Mature murine supraspinatus tendons demonstrate regional differences in multiscale structure, function and gene...

Area of Science:

• Biomedical Engineering
• Musculoskeletal Biology
• Connective Tissue Research

Background:

• Tendon structure is hierarchical, enabling muscle-to-bone load transmission.
• Site-specific mechanical loading influences tendon structure, composition, and remodeling during development and healing.
• Previous studies noted regional differences in collagen fibril responses to mechanical loading in mouse supraspinatus tendons.

Purpose of the Study:

• To comprehensively investigate site-specific differences in hierarchical structure, function, and gene expression within the mouse supraspinatus tendon.
• To link multiscale structural, functional, and gene expression characteristics between the tendon's insertion and midsubstance regions.

Main Methods:

• Harvesting supraspinatus tendons from day 150 wild-type C57BL/6 mice.
• Employing regional mechanics testing, histology, transmission electron microscopy (TEM), and quantitative polymerase chain reaction (qPCR).

Main Results:

• The midsubstance exhibited a higher modulus and greater collagen fiber realignment than the insertion region.
• Histology revealed increased cellularity and rounder cells at the insertion site.
• TEM showed a shift towards smaller collagen fibril diameters at the insertion.
• Gene expression analysis identified differentially expressed genes, with distinct regional clustering via principal component analysis.

Conclusions:

• Significant regional heterogeneity exists in the mouse supraspinatus tendon's structure, mechanics, and gene expression.
• These site-specific differences are critical for understanding tendon pathology, injury, and repair mechanisms.
• Findings provide a foundation for future research into tendon healing and therapeutic strategies.