National Institute of Dental and Craniofacial Research

Studies of the human microbiome have revealed that even healthy individuals differ remarkably in the microbes that occupy habitats such as the gut, skin and vagina. Much of this diversity remains unexplained, although diet, environment, host genetics and early microbial exposure have all been implicated. Accordingly, to characterize the ecology of human-associated microbial communities, the Human Microbiome Project has analysed the largest cohort and set of distinct, clinically relevant body habitats so far. We found the diversity and abundance of each habitat’s signature microbes to vary widely even among healthy subjects, with strong niche specialization both within and among individuals. The project encountered an estimated 81–99% of the genera, enzyme families and community configurations occupied by the healthy Western microbiome. Metagenomic carriage of metabolic pathways was stable among individuals despite variation in community structure, and ethnic/racial background proved to be one of the strongest associations of both pathways and microbes with clinical metadata. These results thus delineate the range of structural and functional configurations normal in the microbial communities of a healthy population, enabling future characterization of the epidemiology, ecology and translational applications of the human microbiome. The Human Microbiome Project Consortium reports the first results of their analysis of microbial communities from distinct, clinically relevant body habitats in a human cohort; the insights into the microbial communities of a healthy population lay foundations for future exploration of the epidemiology, ecology and translational applications of the human microbiome. The Human Microbiome Project (HMP), supported by the National Institutes of Health Common Fund, has the goal of characterizing the microbial communities that inhabit and interact with the human body in sickness and in health. In two Articles in this issue of Nature, the HMP Consortium presents the first population-scale details of the organismal and functional composition of the microbiota across five areas of the body. An associated News & Views discusses the initial results — which, along with those of a series of co-publications, already constitute the most extensive catalogue of organisms and genes related to the human microbiome yet published — and highlights some of the major questions that the project will tackle in the next few years.

Microbiology Society journals contain high-quality research papers and topical review articles. We are a not-for-profit publisher and we support and invest in the microbiology community, to the benefit of everyone. This supports our principal goal to develop, expand and strengthen the networks available to our members so that they can generate new knowledge about microbes and ensure that it is shared with other communities.

A peripheral mononeuropathy was produced in adult rats by placing loosely constrictive ligatures around the common sciatic nerve. The postoperative behavior of these rats indicated that hyperalgesia, allodynia and, possibly, spontaneous pain (or dysesthesia) were produced. Hyperalgesic responses to noxious radiant heat were evident on the second postoperative day and lasted for over 2 months. Hyperalgesic responses to chemogenic pain were also present. The presence of allodynia was inferred from the nocifensive responses evoked by standing on an innocuous, chilled metal floor or by innocuous mechanical stimulation, and by the rats' persistence in holding the hind paw in a guarded position. The presence of spontaneous pain was suggested by a suppression of appetite and by the frequent occurrence of apparently spontaneous nocifensive responses. The affected hind paw was abnormally warm or cool in about one-third of the rats. About one-half of the rats developed grossly overgrown claws on the affected side. Experiments with this animal model may advance our understanding of the neural mechanisms of neuropathic pain disorders in humans.

SUMMARY: An improved growth medium for lactobacilli is described. It supports good growth of lactobacilli generally and also is particularly useful for a number of fastidious strains which grow only poorly in other general media. In addition, tomato juice, a highly variable material, is not required. In a slightly modified form, it can also be used as a basal medium for fermentation tests.

(R)-Roscovitine, a pharmacological inhibitor of kinases, is currently in phase II clinical trial as a drug candidate for the treatment of cancers, Cushing's disease and rheumatoid arthritis. We here review the data that support the investigation of (R)-roscovitine as a potential therapeutic agent for the treatment of cystic fibrosis (CF). (R)-Roscovitine displays four independent properties that may favorably combine against CF: (1) it partially protects F508del-CFTR from proteolytic degradation and favors its trafficking to the plasma membrane; (2) by increasing membrane targeting of the TRPC6 ion channel, it rescues acidification in phagolysosomes of CF alveolar macrophages (which show abnormally high pH) and consequently restores their bactericidal activity; (3) its effects on neutrophils (induction of apoptosis), eosinophils (inhibition of degranulation/induction of apoptosis) and lymphocytes (modification of the Th17/Treg balance in favor of the differentiation of anti-inflammatory lymphocytes and reduced production of various interleukins, notably IL-17A) contribute to the resolution of inflammation and restoration of innate immunity, and (4) roscovitine displays analgesic properties in animal pain models. The fact that (R)-roscovitine has undergone extensive preclinical safety/pharmacology studies, and phase I and II clinical trials in cancer patients, encourages its repurposing as a CF drug candidate.

