Differential Effects of Mitochondrial Heat Shock Protein 60 and Related Molecular Chaperones to Prevent Intracellular β-Amyloid-induced Inhibition of Complex IV and Limit Apoptosis

Abstract

Defects in mitochondrial oxidative metabolism, in particular decreased activity of cytochrome c oxidase, have been reported in Alzheimer disease tissue and in cultured cells that overexpress amyloid precursor protein. Mitochondrial dysfunction contributes to neurodegeneration in Alzheimer disease partly through formation of reactive oxygen species and the release of sequestered molecules that initiate programmed cell death pathways. The heat shock proteins (HSP) are cytoprotective against a number of stressors, including accumulations of misfolded proteins and reactive oxygen species. We reported on the property of Hsp70 to protect cultured neurons from cell death caused by intraneuronal ␤-amyloid. Here we demonstrate that Hsp60, Hsp70, and Hsp90 both alone and in combination provide differential protection against intracellular ␤-amyloid stress through the maintenance of mitochondrial oxidative phosphorylation and functionality of tricarboxylic acid cycle enzymes. Notably, ␤-amyloid was found to selectively inhibit complex IV activity, an effect selectively neutralized by Hsp60. The combined effect of HSPs was to reduce the free radical burden, preserve ATP generation, decrease cytochrome c release, and prevent caspase-9 activation, all important mediators of ␤-amyloid-induced neuronal dysfunction and death.Current evidence indicates that intracellular accumulation of ␤-amyloid in neurons leads to the formation of an insoluble pool in which the peptide is highly aggregated as well as a soluble pool in which toxic oligomers are found (1-3). A␤-(1-42) 2 is generated in both the endoplasmic reticulum and the intermediate compartment (4). Because neuronal mitochondria are frequently found in close association with the endoplasmic reticulum (5), it is possible that the local concentration of A␤ is relatively higher in their vicinity compared with other cellular locations. Conceivably, exposure of mitochondria to A␤ alters membrane stability and/or their normal oxidative phosphorylation functions. These considerations make it feasible that a direct impact of intracellular ␤-amyloid on mitochondrial function may contribute to neurodegeneration in AD through energy failure and activation of apoptosis.A recent study of mitochondrial function in a transgenic model and in AD patients has shown that oxidative phosphorylation is inhibited by the presence of intracellular ␤-amyloid (6), leading to a reduction in ATP production. ATP depletion leads to partial membrane depolarization, release of the voltagedependent Mg 2ϩ block of NMDA receptors, increase in calcium influx, and a decrease in calcium buffering capacity (7). The increase in intracellular calcium enhances free radical generation and triggers several pathways that lead to cellular dysfunction and death (8). Examination of brains from patients suffering from AD identifies a high fraction of cells undergoing apoptosis, which is suggested as an important mechanism for neuronal cell loss (9). One of the major events related to activation of the intrinsic programmed ce...

Proteomic analysis of cells exposed to prefibrillar aggregates of HypF-N

“…In a recent study, Hsp60, Hsp70, and Hsp90 were shown to provide differential protection against intracellular stress caused by β-amyloid by maintaining the efficiency of the mitochondrial oxidative phosphorylation and the tricarboxylic acid cycle enzymes. In particular, Hsp60 was shown to prevent the inhibition of complex IV activity by β-amyloid, thus preventing apoptosis [39]. We also found significantly increased levels of Gapdh and actin.…”

Upon oxidative stress, the antiapoptotic Hsp60/procaspase-3 complex persists in mucoepidermoid carcinoma cells

“…Hsp60, including probably the mitochondrial Cpn60, can be elevated in a number of human tumors (Czarnecka et al, 2006;Cappello et al, 2007;2008) and in the extracellular milieu, which can cause activation of an antitumor immune response (Calderwood et al, 2007). Whether and when mitochondrial and cytosolic Hsp60 have pro-or anti-apoptotic roles is still unclear, since there is evidence supporting both possibilities (Samali et al, 1999;Xanthoudakis et al, 1999;Gupta et al, 2005;Veereshwarayya et al, 2006;Chandra et al, 2007). In addition, it was demonstrated that increased expression of Hsp60, Hsp70, and Hsp90 interferes with mitochondrial apoptotic pathways in human neuroblastoma cells (Veereshwarayya et al, 2006).…”

“…Whether and when mitochondrial and cytosolic Hsp60 have pro-or anti-apoptotic roles is still unclear, since there is evidence supporting both possibilities (Samali et al, 1999;Xanthoudakis et al, 1999;Gupta et al, 2005;Veereshwarayya et al, 2006;Chandra et al, 2007). In addition, it was demonstrated that increased expression of Hsp60, Hsp70, and Hsp90 interferes with mitochondrial apoptotic pathways in human neuroblastoma cells (Veereshwarayya et al, 2006).…”

Alzheimer's Disease and Molecular Chaperones: Current Knowledge and the Future of Chaperonotherapy

“…Expression of Hsp60 is significantly decreased in the parietal cortex of AD subjects and in the cerebella of a rat model of AD, suggesting a defect in the protective role of this chaperonin in the AD brain [81,83]. In support of the neuroprotective effects of Hsp60, it has been demonstrated that in a human neuroblastoma cell line, induced expression of the chaperonin prevented intracellular -amyloid-induced inhibition of complex IV and consequently reduced apoptosis [84]. A 25-35 induced oxidation of Hsp60 in fibroblasts derived from AD patients [85] and, also, Hsp60 was oxidized by A 1-42 leading to a loss of function of the chaperonin, which caused an increase in protein misfolding and aggregation [86].…”