosis of two cases

Until 17 years ago the diagnosis of the cerebrohepatorenal Zellweger syndrome (ZS) rested largely on clinical grounds confirmed by pathologic findings at autopsy. The observation that peroxisomes are not detectable morphologically or histochemically in liver or kidney of patients with this syndrome gave histopathologists the opportunity to make the diagnosis of this complex syndrome at biopsy. Catalase reaction of the peroxisomes can be used as a rapid and accurate method to differentiate between ZS and other clinical conditions in which the peroxisomes are present in normal or reduced number. We describe two patients in whom the diagnosis of ZS was made by the absence of histochemical staining for catalase in a liver biopsy. The findings were subsequently confirmed using standard biochemical tests.

Immunochemical analysis of the peroxisomal beta-oxidation enzymes in rat and human heart and skeletal muscle and in skeletal muscle of Zellweger patients

Immunoblot analyses with antibodies against the peroxisomal beta-oxidation enzymes from rat liver showed the presence of these enzymes in rat and human liver and kidney and rat adrenal gland. The bifunctional protein could not be detected in muscle tissues or cultured muscle cells. Acyl-CoA oxidase was detected in rat heart and cultured human muscle cells. 3-Ketoacyl-CoA thiolase was also detected in human and rat heart and skeletal muscle; however, this enzyme was not detectable in skeletal muscle of Zellweger patients, in agreement with the absence of peroxisomal fatty acid oxidation.

Acyl-CoA oxidase, peroxisomal thiolase and dihydroxyacetone phosphate acyltransferase: aberrant subcellular localization in Zellweger syndrome

We have studied the presence and subcellular localization of peroxisomal 3-oxoacylcoenzyme A thiolase, acylcoenzyme A oxidase and acyl-CoA: dihydroxyacetonephosphate acyltransferase (DHAPAT) in fibroblasts from control subjects and patients with an inherited deficiency of peroxisomes (Zellweger syndrome), using immunofluorescence spectroscopy and density gradient centrifugation techniques. The results show that Zellweger cells contain unprocessed thiolase and unprocessed acyl-CoA oxidase which are associated with structures containing a peroxisomal integral membrane protein of 69 kDa and having a density much lower than that of normal peroxisomes. The residual DHAPAT activity present in Zellweger cells is also contained in these structures. We conclude that these structures represent defectively assembled peroxisomes which may still be capable of importing some peroxisomal proteins.

Identification of pristanoyl-CoA oxidase activity in human liver and its deficiency in the Zellweger syndrome

The ability of human liver to oxidize pristanic acid was investigated. Liver from control subjects was found to contain pristanic acid oxidase activity, an H2O2-producing enzyme activity not previously demonstrated in mammals. In livers from patients with the cerebro-hepato-renal syndrome of Zellweger, a genetic disease characterized by the absence of morphologically distinguishable peroxisomes, pristanic acid oxidase activity was found to be deficient. These results indicate that pristanic acid is oxidized in peroxisomes rather than in mitochondria as believed until now. Furthermore, our findings provide an explanation for the elevated levels of pristanic acid in body fluids from patients lacking peroxisomes.

The Zellweger syndrome: deficient conversion of docosahexaenoic acid (22:6(n-3)) to eicosapentaenoic acid (20:5(n-3)) and normal delta 4-desaturase activity in cultured skin fibroblasts

The metabolism of docosahexaenoic acid (22:6(n-3)) and adrenic acid (22:4(n-6)) was studied in cultured fibroblasts from patients with the Zellweger syndrome, X-linked adrenoleukodystrophy (X-ALD) and normal controls. It was shown that [4,5- 3H]22:6(n-3) is retroconverted to labelled eicosapentaenoic acid (20:5(n-3)) in normal and X-ALD fibroblasts, while this conversion is deficient in Zellweger fibroblasts. [U- 14C]Eicosapentaenoic acid (20:5(n-3)) is elongated to docosapentaenoic acid (22:5(n-3)) in all three cell lines. With [U- 14C]20:5(n-3) as the substrate, shorter fatty acids were not detected. With [4,5- 3H]22:6(n-3) as the substrate, labelled fatty acids were esterified in the phospholipid- and triacylglycerol-fraction to approximately the same extent in all three cell lines. [2- 14C]Adrenic acid (22:4(n-6)) was desaturated to 22:5(n-6) and elongated to 24:4(n-6) in all three cell lines and to the largest extent in the Zellweger fibroblasts. This agrees with the view that the delta 4-desaturase is not a peroxisomal enzyme. The observation that the retroconversion of 22:6(n-3) to 20:5(n-3) is deficient in Zellweger fibroblasts strongly suggest that the beta-oxidation step in the retroconversion is a peroxisomal function. Peroxisomal very-long-chain (lignoceroyl) CoA ligase is probably not required for the activation of 22:6(n-3), since the retroconversion to 20:5(n-3) is normal in X-ALD fibroblasts.

Aberrant subcellular localization of peroxisomal 3-ketoacyl-CoA thiolase in the Zellweger syndrome and rhizomelic chondrodysplasia punctata

Fibroblasts from patients with the inherited disorder Zellweger syndrome have few or no peroxisomes; multiple biochemical processes that normally occur in this organelle are defective. Rhizomelic chondrodysplasia punctata (RCDP) is another inherited disorder in which two unrelated peroxisomal metabolic processes, plasmalogen synthesis and phytanic acid oxidation, are impaired despite the normal appearance of peroxisomal structure. It was previously reported that one of the enzymes of peroxisomal fatty acid beta-oxidation, 3-ketoacyl-CoA thiolase (beta-keto-thiolase), was present in precursor rather than mature form in both of these diseases. Immunofluorescent staining for peroxisomal beta-ketothiolase showed the immunoreactivity to be localized in subcellular particles in fibroblasts from both Zellweger syndrome and RCDP patients, even though the former lack normal peroxisomes. Immunoblot studies were performed to determine the subcellular location of the thiolase precursor in fractionated fibroblasts from Zellweger and RCDP patients. In both disorders, thiolase immunoreactivity was detected in subcellular fractions having a lower density than normal peroxisomes and mitochondria, and was resistant to digestion by proteinase K. The density of the thiolase precursor-containing fractions was similar to that of peroxisomal membrane "ghost" fractions recently described by Santos et al. (J Biol Chem 263:10502-10509, 1988). Our results suggest that these are not empty membrane vesicles but contain at least one peroxisomal matrix protein. Furthermore, they exist not only in cells in which normal peroxisomes fail to form (Zellweger syndrome), but also in some cells which have catalase-containing peroxisomes (RCDP).