Disruption of Innate Immunity Responses in Monocytes: Contribution to Neurodegeneration ABSTRACT Alzheimer’s disease (AD), characterized by elevated levels of β-amyloid (Aβ40 and Aβ42), is the leading cause of dementia, prevailing in approximately 12% of the population worldwide. In turn, HIV-associated neurocognitive disorders (HAND) prevail in 20-50% of people with HIV (PWH)1,2, despite the access to combined antiretroviral therapy (cART). Monocyte recruitment to the brain promotes macrophage phagocytic clearance of Aβ plaques and restoration of central nervous system (CNS) homeostasis (reviewed in3). However, in HIV infection, peripheral monocytes infiltrate the compromised blood brain barrier (BBB) into the CNS, triggering inflammation and neuronal damage4–7. Interestingly, HAND patients exhibit accumulation of Aβ in the blood8 and in the brain9–12, despite the presence of infiltrated monocytes. HIV hijacks its target cells to promote viral replication by impairing the interferon type I (IFN-1) signaling13,14. In AD, altered IFN-1 response decreases the recruitment of monocytes to the CNS15. IFN-1 signaling impairs insulin production16– 18, and dysregulated insulin signaling exacerbates Aβ plaque formation19,20. In turn, elevated levels of Aβ contribute to insulin resistance and cognitive decline21. In HIV patients on cART, insulin resistance prevalence is higher, compared to healthy individuals, which in turn is associated with worse neuropsychological performance, suggesting that metabolic alterations could also contribute to the development of HAND22,23. Thus, Aβ metabolism, insulin signaling, and cognitive impairment are interconnected. Due to their different etiologies, the shared mechanisms underlying AD pathology and HIV neuropathogenesis are not well understood. I hypothesize that impaired IFN-1 signaling in monocyte/macrophage (Mφs) alters their phenotype and insulin receptor (IR) metabolism, contributing to cognitive impairment in HAND and in AD patients. In this study, I will determine the contribution of the Mφs IFN-1 response to cognitive decline, through the following aims: 1) Characterization of IFN-1 signaling and insulin receptor biology in monocytes from the blood of AD and HAND patients, stratified by cognitive status; 2) using brain organoid models I will determine whether monocytes are neuroprotective or neuroinflammatory upon HIV infection, using HIV-negative and positive subjects’ monocytes; 3) I will determine the effect(s) of IFN-1 receptor modulation on Mφs phenotype, and neuronal dysfunction in vitro using brain organoids. Results from this study will uncover novel mechanisms involved in the crosstalk between the peripheral and CNS in neurodegenerative disorders. Further, our results will help identifying candidates and/or targets for the development of effective therapies against cognitive decline in HAND andAD. The proposed training plan is tailored to capitalize on my expertise in cellular biology and viral immunology, and to expand my skill set with novel 3D brain organoids methodologies. The multidisciplinary mentoring team is committed to provide career guidance, enrich my knowledge on new techniques, and ensure my transition to independence in academia, specializing in neuroimmunology.

PROJECT NARRATIVE Alzheimer’s disease (AD) is the leading cause of dementia worldwide in older individuals, while HIV associated neurocognitive disorder (HAND) is prevalent in 20-50% of people with HIV, who live longer due to successful antiviral therapy, being the leading cause of dementia in younger individuals. The crosstalk between the signaling pathways of AD and HAND warrant studies to better understand the neuropathologic mechanisms and identify novel candidates for therapies. Studying the altered interferon type 1 immune response in monocytes will yield novel information on how interactions between immunologic signaling and the CNS contribute to cognitive impairment.