Tissue inhibitor of metalloproteinase 1 regulates matrix metalloproteinase activity during newt limb regeneration

Tail and Spinal Cord Regeneration in Urodelean Amphibians

Urodelean amphibians can regenerate the tail and the spinal cord (SC) and maintain this ability throughout their life. This clearly distinguishes these animals from mammals. The phenomenon of tail and SC regeneration is based on the capability of cells involved in regeneration to dedifferentiate, enter the cell cycle, and change their (or return to the pre-existing) phenotype during de novo organ formation. The second critical aspect of the successful tail and SC regeneration is the mutual molecular regulation by tissues, of which the SC and the apical wound epidermis are the leaders. Molecular regulatory systems include signaling pathways components, inflammatory factors, ECM molecules, ROS, hormones, neurotransmitters, HSPs, transcriptional and epigenetic factors, etc. The control, carried out by regulatory networks on the feedback principle, recruits the mechanisms used in embryogenesis and accompanies all stages of organ regeneration, from the moment of damage to the completion of morphogenesis and patterning of all its structures. The late regeneration stages and the effects of external factors on them have been poorly studied. A new model for addressing this issue is herein proposed. The data summarized in the review contribute to understanding a wide range of fundamentally important issues in the regenerative biology of tissues and organs in vertebrates including humans.

Matrisomal components involved in regenerative wound healing in axolotl and Acomys: implications for biomaterial development

Achieving regeneration in humans has been a long-standing goal of many researchers. Whereas amphibians like the axolotl (Ambystoma mexicanum) are capable of regenerating whole organs and even limbs, most mammals heal their wounds via fibrotic scarring. Recently, the African spiny mouse (Acomys sp.) has been shown to be injury resistant and capable of regenerating several tissue types. A major focal point of research with Acomys has been the identification of drivers of regeneration. In this search, the matrisome components related to the extracellular matrix (ECM) are often overlooked. In this review, we compare Acomys and axolotl skin wound healing and blastema-mediated regeneration by examining their wound healing responses and comparing the expression pattern of matrisome genes, including glycosaminoglycan (GAG) related genes. The goal of this review is to identify matrisome genes that are upregulated during regeneration and could be potential candidates for inclusion in pro-regenerative biomaterials. Research papers describing transcriptomic or proteomic coverage of either skin regeneration or blastema formation in Acomys and axolotl were selected. Matrisome and GAG related genes were extracted from each dataset and the resulting lists of genes were compared. In our analysis, we found several genes that were consistently upregulated, suggesting possible involvement in regenerative processes. Most of the components have been implicated in regulation of cell behavior, extracellular matrix remodeling and wound healing. Incorporation of such pro-regenerative factors into biomaterials may help to shift pro-fibrotic processes to regenerative responses in treated wounds.

The salamander blastema within the broader context of metazoan regeneration

Throughout the animal kingdom regenerative ability varies greatly from species to species, and even tissue to tissue within the same organism. The sheer diversity of structures and mechanisms renders a thorough comparison of molecular processes truly daunting. Are "blastemas" found in organisms as distantly related as planarians and axolotls derived from the same ancestral process, or did they arise convergently and independently? Is a mouse digit tip blastema orthologous to a salamander limb blastema? In other fields, the thorough characterization of a reference model has greatly facilitated these comparisons. For example, the amphibian Spemann-Mangold organizer has served as an amazingly useful comparative template within the field of developmental biology, allowing researchers to draw analogies between distantly related species, and developmental processes which are superficially quite different. The salamander limb blastema may serve as the best starting point for a comparative analysis of regeneration, as it has been characterized by over 200 years of research and is supported by a growing arsenal of molecular tools. The anatomical and evolutionary closeness of the salamander and human limb also add value from a translational and therapeutic standpoint. Tracing the evolutionary origins of the salamander blastema, and its relatedness to other regenerative processes throughout the animal kingdom, will both enhance our basic biological understanding of regeneration and inform our selection of regenerative model systems.

Novel Expansion of Matrix Metalloproteases in the Laboratory Axolotl (Ambystoma mexicanum) and Other Salamander Species

Matrix metalloprotease (MMP) genes encode endopeptidases that cleave protein components of the extracellular matrix (ECM) as well as non-ECM proteins. Here we report the results of a comprehensive survey of MMPs in the laboratory axolotl and other representative salamanders. Surprisingly, 28 MMPs were identified in salamanders and 9 MMP paralogs were identified as unique to the axolotl and other salamander taxa, with several of these presenting atypical amino acid insertions not observed in other tetrapod vertebrates. Furthermore, as assessed by sequence information, all of the novel salamander MMPs are of the secreted type, rather than cell membrane anchored. This suggests that secreted type MMPs expanded uniquely within salamanders to presumably execute catalytic activities in the extracellular milieu. To facilitate future studies of salamander-specific MMPs, we annotated transcriptional information from published studies of limb and tail regeneration. Our analysis sets the stage for comparative studies to understand why MMPs expanded uniquely within salamanders.

