Pathogenic Role of Mechanical Stress in Fibrosis and Tissue Remodeling in Crohn's Disease

由于组织纤维化和平滑肌增生导致的血管形成是严重克罗恩病的标志 疾病（CD）。虽然狭窄形成与慢性炎症有关，但没有抗炎药物。 除手术治疗外，其他治疗方法均有效。然而，术后狭窄前的复发 该地区几乎是100%。非炎症依赖性机制在纤维化中可能作用的研究 和增生。机械应力（MS）与组织变形、水肿、纤维化和 扩张在CD中常见。我们假设MS在纤维化中起关键作用， CD增生。我们在明确的啮齿动物CD模型中发现，结肠内注射TNBS诱导了CD的表达。 局部透壁性炎症，远端结肠管腔狭窄， 靠近炎症的节段。我们发现结缔组织生长因子（CTGF）和 结肠平滑肌细胞（SMC）中的脑源性神经营养因子（BDNF）不仅明显诱导， 在炎症部位，但在炎症近端的扩张节段。我们还检测到 炎症部位和炎症近端节段的纤维化和增生。的 炎症远端的非扩张节段没有显示出任何CTGF和BDNF的增加，或纤维化， 增生，表明MS依赖性机制。此外，如果机械扩张被阻止， 仅用流质饮食喂养大鼠，其模拟CD管理中的排他肠内营养（EEN）， CTGF和BDNF的表达显著减弱，纤维化显著改善。 体外机械牵张诱导结肠平滑肌细胞表达CTGF和BDNF并激活转录 激活子γ-相关蛋白1（雅普）。此外，发现在纤维狭窄的血管中雅普活性显著增加， 人体CD组织。我们认为CD的透壁炎症导致炎症部位的MS， 扩张的节段近端炎症，MS诱导YAP依赖性机械敏感性 CTGF和BDNF的表达，这有助于纤维化和增生。研究的具体目标 是：1.确定MS是否在CD的肠纤维化和SMC增生中起作用。我们将区分 通过评估纤维化、SMC生长和表达的位点特异性变化来评估MS对炎症的影响 CTGF和BDNF在炎症部位（炎症和MS），近端节段（MS）， MS）和CD模型中炎症部位的远端（既没有炎症也没有MS）。MS的作用 将在不含MS的CD中进一步评估ECM产生和SMC增生（饲喂流质饮食的大鼠）， 在仅具有MS的模型中（机械阻塞）。2.研究MS诱导的细胞凋亡的信号转导机制， CTGF和BDNF的雅普激活和YAP依赖性表达。3.为了研究致病作用， 雅普介导纤维化和增生中CTGF和BDNF的机械敏感性表达。可能的 还将研究炎症和MS在纤维化和增生中的协同作用。

Stricture formation due to tissue fibrosis and smooth muscle hyperplasia is a hallmark of severe Crohn’s disease (CD). Although stricture formation is associated with chronic inflammation, no anti-inflammatory treatment is effective for it, except surgical approaches. However, post-surgery recurrences in the pre-stenotic region are almost 100%. Studies into the possible role of inflammation-independent mechanisms in fibrosis and hyperplasia are needed. Mechanical stress (MS) associated with tissue deformation, edema, fibrosis, and distention are commonly encountered in CD. We hypothesize that MS plays a critical role in fibrosis and hyperplasia in CD. We found in a well-defined rodent model of CD that intracolonic injection of TNBS induced a localized transmural inflammation with lumen narrowing in the distal colon and marked distention in the segment proximal to inflammation. We found that expression of connective tissue growth factor (CTGF) and brain-derived neurotrophic factor (BDNF) in colon smooth muscle cells (SMC) was markedly induced not only in the inflammation site but in the distended segment proximal to inflammation. We also detected significant fibrosis and hyperplasia in the inflammation site and the segment proximal to inflammation by 21 days. The non-distended segment distal to inflammation did not show any increased CTGF and BDNF, or fibrosis and hyperplasia, indicating a MS dependent mechanism. Furthermore, if mechanical distention was prevented by feeding rats with only liquid diet, which mimics exclusive enteral nutrition (EEN) in CD management, expression of CTGF and BDNF was dramatically attenuated and fibrosis was significantly improved. Mechanical stretch in vitro induced expression of CTGF and BDNF in colon SMC, and activated transcription activator yes-associated protein-1 (YAP). Moreover, YAP activity is found markedly increased in fibrostenotic CD tissues in humans. We propose that transmural inflammation in CD causes MS in the inflammation site and the distended segment proximal to inflammation, and the MS induces YAP-dependent mechanosensitive expression of CTGF and BDNF, which contribute to fibrosis and hyperplasia. The specific aims of the study are: 1. To determine if MS plays a role in intestinal fibrosis and SMC hyperplasia in CD. We will differentiate the effect of MS from inflammation by assessing site-specific changes of fibrosis, SMC growth, and expression of CTGF and BDNF in the site of inflammation (with both inflammation and MS), the segments proximal (with MS) and distal (with neither inflammation nor MS) to the inflammation site in the CD model. The role of MS in ECM production and SMC hyperplasia will be further assessed in CD without MS (rats fed with liquid diet) and in a model with MS only (mechanical obstruction). 2. To investigate the signaling mechanisms of MS-induced YAP activation and YAP-dependent expression of CTGF and BDNF. 3. To examine the pathogenic roles of YAP mediated mechanosensitive expression of CTGF and BDNF in fibrosis and hyperplasia. The possible cooperation between inflammation and MS in fibrosis and hyperplasia will be investigated as well.