Characterization of the molecular function of the human genome and its variation across individuals is essential for identifying the cellular mechanisms that underlie human genetic traits and diseases. The Genotype-Tissue Expression (GTEx) project aims to characterize variation in gene expression levels across individuals and diverse tissues of the human body, many of which are not easily accessible. Here we describe genetic effects on gene expression levels across 44 human tissues. We find that local genetic variation affects gene expression levels for the majority of genes, and we further identify inter-chromosomal genetic effects for 93 genes and 112 loci. On the basis of the identified genetic effects, we characterize patterns of tissue specificity, compare local and distal effects, and evaluate the functional properties of the genetic effects. We also demonstrate that multi-tissue, multi-individual data can be used to identify genes and pathways affected by human disease-associated variation, enabling a mechanistic interpretation of gene regulation and the genetic basis of disease.

CD4+CD25+ regulatory T cells (Treg) are instrumental in the maintenance of immunological tolerance. One critical question is whether Treg can only be generated in the thymus or can differentiate from peripheral CD4+CD25- naive T cells. In this paper, we present novel evidence that conversion of naive peripheral CD4+CD25- T cells into anergic/suppressor cells that are CD25+, CD45RB-/low and intracellular CTLA-4+ can be achieved through costimulation with T cell receptors (TCRs) and transforming growth factor beta (TGF-beta). Although transcription factor Foxp3 has been shown recently to be associated with the development of Treg, the physiological inducers for Foxp3 gene expression remain a mystery. TGF-beta induced Foxp3 gene expression in TCR-challenged CD4+CD25- naive T cells, which mediated their transition toward a regulatory T cell phenotype with potent immunosuppressive potential. These converted anergic/suppressor cells are not only unresponsive to TCR stimulation and produce neither T helper cell 1 nor T helper cell 2 cytokines but they also express TGF-beta and inhibit normal T cell proliferation in vitro. More importantly, in an ovalbumin peptide TCR transgenic adoptive transfer model, TGF-beta-converted transgenic CD4+CD25+ suppressor cells proliferated in response to immunization and inhibited antigen-specific naive CD4+ T cell expansion in vivo. Finally, in a murine asthma model, coadministration of these TGF-beta-induced suppressor T cells prevented house dust mite-induced allergic pathogenesis in lungs.

Dentinal repair in the postnatal organism occurs through the activity of specialized cells, odontoblasts, that are thought to be maintained by an as yet undefined precursor population associated with pulp tissue. In this study, we isolated a clonogenic, rapidly proliferative population of cells from adult human dental pulp. These DPSCs were then compared with human bone marrow stromal cells (BMSCs), known precursors of osteoblasts. Although they share a similar immunophenotype in vitro, functional studies showed that DPSCs produced only sporadic, but densely calcified nodules, and did not form adipocytes, whereas BMSCs routinely calcified throughout the adherent cell layer with clusters of lipid-laden adipocytes. When DPSCs were transplanted into immunocompromised mice, they generated a dentin-like structure lined with human odontoblast-like cells that surrounded a pulp-like interstitial tissue. In contrast, BMSCs formed lamellar bone containing osteocytes and surface-lining osteoblasts, surrounding a fibrous vascular tissue with active hematopoiesis and adipocytes. This study isolates postnatal human DPSCs that have the ability to form a dentin/pulp-like complex.

