The focus of our research is to understand diseases of the central nervous system (CNS) and how risk factors such as metabolic dysfunction, sleep impairment, and vascular damage disrupt healthy brain function to cause neurodegenerative disease. Ultimately, the goal is to leverage these mechanistic findings as therapeutic targets for treating CNS disease.
My work focuses on two main areas: 1) the mechanistic interplay between Alzheimer’s disease (AD) and type-2-diabetes (T2D) and 2) the treatment of neurodegenerative disorders, including AD and lysosomal storage diseases (LSDs). To study AD, my laboratory uses rodent models, non-human primates, and human data to understand how metabolic or vascular perturbations affect the progression of Alzheimer’s-related pathology. For our rodent studies, we use a variety of in vivo techniques, including glucose clamps, in vivo microdialysis, in vivo biosensors, EEG/EMG recordings, and small animal neuroimaging to study the acute effects of metabolic challenges on cerebral metabolism, neuronal activity, Aβ/tau dynamics, and sleep. For our chronic studies, we use rodent models and non-human primates to investigate how Alzheimer’s disease risk factors, like metabolic dysfunction or sleep disruptions, impact Aβ/tau pathology, learning and memory, cerebral metabolism, and brain network connectivity. Our lab is using both pharmacological and non-pharmacological interventions to target metabolic dysfunction to reverse Alzheimer's pathology and rescue sleep.
In addition to my interests in T2D and AD, we study mechanisms of neurometabolism, neurodegeneration, and neuroinflammation in lysosomal storage diseases (LSD) and how targeting different aspects of pathology with combination therapies enhances efficacy. Our findings not only characterized the temporal-spatial spread of CNS disease and functional deficits in mouse models of Niemann-Pick Type A, infantile neuronal ceroid lipofuscinosis, Pompe disease, Krabbe disease, and late-infantile neuronal ceroid lipofuscinosis, but also identified secondary disease mechanisms associated with neurodegeneration that need to be addressed in treatment strategies for these disorders.
Lastly, a significant portion of our laboratory is dedicated to developing novel biomarkers, tools, and technology to improve our studies in the field of Alzheimer's disease. Through a network of collaborations, we are developing novel exosome- and imaging-based biomarkers for staging Alzheimer's disease as well as generating improved mouse and non-human primate models of Alzheimer's disease pathology and resilience.
Alzheimer's Disease and Type-2-Diabetes
Metabolic dysfunction is central to the development of Alzheimer’s disease. Moreover, epidemiological studies suggest that patients with type 2 diabetes (T2D) have an increased risk for developing Alzheimer’s disease (AD). Therefore, a large focus of our laboratory is how metabolic dysfunction, like glycemic variability and glucose intolerance, affects the production, clearance, and aggregation of Aβ and tau (Macauley et al, 2015; Stanley, Macauley et al, 2016; Harris et al, 2016; Kavanagh et al, 2019).
Our initial work investigated whether hyperglycemia, or elevated blood glucose levels, or hyperinsulinemia, elevated blood insulin levels, increased amyloid-β (Aβ) levels in the brain's interstitial fluid (ISF). By coupling in vivo microdialysis and glucose clamps, we developed a novel approach to dynamically modulate systemic blood glucose and/or insulin levels while sampling proteins and metabolites within the brain’s interstitial fluid (ISF) in unanesthetized, freely moving mice. We found that hyperglycemia increased Aβ production in the hippocampus through an activity dependent mechanism; an effect that is exacerbated in mice with amyloid plaques. Interestingly, hyperinsulinemia did not have the same effect, suggesting hyperglycemia is a more potent driver of Aβ production than hyperinsulinemia. We also found a direct correlation between ISF glucose and ISF Aβ concentrations, providing a causal relationship between T2D and AD. Recently, we extended these studies to non-human primates to demonstrate the same phenomenon- peripheral hyperglycemia, not hyperinsulinemia, in vervet monkeys with type-2-diabetes correlates with decreased CSF Aβ40 and Aβ42, a biomarker of Alzheimer’s disease pathology in the brain.
