Nell-1在骨组织工程中的作用与应用

文题释义：Nel样分子Ⅰ型(Nell-1)：是与人颅缝早闭症相关的一种外分泌型蛋白,一系列研究表明Nell-1可以有效促进骨的生长。相比于其他骨生长因子,在促进骨生长方面具有特异性高、不良反应少的优点。 骨形态发生蛋白2：一种促进骨生长的蛋白,是目前唯一被美国FDA批准应用于临床的促进骨再生及修复的骨形态发生蛋白,可以有效促进骨再生,但不良反应较多。 背景：Nel样分子Ⅰ型是一种外分泌型糖蛋白蛋白,一系列体内、体外研究表明Nel样分子Ⅰ型是一种有效的骨诱导因子,可以有效地促进骨的生长。此外,Nel样分子Ⅰ型还抑制脂肪分化和炎症反应。 目的：就Nel样分子Ⅰ型目前在骨组织工程中的研究进展进行综述。 方法：检索 PubMed数据库1996年1月至 2019 年6月相关文献,检索词为“Nell-1;bone regeneration and repair;regulatory factor;signal path;bone morphogenetic protein;osteoporosis;marrow derived mesenchymal stem cells”。排除重复研究及与综述内容关系不密切的文献,对最终纳入的61篇文献进行分析。 结果与结论：经过研究,Nel样分子Ⅰ型已被证实为是一种可以有效促进骨组织生长的因子,局部应用对长骨、脊柱生长及颅缝闭合和软骨生长具有良好的促进作用。作为一种全新的生长因子,Nel样分子Ⅰ型的生物学效应相对单一,所以相比其他骨生长因子Nel样分子Ⅰ型的生物安全性和精准性更高。Nel样分子Ⅰ型可与骨形态发生蛋白2,9等其他成骨因子产生协同作用,Nel样分子Ⅰ型抑制骨形态发生蛋白2引起的炎症反应及脂肪生成并促进其成骨作用,为Nel样分子Ⅰ型和骨形态发生蛋白2结合提高临床骨再生的安全性和有效性提供了理论基础。 ORCID:0000-0002-0489-852X(靳良宇) 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     

Multilineage cells from human adipose tissue: implications for cell-based therapies

Future cell-based therapies such as tissue engineering will benefit from a source of autologous pluripotent stem cells. For mesodermal tissue engineering, one such source of cells is the bone marrow stroma. The bone marrow compartment contains several cell populations, including mesenchymal stem cells (MSCs) that are capable of differentiating into adipogenic, osteogenic, chondrogenic, and myogenic cells. However, autologous bone marrow procurement has potential limitations. An alternate source of autologous adult stem cells that is obtainable in large quantities, under local anesthesia, with minimal discomfort would be advantageous. In this study, we determined if a population of stem cells could be isolated from human adipose tissue. Human adipose tissue, obtained by suction-assisted lipectomy (i.e., liposuction), was processed to obtain a fibroblast-like population of cells or a processed lipoaspirate (PLA). These PLA cells can be maintained in vitro for extended periods with stable population doubling and low levels of senescence. Immunofluorescence and flow cytometry show that the majority of PLA cells are of mesodermal or mesenchymal origin with low levels of contaminating pericytes, endothelial cells, and smooth muscle cells. Finally, PLA cells differentiate in vitro into adipogenic, chondrogenic, myogenic, and osteogenic cells in the presence of lineage-specific induction factors. In conclusion, the data support the hypothesis that a human lipoaspirate contains multipotent cells and may represent an alternative stem cell source to bone marrow-derived MSCs.     

Matrix-mediated retention of in vitro osteogenic differentiation potential and in vivo bone-forming capacity by human adult bone marrow-derived mesenchymal stem cells during ex vivo expansion

