Neuroprotective Sirtuin ratio reversed by ApoE4
The Buck Institute for Research on Aging, Novato, CA 94945.Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 10/2013; 110(45). DOI: 10.1073/pnas.1314145110
The canonical pathogenesis of Alzheimer's disease links the expression of apolipoprotein E ε4 allele (ApoE) to amyloid precursor protein (APP) processing and Aβ peptide accumulation by a set of mechanisms that is incompletely defined. The development of a simple system that focuses not on a single variable but on multiple factors and pathways would be valuable both for dissecting the underlying mechanisms and for identifying candidate therapeutics. Here we show that, although both ApoE3 and ApoE4 associate with APP with nanomolar affinities, only ApoE4 significantly (i) reduces the ratio of soluble amyloid precursor protein alpha (sAPPα) to Aβ; (ii) reduces Sirtuin T1 (SirT1) expression, resulting in markedly differing ratios of neuroprotective SirT1 to neurotoxic SirT2; (iii) triggers Tau phosphorylation and APP phosphorylation; and (iv) induces programmed cell death. We describe a subset of drug candidates that interferes with the APP-ApoE interaction and returns the parameters noted above to normal. Our data support the hypothesis that neuronal connectivity, as reflected in the ratios of critical mediators such as sAPPα:Aβ, SirT1:SirT2, APP:phosphorylated (p)-APP, and Tau:p-Tau, is programmatically altered by ApoE4 and offer a simple system for the identification of program mediators and therapeutic candidates.
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ABSTRACT: Our understanding of the magnitude and physiological significance of proteome lysine acetylation remained incipient for five decades since it was first described. State of the art methodologies, ranging from functional genomics to large-scale proteomics, have recently uncovered that this modification is more broadly represented in proteins than previously recognized, thus constituting the "acetylome". At present, it is estimated that acetylome covers only one tenth of the proteome, however, due its potential significance in physiology, is capturing great attention. The first components of the cellular machinery, which finely orchestrate acetylome homeostasis, were identified by the end of last century. Since then, the majority of our growing knowledge concerning the physiological relevance of proteome reversible acetylation comes from the study of sirtuins, a unique type of lysine deacetylases that use NAD+. Sirtuins participate in a variety of cellular processes, ranging from transcription, DNA repair, energy balance, mitochondrial biogenesis and cell division, to apoptosis, autophagy and aging. Within the brain, besides their widespread epigenetic effects of dynamically modifying histones, sirtuins also target a variety of non-histone proteins either commonly deregulated in pathologies, or that participate in normal cerebral functions. For example, they modulate critical elements of the circadian rhythms, neurogenesis, synapses, cognition, serotonin synthesis, myelination, and proteins involved in neuropathology. Acetylome dynamics, and its regulation by sirtuins, may also help to better understand the molecular mechanisms underlying brain aging. Thus, this work reviews the pathways as orchestrated by the interplay between acetylome and sirtuins in the brain, from physiology involvement, to aging processes, and pathological settings.Current pharmaceutical design 03/2013; 19(38). DOI:10.2174/1381612811319380014 · 3.45 Impact Factor
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ABSTRACT: Tropisetron was identified in a screen for candidates that increase the ratio of the trophic, neurite-extending peptide sAPPα to the anti-trophic, neurite-retractive peptide Aβ, thus reversing this imbalance in Alzheimer's disease (AD). We describe a hierarchical screening approach to identify such drug candidates, moving from cell lines to hippocampal neuronal cultures to in vivo studies. By screening a clinical compound library in the primary assay using CHO-7W cells stably transfected with human APPwt, we identified tropisetron as a candidate that consistently increased sAPPα. Secondary assay testing in neuronal cultures from J20 (PDAPP, huAPP(Swe/Ind)) mice showed that tropisetron consistently increased the sAPPα/Aβ 1-42 ratio. In in vivo studies in J20 mice, tropisetron improved the sAPPα/Aβ ratio along with spatial and working memory in mice, and was effective both during the symptomatic, pre-plaque phase (5-6 months) and in the late plaque phase (14 months). This ameliorative effect occurred at a dose of 0.5mg/kg/d (mkd), translating to a human-equivalent dose of 5mg/day, the current dose for treatment of postoperative nausea and vomiting (PONV). Although tropisetron is a 5-HT3 antagonist and an α7nAChR partial agonist, we found that it also binds to the ectodomain of APP. Direct comparison of tropisetron to the current AD therapeutics memantine (Namenda) and donepezil (Aricept), using similar doses for each, revealed that tropisetron induced greater improvements in memory and sAPPα/Aβ1-42. The improvements observed with tropisetron in the J20 AD mouse model, and its known safety profile, suggest that it may be suitable for transition to human trials as a candidate therapeutic for mild cognitive impairment (MCI) and AD, and therefore it has been approved for testing in clinical trials to begin in 2014.Brain research 12/2013; 1551. DOI:10.1016/j.brainres.2013.12.029 · 2.84 Impact Factor
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