Disease relevance of ACAN

• A mutation in the variable repeat region of the aggrecan gene (AGC1) causes a form of spondyloepiphyseal dysplasia associated with severe, premature osteoarthritis [1].
• This proximal location for AGC1 is further supported by linkage data from a second family with an autosomal recessive form of multiple epiphyseal dysplasia that also maps to the SED locus [2].
• ADAMTS-4, also referred to as aggrecanase-1, is a glutamyl endopeptidase capable of generating catabolic fragments of aggrecan analogous to those released from articular cartilage during degenerative joint diseases such as osteoarthritis [3].
• Human p135 (p135H) and mouse p135 (p135M) synthetic peptides of the G3 domain of aggrecan were used to prime lymphocytes, which were then used for adoptive transfer of arthritis into "presensitized" SCID mice, determining cross-reactivity among p135 peptides and their analogous sequences, and generating T cell hybridomas [4].
• Studies in vitro with retinoic acid-stimulated rat chondrosarcoma cells indicated that the rAgg1mut substrate was cleaved at the 'aggrecanase' site equivalent to Glu373-Ala374 (human aggrecan sequence enumeration) in its interglobular domain sequence segment [5].

Psychiatry related information on ACAN

• Human aggrecan keratan sulfate undergoes structural changes during adolescent development [6].
• In an immunocytochemical study, three monoclonal antibodies to different sulfation states of the chondroitin glycosaminoglycan were used to localize CSPG in cases of Alzheimer's disease [7].
• Reacting astrocytes in each of these neurodegenerative diseases and Huntington's disease showed immunoreactivity for CSPG [8].

High impact information on ACAN

• This defines the consensus fold for the Link module superfamily, which includes CD44, cartilage link protein, and aggrecan [9].
• Arthritis induced by proteoglycan aggrecan G1 domain in BALB/c mice. Evidence for t cell involvement and the immunosuppressive influence of keratan sulfate on recognition of t and b cell epitopes [10].
• In this study, two T cell epitopes residing on G1 within residues 70-84 (peptide G5) and 150-169 (peptide G9) were identified using synthetic peptides and aggrecan-specific T cell lines [10].
• Our results are consistent with the presence in both normal and arthritic joint cartilage of proteolytic activity against aggrecan based on both classical MMPs and "aggrecanase."[11]
• The levels of extracted VDIPEN neoepitope relative to collagen or aggrecan in both OA and RA samples were similar to those seen in age-matched control specimens [11].

Chemical compound and disease context of ACAN

• Glucosamine sulfate modulates the levels of aggrecan and matrix metalloproteinase-3 synthesized by cultured human osteoarthritis articular chondrocytes [12].
• Analysis of enzyme activity confirmed different melanoma cell proteolytic potentials based on engagement of either the alpha2beta1 integrin or CD44/CSPG [13].
• Rat chondrosarcoma tumour contained full-length aggrecan and all of the individual peptides expected from single independent cleavages at each of the four aggrecanase sites in the chondroitin sulphate (CS) domain [14].
• METHODS: One trochlea and its tendon from 11 dissecting-room cadavers were fixed in methanol, cryosectioned, and immunolabeled with a panel of monoclonal antibodies against types I, II, III, V, and VI collagens, chondroitin-4 and -6, keratan and dermatan sulfates, aggrecan, link protein, versican, and tenascin [15].
• OBJECTIVE: To characterize the time course of aggrecan and type II collagen degradation in the rat iodoacetate model of cartilage degeneration in relationship to the temporal sequence that has been described in human osteoarthritis (OA) [16].

Biological context of ACAN

• Following BMP-6 induction, AGC1 gene expression in P9 cells increased 290-fold over P4 cells [17].
• In response to specific media formulations, including transforming growth factor beta1 (TGFbeta1), these cells exhibit significant ability to differentiate into a chondrocyte-like phenotype, expressing cartilage-specific genes and proteins such as aggrecan and type II collagen [18].
• The inverse correlation between serum levels of TIMP-1 and antigenic KS suggests that an upregulation of TIMP-1 synthesis might be responsible for the apparent suppression of cartilage aggrecan catabolism in patients with severe inflammatory changes [19].
• In aggrecan, these are subject to alternative splicing [20].
• Genomic structures revealed that all four HAPLN genes were similar in exon-intron organization and were also similar in genomic organization to the 5' exons for the CSPG core protein genes [21].

Anatomical context of ACAN

• RESULTS: In normal adult articular chondrocytes the expression of both aggrecan and type II collagen genes was significantly down-regulated, whereas matrix-degrading proteases (except MMP-2), as well as the investigated cytokines, were induced by IL-1beta in a dose-dependent manner [22].
• The proteoglycan aggrecan is an important major component of cartilage matrix that gives articular cartilage the ability to withstand compression [23].
• We have analysed the aggrecan core protein species present in vivo in both articular cartilage and synovial fluids from normal, acutely injured and osteoarthritic joints [24].
• Interaction of lumican with aggrecan in the aging human sclera [25].
• The presence of fibrin glue positively influences on mRNA levels of collagen type II and aggrecan, while blood plasma enhanced only the level of collagen type II expression [26].

