The p3 peptide [amyloid beta-peptide (Abeta) 17-40/42], derived by alpha- and gamma-secretase cleavage of the amyloid precursor protein (APP), is a major constituent of diffuse plaques in Alzheimer's disease and cerebellar pre-amyloid in Down's syndrome. However, the importance of p3 peptide accumulation in Alzheimer's disease and its toxic properties is not clear. Here, we demonstrate that treatment of cells with Abeta 17-42 leads to apoptosis in two human neuroblastoma cell lines, SH-SY5Y and IMR-32. Abeta 17-42 activated caspase-8 and caspase-3, induced poly(ADP-ribose) polymerase cleavage, but did not activate caspase-9. Selective caspase-8 and caspase-3 inhibitors completely blocked Abeta 17-42-induced neuronal death. Abeta 17-42 moderately activated c-Jun N-terminal kinase (JNK); however, overexpression of a dominant-negative mutant of SEK1, the upstream kinase of JNK, protected against Abeta 17-42 induced neuronal death. These results demonstrate that Abeta 17-42 induced neuronal apoptosis via a Fas-like/caspase-8 activation pathway. Our findings reveal the previously unrecognized toxic effect of Abeta 17-42. We propose that Abeta 17-42 constitutes an additional toxic peptide derived from APP proteolysis and may thus contribute to the neuronal cell loss characteristic of Alzheimer's disease.

Excessive accumulation of amyloid β-peptide (Aβ) plays an early and critical role in synapse and neuronal loss in Alzheimer's Disease (AD). Increased oxidative stress is one of the mechanisms whereby Aβ induces neuronal death. Given the lessened susceptibility to oxidative stress exhibited by mice lacking p66Shc, we investigated the role of p66Shc in Aβ toxicity. Treatment of cells and primary neuronal cultures with Aβ caused apoptotic death and induced p66Shc phosphorylation at Ser36. Ectopic expression of a dominant-negative SEK1 mutant or chemical JNK inhibition reduced Aβ-induced JNK activation and p66Shc phosphorylation (Ser36), suggesting that JNK phosphorylates p66Shc. Aβ induced the phosphorylation and hence inactivation of forkhead transcription factors in a p66Shc-dependent manner. Ectopic expression of p66ShcS36A or antioxidant treatment protected cells against Aβ-induced death and reduced forkhead phosphorylation, suggesting that p66Shc phosphorylation critically influences the redox regulation of forkhead proteins and underlies Aβ toxicity. These findings underscore the potential usefulness of JNK, p66Shc, and forkhead proteins as therapeutic targets for AD.

The induction of heat shock proteins (HSP) by cellular stress and the activation of the hypothalamicpituitary-adrenal axis by physiologic stress are biological responses that aid in the maintenance of cellular and organismal homeostasis, respectively. In this report, restraint stress, known to activate the hypothalamic-pituitary-adrenal axis, is shown to induce expression of HSP70 mRNA selectively in the adrenal cortex of the rat. Restraint-induced HSP70 expression in the adrenals is rapid and is preceded by the activation of a protein factor capable of binding to the heat shock transcriptional control element. The ability of restraint to induce HSP70 expression in the adrenal is virtually eliminated in hypophysectomized rats but can be restored by the exogenous administration of adrenocorticotropic hormone. The magnitude of this induction declines as a function of increasing age, which may contribute to a reduced stress tolerance by aged animals. These results support a role for HSP70 in the physiologic stress response mediated by the hypothalamic-pituitary-adrenal axis.The ability of an organism to adapt to stress is a requisite for its survival in an everchanging environment (1). In higher organisms stress results in the activation of the hypothalamic-pituitary-adrenal (HPA) axis. This response is characterized by the secretion ofcorticotropin-releasing hormone from hypothalamic nuclei into the hypophyseal portal system, which, in turn, stimulates the release of adrenocorticotropic hormone (ACTH) from the anterior pituitary into the peripheral circulation. ACTH binds to specific adrenocortical receptors, resulting in the rapid release of glucocorticoids into the bloodstream. Glucocorticoids act on a variety of tissues to give rise to their numerous homeostatic effects (2).At the cellular level, heat and other metabolic stressors induce the synthesis of a set of highly conserved proteins termed heat shock proteins (HSPs) (3). This enhanced gene expression occurs as a result of stress-induced activation of one or more heat shock transcription factors (HSFs) (4-6). These proteins bind to a specific DNA sequence, the heat shock element (HSE) (7-10), in the promotor regions of the HSP genes to increase their rate of transcription. HSPs interact with other cellular proteins under normal and stress conditions and are thought to aid in the maintenance of cellular homeostasis (3).Our current knowledge of HSP function is derived largely from studies in cultured cells. Few investigations have used in vivo stress models that might have direct physiologic relevance. In a previous study we demonstrated that, in response to heat stress, HSP70 is preferentially induced in specific brain regions involved in the regulation of HPA function and hypothesized that HSPs are an integral component of the mammalian physiologic stress response (11). In support of this hypothesis, this report demonstrates that a mild physiologic stress, restraint, induces the expression of the major HSP, HSP70, in rat adrenal cortex. We provide ...