Imai Shinji, Matsusue Yoshitaka
Department of Orthopeadic Surgery, Shiga University of Medical Science, Setatsukinowa-cho, Otsu-city, 520-2192, Shiga-ken, Japan.
Microsc Res Tech. 2002 Jul 15;58(2):61-9. doi: 10.1002/jemt.10119.
Bone alters its metabolic and anabolic activities in response to the variety of systemic and local factors such as hormones and growth factors. Classical observations describing abundance of the nerves fibers in bone also predict a paradigm that the nervous system influences bone metabolism and anabolism. Identification of the nerve-derived signaling molecules, capable of modulating cellular activities of the bone cells, facilitates a novel approach to study the biology of skeletal innervation. Many of the signaling molecules that may act as efferent agents on the bone cells fall into the category of neuropeptides. The present article reviews current understanding of the skeletal innervation and their proposed physiological effects on bone metabolism, with a special interest to calcitonin gene-related peptide (CGRP)-containing nerves fibers. CGRP is abundantly distributed in bone via sensory nerves, especially in the epiphyseal trabecular bones. Its in vitro actions to the cultured osteoblasts and osteoclasts, together with its in vivo localization, strongly support the paradigm that the nervous system influences bone metabolism. In addition, CGRP is recently shown to be expressed endogenously by the osteoblasts. Transgenic mice with osteoblasts overexpressing CGRP are characterized by increased bone formation rate and enhanced bone volume, suggesting that CGRP indeed acts on bone metabolism not only via nervous route but also via autocrine loop. The current article also reviews the distribution of nerve fibers containing substance P (SP), another sensory nerve-specific neuropeptide, and tyrosine hydroxylase (TH), the rate-limiting enzyme of catecholamine. The distinct effects of SP and catecholamines on the bone cells together with their in vivo influences manifested by experimental denervation studies suggest that the sensory and sympathetic nerves play important roles in bone metabolism.
骨骼会根据多种全身和局部因素(如激素和生长因子)改变其代谢和合成代谢活动。经典观察描述了骨骼中丰富的神经纤维,这也预示着一种神经系统影响骨代谢和合成代谢的模式。能够调节骨细胞活动的神经源性信号分子的鉴定,为研究骨骼神经支配生物学提供了一种新方法。许多可能作为骨细胞传出因子的信号分子属于神经肽类别。本文综述了目前对骨骼神经支配及其对骨代谢的拟议生理作用的理解,特别关注含降钙素基因相关肽(CGRP)的神经纤维。CGRP通过感觉神经大量分布于骨骼中,尤其是在骨骺小梁骨中。它对培养的成骨细胞和破骨细胞的体外作用,以及其在体内的定位,有力地支持了神经系统影响骨代谢这一模式。此外,最近发现CGRP由成骨细胞内源性表达。成骨细胞过表达CGRP的转基因小鼠的特征是骨形成率增加和骨量增加,这表明CGRP确实不仅通过神经途径,而且通过自分泌环作用于骨代谢。本文还综述了含P物质(SP)(另一种感觉神经特异性神经肽)和酪氨酸羟化酶(TH)(儿茶酚胺的限速酶)的神经纤维的分布。SP和儿茶酚胺对骨细胞的不同作用以及实验性去神经研究显示的它们在体内的影响表明,感觉神经和交感神经在骨代谢中起重要作用。