破骨细胞血系起源的活细胞成像观察

目的:采用活细胞成像技术,观察血系单核细胞诱导形成破骨细胞的全过程,旨在进一步阐明破骨细胞血系起源的发生及其细胞动力学。方法:取成年SPF级纯种雄性SD大鼠1只,体重280 g,腹主动脉采血8 ml,经密度梯度离心分离单个核细胞,在RANKL与M-CSF诱导下,分为倒置相差显微镜观察组、抗酒石酸酸性磷酸酶染色组、噬骨试验扫描电镜观察组、活细胞成像组4组进行培养。倒置相差显微镜观察组从培养开始,在数字显微成像系统下,每天观察记录1次;抗酒石酸酸性磷酸酶染色组培养21 d作酶活性染色鉴定;噬骨试验扫描电镜观察组培养21 d取出骨磨片作扫描电镜观察;活细胞成像组采用多点位缩时电影法对整个培养过程进行长达35 d的连续观察记录。结果:诱导培养2周后,倒置相差显微镜观察可见大量多核细胞形成,外形呈圆形、梭形、扇形、椭圆形及不规则突起状;抗酒石酸酸性磷酸酶染色绝大部分多核细胞与单核细胞均呈阳性反应;骨磨片扫描电镜观察可见较多骨吸收陷窝、坑洼及沟道,还有位于陷窝及沟道内正在行使骨吸收功能的破骨细胞;活细胞成像观察到起源于周围血的多核破骨细胞是由单核细胞、单核细胞与多核细胞及多核细胞之间相互融合而成,其细胞间的融合均发生在贴壁状态,显微缩时电影观察显示破骨细胞形态表现复杂多变。结论:大鼠周围血单核细胞在RANKL和M-CSF诱导下,可以向破骨细胞分化,形成具有骨吸收功能的多核破骨细胞。破骨细胞的形成是发生在贴壁状态下多种形式的细胞融合过程,破骨细胞的粘附特性对其存活及功能发挥至关重要。破骨细胞具有吞噬功能,其形态结构动态多变。破骨细胞不仅是一种多核细胞,还可能包括单核破骨细胞。破骨细胞通过融合形成多核巨细胞的特性,可能是其适应功能需求与骨吸收效率的一种特殊生物学行为。实验结果进一步证实了破骨细胞的血系起源学说,并为深入阐明破骨细胞的细胞动力学与细胞生物学特性提供了新的实验研究依据。     

诱导小鼠破骨前体细胞成熟分化的实验条件探讨

目的探讨小鼠单核细胞RAW264.7能否在RANKL诱导下向破骨细胞成熟分化。方法 RANKL作用RAW264.7细胞7天～9天,光镜、透射电镜、扫描电镜(scanning electron microscope,SEM)分别观察其细胞形态学变化,用抗酒石酸酸性磷酸酶(tartrate-resistant acid phosphatase,TRAP)染色法观察TRAP阳性的多核细胞,RT-PCR检测破骨细胞表型和功能基因表达变化情况,扫描电镜观察破骨细胞在骨片上形成骨吸收陷窝。结果光镜、透射电镜下可见细胞胞体增大,为椭圆形或不规则形,胞核5～10个,扫描电镜下可见细胞表面大量的伪足样突起;此外,RANKL能诱导RAW264.7细胞分化为TRAP染色阳性的多核破骨细胞,细胞多为超过5个核的多核巨细胞;RAW264.7细胞成熟分化后具有骨吸收功能,并且能上调Cathepsin-K、TRAP、RANK等典型破骨细胞表型和功能基因mRNA的表达。结论 RAW264.7细胞是一种较好的破骨前体细胞模型,单用50ng/ml的RANKL体外连续诱导7天以上,能明显促进它向成熟的破骨细胞分化。     

