Post-natal bone physiology

Post-natal bone development is characterized by substantial longitudinal bone growth and changes in skeletal size and shape. Bone is in a dynamic process of continuous remodeling which helps to regulate calcium homeostasis, repair micro-damage to bones from everyday stress, and to shape the skeleton during growth. Bone growth is regulated by systemic hormones and locally generated factors. Understanding their mechanisms of action enables us to obtain a better appreciation of the cellular and molecular basis of bone remodeling and could therefore be valuable in approaches to new therapies. This article will review molecular and cellular control of skeletal growth in the post-natal period, the physiology of each bone cell with their systemic and local regulators, as well as the physiology of bone remodeling.     

NDRG2 Expression Decreases Tumor-Induced Osteoclast Differentiation by Down-regulating ICAM1 in Breast Cancer Cells

Bone matrix is properly maintained by osteoclasts and osteoblasts. In the tumor microenvironment, osteoclasts are increasingly differentiated by the various ligands and cytokines secreted from the metastasized cancer cells at the bone metastasis niche. The activated osteoclasts generate osteolytic lesions. For this reason, studies focusing on the differentiation of osteoclasts are important to reduce bone destruction by tumor metastasis. The N-myc downstream-regulated gene 2 (NDRG2) has been known to contribute to the suppression of tumor growth and metastasis, but the precise role of NDRG2 in osteoclast differentiation induced by cancer cells has not been elucidated. In this study, we demonstrate that NDRG2 expression in breast cancer cells has an inhibitory effect on osteoclast differentiation. RAW 264.7 cells, which are monocytic preosteoclast cells, treated with the conditioned media (CM) of murine breast cancer cells (4T1) expressing NDRG2 are less differentiated into the multinucleated osteoclast-like cells than those treated with the CM of 4T1-WT or 4T1-mock cells. Interestingly, 4T1 cells stably expressing NDRG2 showed a decreased mRNA and protein level of intercellular adhesion molecule 1 (ICAM1), which is known to enhance osteoclast maturation. Osteoclast differentiation was also reduced by ICAM1 knockdown in 4T1 cells. In addition, blocking the interaction between soluble ICAM1 and ICAM1 receptors significantly decreased osteoclastogenesis of RAW 264.7 cells in the tumor environment. Collectively, these results suggest that the reduction of ICAM1 expression by NDRG2 in breast cancer cells decreases osteoclast differentiation, and demonstrate that excessive bone resorption could be inhibited via ICAM1 down-regulation by NDRG2 expression.     

A delivery system specifically approaching bone resorption surfaces to facilitate therapeutic modulation of microRNAs in osteoclasts

Dysregulated microRNAs in osteoclasts could cause many skeletal diseases. The therapeutic manipulation of these pathogenic microRNAs necessitates novel, efficient delivery systems to facilitate microRNAs modulators targeting osteoclasts with minimal off-target effects. Bone resorption surfaces characterized by highly crystallized hydroxyapatite are dominantly occupied by osteoclasts. Considering that the eight repeating sequences of aspartate (D-Asp₈) could preferably bind to highly crystallized hydroxyapatite, we developed a targeting system by conjugating D-Asp₈ peptide with liposome for delivering microRNA modulators specifically to bone resorption surfaces and subsequently encapsulated antagomir-148a (a microRNA modulator suppressing the osteoclastogenic miR-148a), i.e. (D-Asp₈)-liposome-antagomir-148a. Our results demonstrated that D-Asp₈ could facilitate the enrichment of antagomir-148a and the subsequent down-regulation of miR-148a in osteoclasts in vivo, resulting in reduced bone resorption and attenuated deterioration of trabecular architecture in osteoporotic mice. Mechanistically, the osteoclast-targeted delivery depended on the interaction between bone resorption surfaces and D-Asp₈. No detectable liver and kidney toxicity was found in mice after single/multiple dose(s) treatment of (D-Asp₈)-liposome-antagomir-148a. These results indicated that (D-Asp₈)-liposome as a promising osteoclast-targeting delivery system could facilitate clinical translation of microRNA modulators in treating those osteoclast-dysfunction-induced skeletal diseases.     

