• basic
    • Cell-ECM interactions
      • Dynamic reciprocity 动态互作
        • the mechanism of ECM is an important component in embryonic inductions
          动态互作解释了ECM在胚胎诱导过程中的机制
        • 整体就是ECM与细胞表面受体分子作用, 受体分子调控细胞表达蛋白反过来影响ECM
        • ECM molecules interact with receptors on the surface of cells
        • Receptors transmit signals across the cell membrane to molecules in the cytoplasm细胞质.
        • These signals initiate a cascade级联 of events through the cytoskeleton into the nucleus, resulting in the expression of specific genes
        • Products of these genes, in turn, affect the ECM in various ways
      • participate in promoting
        • cell adhesion
        • migration
        • growth
        • differentiation
        • apoptosis凋亡 (a form of programmed cell death)
        • modulating the activities of cytokines细胞因子 and growth factors生长因子 and indirectly间接 activating intracellular signaling
    • The life cycle of extracellular matrix molecules
      • 图
    • 各类细胞与ECM位置
      • 图
      • mesenchymal cells 间充质细胞
        • 比如fibroblast成纤维细胞
        • are immersed in an interstitial matrix
        • 浸没在间质基质中
        • interstitial matrix confers specific biomechanical and functional properties to connective tissue
        • 间质基质赋予结缔组织特定的生物力学特性和功能特性
      • epithelial and endothelial cells 上皮细胞和内皮细胞
        • contact the basement membrane via their basal surfaces only
        • 仅通过其基底面与基底膜接触
        • the basement membrane conferring mechanical strength and specific physiological properties on the epithelia
        • 基底膜为上皮组织提供机械强度和特定的生理特性
  • Composition
    • proteins
      • Collagens
        • 分类
          • 已经发现了28类, 主要关注3类
          • Type I
            • 占人体总胶原蛋白90%以上
            • skin
            • tendon
            • bone
          • Type II
            • cartilage 软骨
          • Type III
            • blood vessel wall
            • minor contaminant in skin皮肤中的次要杂质
        • Triple helix structure
          • 蛋白质的四级结构
            • Primary structure
              • sequence of amino acids along polypeptide chains and the location of interchain cross-links
            • Secondary structure
              • local configuration of a polypeptide chain
              • 多肽链的局部构象
            • Tertiary structure
              • global configuration of the polypeptide chains, a physicochemically stable entity in solution
              • 多肽链的整体构象，是溶液中理化性质稳定的实体
            • Quaternary structure
              • repeating supermolecular unit structure comprising several molecules packed in a specific lattice
              • 由多个分子按特定晶格排列形成的重复超分子单元结构
          • collagen的四级结构
            • 图
            • Most of collagens (except Type IV) form fibrils with the distinct collagen periodicity
              大多数胶原蛋白(Ⅳ 型除外)会形成原纤维，且具有独特的胶原蛋白周期性
            • collagens consists of about 300 Gly-X-Y tripeptide repeats, where X and Y can be any residue but Y is frequently proline or hydroxyproline
              胶原蛋白包含约 300 个甘氨酸 - X - Y 三肽重复序列，其中 X 和 Y 可为任意残基，但 Y 位常为脯氨酸或羟脯氨酸
            • 图
          • 组装过程
              1. Procollagen chains前胶原链 are synthesized in the endoplasmic reticulum (ER)
              1. brought together by interactions between the C-propeptides and fold to form a rod-like triple-helical domain flanked by globular N- and C-propeptides.
                各前胶原链通过 C 端前肽间的相互作用结合，折叠形成杆状三螺旋结构域，其两端分别连接球状的 N 端前肽和 C 端前肽
              1. Removal of the N- and C propeptides occurs after transport of procollagen across the Golgi高尔基体 stacks堆叠
              1. collagen molecules then assemble into fibrils.