M-CSF和RANKL体外诱导培养小鼠破骨样细胞及其骨吸收功能的动态观察

目的以巨噬细胞集落刺激因子(Macrophage colony-stimulating factor,M-CSF)和核因子κB受体激动剂配体(Ligand of receptor activator of NF-κB,RANKL)联合体外诱导小鼠骨髓干细胞分化为破骨样细胞,并对其骨吸收功能进行动态观察。方法分离小鼠四肢骨获取骨髓干细胞,以M-CSF和RANKL诱导培养,将盖玻片及骨磨片置入培养基内,在诱导培养的第3,6,9天分别对盖玻片行抗酒石酸酸性磷酸酶(The tartrate-resistant acid phosphatase TRAP)染色,观察细胞形态和染色情况,并计算破骨样细胞数量;同时对骨磨片进行骨吸收陷窝的观察。结果诱导培养3 d后出现含TRAP(+)颗粒的细胞,可见淡染单核和双核;诱导培养6 d后可见TRAP(+)细胞较诱导培养3 d时增多,仍以双核为主;诱导培养9 d后出现多核巨型TRAP(+)细胞,细胞核达到3个以上。并且随着诱导培养的时间延长,破骨样细胞数量逐渐增长。诱导培养第3,6天骨磨片上均未发现骨吸收陷窝,第九天出现不同形态的呈蓝紫色的吸收陷窝。结论 M-CSF和RANKL联合体外诱导小鼠骨髓干细胞形成破骨样细胞是一种有效的诱导培养方法,本实验在诱导培养第九天发现破骨样细胞具有骨吸收功能。     

骨保护素体外抑制小鼠单核巨噬细胞 成熟分化的实验研究

目的研究骨保护素（Osteoprotegerin, 0PG)抑制核因子NF-KB受体活化因子配体（Receptor activator of nuclear kappa B ligand,RANKL)诱导小鼠单核细胞RAW264. 7成熟分化而导致的溶骨效 应。方法50 ng/mL RANKL诱导RAW264. 7细胞1 d后,加人100 ng/mL 0PG(实验组,即0PG + RANKL组）或不加人0PG(对照组,即RANKL组）分别培养7 d和9 d,经细胞形态学观察其变化,抗 酒石酸酸性碟酸酶（Tartrate resistant acid phosphatase, TRAP)染色法观察TRAP阳性多核细胞,扫描 电镜下观察在骨片上的破骨细胞所致的骨吸收陷窝形成情况。结果对照组培养7 d时,在倒置相 差显微镜、透射电镜、光镜下可见细胞形状为椭圆形或不规则形,胞体明显较KAW264.7细胞增大, 胞核多为6 ~ 10个,扫描电镜下还可见大量伪足形成,而实验组培养7 d后,细胞形状多为圆形,且扫 描电镜下未见明显伪足形成;对照组9 d时可见大量TRAP染色阳性的多核巨细胞（含3个或3个以 上的细胞核）,而实验组中TRAP染色阳性的多核破骨细胞偶见多核巨细胞,培养9 d时很难找到多 核巨细胞;仅用RANKL诱导RAW264.7细胞分化7 d时,对照组中破骨细胞表面可见大量伪足伸出, 并形成明显的骨吸收陷窝,实验组中破骨细胞见少许伪足突出,不能看到明显的骨陷窝形成。结论 单用50 ng/mL RANKL体外连续诱导RAWM4.7细胞7 d时,可以促进成熟的破骨细胞显著分化。 100 ng/mL 0PG培养9 d能有效地抑制破骨细胞的分化,减少破骨细胞的骨吸收效应。     

RANKL诱导小鼠单核细胞RAW264.7分化成成熟破骨细胞

目的观察小鼠的单核／巨噬细胞RAW264．7的一般生物学特征及在RANKL诱导下形成成熟破骨细胞的特征。方法RANKI，诱导RAW264．7细胞6d后，用抗酒石酸酸性磷酸酶(TRAP)染色法观察TRAP阳性多核细胞，吖啶橙染色激光共聚焦显微镜(LCSM)观察多核细胞形态；诱导RAW264．7细胞9d后，RT、PCR检测RAW264．7细胞的破骨细胞表型和功能基因表达及其RANKL诱导后变化；诱导RAW264．7细胞12d后，钙磷覆盖的破骨细胞活性分析板观察破骨细胞的骨吸收功能。结果RAW264．7细胞TRAP染色阴性，单核或2个核，能表达破骨细胞表型和功能基因，无骨吸收功能。RANKL可诱导RAW264．7细胞形成TRAP阳性成熟的多核破骨细胞，上调CathepsinK、CAⅡ、integrinβ3等基因mRNA的表达。结论RAW264．7具有破骨细胞特征性基因表达谱，是一种较好的破骨前体细胞模型。RANKL可诱导RAW264．7细胞形成成熟破骨细胞。     

