Solid-State NMR Spectroscopy Investigation of Structural Changes of Mechanically Strained Mouse Tail Tendons

Structural tissues like tendon are subjected to repeated tensile strains in vivo and excessive strains cause irreversible changes to the tissue. Large strains affect the molecular structure and organization of the extracellular matrix, and these are the parameters that drive cell behavior, including tissue repair. Here we describe a method to perform solid-state NMR spectroscopy on in situ strained tissue samples under magic-angle spinning to achieve high-resolution NMR spectra while maintaining the tissue's native hydration state. The changes observed in the NMR spectra are interpreted using quantum mechanics molecular mechanics (QM/MM) chemical shift calculations on strained collagen triple-helix structures and consideration of changes in the distribution of molecular orientations between strained and relaxed mechanical states. We demonstrate that our tissue strain method in combination with spectral simulations can detect changes in collagen organization between tendons loaded to plastic deformation and subsequent structural relaxation in the unloaded state.