Background: Hypoxia-induced pulmonary hypertension (HPH) is one of the most common forms of PH.The hallmark of HPH is the pulmonary arterioles remodeling especially medial thickening.Excessive pulmonary arterial smooth muscle cells (PASMCs)proliferation have been implicated to play a very important role in the medial thickening.Hyperactivation of mammalian target of rapamycin (mTOR) and Notch3 signaling have been identified in HPH respectively.The activation of mTOR signaling has been shown to impair cell differentiation of murine and human by positively regulating Notch signaling.Therefore, we hypothesized that hypoxia activated mTOR was involved in HPH through regulating Notch3 signaling activity.