Discoidin domain receptors and their ligand, collagen, are temporally regulated in fetal rat fibroblasts in vitro

Mesodermal Derivatives of Pluripotent Stem Cells Route to Scarless Healing

Scar formation during normal tissue regeneration in adults may result in noticeable cosmetic and functional defects and have a significant impact on the quality of life. In contrast, fetal tissues in the mid-gestation period are known to be capable of complete regeneration with the restitution of the initial architecture, organization, and functional activity. Successful treatments that are targeted to minimize scarring can be realized by understanding the cellular and molecular mechanisms of fetal wound regeneration. However, such experiments are limited by the inaccessibility of fetal material for comparable studies. For this reason, the molecular mechanisms of fetal regeneration remain unknown. Mesenchymal stromal cells (MSCs) are central to tissue repair because the molecules they secrete are involved in the regulation of inflammation, angiogenesis, and remodeling of the extracellular matrix. The mesodermal differentiation of human pluripotent stem cells (hPSCs) recapitulates the sequential steps of embryogenesis in vitro and provides the opportunity to generate the isogenic cell models of MSCs corresponding to different stages of human development. Further investigation of the functional activity of cells from stromal differon in a pro-inflammatory microenvironment will procure the molecular tools to better understand the fundamental mechanisms of fetal tissue regeneration. Herein, we review recent advances in the generation of clonal precursors of primitive mesoderm cells and MSCs from hPSCs and discuss critical factors that determine the functional activity of MSCs-like cells in a pro-inflammatory microenvironment in order to identify therapeutic targets for minimizing scarring.

Discoidin domain receptor 1 may be involved in biological barrier homeostasis

WHAT IS KNOWN AND OBJECTIVE

Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase involved in the pathological processes of several diseases, such as keloid formation, renal fibrosis, atherosclerosis, tumours, and inflammatory processes. The biological barrier is the first line of defence against pathogens, and its disruption is closely related to diseases. In this review, we attempt to elucidate the relationship between DDR1 and the biological barrier, explore the potential biological value of DDR1, and review the current research status and clinical potential of DDR1-selective inhibitors.

METHODS

We conducted an extensive literature search on PubMed to collect studies on the relevance of DDR1 to biological barriers and DDR1-selective inhibitors. With these studies, we explored the relationship between DDR1 and biological barriers and briefly reviewed representative DDR1-selective inhibitors that have been reported in recent years.

RESULTS AND DISCUSSION

First, the review of the potential mechanisms by which DDR1 regulates biological barriers, including the epithelial, vascular, glomerular filtration, blood-labyrinth, and blood-brain barriers. In the body, DDR1 dysfunction and aberrant expression may be involved in the homeostasis of the biological barrier. Secondly, the review of DDR1 inhibitors reported in recent years shows that DDR1-targeted inhibition is an attractive and promising pharmacological intervention.

WHAT IS NEW AND CONCLUSIONS

This review shows that DDR1 is involved in various physiological and pathological processes and in the regulation of biological barrier homeostasis. However, studies on DDR1 and biological barriers are still scarce, and further studies are needed to elucidate their specific mechanisms. The development of targeted inhibitors provides a new direction and idea to study the mechanism of DDR1.

Dermal Fibroblast Heterogeneity and Its Contribution to the Skin Repair and Regeneration

Significance: Dermal fibroblasts are the major cell type in the skin's dermal layer. These cells originate from distinct locations of the embryo and reside in unique niches in the dermis. Different dermal fibroblasts exhibit distinct roles in skin development, homeostasis, and wound healing. Therefore, these cells are becoming attractive candidates for cell-based therapies in wound healing. Recent Advances: Human skin dermis comprises multiple fibroblast subtypes, including papillary, reticular, and hair follicle-associated fibroblasts, and myofibroblasts after wounding. Recent studies reveal that these cells play distinct roles in wound healing and contribute to diverse healing outcomes, including nonhealing chronic wound or excessive scar formation, such as hypertrophic scars (HTS) and keloids, with papillary fibroblasts having antiscarring and reticular fibroblast scar-forming properties. Critical Issues: The identities and functions of dermal fibroblast subpopulations in many respects remain unknown. In this review, we summarize the current understanding of dermal fibroblast heterogeneity, including their defined cell markers and dermal niches, dynamic changes, and contributions to skin wound healing, with the emphasis on scarless healing, healing with excessive scars (HTS and keloids), chronic wounds, and the potential application of this heterogeneity for developing cell-based therapies that allow wounds to heal faster with less scarring. Future Directions: Heterogeneous dermal fibroblast populations and their functions are poorly characterized. Refining and advancing our understanding of dermal fibroblast heterogeneity and their participation in skin homeostasis and wound healing may create potential therapeutic applications for nonhealing chronic wounds or wounds that heal with excessive scarring.

