Idiopathic Pulmonary Arterial Hypertension in human patients is associated with mutations in BMPR2. Mice expressing an inducible dominant negative form of BMPR2 in smooth muscle develop elevated right ventricular pressures when the transgene is activated. We hypothesized that transcriptional changes in these mice may allow insight into the early molecular events leading to Idiopathic Pulmonary Arterial Hypertension (IPAH). Microarray analysis was used to examine the transcriptional changes induced in whole lung by loss of normal smooth muscle cell (SMC) BMPR2 signaling in adult male or female mice (12 weeks at sacrifice) expressing the transgene for either 1 or 8 weeks. Our key results include a decrease in markers of smooth muscle differentiation, an increase in cytokines and markers of immune response, particularly in female mice, and a decrease in angiogenesis-related genes. These broad patterns of gene expression appear as early as 1 week, and are well established by 8 weeks. Results were confirmed by quantitative RT-PCR to RNA from individual mice. Primary pulmonary artery SMC cultures transfected with siRNA to BMPR2 also show loss of SMC markers Myosin Heavy Chain 11 (Myh11) and Calponin (Cnn1) by quantitative RT-PCR and western blot. These studies show classes of genes differentially regulated in response to loss of BMPR2 in SMC in vivo with clear relevance to the IPAH disease process, suggesting that the relevance of BMPR2 dysregulation may extend beyond proliferation.