ChileAlzheimer's disease (AD) is a progressive neurodegenerative disorder, which is probably caused by the cytotoxic effect of the amyloid b-peptide (Ab). We report here molecular changes induced by Ab, both in neuronal cells in culture and in rats injected in the dorsal hippocampus with preformed Ab fibrils, as an in vivo model of the disease. Results indicate that in both systems, Ab neurotoxicity resulted in the destabilization of endogenous levels of b-catenin, a key transducer of the Wnt signaling pathway. Lithium chloride, which mimics Wnt signaling by inhibiting glycogen synthase kinase-3b promoted the survival of post-mitotic neurons against Ab neurotoxicity and recovered cytosolic b-catenin to control levels. Moreover, the neurotoxic effect of Ab fibrils was also modulated with protein kinase C agonists/inhibitors and reversed with conditioned medium containing the Wnt-3a ligand. We also examined the spatial memory performance of rats injected with preformed Ab fibrils in the Morris water maze paradigm, and found that chronic lithium treatment protected neurodegeneration by rescuing b-catenin levels and improved the deficit in spatial learning induced by Ab. Our results are consistent with the idea that Ab-dependent neurotoxicity induces a loss of function of Wnt signaling components and indicate that lithium or compounds that mimic this signaling cascade may be putative candidates for therapeutic intervention in Alzheimer's patients.

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Peroxisome proliferator-activated receptor ␥ (PPAR␥) has been proposed as a therapeutic target for neurodegenerative diseases because of its anti-inflammatory action in glial cells. However, PPAR␥ agonists prevent ␤-amyloid (A␤)-induced neurodegeneration in hippocampal neurons, and PPAR␥ is activated by the nerve growth factor (NGF) survival pathway, suggesting a neuroprotective anti-inflammatory independent action. Here we show that the PPAR␥ agonist rosiglitazone (RGZ) protects hippocampal and dorsal root ganglion neurons against A␤-induced mitochondrial damage and NGF deprivation-induced apoptosis, respectively, and promotes PC12 cell survival. In neurons and in PC12 cells RGZ protective effects are associated with increased expression of the Bcl-2 anti-apoptotic protein. NGF-differentiated PC12 neuronal cells constitutively overexpressing PPAR␥ are resistant to A␤-induced apoptosis and morphological changes and show functionally intact mitochondria and no increase in reactive oxygen species when challenged with up to 50 M H 2 O 2 . Conversely, cells expressing a dominant negative mutant of PPAR␥ show increased A␤-induced apoptosis and disruption of neuronal-like morphology and are highly sensitive to oxidative stress-induced impairment of mitochondrial function. Cells overexpressing PPAR␥ present a 4-to 5-fold increase in Bcl-2 protein content, whereas in dominant negative PPAR␥-expressing cells, Bcl-2 is barely detected. Bcl-2 knockdown by small interfering RNA in cells overexpressing PPAR␥ results in increased sensitivity to A␤ and oxidative stress, further suggesting that Bcl-2 up-regulation mediates PPAR␥ protective effects. PPAR␥ prosurvival action is independent of the signal-regulated MAPK or the Akt prosurvival pathways. Altogether, these data suggest that PPAR␥ supports survival in neurons in part through a mechanism involving increased expression of Bcl-2.