Associations of ACAN with chemical compounds

• The chondroitin sulfate proteoglycan aggrecan forms link protein-stabilized complexes with hyaluronan (HA), via its N-terminal G1-domain, that provide cartilage with its load bearing properties [27].
• Binding-competition experiments conducted using native and deglycosylated aggrecan provided direct evidence for interaction of the ADAMTS-4 cysteine-rich/spacer domains with aggrecan GAGs [3].
• ACECLO and INDO increased AGG content by 25% in the alginate beads, while the other NSAID were without significant effect [28].
• They fully blocked PGE2 production, inhibited IL-6 synthesis, and increased aggrecan synthesis [28].
• Both aggrecanases showed a similar ability to cleave within the CS2 domain of bovine aggrecan irrespective of age, but showed a much lower ability to cleave within the CS2 domain of human aggrecan [29].

Physical interactions of ACAN

• Efficient aggrecanase activity requires the presence of sulfated glycosaminoglycans (GAGs) attached to the aggrecan core protein, implying the contribution of substrate recognition/binding site(s) to ADAMTS-4 activity [3].
• Fibulin-1 has affinity for the common site on versican but may bind to a different site on the aggrecan lectin domain [30].
• TSG-6 also interacts with aggrecan, with a similar pH dependence, and this can be inhibited by HA [31].
• Link protein (LP) is an abundant protein of cartilage which stabilizes the interaction of aggrecan with hyaluronic acid (HA) [32].
• In this study, the rupture force of the single bond between hyaluronan and hyaluronan binding protein - the complex of the hyaluronan binding region of aggrecan and link protein - was directly measured with a nanomechanical testing system as 40+/-11 pN [33].

Enzymatic interactions of ACAN

• ADAMTS4 cleaves at the aggrecanase site (Glu373-Ala374) and secondarily at the matrix metalloproteinase site (Asn341-Phe342) in the aggrecan interglobular domain [34].
• ADAM-TS5 cleaved aggrecan approximately 2-fold slower than ADAM-TS4 [35].
• Membrane-type 1 MMP (MMP-14) cleaves at three sites in the aggrecan interglobular domain [36].
• Several members of the matrix metalloproteinase family have been reported to cleave aggrecan in the interglobular domain between Asn-341 and Phe-342 [37].
• Recombinant human MMP-8 catalytic domain cleaved native aggrecan in a concentration-related manner between 0.2 and 2 microg/ml, with complete release of glycosaminoglycan at 2 microg/ml or greater [38].

Regulatory relationships of ACAN

• Matrix metalloproteinase (MMP) inhibitors inhibited aggrecan loss from bovine nasal explants incubated in the presence of recombinant human interleukin 1alpha [39].
• Alternative splicing in the aggrecan G3 domain influences binding interactions with tenascin-C and other extracellular matrix proteins [20].
• In addition, B cell CSPG blocked C1q receptor binding in a dose-dependent manner [40].
• Recombinant MMP-2 inactivated the neurite-inhibiting CSPG without hindering the neurite-promoting potential of laminin [41].
• Chondrocytes expanded with FGF-2/TGF beta 1 and redifferentiated in SFM TD expressed the largest mRNA amounts of CII and aggrecan and generated cartilaginous tissues with the highest accumulation of glycosaminoglycans and collagen type II [42].

Other interactions of ACAN

• We show here, in digests with native human aggrecan, that purified ADAMTS4 cleaves primarily at the Glu(373)-Ala(374) site, but also, albeit slowly and secondarily, at the Asn(341)-Phe(342) site [34].
• Surprisingly, the length of HA required to accommodate two G1-domains was found to be significantly larger for aggrecan than versican, which may reflect differences in the conformation of HA stabilized on binding these proteins [27].
• RESULTS: Normal chondrocytes showed an increase in aggrecan mRNA and a decrease in MMP-3 mRNA within 1 hour following stimulation, with a return to baseline levels within 24 hours [43].
• Accordingly, the presence of the cleavage products globular domain 1 (G1)-NITEGE(373) and G1-VDIPEN(341) in vivo has been widely interpreted as evidence for the specific involvement of ADAMTS enzymes and MMPs/cathepsin B, respectively, in aggrecan proteolysis in situ [34].
• Bovine nasal cartilage was treated with affinity-purified fibronectin fragments and assayed for aggrecan breakdown by monitoring the release of glycosaminoglycans and the aggrecan neoepitope (1771)AGEG [44].

Analytical, diagnostic and therapeutic context of ACAN

• This new structural information on aggrecan may account for the previously observed stiffness of the interglobular domains when viewed by rotary shadowing electron microscopy (Paulsson, M., Morgelin, M., Wiedemann, H., Beardmore-Gray, M., Dunham, D. G., Hardingham, T. E., Heinegard, D., Timpl, R., and Engel, J. (1987) Biochem. J. 245, 763-772) [45].
• Gel filtration and protein cross-linking/matrix-assisted laser desorption ionization time-of-flight peptide fingerprinting showed that cLP and AG1 interact in the absence or presence of HA [27].
• The reliability of the newly established coculture systems is confirmed by causing a clear decrease of intact aggrecan in the coculture medium plus concurrent appearance of additional smaller fragments and a reduction of chondrocyte aggrecan and collagen II gene expression in the presence of monocytes [46].
• The mRNA of Sox9, type II collagen, and aggrecan were all significantly upregulated by PRP through RT-PCR [47].
• Analysis of proteoglycan degradation products, both released into culture media and retained within the cartilage matrix, was performed by Western blotting using antibodies specific for the N- and C-terminal neoepitopes generated by aggrecanase- and MMP-related catabolism of the interglobular domain of the aggrecan core protein (IGD) [48].

References