Olivier Thibault, Ph.D. - US grants

[unreadable] DESCRIPTION (provided by applicant): Alzheimer's disease (AD), the third most costly disease in the United States after cardiac disease and cancer, has shown an increase in incidence recently, moving from 7th to 5th as a leading cause of death among the elderly. Currently available medical strategies treat the symptoms rather than address the underlying processes responsible for the progressive decline in cognitive function seen in AD patients. However, results from both clinical and basic science research suggest that antidiabetic agents (e.g., thiazolidinediones - TZDs) may be beneficial in the treatment of AD, and a few human and animal studies have shown that use of rosiglitazone (a TZD) can improve memory and lead to cognitive improvements. These results appear to provide compelling preliminary evidence to support the use of antidiabetic drugs to combat the cognitive impairment associated with AD. However, little is known about the underlying molecular mechanisms, or about the identity of the CNS targets of TZDs. Some of the proposed beneficial effects of TZDs include reestablishment of insulin sensitivity and associated peripheral and/or CNS glucose utilization, along with reductions in inflammatory cytokines, Ab1-42 deposits, microglial activation, and intracellular Ca2+ levels. Given that Ca2+ dysregulation is considered a hallmark of brain aging and AD, and is also present in animal models of diabetes, we propose that some Ca2+ biomarkers of brain aging may be targets for intervention with TZDs. Using electrophysiological, molecular and Ca2+ imaging techniques along with a team of qualified scientists, this project will test the overall hypothesis that some TZDs can improve cognitive status in aged animals, by reducing key biomarkers of brain aging and neurodegeneration in the hippocampus. We will determine the molecular bases underlying the potential use of TZDs for the treatment of AD by the following Specific Aims: 1) to test the hypothesis that TZDs act as neuroprotective agents by normalizing Ca2+ levels within neurons and/or glial cells; and 2) to test the prediction that in vivo TZD treatment can improve cognition in aged animals and restore Ca2+ homeostasis. Results form our studies may provide support for the therapeutic application of TZDs in preventing/retarding the cognitive decline seen in AD. Furthermore, these studies will contribute to future drug discovery efforts to generate new TZD-derived or similar drugs for the treatment of AD. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Increasing epidemiological and experimental evidence shows that factors associated with metabolic syndrome, including glucose dysregulation, insulin insensitivity, and/or obesity, are linked to cognitive decline in aging. Moreover, the incidence of obesity and metabolic syndrome are approaching epidemic proportions. The thiazolidinediones (TZD), selective peroxisome proliferator-activated receptor-gamma (PPAR3) agonists, improve several aspects of metabolic syndrome including lowering insulin resistance, glucose and cholesterol levels in Type 2 diabetics, and have also been linked to decreased inflammation and 2-amyloid load in models of Alzheimer's disease (AD). However, the mechanisms that link peripheral metabolic syndrome to brain dysfunction are still poorly understood, and few studies have analyzed these periphery-brain relationships in aged animals. Over the past years, we and others have found considerable electrophysiological and imaging evidence that hippocampal Ca2+ dysregulation with aging correlates with cognitive decline. Recently, our gene microarray studies also revealed downregulation of hippocampal insulin and glucose signaling that correlated with aging-related memory impairment. Here, we will test the working hypothesis that peripheral components of metabolic syndrome induce alterations in Ca2+ homeostasis in the hippocampus by acting on L-type voltage-gated Ca2+ channels (L-VGCCs), NMDARs, Ca2+-induced Ca2+ release (CICR), and the Ca2+-dependent afterhyperpolarization (AHP), thereby negatively affecting synaptic plasticity (LTP) and cognitive function. We will also test the hypothesis that these actions are mediated in part by changes in brain insulin/glucose signaling pathways and can be counteracted by TZDs. Specific Aim # 1 will study F344 male rats fed a normal diet and determine, at 7-8 and 18-20 months of age, which component of metabolic dysregulation most closely associates with measures of cognitive function, and hippocampal electrophysiological/imaging function (L-VGCCs, NMDARs, CICR, AHPs, and LTP). Specific Aim #2 will test whether diet-induced obesity (DIO) exacerbates neurobiological, cognitive, gene expression and neuropathological indices of brain aging and whether interventions with TZDs can slow or reverse this process. Specific Aim #3 will analyze the effects of insulin on hippocampal slices, testing for direct effects on electrophysiological markers of aging, and will test the sub-hypothesis that neurons from aged animals exhibit insulin resistance. Together, these multidisciplinary studies will provide one of the first systematic analyses of links between variables contributing to peripheral metabolic syndrome and cellular mechanisms of brain aging. Therefore, even if the central hypothesis is rejected, the studies proposed will provide more definitive evidence for the impact o metabolic syndrome, as well as the actions of TZDs, on the brain. PUBLIC HEALTH RELEVANCE Metabolic syndrome and diabetes are age- and obesity-related diseases that are rapidly approaching epidemic proportions in our society. Recent studies indicate that there may be a link between metabolic syndrome and cognitive decline. The underlying mechanisms through which individual components of peripheral metabolic dysregulation can negatively impact brain function are not known. Our research will identify new links between brain aging, diabetes and obesity. If successful, our project could impact public health by providing strong clues to help identify novel therapeutic targets and prevent cognitive decline in aging.

