Abstract 3464: The Oncoprotein Kinase Pim-1 Play a Key Role in Human Pulmonary Hypertension
Pulmonary arterial hypertension (PAH) is a proliferative remodeling disease characterized by enhanced pulmonary artery smooth muscle (PASMC) proliferation and suppressed apoptosis. We described that human PAH is associated with the activation of the transcription factor NFAT (nuclear factor of activated T-cells) accounting for a number of diverse features of PAH PASMC including: the downregulation of Kv1.5, (which by increasing [Ca2+]i promotes proliferation), the mitochondrial membrane potential, (ΔΨm) hyperpolarization (suppressing apoptosis). Because NFAT is implicated in several physiological processes (immune response), its inhibition in PAH patients could be associated with detrimental effects. Therefore a better understanding of the mechanism accounting for NFAT activation in PAH-PASMC is of a great therapeutic interest. Pim-1 is a kinase previously thought to be expressed primarily in cancer cells and is recognized as a strong “NFAT activator”. Because of the multiple similarities between cancer and PAH, we hypothesized that Pim-1 activation is involved in the pathogenesis of PAH. Using immunoblot & qRT-PCR (n=3;p<0.05) we found that Pim-1 is expressed in humans PAH-PASMC and rats with monocrotaline-induced PAH (M-PAH), but not in healthy-PASMC and control rats. Using either siRNA and dominant-negative adenovirus (DN-Pim-1) we demonstrated that Pim-1 inhibition in PAH-PASMC
decreases NFAT activation (luciferase assay); depolarizes ΔΨm (TMRM; n=150 p<0.05), increasing apoptosis by 25% (n=150 p<0.05, TUNEL).
By decreasing [Ca2+]i (FLUO3AM n=150, p<0.05) Pim-1 inhibition decreases proliferation by 30% (PCNA).
Opposite results were observed in healthy-PASMC infected with Pim-1 adenovirus. Finally, In vivo experiments with inhalation of DN-Pim1 or injection of Pim-1 siRNA in rats with M-PAH (N=10; p<0.05) support a putative therapeutic effect of Pim-1 inhibition characterized by
a PA specific NFAT inhibition,
decreased PA pressure, wall thickness and right ventricular hypertrophy (Echo and catheterization).
We demonstrated for the first time that the inhibition of the inappropriate activation of Pim-1 that accompanies human and experimental PAH is a novel and attractive therapeutic strategy to reverse PAH.