OBJECTIVE: To provide recommendations for the core outcome domains that should be considered by investigators conducting clinical trials of the efficacy and effectiveness of treatments for chronic pain. Development of a core set of outcome domains would facilitate comparison and pooling of data, encourage more complete reporting of outcomes, simplify the preparation and review of research proposals and manuscripts, and allow clinicians to make informed decisions regarding the risks and benefits of treatment. METHODS: Under the auspices of the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT), 27 specialists from academia, governmental agencies, and the pharmaceutical industry participated in a consensus meeting and identified core outcome domains that should be considered in clinical trials of treatments for chronic pain. CONCLUSIONS: There was a consensus that chronic pain clinical trials should assess outcomes representing six core domains: (1) pain, (2) physical functioning, (3) emotional functioning, (4) participant ratings of improvement and satisfaction with treatment, (5) symptoms and adverse events, (6) participant disposition (e.g. adherence to the treatment regimen and reasons for premature withdrawal from the trial). Although consideration should be given to the assessment of each of these domains, there may be exceptions to the general recommendation to include all of these domains in chronic pain trials. When this occurs, the rationale for not including domains should be provided. It is not the intention of these recommendations that assessment of the core domains should be considered a requirement for approval of product applications by regulatory agencies or that a treatment must demonstrate statistically significant effects for all of the relevant core domains to establish evidence of its efficacy.

To isolate high-quality human postnatal stem cells from accessible resources is an important goal for stem-cell research. In this study we found that exfoliated human deciduous tooth contains multipotent stem cells [stem cells from human exfoliated deciduous teeth (SHED)]. SHED were identified to be a population of highly proliferative, clonogenic cells capable of differentiating into a variety of cell types including neural cells, adipocytes, and odontoblasts. After in vivo transplantation, SHED were found to be able to induce bone formation, generate dentin, and survive in mouse brain along with expression of neural markers. Here we show that a naturally exfoliated human organ contains a population of stem cells that are completely different from previously identified stem cells. SHED are not only derived from a very accessible tissue resource but are also capable of providing enough cells for potential clinical application. Thus, exfoliated teeth may be an unexpected unique resource for stem-cell therapies including autologous stem-cell transplantation and tissue engineering.

Adhesions between fibroblastic cells and extracellular matrix have been studied extensively in vitro, but little is known about their in vivo counterparts. Here, we characterized the composition and function of adhesions in three-dimensional (3D) matrices derived from tissues or cell culture. "3D-matrix adhesions" differ from focal and fibrillar adhesions characterized on 2D substrates in their content of alpha5beta1 and alphavbeta3 integrins, paxillin, other cytoskeletal components, and tyrosine phosphorylation of focal adhesion kinase (FAK). Relative to 2D substrates, 3D-matrix interactions also display enhanced cell biological activities and narrowed integrin usage. These distinctive in vivo 3D-matrix adhesions differ in structure, localization, and function from classically described in vitro adhesions, and as such they may be more biologically relevant to living organisms.

The genetics underlying severe COVID-19 The immune system is complex and involves many genes, including those that encode cytokines known as interferons (IFNs). Individuals that lack specific IFNs can be more susceptible to infectious diseases. Furthermore, the autoantibody system dampens IFN response to prevent damage from pathogen-induced inflammation. Two studies now examine the likelihood that genetics affects the risk of severe coronavirus disease 2019 (COVID-19) through components of this system (see the Perspective by Beck and Aksentijevich). Q. Zhang et al. used a candidate gene approach and identified patients with severe COVID-19 who have mutations in genes involved in the regulation of type I and III IFN immunity. They found enrichment of these genes in patients and conclude that genetics may determine the clinical course of the infection. Bastard et al. identified individuals with high titers of neutralizing autoantibodies against type I IFN-α2 and IFN-ω in about 10% of patients with severe COVID-19 pneumonia. These autoantibodies were not found either in infected people who were asymptomatic or had milder phenotype or in healthy individuals. Together, these studies identify a means by which individuals at highest risk of life-threatening COVID-19 can be identified. Science , this issue p. eabd4570 , p. eabd4585 ; see also p. 404

