器官纖維化是組織損傷、感染或發炎所引發的異常修復過程，纖維母細胞過度活化及胞外基質大量累積，最終導致組織硬化與功能喪失，嚴重時甚至引發器官衰竭。心臟纖維化可導致心肌肥厚與擴張、腎臟纖維化會誘發慢性腎病、肝臟纖維化可能演變成肝硬化與肝癌，而肺纖維化則使呼吸功能下降。據統計，已開發國家中因嚴重器官纖維化所致之器官衰竭約佔死亡率45%，然現有治療選擇十分有限，亟需從病理機轉中尋找新型治療標的。

近年來，我們團隊針對內質網蛋白TXNDC5在器官纖維化中的作用展開深入研究。透過對人類心臟衰竭組織之轉錄體分析，我們發現TXNDC5在心臟纖維化中高度表達，主要存在於心臟纖維母細胞，並促進其活化與增生。進一步結合生物資訊學分析及人類、小鼠肺、腎及肝臟組織檢體實驗，我們發現TXNDC5基因及蛋白在纖維化組織中顯著上調，且與COL1A1、ELN及ACTA2等促纖維化因子呈現正相關。在體外實驗中，敲低TXNDC5能有效抑制TGFβ誘導的細胞外基質蛋白生成及纖維母細胞的活化，同時降低細胞增生；反之，過量表達TXNDC5則明顯促進纖維化進程。我們進一步利用CRISPR/Cas9基因編輯技術，在小鼠肺、腎及肝臟纖維化模型中專一性剔除纖維母細胞內的TXNDC5基因，結果顯示纖維化進程大幅減緩，器官功能獲得改善。相關成果分別發表於Circulation Research、Nature Communications、Journal of Clinical Investigation與Gut等國際頂尖期刊，充分證實TXNDC5在器官纖維化中的致病角色，並提供了新的治療靶點。

除了器官纖維化外，我們也發現TXNDC5在動脈硬化血管病中也具有重要角色。動脈粥狀硬化常發生於血管彎曲與分叉處，這些區域因產生擾流（disturbed flow）而引起內皮細胞功能失常，進而誘發動脈硬化。我們的研究發現，TXNDC5在動脈內皮細胞中表現豐富，尤其在發生動脈粥狀硬化的區域，其於內皮細胞受擾流刺激後更顯著上調。機制上，TXNDC5透過調控HSF1-HSP90-eNOS訊號軸，促使eNOS蛋白降解，導致內皮功能障礙，進而誘發血管病變。動物實驗中，內皮細胞專一性剔除TXNDC5能有效抑制高脂飲食誘導的小鼠頸動脈及主動脈粥狀硬化，進一步證實了TXNDC5在動脈硬化血管病中的關鍵作用。此外，我們採用靶向TXNDC5的CRISPR/Cas9奈米粒子治療策略，同樣在高血脂與擾流模型中顯示出抑制動脈硬化的潛力，相關成果已於2022年發表在Science Advances頂尖期刊。。我們目前也進一步將此策略延伸至腹部主動脈瘤及洗腎患者動靜脈瘻管內膜異常增生等病變，目前已經觀察到有不錯的治療效果。

基於上述發現，我們也已經開發靶向TXNDC5的新型治療藥物，包括高效且專一性抑制TXNDC5蛋白活性的核醣核酸適體 (DNA aptamer)及反義寡核苷酸(anti-sense oligo/ASO)，並取得美國、台灣及日本等多國專利，同時獲得吳火獅醫學獎與百靈佳殷格翰生醫新創獨角獸支持計畫的肯定。未來我們將進一步的推動臨床試驗，期望能將這些針對TXNDC5的新藥應用於肺、腎、肝等器官纖維化及動脈硬化等血管病患者的治療中，提供安全、有效的新型療法，改善患者器官功能、降低纖維化及動脈硬化相關死亡率，最終提升患者生活品質。

綜上所述，TXNDC5在器官纖維化與血管病變中皆扮演關鍵角色，我們的研究釐清了該分子促進纖維母細胞及內皮細胞功能異常的病理機轉。開發抑制TXNDC5表現或功能的治療藥物，不僅能減緩器官纖維化進程，更可改善動脈血管功能，為臨床上器官纖維化及動脈硬化血管病的治療帶來革命性的新方向，有望成為未來臨床上一項突破性療法，為廣大患者帶來福音。

（114年度TBF學術講座、台大醫學院藥理所　楊鎧鍵教授）

【Targeting ER Protein TXNDC5 as a Novel Therapeutic Approach against Organ Fibrosis and Atherosclerotic Vascular Diseases】

Fibrosis is a condition that poses a significant global health challenge, contributing to organ dysfunction, failure and even death. It occurs when the normal healing process becomes overactive following tissue damage, infection, or inflammation. Instead of restoring tissue integrity, the body excessively produces extracellular matrix (ECM) proteins, leading to the formation of scar tissue. Over time, this scar tissue disrupts the normal architecture and function of vital organs—including the heart, lungs, kidneys, and liver—eventually causing organ failure. Unfortunately, effective treatments specifically targeting fibrosis are very limited, which makes the discovery of novel therapeutic targets critically important.