Mesenchymal stem cells (MSCs) represent an attractive cell source for tissue engineering applications, since they are readily isolated from adult bone marrow and have the ability to differentiate along multiple mesenchymal lineages, including osteogenic. Currently, utilization of MSCs for bone tissue engineering is limited because of the attenuation of their osteogenic differentiation potential and in vivo bone-forming capacity following ex vivo expansion on conventional tissue culture plastic (TCP). Previously, we demonstrated that a denatured type I collagen (DC) matrix promotes the maintenance of MSC in vitro osteogenic differentiation potential during ex vivo expansion in contrast to TCP. In this study, we further demonstrate that the maintenance of MSC osteogenic differentiation potential is primarily due to the ability of DC matrix to influence the retention of early passage osteogenic functions in late passage (LP) cells during ex vivo expansion, in contrast to solely enhancing attenuated LP cellular functions during osteogenic differentiation. Serum-associated factors played a significant role in influencing the retention of MSC osteogenic differentiation potential during expansion on the DC matrix. Significantly, the results show that although LP cells expanded ex vivo on TCP highly attentuate their in vivo bone-forming capacity, the expansion of MSCs on DC matrix preserves this ability as determined by histological, histomorphometric, and bone mineral density evaluations of MSC-seeded hydroxyapatite/tricalcium phosphate scaffolds following an 8-week implantation period within a heterotopic muscle pouch model. These findings provide further insight into the importance of matrix-mediated effects on MSC function and selective factors important in this process.     

Nell-1-induced bone regeneration in calvarial defects

Many craniofacial birth defects contain skeletal components requiring bone grafting. We previously identified the novel secreted osteogenic molecule NELL-1, first noted to be overexpressed during premature bone formation in calvarial sutures of craniosynostosis patients. Nell-1 overexpression significantly increases differentiation and mineralization selectively in osteoblasts, while newborn Nell-1 transgenic mice significantly increase premature bone formation in calvarial sutures. In the current study, cultured calvarial explants isolated from Nell-1 transgenic newborn mice (with mild sagittal synostosis) demonstrated continuous bone growth and overlapping sagittal sutures. Further investigation into gene expression cascades revealed that fibroblast growth factor-2 and transforming growth factor-beta1 stimulated Nell-1 expression, whereas bone morphogenetic protein (BMP)-2 had no direct effect. Additionally, Nell-1-induced osteogenesis in MC3T3-E1 osteoblasts through reduction in the expression of early up-regulated osteogenic regulators (OSX and ALP) but induction of later markers (OPN and OCN). Grafting Nell-1 protein-coated PLGA scaffolds into rat calvarial defects revealed the osteogenic potential of Nell-1 to induce bone regeneration equivalent to BMP-2, whereas immunohistochemistry indicated that Nell-1 reduced osterix-producing cells and increased bone sialoprotein, osteocalcin, and BMP-7 expression. Insights into Nell-1-regulated osteogenesis coupled with its ability to stimulate bone regeneration revealed a potential therapeutic role and an alternative to the currently accepted techniques for bone regeneration.     

Adult mesenchymal stem cells: differentiation potential and therapeutic applications

Adult mesenchymal stem cells (MSCs) are a population of multipotent cells found primarily in the bone marrow. They have long been known to be capable of osteogenic, adipogenic and chondrogenic differentiation and are currently the subject of a number of trials to assess their potential use in the clinic. Recently, the plasticity of these cells has come under close scrutiny as it has been suggested that they may have a differentiation potential beyond the mesenchymal lineage. Myogenic and in particular cardiomyogenic potential has been shown in vitro. MSCs have also been shown to have the ability to form neural cells both in vitro and in vivo, although the molecular mechanisms underlying these apparent transdifferentiation events are yet to be elucidated. We describe here the cellular characteristics and differentiation potential of MSCs, which represent a promising stem cell population for future applications in regenerative medicine.     

Bone tissue engineering with bone marrow-derived stromal cells integrated with concentrated growth factor in Rattus norvegicus calvaria defect model

Concentrated growth factor (CGF) is an autologous leukocyte-rich and platelet-rich fibrin (L-PRF) biomaterial termed “second-generation platelet concentrate”. CGF contains autologous osteoinductive platelet growth factors and an osteoconductive fibrin matrix. The purpose of this study was to assess the ability of CGF combined with bone marrow stromal cells (BMSCs) to heal critical-size rat calvaria defects in vivo and to modulate the proliferation and osteogenic differentiation of mesenchymal stem cells (MSCs) in vitro. In the in-vivo study, the CGF group regenerated bone better than the control group, and combined therapy with CGF and BMSCs almost completely repaired critical-size bone defects within 12 weeks after surgery. In the in-vitro study, the CGF extract, at concentrations between 1 and 10 %, promoted proliferation, osteogenic maturation, and mineralization of hTERT-E6/E7 human MSCs in a dose-dependent manner but had an inhibitory effect at higher concentrations. In conclusion, a CGF extract promoted the proliferation, osteogenic maturation, and mineralization of mesenchymal stem cells in vitro, and combination therapy with CGF and BMSCs resulted in excellent healing of critical-size bone defects in vivo.     

