ABSTRACT
Cherubism, a case of bone remodeling gone haywire, is associated with mutations in the adaptor protein SH3BP2. Two papers in this issue of Cell (Guettler et al. and Levaot et al.) demonstrate that these mutations disrupt the interaction between SH3BP2 and Tankyrase and describe rules for substrate recognition by this poly(ADP-ribose) polymerase. Establishing such rules paves the way to identifying all Tankyrase-regulated pathways in cells.
ABSTRACT
OBJECTIVES: The project aims were to identify infectious mechanisms responsible for an extreme form of mandibular osteonecrosis and osteomyelitis in West African populations and test the hypothesis that Mycobacterium tuberculosis plays a pivotal role. MATERIALS AND METHODS: DNA was extracted from mandibular fragments of 9 of 19 patients previously included in a prospective study leading to the mycobacterial hypothesis. Amplified DNAs were used for preparing libraries suitable for next-generation sequencing. For comparison of the whole-genome sequencing data of the 9 patients with DNAs of both microbiota and human tissues, DIAMOND v0.9.26 was used to align sequencing reads to NCBI-nr database and MEGAN 6 for taxonomy binning and identification of Mycobacterium tuberculosis strains. RESULTS: The data show that mandibular bone fragments of all 9 patients not only contain Homo sapiens and Mycobacterium tuberculosis DNAs; they also contain DNAs of Plasmodium ovale wallikeri, Staphylococcus aureus, Staphylococcus hominis, and Prevotella P3-120/intermedia; as well as large numbers of DNAs from other infectious components. CONCLUSIONS: The data obtained provide direct evidence to support the conclusion that combinations of Mycobacterium tuberculosis, Plasmodium ovale wallikeri, and other oral bacteria are involved in this particular type of mandibular destruction in West African individuals of many ages.
Subject(s)
Malaria , Plasmodium ovale , Humans , Malaria/complications , Plasmodium ovale/genetics , Prospective StudiesABSTRACT
Ligaments serve as compliant connectors between hard tissues. In that role, they function under various load regimes and directions. The 3D structure of ligaments is considered to form as a uniform entity that changes due to function. The periodontal ligament (PDL) connects the tooth to the bone and sustains different types of loads in various directions. Using the PDL as a model, employing a fabricated motorized setup in a microCT, we demonstrate that the fibrous network structure within the PDL is not uniform, even before the tooth becomes functional. Utilizing morphological automated segmentation methods, directionality analysis, as well as second harmonic generation imaging, we find high correlation between blood vessel distribution and fiber density. We also show a structural feature in a form of a dense collar around the neck of the tooth as well as a preferred direction of the fibrous network. Finally, we show that the PDL develops as a nonuniform structure, with an architecture designed to sustain specific types of load in designated areas. Based on these findings, we propose that ligaments in general should be regarded as nonuniform entities, structured already at developmental stages for optimal functioning under variable load regimes.
Subject(s)
Periodontal Ligament/diagnostic imaging , Tooth/diagnostic imaging , X-Ray Microtomography , Animals , Mice , Mice, Transgenic , Periodontal Ligament/blood supply , Periodontal Ligament/metabolism , Tooth/blood supply , Tooth/metabolismABSTRACT
Pathologic extraskeletal bone formation, or heterotopic ossification (HO), occurs following mechanical trauma, burns, orthopedic operations, and in patients with hyperactivating mutations of the type I bone morphogenetic protein receptor ACVR1 (Activin type 1 receptor). Extraskeletal bone forms through an endochondral process with a cartilage intermediary prompting the hypothesis that hypoxic signaling present during cartilage formation drives HO development and that HO precursor cells derive from a mesenchymal lineage as defined by Paired related homeobox 1 (Prx). Here we demonstrate that Hypoxia inducible factor-1α (Hif1α), a key mediator of cellular adaptation to hypoxia, is highly expressed and active in three separate mouse models: trauma-induced, genetic, and a hybrid model of genetic and trauma-induced HO. In each of these models, Hif1α expression coincides with the expression of master transcription factor of cartilage, Sox9 [(sex determining region Y)-box 9]. Pharmacologic inhibition of Hif1α using PX-478 or rapamycin significantly decreased or inhibited extraskeletal bone formation. Importantly, de novo soft-tissue HO was eliminated or significantly diminished in treated mice. Lineage-tracing mice demonstrate that cells forming HO belong to the Prx lineage. Burn/tenotomy performed in lineage-specific Hif1α knockout mice (Prx-Cre/Hif1α(fl:fl)) resulted in substantially decreased HO, and again lack of de novo soft-tissue HO. Genetic loss of Hif1α in mesenchymal cells marked by Prx-cre prevents the formation of the mesenchymal condensations as shown by routine histology and immunostaining for Sox9 and PDGFRα. Pharmacologic inhibition of Hif1α had a similar effect on mesenchymal condensation development. Our findings indicate that Hif1α represents a promising target to prevent and treat pathologic extraskeletal bone.
