The role of extracellular matrix in vascular branching morphogenesis

Angiogenesis requires the development of a hierarchically branched network of vessels, which undergoes radial expansion and anastomosis to form a close circuit. Branching is achieved by coordinated behavior of endothelial cells that organize into leading “tip” cells and trailing “stalk” cells. Such organization is under control of the Dll4-Notch signaling pathway, which sets a hierarchy in receptiveness of cells to VEGF-A. Recent studies have shed light on a control of the Notch pathway by basement membrane proteins and integrin signaling, disclosing that extracellular matrix exerts active control on vascular branching morphogenesis. We will survey in the present review how extracellular matrix is a multifaceted substrate, which behind a classical structural role hides a powerful conductor function to shape the branching pattern of vessels.     

The role of urokinase in vascular cell migration and in regulation of growth and branching of capillaries

The urokinase system, represented by a plasminogen activator of urokinase type (urokinase, uPA), urokinase receptor (uPAR), and inhibitors of plasminogen activator (PAI-1 and PAI-2), plays an important role in the regulation of vascular wall functioning. Urokinase signaling initiates proteolytic cascade and degradation of the extracellular matrix; and also activates intracellular signaling in vascular cells. This study is the first to reveal a urokinase-mediated fundamental mechanism that regulates the growth trajectory and branching morphogenesis of blood vessels. This mechanism may be of particular importance during vessel growth in early embryogenesis and in the adult during tissue regeneration.     

Expression profiles of microRNAs in oxidized low-density lipoprotein-stimulated RAW 264.7 cells

Macrophage-derived foam cells were one of the hallmarks of atherosclerosis, and microRNAs played an important role in the formation of foam cells. In order to explore the roles of miRNA in the formation of foam cells, we investigated miRNA expression profiles in foam cells through high-throughput sequencing technology. A total of 84 miRNAs were differentially expressed between RAW 264.7 macrophages and foam cells induced by ox-LDL. Thirty miRNAs were upregulated and 54 miRNAs were downregulated. GO terms and KEGG pathways analysis revealed that the target genes of most of DE miRNAs were mainly enriched in “cell differentiation,” “endocytosis,” “MAPK signaling pathway,” and “FoxO signaling pathway.” The target genes of some DE miRNAs were enriched in “Insulin signaling pathway,” “Hippo signaling pathway,” “TNF signaling pathway,” “NF-kappa B signaling pathway,” and “cell death.” Using bioinformatics analyses and dual-luciferase reporter assays, we found that miR-28a-5p and miR-30c-1-3p directly inhibited LRAD3 and LOX-1 mRNA expression through targeting the 3’UTR of LRAD3 and LOX-1 mRNA, respectively. Our study indicates that miRNAs are extensively involved in the formation of foam cells, and provides a valuable resource for further study the role of miRNAs in atherosclerosis.     

Parabronchial smooth muscle cells and alveolar myofibroblasts in lung development

Epithelial-mesenchymal interactions and extracellular matrix remodeling are key processes of embryonic lung development. Lung smooth muscle cells, which are derived from the mesenchyme, form a sheath around bronchi and blood vessels. During lung organogenesis, smooth muscle differentiation coincides with epithelial branching morphogenesis and closely follows developing airways spatially and temporally. The precise function of parabronchial smooth muscle (PBSM) cells in healthy adult lung remains unclear. However, PBSM may regulate epithelial branching morphogenesis during lung development by the induction of mechanical stress or through regulation of paracrine signaling pathways. Alveolar myofibroblasts are interstitial contractile cells that share features and may share an origin with smooth muscle cells. Alveolar myofibroblasts are essential for secondary septation, a process critical for the development of the gas-exchange region of the lung. Dysregulation of PBSM or alveolar myofibroblast development is thought to underlie the pathogenesis of many lung diseases, including bronchopulmonary dysplasia, asthma, and interstitial fibrosis. We review the current understanding of the regulation of PBSM and alveolar myofibroblast development, and discuss the role of PBSM in lung development. We specifically focus on the role of these cells in the context of fibroblast growth factor-10, sonic hedgehog, bone morphogenetic protein-4, retinoic acid, and Wnt signaling pathways in the regulation of lung branching morphogenesis.     

