Analysing the cell biology of SNX10 in endosomal sorting and signaling: implications for osteoclast function in osteopetrosis

所有人类细胞都由一个外部边界组成，这个外部边界是由一种称为质膜的蛋白质和脂质的复杂混合物所定义的。这包围了一个充满流体的三维空间，称为胞浆，它包含额外的富含膜的隔室，每个隔室由蛋白质和脂类的独特组合组成。为了让细胞正常运作，蛋白质和脂类必须被有效地输送到这个迷宫般的膜中正确的富含膜的隔室。毫不奇怪，如果这种转运受到干扰，以至于错误的蛋白质和脂类被输送到错误的膜富集室，细胞功能可能会受到不利影响，进而导致各种疾病的发生。因此，建立细胞实现蛋白质和脂类调节运输的机制是细胞生物学中的一个主要挑战，它直接影响我们对人类疾病的理解。10多年来，我们的实验室一直专注于描述在细胞膜迷宫的特定方面控制蛋白质和脂类调节运输的机制细节，称为内吞网络。特别是，我们研究了一个古老的、进化保守的蛋白质家族--分类连接素。在这个家族中，我们广泛地分析了逆转录复合体的功能，这对内体网络在各种病原体以及包括阿尔茨海默病和帕金森病在内的各种疾病感染过程中的扰动功能产生了新的见解。在当前的提案中，我们试图利用我们在研究分类连接蛋白方面的丰富经验来定义分类连接蛋白-10(SNX10)在骨重建调节中的功能。这源于一项研究表明，SNX10的突变与常染色体隐性遗传性骨化症有关，这是一种遗传异质性疾病，由一种名为破骨细胞的特定细胞减少骨吸收引起。然而，目前我们还不了解SNX10的基本功能，因此对其突变导致这种衰弱疾病的原因了解非常有限。我们提出的研究将解决以下问题：1)RANK和RANKL下游信号的内体分选是否需要SNX10？其他受体的细胞表面表达是否也受SNX10的调节？SNX10介导的内体分选的分子细节是什么？SNX10介导的内体分选的分子细节是否有助于进一步洞察骨内稳态疾病？总体而言，这项拟议研究的数据将通过同行评议出版物和国际会议上的口头报告进行传播，将定义SNX10在破骨细胞功能中的作用，这些知识将更好地了解导致骨化病和其他相关骨骼疾病的细胞缺陷。从长远来看，这项研究可能会为携带SNX10突变和其他骨化病相关突变的患者进行治疗干预提供理论依据。

All human cells are composed of an outer boundary that is defined by a complex mixture of protein and lipids called the plasma membrane. This encircles a fluid filled 3-dimensional space, termed the cytosol, which contains additional membrane-enriched compartments each composed of a unique combination of proteins and lipids. For cells to functional normally, proteins and lipids must be efficiently transported to the correct membrane-enriched compartment within this maze of membranes. Not surprisingly, if such transport is perturbed, so that the wrong proteins and lipids are delivered to the incorrect membrane-enriched compartment, cell function can be adversely affected which in turn leads to the development of various diseases. Establishing the mechanisms through which cells achieve regulated protein and lipid transport is therefore a major challenge in cell biology with direct implication for our understanding of human disease.For over 10 years our laboratory has focused on describing the mechanistic details that control regulated transport of proteins and lipids within a specific aspect of the cell's membranous maze termed the endocytic network. In particular, we have studied a family of ancient, evolutionary conserved proteins, the sorting nexins. Within this family we have extensively analysed the function of retromer complexes, and this is generating new insight into the perturbed function of the endosomal network during cell infection by various pathogens, as well as a variety of diseases including Alzheimer's disease and Parkinson's disease.In the current proposal we seek to utilize our extensive experience of studying sorting nexins to define the function of sorting nexin-10 (SNX10) in the regulation of bone re-modeling. This stems from research showing that mutations in SNX10 are linked with autosomal recessive osteopetrosis, a genetically heterogenous disorder caused by reduced bone resorption by a specific class of cells termed osteoclasts. However, at present we do not understand the basic function of SNX10, and hence have a very limited appreciation of why its mutation leads to this debilitating disease.Our proposed research will address the following questions:1). Is SNX10 required for endosomal sorting of RANK and downstream RANKL signaling?2). Is the cell surface expression of other receptors also regulated by SNX10?3). What are the molecular details of SNX10-mediated endosomal sorting?4). Do the molecular details of SNX10-mediated endosomal sorting generate further insight into diseases of bone homeostasis?Overall, data derived from the proposed research, which will be disseminated through peer-review publications and oral presentation at international meetings, will define the role of SNX10 in osteoclast function, knowledge that will achieve a greater appreciation of the cellular defects that lead to osteopetrosis and possibly other related bone diseases. Longer term, the research may provide a rationale for therapeutic intervention in patients carrying the SNX10 mutations and other osteopetrosis-linked mutations.