Morphogenesis defects are associated with abnormal nervous system regeneration following roboA RNAi in planarians

The process by which the proper pattern is restored to newly formed tissues during metazoan regeneration remains an open question. Here, we provide evidence that the nervous system plays a role in regulating morphogenesis during anterior regeneration in the planarian Schmidtea mediterranea. RNA interference (RNAi) knockdown of a planarian ortholog of the axon-guidance receptor roundabout (robo) leads to unexpected phenotypes during anterior regeneration, including the development of a supernumerary pharynx (the feeding organ of the animal) and the production of ectopic, dorsal outgrowths with cephalic identity. We show that Smed-roboA RNAi knockdown disrupts nervous system structure during cephalic regeneration: the newly regenerated brain and ventral nerve cords do not re-establish proper connections. These neural defects precede, and are correlated with, the development of ectopic structures. We propose that, in the absence of proper connectivity between the cephalic ganglia and the ventral nerve cords, neurally derived signals promote the differentiation of pharyngeal and cephalic structures. Together with previous studies on regeneration in annelids and amphibians, these results suggest a conserved role of the nervous system in pattern formation during blastema-based regeneration.     

Morphology of the nervous system of Polychaeta (Annelida)

The article summarizes our up to date knowledge about the morphology of the annelid, especially the polychaete, central and peripheral nervous system. Since the cephalic nervous system was in the focus of controversial discussions for decades, the structure of its neuropile, associated ganglia and nerves is reviewed in detail. The enormous variation of the ventral nerve cord and peripheral nerves is presented as well as a theory how this might have evolved. A ground pattern of the polychaete nervous system is suggested, based on developmental and regeneration studies.     

Experiments on anterior regeneration in<Emphasis Type="Italic"> Eurythoe complanata</Emphasis> ("Polychaeta", Amphinomidae): reconfiguration of the nervous system and its function for regeneration

In the polychaete Eurythoe complanata (Amphinomidae) regeneration of the nervous system has been monitored after amputation of anterior segments and after amputation plus extirpation of one to a few anterior ganglia of the ventral nerve cord. The serotonergic subunit of the nervous system was visualized with an antibody directed against the bioamine 5-HT. Cell proliferation could be demonstrated by incorporation of 5-bromo-2'-deoxyuridine. Antibody binding was visualized by fluorescence labeling and confocal laser scanning microscopy. The results show that regeneration of the nervous system occurs in two phases: (1) formation of primary neuronal structures by the "old" cord and (2) formation of new neurons in the regenerate that link up with the "old" system by their outgrowing axons. It is demonstrated that the nervous system is essential for regeneration: it induces cell proliferation in the blastema and subsequently in the regenerate. Extirpation of one ganglion retards regeneration, and extirpation of more than one ganglion prevents it completely, unless the affected segments are autotomized.     

TINP1 homolog is required for planarian regeneration

The planarian flatworm is an ideal system for the study of regeneration in vivo. In this study, we focus on TINP1, which is one of the most conserved proteins in eukaryotic organisms. We found that TINP1 was expressed in parenchymal region through whole body as well as central nervous system (CNS) during the course of regeneration. RNA interference targeting DjTINP1 caused lysis defects in regenerating tissues and a decreased in cell division and expression levels of DjpiwiA and Djpcna. Furthermore, the expression levels of DjTINP1 were decreased when we inhibited the TGF-β signal by knockdown of smad4, which is the sole co-smad and has been proved to control the blastema patterning and central nervous system (CNS) regeneration in planarians. These findings suggest that DjTINP1 participate in the maintenance of neoblasts and be required for proper cell proliferation in planarians as a downstream gene of the TGF-β signal pathway.     