Subject(s)
Hypoxia-Inducible Factor 1, alpha Subunit/antagonists & inhibitors , Ossification, Heterotopic/genetics , Ossification, Heterotopic/prevention & control , Wounds and Injuries/complications , Activin Receptors, Type I/metabolism , Adipose Tissue/drug effects , Adipose Tissue/metabolism , Animals , Burns/complications , Burns/genetics , Chondrogenesis/drug effects , Chondrogenesis/genetics , Disease Models, Animal , Gene Regulatory Networks/drug effects , Humans , Hypoxia-Inducible Factor 1, alpha Subunit/genetics , Hypoxia-Inducible Factor 1, alpha Subunit/metabolism , Integrases/metabolism , Luminescent Measurements , Mesenchymal Stem Cells/drug effects , Mice, Knockout , Models, Biological , Mustard Compounds/pharmacology , Ossification, Heterotopic/diagnostic imaging , Ossification, Heterotopic/drug therapy , Phenylpropionates/pharmacology , RNA, Messenger/genetics , RNA, Messenger/metabolism , Receptor, Platelet-Derived Growth Factor alpha/metabolism , SOX9 Transcription Factor/metabolism , Signal Transduction/drug effects , Sirolimus/pharmacology , Tendons/drug effects , Tendons/pathology , Tendons/surgery , Tenotomy , Up-Regulation/drug effects , Wound Healing/drug effects , Wounds and Injuries/pathology , X-Ray MicrotomographyABSTRACT
Vascular endothelial growth factor A (Vegfa) has important roles in endochondral bone formation. Osteoblast precursors, endothelial cells and osteoclasts migrate from perichondrium into primary ossification centers of cartilage templates of future bones in response to Vegfa secreted by (pre)hypertrophic chondrocytes. Perichondrial osteolineage cells also produce Vegfa, but its function is not well understood. By deleting Vegfa in osteolineage cells in vivo, we demonstrate that progenitor-derived Vegfa is required for blood vessel recruitment in perichondrium and the differentiation of osteoblast precursors in mice. Conditional deletion of Vegfa receptors indicates that Vegfa-dependent effects on osteoblast differentiation are mediated by Vegf receptor 2 (Vegfr2). In addition, Vegfa/Vegfr2 signaling stimulates the expression and activity of Indian hedgehog, increases the expression of ß-catenin and inhibits Notch2. Our findings identify Vegfa as a regulator of perichondrial vascularity and osteoblast differentiation at early stages of bone development.
Subject(s)
Bone Development , Bone and Bones/blood supply , Cell Differentiation , Neovascularization, Physiologic , Osteoblasts/cytology , Osteoblasts/metabolism , Vascular Endothelial Growth Factor A/metabolism , Animals , Bone and Bones/metabolism , Calcification, Physiologic , Cell Count , Cell Lineage , Hedgehog Proteins/metabolism , Kruppel-Like Transcription Factors/metabolism , Mice , Osteogenesis , Receptor, Notch2/metabolism , Signal Transduction , Stem Cells/cytology , Vascular Endothelial Growth Factor Receptor-2/metabolism , Zinc Finger Protein GLI1 , beta Catenin/metabolismABSTRACT
Vascular endothelial growth factor A (VEGF) is a critical regulator of vascular development and postnatal angiogenesis and homeostasis, and it is essential for bone development and repair. Blood vessels serve both as structural templates for bone formation and they provide essential cells, growth factors and minerals needed for synthesis and mineralization, as well as turnover, of the extracellular matrix in bone. Through its regulation of angiogenesis, VEGF contributes to coupling of osteogenesis to angiogenesis, and it directly controls the differentiation and function of osteoblasts and osteoclasts. In this review, we summarize the properties of VEGF and its receptors that are relevant to bone formation and repair; the roles of VEGF during development of endochondral and membranous bones; and the contributions of VEGF to bone healing during different phases of bone repair. Finally, we discuss contributions of altered VEGF function in inherited disorders with bone defects as part of their phenotypes, and we speculate on what will be required before therapeutic strategies based on VEGF modulation can be developed for clinical use to treat patients with bone growth disorders and/or compromised bone repair. Developmental Dynamics 246:227-234, 2017. © 2016 Wiley Periodicals, Inc.