              1. Covalent crosslinks occur within and between triple-helical collagen molecules in fibrils.
            • 图
          • 连接
            • 氢键
              • 形成位置
                • 在三螺旋之间形成, 稳定三螺旋
                • The extended conformation of each α-chain does not allow the formation of intrachain (chain here refers to each collagen peptide) hydrogen bonds, the stability of the triple helix is instead due to interchain hydrogen bonds.
                  三螺旋的每个螺旋不能和自己形成氢键, 但是互相形成的氢键是提供稳定的基础
                • Such interchain bonds can form only if every third residue of each α-chain does not have a side chain and is packed close to the triple helical axis.
                  仅当每条 α 链中每三个残基无侧链，且紧密靠近三螺旋轴心时，这类链间氢键才能形成
                • Only glycine residues甘氨酸残基 can therefore be accommodated in this position.
                • hydrogen-bonds formed between glycine NH (or OH group of hydroxylproline羟脯氨酸) & Proline脯氨酸 C=O
              • 酶
                • Enzymes (prolyl-3-hydroxylase, prolyl-4-hydroxylase, and lysyl hydroxylase) catalyze the reactions that add -OH to the amino acids proline or lysine in the collagen molecule
                • These enzymes require vitamin C as a cofactor辅因子
                • Hydroxylation -OH allows the collagen molecule to assume its triple helix structure, and thus vitamin C is essential to the development and maintenance of scar tissue, blood vessels, and cartilage
              • vitamin C
                • 是形成三螺旋之间氢键的cofactor辅因子
                • Scurvy坏血病 is a disease resulting from a deficiency of vitamin C, which is required for the synthesis of collagen in humans.
                • As scurvy advances, there can be open, suppurating化脓 wounds, loss of teeth, jaundice黄疸, fever, neuropathy神经病变 and death.
                • So vitamin C (ascobic acid抗坏血酸) is generally supplemented in the culture media for tissue engineering.
            • 共价交联
              • Inter-collagen helix cross-link is formed by a reaction involving lysine and hydroxylysine residues
                胶原蛋白链间螺旋交联通过赖氨酸和羟赖氨酸残基参与的反应形成
              • Lysine-Lysine, lysine-hydroxylysine cross-links (formed by lysyl oxidase)
                赖氨酸 - 赖氨酸交联、赖氨酸 - 羟赖氨酸交联（由赖氨酰氧化酶催化形成）
              • 形成共价键
              • 三条α链内可形成, 相邻的三螺旋之间可形成
        • 辅助
          • Type IX collagen
            • Type IX molecules are located on the surface of type II/XI containing fibrils with the long arm parallel to the fibril surface and the short arm projecting into the perifi brillar space
            • Ⅸ 型胶原蛋白分子位于含 Ⅱ 型 /Ⅺ 型胶原蛋白的原纤维表面，其长臂与原纤维表面平行，短臂则伸入原纤维周间隙中
            • Collagen IX functions as a bridging molecule between fibrils, between fibrils and other matrix constituents
            • Ⅸ 型胶原蛋白充当 “桥接分子”，可在原纤维之间、原纤维与其他基质成分之间发挥连接作用
            • 图
          • Type V/XI collagen
            • Regulators of Fibril Assembly
            • Collagen fibrils are heterotypic, i.e., contain more than one collagen type
            • 胶原蛋白原纤维为异质性原纤维，即包含一种以上胶原蛋白类型
            • 比如
              • collagen I fibrils in skin, ligaments, and bone contain 5–10% collagen V
              • collagen II fibrils in cartilage contain 5–10% collagen XI.
              • 皮肤、韧带和骨骼中的 Ⅰ 型胶原蛋白原纤维含 5%-10% 的 Ⅴ 型胶原蛋白
              • 软骨中的 Ⅱ 型胶原蛋白原纤维含 5%-10% 的 Ⅺ 型胶原蛋白
            • The presence of N-propeptide domains on V/XI molecules represents a steric hindrance to addition of molecules at fibril surfaces.