Heparan sulfate mediates the proliferation and differentiation of rat mesenchymal stem cells

The growth and differentiation of mesenchymal stem cells (MSCs) is controlled by various growth factors, the activities of which can be modulated by heparan sulfates (HSs). We have previously noted the necessity of sulfated glycosaminoglycans for the fibroblast growth factor type 2 (FGF-2)-stimulated differentiation of osteoprogenitor cells. Here we show that exogenous application of HS to cultures of primary rat MSCs stimulates their proliferation, leading to increased expression of osteogenic markers and enhanced bone nodule formation. FGF-2 can also increase the proliferation, and osteogenic differentiation of rat bone marrow stem cells (rMSCs) when applied exogenously during their linear growth. However, as opposed to exogenous HS, the continuous use of FGF-2 during in vitro differentiation completely blocked rMSC mineralization. We show that the effects of both FGF-2 and HS are mediated through FGF receptor 1 (FGFR1) and that inhibition of signaling through this receptor arrests cell growth, resulting in the cells being unable to reach the critical density necessary to induce differentiation. Blocking FGFR1 signaling in postconfluent osteogenic cultures significantly increased calcium deposition. Taken together our data suggest that FGFR1 signaling plays an important role during osteogenic differentiation, first by stimulating cell growth that is closely followed by an inhibitory effect once the cells have reached confluence. It also confirms the importance of HS as a coreceptor for the signaling of endogenous FGF-2 and suggests that purified glycosaminoglycans may be attractive alternatives to growth factors for improved ex vivo growth and differentiation of MSCs.     

Additive effects of sonic hedgehog and Nell-1 signaling in osteogenic versus adipogenic differentiation of human adipose-derived stromal cells

A theoretical inverse relationship exists between osteogenic (bone forming) and adipogenic (fat forming) mesenchymal stem cell (MSC) differentiation. This inverse relationship in theory partially underlies the clinical entity of osteoporosis, in which marrow MSCs have a preference for adipose differentiation that increases with age. Two pro-osteogenic cytokines have been recently studied that each also possesses antiadipogenic properties: Sonic Hedgehog (SHH) and NELL-1 proteins. In the present study, we assayed the potential additive effects of the biologically active N-terminus of SHH (SHH-N) and NELL-1 protein on osteogenic and adipogenic differentiation of human primary adipose-derived stromal cell (hASCs). We observed that both recombinant SHH-N and NELL-1 protein significantly enhanced osteogenic differentiation and reduced adipose differentiation across all markers examined (alkaline phosphatase, Alizarin red and Oil red O staining, and osteogenic gene expression). Moreover, SHH-N and NELL-1 directed signaling produced additive effects on the pro-osteogenic and antiadipogenic differentiation of hASCs. NELL-1 treatment increased Hedgehog signaling pathway expression; coapplication of the Smoothened antagonist Cyclopamine reversed the pro-osteogenic effect of NELL-1. In summary, Hedgehog and Nell-1 signaling exert additive effects on the pro-osteogenic and antiadipogenic differentiation of ASCs. These studies suggest that the combination cytokines SHH-N+NELL-1 may represent a viable future technique for inducing the osteogenic differentiation of MSCs.     