Subject(s)
Bone Development , Bone Regeneration , Vascular Endothelial Growth Factor A/physiology , Vascular Endothelial Growth Factors/physiology , Animals , Bone Diseases, Developmental/congenital , Bone Remodeling , Bone and Bones , HumansABSTRACT
Studies of proliferative hemangiomas have led to the discovery that interactions of endothelial cells with extracellular matrix and/or Vascular Endothelial Growth Factor (VEGF)-A stimulate the expression of VEGFR1, the VEGF decoy receptor, and suppress VEGF-dependent VEGFR2 signalling by a mechanism that requires the matrix-binding receptor Anthrax Toxin Receptor (ANTXR)1, VEGFR2, ß1 integrin and the Nuclear Factor of Activated T cells (NFAT). In hemangioma endothelial cells, all these components are present, but are functionally compromised, so that the levels of VEGFR1 are extremely low and VEGFR2 signalling is constitutively active. Consequently, the levels of Hypoxia Inducible Factor (HIF)-1α and its transcriptional targets, VEGF-A and C-X-C motif chemokine 12 (CxCl12), are elevated and a positive VEGF-A feedback loop is established. Overexpression of ANTXR1, carrying a heterozygous Ala-to-Thr mutation, induces hemangioma-like signalling in control endothelial cells; VEGF signalling is normalized when wild-type ANTXR1 is overexpressed in hemangioma cells. These findings suggest that ANTXR1 functions as a negative regulator of VEGF-A signalling. Studies of a mouse model of the Growth Retardation, Alopecia, Pseudo-anodontia and Optic Atrophy (GAPO) syndrome, caused by the loss-of-function mutations in ANTXR1, as well as knock-in mice carrying the Ala-to-Thr ANTXR1 mutation, confirm that ANTXR1 functions as a suppressor of VEGF-A signalling. Cutaneous endothelial cells isolated from ANTXR1-deficient mice exhibit low levels of VEGFR1, elevated levels of VEGF-A, HIF-1α and CxCl12 and activated VEGFR2 signalling as in hemangioma. Increased numbers of myeloid cells in the skin of ANTXR1-deficient mice are associated with reduced vascularity and increased skin fibrosis, suggesting a mechanism for hemangioma involution and replacement by fibrotic scars. Through controlling VEGF-A signalling and extracellular matrix synthesis, ANTXR1 is emerging as a key regulator of skeletal and connective tissue development and homeostasis.
Subject(s)
Bone Development/physiology , Connective Tissue/growth & development , Hemangioma/metabolism , Homeostasis/physiology , Animals , Hemangioma/pathology , Humans , Microfilament Proteins , Neoplasm Proteins/physiology , Receptors, Cell Surface/physiology , Signal Transduction/physiology , Vascular Endothelial Growth Factor A/metabolism , Vascular Endothelial Growth Factor Receptor-2/metabolismABSTRACT
Recent advances in extracellular signaling suggest that extracellular protein phosphorylation is a regulatory mechanism outside the cell. The list of reported active extracellular protein kinases and phosphatases is growing, and phosphorylation of an increasing number of extracellular matrix molecules and extracellular domains of trans-membrane proteins is being documented. Here, we use public proteomic databases, collagens - the major components of the extracellular matrix, extracellular signaling molecules and proteolytic enzymes as examples to assess what the roles of extracellular protein phosphorylation may be in health and disease. We propose that novel tools be developed to help assess the role of extracellular protein phosphorylation and translate the findings for biomedical applications. Furthermore, we suggest that the phosphorylation state of extracellular matrix components as well as the presence of extracellular kinases be taken into account when designing translational medical applications.
