beta 25-35 alters calcium homeostasis and induces neurotoxicity in cerebellar granule cells.

We studied the neurotoxic effects of beta 25-35 amyloid fragment (beta 25-35) on cerebellar granule cells and the intracellular mechanisms involved. Treatment for 3 days with peptide greatly reduced the survival of 1 day in vitro (DIV) cultures kept in 5 mM KCI but slightly modified the survival of 25 mM KCI-cultured cerebellar granule cells. We also studied the effect of glutamate on survival of undifferentiated cerebellar granules. We report no neurotoxic effect of glutamate on 3-DIV-treated cultures; whereas in beta 25-35-pretreated cells, a significant glutamate toxicity was observed. Treatment of 6-DIV cells with beta 25-35, performed with 25 mM KCI, induced a late but significant neurotoxic effect after 5 days of exposure, and death occurred within 8 days. Differentiated cerebellar granule cells were also sensitive to glutamate-related neurotoxicity, and this effect was enhanced by beta 25-35 pretreatment. To study the molecular mechanisms underlying the neurotoxic effects of beta 25-35, changes in calcium homeostasis after glutamate stimulation were evaluated in control and beta 25-35-treated cells. beta 25-35 did not affect basal [Ca2+]i but modified glutamate-induced [Ca2+]i increase, causing a sustained plateau phase that persisted even after the removal of the agonist. These results show that beta 25-35 induces neurotoxicity in cerebellar granule cells and that this effect is related to modifications in the control of calcium homeostasis.