Secretory and endo/exocytic trafficking in invadopodia formation: The MT1-MMP paradigm

Invadopodia are actin-rich, adhesive protrusions that extend into and remodel the extracellular matrix. They are associated with high levels of pericellular proteolysis and correlate with the invasive capacity of a variety of tumour cells. Invadopodia have, thus, been proposed to recapitulate key events of the metastatic process. Although our understanding of the patho-physiology of invadopodia is still in its infancy, the molecular components and signalling pathways leading to their formation have received increasing attention. Recent studies have revealed that diverse membrane polarized secretory and endo/exocytic trafficking pathways converge at these structures for the delivery, in a temporally controlled and spatially confined manner, of key proteolytic enzymes. Here, we will focus our attention on MT1-MMP, a paradigmatic metalloprotease that is primarily responsible for the proteolytic activity of invadopodia. We propose that the biosynthetic/secretory pathway might be critical for the polarized delivery of MT1-MMP to invadopodia that form as “default response” whenever cells have to deal with extracellular matrix (ECM) of variable composition and stiffness. Conversely, “inducible” endo/exocytic trafficking routes might primarily control the delivery of MT1-MMP to invadopodia when cells need to respond in a fast and transient manner to soluble motogenic factors, rather than the insoluble ECM.     

Radiation induces apoptosis primarily through the intrinsic pathway in mammalian cells

Radiation-induced tumor cells death is the theoretical basis of tumor radiotherapy. Death signaling disorder is the most important factor for radioresistance. However, the signaling pathway(s) leading to radiation-triggered cell death is (are) still not completely known. To better understand the cell death signaling induced by radiation, the immortalized mouse embryonic fibroblast (MEF) deficient in “initiator” caspases, “effector” caspases or different Bcl-2 family proteins together with human colon carcinoma cell HCT116 were used. Our data indicated that radiation selectively induced the activation of caspase-9 and caspase-3/7 but not caspase-8 by triggering mitochondrial outer membrane permeabilization (MOMP). Importantly, the role of radiation in MOMP is independent of the activation of both “initiator” and “effector” caspases. Furthermore, both proapoptotic and antiapoptotic Bcl-2 family proteins were involved in radiation-induced apoptotic signaling. Overall, our study indicated that radiation specifically triggered the intrinsic apoptotic signaling pathway through Bcl-2 family protein-dependent mitochondrial permeabilization, which indicates targeting mitochondria is a promising strategy for cancer radiotherapy.     

Contact-inhibited chemotaxis in de novo and sprouting blood-vessel growth

Blood vessels form either when dispersed endothelial cells (the cells lining the inner walls of fully formed blood vessels) organize into a vessel network (vasculogenesis), or by sprouting or splitting of existing blood vessels (angiogenesis). Although they are closely related biologically, no current model explains both phenomena with a single biophysical mechanism. Most computational models describe sprouting at the level of the blood vessel, ignoring how cell behavior drives branch splitting during sprouting. We present a cell-based, Glazier-Graner-Hogeweg model (also called Cellular Potts Model) simulation of the initial patterning before the vascular cords form lumens, based on plausible behaviors of endothelial cells. The endothelial cells secrete a chemoattractant, which attracts other endothelial cells. As in the classic Keller-Segel model, chemotaxis by itself causes cells to aggregate into isolated clusters. However, including experimentally observed VE-cadherin-mediated contact inhibition of chemotaxis in the simulation causes randomly distributed cells to organize into networks and cell aggregates to sprout, reproducing aspects of both de novo and sprouting blood-vessel growth. We discuss two branching instabilities responsible for our results. Cells at the surfaces of cell clusters attempting to migrate to the centers of the clusters produce a buckling instability. In a model variant that eliminates the surface-normal force, a dissipative mechanism drives sprouting, with the secreted chemical acting both as a chemoattractant and as an inhibitor of pseudopod extension. Both mechanisms would also apply if force transmission through the extracellular matrix rather than chemical signaling mediated cell-cell interactions. The branching instabilities responsible for our results, which result from contact inhibition of chemotaxis, are both generic developmental mechanisms and interesting examples of unusual patterning instabilities.     