DESCRIPTION (provided by applicant): Increasing epidemiological and experimental evidence shows that factors associated with metabolic syndrome, including glucose dysregulation, insulin insensitivity, and/or obesity, are linked to cognitive decline in aging. Moreover, the incidence of obesity and metabolic syndrome are approaching epidemic proportions. The thiazolidinediones (TZD), selective peroxisome proliferator-activated receptor-gamma (PPAR3) agonists, improve several aspects of metabolic syndrome including lowering insulin resistance, glucose and cholesterol levels in Type 2 diabetics, and have also been linked to decreased inflammation and 2-amyloid load in models of Alzheimer's disease (AD). However, the mechanisms that link peripheral metabolic syndrome to brain dysfunction are still poorly understood, and few studies have analyzed these periphery-brain relationships in aged animals. Over the past years, we and others have found considerable electrophysiological and imaging evidence that hippocampal Ca2+ dysregulation with aging correlates with cognitive decline. Recently, our gene microarray studies also revealed downregulation of hippocampal insulin and glucose signaling that correlated with aging-related memory impairment. Here, we will test the working hypothesis that peripheral components of metabolic syndrome induce alterations in Ca2+ homeostasis in the hippocampus by acting on L-type voltage-gated Ca2+ channels (L-VGCCs), NMDARs, Ca2+-induced Ca2+ release (CICR), and the Ca2+-dependent afterhyperpolarization (AHP), thereby negatively affecting synaptic plasticity (LTP) and cognitive function. We will also test the hypothesis that these actions are mediated in part by changes in brain insulin/glucose signaling pathways and can be counteracted by TZDs. Specific Aim # 1 will study F344 male rats fed a normal diet and determine, at 7-8 and 18-20 months of age, which component of metabolic dysregulation most closely associates with measures of cognitive function, and hippocampal electrophysiological/imaging function (L-VGCCs, NMDARs, CICR, AHPs, and LTP). Specific Aim #2 will test whether diet-induced obesity (DIO) exacerbates neurobiological, cognitive, gene expression and neuropathological indices of brain aging and whether interventions with TZDs can slow or reverse this process. Specific Aim #3 will analyze the effects of insulin on hippocampal slices, testing for direct effects on electrophysiological markers of aging, and will test the sub-hypothesis that neurons from aged animals exhibit insulin resistance. Together, these multidisciplinary studies will provide one of the first systematic analyses of links between variables contributing to peripheral metabolic syndrome and cellular mechanisms of brain aging. Therefore, even if the central hypothesis is rejected, the studies proposed will provide more definitive evidence for the impact o metabolic syndrome, as well as the actions of TZDs, on the brain.