            • Ⅴ 型 /Ⅺ 型胶原蛋白分子上的 N 端前肽结构域，会对原纤维表面添加新分子形成空间位阻
            • This heterotypic/steric hindrance model predicts that collagen fibril diameters in a tissue are determined by the ratio of the minor component (V/XI) to the major component (I or II).
            • 该异质性 / 空间位阻模型认为，组织中胶原蛋白原纤维的直径由次要成分（Ⅴ 型 /Ⅺ 型胶原蛋白）与主要成分（Ⅰ 型或 Ⅱ 型胶原蛋白）的比例决定
            • A high ratio results in thin fibrils, a low ratio results in thick fibrils.
            • 比例越高，原纤维越细, 比例越低，原纤维越粗
        • organization
          • interstitial collagens 间隙胶原
            • e.g. types I, III
            • self assemble into 3D lattices网格结构, which, in turn, bind fibronectin纤连蛋白 and proteoglycans蛋白聚糖
            • This type of native ECM forms the backbone of loose connective tissues, such as dermis真皮
          • basement membrane collagens 基底膜胶原
            • e.g. types IV, V
            • assemble into planar arrays平面阵列
            • when these collagenous sheets interact with fibronectin纤连蛋白, laminin层粘连蛋白, and proteoglycan蛋白聚糖, a planar ECM formed (i.e., the basement membrane)
              i.e. 是拉丁语 id est 的缩写，意思是 “也就是说”
          • 图
        • Diseases
          • Fibrosis纤维化 - excessive collagen deposition胶原蛋白过度沉积
            • Lung fibrosis
            • Liver fibrosis
            • Cancer
      • Elastin 弹性蛋白
        • 与collagen对比
          • Collagen
            • collagen fibers evolved as structures of high tensile strength
            • 胶原蛋白纤维进化为高抗拉强度结构
            • equivalent to that of steel when compared on the basis of the same cross-sectional area but three times lighter
            • 在横截面积相同的情况下，其抗拉强度与钢材相当，但重量仅为钢材的三分之一
          • Elastic fibers
            • composed of molecules of elastin
            • 由弹性蛋白分子构成
            • provide tissues with elasticity so that they can recoil after transient stretch
            • 为组织赋予弹性，使其在短暂拉伸后能够回弹
            • 图
        • In organs such as the large arteries大动脉, skin, and lungs, elasticity is obviously crucial for normal functioning.
        • Elastin fibers are about five times as extensible compared to a rubber band with the same crosssectional area
          弹性蛋白纤维的伸展性约为相同横截面积橡皮筋的五倍
        • Each molecule is composed of alternating segments of hydrophobic and α-helical Ala- and Lys rich sequences.
        • 由疏水片段与富含丙氨酸（Ala）和赖氨酸（Lys）的 α- 螺旋片段交替构成
        • the elasticity of the fiber is due to the tendency of the hydrophobic segments to adopt a randomcoil configuration following stretch.
        • 纤维的弹性源于拉伸后，疏水片段倾向于形成无规卷曲构象
    • glycoproteins 糖蛋白
      主要是蛋白
      • basic
        • more protein and less carbohydrate(oligosaccharides寡聚糖)
      • 作用
        • Contribute to both organizing the matrix and helping cells attach to it
        • Guide cell movements in developing tissues
        • Bind and influence the function of peptide肽 growth factors and other small molecules
      • Fibronectin 纤连蛋白
        • Fibronectin is a multidomain多结构域, multifunctional多功能 adhesive黏附性 glycoprotein糖蛋白
        • Binds to other ECM molecules including collagen, chondroitin sulfate硫酸软骨素, fibrin纤维蛋白 etc.