Our research has focused on an endoplasmic reticulum (ER) protein called thioredoxin domain containing 5 (TXNDC5) as a potential key player in the development of organ fibrosis and atherosclerosis. The ER is an essential cellular organelle that ensures proteins are properly folded and processed before they are sent to their final destinations. When the ER is under stress, as occurs during chronic injury or inflammation, its ability to manage protein folding becomes compromised. This state, known as ER stress, has been linked to various diseases, including fibrosis and atherosclerosis. Employing a combination of systems biology and transcriptome profiling of fibrotic and atherosclerotic tissues from human and mouse models, we identified TXNDC5 as being significantly upregulated in diseased tissues. Our experiments, conducted both in vitro (in the laboratory using cell cultures) and in vivo (using animal models), allowed us to dissect the molecular mechanisms through which TXNDC5 contributes to fibrosis. Our findings indicate that TXNDC5 is both necessary and sufficient to drive fibrosis in multiple organs. In fibrotic tissues, TXNDC5 enhances the folding and stability of critical proteins involved in the fibrotic process. One such protein is the TGFβ receptor 1 (TGFBR1), which plays a central role in the transforming growth factor beta (TGFβ) signaling pathway. TGFβ is a well-known pro-fibrotic cytokine that stimulates fibroblasts—the cells responsible for producing ECM proteins—to become activated and proliferate. TXNDC5 aids in the proper folding of TGFBR1 and ECM proteins, thereby strengthening the TGFβ signaling cascade. This results in increased activation of fibroblasts and subsequent overproduction of ECM, ultimately leading to the development and progression of fibrosis in organs including the heart, lung, kidney, and liver. Moreover, our research revealed an intriguing feedback mechanism. TGFβ not only utilizes TXNDC5 to amplify its signaling but also induces the upregulation of TXNDC5 in tissue fibroblasts. This occurs through increased ER stress, which activates a transcription factor called ATF6 that, in turn, boosts TXNDC5 production. This positive feedback loop can exacerbate the fibrotic response, making it a particularly attractive target for therapeutic intervention. In our in vivo studies, we used a technique called conditional knockout to delete the TXNDC5 gene specifically in fibroblasts of animal models. The results were striking: animals lacking TXNDC5 in their fibroblasts showed significantly reduced fibrosis in the heart, lung, kidney, and liver following injury. This evidence strongly supports the concept that TXNDC5 is not only a marker of fibrosis but also a driving force behind the fibrotic process. In addition to its role in fibrosis, TXNDC5 is also implicated in atherosclerosis—a disease characterized by the buildup of plaques in the arteries, which can lead to heart attacks and strokes. In regions of blood vessels where flow is disturbed, such as bends and bifurcations, TXNDC5 is induced in arterial endothelial cells. Endothelial cells, which line the inner walls of blood vessels, are particularly sensitive to changes in blood flow. Disturbed flow conditions lead to increased mechanical stress on these cells, triggering TXNDC5 upregulation through the action of a mechanosensitive transcription factor known as KLF2. Elevated TXNDC5 in endothelial cells disrupts normal cellular function by downregulating the enzyme endothelial nitric oxide synthase (eNOS). eNOS is critical for producing nitric oxide (NO), a molecule that maintains blood vessel flexibility and inhibits plaque formation. Reduced eNOS levels contribute to endothelial dysfunction, creating a pro-atherogenic environment that fosters plaque formation and vascular inflammation. In our studies, mice with an endothelial-specific deletion of TXNDC5, as well as those treated with TXNDC5-targeting CRISPR-nanoparticles, showed a significant reduction in atherosclerotic lesions, indicating that TXNDC5 is a major contributor to atherosclerosis as well as fibrosis. Based on these findings, targeting TXNDC5 presents a novel and promising therapeutic approach for both organ fibrosis and atherosclerotic vascular diseases. By interfering with TXNDC5 function, it may be possible to break the vicious cycle of excessive TGFβ signaling and fibroblast activation that drives fibrosis, while also restoring endothelial function and reducing plaque buildup in arteries. Our team is actively developing new pharmaceutical agents that specifically inhibit TXNDC5. Two promising strategies are under investigation: DNA aptamers and antisense oligonucleotides (ASOs). DNA aptamers are short, single-stranded DNA molecules engineered to bind selectively to TXNDC5, thereby blocking its function. ASOs, on the other hand, are short strands of modified DNA or RNA designed to bind to TXNDC5 mRNA, reducing its translation into protein. These approaches aim to lower TXNDC5 levels or inhibit its activity in diseased tissues. Preclinical studies using these TXNDC5 inhibitors have yielded encouraging results. For example, in animal models of pulmonary fibrosis, treatment with a TXNDC5-targeting agent led to a significant reduction in lung scarring and improved lung function. Similarly, interventions targeting TXNDC5 in the vasculature have demonstrated a reduction in atherosclerotic plaque formation. These findings pave the way for future clinical trials that could eventually offer new treatment options for patients suffering from fibrosis-related organ dysfunction and atherosclerotic vascular disease.