A window into intracellular events in myositis through subcellular proteomics

Area of Science:

• Muscle Biology
• Proteomics
• Molecular Medicine

Background:

• Idiopathic inflammatory myopathies (IIM) are complex muscle disorders with unknown causes.
• Mitochondrial dysfunction and protein aggregation are implicated in skeletal muscle degeneration in IIM.
• The precise molecular pathways driving protein aggregation in skeletal muscle remain unclear.

Purpose of the Study:

• To investigate molecular alterations in skeletal muscle of patients with idiopathic inflammatory myopathies (IIM).
• To identify novel protein changes in various cellular compartments of affected muscle tissue.
• To explore the role of mitochondrial dysfunction and protein aggregation in IIM pathogenesis.

Main Methods:

• Isolation of membrane-bound organelles (nuclei, mitochondria, ER, Golgi, plasma membrane) from muscle biopsies.
• Global proteomic analysis using Orbitrap Fusion mass spectrometry.
• Unsupervised clustering of proteomic data to differentiate between normal, mitochondrial myopathy, and IIM muscle samples.

Main Results:

• Confirmed known protein alterations and identified numerous new ones in IIM skeletal muscle.
• Found differential expression of nuclear proteins involved in cell division, transcription, and RNA regulation.
• Observed altered expression of ER/Golgi proteins related to protein folding and trafficking, and mitochondrial proteins in energy metabolism.
• Identified changes in the cytoskeletal and contractile machinery of muscle.

Conclusions:

• Molecular alterations in IIM skeletal muscle extend beyond cytosolic protein aggregates.
• Significant changes occur in nuclear, mitochondrial, and membrane-bound compartments.
• These findings provide a broader understanding of the molecular pathology in IIM.