? DESCRIPTION (provided by applicant): Peripheral metabolic dysregulation appears to increase the risk for cognitive decline with aging and susceptibility to dementing neurodegenerative disorders such as Alzheimer's disease. However, the pathways and mechanisms underlying the relationship between metabolic dysregulation and age-related cognitive impairment are not clearly defined. Here we propose that insulin resistance in the brain can destabilize tightly regulated processes which maintain normal calcium homeostasis in neurons resulting in neuronal dysfunction and impaired cognition. Age-related neuronal calcium dysregulation is a well-recognized mechanism contributing to neurologic dysfunction and cognitive decline and we and others have extensively characterized this dysfunction in brain structures important for learning and memory. Interestingly, peripheral tissues that are insulin resistant also show calcium dysregulation and provide supporting evidence for a similar relationship in the brain. In the prior funding cycle, we identified a previously unrecognized link between metabolic dysregulation and altered calcium signaling in hippocampal neurons. Together, these findings provide support for the notion that overcoming insulin resistance in the hippocampus with insulin-raising strategies will reestablish neuronal calcium homeostasis. Several innovative approaches will be used to increase brain insulin signaling in aging. Specifically, we will 1) utilize intranasal insulin delivery to increas insulin availability at the brain insulin receptor in vivo, 2) increase insulin receptor signaling n the brain via AAV-mediated expression of a constitutively active human insulin receptor mutant (? subunit), and 3) increase endogenous insulin receptor trafficking through the use of a novel pharmacologic strategy. Using these approaches in the F344 rat model of aging, we will investigate cognitive functions using different behavioral paradigms. In hippocampal tissue from these animals, we will use single cell electrophysiology/imaging to directly measure calcium status (recordings of calcium-dependent potentials and calcium imaging), and complement these studies with molecular/biochemical assays. To determine whether increasing insulin in the brain affects other pathways independent of Ca2+, we will also quantify p-Akt signaling, tyrosine phosphorylation, glucose homeostasis (glucose imaging), and adiponectin levels. Type 2 diabetes has reached epidemic proportions among older adults accounting for approximately 26 million people and a $175 billion dollar toll to our health care system (CDC statistics). Our studies are designed to determine whether enhancing insulin action in the brain reduces the burden of cognitive decline in aging and helps to maintain healthy cognitive function. The outcomes from our studies will inform related clinical studies and may have significant impact for the aging population, especially for those at increased risk for neurodegenerative diseases such as Alzheimer's disease. This work is clinically-oriented and directly addresses one of the missions of the NIA by establishing novel targets for the treatment of cognitive decline and/or dementia in brain aging.

Project Summary / Abstract: There is an urgent need for disease-modifying treatment of Alzheimer's disease (AD) starting at its very onset. This knowledge gap remains because conventional approaches cannot measure in vivo brain region-specific biomarkers of the earliest relevant dysfunction underlying abnormal behavior. Often, spatial disorientation is observed during prodromal AD, and its occurrence predicts later dementia. A brain region contributing to this spatial confusion is the CA1 subfield of hippocampus because of its essential role in encoding spatial information. HC oxidative stress is most commonly identified at the very start of AD, and in experimental models of AD. Yet, it has not been possible to prove that prodromal oxidative stress in the relevant CA1 subfield plays a pathogenic role in at-risk patients showing impaired spatial memory because conventional methods only measure oxidative stress from post-mortem tissue. Addressing this major knowledge gap requires a new paradigm that compares antioxidant treatment efficacy in HC CA1 subregions in vivo with improved spatial learning and memory in experimental models, and that can then be translated into patients. In this proposal, we present a transformative solution to this problem based on a novel method recently discovered by our lab: QUEnch-assiSTed MRI (QUEST MRI). QUEST MRI is a robust and sensitive tool that has been validated against ?gold standard? methods and maps in vivo excessive free radical production in, for example, murine dorsal CA1. The QUEST MRI index of abnormally high production of paramagnetic free radicals in specific brain regions is a greater- than-normal spin-lattice relaxation rate R1 (1/T1) that can be returned to baseline after acute antioxidant administration. Our QUEST MRI studies have confirmed dorsal HC CA1-specific oxidative stress in spontaneous and familial AD mouse models with declines in spatial learning and memory in conjunction with HC CA1 oxidative stress measured ex vivo. We also find downstream consequences of oxidative stress such as greater-than-normal amounts of the lipid peroxidation product 4-hydroxynonenal (HNE), dorsal HC CA1 calcium dysregulation and reductions in dorsal HC CA1 calcium-dependent afterhyperpolarization (AHP). To improve statistical power, this proposal is tightly focused on uniquely testing a specific working hypothesis that oxidative stress in dorsal CA1 in vivo causes deterioration of spatial memory in experimental models. Our highly innovative studies by an experienced team of experts will validate a new bridging tool for testing in vivo antioxidant therapeutic strategies to mitigate a clinically important early decline in spatial memory preceding later loss of personhood in AD.