A variety of microbial communities and their genes (the microbiome) exist throughout the human body, with fundamental roles in human health and disease. The National Institutes of Health (NIH)-funded Human Microbiome Project Consortium has established a population-scale framework to develop metagenomic protocols, resulting in a broad range of quality-controlled resources and data including standardized methods for creating, processing and interpreting distinct types of high-throughput metagenomic data available to the scientific community. Here we present resources from a population of 242 healthy adults sampled at 15 or 18 body sites up to three times, which have generated 5,177 microbial taxonomic profiles from 16S ribosomal RNA genes and over 3.5 terabases of metagenomic sequence so far. In parallel, approximately 800 reference strains isolated from the human body have been sequenced. Collectively, these data represent the largest resource describing the abundance and variety of the human microbiome, while providing a framework for current and future studies. The Human Microbiome Project Consortium has established a population-scale framework to study a variety of microbial communities that exist throughout the human body, enabling the generation of a range of quality-controlled data as well as community resources. The Human Microbiome Project (HMP), supported by the National Institutes of Health Common Fund, has the goal of characterizing the microbial communities that inhabit and interact with the human body in sickness and in health. In two Articles in this issue of Nature, the HMP Consortium presents the first population-scale details of the organismal and functional composition of the microbiota across five areas of the body. An associated News & Views discusses the initial results — which, along with those of a series of co-publications, already constitute the most extensive catalogue of organisms and genes related to the human microbiome yet published — and highlights some of the major questions that the project will tackle in the next few years.

In this study, we characterized the self-renewal capability, multi-lineage differentiation capacity, and clonogenic efficiency of human dental pulp stem cells (DPSCs). DPSCs were capable of forming ectopic dentin and associated pulp tissue in vivo. Stromal-like cells were reestablished in culture from primary DPSC transplants and re-transplanted into immunocompromised mice to generate a dentin-pulp-like tissue, demonstrating their self-renewal capability. DPSCs were also found to be capable of differentiating into adipocytes and neural-like cells. The odontogenic potential of 12 individual single-colony-derived DPSC strains was determined. Two-thirds of the single-colony-derived DPSC strains generated abundant ectopic dentin in vivo, while only a limited amount of dentin was detected in the remaining one-third. These results indicate that single-colony-derived DPSC strains differ from each other with respect to their rate of odontogenesis. Taken together, these results demonstrate that DPSCs possess stem-cell-like qualities, including self-renewal capability and multi-lineage differentiation.

The Human Microbiome Project (HMP), funded as an initiative of the NIH Roadmap for Biomedical Research (http://nihroadmap.nih.gov), is a multi-component community resource. The goals of the HMP are: (1) to take advantage of new, high-throughput technologies to characterize the human microbiome more fully by studying samples from multiple body sites from each of at least 250 "normal" volunteers; (2) to determine whether there are associations between changes in the microbiome and health/disease by studying several different medical conditions; and (3) to provide both a standardized data resource and new technological approaches to enable such studies to be undertaken broadly in the scientific community. The ethical, legal, and social implications of such research are being systematically studied as well. The ultimate objective of the HMP is to demonstrate that there are opportunities to improve human health through monitoring or manipulation of the human microbiome. The history and implementation of this new program are described here.

