Notch signaling is critically important for proper architecture of the vascular system, and mutations in NOTCH3 are associated with CADASIL, a stroke and dementia syndrome with vascular smooth muscle cell (VSMC) dysfunction. In this report, we link Notch signaling to platelet-derived growth factor (PDGF) signaling, a key determinant of VSMC biology, and show that PDGF receptor (PDGFR)-ß is a novel immediate Notch target gene. PDGFR-ß expression was upregulated by Notch ligand induction or by activated forms of the Notch receptor. Moreover, upregulation of PDGFR-ß expression in response to Notch activation critically required the Notch signal integrator CSL. In primary VSMCs, PDGFR-ß expression was robustly upregulated by Notch signaling, leading to an augmented intracellular response to PDGF stimulation. In newborn Notch3-deficient mice, PDGFR-ß expression was strongly reduced in the VSMCs that later develop an aberrant morphology. In keeping with this, PDGFR-ß upregulation in response to Notch activation was reduced also in Notch3-deficient embryonic stem cells. Finally, in VSMCs from a CADASIL patient carrying a NOTCH3 missense mutation, upregulation of PDGFR-ß mRNA and protein in response to ligand-induced Notch activation was significantly reduced. In sum, these data reveal a hierarchy for 2 important signaling systems, Notch and PDGF, in the vasculature and provide insights into how dysregulated Notch signaling perturbs VSMC differentiation and function. © 2008 American heart association, Inc.