Cytoprotective Role of Heat Shock Proteins in IBD

描述（由申请人提供）：肠道内稳态是维持正常粘膜功能、完整性、自我更新和宿主防御的要素的基本和动态平衡。在急性疾病中，致病性损伤是自限性的，肠道内平衡得以恢复。在炎症性肠病（IBD）中，由于慢性破坏性粘膜炎症的持续存在，肠道稳态无法恢复。然而，较少考虑的可能性是，恢复肠道稳态所必需的对抗机制在冒犯性侮辱解决期间甚至之后受损。因此，本研究将检验诱导热休克蛋白Hsp70对维持肠道稳态至关重要的假设，以及炎症期间其表达不足导致慢性结肠炎和结肠炎相关结肠癌的发展。对这一观点的支持来自以下观察：(1) Hsp70具有强大的细胞保护和抗炎特性；(2)在实验和人类结肠炎中观察到Hsp70的下调表达，使粘膜更容易受到损伤，并加剧炎症反应；(3)基因靶向缺失Hsp70可将自限性DSS诱导的结肠炎转变为慢性IBD样结肠炎；Hsp70基因缺失的小鼠会发生扁平型发育不良至癌症序列的结肠癌，而野生型小鼠则会发生散发性息肉至癌症序列的结肠癌。5)Hsp70基因的表达与散发性人类结肠癌相关，但与IBD癌症无关。研究人员提出了三个特定的目的来研究Hsp70（在上皮细胞和免疫来源细胞中）在肠道稳态中的作用，以及炎症引起的表达受损是否有助于慢性结肠炎和ibd样结肠癌的发展。首先，我们将确定Hsp70是否对维持肠道稳态至关重要，以及它在急性炎症性结肠炎和基于免疫的结肠炎模型中的下调表达是否会导致慢性或更严重的ibd样结肠炎。其次，明确观察到的与肠道炎症和促炎细胞因子相关的Hsp70选择性翻译下调的机制。最后，我们将研究Hsp70表达/功能的丧失对于慢性结肠炎小鼠自发性和致癌物诱导的结肠癌的发展是否必要和充分。将采用体外和体内相结合的方法，后者包括基因靶向Hsp70缺失和上皮或髓细胞特异性Hsp70转基因表达的新模型。通过这些研究获得的见解将为损害肠道内稳态的过程可能导致IBD和炎症相关结肠癌的发展提供原理证明。因此，恢复肠道稳态的策略对于预防、治疗和改变炎症性肠病的自然史非常重要。

DESCRIPTION (provided by applicant): Intestinal homeostasis is the essential and dynamic equilibrium of factors that maintain normal mucosal function, integrity, self-renewal, and host defense. In acute diseases, the pathogenic insult is self- limited and intestinal homeostasis is restored. In inflammatory bowel diseases (IBD), intestinal homeostasis cannot be restored because of the persistence of chronic, destructive mucosal inflammation. However, less well considered is the possibility that countering mechanisms necessary for restoring intestinal homeostasis are impaired during and even after resolution of the offending insult. This proposal will therefore examine the hypothesis that the inducible heat shock protein, Hsp70, is essential for maintaining intestinal homeostasis and that its deficient expression during inflammation contributes to the development of chronic colitis and colitis-associated colon cancer. Support for this notion comes from the following observations: (1) Hsp70 has both potent cytoprotective and anti-inflammatory properties, (2) down-regulated expression of Hsp70 is observed in experimental and human colitis, rendering the mucosa more susceptible to injury and intensifying the inflammatory response, (3) gene-targeted deletion of Hsp70 transforms the otherwise, self-limited, DSS-induced colitis to a chronic, IBD -like colitis, and (4) after AOM/DSS challenge, multi-focal, flat dysplasia-to-cancer sequence colon cancer develops in Hsp70- deficient mice as opposed to their wild-type counterparts that develop sporadic polyp-to-cancer sequence colon cancer, and 5) robust Hsp70 expression is associated with sporadic human colon cancer, but not IBD cancer. Three specific aims are proposed to investigate the role of Hsp70 (in epithelial versus immune-derived cells) in intestinal homeostasis and whether impaired expression caused by inflammation contributes to the development of chronic colitis and IBD-like colon cancer. First, we will determine if Hsp70 is essential for maintenance of intestinal homeostasis and whether it down-regulated expression in acute inflammatory and in immune-based models of colitis leads to chronic or more severe IBD-like colitis. Second, the mechanism(s) causing the observed selective translational down-regulation of Hsp70 associated with intestinal inflammation and pro-inflammatory cytokines will be defined. Finally, we will investigate whether the loss of Hsp70 expression/function is necessary and sufficient for development of spontaneous and carcinogen-induced colon cancer in mice with chronic colitis. A combination of in vitro and in vivo approaches will be employed, the latter including novel models of gene-targeted-Hsp70 deletion and epithelial- or myeloid cell-specific Hsp70 transgene expression. The insights gained through these studies will provide proof of principle that processes that impair intestinal homeostasis can contribute to the development of IBD and inflammation-associated colon cancer. Strategies to restore intestinal homeostasis would therefore be important for preventing, treating, and changing the natural history of inflammatory bowel diseases. PUBLIC HEALTH RELEVANCE This proposal will examine the hypothesis that the inducible heat shock protein, Hsp70, is essential for maintaining intestinal homeostasis and that its deficient expression in inflamed mucosa contributes to the development of chronic colitis and colitis-associated colon cancer. Strategies to restore Hsp70 expression in inflamed mucosa would be important for preventing, treating, and changing the natural history of inflammatory bowel diseases.