        • The binding of fibronectin to some integrins整合素, especially integrin α5β1, involves涉及 the tripeptide三肽 sequence Arg-Gly-Asp (RGD) in Fn3 module 结构域
        • 多个结合域
        • The most important activity of fibronectin is its ability to serve as a substrate for cell adhesion, spreading, and migration
        • 纤连蛋白最重要的功能是能够作为细胞黏附、铺展和迁移的底物
        • Fibronectin can assemble into a fibrous network(上面可以举着一个collagen) in the ECM through interactions involving cell surface receptors(integrins)

          • 纤连蛋白可通过与细胞表面受体的相互作用，在细胞外基质中组装形成纤维网络
      • Laminin 层粘连蛋白
        • The primary organizer of basal lamina基底膜
        • Laminins are trimeric basement membrane molecules of α-, β-, and γ-chains
        • 层粘连蛋白是由 α 链、β 链和 γ 链构成的三聚体基底膜分子
        • most significant interactions of laminin involve a variety of both integrin and nonintegrin cell surface receptors.
        • 层粘连蛋白最重要的相互作用，涉及多种整合素及非整合素类细胞表面受体
        • Several integrins are laminin receptors
        • 多种整合素均为层粘连蛋白受体
        • 图
      • Thrombospondins 血小板反应蛋白
        • Thrombospondins (TSPs) are a group of homologous matrix proteins
          是一组同源基质蛋白
          • trimeric三聚体 (TSP-1 and TSP-2)
          • pentameric五聚体 (TSP-3, TSP-4 and TSP-5/COMP)
          • 图
        • composed of several Ca2+ -binding domains, EGF-like repeats, etc.
        • 由多个钙结合结构域、表皮生长因子样重复序列等构成
        • The highly conserved carboxyl regions of thrombospondins can bind to a variety of ECM molecules and cell surface components like integrins
        • 血小板反应蛋白高度保守的羧基端区域, 可结合多种细胞外基质分子及细胞表面成分, 比如整合素
        • All thrombospondins support attachment of cells in a Ca2+ -dependent manner
        • 所有血小板反应蛋白均以钙依赖的方式支持细胞黏附
        • stimulate cell migration, proliferation, chemotaxis, and phagocytosis
        • 能刺激细胞迁移、增殖、趋化及吞噬作用
      • Tenascin 肌腱蛋白
        • The four members of the vertebrate tenascin family (C, R, W, and X) are large multimeric proteins with subunits composed of multiple protein modules
        • 脊椎动物肌腱蛋白家族的四个成员（C、R、W 和 X）均为大型多聚体蛋白，其亚基由多个蛋白质结构域组成
        • The tenascins are differentially expressed in different tissues and at different times during development and growth
        • 肌腱蛋白在发育和生长过程中，于不同组织及不同时期呈现差异表达
        • Tenascin-C expression is high during development and inflammation and around tumors, but it is otherwise relatively low in postnatal tissues.
        • 肌腱蛋白 - C 在发育阶段、炎症状态下及肿瘤周围表达量较高，而在出生后组织中表达量通常较低
        • In tissue regions of high mechanical stress, the levels of tenascin-C expression are high
        • 在机械应力较高的组织区域，肌腱蛋白 - C 的表达水平会升高
        • The interactions between tenascins and cells are relatively weak compared to other proteins, such as fibronectin and thrombospondin.
        • 与纤连蛋白、血小板反应蛋白等其他蛋白质相比，肌腱蛋白与细胞的相互作用相对较弱
    • proteoglycans 蛋白聚糖
      主要是糖
      • basic
        • more carbohydrate (glycosaminoglycans糖胺聚糖, GAG) and less protein

          • hyaluronic acid backbone作为骨架，没有S
      • GAGs
        • basic
          • Glycosaminoglycans (GAGs) are polysaccharide branches of a protein core
          • 糖胺聚糖(GAGs)是蛋白核心上的多糖侧链
          • covalently attached via a specific linkage.
