Reactive oxygen species generated from skeletal muscles are required for gecko tail regeneration

Glycyrrhiza uralensis crude water extract and licochalcone A and B to enhance chicken muscle satellite cell differentiation for cultured meat production

Muscle satellite cells (MSCs) are the most commonly used cells in cultured meat research and development. Enhancing MSC proliferation and differentiation while reducing cell culture costs is requisite to commercializing cultured meat. This study explored the effects of Glycyrrhiza uralensis crude water extract (GU-CWE) and licochalcone A and B (Lic A or B) on the proliferation and differentiation of chicken, bovine, and porcine MSCs. While GU-CWE and Lic A and B had negligible effects on bovine and porcine MSCs, GU-CWE significantly enhanced chicken MSC differentiation, and Lic A and B promoted both the proliferation and differentiation of chicken MSCs. Furthermore, GU-CWE was found to mitigate reactive oxygen species activity during chicken MSC differentiation and promote cell proliferation and adhesion in spheroid culture, thereby maintaining a spherical shape. Collectively, this study suggests that GU-CWE and Lic A and B can significantly reduce costs and safely increase the productivity of chicken MSCs in cultured meat production processes.

Autophagy mediated by ROS-AKT-FoxO pathway is required for intestinal regeneration in echinoderms

Autophagy is essential for maintaining material balance and energy circulation and plays a critical role as a regulatory mechanism in tissue regeneration. However, current studies primarily describe this phenotype, with limited exploration of its molecular mechanisms. In this study, we provided the first evidence that autophagy is required for intestinal regeneration in Apostichopus japonicus and identified a previously unrecognized regulatory mechanism involved in this process. We observed that autophagy activation was significantly associated with enhanced regeneration, and its upregulation was shown to be regulated by reactive oxygen species (ROS) bursts. Mechanistically, ROS induced the dephosphorylation of Forkhead box protein O (FoxO) through AjAKT dephosphorylation. The dephosphorylated AjFoxO translocated to the nucleus, where it bound to the promoters of AjLC3 and AjATG4, inducing their transcription. This study highlights the ROS-AjAKT-AjFoxO-AjATG4/AjLC3 pathway as a novel regulatory mechanism underlying autophagy-mediated intestinal regeneration in echinoderms, providing a reference for studying regenerative processes and cytological mechanisms in economically important echinoderms.

Eccentric contraction increases hydrogen peroxide levels and alters gene expression through Nox2 in skeletal muscle of male mice

Hydrogen peroxide (H2O2) is one of the key signaling factors regulating skeletal muscle adaptation to muscle contractions. Eccentric (ECC) and concentric (CONC) contractions drive different muscle adaptations with ECC resulting in greater changes. The present investigation tested the hypothesis that ECC produces higher cytosolic and mitochondrial H2O2 concentrations [H2O2] and alters gene expression more than CONC. Cytosolic and mitochondrial H2O2-sensitive fluorescent proteins, HyPer7 and MLS-HyPer7, were expressed in the anterior tibialis muscle of C57BL6J male mice. Before and for 60 min after either CONC or ECC (100 Hz, 50 contractions), [H2O2]cyto and [H2O2]mito were measured by in vivo fluorescence microscopy. RNA sequencing was performed in control (noncontracted), CONC, and ECC muscles to identify genes impacted by the contractions. [H2O2]cyto immediately after ECC was greater than after CONC (CONC: +6%, ECC: +11% vs. rest, P < 0.05) and remained higher for at least 60 min into recovery. In contrast, the elevation of [H2O2]mito was independent of the contraction modes (time; P < 0.0042, contraction mode; P = 0.4965). The impact of ECC on [H2O2]cyto was abolished by NADPH oxidase 2 (Nox2) inhibition (GSK2795039). Differentially expressed genes were not present after CONC or ECC + GSK but were found after ECC and were enriched for vascular development and apoptosis-related genes, among others. In conclusion, in mouse anterior tibialis, ECC, but not CONC, evokes a pronounced cytosolic H2O2 response, caused by Nox2, that is mechanistically linked to gene expression modifications.NEW & NOTEWORTHY This in vivo model successfully characterized the effects of eccentric (ECC) and concentric (CONC) contractions on cytosolic and mitochondrial [H2O2] in mouse skeletal muscle. Compared with CONC, ECC induced higher and more sustained [H2O2]cyto-an effect that was abolished by Nox2 inhibition. ECC-induced [H2O2]cyto elevations were requisite for altered gene expression.