复合振动抑制RAW264.7细胞分化成熟

目的研究复合振动对核因子-κB受体活化因子配体(RANKL)诱导的RAW264.7细胞分化的影响,探讨复合振动对破骨细胞分化的影响及机制。方法 RAW264.7细胞RANKL诱导培养3或4d并施加复合振动干预,通过抗酒石酸酸性磷酸酶(TRAP)染色观察TRAP阳性多核细胞形成的变化,real-time RT-PCR分析破骨细胞特异性基因组织蛋白酶K(cathepsin K),金属蛋白酶-9(MMP-9)和TRAP表达的变化。结果复合振动能抑制RANKL诱导破骨细胞形成,下调破骨细胞特异基因cathepsin K,MMP-9和TRAP的表达。结论 RANKL促进RAW264.7细胞向破骨细胞分化,并增加特异基因的表达,但RANKL的促进作用受复合振动抑制。这进一步的阐释复合振动抗骨质疏松的作用机制。     

兔原代破骨细胞与鼠单核细胞诱导破骨细胞的形态学观察及比较分析

目的 通过提取新生兔骨髓破骨细胞及诱导鼠单核细胞破骨分化，比较原代破骨细胞与诱导形成的破骨细胞之间的形态差异,阐明单核细胞-破骨分化融合过程中的阶段变化特点。方法 取2～4 d龄新西兰乳兔骨髓细胞，贴壁法富集原代破骨细胞。取6～8周龄SD大鼠骨髓细胞，M-CSF与RANKL诱导单核细胞破骨细胞分化。HE染色，Actin-red、Lyso-tracker Green、TRAP染色分别对细胞骨架、溶酶体、抗酒石酸酶进行观察。结果 兔原代破骨细胞贴壁速度快，呈现多核(10～50个）煎饼状外观，溶酶体荧光染色呈现强阳性，抗酒石酸酶染色阳性；鼠单核细胞诱导形成的巨噬细胞，贴壁过程较慢，表现为胞质逐渐伸展，细胞折光性逐渐降低，胞浆嗜酸性，溶酶体荧光染色强阳性，细胞内肌动蛋白微丝分布散在。诱导后期TRAP阳性的单核破骨细胞，部分细胞发生融合形成胞质紧贴皿底，形态巨大的多核，细胞骨架染色可呈现典型的“封闭环”样结构。结论 兔原代破骨细胞与鼠单核细胞诱导形成的破骨细胞形态具有一定相似度，但后者诱导过程中细胞形态变化大，形态复杂多变，在诱导早期阶段可借助细胞光镜下的形态特征，溶酶体荧光染色及细胞骨架染色与杂细胞-间充质细胞鉴别。     

痩素对小鼠破骨细胞分化及功能的影响

目的 观察瘦素（leptin）对体外骨髓诱导培养的小鼠破骨细胞分化和功能的作用效应,探索leptin和骨吸收之间的关联.方法 建立由巨噬细胞集落刺激因子（M-CSF）和骨保护素配体（RANKL）为共同细胞因子的小鼠破骨细胞骨髓诱导培养体系,将不同浓度的leptin作用于破骨细胞.实验中根据培养液中是否加入M-CSF和RANKL并依据leptin浓度的不同分为：A组,M-CSF和RANKL;B组,M-CSF、RANKL和leptin（80 ng/ml）;C组,M-CSF、RANKL和leptin（160 ng/ml）;D组,M-CSF、RANKL和leptin（240 ng/ml）;E组,M-CSF、RANKL和leptin（320 ng/ml）;F组,M-CSF、RANKL和leptin（400 ng/ml）;同时设立空白对照组G组.于作用后第7天取细胞玻片进行抗酒石酸酸性磷酸酶（TRAP）染色,观察破骨细胞并计数;于第10天取出骨片进行甲苯胺蓝染液染色,在光镜和扫描电镜观察骨吸收陷窝形态.结果：诱导培养的小鼠破骨细胞形态特征明显;A组在破骨细胞数量与D、E、F组相比较有明显的统计学差异（P＜0.05）;A组骨吸收面积比与B、C、D、E、F组都有明显的统计学差异（P＜0.05）.结论：leptin抑制体外培养的破骨细胞的分化和骨吸收功能.     

