Role of cartilage and bone matrix regulation in early equine osteochondrosis

The objective of this study is to better understand the pathogenesis of early equine osteochondrosis (OC) by identifying differences in gene and protein expression of extracellular matrix components and regulators in normal and diseased cartilage and bone, focusing on the osteochondral junction and cells surrounding the cartilage canals. We expected to find an upregulation of matrix metalloproteinases and a decrease in extracellular matrix constituent expression along the osteochondral junction and cells surrounding the cartilage canals in OC samples. Paraffin-embedded osteochondral samples (6 OC-affected, 8 normal controls) and cDNA from chondrocytes captured with laser capture microdissection from frozen sections (4 OC-affected, 5 normal controls) were used in this study. Quantitative real-time polymerase chain reaction was performed on 16 target genes. Immunohistochemistry was performed on osteochondral samples for Sox-9, lubricin, osteocalcin, and collagen type IIB. In OC-affected samples, there was significantly (P ≤ 0.05) decreased gene expression of collagen type IIB, aggrecan, and SOX-9 in chondrocytes surrounding the cartilage canals and decreased gene expression of PRG4 (Lubricin) and collagen type IIB in chondrocytes along the osteochondral junction. We found significantly lower collagen type IIB total matrix percentages in the middle and deep cartilage layers, lower lubricin total cellular percentage in the superficial layer, and higher Sox-9 total cellular percentage in bone of OC samples. No significant differences were found in matrix degradation molecules or HSCORE protein expression at any locations between normal and OC-affected samples in our study.