MSC frequency correlates with blood vessel density in equine adipose tissue

Mesenchymal stem cells (MSCs) are multipotent cells that have the capacity to develop into different mature mesenchymal cell types. They were originally isolated from bone marrow, but MSC-like cells have also been isolated from other tissues. The common feature of all of these tissues is that they all house blood vessels. It is, thus, possible that MSCs are associated with perivascular locations. The objective of this work was to test the hypothesis that MSCs are associated with blood vessels by verifying if MSC frequency positively correlates with blood vessel density. To this end, samples from highly and poorly vascularized adipose tissue sites of two equine donors were collected and processed for histology and cell isolation. MSC frequency in these samples was estimated by means of CFU-F assays, which were performed under MSC conditions. Culture-adherent cells from equine adipose tissue and bone marrow were culture expanded, tested for differentiation into mesenchymal cell types in vitro, and implanted in vivo in porous ceramic vehicles to assess their osteogenic capacity, using human MSCs and brain pericytes as controls. The differentiation assays showed a difference between adipose tissue-derived cells as compared to equine bone marrow MSCs. While differences in CFU-F frequencies between both donors were evident, the CFU-F numbers correlated directly with blood vessel densities (r(2) = 0.86). We consider these preliminary data as further evidence linking MSCs to blood vessels.     

间充质干细胞体外成骨及成脂肪分化中sortilin基因表达的研究

目的:研究间充质干细胞(MSC)体外成骨、成脂肪分化时sortilin基因表达变化。方法:从骨髓中分离培养人间充质干细胞,流式细胞术鉴定其表型,加入成骨和成脂肪诱导剂,RT-PCR检测成骨标志骨桥蛋白(Op)和成脂肪标志脂蛋白脂肪酶(LpL)表达,半定量RT-PCR分析sortilin基因随诱导时间的表达变化。结果:①体外分离培养的人间充质干细胞能向成骨细胞和脂肪细胞分化,分别表达Op和LpL。②在体外成骨分化过程中,sortilin基因表达第1d开始上调,持续约1周后恢复至原水平;在培养3d时,sortilin基因表达明显上调,与未诱导组相比,差异明显(P＜0.01)。③体外成脂肪分化时,sortilin基因表达无明显的改变(P＞0.05)。结论:sortilin基因可能参与间充质干细胞成骨分化的调节,而与成脂肪分化无关,通过调控sortilin基因的表达,有可能为成骨障碍性疾病的治疗,提供新的思想和策略。     

间充质干细胞——现代组织工程的新资源

间充质干细胞 ( mesenchymal stem cells,MSC)存在于人类、鸟类、啮齿类等生物的骨髓中 ,它具有向骨、软骨、脂肪、肌肉及肌腱等组织分化的潜能。人们可利用它的这一特性建立多种细胞或组织的体外分化模型 ,从而为人类的细胞移植或组织移植提供可能的自体资源。本文就 MSC的生物学特性、体外分离方法、向各中胚层组织的分化条件及检测作一简要综述     

A comprehensive analysis of the dual roles of BMPs in regulating adipogenic and osteogenic differentiation of mesenchymal progenitor cells

Pluripotent mesenchymal stem cells (MSCs) are bone marrow stromal progenitor cells that can differentiate into osteogenic, chondrogenic, adipogenic, and myogenic lineages. Several signaling pathways have been shown to regulate the lineage commitment and terminal differentiation of MSCs. Here, we conducted a comprehensive analysis of the 14 types of bone morphogenetic protein (BMPs) for their abilities to regulate multilineage specific differentiation of MSCs. We found that most BMPs exhibited distinct abilities to regulate the expression of Runx2, Sox9, MyoD, and PPARgamma2. Further analysis indicated that BMP-2, BMP-4, BMP-6, BMP-7, and BMP-9 effectively induced both adipogenic and osteogenic differentiation in vitro and in vivo. BMP-induced commitment to osteogenic or adipogenic lineage was shown to be mutually exclusive. Overexpression of Runx2 enhanced BMP-induced osteogenic differentiation, whereas knockdown of Runx2 expression diminished BMP-induced bone formation with a decrease in adipocyte accumulation in vivo. Interestingly, overexpression of PPARgamma2 not only promoted adipogenic differentiation, but also enhanced osteogenic differentiation upon BMP-2, BMP-6, and BMP-9 stimulation. Conversely, MSCs with PPARgamma2 knockdown or mouse embryonic fibroblasts derived from PPARgamma2(-/-) mice exhibited a marked decrease in adipogenic differentiation, coupled with reduced osteogenic differentiation and diminished mineralization upon BMP-9 stimulation, suggesting that PPARgamma2 may play a role in BMP-induced osteogenic and adipogenic differentiation. Thus, it is important to understand the molecular mechanism behind BMP-regulated lineage divergence during MSC differentiation, as this knowledge could help us to understand the pathogenesis of skeletal diseases and may lead to the development of strategies for regenerative medicine.     

