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

描述(申请人提供)：酗酒者易受细菌感染。严重感染的酗酒患者，特别是败血症患者，经常出现粒细胞减少症，这是死亡率增加的指标。我们最近的研究表明，作为对细菌感染的响应，小鼠的骨髓库中的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细胞群体的紧急扩张与这些原始前体细胞的重新编程有关，以增强它们对粒细胞谱系发展的承诺。酒精损害了粒细胞反应的这一关键步骤。目前，潜在的细胞信号机制仍不清楚。据报道，Hedgehog信号转导通路参与了胚胎发育和成年期正常状态下某些干/祖细胞功能的调节。在初步实验中，我们观察到Sonic hedgehog(SHH)在败血症小鼠骨髓中的表达显著上调。Toll样受体(TLR)4-细胞外信号调节蛋白(ERK)1/2-特异性蛋白1(Sp1)信号通路为骨髓细胞上调SHH表达提供了重要信号。LKS细胞是SHH反应最活跃的细胞。SHH-胶质瘤锌指转录因子1(Gli1)-细胞周期蛋白D1信号的激活促进了LKS细胞的增殖，而SHH-Gli1-PU.1(SPI1基因编码的Ets区转录因子)信号的激活则介导了LKS细胞的重编程，以增强对粒系发育的承诺。酒精暴露扰乱了这个信号系统。因此，我们建议系统地研究酒精对SHH信号在原始造血祖细胞调节中的作用。 败血症时粒系反应过程中的激活。我们的中心假设是，酒精通过干扰SHH信号，在对全身感染的粒细胞反应中损害原始造血祖细胞的功能。三个特定的目的是：1)验证酒精抑制败血症反应中LKS细胞SHH信号通路激活的预测；2)测试酒精通过损害GLI1-Cyclin D1途径抑制败血症反应中LKS细胞增殖的预测；3)测试酒精通过损害Gli1-PU.1信号通路而抑制LKS细胞重编程以增强败血症时粒细胞系承诺的预测。本次调查结果将极大地促进我们对酒精滥用者对严重感染的宿主防御能力受损的认识。它还将确定开发新的治疗干预措施的关键目标，以治疗这些免疫受损宿主的致命感染。

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.