Deciphering the role of CD44 astrocytes in Alzheimer's disease - Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder, characterized by neurofibrillary tangles, β-amyloid (Aβ) plaques, and astrocyte dysfunction. Astrocytes play critical roles in AD pathophysiology, including Aβ clearance and modulation of neuroinflammation. Thus, astrocytes are essential in the pathogenesis of AD, yet the molecular mechanisms underlying astrocyte pathology in AD are not fully understood. Robust evidence from the literature and our preliminary data in human AD tissue and an AD mouse model shows an increase in a population of astrocytes characterized by expression of the matrix-protein receptor CD44. However, the precise contributions of CD44 astrocytes to AD pathology are unknown. Our detailed initial investigations revealed an elevated spatial correlation between CD44 expression and Aβ plaques in both human AD patients and a murine AD model - suggesting a potential role for CD44 in disease initiation or progression. This proposal builds on this foundation and aims to comprehensively define the functional role of CD44 in AD disease- associated astrocyte states. Overarching hypothesis: CD44 upregulation in astrocytes drives a specific disease-associated astrocytes state and promotes AD pathology. Aim 1 will elucidate the signaling mechanisms by which CD44 alters astrocyte phenotype and function in vitro. This will involve genetic and pharmacological manipulation of CD44 cleavage and CD44 intracellular domain (ICD) signaling pathways, evaluating downstream effects on astrocyte biology, including morphology, gene expression, and functional responses. Aim 2 will investigate the impact of astrocytic CD44 on neuronal dysfunction using AD cellular models. Co-culture experiments with cortical murine and induced pluripotent stem cell (iPSC)-derived neuronal AD models will assess how astrocyte CD44 perturbations affect neuronal viability, synaptic function, and transcriptomic profiles. Leveraging single-nucleus RNA sequencing (snRNAseq), this aim will correlate in vitro findings with changes observed in AD patient brains to validate the relevance of CD44-dependent mechanisms in disease pathogenesis. Aim 3 will explore the in vivo effects of modifying CD44 in an AD mouse model, utilizing a novel astrocyte-specific Cd44 knockout mouse and targeted viral expression strategies. We will employ multiplex immunofluorescence, snRNAseq, spatial transcriptomics, and behavioral assays to quantify changes in astrocyte states, Aβ pathology, and cognitive decline. By targeting CD44 at early and late stages of pathology, this aim will determine how manipulating CD44 can mitigate or exacerbate neurodegenerative outcomes. Impact: This study will advance our understanding of CD44-mediated mechanisms in AD, proposing CD44 as a potential therapeutic target for modulating astrocyte-driven neurodegeneration and improving outcomes in AD patients.
