Morphological and molecular cell biology studies on aging changes and reconstruction of bone tissue.

【利用新的骨形态测量方法研究骨组织的衰老】为了建立研究颌骨衰老现象的基本体系，我们开发了一种新的共聚焦激光显微镜形态测量方法，并将muCT应用于骨形态测量研究。结果表明，由于不同区域对雌激素缺乏的反应性和咬合力对骨形成的刺激不同，下颌髁在雌激素缺乏后发生骨质流失，髁维持骨量并发生动态结构改变。【老化骨的组织化学研究】随着年龄的增长，产生II型胶原纤维的下颌软骨变成产生I型胶原纤维的纤维软骨样组织。随着年龄的增长，髁突内肥大软骨细胞逐渐消失。老龄大鼠骨髓中脂肪细胞明显增多。这些结果进一步表明，骨组织老化现象是通过控制软骨细胞、成骨细胞和破骨细胞的增殖和分化机制发生的。【老化骨的分子和细胞生物学研究】采用原位杂交方法，我们评估了骨组织中基因表达模式随年龄增长的变化。在OVX大鼠和PTHrP基因敲除小鼠的骨骼中，骨连接素、ALPase、PTHrP、FGF及其受体的基因表达模式在衰老过程中受到抑制。随着年龄的增长，骨骼中的基因表达模式可能与细胞分化的抑制有关。【诱导骨实验】为了预防和恢复随着衰老而发生的骨质流失，我们评估了间歇给药甲状旁腺激素和植入BMP-2微球对实验动物下颌骨的影响。去势大鼠预防性和治疗性间歇给予甲状旁腺激素可增加大鼠下颌髁骨形成，但不加速骨吸收活性。将BMP-2微球植入牙腔后，诱导牙腔内间充质细胞增殖，成骨前细胞向成骨细胞分化，牙腔内快速成骨。此外，BMP-2微球植入后应用e-PTFE膜可以有效地将新骨形成设计的骨形。少

[Studies on aging in bone tissue using new bone morphometrical methods] In order to establish the basic system for the research on aging phenomena in the jaw bone, we developed a new morphometrical method using confocal laser microscope and applied muCT on the bone morphometrical studies. From the results using the system, it is demonstrated that the bone loss occurred in mandibular condyle following estrogen deficiency and the condyle maintained the bone mass with dynamic structural alterations, due to regionally different reactivity against estrogen deficiency and the bone formative stimulus by occlusal force. [Histochemical studies on aging bones] With advancing age, the mandibular chondylar cartilage, which produced type II collagen fibers, became fibrocartilage-like tissue which produced type I collagen fibers. Hypertrophic chondrocytes in the condyle disappeared in the course of aging. Adipocytes were found prominently in the bone marrow of aged rat. From these results, it is sug … More gested that aging phenomena in bone tissue occurred through the control mechanisms in proliferation and differentiation of chondrocytes, osteoblasts and osteoclasts. [Molecular and cell biological studies on aging bones] Using the in situ hybridization method, we assessed the changing of the gene expression patterns in bone tissue with advancing age. In bones of OVX rats and PTHrP gene-knock out mice, gene expression patterns of osteonectin, ALPase, PTHrP, FGF and their receptor were suppressed in the course of aging. Gene expression patterns in bones with advancing age may change in association with the suppression of cell differentiation. [Inducing bone experiments] In order to prevent and recover the bone loss which occurred with aging, we assessed the effects of intermittent administration of PTH and implantation of BMP-2 pellets on mandibles of experimental animals. The preventive and therapeutic intermittent administrations of PTH in ovariectomized rats increased the bone formation in rat mandibular condyle without accelerating bone resorptive activity. When BMP-2 pellets were implanted into the extracted teeth cavities, proliferation of mesenchymal cells and differentiation of preosteoblasts into osteoblasts were induced and rapid bone formation occurred in the cavities. Furthermore, application of e-PTFE membrane after the implantation of BMP-2 pellets was effective to form the new bone into the designed bone shape. Less