Immunolocalization of the angiogenetic factor pleiotrophin (PTN) in the growth plate of mice

The aim of this study was to find out whether and where the angiogenic agent pleiotrophin (PTN) occurs within the growth plate. We investigated paraffin-embedded tissue sections of ten male mice with an antibody directed against the recombinant PTN. Immunostaining for PTN was positive within the cytoplasm and the pericellular matrix of osteoblasts which lined the longitudinal mineralized septae of the epiphyseal plate. Within the zone of hypertrophic chondrocytes, immunolabelling for PTN was positive in the pericellular matrix of hypertrophic chondrocytes and within the opened lacunae of the apoptotic hypertrophic chondrocytes. The resting zone and the proliferation zone were PTN negative. The results of our study suggest that the known angiogenetic peptide PTN plays a role in the process of angiogenesis in the growth plate.