小鼠骨髓基质干细胞体外成骨的实验研究

目的　建立一种良好的分离和培养小鼠骨髓基质干细胞 (moasebonemarrow derivedmesenchymalstemcells ,mMSCs)的方法 ,观察小鼠骨髓基质干细胞体外成骨潜能。方法　应用贴壁选择法结合细胞克隆收集法进行mMSCs的分离纯化 ,应用细胞生长因子 (EGF和PDGF BB)刺激法进行MSCs的体外培养和传代 ,并在低糖DMEM (DMEM LG)培养液中培养。为促进mMSCs体外成骨性分化 ,传代培养到一定时期时加入成骨性添加剂和 1 0 %胎牛血清。培养第 2 0天分别用Gomori钙钴法显示碱性磷酸酶和VonKossa改良法显示钙化结节。结果　mMSCs呈克隆化增殖并贴壁生长形成形态均一的梭形细胞群。成骨性添加剂可有效作用于传代培养的mMSCs,表现为细胞之间相互连接形成结节状聚合体 ,碱性磷酸酶阳性细胞数量增多 ,VonKossa染色可见钙化结节的形成。结论　建立的mMSCs的分离、培养和成骨条件有效 ,所分离培养的mMSCs具有良好的体外成骨潜能     

兔骨髓间充质干细胞定向诱导分化为脂肪细胞及成骨细胞的研究

用密度梯度离心和贴壁法分离和纯化兔骨髓间充干细胞，建立诱导兔MSCs向脂肪细胞及成骨细胞表型转化的方法及条件。在成脂诱导剂或成骨诱导剂作用下，对原代和第2代兔MSCs进行成脂和成骨诱导培养，并鉴定成脂及成骨表型。结果表明：原代及第2代兔MSCs均有一定的成脂、成骨能力，且第2代细胞的分化能力较原代低。在诱导培养条件下，原代及第2代兔MSCs均能分化，成脂诱导21d，75％的兔MSCs转化为脂肪细胞；成骨诱导21d，75％的兔MSCs转化为成骨细胞。兔MSCs在适当的诱导条件下可快速分化为脂肪细胞或成骨细胞。     

Autocrine fibroblast growth factor 2 increases the multipotentiality of human adipose-derived mesenchymal stem cells

Multipotent mesenchymal stem cells (MSCs), first identified in the bone marrow, have subsequently been found in many other tissues, including fat, cartilage, muscle, and bone. Adipose tissue has been identified as an alternative to bone marrow as a source for the isolation of MSCs, as it is neither limited in volume nor as invasive in the harvesting. This study compares the multipotentiality of bone marrow-derived mesenchymal stem cells (BMSCs) with that of adipose-derived mesenchymal stem cells (AMSCs) from 12 age- and sex-matched donors. Phenotypically, the cells are very similar, with only three surface markers, CD106, CD146, and HLA-ABC, differentially expressed in the BMSCs. Although colony-forming units-fibroblastic numbers in BMSCs were higher than in AMSCs, the expression of multiple stem cell-related genes, like that of fibroblast growth factor 2 (FGF2), the Wnt pathway effectors FRAT1 and frizzled 1, and other self-renewal markers, was greater in AMSCs. Furthermore, AMSCs displayed enhanced osteogenic and adipogenic potential, whereas BMSCs formed chondrocytes more readily than AMSCs. However, by removing the effects of proliferation from the experiment, AMSCs no longer out-performed BMSCs in their ability to undergo osteogenic and adipogenic differentiation. Inhibition of the FGF2/fibroblast growth factor receptor 1 signaling pathway demonstrated that FGF2 is required for the proliferation of both AMSCs and BMSCs, yet blocking FGF2 signaling had no direct effect on osteogenic differentiation. Disclosure of potential conflicts of interest is found at the end of this article.     

