LPS-induced decrease in intracellular labile zinc, [Zn]i, contributes to apoptosis in cultured sheep pulmonary artery endothelial cells.

Thambiayya K, Wasserloos KJ, Huang Z, Kagan VE, St. Croix CM, Pitt BR. LPS-induced decrease in intracellular labile zinc, [Zn](i), contributes to apoptosis in cultured sheep pulmonary artery endothelial cells. Am J Physiol Lung Cell Mol Physiol 300: L624-L632, 2011. First published January 14, 2011; doi:10.1152/ajplung.00376.2010.-A role in signal transduction for a vanishingly small labile pool of intracellular zinc ([Zn](i)) has been inferred by the sensitivity of various physiological pathways to zinc chelators such as N, N, N', N'-tetrakis(2-pyridylmethyl) ethylenediamine (TPEN) and/or associations with changes in nonprotein-bound zinc-sensitive fluorophores. Although we (44) reported that LPS-induced apoptosis in cultured sheep pulmonary artery endothelial cells (SPAEC) was exacerbated by TPEN, 1) we did not detect acute (30 min) changes in [Zn](i), and 2) it is unclear from other reports whether LPS increases or decreases [Zn](i) and whether elevations or decreases in [Zn](i) are associated with cell death and/or apoptosis. In the present study, we used both chemical (FluoZin-3 via live cell epifluorescence microscopy and fluorescence-activated cell sorting) and genetic (luciferase activity of a chimeric reporter encoding zinc-sensitive metal-response element and changes in steady-state mRNA of zinc importer, SLC39A14 or ZIP14) techniques to show that LPS caused a delayed time-dependent (2-4 h) decrease in [Zn](i) in SPAEC. A contributory role of decreases in [Zn](i) in LPS-induced apoptosis (as determined by caspase-3/7 activation, annexin-V binding, and cytochrome c release) in SPAECs was revealed by mimicking the effect of LPS with the zinc chelator, TPEN, and inhibiting LPS- (or TPEN)-induced apoptosis with exogenous zinc. Collectively, these are the first data demonstrating a signaling role for decrease in [Zn](i) in pulmonary endothelial cells and suggest that endogenous levels of labile zinc may affect sensitivity of pulmonary endothelium to the important and complex proapoptotic stimulus of LPS.