Disease relevance of Acan

• Homozygous cmd/cmd mice are characterized by disorganisation of chondrocytes in the growth plate, disproportionate dwarfism, cleft palate, and perinatal lethality [1].
• The kinetics of expression of the genes encoding type II, IX, X, and XI collagens, aggrecan and link protein during the conversion toward cartilage hypertrophy resembles that accompanying in vivo chondrogenesis [2].
• Dwarfism and age-associated spinal degeneration of heterozygote cmd mice defective in aggrecan [3].
• Both type II collagen and the proteoglycan aggrecan are capable of inducing an erosive inflammatory polyarthritis in mice [4].
• SOX9 enhancement of aggrecan gene promoter activity and SOX9 transactivation through the Sry/Sox consensus sequence were not observed in osteoblastic osteosarcoma cells (ROS17/2.8), indicating the dependence on the cellular background [5].

High impact information on Acan

• Link protein (LP), an extracellular matrix protein in cartilage, stabilizes aggregates of aggrecan and hyaluronan, giving cartilage its tensile strength and elasticity [6].
• The cartilage contained significantly reduced aggrecan depositions in the hypertrophic zone, and decreased numbers of prehypertrophic and hypertrophic chondrocytes [6].
• Mouse cartilage matrix deficiency (cmd) is an autosomal recessive mutation characterized by cleft palate, short limbs, tail and snout [7].
• Here, we have mapped the aggrecan gene to a region of mouse chromosome 7 near the cmd locus [7].
• These nodules stained intensely with Alcian blue and collagen type II antibodies. mRNA encoding chondrocyte markers including collagen type II, aggrecan, and Pln was elevated in 10T1/2 cells cultured on Pln [8].

Chemical compound and disease context of Acan

• Monoclonal antibodies that recognize epitopes in these domains were raised against Swarm rat chondrosarcoma aggrecan that was either denatured through reduction and alkylation or partially deglycosylated through chondroitinase ABC digestion or alkali elimination, the latter with or without sulfite addition [9].

Biological context of Acan

• The discordance of gene expression in cmd chondrocytes may be additional factors contributing to the disrupted cellular architecture of the growth plate resulting from the primary absence of aggrecan [1].
• To investigate transcriptional regulation of the aggrecan gene by OP-1, we constructed a clone containing a 1 kb region of the 5'-upstream sequence of the mouse aggrecan gene fused to the promoter-less luciferase reporter gene in pGL2-Basic vector [10].
• The G3 domain of aggrecan, which does not contain an EGF-like motif, did not inhibit mesenchymal chondrogenesis [11].
• Although the function of these domains is not understood, the uniform expression of the EGF2 domain may indicate a general role of this aggrecan module, while the expression of the EGF1 domain may reflect species specificity [12].
• The overall amino acid sequence of the mouse aggrecan shows 91.6% identity to rat and 72.5% to human aggrecan [13].

Anatomical context of Acan

• Immunostaining showed that versican was mainly localized in the interterritorial zone of the articular surface at 2 weeks in mice, whereas aggrecan was in the pericellular zone of prehypertrophic and hypertrophic cells of the growth plate [14].
• Biochemical analysis of normal articular cartilage and aggrecan-null cartilage from cmd (cartilage matrix deficiency)/cmd mice revealed that versican was present as a proteoglycan aggregate with both link protein and hyaluronan [14].
• In vitro studies using primary chondrocyte cultures showed that both CDMP-1 and CDMP-2 stimulated equally de novo synthesis of proteoglycan aggrecan in a concentration-dependent manner [15].
• We investigated the expression pattern of versican, aggrecan, link protein and hyaluronan in the developing limb bud cartilage of the fetal mouse using in situ hybridization and/or immunohistochemistry [16].
• Versican mRNA expression rapidly disappeared from the tibial cartilage, as cartilage formation progressed during E13-15, but the immunostaining was gradually replaced by aggrecan immunostaining from the diaphysis [16].

