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 i nvolved. Treatment for 3 days with peptide greatly reduced the surviva l of 1 day in vitro (DIV) cultures kept in 5 mM KCI but slightly modif ied the survival of 25 mM KCI-cultured cerebellar granule cells, We al so studied the effect of glutamate on survival of undifferentiated cer ebellar granules, We report no neurotoxic effect of glutamate on 3-DIV -treated cultures; whereas in beta 25-35-pretreated cells, a significa nt glutamate toxicity was observed. Treatment of 6-DIV cells with beta 25-35, performed with 25 mM KCI, induced a late but significant neuro toxic effect after 5 days of exposure, and death occurred within 8 day s, Differentiated cerebellar granule cells were also sensitive to glut amate-related neurotoxicity, and this effect was enhanced by beta 25-3 5 pretreatment. To study the molecular mechanisms underlying the neuro toxic effects of beta 25-35, changes in calcium homeostasis after glut amate stimulation were evaluated in control and beta 25-35-treated cel ls, beta 25-35 did not affect basal [Ca2+](i) but modified glutamate-i nduced [Ca2+](i) increase, causing a sustained plateau phase that pers isted even after the removal of the agonist. These results show that b eta 25-35 induces neurotoxicity in cerebellar granule cells and that t his effect is related to modifications in the control of calcium homeo stasis.