Alzheimer’s Presenilin Mutation Sensitizes Neural Cells to Apoptosis Induced by Trophic Factor Withdrawal and Amyloid β-Peptide: Involvement of Calcium and Oxyradicals

Abstract

Most autosomal dominant inherited forms of early onset Alzheimer’s disease (AD) are caused by mutations in the presenilin-1 (PS-1) gene on chromosome 14. PS-1 is an integral membrane protein with six to nine membrane-spanning domains and is expressed in neurons throughout the brain wherein it is localized mainly in endoplasmic reticulum (ER). The mechanism or mechanisms whereby PS-1 mutations promote neuron degeneration in AD are unknown. Recent findings suggest links among deposition of amyloid β-peptide (Aβ), oxidative stress, disruption of ion homeostasis, and an apoptotic form of neuron death in AD. We now report that expression of the human PS-1 L286V mutation in PC12 cells increases their susceptibility to apoptosis induced by trophic factor withdrawal and Aβ. Increases in oxidative stress and intracellular calcium levels induced by the apoptotic stimuli were exacerbated greatly in cells expressing the PS-1 mutation, as compared with control cell lines and lines overexpressing wild-type PS-1. The antiapoptotic gene product Bcl-2 prevented apoptosis after NGF withdrawal from differentiated PC12 cells expressing mutant PS-1. Elevations of [Ca2+]iin response to thapsigargin, an inhibitor of the ER Ca2+-ATPase, were increased in cells expressing mutant PS-1, and this adverse effect was abolished in cells expressing Bcl-2. Antioxidants and blockers of calcium influx and release from ER protected cells against the adverse consequences of the PS-1 mutation. By perturbing cellular calcium regulation and promoting oxidative stress, PS-1 mutations may sensitize neurons to apoptotic death in AD.

Increased susceptibility to amyloid toxicity in familial Alzheimer's fibroblasts

“…Correspondingly, we found prompt and sharp ROS production in APPV717I fibroblasts exposed to A␤ 1-40 and A␤ 1-42 aggregates. Accordingly, addition of A␤ to PC12 cells induces increased ROS production and apoptosis [12,27,50]. In contrast, treatment of healthy control fibroblasts with small prefibrillar aggregates induced a later and more moderate ROS increase.…”

Wild-Type But Not FAD Mutant Presenilin-1 Prevents Neuronal Degeneration by Promoting Phosphatidylinositol 3-Kinase Neuroprotective Signaling

“…For example, neurons from PS1 M146L knock-in mice show increased vulnerability to glucose deprivation and chemical hypoxia of (Mattson et al, 2000) whereas overexpression of PS1 FAD mutants A246E and C410Y in primary neurons inhibits Akt and increases apoptosis (Weihl et al, 1999). In addition, mutant L286V increases susceptibility to apoptosis induced by trophic factor withdrawal or amyloid ␤-peptides (Guo et al, 1997). Here we used primary neuronal cultures heterozygous for WT PS1 to examine the effects of eight PS1 FAD mutants on PI3K/Akt signaling and apoptosis in the presence of a WT PS1 allele, a situation closely resembling the in vivo FAD condition.…”

Protection against hydrogen peroxide cytotoxicity in Rat-1 fibroblasts provided by the oncoprotein Bcl-2: maintenance of calcium homoeostasis is secondary to the effect of Bcl-2 on cellular glutathione

“…The observation that Bcl-2 does not directly regulate cellular Ca# + compartmentation and fluxes but modulates sensitivity to Ca# + -dependent injurious processes through the intermediary glutathione may also help to explain the contradictory results reported for the action of Bcl-2 on cellular Ca# + homoeostasis and on Ca# + -mediated cell death [5][6][7][8][9][10][11][12]. According to the results obtained here with Rat-1 fibroblasts, Bcl-2 should only affect those Ca# + -mediated processes that are triggered by alterations in cellular glutathione homoeostasis, but should leave nonglutathione-dependent processes unaffected.…”

“…In some of these injurious processes, disruption of cellular Ca# + homoeostasis, especially elevations of cytosolic Ca# + concentration, is considered to play a decisive intermediary role [4]. Accordingly, effects of Bcl-2 on Ca# + homoeostasis and on Ca# + -mediated cell death have been studied in a number of experimental models [5][6][7][8][9][10][11][12]. These studies, however, led to contradictory results and no clear picture emerged as to how Bcl-2 may affect Ca# + -mediated cell-injurious processes.…”