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Functional genomic analysis of frataxin deficiency, Illumina data

ABSTRACT: Functional genomic analysis of frataxin deficiency reveals tissue-specific alterations and identifies the PPARγ pathway as a therapeutic target in Friedreich's ataxia Friedreich's ataxia (FRDA), the most common inherited ataxia, is characterized by focal neurodegeneration, diabetes mellitus, and life-threatening cardiomyopathy. Frataxin, which is significantly reduced in patients with this recessive disorder, is a mitochondrial iron-binding protein, but how its deficiency leads to neurodegeneration and metabolic derangements is not known. We performed microarray analysis of heart and skeletal muscle in a mouse model of frataxin deficiency, and found molecular evidence of increased lipogenesis in skeletal muscle, and alteration of fiber-type composition in heart, consistent with insulin resistance and cardiomyopathy, respectively. Since the peroxisome proliferator-activated receptor gamma (PPARγ) pathway is known to regulate both processes, we hypothesized that dysregulation of this pathway could play a key role in frataxin deficiency. We confirmed this by showing a coordinate dysregulation of the PPARγ coactivator Pgc1a and transcription factor Srebp1 in cellular and animal models of frataxin deficiency, and in cells from FRDA patients, who have marked insulin resistance. Finally, we show that genetic modulation of the PPARγ pathway affects frataxin levels in vitro, supporting PPARγ as a novel therapeutic target in FRDA.

ORGANISM(S): Mus musculus

PROVIDER: GSE15848 | GEO | 2009/06/02

SECONDARY ACCESSION(S): PRJNA123051

REPOSITORIES: GEO

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Project description:Friedreich's Ataxia (FRDA), a rare, inherited, progressive degenerative disease, is caused by a defective expression of mitochondrial protein frataxin (FXN), due to homozygous hyper-expansion of GAA triplets in the gene which severely reduce its transcription. FXN is crucial for cell survival and its deficiency in humans critically affects viability of neurons, cardiomyocytes and pancreatic beta cells. Around two thirds of individuals with FRDA show typical manifestation of hypertrophic cardiomyopathy, that can progress in heart failure and death. Except for FXN, very few genes have been correlated with ataxia and cardiac disease in FRDA. To identify other genes involved in pathogenesis of FRDA, a microarray analysis on FRDA patient's lymphoblastoid cells stably reconstituted with FXN was performed. HS-1 associated protein X-1 (HAX-1), a family of proteins playing important roles in the protection of cardiomyocytes from apoptosis, is the highest up-regulated transcript (FC=+2, p<0.0006). HAX-1 is highly expressed in heart and HAX-1 heterozygous-deficient hearts exhibit increases in infarct size. The microarray result was further assessed with qRT-PCR and western blot analysis performed on HEK293 stably transfected with empty vector or FXN-vector and lymphoblasts from FRDA patients compared to clinically unaffected heterozygous parents, confirming a strong co-expression of HAX-1 and FXN both at mRNA and protein level. Moreover, analysis of FXN and HAX-1 in peripheral blood mononuclear cells (PBMCs) of FRDA patients (n=13), heterozygous parents (n=6) and non-correlated healthy controls (n=13) revealed that their expressions are correlated. The positive correlation is more significant in FRDA patients showing a cardiac disease (10/13). The positive correlation between frataxin and HAX-1 expression level suggests a potential link of HAX-1 expression to pro-survival or protective cellular pathways related to frataxin. Thus, HAX-1 may be considered a specific biomarker of cardiomyopathy in FRDA and may represent a prognostic implement in these patients. Moreover, the discovery of novel genetic "risk" or "protective" factors in cardiomyopathy is crucial to improve risk stratification strategies and to identify new therapeutic targets.

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Functional genomic analysis of frataxin deficiency, Illumina data

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