益气化瘀方减轻HIF-1α条件性基因敲除小鼠膝关节软骨退变的研究

目的:观察低氧诱导因子-1α(HIF-1α)条件性基因敲除(HIF-1αcKO)小鼠膝关节软骨退变情况,以及中药复方益气化瘀方对减缓HIF-1αcKO小鼠椎间盘软骨退变的作用。方法:①将杂交繁殖获得同窝的HIF-1α+/+小鼠和HIF-1α-/-小鼠,分为HIF-1α+/+小鼠4月龄组、HIF-1α-/-小鼠4月龄组,HIF-1α+/+小鼠6月龄组、HIF-1α-/-小鼠6月龄组,每组3只。在4、6月龄依次处死相应的小鼠,取膝关节软骨,分别进行Mankin评分、藏红固绿、HE及免疫组化相关指标染色及分析,研究软骨组织的改变情况。②将2月龄HIF-1α-/-小鼠随机分为生理盐水组和益气化瘀方组,以生理盐水组小鼠作为正常对照,每组6只,共12只。灌胃给药2个月后,取各组小鼠的膝关节,分别进行Mankin评分、HE染色和藏红固绿染色,ColⅡ、ColX、VEGF、MMP-13和Sox9免疫组化染色及分析。结果:①HIF-1α-/-小鼠4月龄组膝关节软骨组织出现破损和骨化,细胞分布不均匀,软骨细胞减少。HIF-1α-/-小鼠6月龄组膝关节软骨损伤更加严重。HIF-1α-/-小鼠4月龄组椎间盘软骨中Ⅱ型胶原(ColⅡ)和Sox9表达降低,X型胶原(ColX)、基质金属蛋白酶-13(MMP-13)、VEGF蛋白表达增加。HIF-1α-/-小鼠6月龄组ColⅡ蛋白与Sox9表达进一步降低,ColX、MMP13、VEGF蛋白表达进一步上升。②与生理盐水组比较,益气化瘀方干预后膝关节软骨部位的骨化和缺损减轻,软骨细胞分布较均匀,细胞总数增加。免疫组化染色显示,益气化瘀方组ColⅡ和Sox9蛋白的表达升高,ColX、VEGF、MMP-13蛋白表达减少。结论:HIF-1α基因敲除小鼠出现了膝关节软骨退变,并且这种退变随着小鼠增龄而加重;益气化瘀方可以减轻HIF-1α基因敲除小鼠的膝关节软骨退变。     

低氧诱导因子1α调控骨代谢和骨微环境血管生成的研究进展

骨微环境血管生成能力的衰退是造成老年性骨质疏松的重要原因之一。老年化导致的骨血管生成能力下降致使骨形成能力减弱,导致骨量流失并诱发骨质疏松。在骨微环境中,骨血管生成能够促进成骨细胞分化,增强骨形成。而成骨细胞则通过分泌VEGF以及FGF2等血管生成因子促进血管内皮细胞的增殖及分化,进而促进骨血管生成。低氧诱导因子1α(HIF-1α)广泛参与骨代谢及血管生成等多个生理过程的调控,且参与骨形成及骨血管生成偶联的调控,在骨血管生成的调控中有着举足轻重的作用。本文主要综述HIF-1α在骨代谢和骨微环境血管生成中的作用机制,为骨血管生成防治骨质疏松的机制研究及骨相关疾病的靶向治疗提供理论基础及研究思路。     

条件性敲除Osterix基因获得先天性脊柱侧凸小鼠动物模型及表型分析

目的 通过Osterix基因敲除获得先天性脊柱侧凸动物模型及表型分析.方法 应用Cre-LoxP系统繁育成骨细胞特异性敲除Osterix基因小鼠.取4、12周龄的敲除小鼠各10只,以同龄同系野生型小鼠各10只为对照,行全身及脊柱X线摄像观察;收集脊柱标本行苏木素-伊红(HE)染色及抗酒石酸酸性磷酸酶(TRAP)染色观察并检测.结果 成功获得成骨细胞特异性敲除Osterix基因小鼠,X线显示敲除小鼠中75％出现严重的脊柱侧凸,Cobb角平均值为35..HE染色显示敲除小鼠椎体生长板增宽,椎体骨量增加,TRAP染色显示腰椎中破骨细胞数量显著减少(P＜0.05).结论 小鼠成骨细胞中条件性敲除Osterix基因后成功获得先天性脊柱侧凸模型,提示Osterix在先天性脊柱侧凸的发病中有重要作用.     

