Role of C-type lectin molecules in bone homeostasis

本项目旨在了解C型凝集素受体，如Mincle和Dectin-1如何影响骨骼的动态平衡。正常情况下，Mincle与抵御真菌或细菌感染有关。最近，Mincle被发现在清除死亡细胞后对组织维持和组织动态平衡也很重要。Mincle通常由单核细胞和巨噬细胞表达。由于骨吸收细胞、破骨细胞是髓系祖细胞融合的产物，我推测Mincle也可能在骨组织维持过程中发挥作用。根据这一假说，C型凝集素受体的下游通路与ITAM/FcRg和SYK信号的激活有关，而SYK信号被认为是破骨细胞形成的基本途径。为了支持这一概念，对Mincle基因敲除小鼠和它们的仔鼠对照的初步分析表明，Mincle基因敲除小鼠可能由于较少的破骨细胞而具有骨质疏松症。事实上，Mincle被已知通过SAP130的结合而激活，SAP130是在坏死过程中释放的小核核糖核蛋白的一种成分。由于晚期成骨细胞和骨细胞在骨更新过程中会发生坏死，我认为Mincle通过感知骨细胞释放的坏死碎片来促进破骨细胞的形成，从而增加骨丢失。因此，本应用的目的是：(1)鉴定缺乏Mincle和缺乏另一种C型凝集素Dectin-1的小鼠的骨表型和破骨细胞分化能力；(2)破译Mincle促进破骨细胞形成的分子机制，重点关注体内和体外死亡的骨细胞积聚的过程；(3)确定Mincle和Dectin-1在卵巢切除诱导的骨质疏松和骨折愈合过程中在破骨细胞中的作用；以及(4)通过确定人破骨细胞中C型凝集素分子的分子机制，将这些发现转化为人类。总之，这些实验旨在揭示C型凝集素受体Mincle和Dectin-1在骨骼健康和疾病中的作用。

This project aims to understand how C-type lectin receptors such as Mincle and Dectin-1 affect the bone homeostasis. Normally, Mincle is associated with defense against fungal or bacterial infections. Recently, Mincle was found also important for tissue maintenance and tissue homeostasis after clearance of dead cells. Mincle is usually expressed by monocytes and macrophages. Since the bone resorbing cells, osteoclasts are a product of the fusion of myeloid progenitor cells, I hypothesized that Mincle could also play a role during bone tissue maintenance. In accordance with this hypothesis, the downstream pathway of C-type lectin receptors is associated with ITAM/FcRg and activation of SYK signaling, which was previously described as essential pathway for osteoclastogenesis. In support of this concept, preliminary analysis of Mincle knock-out mice and their littermate controls showed that Mincle knock-out mice are osteopetrotic likely due to fewer osteoclasts. In fact, Mincle is known to be activated by the binding of SAP130, a component of small nuclear ribonucleoprotein released during necrosis. Since late osteoblasts and osteocytes undergo necrosis during bone renewal, I assume that Mincle enhances osteoclastogenesis by sensing necrotic debris released by osteocytes and in this way increases bone loss. Hence, the aim of this application is: (1) to characterize the bone phenotype and the ability for osteoclast differentiation in mice lacking Mincle and mice lacking the other C-type lectin, Dectin-1; (2) to decipher the molecular mechanism, by which Mincle enhances osteoclast formation focusing on the process of dead osteocyte accumulation upon bone renewal, in vivo and in vitro; (3) to determine the importance of Mincle and Dectin-1 functions in osteoclasts during ovariectomy-induced osteoporosis and fracture healing and (4) to translate these findings into humans by determining the molecular mechanism of C-type lectin molecules in human osteoclasts. In summary, these experiments aim to unravel the role of C-type lectin receptors, Mincle and Dectin-1, in bone health and disease.