调控骨髓间充质干细胞成骨分化的Wnt/β-catenin信号通路及相关因素

背景:骨髓间充质干细胞诱导成骨而抑制成脂分化是骨质疏松症防治的关键,也是骨组织修复工程种子细胞的来源,Wnt信号通路对骨形成起着重要作用.目的:综述Wnt/β-catenin信号通路调控骨髓间充质干细胞成骨分化的相关因素及分子机制.方法:应用计算机检索CNKI、PubMed及万方医学数据库建库至2020年2月发表的相关...     

Effects of Wnt signaling on proliferation and differentiation of human mesenchymal stem cells

Mesenchymal stem cells are pluripotent cells from bone marrow, which can be differentiated into the osteogenic, chondrogenic, and adipogenic lineages in vitro and are a source of cells in bone and cartilage tissue engineering. An improvement in current tissue-engineering protocols requires more detailed insight into the molecular cues that regulate the distinct steps of osteochondral differentiation. Because Wnt signaling has been widely implicated in mesenchymal differentiation, we analyzed the role of Wnt signaling in human mesenchymal stem cell (hMSC) biology by stimulation of the pathway with lithium chloride and Wnt3A-conditioned medium. We demonstrate a role for low levels of Wnt signaling in proliferation of uncommitted hMSCs and confirm that Wnt signaling controls osteoprogenitor proliferation. On the other hand, at high Wnt levels we observed a block in adipogenic differentiation and an increase in the expression of alkaline phosphatase, suggesting a role in the initiation of osteogenesis. The results of this study suggest that bone tissue engineering could benefit from the activation of critical levels of Wnt signaling at defined stages of differentiation. Moreover, our data suggest that hMSCs provide a valid in vitro model to study the role of Wnt signaling in mesenchymal biology.     

Mediation of osteogenic differentiation of human mesenchymal stem cells on titanium surfaces by a Wnt-integrin feedback loop

Peri-implant bone formation depends on the ability of mesenchymal cells to colonize the implant surface and differentiate into osteoblasts. Human mesenchymal stem cells (HMSCs) undergo osteoblastic differentiation on microstructured titanium (Ti) surfaces in the absence of exogenous factors, but the mechanisms are unknown. Wnt proteins are associated with an osteoblast phenotype, but how Wnt signaling regulates HMSC differentiation on microstructured Ti surfaces is not known. HMSCs were cultured on tissue culture polystyrene or Ti (PT [Sa = 0.33 μm, θ = 96°], SLA [Sa = 2.5 μm, θ = 132°], modSLA [hydrophilic-SLA]). Expression of calcium-dependent Wnt ligand WNT5A increased and canonical Wnt pathway ligands decreased on microstructured Ti in a time-dependent manner. Treatment of HMSCs with canonical ligand Wnt3a preserved the mesenchymal phenotype on smooth surfaces. Treatment with Wnt5a increased osteoblastic differentiation. Expression of integrins ITGA1, ITGA2, and ITGAV increased over time and correlated with increased WNT5A expression. Treatment of HMSCs with Wnt5a, but not Wnt3a, increased integrin expression. Regulation of integrin expression due to surface roughness and energy was ablated in WNT5A-knockdown HMSCs. This indicates that surface properties regulate stem cell fate and induce osteoblast differentiation via the Wnt calcium-dependent pathway. Wnt5a enhances osteogenesis through a positive feedback with integrins and local factor regulation, particularly though BMP signaling.     

经典Wnt信号通路对细胞成骨分化的调控作用

Wnt信号通路是参与体内多种器官发育和组织新陈代谢的保守性通路,可分为经典和非经典Wnt信号通路.其中,经典Wnt信号通路通过调节下游的成骨相关转录因子调控细胞成骨分化、骨基质形成和矿化,且在细胞分化的不同阶段发挥不同的调控作用.此外,经典Wnt信号通路还调控牙周组织干细胞成骨分化,该作用受外界微环境的影响.加深对经典Wnt信号通路的认识有助于治疗相关的骨疾病.     