Shaping Pancreatic β-Cell Differentiation and Functioning: The Influence of Mechanotransduction

Embryonic and pluripotent stem cells hold great promise in generating β-cells for both replacing medicine and novel therapeutic discoveries in diabetes mellitus. However, their differentiation in vitro is still inefficient, and functional studies reveal that most of these β-like cells still fail to fully mirror the adult β-cell physiology. For their proper growth and functioning, β-cells require a very specific environment, the islet niche, which provides a myriad of chemical and physical signals. While the nature and effects of chemical stimuli have been widely characterized, less is known about the mechanical signals. We here review the current status of knowledge of biophysical cues provided by the niche where β-cells normally live and differentiate, and we underline the possible machinery designated for mechanotransduction in β-cells. Although the regulatory mechanisms remain poorly understood, the analysis reveals that β-cells are equipped with all mechanosensors and signaling proteins actively involved in mechanotransduction in other cell types, and they respond to mechanical cues by changing their behavior. By engineering microenvironments mirroring the biophysical niche properties it is possible to elucidate the β-cell mechanotransductive-regulatory mechanisms and to harness them for the promotion of β-cell differentiation capacity in vitro.

Advances in Fetal Surgery: Current and Future Relevance in Plastic Surgery

Scarless healing has long been the holy grail for plastic surgery. While historically fetal surgery has tempted plastic surgeons with the allure of scarless correction of congenital abnormalities, the risks far outweighed the benefits and these interventions never materialized. Current advances in fetal surgery with minimally invasive fetoscopic surgery have made these early fetal interventions safer, leading to expanding applications. While the plastic surgeon's role is limited as of yet, this article provides a review of the history of fetal surgery and the advances that may become relevant to the future plastic surgeon.

DDR1 role in fibrosis and its pharmacological targeting

Discoidin domain receptor1 (DDR1) is a collagen activated receptor tyrosine kinase and an attractive anti-fibrotic target. Its expression is mainly limited to epithelial cells located in several organs including skin, kidney, liver and lung. DDR1's biology is elusive, with unknown downstream activation pathways; however, it may act as a mediator of the stromal-epithelial interaction, potentially controlling the activation state of the resident quiescent fibroblasts. Increased expression of DDR1 has been documented in several types of cancer and fibrotic conditions including skin hypertrophic scars, idiopathic pulmonary fibrosis, cirrhotic liver and renal fibrosis. The present review article focuses on: a) detailing the evidence for a role of DDR1 as an anti-fibrotic target in different organs, b) clarifying DDR1 tissue distribution in healthy and diseased tissues as well as c) exploring DDR1 protective mode of action based on literature evidence and co-authors experience; d) detailing pharmacological efforts attempted to drug this subtle anti-fibrotic target to date.

Wound Healing: A Cellular Perspective

Wound healing is one of the most complex processes in the human body. It involves the spatial and temporal synchronization of a variety of cell types with distinct roles in the phases of hemostasis, inflammation, growth, re-epithelialization, and remodeling. With the evolution of single cell technologies, it has been possible to uncover phenotypic and functional heterogeneity within several of these cell types. There have also been discoveries of rare, stem cell subsets within the skin, which are unipotent in the uninjured state, but become multipotent following skin injury. Unraveling the roles of each of these cell types and their interactions with each other is important in understanding the mechanisms of normal wound closure. Changes in the microenvironment including alterations in mechanical forces, oxygen levels, chemokines, extracellular matrix and growth factor synthesis directly impact cellular recruitment and activation, leading to impaired states of wound healing. Single cell technologies can be used to decipher these cellular alterations in diseased states such as in chronic wounds and hypertrophic scarring so that effective therapeutic solutions for healing wounds can be developed.

