Collagen is a key structural protein in the extracellular matrix of many tissues. It provides biological tissues with tensile mechanical strength and is enzymatically cleaved by a class of matrix metalloproteinases (MMPs) known as collagenases. Collagen enzymatic kinetics has been well characterized in solubilized, gel and reconstituted forms. However limited information exists on enzyme degradation of structurally intact collagen fibers and, more important, on the effect of mechanical deformation on collagen cleavage. We studied the degradation of native rat tail tendon fibers by collagenase after the fibers were mechanically elongated to strains of ε = 1-10%. After the fibers were elongated and the stress allowed to relax, the fiber was immersed in Clostridium histolyticum collagenase and the decrease in stress (σ) monitored as a means of calculating the rate of enzyme cleavage of the fiber. An enzyme mechanokinetic (EMK) relaxation function TE(ε) in sec-1 was calculated from the linear stress-time response during fiber cleavage, where TE(ε) corresponds to the zero-order Michaelis-Menten enzyme-substrate kinetic response. The EMK relaxation function TE(ε) was found to decrease with applied strain at a rate of ~9% per percent strain, with complete inhibition of collagen cleavage predicted to occur at a strain of ~11%. However, comparison of the EMK response (TE vs ε) to collagen’s stress-strain response (σ vs ε) suggested the possibility of three different EMK responses; (1) constant TE(ε) within the toe region (ε<3%), (2) a rapid decrease (~50%) at the transition of the toe-to-heel region (ε≅3%) followed by (3) a constant value throughout the heel (ε=3 to 5%) and linear (ε=5 to 10%) regions. This observation suggests that the mechanism for the strain-dependent inhibition of enzyme cleavage of the collagen triple helix may be by a conformational change in the triple helix since the decrease in TE(ε) appeared concomitant with stretching of the collagen molecule.

Molecular mechanisms leading to pressure ulcer development are scarce in spite of high mortality of patients. Development of pressure ulcers that is initially observed as deep tissue injury is multifactorial. We postulate that biomechanical forces and inflammasome activation, together with ischemia and aging, may play a role in pressure ulcer development. To test this we used a newly-developed bio-mechanical model in which ischemic young and aged human skin was subjected to a constant physiological compressive stress (load) of 300 kPa (determined by pressure plate analyses of a person in a reclining position) for 0.5–4 hours. Collagen orientation was assessed using polarized light, whereas inflammasome proteins were quantified by immunoblotting. Loaded skin showed marked changes in morphology and NLRP3 inflammasome protein expression. Sub-epidermal separations and altered orientation of collagen fibers were observed in aged skin at earlier time points. Aged skin showed significant decreases in the levels of NLRP3 inflammasome proteins. Loading did not alter NLRP3 inflammasome proteins expression in aged skin, whereas it significantly increased their levels in young skin. We conclude that aging contributes to rapid morphological changes and decrease in inflammasome proteins in response to tissue damage, suggesting that a decline in the innate inflammatory response in elderly skin could contribute to pressure ulcer pathogenesis. Observed morphological changes suggest that tissue damage upon loading may not be entirely preventable. Furthermore, newly developed model described here may be very useful in understanding the mechanisms of deep tissue injury that may lead towards development of pressure ulcers.

Tumor metastases and epithelial to mesenchymal transition (EMT) involve tumor cell invasion and migration through the dense collagen-rich extracellular matrix surrounding the tumor. Little is known about the mechanobiological mechanisms involved in this process, nor the role of the mechanical forces generated by the cells in their effort to invade and migrate through the stroma. In this paper we propose a new fundamental mechanobiological mechanism involved in cancer growth and metastasis, which can be both protective or destructive depending on the magnitude of the forces generated by the cells. This new mechanobiological mechanism directly challenges current paradigms that are focused mainly on biological and biochemical mechanisms associated with tumor metastasis. Our new mechanobiological mechanism describes how tumor expansion generates mechanical forces within the stroma to not only resist tumor expansion but also inhibit or enhance tumor invasion by, respectively, inhibiting or enhancing matrix metalloproteinase (MMP) degradation of the tensed interstitial collagen. While this mechanobiological mechanism has not been previously applied to the study of tumor metastasis and EMT, it may have the potential to broaden our understanding of the tumor invasive process and assist in developing new strategies for preventing or treating cancer metastasis.