Functional genomic analysis of frataxin deficiency reveals tissue-specific alterations and identifies the PPARgamma 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 (PPARgamma) 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 PPARgamma 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 PPARgamma pathway affects frataxin levels in vitro, supporting PPARgamma as a novel therapeutic target in FRDA.

Cerebellar ataxias.

PURPOSE OF REVIEW: The term 'cerebellar ataxias' encompasses the various cerebellar disorders encountered during daily practice. Patients exhibit a cerebellar syndrome and can also present with pigmentary retinopathy, extrapyramidal movement disorders, pyramidal signs, cortical symptoms (seizures, cognitive impairment/behavioural symptoms), and peripheral neuropathy. The clinical diagnosis of subtypes of ataxias is complicated by the salient overlap of the phenotypes between genetic subtypes. The identification of the causative mutations of many hereditary ataxias and the development of relevant animal models bring hope for effective therapies in neurodegenerative ataxias. RECENT FINDINGS: We describe the current classification of cerebellar ataxias and underline the recent discoveries in molecular pathogenesis. Cerebellar disorders can be divided into sporadic forms and inherited diseases. Inherited ataxias include autosomal recessive cerebellar ataxias, autosomal dominant cerebellar ataxias/spinocerebellar ataxia) and episodic ataxias, and X-linked ataxias. From a motor control point of view, the leading theories of ataxia are based on neural representations or 'internal models' to emulate fundamental natural processes such as body motion. SUMMARY: Recent molecular advances have direct implications for research and daily practice. We provide a framework for the diagnosis of ataxias. For the first time, the therapeutic agents under investigation are targeted to deleterious pathways.

Friedreich's Ataxia: from the (GAA)n repeat mediated silencing to new promising molecules for therapy.

Friedreich's ataxia (FRDA) is a neurodegenerative disease due to a pathological expansion of a GAA triplet repeat in the first intron of the FXN gene encoding for the mitochondrial protein frataxin. The expansion is responsible for most cases of FRDA through the formation of a nonusual B-DNA structure and heterochromatin conformation that determine a direct transcriptional silencing and the subsequent reduction in frataxin expression. Among other functions, frataxin is an iron chaperone central for the assembly of iron-sulfur clusters in mitochondria; its reduction is associated with iron accumulation in mitochondria, increased cellular sensitivity to oxidative stress and cell damage. There is, nowadays, no effective therapy for FRDA and current therapeutic strategies mainly act to slow down the consequences of frataxin deficiency. Therefore, drugs that are able to increase the amount of frataxin are excellent candidates for a rational approach to FRDA therapy. Recently, several drugs have been assessed for their ability to increase the amount of cellular frataxin, including human recombinant erythropoietin, histone deacetylase inhibitors, and the PPAR-gamma agonists.

Animal models of human cerebellar ataxias: a cornerstone for the therapies of the twenty-first century.

Cerebellar ataxias represent a group of disabling neurological disorders. Our understanding of the pathogenesis of cerebellar ataxias is continuously expanding. A considerable number of laboratory animals with neurological mutations have been reported and numerous relevant animal models mimicking the phenotype of cerebellar ataxias are becoming available. These models greatly help dissecting the numerous mechanisms of cerebellar dysfunction, a major step for the assessment of therapeutics targeting a given deleterious pathway and for the screening of old or newly synthesized chemical compounds. Nevertheless, differences between animal models and human disorders should not be overlooked and difficulties in terms of characterization should not be occulted. The identification of the mutations of many hereditary ataxias, the development of valuable animal models, and the recent identifications of the molecular mechanisms underlying cerebellar disorders represent a combination of key factors for the development of anti-ataxic innovative therapies. It is anticipated that the twenty-first century will be the century of effective therapies in the field of cerebellar ataxias. The animal models are a cornerstone to reach this goal.

PPAR-gamma agonist Azelaoyl PAF increases frataxin protein and mRNA expression: new implications for the Friedreich's ataxia therapy.

Friedreich's ataxia is a neurodegenerative disease due to frataxin deficiency, and thus, drugs increasing the frataxin amount are excellent candidates for therapy. By screening Gene Expression Omnibus profiles, we identified records showing a frataxin response to the peroxisome proliferator-activated receptors gamma (PPAR-gamma) agonist rosiglitazone. We decided to investigate the effect of the PPAR-gamma agonist Azelaoyl PAF on the frataxin protein and mRNA expression profile. We treated human neuroblastoma cells SKNBE and primary fibroblasts from skin biopsies from Friedreich's ataxia (FRDA) patients and healthy controls with the PPAR-gamma agonist Azelaoyl PAF. We show in this paper for the first time that Azelaoyl PAF significantly increases the intracellular frataxin levels by twofold in the neuroblastoma cell line SKNBE and fibroblasts from FRDA patients and that Azelaoyl PAF increases frataxin protein through a transcriptional mechanism. PPAR-gamma agonist Azelaoyl PAF increases both messenger RNA and protein levels of frataxin. We hypothesize that PPAR-gamma agonists could play a role in the treatment of FRDA, and our results offer the logical bases to further investigate the usefulness of this group of agents for the treatment of the FRDA.

