Human HtrA1 belongs to a widely conserved family of serine proteases involved in various aspects of protein quality control and cell fate. Although HtrA1 has been implicated in the pathology of several diseases, its precise biological functions remain to be established. Through identification of potential HtrA1 targets, studies presented herein propose that within the context of arthritis pathology HtrA1 contributes to cartilage degradation. Elevated synovial HtrA1 levels were detected in fluids obtained from rheumatoid and osteoarthritis patients, with synovial fibroblasts identified as a major source of secreted HtrA1. Mass spectrometry analysis of potential HtrA1 substrates within synovial fluids identified fibronectin as a candidate target, and treatment of fibronectin with recombinant HtrA1 led to the generation of fibronectin-degradation products that may be involved in cartilage catabolism. Consistently, treatment of synovial fibroblasts with HtrA1 or HtrA1-generated fibronectin fragments resulted in the specific induction of matrix metalloprotease 1 and matrix metalloprotease 3 expression, suggesting that HtrA1 contributes to the destruction of extracellular matrix through both direct and indirect mechanisms.Human HtrA1 (L56) is a member of the HtrA 3 (High temperature requirement) family of serine proteases, a well defined group of proteases sharing many of the characteristics associated with bacterial HtrAs (1). Such features include a highly conserved trypsin-like serine protease domain and at least one PDZ domain at the C terminus. In addition, HtrA1 contains an insulin-like growth factor-binding protein domain and a Kazal-type serine protease inhibitor motif at its N terminus (2). Originally identified as a gene down-regulated in SV40-transformed fibroblasts (2), HtrA1 has since been implicated in the modulation of various disease pathologies. Recent reports suggest that HtrA1 plays a protective role in various malignancies because of its tumorsuppressive properties (3-6). Studies have shown that HtrA1 is downregulated in cancerous tissue as compared with normal tissue and that overexpression results in the inhibition of tumor cell growth and proliferation both in vitro and in vivo (5). In contrast to tumor tissue, HtrA1 expression is up-regulated in skeletal muscle of Duchenne muscular dystrophy (7) and in cartilage of osteoarthritic joints (8). Therefore, up-regulation of HtrA1 in osteoarthritic joints may contribute to the development of this debilitating disease.Progressive degradation of components of the extracellular matrix plays an important role in the pathogenesis of arthritic diseases (9, 10). The destruction of the major cartilage components is driven by members of all classes of proteases, including serine proteases, although the matrix metalloproteases (MMPs) are considered to be the primary instigators (11-13). Elevated levels of various MMPs have been identified in the diseased joints of both osteoarthritis (OA) (14 -16) and rheumatoid arthritis (RA) (17) patients, originating primar...

Objective: Mutations of the SPRED1 gene, one of a family of Sprouty (Spry)/Spred proteins known to ''downregulate'' mitogen activated protein kinase (MAPK) signalling, have been identified in patients with a mild neurofibromatosis type 1 (NF1) phenotype with pigmentary changes but no neurofibromas (Legius syndrome).To ascertain the frequency of SPRED1 mutations as a cause of this phenotype and to investigate whether other SPRED/SPRY genes may be causal, a panel of unrelated mild NF1 patients were screened for mutations of the SPRED1-3 and the SPRY1-4 genes. Methods: 85 patients with a mild NF1 phenotype were screened for SPRED1 mutations. 44 patients negative for both NF1 and SPRED1 mutations were then screened for SPRED2-3 and SPRY1-4 mutations. Complexity analysis was applied to analyse the flanking sequences surrounding the identified SPRED1 mutations for the presence of direct and inverted repeats or symmetric sequence elements in order to infer probable mutational mechanism.

Introduction The small leucine-rich proteoglycans (SLRPs) modulate tissue organization, cellular proliferation, matrix adhesion, growth factor and cytokine responses, and sterically protect the surface of collagen type I and II fibrils from proteolysis. Catabolism of SLRPs has important consequences for the integrity of articular cartilage and meniscus by interfering with their tissue homeostatic functions.

Matrix assembly and homeostasis in collagen-rich tissues are mediated by interactions with proteoglycans (PGs) substituted with sulfated glycosaminoglycans (GAGs). The major GAG in cornea is keratan sulfate (KS), which is N-linked to one of three PG core proteins. To ascertain the importance of the carbohydrate chain sulfation step in KS functionality, we generated a strain of mice with a targeted gene deletion in Chst5, which encodes an N-acetylglucosamine-6-O-sulfotransferase that is integral to the sulfation of KS chains. Corneas of homozygous mutants were significantly thinner than those of WT or heterozygous mice. They lacked high-sulfated KS, but contained the core protein of the major corneal KSPG, lumican. Histochemically stained KSPGs coassociated with fibrillar collagen in WT corneas, but were not identified in the Chst5-null tissue. Conversely, abnormally large chondroitin sulfate͞dermatan sulfate PG complexes were abundant throughout the Chst5-deficient cornea, indicating an alteration of controlled PG production in the mutant cornea. The corneal stroma of the Chst5-null mouse exhibited widespread structural alterations in collagen fibrillar architecture, including decreased interfibrillar spacing and a more spatially disorganized collagen array. The enzymatic sulfation of KS GAG chains is thus identified as a key requirement for PG biosynthesis and collagen matrix organization.collagen ͉ glycosaminoglycans ͉ proteoglycans G lycosaminoglycans (GAGs) substituted on proteoglycans (PGs) are influential in defining collagen fibrillar architecture in a wide range of connective tissue matrices. Keratan sulfate (KS) is an important constituent of several collagen-rich tissues and is the major GAG in cornea where it is N-linked to asparagine residues in one of three PG core proteins: lumican (1), keratocan (2), and mimecan͞osteoglycin (3). Human corneal GlcNAc 6-O-sulfotransferase (also known as human GlcNAc6ST-5 and GST4␤) is the responsible enzyme for the synthesis of high-sulfated KS via the transfer of sulfate onto the GlcNAc 6-O position of the KS backbone (4).Fairly compelling evidence exists for a regulatory role for KSPGs in the maintenance of corneal matrix structure in a number of species. The avian cornea in ovo, for example, synthesizes an unsulfated form of KS midway through development when it is structurally disorganized and transmits relatively little light, but switches to produce a sulfated KS GAG as it becomes transparent and attains a more well ordered collagen fibrillar ultrastructure (5, 6). KS sulfation patterns are also altered in opaque, structurally disorganized corneal scar tissue in rabbits (7,8) and in cloudy human corneas with the inherited disease, macular corneal dystrophy (9), which is caused by mutations in CHST6, a gene encoding human corneal GlcNAc 6-O-sulfotransferase (10).Hybrid type I͞V collagen fibrils are the cornea's main nonspecular light-scattering elements and are formed into wide, interweaving belts or lamellae that lie approximately in the tissue plane (11). Wit...