破骨细胞分化过程中的信号通路及信号因子的研究进展

破骨细胞（osteoclast,OC）来源于骨髓,在生长发育过程中,起着骨吸收的重要功能,其增多或减少会引起骨质疏松或骨质硬化等相关的骨代谢性疾病。本文将从OC分化过程中所涉及的信号通路（NF-κB、Src-PI3K-Akt、MAPK、CN/NFAT、IDO/Tryptophan通路等）及相关信号因子（PU 1、 Lhx2、TNF-α、 M-CSF、TGF-β等）方面,对OC分化的信号通路及相关信号因子的研究进展进行简要综述,以期能为相关骨代谢性疾病的治疗提供新的思路。     

小鼠骨髓细胞和脾细胞诱导形成破骨细胞潜能的比较

目的在体外破骨细胞分化因子(RANKL)和巨噬细胞集落刺激因子(M-CSF)联合应用的情况下,比较小鼠骨髓细胞和脾细胞形成破骨细胞的能力。方法选用小鼠M-CSF依赖性非附着性骨髓细胞和脾细胞,以不同的细胞密度在含有25ng/mlsM-CSF和30ng/mlsRANKL的(-MEM培养液中培养5、9天后,计数形成的抗酒石酸酸性磷酸酶染色(TRAP)阳性多核细胞的数目和骨吸收面积。结果脾细胞形成的破骨样细胞与骨髓形成的细胞形态与功能均无明显差异,但所需的细胞密度为骨髓细胞的10~20倍。结论在特殊情况下,脾细胞可替代骨髓细胞进行体外破骨细胞实验,但培养条件应适当调整。     

1,25-二羟维生素D3对骨髓破骨细胞形成和破骨细胞分化因子mRNA表达的影响

目的：观察不同浓度的1，25-(0H)2D3对骨髓单个核细胞诱导形成破骨细胞和对单个核细胞ODF mRNA表达的影响。进一步阐明骨吸收刺激因子在破骨细胞性骨吸收中的作用机制。方法：应用不同浓度的1，25-(0H)2D3(0、10^-10、10^-8、10^-6moL／L)诱导大鼠破骨细胞的形成，观察形成破骨细胞的数目，并采用原位杂交技术检测骨髓细胞ODF mRNA的表达。结果：随着l，25-(0H)：D，浓度的增加，多核细胞计数增多；ODF mRNA表达的阳性信号显著增强。结论：1，25-(0H)2D3通过调节骨髓细胞ODF mRNA的表达，影响破骨细胞的形成和功能，进而调节局部骨微环境内骨吸收与骨形成平衡的变化，影响骨组织改建。     

重组人生长激素对去势大鼠正畸牙牙周组织改建的影响

目的:探讨重组人生长激素(recombinanthumangrowthhormone,rh-GH)对去势(ovariectomy,OVX)大鼠正畸牙移动后牙周组织细胞变化的影响。方法:30只7周龄SPF级雌性Wistar大鼠随机分为3组:对照组、去势盐水组(OVX-NS组)和去势生长激素组(OVX-GH组)。将去势摘除双侧卵巢和腹部皮下注射rh-GH作为不同处理因素,观察第15天和第30天时3组大鼠正畸牙移动引起牙槽骨受压侧破骨细胞数的变化,并进行组织学观察。用SPSS12.0软件包对数据进行完全随机设计资料的方差分析。结果:对3组大鼠不同时间正畸牙牙槽骨受压侧破骨细胞计数进行比较,发现同一时间3组数据的差异有统计学意义(P<0.05);OVX-NS组比OVX-GH组显著增多(P<0.05),对照组最少;同组相比,第15天处死的大鼠与第30天处死的大鼠其破骨细胞数无显著差异(P>0.05);牙周组织学观察见,OVX-GH组牙周膜的损伤和创伤性炎症较OVX-NS组明显减轻。结论:去势(成年)大鼠腹部皮下注射rh-GH,能够减少其正畸牙移动引起的受压侧破骨细胞数目,同时可促进牙周组织因正畸力所致的病理性变化的恢复,对成年正畸治疗有良好的协同作用。     

