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 increase insulin availability at the brain insulin receptor in vivo, 2) increase insulin receptor signaling in 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.
Our work will test if the mechanism of insulin actions in the brain modulates calcium-related functions inside cells. We will focus on one area of the brain that is known for its role in memory function, the hippocampus. We propose new ways to increase insulin signals in the brain.
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