The osteochondral interface as a gradient tissue: From development to the fabrication of gradient scaffolds for regenerative medicine

The osteochondral (OC) interface is not only the interface between two tissues, but also the evolution of hard and stiff bone tissue to the softer and viscoelastic articular cartilage covering the joint surface. To generate a smooth transition between two tissues with such differences in many of their characteristics, several gradients are recognizable when moving from the bone side to the joint surface. It is, therefore, necessary to implement such gradients in the design of scaffolds to regenerate the OC interface, so to mimic the anatomical, biological, and physicochemical properties of bone and cartilage as closely as possible. In the past years, several scaffolds were developed for OC regeneration: biphasic, triphasic, and multilayered scaffolds were used to mimic the compartmental nature of this tissue. The structure of these scaffolds presented gradients in mechanical, physicochemical, or biological properties. The use of gradient scaffolds with already differentiated or progenitor cells has been recently proposed. Some of these approaches have also been translated in clinical trials, yet without the expected satisfactory results, thus suggesting that further efforts in the development of constructs, which can lead to a functional regeneration of the OC interface by presenting gradients more closely resembling its native environment, will be needed in the near future. The aim of this review is to analyze the gradients present in the OC interface from the early stage of embryonic life up to the adult organism, and give an overview of the studies, which involved gradient scaffolds for its regeneration. Birth Defects Research (Part C) 105:34–52, 2015. © 2015 Wiley Periodicals, Inc.     

Melanocytes in development, regeneration, and cancer

The genes required for stem cell specification and lineage restriction during embryogenesis also play fundamental roles in adult tissue regeneration and cancer. This "development-regeneration-cancer" axis is exemplified by the vertebrate pigmentation system. Melanocytes exhibit almost unlimited self-renewal capacity during regenerative processes such as mammalian hair recoloration and zebrafish fin regeneration. Melanoma utilizes many regulatory signals and pathways required during ontogeny and regeneration. A discussion of these interconnections highlights how studies of stem cell function in embryonic and regenerative contexts can yield insights into melanoma biology.     

生物活性材料与牙周组织再生

生物活性材料是一类经由材料表面或界面产生特殊生物或化学反应,从而影响组织和材料间的结合、诱发细胞活性或引导组织再生的生物材料。近年来,生物活性材料已广泛应用于牙周组织再生。本文对不同类型生物活性材料的特点及其在牙周组织再生中的作用进行综述,为推动其在牙周组织再生领域中的应用提供参考。     

Electroconductive materials as biomimetic platforms for tissue regeneration

In many diseases, tissue regeneration is compromised and/or insufficient to restore tissue/organ function. Therefore, novel regenerative therapies are being developed to enhance resident and transplanted cell proliferation and functional differentiation. Numerous biomaterials engineered to include nanocomponents have emerged as promising candidates to fulfil the need of mimicking the properties of the healthy extracellular matrix. This is particularly important for tissues that require electroconductive support to achieve optimal cellular function, such as muscles and neurons. In this review, we summarize and discuss the current state-of-the-art for electroconductive materials in tissue regeneration, with particular emphasis on materials containing nanocomponents.     

In situ guided tissue regeneration in musculoskeletal diseases and aging

In situ guided tissue regeneration, also addressed as in situ tissue engineering or endogenous regeneration, has a great potential for population-wide “minimal invasive” applications. During the last two decades, tissue engineering has been developed with remarkable in vitro and preclinical success but still the number of applications in clinical routine is extremely small. Moreover, the vision of population-wide applications of ex vivo tissue engineered constructs based on cells, growth and differentiation factors and scaffolds, must probably be deemed unrealistic for economic and regulation-related issues. Hence, the progress made in this respect will be mostly applicable to a fraction of post-traumatic or post-surgery situations such as big tissue defects due to tumor manifestation. Minimally invasive procedures would probably qualify for a broader application and ideally would only require off the shelf standardized products without cells. Such products should mimic the microenvironment of regenerating tissues and make use of the endogenous tissue regeneration capacities. Functionally, the chemotaxis of regenerative cells, their amplification as a transient amplifying pool and their concerted differentiation and remodeling should be addressed. This is especially important because the main target populations for such applications are the elderly and diseased. The quality of regenerative cells is impaired in such organisms and high levels of inhibitors also interfere with regeneration and healing. In metabolic bone diseases like osteoporosis, it is already known that antagonists for inhibitors such as activin and sclerostin enhance bone formation. Implementing such strategies into applications for in situ guided tissue regeneration should greatly enhance the efficacy of tailored procedures in the future.     