Awakening adult neural stem cells: NOX signalling as a positive regulator of the quiescence-to-proliferation transition in the Xenopus retina

A growing wealth of data suggest that reactive oxygen species (ROS) signalling might be crucial in conferring embryonic or adult stem cells their specific properties. However, how stem cells control ROS production and scavenging, and how ROS in turn contribute to stemness, remain poorly understood. Using the Xenopus retina as a model system, we first investigated the redox status of retinal stem cells (RSCs). We discovered that they exhibit higher ROS levels compared with progenitors and retinal neurons, and express a set of specific redox genes. We next addressed the question of ROS functional involvement in these cells. Using pharmacological or genetic tools, we demonstrate that inhibition of NADPH oxidase-dependent ROS production increases the proportion of quiescent RSCs. Surprisingly, this is accompanied by an apparent acceleration of the mean division speed within the remaining proliferating pool. Our data further unveil that such impact on RSC cell cycling is achieved by modulation of the Wnt/Hedgehog signalling balance. Altogether, we highlight that RSCs exhibit distinctive redox characteristics and exploit NADPH oxidase signalling to limit quiescence and fine-tune their proliferation rate.

Genome-wide characterization of the TGF-β gene family and their expression in different tissues during tail regeneration in the Schlegel's Japanese gecko Gekko japonicus

The transforming growth factor-β (TGF-β) gene family is unique to animals and is involved in various important processes including tissue regeneration. Here, we identified 52 TGF-β family genes based on genome sequences of the gecko (Gekko japonicus), compared TGF-β genes between G. japonicus and other four reptilian species, and evaluated the expression of 14 randomly selected genes in muscle, kidney, liver, heart, and brain during tail regeneration to investigate whether their expression was tissue-dependent. We detected 23 conserved domains, 13 in the TGF-β ligand subfamily, and 10 in the receptor subfamily. The pattern of higher genetic variation in the ligand subfamily than in the receptor subfamily in vertebrates might result from the precise localization of agonists and antagonists in the cell surface and intracellular compartment. TGF-β genes were unevenly distributed across 15 chromosomes in G. japonicus, presumably resulting from gene losses and gains during evolution. Genes in the TGF-β receptor subfamily (ACVR2A, ACVR2B, ACVR1, BMPR1A, ACVRL1, BMPR2 and TGFBR1) played a vital role in the TGF-β signal pathway. The expression of all 14 randomly selected TGF-β genes was tissue-specific. Our study supports the speculation that some TGF-β family genes are involved in the early stages of tail regeneration.

Duox is the primary NADPH oxidase responsible for ROS production during adult caudal fin regeneration in zebrafish

Sustained elevated levels of reactive oxygen species (ROS) have been shown to be essential for regeneration in many organisms. This has been shown primarily via the use of pharmacological inhibitors targeting the family of NADPH oxidases (NOXes). To identify the specific NOXes involved in ROS production during adult caudal fin regeneration in zebrafish, we generated nox mutants for duox, nox5 and cyba (a key subunit of NOXes 1-4) and crossed these lines with a transgenic line ubiquitously expressing HyPer, which permits the measurement of ROS levels. Homozygous duox mutants had the greatest effect on ROS levels and rate of fin regeneration among the single mutants. However, duox:cyba double mutants showed a greater effect on fin regeneration than the single duox mutants, suggesting that Nox1-4 also play a role during regeneration. This work also serendipitously found that ROS levels in amputated adult zebrafish fins oscillate with a circadian rhythm.

Live Imaging in Planarians: Immobilization and Real-Time Visualization of Reactive Oxygen Species

Imaging of living animals allows the study of metabolic processes in relation to cellular structures or larger functional entities. To enable in vivo imaging during long-term time-lapses in planarians, we combined and optimized existing protocols, resulting in an easily reproducible and inexpensive procedure. Immobilization with low-melting-point agarose eliminates the use of anesthetics, avoids interfering with the animal during imaging-functionally or physically-and allows recovering the organisms after the imaging procedure. As an example, we used the immobilization workflow to image the highly dynamic and fast-changing reactive oxygen species (ROS) in living animals. These reactive signaling molecules can only be studied in vivo and mapping their location and dynamics during different physiological conditions is crucial to understand their role in developmental processes and regeneration. In the current protocol, we describe both the immobilization and ROS detection procedure. We used the intensity of the signals together with pharmacological inhibitors to validate the signal specificity and to distinguish it from the autofluorescent nature of the planarian.