Extracellular matrix gene expression during arm regeneration in Amphiura filiformis

Extracellular matrix (ECM) plays a dynamic role during tissue development and re-growth. Body part regeneration efficiency relies also on effective ECM remodelling and deposition. Among invertebrates, echinoderms are well known for their striking regenerative abilities since they can rapidly regenerate functioning complex structures. To gather insights on the involvement of ECM during arm regeneration, the brittle star Amphiura filiformis was chosen as experimental model. Eight ECM genes were identified and cloned, and their spatio-temporal and quantitative expression patterns were analysed by means of whole mount in situ hybridisation and quantitative PCR on early and advanced regenerative stages. Our results show that almost none of the selected ECM genes are expressed at early stages of regeneration, suggesting a delay in their activation that may be responsible for the high regeneration efficiency of these animals, as described for other echinoderms and in contrast to most vertebrates. Moreover, at advanced stages, these genes are spatially and temporally differentially expressed, suggesting that the molecular regulation of ECM deposition/remodelling varies throughout the regenerative process. Phylogenetic analyses of the identified collagen-like genes reveal complex evolutionary dynamics with many rounds of duplications and losses and pinpointed their homologues in selected vertebrates. The study of other ECM genes will allow a better understanding of ECM contribution to brittle star arm regeneration.

Mechanisms of urodele limb regeneration

This review explores the historical and current state of our knowledge about urodele limb regeneration. Topics discussed are (1) blastema formation by the proteolytic histolysis of limb tissues to release resident stem cells and mononucleate cells that undergo dedifferentiation, cell cycle entry and accumulation under the apical epidermal cap. (2) The origin, phenotypic memory, and positional memory of blastema cells. (3) The role played by macrophages in the early events of regeneration. (4) The role of neural and AEC factors and interaction between blastema cells in mitosis and distalization. (5) Models of pattern formation based on the results of axial reversal experiments, experiments on the regeneration of half and double half limbs, and experiments using retinoic acid to alter positional identity of blastema cells. (6) Possible mechanisms of distalization during normal and intercalary regeneration. (7) Is pattern formation is a self-organizing property of the blastema or dictated by chemical signals from adjacent tissues? (8) What is the future for regenerating a human limb?

Regeneration and Regrowth Potentials of Digit Tips in Amphibians and Mammals

Tissue regeneration and repair have received much attention in the medical field over the years. The study of amphibians, such as newts and salamanders, has uncovered many of the processes that occur in these animals during full-limb/digit regeneration, a process that is highly limited in mammals. Understanding these processes in amphibians could shed light on how to develop and improve this process in mammals. Amputation injuries in mammals usually result in the formation of scar tissue with limited regrowth of the limb/digit; however, it has been observed that the very tips of digits (fingers and toes) can partially regrow in humans and mice under certain conditions. This review will summarize and compare the processes involved in salamander limb regeneration, mammalian wound healing, and digit regeneration in mice and humans.

Hyperbaric Oxygen Promotes Proximal Bone Regeneration and Organized Collagen Composition during Digit Regeneration

Oxygen is critical for optimal bone regeneration. While axolotls and salamanders have retained the ability to regenerate whole limbs, mammalian regeneration is restricted to the distal tip of the digit (P3) in mice, primates, and humans. Our previous study revealed the oxygen microenvironment during regeneration is dynamic and temporally influential in building and degrading bone. Given that regeneration is dependent on a dynamic and changing oxygen environment, a better understanding of the effects of oxygen during wounding, scarring, and regeneration, and better ways to artificially generate both hypoxic and oxygen replete microenvironments are essential to promote regeneration beyond wounding or scarring. To explore the influence of increased oxygen on digit regeneration in vivo daily treatments of hyperbaric oxygen were administered to mice during all phases of the entire regenerative process. Micro-Computed Tomography (μCT) and histological analysis showed that the daily application of hyperbaric oxygen elicited the same enhanced bone degradation response as two individual pulses of oxygen applied during the blastema phase. We expand past these findings to show histologically that the continuous application of hyperbaric oxygen during digit regeneration results in delayed blastema formation at a much more proximal location after amputation, and the deposition of better organized collagen fibers during bone formation. The application of sustained hyperbaric oxygen also delays wound closure and enhances bone degradation after digit amputation. Thus, hyperbaric oxygen shows the potential for positive influential control on the various phases of an epimorphic regenerative response.