Hedgehog signaling alters adipocyte maturation of human mesenchymal stem cells

Human stem cells are powerful tools by which to investigate molecular mechanisms of cell growth and differentiation under normal and pathological conditions. Hedgehog signaling, the dysregulation of which causes several pathologies, such as congenital defects and cancer, is involved in several cell differentiation processes and interferes with adipocyte differentiation of rodent cells. The present study was aimed at investigating the effect of Hedgehog pathway modulation on adipocyte phenotype using different sources of human mesenchymal cells, such as bone marrow stromal cells and human multipotent adipose-derived stem cells. We bring evidence that Hedgehog signaling decreases during human adipocyte differentiation. Inhibition of this pathway is not sufficient to trigger adipogenesis, but activation of Hedgehog pathway alters adipocyte morphology as well as insulin sensitivity. Analysis of glycerol-3-phosphate dehydrogenase activity and expression of adipocyte marker genes indicate that activation of Hedgehog signaling by purmorphamine impairs adipogenesis. In sharp contrast to reports in rodent cells, the maturation process, but not the early steps of human mesenchymal stem cell differentiation, is affected by Hedgehog activation. Hedgehog interferes with adipocyte differentiation by targeting CCAAT enhancer-binding protein alpha and peroxisome proliferator-activated receptor (PPAR) gamma2 expression, whereas PPARgamma1 level remains unaffected. Although Hedgehog pathway stimulation does not modify the total number of adipocytes, adipogenesis appears dramatically impaired, with reduced lipid accumulation, a decrease in adipocyte-specific markers, and acquisition of an insulin-resistant phenotype. This study indicates that a decrease in Hedgehog signaling is necessary but not sufficient to trigger adipocyte differentiation and unveils a striking difference in the adipocyte differentiation process between rodent and human mesenchymal stem cells.     

山羊骨髓间充质干细胞的分离培养及鉴定

目的分离培养山羊的问充质干细胞，并为其在骨组织工程研究中的应用奠定基础。方法应用常规的密度梯度离心法结合贴壁培养法从山羊骨髓中分离间充质干细胞，并通过观察分离培养细胞的形态，检测其表面的CD分子表达，以及RT—PCR和免疫组化病理染色方法证实成骨、成软骨、成脂肪多方向分化潜能来对细胞进行鉴定。结果分离的细胞具有成纤维细胞样形态，第三代细胞的表面分子CD29和CD44阳性率为98．70％、99．54％，而CD62L和CD45阳性率为1．10％和0．73％。RT-PCR和免疫组化病理染色证实分离细胞具有成骨、成软骨、成脂肪多方向分化潜能。结论成功地分离培养山羊的骨髓间充质干细胞，使山羊间充质干细胞应用于骨组织工程的研究成为可能。     

杜仲醇提取物诱导骨髓间充质干细胞成骨分化中的Wnt信号途径

背景：近年来,中药及中药有效部分对骨质疏松的干预和治疗作用的报道较多,但涉及细胞成骨分化调控的信号途径的报道较少。 目的：观察杜仲诱导大鼠骨髓间充质干细胞成骨分化过程中Wnt信号途径相关基因表达的变化。 方法：将第3代SD大鼠骨髓间充质干细胞,接种到6孔培养板中,每孔1×103个细胞,24 h后更换诱导培养基(含体积分数为7.5%胎牛血清的DMEM/F12(1∶1)加1/1 000浓度的杜仲醇提取物)。阴性对照组仍为正常培养基培养。诱导8 h,1 d,3 d和7 d时采用RT-qPCR法测定Wnt信号途径中Fzd和LRP受体系列、β-catenin、核内Wnt调控靶基因系列及Wnt抑制因子(WIF1)等表达变化。 结果与结论：与阴性对照组比较,诱导3 d后Fzd2表达升高11.86倍,Fzd3升高达到2倍;诱导7 d后,Fzd2表达升高5.12倍,Fzd3恢复到正常水平;β-catenin 在诱导3 d时表达升高达2倍;WIF1在诱导3 d和7 d后表达显著下降。结果提示Wnt信号途径可能参与了杜仲促骨髓间充质干细胞成骨分化过程。     

