Increased neuronal excitability contributes to amyloid-β (Aβ) production and aggregation in the Alzheimer's disease (AD) brain. Previous work from our lab demonstrated that hyperglycemia, or elevated blood glucose levels, increased brain excitability and Aβ release potentially through inward rectifying, ATP-sensitive potassium (KATP) channels. KATP channels are present on several different cell types and help to maintain excitatory thresholds throughout the brain. KATP channels are sensitive to changes in the metabolic environment, which are coupled to changes in cellular excitability. Therefore, we hypothesized that neuronal KATP channels are necessary for the hyperglycemic-dependent increases in extracellular Aβ and eliminating KATP channel activity will uncouple the relationship between metabolism, excitability, and Aβ pathology. First, we demonstrate that Kir6.2/KCNJ11, the pore forming subunits, and SUR1/ABCC8, the sulfonylurea receptors, are predominantly expressed on excitatory and inhibitory neurons in the human brain and that cortical expression of KCNJ11 and ABCC8 change with AD pathology in humans and rodent models. Next, we crossed APP/PS1 mice with Kir6.2 -/- mice, which lack neuronal KATP channel activity, to define the relationship between KATP channels, Aβ, and hyperglycemia. Using in vivo microdialysis and hyperglycemic clamps, we explored how acute elevations in peripheral blood glucose levels impacted hippocampal interstitial fluid (ISF) glucose, lactate, and Aβ levels in APP/PS1 mice with or without KATP channels. Kir6.2+/+, APP/PS1 mice and Kir6.2-/-, APP/PS1 mice were exposed to a high sucrose diet for 6 months to determine the effects of chronic hyperglycemia on Aβ deposition. We found that elevations in blood glucose levels correlate with increased ISF Aβ, amyloidogenic processing of amyloid precursor protein (APP), and amyloid plaque pathology in APP/PS mice with intact KATP channels. However, neither acute hyperglycemia nor chronic sucrose overconsumption raised ISF Aβ or increased Aβ plaque burden in APP/PS1 mice lacking Kir6.2-KATP channel activity. Mechanistic studies demonstrate ISF glucose not only correlates with ISF Aβ but also ISF lactate. Without KATP channel activity, ISF lactate does not increase during hyperglycemia, which correlates with decreased monocarboxylate transporter 4 (MCT4) expression, a lactate transporter responsible for astrocytic lactate release. This suggests that KATP channel activity regulates ISF lactate during hyperglycemia, which is important for Aβ release and aggregation. These studies identify a new role for Kir6.2-KATP channels in Alzheimer's disease pathology and suggest that pharmacological antagonism of Kir6.2-KATP channels holds therapeutic promise in reducing Aβ pathology, especially in diabetic and prediabetic patients.

Brain-derived extracellular vesicles (EVs) play an active role in Alzheimer's disease (AD), relaying important physiological information about their host tissues. Circulating EVs are protected from degradation, making them attractive AD biomarkers. However, it is unclear how circulating EVs relate to EVs isolated from disease-vulnerable brain regions. We developed a novel method for collecting EVs from the hippocampal interstitial fluid (ISF) of live mice. EVs (EVISF) were isolated via ultracentrifugation and characterized by nanoparticle tracking analysis, immunogold labeling, and flow cytometry. Mass spectrometry and proteomic analyses were performed on EVISF cargo. EVISF were 40-150 nm in size and expressed CD63, CD9, and CD81. Using a model of cerebral amyloidosis (e.g. APPswe,PSEN1dE9 mice), we found protein concentration increased but protein diversity decreased with A deposition. Genotype, age, and Aβ deposition modulated proteostasis- and immunometabolic-related pathways. Changes in the microglial EVISF proteome were sexually dimorphic and associated with a differential response of plaque associated microglia. We found that female APP/PS1 mice have more amyloid plaques, less plaque associated microglia, and a less robust- and diverse- EVISF microglial proteome. Thus, in vivo microdialysis is a novel technique for collecting EVISF and offers a unique opportunity to explore the role of EVs in AD.