Expression of the G1 domain of aggrecan interferes with chondrocyte attachment and adhesion

The proteoglycan aggrecan is a major component of cartilage, and degradation of aggrecan is associated with aging and a number of pathological conditions. To investigate the effects of the accumulation of G1 domain from degraded aggrecan, we overexpressed the G1 domain in cell culture. Exogenous addition of the expressed GI gene product to chondrocyte cultures retarded the attachment of chondrocytes to tissue culture plates, type II collagen and hyaluronan. Expression of the G1 construct, aggrecan or link protein in chondrocytes led to decreased cell adhesion. Interestingly, aggrecan land specifically G1) and link protein, when applied simultaneously, seem to be able to interact and inhibit the destabilization of chondrocyte adhesion observed when either is applied alone. The G3 domain of aggrecan has little effect on chondrocyte adhesion and did not change the effects of link protein and the G1 domain on chondrocyte adhesion. These effects probably involve the binding of G1 to cell surface molecules, since FAGS (fluorescence-activated cell sorter) analysis demonstrated that the G1 domain binds to the chondrocyte surface with high affinity.