mRNA deregulation upon BRAFV600E induction in mouse thyrocytes

Papillary thyroid carcinoma (PTC) is the most frequent histological subtype of thyroid cancers (TC), and BRAFV600E genetic alteration is found in 60% of this endocrine cancer. This oncogene is associated with poor prognosis, resistance to radioiodine therapy and tumor progression. His-tological follow-up by anatomo-pathologists reveals that 2/3 of surgically-removed thyroids do not present malignant lesions. Continued fundamental research into the molecular mechanisms of TC downstream of BRAFV600E remains thus central to better understand the clinical behavior of these tumors. To study PTC, we used a mouse model in which expression of BRAFV600E is specifi-cally switched on in thyrocytes by doxycycline administration. Upon daily intraperitoneal doxycycline injection, thyroid tissue rapidly acquired histological features mimicking human PTC. Transcriptomic analysis revealed major changes in immune signaling pathways upon BRAFV600E induction. Multiplex immunofluorescence confirmed the abundant recruitment of macrophages, among which a population of LYVE-1+/CD206+/STABILIN-1+ was dramatically increased. By genetically inactivating the gene coding for the scavenger receptor STABILIN-1, we showed an increase of CD8+ T cells in this in-situ BRAFV600E dependent TC. Finally, we demon-strated the presence of CD206+/STABILIN-1+ macrophages in human thyroid pathologies. Alto-gether, we revealed the recruitment of immunosuppressive STABILIN-1 macrophages a PTC mouse model and the relevance of observations in human thyroid tissues.

甲状腺乳头状癌（Papillary thyroid carcinoma, PTC）是甲状腺癌（thyroid cancers, TC）最常见的组织学亚型，BRAFV600E基因变异在这类内分泌恶性肿瘤中的检出率可达60%。该癌基因与不良预后、放射性碘治疗耐药及肿瘤进展密切相关。解剖病理学家开展的组织学随访显示，三分之二的手术切除甲状腺组织并无恶性病变。因此，深入探究BRAFV600E下游甲状腺癌的分子机制，仍是阐明此类肿瘤临床行为的核心研究方向。为研究PTC，我们构建了一种小鼠模型，该模型可通过给予多西环素（doxycycline）特异性激活甲状腺滤泡细胞中BRAFV600E的表达。每日腹腔注射多西环素后，小鼠甲状腺组织快速出现与人PTC相似的组织学特征。转录组学分析显示，BRAFV600E诱导后免疫信号通路发生显著改变。多重免疫荧光染色证实，巨噬细胞大量招募，其中LYVE-1阳性/CD206阳性/STABILIN-1阳性的巨噬细胞亚群比例显著升高。通过遗传学手段敲除编码清道夫受体STABILIN-1的基因，我们发现该原位BRAFV600E依赖性甲状腺癌模型中CD8阳性T细胞的数量有所增加。最后，我们在人类甲状腺病变组织中检测到了CD206阳性/STABILIN-1阳性巨噬细胞的存在。综上，我们在PTC小鼠模型中揭示了免疫抑制型STABILIN-1阳性巨噬细胞的招募现象，并证实了该观察结果在人类甲状腺组织中的临床相关性。