The glycogen synthase kinase-3␤ (GSK3␤) pathway plays an important role in mediating neuronal fate and synaptic plasticity. In Alzheimer's disease (AD), abnormal activation of this pathway might play an important role in neurodegeneration, and compounds such as lithium that modulate GSK3␤ activity have been shown to reduce amyloid production and tau phosphorylation in amyloid precursor protein (APP) transgenic (tg) mice. However, it is unclear whether regulation of GSK3␤ is neuroprotective in APP tg mice. In this context, the main objective of the present study was to determine whether pharmacological or genetic manipulations that block the GSK3␤ pathway might ameliorate the neurodegenerative alterations in APP tg mice and to better understand the mechanisms involved. For this purpose, two sets of experiments were performed. First, tg mice expressing mutant human APP under the Thy1 promoter (hAPP tg) were treated with either lithium chloride or saline alone. Second, hAPP tg mice were crossed with GSK3␤ tg mice, in which overexpression of this signaling molecule results in a dominant-negative (DN) effect with inhibition of activity. hAPP tg mice that were treated with lithium or that were crossed with DN-GSK3␤ tg mice displayed improved performance in the water maze, preservation of the dendritic structure in the frontal cortex and hippocampus, and decreased tau phosphorylation. Moreover, reduced activation of GSK3␤ was associated with decreased levels of APP phosphorylation that resulted in decreased amyloid-␤ production. In conclusion, the present study showed that modulation of the GSK3␤ signaling pathway might also have neuroprotective effects in tg mice by regulating APP maturation and processing and further supports the notion that GSK3␤ might be a suitable target for the treatment of AD.

In recent years, new hope for understanding the pathogenesis of Parkinson's disease (PD) and Lewy body dementia (LBD) has emerged with the discovery of mutations and duplications in the a-synuclein (a-syn) gene that are associated with rare familial forms of Parkinsonism [1][2][3]. Moreover, it has been shown that a-syn is centrally involved in the pathogenesis of both sporadic and inherited forms of PD and LBD because this molecule accumulates in Lewy bodies (LBs) [4][5][6], synapses, and axons, and its expression in transgenic (tg) mice [7][8][9] and Drosophila [10] mimics several aspects of PD.The mechanisms through which a-syn leads to neurodegeneration and the characteristic symptoms of LBD are unclear. However, recent evidence indicates that abnormal accumulation of misfolded a-syn in the Accumulation of a-synuclein resulting in the formation of oligomers and protofibrils has been linked to Parkinson's disease and Lewy body dementia. In contrast, b-synuclein (b-syn), a close homologue, does not aggregate and reduces a-synuclein (a-syn)-related pathology. Although considerable information is available about the conformation of a-syn at the initial and end stages of fibrillation, less is known about the dynamic process of a-syn conversion to oligomers and how interactions with antiaggregation chaperones such as b-synuclein might occur. Molecular modeling and molecular dynamics simulations based on the micelle-derived structure of a-syn showed that a-syn homodimers can adopt nonpropagating (head-to-tail) and propagating (head-to-head) conformations. Propagating a-syn dimers on the membrane incorporate additional a-syn molecules, leading to the formation of pentamers and hexamers forming a ring-like structure. In contrast, b-syn dimers do not propagate and block the aggregation of a-syn into ring-like oligomers. Under in vitro cell-free conditions, a-syn aggregates formed ring-like structures that were disrupted by b-syn. Similarly, cells expressing a-syn displayed increased ion current activity consistent with the formation of Zn 2+ -sensitive nonselective cation channels. These results support the contention that in Parkinson's disease and Lewy body dementia, a-syn oligomers on the membrane might form pore-like structures, and that the beneficial effects of b-synuclein might be related to its ability to block the formation of pore-like structures.Abbreviations aa, amino acid; a-syn, a-synuclein; b-syn, b-synuclein; GFP, green fluorescent protein; LBD, Lewy body disease; PD, Parkinson's disease; POPC, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine; tg, transgenic.

