BACKGROUND: Enhanced proliferation, resistance to apoptosis, and metabolic shift 
to glycolysis of pulmonary arterial vascular smooth muscle cells (PAVSMCs) are 
key pathophysiological components of pulmonary vascular remodeling in idiopathic 
pulmonary arterial hypertension (PAH). The role of the distinct mammalian target 
of rapamycin (mTOR) complexes mTORC1 (mTOR-Raptor) and mTORC2 (mTOR-Rictor) in 
PAVSMC proliferation and survival in PAH and their therapeutic relevance are 
unknown.
METHODS AND RESULTS: Immunohistochemical and immunoblot analyses revealed that 
mTORC1 and mTORC2 pathways are markedly upregulated in small remodeled pulmonary 
arteries and isolated distal PAVSMCs from subjects with idiopathic PAH that have 
increased ATP levels, proliferation, and survival that depend on glycolytic 
metabolism. Small interfering RNA- and pharmacology-based analysis showed that 
although both mTORC1 and mTORC2 contribute to proliferation, only mTORC2 is 
required for ATP generation and survival of idiopathic PAH PAVSMCs. mTORC2 
downregulated the energy sensor AMP-activated protein kinase, which led to 
activation of mTORC1-S6 and increased proliferation, as well as a deficiency of 
the proapoptotic protein Bim and idiopathic PAH PAVSMC survival. NADPH oxidase 4 
(Nox4) protein levels were increased in idiopathic PAH PAVSMCs, which was 
necessary for mTORC2 activation, proliferation, and survival. Nox4 levels and 
mTORC2 signaling were significantly upregulated in small pulmonary arteries from 
hypoxia-exposed rats at days 2 to 28 of hypoxia. Treatment with the mTOR kinase 
inhibitor PP242 at days 15 to 28 suppressed mTORC2 but not Nox4, induced smooth 
muscle-specific apoptosis in small pulmonary arteries, and reversed 
hypoxia-induced pulmonary vascular remodeling in rats.
CONCLUSIONS: These data provide a novel mechanistic link of Nox4-dependent 
activation of mTORC2 via the energy sensor AMP-activated protein kinase to 
increased proliferation and survival of PAVSMCs in PAH, which suggests a new 
potential pathway for therapeutic interventions.