          • 它们通过特定连接键与蛋白核心共价结合
          • The entire branched macromolecule, has a “bottle brush” configuration
          • 这种完整的分支大分子呈 “瓶刷状” 结构
          • a major component of the extracellular matrix, the “filler” substance existing between cells in an organism
          • 它是细胞外基质的主要成分，也是生物体内细胞间的 “填充” 物质
        • 结构
          • 大部分GAG都有sulfated硫酸化修饰, 除了Hyaluronic acid透明质酸(玻尿酸)
            • 都是一个氨基糖和一个非氨基糖的重复单元, 大部分sulfated
          • Alternating copolymer
            • 一个氨基糖a hexosamine (glucosamine or galactosamine葡萄糖胺或半乳糖胺)
            • 一个非氨基糖another sugar (galactose, glucuronic acid, or iduronic acid半乳糖, 葡萄糖醛酸或艾杜糖醛酸)
            • 图
      • Syndecan
        • Syndecan family, transmembrane molecules with highly conserved cytoplasmic domains
        • 是一类跨膜分子，其胞质域具有高度保守性(在不同物种保持一致)
        • Through their heparan sulfate side chains it can bind growth factors, protease inhibitors, enzymes, and matrix macromolecules.
        • 它们通过硫酸乙酰肝素侧链，能够结合生长因子、蛋白酶抑制剂、酶类及基质大分子
        • They are therefore important modulators of cell signaling pathways and cell–matrix
        • 因此，该家族蛋白是细胞信号通路及细胞 - 基质相互作用的重要调控因子
        • 在细胞表面, 胞外域共价连接多个GAGs
      • small proteoglycans
        • They include decorin, biglycan, lumican, and fibromodulin.
        • 包括核心蛋白聚糖(decorin)、双糖链蛋白聚糖(biglycan)、光蛋白聚糖(lumican)和纤调蛋白聚糖(fibromodulin)
        • the small proteoglycans help sequester growth factors within the ECM and thus regulate their activities
        • 这些小分子蛋白聚糖有助于将生长因子封存于细胞外基质中，进而调控生长因子的活性
        • Decorin 核心蛋白聚糖
          • binds along collagen fibrils
          • 沿胶原原纤维结合
          • plays a role in regulating fibril assembly and mechanical properties
          • 既能调控原纤维的组装过程，也能影响其机械性能
          • It also modulates the binding of cells to matrix constituents such as collagen, fibronectin
          • 还能调节细胞与基质成分(如胶原蛋白、纤连蛋白)的结合作用
    • others
      • growth factors, cytokines, and matrixdegrading enzymes and their inhibitors
  • ECM diversity
    • This diversity of composition, organization, and distribution of ECM results from
      • differential gene expression of the various molecules in specific tissues
      • the existence of differential splicing and post-translational modifications of those molecules.
    • For example, alternative splicing may change the binding potential of proteins to other matrix molecules
      • 图
  • ECM-soluble factor interactions
    • basic
      • ECM regulates local concentration and biological activity of growth factors and cytokines
      • ECM serves as a reservoir容器 that binds these molecules
        • Protects them from being degraded
        • Presents them more efficiently to their receptors
        • Modulates their synthesis
      • eg. Specific binding of FGF(fibroblast growth factor) to GAG
      • Binding to ECM molecules may sometimes inhibit growth factor activity
    • ECM promotes spatial presentation of soluble factors
      • Binding of growth factors (GFs) to ECM can lead to the localization GFs to particular regions within tissues to establish the spatial gradient of GF concentration
      • eg.人造的ECM可以用GF浓度引导stem cell过去
        • 图
      • eg.Cell-fibronectin interaction strains and aligns the fibronectin
        • 细胞与纤连蛋白（FN）的相互作用可牵拉并对齐纤连蛋白
        • 图
        • 肌成纤维细胞收缩让 ECM 产生预应变，会激活 TGF-β1。这个过程会推动成纤维细胞变成肌成纤维细胞，而肌成纤维细胞又会进一步给 ECM 施加机械力，形成正反馈
        • ECM prestrain generated by myofibroblast contraction affects TGF-β1 activation. Fibroblasts secrete ECM that is rich in FN (green) and the large latent complex of TGF-β1 (LTBP-1, LAP, and TGF-β1). Fibroblastto- myofibroblast differentiation occurs during physiological (normal wound healing) and pathological (fibrosis) tissue remodeling. Myofibroblasts are characterized by αSMA–positive stress fibers (red) enabling these cells to exert high contractile activity and forces transmitted to the ECM at sites of integrins. The gradual straitening and straining of ECM fibrils, containing FN and LTBP-1, prime the latent TGF complex for subsequent activation. At sufficient prestrain, minimal additional length changes in the ECM (i.e., small contractions) will be sufficient to release active TGF-β1 by inducing a conformational change in LAP. Hence, the mechanical preloading of the ECM determines the trigger point for TGF-β1 activation driving the vicious loop of myofibroblast self-activation.