DDR1 signaling is essential to sustain Stat5 function during lactogenesis

Postnatal development of the mammary gland is achieved by an interplay of endocrine and extracellular matrix-derived signals. Despite intense research, a comprehensive understanding of the temporal and spatial coordination of these hormonal and basement membrane stimuli is still lacking. Here, we address the role of the collagen-receptor DDR1 in integrating extracellular matrix-derived signaling with the lactogenic pathway initiated by the prolactin receptor. We found that stimulation of DDR1-overexpressing mammary epithelial HC11 cells with collagen and prolactin resulted in stronger and more sustained induction of Stat5 phosphorylation as compared to control cells. Enhanced Stat5 activity in HC11-DDR1 cells correlated with increased beta-casein gene expression. In contrast, cells derived from DDR1-null mice showed reduced Stat5 activation upon lactogenic stimulation and completely failed to induce beta-casein expression. The cell-autonomous role of DDR1 in controlling ductal branching and alveologenesis prior to the onset of lactogenesis was corroborated by mammary tissue transplantation experiments. Our results show that aside from hormone- and cytokine receptors, DDR1 signaling establishes a third matrix-derived pathway vital to maintain mammary gland function.     

NFATC1 promotes epicardium-derived cell invasion into myocardium

Epicardium-derived cells (EPDCs) contribute to formation of coronary vessels and fibrous matrix of the mature heart. Nuclear factor of activated T-cells cytoplasmic 1 (NFATC1) is expressed in cells of the proepicardium (PE), epicardium and EPDCs in mouse and chick embryos. Conditional loss of NFATC1 expression in EPDCs in mice causes embryonic death by E18.5 with reduced coronary vessel and fibrous matrix penetration into myocardium. In osteoclasts, calcineurin-mediated activation of NFATC1 by receptor activator of NFκB ligand (RANKL) signaling induces cathepsin K (CTSK) expression for extracellular matrix degradation and cell invasion. RANKL/NFATC1 pathway components also are expressed in EPDCs, and loss of NFATC1 in EPDCs causes loss of CTSK expression in the myocardial interstitium in vivo. Likewise, RANKL treatment induces Ctsk expression in PE-derived cell cultures via a calcineurin-dependent mechanism. In chicken embryo hearts, RANKL treatment increases the distance of EPDC invasion into myocardium, and this response is calcineurin dependent. Together, these data demonstrate a crucial role for the RANKL/NFATC1 signaling pathway in promoting invasion of EPDCs into the myocardium by induction of extracellular matrix-degrading enzyme gene expression.     

Repulsion or adhesion: receptors make the call

Repulsive signaling plays a prominent role in regulating cell-cell interactions and is fundamental to multiple developmental processes. A proper balance between repulsion from and adhesion to other cells or the extracellular matrix is also important. Semaphorin-Plexin and ephrin-Eph ligand-receptor pairs compose two major repulsive signaling systems. Recent advances have elucidated mechanisms by which Semaphorin-Plexin and ephrin-Eph signaling control repulsion versus adhesion. Semaphorins act through a complex signaling pathway to inhibit integrin-mediated adhesion, allowing cell repulsion. Ephrin-Eph interactions can directly mediate cell adhesion and several mechanisms control whether ephrin-Eph binding and signaling induces repulsion or adhesion.     

Thromboxane receptor signaling is required for fibronectin-induced matrix metalloproteinase 9 production by human and murine macrophages and is attenuated by the Arhgef1 molecule

During an inflammatory response, resident and newly recruited tissue macrophages adhere to extracellular matrix and cell-bound integrin ligands. This interaction induces the expression of pro-inflammatory mediators that include matrix metalloproteinases (MMPs). Arhgef1 is an intracellular signaling molecule expressed by myeloid cells that normally attenuates murine macrophage MMP production in vivo and in vitro after cell culture on the extracellular matrix protein, fibronectin. In this study, we have extended the characterization of this fibronectin-induced Arhgef1-regulated signaling pathway in both human and murine myeloid cells. Our results show that MMP9 production by fibronectin-stimulated monocytes and macrophages depends on autocrine thromboxane receptor signaling and that under normal conditions, this signaling pathway is attenuated by Arhgef1. Finally, we show that the expression of ARHGEF1 by human peripheral blood monocytes varies between individuals and inversely correlates with fibronectin-mediated MMP9 production.     