We continue to explore how changes in peripheral or cerebral metabolism affect brain excitability and Aβ/tau metabolism. First, our initial work demonstrated that hyperglycemia modulates extracellular concentrations of amyloid-β (Aβ) in an activity-dependent manner by altering the activity of inward rectifying, ATP-sensitive potassium (KATP) channels. Using pharmacological and genetic approaches, we are exploring the role of KATP channel activity in Alzheimer's disease. Second, our work investigates how hyperglycemia impacts neuronal activity, synaptic plasticity and network connectivity during healthy aging. Third, we are exploring how hyper- and hypoglycemia affects cerebral metabolism, brain excitability, and Aβ/tau pathology in order to further understand the complex relationship between T2D and AD. Lastly, we are exploring why regions vulnerable to Aβ deposition are uniquely reliant on glucose compared to regions resilient to Aβ pathology. Through collaborative studies, we found that alterations in key glycolytic enzymes involved in aerobic glycolysis are altered as a function of age and Aβ, impacting learning and memory differentially. The ultimate goal of our work is to elucidate the role of glucose metabolism in Alzheimer's disease.
Sleep, Metabolism, and Alzheimer's disease
Carroll & Macauley, 2019
A bidirectional relationship exists between Alzheimer’s disease and sleep, where disrupted sleep increases amyloid-beta (Aβ) and tau pathology and conversely, Aβ and tau aggregation disrupt sleep. The sleep/wake cycle is a master regulator of metabolic and neuronal activity, where daily oscillations in activity are coupled to the production and clearance of Aβ and tau. Although modulating neuronal activity alters both sleep/wake cycles and Aβ/tau release, less is known about how fluctuations in glucose metabolism drive changes in sleep and Alzheimer’s disease related pathology.
The goal of our work is 1) to determine whether changes in metabolic activity lead to changes in neuronal activity to disrupt sleep in Alzheimer’s disease and 2) whether metabolic dysfunction can serve as a novel therapeutic target to rescue sleep and Alzheimer’s pathology.
Using hippocampal biosensors coupled with EEG/EMG recordings, our work will investigate how glycemic variability and peripheral glucose intolerance affect sleep and Alzheimer’s disease in rodent models of Alzheimer’s related pathology. Moreover, we will establish whether normalizing peripheral glucose homeostasis through treatment with the diabetic medication, metformin, is sufficient to preserve and restore sleep architecture in the setting of Alzheimer’s disease.
KATP channel activity in Alzheimer's disease:
from pathology to treatment
Inward rectifying, ATP-sensitive potassium (KATP) channels are found on the plasma membranes of excitable cells and link changes in metabolism with cellular excitability. We demonstrated that hyperglycemia, a key feature of diabetes, increased brain glucose levels (ISF glucose), neuronal activity (ISF lactate), and, as a byproduct, hippocampal ISF Aβ release (Macauley et al, 2015); an effect that was modulated by KATP channel activation and inhibition. Pharmacological manipulation of neuronal KATP channels altered Aβ levels, reinforcing the connection between KATP channels, diabetes, and Alzheimer’s disease. However, it is unclear if brain KATP channels are required for hyperglycemia-dependent increases ISF Aβ and whether chronic hyperexcitability due to KATP channels can alter AD pathology. Therefore, current work in the laboratory is using genetic models of KATP channel deficiency to explore their role in the development of Alzheimer's disease.
Inward rectifying, ATP-sensitive potassium (KATP) channels are not restricted to neurons but found through the body. They also regulate excitability in 1) the vasculature, where they modulate vasodilation and vasoconstriction; and 2) pancreatic beta cells, where rising blood glucose triggers KATP channel closure and insulin release. Thus, KATP channel activity in different cell types cause different physiological effects.
