Regulation of Collagenase Activities of Human Cathepsins by Glycosaminoglycans

Abstract

Cathepsin K, a lysosomal papain-like cysteine protease, forms collagenolytically highly active complexes with chondroitin sulfate and represents the most potent mammalian collagenase. Here we demonstrate that complex formation with glycosaminoglycans (GAGs) is unique for cathepsin K among human papain-like cysteine proteases and that different GAGs compete for the binding to cathepsin K. GAGs predominantly expressed in bone and cartilage, such as chondroitin and keratan sulfates, enhance the collagenolytic activity of cathepsin K, whereas dermatan, heparan sulfate, and heparin selectively inhibit this activity. Moreover, GAGs potently inhibit the collagenase activity of other cysteine proteases such as cathepsins L and S at 37°C. Along this line MMP1-generated collagen fragments in the presence of GAGs are stable against further degradation at 28°C by all cathepsins but cathepsin K, whereas thermal destabilization at 37°C renders the fragments accessible to all cathepsins. These results suggest a novel mechanism for the regulation of matrix protein degradation by GAGs. It further implies that cathepsin K represents the only lysosomal collagenolytic activity under physiologically relevant conditions.Controlled degradation of collagen is observed in bone remodeling, wound healing, angiogenesis, and during organ development (1-3). On the other hand excessive collagen degradation leads to pathological phenotypes such as osteoporosis (4), various forms of arthritis (5), or aneurysms of blood vessels (6), or it is characteristic for tumor invasion (7). However, triple helical collagens, in particular type I and II collagens, are highly resistant to general proteolysis and require specific proteases for their degradation. Known mammalian collagenolytic activities include members of the matrix metalloprotease family such as MMP-1, -2, -8, -13, and -14 (8), the serine protease, human neutrophil elastase (9), and thiol-dependent cathepsins (1). Collagenases of the MMP family cleave triple helical collagen at a specific single site and release 3 ⁄4 and 1 ⁄4 fragments. Similar to MMPs, human neutrophil elastase generates 3 ⁄4 fragments from type I collagen but is unable to degrade type II collagen (9). Lysosomal cysteine proteases such as cathepsins L and B have also been discussed as collagenolytic activities, but these data were mostly based on inhibitor experiments in cell extracts or on early preparations of cathepsins, which may not have excluded contaminating activities (10 -13). Thorough enzymatic studies suggested that cathepsins B and L primarily cleave in the non-helical telopeptide extensions of collagens (14, 15). A truly triple helical collagenase activity is found in cathepsin K, which is predominantly expressed in osteoclasts and to a lower degree in various other cell types including fibroblasts (16 -19). It was demonstrated that cathepsin K, similar to the bacterial Clostridium collagenase, cleaves at multiple sites within the triple helical region of types I and II collagens (20,21). The biological relevan...

Liver-Directed Human Amniotic Epithelial Cell Transplantation Improves Systemic Disease Phenotype in Hurler Syndrome Mouse Model

“…Previous studies have shown that excess GAG accumulation inhibits the degradation of collagen type II by cathepsin K, resulting in impaired osteoclast activity and decreased cartilage resorption. This contributes to the skeletal abnormalities seen in the MPS1 human disease and the mouse model 43, 44. Significant normalization of bone volume and density values in our treated mice is further evidence of the therapeutic reduction of systemic GAGs achieved via liver‐directed hAEC transplantation.…”

Membrane-Type I Matrix Metalloproteinase-Dependent Regulation of Rheumatoid Arthritis Synoviocyte Function

“…Although the human genome encodes .500 proteases, only a small subset of these gene products-confined largely to the MMP and cysteine proteinase families-can degrade intact type I or II collagen molecules within their triple-helical domains (5)(6)(7)(8)(9)(10)(11). RA synoviocytes have been reported to express multiple collagenases (1-3, 12-19), but the dominant effectors capable of supporting either collageninvasive or collagen-destructive phenotypes under pathophysiologically relevant conditions have remained the subject of controversy (3).…”

“…Although the cartilaginous matrix is dominated by type II collagen, the extracellular matrix of ligaments, tendons, and bone is largely composed of type I collagen (1)(2)(3). Presently, triple-helical collagenases (i.e., those proteinases that are able to hydrolyze collagen by cleaving within triplehelical domains) are limited to members of the matrix metalloproteinase (MMP) and cysteine proteinase families (5)(6)(7)(8). Within the MMP family, four secreted collagenases have been identified: MMP-1 (the so-called fibroblast collagenase), MMP-8 (collagenase-2), MMP-13 (collagenase-3), and MMP-2 (gelatinase A) (3,5,9).…”

Glycosaminoglycan-Mediated Loss of Cathepsin K Collagenolytic Activity in MPS I Contributes to Osteoclast and Growth Plate Abnormalities

“…HS and DS both accumulate during the pathology of MPS I disease 1 and have both been shown to inhibit the type I collagenolytic activity of cathepsin K. 11 However, due to the lack of an appropriate antibody for DS, we have only described HS staining. The growth plate of the femur at the shoulder joint, the tibia at the knee joint, and the spine, were stained for cathepsin K and HS, and the overlapping area resulting in orange fluorescence was measured ( Figure 3A).…”

“…10 However other GAGs, like DS and HS, were shown to inhibit the collagenolytic activity of cathepsin K. 11 As both DS and HS are present in high concentrations in MPS I tissue, we investigated the effect these concentrations would have on cathepsin K activity. During endochondral ossification, cathepsin K degrades type II collagen (cartilage) below the growth plate area to provide room for new bone to be laid down by osteoblasts.…”