MECHANISMS OF DMBA INDUCED BONE MARROW TOXICITY

描述：（改编自研究者摘要）7,12-二甲基苯并[a]蒽作为致癌和免疫抑制多环芳烃的模型被广泛研究。DMBA的大多数生物学效应需要一些细胞色素P450家族成员的激活。DMBA对免疫系统最显著的影响之一是骨髓毒性，导致祖细胞B淋巴细胞严重耗竭。该项目的长期目标是确定DMBA骨髓毒性的机制。在初步研究中，研究人员发现骨髓基质细胞具有高组成水平的细胞色素P450lBl (CYPlBl)，其在体外将DMBA代谢为致癌代谢物。研究者还观察到祖细胞B-淋巴细胞在体外与DMBA和骨髓基质细胞共培养时发生凋亡，而与DMBA单独孵育时没有发生凋亡。核心假设是骨髓基质细胞中CYP1B1代谢DMBA导致代谢物的释放，这些代谢物直接或间接地导致祖细胞B-淋巴细胞凋亡。这项研究的基本原理是基于：i)基质细胞-B细胞相互作用在正常B细胞发育中的关键重要性；ii)基质细胞中CYPlBl的高组成水平和前B细胞中CYPlBl的缺失；iii) DMBA仅在与骨髓基质细胞共培养时才引起前b细胞凋亡的能力。前B细胞中dba - dna加合物的形成可能导致前B细胞死亡；dmba处理的骨髓基质细胞的强制性生长信号缺失；或经DMBA处理的骨髓基质细胞释放前B细胞的有毒部分。为了解决这些可能性，研究人员将追求以下三个具体目标：1)在一系列体内和体外实验中使用基因敲除小鼠来描述CYP1B1和AhR在dba诱导的前B细胞凋亡中的作用。2)区分可能的机制（即dna加合物的形成，生长信号的丢失，Fas配体或其他介质的释放），这些机制可能负责dba处理骨髓基质细胞导致前b细胞凋亡的能力；3)明确影响骨髓基质细胞CYP1B1表达的生长因子及其相关调控机制。在该项目完成后，研究人员希望能够评估骨髓基质细胞CYP1B1在dba介导的祖B细胞凋亡中的作用及其效应机制。这些发现可能会对毒物引起骨髓毒性的机制产生新的见解。

DESCRIPTION: (Adapted from the Investigator's Abstract) 7,12-Dimethylbenzo[a]anthracene has been studied extensively as a model for carcinogenic and immuno-suppressive polycyclic aromatic hydrocarbons. Most of the biological effects of DMBA require activation by some member of the cytochrome P450 family. One of the most striking effects of DMBA on the immune system is bone marrow toxicity, resulting in severe depletion of progenitor B- lymphocytes. The long-term goal of this project is to identify the mechanisms involved in the bone marrow toxicity of DMBA. In preliminary studies, the investigators found that bone marrow stromal cells have high constitutive levels of cytochrome P450lBl (CYPlBl) that metabolizes DMBA to carcinogenic metabolites in vitro. The investigators also observed that progenitor B- lymphocytes undergo apoptosis when co-cultured with DMBA and bone marrow stromal cells in vitro, but not when incubated with DMBA alone. The central hypothesis is that DMBA metabolism by CYP1B1 in bone marrow stromal cells results in release of metabolites that, directly or indirectly, cause apoptosis in progenitor B- lymphocytes. The rationale for this study is based on: i) the critical importance of stromal cell-B cell interactions in normal B cell development; ii) the high constitutive levels of CYPlBl in stromal cells and its absence in pre B cells; and iii) the ability of DMBA to cause apoptosis in pre-B cells only when co-cultured with bone marrow stromal cells. Death of progenitor B cells might result from: DMBA-DNA adduct formation in pre B cells; loss of an obligatory growth signal from DMBA-treated bone marrow stromal cells; or the release of a toxic moiety for pre B cells by DMBA- treated bone marrow stromal cells. To resolve these possibilities, the investigators will pursue to following three specific aims: 1) Use gene knockout mice in a series of in vivo and in vitro experiments to delineate the roles of CYP1B1, and the AhR, in DMBA-induced pre B cell apoptosis. 2) Distinguish possible mechanisms (i.e., DNA-adduct formation, loss of growth signals, release of Fas ligand or other mediators) that could be responsible for the ability of DMBA-treated bone marrow stromal cells to cause apoptosis in pre-B cells; 3) Identify growth factors and associated regulatory mechanisms that affect CYP1B1 expression in bone marrow stromal cells. At the completion of this project, the investigators expect to have evaluated the role of bone marrow stromal cell CYP1B1, and resulting effector mechanisms, in DMBA-mediated apoptosis in progenitor B cells. These findings could lead to new insights into the mechanisms by which the toxicants cause bone marrow toxicity.