门静脉高压症大鼠断流术后胃黏膜缺氧诱导因子-1α和血管内皮生长因子的表达

目的 观察缺氧诱导因子-1α（HIF-1α）和血管内皮生长因子（VEGF）在断流术前后肝前性门静脉高压症（PHPH）大鼠胃黏膜的表达，探讨HIF-1α和VEGF在门静脉高压胃病（PHG）的发生发展的作用。方法 取Wistar大鼠制备PHPH模型80只，设假手术组（SO）60只，在术后3周施断流术。检测HIF-1α、VEGF和CD34在大鼠胃壁组织中的表达。结果 断流术前PHPH组大鼠胃壁中HIF-1α（5．8±1．3）和VEGF（12．0±3．0）的表达均明显高于SO组[HIF-1α（0．03750±0．05175），VEGF（0．7±0．1），P〈0．01]。术后HIF-1α、VEGF和MVD均有升高趋势。结论 HIF-1α和VEGF可能参与了PHG的发生发展，断流术本身能通过某种机制影响HIF-1α和VEGF的表达，加重PHG。     

低氧诱导因子-α信号通路与骨形成

 在组织细胞缺血、缺氧状态下表达的低氧诱导因子（Hypoxia-inducible factor-α,HIF-α）是诱导低氧基因和维持细胞内氧环境稳定的核心转录因子,参与调控血管生成、炎性细胞及干细胞归巢、细胞分化、糖代谢等众多生理病理反应。机体内多数组织器官在生理条件下都维持20%左右的氧分压,而骨骼及骨髓腔却处于低氧状态,氧分压只有1%~7%,因此骨骼内的多种细胞,如成骨细胞、骨细胞等在生理状态下都表达HIF-α。近年来的研究表明,HIF-α信号通路对骨发育及骨重塑均有至关重要的作用。通过对骨形成、血管形成的影响,HIF-α信号通路能够调控骨发育时的骨量;在骨折愈合时,HIF-α信号通路也存在着时空上的特异性改变,从而成为骨折愈合的必要条件。鉴于HIF-α信号通路的重要作用,很多学者都致力于研究通过调控HIF-α信号通路促进骨折愈合及骨缺损的修复。局部应用低氧信号通路激活剂,或者移植过表达HIF-α的间质干细胞对骨折、骨缺损的愈合有一定的促进作用。另一方面,在动物模型上全身应用低氧信号通路激活剂对雌激素缺乏性骨质疏松、老年性骨质疏松具有一定的防治作用。本文就HIF-α信号通路对骨发育、骨重塑的作用,调控HIF-α信号通路在骨折、骨缺损愈合及骨质疏松防治方面的应用进行综述。     

二至丸促进围绝经期妇女成骨细胞增殖的分子机制

目的观察二至丸对围绝经期妇女成骨细胞分化过程的影响,并探讨其可能的分子机制。方法随机收集临床不同年龄段符合纳入标准的围绝经期妇女松质骨,分为绝经前骨量正常组、绝经前骨量减少组、绝经后骨量正常组、绝经后骨质疏松组,分离培养体外成骨细胞,对二至丸干预前后成骨细胞的增殖分化,采用MTT法检测各组细胞增殖能力,比色法测AKP,ELISA法检测BMP-2和OCN表达,实时荧光定量PCR-SYBR GREEN法检测核心结合因子BMP-2mRNA、ER-αmRNA、OCNmRNA的表达。结果二至丸干预后,各组成骨细胞增殖能力、AKP、BMP-2和OCN的表达量及BMP-2mRNA、OCNmRNA和ER-αmRNA的表达量总体由高到低依次为绝经前骨量正常组、绝经后骨量正常组、绝经前骨量减少组、绝经后骨质疏松组,且均较同组干预前显著上升,差异有统计学意义(P0.05)。结论二至丸能在一定程度上促进成骨细胞增殖分化,对防治骨质疏松起到积极作用。     

