The effects of bisphosphonates on the resorption cycle of isolated osteoclasts

Binding sites for wheat germ agglutinin (WGA)-lectin have been shown to become revealed in the demineralized resorption lacunae that osteoclasts excavate on bone substrate. Peroxidase-conjugated WGA-lectin, which binds to bone matrix glycoconjugates and proteoglycans, was used in pit formation assays to assess the activity of isolated osteoclasts cultured on either 3-amino-1,1-hydroxy-propylidene-bisphosphonate (APD)-or dichloromethylene bisphosphonate (Cl₂MBP)-covered bone slices. Immunofluorescence and histochemical techniques were also used to study the effects of bone-bound bisphosphonates on isolated rat osteoclasts. Neither APD nor Cl₂MBP interfered with the special organization of actin or vinculin in osteoclasts when the cells were initializing their resorption cycle. After 24 hours of culture, the number of resorbing osteoclasts increased strongly on control slices, but remained low on either APD- or Cl₂MBP-treated slices. At this time, the actin and vinculin rings in osteoclasts also started to exhibit abnormal, more diffuse staining. Both bisphosphonates studied resulted in signs of cytotoxicity: the number of osteoclasts decreased on APD- or Cl₂MBP-covered bone during the course of the study and those remaining attached exhibited severe cytoplasmic retractions. The total areas of resorption remained at significantly lower levels in both experimental groups studied, and this was due to decreases in both the number and sizes of individual resorption pits. The size of the most extensive lacunae detected on the Cl₂MBP slices did not exceed 5x10³ m², whereas on the control slices, resorption pits bigger than 15x10^{3 2} were frequently discovered.     

OPG/RANKL/RANK系统在成骨细胞和破骨细胞相互调节中的作用

骨组织平衡由行使骨形成和骨吸收的成骨细胞(osteoblast,OB)和破骨细胞(osteoclast,OC)共同维持。在骨重建中两种细胞之间相互调节,一方面,OB、前体细胞、基质细胞调节OC的数量和活性;另一方面,OC反过来也可以调节OB的功能,从而形成一个反馈通路。OB和OC之间的相互调节有助于骨重建过程中骨吸收和骨形成的偶联。近年来,OB对OC骨吸收的调节已有较多研究,尤其是,OPG/RANKL/RANK信号系统的发现对于理解OB对OC骨吸收的调节是一个巨大的飞跃。但OC对OB的调节研究相对较少。本综述讨论了OB和OC之间的相互调节作用,综述了RANKL/RANK/OPG系统在骨形成和骨重建中的作用。     

骨细胞分离培养及其与成骨细胞鉴别比较的实验研究

目的:建立比较稳定的骨细胞实验室分离培养方法,并将其部分生物学特性与实验室培养的成骨细胞进行比较研究,明确两者区别.方法:采用序列酶消化法,分别从3只3dSD乳鼠骨骼中分离培养骨细胞和成骨细胞,培养24 h后进行细胞形态学观察.第1代细胞用碱性磷酸酶试剂盒采用重氮盐法(改良Kaplow氏法)染色,采用免疫细胞化学法对细胞的骨钙素(BGP)染色,测定碱性磷酸酶并计算其活性.结果:骨细胞多呈星状或树枝状,且有很多的突触;成骨细胞呈长梭形,有少量的突触.骨细胞碱性磷酸酶染色,胞浆内cAKP颗粒不明显;成骨细胞碱性磷酸酶染色,胞浆内可见众多cAKP颗粒.骨细胞BGP染色阳性明显,成骨细胞BGP染色阳性不如骨细胞明显.ALP在骨细胞中分泌较成骨细胞低,且有统计学差异.结论:实验室条件下能培养出骨细胞,该类细胞和成骨细胞有明显区别.     

Endogenous PKI gamma limits the duration of the anti-apoptotic effects of PTH and beta-adrenergic agonists in osteoblasts.

