Ascorbic Acid Ameliorates Molecular and Developmental Defects in Human-Induced Pluripotent Stem Cell and Cerebral Organoid Models of Fragile X Syndrome

Fragile X Syndrome (FX) is the most common form of inherited cognitive impairment and falls under the broader category of Autism Spectrum Disorders (ASD). FX is caused by a CGG trinucleotide repeat expansion in the non-coding region of the X-linked <i>Fragile X Messenger Ribonucleoprotein 1</i> (<i>FMR1</i>) gene, leading to its hypermethylation and epigenetic silencing. Animal models of FX rely on the deletion of the <i>Fmr1</i> gene, which fails to replicate the epigenetic silencing mechanism of the <i>FMR1</i> gene observed in human patients. Human stem cells carrying FX repeat expansions have provided a better understanding of the basis of epigenetic silencing of <i>FMR1</i>. Previous studies have found that 5-Azacytidine (5Azac) can reverse this methylation; however, 5Azac can be toxic, which may limit its therapeutic potential. Here, we show that the dietary factor Ascorbic Acid (AsA) can reduce DNA methylation in the <i>FMR1</i> locus and lead to an increase in <i>FMR1</i> gene expression in FX iPSCs and cerebral organoids. In addition, AsA treatment rescued neuronal gene expression and morphological defects observed in FX iPSC-derived cerebral organoids. Hence, we demonstrate that the dietary co-factor AsA can partially revert the molecular and morphological defects seen in human FX models in vitro. Our findings have implications for the development of novel therapies for FX in the future.