Fibronectin (FN) mediates a wide variety of cellular interactions with the extracellular matrix (ECM) and plays important roles in cell adhesion,migration, growth and differentiation(Mosher, 1989;Carsons, 1989;Hynes, 1990;Yamada and Clark, 1996). FN is widely expressed by multiple cell types and is critically important in vertebrate development, as demonstrated by the early embryonic lethality of mice with targeted inactivation of the FN gene(George et al., 1993). Although FN has been studied for more than two decades, this remarkably complex molecule is still the subject of exciting discoveries, such as finding new integrin- and heparin-binding sites(Mostafavi-Pour et al., 2001;Liao et al., 2002) or even a new form of the molecule (Zhao et al.,2001) that mediates a particular viral infection(Liu and Collodi, 2002).FIG1FN usually exists as a dimer composed of two nearly identical ∼250 kDa subunits linked covalently near their C-termini by a pair of disulfide bonds(see poster). Each monomer consists of three types of repeating units (termed FN repeats): type I (purple rectangles), type II (green octagons) and type III(red ovals). FN contains 12 type I repeats, two type II repeats and 15-17 type III repeats, which together account for approximately 90% of the FN sequence. Type I repeats are about 40 amino-acid residues in length and contain two disulfide bonds; type II repeats comprise a stretch of approximately 60 amino acids and two intrachain disulfide bonds; and type III repeats are about 90 residues long without any disulfide bonds. All three types of FN repeat are also found in other molecules, suggesting that FN evolved through exon shuffling (Patel et al.,1987).Although FN molecules are the product of a single gene, the resulting protein can exist in multiple forms that arise from alternative splicing of a single pre-mRNA that can generate as many as 20 variants in human FN (for reviews, see ffrench-Constant,1995; Kosmehl et al.,1996) (left panel, Plasma and Cellular fibronectin). A major type of splicing occurs within the central set of type III repeats (left panel, FN III7 to FN III15). Exon usage or skipping leads to inclusion or exclusion of either of two type III repeats — EDB (also termed EIIIB or EDII and located between FN repeats III7 and III8) and EDA (also called EIIIA or EDI and located between FN repeats III11 and III12). This `yes or no' type of splicing of FN ED domains is found in many vertebrates, including Xenopus, chickens, rats and humans.A third region of alternative splicing is localized to a non-homologous stretch called the V (variable in length) or IIICS (type III connecting segment) region. The structural variations in this region are more complex and species dependent (left panel, lower four gray boxes). In most species studied to date, except chicken, this region can be either partially or completely included or excluded; for example, in human FN, there can be five different V region variants.1 A fourth type of splicing is found in cartilage, where the predominant form of FN [termed (V+C)-] lacks the entire V region along with the FN III15 and FN I10 repeats. Interestingly, this FN isoform exists not only as a homodimer but also in an unusual monomeric configuration(left panel, Single-chain fibronectins). Recently, another single-chain FN(termed FN2) has been described in zebrafish, together with a FN1 form that is very similar to FNs identified in other vertebrates. The truncated FN2 form results from a fifth type of splicing in zebrafish (left panel, Single-chain fibronectins).1In chicken, the whole 120 amino acid residues of the V region can be included or a 44 amino acid segment from the 5′ end can be excluded(creating V76), but the whole V region is never missing. A similar mechanism leads to exclusion of a 25 amino acid fragment in rat, generating V95 that can be detected together with V0 and V120 forms. Splicing of the V region is even more complicated in human where segments from both 5′ (25aa) and 3′ (31aa) ends can be omitted independently (creating V95 and V89 correspondingly) or together (V64) producing five different V regions.FN is an abundant soluble constituent of plasma (300 μg/ml) and other body fluids and also part of the insoluble extracellular matrix. On the basis of its solubility, FN can be subdivided into two forms — soluble plasma FN (pFN) and less-soluble cellular (cFN) FN. Plasma FN is synthesized predominantly in the liver by hepatocytes and shows a relatively simple splicing pattern. The alternatively spliced EDA and EDB domains are almost always absent from plasma FN, although both V0 and V+ are present (left panel,Plasma fibronectin). Cellular FN consists of a much larger and more heterogeneous group of FN isoforms that result from cell-type-specific and species-specific splicing patterns (left panel, Cellular fibronectin). Thus,alternative splicing of precursor mRNA from the single FN gene has the capacity to produce a large number of variants, generating FNs with different cell-adhesive, ligand-binding, and solubility properties that provide a mechanism for cells to precisely alter the composition of the ECM in a developmental and tissue-specific manner.FN can be a ligand for a dozen members of the integrin receptor family (for a recent review, see Plow et al.,2000). Integrins are structurally and functionally related cell-surface heterodimeric receptors that link the ECM with the intracellular cytoskeleton. A large number of different integrins bind to FN, including the classic FN receptor α5β1 (middle panel,Integrin interaction sites). Extensive analyses have narrowed down the regions involved in cell adhesion along the lengthy FN molecule to several minimal integrin-recognition sequences (middle panel, single amino-acid sequences in red). The best known of these — RGD — is located in FN repeat III10. The recognition of this simple tripeptide sequence is complex and depends on flanking residues, its three-dimensional presentation and individual features of the integrin-binding pockets. For example, a second site in FN repeat III9 (the `synergy site' PHSRN, green) promotes specific α5β1 integrin binding to FN,apparently via interactions with the α5 subunit. However,binding of the FN receptor α5β1 to FN is not restricted only to repeats III9 and III10. It