Heterogeneous muscle gene expression patterns in patients with massive rotator cuff tears

Area of Science:

• Orthopedics
• Muscle Biology
• Molecular Pathology

Background:

• Rotator cuff (RC) disease is characterized by muscle composition and function changes.
• Muscle atrophy and degeneration are observed in advanced RC disease.
• The link between gene expression and RC muscle pathology is not well understood due to limited correlation studies.

Purpose of the Study:

• To investigate the relationship between tissue composition and gene expression in RC muscle biopsies.
• To analyze gene expression patterns in patients undergoing reverse shoulder arthroplasty (RSA).

Main Methods:

• Analyzed gene expression (myogenesis, atrophy, apoptosis, adipogenesis, metabolism, inflammation, fibrosis) in 40 RC muscle biopsies (31 RSA, 9 control).
• Used linear regression to correlate gene expression with histological tissue composition.
• Employed hierarchical clustering and principal component analysis (PCA) to identify sample clusters and differences.

Main Results:

• Muscle fraction was the only histological parameter significantly correlated with gene expression.
• Samples with muscle tissue clustered separately from those without muscle.
• Identified two subgroups within RSA biopsies suggesting distinct disease phases: one with atrophy/regeneration markers, another similar to controls or muscle-absent samples.

Conclusions:

• Muscle presence is a key determinant of gene expression profiles in RC disease.
• The study provides context for interpreting gene expression in degenerating muscle.
• Findings suggest distinct stages of human rotator cuff disease progression.