Endocytic Regulation of Inflammation

描述（由申请人提供）：CD13是一种大的、多功能的细胞表面肽酶，在所有髓系细胞（以及其他细胞）中组成性表达，并在血管生成和炎症部位的内皮细胞中上调。总的来说，我们最近的研究表明，CD13调节不同细胞类型中不同类别受体的内吞作用，以控制下游信号转导途径，这暗示了CD13在基本细胞过程中的作用。最近，我们发现在树突状细胞（dc）中，CD13调节toll样受体TLR4的内噬作用，TLR4是通过PAMPs（病原体相关分子模式）和DAMPs（危险相关分子模式）对病原体进行先天免疫反应的关键哨兵。在缺乏CD13的情况下，DAMPs与巨噬细胞和DC TLR4的结合导致细胞因子反应不平衡，由于内吞信号通路扭曲，I型干扰素（ifn）水平异常高。虽然对抗病毒应答有益，但强烈的IFN应答明显加剧了tlr4结合的PAMPs和DAMPs的发病机制。此外，我们有额外的证据表明CD13在受体循环到细胞表面。为了在体内建立这种模型，我们对野生型和cd13缺失的动物进行永久性股动脉解剖，这释放了内源性配体，TLR4将其识别为DAMPs。在功能上，CD13null小鼠的活动和灌注恢复明显受损，坏死更多，与愈合受损一致。此外，缺血肌肉中的细胞因子谱显示IFN-ß和IL-10水平显著升高，这与我们的体外数据一致，也与TLR4参与PAMPs或DAMPs导致夸大病理的研究一致，这表明CD13调节髓细胞中促炎和IFN生成信号转导之间的平衡。此外，骨髓移植研究表明，CD13null供体造血细胞无法在野生型缺血肌肉中恢复灌注和功能，这证实了这一观点，并强调了充分了解这种新型调节因子的机制基础的重要性。最后,虽然

DESCRIPTION (provided by applicant): CD13 is a large, multifunctional cell surface peptidase that is constitutively expressed on all lineages of myeloid cells (among others) and upregulated on endothelial cells at sites of angiogenesis and inflammation. Collectively, our recent studies demonstrate that CD13 regulates endocytosis of receptors of disparate classes in different cell types to control downstream signal transduction pathways, implicating a role for CD13 in fundamental cellular processes. More recently, we showed that in dendritic cells (DCs) CD13 regulates endocytosis of the toll-like receptor TLR4 which is a critical sentinel of the innate immune response to pathogens via PAMPs (pathogen-associated molecular patterns) and DAMPs (danger associated molecular patterns). Binding of DAMPs to macrophage and DC TLR4 in the absence of CD13 leads to an unbalanced cytokine response and aberrantly high levels of type I interferons (IFNs) due to skewed endocytic-signaling pathways. Although beneficial in anti-viral responses, strong IFN responses clearly exacerbate the patho- genesis of TLR4-binding PAMPs and DAMPs. Furthermore, we have additional evidence implicating CD13 in receptor recycling to the cell surface. To model this in vivo we subjected wild type and CD13null animals to permanent femoral artery dissection, which releases endogenous ligands that TLR4 recognizes as DAMPs. Functionally, CD13null mice have strikingly impaired ambulation and perfusion recovery and more necrosis consistent with impaired healing. Furthermore, cytokine profiles in the ischemic muscle showed markedly increased levels of IFN-ß and IL-10 consistent with our in vitro data and with studies where TLR4 engagement by PAMPs or DAMPs leads to exaggerated pathology suggesting that CD13 regulates the balance between pro-inflammatory and IFN-generating signal transduction in myeloid cells. Furthermore, marrow transplant studies demonstrating that CD13null donor hematopoietic cells are unable to rescue perfusion and function in wild type ischemic muscles validate this notion and highlights the importance of fully understanding the mechanistic basis of this novel regulator. Finally, while it is clear that the individual subsets of myeloid cells of the innate immune response orchestrate subsequent steps in the healing process, their relative contributions and specific roles are largely unknown. Pertinent to this proposal, macrophage and DC TLR4 signaling occurs via both cell surface and endocytic mechanisms supporting discrete regulatory processes and cell-specific roles for these largely uncharacterized pathways in distinct cell types. Therefore, through its regulation of endocytosis, we propose that myeloid CD13 is a functional regulator of innate immunity and dissection of the relative contributions of CD13 expressed on pan-myeloid (lysM-cre) and DCs (CD11c-cre) to these regulatory processes will clearly increase our understanding of myeloid cells in response to ischemia, information essential to the design of strategies to regulate healing by manipulating this novel target.