Targeted Deletion of Hepatocyte Abca1 Increases Plasma HDL (High-Density Lipoprotein) Reverse Cholesterol Transport via the LDL (Low-Density Lipoprotein) Receptor.

OBJECTIVE: The role of hepatocyte Abca1 (ATP binding cassette transporter A1) in trafficking hepatic free cholesterol (FC) into plasma versus bile for reverse cholesterol transport (RCT) is poorly understood. We hypothesized that hepatocyte Abca1 recycles plasma HDL-C (high-density lipoprotein cholesterol) taken up by the liver back into plasma, maintaining the plasma HDL-C pool, and decreasing HDL-mediated RCT into feces. Approach and Results: Chow-fed hepatocyte-specific Abca1 knockout (HSKO) and control mice were injected with human HDL radiolabeled with 125I-tyramine cellobiose (125I-TC; protein) and 3H-cholesteryl oleate (3H-CO). 125I-TC and 3H-CO plasma decay, plasma HDL 3H-CO selective clearance (ie, 3H-125I fractional catabolic rate), liver radiolabel uptake, and fecal 3H-sterol were significantly greater in HSKO versus control mice, supporting increased plasma HDL RCT. Twenty-four hours after 3H-CO-HDL injection, HSKO mice had reduced total hepatic 3H-FC (ie, 3H-CO hydrolyzed to 3H-FC in liver) resecretion into plasma, demonstrating Abca1 recycled HDL-derived hepatic 3H-FC back into plasma. Despite similar liver LDLr (low-density lipoprotein receptor) expression between genotypes, HSKO mice treated with LDLr-targeting versus control antisense oligonucleotide had slower plasma 3H-CO-HDL decay, reduced selective 3H-CO clearance, and decreased fecal 3H-sterol excretion that was indistinguishable from control mice. Increased RCT in HSKO mice was selective for 3H-CO-HDL, since macrophage RCT was similar between genotypes. CONCLUSIONS: Hepatocyte Abca1 deletion unmasks a novel and selective FC trafficking pathway that requires LDLr expression, accelerating plasma HDL-selective CE uptake by the liver and promoting HDL RCT into feces, consequently reducing HDL-derived hepatic FC recycling into plasma.

Upsetting the Balance: How Modifiable Risk Factors Contribute to the Progression of Alzheimer's Disease.

Alzheimer's disease (AD) is a neurodegenerative disorder affecting nearly one in nine older adults in the US. This number is expected to grow exponentially, thereby increasing stress on caregivers and health systems. While some risk factors for developing AD are genetic, an estimated 1/3 of AD cases are attributed to lifestyle. Many of these risk factors emerge decades before clinical symptoms of AD are detected, and targeting them may offer more efficacious strategies for slowing or preventing disease progression. This review will focus on two common risk factors for AD, metabolic dysfunction and sleep impairments, and discuss potential mechanisms underlying their relationship to AD pathophysiology. Both sleep and metabolism can alter AD-related protein production and clearance, contributing to an imbalance that drives AD progression. Additionally, these risk factors have bidirectional relationships with AD, where the presence of AD-related pathology can further disrupt sleep and worsen metabolic functioning. Sleep and metabolism also appear to have a bidirectional relationship with each other, indirectly exacerbating AD pathophysiology. Understanding the mechanisms involved in these relationships is critical for identifying new strategies to slow the AD cascade.

Novel method for collecting hippocampal interstitial fluid extracellular vesicles (EVISF ) reveals sex-dependent changes in microglial EV proteome in response to Aß pathology.

Brain-derived extracellular vesicles (EVs) play an active role in Alzheimer's disease (AD), relaying important physiological information about their host tissues. The internal cargo of EVs is protected from degradation, making EVs 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 labelling, 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 Aß deposition. Genotype, age, and Aß 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.

Kir6.2-K ATP channels alter glycolytic flux to modulate cortical activity, arousal, and sleep-wake homeostasis.