    • ECM-growth factor receptor interactions
      • 总结来说ECM也有receptor可以抓着soluble factor然后一直给细胞作用
      • specific domains of ECM molecules can bind and activate growth factor receptors
      • ECM 分子的特定结构域可以结合并激活生长因子受体
      • For example, the EGF-like repeats of laminin and tenascin-C bind and activate the EGF receptor (EGFR).
      • 例如，层粘连蛋白和腱生蛋白 - C 的表皮生长因子(EGF)样重复序列可结合并激活表皮生长因子受体(EGFR)
      • Basically, ECM molecules can serve as ligands for growth factor receptors
      • 从本质上讲，ECM 分子可作为生长因子受体的配体
      • This may facilitate a long-term signaling events (pro-migratory and/or pro-proliferative) to the cells due to the inability of the ligand either to diffuse or to be internalized
      • 由于这类配体既无法扩散也不能被细胞内化，这可能会为细胞促成长期的信号事件
  • ECM-cell interactions
    • basic
      • During development, the cellular cross-talk with the surrounding ECM promotes the formation of patterns, the development of form (morphogenesis), and the acquisition and maintenance of differentiated phenotypes during embryogenesis.
      • 发育过程中，细胞与周围ECM的相互交流，会促进胚胎发生期的模式形成、形态构建(形态发生)，以及分化表型的获得与维持
      • During wound healing these interactions contribute to the processes of clot formation, inflammation, granulation tissue development, and remodeling.
      • 伤口愈合过程中，这些相互作用会参与凝血形成、炎症反应、肉芽组织生长及组织重塑等过程
    • ECM receptors
      细胞表面能与ECM结合的受体
      • integrins 整合素
        • Link the ECM to the cytoskeleton and transmit signals in both directions
        • Integrins, a family of heterodimeric transmembrane proteins composed of α and β subunits, the first ECM receptors identified
        • 整合素是一类异二聚体跨膜蛋白，由 α 亚基和 β 亚基组成，是最早被发现的细胞外基质受体
        • 可以通过构型变换开关
        • At least 18 α and 8 β subunits have been identified so far
        • 目前已鉴定出至少 18 种 α 亚基和 8 种 β 亚基
        • a variety of combinations α and β give rise to a large family of integrins
        • α 亚基与 β 亚基的多种组合，构成了庞大的整合素家族
        • Some integrin receptors are very specific, and others bind several different epitopes, affording plasticity and redundancy
        • 部分整合素受体具有高度特异性，另一些则可结合多种不同表位，赋予其功能可塑性和冗余性
      • glycoproteins
        • Transmembrane glycoproteins typically serve as receptors for ECM molecules.
        • CD44
          • interact directly with hyaluronan 透明质酸(玻尿酸), 连接GAG
      • Syndecan
        • 一种proteoglycans
        • binds cells to ECM via its chondroitin- and heparan-sulfate glycosaminoglycan side chains.