Subject(s)
Data Mining , Databases, Protein , Extracellular Space/chemistry , Proteins/therapeutic use , Proteomics , Amino Acid Sequence , Humans , Molecular Sequence Data , Phosphorylation , Proteins/chemistryABSTRACT
Cre/loxP recombination is a powerful strategy widely used for in vivo conditional gene targeting. This technique has made possible many important discoveries of gene function in normal and disease biology. However, due to the transgenic nature of most Cre mouse strains undesired phenotypes occasionally occur in Cre mice. Here we report skeletal defects in Osterix-Cre (Osx-Cre) transgenic mice including delayed calvarial ossification and fracture calluses at multiple skeletal sites. These data suggest that Osx-Cre containing controls should be used for both in vivo and in vitro skeletal analyses of conditional knockout mice generated with this Osx-Cre mouse strain.
Subject(s)
Bone and Bones/injuries , Integrases/genetics , Mice, Transgenic , Transcription Factors/genetics , Animals , Bone and Bones/physiopathology , Female , Mice , Mice, Knockout , Phenotype , Sp7 Transcription FactorSubject(s)
Achondroplasia/drug therapy , Achondroplasia/pathology , Hydroxymethylglutaryl-CoA Reductase Inhibitors/therapeutic use , Receptor, Fibroblast Growth Factor, Type 3/deficiency , Receptor, Fibroblast Growth Factor, Type 3/genetics , Thanatophoric Dysplasia/drug therapy , Thanatophoric Dysplasia/pathology , Animals , Female , MaleABSTRACT
Osteoblasts and adipocytes share a common precursor in adult bone marrow and there is a degree of plasticity between the two cell lineages. This has important implications for the etiology of not only osteoporosis but also several other diseases involving an imbalance between osteoblasts and adipocytes. Understanding the process of differentiation of osteoblasts and adipocytes and their trans-differentiation is crucial in order to identify genes and other factors that may contribute to the pathophysiology of such diseases. Several transcriptional regulators have been shown to control osteoblast and adipocyte differentiation and function. Regulation of cell commitment occurs at the level of the progenitor cell through cross talk between complex signaling pathways and epigenetic mechanisms such as DNA methylation, chromatin remodeling, and microRNAs. Here we review the complex precursor cell microenvironment controlling osteoblastogenesis and adipogenesis during tissue development, maintenance, and pathology.
Subject(s)
Adipocytes/cytology , Bone Marrow Cells/cytology , Cell Differentiation/physiology , Cell Lineage/physiology , Cellular Microenvironment/physiology , Osteoblasts/cytology , Regulatory Elements, Transcriptional/physiology , Animals , Epigenesis, Genetic/physiology , Humans , Regulatory Elements, Transcriptional/geneticsABSTRACT
ADAMTS9 is the most conserved member of a large family of secreted metalloproteases having diverse functions. Adamts9 null mice die before gastrulation, precluding investigations of its roles later in embryogenesis, in adult mice or disease models. We therefore generated a floxed Adamts9 allele to bypass embryonic lethality. In this mutant, unidirectional loxP sites flank exons 5-8, which encode the catalytic domain, including the protease active site. Mice homozygous for the floxed allele were viable, lacked an overt phenotype, and were fertile. Conversely, mice homozygous for a germ-line deletion produced from the floxed allele by Cre-lox recombination did not survive past gastrulation. Hemizygosity of the deleted Adamts9 in combination with mutant Adamts20 led to cleft palate and severe white spotting as previously described. Previously, Adamts9 haploinsufficiency combined with either Adamts20 or Adamts5 nullizygosity suggested a cooperative role in interdigital web regression, but the outcome of deletion of Adamts9 alone remained unknown. Here, Adamts9 was conditionally deleted in limb mesoderm using Prx1-Cre mice. Unlike other ADAMTS single knockouts, limb-specific Adamts9 deletion resulted in soft-tissue syndactyly (STS) with 100% penetrance and concurrent deletion of Adamts5 increased the severity of STS. Thus, Adamts9 has both non-redundant and cooperative roles in ensuring interdigital web regression. This new allele will be useful for investigating other biological functions of ADAMTS9.