PKI gamma knockdown substantially extended the anti-apoptotic effects of PTH and beta-adrenergic agonists, whereas PKI gamma overexpression decreased these effects. Therefore, inhibition of PKI gamma activity may provide a useful co-therapy in combination with intermittent PTH or beta-adrenergic agonists for bone loss in conditions such as osteoporosis. INTRODUCTION: PTH has both catabolic and anabolic effects on bone, which are primarily caused by cAMP/protein kinase A (PKA) signaling and regulation of gene expression. We previously showed that protein kinase inhibitor-gamma (PKI gamma) is required for efficient termination of cAMP/PKA signaling and gene expression after stimulation with PTH or beta-adrenergic agonists. Inhibition of osteoblast apoptosis is thought to be an important, but transient, mechanism partly responsible for the anabolic effects of intermittent PTH. Therefore, we hypothesized that endogenous PKI gamma also terminates the anti-apoptotic effect of PTH. MATERIALS AND METHODS: PKI gamma knockdown by antisense transfection or siRNA was used to examine the ability of endogenous PKI gamma to modulate the anti-apoptotic effects of PTH and beta-adrenergic agonists in ROS 17/2.8 cells. RESULTS: Knockdown of PKI gamma substantially extended the anti-apoptotic effects of PTH, whether apoptosis was induced by etoposide or dexamethasone. In contrast, overexpression of PKI gamma decreased the anti-apoptotic effect of PTH pretreatment. This study is also the first demonstration that beta-adrenergic agonists mimic the anti-apoptotic effects of PTH in osteoblasts. Moreover, PKI gamma knockdown also substantially extended this anti-apoptotic effect of beta-adrenergic agonists. Taken together, these results show that endogenous PKI gamma limits the duration of the anti-apoptotic effects of cAMP/PKA signaling in osteoblasts. CONCLUSIONS: Because significant individual variability exists in the anabolic responses to PTH therapy in current clinical treatment of osteoporosis, inhibition of PKI gamma activity may provide a useful co-therapy in combination with intermittent PTH or beta-adrenergic agonists for bone loss in conditions such as osteoporosis. However, the potential use of such a co-therapy would depend on it not adversely affecting bone formation or other organ systems.     

Cells with Fc receptors in the cell layer next to osteoblasts and osteoclasts on bone

Cells on and near the endocranial aspect of the rat calvarium were examined for the presence of immunoglobulin (Fc) receptors ordinarily found on cells of the monocyte-macrophage lineage, from which osteoclasts are supposed to originate. Fc receptors were detected by sheep red blood cells coated with immunoglobulin (IgG). Bones were fixed, washed, freeze dried, coated with Au and examined by SEM. Neither osteoclasts nor osteoblasts showed RBC rosettes (Fc receptors). Rosetting cells were found on the bone surface near sutural areas and on the surface of the periosteal flap which was partly folded back to reveal the bone in both control and 1–34 PTH stimulated animals. Thus the layer of cells next to the osteoblasts and osteoclasts does contain cells with immunoglobulin receptors. Further work is necessary to establish whether these are only monocyte-macrophages or include some B-lymphocytes. These findings indicate that Fc receptors are not present on bone resorbing cells. If osteoclasts prove to originate from the same mononuclear precursor cells as monocytes then they loose these hallmark receptors before acquiring any of the characters by which they are commonly recognised.     

The alteration of a mechanical property of bone cells during the process of changing from osteoblasts to osteocytes

Osteocytes acquire their stellate shape during the process of changing from osteoblasts in bone. Throughout this process, dynamic cytoskeletal changes occur. In general, changes of the cytoskeleton affect cellular mechanical properties. Mechanical properties of living cells are connected with their biological functions and physiological processes. In this study, we for the first time analyzed elastic modulus, a mechanical property of bone cells. Bone cells in embryonic chick calvariae and in isolated culture were identified using fluorescently labeled phalloidin and OB7.3, a chick osteocyte-specific monoclonal antibody, and then observed by confocal laser scanning microscopy. The elastic modulus of living cells was analyzed with atomic force microscopy. To examine the consequences of focal adhesion formation on the elastic modulus, cells were pretreated with GRGDS and GRGES, and then the elastic modulus of the cells was analyzed. Focal adhesions in the cells were visualized by immunofluorescence of vinculin. From fluorescence images, we could distinguish osteoblasts, osteoid osteocytes and mature osteocytes both in vivo and in vitro. The elastic modulus of peripheral regions of cells in all three populations was significantly higher than in their nuclear regions. The elastic modulus of the peripheral region of osteoblasts was 12053+/-934 Pa, that of osteoid osteocytes was 7971+/-422 Pa and that of mature osteocytes was 4471+/-198 Pa. These results suggest that the level of elastic modulus of bone cells was proportional to the stage of changing from osteoblasts to osteocytes. The focal adhesion area of osteoblasts was significantly higher than that of osteocytes. The focal adhesion area of osteoblasts was decreased after treatment with GRGDS, however, that of osteocytes was not. The elastic modulus of osteoblasts and osteoid osteocytes were decreased after treatment with GRGDS. However, that of mature osteocytes was not changed. There were dynamic changes in the mechanical property of elastic modulus and in focal adhesions of bone cells.     

