THE FUNCTION AND REGULATION OF HISTIDINE DECARBOXYLASE IN GUT INFLAMMATION

描述（由申请人提供）：组氨酸脱羧酶（HDC）将l -组氨酸转化为组胺，组胺是一种生物胺，在许多生理过程中起作用，但越来越多地与免疫调节有关。我们实验室使用HDC- egfp BAC转基因报告小鼠的研究表明，HDC在CD11b+Ly6G+未成熟髓样细胞（IMCs）中高度表达，这些细胞表面标记类似于髓源性抑制细胞（MDSCs）或肿瘤相关中性粒细胞（TAN）。这些表达hdc的细胞在AOM/DSS结肠直肠癌发生模型的早期被募集。组胺分泌不足的HDC-/-小鼠对AOM/DSS的炎症反应明显增加，因此结肠癌发生增加，这主要是由于髓细胞成熟不足。HDC-/-小鼠显示循环CD11b+Ly6G+ IMCs增加，成熟中性粒细胞和巨噬细胞减少，这是由于CD11b+Ly6G+骨髓祖细胞的正常成熟和分化需要组胺。将HDC缺失的骨髓移植给野生型受体，可增加CD11b+Ly6G+细胞的动员，重现癌症易感表型。来自hdl - ko小鼠的CD11b+Ly6G+ IMCs显示促炎细胞因子表达增加，并诱导结肠癌异种移植物生长。IMCs在小鼠和人类结肠肿瘤早期积累，这是由于癌细胞下调HDC基因表达导致髓细胞成熟受到抑制，提示肿瘤促进活跃肿瘤微环境的新机制。综上所述，这些数据表明HDC/组胺在骨髓细胞分化中的关键作用，以及CD11b+Ly6G+ IMCs在早期结肠癌发展中的关键作用。我们提出了四个具体目标：(1)表达hdl的CD11b+Gr1+细胞是产生成熟单核细胞、粒细胞和其他细胞类型的髓系前体吗？我们将利用我们实验室开发的HDC-BAC-Cre-ERTM小鼠，在体外和体内追踪骨髓细胞谱系的发育和分化。(2)在致癌刺激过程中表达hdc的IMCs是如何募集的？我们将研究il -1 β、IL-6和RAGE配体（S100A8/A9）的作用，并测试il -1 β阻断和RAGE缺失对IMC募集的影响。(3)肿瘤如何下调HDC抑制髓细胞分化成熟？我们将研究在IMCs与肿瘤细胞共培养过程中HDC CpG启动子位点的甲基化变化，并探讨tgf - β在调节髓细胞分化中的可能作用。(4)表达hdc的IMC细胞对结直肠癌的发生和促进是否至关重要？我们将把HDC-BAC-Cre-ERTM小鼠与Ikkbeta F/F和DTR F/F小鼠杂交，并探讨组胺在癌变中的重要性。

DESCRIPTION (provided by applicant): The enzyme histidine decarboxylase (HDC) converts L-histidine to histamine, a biogenic amine that functions in numerous physiologic processes, but has increasingly been linked to immune regulation. Work from our laboratory using HDC-EGFP BAC transgenic reporter mice has demonstrated that HDC is highly expressed in CD11b+Ly6G+ immature myeloid cells (IMCs) that exhibit cell surface markers similar to myeloid-derived suppressor cells (MDSCs) or tumor-associated neutrophils (TAN). These HDC-expressing cells are recruited early on in an AOM/DSS model of colorectal carcinogenesis. HDC-/- mice that are deficient in histamine production exhibit markedly increased inflammatory responses to AOM/DSS and thus increased colon carcinogenesis, due largely to deficient myeloid maturation. HDC-/- mice show increased circulating CD11b+Ly6G+ IMCs and decreased mature neutrophils and macrophages, due to a requirement for histamine for normal maturation and differentiation of CD11b+Ly6G+ myeloid progenitors. Transplant of HDC deficient bone marrow to wild type recipients results in increased CD11b+Ly6G+ cell mobilization and reproduces the cancer susceptibility phenotype. CD11b+Ly6G+ IMCs from HDC-KO mice show increased proinflammatory cytokine expression and induce greater growth of colon cancer xenografts. IMCs accumulate in early stages of mouse and human colonic neoplasia, due to downregulation of HDC gene expression by cancer cells leading to inhibition of myeloid cell maturation, suggesting a novel mechanism by which tumors promote an active tumor microenvironment. Taken together, these data indicate key roles for HDC/histamine in myeloid cell differentiation, and CD11b+Ly6G+ IMCs in early colon cancer development. We are proposing four specific aims: (1) Are HDC-expressing CD11b+Gr1+ cells myeloid precursors that give rise to mature monocytes and granulocytes and other cell types? We will utilize HDC-BAC-Cre-ERTM mice developed in our laboratory to trace the development and differentiation of the myeloid cell lineage, both in vitro and in vivo. (2) How are HDC-expressing IMCs recruited during carcinogenic stimuli? We will examine the role of IL-1beta, IL-6, and RAGE ligands (S100A8/A9), and test the effect of IL-1beta blockade and RAGE deletion on IMC recruitment. (3) How do tumors downregulate HDC to inhibit myeloid cell differentiation and maturation? We will examine changes in methylation of the HDC CpG promoter sites during co-culture of IMCs with tumor cells, and explore the possible role of TGF-beta in modulating myeloid cell differentiation. (4) Are HDC-expressing IMC cells critical to the initiation and promotion of colorectal cancer? HDC-BAC-Cre-ERTM mice will be crossed to Ikkbeta F/F and DTR F/F mice, and we will also explore the importance of histamine in carcinogenesis.