Subject(s)
ADAM Proteins/genetics , Alleles , Syndactyly/genetics , ADAMTS9 Protein , Animals , Exons , Extremities/embryology , Mesoderm/metabolism , Mice , Mice, Inbred C57BL , PhenotypeABSTRACT
Progress in translational research has led to effective new treatments of a large number of diseases. Despite this progress, diseases including cancer and cardiovascular disorders still are at the top in death statistics and disorders such as osteoporosis and osteoarthritis represent an increasing disease burden in the aging population. Novel strategies in research are needed more than ever to overcome such diseases. The growing field of extracellular protein phosphorylation provides excellent opportunities to make major discoveries of disease mechanisms that can lead to novel therapies. Reversible phosphorylation/dephosphorylation of sites in the extracellular domains of matrix, cell-surface and trans-membrane proteins is emerging as a critical regulatory mechanism in health and disease. Moreover, a new concept is emerging from studies of extracellular protein phosphorylation: in cells where ATP is stored within secretory vesicles and released by exocytosis upon cell-stimulation, phosphorylation of extracellular proteins can operate as a messenger operating uniquely in signaling pathways responsible for long-term cellular adaptation. Here, we highlight new concepts that arise from this research, and discuss translation of the findings into clinical applications such as development of diagnostic disease markers and next-generation drugs.
Subject(s)
Phosphoprotein Phosphatases/metabolism , Translational Research, Biomedical , Humans , Phosphorylation , Protein Kinases/metabolismABSTRACT
Cranial base growth plates are important centers of longitudinal growth in the skull and are responsible for the proper anterior placement of the face and the stimulation of normal cranial vault development. We report that the presphenoidal synchondrosis (PSS), a midline growth plate of the cranial base, closes in the DBA/2J mouse strain but not in other common inbred strains. We investigated the genetics of PSS closure in DBA/2J mice by evaluating F1, F1 backcross, and/or F1 intercross offspring from matings with C57BL/6J and DBA/1J mice, whose PSS remain open. We observed that PSS closure is genetically determined, but not inherited as a simple Mendelian trait. Employing a genome-wide SNP array, we identified a region on chromosome 11 in the C57BL/6J strain that affected the frequency of PSS closure in F1 backcross and F1 intercross offspring. The equivalent region in the DBA/1J strain did not affect PSS closure in F1 intercross offspring. We conclude that PSS closure in the DBA/2J strain is complex and modified by different loci when outcrossed with C57BL/6J and DBA/1J mice.
Subject(s)
DNA/isolation & purification , Embryonic Development/genetics , Gene Fusion , Inheritance Patterns , Skull/embryology , Alleles , Animals , Chromosome Mapping , Chromosomes/genetics , Chromosomes/metabolism , Crosses, Genetic , DNA/genetics , Female , Genetic Linkage , Genomics/methods , Genotype , Liver/metabolism , Male , Mice , Mice, Inbred C57BL , Mice, Inbred DBA , Microsatellite Repeats , Models, Animal , Phenotype , Polymorphism, Single Nucleotide , Sequence Analysis, DNAABSTRACT
Osteoporosis results from an imbalance in skeletal remodeling that favors bone resorption over bone formation. Bone matrix is degraded by osteoclasts, which differentiate from myeloid precursors in response to the cytokine RANKL. To gain insight into the transcriptional regulation of bone resorption during growth and disease, we generated a conditional knockout of the transcription factor nuclear factor of activated T cells c1 (Nfatc1). Deletion of Nfatc1 in young mice resulted in osteopetrosis and inhibition of osteoclastogenesis in vivo and in vitro. Transcriptional profiling revealed NFATc1 as a master regulator of the osteoclast transcriptome, promoting the expression of numerous genes needed for bone resorption. In addition, NFATc1 directly repressed osteoclast progenitor expression of osteoprotegerin, a decoy receptor for RANKL previously thought to be an osteoblast-derived inhibitor of bone resorption. "Cherubism mice", which carry a gain-of-function mutation in SH3-domain binding protein 2 (Sh3bp2), develop osteoporosis and widespread inflammation dependent on the proinflammatory cytokine, TNF-alpha. Interestingly, deletion of Nfatc1 protected cherubism mice from systemic bone loss but did not inhibit inflammation. Taken together, our study demonstrates that NFATc1 is required for remodeling of the growing and adult skeleton and suggests that NFATc1 may be an effective therapeutic target for osteoporosis associated with inflammatory states.