Extracellular matrix proteoglycans control the fate of bone marrow stromal cells

Extracellular matrix glycoproteins and proteoglycans bind a variety of growth factors and cytokines thereby regulating matrix assembly as well as bone formation. However, little is known about the mechanisms by which extracellular matrix molecules modulate osteogenic stem cells and bone formation. Using mice deficient in two members of the small leucine-rich proteoglycans, biglycan and decorin, we uncovered a role for these two extracellular matrix proteoglycans in modulating bone formation from bone marrow stromal cells. Our studies showed that the absence of the critical transforming growth factor-beta (TGF-beta)-binding proteoglycans, biglycan and decorin, prevents TGF-beta from proper sequestration within the extracellular matrix. The excess TGF-beta directly binds to its receptors on bone marrow stromal cells and overactivates its signaling transduction pathway. Overall, the predominant effect of the increased TGF-beta signaling in bgn/dcn-deficient bone marrow stromal cells is a "switch in fate" from growth to apoptosis, leading to decreased numbers of osteoprogenitor cells and subsequently reduced bone formation. Thus, biglycan and decorin appear to be essential for maintaining an appropriate number of mature osteoblasts by modulating the proliferation and survival of bone marrow stromal cells. These findings underscore the importance of the micro-environment in controlling the fate of adult stem cells and reveal a novel cellular and molecular basis for the physiological and pathological control of bone mass.     

单细胞测序分析人类胚胎干细胞神经分化的分子机制

目的 探讨人类胚胎干细胞(ESCs)分化为神经细胞的关键性靶基因及分子机制,为临床靶向治疗神经康复患者提供分子理论依据.方法 基于GEO数据平台芯片,采用单细胞测序方法(scRNA-seq),利用R语言从多分子维度(单细胞差异基因、蛋白互作网络和基因通路等)分析人类ESCs分化过程中的关键Marker基因并利用质控和数...     

Fibroblasts as architects of cancer pathogenesis

Studies of epithelial cancers (i.e., carcinomas) traditionally focused on transformation of the epithelium (i.e., the cancer cells) and how aberrant signaling within the cancer cells modulates the surrounding tissue of origin. In more recent decades, the normal cells, blood vessels, molecules, and extracellular components that surround the tumor cells, collectively known as the “tumor microenvironment” or “stroma”, have received increasing attention and are now thought to be key regulators of tumor initiation and progression. Of particular relevance to the work reviewed herein are the fibroblasts, which make up the major cell type within the microenvironment of most carcinomas. Due to their inherent heterogeneity, plasticity, and function, it is perhaps not surprising that fibroblasts are ideal modulators of normal and cancerous epithelium; however, these aspects also present challenges if we are to interrupt their tumor-supportive functions. Here, we review the current body of knowledge and the many questions that still remain about the special entity known as the cancer-associated fibroblast. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.     

Focal adhesion kinase signaling controls cyclic tensile strain enhanced collagen I-induced osteogenic differentiation of human mesenchymal stem cells

Focal adhesion kinase (FAK) is a key integrator of integrin-mediated signals from the extracellular matrix to the cytoskeleton and downstream signaling molecules. FAK is activated by phosphorylation at specific tyrosine residues, which then stimulate downstream signaling including the ERK1/2 pathway, leading to a variety of cellular responses. In this study, we examined the effects of FAK point mutations at tyrosine residues (Y397, Y925, Y861, and Y576/7) on osteogenic differentiation of human mesenchymal stem cells exposed to collagen I and cyclic tensile strain. Our results demonstrate that FAK signaling emanating from Y397, Y925, and to a lesser extent Y576/7, but not from Y861, controls osteogenic differentiation through an ERK1/2 pathway, as measured by expression levels of key osteogenesis marker genes and subsequent matrix mineralization. These data indicate that FAK is a critical decision maker in extracellular matrix/strain-enhanced osteogenic differentiation.     

