Monitoring uptake of palmitic acid by glioma cells using stimulated Raman scattering microscopy

Glioblastoma (GBM) is one of the most aggressive cancer types in nervous system. Due to the limited effectiveness of current treatments, prognosis remains poor for GBM patients. Altered lipid metabolism is a hallmark of GBM. Previous studies show that increased lipid droplets (LDs) could protect cancer cells from chemotherapy and other extracellular stresses. In this study, we apply stimulated Raman scattering (SRS) microscopy to image LDs to monitor uptake of palmitic acid (PA) by U-87 glioma cells. We observe that uptake of free PA rapidly upregulates adipogenesis in glioma cells. We find that glioma cells exhibit distinctive time-dependent and dose-dependent patterns in PA uptake and adipogenesis. Uptake of extra PA significantly decreases the unsaturation degree of LDs. The decreased unsaturation degree and other lipotoxicity effects lead to clear cell death upon PA treatment at a high concentration. The results indicate that inhibition of adipogenesis may have therapeutic effects for GBM utilizing the lipotoxicity effects induced by free fatty acids. This work demonstrates that SRS microscopy for label-free imaging of LDs distribution and their composition is a promising tool for lipid metabolism studies in cancer.

胶质母细胞瘤（GBM）是神经系统中最具侵袭性的癌症类型之一。由于当前治疗方法的效果有限，GBM患者的预后仍然不佳。脂质代谢改变是GBM的一个特征。先前的研究表明，增加的脂滴（LDs）可以保护癌细胞免受化疗和其他细胞外应激的影响。在这项研究中，我们应用受激拉曼散射（SRS）显微镜对脂滴进行成像，以监测U - 87胶质瘤细胞对棕榈酸（PA）的摄取。我们观察到游离PA的摄取迅速上调胶质瘤细胞中的脂肪生成。我们发现胶质瘤细胞在PA摄取和脂肪生成方面呈现出独特的时间依赖性和剂量依赖性模式。额外PA的摄取显著降低了脂滴的不饱和度。在高浓度PA处理时，不饱和度的降低和其他脂毒性作用导致细胞明显死亡。结果表明，利用游离脂肪酸诱导的脂毒性作用，抑制脂肪生成可能对GBM具有治疗效果。这项工作表明，用于脂滴分布及其组成的无标记成像的SRS显微镜是癌症脂质代谢研究的一种有前途的工具。