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 term inal differentiation. We have examined the distribution and gene expression levels of PTHrP in the growth plates of broiler chickens with tibial dysch ondroplasia (TD) in order to determine whether increased expression of PTHr P is responsible for the delayed chondrocyte differentiation that is charac teristic of this skeletal disorder. PTHrP protein distribution and gene exp ression levels were assessed by immunocytochemistry and reverse transcripta se-polymerase chain reaction, respectively. In growth plates of normal bird s, PTHrP was found to be distributed throughout all maturational zones of t he growth plate. In cartilage proximal to the TD lesion, PTHrP immunostaini ng 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 le sion stained poorly for PTHrP and this was reflected in the lower levels of PTHrP mRNA detected in lesion cells. These results suggest that alteration s in PTHrP distribution and gene expression are not primarily responsible f or the delayed chondrocyte differentiation and hypertrophy noted in dyschon droplasia, but are a result of secondary changes due to the pathology of th e condition.