Muscle atrophy after ACL reconstruction involves molecular mechanisms beyond unloading

Area of Science:

• Muscle physiology
• Molecular biology
• Bioinformatics

Background:

• Anterior cruciate ligament reconstruction (ACLR) often results in significant muscle atrophy and weakness that hinders rehabilitation.
• The precise contribution of disuse (limb unloading) to early muscle pathology following ACLR is not fully understood.

Purpose of the Study:

• To compare the early transcriptional responses to disuse versus ACLR in skeletal muscle.
• To differentiate between genes affected by unloading alone and those specifically altered by ACLR.

Main Methods:

• Analysis of publicly available RNA-sequencing datasets from vastus lateralis muscle biopsies.
• Comparison of gene expression profiles from limbs after ACLR and unilateral lower limb suspension (ULLS) against matched control limbs.
• Bioinformatic analyses (intersection and interaction) to identify differentially expressed genes (DEGs).

Main Results:

• Substantial divergence in transcriptomic responses between ACLR and ULLS, despite similar unloading periods.
• Only 16% of DEGs were common to both conditions; ACLR induced over 1,000 more DEGs than ULLS.
• ACLR uniquely showed reduced extracellular matrix (ECM) remodeling and increased expression of denervation-responsive genes.

Conclusions:

• Limb unloading contributes only modestly to the early muscle transcriptomic changes after ACLR.
• ACLR elicits distinct molecular responses beyond disuse, including altered ECM remodeling and denervation signaling.
• Identifying ACLR-specific molecular pathways is crucial for understanding muscle atrophy pathophysiology and improving functional recovery.