Reduced type II collagen mRNA in nanomelic cultured chondrocytes: An example of extracellular matrix/type II collagen feedback regulation?

Aim. Characterization of nanomelic chondrocytes. Method. Examination of cultured chondrocytes by aggrecan and type II collagen mRNA analysis and electron microscopy. Results. Differences in the shape, mobility and attachment were noted between normal and nanomelic sternal chondrocytes in tissue culture. Electron microscopy showed a decrease in extracellular matrix in nanomelic cells after the second passage. Northern blot analysis demonstrated lower levels of mRNA for aggrecan in the nuclear compartment of nanomelic cells, and showed almost no mRNA for aggrecan in the cytoplasm. Direct RNase protection of total mRNA confirmed this decrease in the amount of aggrecan mRNA, but also revealed that a decrease in type II collagen mRNA occurred at the same time. In contrast, type I collagen and GPDH remained at normal levels in both cell types. Conclusion. It appears that the primary failure in aggrecan production by nanomelic chondrocytes has an unexpected secondary effect on type II collagen. The decrease in type II collagen mRNA suggests a possible coordination of transcription between genes that code for interacting extracellular matrix proteins.