Subject(s)
Bone Diseases, Metabolic/pathology , Cherubism/metabolism , Inflammation/pathology , NFATC Transcription Factors/metabolism , Osteoclasts/physiology , Osteoprotegerin/metabolism , Animals , Cherubism/genetics , Mice , Mice, Knockout , Mice, Transgenic , Osteoclasts/metabolism , Osteoprotegerin/geneticsABSTRACT
Endostatin, a C-terminal fragment of collagen XVIII, binds to TG-2 (transglutaminase-2) in a cation-dependent manner. Recombinant human endostatin binds to TG-2 with an affinity in the nanomolar range (Kd=6.8 nM). Enzymatic assays indicated that, in contrast with other extracellular matrix proteins, endostatin is not a glutaminyl substrate of TG-2 and is not cross-linked to itself by the enzyme. Two arginine residues of endostatin, Arg27 and Arg139, are crucial for its binding to TG-2. They are also involved in the binding to heparin [Sasaki, Larsson, Kreuger, Salmivirta, Claesson-Welsh, Lindahl, Hohenester and Timpl (1999) EMBO J. 18, 6240-6248], and to alpha5beta1 and alphavbeta3 integrins [Faye, Moreau, Chautard, Jetne, Fukai, Ruggiero, Humphries, Olsen and Ricard-Blum (2009) J. Biol. Chem. 284, 22029-22040], suggesting that endostatin is not able to interact simultaneously with TG-2 and heparan sulfate, or with TG-2 and integrins. Inhibition experiments support the hypothesis that the GTP-binding site of TG-2 is a potential binding site for endostatin. Endostatin and TG-2 are co-localized in the extracellular matrix secreted by endothelial cells under hypoxia, which stimulates angiogenesis. This interaction, occurring in a cellular context, might participate in the concerted regulation of angiogenesis and tumorigenesis by the two proteins.
Subject(s)
Endostatins/metabolism , Endothelial Cells/metabolism , Extracellular Matrix/metabolism , GTP-Binding Proteins/metabolism , Transglutaminases/metabolism , Cells, Cultured , Collagen Type XVIII/chemistry , Collagen Type XVIII/metabolism , Humans , Immunohistochemistry , Protein Binding , Protein Glutamine gamma Glutamyltransferase 2 , Protein Structure, Tertiary , Surface Plasmon ResonanceABSTRACT
Collagen assembly during development is essential for successful matrix mineralisation, which determines bone quality and mechanocompetence. However, the biochemical and structural perturbations that drive pathological skeletal collagen configuration remain unclear. Deletion of vascular endothelial growth factor (VEGF; also known as VEGFA) in bone-forming osteoblasts (OBs) induces sex-specific alterations in extracellular matrix (ECM) conformation and mineralisation coupled to vascular changes, which are augmented in males. Whether this phenotypic dimorphism arises as a result of the divergent control of ECM composition and its subsequent arrangement is unknown and is the focus of this study. Herein, we used murine osteocalcin-specific Vegf knockout (OcnVEGFKO) and performed ex vivo multiscale analysis at the tibiofibular junction of both sexes. Label-free and non-destructive polarisation-resolved second-harmonic generation (p-SHG) microscopy revealed a reduction in collagen fibre number in males following the loss of VEGF, complemented by observable defects in matrix organisation by backscattered electron scanning electron microscopy. This was accompanied by localised divergence in collagen orientation, determined by p-SHG anisotropy measurements, as a result of OcnVEGFKO. Raman spectroscopy confirmed that the effect on collagen was linked to molecular dimorphic VEGF effects on collagen-specific proline and hydroxyproline, and collagen intra-strand stability, in addition to matrix carbonation and mineralisation. Vegf deletion in male and female murine OB cultures in vitro further highlighted divergence in genes regulating local ECM structure, including Adamts2, Spp1, Mmp9 and Lama1. Our results demonstrate the utility of macromolecular imaging and spectroscopic modalities for the detection of collagen arrangement and ECM composition in pathological bone. Linking the sex-specific genetic regulators to matrix signatures could be important for treatment of dimorphic bone disorders that clinically manifest in pathological nano- and macro-level disorganisation. This article has an associated First Person interview with the first author of the paper.