去骨瓣减压术对大鼠缺血缺氧性脑损伤后缺氧诱导因子-1α、血管内皮生长因子表达的影响

缺氧诱导因子-1(HIF-1)是缺氧条件下广泛存在于哺乳动物和人体内的一种转录因子,它通过对下游靶基因的调控,使细胞对缺氧产生适应性反应[1].有研究结果显示,脑组织缺血缺氧可导致脑缺血半暗带HIF-1α的表达增加,并诱导血管内皮生长因子(VEGF)过量表达,刺激血管新生,改善局部血供,减轻缺血后的脑损伤[2]1.本研究旨在观察去骨瓣减压术对局灶性脑缺血大鼠梗死灶周HIF-1α、VEGF表达的影响,探讨该手术脑保护作用的可能机制.     

不同发育阶段Fmr1基因敲除小鼠睾丸组织iNOS的变化

目的:对不同周龄的Fmr1(fragile X mental retardation 1)基因敲除和野生型雄性小鼠睾丸组织诱导型一氧化氮合酶(inducible nitric oxide synthase,iNOS)的表达进行分析比较,探讨Fmr1基因敲除小鼠睾丸组织中iNOS表达的差异,为脆性X综合征的研究提供背景资料。方法:不同周龄(4、6、8、10周)的Fmr1基因敲除型和野生型雄性小鼠各6只,先采用PCR技术对基因敲除和野生型小鼠进行基因型鉴定,之后所有小鼠麻醉取睾丸组织,采用石蜡包埋切片免疫组化染色技术对基因敲除和野生型小鼠睾丸iNOS的表达进行检测并作对比分析。结果:iNOS在4周野生型小鼠睾丸间质细胞呈弱阳性表达,在6周小鼠呈阳性表达,在8周和10周小鼠呈强阳性表达,且基因敲除小鼠睾丸的iNOS表达均弱于野生型小鼠。结论:Fmr1基因敲除小鼠在缺失FMR1蛋白(FMRP)后的睾丸组织中iNOS的表达降低。     

柚皮苷通过HIF-1α/VEGF信号促进H型血管抗骨质疏松的研究

目的 观察柚皮苷对去卵巢骨质疏松大鼠骨组织HIF-1α/VEGF信号通路和H型血管形成的影响,探讨柚皮苷防治骨质疏松症的作用机制。方法 建立去卵巢骨质疏松大鼠模型（随机将36只大鼠分为去卵巢组、假手术组和柚皮苷治疗组）。柚皮苷治疗３个月后,检测血清和骨髓上清骨代谢指标和HIF-1α/VEGF信号通路变化,检测骨密度(bone mineral density, BMD)、骨微结构及H型血管变化。结果 柚皮苷治疗组大鼠血清中成骨代谢指标[骨特异性碱性磷酸酶(BALP)、骨钙素(BGP)、I型原胶原分子N 端前肽(PINP)]升高;而骨吸收标志物血清C端交联肽（CTX）降低;HIF-1α在血清和骨髓上清中表达均升高;VEGF在骨髓上清中表达升高,而血清中无明显改变;BMD和Micro-CT结果显示柚皮苷治疗组大鼠骨密度和骨量增加;同时股骨近端H型血管表达升高。结论 柚皮苷可以调节骨代谢,改善骨质疏松大鼠骨密度,发挥抗骨质疏松作用,其作用机制可能是通过调节HIF-1α/VEGF信号通路、促进H型血管形成来实现的。     

