Expression of calbindin-D(28k) in C6 glial cells stabilizes intracellular calcium levels and protects against apoptosis induced by calcium ionophore and amyloid β-peptide

The calcium binding protein, calbindin-D(28k) is normally present in neurons. Recently we reported that brain injury and tumor necrosis factors (TNFs) induce calbindin-D(28k) in astrocytes. TNF-treated calbindin expressing astrocytes were resistant to acidosis and calcium ionophore toxicity, suggesting that calbindin may have a cytoprotective role in astrocytes in the injured brain (M.P. Mattson, B. Cheng, S.A. Baldwin, V.L. Smith-Swintosky, J. Keller, J. Geddes, Scheft, J.W., Christakos, S., Brain injury and tumor necrosis factors induce calbindin-D(28k) in astrocytes: evidence for a cytoprotective response, J. Neurosci. Res., 42 (1995) 257). In order to obtain direct evidence for a role of calbindin, using the eukaryotic expression vector pREP4, rat calbindin-D(28k) was stably expressed in C6 rat astocytoma glial cells. Cytotoxicity in response to calcium ionophore or amyloid β-peptide (which accumulates in the brain in Alzheimer's disease and has been reported to be neurotoxic) was measured by MTT reduction in vector transfected cells and in calbindin transfected clones. Stably expressed calbindin resulted in increased cell survival in the presence of calcium ionophore (1-10 μM) or amyloid β-peptide (10-100 μM). In addition, the calcium ionophore or amyloid β-peptide mediated rise in intracellular calcium in vector transfected cells was significantly attenuated in calbindin expressing cells. Apoptotic cell death was detected by the Hoechst method in vector transfected C6 glial cells treated with calcium ionophore or β- amyloid (34-36% apoptotic cells/culture). The number of apoptotic nuclei was significantly attenuated in similarly treated calbindin-D(28k) transfected clones (10-13% apoptotic cells/culture; p <0.01). Our results support the involvement of calcium fluxes in apoptosis and suggest that calbindin- D(28k), by buffering calcium, can suppress death in apoptosis susceptible cells in the central nervous system.