An insight into planarian regeneration

BackgroundPlanarian has attracted increasing attentions in the regeneration field for its usefulness as an important biological model organism attributing to its strong regeneration ability. Both the complexity of multiple regulatory networks and their coordinate functions contribute to the maintenance of normal cellular homeostasis and the process of regeneration in planarian. The polarity, size, location and number of regeneration tissues are regulated by diverse mechanisms. In this review we summarize the recent advances about the importance genetic and molecular mechanisms for regeneration control on various tissues in planarian.MethodsA comprehensive literature search of original articles published in recent years was performed in regards to the molecular mechanism of each cell types during the planarian regeneration, including neoblast, nerve system, eye spot, excretory system and epidermal.ResultsAvailable molecular mechanisms gave us an overview of regeneration process in every tissue. The sense of injuries and initiation of regeneration is regulated by diverse genes like follistatin and ERK signaling. The Neoblasts differentiate into tissue progenitors under the regulation of genes such as egfr‐3. The regeneration polarity is controlled by Wnt pathway, BMP pathway and bioelectric signals. The neoblast within the blastema differentiate into desired cell types and regenerate the missing tissues. Those tissue specific genes regulate the tissue progenitor cells to differentiate into desired cell types to complete the regeneration process.ConclusionAll tissue types in planarian participate in the regeneration process regulated by distinct molecular factors and cellular signaling pathways. The neoblasts play vital roles in tissue regeneration and morphology maintenance. These studies provide new insights into the molecular mechanisms for regulating planarian regeneration.

Genetic and molecular mechanisms for regeneration control on various tissues in planarian.     

Regenerating articular tissue by converging technologies

Scaffolds for osteochondral tissue engineering should provide mechanical stability, while offering specific signals for chondral and bone regeneration with a completely interconnected porous network for cell migration, attachment, and proliferation. Composites of polymers and ceramics are often considered to satisfy these requirements. As such methods largely rely on interfacial bonding between the ceramic and polymer phase, they may often compromise the use of the interface as an instrument to direct cell fate. Alternatively, here, we have designed hybrid 3D scaffolds using a novel concept based on biomaterial assembly, thereby omitting the drawbacks of interfacial bonding. Rapid prototyped ceramic particles were integrated into the pores of polymeric 3D fiber-deposited (3DF) matrices and infused with demineralized bone matrix (DBM) to obtain constructs that display the mechanical robustness of ceramics and the flexibility of polymers, mimicking bone tissue properties. Ostechondral scaffolds were then fabricated by directly depositing a 3DF structure optimized for cartilage regeneration adjacent to the bone scaffold. Stem cell seeded scaffolds regenerated both cartilage and bone in vivo.     

Early events of peripheral nerve regeneration

Early regeneration of injured peripheral nerves involves a series of events that are important in the success of eventual reconnection. In many nerve injuries, such as transections with gaps, axons and Schwann cells (SCs) penetrate into new microenvironments de novo, not involving zones of Wallerian degeneration. We studied unexplored axon-SC interactions by sampling of newly forming connections through a silicone conduit across transected rat sciatic peripheral nerve gaps. Axon and SC participation in bridge formation was addressed by light microscopy, electron microscopy and by double-labeling immunohistochemistry,including confocal imaging, and several, less appreciated aspects of early regrowth were identified. There are limitations to early and widespread regeneration of axons and SCs into bridges initially formed from connective tissue and blood vessels.Regrowth is 'staggered' such that only a small percentage of parent axons sampled the early bridge. There is an intimate, almost invariable relationship between SCs and extension of axons, which challenges the concept that axons lead and SCs follow.'Naked' axons were infrequent and limited in scope. Axons did not seek out and adhere to vascular laminin but intimately followed laminin deposits associated with apposed SCs. Growth cones identified by labeling of beta III tubulin, PGP(9 x 5) and GAP(43)/B(50) were complex, implying a pause in their regrowth, and were most prominent at the proximal stump-regenerative bridge interface. There is surprising and substantial hostility to local regrowth of axons into newly forming peripheral nerve bridges.Early axon outgrowth, associated with apposed Schwann cell processes, is highly constrained even when not exposed to adjacent myelin and products of Wallerian degeneration.     