can also interact with an N-terminal fragment containing repeats I1-9 and II1,2, which also promotesα 5β1-integrin-mediated cell adhesion. Interestingly, interaction with this N-terminal region can trigger integrin-mediated intracellular signals that are distinct from those generated in response to ligation with the RGD sequence.A second set of FN sequences, which are bound by theα 4β1 integrin, has also received considerable attention. Two cell-recognition sequences (LDV and REDV) were originally identified in the alternatively spliced V region. Both of them are recognized by α4β1 andα 4β7. Additional sites recognized by theα 4β1 integrin — IDAPS and KLDAPT— are also present in repeats III14 and III5,respectively (the latter also binds to theα 4β7 integrin). Recently, binding ofα 4β1 as well asα 9β1 to an EDGIHEL sequence located within the alternatively spliced EDA segment has been reported, suggesting a possible adhesive function for the increased EDA-containing FN species observed during wound healing (Liao et al.,2002).Elucidation of the sites of integrin binding as well as other functionally important domains within the FN molecule was greatly facilitated by the early discovery that all FNs are cleaved only in specific regions when subjected to limited proteolytic digestion (reviewed byMosher, 1989;Hynes, 1990). Even a protease capable of cleaving proteins at many sites (such as pronase) will initially cleave FN, and it will only do this at highly specific, probably non-folded,unprotected locations. A simplified scheme of the major proteolytic cleavage sites is shown in the middle panel (see Major proteolytic digestion sites). The binding activities of FN are often preserved after such proteolysis and can be identified within particular fragments.FN has a remarkably wide variety of functional activities besides binding to cell surfaces through integrins. It binds to a number of biologically important molecules that include heparin, collagen/gelatin, and fibrin. These interactions are mediated by several distinct structural and functional domains, which have been defined by proteolytic fragmentation or recombinant DNA analyses (see Mosher,1989; Hynes, 1990;Yamada and Clark, 1996; and the website http://www.gwumc.edu/biochem/ingham/fnpage.htm).FN contains two major heparin-binding domains that interact with heparan sulfate proteoglycans (right panel, Ligand interaction sites). The strongest heparin-binding site is located in the C-terminal part (Heparin II) and a weaker binding domain is situated at the N-terminal end of the protein(Heparin I). The high-affinity heparin II domain can also bind to a widely distributed glycosaminoglycan, chondroitin sulfate, whereas the weaker heparin-binding domain contains a Staphylococus-aureus-binding site that mediates FN interactions with bacteria. Recently, a novel glycosaminoglycan-binding site has been identified within the V region of FN(Mostafavi-Pour et al., 2001)(marked as `Heparin' at the V domain). In at least some cell types, the heparin-binding domains of FN potentiate cell adhesion.The collagen-binding domain includes repeats I6-9 and II1,2, and it binds far more effectively to denatured collagen(gelatin) than to native collagen. Thus, FN interactions with collagens in general may be due to its binding to unfolded regions of the collagen triple helix. It has been suggested that the physiological function of the collagen/gelatin-binding domain is related more to binding and clearance of denatured collagenous materials from blood and tissue than to mediating cell adhesion to collagen. Interestingly, however, a recent analysis of the physiological state of collagen indicates that the triple helix is likely to unfold locally at body temperature (Leikina et al., 2002), which suggests that this FN domain could be involved in interactions with native collagen in vivo.FN also contains two major fibrin-binding sites (Fibrin I and Fibrin II). The major site is in the N-terminal domain and is formed by type I repeats 4 and 5. The interaction of FN with fibrin is thought to be important for cell adhesion or cell migration into fibrin clots. In both cases, cross-linking between FN and fibrin mediated by factor XIII transglutaminase is proposed to mediate the effect (the cross-linking site on the FN molecule is marked by factor XIIIa and an arrow). The interaction of FN with fibrin may also be involved in macrophage clearance of fibrin from circulation after trauma or in inflammation.FNs are glycoproteins that contain 4-9% carbohydrate, depending on the cell source. Glycosylation sites that are either N-linked (red stars) or O-linked(green star) reside predominantly within type III repeats and the collagen-binding domain. The physiological role of the carbohydrates is not certain, although they appear to stabilize FN against hydrolysis and modulate its affinity to some substrates.Although the plasma FN that circulates in blood is in a closed, reportedly non-active form, most of the FN activities in the body have been ascribed to the insoluble form of FN that exists as part of the extracellular matrix (see the immunofluorescence image obtained with anti-FN antibodies at the bottom of the middle panel labeled Fibronectin-based matrix). The creation and deposition of insoluble FN fibrils into the ECM is a tightly regulated,cell-mediated process termed FN fibrillogenesis or FN matrix assembly (for a review, see Geiger et al.,2001). A critical step in this process is self-association of FN into aggregates and fibrils, which is directed by multiple binding sites that have been identified along the molecule (right panel, Sites involved in fibronectin fibrillogenesis). Some of these self-interaction sites are exposed and available for binding (marked in yellow), while others are cryptic (marked in light brown) and become accessible only after conformational changes, for example, by cell-driven mechanical stretching of the FN molecule.FN is one of the largest multi-domain proteins for which domain organization, molecular interactions, and key functions have been established in great detail. Exploration of the cell-type-specific splicing variants,glycosylation patterns and their relationship to health and disease will be further challenges in the study of this fascinating molecule.

