支链氨基酸转氨酶BCAT1在慢性髓系白血病耐药中的功能

Although most of chronic myeloid leukemia (CML) patients can be effectively treated by the tyrosine kinase inhibitors (TKIs), such as Imatinib, TKI-resistance still occurs in approximately 15-17% of cases, which may be due to the existence of the leukemia-initiating cells (LICs) in CML cells. Although many studies indicate that metabolisms of different nutrients may be involved in the regulation of drug resistance in CML, the detailed mechanisms await for the further investigations. In our previous report, we established a dynamic and precise metabolic analysis system with a genetically coded branched-chain amino acid sensor and revealed that the catabolism of branched-chain amino acids plays important roles in the cell fate determinations of both hematopoietic stem cells and acute myeloid leukemia-initiating cells. Based on these findings, we further demonstrated that branched-chain amino acid levels were significantly reduced in TKI-resistant CML cells with a dramatic up-regulation of BCAT1 expression, which is the rate-limiting enzyme for the branched-chain amino acid degradation. Both in vitro and in vivo proliferation capacities of TKI-resistant CML cell lines or primary bone marrow cells from a mouse CML model were markedly inhibited upon the BCAT1-knockdown or the branch-chain amino acid diet restriction. BCAT1-mediated TKI-resistance in CML may be potentially fine-tuned by CDC20. In current project, we will further unravel the metabolic profiles of branched chain amino acids of CML-LICs. We will also evaluate the roles of BCAT1 in the cell fate commitments and TKI-resistance of CML-LICs. Eventually, we will test the potential effects of the branch-chain amino acid diet restriction in the treatment of TKI-resistant CML model. These studies may provide the novel angle or targets for understanding the underlying mechanisms related to TKI-resistance and potential therapeutic strategies for TKI-resistant CML.

虽然伊马替尼等酪氨酸激酶抑制剂治疗对多数慢性髓系白血病（CML）患者效果良好，但约有15%病人仍发生耐药，这可能与其存在的白血病起始细胞（LICs）密切相关。研究提示诸多代谢途径可能参与了CML耐药的调控，但相关机制亟待阐明。我们前期构建了基于遗传编码的支链氨基酸感受器的精准代谢研究体系，并揭示了支链氨基酸代谢对造血干细胞和急性髓系白血病起始细胞命运的关键作用。基于此，我们后续发现了耐药性CML细胞支链氨基酸水平明显降低，而介导其降解的限速酶BCAT1急剧上调的新规律；干扰BCAT1表达或限制支链氨基酸饮食能有效抑制CML细胞系或原代骨髓细胞的体内外增殖，并受到CDC20的潜在调控。本项目拟进一步明确CML-LICs支链氨基酸代谢规律，及BCAT1调控CML-LICs命运和耐药的作用与机制；探讨支链氨基酸摄入限制对CML耐药的疗效，为理解CML耐药机制和探讨潜在治疗策略提供新的思路和靶点。

研究提示诸多代谢途径可能参与调控造血干细胞（Hematopoietic stem cells, HSCs）干性维持及恶性转化过程，我们前期利用多种遗传编码的代谢感受器揭示了不同类型白血病起始细胞（Leukemia initiation cells，LICs）具有独特的代谢特征，参与调控LICs自我更新、耐药等命运决定。课题围绕着支链氨基酸转氨酶1（branched-chain amino acid transaminase 1，BCAT1）在耐药慢性髓系白血病(Chronic myeloid leukemia, CML)细胞中的作用，利用遗传编码的代谢感受器、分子生物学、转录组学、疾病动物模型等手段，揭示了BCAT1对CML-LICs耐药细胞命运决定具有重要调控作用，干扰BCAT1表达及酶活性或限制支链氨基酸饮食能有效抑制伊马替尼耐药CML细胞系或原代耐药CML模型骨髓细胞在体内外增殖，并显著延长受体小鼠生存期。机制上，BCAT1通过调控CREB（AMP response element-binding protein）磷酸化水平精细调控CML细胞耐药。我们进一步拓展研究骨髓微环境成分与HSC/LICs内在代谢特征及其命运决定之间的互作规律。我们发现，内皮细胞来源的血管生成素样蛋白2是骨髓Niche的重要组成成分，通过PPARD/G0S2信号精准调控HSCs的静息状态、骨髓血管周微环境定位及干自我更新。急性髓系白血病小鼠骨髓液中ATP浓度显著高于正常小鼠，且LICs更倾向定位于靠近骨内膜高浓度ATP处，微环境中ATP 可通过激活灵敏度不同的嘌呤能受体离子通道P2X1、P2X7所介导的下游代谢性信号通路显著促进白血病的发生发展。以上研究，不仅有助于为理解骨髓微环境中HSCs/LICs干性维持的分子基础，也为探讨CML/AML潜在治疗策略提供新的思路和靶点，并为HSCs体外扩增和临床应用提供了潜在路径。