辛伐他汀联合雷奈酸锶对成骨细胞及破骨细胞生物学特性的影响

目的 探讨辛伐他汀(simvastatin,SIM)联合雷奈酸锶(strontium ranelate,SR)治疗对大鼠成骨细胞及破骨细胞生物学特性的影响.方法 分离和培养大鼠成骨细胞和破骨细胞;使用SIM或SR和较低剂量SIM联合较低剂量SR处理大鼠成骨细胞和破骨细胞;用Western blot方法检测成骨细胞和破骨...     

血小板衍生生长因子-AA对破骨细胞功能的影响

目的　研究血小板衍生生长因子 (PDGF) AA对破骨细胞功能的影响。　方法　利用免疫电镜技术证明PDGF α受体在破骨细胞膜得以表达 ;酶动力学法测定培养基中酸性磷酸酶与抗酒石酸酸性磷酸酶活性 ;通过荧光探针在共聚焦显微镜下观察破骨细胞内氢离子随PDGF AA浓度的变化情况 ;利用甲苯胺蓝对骨吸收陷窝染色并在图像分析仪下测定其面积和数目。　结果　破骨细胞膜有胶体金颗粒沉着 ,抗酒石酸酸性磷酸酶的活性无显著变化 (P >0 0 5 ) ,细胞内氢离子显著增加 ,但PDGF AA不能促进其释放 ;骨吸收陷窝的面积与数目均无显著变化。　结论　PDGF AA虽然能够促进氢离子在细胞内产量增加 ,但由于不能显著改变抗酒石酸酸性磷酸酶活性 ,因而不能直接促进破骨细胞的骨吸收功能。     

Isolation of human osteoclasts formed in vitro: hormonal effects on the bone-resorbing activity of human osteoclasts

Osteoclasts are multinucleated cells that carry out bone resorption. Analysis of the direct effect of hormones on the bone-resorbing activity of human osteoclasts has been limited by difficulties in isolating these cells from the human skeleton. In this study, human osteoclasts formed from cultures of peripheral blood mononuclear precursors (PBMCs) on a Type-I collagen gel were isolated by collagenase treatment for investigating their resorptive activity. PBMCs were cultured in the presence of M-CSF, soluble RANKL, dexamethasone, and 1,25(OH)2D3. The isolated multinucleated cells expressed the osteoclast markers, TRAP, VNR, cathepsin K, calcitonin receptors and were capable of extensive lacunar resorption. Calcitonin inhibited the motility and resorptive activity of osteoclasts. RANKL significantly stimulated osteoclast resorption, but 1,25(OH)2D3, PTH, and OPG did not. These findings indicate that calcitonin and RANKL act directly on human osteoclasts to inhibit and stimulate osteoclast bone-resorbing activity, respectively, and that PTH, 1,25(OH)2D3, and OPG are more likely to influence osteoclast activity indirectly. This technique of human osteoclast isolation should permit the effects of cellular and hormonal/humoral factors on the bone-resorbing activity of mature human osteoclasts to be assessed independently of any effect such factors have on osteoclast formation. It should also make it possible to examine directly the resorptive activity and other characteristics of osteoclasts in specific bone disorders such as Paget's disease.     

Suppression of autophagy in osteocytes does not modify the adverse effects of glucocorticoids on cortical bone

