Determining the role of lipid droplets in glioblastoma and their therapeutic potential

摘要 胶质母细胞瘤（GBM）是最具侵袭性的脑肿瘤，尽管有肿瘤，但中位生存期仅为12-15个月。 强化治疗，表明迫切需要确定有效的方法来治疗GBM和规避 对治疗的抵抗，以显着提高患者的生存。我们最近的研究表明， 脂质合成和摄取在GBM中大大增强并促进肿瘤生长。据了解， 游离脂肪酸（FFA）和胆固醇可引起内质网（ER）应激和脂毒性， 细胞死亡，这就提出了一个有趣的问题，即GBM细胞如何防止可能由 增加脂质代谢。我们最近发现来自GBM患者的肿瘤组织含有大量的 脂滴（LDs）、甘油三酯（TG）和胆固醇酯（CE），表明GBM细胞可能储存过量 FFA和胆固醇转化为LD，以避免毒性并维持肿瘤生长。进一步分析表明， 肿瘤组织中含有较高水平的LD和DGAT 1（甘油二酯酰基转移酶）的患者，或 SOAT 1（固醇O-酰基转移酶），两种ER膜结合酶，催化过量的 FFA和胆固醇转化为TG和CE形成LDs，生存率较差，提示LDs可能具有一定的 促肿瘤功能与我们的发现一致，一些研究小组最近报道，抑制胆固醇 在前列腺癌、胰腺癌或肾癌细胞中，酯化或抑制LD形成显著增强ER 应力然而，癌细胞中许多重要的LD功能仍然未被探索，例如它们的功能。 支持肿瘤抵抗的积极作用和潜力。我们的初步数据表明，LD可能 为营养减少或辐射/替莫唑胺（TMZ）下的GBM生存提供关键的能量来源 治疗，GBM的标准疗法。基于目前对癌细胞中LD的理解和我们的新研究， 根据初步数据，我们假设GBM中LD的形成阻止了ER应激和脂毒性， 作为能量库，以支持肿瘤在能量挑战下存活。我们进一步假设， LD的形成会引起ER应激、脂毒性和能量不足，这可能与LD的形成有强烈的协同作用。 放射/TMZ处理以诱导GBM细胞死亡。在本研究中，我们将：（1）描绘潜在的保护性 LD形成在GBM细胞中的作用;（2）确定LD是否在GBM细胞中发挥重要的能量作用;（3） 检查是否遗传性或非遗传性抑制LD形成有效地抑制肿瘤生长 并在GBM原位小鼠模型中使GBM对放射/TMZ治疗敏感。这项研究将揭示 LDs在GBM中以前未表征的作用和分子调控。重要的是，它还将证明 抑制LD形成可能是特异性靶向GBM的非常有效的方法， 正常脑组织中没有检测到LD。这项研究的完成将大大促进我们的 了解脂质代谢重编程，并可能带来新的方法来拮抗GBM。

ABSTRACT Glioblastoma (GBM) is the most aggressive brain tumor, and has a median survival of only 12-15 months despite intensive therapies, indicating the urgent need to identify effective approaches to treat GBM and circumvent resistance to therapies in order to significantly improve patient survival. Our recent studies demonstrated that lipid synthesis and uptake are greatly enhanced in GBM and promote tumor growth. It is known that increased free fatty acids (FFA) and cholesterol can cause endoplasmic reticulum (ER) stress and lipotoxicity that lead to cell death, which raises the intriguing question of how GBM cells can prevent the toxicity potentially induced by increased lipid metabolism. We recently found that tumor tissues from GBM patients contain large amount of lipid droplets (LDs), triglycerides (TG) and cholesteryl esters (CE), suggesting that GBM cells may store excess FFA and cholesterol into LDs to avoid toxicity and maintain tumor growth. Further analysis showed that GBM patients whose tumor tissues contained higher levels of LDs and of DGAT1 (diglyceride acyltransferase) or SOAT1 (sterol O-acyltransferase), two ER membrane-bound enzymes that catalyze the conversion of excess FFA and cholesterol into TG and CE to form LDs, had the worse survival, suggesting that LDs may have a protumoral function. Consistent with our findings, several groups have recently reported that inhibiting cholesterol esterification or suppressing LD formation in prostate, pancreatic or renal cancer cells significantly enhanced ER stress. Nevertheless, many important LD functions in cancer cells remain unexplored, such as their energetic role and potential for supporting tumor resistance. Our preliminary data suggest that LDs may provide a critical energy source for GBM survival under nutrient reduction or radiation/temozolomide (TMZ) treatment, the standard therapy for GBM. Based on current understanding of LDs in cancer cells and our novel preliminary data, we hypothesize that LD formation in GBM prevents ER stress and lipotoxicity, and also serves as energy reservoir to support tumor survival upon energy challenges. We further hypothesize that inhibiting LD formation will cause ER stress, lipotoxicity and energy shortage, which may strongly synergize with radiation/TMZ treatment to induce GBM cell death. In this study, we will: (1) delineate the underlying protective role of LD formation in GBM cells; (2) determine whether LDs play an important energetic role in GBM cells; (3) examine whether genetically or pharmacologically inhibiting LD formation effectively suppresses tumor growth and sensitizes GBM to radiation/TMZ treatment in GBM orthotopic mouse models. This study will reveal the previously uncharacterized role and molecular regulation of LDs in GBM. Importantly, it will also demonstrate that inhibiting LD formation may be a very effective approach to specifically target GBM with little toxicity on normal brain tissues where no LDs could be detected. Completion of this study will significantly advance our understanding of lipid metabolism reprogramming and may bring about new approaches to antagonize GBM.