肿瘤细胞群体适应性权衡的生态进化机制

Different biotopes result creatures in different phenotypic characteristics to adapt the various natural environment. The r-/K-selection theory, which was introduced to the life history theory and based on density-dependent selection, was used to elucidate the population dynamics in ecology. The r-selected populations live at loose density without resource limitation, while the K-selected populations live at density close to carrying capacity. This theory suggests that many living things under r-/K-selection were subjected to ecological trade-offs between many features. The high heterogeneity of tumor has been shown at different levels. It would have been reflected on the phenotype of cells and enabled the cell populations to have diverse biological characteristics, suggesting that the cancer cells may be subject to trade-offs between cell proliferation and survival, which emerged during somatic evolution driven by r/K selection. Here we platformed an evolutionary experiment system to select the cancer cell-lines under two different culture conditions and obtained two cell-lines with stable phenotypic differentiation finally. It is meaningful to analyze the characteristics and mechanism of phenotypic diversity of tumor cell populations for understanding the tumor evolutionary process. The molecular or cytological markers of different cell lines could be identified via detect the variances between the genomes, epigenomes and transcriptomes of phenotypic divergence cell-lines. The cluster analysis based on the differentially expressed genes, combined with a large number of cancer data in TCGA, could not only demonstrate that whether the cell phenotypic differentiation was involved in cancer tissues in vivo but also identify the characteristics and the key genes or regulatory pathways of cell phenotypic differentiation. Meanwhile, a mouse model of cell proliferation and a drug delivery system could be established to explore the relationship between the phenotypic differentiation and adaptation in vivo. In addition, a competitive Lotka–Volterra model would be developed. Based on this ecological model and combined with the data of cell proliferation in vivo and in vitro, the driving force of the phenotypic evolving process of the population could be well explained. The genomic and ecological interpretation of trade-off in cancer cells will shed light on the understandings of the process and mechanism of tumor evolution and the clinical treatment of tumors.

生物在不同的生境中具有不同的表型，以适应复杂多样的环境。生态学中的r/K选择理论可以阐述种群的动态变化。r/K选择下的种群在许多特征上体现出适应性权衡。肿瘤高度的异质性也体现在细胞表型方面，使之具有多样的生物学特征。通过建立实验进化学系统，将肿瘤细胞系在两种不同培养条件下进行筛选，得到了两种具有稳定表型分化的细胞系。通过表型分析，发现细胞系在进化中出现细胞增殖与细胞存活之间的适应性权衡。解析表型多样性的特征及产生机制，对深入理解肿瘤群体演化有重要意义。通过检测表型分化群体的基因组、表观和转录组变异，结合TCGA组学数据，以寻找种群特异的分子或细胞学标记，探究癌组织中细胞的表型分化及其涉及到的关键基因或调控通路；建立细胞增殖的小鼠模型与给药体系，解析表型分化与适应性的关系；建立竞争L-V生态学模型，分析群体表型演化的驱动力。通过上述系统的实验及分析，将对肿瘤临床治疗提供新的组学及细胞学线索。

生物在不同的生境中具有不同的表型，以适应复杂多样的环境。生态学中的r/K选择理论可以阐述种群的动态变化。r/K选择下的种群在许多特征上体现出适应性权衡。肿瘤高度的异质性也体现在细胞表型方面，使之具有多样的生物学特征。在本项目中，以密度依赖性选择中的经典理论——r-vs.K-选择理论为基础，利用实验进化的手段，选择出r或K癌细胞系，获得了具有快速增殖能力的r细胞和具有高度竞争力的K细胞，证实了癌症细胞群体中存在表型亚群分化，并系统地揭示了不同表型之间的适应性权衡。RNA-seq表明，这种权衡与细胞周期、粘附、凋亡和接触抑制相关基因的不同表达有关。此外，我们还建立了具有空间结构制约的肿瘤细胞系亚群竞争实验，当r细胞和K细胞混合时，它们表现出明显不同的时空分布。这是领域内首次观察到癌症细胞不同表型亚群之间的生态位分离事件。之后，我们以L-V竞争模型为基础，构建了一个基于密度依赖性选择的细胞竞争性群体动力学模型，探究细胞群体的种群动力学规律，结果表明细胞群体内表型权衡的共存可能有助于群体的增长。.肿瘤发展过程中的体细胞进化使肿瘤细胞发生的表型分化，那么这些表型上的差异会不会影响肿瘤内的遗传异质性和克隆结构？为回答此问题，我们提出了一个中性空间(NS)模型，在该模型中，突变积累随着肿瘤的向外生长而增加，谱系关系是由空间位置决定的，自然选择的效能微弱(由于亲缘竞争)。为了检验NS模型，我们对一个肝细胞癌病例的两个肿瘤（T1和T2）进行了三维多点微采样和全基因组测序。结果显示，肿瘤外缘细胞具有更高的分裂速度，从而积累更多的突变。肿瘤这种外围细胞比内部细胞分裂速度快的现象可能对肿瘤的治疗有一定的影响，提示临床上可能需要针对不同表型和肿瘤微环境的治疗方法联合使用。