Revealing simulated microgravity-induced abnormal accumulation of lipid droplets in nerve cells with long-term tracking probe

During spaceflight, microgravity impacts the functions of central nervous system (CNS). Lipid droplets can respond to stress-induced cell damage, but the role of them in the effect of space microgravity on CNS remains unclear. Herein, we construct two lipophilic fluorescent probes, LD-T and LD-C, with similar chemical structures but different cell staining behaviors. LD-T exclusively targets lipid droplets and is well retained in living cells for 72 h. While LD-C stains both lipid droplets and endoplasmic reticulum (ER), and is excluded gradually by living cells within 72 h. With superior long-term tracking ability, LD-T is successfully used to monitor lipid droplets abnormal accumulation in nerve cells under simulated microgravity (SMG) exposure. The expression levels of lipid droplet-related genes are also upregulated responding to SMG treatment. Inhibiting lipid droplet accumulation can effectively alleviate SMG-induced nerve cell damage. This work discovers that ER-targeting dyes are facilely excluded from the cells, but exclusive lipid droplet-targeting probes are potential to be retained and applied for long-term tracking. Furthermore, we find that SMG causes lipid droplets abnormal accumulation in nerve cells for the first time, which mediates SMG-induced nerve injury. Therefore, lipid droplets may serve as potential targets for neuroprotection in space environment.