Adolescent Binge Alcohol Exposure Accelerates Alzheimer's disease-associated Basal Forebrain Neuropathology through Proinflammatory HMGB1 Signaling

Rachael P Fisher Lindsay Matheny Sarrah Ankeny Liya Qin Leon Coleman Jr Ryan P. Vetreno ^*

• University of North Carolina at Chapel Hill, Chapel Hill, United States

Human studies suggest that heavy alcohol use may be an etiological factor contributing to the development of Alzheimer’s disease (AD) neuropathology. Both alcohol use disorder (AUD) and AD share common underlying neuropathology, including proinflammatory high-mobility group box 1 (HMGB1)-mediated neuroimmune signaling and basal forebrain cholinergic neuron degeneration, and evidence suggests these systems are particularly sensitive to adolescent alcohol exposure. Therefore, we sought to test the hypothesis that adolescent binge alcohol exposure increases AD-associated neuropathology through proinflammatory HMGB1 signaling. In Experiment 1, AD-associated neuropathology was assessed in the post-mortem human basal forebrain of individuals with AUD and an adolescent age of drinking onset relative to age-matched moderate drinking controls (CONs). In Experiment 2, non-transgenic and 5xFAD male and female mice, which overexpress both mutant human APP and PS1, received adolescent intermittent ethanol (AIE; 5.0 g/kg, i.g. 2-days on/2-days off; postnatal day [P]30 – P55) and basal forebrain tissue collected on P100 for assessment of AD-associated neuropathology. In Experiment 3, 5xFAD female mice received AIE treatment followed by glycyrrhizic acid (150 mg/L), an HMGB1 inhibitor, in drinking water from P56 to P100, and basal forebrain tissue collected on P100 for assessment of AD-associated neuropathology. In the post-mortem human AUD basal forebrain, we report upregulation of Hmgb1 and the HMGB1 receptors Rage and Tlr4 as well as microglial activation and increased intraneuronal Aβ1-42 in association with reduced cholinergic neuron marker expression (ChAT). In the 5xFAD mouse model, AIE accelerated AD-associated induction of Hmgb1 proinflammatory neuroimmune genes, microglial activation, and reductions of ChAT+ basal forebrain cholinergic neurons in the adult female, but not male, basal forebrain. Post-AIE treatment with glycyrrhizic acid rescued the AIE-induced acceleration of AD-associated increases in proinflammatory HMGB1 neuroimmune signaling, microglial activation, and persistent reductions of basal forebrain cholinergic neurons in adult 5xFAD female mice. Together, these data suggest that adolescent binge ethanol exposure may represent an underappreciated etiological factor contributing to onset of AD-associated neuropathology in adulthood through HMGB1-mediated neuroimmune signaling.