Post-amputation reactive oxygen species production is necessary for axolotls limb regeneration

Introduction: Reactive oxygen species (ROS) represent molecules of great interest in the field of regenerative biology since several animal models require their production to promote and favor tissue, organ, and appendage regeneration. Recently, it has been shown that the production of ROS such as hydrogen peroxide (H₂O₂) is required for tail regeneration in Ambystoma mexicanum. However, to date, it is unknown whether ROS production is necessary for limb regeneration in this animal model. Methods: forelimbs of juvenile animals were amputated proximally and the dynamics of ROS production was determined using 2′7- dichlorofluorescein diacetate (DCFDA) during the regeneration process. Inhibition of ROS production was performed using the NADPH oxidase inhibitor apocynin. Subsequently, a rescue assay was performed using exogenous hydrogen peroxide (H₂O₂). The effect of these treatments on the size and skeletal structures of the regenerated limb was evaluated by staining with alcian blue and alizarin red, as well as the effect on blastema formation, cell proliferation, immune cell recruitment, and expression of genes related to proximal-distal identity. Results: our results show that inhibition of post-amputation limb ROS production in the A. mexicanum salamander model results in the regeneration of a miniature limb with a significant reduction in the size of skeletal elements such as the ulna, radius, and overall autopod. Additionally, other effects such as decrease in the number of carpals, defective joint morphology, and failure of integrity between the regenerated structure and the remaining tissue were identified. In addition, this treatment affected blastema formation and induced a reduction in the levels of cell proliferation in this structure, as well as a reduction in the number of CD45⁺ and CD11b + immune system cells. On the other hand, blocking ROS production affected the expression of proximo-distal identity genes such as Aldha1a1, Rarβ, Prod1, Meis1, Hoxa13, and other genes such as Agr2 and Yap1 in early/mid blastema. Of great interest, the failure in blastema formation, skeletal alterations, as well as the expression of the genes evaluated were rescued by the application of exogenous H₂O₂, suggesting that ROS/H₂O₂ production is necessary from the early stages for proper regeneration and patterning of the limb.

The Role of Oxidative Stress in Skeletal Muscle Myogenesis and Muscle Disease

The contractile activity, high oxygen consumption and metabolic rate of skeletal muscle cause it to continuously produce moderate levels of oxidant species, such as reactive oxygen species (ROS) and reactive nitrogen species (RNS). Under normal physiological conditions, there is a dynamic balance between the production and elimination of ROS/RNS. However, when the oxidation products exceed the antioxidant defense capacity, the body enters a state of oxidative stress. Myogenesis is an important process to maintain muscle homeostasis and the physiological function of skeletal muscle. Accumulating evidence suggests that oxidative stress plays a key role in myogenesis and skeletal muscle physiology and pathology. In this review, we summarize the sources of reactive oxygen species in skeletal muscle and the causes of oxidative stress and analyze the key role of oxidative stress in myogenesis. Then, we discuss the relationship between oxidative stress and muscle homeostasis and physiopathology. This work systematically summarizes the role of oxidative stress in myogenesis and muscle diseases and provides targets for subsequent antioxidant therapy and repair of inflammatory damage in noninflammatory muscle diseases.

An early Shh-H2O2 reciprocal regulatory interaction controls the regenerative program during zebrafish fin regeneration

Reactive oxygen species (ROS), originally classified as toxic molecules, have attracted increasing interest given their actions in cell signaling. Hydrogen peroxide (H2O2), the major ROS produced by cells, acts as a second messenger to modify redox-sensitive proteins or lipids. After caudal fin amputation, tight spatiotemporal regulation of ROS is required first for wound healing and later to initiate the regenerative program. However, the mechanisms carrying out this sustained ROS production and their integration with signaling pathways are still poorly understood. We focused on the early dialog between H2O2 and Sonic Hedgehog (Shh) during fin regeneration. We demonstrate that H2O2 controls Shh expression and that Shh in turn regulates the H2O2 level via a canonical pathway. Moreover, the means of this tight reciprocal control change during the successive phases of the regenerative program. Dysregulation of the Hedgehog pathway has been implicated in several developmental syndromes, diabetes and cancer. These data support the existence of an early positive crosstalk between Shh and H2O2 that might be more generally involved in various processes paving the way to improve regenerative processes, particularly in vertebrates.

Tissue Regeneration: The Dark Side of Opioids

Opioids are regarded as among the most effective analgesic drugs and their use for the management of pain is considered standard of care. Despite their systematic administration in the peri-operative period, their impact on tissue repair has been studied mainly in the context of scar healing and is only beginning to be documented in the context of true tissue regeneration. Indeed, in mammals, growing evidence shows that opioids direct tissue repair towards scar healing, with a loss of tissue function, instead of the regenerative process that allows for recovery of both the morphology and function of tissue. Here, we review recent studies that highlight how opioids may prevent a regenerative process by silencing nociceptive nerve activity and a powerful anti-inflammatory effect. These data open up new perspectives for inducing tissue regeneration and argue for opioid-restricted strategies for managing pain associated with tissue injury.