DDR1 and DDR2 in skin

DDR1 and DDR2 are expressed in skin but their expression differs according to the skin compartment, epidermis, dermis, hypodermis and to the embryonic origin of the cells. In skin, it seems that during physiological processes such as wound healing or pathological processes such as tumorigenesis or systemic sclerosis development only one of the DDR is dysregulated. Furthermore, the altered DDR in pathological process is not necessarily the DDR implicated in basal homeostasis. Indeed, in epidermis, while DDR1 is the main DDR involved in melanocyte homeostasis, DDR2 seems to be the main DDR implicated in melanoma. On the contrary, in dermis, while DDR2 is necessary for normal wound healing, dysregulation of DDR1 is associated with abnormal wound healing leading to keloid. In conclusion, targeting DDR could be a therapeutic solution, however side effects have to be managed carefully.

Therapeutic Strategies for Modulating the Extracellular Matrix to Improve Pancreatic Islet Function and Survival After Transplantation

PURPOSES OF REVIEW

Extracellular matrix (ECM) components modulate the interaction between pancreatic islet cells. During the islet isolation prior to transplantation as treatment for type 1 diabetes, the ECM is disrupted impacting functional graft survival. Recently, strategies for restoring ECM have shown to improve transplantation outcomes. This review discusses the current therapeutic strategies to modulate ECM components to improve islet engraftment.

RECENT FINDINGS

Approaches applied are seeding islets in ECM of decellularized organs, supplementation of specific ECM components in polymeric scaffolds or immunoisolating capsules, and stimulating islet ECM production with specific growth factors or ECM-producing cells. These strategies have shown success in improving functional islet survival. However, the same experiments show that caution should be taken as some ECM components may negatively impact islet function and engraftment. ECM restoration resulted in improved transplantation outcomes, but careful selection of beneficial ECM components and strategies is warranted.

Scarless wound healing: Transitioning from fetal research to regenerative healing

Since the discovery of scarless fetal skin wound healing, research in the field has expanded significantly with the hopes of advancing the finding to adult human patients. There are several differences between fetal and adult skin that have been exploited to facilitate scarless healing in adults including growth factors, cytokines, and extracellular matrix substitutes. However, no one therapy, pathway, or cell subtype is sufficient to support scarless wound healing in adult skin. More recently, products that contain or mimic fetal and adult uninjured dermis were introduced to the wound healing market with promising clinical outcomes. Through our review of the major experimental targets of fetal wound healing, we hope to encourage research in areas that may have a significant clinical impact. Additionally, we will investigate therapies currently in clinical use and evaluate whether they represent a legitimate advance in regenerative medicine or a vulnerary agent. WIREs Dev Biol 2018, 7:e309. doi: 10.1002/wdev.309 This article is categorized under: Adult Stem Cells, Tissue Renewal, and Regeneration > Regeneration Plant Development > Cell Growth and Differentiation Adult Stem Cells, Tissue Renewal, and Regeneration > Environmental Control of Stem Cells.

Signals in the pancreatic islet microenvironment influence β-cell proliferation

The progressive loss of pancreatic β-cell mass that occurs in both type 1 and type 2 diabetes is a primary factor driving efforts to identify strategies for effectively increasing, enhancing or restoring β-cell mass. While factors that seem to influence β-cell proliferation in specific contexts have been described, reliable stimulation of human β-cell proliferation has remained a challenge. Importantly, β-cells exist in the context of a complex, integrated pancreatic islet microenvironment where they interact with other endocrine cells, vascular endothelial cells, extracellular matrix, neuronal projections and islet macrophages. This review highlights different components of the pancreatic microenvironment, and reviews what is known about how signaling that occurs between β-cells and these other components influences β-cell proliferation. Future efforts to further define the role of the pancreatic islet microenvironment on β-cell proliferation may lead to the development of successful approaches to increase or restore β-cell mass in diabetes.

