Alleviating GAA Repeat Induced Transcriptional Silencing of the Friedreich's Ataxia Gene During Somatic Cell Reprogramming.
Friedreich's ataxia (FRDA) is the most common autosomal recessive ataxia. This severe neurodegenerative disease is caused by an expansion of guanine-adenine-adenine (GAA) repeats located in the first intron of the frataxin (FXN) gene, which represses its transcription. Although transcriptional silencing is associated with heterochromatin-like changes in the vicinity of the expanded GAAs, the exact mechanism and pathways involved in transcriptional inhibition are largely unknown. As major remodeling of the epigenome is associated with somatic cell reprogramming, modulating chromatin modification pathways during the cellular transition from a somatic to a pluripotent state is likely to generate permanent changes to the epigenetic landscape. We hypothesize that the epigenetic modifications in the vicinity of the GAA repeats can be reversed by pharmacological modulation during somatic cell reprogramming. We reprogrammed FRDA fibroblasts into induced pluripotent stem cells (iPSCs) in the presence of various small molecules that target DNA methylation and histone acetylation and methylation. Treatment of FRDA iPSCs with two compounds, sodium butyrate (NaB) and Parnate, led to an increase in FXN expression and correction of repressive marks at the FXN locus, which persisted for several passages. However, prolonged culture of the epigenetically modified FRDA iPSCs led to progressive expansions of the GAA repeats and a corresponding decrease in FXN expression. Furthermore, we uncovered that differentiation of these iPSCs into neurons also results in resilencing of the FXN gene. Taken together, these results demonstrate that transcriptional repression caused by long GAA repeat tracts can be partially or transiently reversed by altering particular epigenetic modifications, thus revealing possibilities for detailed analyses of silencing mechanism and development of new therapeutic approaches for FRDA.
1 Department of Molecular Carcinogenesis, Center for Cancer Epigenetics, University of Texas MD Anderson Cancer Center , Smithville, Texas.
Urszula
U
Polak
2 Department of Biochemistry and Molecular Genetics, UAB Stem Cell Institute, University of Alabama at Birmingham , Birmingham, Alabama.
Yanjie
Y
Li
2 Department of Biochemistry and Molecular Genetics, UAB Stem Cell Institute, University of Alabama at Birmingham , Birmingham, Alabama.
Jill Sergesketter
JS
Butler
2 Department of Biochemistry and Molecular Genetics, UAB Stem Cell Institute, University of Alabama at Birmingham , Birmingham, Alabama.|3 Department of Molecular Biomedicine, Institute of Bioorganic Chemistry , Polish Academy of Sciences, Poznan, Poland .
Marek
M
Napierala
D020148:Butyric Acid / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects; D019070:Cell Lineage / Q000187:drug effects; D002478:Cells, Cultured; D065150:Cellular Reprogramming / Q000187:drug effects / Q000235:genetics*; D002843:Chromatin / Q000378:metabolism; D044127:Epigenesis, Genetic / Q000187:drug effects; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D005621:Friedreich Ataxia / Q000235:genetics*; D020868:Gene Silencing / Q000187:drug effects; D056426:Genetic Loci; D006801:Humans; D057026:Induced Pluripotent Stem Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D033862:Iron-Binding Proteins / Q000235:genetics*; D009474:Neurons / Q000166:cytology / Q000187:drug effects; D014158:Transcription, Genetic / Q000187:drug effects; D014191:Tranylcypromine / Q000494:pharmacology; D019680:Trinucleotide Repeat Expansion / Q000235:genetics*; D000096923:Frataxin
D020148:Butyric Acid; D002843:Chromatin; D033862:Iron-Binding Proteins; D014191:Tranylcypromine; D000096923:Frataxin
FXN silencing; Friedreich's ataxia; expanded GAA repeats; induced pluripotent stem cells; somatic cell reprogramming