Tails of reproduction: Regeneration leads to increased reproductive investment

Trade-offs between life-history traits are due to limited resources or constraints in the regulation of genetic and physiological networks. Tail autotomy, with subsequent regeneration, is a common anti-predation mechanism in lizards and is predicted to trade-off with life-history traits, such as reproduction. We utilize the brown anole lizard with its unusual reproductive pattern of single-egg clutches every 7-10 days to test for a trade-off in reproductive investment over 8 weeks of tail regeneration on a limited diet. In contrast to predictions, we found that investing in tissue regeneration had a positive effect on reproduction in terms of egg size (11.7% relative to controls) and hatchling size (11.5% relative to controls), and no effect on egg number or survival, with the increase in reproduction starting at peak regeneration. We discuss mechanistic hypotheses that the process of regeneration may cause increased energetic efficiency or utilized shared physiological pathways with reproductive investment.

Unlocking mammalian regeneration through hypoxia inducible factor one alpha signaling

Historically, the field of regenerative medicine has aimed to heal damaged tissue through the use of biomaterials scaffolds or delivery of foreign progenitor cells. Despite 30 years of research, however, translation and commercialization of these techniques has been limited. To enable mammalian regeneration, a more practical approach may instead be to develop therapies that evoke endogenous processes reminiscent of those seen in innate regenerators. Recently, investigations into tadpole tail regrowth, zebrafish limb restoration, and the super-healing Murphy Roths Large (MRL) mouse strain, have identified ancient oxygen-sensing pathways as a possible target to achieve this goal. Specifically, upregulation of the transcription factor, hypoxia-inducible factor one alpha (HIF-1α) has been shown to modulate cell metabolism and plasticity, as well as inflammation and tissue remodeling, possibly priming injuries for regeneration. Since HIF-1α signaling is conserved across species, environmental or pharmacological manipulation of oxygen-dependent pathways may elicit a regenerative response in non-healing mammals. In this review, we will explore the emerging role of HIF-1α in mammalian healing and regeneration, as well as attempts to modulate protein stability through hyperbaric oxygen treatment, intermittent hypoxia therapy, and pharmacological targeting. We believe that these therapies could breathe new life into the field of regenerative medicine.

Reactive oxygen species during heart regeneration in zebrafish: Lessons for future clinical therapies

In humans, myocardial infarction (MI) is associated with irreversible damage to heart tissue, resulting in increased morbidity and mortality in patients. By comparison, the zebrafish (Danio rerio) is capable of repairing damaged and injured hearts by activating a full regenerative response. By studying model organisms that can regenerate loss heart tissue following injury, such as the zebrafish, a greater insight will be gained into the molecular pathways that can induce and sustain a regenerative response following injury. There is hope that such information may lead to new treatments or therapies aimed at stimulating a better regenerative response in humans that have suffered heart attacks. Recent findings in zebrafish have highlighted an important role for sustained elevated levels of Reactive Oxygen Species (ROS), including hydrogen peroxide (H₂O₂) in the promotion of a regenerative response. Given that elevated levels of H₂O₂ can be harmful, simply elevating ROS levels directly may not be easy or practical to translate clinically. An alternative approach would be to identify the critical downstream targets of ROS in the promotion of heart regeneration, and then target these clinically using drugs. One such family of potential downstream targets of ROS during heart regeneration are the family of protein tyrosine phosphatases (PTPs), which are known to be exquisitely sensitive to redox regulation and whose inhibition have been linked to the promotion of heart regeneration in zebrafish. In this review, we present an overview of the zebrafish as a model organism for studying cardiac regeneration, including the molecular mechanisms by which cardiac regeneration occurs in response to injury. We then present recent findings linking elevated ROS levels to heart regeneration and their potential downstream targets, the PTPs, including protein tyrosine phosphatase 1B (PTP1B) and the dual specificity phosphatase 6 (DUSP6) in the promotion of heart regeneration.

Transcriptomic analysis of early stages of intestinal regeneration in Holothuria glaberrima

Echinoderms comprise a group of animals with impressive regenerative capabilities. They can replace complex internal organs following injury or autotomy. In holothurians or sea cucumbers, cellular processes of intestinal regeneration have been extensively studied. The molecular machinery behind this faculty, however, remains to be understood. Here we assembled and annotated a de novo transcriptome using RNA-seq data consisting of regenerating and non-regenerating intestinal tissues from the sea cucumber Holothuria glaberrima. Comparisons of differential expression were made using the mesentery as a reference against 24 h and 3 days regenerating intestine, revealing a large number of differentially expressed transcripts. Gene ontology and pathway enrichment analysis showed evidence of increasing transcriptional activity. Further analysis of transcripts associated with transcription factors revealed diverse expression patterns with mechanisms involving developmental and cancer-related activity that could be related to the regenerative process. Our study demonstrates the broad and diversified gene expression profile during the early stages of the process using the mesentery as the focal point of intestinal regeneration. It also establishes the genes that are the most important candidates in the cellular processes that underlie regenerative responses.

