Antonella Monticelli

Friedreich's Ataxia: Autosomal Recessive Disease Caused by an Intronic GAA Triplet Repeat Expansion

Friedreichs ataxia (FRDA) is an autosomal recessive, degenerative disease that involves the central and peripheral nervous systems and the heart. A gene, X25, was identified in the critical region for the FRDA locus on chromosome 9q13. The gene encodes a 210-amino acid protein, frataxin, that has homologs in distant species such as Caenorhabditis elegans and yeast. A few FRDA patients were found to have point mutations in X25, but the majority were homozygous for an unstable GAA trinucleotide expansion in the first X25 intron.

Increased BDNF Promoter Methylation in the Wernicke Area of Suicide Subjects

CONTEXT Brain-derived neurotrophic factor (BDNF) plays a pivotal role in the pathophysiology of suicidal behavior and BDNF levels are decreased in the brain and plasma of suicide subjects. So far, the mechanisms leading to downregulation of BDNF expression are poorly understood. OBJECTIVES To test the hypothesis that alterations of DNA methylation could be involved in the dysregulation of BDNF gene expression in the brain of suicide subjects. DESIGN Three independent quantitative methylation techniques were performed on postmortem samples of brain tissue. BDNF messenger RNA levels were determined by quantitative real-time polymerase chain reaction. SETTING Academic medical center. PATIENTS OR OTHER PARTICIPANTS Forty-four suicide completers and 33 nonsuicide control subjects of white ethnicity. MAIN OUTCOME MEASURES The DNA methylation degree at BDNF promoter IV and the genome-wide DNA methylation levels in the brains Wernicke area. RESULTS Postmortem brain samples from suicide subjects showed a statistically significant increase of DNA methylation at specific CpG sites in BDNF promoter/exon IV compared with nonsuicide control subjects (P < .001). Most of the CpG sites lying in the -300/+500 region, on both strands, had low or no methylation, with the exception of a few sites located near the transcriptional start site that had differential methylation, while genome-wide methylation levels were comparable among the subjects. The mean methylation degree at the 4 CpG sites analyzed by pyrosequencing was always less than 12.9% in the 33 nonsuicide control subjects, while in 13 of 44 suicide victims (30%), the mean methylation degree ranged between 13.1% and 34.2%. Higher methylation degree corresponded to lower BDNF messenger RNA levels. CONCLUSIONS BDNF promoter/exon IV is frequently hypermethylated in the Wernicke area of the postmortem brain of suicide subjects irrespective of genome-wide methylation levels, indicating that a gene-specific increase in DNA methylation could cause or contribute to the downregulation of BDNF expression in suicide subjects. The reported data reveal a novel link between epigenetic alteration in the brain and suicidal behavior.

A New Locus for Autosomal Recessive Hereditary Spastic Paraplegia Maps to Chromosome 16q24.3

Hereditary spastic paraplegia is a genetically and phenotypically heterogeneous disorder. Both pure and complicated forms have been described, with autosomal dominant, autosomal recessive, and X-linked inheritance. Various loci (SPG1-SPG6) associated with this disorder have been mapped. Here, we report linkage analysis of a large consanguineous family affected with autosomal recessive spastic paraplegia with age at onset of 25-42 years. Linkage analysis of this family excluded all previously described spastic paraplegia loci. A genomewide linkage analysis showed evidence of linkage to chromosome 16q24.3, with markers D16S413 (maximum LOD score 3.37 at recombination fraction [theta] of .00) and D16S303 (maximum LOD score 3.74 at straight theta=.00). Multipoint analysis localized the disease gene in the most telomeric region, with a LOD score of 4.2. These data indicate the presence of a new locus linked to pure recessive spastic paraplegia, on chromosome 16q24.3, within a candidate region of 6 cM.

Progressive gaa expansions in dorsal root ganglia of Friedreich's ataxia patients

Friedreichs ataxia patients are homozygous for expanded alleles of a GAA triplet‐repeat sequence in the FXN gene. Patients develop progressive ataxia due to primary neurodegeneration involving the dorsal root ganglia (DRGs). The selective neurodegeneration is due to the sensitivity of DRGs to frataxin deficiency; however, the progressive nature of the disease remains unexplained. Our objective was to test whether the expanded GAA triplet‐repeat sequence undergoes further expansion in DRGs as a possible mechanism underlying the progressive pathology seen in patients.

PGC-1alpha Down-Regulation Affects the Antioxidant Response in Friedreich's Ataxia

Background Cells from individuals with Friedreichs 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 (PPARγ) Coactivator 1-alpha (PGC-1α), 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-1α. Compared to control cells, PGC-1α and SOD2 levels were decreased in FRDA cells and did not change after addition of hydrogen peroxide. PGC-1α direct silencing with siRNA in control fibroblasts led to a similar loss of SOD2 response to oxidative stress as observed in FRDA fibroblasts. PGC-1α activation with the PPARγ 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-1α 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 PPARγ agonists, suggesting a potential therapeutic approach for FRDA.