Bone marrow stromal cells are progenitors of skeletal tissue components such as bone, cartilage, the hematopoiesis-supporting stroma, and adipocytes. In addition, they may be experimentally induced to undergo unorthodox differentiation, possibly forming neural and myogenic cells. As such, they represent an important paradigm of post-natal nonhematopoietic stem cells, and an easy source for potential therapeutic use. Along with an overview of the basics of their biology, we discuss here their potential nature as components of the vascular wall, and the prospects for their use in local and systemic transplantation and gene therapy.

Periodontal disease is a chronic inflammatory condition characterized by destruction of the periodontal tissues and resulting in loss of connective tissue attachment, loss of alveolar bone, and the formation of pathological pockets around the diseased teeth. Some level of periodontal disease has been found in most populations studied and is responsible for a substantial portion of the tooth loss in adulthood.

Mesenchymal stem cell populations have previously been identified in adult bone marrow and dental pulp that are capable of regenerating the bone marrow and dental pulp microenvironments, respectively. Here we show that these stem cell populations reside in the microvasculature of their tissue of origin. Human bone marrow stromal stem cells (BMSSCs) and dental pulp stem cells (DPSCs) were isolated by immunoselection using the antibody, STRO-1, which recognizes an antigen on perivascular cells in bone marrow and dental pulp tissue. Freshly isolated STRO-1 positive BMSSCs and DPSCs were tested for expression of vascular antigens known to be expressed by endothelial cells (von Willebrand factor, CD146), smooth muscle cells, and pericytes (alpha-smooth muscle actin, CD146), and a pericyte-associated antigen (3G5), by immunohistochemistry, fluorescence-activated cell sorting (FACS), and/or immunomagnetic bead selection. Both BMSSCs and DPSCs lacked expression of von Willebrand factor but were found to be positive for alpha-smooth muscle actin and CD146. Furthermore, the majority of DPSCs expressed the pericyte marker, 3G5, while only a minor population of BMSSCs were found to be positive for 3G5. The finding that BMSSCs and DPSCs both display phenotypes consistent with different perivascular cell populations, regardless of their diverse ontogeny and developmental potentials, may have further implications in understanding the factors that regulate the formation of mineralized matrices and other associated connective tissues.

Recent studies have focused on the potential role of transforming growth factor type beta (TGF-beta) as an immunoregulatory peptide. In this context, we demonstrate that TGF-beta is a potent chemoattractant for human peripheral blood monocytes. At concentrations from 0.1 to 10 pg/ml, TGF-beta induces directed monocyte migration in vitro. Consistent with this observation is the expression of high-affinity TGF-beta receptors on the monocytes with a Kd of 1-10 pM. At higher concentrations of TGF-beta (greater than or equal to 1 ng/ml), monocytes are stimulated to generate biologically active mediator(s) that enhance fibroblast growth. Gene expression for one of these growth factors, interleukin 1, is induced in monocytes within hours after exposure to TGF-beta. Thus, TGF-beta may provide an important signal for monocyte recruitment and for regulation of their synthesis of mediators of fibroblast growth and activity in wound healing.