Reintegration of the regenerated and the remaining tissues during joint regeneration in the newt Cynops pyrrhogaster

Urodele amphibians, such as newts, can regenerate a functional limb, including joints, after amputation at any level along the proximal−distal axis of the limb. The blastema can regenerate the limb morphology largely independently of the stump after proximal−distal identity has been established, but the remaining and regenerated tissues must be structurally reintegrated (matched in size and shape). Here we used newt joint regeneration as a model to investigate reintegration, because a functionally interlocking joint requires structural integration between its opposing skeletal elements. After forelimbs were amputated at the elbow joint, the joint was regenerated between the remaining and regenerated skeletal elements. The regenerated cartilage was thick around the amputated joint to make a reciprocally interlocking joint structure with the remaining bone. Furthermore, during regeneration, the extracellular matrix of the remaining tissues was lost, suggesting that the remaining tissues might contribute to the morphogenesis of regenerating cartilage. Our results showed that the area of the regenerated cartilage matched the area of the apposed remaining cartilage, thus contributing to formation of a functional structure.

FGF2-induced effects on transcriptome associated with regeneration competence in adult human fibroblasts

BACKGROUND

Adult human fibroblasts grown in low oxygen and with FGF2 supplementation have the capacity to tip the healing outcome of skeletal muscle injury - by favoring regeneration response in vivo over scar formation. Here, we compare the transcriptomes of control adult human dermal fibroblasts and induced regeneration-competent (iRC) fibroblasts to identify transcriptional changes that may be related to their regeneration competence.

RESULTS

We identified a unique gene-expression profile that characterizes FGF2-induced iRC fibroblast phenotype. Significantly differentially expressed genes due to FGF2 treatment were identified and analyzed to determine overrepresented Gene Ontology terms. Genes belonging to extracellular matrix components, adhesion molecules, matrix remodelling, cytoskeleton, and cytokines were determined to be affected by FGF2 treatment.

CONCLUSIONS

Transcriptome analysis comparing control adult human fibroblasts with FGF2-treated fibroblasts identified functional groups of genes that reflect transcriptional changes potentially contributing to their regeneration competence. This comparative transcriptome analysis should contribute new insights into genes that characterize cells with greater regenerative potential.

A dynamic spatiotemporal extracellular matrix facilitates epicardial-mediated vertebrate heart regeneration

Unlike humans, certain adult vertebrates such as newts and zebrafish possess extraordinary abilities to functionally regenerate lost appendages and injured organs, including cardiac muscle. Here, we present new evidence that a remodeled extracellular matrix (ECM) directs cell activities essential for cardiac muscle regeneration. Comprehensive mining of DNA microarrays and Gene Ontology term enrichment analyses for regenerating newt and zebrafish hearts revealed that distinct ECM components and ECM-modifying proteases are among the most significantly enriched genes in response to local injury. In contrast, data analyses for mammalian cardiac injury models indicated that inflammation and metabolic processes are the most significantly activated gene groups. In the regenerating newt heart, we show dynamic spatial and temporal changes in tenascin-C, hyaluronic acid, and fibronectin ECM distribution as early as 3 days postamputation. Linked to distinct matrix remodeling, we demonstrate a myocardium-wide proliferative response and radial migration of progenitor cells. In particular, we report dramatic upregulation of a regeneration-specific matrix in the epicardium that precedes the accumulation and migration of progenitor cells. For the first time, we show that the regenerative ECM component tenascin-C significantly increases newt cardiomyocyte cell cycle reentry in vitro. Thus, the engineering of nature-tested extracellular matrices may provide new strategic opportunities for the enhancement of regenerative responses in mammals.

Multi-tissue microarray analysis identifies a molecular signature of regeneration

The inability to functionally repair tissues that are lost as a consequence of disease or injury remains a significant challenge for regenerative medicine. The molecular and cellular processes involved in complete restoration of tissue architecture and function are expected to be complex and remain largely unknown. Unlike humans, certain salamanders can completely regenerate injured tissues and lost appendages without scar formation. A parsimonious hypothesis would predict that all of these regenerative activities are regulated, at least in part, by a common set of genes. To test this hypothesis and identify genes that might control conserved regenerative processes, we performed a comprehensive microarray analysis of the early regenerative response in five regeneration-competent tissues from the newt Notophthalmus viridescens. Consistent with this hypothesis, we established a molecular signature for regeneration that consists of common genes or gene family members that exhibit dynamic differential regulation during regeneration in multiple tissue types. These genes include members of the matrix metalloproteinase family and its regulators, extracellular matrix components, genes involved in controlling cytoskeleton dynamics, and a variety of immune response factors. Gene Ontology term enrichment analysis validated and supported their functional activities in conserved regenerative processes. Surprisingly, dendrogram clustering and RadViz classification also revealed that each regenerative tissue had its own unique temporal expression profile, pointing to an inherent tissue-specific regenerative gene program. These new findings demand a reconsideration of how we conceptualize regenerative processes and how we devise new strategies for regenerative medicine.

