Regulation of Myoblast Fusion

说明(申请人提供)：成肌细胞融合对肌管/肌纤维的形成、生长和维持至关重要。我们以前的工作已经定义了哺乳动物肌管的形成是一个两阶段的过程。最初，成肌细胞彼此融合，形成新生的小肌管。新生肌管的一个亚群分泌细胞因子IL-4，导致更多的成肌细胞的招募和融合，形成大的成熟肌管。关于调控成肌细胞融合的第二阶段的分子机制，人们知之甚少。在几种细胞类型中，IL-4调节甘露糖受体(MR)的表达，甘露糖受体是一种表达在多种细胞类型表面的C型凝集素。MR具有多种作用，重要的是，MR在细胞黏附和识别中发挥作用，并与巨噬细胞融合有关。我们的初步数据表明，MR是成肌细胞融合第二阶段的一种新的调节因子，并提示MR在IL-4信号的下游发挥作用。这项建议的总体目标是了解MR如何调节成肌细胞融合的第二阶段。为此，我们将在体外和体内分析MR NULL小鼠肌肉发生的各个方面。为了分析MR在体外的功能和作用机制(目标1)，分析MR在体内肌肉再生过程中的功能(目标2)，确定MR是否与已知的调节融合的通路相关(目标3)，并确定其配体(目标4)，提出了一套4个特定的目标。我们提出的研究将在骨骼肌中定义一条调控成肌细胞融合的新途径。对MR的研究可能导致在疾病、修复和衰老过程中操纵成肌细胞的新策略，并确定促进肌肉生长的新治疗靶点。

DESCRIPTION (provided by applicant): Myoblast fusion is critical for myotube/myofiber formation, growth and maintenance. Our previous work has defined that myotube formation in mammals occurs in a two-stage process. Initially, myoblasts fuse with one another to form small nascent myotubes. A subset of nascent myotubes secretes the cytokine IL-4 leading to the recruitment and fusion of additional myoblasts and the formation of large mature myotubes. Little is known about the molecular mechanisms regulating this second phase of myoblast fusion. In several cell types IL-4 regulates expression of the mannose receptor (MR), a C-type lectin expressed on the surface of a number of cell types. Several roles have been ascribed to the MR. Importantly for this proposal the MR plays a role in cell adhesion and recognition and is implicated in macrophage fusion. Our preliminary data identify the MR as a novel regulator of the second phase of myoblast fusion and suggest that the MR functions downstream of IL-4 signaling. The overall goal of this proposal is to understand how the MR regulates the second phase of myoblast fusion. Towards this end we will analyze various aspects of myogenesis in MR null mice in vitro and in vivo. A set of 4 specific aims are proposed to analyze MR function and mechanism of action in vitro (Aim 1), analyze MR function during muscle regeneration in vivo (Aim 2), determine if the MR is associated with known pathways that regulate fusion (Aim 3) and identify its ligand (Aim 4). Our proposed studies will define a novel pathway in skeletal muscle for regulating myoblast fusion. Studies of the MR may lead to new strategies for manipulating myoblasts in disease, repair and aging and define novel therapeutic targets for enhancing muscle growth.