Tissue engineering and regenerative repair in wound healing

Wound healing is a highly evolved defense mechanism against infection and further injury. It is a complex process involving multiple cell types and biological pathways. Mammalian adult cutaneous wound healing is mediated by a fibroproliferative response leading to scar formation. In contrast, early to mid-gestational fetal cutaneous wound healing is more akin to regeneration and occurs without scar formation. This early observation has led to extensive research seeking to unlock the mechanism underlying fetal scarless regenerative repair. Building upon recent advances in biomaterials and stem cell applications, tissue engineering approaches are working towards a recapitulation of this phenomenon. In this review, we describe the elements that distinguish fetal scarless and adult scarring wound healing, and discuss current trends in tissue engineering aimed at achieving scarless tissue regeneration.

New insights into vertebrate skin regeneration

Regeneration biology has experienced a renaissance as clinicians, scientists, and engineers have combined forces to drive the field of regenerative medicine. Studies investigating the mechanisms that regulate wound healing in adult mammals have led to a good understanding of the stereotypical processes that lead to scarring. Despite comparative studies of fetal wound healing in which no scar is produced, the fact remains that insights from this work have failed to produce therapies that can regenerate adult human skin. In this review, we analyze past and contemporary accounts of wound healing in a variety of vertebrates, namely, fish, amphibians, and mammals, in order to demonstrate how examples of skin regeneration in adult organisms can impact traditional wound-healing research. When considered together, these studies suggest that inflammation and reepithelialization are necessary events preceding both scarring and regeneration. However, the extent to which these processes may direct one outcome over another is likely weaker than currently accepted. In contrast, the extent to which newly deposited extracellular matrix in the wound bed can be remodeled into new skin, and the intrinsic ability of new epidermis to regenerate appendages, appears to underlie the divergence between scar-free healing and the persistence of a scar. We discuss several ideas that may offer areas of overlap between researchers using these different model organisms and which may be of benefit to the ultimate goal of scar-free human wound healing.

Scarless fetal skin wound healing update

Scar formation, a physiologic process in adult wound healing, can have devastating effects for patients; a multitude of pathologic outcomes, affecting all organ systems, stems from an amplification of this process. In contrast to adult wound repair, the early-gestation fetal skin wound heals without scar formation, a phenomenon that appears to be intrinsic to fetal skin. An intensive research effort has focused on unraveling the mechanisms that underlie scarless fetal wound healing in an attempt to improve the quality of healing in both children and adults. Unique properties of fetal cells, extracellular matrix, cytokine profile, and gene expression contribute to this scarless repair. Despite the great increase in knowledge gained over the past decades, the precise mechanisms regulating scarless fetal healing remain unknown. Herein, we describe the current proposed mechanisms underlying fetal scarless wound healing in an effort to recapitulate the fetal phenotype in the postnatal environment.

A review of fetal scarless healing

Wound healing is a complex process involving a number of processes. Fetal regeneration has been shown to have a number of differences compared to scar-forming healing. This review discusses the number of differences identified in fetal regeneration. Understanding these differences may result in new therapeutic targets which may reduce or even prevent scarring in adult healing.

Discoidin domain receptors regulate the migration of primary human lung fibroblasts through collagen matrices

BACKGROUND

The two discoidin domain receptors (DDRs), DDR1 and DDR2 are receptor tyrosine kinases (RTKs) with the unique ability among RTKs to respond to collagen. We have previously shown that collagen I induces DDR1 and matrix metalloproteinase (MMP)-10 expression through DDR2 activation and a Janus kinase (JAK)2 and extracellular signal-regulated kinase (ERK)1/2-mediated mechanism in primary human lung fibroblasts suggesting that these signaling pathways play a role in fibroblast function. Fibroblasts can traverse basement membrane barriers during development, wound healing and pathological conditions such as cancer and fibrosis by activating tissue-invasive programs, the identity of which remain largely undefined. In the present work, we investigated the role of DDRs and DDR-associated signal transduction in these processes.

RESULTS

Transwell migration experiments showed that normal human lung fibroblast (NHLF) transmigration through collagen I-coated inserts is mediated by DDR2 and the DDR2-associated signaling kinases JAK2 and ERK1/2, but not DDR1. Additionally, experiments with specific small interfering (si)RNAs revealed that collagen I-induced expression of MMP-10 and MMP-2 is DDR2 but not DDR1 dependent in NHLFs. Our data showed that collagen I increases NHLF migration through collagen IV, the main component of basement membranes. Furthermore, basal and collagen I-induced NHLF migration through collagen IV-coated inserts was both DDR2 and DDR1 dependent. Finally, DDR2, but not DDR1 was shown to be involved in fibroblast proliferation.

