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The role of cholesterol in Alzheimer's disease (AD) has been linked to the generation of toxic amyloid β peptides (Aβ). Using genetic mouse models of cholesterol loading, we examined whether mitochondrial cholesterol regulates Aβ neurotoxicity and AD pathology. Isolated mitochondria from brain or cortical neurons of transgenic mice overexpressing SREBP-2 (sterol regulatory element binding protein 2) or NPC1 (Niemann-Pick type C1) knock-out mice exhibited mitochondrial cholesterol accumulation, mitochondrial glutathione (mGSH) depletion and increased susceptibility to Aβ1- 42-induced oxidative stress and release of apoptogenic proteins. Similar findings were observed in pharmacologically GSH-restricted rat brain mitochondria, while selective mGSH depletion sensitized human neuronal and glial cell lines to Aβ1- 42-mediated cell death. Intracerebroventricular human Aβ delivery colocalized with mitochondria resulting in oxidative stress, neuroinflammation and neuronal damage that were enhanced in Tg-SREBP-2 mice and prevented upon mGSH recovery by GSH ethyl ester coinfusion, with a similar protection observed by intraperitoneal administration of GSH ethyl ester. Finally, APP/PS1 (amyloid precursor protein/presenilin 1) mice, a transgenic AD mouse model, exhibited mitochondrial cholesterol loading and mGSH depletion. Thus, mitochondrial cholesterol accumulation emerges as a novel pathogenic factor in AD by modulating Aβ toxicity via mGSH regulation; strategies boosting the particular pool of mGSH may be of relevance to slow down disease progression. [ABSTRACT FROM AUTHOR]

Poly(ADP-ribose) polymerase-1 (PARP-1) and PARP-2 belong to a family of enzymes that, using NAD(+) as a substrate, catalyze poly(ADP-ribosyl)ation of proteins. PARP-1 and PARP-2 catalytic activity is stimulated by DNA-strand breaks targeting mainly proteins involved in chromatin structure and DNA metabolism, providing strong support for a dual role of both PARP-1 and PARP-2 in the DNA damage response as DNA damage sensors and signal transducers to downstream effectors. The DNA damage response has important consequences for genomic stability and tumour development. In order to manipulate DNA damage responses to selectively induce tumour cell death, a considerable effort is centred on defining the molecular mechanisms that allow cells to detect, respond to, and repair DNA damage. PARP inhibitors that compete with NAD+ at the highly conserved enzyme active site are arisen as new potential therapeutic strategies as chemo- and radiopotentiation and for the treatment of cancers with specific DNA repair defects as single-agent therapies. In the present review, we highlight emerging information about the redundant and specific functions of PARP-1 and PARP-2 in genome surveillance and DNA repair pathways. Understanding these roles might provide invaluable clues to design new cancer therapeutic approaches. In addition, we provide an overview of ongoing clinical trials with PARP inhibitors and the value of PARP-1 and PARP-2 expression as prognostic biomarkers in cancer.

Background: Hypoxia-mediated HIF-1alpha stabilization and NF-kappaB activation play a key role in carcinogenesis by fostering cancer cell survival, angiogenesis and tumor invasion. Gangliosides are integral components of biological membranes with an increasingly recognized role as signaling intermediates. In particular, ganglioside GD3 has been characterized as a proapoptotic lipid effector by promoting cell death signaling and suppression of survival pathways. Thus, our aim was to analyze the role of GD3 in hypoxia susceptibility of hepatocarcinoma cells and in vivo tumor growth., Methodology/principal Findings: We generated and characterized a human hepatocarcinoma cell line stably expressing GD3 synthase (Hep3B-GD3), which catalyzes the synthesis of GD3 from GM3. Despite increased GD3 levels (2-3 fold), no significant changes in cell morphology or growth were observed in Hep3B-GD3 cells compared to wild type Hep3B cells under normoxia. However, exposure of Hep3B-GD3 cells to hypoxia (2% O(2)) enhanced reactive oxygen species (ROS) generation, resulting in decreased cell survival, with similar findings observed in Hep3B cells exposed to increasing doses of exogenous GD3. In addition, hypoxia-induced c-Src phosphorylation at tyrosine residues, NF-kappaB activation and subsequent expression of Mn-SOD were observed in Hep3B cells but not in Hep3B-GD3 cells. Moreover, MnTBAP, an antioxidant with predominant SOD mimetic activity, reduced ROS generation, protecting Hep3B-GD3 cells from hypoxia-induced death. Finally, lower tumor growth, higher cell death and reduced Mn-SOD expression were observed in Hep3B-GD3 compared to Hep3B tumor xenografts., Conclusion: These findings underscore a role for GD3 in hypoxia susceptibility by disabling the c-Src/NF-kappaB survival pathway resulting in lower Mn-SOD expression, which may be of relevance in hepatocellular carcinoma therapy.

Nuclear factor (NF)-kappaB participates in ischemia/reperfusion (I/R) hepatic signaling, stimulating both protective mechanisms and the generation of inflammatory cytokines. After analyzing NF-kappaB activation during increasing times of ischemia in murine I/R, we observed that the nuclear translocation of p65 paralleled Src and IkappaB tyrosine phosphorylation, which peaked after 60 minutes of ischemia. After extended ischemic periods (90 to 120 minutes) however, nuclear p65 levels were inversely correlated with the progressive induction of oxidative stress. Despite this profile of NF-kappaB activation, inflammatory genes, such as tumor necrosis factor (TNF) and interleukin (IL)-1beta, predominantly induced by Kupffer cells, increased throughout time during ischemia (30 to 120 minutes), whereas protective NF-kappaB-dependent genes, such as manganese superoxide dismutase (Mn-SOD), expressed in parenchymal cells, decreased. Consistent with this behavior, gadolinium chloride pretreatment abolished TNF/IL-1beta up-regulation during ischemia without affecting Mn-SOD levels. Interestingly, specific glutathione (GSH) up-regulation in hepatocytes by S-adenosylmethionine increased Mn-SOD expression and protected against I/R-mediated liver injury despite TNF/IL-1beta induction. Similar protection was achieved by administration of the SOD mimetic MnTBAP. In contrast, indiscriminate hepatic GSH depletion by buthionine-sulfoximine before I/R potentiated oxidative stress and decreased both nuclear p65 and Mn-SOD expression levels, increasing TNF/IL-1beta up-regulation and I/R-induced liver damage. Thus, the divergent role of NF-kappaB activation in selective liver cell populations underlies the dichotomy of NF-kappaB in hepatic I/R injury, illustrating the relevance of specifically maintaining NF-kappaB activation in parenchymal cells.