Sox2蛋白於造釉細胞瘤的表現及與其臨床病理之相關性

Abstract

造釉細胞瘤是顎骨中最常見之齒源性腫瘤，雖屬於良性但其具有局部侵犯能力而需進行較大範圍之切除，因此，患者常會有顏面部變形並有較高的復發可能，特別是前次手術未將腫瘤完全移除時。有關造釉細胞瘤的來源仍然未有定論，而齒源性上皮殘留體被認為是可能的來源之一。目前對於造釉細胞瘤的致病機轉仍相當有限。許多研究顯示組織特有幹細胞常為腫瘤的啟始細胞，在經過治療後，造成腫瘤復發的細胞也常是腫瘤幹細胞。目前對於牙齒上皮幹細胞在造釉細胞瘤的致病機轉仍不清楚。Sox2為一轉錄因子，表現於胚胎或成人的幹細胞。在許多腫瘤中也常見Sox2的表現，並在腫瘤的生長、侵犯能力、抗藥性、預後都扮演著重要的角色。在先前研究中發現在牙胚中表現Sox2的細胞後續能分化成各類的齒源上皮細胞，因而Sox2被認為是牙齒上皮幹細胞的標記。在本實驗中，我們利用免疫染色的方式來確認齒源性上皮殘留體是否有Sox2的表現，並探查不同亞型之造釉細胞瘤的Sox2表現情形，並觀察造釉細胞瘤其臨床及病理表現與Sox2染色表現程度的相關性。本實驗一共收錄七十四例造釉細胞瘤及六例齒濾泡。依組織學分類，本實驗收集之造釉細胞瘤分為：濾胞型 (27 例，36.5%)；叢狀型 (22例，29.7%)；單室型 (25例，33.8%)。我們首先利用過去研究使用的兩株Sox2的抗體，觀察其在鱗狀上皮與造釉細胞瘤的表現，找出其中較可信賴之抗體用以繼續後續的實驗。所得之結果如下:(1)在6例齒濾泡中，在齒源性上皮殘留體皆有表現Sox2的細胞，表現率為44.7%，Sox2表現細胞呈現於小型圓核細胞。(2)74例的造釉細胞瘤腫瘤細胞，皆有Sox2的表現，叢狀型表現率顯著地高於濾泡型(28.8% vs. 17.2%, 曼惠二氏U檢定法，p=0.031)，但與單室型(20.3%)無顯著差距。Sox2多表現於圓或橢圓形的類造釉母細胞，偶爾表現在有極性的高柱狀型類造釉母細胞; (3)Sox2與臨床情形(顎骨穿孔與否、因腫瘤而牙根吸收與否、腫瘤大小)並無顯著相關。另外也發現不論是復發的病例或是將來有復發情形病例，其Sox2的表現程度與無復發的病例相比並無顯著差異。然而在三對分別為原發與復發的病例中，復發病例的Sox2表現程度明顯大於原發組別。(4)病理觀察方面，出現表現Sox2的高柱狀類造釉母細胞與其他臨床指標也無相關。(5)此外我們也在2例造釉細胞纖維瘤及4例造釉細胞纖維牙瘤上進行Sox2免疫染色，觀察到Sox2+的高柱狀類造釉母細胞在所有表現Sox2腫瘤細胞的比例越高的病例，其腫瘤尺寸越大。以上呈現了Sox2在造釉細胞瘤的表現情形，雖然其表現程度與臨床指標並無顯著相關，但Sox2可能在復發病例扮演重要的角色。而齒源性上皮殘留體具有強烈的Sox2，可能為造釉細胞瘤或是其他齒源性腫瘤的來源。

Ameloblastoma is the most common odontogenic neoplasm. Although ameloblastoma is a benign and slowly growing epithelial odontogenic tumor, it is local invasive with high recurrence rate, especially when the lesion is not adequately removed in the initial surgery. The knowledge of pathogenesis of ameloblastoma remains limited and the cell of origin for ameloblastoma is unclear. It has been suggested that it may arise from the remnants of the odontogenic epithelium. Recent studies point the stem/progenitor cells as both initiators and propagators of the tumors. Sox2 is a transcription factor and plays important roles in many stage of mammalian development, tissue homeostasis and tumor pathogenesis. Sox2+ cells have been showed to give rise to all dental epithelial lineages and therefore has been accepted as a dental epithelial stem cell marker. In this study, we conducted immunohistochemical study to investigate whether there is Sox2+ cells in the remnants of the odontogenic epithelium in dental follicles, and the expression pattern of Sox2 in different subtypes (follicular, plexiform and unicystic) of ameloblastoma. The correlation between Sox2 expression and clinicopathological findings was performed. In this study, we enrolled 6 cases of dental follicle, 74 (27 follicular; 22 plexiform; 25 unicystic type) paraffin-embedded tissues of ameloblastoma. Since previous studies using two different clones of Sox2 antibodies show different results, we first performed a pilot study to determine the antibody we would further used for our study. The results showed as following: (1) Sox2+ cells can be identified in odontogenic epithelial nests in all six dental follicles and the labeling indices is 44.7%. The positive cells are small round cells. (2) Sox2+ cells can be identified in all 74 cases of ameloblastoma with scattered and patchy distribution and variable amount. Majority of positive cells are peripheral basal to pre-ameloblast-like cells. Few Sox2 expression in high columnar ameloblast-like cells can be identified. The plexiform type showed significant higher Sox2 labeling indices than follicular type using Mann-Whitney u test (28.8% vs. 17.2%, p= 0.031). (3) The expression of Sox2 were not correlated with the clinical findings (bone perforation or not, root resorption causing by tumor or not, size of tumor) in ameloblastoma. The expression level also show no difference in cases with recurrent events and cases without recurrence. However, the recurrent cases show much higher Sox2 labeling indices than original ones in three paired cases of three patients. (4) the presence of high-columnar Sox2+ cell was not correlated to any of the clinical parameters in these three type of ameloblastoma. (5) All cases of 2 cases of ameloblastic fibroma and 4 cases of ameloblastic fibro-odontoma showed Sox2+ cells. Sox2+ cells were randomly and scattered distributed in islands or strands of odontogenic epithelium. The cases with more Sox2+ high-columnar cell showed larger tumor size. In this study, we examined the expression pattern of Sox2 in dental follicle and three different types of ameloblastoma and odontogenic tumors with ameloblastic features. Our findings suggested that Sox2+ cells might play some roles in propagation and recurrence of ameloblastoma. Sox2+ cells can be identified in remnants of the odontogenic epithelium in dental follicle, which suggested that these Sox2+ dental epithelial stem cells might be the origin of ameloblastoma and other odontogenic tumors. However, the roles of Sox2 in clinical behavior of ameloblastoma are still not clear and it needs further investigations to uncover what roles Sox2 play in the tumorigenesis of ameloblastoma.