Glucocorticoid excess decreases bone mass and strength in part by acting directly on osteoblasts and osteocytes, but the mechanisms remain unclear. Macroautophagy (herein referred to as autophagy) is a lysosome-based recycling pathway that promotes the turnover of intracellular components and can promote cell function and survival under stressful conditions. Recent studies have shown that glucocorticoids stimulate autophagy in osteocytes, suggesting that autophagy may oppose the negative actions of glucocorticoids on this cell type. To address this possibility, we compared the impact of prednisolone administration on the skeletons of adult mice in which autophagy was suppressed in osteocytes, via deletion of Atg7 with a Dmp1-Cre transgene, to their control littermates. In control mice, prednisolone increased autophagic flux in osteocyte-enriched bone as measured by LC3 conversion, but this change did not occur in the mice lacking Atg7 in osteocytes. Nonetheless, prednisolone reduced femoral cortical thickness, increased cortical porosity, and reduced bone strength to similar extents in mice with and without autophagy in osteocytes. Prednisolone also suppressed osteoblast number and bone formation in the cancellous bone of control mice. As shown previously, Atg7 deletion in osteocytes reduced osteoblast number and bone formation in cancellous bone, but these parameters were not further reduced by prednisolone administration. In cortical bone, prednisolone elevated osteoclast number to a similar extent in both genotypes. Taken together, these results demonstrate that although glucocorticoids stimulate autophagy in osteocytes, suppression of autophagy in this cell type does not worsen the negative impact of glucocorticoids on the skeleton.     

Arachidonic acid for loading induced prostacyclin and prostaglandin E(2) release from osteoblasts and osteocytes is derived from the activities of different forms of phospholipase A(2)

Mechanical loading of bone stimulates resident bone cells to produce prostacyclin (PGI(2)) and prostaglandin (PG)E(2) by a mechanism that can be differentially regulated by ion channel blockers. We have investigated differences in the loading-related PG production mechanisms in rat ulnae explants loaded ex vivo. Loading and aluminium fluoride (AlF(3), a nonselective activator of G-proteins) both increased PGI(2) and PGE(2) release into culture medium. Pertussis toxin (PTX) blocked loading-related release of PGE(2), but not PGI(2), while isotetrandrine, an inhibitor of G-protein-mediated activation of phospholipase (PL)A(2), abolished the loading-related release of both PGs. This suggests both PTX-sensitive and -insensitive G-protein-dependent, PLA(2)-mediated mechanisms for loading-related PG production. Blockade of secretory (s)PLA(2) activity prevented loading-related release of PGE(2) and PGI(2), whereas inhibition of cytosolic (c)PLA(2) activity blocked loading-related release of PGE(2) alone. cPLA(2) was localized immuno-cytochemically to osteoblasts, but not to osteocytes. sPLA(2) was localized to osteocytes and osteoblasts. Exogenous type-IA sPLA(2) and type-IB sPLA(2) stimulated significant increases in PGE(2) and PGI(2) release. PTX reduced the release of both PGs stimulated by type IA PLA(2), but not type IB. Furthermore, inhibition of protein kinase C (PKC) activity blocked loading-related release of PGE(2), but not that of PGI(2). These data suggest that loading-related release of PGI(2) and PGE(2) utilizes arachidonic acid derived from the activity of different PLA(2)s. In osteocytes and osteoblasts, arachidonic acid for PGI(2) synthesis is liberated by PTX-insensitive G-protein-dependent sPLA(2) alone. In osteoblasts, arachidonic acid for PGE(2) synthesis is released by PTX-sensitive, G-protein-dependent, cPLA(2)-mediated activity, which also requires upstream sPLA(2) and PKC activities.     

Autoantibodies against the insulin receptor. Dissociation of the acute effects of the antibodies from the desensitization seen with prolonged exposure

The effect of antibodies against the insulin receptor (anti-R) found in a patient with the type B syndrome of insulin resistance and acanthosis nigricans was characterized using 3T3-L1 cultured fat cells. Anti-R acutely mimicked the action of insulin by stimulating deoxyglucose uptake. With more prolonged exposure, this insulinomimetic effect decayed, glucose metabolism returned to basal levels, and the cells became severely resistant to the actions of insulin. As seen with anti-R from a previous patient, desensitization consisted of both a dramatic decrease in the maximal responsiveness of the cells to insulin and a shift in the dose-response curve for insulin-stimulated glucose oxidation. The acute and chronic effects of anti-R were then compared. The concentration of anti-R required to half-maximally inhibit insulin binding averaged more than twice that required for half-maximal stimulation of deoxyglucose uptake, consistent with the amount of spare receptors in 3T3-L1 cells. After prolonged exposure, the insulinomimetic activity was completely lost at all concentrations of anti-R, even at those that did not completely induce insulin resistance. Thus, loss of the insulinomimetic activity of anti-R is necessary, but not sufficient, to cause desensitization. Less anti-R was required to desensitize cells to insulin than would have been predicted on the basis of the acute inhibition of binding and the number of spare receptors.(ABSTRACT TRUNCATED AT 250 WORDS)     