Associations of Acan with chemical compounds

• Chondroitin sulfate chains of versican digested with chondroitinase ABC contained 71% nonsulfated and 28% 4-sulfated unsaturated disaccharides, whereas those of aggrecan contained 25% nonsulfated and 70% 4-sulfated [14].
• Finally, mice lacking matrilin-1, a non-collagenous glycoprotein that binds to both collagen fibrils and aggrecan, develop normally without detectable abnormalities in their skeleton [17].
• Following retinoic acid or IL-1alpha stimulation of cartilage explants, aggrecan fragments in medium and extracts contained SELE(1279) or FREEE(1467) C-terminal sequences [18].
• No difference in Safranin O staining or aggrecan cleavage site neoepitope abundance was seen [19].
• At confluency, TGF-beta induced Agc expression within 3 h, and cycloheximide blocked this induction, indicating that de novo protein synthesis is essential for this response [20].

Physical interactions of Acan

• Although matrilin 1 interacts with the collagen II and aggrecan networks of cartilage, suggesting that it may play a role in cartilage tissue organization, studies of collagen extractability indicated that collagen fibril maturation and covalent cross-linking were unaffected by the absence of matrilin 1 [21].
• Furthermore, the chondroitin sulfate attachment region of aggrecan received GAG side chains more readily when coupled to the G3 domain of aggrecan than when coupled to domains II and III of perlecan [22].

Enzymatic interactions of Acan

• Further analysis of the media showed the presence of Aggrecanase-cleaved aggrecan fragments, a signature of matrix degradation [23].

Regulatory relationships of Acan

• The purpose of this study was to examine whether SOX9 modulates aggrecan gene expression and to further identify molecules that regulate Sox9 expression in TC6 cells [5].
• Compressive force promotes sox9, type II collagen and aggrecan and inhibits IL-1beta expression resulting in chondrogenesis in mouse embryonic limb bud mesenchymal cells [24].
• Arthritic NADPH oxidase-deficient mice showed irreversible cartilage damage as judged by the enhanced aggrecan VDIPEN expression, and chondrocyte death [25].
• In cultures of the mouse ATDC5 cell line, MTf is developmentally expressed in parallel with the expression of type II collagen and aggrecan, in the pattern commensurate with the onset of chondrogenesis to form cartilage nodules [26].

Other interactions of Acan

• These results suggest that versican is present as an aggregate distinct from the aggrecan aggregate and may play specific roles in the articular surface [14].
• Identification of an osteogenic protein-1 responsive element in the aggrecan promoter [10].
• This conserved segment, however, is not entirely conserved in the mouse and is split between Chr 7 (Igf1r-Agc) and 2 (B2m) [27].
• Changes in gene activity and matrix organization in the growth plate also accompanied deficiencies in aggrecan, perlecan and collagen II [28].
• These cells expressed mRNAs for Sox9 and aggrecan in addition to osteogenic markers [29].

Analytical, diagnostic and therapeutic context of Acan

• In situ hybridization and immunohistochemistry of versican, aggrecan and link protein, and histochemistry of hyaluronan in the developing mouse limb bud cartilage [16].
• A reverse transcription-polymerase chain reaction (RT-PCR) assay also showed that the mRNA levels of aggrecan and type X collagen were reduced compared with nontreated tissues [30].
• Immunofluorescence of proteoglycan was increased in the matrix of cho and Dmm and decreased in cmd [31].
• Northern blot analysis indicated that expression of the PTH/PTHrP receptor gene became detectable at the early stage of chondrogenesis of ATDC5 cells, preceding induction of aggrecan gene expression [32].
• RESULTS: ELISA revealed positive responses to glucose-6-phosphate isomerase, chondroitin sulfate B, collagen I, collagen II, aggrecan, and DNA between 4 and 12 months post-pristane injection [33].

References