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Temperature-sensitive mutation in PEX1 moderates the phenotypes of peroxisome deficiency disorders
A Imamura1, S Tamura, N Shimozawa
1Department of Pediatrics, Gifu University School of Medicine, Gifu 500-8076, Japan.
Insights
Peroxisome biogenesis disorders (PBDs) like infantile Refsum disease (IRD) show mild symptoms due to temperature-sensitive peroxisome assembly. A specific PEX1 gene mutation causes this in PBD complementation group I patients.
Area of Science:
- Cell Biology
- Genetics
- Biochemistry
Background:
- Peroxisome biogenesis disorders (PBDs) are severe genetic conditions affecting peroxisome assembly.
- Infantile Refsum disease (IRD), Zellweger syndrome (ZS), and neonatal adrenoleukodystrophy (NALD) represent a spectrum of PBD severity.
- The PEX1 gene, encoding peroxin Pex1p, is frequently implicated in PBDs, particularly complementation group I (CG1).
Purpose of the Study:
- To investigate the molecular basis for the varying severity of PBDs, specifically focusing on PEX1-defective IRD.
- To determine if temperature sensitivity plays a role in the milder clinical presentation of certain PBDs.
- To identify specific mutations in the PEX1 gene associated with temperature-sensitive peroxisome assembly.
Main Methods:
- Culturing patient-derived fibroblasts (from IRD, ZS, and NALD patients) and complementation group I Chinese hamster ovary (CHO) cell mutants.
- Assessing peroxisome morphology and biochemical function at different temperatures (30°C and 37°C).
- Identifying mutations in the PEX1 gene using genetic sequencing.
- Transfecting mutant CHO cells with the identified mutant PEX1 gene (HsPEX1G843D) to assess its functional impact.
Main Results:
- Fibroblasts from CG1 IRD patients exhibited temperature-sensitive peroxisome formation, with peroxisomes assembling at 30°C but not 37°C.
- ZS and NALD cells showed minimal peroxisome formation even at 30°C.
- A specific missense mutation, G843D, was identified in the PEX1 gene of most CG1 IRD patients.
- Transfection of CG1 CHO cell mutants with the G843D mutant PEX1 gene (HsPEX1G843D) replicated the temperature-sensitive phenotype.
Conclusions:
- Temperature-sensitive peroxisome assembly is a key factor contributing to the milder clinical features observed in PEX1-defective infantile Refsum disease (IRD) within complementation group I.
- The G843D mutation in the PEX1 gene is strongly associated with this temperature-sensitive phenotype and milder PBD presentation.
- Understanding genotype-phenotype correlations, like temperature sensitivity, is crucial for characterizing the spectrum of peroxisome biogenesis disorders.
Abstract:
The peroxisome biogenesis disorders (PBDs), including Zellweger syndrome (ZS), neonatal adrenoleukodystrophy (NALD) and infantile Refsum disease (IRD), are autosomal recessive diseases caused by deficiency of peroxisome assembly as well as malfunction of peroxisomes, where >10 genotypes have been reported. ZS patients manifest the most severe clinical and biochemical abnormalities, while those with NALD and IRD show the least severity and the mildest features, respectively. PEX1 is the causative gene for PBDs of complementation group I (CG1), the highest incidence PBD, and encodes the peroxin, Pex1p, a member of the AAA ATPase family. In the present work, we found that peroxisomes were morphologically and biochemically formed at 30 but not 37 degrees C, in the fibroblasts from all CG1 IRD patients examined, whereas almost no peroxisomes were seen in ZS and NALD cells, even at 30 degrees C. A point missense mutation, G843D, was identified in the PEX1 allele of most CG1 IRD patients. The mutant PEX1, termed HsPEX1G843D, gave rise to the same temperature-sensitive phenotype on CG1 CHO cell mutants upon transfection. Collectively, these results demonstrate temperature-sensitive peroxisome assembly to be responsible for the mildness of the clinical features of PEX1 -defective IRD of CG1.