破骨细胞分化因子诱导小鼠骨髓细胞形成破骨细胞的实验研究

目的:探讨破骨细胞分化因子(ODF)和巨噬细胞集落刺激因子(M-CSF)联合应用进行体外诱导小鼠骨髓细胞形成破骨细胞(OC)的能力。方法:收集5～6周小鼠骨髓细胞,在含M-CSF(10 ng/ml)的α-MEM全培养液中培养24h,然后将悬浮生长的细胞接种到24孔培养板,并加入不同浓度的ODF和M-CSF。,通过观察抗酒石酸盐酸性磷酸酶(TRAP)染色的阳性细胞和能否在骨磨片上形成吸收陷窝来鉴定OC形成情况。结果:在只加入ODF或M-CSF一种细胞因子时,未见有TRAP阳性或CTR阳性细胞形成,同时加入ODF和M-CSF,可形成典型的OC。TRAP阳性多核细胞的数目和培养液中钙离子浓度的增加与ODF的浓度呈正相关。结论:小鼠骨髓来源的单核细胞在ODF和M-CSF共同作用下可形成具有骨吸收功能的OC,为体外研究OC的分化发育和功能调节提供了一种新的方法。     

PERK-eIF2α-ATF4信号通路参与调控磷酸三钙磨损颗粒诱导的假体周围骨溶解

目的 探讨蛋白激酶R样内质网激酶（PERK）-真核细胞起始因子2α（eIF2α）-活化转录因子4（ATF4）介导的内质网应激通路在磷酸三钙（TCP）磨损颗粒诱导假体周围骨溶解中的作用。 方法 取雄性ICR小鼠30只,随机分为3组：假手术组（sham,n=10）、TCP磨损颗粒组（模型组,n=10）和salubrinal干预组(SAL,n=10)。采用TCP磨损颗粒诱导小鼠颅骨溶解模型,于术后第2天颅顶局部注射SAL（1 mg/kg）,每隔2 d 1次,持续干预2周。实验结束后处死动物取颅骨和外周血。Western blotting法检测TCP磨损颗粒植入部位周围骨组织中内质网应激分子伴侣葡萄糖调节蛋白78（GRP78）、C/EBP同源蛋白（CHOP）表达水平及PERK-eIF2α-ATF4信号通路的活化情况;HE染色和抗酒石酸酸性磷酸酶（TRAP）染色观察SAL对假体周围骨溶解和破骨细胞形成的影响;Real-time PCR检测SAL对破骨细胞活化相关基因抗酒石酸酸性磷酸酶（TRAP）、基质金属蛋白酶-9（MMP-9）和 c-fos的mRNA水平;ELISA法检测SAL对血清中肿瘤坏死因子α（TNF-α）、白细胞介素1β（IL-1β）和前列腺素E₂（PGE₂）水平的影响。 结果 TCP磨损颗粒可诱导假体周围骨组织发生内质网应激反应,同时激活PERK-eIF2α-ATF4信号通路,表现为TCP磨损颗粒组小鼠颅骨组织中内质网应激通路蛋白GRP78、CHOP和磷酸化PERK（p-PERK）、磷酸化eIF2α（p-eIF2α）和ATF4蛋白表达均显著上调,而PERK和eIF2α蛋白明显下调（P<0.05）;而颅顶局部注射eIF2α特异性抑制剂SAL可明显阻止TCP磨损颗粒诱导假体周围破骨细胞形成和骨溶解,减少TRAP、MMP-9和cathepsin K 的mRNA水平（P<0.05）;同时抑制TNF-α、PGE2和IL-1β等炎症因子的产生（P<0.05）。 结论 PERK-eIF2α-ATF4介导的内质网应激通路参与调控TCP磨损颗粒诱导的小鼠颅骨溶解;抑制该信号通路可减轻TCP磨损颗粒诱导的假体周围骨溶解和关节松动。     

促红细胞生成素对破骨细胞调控机理的研究

目的研究小鼠单核巨噬细胞在体外向破骨细胞分化的过程中,促红细胞生成素（erythropoietin,EPO）与破骨细胞表面受体Epor结合发挥作用的机理。方法 EPO作用于Epor受体沉默的经诱导的小鼠单核巨噬细胞,观察TRAP阳性多核细胞数目变化。Real-time PCR检测RAW264.7向破骨细胞分化过程中相关基因Epor、Nfatc1、Mmp9、EphrinB2基因的表达。结果与对照组比较,4天后,Epor沉默组的Nfatc1、EphrinB2 mRNA的表达明显升高（P〈0.01）,Ctsk Mmp9 mRNA的表达明显降低（P〈0.01）。结论 EPO通过与破骨细胞表面受体Epor结合,引发破骨细胞内相关基因表达改变,进而影响破骨细胞的分化和活化。