骨髓间充质干细胞诱导分化为肝细胞的方法及机制研究与进展

BACKGROUND:A number of studies have shown that there are many inducible methods by which bone marrow mesenchymal stem cells can differentiate into hepatocytes, but the specific molecular mechanism is unclear yet. OBJECTIVE:To review the programs and underlying mechanisms by which bone marrow mesenchymal stem cells differentiate into hepatocytes. METHODS:A computer-based online search of CNKI, VIP, WanFang and PubMed databases was performed to retrieve articles about directional differentiation of bone marrow mesenchymal stem cells into hepatocytes published between 2004 and 2015. The key words were “hepatocyte (-like) cells, bone marrow mesenchymal stem cells, differentiation” in Chinese and English, respectively. Finally, 62 articles were included in result analysis. RESULTS AND CONCLUSION:There are many programs for hepatic differentiation of bone marrow mesenchymal stem cells, but the specific molecular mechanism is still unclear. Many studies mainly focus on Notch signaling pathway, Wnt/β-catenin signaling pathway, P38 signal pathway, miR-122 and effect of calcium ions. Bone marrow mesenchymal stem cells that can be induced to differentiate into mature hepatocytes provide an ideal cellular source for hepatocyte transplantation and artificial liver, which is proposed to be a new strategy for clinical treatment of end-stage liver disease.     

低氧培养对间充质干细胞生物学的影响

背景：氧参与细胞内ATP的合成以供细胞代谢,氧浓度也是调节细胞生理功能的重要因素。骨髓间充质干细胞的生理病理活动是在低氧状态下进行,其发生机制还不完全清楚。 目的：回顾分析低氧培养对间充质干细胞生物学的影响的研究进展。 方法：应用计算机检索1997-01/2011-10 PubMed 数据库相关文章,检索词为“mesenchymal stem cells,hypoxia,HIF”;同时检索同期万方数据库、维普资讯网数据库和中国知网数据库相关文章,检索词“间充质干细胞,低氧培养,缺氧诱导因子”,共检索到文献1 120篇,最终纳入符合标准的文献48篇进行分析。 结果与结论：低氧预处理的骨髓间充质干细胞凋亡率将降低,其作用机制是通过上调血管内皮生长因子表达、抑制p53凋亡信号的表达以及促进抗凋亡蛋白Bcl-2的高表达来降低细胞凋亡。低氧下骨髓间充质干细胞通过抑制WNT信号通路和骨形态发生蛋白信号通路等通路,增加损伤组织的增殖能力;缺氧组织可诱导间充质干细胞迁移至缺氧区域,参与此过程的主要信号通路包括：血管内皮生长因子信号通路、基质细胞衍生因子1信号通路以及c-Met信号通路;低氧可提高间充质干细胞的黏附性,主要通过诱导细胞骨架蛋白以及细胞间黏附分子的高表达而实现;缺氧下间充质细胞增加Angiopoietin-1和血管内皮生长因子等因子的表达来促进细胞分化。     

成骨信号通路在非创伤性股骨头坏死中的作用

文题释义： 非创伤性股骨头坏死：是一种由多种非创伤因素引起的股骨头血液供应中断或受损,导致成骨细胞和骨细胞的凋亡,骨髓干细胞、骨细胞、脂肪细胞的增殖代谢紊乱,进而出现股骨头局部骨质变性、坏死,骨小梁断裂,最终导致股骨头塌陷和髋关节功能障碍的疾病,目前其发病机制仍不明确,是在国内外常见且尚未解决的难治性骨代谢性疾病之一。 Wnt/β-catenin信号通路：广泛存在于多细胞动物中,是一条在物种进化中高度保守的信号通路,因为有β-catenin参与信号转导故又被称为经典Wnt通路。其构成主要包括：细胞外因子、卷曲蛋白、胞质蛋白、低密度脂蛋白受体相关蛋白5/6、糖原合成酶激酶3β、T细胞因子/淋巴增强因子等。 背景：近年来非创伤股骨头坏死的发病率逐年增高,具有起病隐秘、病情发展迅速、致残率高的特点,给患者及其家庭乃至社会带来极大的负担。若能明确其发病机制,对非创伤股骨头坏死的早期有效治疗有重要意义。 目的：综述国内外相关文献,总结成骨信号通路在非创伤性股骨头坏死发病机制中的研究进展。 方法：以“非创伤性股骨头坏死,成骨,信号通路,发病机制”或“non-traumatic osteonecrosis of femoral head,Osteogenesis,Signaling pathways,pathogenesis,Wnt/β-catenin,PPARγ,TGF-β/Smad,PI3K/AKT,MAPK,Notch”等作为检索词,检索PubMed、Embase、Medline、中国知网、万方、维普等数据库中有关非创伤性股骨头坏死相关成骨信号通路机制及应用的研究文献。 结果与结论：近年来,成骨信号通路在非创伤性股骨头坏死中的作用日益受到重视,非创伤性股骨头坏死发生发展中骨髓间充质干细胞的异常分化亦成为研究的焦点。成骨信号通路转导异常造成的骨髓间充质干细胞异常分化、成骨分化抑制、骨质破坏增加、骨代谢平衡破坏,可能是导致非创伤性股骨头坏死的主要原因。将Wnt/β-catenin、PPARγ、TGF-β/Smad、PI3K/AKT、MAPK、Notch等成骨信号通路作为干预非创伤性股骨头坏死的治疗靶点或许是一种可行的办法,尽管目前已有大量体外及动物实验研究证实成骨信号通路可能具有调控骨髓间充质干细胞分化并逆转股骨头坏死的潜能,但其具体的作用机制尚未明确,且目前相关临床应用研究仍较少,故探索成骨信号通路的作用机制、加快临床的应用研究将是未来研究的方向。 ORCID: 0000-0001-7591-6337(许灿宏) 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