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Current evidence supports the notion that the amyloid beta-peptide (Abeta) plays a major role in the neurotoxicity observed in the brain in Alzheimer's disease. However, the signal transduction mechanisms involved still remain unknown. In the present work, we analyzed the effect of protein kinase C (PKC) on some members of the Wnt signaling pathway and its implications for Abeta neurotoxicity. Activation of PKC by phorbol 12-myristate 13-acetate protected rat hippocampal neurons from Abeta toxicity. This effect was accomplished by inhibition of glycogen synthase kinase-3beta (GSK-3beta) activity, which led to the accumulation of cytoplasmic beta-catenin and transcriptional activation via beta-catenin/T-cell factor/lymphoid enhancer factor-1 (TCF/LEF-1) of Wnt target genes, which in the present study were engrailed-1 (en-1) and cyclin D1 (cycD1,). In contrast, inhibition of Ca2+-dependent PKC isoforms activated GSK-3beta and offered no protection from Ab neurotoxicity. Wnt-3a and lithium salts, classical activators of the Wnt pathway, mimicked PKC activation. Our results suggest that regulation of members of the Wnt signaling pathway by Ca2+-dependent PKC isoforms may be important in controlling the neurotoxic process induced by Ab.

1. The hepatic concentration of several nucleotides and metabolites was measured during the first few minutes after an intravenous load of fructose to mice. The first changes, observed at 30s, were a decrease in the concentration of Pi and a simultaneous accumulation of fructose 1-phosphate. The decrease in the concentrations of ATP and GTP proceeded more slowly. An increase in the concentration of IMP was detected only after 1 min and could therefore not be considered to be the cause of the accumulation of fructose 1-phosphate. 2. To explain the temporary burst of adenine nucleotide breakdown that occurs after a load of fructose, the kinetics of AMP deaminase (EC 3.5.4.6) from rat liver were reinvestigated at physiological (0.2 mM) concentration of substrate. For this purpose, a new radiochemical-assay procedure was developed. At 0.2mM-AMP a low activity could be measured, which was more than 90% inhibited by 5mM-Pi. ATP (3MM) increased the enzyme activity over 200-fold. Pi alone did not influence the ATP-activated enzyme, but 0.5mM-GTP caused a 60% inhibition. The combined effect of both inhibitors at their physiological concentrations reached 95%. 3. It is proposed that the rapid degradation of adenine nucleotides that occurs after a load of fructose is caused by a decrease in the concentration of both inhibitors, Pi and GTP, soon counteracted by the decrease in the concentration of ATP. 4. Some of the kinetic parameters of liver AMP deaminase were computed in terms of the concerted transition theory of Monod, Wyman & Changeux (1965) (J. Mol. Biol. 12, 88-118).

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Peroxisome proliferator-activated receptor-␥ (PPAR␥) is a member of the PPAR family of transcription factors. Synthetic PPAR␥ agonists are used as oral anti-hyperglycemic drugs for the treatment of non-insulin-dependent diabetes. However, emerging evidence indicates that PPAR␥ activators can also prevent or attenuate neurodegeneration. Given these previous findings, the focus of this report is on the potential neuroprotective role of PPAR␥ activation in preventing the loss of mitochondrial function in Huntington disease (HD). For these studies we used striatal cells that express wild-type (STHdh Q7/Q7 ) or mutant (STHdh Q111/Q111 ) huntingtin protein at physiological levels. Treatment of mutant cells with thapsigargin resulted in a significant decrease in mitochondrial calcium uptake, an increase in reactive oxygen species production, and a significant decrease in mitochondrial membrane potential. PPAR␥ activation by rosiglitazone prevented the mitochondrial dysfunction and oxidative stress that occurred when mutant striatal cells were challenged with pathological increases in calcium. The beneficial effects of rosiglitazone were likely mediated by activation of PPAR␥, as all protective effects were prevented by the PPAR␥ antagonist GW9662. Additionally, the PPAR␥ signaling pathway was significantly impaired in the mutant striatal cells with decreases in PPAR␥ expression and reduced PPAR␥ transcriptional activity. Treatment with rosiglitazone increased mitochondrial mass levels, suggesting a role for the PPAR␥ pathway in mitochondrial function in striatal cells. Altogether, this evidence indicates that PPAR␥ activation by rosiglitazone attenuates mitochondrial dysfunction in mutant huntingtin-expressing striatal cells, and this could be an important therapeutic avenue to ameliorate the mitochondrial dysfunction that occurs in HD.