Endocytic Regulation of Inflammation

描述（由申请人提供）：CD 13是一种大型多功能细胞表面肽酶，在所有髓系细胞（其中）上组成型表达，并在血管生成和炎症部位的内皮细胞上上调。总的来说，我们最近的研究表明，CD 13调节不同类型的受体在不同的细胞类型的内吞作用，以控制下游信号转导途径，这意味着CD 13在基本的细胞过程中的作用。最近，我们发现，在树突状细胞（DC）中，CD 13调节toll样受体TLR 4的内吞作用，TLR 4是通过PAMP（病原体相关分子模式）和DAMP（危险相关分子模式）对病原体的先天免疫应答的关键哨兵。在不存在CD 13的情况下，DAMP与巨噬细胞和DC TLR 4的结合导致不平衡的细胞因子应答和异常高水平的I型干扰素（IFN），这是由于偏斜的内吞信号传导途径。尽管在抗病毒应答中是有益的，但强IFN应答明显加剧了TLR 4结合PAMP和DAMP的致病性。此外，我们有额外的证据表明，CD 13在受体再循环到细胞表面。为了在体内对此进行建模，我们将野生型和CD 13缺失动物进行永久性股动脉剥离，其释放TLR 4识别为DAMP的内源性配体。在功能上，CD 13基因敲除的小鼠具有显著受损的动脉硬化和灌注恢复以及与受损愈合一致的更多坏死。此外，缺血肌肉中的细胞因子谱显示IFN-γ和IL-10的水平显著增加，这与我们的体外数据以及PAMP或DAMP与TLR 4接合导致夸大的病理学的研究一致，表明CD 13调节骨髓细胞中促炎性和IFN产生信号转导之间的平衡。此外，骨髓移植研究表明，CD 13空供体造血细胞无法挽救灌注和功能在野生型缺血性肌肉验证了这一概念，并强调了充分理解这种新的调节机制的重要性。最后，虽然 很明显，先天免疫应答的骨髓细胞的各个亚群协调愈合过程中的后续步骤，它们的相对贡献和具体作用在很大程度上是未知的。与该提议相关，巨噬细胞和DC TLR 4信号传导通过细胞表面和内吞机制发生，支持这些在不同细胞类型中基本上未表征的途径的离散调节过程和细胞特异性作用。因此，通过其对内吞作用的调节，我们提出骨髓CD 13是先天免疫的功能调节剂，并剖析了泛骨髓上表达的CD 13的相对贡献（lysM-cre）和DC（CD 11 c-cre）对这些调节过程的作用将明显增加我们对髓系细胞对缺血反应的理解，这些信息对于设计通过操纵这个新目标来调节愈合的策略至关重要。

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.