Mechanisms of axon regeneration: The significance of proteoglycans

BackgroundTherapeutics specific to neural injury have long been anticipated but remain unavailable. Axons in the central nervous system do not readily regenerate after injury, leading to dysfunction of the nervous system. This failure of regeneration is due to both the low intrinsic capacity of axons for regeneration and the various inhibitors emerging upon injury. After many years of concerted efforts, however, these hurdles to axon regeneration have been partially overcome.Scope of reviewThis review summarizes the mechanisms regulating axon regeneration. We highlight proteoglycans, particularly because it has become increasingly clear that these proteins serve as critical regulators for axon regeneration.Major conclusionsStudies on proteoglycans have revealed that glycans not only assist in the modulation of protein functions but also act as main players—e.g., as functional ligands mediating intracellular signaling through specific receptors on the cell surface. By regulating clustering of the receptors, glycans in the proteoglycan moiety, i.e., glycosaminoglycans, promote or inhibit axon regeneration. In addition, proteoglycans are involved in various types of neural plasticity, ranging from synaptic plasticity to experience-dependent plasticity.General significanceAlthough studies on proteins have progressively facilitated our understanding of the nervous system, glycans constitute a new frontier for further research and development in this field. This article is part of a Special Issue entitled Neuro-glycoscience, edited by Kenji Kadomatsu and Hiroshi Kitagawa.     

Refining the Ciona intestinalis Model of Central Nervous System Regeneration

Background

New, practical models of central nervous system regeneration are required and should provide molecular tools and resources. We focus here on the tunicate Ciona intestinalis, which has the capacity to regenerate nerves and a complete adult central nervous system, a capacity unusual in the chordate phylum. We investigated the timing and sequence of events during nervous system regeneration in this organism.

Methodology/Principal Findings

We developed techniques for reproducible ablations and for imaging live cellular events in tissue explants. Based on live observations of more than 100 regenerating animals, we subdivided the regeneration process into four stages. Regeneration was functional, as shown by the sequential recovery of reflexes that established new criteria for defining regeneration rates. We used transgenic animals and labeled nucleotide analogs to describe in detail the early cellular events at the tip of the regenerating nerves and the first appearance of the new adult ganglion anlage.

Conclusions/Significance

The rate of regeneration was found to be negatively correlated with adult size. New neural structures were derived from the anterior and posterior nerve endings. A blastemal structure was implicated in the formation of new neural cells. This work demonstrates that Ciona intestinalis is as a useful system for studies on regeneration of the brain, brain-associated organs and nerves.     

New era of optogenetics: from the central to peripheral nervous system

Abstract

Optogenetics has recently gained recognition as a biological technique to control the activity of cells using light stimulation. Many studies have applied optogenetics to cell lines in the central nervous system because it has the potential to elucidate neural circuits, treat neurological diseases and promote nerve regeneration. There have been fewer studies on the application of optogenetics in the peripheral nervous system. This review introduces the basic principles and approaches of optogenetics and summarizes the physiology and mechanism of opsins and how the technology enables bidirectional control of unique cell lines with superior spatial and temporal accuracy. Further, this review explores and discusses the therapeutic potential for the development of optogenetics and its capacity to revolutionize treatment for refractory epilepsy, depression, pain, and other nervous system disorders, with a focus on neural regeneration, especially in the peripheral nervous system. Additionally, this review synthesizes the latest preclinical research on optogenetic stimulation, including studies on non-human primates, summarizes the challenges, and highlights future perspectives. The potential of optogenetic stimulation to optimize therapy for peripheral nerve injuries (PNIs) is also highlighted. Optogenetic technology has already generated exciting, preliminary evidence, supporting its role in applications to several neurological diseases, including PNIs.     

