Molecular analysis of peroxisomal beta-oxidation enzymes in infants with peroxisomal disorders indicates heterogeneity of the primary defect

The inflammatory response in acyl-CoA oxidase 1 deficiency (pseudoneonatal adrenoleukodystrophy)

Among several peroxisomal neurodegenerative disorders, the pseudoneonatal adrenoleukodystrophy (P-NALD) is characterized by the acyl-coenzyme A oxidase 1 (ACOX1) deficiency, which leads to the accumulation of very-long-chain fatty acids (VLCFA) and inflammatory demyelination. However, the components of this inflammatory process in P-NALD remain elusive. In this study, we used transcriptomic profiling and PCR array analyses to explore inflammatory gene expression in patient fibroblasts. Our results show the activation of IL-1 inflammatory pathway accompanied by the increased secretion of two IL-1 target genes, IL-6 and IL-8 cytokines. Human fibroblasts exposed to very-long-chain fatty acids exhibited increased mRNA expression of IL-1α and IL-1β cytokines. Furthermore, expression of IL-6 and IL-8 cytokines in patient fibroblasts was down-regulated by MAPK, p38MAPK, and Jun N-terminal kinase inhibitors. Thus, the absence of acyl-coenzyme A oxidase 1 activity in P-NALD fibroblasts triggers an inflammatory process, in which the IL-1 pathway seems to be central. The use of specific kinase inhibitors may permit the modulation of the enhanced inflammatory status.

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.

A novel peroxisomal enzyme, D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein: its expression in the developing human brain

D-bifunctional protein, which is a newly recognized peroxisomal enzyme (D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase), demonstrates a characteristic development of pattern in the human brain. At 13 gestational weeks (GW), D-bifunctional protein immunoreactivity first appeared in the brain. Each neuron exhibited increased immunoreactivity along with growth in size as age increased and size with age. Glial cells in the white matter showed immunoreactivity after 30 GW. On the other hand, the L-bifunctional protein immunoreactivity was reported in neurons from 23 or 25 GW and in the white matter from 12 or 14 GW. Because of polymicrogyria in conditions such as infantile Refsum disease and infantile adrenoleukodystrophy, peroxisomal enzymes are thought to play an important role in neuronal migration and possibly myelination. D-bifunctional protein may be relevant to neuronal migration and L-bifunctional protein may be involved in axonal growth and synaptic development. This study is designed to access the ontogeny of D-bifunctional protein in the human brain.

Resistance to erucic acid as a selectable marker for peroxisomal activity: isolation of revertants of an infantile Refsum disease cell line

A system based on the ability of cells to oxidize very long-chain fatty acids (VLCFA) was developed to select in vitro normal human fibroblasts from fibroblasts of patients suffering from peroxisomal disorders with multienzymatic deficiencies: Zellweger syndrome, neonatal adrenoleukodystrophy, infantile Refsum disease (IRD). Cells treated with various concentrations of erucic acid (C22:1 n-9) revealed an enhanced toxicity of this fatty acid for the fibroblasts of patients compared with normal cells. This differential toxicity is correlated with variable accumulations of C22:1 n-9 and the absence of beta-oxidation products in the mutants. Revertants from clonal IRD cell lines were isolated in the selective medium at frequencies ranging from 3 x 10(-7) to 4 x 10(-6) depending on the line. After six weeks of growth in the absence of selective pressure, the variants exhibited a resistance level to C22:1 n-9 identical to that of normal cells. Furthermore, beta-oxidation of VLCFA is re-established in these selected cells as well as dihydroxyacetone phosphate acyltransferase activity. Immunoblot experiments also demonstrated a restored pattern of acyl-CoA oxidase molecular forms. Last, immunofluorescence studies revealed the presence of cytoplasmic structures that were absent in the original IRD cells. Thus, both the deficiencies in metabolic pathways and paucity of the organelle are at least partially corrected in the selected clones.

Structure-function relationships in the peroxisome: implications for human disease

Progress relevant to human peroxisomal disorders over the past 3 years includes improved biochemical delineation of disease phenotypes and new insights into peroxisomal structure and biogenesis. Immunoblotting studies using antibodies to peroxisomal beta-oxidation enzymes have defined mutations affecting each step of the pathway, some with clinical phenotypes as severe as disorders with global peroxisome deficiency. The latter disorders, typified by Zellweger syndrome, often lack matrix proteins but retain major membrane species of 150, 70, 35, and 22 kDa in empty peroxisomal "ghost" structures. The hypothesis that peroxisomal deficiency disorders result from altered targeting or import of peroxisomal matrix proteins has been strengthened by the demonstration of a carboxy terminal peroxisome-targeting signal which is distinct from amino terminal signals directing proteins to mitochondria. A mutation which mistargets alanine/glyoxylate aminotransferase from peroxisomes to mitochondria in primary hyperoxaluria provides a graphic example of these signals. The structural significance of membrane function is supported by the primacy of membrane assembly in normal ontogeny or regenerating liver. The coordinate control, targeting, and striking inducibility of peroxisomal proteins suggests a potential vehicle for gene and enzyme therapy.

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.

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.

Immunocytochemical localization of peroxisomal beta-oxidation enzymes in human fetal liver

In the majority of congenital peroxisomal disorders, beta-oxidation of very long chain fatty acids is deficient. We have investigated the appearance and localization of the three peroxisomal beta-oxidation enzymes in normal fetal liver (fertilization age between 5 and 18 weeks) with protein A-gold immunocytochemistry and silver enhancement for light microscopic visualization. With specificity-tested polyclonal antibodies, acyl-CoA-oxidase, bifunctional enzyme, and 3-oxoacyl-CoA thiolase were localized in the peroxisomes of the parenchymal cells, which appear as brown or black granules. In the youngest specimen, no immunopositive reaction was obtained. A weak reaction with anti-thiolase was obtained at the age of 6-7 weeks. At a fertilization age of 8 weeks, peroxisomes could be distinctly visualized after immunostaining for all three enzymes. From a staining series with anti-thiolase on simultaneously treated slides, it appears that the amount of antigen per peroxisome and the organelle size increase between the seventh and eighteenth weeks. These data should enable a more specific diagnosis in fetal liver biopsies from pregnancies at risk and after termination of pregnancy.