低氧诱导因子-1α参与骨发育及骨代谢调控的研究进展

低氧诱导因子-lα( hypoxia inducible factor-1α,HIF-1α)是组织细胞在低氧状态下激活相应基因转录的核心调节因子之一,在骨发育和代谢过程中起到非常重要的作用。通过敲除Vhl基因高表达HIF-1α可以促进血管和骨组织的生成,但这一过程的分子机制依然不明确。目前巳知HIF-1α在骨的发育过程中可以调节多种蛋白因子和信号通路,如血管内皮生长因子 (vascular endothelial growth factor,VEGF)和经典Wnt信号通路,而这些蛋白因子和信号通路大多能对细胞的分化、增殖及功能进行调节。本文综述骨组织发育和代谢过程中HIF-1α、Wnt信号通路、骨保护素(osteoprotegerin,OPG)等所起的作用以及它们之间的联系,从而进一步探讨HIF-1α在骨发育及骨代谢调控中的机制。     

Sex‐Dependent,Osteoblast Stage‐Specific Effects of Progesterone Receptor on Bone Acquisition

The role of the progesterone receptor (PR) in the regulation of sexual dimorphism in bone has yet to be determined. Here we utilized genetic fate mapping and Western blotting to demonstrate age‐dependent PR expression in the mouse femoral metaphysis and diaphysis. To define sex‐dependent and osteoblast stage–specific effects of PR on bone acquisition, we selectively deleted PR at different stages of osteoblast differentiation. We found that when Prx1‐Cre mice were crossed with PR floxed mice to generate a mesenchymal stem cell (MSC) conditional KO model (Prx1; PRcKO), the mutant mice developed greater trabecular bone volume with higher mineral apposition rate and bone formation. This may be explained by increased number of MSCs and greater osteogenic potential, particularly in males. Age‐related trabecular bone loss was similar between the Prx1; PRcKO mice and their WT littermates in both sexes. Hormone deficiency during the period of rapid bone growth induced rapid trabecular bone loss in both the WT and the Prx1; PRcKO mice in both sexes. No differences in trabecular bone mass was observed when PR was deleted in mature osteoblasts using osteocalcin‐Cre (Bglap‐Cre). Also, there were no differences in cortical bone mass in all three PRcKO mice. In conclusion, PR inactivation in early osteoprogenitor cells but not in mature osteoblasts influenced trabecular bone accrual in a sex‐dependent manner. PR deletion in osteoblast lineage cells did not affect cortical bone mass. © 2017 American Society for Bone and Mineral Research.     

Transgenic mice overexpressing macrophage migration inhibitory factor (MIF) exhibit high-turnover osteoporosis.

The bone phenotype of mice overexpressing MIF was studied. These mice showed decreased trabecular bone, increased bone formation rate, and increased MMP-3, -9, and -13 mRNA expression in the femora and tibias. This model provides evidence of the role played by MIF in bone remodeling and balance in vivo. INTRODUCTION: The role of macrophage migration inhibitory factor (MIF) in in vivo bone remodeling remains unelucidated. We describe disordered bone metabolism in transgenic mice overexpressing MIF. MATERIALS AND METHODS: For in vivo study, muCT, bone histomorphometry, blood and urine biochemical data, and gene expression of MIF transgenic (MIF Tg) mice and littermate wildtype (WT) mice were examined. For in vitro study, osteoclastogenesis in the co-culture of bone marrow cells and osteoblasts from MIF Tg and WT were assessed. RESULTS: muCT analyses revealed a significant reduction in the trabecular bone of distal femur in MIF Tg at 8-12 weeks of age. Histomorphometric analysis revealed increase in several measures of bone formation. Osteoclastogenesis was not influenced by the origin of bone marrow cells or osteoblasts. Urine level of deoxypyridinoline/creatinine and the mRNA levels of matrix metalloproteinase (MMP) -3, -9, and -13 in femurs were elevated in MIF Tg. CONCLUSIONS: Overexpression of MIF causes high-turnover osteoporosis in mice. The increased expression of MMPs in bone was suggested, at least in part, as one cause of this phenotype, because MMPs plays important roles for bone resorption without affecting the formation of osteoclasts. This model provides evidence of the role played by MIF in bone remodeling and balance.     