Spry1在miR-21调控人骨髓间充质干细胞成骨分化中的作用

背景：前期研究发现,miR-21在骨髓间充质干细胞成骨分化中表达上升,但是miR-21在骨髓间充质干细胞成骨分化中的作用及分子机制尚不明确。 目的：验证miR-21的靶基因Spry1,探明Spry1在人骨髓间充质干细胞成骨分化中的作用。 方法：荧光素酶报告验证miR-21靶基因Spry1,Western Blot检测Spry1在人骨髓间充质干细胞成骨过程的表达。构建Spry1慢病毒表达载体,感染人骨髓间充质干细胞。碱性磷酸酶、茜素红染色、RT-PCR和Western Blot分析Spry1高表达后人骨髓间充质干细胞成骨能力的改变。 结果与结论：荧光素酶报告提示Spry1为miR-21的靶基因,在人骨髓间充质干细胞成骨过程中表达量下降。上调Spry1能够抑制人骨髓间充质干细胞的成骨分化。结果表明Spry1作为miR-21的靶基因负向调控人骨髓间充质干细胞的成骨分化,在骨形成过程发挥着重要作用。中国组织工程研究杂志出版内容重点：干细胞;骨髓干细胞;造血干细胞;脂肪干细胞;肿瘤干细胞;胚胎干细胞;脐带脐血干细胞;干细胞诱导;干细胞分化;组织工程全文链接：     

果糖和二硫苏糖醇对骨髓间充质干细胞冻存后活性及多能性的影响

背景:冻存是保证干细胞临床应用的关键步骤之一,但现有冻存技术常导致细胞活性降低、多能性丧失及分化能力下降。目的:探究果糖及二硫苏糖醇是否有助于维持冻存后骨髓间充质干细胞多能性及成骨分化潜能。方法:分离培养SD大鼠骨髓间充质干细胞,在细胞冻存前分别用果糖(200μmol/L),二硫苏糖醇(500μmol/L)μmol/L)及果糖(200μmol/L)+二硫苏糖醇(500预处理1 h。冻存6个月后,复苏细胞并用倒置显微镜观察细胞形态,MTT实验检测细胞活性,定量PCR检测相关干性基因(Nanog,Oct4及Sox2)的表达,碱性磷酸酶活性测试及茜素红染色检测复苏骨髓间充质干细胞成骨分化能力。结果与结论:(1)复苏后各组细胞在形态上无明显差别;(2)果糖预处理及联合预处理有助于骨髓间充质干细胞活性维持;(3)二硫苏糖醇预处理可显著促进骨髓间充质干细胞多能性相关基因Nanog及Sox2的表达;(4)果糖、二硫苏糖醇及联合预处理皆有助于维持骨髓间充质干细胞成骨分化潜能,但以二硫苏糖醇及联合预处理组效果最佳;(5)结果表明,果糖预处理有助于维持冻存骨髓间充质干细胞活性,二硫苏糖醇有助于维持冻存骨髓间充质干细胞多能性及成骨分化能力。     

