LOCALIZATION OF COLLAGEN TYPE-1, TYPE-2, AND TYPE-3 MESSENGER-RNAS IN HUMAN HETEROTOPIC OSSIFICATION BY NONRADIOACTIVE IN-SITU HYBRIDIZATION

Heterotopic ossification is a metabolically active process which shares several properties of orthotopic bone formation and, therefore, represents an excellent model for the investigation of matrix components. A novel tool for studying the ossifying process at the level of transcription is the technique of non-radioactive in situ hybridization. Using digoxigenin labeled cDNA probes we investigated the distribution patterns of types I, II and III collagen mRNAs in heterotopic ossification of pressure sores of paraplegic patients. The three collagen mRNAs exhibited substantially divergent distribution patterns. Type I (al) collagen mRNA was predominantly detectable in preosteoblasts, prechondroblasts and chondrocytes of the ossification zone. Type II (alpha1) collagen mRNA was nearly exclusively found in cells of the chondrogenic lineage. Type III (alpha1) collagen mRNA was detectable at low levels in soft tissue, but was strongly expressed by prechondroblasts and chondrocytes of heterotopic cartilage. Our in situ hybridization experiments provide evidence that chondrogenic cells in heterotopic ossification show a phenotypic alteration in collagen type expression. These results indicate that chondrocytes of heterotopic cartilage show a co-expression of types I (alpha1), II (alpha1) and III (alpha1) collagen mRNAs.