阿司匹林通过抑制大鼠破骨细胞 RANK 表达抑制骨质吸收

目的：研究不同浓度阿司匹林对体外培养大鼠破骨细胞（Osteoclast, OC）RANK（receptor activator of nuclear factor-κB,核因子κB受体活化因子）表达的影响。方法采用RANKL和M-CSF诱导大鼠骨髓单核巨噬细胞破骨分化模型,给予不同浓度的阿司匹林（0.25 mmol/L、0.5 mmol/L、1.0 mmol/L、1.5 mmol/L）和雌激素（雌二醇10-6 mmol/L）处理,而后进行抗酒石酸酸性磷酸酶（ The tartrate-resistant acid phosphatase ,TRAP）染色观察细胞形态特征,扫描电镜观察骨磨片破骨细胞骨吸收陷窝,RT-PCR技术检测破骨细胞表面RANK基因的表达,ELISA法检测RANK蛋白的表达。结果阿司匹林和雌激素都可以使大鼠破骨细胞成熟分化程度和骨吸收活性降低,抑制破骨细胞RANK基因和蛋白的表达,且阿司匹林的抑制作用具有剂量依赖性。结论阿司匹林对大鼠破骨细胞RANK的表达有抑制作用且呈剂量依赖性,从而抑制破骨细胞的成熟分化及骨吸收功能。     

盐酸二甲双胍抑制破骨细胞分化的研究

目的探讨盐酸二甲双胍对破骨细胞分化抑制作用的研究。方法核因子-κB受体活化因子配体(RANKL)诱导小鼠骨髓巨噬细胞分化成破骨细胞,在诱导过程中加入不同浓度的盐酸二甲双胍。培养7 d后固定,抗酒石酸酸性磷酸酶染色,计数破骨细胞的数量,骨吸收培养板观察骨陷窝面积,Western blot检测盐酸二甲双胍对ERK磷酸化的影响。结果盐酸二甲双胍能抑制RANKL诱导的破骨细胞的形成,并且能减少骨陷窝面积,以及抑制ERK磷酸化。结论盐酸二甲双胍可抑制破骨细胞分化及功能,其机制可能与抑制ERK磷酸化有关。     

Arthroplasty membrane-derived fibroblasts directly induce osteoclast formation and osteolysis in aseptic loosening.

PURPOSE: Both macrophages and fibroblasts are the main cell types found in periprosthetic tissues surrounding failed joint arthroplasties. These fibroblasts are known to express RANKL and to produce TNFalpha, factors which promote osteoclast formation and bone resorption. In this study we have analysed the role that arthroplasty membrane-derived fibroblasts (AFb) play in inducing the generation of bone resorbing osteoclasts. METHODS: Fibroblasts were isolated from periprosthetic tissues and co-cultured with human monocytes in an osteoclast differentiation assay in the presence or absence of M-CSF and inhibitors of RANKL (OPG) and/or TNFalpha. RANKL expression by AFbs was determined by RT-PCR and the extent of osteoclast differentiation by the expression of TRAP, VNR and evidence of lacunar resorption. RESULTS: In the presence of M-CSF, large numbers of TRAP(+) and VNR(+) multinucleated cells capable of lacunar resorption, were noted in co-cultures of monocytes and RANKL-expressing AFbs. Cell-cell contact was required for osteoclast formation. The addition of OPG and anti-TNFalpha alone significantly reduced but did not abolish the extent of osteoclast formation, whereas the addition of both together abolished osteoclast formation and lacunar resorption. CONCLUSION: Our results indicate that fibroblasts in periprosthetic tissues are capable of inducing the differentiation of normal human peripheral blood mononuclear cells to mature osteoclasts by a mechanism that involves both RANKL and TNFalpha. Suppression of both RANKL and inflammatory cytokines is likely to be required to control periprosthetic osteolysis.     