        • 可通过其硫酸软骨素和硫酸乙酰肝素GAG侧链，介导细胞与ECM的结合
    • Three types of ECM-cell interactions
      • Type I
        • 整合素, 蛋白聚糖参与, 与黏附, 迁移有关
        • Involve integrin, proteoglycan
        • adhesion/migration
        • 图
      • Type II
        • 基质受体参与, 与细胞因子/生长因子受体协同的, 对细胞命运有关
        • involve matrix–receptor interactions, in conjunction with growth factor or cytokine receptors
        • proliferation, survival, differentiation, maintenance of phenotype
        • 图
      • Type III
        • 降解ECM诱导细胞死亡
        • Integrin receptors bind to fragments of ECM molecules
        • This leads to expression of matrix protease基质蛋白水解酶 which degrade the matrix and release peptides, leading to apoptosis
        • 图
    • Cellular process affected
      受影响的细胞过程
      • cell adhesion/deadhesion
      • migration 迁移
        • e.g.Gastrulation 原肠胚形成
          • an embryo development stage during which the single-layered blastula develops into the trilayered gastrula
          • 胚胎发育的一个阶段，在此过程中单层的囊胚发育为三层的原肠胚
          • Injection of ECM antibodies into embryos disrupt gastrulation
            • Antibody against fibronectin
            • Antibody against GAG
          • 图
        • Micromechanical model of morphogenetic control during epithelial development
          • 这个微力学模型解释了上皮发育中芽体形成的机制 ——ECM 周转局部增加让基底膜出现缺损，相邻上皮和间充质的牵拉给 ECM 施加预应力，使基底膜局部拉伸变薄(形成高应变区). 黏附在该区域的细胞会变形、细胞骨架张力升高，对生长刺激更敏感，再加上细胞分裂与新基底膜沉积同步进行，最终在高应变区形成新芽体，且高应变区域和芽体形成区域完全对应
          • 图
        • e.g.神经嵴细胞 NCC 迁移
          • 使用鸡蛋研究
          • The migration of neural crest cells (NCC) is critical to proper development of embryos
          • 神经嵴细胞(NCC)的迁移对胚胎正常发育至关重要
          • fibronectin appears between chick NCC just prior to their emigration from the neural tube
          • 纤连蛋白(FN)在鸡胚神经嵴细胞即将从神经管迁出前，出现于细胞之间
          • the RGD domain of fibronectin binds to its integrin receptor, promotes secretion of adhesion-degrading enzymes, thereby facilitating emigration
          • 纤连蛋白的 RGD 结构域与整合素受体结合，促进黏附降解酶的分泌，进而助力神经嵴细胞迁出
          • Injection of antibodies targeting fibronectin or its integrin receptor in chick embryos reduces NCC migration and causes abnormal neural tube development.
          • 向鸡胚中注射针对纤连蛋白或其整合素受体的抗体，会减少神经嵴细胞迁移，并导致神经管发育异常
        • e.g.cancer cell migration - metastasis
          • 图
      • angiogenesis 血管形成
        • blood vessel formation
        • HUVEC 脐静脉内皮细胞实验
          • 人脐静脉内皮细胞HUVEC是从人类脐带静脉内壁分离得到的原代内皮细胞，是血管生物学、肿瘤转移、组织工程等领域最常用的体外研究模型之一
          • 在不同环境下培养
            • 基质胶
              • Matrigel基质胶 consists of large amounts of laminin层粘连蛋白, collagen IV, proteoglycans.
              • Human umbilical vein endothelial cells (HUVEC)脐静脉内皮细胞 were cultured培养 on Matrigel基质胶, migrate and form tubelike管状 structures after 12 hours
            • collagen I
              • when cultured with collagen I, they form tubelike structures only after one week
            • 塑料培养基
              • do not form tubular structure at all on tissue culture plastics (no ECM coating)
          • 这表明laminin, was important to endothelial tube formation and angiogenesis.
        • 血管生成过程中内皮细胞(EC)出芽的四个核心阶段
          • 图
          • 选芽 - 部分内皮细胞变尖端细胞，DLL4-Notch、VEGF 信号驱动出芽
          • 长芽 - 尖端细胞引导出芽生长，VEGF、导向信号（如 Semaphorin）调控方向，同时沉积新 ECM
          • 融芽成管 - 相邻出芽融合，形成管腔，PDGF、Integrins 等推动液泡融合和管腔扩张
          • 成熟 - 血管通血流，EC 增殖减少，EGFL7-ECM 和静息信号让血管稳定成熟
      • proliferation 增殖
        • Pro-proliferation 促增殖
          • a domain of laminin that is rich in EGF-like repeats stimulates proliferation of a variety of different cell lines.