The BMP pathway is essential for re-specification and maintenance of the dorsoventral axis in regenerating and intact planarians

The bone morphogenetic protein (BMP) pathway has been shown to play an important role in the establishment of the dorsoventral axis during development in both vertebrate and invertebrate species. In an attempt to unravel the role of BMPs in pattern formation during planarian regeneration, we studied this signaling pathway in Schmidtea mediterranea. Here, we functionally characterize planarian homologues of two key elements of the pathway: Smed-BMP and Smed-Smad1. Whole-mount in situ hybridization showed that Smed-BMP is expressed at the planarian dorsal midline, suggesting a role in dorsoventral patterning, while Smed-Smad1 is widely expressed throughout the mesenchyme and in the central nervous system. RNA interference (RNAi) knockdowns of Smed-BMP or Smed-Smad1 led to the disappearance of dorsal markers along with the ectopic expression of ventral markers on the dorsal side of the treated animals. In almost all cases, a duplicated central nervous system differentiated dorsally after Smed-BMP or Smed-Smad1 RNAi. These defects were observed not only during regeneration but also in intact non-regenerating animals. Our results suggest that the BMP signaling pathway is conserved in planarians and that it plays a key role in the regeneration and maintenance of the dorsoventral axis.     

The DLK signalling pathway—a double‐edged sword in neural development and regeneration

Dual leucine zipper kinase (DLK), a mitogen‐activated protein kinase kinase kinase, controls axon growth, apoptosis and neuron degeneration during neural development, as well as neurodegeneration after various insults to the adult nervous system. Interestingly, recent studies have also highlighted a role of DLK in promoting axon regeneration in diverse model systems. Invertebrates and vertebrates, cold‐ and warm‐blooded animals, as well as central and peripheral mammalian nervous systems all differ in their ability to regenerate injured axons. Here, we discuss how DLK‐dependent signalling regulates apparently contradictory functions during neural development and regeneration in different species. In addition, we outline strategies to fine‐tune DLK function, either alone or together with other approaches, to promote axon regeneration in the adult mammalian central nervous system.     

Regeneration of articular cartilage by adipose tissue derived mesenchymal stem cells: Perspectives from stem cell biology and molecular medicine

Adipose‐derived stem cells (ASCs) have been discovered for more than a decade. Due to the large numbers of cells that can be harvested with relatively little donor morbidity, they are considered to be an attractive alternative to bone marrow derived mesenchymal stem cells. Consequently, isolation and differentiation of ASCs draw great attention in the research of tissue engineering and regenerative medicine. Cartilage defects cause big therapeutic problems because of their low self‐repair capacity. Application of ASCs in cartilage regeneration gives hope to treat cartilage defects with autologous stem cells. In recent years, a lot of studies have been performed to test the possibility of using ASCs to re‐construct damaged cartilage tissue. In this article, we have reviewed the most up‐to‐date articles utilizing ASCs for cartilage regeneration in basic and translational research. Our topic covers differentiation of adipose tissue derived mesenchymal stem cells into chondrocytes, increased cartilage formation by co‐culture of ASCs with chondrocytes and enhancing chondrogenic differentiation of ASCs by gene manipulation. J. Cell. Physiol. © 2012 Wiley Periodicals, Inc.     

Dihydrotestosterone Treatment Accelerates Autograft Reversal Sciatic Nerve Regeneration in Rats

Neuroactive steroids such as progesterone, testosterone, and their derivatives have been widely studied for their neuroprotective roles in the nervous system. Autologous nerve transplantation is considered as the gold standard repair technique when primary suture is impossible; nevertheless, this method is far from ideal. In this study, we aimed to explore the impact of dihydrotestosterone (DHT), a 5α-reduced derivative of testosterone, on the recovery of peripheral nerve injury treated with autologous nerve transplantation. Sprague–Dawley rats were subjected to a 10-mm right side sciatic nerve reversed autologous nerve transplantation and randomly divided into groups that received DHT or DHT?+?flutamide (an androgen receptor blocker) daily for 8 weeks after operation. Our results demonstrated that DHT could speed up the rate of axonal regeneration and increase the expression of myelin protein zero (P0) in autograft reversal sciatic nerves. Thus, our study provided new insights into improving the prognosis of patients with long gap peripheral nerve defects.     