Blastema induction in aneurogenic state and Prrx-1 regulation by MMPs and FGFs in Ambystoma mexicanum limb regeneration

Urodele amphibians can regenerate amputated limbs. It has been considered that differentiated dermal tissues generate multipotent and undifferentiated cells called blastema cells during limb regeneration. In early phases of limb regeneration, blastema cells are induced by nerves and the apical epithelial cap (AEC). We had previously investigated the role of neurotrophic factors in blastema or blastema-like formation consisting of Prrx-1 positive cells. A new system suitable for investigating early phases of limb regeneration, called the accessory limb model (ALM), was recently developed. In this study, we performed a comparative transcriptome analysis between a blastema and wound using ALM. Matrix metalloproteinase (MMP) and fibroblast growth factor (FGF) signaling components were observed to be predominantly expressed in ALM blastema cells. Furthermore, we found that MMP activity induced a blastema marker gene, Prrx-1, in vitro, and FGF signaling pathways worked in coordination to maintain Prrx-1 expression and ALM blastema formation. Furthermore, we demonstrated that these two activities were sufficient to induce an ALM blastema in the absence of a nerve in vivo.

The relationship between inflammation and regeneration in the MRL mouse: potential relevance for putative human regenerative(scarless wound healing) capacities?

The matrix metalloproteinases (MMPs) have been implicated in the regenerative response in amphibians and various mammalian models of regeneration. The neutrophil response is known to bring MMPs and other proteases to the wound to promote bacterial elimination and tissue remodeling. These issues in relation to what is occurring in the MRL mouse model of regeneration/wound healing are discussed, followed by speculation as to their possible relevance for examples of the putative scarless wound healing described by some medical anthropologists and clinicians.

From fish to amphibians to mammals: in search of novel strategies to optimize cardiac regeneration

Different vertebrate species have different cardiac regeneration rates: high in teleost fish, moderate in urodele amphibians, and almost negligible in mammals. Regeneration may occur through stem and progenitor cell differentiation or via dedifferentiation with residual cardiomyocytes reentering the cell cycle. In this review, we will examine the ability of zebrafish and newts to respond to cardiac damage with de novo cardiogenesis, whereas rodents and humans respond with a marked fibrogenic response and virtually no cardiomyocyte regeneration. Concerted strategies are needed to overcome this evolutionarily imposed barrier and optimize cardiac regeneration in mammals.

Characterization of the acute temporal changes in excisional murine cutaneous wound inflammation by screening of the wound-edge transcriptome

This work represents a maiden effort to systematically screen the transcriptome of the healing wound-edge tissue temporally using high-density GeneChips. Changes during the acute inflammatory phase of murine excisional wounds were characterized histologically. Sets of genes that significantly changed in expression during healing could be segregated into the following five sets: up-early (6-24 h; cytokine-cytokine receptor interaction pathway), up-intermediary (12-96 h; leukocyte-endothelial interaction pathway), up-late (48-96 h; cell-cycle pathway), down-early (6-12 h; purine metabolism) and down-intermediary (12-96 h; oxidative phosphorylation pathway). Results from microarray and real-time PCR analyses were consistent. Results listing all genes that were significantly changed at any specific time point were further mined for cell-type (neutrophils, macrophages, endothelial, fibroblasts, and pluripotent stem cells) specificity. Candidate genes were also clustered on the basis of their functional annotation, linking them to inflammation, angiogenesis, reactive oxygen species (ROS), or extracellular matrix (ECM) categories. Rapid induction of genes encoding NADPH oxidase subunits and downregulation of catalase in response to wounding is consistent with the fact that low levels of endogenous H2O2 is required for wound healing. Angiogenic genes, previously not connected to cutaneous wound healing, that were induced in the healing wound-edge included adiponectin, epiregulin, angiomotin, Nogo, and VEGF-B. This study provides a digested database that may serve as a valuable reference tool to develop novel hypotheses aiming to elucidate the biology of cutaneous wound healing comprehensively.

Gene expression signatures in the newt irises during lens regeneration

Lens regeneration in adult newts is possible by transdifferentiation of the pigment epithelial cells (PECs) of the dorsal iris. The same cells in the ventral iris are not capable of such a process. To understand this difference in regenerative competency, we examined gene expression of 373 genes in the intact dorsal and ventral irises as well as in irises during the process of lens regeneration. We found similar signatures of gene expression in dorsal and ventral with several cases of even higher levels in the ventral iris. Such transcriptional activity in the regeneration-incompetent ventral iris was unexpected and calls for a revision of our views about mechanisms of lens regeneration induction.