Parathyroid hormone-related peptide expression in tibial dyschondroplasia

Parathyroid hormone-related peptide (PTHrP) has a key role in the growth of long bones, as it is a negative regulator of growth plate chondrocyte terminal differentiation. We have examined the distribution and gene expression levels of PTHrP in the growth plates of broiler chickens with tibial dyschondroplasia (TD) in order to determine whether increased expression of PTHrP is responsible for the delayed chondrocyte differentiation that is characteristic of this skeletal disorder. PTHrP protein distribution and gene expression levels were assessed by immunocytochemistry and reverse transcriptase-polymerase chain reaction, respectively. In growth plates of normal birds, PTHrP was found to be distributed throughout all maturational zones of the growth plate. In cartilage proximal to the TD lesion, PTHrP immunostaining and the level of PTHrP gene expression were similar to that observed in normal birds. In contrast, many chondrocytes within the centre of the TD lesion stained poorly for PTHrP and this was reflected in the lower levels of PTHrP mRNA detected in lesion cells. These results suggest that alterations in PTHrP distribution and gene expression are not primarily responsible for the delayed chondrocyte differentiation and hypertrophy noted in dyschondroplasia, but are a result of secondary changes due to the pathology of the condition.