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...

Greater penetrations of variable renewable generation on electric grids have resulted in increased levels of curtailment in recent years. Studies of renewable energy grid integration have found that curtailment levels may grow as the penetration of wind and solar energy generation increases. This paper reviews international experience with curtailment of wind and solar energy on bulk power systems in recent years, with a focus on eleven countries in Europe, North America, and Asia. It examines levels of curtailment, the causes of curtailment, curtailment methods and use of market-based dispatch, as well as operational, institutional, and other changes that are being made to reduce renewable energy curtailment.

No abstract

The paramount importance of the homeostasis of the extracellular matrix for pulmonary function is exemplified by two opposing extremes: emphysema and pulmonary fibrosis. This study examined the putative role of cathepsin K (catK) in the pathology of lung fibrosis in mice and its relevance to the human disease activity. We compared the induction of lung fibrosis by administration of bleomycin. CTSK(-/-) mice deposited significantly more extracellular matrix than control mice. Primary lung fibroblasts derived from CTSK(-/-) mice showed a decreased collagenolytic activity indicating the role of catK in collagen degradation. Interestingly, CTSK(+/+) control mice revealed an increased expression of catK in fibrotic lung regions suggesting a protective role of catK to counter the excessive deposition of collagen matrix in the diseased lung. Similarly, in lung specimens obtained from patients with lung fibrosis fibroblasts expressed larger amounts of catK than those obtained from normal lungs. Activation of human pulmonary fibroblasts in primary cell cultures led to an increased activity of catK through enhanced gene transcription and protein expression and to increased intracellular collagenolytic activity. We believe that this is the first study to show that catK plays a pivotal role in lung matrix homeostasis under physiological and pathological conditions.

Atherosclerosis is characterized by a thickening and loss of elasticity of the arterial wall. Loss of elasticity has been attributed to the degradation of the arterial elastin matrix. Cathepsins K and S are papain-like cysteine proteases with known elastolytic activities, and both enzymes have been identified in macrophages present in plaque areas of diseased blood vessels. Here we demonstrate that macrophages express a third elastolytic cysteine protease, cathepsin V, which exhibits the most potent elastase activity yet described among human proteases and that cathepsin V is present in atherosclerotic plaque specimens. Approximately 60% of the total elastolytic activity of macrophages can be attributed to cysteine proteases with cathepsins V, K, and S contributing equally. From this 60%, two-thirds occur extracellularly and one-third intracellularly with the latter credited to cathepsin V. Ubiquitously expressed glycosaminoglycans (GAGs) such as chondroitin sulfate specifically inhibit the elastolytic activities of cathepsins V and K via the formation of specific cathepsin-GAG complexes. In contrast, cathepsin S, which does not form complexes with chondroitin sulfate is not inhibited; thus suggesting a specific regulation of elastolytic activities of cathepsins by GAGs. Because the GAG content is reduced in atherosclerotic plaques, an increase of cathepsins V and K activities may accelerate the destruction of the elastin matrix in diseased arteries.Atherosclerosis is characterized by arterial intimal enlargement and subsequent lipid deposition leading to the formation of blood stream obstructing plaques. The infiltration of monocyte-derived macrophages (MDMs) 1 and smooth muscle cells (SMCs) into the intima of the inflamed artery contributes to the formation of atherosclerotic lesions. Atherosclerotic lesions resident MDMs and SMCs produce a large number of extracellular matrix-degrading enzymes (1), such as cysteine proteases (2-5) and matrix metalloproteinases (MMPs) (6 -8).Elastin and collagen are the two major extracellular matrix components that provide elasticity and tensile strength to the arterial wall. The destruction of elastin and collagen causes a weakening and rupture of blood vessels (9, 10). MMPs, serine, and cysteine proteases have been identified as major elastolytic proteases in arteries (11, 12). Among cysteine proteases, cathepsins S and K have been considered as the most potent elastolytic activities with cathepsin K exhibiting a slightly higher activity than cathepsin S (13, 14). However, cathepsin K-deficient human macrophages derived from patients with pycnodysostosis were shown to retain their high cysteine proteasedependent elastolytic activities (15). This finding implied that additional cathepsins may contribute to the overall elastolytic activity in human macrophages.We and others (16 -18) have identified and partially characterized a novel human cysteine protease closely related to cathepsin L that was named cathepsin V (also known as cathepsin L2). Cathepsin V shares 80% protein s...