PDGF (alpha)-receptor is unresponsive to PDGF-AA in aortic smooth muscle cells from the NG2 knockout mouse

A line of null mice has been produced which fails to express the transmembrane chondroitin sulfate proteoglycan NG2. Homozygous NG2 null mice do not exhibit gross phenotypic differences from wild-type mice, suggesting that detailed analyses are required to detect subtle alterations caused by the absence of NG2. Accordingly, dissociated cultures of aortic smooth muscle cells from null mice were compared to parallel cultures from wild-type mice for their ability to proliferate and migrate in response to specific growth factors. Both null and wild-type smooth muscle cells exhibited identical abilities to proliferate and migrate in response to PDGF-BB. In contrast, only the wild-type cells responded to PDGF-AA in both types of assays. NG2 null cells failed to proliferate or migrate in response to PDGF-AA, implying a defect in the signaling cascade normally initiated by activation of the PDGF (alpha)-receptor. In agreement with this idea, activation of the extracellular signal-regulated kinase (ERK) in response to PDGF-AA treatment occured only in wild-type cells. Failure to observe autophosphorylation of the PDGF (alpha)-receptor in PDGF-AA-treated null cells indicates that the absence of NG2 causes a defect in signal transduction at the level of (alpha)-receptor activation.