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The four murine peroxisomal ABC-transporter genes differ in constitutive, inducible and developmental expression
J Berger1, S Albet, M Bentejac
1Brain Research Institute, University of Vienna, Austria. johannes.berger@univie.ac.at
Abstract:
Four ATP-binding cassette (ABC) half-transporters have been identified in mammalian peroxisomes: adrenoleukodystrophy protein (ALDP), adrenoleukodystrophy-related protein (ALDRP), 70-kDa peroxisomal membrane protein (PMP70) and PMP70-related protein (P70R). Inherited defects in ALDP cause the neurodegenerative disorder X-linked adrenoleukodystrophy (X-ALD). By comparative Northern blot analyses we found each of the four murine peroxisomal ABC transporter mRNA species at maximum abundance only in a few tissues, which differed for each family member. The four genes were also regulated differentially during mouse brain development: ALDP mRNA was most abundant in embryonic brain and gradually decreased during maturation; ALDRP and P70R mRNA accumulated in the early postnatal period; and the amount of PMP70 transcript increased slightly during the second and third postnatal week. The different expression patterns could explain why beta-oxidation is defective in X-ALD, although ALDRP and PMP70 can replace ALDP functionally in fibroblasts. Dietary fenofibrate had no effect on the ALD and P70R genes, but strongly increased expression of the ALDR and PMP70 genes in mouse liver. However, in P-glycoprotein Mdr1a-deficient mice fenofibrate treatment increased ALDR gene expression also in the brain, suggesting that the multidrug-transporter P-glycoprotein restricts entry of fenofibrate to the brain at the blood-brain barrier. Analysis of the promoter sequences revealed a cryptic nuclear hormone receptor response element of the DR+4 type in the ALDR promoter and a novel 18-bp sequence motif present only in the 5' flanking DNA of the ALDR and PMP70 genes. The mouse ALDR gene uses a single transcription start site but alternative polyadenylation sites. These data are of importance for the use of ALDP-deficient mice as a model in pharmacological gene therapy studies.
Insights
Four peroxisomal ATP-binding cassette (ABC) transporters show distinct tissue and developmental expression patterns in mice. Differential gene regulation may explain X-linked adrenoleukodystrophy (X-ALD) and offers insights for therapeutic strategies.
Area of Science:
- Biochemistry
- Genetics
- Cell Biology
Background:
- Mammalian peroxisomes contain four ATP-binding cassette (ABC) half-transporters: adrenoleukodystrophy protein (ALDP), adrenoleukodystrophy-related protein (ALDRP), 70-kDa peroxisomal membrane protein (PMP70), and PMP70-related protein (P70R).
- Defects in ALDP cause X-linked adrenoleukodystrophy (X-ALD), a neurodegenerative disorder.
- Understanding the expression and regulation of these transporters is crucial for comprehending peroxisomal function and disease mechanisms.
Purpose of the Study:
- To investigate the tissue-specific and developmental expression patterns of the four murine peroxisomal ABC transporter genes.
- To explore the regulatory effects of fenofibrate on these genes and the role of P-glycoprotein in modulating drug response.
- To identify potential regulatory elements in the promoter regions of ALDR and PMP70 genes.
Main Methods:
- Comparative Northern blot analyses to determine mRNA abundance in various mouse tissues.
- Analysis of gene expression during different stages of mouse brain development.
- Treatment of mice with fenofibrate and assessment of gene expression changes, including in P-glycoprotein deficient models.
- Bioinformatic analysis of promoter sequences to identify regulatory elements.
Main Results:
- Each of the four peroxisomal ABC transporter mRNAs exhibited unique tissue-specific expression patterns.
- Differential regulation of ALDP, ALDRP, P70R, and PMP70 mRNA levels was observed during mouse brain development.
- Fenofibrate treatment significantly increased ALDR and PMP70 gene expression in mouse liver, with P-glycoprotein influencing brain expression.
- Identification of a nuclear hormone receptor response element in the ALDR promoter and a novel conserved motif in ALDR and PMP70 flanking DNA.
Conclusions:
- The distinct expression profiles of peroxisomal ABC transporters suggest specialized roles and contribute to understanding X-ALD pathophysiology.
- Fenofibrate's differential regulation of these transporters highlights potential therapeutic avenues, with P-glycoprotein acting as a barrier to brain penetration.
- The identified promoter elements provide insights into the transcriptional control of ALDR and PMP70 genes.
- These findings are significant for developing ALDP-deficient mouse models for X-ALD gene therapy research.