骨髓间充质干细胞成骨分化中的微小RNA及Wnt通路

背景：有差异性表达的微小RNA在成骨细胞的增殖和分化中发挥广泛而又重要的作用,但其作用机制、作用靶点还不甚清楚,是近年来的研究热点。 目的：对微小RNA通过Wnt信号通路调节成骨分化方面的研究现状及新进展作一综述。 方法：应用计算机检索2000年1月至2012年1月CNKI和PubMed数据库,在标题和摘要中以“MicroRNA,Wnt通路,成骨分化”或“MicroRNA,Wnt pathway,osteogenesis”为检索词进行检索。选择文章内容与微小RNA经典Wnt通路促进成骨分化有关者,同一领域文献则选择近期发表或发表在权威杂志的文章。初检得到205篇文献,最终选择33篇文献进行综述。 结果与结论：微小RNA是近年来生命科学的研究热点,越来越多的研究表明微小RNA作用于经典Wnt信号通路在成骨分化过程中发挥了重要作用。了解微小RNA在成骨分化中的调控机制是骨组织工程化培养的基础,具有巨大的应用前景。目前关于微小RNA的研究工作还处于起步阶段。     

Wnt/β- catenin信号介导脐带间充质干细胞修复糖尿病创面的应用前景

糖尿病并发创面致病机制复杂,缺乏有效治疗措施。间充质干细胞(MSC)具有促进创面愈合的作用,与骨髓MSC比较,脐带来源的MSC生物学特性优势明显。Wnt是干细胞转归和皮肤再生的强效调节信号分子,而糖尿病创面Wnt信号通路功能低下。Wnt/β- catenin信号介导脐带MSC修复糖尿病创面有潜在的临床应用前景,本文综述了这方面的研究现状及存在问题。     

A Novel Semisynthetic Molecule Icaritin Stimulates Osteogenic Differentiation and Inhibits Adipogenesis of Mesenchymal Stem Cells

Background We previously reported that the constitutional flavonoid glycosides derived from herb Epimedium (EF, composed of seven flavonoid compounds with common nuclear stem) exerted beneficial effects on the bone, including promoting bone formation and inhibiting bone marrow fat deposition. Recent in vivo study showed that Icaritin was a common metabolite of these constitutional flavonoid glycosides, indicating that Icaritin is a bioactive compound. The present study was designed to investigate whether Icaritin could promote osteogenic differentiation and suppress adipogenic differentiation of marrow mesenchymal stem cells (MSCs).Methods Primary MSCs were harvested from adult mice and exposed to Icaritin to evaluate whether it could promote osteogenesis and suppress adipogenesis using the following assays: determination of alkaline phosphatase (ALP) activity and mineralization; mRNA expression of osteogenic differentiation marker Runx2; osteocalcin and bone sialoprotein (BSP) by RT-PCR; quantification of adipocyte-like cells by Oil Red O staining assay and mRNA expression for adipogenic differentiation markers peroxisome proliferator-activated receptor gamma (PPARγ); adipocyte fatty acid binding protein (aP2) and lipoprotein lipase (LPL) by RT-PCR. For the underlying mechanism, glycogen synthase kinase-3beta (GSK3β) and β-catenin were also explored by western blotting.Results Icaritin promoted osteogenic differentiation and maturation of MSCs as indicated by increased mRNA expression for Runx2, osteocalcin and BSP, and enhanced ALP activity and mineralization; Icaritin inhibited adipogenic differentiation, as indicated by decreased mRNA expression for PPARγ, LPL, aP2, and suppressed formation of adipocyte-like cells; Icaritin inactivated GSK3β and suppressed PPARγ expression when promoting osteogenesis and suppressing adipogenesis of MSCs.Conclusion This was the first study demonstrating that the novel semisynthetic molecule Icaritin could stimulate osteogenic differentiation and inhibit adipogenesis of MSCs, which was associated with the suppression of GSK3β and PPARγ.     