Immunomodulatory properties of mesenchymal stem cells: cytokines and factors

Mesenchymal stem cells (MSCs) are defined as undifferentiated cells that are capable of self renewal and differentiation into several cell types such as chondrocyte, adipocyte, osteocyte, myocyte, hepatocyte, and neuron-like cells. MSC can be isolated from bone marrow, umbilical cord blood, adipose tissue, placenta, periosteum, trabecular bone, synovium, skeletal muscle, and deciduous teeth. Immunomodulatory of MSCs is one of the important issues nowadays, because this aspect can be clinically applied for graft-versus-host and autoimmune diseases. In this review, we tried to discuss in detail about cytokines and factors such as members of the transforming growth factor superfamily (transforming growth factor-β), hepatic growth factors (HGF), prostaglandin E2 (PGE2), IL-10, indolamine 2,3-dioxygenase (IDO), nitric oxide (NO), heme oxygenase-1 (HO-1), and human leukocyte antigen-G (HLA-G) that are involved in immunomodulatory of MSCs.     

Mesenchymal stem cells can be differentiated into endothelial cells in vitro

Human bone marrow-derived mesenchymal stem cells (MSCs) have the potential to differentiate into mesenchymal tissues like osteocytes, chondrocytes, and adipocytes in vivo and in vitro. The aim of this study was to investigate the in vitro differentiation of MSCs into cells of the endothelial lineage. MSCs were generated out of mononuclear bone marrow cells from healthy donors separated by density gradient centrifugation. Cells were characterized by flow cytometry using a panel of monoclonal antibodies and were tested for their potential to differentiate along different mesenchymal lineages. Isolated MSCs were positive for the markers CD105, CD73, CD166, CD90, and CD44 and negative for typical hematopoietic and endothelial markers. They were able to differentiate into adipocytes and osteocytes after cultivation in respective media. Differentiation into endothelial-like cells was induced by cultivation of confluent cells in the presence of 2% fetal calf serum and 50 ng/ml vascular endothelial growth factor. Laser scanning cytometry analysis of the confluent cells in situ showed a strong increase of expression of endothelial-specific markers like KDR and FLT-1, and immunofluorescence analysis showed typical expression of the von Willebrand factor. The functional behavior of the differentiated cells was tested with an in vitro angiogenesis test kit where cells formed characteristic capillary-like structures. We could show the differentiation of expanded adult human MSCs into cells with phenotypic and functional features of endothelial cells. These predifferentiated cells provide new options for engineering of artificial tissues based on autologous MSCs and vascularized engineered tissues.     

#br# rhTGF-β1对SD大鼠MSCs骨向分化的影响及机制研究

 目的：通过观察重组人转化生长因子 β1(rhTGF-β1)对大鼠骨髓间充质干细胞(MSCs)增殖和骨向分化能力的影响,以及对骨形态发生蛋白2(BMP-2)、Smad4及核心结合因子α1(Cbfa1)的作用,阐释其对MSCs骨向分化影响以及可能的作用机制。方法：用全骨髓贴壁法分离、纯化SD大鼠MSCs;用MTT法检测0、5、10、20、40、80和100 μg/L rhTGF-β1对MSCs增殖活性的影响;以碱性磷酸酶(ALP)活性及ALP染色阳性率确定rhTGF-β1的最佳促MSCs骨向分化浓度,并以该浓度对MSCs骨向分化进行干预。按是否添加经典成骨诱导液将实验分为：正常组、经典组、rhTGF-β1组和rhTGF-β1+经典组。通过检测ALP、I型胶原、骨钙素表达和钙化结节的数目,评价各组骨向分化能力;通过检测BMP-2、Smad4和Cbfa1 mRNA的表达,评价各组促MSCs骨向分化的可能作用机制。结果：rhTGF-β1最佳促MSCs增殖浓度为10 μg/L,最佳促MSCs骨向分化浓度为5 μg/L。经典组、rhTGF-β1组和rhTGF-β1+经典组均能促进MSCs骨向分化,刺激BMP-2分泌,并上调Smad4和Cbfa1 mRNA的表达,且rhTGF-β1对MSCs成骨分化的早期、中期效果好,而rhTGF-β1+经典组对MSCs成骨分化的晚期效果更为明显。结论:经典组、rhTGF-β1组和rhTGF-β1+经典组均有促MSCs骨向分化的作用,其机制可能是促进BMP-2的分泌,通过TGF-β超家族/Smads信号通路调控骨向分化。