Notch signaling in the pathogenesis of thoracic aortic aneurysms: A bridge between embryonic and adult states

Aneurysms of the thoracic aorta are a “silent killer” with no evident clinical signs until the fatal outcome. Molecular and genetic bases of thoracic aortic aneurysms mainly include transforming growth factor beta signaling, smooth muscle contractile units and metabolism genes, and extracellular matrix genes. In recent studies, a role of Notch signaling, among other pathways, has emerged in disease pathogenesis. Notch is a highly conserved signaling pathway that regulates the development and differentiation of many types of tissues and influences major cellular processes such as cell proliferation, differentiation and apoptosis. Mutations in several Notch signaling components have been associated with a number of heart defects, demonstrating an essential role of Notch signaling both in cardiovascular system development and its maintenance during postnatal life. This review discusses the role of Notch signaling in the pathogenesis of thoracic aortic aneurysms considering development and maintenance of the aortic root and how developmental regulations by Notch signaling may influence thoracic aortic aneurysms.     

Rheostatic signaling by CD44 and hyaluronan

Cellular function and adaptive behavior is often driven by signals generated in response to the local tissue microenvironment. Cell surface receptors that detect changes in extracellular matrix composition and modifications to extracellular matrix components, are ideally positioned to provide highly responsive sensors of changes in the microenvironment and mediate changes in cellular function required to maintain tissue integrity. Receptors can act as “on/off” switches, but ligand/receptor complexes that provide “rheostatic” control may be more sensitive, provide a more rapid mechanism of control and allow for fine-tuning of cellular responses to the microenvironment. Herein, we review evidence that transitions in the physiochemical properties of the extracellular glycosaminoglycan hyaluronan and in the function of its major receptor, CD44, differentially regulate ERK and Rac signal transduction pathways to provide critical rheostatic control of mesenchymal cell proliferation.     

表皮形态发生素(Epimorphin)与表皮形态发生

表皮形态发生素（epimorphin 又称为syntaxin2）是哺乳动物中高度保守的一个间质细胞表面膜蛋白,胞外区包含有1个19个氨基酸残基的部位（NL肽序列）,是其与细胞的结合位点,但发挥效应必须有其它的胞外区存在.目前,已经发现它调控下游的2个分子MMP3和C/EBPβ,但对于其信号通路还知之甚少,推测其可能通过直接或者间接磷酸化表皮生长因子受体（EGFR）而激发MAPK/ERK信号通路.它在多种表皮组织（包括肺、肠、肝、乳腺、胰腺、毛囊、胆囊、血管内皮等）的表皮形态发生,尤其是腺管状结构的形态发生过程中发挥重要作用.依靠极性和非极性2种不同的表达方式,epimorphin可以选择性介导腺管形态发生的2个关键过程:分支形态发生和腔形态发生,分支状形态发生涉及到腺管的发生和延展,腔形态发生涉及到腺管直径的增大.     

Reelin signals through phosphatidylinositol 3-kinase and Akt to control cortical development and through mTor to regulate dendritic growth

Reelin is an extracellular matrix protein with various functions during development and in the mature brain. It activates different signaling cascades in target cells, one of which is the phosphatidylinositol 3-kinase (PI3K) pathway, which we investigated further using pathway inhibitors and in vitro brain slice and neuronal cultures. We show that the mTor (mammalian target of rapamycin)-S6K1 (S6 kinase 1) pathway is activated by Reelin and that this depends on Dab1 (Disabled-1) phosphorylation and activation of PI3K and Akt (protein kinase B). PI3K and Akt are required for the effects of Reelin on the organization of the cortical plate, but their downstream partners mTor and glycogen synthase kinase 3beta (GSK3beta) are not. On the other hand, mTor, but not GSK3beta, mediates the effects of Reelin on the growth and branching of dendrites of hippocampal neurons. In addition, PI3K fosters radial migration of cortical neurons through the intermediate zone, an effect that is independent of Reelin and Akt.