Current and future uses of skeletal stem cells for bone regeneration

The postnatal skeleton undergoes growth, modeling, and remodeling. The human skeleton is a composite of diverse tissue types, including bone, cartilage, fat, fibroblasts, nerves, blood vessels, and hematopoietic cells. Fracture nonunion and bone defects are among the most challenging clinical problems in orthopedic trauma. The incidence of nonunion or bone defects following fractures is increasing. Stem and progenitor cells mediate homeostasis and regeneration in postnatal tissue, including bone tissue. As multipotent stem cells, skeletal stem cells (SSCs) have a strong effect on the growth, differentiation, and repair of bone regeneration. In recent years, a number of important studies have characterized the hierarchy, differential potential, and bone formation of SSCs. Here, we describe studies on and applications of SSCs and/or mesenchymal stem cells for bone regeneration.     

Notch signaling inhibits axon regeneration

Many neurons have limited capacity to regenerate their axons after injury. Neurons in the mammalian central nervous system do not regenerate, and even neurons in the peripheral nervous system often fail to regenerate to their former targets. This failure is likely due in part to pathways that actively restrict regeneration; however, only a few factors that limit regeneration are known. Here, using single-neuron analysis of regeneration in?vivo, we show that Notch/lin-12 signaling inhibits the regeneration of mature C.?elegans neurons. Notch signaling suppresses regeneration by acting autonomously in the injured cell to prevent growth cone formation. The metalloprotease and gamma-secretase cleavage events that lead to Notch activation during development are also required for its activity in regeneration. Furthermore, blocking Notch activation immediately after injury improves regeneration. Our results define a postdevelopmental role for the Notch pathway as a repressor of axon regeneration in?vivo.     

Venous graft-derived cells participate in peripheral nerve regeneration

Background

Based on growing evidence that some adult multipotent cells necessary for tissue regeneration reside in the walls of blood vessels and the clinical success of vein wrapping for functional repair of nerve damage, we hypothesized that the repair of nerves via vein wrapping is mediated by cells migrating from the implanted venous grafts into the nerve bundle.

Methodology/Principal Findings

To test the hypothesis, severed femoral nerves of rats were grafted with venous grafts from animals of the opposite sex. Nerve regeneration was impaired when decellularized or irradiated venous grafts were used in comparison to untreated grafts, supporting the involvement of venous graft-derived cells in peripheral nerve repair. Donor cells bearing Y chromosomes integrated into the area of the host injured nerve and participated in remyelination and nerve regeneration. The regenerated nerve exhibited proper axonal myelination, and expressed neuronal and glial cell markers.

Conclusions/Significance

These novel findings identify the mechanism by which vein wrapping promotes nerve regeneration.     

Requirement of fibroblast growth factor signaling for regeneration of epiphyseal morphology in rabbit full-thickness defects of articular cartilage

The involvement of fibroblast growth factor-2 (FGF-2) during the repair process in rabbit full-thickness defects of articular cartilage was studied. Fibroblast growth factor-2 (50 pg/h) was administered for 2 weeks in a 5mm defect of articular cartilage, which is large enough not to repair spontaneously. The administration of FGF-2 resulted in the regeneration of the articular cartilage and the subchondral bone within 8 weeks. In these defects, undifferentiated mesenchymal cells initiated chondrogenic differentiation coupled with replacement by subchondral bone, resulting in the resurfacing of the defects with hyaline cartilage and the recovery of subchondral bone up to the original bone–articular cartilage junction. In rabbits, full-thickness defects are capable of regenerating articular cartilage as long as the defect size is limited to ≤3 mm in diameter. In the defects, strong immunoreactivity for FGF-2 was observed in the granulation tissue filling the defects in the early stage of repair, in association with the expression of FGF-2 mRNA shown by in situ hybridization. Once the undifferentiated mesenchymal cells had differentiated into chondrocytes, both the immunoreactivity and the in situ hybridization signal declined significantly. Upon the local administration of a monoclonal antibody against FGF-2 (bFM-1, 50ng/h), the defects were filled with fibrous tissue and no resurfacing hyaline cartilage was formed. Compared to the non-treated defects, there were marked increases in FGF-2 immunoreactivity and the overexpression of FGF-2 mRNA in the reparative tissue in the bFM-1 -treated defects. This rebound phenomenon indicates that the autocrine FGF-2 signaling is critically important for the regeneration of articular cartilage.     

