Evidence that species specificity and rate of collagen degradation are properties of collagen, not collagenase

Biochemical signal transduction of mechanical strain in osteoblast-like cells

The responses to mechanical loading of two types of osteoblast-like cells and skin fibroblasts were investigated using two new devices for applying defined and homogeneous strains to cells. The results indicate that only periostal (bone surface) osteoblasts are sensitive to strains within the physiological range and that a specific strain mechanism is responsible. Osteoblasts derived from the haversian system and skin fibroblasts do not respond except at higher, unphysiological strains. The mechanism is located in the cytoskeleton and activates the membrane phospholipase C within milliseconds and may react to distension of a strain sensitive protein. Activation of phospholipase C can account for only some of the observed responses of bone to mechanical loading such as stimulation of cell division, increase in collagen and collagenase production. Application of over 10,000 mu strains results in a de-differentiation of the osteoblasts and a change in cell morphology to become fibroblast-like.

Action of collagenase and elastase from human polymorphonuclear leukocytes on human articular cartilage

Collagenase from human polymorphonuclear leukocytes (neutrophil collagenase) attacks collagen type II in solution at a rate intermediate to those of type I and III collagens. This enzyme alone is not able to initiate degradation of native human articular cartilage. If the cartilage is first treated with leukocyte elastase, collagenase slowly degrades collagen. Confirming earlier findings by other investigators, elastase has a dual action on cartilage: The enzyme removes proteoglycans, thus demasking collagen fibers and giving collagenase access to them, and solubilizes collagen at a sizable rate. Although neutrophil collagenase cleaves collagen type II in solution at a high rate, the native, cross-linked status of collagen in cartilage makes it a relatively poor substrate for this enzyme. On a weight by weight scale, elastase and collagenase display about the same collagenolytic potential on human articular cartilage. The elastase/collagenase system from human polymorphonuclear leukocytes could represent a cooperative proteolytic complex in the destruction of cartilage in rheumatoid arthritis.

Effect of tensile mechanical stress on the synthesis of metalloproteinases by rabbit coronal sutures in vitro

The application of a continuous tensile mechanical stress (30 g) to explants of coronal sutures from newborn rabbits (1-2 days) produced increases in enzyme activity of 33.7% for collagenase, 95.2% for gelatinase, and 35.9% for NMP III over a 4-day culture period. All three activities were in latent form and required activation with either 4-APMA or trypsin. The increases in enzyme activities were not accompanied by an alteration in the degradation of structural proteins. This was due to the ability of the cells to synthesize an inhibitor (mol wt 29,000 daltons) which complexed the increased quantities of enzyme. This necessitated a substantial stimulation of inhibitor production because there was still a residue of free inhibitory activity in the media of stressed cultures after 4 days. We previously showed using the same model system that coronal sutures respond to tensile mechanical stress by a two-fold increase in collagen synthesis. The present data suggest that when the priority of the cell population is the synthesis of structural proteins, the inhibitor, in addition to preventing the hydrolysis of newly synthesized peptides, also maintains matrix degradation at normal turnover levels.