SFRP2-Wnt/β-catenin信号通路在库欣病发生中的作用及机制研究

Cushing's disease (CD), caused by excessive secretion of adrenocorticotropic hormone (ACTH) from pituitary adenoma, induced a series of metabolic disorders; the patients were faced with a double blow- endocrine disorders and tumor growth, which seriously threatened their normal life and survival. Moreover, the mortality of CD is reported four times higher than that in the general population. However, the pathogenesis of CD is still unclear. Our RNA sequencing data shown that SFRP2, the Wnt inhibitor, was remarkedly decreased in human pituitary ACTH-secreting adenoma. In mouse AtT20 pituitary corticotroph cells, forced expression of SFRP2 could down-regulate the proopiomelanocortin (POMC) expression, inhibit ACTH secretion and cellular proliferation. These results suggest that downregulated SFRP2 may promote CD tumorigenesis by activating canonical Wnt signaling pathway. Thus we have established the pituitary tissue specific SFRP2 knockdown mouse model, which is now ready for use. In the present study, by using this mouse model as well as primary cells, analyzing the phenotypes of mice and cells after SFRP2 overexpression and knockdown, we will further explore the significant role and underlying mechanism of SFRP2 in Cushing disease. Lastly, we will compare the serum SFRP2 level between CD patients and normal individuals to establish the correlation of SFRP2 and CD clinical outcome, such as ACTH level, tumor size, invasiveness etc. This study will provide a new tumor suppressive factor for the pathogenesis and therapy of CD.

库欣病是由垂体肿瘤过度分泌ACTH引起的一系列代谢紊乱症候群，患者面临内分泌紊乱及肿瘤生长双重威胁，病死率比一般人群高4倍。然而，其发病机制尚不清楚。我们前期研究发现，Wnt通路天然抑制因子SFRP2在库欣病人肿瘤组织中表达明显下调；在小鼠ACTH垂体腺瘤细胞系AtT20中过表达SFRP2能抑制前阿黑皮原（POMC）基因表达，ACTH分泌及细胞增殖；且SFRP2可下调Wnt通路下游基因表达，表明其可能通过拮抗Wnt通路参与库欣病发生。基于此，我们构建了垂体组织特异性SFRP2敲除小鼠，此项目拟借助此基因修饰小鼠，通过表型观察，SFRP2过表达和下调干预试验，从体内外水平阐明SFRP2/Wnt通路参与库欣病发生的作用机制；同时我们将检测库欣病人血清SFRP2水平，建立SFRP2与库欣病临床后果之间的相关性。这将在库欣病发生机制方面提出一个全新的抑癌因子，并可能为库欣病干预治疗提供新的靶点。

库欣病亦称为垂体依赖性皮质醇增多症，是由垂体腺瘤细胞分泌过多促肾上腺皮质激素所致。除了肿瘤增长引起的占位性损伤，体内过量的促肾上腺皮质激素还导致双侧肾上腺皮质增生进而引起高皮质醇血症，造成患者出现一系列严重的内分泌代谢紊乱症状。目前尚不清楚该疾病发生发展的具体分子机制，因而缺乏有效的靶向治疗方式。本项课题研究中我们对库欣病肿瘤垂体肿瘤组织中SFRP2的表达水平进行了相关的验证，明确其在库欣病中组织中存在表达差异。并且，通过相关基础研究手段，对库欣病肿瘤中SFRP2与Wnt/β-catenin通路活性相关性进行了阐述，明确了二者之间的相关作用关系。除此以外，我们还在前期研究的基础上，拓展了库欣病研究的宽度，对转录组中相关差异基因进行了更深入的筛选，选择TSP-1基因进行了相关研究。研究中，我们在细胞及动物模型水平证实了TSP-1表达能够抑制库欣病肿瘤细胞的增殖、迁移、侵袭、成瘤以及激素分泌能力。除此之外，我们还对库欣病垂体肿瘤中TSP-1表达减少的原因进行了初步探索，发现肿瘤中lncTHBS1能够作为ceRNA，发挥竞争性抑制miR-449c的作用进而调控库欣病肿瘤中TSP-1表达水平的的作用。本课题的相关成果进一步丰富了库欣病发生发展的基础研究理论，为阐明库欣病的致病机理以及研发治疗靶点提供了大量数据和线索。