Reorganization of the nervous system during regeneration in Dugesia tigrina]

The normal structure of the nervous system in Dugesia tigrina Girard and the total morphodynamics of the nervous system during regeneration have been studied by means of choline esterase assay. The nervous system reacts to local damages of the planarian body; accumulations of nervous elements form in the wound region. Following the transverse cut of a planarian, the regeneration of the nervous system is not reduced to the completion of lacking parts. In this case (as well as in that of asexual reproduction) the nervous system manifests a considerable morphological lability and undergoes morphological rearrangements accompanied by the appearance of additional, frequently unpaired, nerve trunks. The data obtained are to be taken into account in neurobiological studies on planarians.     

Current and novel polymeric biomaterials for neural tissue engineering

The nervous system is a crucial component of the body and damages to this system, either by of injury or disease, can result in serious or potentially lethal consequences. Restoring the damaged nervous system is a great challenge due to the complex physiology system and limited regenerative capacity.Polymers, either synthetic or natural in origin, have been extensively evaluated as a solution for restoring functions in damaged neural tissues. Polymers offer a wide range of versatility, in particular regarding shape and mechanical characteristics, and their biocompatibility is unmatched by other biomaterials, such as metals and ceramics. Several studies have shown that polymers can be shaped into suitable support structures, including nerve conduits, scaffolds, and electrospun matrices, capable of improving the regeneration of damaged neural tissues. In general, natural polymers offer the advantage of better biocompatibility and bioactivity, while synthetic or non-natural polymers have better mechanical properties and structural stability. Often, combinations of the two allow for the development of polymeric conduits able to mimic the native physiological environment of healthy neural tissues and, consequently, regulate cell behaviour and support the regeneration of injured nervous tissues.Currently, most of neural tissue engineering applications are in pre-clinical study, in particular for use in the central nervous system, however collagen polymer conduits aimed at regeneration of peripheral nerves have already been successfully tested in clinical trials.This review highlights different types of natural and synthetic polymers used in neural tissue engineering and their advantages and disadvantages for neural regeneration.     

Extracellular vesicles from human umbilical cord mesenchymal stem cells improve nerve regeneration after sciatic nerve transection in rats

Peripheral nerve injury results in limited nerve regeneration and severe functional impairment. Mesenchymal stem cells (MSCs) are a remarkable tool for peripheral nerve regeneration. The involvement of human umbilical cord MSC‐derived extracellular vesicles (hUCMSC‐EVs) in peripheral nerve regeneration, however, remains unknown. In this study, we evaluated functional recovery and nerve regeneration in rats that received hUCMSC‐EV treatment after nerve transection. We observed that hUCMSC‐EV treatment promoted the recovery of motor function and the regeneration of axons; increased the sciatic functional index; resulted in the generation of numerous axons and of several Schwann cells that surrounded individual axons; and attenuated the atrophy of the gastrocnemius muscle. hUCMSC‐EVs aggregated to rat nerve defects, down‐regulated interleukin (IL)‐6 and IL‐1β, up‐regulated IL‐10 and modulated inflammation in the injured nerve. These effects likely contributed to the promotion of nerve regeneration. Our findings indicate that hUCMSC‐EVs can improve functional recovery and nerve regeneration by providing a favourable microenvironment for nerve regeneration. Thus, hUCMSC‐EVs have considerable potential for application in the treatment of peripheral nerve injury.