Myeloid Lineage Differentiation and Osteoclast Priming by a Novel Pax5 Cytokine

描述(申请人提供)：骨髓是成骨、造血细胞和免疫细胞的来源。现在人们普遍认为，破骨细胞与巨噬细胞、粒细胞和树突状细胞一样，是起源于造血干细胞的髓系成员。造血细胞分化早期的多潜能祖细胞 (MPP)细胞既可以分化为髓系祖细胞，也可以分化为B淋巴祖细胞。这些早期的细胞命运决定在一定程度上是由一系列转录因子(TF)控制下的蛋白质表达或抑制所调节的，这些转录因子包括PU.1、Ikaros、E2a、EBF1、Pax5和Gon4样蛋白。除PU.1和Ikaros外，其他TF最常与B细胞分化有关。然而，我们和其他人已经证明，其中一些转录因子在骨细胞发育中发挥着重要作用。然而，这些因子如何调控破骨细胞和B细胞分化之间的早期细胞命运选择才刚刚开始探索，但几乎没有直接的数据可用。这一调节具有额外的意义，因为有数据表明，免疫细胞可以有效地调节破骨细胞的分化。我们已经开始对缺乏Pax5的小鼠进行分析，Pax5是一种承诺和维持B细胞谱系所需的转铁蛋白。这些动物经历了B细胞分化的发育障碍，导致了以大多数B细胞缺失为特征的表型。重要的是，这些小鼠也有严重的疲劳；它们的骨小梁数量显著减少，破骨细胞数量显著增加。我们已经能够从Pax5-/-小鼠的脾中分离并鉴定出一种贴壁细胞群，该细胞群在没有添加生长因子的情况下在培养中持续生长，并能够产生破骨细胞、巨噬细胞和树突状细胞。此外，这些细胞分泌一种细胞因子(S)，诱导增殖，并启动野生型细胞也成为髓系祖细胞。我们的假设是，Pax5的缺失导致特定基因的去抑制，从而允许这种新的细胞因子(S)的分泌，从而诱导髓系祖细胞分化，导致破骨细胞生成增加，进而产生骨表型。更广泛地说，Pax5的缺失可能揭示了一条调控髓系细胞分化的新途径，特别是破骨细胞。这个建议的目的是确定细胞因子(S)，从而确定Pax5调节髓系细胞分化的机制(S)。

DESCRIPTION (provided by applicant): Bone marrow is the source of osteogenic, hematopoietic, and immune cells. It is now well accepted that osteoclasts, like macrophages, granulocytes and dendritic cells, are members of the myeloid lineage arising from hematopoietic stem cells. During the early stages of hematopoietic cell differentiation multipotential progenitor (MPP) cells can give rise to either myeloid progenitors or B lymphocyte progenitors. These early cell fate decisions are regulated, in part, by the expression or repression of proteins under the control of a series of transcription factors (TFs), which include, PU.1, Ikaros, E2A, Ebf1, Pax5 and Gon4-like. With the exception of PU.1 and Ikaros the other TFs are most often associated with B cell differentiation. However, we and others have shown that some of these TFs play an important role in bone cell development. How these TFs regulate the early cell fate choice between osteoclast and B cell differentiation is however only starting to be explored but with little direct data available. This regulation takes on added significance because of data showing that immune cells can be potent regulators of osteoclast differentiation. We have begun an analysis of mice deficient in Pax5, a TF required for commitment and maintenance of the B cell lineage. These animals experience a developmental block in B cell differentiation resulting in a phenotype characterized by the absence of most B cells. Importantly, these mice are also severely runted; they develop strikingly decreased trabecular bone mass with markedly increased numbers of osteoclasts. We have been able to isolate and characterize an adherent cell population from the spleen of Pax5-/- mice that grows continuously in culture without added growth factors and can give rise to osteoclasts, macrophages and dendritic cells. In addition, these cells secrete a cytokine(s) that induces proliferation and primes wild-type cells to also become myeloid progenitor cells. It is our hypothesis that the loss of Pax5 leads to the derepression of specific genes that allow the secretion of this novel cytokine(s), which induces myeloid progenitor cell differentiation resulting in increased osteoclastogenesis and this in turn produces the resultant bone phenotype. In broader terms, loss of Pax5 may have revealed a new pathway that regulates myeloid cell differentiation and specifically osteoclasts. The goal of this proposal is to identify that cytokine(s) and thus the mechanism(s) by which Pax5 regulates myeloid cell differentiation.