Salamander-like tail regeneration in the West African lungfish

Salamanders, frog tadpoles and diverse lizards have the remarkable ability to regenerate tails. Palaeontological data suggest that this capacity is plesiomorphic, yet when the developmental and genetic architecture of tail regeneration arose is poorly understood. Here, we show morphological and molecular hallmarks of tetrapod tail regeneration in the West African lungfish Protopterus annectens, a living representative of the sister group of tetrapods. As in salamanders, lungfish tail regeneration occurs via the formation of a proliferative blastema and restores original structures, including muscle, skeleton and spinal cord. In contrast with lizards and similar to salamanders and frogs, lungfish regenerate spinal cord neurons and reconstitute dorsoventral patterning of the tail. Similar to salamander and frog tadpoles, Shh is required for lungfish tail regeneration. Through RNA-seq analysis of uninjured and regenerating tail blastema, we show that the genetic programme deployed during lungfish tail regeneration maintains extensive overlap with that of tetrapods, with the upregulation of genes and signalling pathways previously implicated in amphibian and lizard tail regeneration. Furthermore, the lungfish tail blastema showed marked upregulation of genes encoding post-transcriptional RNA processing components and transposon-derived genes. Our results show that the developmental processes and genetic programme of tetrapod tail regeneration were present at least near the base of the sarcopterygian clade and establish the lungfish as a valuable research system for regenerative biology.

Integrating Bioelectrical Currents and Ca2+ Signaling with Biochemical Signaling in Development and Pathogenesis

Roles of bioelectrical signals are increasingly recognized in excitable and nonexcitable non-neural tissues. Diverse ion-selective channels, pumps, and gap junctions participate in bioelectrical signaling, including those transporting calcium ions (Ca2+). Ca2+ is the most versatile transported ion, because it serves as an electrical charge carrier and a biochemical regulator for multiple molecular binding, enzyme, and transcription activities. We aspire to learn how bioelectrical signals crosstalk to biochemical/biomechanical signals. In this study, we review four recent studies showing how bioelectrical currents and Ca2+ signaling affect collective dermal cell migration during feather bud elongation, affect chondrogenic differentiation in limb development, couple with mechanical tension in aligning gut smooth muscle, and affect mitochondrial function and skeletal muscle atrophy. We observe bioelectrical signals involved in several developmental and pathological conditions in chickens and mice at multiple spatial scales: cellular, cellular collective, and subcellular. These examples inspire novel concept and approaches for future basic and translational studies.

Model systems for regeneration: Xenopus

Understanding how to promote organ and appendage regeneration is a key goal of regenerative medicine. The frog, Xenopus, can achieve both scar-free healing and tissue regeneration during its larval stages, although it predominantly loses these abilities during metamorphosis and adulthood. This transient regenerative capacity, alongside their close evolutionary relationship with humans, makes Xenopus an attractive model to uncover the mechanisms underlying functional regeneration. Here, we present an overview of Xenopus as a key model organism for regeneration research and highlight how studies of Xenopus have led to new insights into the mechanisms governing regeneration.

Common themes in tetrapod appendage regeneration: a cellular perspective

Complete and perfect regeneration of appendages is a process that has fascinated and perplexed biologists for centuries. Some tetrapods possess amazing regenerative abilities, but the regenerative abilities of others are exceedingly limited. The reasons underlying these differences have largely remained mysterious. A great deal has been learned about the morphological events that accompany successful appendage regeneration, and a handful of experimental manipulations can be reliably applied to block the process. However, only in the last decade has the goal of attaining a thorough molecular and cellular biological understanding of appendage regeneration in tetrapods become within reach. Advances in molecular and genetic tools for interrogating these remarkable events are now allowing for unprecedented access to the fundamental biology at work in appendage regeneration in a variety of species. This information will be critical for integrating the large body of detailed observations from previous centuries with a modern understanding of how cells sense and respond to severe injury and loss of body parts. Understanding commonalities between regenerative modes across diverse species is likely to illuminate the most important aspects of complex tissue regeneration.

Weak magnetic fields alter stem cell-mediated growth

Biological systems are constantly exposed to electromagnetic fields (EMFs) in the form of natural geomagnetic fields and EMFs emitted from technology. While strong magnetic fields are known to change chemical reaction rates and free radical concentrations, the debate remains about whether static weak magnetic fields (WMFs; <1 mT) also produce biological effects. Using the planarian regeneration model, we show that WMFs altered stem cell proliferation and subsequent differentiation via changes in reactive oxygen species (ROS) accumulation and downstream heat shock protein 70 (Hsp70) expression. These data reveal that on the basis of field strength, WMF exposure can increase or decrease new tissue formation in vivo, suggesting WMFs as a potential therapeutic tool to manipulate mitotic activity.

