VEGFR‐2‐mediated increased proliferation and survival in response to oxygen and glucose deprivation in PlGF knockout astrocytes

Abstract In hypoxic/ischemic conditions, astrocytes are involved in neuroprotection and angiogenesis. Vascular endothelial growth factor (VEGF) induces angiogenesis and exhibits neuroprotective and neurotrophic properties. However, the role of placental growth factor (PlGF), a VEGF homolog, in these processes is unclear. Therefore, proliferation and survival studies were performed on PlGF knockout (PlGF−/−) and wild‐type (PlGF+/+) mouse astrocytes. A significant increase in cell proliferation and survival to oxygen and glucose deprivation (OGD) was observed in PlGF−/− compared to PlGF+/+ astrocytes. Interestingly, no PlGF protein expression was detected in PlGF+/+ astrocytes and no changes in VEGF protein levels were observed between the two genotypes. Real‐time PCR and immunocytochemistry showed over‐expression of VEGF receptor‐2 (VEGFR‐2) in PlGF−/− compared with PlGF+/+ astrocytes. Confocal microscopy revealed nuclear, membrane, and cytoplasmic localization of VEGFR‐2. In vivo over‐expression of VEGFR‐2 mRNA was also detected in PlGF−/− compared with PlGF+/+ astrocytes. Stimulation with VEGF165 resulted in increased proliferation in PlGF−/− compared with PlGF+/+ astrocytes. This effect was blocked by the VEGFR‐2 antagonist, VEGF165b. The enhanced proliferation of PlGF−/− astrocytes correlated with increased phospho‐extracellular‐signal‐regulated kinase‐1/2 levels, while the resistance to OGD was independent of the phosphatidylinositol 3′‐kinase/Akt pathway. These results suggest that VEGFR‐2 mediates the enhanced proliferative/OGD resistant phenotype observed in PlGF−/− astrocytes.