CONCLUSIONS

Our results suggest a mechanism by which the presence of collagen I in situations of excessive matrix deposition could induce fibroblast migration through basement membranes through DDR2 activation and subsequent DDR1 and MMP-2 gene expression. This work provides new insights into the role of DDRs in fibroblast function.

Matrix components and scaffolds for sustained islet function

The clinical treatment of diabetes by islet transplantation is limited by low islet survival rates. A fundamental reason for this inefficiency is likely due to the removal of islets from their native environment. The isolation process not only disrupts interactions between blood vessels and endocrine cells, but also dramatically changes islet cell interaction with the extracellular matrix (ECM). Biomolecular cues from the ECM are important for islet survival, proliferation, and function; however, very little is known about the composition of islet ECM and the role each component plays. Without a thorough understanding of islet ECM, current endeavors to prolong islet survival via scaffold engineering lack a systematic basis. The following article reviews current knowledge of islet ECM and attempts to explain the roles they play in islet function. In addition, the effects of in vitro simulations of the native islet scaffold will be evaluated. Greater understanding in these areas will provide a preliminary platform from which a sustainable bioartificial pancreas may be developed.

Collagen I induces discoidin domain receptor (DDR) 1 expression through DDR2 and a JAK2-ERK1/2-mediated mechanism in primary human lung fibroblasts

Discoidin domain receptors (DDRs) DDR1 and DDR2 are receptor tyrosine kinases with the unique ability among receptor tyrosine kinases to respond to collagen. Several signaling molecules have been implicated in DDR signaling, including Shp-2, Src, and MAPK pathways, but a detailed understanding of these pathways and their transcriptional targets is still lacking. Similarly, the regulation of the expression of DDRs is poorly characterized with only a few inflammatory mediators, such as lipopolysaccharide and interleukin-1β identified as playing a role in DDR1 expression. DDRs have been reported to induce the expression of various genes including matrix metalloproteinases and bone morphogenetic proteins, but the regulatory mechanisms underlying DDR-induced gene expression remain to be determined. The aim of the present work was to elucidate the molecular mechanisms implicated in the expression of DDRs and to identify DDR-induced signaling pathways and target genes. Our data show that collagen I induces the expression of DDR1 in a dose- and time-dependent manner in primary human lung fibroblasts. Furthermore, activation of DDR2, JAK2, and ERK1/2 MAPK signaling pathways was essential for collagen I-induced DDR1 and matrix metalloproteinase 10 expression. Finally, inhibition of the ERK1/2 pathway abrogated DDR1 expression by blocking the recruitment of the transcription factor polyoma enhancer A-binding protein 3 to the DDR1 promoter. Our data provide new insights into the molecular mechanisms of collagen I-induced DDR1 expression and demonstrate an important role for ERK1/2 activation and the recruitment of polyoma enhancer-A binding protein 3 to the DDR1 promoter.

Epithelial-mesenchymal transition in primary human bronchial epithelial cells is Smad-dependent and enhanced by fibronectin and TNF-alpha

Background

Defective epithelial repair, excess fibroblasts and myofibroblasts, collagen overproduction and fibrosis occur in a number of respiratory diseases such as asthma, chronic obstructive pulmonary disease (COPD) and pulmonary fibrosis. Pathological conversion of epithelial cells into fibroblasts (epithelial-mesenchymal transition, EMT) has been proposed as a mechanism for the increased fibroblast numbers and has been demonstrated to occur in lung alveolar epithelial cells. Whether other airway cell types also have the capability to undergo EMT has been less explored so far. A better understanding of the full extent of EMT in airways, and the underlying mechanisms, can provide important insights into airway disease pathology and enable the development of new therapies. The main aim of this study was to test whether primary human bronchial epithelial cells are able to undergo EMT in vitro and to investigate the effect of various profibrotic factors in the process.

