Spatiotemporal localization of VEGF-A isoforms in the mouse postnatal growth plate

Vascular endothelial growth factor (VEGF) is implicated as a key angiogenic factor in the development of endochondral long bone. Several studies have evaluated the role of VEGF in prenatal endochondral bone development, but few have evaluated VEGF postnatally. Growth plates from mice at postnatal ages 14 (P14), 35 (P35), 49 (P49), and 77 (P77) days were examined for differential expression of the primary VEGF-A mRNA isoforms: VEGF 120, VEGF 164, and VEGF 188. VEGF 120 isoform expression was stable across all ages, whereas VEGF 164 had significantly less expression at P35 and P49 and VEGF l88 expression increased with increasing age. The proportion of transcript isoforms expressed at a given age also changed with VEGF 120 being expressed more highly at P35 and P49 than the other two isoforms. Changes in VEGF mRNA isoforms across cell types within the growth plate were assessed by Percoll fractionation of growth plate cells at age P28. Cells of the proliferative and early hypertrophic regions had significantly higher total VEGF mRNA expression relative to the resting and late hypertrophic regions. VEGF protein expression assessed by immunohistochemistry showed variable expression patterns with increasing postnatal age. In contrast, FLK-1 (VEGF Receptor-2) expression was restricted to the hypertrophic region. These results indicate that VEGF continues to play a significant role in endochondral bone development throughout the entire growth phase of postnatal bone development.