Department of Orthopaedic Surgery, Boston School of Medicine, Boston, Massachusetts, USA.
Department of Orthopaedic Surgery, Stanford University School of Medicine, Redwood City, California.
J Cell Physiol. 2024 Aug;239(8):e31285. doi: 10.1002/jcp.31285. Epub 2024 Jun 11.
The mechanistic relationships between the progression of growth chondrocyte differentiation, matrix mineralization, oxidative metabolism, and mitochondria content and structure were examined in the ATDC5 murine chondroprogenitor cell line. The progression of chondrocyte differentiation was associated with a statistically significant (p ≤ 0.05) 2-fold increase in oxidative phosphorylation. However, as matrix mineralization progressed, oxidative metabolism decreased. In the absence of mineralization, cartilage extracellular matrix mRNA expression for Col2a1, Aggrecan, and Col10a1 were statistically (p ≤ 0.05) ~2-3-fold greater than observed in mineralizing cultures. In contrast, BSP and Phex that are associated with promoting matrix mineralization showed statistically (p ≤ 0.05) higher ~2-4 expression, while FGF23 phosphate regulatory factor was significantly lower (50%) in mineralizing cultures. Cultures induced to differentiate under both nonmineralizing and mineralizing media conditions showed statistically greater basal oxidative metabolism and ATP production. Maximal respiration and spare oxidative capacity were significantly elevated (p ≤ 0.05) in differentiated nonmineralizing cultures compared to those that mineralized. Increased oxidative metabolism was associated with both an increase in mitochondria volume per cell and mitochondria fusion, while mineralization diminished mitochondrial volume and appeared to be associated with fission. Undifferentiated and mineralized cells showed increased mitochondrial co-localization with the actin cytoskeletal. Examination of proteins associated with mitochondria fission and apoptosis and mitophagy, respectively, showed levels of immunological expression consistent with the increasing fission and apoptosis in mineralizing cultures. These results suggest that chondrocyte differentiation is associated with intracellular structural reorganization, promoting increased mitochondria content and fusion that enables increased oxidative metabolism. Mineralization, however, does not need energy derived from oxidative metabolism; rather, during mineralization, mitochondria appear to undergo fission and mitophagy. In summary, these studies show that as chondrocytes underwent hypertrophic differentiation, they increased oxidative metabolism, but as mineralization proceeds, metabolism decreased. Mitochondria structure also underwent a structural reorganization that was further supportive of their oxidative capacity as the chondrocytes progressed through their differentiation. Thus, the mitochondria first underwent fusion to support increased oxidative metabolism, then underwent fission during mineralization, facilitating their programed death.
我们研究了 ATDC5 鼠类软骨祖细胞系中生长板软骨细胞分化、基质矿化、氧化代谢和线粒体含量与结构之间的作用关系。软骨细胞分化过程与氧化磷酸化呈统计学显著相关（p≤0.05），增加约 2 倍。然而，随着基质矿化的进行，氧化代谢下降。在不存在矿化的情况下，软骨细胞外基质中 Col2a1、Aggrecan 和 Col10a1 的 mRNA 表达量比矿化培养物中的观察值高统计学显著（p≤0.05）约 2-3 倍。相比之下，与促进基质矿化相关的 BSP 和 Phex 的表达量高统计学显著（p≤0.05）约 2-4 倍，而矿化培养物中的 FGF23 磷酸盐调节因子则显著降低（~50%）。在非矿化和矿化培养基条件下诱导分化的培养物显示出统计学上更高的基础氧化代谢和 ATP 产生。与矿化的培养物相比，非矿化培养物的最大呼吸作用和备用氧化能力显著升高（p≤0.05）。氧化代谢的增加与细胞内线粒体体积的增加和线粒体融合有关，而矿化则减少了线粒体体积，并且似乎与裂变有关。未分化和矿化的细胞显示出线粒体与肌动蛋白细胞骨架的共定位增加。对与线粒体裂变和细胞凋亡以及自噬相关的蛋白质进行检测，显示免疫表达水平与矿化培养物中不断增加的裂变和细胞凋亡一致。这些结果表明，软骨细胞分化与细胞内结构重排有关，促进了线粒体含量和融合的增加，从而增强了氧化代谢。然而，矿化并不需要来自氧化代谢的能量；相反，在矿化过程中，线粒体似乎经历了裂变和自噬。总之，这些研究表明，随着软骨细胞向肥大分化，它们增加了氧化代谢，但随着矿化的进行，代谢减少。线粒体结构也经历了结构重排，这进一步支持了它们的氧化能力，因为软骨细胞在分化过程中。因此，线粒体首先融合以支持增加的氧化代谢，然后在矿化过程中发生裂变，促进它们的程序性死亡。
