Neural Mechanisms in Heterotopic Ossification

描述（由申请人提供）：我们最近证明了外周神经系统（PNS）中的感觉神经与被称为异位骨化（HO）的异常骨形成之间的联系。从这些研究中，骨形态发生蛋白2 （BMP2）似乎直接诱导神经炎症的表达，从而导致神经周围祖细胞的扩张和迁移。这些细胞随后发生棕色脂肪生成和神经炎症抑制，两者都消融了它们的扩张并显著减弱了HO。同样值得注意的是，这些棕色脂肪细胞样细胞表达了许多软骨细胞标记物，表明它们可能正在发生软骨形成。这些神经周围祖细胞在HO诱导48小时内也表达VEGF A和D，这与新骨形成区域出现新的flk1+血管一致。同时，来自神经内膜室的其他细胞被发现表达成骨细胞转录因子osterix。这些细胞也表达claudin 5，它存在于神经内皮细胞上。这些数据共同引导我们进一步假设；外周神经可能通过常驻祖细胞的迁移，形成异位软骨和骨，直接促进HO的发生。此外，这些细胞的扩张和迁移可能是它们共同调节的产物，包括内皮细胞在神经内膜内。我们设计了三个具体目标来验证这一假设。(1)确定神经周围祖细胞是否发生软骨形成。星形细胞标记物GLAST在神经内的神经周围祖细胞上独特表达，我们将使用他莫昔芬调节（Ert） GLAST- yfp小鼠来评估它们的谱系命运。我们还将在UCP-DTA小鼠中诱导HO，在白喉毒素存在的情况下，将UCP1+细胞消融，并在没有白喉毒素的情况下表征软骨的形成。(2)确定HO期间周围神经内的内皮样祖细胞是否发生成骨。我们将进一步表征与神经祖细胞、内皮细胞和成骨细胞相关的细胞标记。此外，我们将使用Ert-Wnt1-YFP小鼠和/或Ert-PDGFR？并对YFP+细胞形成的异位骨进行分析。此外，我们使用Ert-Wnt1-Cre x Floxed osterix选择性地去除这些细胞中的osterix表达，并分析下游骨形成。(3)观察HO期间神经周围扩张、血管发芽和神经内膜祖细胞扩张和迁移的调控。我们将测试特定生长因子（如LIF， PDGF，VEGF， CSF）的表达是否在HO的早期阶段受到调节，从而导致紧密连接的溶解以及神经周围细胞的扩张，随后是棕色脂肪的形成以及轴突和新血管的发芽。

DESCRIPTION (provided by applicant): We have recently demonstrated a connection between sensory nerves in the peripheral nervous system (PNS) and the aberrant bone formation known as heterotopic ossification (HO). From these studies bone morphogenetic protein type 2 (BMP2) appears to directly induce expression of neural inflammation, that leads to the expansion and migration of perineurial progenitors. These cells then undergo brown adipogenesis and suppression of neural inflammation, both ablated their expansion and significantly attenuate HO. Also of note, these brown adipocyte-like cells expressed many chondrocyte markers suggesting that they may be undergoing chondrogenesis. These perineurial progenitors also express VEGF A and D within 48 hours of induction of HO, which coincides with the appearance of new flk1+ vessels in the region of new bone formation. Simultaneously, other cells from the endoneurial compartment of the nerve were found to express the osteoblast transcription factor osterix. These cells also express claudin 5, which is present on endoneurial endothelial cells. The data collectively has led us to further hypothesize; that peripheral nerves may directly contribute to HO through the migration of resident progenitors to form both the heterotopic cartilage and bone. Further, the expansion of these cells and their migration may be a product of their co-regulation involving the endothelium within the endoneurium. We have devised three specific aims to test this hypothesis. (1) To determine whether perineurial progenitors are undergoing chondrogenesis. The astrocytic marker GLAST is uniquely expressed on the perineurial progenitors within the nerve, and we will use tamoxifen-regulated (Ert) GLAST-YFP mice to evaluate their lineage fate. We will also induce HO in UCP-DTA mice, where UCP1+ cells are ablated in the presence of diptheria toxin and characterize the formation of cartilage in their absence. (2) To determine if endoneurial endothelial-like progenitors within peripheral nerves undergo osteogenesis during HO. We will further characterize the cells for markers associated with neural progenitors, endothelial cells, and osteoblasts. Additionally, we will use Ert-Wnt1-YFP mice and/or Ert-PDGFR?-YFP mice to trace the tentative neural lineage of these cells, and analyze the resultant heterotopic bone for YFP+ cells. Further, we selectively remove osterix expression in these cells, using an Ert-Wnt1-Cre x Floxed osterix and analyze downstream bone formation. (3) To characterize the regulation of perineurial expansion, vascular sprouting and endoneurial progenitor expansion and migration during HO. We will test whether specific growth factors (such as LIF, PDGF,VEGF, CSF) expression are regulated during the early stages of HO, leading to the dissolution of the tight junctions as well as expansion of perineurial cells followed by brown adipogenesis as well as sprouting of axons and new vessels.