Wnt/β‐catenin signaling of cartilage canal and osteochondral junction chondrocytes and full thickness cartilage in early equine osteochondrosis

The objective of this study was to elucidate gene and protein expression of Wnt signaling molecules in chondrocytes of foals having early osteochondrosis (OC) versus normal controls. The hypothesis was that increased expression of components of Wnt signaling pathway in osteochondral junction (OCJ) and cartilage canal (CC) chondrocytes would be found in early OC when compared to controls. Paraffin‐embedded osteochondral samples (7 OC, 8 normal) and cDNA from whole cartilage (7 OC, 10 normal) and chondrocytes surrounding cartilage canals and osteochondral junctions captured with laser capture microdissection (4 OC, 6 normal) were obtained from femoropatellar joints of 17 immature horses. Equine‐specific Wnt signaling molecule mRNA expression levels were evaluated by two‐step real‐time qPCR. Spatial tissue protein expression of β‐catenin, Wnt‐11, Wnt‐4, and Dkk‐1 was determined by immunohistochemistry. There was significantly decreased Wnt‐11 and increased β‐catenin, Wnt‐5b, Dkk‐1, Lrp6, Wif‐1, Axin1, and SC‐PEP gene expression in early OC cartilage canal chondrocytes compared to controls. There was also significantly increased β‐catenin gene expression in early OC osteochondral junction chondrocytes compared to controls. Based on this study, abundant gene expression differences in OC chondrocytes surrounding cartilage canals suggest pathways associated with catabolism and inhibition of chondrocyte maturation are targeted in early OC pathogenesis. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1433–1438, 2015.