Role of inflammatory response in aortic valve lesions

总结 外科瓣膜置换术是钙化性主动脉瓣狭窄的唯一有效治疗方法。 虽然慢性炎症被认为在发病机制和进展中起主要作用， 主动脉瓣病变，启动和维持炎症过程的信号机制， 目前尚不清楚。了解炎症和成骨反应， 瓣膜细胞对于预防主动脉瓣病变及其进展是重要的。我们证明 用内毒素刺激Toll样受体4（TLR 4）， 形态发生蛋白2（BMP-2）在人主动脉瓣肌成纤维细胞（HAVMFs）中的表达， 在TLR 4诱导的成骨反应中起主要作用，其特征在于Runx 2的表达， 碱性磷酸酶（ALP）和骨桥蛋白。此外，我们发现TLR 4的慢性刺激 促进老年小鼠的主动脉瓣钙化和增厚。初步研究表明，TLR 4 Notch 1信号转导上调HAVMF中Notch 1胞内结构域（NICD 1）的水平。中和 INF是一种TRIF调节的1型干扰素，可消除细胞NICD 1的增加， 刺激TLR 4后的BMP-2水平。此外，Notch 1的抑制也减少BMP-2 在TLR 4刺激后表达。总之，这些新的发现表明，INF激活 Notch 1和NICD 1增强TLR 4诱导的BMP-2表达。有趣的是，水平升高 TLR 4刺激后24 h，ILCD 1和BMP-2在人AVMF中共存。很可能 NICD 1不仅在早期阶段调节BMP-2表达，而且在 调节BMP-2信号传导。事实上，初步研究表明，Notch 1的激活增强了 BMP-2诱导Runx 2表达。因此，TLR 4信号传导诱导成骨反应， 人AVMF，其机制涉及BMP-2和Notch 1通路之间的相互作用。 我们制定了三个相互关联的目标，以确定TLR 4诱导的瓣膜病变的机制。 成骨反应：1）检验TLR 4信号传导诱导主动脉瓣成骨的假设 通过BMP-2介导的Runx上调2，2）来测试NICD 1 通过调节NF-B活性增强BMP-2的表达，以及3）检验以下假设： NICD 1通过与Smad 1/5/8相互作用增强BMP-2信号传导。这些研究将提供 对促炎信号介导的分子机制的重要见解 AVMF成骨反应和主动脉瓣病变。

Summary Surgical valve replacement is the only available therapy for calcific aortic valve stenosis. Although chronic Inflammation is believed to play a major role in the pathogenesis and progression of aortic valve lesions, the signaling mechanisms that initiate and sustain the inflammatory process in valvular cells remain unclear. Understanding of the inflammatory and osteogenic responses in valvular cells is important for prevention aortic valve lesions and their progression. We demonstrate that stimulating Toll-like receptor 4 (TLR4) with endotoxin up-regulates the expression of bone morphogenetic protein 2 (BMP-2) in human aortic valve myofibroblasts (HAVMFs) and that BMP-2 plays a major role in TLR4-induced osteogenic responses, characterized by expression of Runx2, alkaline phosphatase (ALP) and osteopontin. Further, we found that chronic stimulation of TLR4 promotes aortic valve calcification and thickening in old mice. Preliminary studies show that TLR4 signaling up-regulates the levels of Notch1 intracellular domain (NICD1) in HAVMFs. Neutralizing INF¿, a TRIF-regulated type 1 interferon, abrogates the increase in cellular NICD1 and reduces BMP-2 levels following stimulation of TLR4. Further, inhibition of Notch1 also reduces BMP-2 expression following TLR4 stimulation. Together, these novel findings indicate that INF¿ activates Notch1 and that NICD1 enhances TLR4-induced BMP-2 expression. Interestingly, elevated levels of lNICD1 and BMP-2 coexist in human AVMFs at 24 h following TLR4 stimulation. It is likely that NICD1 plays a role not only in regulating BMP-2 expression in the early phase but also in modulating BMP-2 signaling. Indeed, preliminary studies show that activation of Notch1 enhances BMP-2-induced expression of Runx2. Thus, TLR4 signaling induces the osteogenic responses in human AVMFs, and mechanisms involve the interplay between the BMP-2 and Notch1 pathways. We formulated three interrelated aims to determine the mechanisms of TLR4-induced valvular osteogenic responses: 1) to test the hypothesis that TLR4 signaling induces aortic valve osteogenic responses through BMP-2-mediated up-regulation of Runx2, 2) to test the hypothesis that NICD1 enhances BMP-2 expression through modulation of NF-¿B activity and 3) to test the hypothesis that NICD1 enhances BMP-2 signaling via interaction with Smad1/5/8. These studies will provide important insights into the molecular mechanisms by which pro-inflammatory signaling mediates AVMF osteogenic responses and aortic valve lesions.