Uniaxial tension inhibits tendon collagen degradation by collagenase in vitro

Abstract

Tendon structure is governed largely by factors regulating the anabolic and catabolic phases of tenocyte metabolism. Little is known about the mechanisms that regulate the synthesis, activation, and action of metalloproteinases, which are key enzymes in a multifactorial cascade controlling homeostasis of the extracellular matrix. In the present study, we investigated the effect of tension on collagenase-induced degradation of the tendon in vitro by assessing changes in structural and material properties measured during tensile failure tests. Devitalized right-left pairs of rabbit patella-patellar tendon-tibia units were maintained under culture conditions in the presence of 60 U/ml highly purified collagenase for 20 hours. One randomly selected unit from each animal was subjected to a tension that produced a constant 4% elongation or strain (n = 10); the contralateral unit served as a slack comparison (n = 10). In one series of experiments (immediate, n = 5), the tension was applied immediately prior to collagenase exposure. In a second series (delayed, n = 5), it was delayed for 4 hours to allow time for the collagenase to diffuse into the tendon. Additional devitalized and nonincubated units (n = 6) were used as normal controls. Collagenase exposure caused large decreases in stiffness and elongation to failure in slack units. This resulted in greater than 80% reductions in both maximum failure force and energy to failure. In contrast, the loaded unit in both experimental protocols had significantly greater stiffness than control units. In both the immediate and the delayed protocols, the loaded tendons had significantly higher stiffness and failed at significantly higher elongations and maximum forces than the slack tendons. Diffusion studies with and without tension showed the tension did not inhibit diffusion of collagenase into the tendon but did significantly decrease the water content from 64.6 to 57.8%. The data suggest that stresses and strains of the extracellular matrix may modify the kinetics of the bacterial collagenase-collagen interaction. Matrix stress and strain may be an important and overlooked factor that modulates the susceptibility of collagen to proteolytic degradation.

Internal strain drives spontaneous periodic buckling in collagen and regulates remodeling

“…Filled data points were included in the fit of P(x) (Supporting Information), returning estimates for the spring constant, k = k B T/σ 2 (effective stiffness of the potential well), the average buckle separation, often occurs without subsequent cleavage but is an obligatory and rate-limiting step in the proteolysis of fibrillar collagen (23). An implication of this model is that degradation will be strongly inhibited by mechanical strain through a switch-like removal of buckle sites (16), consistent with the well-documented, but poorly understood, finding that fibrillar collagen under tension is resistant to degradation by MMP-1, MMP-8, and bacterial collagenase (15)(16)(17)(38)(39)(40)(41). External tension on the fibril would decrease the internal strain energy that drives the formation of buckles.…”

The Role of Mechanical Loading in Tendon Development, Maintenance, Injury, and Repair

“…Normal, physiologic loads are required to maintain tendon homeostasis and prevent excessive degradation of the extracellular matrix [25][26][27] . Nabeshima et al found that culturing nontensioned rabbit patellar tendon explants in the presence of collagenase over a period of twenty hours significantly decreased linear stiffness (p < 0.0001), elongation to failure (p < 0.002), and maximum failure force (p < 0.002) by 80% compared with explants tensioned with constant 4% strain 26 .…”

“…Nabeshima et al found that culturing nontensioned rabbit patellar tendon explants in the presence of collagenase over a period of twenty hours significantly decreased linear stiffness (p < 0.0001), elongation to failure (p < 0.002), and maximum failure force (p < 0.002) by 80% compared with explants tensioned with constant 4% strain 26 . Further, Flynn et al found that reconstituted type-I collagen micronetworks, strained between micropipettes, degraded significantly slower (p < 0.05) than unloaded controls when exposed to mammalian collagenase matrix metalloproteinase 8 27 .…”

Inflammation et réparation tendineuse

“…En effet, différents groupes de recherche ont observé une activation des MMP et une expression subséquente ou concomitante de TIMP consécutive à un stress de l'appareil tendineux [7,8]. Certaines observations suggèrent également que la tension axiale protège les fibres de collagène contre la dégradation protéolytique [9]. Bien que le débat entourant la théorie des dommages inflammatoires ne soit pas clos, des travaux récents montrent que l'accumulation maximale des cellules inflammatoires précède le don : macrophages résidents, fibroblastes et mastocytes, qui libéreront une vaste gamme de molécules pro-inflammatoires ( Figure 2B).…”