Results

Our data demonstrate that primary human bronchial epithelial cells (HBECs) are able to undergo EMT in response to transforming growth factor-beta 1 (TGF-β1), as revealed by typical morphological alterations and EMT marker progression at the RNA level by real-time quantitative polymerase chain reaction and, at the protein level, by western blot. By using pharmacological inhibitors we show that this is a Smad-dependent mechanism and is independent of extracellular signal-related kinase pathway activation. Additional cytokines and growth factors such as tumour necrosis factor-alpha (TNF-α), interleukin-1 beta (IL1β) and connective tissue growth factor (CTGF) were also tested, alone or in combination with TGF-β1. TNF-α markedly enhances the effect of TGF-β1 on EMT, whereas IL1β shows only a very weak effect and CTGF has no significant effect. We have also found that cell-matrix contact, in particular to fibronectin, an ECM component upregulated in fibrotic lesions, potentiates EMT in both human alveolar epithelial cells and HBECs. Furthermore, we also show that the collagen discoidin domain receptor 1 (DDR1), generally expressed in epithelial cells, is downregulated during the EMT of bronchial epithelium whereas DDR2 is unaffected. Our results also suggest that bone morphogenetic protein-4 is likely to have a context dependent effect during the EMT of HBECs, being able to induce the expression of EMT markers and, at the same time, to inhibit TGF-β induced epithelial transdifferentiation.

Conclusions

The results presented in this study provide additional insights into EMT, a potentially very important mechanism in fibrogenesis. We show that, in addition to alveolar epithelial type II cells, primary HBECs are also able to undergo EMT in vitro upon TGF-β1 stimulation via a primarily Smad 2/3 dependent mechanism. The effect of TGF-β1 is potentiated on fibronectin matrix and in the presence of TNF-α, representing a millieu reminiscent of fibrotic lesions. Our results can contribute to a better understanding of lung fibrosis and to the development of new therapeutic approaches.

How does amniotic membrane work?

Transplantation of amniotic membrane as a temporary or permanent graft promotes epithelial wound healing and exerts potent anti-inflammatory and anti-scarring effects on the ocular surface. These actions depend on the killing of allogeneic amniotic cells and preservation of the cytokine-containing matrix during the preparation of the amniotic membrane. This review describes how these actions inherently operate in utero and how amniotic membrane transplantation aims to recreate such a fetal environment to exert these actions by insulating the surgical site from the host environment. These actions also render the amniotic membrane a unique niche capable of expanding both epithelial and mesenchymal progenitor cells ex vivo, while maintaining their normal cell phenotypes. As a result, the amniotic membrane becomes an ideal substrate for engineering different types of ocular surface tissues for transplantation. Further studies investigating the exact molecular mechanism by which the amniotic membrane works will undoubtedly unravel additional applications in reconstruction and engineering of both ocular and nonocular tissues in the burgeoning field of regenerative medicine.

Differential expression of matrix metalloproteinases and tissue-derived inhibitors of metalloproteinase in fetal and adult skins

Matrix metalloproteinases and their tissue-derived inhibitors determine the architecture of the extracellular matrix. In early gestation, the amount and organization of extracellular matrix may be associated with scarless repair of fetal skin wounds. To elucidate the part of the mechanism(s) underlying the phenotypic transition from scarless to scar-forming healing observed during fetal gestation, the ontogeny of matrix metalloproteinase-2, -9, -14 and their tissue inhibitors was characterized in non-wounded fetal human skin with different gestational ages from 13 to 33 weeks and adult skin using reverse transcriptase-polymerase chain reaction, immunohistochemical staining and western blot protocols. We showed that the levels of gene expressions for matrix metalloproteinase-2, -9, -14 and their endogenous inhibitors were significantly more in late gestational and adult skins than that in early gestational skin. Similar results were noted in terms of protein contents of these enzymes and inhibitors in fetal and adult skins. We concluded that the endogenous matrix metalloproteinase-2, -9, -14 and their endogenous inhibitors might be involved in skin development and in maintenance of cutaneous structure and function. Lower protein contents of tissue-derived inhibitor-1, -2 in early gestational skin might provide a predominantly antiscarring signal while higher protein expression of these two inhibitors might be associated with scar-forming healing in late gestational and adult skins.