Sulfonylureas are KATP channel antagonists and widely used anti-hyperglycemic medications to treat T2D. However, their effect on the neurovasculature and Alzheimer’s related pathology is unknown. Thus, we investigated the effects of the KATP channel antagonist, glyburide, on Alzheimer’s related pathology in a mouse model of Aβ overexpression (e.g. APPswe/PSEN1dE9 mice). We found that peripheral glyburide treatment: 1) decreased Aβ pathology; 2) reduced the activity dependent release of Aβ; and 3) altered the neurovascular response, reduced arterial stiffness, and normalized pericyte-endothelial cell morphology. These preliminary data suggest that KATP channels play a critical and previously unappreciated role linking Aβ with neurovascular dysfunction in AD. Ongoing work in the lab is exploring whether KATP channels are a druggable target for modulating Aβ and tau pathology in AD.
pathogenic mechanism to AD biomarker
Exosomes are small extracellular vesicles (EVs) that originate from the endosomal system and are secreted extracellularly. Exosome cargo is unique to their cell of origin and protected from degradation as the vesicles move throughout the circulation. Thus, exosomes act as messengers of pathological conditions and are being pursued as biomarkers in Alzheimer’s disease. To date, studies investigating exosome changes in AD have focused on exosomes isolated from the CSF, blood, or post-mortem brain tissue. However, these studies fail to fully capture 1) whether extracellular vesicle (EV) and exosome release into the brain’s ISF is impaired in AD in vivo, 2) how the progression of Alzheimer’s disease affects the exosome proteome in a brain region- and cell type-specific manner in vivo, 3) whether the ISF exosome population mirrors the blood or CSF pool, and 5) how exosome secretion from specific cell types, like neurons and glia, is altered in AD. Therefore, it is vital to uncover whether these changes in ISF-derived EVs are truly exosome specific, how the ISF population of exosomes changes during AD pathogenesis, and whether the local changes in ISF exosomes can be captured in the blood for biomarker development.
We leveraged our expertise in lysosomal biology with our technical expertise with in vivo microdialysis to develop a novel method for isolating exosomes from the hippocampal interstitial fluid (ISF) of unanesthetized, freely moving mice. Coupled with proteomic profiling, we can characterize brain region- and cell type-specific changes in exosomes relative to Alzheimer’s-like pathology in vivo. Moreover, we can identify unique proteins on the exosome surface that change with amyloid-beta (Aβ) or tau and explore their use as novel blood based biomarkers in AD. We feel this novel approach will yield novel insights into the role of exosomes in AD pathogenesis.
Exploring the link between alcohol use disorder and Alzheimer's disease
Epidemiological studies suggest alcohol use disorder (AUD) is a risk factor for Alzheimer’s disease (AD), yet the mechanisms underlying this relationship are poorly understood. AD is characterized by the accumulation of extracellular amyloid-β (Aβ) into amyloid plaques and intracellular tau into neurofibrillary tangles (NFTs), both beginning ~15 years before cognitive decline. Given this long presymptomatic period in AD, risk factors can affect the age of onset and progression of AD. In particular, it is unknown whether ethanol exposure during this critical period directly modulates Aβ and tau or whether ethanol acts via an alternative pathway to accelerate AD pathogenesis. The goal of our work is to determine whether acute ethanol exposure is sufficient to alter the interstitial fluid (ISF) levels of Aβ and tau in unanesthetized, freely moving mice. Moreover, we are exploring whether the presence of amyloid plaques and neurofibrillary tangles impacts the brain's response to an acute ethanol challenge.
NIA R01 AG068330 (PI)
NIA R01 AG061805 (CoI)
NIA R01 AG065839 (CoI)
BrightFocus Foundation (PI)
WF-TARC Pilot Grant (PI)
ADRC Pilot Grant (PI)
CTSI Pilot Grant (CoI)
NIA K01 AG050719 (PI)
ADRC Pilot Grant (CoI)
Donors Cure New Vision Award (PI)
NINDS F32 NS080320 (PI)
McDonnell Center for Systems Neuroscience Small Grant (PI: Macauley/Bauer)
Batten Disease Research and Support Association Research Fellowship
NINDS F31 NS056718 (PI)