Metabolism plays an important role in the maintenance of vigilance states (e.g. wake, NREM, and REM). Brain lactate fluctuations are a biomarker of sleep. Increased interstitial fluid (ISF) lactate levels are necessary for arousal and wake-associated behaviors, while decreased ISF lactate is required for sleep. ATP-sensitive potassium (K ATP ) channels couple glucose-lactate metabolism with neuronal excitability. Therefore, we explored how deletion of neuronal K ATP channel activity (Kir6.2-/- mice) affected the relationship between glycolytic flux, neuronal activity, and sleep/wake homeostasis. Kir6.2-/- mice shunt glucose towards glycolysis, reduce neurotransmitter synthesis, dampen cortical EEG activity, and decrease arousal. Kir6.2-/- mice spent more time awake at the onset of the light period due to altered ISF lactate dynamics. Together, we show that Kir6.2-K ATP channels act as metabolic sensors to gate arousal by maintaining the metabolic stability of each vigilance state and providing the metabolic flexibility to transition between states. Highlights: Glycolytic flux is necessary for neurotransmitter synthesis. In its absence, neuronal activity is compromised causing changes in arousal and vigilance states despite sufficient energy availability. With Kir6.2-K ATP channel deficiency, the ability to both maintain and shift between different vigilance states is compromised due to changes in glucose utilization. Kir6.2-K ATP channels are metabolic sensors under circadian control that gate arousal and sleep/wake transitions.

Novel method for collecting hippocampal interstitial fluid extracellular vesicles (EV-ISF) reveals sex-dependent changes in microglial EV proteome in response to Aß pathology.

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 Aß 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.

KATP channels are necessary for glucose-dependent increases in amyloid-ß and Alzheimer's disease-related pathology.

Elevated blood glucose levels, or hyperglycemia, can increase brain excitability and amyloid-ß (Aß) release, offering a mechanistic link between type 2 diabetes and Alzheimer's disease (AD). Since the cellular mechanisms governing this relationship are poorly understood, we explored whether ATP-sensitive potassium (KATP) channels, which couple changes in energy availability with cellular excitability, play a role in AD pathogenesis. First, we demonstrate that KATP channel subunits Kir6.2/KCNJ11 and SUR1/ABCC8 were expressed on excitatory and inhibitory neurons in the human brain, and cortical expression of KCNJ11 and ABCC8 changed with AD pathology in humans and mice. Next, we explored whether eliminating neuronal KATP channel activity uncoupled the relationship between metabolism, excitability, and Aß pathology in a potentially novel mouse model of cerebral amyloidosis and neuronal KATP channel ablation (i.e., amyloid precursor protein [APP]/PS1 Kir6.2-/- mouse). Using both acute and chronic paradigms, we demonstrate that Kir6.2-KATP channels are metabolic sensors that regulate hyperglycemia-dependent increases in interstitial fluid levels of Aß, amyloidogenic processing of APP, and amyloid plaque formation, which may be dependent on lactate release. These studies identify a potentially new role for Kir6.2-KATP channels in AD and suggest that pharmacological manipulation of Kir6.2-KATP channels holds therapeutic promise in reducing Aß pathology in patients with diabetes or prediabetes.

The Interaction Between Sleep and Metabolism in Alzheimer's Disease: Cause or Consequence of Disease?

Alzheimer's disease (AD) is the most common form of dementia and affects over 45 million people worldwide. Both type-2-diabetes (T2D), a metabolic condition associated with aging, and disrupted sleep are implicated in the pathogenesis of AD, but how sleep and metabolism interact to affect AD progression remains unclear. In the healthy brain, sleep/wake cycles are a well-coordinated interaction between metabolic and neuronal activity, but when disrupted, are associated with a myriad of health-related issues, including metabolic syndrome, cardiovascular disease, T2D, and AD. Therefore, this review will explore our current understanding of the relationship between metabolism, sleep, and AD-related pathology to identify the causes and consequences of disease progression in AD. Moreover, sleep disturbances and metabolic dysfunction could serve as potential therapeutic targets to mitigate the increased risk of AD in individuals with T2D or offer a novel approach for treating AD.

Cortical zeta-inhibitory peptide injection reduces local sleep need.

Local sleep need within cortical circuits exhibits extensive interregional variability and appears to increase following learning during preceding waking. Although the biological mechanisms responsible for generating sleep need are unclear, this local variability could arise as a consequence of wake-dependent synaptic plasticity. To test whether cortical synaptic strength is a proximate driver of sleep homeostasis, we developed a novel experimental approach to alter local sleep need. One hour prior to light onset, we injected zeta-inhibitory peptide (ZIP), a pharmacological antagonist of protein kinase Mζ, which can produce pronounced synaptic depotentiation, into the right motor cortex of freely behaving rats. When compared with saline control, ZIP selectively reduced slow-wave activity (SWA; the best electrophysiological marker of sleep need) within the injected motor cortex without affecting SWA in a distal cortical site. This local reduction in SWA was associated with a significant reduction in the slope and amplitude of individual slow waves. Local ZIP injection did not significantly alter the amount of time spent in each behavioral state, locomotor activity, or EEG/LFP power during waking or REM sleep. Thus, local ZIP injection selectively produced a local reduction in sleep need; synaptic strength, therefore, may play a causal role in generating local homeostatic sleep need within the cortex.