Fragile X syndrome (FXS) is the most common genetic disorder. The main cause of FXS is the increase of CGG repeats in the 5' non-translated region of FMR1 gene encoding fragile X chromosome low intelligence protein (FMRP).An important feature of FXS is abnormal and active mRNA translation in the brain.FMRP is often considered an inhibitor of mRNA translation; some studies have reported that FMRP may enhance mRNA translation by binding to mRNA coding sequences (CDS) and inhibiting ribosomes from moving over mRNAs.The conflicting regulation of FMRP in target mRNA translation suggests that there may be several regulatory pathways involved in the regulation of mRNA translation, some of which may play a more decisive role in the pathology of FXS.
In response to these problems, Luo Cheng, a researcher at the Shanghai Institute of Pharmacy, Chinese Academy of Sciences, and Professor He Chuan of the University of Chicago (Nature Chem 2015, Cancer Cell 2023, Gut 2023), formed a joint team.This study demonstrated a pathway in which YTHDF1 translation function was regulated by FMRP phosphorylation in neurons. It was found that YTHDF1 could be used as a potential drug target for FXS treatment.
The researchers used Fmr1 knock-out and phosphorylation site mutation (S499A) in mouse neurons to find that unphosphorylated FMRP inhibited YTHDF1-mediated mRNA translation, which eliminated this inhibition and thus activated YTHDF1.The researchers then also observed YTHDF1 activation by lowering FMRP expression in HEK293T cells.Therefore, the researchers hypothesized that the expression level of FMRP protein and its phosphorylation play an important role in the regulation of YTHDF1 translation-related functions.Furthermore, the researchers studied the YTHDF1 interaction protein in YTHDF1 phase separation droplet by RNAase processing, and found that nonphosphorylation FMRP binds to YTHDF1 and inhibits YTHDF1 phase separation.To further demonstrate the relationship between YTHDF1 phase separation and its regulation of mRNA translation, the researchers constructed a series of YTHDF1 mutants.This result explains the high translation activity of YTHDF1 due to FMRP protein deficiency and suggests that inhibition of YTHDF1 may be a new strategy for treatment of FXS.
To further demonstrate that YTHDF1 is a potential mitigation target for FXS, the researchers conducted chemical intervention studies targeting YTHDF1.Based on the establishment of a high-throughput screening method, small molecule inhibitors were screened to obtain the active compound SAC of YTHDF1.SAC inhibits YTHDF1 phase separation and YTHDF1-based translation activity in nerve cells and specifically inhibits YTHDF1 target transcriptome translation in FXS-like organs (from reprogrammed induced pluripotent stem cell differentiation in FXS patients).At the same time, the same effect can be achieved by knocking down YTHDF1 in organoid.
In conclusion, this study reveals that inhibition of m6A "reader" YTHDF1 improves the regulatory mechanism and potential intervention effect of brittle X chromosome syndrome, and provides a new potential target for clinical treatment.The obtained small molecule inhibitor of YTHDF1 not only provides a tool for YTHDF1 functional research, but also provides a leading structure for drug development targeting YTHDF1.At the same time, this study also provides clues to the potential therapeutic effect of the important components of Salvia miltiorrhiza on complex diseases.
Professor He Chuan of the University of Chicago, Professor Luo Cheng of Shanghai Pharmaceutical Institute and Professor Jin Peng of Emory University are co-authors of the FXS paper.The research was supported by Academician Jiang Hualiang of Shanghai Institute of Pharmacy and funded by the National Science and Technology Innovation 2030 "brain science and brain like research", the National Key R&D Program, the Foundation Committee and the State Administration of Traditional Chinese Medicine.