Down-regulation of N-methyl D-aspartate receptor in rat-modeled disuse osteopenia

Lack of mechanical stress may result in osteoporosis; however, the underlying mechanisms of disuse osteoporosis remain unclear. It has been indicated that mechanical loading causes extracellular glutamate accumulation in osteoblasts. We hypothesized that the glutamate receptor mediation on bone cells might also be involved in mechanically stimulated osteogenesis. In this study, we investigated the changes of bone formation and the expressions of osteogenic genes and N-methyl D-aspartate (NMDA) receptors, the major glutamate receptors, in disused bones. Rat modeled disuse osteopenia in hind limbs was induced by a 3-week tail suspension in Sprague-Dawley rats. Bone mineral density and trabecular bone volume of distal femurs were measured to verify the osteopenia of disused bones. The mRNA expressions of cbfa1/Runx2, type I collagen, alkaline phosphatase (ALP) and osteocalcin (OC) in bones were measured as osteogenic markers. The influences of mechanical unloading on the expressions of NMDA receptors (NR₁ and NR₂D) in bones were also examined. The effects of NMDA mediation on osteogenesis were tested by a treatment of MK-801, a non-competitive NMDA receptor antagonist, in cultured osteoblasts and bone marrow stroma cells. Our result showed that mRNA expressions of cbfa1/Runx2, type I collagen, ALP and OC were significantly decreased in disused bones. The mRNA and protein expressions of NR₁ and NR₂D were significantly decreased in disused bones; furthermore, immunolocalization of both receptors showed decreases in osteoblasts, but not in osteoclasts. The results from the in vitro study showed that MK-801 inhibited mRNA expression of cbfa1/Runx2 in bone marrow stroma cells and also inhibited those of collagen type I, ALP and OC of osteoblasts in a dose-dependent manner. These results suggest that NMDA receptor mediation may play an important role in transmitting mechanical loading in bones, and decreases of the expressions of NMDA receptors in disused bones, especially in osteoblasts, may contribute to the decrease of osteogenesis.     

Poncirin prevents bone loss in glucocorticoid-induced osteoporosis in vivo and in vitro

Poncirin, a flavonoid isolated from the fruit of Poncirus trifoliata, possesses anti-bacterial and anti-inflammatory activities. However, the action of poncirin in bone biology is unclear. In this study, the in vivo and in vitro effects of poncirin in a glucocorticoid-induced osteoporosis (GIO) mouse model were investigated. Seven-month-old male mice were assigned to the following five groups: (1) sham-implantation (sham), (2) prednisolone 2.1?mg/kg/day (GC), (3) GC treated with 10?mg/kg/day of genistein, (4) GC treated with 3?mg/kg/day of poncirin, (5) and GC treated with 10?mg/kg/day of strontium (GC?+?SrCl(2)). After 8?weeks, bone loss was measured by microcomputed tomography. Osteocalcin (OC) and C-terminal telopeptides of type I collagen (CTX) were evaluated in sera. Runx2 protein, OC and osteoprotegerin (OPG) mRNA expression, alkaline phosphatase (ALP) activity, and mineral nodule assay were performed in C3H10T1/2 or primary bone marrow stromal cells. Poncirin significantly increased the bone mineral density and improved the microarchitecture. Poncirin increased serum OC, Runx2 protein production, expression of OC and OPG mRNA, ALP activity, and mineral nodule formation; and decreased serum CTX. These effects were more prominent in the poncirin group compared to the other positive control groups (genistein and strontium). The poncirin-mediated restoration of biochemical bone markers, increased bone mineral density, and improved trabecular microarchitecture likely reflect increased bone formation and decreased bone resorption in GIO mice.     

