RAN Translation Regulated by Muscleblind Proteins in Myotonic Dystrophy Type 2

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• Microsatellite-expansion diseases often feature RNA foci and repeat-associated non-translation (RAN) proteins.
• Myotonic dystrophy type 2 (DM2) is a multisystemic disorder primarily attributed to RNA gain-of-function effects.

Purpose of the Study:

• To investigate the mechanistic connection between RNA foci and RAN proteins in DM2.
• To explore the role of RAN protein toxicity in DM2 pathogenesis.

Main Methods:

• Analysis of DM2 autopsy brains to detect and localize RAN proteins (LPAC and QAGR).
• Cellular toxicity assays to assess the impact of LPAC and QAGR.
• Correlation analysis between RNA foci, MBNL1 sequestration, and LPAC expression.

Main Results:

• DM2 CCTG⋅CAGG expansion produces sense (LPAC) and antisense (QAGR) RAN proteins.
• LPAC localizes to gray matter (neurons, astrocytes, glia), while QAGR accumulates in white matter.
• LPAC and QAGR proteins exhibit cellular toxicity independent of RNA gain-of-function.
• LPAC expression is inversely correlated with RNA foci and MBNL1 sequestration of CCUG transcripts.

Conclusions:

• A model is proposed where excess expansion RNAs overwhelm RNA-binding protein (RBP) sequestration, leading to cytoplasmic export and RAN translation.
• RAN protein toxicity is a significant factor in DM2, potentially independent of RNA gain-of-function.
• Understanding RAN translation provides new insights into DM2 pathophysiology and potential therapeutic targets.