Wnt10b Promotes Differentiation of Mouse Hair Follicle Melanocytes

Previous research has revealed that Wnt10b activates canonical Wnt signaling, which is integral to melanocyte differentiation in hair follicles (HFs). However, the function of Wnt10b in HF melanocytes remains poorly understood. We determined using Dct-LacZ transgenic mice that Wnt10b is mainly expressed near and within melanocytes of the hair bulbs during the anagen stage of the hair cycle. We also found that Wnt10b promotes an increase in melanocyte maturation and pigmentation in the hair bulbs of the mouse HF. To further explore the potential functions of Wnt10b in mouse HF melanocytes, we infected iMC23 cells with Ad-Wnt10b to overexpress Wnt10b. We demonstrated that Wnt10b promotes the differentiation of melanocytes by activating canonical Wnt signaling in melanocytes.     

3种不同来源CD146阳性间充质干细胞亚群的生物学特性比较

目的比较脐带间充质干细胞(UCMSCs)、脂肪间充质干细胞(AMSCs)以及骨髓间充质干细胞(BM-MSCs)中CD146^+细胞亚群的生物学特性。方法用磁珠分选法分选不同组织来源的间充质干细胞,获得高纯度CD146^+亚群;用流式细胞计量术分析表型;透射电子显微镜观察细胞结构;成脂诱导分化后油红O染色;RT-qPCR检测成脂相关基因LPL、C/EBPα和PPARγ表达;成骨诱导分化后ALP染色,检测成骨相关基因ALP、OPN和RUNX2表达;检测细胞干性基因及血管生成相关基因表达;检测细胞体外成管能力。结果3种组织来源CD146^+MSCs具有相似的形态,表达除CD106外相似的细胞表面标志分子。与其他两种细胞比较,CD146^+AMSCs表达更高的干性基因OCT-4、SOX2和NANOG。在相同的诱导时间,CD146^+UCMSCs成脂和成骨能力较其他两种来源的CD146^+MSCs弱。3种组织来源的CD146^+MSCs均可表达血管内皮相关刺激因子BFGF、VEGF、Ang-1和EGF,但CD146^+BM-MSCs具有更强的体外成管能力。结论3种不同来源的CD146^+MSC具有不同的生物学特性,为进一步研究不同组织来源的间充质干细胞的特定应用提供了基础。     

Loss of β-catenin triggers oxidative stress and impairs hematopoietic regeneration

Accidental or deliberate ionizing radiation exposure can be fatal due to widespread hematopoietic destruction. However, little is known about either the course of injury or the molecular pathways that regulate the subsequent regenerative response. Here we show that the Wnt signaling pathway is critically important for regeneration after radiation-induced injury. Using Wnt reporter mice, we show that radiation triggers activation of Wnt signaling in hematopoietic stem and progenitor cells. β-Catenin-deficient mice, which lack the ability to activate canonical Wnt signaling, exhibited impaired hematopoietic stem cell regeneration and bone marrow recovery after radiation. We found that, as part of the mechanism, hematopoietic stem cells lacking β-catenin fail to suppress the generation of reactive oxygen species and cannot resolve DNA double-strand breaks after radiation. Consistent with the impaired response to radiation, β-catenin-deficient mice are also unable to recover effectively after chemotherapy. Collectively, these data indicate that regenerative responses to distinct hematopoietic injuries share a genetic dependence on β-catenin and raise the possibility that modulation of Wnt signaling may be a path to improving bone marrow recovery after damage.     

Disparate mesenchyme-lineage tendencies in mesenchymal stem cells from human bone marrow and umbilical cord blood

Bone marrow and umbilical cord blood are reported to be the main sources of mesenchymal stem cells (MSCs), which have been proposed for many clinical applications. This study evaluated and quantitated the differentiation potential of bone marrow-derived MSCs (bmMSCs) and cord blood-derived MSCs (cbMSCs) by in vitro induction. Results indicated that cbMSCs had a significantly stronger osteogenic potential but lower capacity for adipogenic differentiation than bmMSCs. Leptin, an important regulator of mesenchymal differentiation, has a significantly stronger effect of promoting osteogenesis and inhibiting adipogenesis in bmMSCs than in cbMSCs. Moreover, Cbfa1 mRNA expression in bmMSCs and cbMSCs was affected to different degrees by leptin during osteogenesis. In contrast, leptin reduced PPARgamma2 mRNA expression to the same level during adipogenesis in both types of MSCs. These results demonstrate the disparate capacities of MSCs from bone marrow and cord blood and suggest that they be used differently in experimental and therapeutic studies. In addition, the disparate differentiation tendencies of MSCs from different sources should be considered in further applications.