Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, Ann Arbor, MI, USA.
J Bone Miner Res. 2013 Nov;28(11):2414-30. doi: 10.1002/jbmr.1971.
Autophagy is a conserved lysosomal degradation process that has important roles in both normal human physiology and disease. However, the function of autophagy in bone homeostasis is not well understood. Here, we report that autophagy is activated during osteoblast differentiation. Ablation of focal adhesion kinase family interacting protein of 200 kD (FIP200), an essential component of mammalian autophagy, led to multiple autophagic defects in osteoblasts including aberrantly increased p62 expression, deficient LC3-II conversion, defective autophagy flux, absence of GFP-LC3 puncta in FIP200-null osteoblasts expressing transgenic GFP-LC3, and absence of autophagosome-like structures by electron microscope examination. Osteoblast-specific deletion of FIP200 led to osteopenia in mice. Histomorphometric analysis revealed that the osteopenia was the result of cell-autonomous effects of FIP200 deletion on osteoblasts. FIP200 deletion led to defective osteoblast terminal differentiation in both primary bone marrow and calvarial osteoblasts in vitro. Interestingly, both proliferation and differentiation were not adversely affected by FIP200 deletion in early cultures. However, FIP200 deletion led to defective osteoblast nodule formation after initial proliferation and differentiation. Furthermore, treatment with autophagy inhibitors recapitulated the effects of FIP200 deletion on osteoblast differentiation. Taken together, these data identify FIP200 as an important regulator of bone development and reveal a novel role of autophagy in osteoblast function through its positive role in supporting osteoblast nodule formation and differentiation.
自噬是一种保守的溶酶体降解过程，在人类生理和疾病中都具有重要作用。然而，自噬在骨稳态中的功能尚不清楚。在这里，我们报告自噬在成骨细胞分化过程中被激活。粘着斑激酶家族相互作用蛋白 200kD（FIP200）是哺乳动物自噬的必需成分，其缺失导致成骨细胞中出现多种自噬缺陷，包括 p62 表达异常增加、LC3-II 转化缺陷、自噬流缺陷、GFP-LC3 转基因成骨细胞中 GFP-LC3 点状结构缺失以及电镜检查时自噬体样结构缺失。成骨细胞特异性缺失 FIP200 导致小鼠出现骨质疏松症。组织形态计量学分析表明，骨质疏松症是 FIP200 缺失对成骨细胞的细胞自主效应所致。FIP200 缺失导致原代骨髓和颅骨成骨细胞体外成骨细胞终末分化缺陷。有趣的是，在早期培养物中，FIP200 的缺失并没有对增殖和分化产生不利影响。然而，FIP200 缺失导致成骨细胞初始增殖和分化后形成的骨结节形成缺陷。此外，自噬抑制剂的处理再现了 FIP200 缺失对成骨细胞分化的影响。总之，这些数据表明 FIP200 是骨发育的重要调节因子，并揭示了自噬通过支持成骨细胞结节形成和分化在成骨细胞功能中的新作用。
