Abstract 1394: Sublethal Levels of Aldehydes Augmented Cardiac Anti-Oxidant Defense through Activation of eIF2α-ATF4 Pathway via GCN2 Kinase
[Introduction] Despite an increase in the levels of aldehydes, the heart from aldehyde dehydrogenase (ALDH)2*2-transgenic (Tg) mice, loss of function model of ALDH, exhibited a greater tolerance to oxidative stress via activation of amino acid metabolism leading to glutathione biosynthesis. This study was designed to identify the signaling cascades responsible for the activation of amino acid metabolism by aldehydes. [Methods & Results] (1) Phosphorylation of α-subunit of eukaryotic translation initiation factor 2 (eIF2α) and subsequent translational activation of ATF4 have been shown to induce amino acid metabolism as a common response to a wide variety of stressors. Consistent with this, phosphorylation levels of eIF2α and protein expression of ATF4 were increased in ALDH2*2-Tg hearts. (2) Among four eIF2α kinases, general control non-depressible (GCN)2 kinase, a sensor for amino acid insufficiency, was activated in ALDH2*2-Tg heart. (3) Quantification of intracellular amino acid demonstrated that free histidine concentration in ALDH2*2-Tg heart was selectively reduced by 50% compared to that in non-Tg littermates. (4) To clarify the functional significance of observed reduction in histidine, ALDH2*2-Tg mice were fed a high histidine diet. The phosphorylation levels of eIF2α and the protein levels of ATF4 were diminished by 50% in ALDH2*2-Tg mice fed the high histidine diet, in agreement with the normalization of histidine concentration. Accordingly, both enhanced tolerance to ischemia-reperfusion injury and elevated levels of glutathione were partially diminished in the heart from ALDH2*2-Tg mice fed the high histidine diet compared to ALDH2*2-Tg mice fed normal chow. (5) In culture, exposure to 4-hydroxy-2-nonenal (4-HNE) phosphorylated GCN2 and eIF2α and increased protein levels of ATF4 in a time-dependent manner. (6) siRNA-mediated knockdown of GCN2 abrogated 4-HNE-induced induction of amino acid metabolic genes. [Conclusions] Activation of eIF2α-ATF4 pathway via GCN2 kinase might be of special importance in the transcriptional control that coordinately promotes amino acid metabolism in response to aldehydes. Intracellular depletion of free histidine is at least partly involved in the activation of GCN2 kinase by aldehydes.