Profiling of genes differentially expressed in a rat of early and later gestational ages with high-density oligonucleotide DNA array

The early gestational fetus heals dermal wounds rapidly and scarlessly. This phenomenon appears to be intrinsic to fetal skin and is probably modulated by interplay of many genes. We ventured to study differences in gene expression between earlier gestational skin (EGS) and later gestational skin (LGS) with the aid of high-density oligonucleotide DNA array to explore the molecular mechanism underlying scarless healing. Total RNA was isolated from fetal Wistar rat skin of the scarless (E15) and scar-forming (E18) periods of gestation (term=21.5 days), and purified to mRNAs. Both the mRNAs from EGS and LGS were reversely transcribed to cDNAs, and were labeled with the incorporation of fluorescent dCTP for preparing the hybridization probes through single primer amplification reaction and Klenow labeling methods. The mixed probes were then hybridized to the oligonucleotide DNA arrays that contained 5,705 DNA fragments representing 5,705 rat genes. After highly stringent washing, the microarray was scanned for fluorescent signals to display the differentially expressed genes between two groups of tissues. Among 5,705 rat genes, there were 53 genes (0.93%) with differentially expressed levels between EGS and LGS; 27 genes, including fibroblast growth factor 8 and follistatin, were up-regulated (0.47%); and 26 genes, containing lymphoid enhancer binding factor-1 and beta-catenin, were down-regulated (0.46%) in fetal skin of scarless period vs. scar-forming period. Analyses of genes related to ion channels, growth factors, extracellular matrix and cellular skeleton, and movement confirmed that our molecular data obtained by oligonucleotide DNA array were consistent with the published biochemical and clinical findings of fetal scarless healing. Stronger expression of fibroblast growth factor 8, follistatin, and weaker expression of lymphoid enhancer binding factor-1 and beta-catenin in EGS vs. LGS were also testified with reverse transcription-polymerase chain reaction and Western blotting methods. Oligonucleotide DNA array was a powerful tool for investigating different gene expression between scarless and scar-forming periods of gestation in the rat fetal skin. Many genes were involved in the phenotypic transition from scarless to scar-forming wound repair during gestation. Further analysis of the obtained genes will help to understand the molecular mechanism of fetal scarless healing.

Sensing extracellular matrix: an update on discoidin domain receptor function

Discoidin Domain Receptors (DDRs) have recently emerged as non-integrin-type receptors for collagen. The two mammalian gene products Discoidin Domain Receptor 1 and -2 constitute a subfamily of tyrosine kinase receptors that are selectively expressed in a number of different cell types and organs. Upon collagen activation, DDRs regulate cell adhesion, proliferation and extracellular matrix remodeling. Here we review the various signaling pathways and cellular responses evoked by activated DDRs. Additionally, we give an overview of the more recent advances in understanding the role of DDRs in various human diseases, in particular during tumor progression, atherosclerosis, inflammation and tissue fibrosis. Furthermore, we discuss potential roles of genes homologous to mammalian DDRs identified in flies, worms and sponges. We show that the structural organization of these DDR-related genes is highly conserved throughout evolution suggesting that invertebrate DDRs may also function as receptors for collagen. By highlighting current questions about these unusual collagen receptors, we hope to attract new research on DDRs from a variety of different fields.

Expression of Discoidin Domain Receptor 2 (DDR2) in the developing heart

Interactions between cells and the surrounding extracellular matrix are important for a number of developmental events. In the heart, cardiac fibroblasts produce the majority of extracellular matrix proteins, particularly collagen types I and III. Cells originating from the proepicardial organ migrate over the surface of the heart, invade the underlying myocardium and ultimately give rise to smooth muscle cells, fibroblasts, and coronary endothelium. Although integrin expression in the developing heart has been well characterized, the expression of Discoidin Domain Receptor 2 (DDR2) remains to be defined. Using confocal microscopy, the expression of DDR2 was examined at several points during cardiac development. Initially, DDR2 expression was detected on the epicardial surface of the heart and on endothelial and mesenchymal cells within the cardiac cushions. As development progressed, DDR2 expression increased at localized regions in the apex and atrioventricular sulcus, although this expression decreased from epicardial to endocardial surface. Eventually, DDR2 expression spanned the myocardial free wall and was detected within the septum. Not until postnatal development was DDR2 expression detected uniformly throughout the myocardium and this distribution was maintained in the adult heart. In summary, the data presented demonstrate that the distribution of DDR2-positive cells changes within the heart during development.

