Ethanol exposure alters Alzheimer’s-related pathology, behavior, and metabolism in APP/PS1 mice

Abstract

Epidemiological studies suggest that alcohol use disorder (AUD) is a risk factor for Alzheimer's disease (AD), yet the mechanisms underlying this relationship are poorly understood. Preclinical studies consistently show that chronic, high dose ethanol exposure increases amyloid-β (Aβ) and tau pathology, hallmarks of AD, in rodent models. Conversely, other studies suggest that moderate ethanol consumption may also be protective against AD-related pathology. Thus, we used a modified two-bottle choice paradigm to identify how chronic ethanol exposure, at moderate levels, alters Aβ-related pathology, cognitive performance, and metabolism. Over the course of the experiment, APP/PS1 mice consumed more ethanol than wild-type mice. This led to changes in food and water consumption in APP/PS1 mice, where ethanol-exposed APP/PS1 mice displayed a circadian shift in eating behavior. Ethanol-exposed APP/PS1 mice displayed glucose intolerance, a marker of insulin resistance, even though fasting blood glucose levels and body weights were comparable across all groups. Ethanol-exposed APP/PS1 mice exhibited deficits in nest building, a metric of self-care, as well as increased locomotor activity and central zone exploration in an open field test. Ethanol exposure also led to decreased brain mass, specifically in APP/PS1 mice, suggesting an interaction between ethanol exposure, amyloid pathology, and neurodegeneration. While there was a trend towards increased cortical Aβ deposition, there was a shift in the distribution of plaque size and numbers, with ethanol-exposed APP/PS1 mice showing a greater number of smaller plaques than H2O-exposed APP/PS1 mice. Finally, we used in vivo microdialysis to explore whether acute ethanol modulates hippocampal interstitial fluid (ISF) Aβ and ISF glucose levels in unrestrained, APP/PS1 mice. Acute intraperitoneal injection of ethanol led to a rapid rise in ISF ethanol and directly ISF Aβ (e.g. decreasing during acute exposure and increasing during acute withdrawal), and ISF glucose levels in the hippocampus. Together, these studies indicate that chronic ethanol, even at moderate doses, is sufficient to exacerbate an Alzheimer's-like phenotype in APP/PS1 mice through the direct modulation of Aβ.

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

“…Historically, in vivo microdialysis has successfully collected proteins and metabolites directly from the brain's ISF (35,39,41,51,52) yielding novel insights into how this dynamic pool is regulated. To date, Aβ 1-x (35,37,39), Aβ38 (78), Aβ40 (37,39,42,78), Aβ42 (37,39,78), tau (41,52), ApoE (63), glucose (35,42), lactate (35,37), and ethanol ( 42) are all detectable in the ISF of mouse models of AD-related pathology. For the first time, we collected EV ISF via in vivo microdialysis and analyzed their size, concentration, and proteome.…”

“…In vivo microdialysis was performed on mixed 3-month-old APP/PS1 and WT male and female mice (n=6) as previously described (42,43,50). Briefly, a guide cannula (BRstyle, BASi Instruments) was stereotaxically implanted into the hippocampus (from bregma, A/P: -3.1 mm; M/L: -2.5 mm; D/V: -1.2 mm; at 12° angle) and secured into place with dental cement.…”

“…Thus, we developed a novel method for collecting EVs from the hippocampal ISF of unanesthetized, freely-moving mice using in vivo microdialysis. To date, in vivo microdialysis is widely utilized in animal models of AD-like pathology for collecting Aβ, tau, and other proteins and metabolites but heretofore untested as a method for collecting EVs from the ISF (35)(36)(37)(38)(39)(40)(41)(42)(43)(44). By coupling in vivo microdialysis and EV isolation with proteomic profiling and bioinformatics, we hypothesized that this approach would allow us to characterize brain region-and cell type-specific changes in EVs relative to Alzheimer's-like pathology in vivo.…”