巴斯德毕赤酵母菌株分泌表达的重组骨保护素融合蛋白生物学活性的研究

目的探讨巴斯德毕赤酵母菌株分泌表达的重组骨保护素融合蛋白(recombiant humanosteoprogerin-human serum album,rhOPG-HSA)对破骨细胞的抑制效应。方法利用巨噬细胞集落刺激因子(macrophage colony stimulating factor,M-CSF)以及破骨细胞分化因子(receptor activator ofnuclear factor-kβligand,RANKL)诱导骨髓单核细胞Raw264.7分化为破骨细胞,通过抗酒石酸酸性磷酸酶(tartrate-resistant acid phosphatase,TRAP)染色和甲苯胺蓝染色法鉴定rhOPG-HSA抑制破骨细胞及其骨吸收能力。结果 rhOPG-HSA组与阴性对照组相比,Raw264.7细胞诱导3d,4d,5d后,TRAP阳性染色的破骨细胞明显减少;Raw264.7细胞与骨薄片共培养诱导10d后,骨吸收陷窝明显减少。结论 rhOPG-HSA能够抑制破骨细胞的分化及骨吸收。     

Osteoclast differentiation from circulating mononuclear precursors in Paget's disease is hypersensitive to 1,25-dihydroxyvitamin D(3) and RANKL

A characteristic feature of Paget's disease is an increase in the number of osteoclasts in bone. Osteoclasts are formed from mononuclear phagocyte precursors that circulate in the monocyte fraction of peripheral blood. These cells require the presence of RANK ligand (RANKL)-expressing osteoblastic cells and human macrophage colony-stimulating factor (M-CSF) to form osteoclasts in vitro. To determine the role of osteoclast differentiation from circulating precursors in Paget's disease, we cultured monocytes from Paget's patients and gender- and age-matched normal controls with no evidence of bone disease for up to 21 days in the presence of UMR 106 cells and various concentrations of M-CSF (1-25 ng/mL) and 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] (10(-10) to 10(-7) mol/L). Relative to controls, there was a significant increase in the extent of osteoclast differentiation from pagetic monocytes as assessed by expression of tartrate-resistant acid phosphatase (TRAP), vitronectin receptor (VNR), and lacunar bone resorption. Serial dilution experiments (2 x 10(5) to 2 x 10(2) cells/well) showed no difference in the concentration of osteoclast precursors in the peripheral blood. In Paget's patients with high serum alkaline phosphatase (sAP) levels, increased sensitivity to the osteoclastogenic effect of 1,25(OH)(2)D(3) was noted. Osteoclast differentiation did not occur when M-CSF was substituted by interleukin-6 (IL-6) and soluble IL-6 receptor (sIL-6R), and these factors did not stimulate osteoclast differentiation in the presence of M-CSF. In this in vitro coculture system, osteoclast formation was inhibited by osteoprotegerin in a dose-dependent manner. In the presence of RANKL (5-30 ng/mL) and M-CSF (25 ng/mL), osteoclast formation and bone resorption were significantly increased in cultures of monocytes from patients with high and low sAP levels as compared with normal controls. Our findings suggest that the increase in osteoclast numbers seen in Paget's disease results not from an increase in the number of circulating precursors in peripheral blood but rather from an increased sensitivity of osteoclast precursors to the humoral factors, 1,25(OH)(2)D(3) and RANKL, which regulate osteoclast formation.     

