HSP90 Inhibition Partially Rescues Alternative Splicing Dysregulation in Cell Models of Myotonic Dystrophy

Area of Science:

• Molecular Biology
• Genetics
• Pharmacology

Background:

• Myotonic dystrophy (DM) types 1 and 2 are genetic disorders caused by toxic RNA expansions.
• These expansions disrupt muscleblind-like (MBNL) protein function, leading to widespread alternative splicing errors.
• Currently, no disease-modifying treatments exist for DM.

Purpose of the Study:

• To identify compounds that can correct the splicing dysregulation in DM.
• To investigate the role of heat shock protein 90 (HSP90) in DM pathogenesis and potential therapeutic targeting.

Main Methods:

• A medium-throughput splicing screen of 1,584 compounds using DM1 patient fibroblasts.
• Utilized RT-PCR, siRNA knockdown, RT-qPCR, immunoblotting, and RNA fluorescence in situ hybridization.
• Tested HSP90 inhibitors (macbecin II, CCT018159) in DM cell and myotube models.

Main Results:

• Identified macbecin II, an HSP90 inhibitor, as a compound that rescues splicing defects in DM1 models.
• HSP90 inhibition increased MBNL1/2 transcript levels, MBNL2 protein, and reduced toxic RNA foci in DM1 cells.
• HSP90 inhibitors also corrected mis-splicing in DM2 myotubes, with specific isoform knockdown yielding varied effects.

Conclusions:

• HSP90 is identified as a key modifier of RNA toxicity and alternative splicing in myotonic dystrophy.
• HSP90 inhibitors demonstrate therapeutic potential for both DM1 and DM2 by correcting underlying splicing defects.
• Further investigation of HSP90-targeted therapies for DM is warranted.