Hyaluronan as an innate ligand that induces inflammation after transplantation

描述（由申请人提供）：先天免疫系统的组分可导致长期同种异体移植耐受性受损。然而，触发先天免疫系统启动同种异体移植排斥反应的分子激活剂是难以捉摸的。我们先前的工作表明，通过MyD88（先天免疫细胞上大多数Toll样受体下游的衔接蛋白）的信号传导，可防止移植耐受。此外，我们有初步证据表明，透明质酸（HA）是一种先天性配体，激活MyD88炎症通路，启动同种异体移植排斥反应和移植耐受抗性。我们推测，不同组织中HA的表达水平差异可能解释了为什么一些器官，如皮肤，表现出受损的移植耐受性，而其他组织，如心脏同种异体移植物，易受耐受诱导。解读这些差异可以为新疗法的产生提供信息，以抑制损伤部位的先天免疫反应（即，在同种异体移植物内）。在本提案的目标1中，我们将采用药理学方法来阻断急性移植排斥和移植耐受的实验模型中的HA活性，其中MyD88信号传导对于移植排斥至关重要。在目标2中，我们将产生皮肤同种异体移植物中HA可诱导缺失的小鼠。这种小鼠模型将是未来实验的有用资源，以确定HA是否介导MyD88依赖性皮肤移植物排斥反应。我们将通过产生HA在心脏组织内过表达的小鼠来补充这种方法。这将使我们能够检查是否HA过度表达足以损害心脏同种异体移植物的移植耐受性。因此，这一建议将产生新的试剂来检查HA在急性移植排斥反应和移植耐受诱导中的作用。此外，这些资源还将影响HA可能发挥重要作用的其他炎症模型。

DESCRIPTION (provided by applicant): Components of the innate immune system can contribute to impairment of long term allograft tolerance. However, the molecular activators that trigger the innate immune system to initiate allograft rejection are elusive. Our prior work demonstrates that signaling via MyD88 an adaptor protein downstream of most Toll like receptors on innate immune cells, prevents transplant tolerance. In addition, we have preliminary evidence to suggest that hyaluranan (HA) is an innate ligand that activates the MyD88 inflammatory pathway to initiate allograft rejection and transplant tolerance resistance. We hypothesize that differential HA expression levels in various tissues may explain why some organs, such as the skin, exhibit impaired transplant tolerance, while other tissues, e.g. cardiac allografts, are susceptible to tolerance induction. Deciphering such differences could inform on the generation of novel therapies to inhibit the innate immune response at the site of injury (i.e., within the allograft). In Aim 1 of this proposal, we will employ pharmacological approaches to block HA activity in experimental models of acute transplant rejection and transplantation tolerance for which MyD88 signaling is critical for graft rejection. In Aim 2, we will generate mice in which HA is inducibly deleted within skin allografts. This mouse model will be a useful resource for future experiments to determine if HA mediates MyD88 dependent rejection of skin allografts. We will complement this approach by generating mice in which HA is over-expressed within cardiac tissue. This will allow us to examine whether HA over-expression is sufficient to impair transplant tolerance of cardiac allografts. Hence, this proposal will generate novel reagents to examine the role of HA in acute graft rejection and transplant tolerance induction. Moreover, these resources would also impact other models of inflammation for which HA may play a major role.