Osteoclast formation and bone resorption are inhibited by megakaryocytes

It has been previously reported that addition of megakaryocytes (MKs) to osteoblasts in vitro results in increased osteoblastic collagen and osteoprotegerin (OPG) production, suggesting a role for MKs in bone formation. To further investigate this role, we have studied the effects of MKs on osteoclast formation and activity. Human osteoclasts were generated from CD14 monocytes isolated from peripheral blood and cultured in the presence of M-CSF and sRANKL on dentine and calcium phosphate substrates. MKs were generated from CD34+ cells isolated from either human peripheral blood or cord blood and cultured in liquid medium for 6 days, after which time maturing MKs (CD61-positive cells) were isolated and added to monocyte cultures. After 6 and 9 days of culture, the number of osteoclasts identified morphologically and by TRAP staining was counted. Cells were removed and the area of resorption was identified by von Kossa staining and quantitatively assessed by image analysis. The addition of MKs to osteoclast cultures at day 0 inhibited the number of osteoclasts formed 1.9-fold (p>0.003), whereas addition at 3 days had no effect on osteoclast number. The presence of MKs inhibited resorption 8.7-fold when co-cultured with osteoclasts from day 0 (p>0.004), but only by 3.1-fold when co-cultured from day 3 (p>0.01). In dose-response experiments, it was found that 1-10% of MKs added to monocyte cultures elicited the greatest inhibition of resorption. Similar osteoclast cultures were treated with CD61-negative cells (non-MKs) to confirm that the inhibition of osteoclast formation and activity was specifically due to MKs. Experiments with a cell-impermeable membrane indicated that both cell to cell contact and release of soluble factor(s) were involved in mediating these effects. These results show that MKs inhibit osteoclast formation and activity. The most pronounced effects were seen when MKs and osteoclasts were co-cultured from day 0, suggesting that MKs act primarily on osteoclast precursors.     

Characterization of Circulating Human Osteoclast Progenitors: Development of In Vitro Resorption Assay

Several cell surface markers were used to isolate monocytes as osteoclast progenitors with an immunomagnetic cell separation system. Use of this system with specific monocyte antibodies produced 99% pure monocytes. When purified monocytes were cultured on bovine bone slices in the presence of receptor activator of nuclear factor-B (RANKL), macrophage-colony stimulating factor (M-CSF), tumor necrocis factor alpha (TNF-), and dexamethasone for 14 days, CD14⁺ CD11b⁺, and CD61⁺ monocytes had approximately 90-, 30- and 20-fold higher osteoclast formation capacities/plated cells compared to the control culture. CD15⁺ monocytes generated few tartrate-resistant acid phosphatase-positive multinucleated cells (TRACP+ MNC), and CD169⁺ monocytes generated no TRACP+ MNC. This suggests, that there are various subsets of monocytes in the blood circulation and that they have different capacities in osteoclast formation. These results show that circulating human osteoclast progenitors can be efficiently purified by immunomagnetic cell separation system using anti-CD14, -CD11b, and -CD61 antibodies. These purified monocyte fractions had different ability to give rise to osteoclasts. CD169 was not found to be suitable for osteoclast progenitor isolation. Optimal concentration of dexamethasone for osteoclast formation and bone resorption was 10 nM. To develop a human resorption assay, osteoclasts were first induced for 7 days, whole media were replaced, cultures were continued for additional 3 days and C-terminal telopeptide of type I collagen was determined from culture media. This assay was shown to be functional, since two well-known resorption inhibitors, bafilomycin A₁ and calcitonin, dose-dependently inhibited the resorption activity of osteoclasts.     

Osteoclastogenesis is Influenced by Modulation of Gap Junctional Communication with Antiarrhythmic Peptides

Osteoclasts are formed by the fusion of mononuclear precursor cells of the monocyte–macrophage lineage. Among several putative mechanisms, gap-junctional intercellular communication (GJC) has been proposed to have a role in osteoclast fusion and bone resorption. We examined the role of GJC in osteoclastogenesis and in vitro bone resorption with mouse bone marrow hematopoietic stem cells and RAW 264.7 cells. Blocking of gap junctions with 18-α-glycyrrhetinic acid (18GA) led to inhibition of osteoclastogenesis and in vitro bone resorption. Similarly, the GJC inhibitor GAP27 inhibited osteoclast formation. GJC modulation with the antiarrhythmic peptides (AAPs) led to increased amounts of multinuclear RAW 264.7 osteoclasts as well as increased number of nuclei per multinuclear cell. In the culture of bone marrow hematopoietic stem cells in the presence of bone marrow stromal cells AAP reduced the number of osteoclasts, and coculture of MC3T3-E1 preosteoblasts with RAW 264.7 macrophages prevented the action of AAPs to promote osteoclastogenesis. The present data indicate that AAPs modulate the fusion of the pure culture of cells of the monocyte–macrophage lineage. However, the fusion is influenced by GJC in cells of the osteoblast lineage.     