Ask1 and Akt act synergistically to promote ROS-dependent regeneration in Drosophila

How cells communicate to initiate a regenerative response after damage has captivated scientists during the last few decades. It is known that one of the main signals emanating from injured cells is the Reactive Oxygen Species (ROS), which propagate to the surrounding tissue to trigger the replacement of the missing cells. However, the link between ROS production and the activation of regenerative signaling pathways is not yet fully understood. We describe here the non-autonomous ROS sensing mechanism by which living cells launch their regenerative program. To this aim, we used Drosophila imaginal discs as a model system due to its well-characterized regenerative ability after injury or cell death. We genetically-induced cell death and found that the Apoptosis signal-regulating kinase 1 (Ask1) is essential for regenerative growth. Ask1 senses ROS both in dying and living cells, but its activation is selectively attenuated in living cells by Akt1, the core kinase component of the insulin/insulin-like growth factor pathway. Akt1 phosphorylates Ask1 in a secondary site outside the kinase domain, which attenuates its activity. This modulation of Ask1 activity results in moderate levels of JNK signaling in the living tissue, as well as in activation of p38 signaling, both pathways required to turn on the regenerative response. Our findings demonstrate a non-autonomous activation of a ROS sensing mechanism by Ask1 and Akt1 to replace the missing tissue after damage. Collectively, these results provide the basis for understanding the molecular mechanism of communication between dying and living cells that triggers regeneration.

Amputation-induced reactive oxygen species signaling is required for axolotl tail regeneration

BACKGROUND

Among vertebrates, salamanders are unparalleled in their ability to regenerate appendages throughput life. However, little is known about early signals that initiate regeneration in salamanders.

RESULTS

Ambystoma mexicanum embryos were administered tail amputations to investigate the timing of reactive oxygen species (ROS) production and the requirement of ROS for regeneration. ROS detected by dihydroethidium increased within minutes of axolotl tail amputation and levels remained high for 24 hr. Pharmacological inhibition of ROS producing enzymes with diphenyleneiodonium chloride (DPI) and VAS2870 reduced ROS levels. Furthermore, DPI treatment reduced cellular proliferation and inhibited tail outgrowth.

CONCLUSIONS

The results show that ROS levels increase in response to injury and are required for tail regeneration. These findings suggest that ROS provide instructive, if not initiating cues, for salamander tail regeneration. Developmental Dynamics 248:189-196, 2019. © 2018 Wiley Periodicals, Inc.

Hydrogen Peroxide and Redox Regulation of Developments

Reactive oxygen species (ROS), which were originally classified as exclusively deleterious compounds, have gained increasing interest in the recent years given their action as bona fide signalling molecules. The main target of ROS action is the reversible oxidation of cysteines, leading to the formation of disulfide bonds, which modulate protein conformation and activity. ROS, endowed with signalling properties, are mainly produced by NADPH oxidases (NOXs) at the plasma membrane, but their action also involves a complex machinery of multiple redox-sensitive protein families that differ in their subcellular localization and their activity. Given that the levels and distribution of ROS are highly dynamic, in part due to their limited stability, the development of various fluorescent ROS sensors, some of which are quantitative (ratiometric), represents a clear breakthrough in the field and have been adapted to both ex vivo and in vivo applications. The physiological implication of ROS signalling will be presented mainly in the frame of morphogenetic processes, embryogenesis, regeneration, and stem cell differentiation. Gain and loss of function, as well as pharmacological strategies, have demonstrated the wide but specific requirement of ROS signalling at multiple stages of these processes and its intricate relationship with other well-known signalling pathways.

Early redox activities modulate Xenopus tail regeneration

Redox state sustained by reactive oxygen species (ROS) is crucial for regeneration; however, the interplay between oxygen (O2), ROS and hypoxia-inducible factors (HIF) remains elusive. Here we observe, using an optic-based probe (optrode), an elevated and steady O2 influx immediately upon amputation. The spatiotemporal O2 influx profile correlates with the regeneration of Xenopus laevis tadpole tails. Inhibition of ROS production but not ROS scavenging decreases O2 influx. Inhibition of HIF-1α impairs regeneration and stabilization of HIF-1α induces regeneration in the refractory period. In the regeneration bud, hypoxia correlates with O2 influx, ROS production, and HIF-1α stabilization that modulate regeneration. Further analyses reveal that heat shock protein 90 is a putative downstream target of HIF-1α while electric current reversal is a de facto downstream target of HIF-1α. Collectively, the results show a mechanism for regeneration via the orchestration of O2 influx, ROS production, and HIF-1α stabilization.

