AUTHOR=Fang Minggang , Deibler Sara K. , Krishnamurthy Pranathi Meda , Wang Feng , Rodriguez Paola , Banday Shahid , Virbasius Ching-Man , Sena-Esteves Miguel , Watts Jonathan K. , Green Michael R. 

TITLE=EZH2 inhibition reactivates epigenetically silenced FMR1 and normalizes molecular and electrophysiological abnormalities in fragile X syndrome neurons

JOURNAL=Frontiers in Neuroscience

VOLUME=18

YEAR=2024

URL=https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2024.1348478

DOI=10.3389/fnins.2024.1348478

ISSN=1662-453X

ABSTRACT=<p>Fragile X Syndrome (FXS) is a neurological disorder caused by epigenetic silencing of the <italic>FMR1</italic> gene. Reactivation of <italic>FMR1</italic> is a potential therapeutic approach for FXS that would correct the root cause of the disease. Here, using a candidate-based shRNA screen, we identify nine epigenetic repressors that promote silencing of <italic>FMR1</italic> in FXS cells (called <italic>FMR1</italic> Silencing Factors, or <italic>FMR1</italic>- SFs). Inhibition of <italic>FMR1</italic>-SFs with shRNAs or small molecules reactivates <italic>FMR1</italic> in cultured undifferentiated induced pluripotent stem cells, neural progenitor cells (NPCs) and post-mitotic neurons derived from FXS patients. One of the <italic>FMR1</italic>-SFs is the histone methyltransferase EZH2, for which an FDA-approved small molecule inhibitor, EPZ6438 (also known as tazemetostat), is available. We show that EPZ6438 substantially corrects the characteristic molecular and electrophysiological abnormalities of cultured FXS neurons. Unfortunately, EZH2 inhibitors do not efficiently cross the blood-brain barrier, limiting their therapeutic use for FXS. Recently, antisense oligonucleotide (ASO)-based approaches have been developed as effective treatment options for certain central nervous system disorders. We therefore derived efficacious ASOs targeting EZH2 and demonstrate that they reactivate <italic>FMR1</italic> expression and correct molecular and electrophysiological abnormalities in cultured FXS neurons, and reactivate <italic>FMR1</italic> expression in human FXS NPCs engrafted within the brains of mice. Collectively, our results establish EZH2 inhibition in general, and EZH2 ASOs in particular, as a therapeutic approach for FXS.</p>