Characterization of osteoclasts derived from CD14+ monocytes isolated from peripheral blood

Bone resorption is solely mediated by osteoclasts. Therefore, a pure osteoclast population is of high interest for the investigation of biological aspects of the osteoclasts, such as the direct effect of growth factors and hormones, as well as for testing and characterizing inhibitors of bone resorption. We have established a pure, stable, and reproducible system for purification of human osteoclasts from peripheral blood. We isolated CD14-positive (CD14+) monocytes using anti-CD14-coated beads. After isolation, the monocytes are differentiated into mature osteoclasts by stimulation with macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor κB ligand (RANKL). Osteoclast formation was only observed in the CD14+ population, not in the CD14− population, and only in the presence of both M-CSF and RANKL, confirming that the CD14+ system is a pure population of osteoclast precursors. No expression of osteoclast markers was observed in the absence of RANKL, whereas RANKL dose-dependently induced the expression of cathepsin K, tartrate-resistant acid phosphatase (TRACP), and matrix metallo proteinase (MMP)-9. Furthermore, morphological characterization of the cells demonstrated that actin rings were only formed in the presence of RANKL. Moreover, the osteoclasts were capable of forming acidic resorption lacunae, and inhibitors of lysosomal acidification attenuated this process. Finally, we measured the response to known bone resorption inhibitors, and found that the osteoclasts were sensitive to these and thereby provided a robust and valid method for interpretation of the effect of antiresorptive compounds. In conclusion, we have established a robust assay for developing osteoclasts that can be used to study several biological aspects of the osteoclasts and which in combination with the resorption marker CTX-I provides a useful tool for evaluating osteoclast function in vitro.     

Fibroblastic stromal cells express receptor activator of NF-kappa B ligand and support osteoclast differentiation.

Osteoclast formation in bone is supported by osteoblasts expressing receptor activator of NF-kappa B ligand (RANKL) and macrophage colony-stimulating factor (M-CSF) expression. Numerous osteotropic factors regulate expression levels of RANKL and the RANKL decoy receptor osteoprotegerin (OPG) in osteoblasts, thereby affecting osteoclast differentiation. However, not only in RANKL widely expressed in soft tissues, but osteoclasts have been noted in extraskeletal lesions. We found that cultured skin fibroblastic cells express RANKL, M-CSF, and OPG messenger (mRNA). Stimulation by 1 alpha,25 dihydroxyvitamin D3 [1,25(OH)2D3] plus dexamethasone (Dex) augmented RANKL and diminished OPG mRNA expression in fibroblastic cells and caused the formation of numerous osteoclasts in cocultures of skin fibroblastic cells with hemopoietic cells or monocytes. The osteoclasts thus formed expressed tartrate-resistant acid phosphatase (TRAP) and calcitonin (CT) receptors and formed resorption pits in cortical bone. Osteoclast formation also was stimulated (in the presence of Dex) by prostaglandin E2 (PGE2), interleukin-11 (IL-11), IL-1, tumor necrosis factor-alpha (TNF-alpha), and parathyroid hormone-related protein (PTHrP), factors which also stimulate osteoclast formation supported by osteoblasts. In addition, granulocyte-macrophage-CSF (GM-CSF), transforming growth factor-beta (TGF-beta), and OPG inhibited osteoclast formation in skin fibroblastic cell-hemopoietic cell cocultures; CT reduced only osteoclast nuclearity. Fibroblastic stromal cells from other tissues (lung, respiratory diaphragm, spleen, and tumor) also supported osteoclast formation. Thus, RANKL-positive fibroblastic cells in extraskeletal tissues can support osteoclastogenesis if osteolytic factors and osteoclast precursors are present. Such mesenchymally derived cells may play a role in pathological osteolysis and may be involved in osteoclast formation in extraskeletal tissues.