Alcohol, hedgehog signal, and HSC dysfunction in host defense against septicemia

描述（由申请人提供）：酗酒者易受细菌感染。严重感染的酒精患者，特别是败血症患者，经常出现粒细胞减少，这是死亡率增加的一个指标。我们最近的研究表明，在细菌感染的反应下，小鼠骨髓谱系(lin)-干细胞因子受体(ckit)+干细胞抗原-1(Sca1)+细胞（LKS细胞，一种富含造血干细胞的细胞群）迅速增加。LKS细胞群的紧急扩张与这些原始前体的重编程有关，以增强它们对粒细胞谱系发育的承诺。酒精会损害这一关键的粒细胞生成反应。目前，潜在的细胞信号传导机制尚不清楚。据报道，hedgehog信号转导通路参与胚胎发生和成年期正常状态下某些干/祖细胞功能的调控。在初步实验中，我们观察到败血症小鼠骨髓中Sonic hedgehog （SHH）的表达显著上调。toll样受体（TLR）4-胞外信号调节激酶（ERK）1/2特异性蛋白1（Sp1）信号级联是骨髓细胞上调SHH表达的重要信号。LKS细胞是对SHH反应最活跃的细胞。激活shh -胶质瘤锌指转录因子1 (Gli1)-cyclin D1信号可促进LKS细胞增殖，而激活SHH-Gli1-PU.1信号则可促进LKS细胞增殖（一种由SPI1基因编码的ets结构域转录因子）信号介导LKS细胞重编程，以增强对粒细胞谱系发育的承诺。酒精会破坏这个信号系统。因此，我们建议系统地研究酒精对SHH信号在原始造血前体细胞调节中的作用

DESCRIPTION (provided by applicant): Alcohol abusers are susceptible to bacterial infection. Alcoholic patients with serious infection, particularly septicemia, frequently present with granulocytopenia which is an indicator for increased mortality. Our recent studies have revealed that in response to bacterial infection, bone marrow pool of lineage(lin)-stem cell factor receptor(ckit)+stem cell antigen-1(Sca1)+ cells (LKS cells, a cell population enriched with hematopoietic stem cells) is rapidly increased in mice. The emergency expansion of LKS cell population is associated with reprogramming of these primitive precursors to enhance their commitment to granulocyte lineage development. Alcohol impairs this critical step of the granulopoietic response. At the present time, the underlying cell signaling mechanisms remain unclear. The hedgehog signal transduction pathway has been reported to participate in the regulation of certain stem/progenitor cell functions in normal state during embryogenesis and in adulthood. In preliminary experiments, we observed that Sonic hedgehog (SHH) expression was significantly up-regulated in the bone marrow of mice with septicemia. The Toll-like receptor (TLR)4-extracellular signal-regulated kinases (ERK)1/2-specificity protein 1(Sp1) signal cascade provided the essential signal for up-regulation of SHH expression by marrow cells. LKS cells were the most active cells responding to SHH. Activation of SHH-glioma zinc finger transcription factor 1 (Gli1)-cyclin D1 signaling promoted LKS cell proliferation, whereas activation of SHH-Gli1-PU.1 (an ETS-domain transcription factor encoded by the SPI1 gene) signaling mediated LKS cell reprogramming for enhanced commitment to granulocyte lineage development. Alcohol exposure disrupted this signaling system. Therefore, we propose to systematically investigate the effects of alcohol on SHH signaling in the regulation of primitive hematopoietic precursor cell activation during the granulopoietic response to septicemia. Our central hypothesis is that alcohol impairs primitive hematopoietic precursor cell function during the granulopoietic response to systemic infection by disrupting SHH signaling. Three specific aims are: 1) to test the prediction that alcohol inhibits activation of the SHH signal pathway in LKS cells in response to septicemia; 2) to test the prediction that alcohol inhibits LKS cell proliferation in response t septicemia via impairing the GLI1-cyclin D1 pathway; and 3) to test the prediction that alcohol inhibits LKS cell reprogramming for enhancing granulocyte lineage commitment during septicemia via impairing the Gli1-PU.1 signal cascade. Results obtained from this investigation will greatly advance our knowledge about the impairment of host defense against serious infections in alcohol abusers. It will also identify key targets for developing novel therapeutic interventions to treat fatal infections in these immunocompromised hosts.