A Polarity-Sensitive Lipid Droplet Probe Reveals Aβ Species-Dependent Lipid Droplet Remodeling in Microglia

Microglial lipid metabolic alterations are increasingly implicated in Alzheimer’s disease (AD), yet the specific β-amyloid (Aβ) species involved in lipid droplet (LD) remodeling remain unclear. Precise visualization of LD morphology in complex biological systems is limited by the availability of selective and photostable probes. Herein, we report a polarity-sensitive LD probe, BODIPY-LD, constructed with a donor−π−acceptor−π−donor (D−π−A−π−D) framework that enables hydrophobic targeting and intramolecular charge transfer (ICT)-based fluorescence activation in low-polarity environments. The probe allows high-contrast visualization and quantitative assessment of LD morphology in cells and brain tissues. Using BODIPY-LD, we observed increased LD burden in hippocampal microglia of APP/PS1 mice and systematically compared the effects of different Aβ 2 5–3 5 assembly states on LD accumulation in BV2 microglia. Among monomeric, oligomeric, and fibrillar Aβ 2 5–3 5 forms, the monomer-treated BV2 cells showed the most pronounced LD enrichment under our experimental conditions. This LD-rich phenotype was associated with reduced phagocytic capacity and was partially reversible upon inhibition of LD synthesis using the long-chain acyl-CoA synthetases (ACSL) inhibitor Triacsin C. Together, these findings suggest that monomeric Aβ 25−35 is associated with an LD-rich microglial phenotype and impaired phagocytic function in vitro model. Beyond this biological observation, BODIPY-LD provides a useful tool for studying lipid remodeling in neuroinflammatory contexts.