肺氣腫 (Emphysema) 是慢性阻塞性肺疾病 (Chronic Obstructive Pulmonary Disease, COPD) 的主要亞型之一，其病理特徵為肺泡異常擴張、肺泡壁瓦解、喪失肺臟彈性等，最後導致呼吸系統失能。臨床研究發現，病人肺臟的組蛋白去乙醯化酶 2 (histone deacetylase 2, HDAC2) 之表現量及活性有明顯的下降，並且與病情的嚴重程度呈現負相關，但造成 HDAC2 表現量減少的機制仍不清楚。越來越多的研究指出表觀遺傳學 (epigenetics) 與疾病的致病機轉有很大的關係，例如組蛋白乙醯化、DNA 甲基化、訊息核醣核酸的穩定度以及蛋白質的轉譯後修飾。MicroRNA (miRNA) 是一種非編碼的微小 RNA ，可與訊息核醣核酸結合、進而影響訊息核醣核酸之穩定度與功能。文獻報導指出，在肺氣腫檢體中會偵測到高表現量的 MiRNA-223 (miR-223)，我們進一步利用生物資訊軟體分析 miR-223 的標定核酸序列，結果發現 miR-223 可以和 HDAC2 的訊息核醣核酸結合，因此我們假設肺氣腫藉由 miR-223 的調控使 HDAC2 表現量下降。前胸腺素 (Prothymosin α, ProT) 是一種酸性核蛋白，參與調節細胞中的許多生理功能，包括染色質重組、細胞增生、免疫與氧化壓力等。前胸腺素過量表現的基因轉殖小鼠會產生自發性的肺氣腫，且實驗證實其 HDAC2 表現量下降，與臨床研究結果相吻合，同時也暗示前胸腺素過量表現可能會導致 miR-223 表現量升高。因此本論文主要在探討前胸腺素、 miR-223 與 HDAC2 之間的關係，藉由此研究提出在臨床上，肺氣腫病患之 HDAC2 下降的可能原因。在細胞實驗中，我們發現前胸腺素過量表現可以透過 NF-κB 的調控，導致 miR-223 表現上升，進而讓 HDAC2 表現降低；另外動物實驗中，前胸腺素過量表現的轉殖肺臟有同樣的現象。最後我們將臨床肺氣腫檢體，利用免疫染色以及原位核酸雜合技術 (in situ hybridization)，觀察前胸腺素、HDAC2 和 miR-223 的表現，結果亦與細胞實驗及動物實驗吻合。本論文研究之重要性在於提出了肺氣腫病患之 HDAC2 表現量下降的可能原因。

Emphysema, a major subtype of chronic obstructive pulmonary disease (COPD), results from histone deacetylase 2 (HDAC2) dysfunction and inflammatory responses. However, the underlying mechanism is still unclear. We have previously demonstrated that the expression of HDAC2 is decreased in prothymosin α (ProT) transgenic mice, which exhibit an emphysema-like phenotype. Moreover, microarray data show that expression of miR-223 is increased in ProT transgenic mice, which is consistent with clinical reports. Bioinformatic prediction revealed that HDAC2 mRNA may contain miR-223 target sequences. Here, we proposed that ProT may contribute to the pathogenesis of emphysema by inhibiting HDAC2 expression through upregulating miR-223 expression. We show that miR-223 expression was elevated in ProT transgenic mice and patients with emphysema. HDAC2 expression was decreased in miR-223-overexpressing A549 cells. ProT overexpression decreased HDAC2 expression, whereas treatment with lentiviral vectors expressing the miR-223 target sequence (miR-223 sponge) abrogated the downregulation of HDAC2 expression in ProT-overexpressing cells. Notably, suppression of miR-223 activity reduces progression of emphysema in ProT transgenic mice. Taken together, our results provide a novel mechanism of emphysema pathogenesis whereby ProT inhibits HDAC2 expression through enhancing miR-223 expression.

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