Opioids prevent regeneration in adult mammals through inhibition of ROS production

Inhibition of regeneration and induction of tissue fibrosis are classic outcomes of tissue repair in adult mammals. Here, using a newly developed model of regeneration in adult mammals i.e. regeneration after massive resection of an inguinal fat pad, we demonstrate that both endogenous and exogenous opioids prevent tissue regeneration in adults, by inhibiting the early production of reactive oxygen species (ROS) that generally occurs after lesion and is required for regeneration. These effects can be overcome and regeneration induced by the use of an opioid antagonist. The results obtained in both our new model and the gold standard adult zebrafish demonstrate that this mechanism can be considered as a general paradigm in vertebrates. This work clearly demonstrates that ROS is required for tissue regeneration in adult mammals and shows the deleterious effect of opioids on tissue regeneration through the control of this ROS production. It thus raises questions about opioid-based analgesia in perioperative care.

The role of autophagy induction in the mechanism of cytoprotective effect of resveratrol

We aimed at studying the potential mechanisms in the preventive effect of resveratrol on serum deprivation induced caspase 3 activation on non-transformed cells.

METHODS

Apoptosis was induced by serum deprivation in primary mouse embryonic fibroblasts. Caspase 3 activation, reactive oxygen species production and depolarization of the mitochondrial membrane were measured by fluorescence methods. The involvement of intracellular receptors and autophagy in the effect of resveratrol were analyzed by using specific agonists and antagonists. The role of autophagy was further examined by Western Blot analysis of its protein markers, LC3-II and p62 as well as by acridine orange staining of acidic vacuoles.

RESULTS

We found that neither aromatic hydrocarbon receptors nor estrogen receptors play an important role in the cytoprotective effect of resveratrol. Reactive oxygen species production was not significantly altered by either serum deprivation or resveratrol treatment. In the presence of serum deprivation resveratrol however, induced a significant depolarization in mitochondrial membrane potential. The autophagy inhibitor, chloroquine not only eliminated the preventive effect of resveratrol, but also turned it to deleterious suggesting the prominent role of autophagy induction in the cytoprotective effect. Resveratrol did not alter LC3-II expression, but facilitated p62 degradation in serum deprived cells, suggesting its ability to augment the late phase of autophagy and thus promote the autophagic flux.

CONCLUSION

We have demonstrated that resveratrol can protect primary fibroblasts against serum deprivation induced apoptosis by provoking mild mitochondrial stress and consequent up-regulation of autophagic flux.

Concise Review: Translating Regenerative Biology into Clinically Relevant Therapies: Are We on the Right Path?

Despite approaches in regenerative medicine using stem cells, bio‐engineered scaffolds, and targeted drug delivery to enhance human tissue repair, clinicians remain unable to regenerate large‐scale, multi‐tissue defects in situ. The study of regenerative biology using mammalian models of complex tissue regeneration offers an opportunity to discover key factors that stimulate a regenerative rather than fibrotic response to injury. For example, although primates and rodents can regenerate their distal digit tips, they heal more proximal amputations with scar tissue. Rabbits and African spiny mice re‐grow tissue to fill large musculoskeletal defects through their ear pinna, while other mammals fail to regenerate identical defects and instead heal ear holes through fibrotic repair. This Review explores the utility of these comparative healing models using the spiny mouse ear pinna and the mouse digit tip to consider how mechanistic insight into reparative regeneration might serve to advance regenerative medicine. Specifically, we consider how inflammation and immunity, extracellular matrix composition, and controlled cell proliferation intersect to establish a pro‐regenerative microenvironment in response to injuries. Understanding how some mammals naturally regenerate complex tissue can provide a blueprint for how we might manipulate the injury microenvironment to enhance regenerative abilities in humans. Stem Cells Translational Medicine2018;7:220–231

Changes in inflammatory and oxidative stress factors and the protein synthesis pathway in injured skeletal muscle after contusion

Injury of skeletal muscle, and particularly mechanically-induced damage, including contusion injury, frequently occurs in contact sports as well as in sports with accidental contact. Although the mechanisms of skeletal muscle regeneration are well understood, those involved in muscle contusion are not. A total of 40 male mice were randomly divided into control (n=8) and muscle contusion (n=32) groups. A muscle contusion model was established by weight-drop injury. Subsequently, the gastrocnemius muscles in the two groups were harvested at different times (1, 3, 7 and 14 days) post-injury. The changes in skeletal muscle morphology were assessed by hematoxylin and eosin (H&E) stains. Furthermore, quantitative polymerase chain reaction and western blotting were used to analyze inflammatory cytokines, oxidative stress factors and the Akt/mechanistic target of rapamycin (mTOR) pathway. The results revealed that pro-inflammatory cytokines [tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and interferon-γ (IFN-γ)] increased significantly at day 1 and 3 and still exhibited high levels of expression at days 7 and 14 (except IL-6) post-injury. Additionally, the anti-inflammatory cytokine IL-10 increased significantly at 1, 3 and 7 days and reached its peak levels at 7 days post-injury. It was revealed that gp91phox mRNA increased significantly at all time points and gp91phox protein increased significantly at day 3 post-injury. Furthermore, it was observed that p-Akt/Akt increased significantly at 1 day post-injury. P-mTOR/mTOR increased significantly at day 1 and 7, and p-p70s6k/p70s6k and P-4EBP1/4EBP1 increased significantly at 1, 3, 7 and 14 days post-injury. These results indicate that inflammatory and oxidative stress factors and the Akt/mTOR pathway may serve important roles in the regeneration of muscle contusion. In addition, certain inflammatory factors and oxidative stress factors maintained high levels of expression at 14 days after injury, indicating that the healing process of muscle was still not fully achieved at this time.