Recombinant human erythropoietin increases frataxin protein expression without increasing mRNA expression.

Friedreich's ataxia is an autosomal recessive neurodegenerative disease that is due to the loss of function of the frataxin protein. The molecular basis of this disease is still a matter of debate and treatments have so far focused on managing symptoms. Drugs that can increase the amount of frataxin protein offer a possible therapy for the disease. One such drug is recombinant human erythropoietin (rhu-EPO). Here, we report the effects of rhu-EPO on frataxin mRNA and protein in primary fibroblast cell cultures derived from Friedreich's ataxia patients. We observed a slight but significant increase in the amount of frataxin protein. Interestingly, we did not observe any increase in the messenger RNA expression at any of the times and doses tested, suggesting that the regulatory effects of rhu-EPO on the frataxin protein was at the post-translational level. These findings could help the evaluation of the treatment with erythropoietin as a potential therapeutic agent for Friedreich's ataxia.

Friedreich's ataxia: past, present and future.

Friedreich's ataxia (FRDA) is an autosomal recessive inherited disorder characterized by progressive gait and limb ataxia, dysarthria, areflexia, loss of vibratory and position sense, and a progressive motor weakness of central origin. Additional features include hypertrophic cardiomyopathy and diabetes. Large GAA repeat expansions in the first intron of the FXN gene are the most common mutation underlying FRDA. Patients show severely reduced levels of a FXN-encoded mitochondrial protein called frataxin. Frataxin deficiency is associated with abnormalities of iron metabolism: decreased iron-sulfur cluster (ISC) biogenesis, accumulation of iron in mitochondria and depletion in the cytosol, enhanced cellular iron uptake. Some models have also shown reduced heme synthesis. Evidence for oxidative stress has been reported. Respiratory chain dysfunction aggravates oxidative stress by increasing leakage of electrons and the formation of superoxide. In vitro studies have demonstrated that Frataxin deficient cells not only generate more free radicals, but also show a reduced capacity to mobilize antioxidant defenses. The search for experimental drugs increasing the amount of frataxin is a very active and timely area of investigation. In cellular and in animal model systems, the replacement of frataxin function seems to alleviate the symptoms or even completely reverse the phenotype. Therefore, drugs increasing the amount of frataxin are attractive candidates for novel therapies. This review will discuss recent findings on FRDA pathogenesis, frataxin function, new treatments, as well as recent animal and cellular models. Controversial aspects are also discussed.

PGC-1alpha down-regulation affects the antioxidant response in Friedreich's ataxia.

BACKGROUND: Cells from individuals with Friedreich's ataxia (FRDA) show reduced activities of antioxidant enzymes and cannot up-regulate their expression when exposed to oxidative stress. This blunted antioxidant response may play a central role in the pathogenesis. We previously reported that Peroxisome Proliferator Activated Receptor Gamma (PPARgamma) Coactivator 1-alpha (PGC-1alpha), a transcriptional master regulator of mitochondrial biogenesis and antioxidant responses, is down-regulated in most cell types from FRDA patients and animal models. METHODOLOGY/PRINCIPAL FINDINGS: We used primary fibroblasts from FRDA patients and the knock in-knock out animal model for the disease (KIKO mouse) to determine basal superoxide dismutase 2 (SOD2) levels and the response to oxidative stress induced by the addition of hydrogen peroxide. We measured the same parameters after pharmacological stimulation of PGC-1alpha. Compared to control cells, PGC-1alpha and SOD2 levels were decreased in FRDA cells and did not change after addition of hydrogen peroxide. PGC-1alpha direct silencing with siRNA in control fibroblasts led to a similar loss of SOD2 response to oxidative stress as observed in FRDA fibroblasts. PGC-1alpha activation with the PPARgamma agonist (Pioglitazone) or with a cAMP-dependent protein kinase (AMPK) agonist (AICAR) restored normal SOD2 induction. Treatment of the KIKO mice with Pioglitazone significantly up-regulates SOD2 in cerebellum and spinal cord. CONCLUSIONS/SIGNIFICANCE: PGC-1alpha down-regulation is likely to contribute to the blunted antioxidant response observed in cells from FRDA patients. This response can be restored by AMPK and PPARgamma agonists, suggesting a potential therapeutic approach for FRDA.