Expression of VEGF and pleiotrophin in deer antler

Deer antlers represent a unique model of mammalian regeneration in that they cast and fully regenerate every year. The deer antler thus provides a fascinating model of both rapid angiogenesis and chondrogenesis and the opportunity to investigate unique growth regulatory processes. One such phenomenon is the presence of vascularized cartilage in the growing antler tip-unlike other cartilage, which is typically avascular. The mechanisms by which blood vessels grow in the cartilage as well as the factors that drive antler extension at approximately 1 cm a day have been hitherto largely unknown. The aim of this study was to determine the expression of VEGF and pleiotrophin within the growing antler tip. We isolated cervine VEGF121 and VEGF165 from deer antler and found that mRNA is produced for VEGF in the precartilage and cartilage regions. By in situ hybridization, we examined whether the VEGF receptors Flt-1 and KDR are present in deer antler and found only KDR mRNA within the endothelial cells of the precartilage region. This finding is compatible with VEGF having an angiogenic effect within antler. Pleiotrophin mRNA was found in the vascular smooth muscle cells of the dermis, thus supporting a possible role in vascular growth. High levels of pleiotrophin mRNA were also detected in the precartilage region with possible implications for both angiogenesis and chondrogenesis. This is the first report of cervine angiogenic growth factors within the growing antler tip.