Regeneration Genetics

Understanding how and why animals regenerate complex tissues has the potential to transform regenerative medicine. Here we present an overview of genetic approaches that have recently been applied to dissect mechanisms of regeneration. We describe new advances that relate to central objectives of regeneration biologists researching different tissues and species, focusing mainly on vertebrates. These objectives include defining the cellular sources and key cell behaviors in regenerating tissue, elucidating molecular triggers and brakes for regeneration, and defining the earliest events that control the presence of these molecular factors.

Nerves, H2O2 and Shh: Three players in the game of regeneration

The tight control of reactive oxygen species (ROS) levels is required during regeneration. H₂O₂ in particular assumes clear signalling functions at different steps in this process. Injured nerves induce high levels of H₂O₂ through the activation of the Hedgehog (Shh) pathway, providing an environment that promotes cell plasticity, progenitor recruitment and blastema formation. In turn, high H₂O₂ levels contribute to growing axon attraction. Once re-innervation is completed, nerves subsequently downregulate H₂O₂ levels to their original state. A similar regulatory loop between H₂O₂ levels and nerves also exists during development. This suggests that redox signalling is a major actor in cell plasticity.

Anti-inflammatory and Analgesic Activities of Topical Formulations of Pterocarpus Santalinus Powder in Rat Model of Chronic Inflammation

INTRODUCTION

The incidence of arthritis is quite high and there is a need for the search of natural products to halt the progression of disease or provide symptomatic relief without significant adverse effects.

AIM

This study aimed at evaluating the anti-inflammatory and analgesic activities of topical Pterocarpus santalinus in an animal model of chronic inflammation.

MATERIALS AND METHODS

Albino rats of either sex were divided into five groups of six rats each (Group I - Control, Group II -Gel base, Group III -P. santalinus paste, Group IV -P. santalinus gel, Group V- Diclofenac gel). Chronic inflammation was induced on day 0 by injecting 0.1 ml Complete Freund's Adjuvant (CFA) in sub-plantar tissue of left hind paw of the rats. Topical treatment was started from day 12 till day 28. Body weight and paw volume (Plethysmometer) were assessed on day 0, 12 and 28. Pain assessment was done using Randall and Selitto paw withdrawal method. Data was analysed using GraphPad Prism version 5. Unpaired students t-test and ANOVA followed by Tukey's test was used for comparison among groups.

RESULTS

Only topical P.santalinus gel significantly reduced the body weight (p=0.02) due to reduction in inflammatory oedema of the left limb. P. santalinus gel also showed significant reduction (p=0.03) in paw volume of rats compared to the other groups. There was significant reduction in pain threshold (gm/sec) due to chronic inflammation, with all the study drugs (p<0.05) but with P. santalinus gel, this reduction was less (p<0.001).

CONCLUSION

Gel showed significant anti-inflammatory and mild analgesic activity on topical application in rat model of chronic inflammation.

Early bioelectric activities mediate redox-modulated regeneration

Reactive oxygen species (ROS) and electric currents modulate regeneration; however, the interplay between biochemical and biophysical signals during regeneration remains poorly understood. We investigate the interactions between redox and bioelectric activities during tail regeneration in Xenopus laevis tadpoles. We show that inhibition of NADPH oxidase-mediated production of ROS, or scavenging or blocking their diffusion into cells, impairs regeneration and consistently regulates the dynamics of membrane potential, transepithelial potential (TEP) and electric current densities (J_I) during regeneration. Depletion of ROS mimics the altered TEP and J_I observed in the non-regenerative refractory period. Short-term application of hydrogen peroxide (H₂O₂) rescues (from depleted ROS) and induces (from the refractory period) regeneration, TEP increase and J_I reversal. H₂O₂ is therefore necessary for and sufficient to induce regeneration and to regulate TEP and J_I Epistasis assays show that voltage-gated Na⁺ channels act downstream of H₂O₂ to modulate regeneration. Altogether, these results suggest a novel mechanism for regeneration via redox-bioelectric orchestration.