Osteopontin,inflammation and myogenesis: influencing regeneration,fibrosis and size of skeletal muscle

Osteopontin is a multifunctional matricellular protein that is expressed by many cell types. Through cell-matrix and cell-cell interactions the molecule elicits a number of responses from a broad range of target cells via its interaction with integrins and the hyaluronan receptor CD44. In many tissues osteopontin has been found to be involved in important physiological and pathological processes, including tissue repair, inflammation and fibrosis. Post-natal skeletal muscle is a highly differentiated and specialised tissue that retains a remarkable capacity for regeneration following injury. Regeneration of skeletal muscle requires the co-ordinated activity of inflammatory cells that infiltrate injured muscle and are responsible for initiating muscle fibre degeneration and phagocytosis of necrotic tissue, and muscle precursor cells that regenerate the injured muscle fibres. This review focuses on the current evidence that osteopontin plays multiple roles in skeletal muscle, with particular emphasis on its role in regeneration and fibrosis following injury, and in determining the severity of myopathic diseases such as Duchenne muscular dystrophy.     

In vivo imaging indicates muscle fiber dedifferentiation is a major contributor to the regenerating tail blastema.

During tail regeneration in urodele amphibians such as axolotls, all of the tissue types, including muscle, dermis, spinal cord, and cartilage, are regenerated. It is not known how this diversity of cell types is reformed with such precision. In particular, the number and variety of mature cell types in the remaining stump that contribute to the blastema is unclear. Using Nomarski imaging, we followed the process of regeneration in the larval axolotl tail. Combining this with in vivo fluorescent labeling of single muscle fibers, we show that mature muscle dedifferentiates. Muscle dedifferentiation occurs by the synchronous fragmentation of the multinucleate muscle fiber into mononucleate cells followed by rapid cell proliferation and the extension of cell processes. We further show that direct clipping of the muscle fiber and severe tissue damage around the fiber are both required to initiate dedifferentiation. Our observations also make it possible to estimate for the first time how many of the blastema cells arise specifically from muscle dedifferentiation. Calculations based on our data suggest that up to 29% of nondermal-derived cells in the blastema come from dedifferentiation of mature muscle fibers. Overall, these results show that endogenous multinucleate muscle fibers can dedifferentiate into mononucleate cells and contribute significantly to the blastema.     

Cellular and molecular processes of regeneration, with special emphasis on fish fins

The phenomenon of 'epimorphic regeneration', a complete reformation of lost tissues and organs from adult differentiated cells, has been fascinating many biologists for many years. While most vertebrate species including humans do not have a remarkable ability for regeneration, the lower vertebrates such as urodeles and fish have exceptionally high regeneration abilities. In particular, the teleost fish has a high ability to regenerate a variety of tissues and organs including scales, muscles, spinal cord and heart among vertebrate species. Hence, an understanding of the regeneration mechanism in teleosts will provide an essential knowledge base for rational approaches to tissue and organ regeneration in mammals. In the last decade, small teleost fish such as the zebrafish and medaka have emerged as powerful animal models in which a variety of developmental, genetic and molecular approaches are applicable. In addition, rapid progress in the development of genome resources such as expressed sequence tags and genome sequences has accelerated the speed of the molecular analysis of regeneration. This review summarizes the current status of our understanding of the cellular and molecular basis of regeneration, particularly that regarding fish fins.     

A compliance-independent pressure transducer for biomedical device-tissue interfaces

The measurement of the interface pressure between a biomedical device and part of the human body is useful to improve the performance and safety of such devices during design. Testing of a selection of existing interface pressure transducers has demonstrated that many are dependent on device and tissue compliance. Such a transducer is useful only in an application where it has been calibrated for specific device-tissue compliance combinations. To overcome this limitation, the authors developed an interface pressure transducer whose output signal is not affected by changes in interface compliance. This enables the transducer to quantitatively measure pressure in many applications without the need to calibrate it for varying compliance conditions. Surgical retraction and surgical tourniquets were selected as demonstration applications for the developed transducer, because they represent a wide spectrum of device and tissue characteristics and properties, and are in common use.     

Regeneration: The ultimate example of wound healing

The outcome of wound repair in mammals is often characterized by fibrotic scaring. Vertebrates such as zebrafish, frogs, and salamanders not only heal scarlessly, but also can regenerate lost appendages. Decades of study on the process of animal regeneration has produced key insights into the mechanisms of how complex tissue is restored. By examining our current knowledge of regeneration, we can draw parallels with mammalian wound healing to identify the molecular determinants that produce such differing outcomes.     