丹仙康骨胶囊对培养成骨细胞影响的观察

目的：为了解补肾活血中药丹仙康骨胶囊对体外培养成骨细胞的作用。方法：应用透射电镜、MTT、对硝基苯磷酸盐法(PNPP)及骨钙素(BGP)含量放免测定法，观察丹仙康骨胶囊对成骨细胞超微结构、增殖与分化作用的影响。结果：丹仙康骨胶囊刺激(20mg／ml)的成骨细胞，ALP活性提高及骨钙素含量增多；透射电镜观察其细胞线粒体致密、游离核糖体增多、内质网丰富扩大增粗呈中等电子密度，而糖原溶解与脂肪空泡均较少。结论：丹仙康骨胶囊具有促进成骨细胞的代谢、增殖和分化的作用。     

Comparison of the effects of calcitonin gene-related peptide and amylin on osteoblasts.

Calcitonin gene-related peptide (CGRP) and amylin are homologous 37-amino-acid peptides which have been demonstrated to have anabolic effects on bone. It is not clear whether these effects are mediated by a common receptor, nor is it known which ligand is the more potent. These questions are addressed in the present study using cultures of fetal rat osteoblasts. CGRP increased cell number when present in a concentration >/=10-9 M, but 10-8 M CGRP was required to stimulate thymidine and phenylalanine incorporation. Amylin was effective on these indices at 100-fold lower concentrations, and its maximal effects were about twice as great as those of CGRP. ED50's for the effects of amylin and CGRP on cell number were 10-12 M and 10-10 M, respectively. There was no additivity between maximal doses of the peptides on these indices. The effects of specific receptor blockers on the maximal stimulation of cell number by these peptides were also studied. The CGRP receptor-blocker, CGRP-(8-37), completely blocked the effect of CGRP at blocker concentrations >/=10-9 M. In contrast, the amylin receptor blocker, amylin-(8-37), completely blocked the effects of CGRP when the blocker was present in concentrations as low as 10-11 M. The KI of CGRP-(8-37) was 2 x 10-10 M and that of amylin-(8-37) was 7 x 10-12 M. In converse experiments studying the blockade of maximal doses of amylin, amylin-(8-37) 10-10 M was effective (KI 1 x 10-10 M), whereas a 100-fold greater concentration of CGRP-(8-37) was necessary to achieve the same effect (KI 6 x 10-9 M). It is concluded that amylin and CGRP probably act through a common receptor to stimulate osteoblast growth, and that this receptor has a higher affinity for amylin than for CGRP.     

The effects of inhibitors of cysteine-proteinases and collagenase on the resorptive activity of isolated osteoclasts

The effects of specific inhibitors of cysteine-proteinases ((Z-Phe-Ala-CHN2: benzyloxycarbonyl-phenyl-alanyl alanyl diazomethane and E-64: trans-epoxy-succinyl-L-leucylamido(4-guanidino)-butane) and collagenase and collagenase ((Cl-1: N-(3-N-benzyloxycarbonyl amino-1-R-carboxypropyl)-L-leucyl-O-methyl-L-tyrosine N-methylamide) have been tested on the osteoclastic resorption of dentine. Chick osteoclasts were cultured in the presence or absence of 12.5 microM Z-Phe-Ala-CHN2, 40 or 60 microM E-64, or 40 or 100 microM Cl-1 for 1 or 2 days. In addition, osteoclasts were cultured on oyster shell calcitostracum with or without 12.5 microM Z-Phe-Ala-CHN2. Specimens were studied by light microscopy to count cells and resorption features and by scanning electron microscopy (SEM) stereophotogrammetry for the measurement of the depths, plan-areas and volumes of resorption pits. The numbers, depths and volumes (but not the plan-areas) of the resorption pits in dentine were significantly reduced by Z-Phe-Ala-CHN2 and E-64. Thus, for a given plan-area, the volumes and the depths of resorption pits were smaller in these experimental groups compared with control dentine specimens. The overall inhibition of resorption was at least 75%. Cl-1 did not have this inhibitory effect on the numbers or sizes of resorption pits in dentine. When the oyster calcitostracum was used as a substrate for the osteoclasts, Z-Phe-Ala-CHN2 did not reduce the numbers or volumes of pits, but increased the plan-areas and prevented the formation of deeper pits.(ABSTRACT TRUNCATED AT 250 WORDS)