DNA methylation in intron 1 of the frataxin gene is related to GAA repeat length and age of onset in Friedreich ataxia patients

Background: The most frequent mutation of Friedreich ataxia (FRDA) is the abnormal expansion of a GAA repeat located within the first intron of FXN gene. It is known that the length of GAA is directly correlated with disease severity. The effect of mutation is a severe reduction of mRNA. Recently, a link among aberrant CpG methylation, chromatin organisation and GAA repeat was proposed. Methods: In this study, using pyrosequencing technology, we have performed a quantitative analysis of the methylation status of five CpG sites located within the region upstream of GAA repeat, in 67 FRDA patients. Results: We confirm previous observation about differences in the methylation degree between FRDA individuals and controls. We showed a direct correlation between CpG methylation and triplet expansion size. Significant differences were found for each CpG tested (ANOVA p<0.001). These differences were largest for CpG1 and CpG2: 84.45% and 76.80%, respectively, in FRDA patients compared to 19.65% and 23.34% in the controls. Most importantly, we found a strong inverse correlation between CpG2 methylation degree and age of onset (Spearman’s ρ  =  −0.550, p<0.001). Conclusion: Because epigenetic changes may cause or contribute to gene silencing, our data may have relevance for the therapeutic approach to FRDA. Since the analysis can be performed in peripheral blood leucocytes (PBL), evaluation of the methylation status of specific CpG sites in FRDA patients could be a convenient biomarker.

A novel mutation in SACS gene in a family from southern Italy

A form of autosomal recessive spastic ataxia (ARSACS) has been described in the Charlevoix and Saguenay regions of Quebec. So far a frameshift and a nonsense mutation have been identified in the SACS gene. The authors report a new mutation (1859insC), leading to a frameshift with a premature termination of the gene product sacsin, in two sisters from consanguineous parents. The phenotype is similar to previously described patients with ARSACS.

Real time PCR quantification of frataxin mRNA in the peripheral blood leucocytes of Friedreich ataxia patients and carriers

The most common causative mutation of Friedreich ataxia (FRDA) is the unstable hyperexpansion of an intronic GAA triplet repeat that impairs frataxin transcription. Using real time quantitative PCR, we showed that FRDA patients had residual levels of frataxin mRNA ranging between 13% and 30% and that FRDA carriers had about 40% of that of controls. Asymptomatic carriers also showed reduced frataxin mRNA levels. We found an inverse correlation between the number of GAA repeats and frataxin mRNA levels. Real-time quantitative PCR may represent an alternative assay for FRDA molecular diagnosis.

The level of thyroglobulin mRNA is regulated by TSH both in vitro and in vivo

We have studied the effect of thyrotropin on the intracellular concentration of thyroglobulin and of its mRNA both in a differentiated rat thyroid cell line and in the rat thyroid in vivo. Our data demonstrate that the absence of thyrotropin causes a two fold decrease of both thyroglobulin and of its mRNA suggesting that thyroglobulin synthesis in thyroid cells is 50% constitutive.

Extra-mitochondrial localisation of frataxin and its association with IscU1 during enterocyte-like differentiation of the human colon adenocarcinoma cell line Caco-2.

Friedreichs ataxia is a recessive neurodegenerative disease due to insufficient expression of the mitochondrial protein frataxin. Although it has been shown that frataxin is involved in the control of intracellular iron metabolism, by interfering with the mitochondrial biosynthesis of proteins with iron/sulphur (Fe/S) clusters its role has not been well established. We studied frataxin protein and mRNA expression and localisation during cellular differentiation. We used the human colon adenocarcinoma cell line Caco-2, as it is considered a good model for intestinal epithelial differentiation and the study of intestinal iron metabolism. Here we report that the protein, but not the mRNA frataxin levels, increase during the enterocyte-like differentiation of Caco-2 cells, as well as in in-vivo-differentiated enterocytes at the upper half of the crypt-villus axis. Furthermore, subcellular fractionation and double immunostaining, followed by confocal analysis, reveal that frataxin localisation changes during Caco-2 cell differentiation. In particular, we found an extramitochondrial localisation of frataxin in differentiated cells. Finally, we demonstrate a physical interaction between extramitochondrial frataxin and IscU1, a cytoplasmic isoform of the human Fe/S cluster assembly machinery. Based on our data, we postulate that frataxin could be involved in the biosynthesis of iron-sulphur proteins not only within the mitochondria, but also in the extramitochondrial compartment. These findings might be of relevance for the understanding of both the pathogenesis of Friedreichs ataxia and the basic mechanism of Fe/S cluster biosynthesis.