Interaction between Human Cathepsins K, L, and S and Elastins

Abstract

Proteolytic degradation of elastic fibers is associated with a broad spectrum of pathological conditions such as atherosclerosis and pulmonary emphysema. We have studied the interaction between elastins and human cysteine cathepsins K, L, and S, which are known to participate in elastinolytic activity in vivo. The enzymes showed distinctive preferences in degrading elastins from bovine neck ligament, aorta, and lung. Different susceptibility of these elastins to proteolysis was attributed to morphological differences observed by scanning electron microscopy. Kinetics of cathepsin binding to the insoluble substrate showed that the process occurs in two steps. The enzyme is initially adsorbed on the elastin surface in a nonproductive manner and then rearranges to form a catalytically competent complex. In contrast, soluble elastin is bound directly in a catalytically productive manner. Studies of enzyme partitioning between the phases showed that cathepsin K favors adsorption on elastin; cathepsin L prefers the aqueous environment, and cathepsin S is equally distributed among both phases. Our results suggest that elastinolysis by cysteine cathepsins proceeds in cycles of enzyme adsorption, binding of a susceptible peptide moiety, hydrolysis, and desorption. Alternatively, the enzyme may also form a new catalytic complex without prior desorption and re-adsorption. In both cases the active center of the enzymes remains at least partly accessible to inhibitors. Elastinolytic activity was readily abolished by cystatins, indicating that, unlike enzymes such as leukocyte elastase, pathological elastinolytic cysteine cathepsins might represent less problematic drug targets. In contrast, thyropins were relatively inefficient in preventing elastinolysis by cysteine cathepsins.Elastic fibers are the key extracellular matrix component conferring elasticity to tissues such as blood vessels, lungs, and skin. The fibers are composed of a rubber-like network of highly stable and hydrophobic polymers of the protein elastin, associated with peripheral microfibrils (1, 2). Proteolytic degradation of elastic fibers leads to loss of tissue elasticity, which is associated with the development of different pathological conditions. A large repertoire of elastinolytic peptidases has been identified in human cells and tissues, including enzymes from four of the five catalytic classes of peptidases. The molecular mechanism underlying the process of elastinolysis has been thoroughly studied for human leukocyte elastase (HLE) 2 (3-9), a serine peptidase produced by neutrophils, whose activity has been associated with the development of atherosclerosis and pulmonary diseases (10, 11). In addition, two other elastinolytic serine peptidases are present in neutrophils, cathepsin G and myeloblastin (leukocyte proteinase 3) (12).Extracellular matrix degradation by monocyte-derived macrophages is because of the action of serine peptidases, matrix metalloproteases, and papain-like cysteine peptidases (cysteine cathepsins) (13-16). In inflammation, m...

Increased Serum Cathepsin K in Patients with Coronary Artery Disease

“…Among the cathepsin family members, cathepsin K has been shown to be one of the most potent mammalian collagenases in vivo and in vitro 11,13,14,15. Data from our group and others have shown that cathepsin K abounds in vascular cells (including smooth muscle cells and endothelial cells) and infiltrated macrophages of human and animal atherogenic lesions 3,16,17,18.…”

Pathogenesis of aortic dilatation in mucopolysaccharidosis VII mice may involve complement activation

“…CtsK is a very important enzyme, as it maintains activity at pH 7.5 (Supplementary Fig. 1), it has elastin-degrading activity [42], and is activated by chondroitin sulfate [43], which is one of the GAGs that accumulates in MPS VII. A CtsK substrate was obtained that was not cleaved by CtsB or CtsS to an appreciable extent, although it was cleaved by CtsL 1% as efficiently as CtsK (data not shown).…”

Carotid intima–media thickness is increased in patients with treated mucopolysaccharidosis types I and II, and correlates with arterial stiffness

“…Multiple studies have demonstrated dilatation of the aortic root and elastin fiber fragmentation in human MPS VII [27], canine MPS I and VII [24,27], feline MPS I and VI [29], and murine MPS I and VII [28,30,31]. Since elastin is a substrate of both metalloproteinase and cathepsin protease families [32,33], the loss of vascular elastin integrity and subsequent increase in arterial stiffness in MPS may be a result of GAG-TLR4 mediated inflammatory signaling. We are currently studying the roles played by HS or DS-derived oligosaccharides, TLR4, and downstream inflammatory mediators, in the aortic phenotype of the MPS I murine model.…”