Developmental aspects of spinal cord and limb regeneration

The ability of birds and mammals to regenerate tissues is limited. By contrast, urodele amphibians can regenerate a variety of injured tissues such as intestine, cardiac muscle, lens and neural retina, as well as entire structures such as limbs, tail and lower jaw. This regenerative capacity is associated with the ability to form masses of mesenchyme cells (blastemas) that differentiate into the missing tissues or parts. Understanding the mechanisms that underlie blastema formation in urodeles will provide valuable tools with which to achieve the goal of stimulating regeneration in mammalian tissues that do not naturally regenerate. Here we discuss an example of tissue regeneration (spinal cord) and an example of epimorphic appendage regeneration (limb) in the axolotl Ambystoma mexicanum , emphasizing analysis of the processes that produce the regeneration blastema and of the tissue interactions and blastemal products that contribute to the regeneration-promoting environment.     

The influence of ethylene in plant tissue culture

Ethylene produced by plant tissues grown in vitro may accumulate in large quantities in the culture vessels, particularly from rapidly growing non-differentiated callus or suspension cultures, and hence is likely to influence growth and development in such systems. Research into this aspect of tissue culture has been sparse, although it has grown recently with the increasing importance of in vitro regeneration. This review deals with the measurement and relevance of the accumulated ethylene, and the influence of both exogenous and endogenous ethylene in the different types of tissue culture systems. The relationships between ethylene and other growth regulators in tissue culture growth and development are also discussed. Although in some cases its influence seems negligible, in many types of tissue culture ethylene may act either as a promoter or inhibitor depending on the species used. Thus ethylene has an important influence on many aspects of in vitro regeneration, but it is also clear that we cannot at present describe a specific role or roles for ethylene in tissue culture which can be applied at a general, species-wide level. If its effects are to be enhanced or diminished in order to improve the efficiency and range of plant tissue culture, then more research is needed to clarify what its fundamental role might be in in vitro growth and development.Abbreviations ABA abscisic acid - ACC 1-aminocyclopropane-1-carboxylic acid - AOA aminooxyacetic acid - ASA acetylsalicyclic acid - AVG aminoethoxyvinylglycine - BA N⁶ benzylaminopurine; 2,4-D, 2,4-dichlorophenoxyacetic acid - DNP 2,4-dinitrophenol - GA gibberellin - IAA indole-3-acetic acid - IBA indole-3-butyric acid - NAA naphthaleneacetic acid - SAM S-adenosylmethionine - STS silver thiosulphate - TIBA 2,3,5-triidobenzoic acid     

Mass Spectrometry Imaging and Identification of Peptides Associated with Cephalic Ganglia Regeneration in Schmidtea mediterranea

Tissue regeneration is a complex process that involves a mosaic of molecules that vary spatially and temporally. Insights into the chemical signaling underlying this process can be achieved with a multiplex and untargeted chemical imaging method such as mass spectrometry imaging (MSI), which can enable de novo studies of nervous system regeneration. A combination of MSI and multivariate statistics was used to differentiate peptide dynamics in the freshwater planarian flatworm Schmidtea mediterranea at different time points during cephalic ganglia regeneration. A protocol was developed to make S. mediterranea tissues amenable for MSI. MS ion images of planarian tissue sections allow changes in peptides and unknown compounds to be followed as a function of cephalic ganglia regeneration. In conjunction with fluorescence imaging, our results suggest that even though the cephalic ganglia structure is visible after 6 days of regeneration, the original chemical composition of these regenerated structures is regained only after 12 days. Differences were observed in many peptides, such as those derived from secreted peptide 4 and EYE53-1. Peptidomic analysis further identified multiple peptides from various known prohormones, histone proteins, and DNA- and RNA-binding proteins as being associated with the regeneration process. Mass spectrometry data also facilitated the identification of a new prohormone, which we have named secreted peptide prohormone 20 (SPP-20), and is up-regulated during regeneration in planarians.     

