Study of the epigenetic regulation of HAX-1 in Friedreich's ataxia

F the deficiency of the mitochondrial protein Frataxin (FXN), as a result of a GAA triplet expansion mutation. Frataxin is required for cell survival and is involved in iron metabolism, with proposed function in iron-sulfur clusters biogenesis, heme biosynthesis and redox regulation. Its deficiency gives rise to a complex pathophysiology that affects not only the nervous system but also cardiac function. Two thirds of patients develop hypertrophic cardiomyopathy that often progresses to heart failure and represents the most common cause of mortality. For this reason, there is a growing need for biological markers to evaluate cardiac disease progression and measure the response of potential therapeutic interventions. On the basis of a microarray analysis, we have previously described that low levels of FXN correspond to reduced levels of HCLS-1 associated protein X-1 (HAX-1), an ubiquitously expressed protein which plays a key role in cardiomyocytes survival, protects cells from apoptosis and promotes cell migration. To date, the specific mechanism acting in regulating frataxin and HAX-1 expression is still lacking. Epigenetic modifications, such as microRNA, might play an important role in the disease. Several microRNAs have yet been described as modulators of frataxin and putative biomarkers for cardiomyopathy. Here, a miRNA PCR-array analysis was carried out on plasma samples of early-, intermediate- and late-onset FRDA patients, defining a set of differentially expressed miRNAs. HsamiR223-3p is the only one shared between the three FRDA patient groups and appears upregulated in all of them. The upregulation of hsa-miR223-3p was further validated in all enrolled patients and, 7 using a ROC curve analysis, was quantified the predictive value of circulating hsa-miR223-3p for FRDA. Interestingly, we report a significant positive correlation between hsa-miR223-3p expression and cardiac parameters in typical FRDA patients. Moreover, in silico analyses also indicated that HAX-1 is a target gene of hsa-miR223-3p and a significant negative correlation between hsamiR223-3p expression and HAX-1 at mRNA and protein level was observed in PBMCs from FRDA patients. Accordingly, overexpression of hsa-miR223-3p negatively regulates HAX-1 in cardiomyocytes and neuronal cells, which are critically affected cell types in FRDA. This study was aimed to investigate if miRNAs could be involved as a specific epigenetic mechanism that coordinates FXN and HAX-1 expression, which leads to the identification of hsa-miR223-3p. The correlation of circulating levels of hsa-miR223-3p with clinical features, along with its capacity to discriminate patients from control individuals, provide the basis for a potential role of this miRNA as non-invasive epigenetic biomarker for FRDA. In this regard, further investigations in a larger cohort is of crucial importance to validate its potential as a diagnostic tool and understand the mechanisms underlying the differential modulation on HAX-1 and FXN expression.