Alzheimer's disease presenilin-1 exon 9 deletion and L250S mutations sensitize SH-SY5Y neuroblastoma cells to hyperosmotic stress-induced apoptosis

Mutations in the presenilin-1 (PS1) and presenilin-2 (PS2) genes account fo r the majority of early-onset familial Alzheimer's disease cases. Recent st udies suggest that presenilin gene mutations predispose cells to apoptosis by mechanisms involving altered calcium homeostasis and oxidative damage. I n the present study, we determined whether PS1 mutations also sensitize cel ls to hyperosmotic stress-induced apoptosis. For this, we established SH-SY 5Y neuroblastoma cell lines stably transfected with wild-type PS1 or either the PS1 exon 9 deletion (Delta E9) or PS1 L250S mutants. Cultured cells we re exposed to an overnight (17 h) serum deprivation, followed by a 30 min t reatment with either 20 mM glucose, 10 nM insulin-like growth factor-1 or 2 0 mM glucose +10 nM insulin-like growth factor-1. Cells were then cultured for a further 3, 6 or 24 h and stained for apoptotic condensed nuclei using propidium iodide. Confirmation that cells were undergoing an active apopto tic process was achieved by labelling of DNA strand breaks using the termin al dUTP nick end labelling (TUNEL) technique. We also determined cell viabi lity using 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide (M TT) reduction. Propidium iodide staining revealed that all cell lines and c ontrols showed an increased number of apoptotic cells appearing with conden sed nuclei at 24 h compared with 6 h and 3 h. High glucose-induced hyperosm otic stress resulted in significantly more apoptotic cells in the PS1 Delta E9 and PS1 L250S mutation cell lines at 24 h, compared with the wild-type PS1 lines (P < 0.001, ANOVA for both comparisons). Mean values (+/- S.D.) f or the percentage number of apoptotic cells at 24 h following high glucose treatment were 16.1 +/- 3.5%, 26.7 +/- 5.5% and 31.0 +/- 5.7% for the wild- type PS1, PS1 Delta E9 and PS1 L250S lines, respectively. The pro-apoptotic effects of high glucose treatment were reversed by 10 nM insulin-like grow th factor-1, although to a lesser extent in the mutation cell Lines (5.8 +/ - 2.4%, 15.2 +/- 7.3% and 13.2 +/- 2.0% for the wild-type PS1, PS1 Delta E9 (P < 0.01 for comparison with wild-type PS1) and PS1 L250S (P < 0.01 for c omparison with wild-type PS1) transfected lines, respectively. TUNEL labell ing of cells at 24 h following treatment gave essentially the same results pattern as obtained using propidium iodide. The percentage number of apopto tic cells with DNA strand breaks (means +/- S.D.) following high glucose tr eatment was 15.4 +/- 2.6% for the wild-type PS1, 26.8 +/- 3.2% for the PS1 Delta E9 (P < 0.001 for comparison with wild-type PS1) and 29.7 +/- 6.1% fo r the PS1 L250S transfected lines (P < 0.001 for comparison with wild-type PS1). The PS1 Delta E9 and PS1 L250S transfected lines also showed a higher number of apoptotic cells with DNA strand breaks at 24 h following high gl ucose plus insulin-like growth factor-1 treatment (11.4 +/-: 2.0% and 14.3 +/- 2.8%, respectively), compared with values for the wild-type PS1 lines ( 8.5 +/- 2.4%). These differences were significant (P < 0.01) for the compar ision of wild-type PS1 and PS1 L250S, but not PS1 Delta E9 lines. The mutat ion-related increases in number of apoptotic cells at 24 h following high g lucose treatment were not accompanied by significant differences in cell vi ability at this time-point. Our results indicate that PS1 mutations predispose to hyperosmotic stress-i nduced apoptosis and that the anti-apoptotic effects of insulin-like growth factor-1 are compromised by these mutations. Perturbations of insulin-like growth factor-1 signalling may be involved in PS1 mutation-related apoptot ic neuronal cell death in Alzheimer's disease. (C) 1999 IBRO. Published by Elsevier Science Ltd.