          • 层粘连蛋白中富含表皮生长因子(EGF)样重复序列的结构域，可刺激多种不同细胞系的增殖
          • EGF - Epidermal Growth Factor
        • Anti-proliferation 抗增殖
          • Heparin and heparin-like molecules are inhibitors of vascular smooth muscle cell (VSMC) proliferation.
          • 肝素及类肝素分子是血管平滑肌细胞(VSMC)增殖的抑制剂
          • normal human breast cells do not growth arrest when cultured on plastic, but they do so if grown in a basement membrane matrix
          • 正常人乳腺细胞在塑料皿中培养时不会生长停滞，但在基底膜基质中培养时会出现生长停滞
      • differentiation 分化
        • e.g. keratinocytes角质形成细胞
          • The basal layer keratinocytes角质形成细胞 in skin is highly proliferative增殖能力强, remain undifferentiated, and is the only cell layer in contact with the basement membrane.
          • As these cells divide, the daughter cells move up and lose contact with the basement membrane, and begin to differentiate
          • keratinocytes adhesion to fibronectin via its α5β1 integrin receptor suppress differentiation
          • 角质形成细胞通过其 α5β1 整合素受体与纤连蛋白结合，会抑制自身分化
          • Keratinocytes cultured on feeder fibroblasts remain undifferentiated due to the ECM secreted by the underlying feeder cells
          • 在饲养层成纤维细胞上培养的角质形成细胞，因底层饲养细胞分泌的ECM，会维持未分化状态
          • Keratinocytes 在 basal layer 高增殖不分化, 子代细胞向上迁移然后开始分化
        • ECM stiffness
          • durotaxis硬度趋向性, Engrafted MSC定植的间充质干细胞
          • a
            • 间充质干细胞(MSC)会向硬度高的组织(如纤维化瘢痕)迁移，并在硬组织中定植、分化
            • 这说明 ECM 硬度是引导干细胞迁移和分化的物理信号
          • b
            • 不同组织的 ECM 弹性差异极大(如脑是软组织，骨是硬组织)
            • 这种硬度差异对应不同细胞的分化方向(如软 ECM 支持神经分化，硬 ECM 支持骨分化)
          • C
            • 细胞在软基质(Soft gel)和硬基质(Stiff substrates)上的形态、细胞骨架差异显著
            • 硬基质通过激活 Rac、Rho 等信号通路，驱动细胞收缩、增殖并向特定表型分化（如成骨分化）
        • ECM-cell receptor binding
          • 图
          • 干细胞通过与 ECM、 niche 细胞(微环境支持细胞)的黏附分子结合，维持干细胞特性
          • 受到receptor干预, 干细胞会增殖并分化为子代细胞Progeny cell
        • ECM structure
          • 图
      • apoptosis 凋亡
        • Cell to ECM adhesion imparts critical cell survival signals
        • 细胞与ECM的黏附会传递关键的细胞存活信号
        • During apoptosis, cell–ECM interactions are decreased due to both matrix degradation and reduced expression of integrin β1
        • 在细胞凋亡过程中，由于基质降解和整合素 β1 表达减少，细胞与 ECM 的相互作用会降低
        • Disruption of cell–ECM interactions may lead to an increase in the expression or activation of pro-apoptotic molecules, and may also lead to the removal of pro-survival signals
        • 破坏细胞与 ECM 的相互作用可能会增加促凋亡分子的表达或激活，也可能导致促存活信号的丧失
  • Relevance in tissue engineering
    • Creating the proper substrate for cell survival and differentiation.
    • Providing the appropriate environmental conditions for tissue maintenance.
    • Avoiding an immune response that can cause inflammation and/or rejection