Regeneration and clonality in Metazoa. The price to pay for evolving complexity

Explaining the high variability of regenerative ability across metazoan taxa is one of the major challenges in modern biology. Although common and widespread, regeneration shows a heterogeneous distribution and most authors consider regeneration capacity to be an ancestral trait that has been restricted or completely lost over the course of metazoan evolution. Basal Metazoans show the highest capacity for regeneration. By contrast, this feature is highly variable within bilaterians, with many taxa limited in their capacity for regeneration or not regenerating at all. The causes of the loss and/or maintenance of regeneration remain poorly understood, with most explanations invoking adaptive mechanisms. In the present study Metazoan regeneration is discussed with reference to stem cell biology, tissue plasticity, evolution of tissue complexity, cell turnover and lifespan. The presence or absence of regenerative ability cannot be seen only as an adaptation to a particular environment but can also be a consequence of body plan and developmental constraints such as may arise from the evolution of an adaptive immune system.     

Role of the lesion scar in the response to damage and repair of the central nervous system

Traumatic damage to the central nervous system (CNS) destroys the blood-brain barrier (BBB) and provokes the invasion of hematogenous cells into the neural tissue. Invading leukocytes, macrophages and lymphocytes secrete various cytokines that induce an inflammatory reaction in the injured CNS and result in local neural degeneration, formation of a cystic cavity and activation of glial cells around the lesion site. As a consequence of these processes, two types of scarring tissue are formed in the lesion site. One is a glial scar that consists in reactive astrocytes, reactive microglia and glial precursor cells. The other is a fibrotic scar formed by fibroblasts, which have invaded the lesion site from adjacent meningeal and perivascular cells. At the interface, the reactive astrocytes and the fibroblasts interact to form an organized tissue, the glia limitans. The astrocytic reaction has a protective role by reconstituting the BBB, preventing neuronal degeneration and limiting the spread of damage. While much attention has been paid to the inhibitory effects of the astrocytic component of the scars on axon regeneration, this review will cover a number of recent studies in which manipulations of the fibroblastic component of the scar by reagents, such as blockers of collagen synthesis have been found to be beneficial for axon regeneration. To what extent these changes in the fibroblasts act via subsequent downstream actions on the astrocytes remains for future investigation.     

Osteochondral tissue engineering: Current strategies and challenges

Osteochondral defect management and repair remain a significant challenge in orthopedic surgery. Osteochondral defects contain damage to both the articular cartilage as well as the underlying subchondral bone. In order to repair an osteochondral defect the needs of the bone, cartilage and the bone-cartilage interface must be taken into account. Current clinical treatments for the repair of osteochondral defects have only been palliative, not curative. Tissue engineering has emerged as a potential alternative as it can be effectively used to regenerate bone, cartilage and the bone-cartilage interface. Several scaffold strategies, such as single phase, layered, and recently graded structures have been developed and evaluated for osteochondral defect repair. Also, as a potential cell source, tissue specific cells and progenitor cells are widely studied in cell culture models, as well with the osteochondral scaffolds in vitro and in vivo. Novel factor strategies being developed, including single factor, multi-factor, or controlled factor release in a graded fashion, not only assist bone and cartilage regeneration, but also establish osteochondral interface formation. The field of tissue engineering has made great strides, however further research needs to be carried out to make this strategy a clinical reality. In this review, we summarize current tissue engineering strategies, including scaffold design, bioreactor use, as well as cell and factor based approaches and recent developments for osteochondral defect repair. In addition, we discuss various challenges that need to be addressed in years to come.     

Alternate glucocorticoid receptor ligand binding structures influence outcomes in an in vivo tissue regeneration model

Since their characterization, glucocorticoids (GCs), the most commonly prescribed immunomodulatory drugs, have undergone numerous structural modifications designed to enhance their activity. In vivo assessment of these corticosteroid analogs is essential to understand the difference in molecular signaling of the ligands that share the corticosteroid backbone. Our research identified a novel function of GCs as modulators of tissue regeneration and demonstrated that GCs activate the glucocorticoid receptor (GR) to inhibit early stages of tissue regeneration in zebrafish (Danio rerio). We utilized this phenomenon to assess the effect of different GC analogs on tissue regeneration and identified that some GCs such as beclomethasone dipropionate (BDP) possess inhibitory properties, while others, such as dexamethasone and hydrocortisone have no effect on regeneration. We performed in silico molecular docking and dynamic studies and demonstrated that type and size of substitution at the C17 position of the cortisol backbone confer a unique stable conformation to GR on ligand binding that is critical for inhibitory activity. In the field of tissue regeneration, our study is one of the first Structure Activity Relationship (SAR) investigations performed in vertebrates demonstrating that the in vivo tissue regeneration model is a powerful tool to probe structure function relationships, to understand regenerative biology, and to assist in rational drug design.