Pulmonary hypertension (PH) is a progressive disorder whose cellular pathogenesis involves enhanced smooth muscle cell (SMC) proliferation and resistance to apoptosis signals. Existing evidence demonstrates that the tumor suppressor, programmed cell death 4 (PDCD4) affects patterns of cell growth and repair responses in the systemic vasculature following experimental injury. In the current study, the regulation PDCD4 and its functional effects on growth and apoptosis susceptibility in pulmonary artery smooth muscle cells was explored. We previously demonstrated that pharmacological activation of the nuclear transcription factor, peroxisome proliferator-activated receptor gamma (PPAR), attenuated hypoxia-induced proliferation of human pulmonary artery smooth muscle cells (HPASMC) by inhibiting the expression and mitogenic functions of microRNA-21 (miR-21). In the current study, we hypothesize that PPAR stimulates PDCD4 expression and HPASMC apoptosis by inhibiting miR-21. Our findings demonstrate that PDCD4 is reduced in the mouse lung upon exposure to chronic hypoxia (10% O₂ x 3-weeks) and in hypoxia-exposed HPASMC (1% O₂). HPASMC apoptosis was reduced by hypoxia, by miR-21 overexpression, or by siRNA-mediated PPAR and PDCD4 depletion. Activation of PPAR inhibited miR-21 expression and resultant proliferation, while restoring PDCD4 levels and apoptosis to baseline. Additionally, pharmacological activation of PPAR with rosiglitazone enhanced PDCD4 protein expression and apoptosis in a dose-dependent manner as demonstrated by increased annexin V detection by flow cytometry. Collectively, these findings demonstrate that PPAR confers growth inhibitory signals in hypoxia-exposed HPASMC through suppression of miR-21 and the accompanying de-repression of PDCD4 which augments HPASMC susceptibility to undergo apoptosis.