12/15-Lipoxygenase debilitates mitochondrial health in intermittent hypobaric hypoxia induced neuronal damage: An in vivo study

Abstract

High altitude cerebral edema does not fall in routine definition of hypoxia and requires alternative therapeutic strategies. 12/15-Lipoxygenase (12/15 LOX), a key proinflammatory lipid peroxidative enzyme which site specifically inserts into cellular and subcellular membranes and plays an instrumental role in hypobaric hypoxia induced neuropathogenesis. Mitochondria, the master regulator organelles for oxygen consumption and ATP generation are sensitive to intracellular oxygen perturbations and are associated with activation of apoptosis based cell death cascades that seal the fate of the cell. The mechanistic involvement of 12/15 LOX in mitochondria mediated cell death in brain microenvironment during hypobaric hypoxia conditions can be an interesting preposition. In the present study, we have investigated underlying involvement of 12/15 LOX in hypobaric hypoxia (HH) induced disturbance in mitochondrial integrity and its relation with neuronal apoptosis. Male Balb/c mice subjected to simulated HH condition for three consecutive days showed robust increase in intra-hippocampal 12(S)HETE (12/15 LOX metabolite), which was significantly reduced following baicalein (12/15 LOX Inhibitor) treatment. The elevated level of 12(S)HETE following hypobaric hypoxia condition correlated with simultaneous increase in expression of 12/15 LOX in neurons and microglia lining the hippocampal CA3 region. Further, 12/15 LOX gets embedded onto the periphery of mitochondria following HH and a strong correlation has been observed with loss of mitochondrial integrity as evident from increased cytochrome-c in the cytosolic compartment and a subsequent upregulated activity of Caspase-3 and Caspase-9 as well as Bax/Bcl-2 expression ratio. The observed effects seen under HH were reversed upon treatment with baicalein suggesting a critical role of 12/15 LOX in HH induced mitochondrial damage Further, the hypobaric hypoxia-mediated increase in hippocampal pAKT and pmTOR protein expression were significantly ameliorated following 12/15 LOX inhibition, suggesting a mitochondrial involvement. We hereby demonstrate the contribution of 12/15 LOX in disorienting mitochondrial integrity with subsequent release of cytochrome-c in cytosol which drives the neuronal cells to intrinsic mode of cell death during hypobaric hypoxia. The protective role of baicalein by inhibition of 12/15 LOX dependent neuronal cell death and preservation of mitochondrial integrity suggests it to be a plausible therapeutic target in CNS related disorders.

Keywords: 12/15-Lipoxygenase; Hippocampus; Hypobaric hypoxia; Mitochondrial integrity; Neuroprotection.