Aggregation of a-synuclein (a-syn) is believed to play a critical role in the pathogenesis of disorders such as dementia with Lewy bodies and Parkinson's disease. The function of a-syn remains unclear, although several lines of evidence suggest that a-syn is involved in synaptic vesicle trafficking probably via lipid binding. Moreover, interactions with cholesterol and lipids have been shown to be involved in a-syn aggregation. In this context, the main objective of this study was to determine if statins -cholesterol synthesis inhibitors -might interfere with a-syn accumulation in cellular models. For this purpose, we studied the effects of lovastatin, simvastatin, and pravastatin on the accumulation of a-syn in a stably transfected neuronal cell line and in primary human neurons. Statins reduced the levels of a-syn accumulation in the detergent insoluble fraction of the transfected cells. This was accompanied by a redistribution of a-syn in caveolar fractions, a reduction in oxidized a-syn, and enhanced neurite outgrowth. In contrast, supplementation of the media with cholesterol increased a-syn aggregation in detergent insoluble fractions of transfected cells and was accompanied by reduced neurite outgrowth. Taken together, these results suggest that regulation of cholesterol levels with cholesterol inhibitors might be a novel approach for the treatment of Parkinson's disease.

Current experimental gene therapy approaches for Parkinson's disease (PD) and dementia with Lewy bodies (DLB) include the use of viral vectors expressing antiapoptosis genes, neurotrophic factors and dopaminergic system enzymes. However, since increasing evidence favors a role for a-synuclein accumulation in the pathogenesis of these disorders, an alternative therapy might require the transfer of genes that might block a-synuclein accumulation. b-Synuclein, the nonamyloidogenic homologue of a-synuclein, has recently been identified as a potential candidate. Thus, in vivo transfer of genes encoding b-synuclein might provide a novel approach to the development of experimental treatments for PD and DLB. To assess this possibility and to better understand the mechanisms involved, a lentiviral vector expressing human (h) b-synuclein (lenti-b-synuclein) was tested in a transgenic (tg) mouse model of ha-synuclein aggregation. This study showed that unilateral intracerebral injection of lenti-b-synuclein reduced the formation of hasynuclein inclusions and the accumulation of ha-synuclein in synapses and ameliorated the neurodegenerative alterations in the tg mice. Both in vivo and in vitro coimmunoprecipitation and immunoblot experiments show that the mechanisms of b-synuclein neuroprotection involve binding of this molecule to ha-synuclein and Akt, resulting in the decreased aggregation and accumulation of ha-synuclein in the synaptic membrane. Together, these data further support a role for b-synuclein in regulating the conformational state of a-synuclein and suggest that this gene transfer approach might have potential for the development of alternative therapies for PD and DLB.

The aggregation of a-synuclein (a-syn) is believed to play a critical role in the pathogenesis of disorders such as dementia with Lewy bodies and Parkinson's disease. The function of asyn remains unclear, although several lines of evidence suggest that a-syn is involved in synaptic vesicle trafficking, probably via lipid binding, and interactions with lipids have been shown to regulate a-syn aggregation. In this context, the main objective of this study was to determine whether methylb-cyclodextrin (MbCD), a cholesterol-extracting agent, interfered with a-syn accumulation in models of synucleinopathy. For this purpose, we studied the effects of MbCD on the accumulation of a-syn in a transfected neuronal cell line and in transgenic mice. Immunoblot analysis showed that MbCD reduced the level of a-syn in the membrane fraction and detergent-insoluble fraction of transfected cells. In agreement with the in vitro studies, treatment of mice with MbCD resulted in decreased levels of a-syn in membrane fractions and reduced accumulation of a-syn in the neuronal cell body and synapses. Taken together, these results suggest that changes in cholesterol and lipid composition using cholesterol-lowering agents may be used as a tool for the treatment of synucleinopathies.