Investigating Sex-Specific Hypothalamic Pathology and Immune Infiltration in Alzheimer's Disease

PROJECT SUMMARY Nearly two-thirds of all Alzheimer’s disease (AD) cases are in females, suggesting sex differences in both prevalence and presentation. Yet, the mechanisms underlying sex disparities in AD remain unknown. The hypothalamus plays a key role in regulating numerous physiological processes that are disrupted in AD, such as sleep-wake cycle, appetite, and sex-hormone production. The hypothalamus is also uniquely positioned as a hub for peripheral signals in the brain due to its leaky blood-cerebrospinal fluid-barrier (BCSFB), central position in the neuroendocrine axis, and bi-directional neuronal circuits. Recent evidence suggests tanycytes, specialized ependymal cells that comprise the hypothalamic BCSFB, transport tau out of the cerebrospinal fluid (CSF) and may be dysfunctional in AD. However, hypothalamic involvement and mechanisms of immune cell infiltration in this region remain critically understudied in AD. Thus, interrogating the link between peripheral immune infiltration and hypothalamic pathology is essential to understanding clinical symptoms underlying sex disparities in AD. Preliminary data indicates uniquely altered populations of clonally expanded CD8 T cells exist in both the blood and CSF of AD patients. Notably, these altered T cell populations could have increased access to the hypothalamus due to the leaky BCSFB in AD patients. This led to the hypothesis that BCSFB dysfunction in the hypothalamus results in increased peripheral immune infiltration and subsequent neuroinflammation in AD. Therefore, the goals of this project are to investigate sex-specific transcriptomic alterations in the AD hypothalamus (Aims 1 and 2) and explore how altered hormonal signaling may influence neuroinflammation in the brain (Aim 3). Specific Aim 1 will utilize single-cell fixed RNA profiling to identify and evaluate cell-specific transcriptomic alterations in AD hypothalamus, according to sex and disease severity. Specific Aim 2 will use spatial transcriptomics to elucidate the spatial relationship between BCSFB dysfunction, neuroinflammation, and AD pathology in the hypothalamus. Specific Aim 3 will use human induced pluripotent stem cells, phagocytosis assays, flow cytometry, and qRT-PCR to delineate the effect of hormones on microglia. The proposed studies will work towards establishing a mechanistic link between peripheral immunity and AD pathobiology in the hypothalamus. They work to aid therapeutic approaches by providing deeper understanding about how BCSFB function may exacerbate neuroinflammation and promote sex disparities in AD.