Abstract 3159: A Critical Role of Glycogen Synthase Kinase-β (GSK3β) in Pulmonary Arterial Hypertension
Pulmonary Arterial Hypertension (PAH) is characterized by resistance to apoptosis in PA smooth muscle cells (PASMC), strikingly similar to cancer. PAH is characterized by the activation of the transcription factor NFAT, responsible for the down-regulation of Kv channels and up-regulation of bcl-2. The metabolic enzyme glycogen synthase kinase-3β (GSK3β) inhibits NFAT activity. GSK3β is inhibited by PI3K/Akt and has been shown to be inhibited in the glycolytic environment of cancer. In cancer, the GSK3β inhibition also promotes the translocation and binding of hexokinase II (HKII) to the mitochondrial voltage dependent anion channel (VDAC), inhibiting it and resulting in mitochondrial hyperpolarization and apoptosis resistance. We hypothesized that GSK3β is inhibited in PAH and that this can explain the NFAT activation. Resistance PA mouse PASMC exposed to 48 hr hypoxia had significant GSK3β inhibition compared to normoxic controls and this was associated with NFAT activation (nuclear localization), HKII-mitochondrial translocation, mitochondrial hyperpolarization and resistance to serum starved apoptosis. GSK3β activation by wortmanin or LY294002 (PI3K inhibitors) blocked all the above hypoxia-induced effects. A HKII-VDAC competitive peptide (prevents HKII binding) specifically prevented the hypoxia-induced mitochondrial hyperpolarization, mimicking GSK3β activation. In vivo, mice exposed to chronic hypoxia for 3 weeks developed PAH (n=8, mPA=32±2 mmHg) and compared to their normoxic controls (n=8, mPA=11±2mmHg), their resistance PAs showed evidence of 45% GSK3β inhibition (immunoblot P-GSK3β/GSK3β). The metabolic modulator Dichloroacetate that inhibits the glycolytic environment ( activating GSK3β) reversing both rat PAH and cancer growth, completely reversed mouse hypoxia induced PAH (n=8, mPA=18±2mmHg). DCA also reversed the NFAT activation, the Kv1.5 down-regulation and the mitochondrial hyperpolarization that was present in the untreated hypoxic mice resistance PAs and PASMC. We show that the mitochondrial hyperpolarization in PAH as well as the activation of NFAT, are due to GSK3β inhibition and that this is secondary to the overall metabolic remodeling. Like in cancer, GSK3β can be a novel therapeutic target in PAH.