Exendin‐4, a Glucagon‐Like Peptide‐1 Receptor Agonist,Prevents Osteopenia by Promoting Bone Formation and Suppressing Bone Resorption in Aged Ovariectomized Rats

Osteoporosis mainly affects postmenopausal women and older men. Gastrointestinal hormones released after meal ingestion, such as glucose‐dependent insulinotropic peptide (GIP) and glucagon‐like peptide (GLP)‐2, have been shown to regulate bone turnover. However, whether GLP‐1, another important gastrointestinal hormone, and its analogues also have antiosteoporotic effects, especially in aged postmenopausal situation, has not been confirmed. In the present study, we evaluated the effects of the GLP‐1 receptor agonist exendin‐4 on ovariectomy (OVX)‐induced osteoporosis in old rats. Twelve‐month‐old female Sprague‐Dawley rats were subjected to OVX, and exendin‐4 was administrated 4 weeks after the surgery and lasted for 16 weeks. Bone characters and related serum and gene biomarkers were analyzed. Sixteen weeks of treatment with exendin‐4 slowed down body weight gain by decreasing fat mass and prevented the loss of bone mass in old OVX rats. Exendin‐4 also enhanced bone strength and prevented the deterioration of trabecular microarchitecture. Moreover, exendin‐4 decreased the urinary deoxypyridinoline (DPD)/creatinine ratio and serum C‐terminal cross‐linked telopeptides of type I collagen (CTX‐I) and increased serum alkaline phosphatase (ALP), osteocalcin (OC), and N‐terminal propeptide of type 1 procollagen (P1NP) levels, key biochemical markers of bone turnover. Interestingly, gene expression results further showed that exendin‐4 not only inhibited bone resorption by increasing the osteoprotegerin (OPG)/receptor activator of NF‐κB ligand (RANKL) ratio, but also promoted bone formation by increasing the expression of OC, Col1, Runx2, and ALP, which exhibited dual regulatory effects on bone turnover as compared with previous antiosteoporotic agents. In conclusion, these findings demonstrated for the first time the antiosteoporotic effects of exendin‐4 in old OVX rats and that it might be a potential candidate for treatment of aged postmenopausal osteoporosis.     

二甲双胍对去卵巢大鼠骨质疏松症的影响及机制研究

目的 以雌二醇为对照,观察二甲双胍(metformin, MF)对去卵巢大鼠骨密度及骨矿含量的影响,并从细胞、分子水平探究MF可能的骨保护机制。方法 将60只雌性SD大鼠随机均分4组：假手术（SHAM）组、去卵巢（OVX）组、去卵巢+二甲双胍（OVX+MF）组和去卵巢+雌二醇(OVX+E2 )组。分组灌胃给药60 d后测量大鼠右侧胫骨骨密度和骨矿含量;分离培养各组大鼠骨髓间充质干细胞（BMSCs）并诱导其向成骨细胞分化,用MTT法测定细胞活性及增殖能力;测定各组碱性磷酸酶（ALP）活性、矿化结节数目、钙含量以及I型胶原（collagen type I）、骨钙素（OC）、骨保护素 (OPG)、NFκB受体的配体 (RANKL)、白细胞介素-6（IL-6）基因表达水平。结果 与OVX组相比,OVX+MF组和OVX+E2组成骨细胞的增殖能力与ALP活性明显增强,骨密度、骨矿含量以及钙沉积量显著增加(P均<0.05),且两组collagen type I、OC、OPG mRNA的表达水平显著升高,而RANKL、IL-6mRNA表达明显受到抑制;但OVX+MF组去卵巢大鼠成骨细胞的增殖能力、ALP活性、钙沉积量、collagen type I、OC、OPG mRNA表达水平低于OVX+E2组,RANKL、IL-6mRNA表达高于OVX+E2组（P均<0.05）;与SHAM组比较,OVX+MF组的collagen type I、OC、OPG mRNA的表达水平更高（P<0.05）。结论 二甲双胍可能通过OPG/RANKL/RANK信号通路促进BMSCs向成骨细胞分化,有效逆转去卵巢大鼠骨质疏松的状态,这种潜在的骨保护作用可能会改善糖尿病引起的骨质疏松。     

Sustained RANKL response to parathyroid hormone in oncostatin M receptor-deficient osteoblasts converts anabolic treatment to a catabolic effect in vivo

