# Reactivation of Epigenetically Silenced FMR1 as a Therapeutic Approach for Fragile X Syndrome

> **NIH NIH R01** · UNIV OF MASSACHUSETTS MED SCH WORCESTER · 2021 · $418,750

## Abstract

Fragile X Syndrome (FXS) is the most common inherited form of mental insufficiency and most prevalent
monogenic cause of autism, occurring in ~1 in 4,000 males and ~1 in 5,000 females. The disease is caused by
a CGG repeat expansion in the 5' untranslated region of the X-linked FMR1 gene that results in epigenetic
silencing of FMR1. As a consequence, the product of FMR1, the fragile X mental retardation protein (FMRP), is
not produced. FMRP is an RNA-binding protein that normally represses mRNA translation in the brain; in its
absence, protein synthesis is excessive, which results in disease pathology. Reactivation of epigenetically
silenced FMR1 is a promising new therapeutic approach for FXS that aims to correct the root cause of the
disease rather than a secondary, downstream consequence of the FMRP deficiency. In preliminary
experiments my laboratory has performed a small-scale candidate-based screen to identify eight repressive
epigenetic regulators that promote silencing of FMR1 in FXS cells (called FMR1 Silencing Factors, or FMR1-
SFs). Inhibition of FMR1-SFs by short hairpin RNAs (shRNAs) or small molecules reactivates epigenetically
silenced FMR1 in undifferentiated induced pluripotent stem cells, neural progenitor cells, and post-mitotic
neurons derived from FXS patients. These preliminary results provide important proof-of-concept regarding the
feasibility of reactivating the epigenetically silenced FMR1 gene as a therapeutic approach for FXS. In this
application we propose experiments using large-scale candidate-based and unbiased loss-of-function screens
to identify additional FMR1-SFs, some of which may provide more desirable targets for the development of
drugs that function by reactivating FMR1. To determine whether the level of FMR1 reactivation obtained with
shRNA and small molecule FMR1-SF inhibitors is likely to be therapeutic, we will undertake several
complementary approaches. First, we will determine the minimal level of FMRP required to normalize the well-
characterized transcriptional, translational and morphological abnormalities of FXS neurons. In these
experiments we will ectopically express FMRP at varying levels and analyze the effect on FXS neuronal
phenotypes. Second, we will determine whether the level of FMR1 reactivation we obtain with shRNA and
small molecule inhibitors of the FMR1-SFs we identify is sufficient to normalize dysfunctional phenotypes of
human FXS neurons. In summary, the results of the proposed experiments will: (1) identify new targets whose
inhibition leads to FMR1 reactivation, (2) determine the minimal levels of FMRP required to correct FXS
neuronal dysfunctions, and (3) test whether FMR1 reactivation by shRNA and small molecule FMR1-SF
inhibitors can normalize dysfunctional phenotypes of human FXS neurons. We believe the results of the
experiments proposed in this application will have a major impact on the field of FXS therapeutics and have the
potential to lead to development of a new clas...

## Key facts

- **NIH application ID:** 10217959
- **Project number:** 5R01MH113874-05
- **Recipient organization:** UNIV OF MASSACHUSETTS MED SCH WORCESTER
- **Principal Investigator:** MICHAEL R GREEN
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $418,750
- **Award type:** 5
- **Project period:** 2017-07-01 → 2022-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10217959

## Citation

> US National Institutes of Health, RePORTER application 10217959, Reactivation of Epigenetically Silenced FMR1 as a Therapeutic Approach for Fragile X Syndrome (5R01MH113874-05). Retrieved via AI Analytics 2026-05-26 from https://api.ai-analytics.org/grant/nih/10217959. Licensed CC0.

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