Subject(s)
Extracellular Matrix , Vascular Endothelial Growth Factor A , Animals , Bone and Bones/metabolism , Collagen/metabolism , Extracellular Matrix/metabolism , Female , Humans , Male , Mice , Osteoblasts , Vascular Endothelial Growth Factor A/metabolismABSTRACT
The piezoelectric properties of single collagen type I fibrils in fascia were imaged with sub-20 nm spatial resolution using piezoresponse force microscopy. A detailed analysis of the piezoresponse force microscopy signal in controlled tip-fibril geometry revealed shear piezoelectricity parallel to the fibril axis. The direction of the displacement is preserved along the whole fiber length and is independent of the fiber conformation. It is shown that individual fibrils within bundles in skeletal muscle fascia can have opposite polar orientations and are organized into domains, i.e., groups of several fibers having the same polar orientation. We were also able to detect piezoelectric activity of collagen fibrils in the high-frequency range up to 200 kHz, suggesting that the mechanical response time of biomolecules to electrical stimuli can be approximately 5 micros.
Subject(s)
Collagen Type I/metabolism , Collagen Type I/ultrastructure , Molecular Imaging , Animals , Anisotropy , Biomechanical Phenomena , Collagen Type I/chemistry , Electricity , Mice , Microscopy, Atomic Force , Models, Molecular , Nanotechnology , Protein Structure, Tertiary , Time FactorsABSTRACT
Three exciting papers in this issue of Developmental Cell provide new insights into the regulation of chondrocytic, osteoblastic, and osteoclastic differentiation during skeletal development and postnatal growth. The studies demonstrate that Wnt/beta-catenin signaling represents both a mechanism in mesenchymal precursor cells for selecting between chondrocytic and osteoblastic fates as well as a mechanism in osteoblasts for stimulating the production of an inhibitor of osteoclast formation.
Subject(s)
Bone Development/physiology , Cytoskeletal Proteins/physiology , Intercellular Signaling Peptides and Proteins/physiology , Trans-Activators/physiology , Animals , Bone Development/genetics , Cell Differentiation , Chondrocytes/cytology , Chondrocytes/metabolism , Chondrogenesis , Cytoskeletal Proteins/genetics , Intercellular Signaling Peptides and Proteins/genetics , Mice , Osteoblasts/cytology , Osteoblasts/metabolism , Osteogenesis , Signal Transduction , Trans-Activators/genetics , Wnt Proteins , beta CateninABSTRACT
Within the framework of a broad definition of the extracellular matrix (ECM), this review discusses three genetic disorders in which major pathogenetic features have been traced back to alterations in the levels/activities of matrix components. In each case, disease-associated alterations are found both intra- and extracellularly. The nature of the ECM involvement is surprising, offers an exciting therapeutic opportunity, and deepens our understanding of ECM-cell interactions. The first of these disorders, cherubism, is a case of inflammatory bone loss in the jaws of children for reasons that are surprisingly systemic in nature, considering the local nature of the disease. The primary defect involves an intracellular signaling molecule, but a major pathogenetic component and therapeutic target of the disease is the extracellular cytokine tumor necrosis factor alpha. The second disorder, Knobloch syndrome, is caused by recessive mutations in collagen XVIII. Although this protein has been classified as belonging to a group of structural macromolecules, the consequence of the mutations is impairment of cellular metabolism. The third disorder, infantile hemangioma, is a common tumor of capillary endothelial cells in infancy. The tumor appears within a few days/weeks after birth, grows rapidly over several months, and regresses over several years. The proliferative phase is the result of constitutively high levels of vascular endothelial cell growth factor (VEGF)-dependent signaling through VEGF receptor 2 (VEGFR2), but recent studies have led to the surprising conclusion that abnormalities in a cell-surface receptor complex controlling expression of the VEGF decoy receptor VEGFR1 is the underlying cause.