衰老进程中骨髓巨噬细胞分泌GCA调控骨髓间充质干细胞命运的机制研究

Skeletal aging always brings change in bone marrow microenvironment. Subsequently, the changed niche will result in an obvious cell fate shift characterized by decreasing differentiation direction of osteoblasts in Bone Marrow Stem Cells (BMSCs). Our previous studies find that bone marrow macrophages (BMMs) can secrete a large amount of grancalcin (GCA) during aging. Based on these results, we hypothesize that the excessive GCA secreted by BMMs will cause the cell fate shift in BMSCs. To test this hypothesis, we firstly construct GCA transgenic mice to observe the process of homing-osteogenesis events. We will also perform COIP-MS and RNA-Seq to identify the interaction proteins and downstream signaling pathway. Furthermore, we will confirm its therapeutic effect on senile osteoporosis or age-related bone loss through treating with GCA neutralizing antibody in aged mice. This study plays a great role in the mechanism of cell fate shift during aging, and absolutely provides a new target for the prevention and treatment of senile osteoporosis and age-related bone loss.

衰老进程中骨髓微环境的改变，导致骨髓间充质干细胞(bone marrow stem cells,BMSCs)命运偏移，向成骨分化减弱。我们前期研究发现在衰老过程中骨髓巨噬细胞(bone marrow macrophages,BMMs)分泌大量颗粒钙蛋白(grancalcin,GCA)。本研究提出“衰老进程中，BMMs分泌GCA增加，导致BMSCs命运偏移”的科学假设。为了验证这一猜想，本研究首先构建BMMs特异性GCA过表达小鼠，观察GCA分泌变化对BMSCs归巢、命运偏移及骨形成的作用；进而采用免疫共沉淀和质谱分析、RNA-seq等技术识别与GCA相互作用的关键蛋白和下游信号通路；并用GCA中和抗体抑制老年小鼠骨髓中GCA功能，观察对老年性骨质疏松的治疗效果。本研究有助于阐明衰老过程BMSCs的命运偏移机制，为老年性骨质疏松的防治提供新靶点。

骨骼老化的特征是骨转换低下和骨髓脂肪堆积。然而，这种不平衡的潜在机制尚不清楚。在本研究中，我们发现在大鼠和小鼠的衰老过程中，包括巨噬细胞和中性粒细胞在内的促炎和衰老免疫细胞亚型在骨髓中累积并分泌丰富的颗粒钙蛋白。在年轻小鼠体内注射重组颗粒钙蛋白足以诱导过早的骨骼衰老。相反，中性粒细胞和巨噬细胞的颗粒钙蛋白基因缺失延缓了骨骼衰老。机制上，我们发现颗粒钙蛋白与plexin-b2受体结合并部分失活其下游信号通路，从而抑制骨髓间充质基质细胞的成骨和促进成脂。在骨骼干细胞中杂合性缺失Plexnb2基因导致颗粒钙蛋白基因敲除小鼠的骨表型改善。最后，我们开发了一种颗粒钙蛋白中和抗体，并表明其对老年小鼠的治疗改善了骨骼健康。综上所述，我们的数据表明，颗粒钙蛋白可能是治疗年龄相关性骨质疏松的潜在靶点。