Mast cells have been linked to osteoporosis and bone fractures, and in a previous study we found that mice lacking a major mast cell protease, chymase, develop increased diaphyseal bone mass. These findings introduce the possibility that mast cell chymase can regulate bone formation, but the underlying mechanism(s) has not previously been investigated. Here we hypothesized that chymase might exert such effects through a direct negative impact on osteoblasts, i.e., the main bone-building cells. Indeed, we show that chymase has a distinct impact on human primary osteoblasts. Firstly, chymase was shown to have pronounced effects on the morphological features of osteoblasts, including extensive cell contraction and actin reorganization. Chymase also caused a profound reduction in the output of collagen from the osteoblasts, and was shown to degrade osteoblast-secreted fibronectin and to activate pro-matrix metallopeptidase-2 released by the osteoblasts. Further, chymase was shown to have a preferential impact on the gene expression, protein output and phosphorylation status of TGFβ-associated signaling molecules. A transcriptomic analysis was conducted and revealed a significant effect of chymase on several genes of importance for bone metabolism, including a reduction in the expression of osteoprotegerin, which was confirmed at the protein level. Finally, we show that chymase interacts with human osteoblasts and is taken up by the cells. Altogether, the present findings provide a functional link between mast cell chymase and osteoblast function, and can form the basis for a further evaluation of chymase as a potential target for intervention in metabolic bone diseases.

肥大细胞与骨质疏松症和骨折有关，在之前的一项研究中，我们发现缺乏主要肥大细胞蛋白酶食糜酶的小鼠骨干骨量增加。这些发现介绍了肥大细胞糜酶可以调节骨形成的可能性，但之前尚未研究其潜在机制。在这里，我们假设食糜酶可能通过对成骨细胞（即主要的造骨细胞）的直接负面影响来发挥这种作用。事实上，我们表明食糜酶对人类原代成骨细胞具有明显的影响。首先，食糜酶被证明对成骨细胞的形态特征有显着影响，包括广泛的细胞收缩和肌动蛋白重组。胃糜酶还导致成骨细胞中胶原蛋白产量的显着减少，并显示可降解成骨细胞分泌的纤连蛋白并激活成骨细胞释放的前基质金属肽酶 2。此外，食糜酶显示对 TGFβ 相关信号分子的基因表达、蛋白质输出和磷酸化状态有优先影响。进行了转录组学分析，揭示了糜蛋白酶对骨代谢重要的几个基因的显着影响，包括骨保护素表达的减少，这在蛋白质水平上得到了证实。最后，我们证明食糜酶与人类成骨细胞相互作用并被细胞吸收。总而言之，本研究结果提供了肥大细胞糜酶和成骨细胞功能之间的功能联系，