Organization of fibroblasts in the heart

Cardiac fibroblasts are organized into a three-dimensional network in the heart. This organization follows the endomysial weave network that surrounds groups of myocytes. Reverse transcriptase-polymerase chain reaction, Western blots, and immunohistochemistry were used to show that discoidin domain receptor 2 (DDR2) was specific for cardiac fibroblasts and not expressed on endothelial cells, smooth muscle cells, or cardiac myocytes. DDR2 is expressed early in development and in the adult heart. High voltage electron microscopy (HVEM), scanning electron microscopy, and laser scanning confocal microscopy document the three-dimensional organization of fibroblasts in the heart. Antibodies against connexin 43 and 45 showed different patterns but confirmed, along with HVEM, that fibroblasts are connected to each other as well as cardiac myocytes. The implications of this arrangement of fibroblasts can be important to cardiac function. The signaling of DDR2 and the expression of matrix metalloproteinase 2 in relation to collagen turnover and remodeling is discussed.

Fetal wound healing current perspectives

Early in gestation, fetal wounds are capable of healing scarlessly. Scarless healing in the fetus is characterized by regeneration of an organized dermis with normal appendages and by a relative lack of inflammation. Although there is a transition period between scarless and scar-forming repair, scarless healing also depends on wound size and the organ involved. The ability to heal scarlessly, furthermore, appears to be intrinsic to fetal skin. Unique characteristics of fetal fibroblasts, inflammatory cells, extra-cellular matrix, cytokine profile, and developmental gene regulation may be responsible for the scarless phenotype of early gestation fetal wounds. With the current knowledge, only minimal success has been achieved with the topical application of neutralizing antibodies, antisense oligonucleotides, and growth factors to improve wound-healing outcomes. Thus, further investigation into the mechanisms underlying scarless repair is crucial in order to devise more effective therapies for scar reduction and the treatment of cirrhosis, scleroderma, and other diseases of excessive fibrosis.

Discoidin domain receptor 1 controls growth and adhesion of mesangial cells

Various types of collagen are known as modulators of mesangial cell proliferation. Here the function of the collagen-binding tyrosine kinase receptor discoidin domain receptor 1 (DDR1) in mesangial cells is investigated. The expression of DDR1 in the mouse kidney is confirmed by Northern analysis. In primary mesangial cells isolated from wild-type and DDR1-null mice, tyrosine phosphorylation in response to collagen-stimulation, adhesion to collagen, and cellular proliferation were measured. DDR1 phosphorylation was induced after overnight incubation of cells with type I collagen. Compared with wild-type cells, the adhesion of DDR1-null cells was drastically reduced. In contrast, DDR1-knockout cells showed significantly enhanced proliferation compared with wild-type cells. Both effects were largely independent of the collagen-binding alpha1/beta1 integrin function. This study found that the increased proliferation rate of DDR1-null cells is caused by a constitutive upregulation of p42/p44 and p38 mitogen-activated protein kinases (MAPK) activity. This is the first evidence indicating that DDR1 could be involved in the proliferative stage of renal disorders.

Ligand-induced shedding of discoidin domain receptor 1

Tyrosine kinases belonging to the discoidin domain receptor (DDR) family are activated upon stimulation with various types of collagen. In response to collagen treatment, immunoprecipitation of DDR1 with an antibody specific to the juxtamembrane region results in co-purification of a previously unrecognized tyrosine phosphorylated protein of 62 kDa molecular weight. Here, this protein is identified as C-terminal cleavage product of the full-length DDR1 receptor and a DDR1-specific shedding enzyme postulated. Shedding of DDR1 can be partially blocked by the furin inhibitor decanoyl-RVKR-chloromethylketone and completely inhibited by the hydroxamate-based inhibitor batimastat. The characteristic of the DDR1 sheddase to be blocked by batimastat suggests that it belongs to the membrane-bound matrix metalloproteinase or disintegrin and metalloproteinase family of proteases.