Parathyroid hormone (PTH) is the only approved anabolic agent for osteoporosis treatment. It acts via osteoblasts to stimulate both osteoclast formation and bone formation, with the balance between these two activities determined by the mode of administration. Oncostatin M (OSM), a gp130‐dependent cytokine expressed by osteoblast lineage cells, has similar effects and similar gene targets in the osteoblast lineage. In this study, we investigated whether OSM might participate in anabolic effects of PTH. Microarray analysis and quantitative real‐time polymerase chain reaction (qPCR) of PTH‐treated murine stromal cells and primary calvarial osteoblasts identified significant regulation of gp130 and gp130‐dependent coreceptors and ligands, including a significant increase in OSM receptor (OSMR) expression. To determine whether OSMR signaling is required for PTH anabolic action, 6‐week‐old male Osmr^?/? mice and wild‐type (WT) littermates were treated with hPTH(1–34) for 3 weeks. In WT mice, PTH increased trabecular bone volume and trabecular thickness. In contrast, the same treatment had a catabolic effect in Osmr^?/? mice, reducing both trabecular bone volume and trabecular number. This was not explained by any alteration in the increased osteoblast formation and mineral apposition rate in response to PTH in Osmr^?/? compared with WT mice. Rather, PTH treatment doubled osteoclast surface in Osmr^?/? mice, an effect not observed in WT mice. Consistent with this finding, when osteoclast precursors were cultured in the presence of osteoblasts, more osteoclasts were formed in response to PTH when Osmr^?/? osteoblasts were used. Neither PTH1R mRNA levels nor cAMP response to PTH were modified in Osmr^?/? osteoblasts. However, RANKL induction in PTH‐treated Osmr^?/? osteoblasts was sustained at least until 24 hours after PTH exposure, an effect not observed in WT osteoblasts. These data indicate that the transient RANKL induction by intermittent PTH administration, which is associated with its anabolic action, is changed to a prolonged induction in OSMR‐deficient osteoblasts, resulting in bone destruction. © 2012 American Society for Bone and Mineral Research.     

Expression of VEGF isoforms by epiphyseal chondrocytes during low-oxygen tension is HIF-1 alpha dependent

OBJECTIVE: To establish the role of hypoxia and HIF-1 alpha for VEGF expression of murine epiphyseal chondrocytes. To analyze the effect of hypoxia on VEGF isoform expression. MATERIALS AND METHODS: VEGF mRNA and VEGF isoform expression was investigated in epiphyses of murine newborns by in situ hybridization and real-time PCR. Further, epiphyseal chondrocytes were isolated from newborn mice with homozygous flanking of the HIF-1 alpha gene with lox-P sites. HIF-1 alpha was deleted by infection with adenovirus containing cre-recombinase. After chondrocytes reached confluency they were exposed to 0.5% or 20% oxygen, respectively. Total VEGF and VEGF isoform mRNA expression levels were measured by real-time PCR. Secreted VEGF protein was determined by ELISA. RESULTS: VEGF mRNA signals were detected in the hypertrophic zone and in the center of the proliferative zone of the murine epiphysis, which is considered to be hypoxic. Real-time PCR revealed that VEGF(120)is the dominant isoform in vivo. In cultured epiphyseal chondrocytes strongly increased VEGF gene expression levels were detected after exposure to hypoxia. Furthermore, secretion of VEGF protein was significantly enhanced under 0.5% oxygen. Remarkably, functional inactivation of HIF-1 alpha abolished the hypoxic increase of VEGF expression in chondrocytes completely. Furthermore, the soluble isoforms VEGF(120)and VEGF(164)are the most abundantly expressed splice variants in chondrocytes exposed to low oxygen levels. CONCLUSIONS: The data presented here clearly indicate that hypoxia is able to induce the synthesis of soluble VEGF isoforms by epiphyseal chondrocytes, most likely through stabilization of HIF-1 alpha. Thus it can be speculated that HIF-1 alpha is an essential prerequisite for hypoxic VEGF synthesis in the epiphysis, thereby contributing to the formation and invasion of blood vessels in long bone development.