Dedifferentiated Schwann Cell Precursors Secreting Paracrine Factors Are Required for Regeneration of the Mammalian Digit Tip

Cellular dedifferentiation. Revisiting Betty Hay's legacy

The concept of mature specialized cells and the stability of the differentiated state was fundamentally challenged by Elizabeth Hay's groundbreaking observations on amphibian limb regeneration, published in 1959. Building on previous work by C.S. Thornton, she discovered that muscle cells could dedifferentiate and transform into progenitor cells within the regeneration blastema reshaping our understanding of cell differentiation. This pivotal finding reshaped our understanding of cell differentiation, opening new avenues of research. Though controversial, her findings significantly advanced the fields of cell plasticity and regenerative biology.

Lacking TRPA1 cation channel impairs primary closure of a stromal incision injury in a mouse cornea

The cornea is a high sensory, innervated, avascular tissue that consists of epithelium, keratocytes, endothelium, and extracellular matrix. We evaluated the effects of gene knockout of the transient receptor potential ankyrin 1 (TRPA1), a membrane cation channel potentially activated by various external stimuli on the wound-healing process in corneal stroma following an incision injury in mice. TRPA1 protein was detected markedly in corneal epithelium and cells in the stroma in a healthy uninjured wild-type (WT) cornea. Deletion of TRPA1 gene function delayed wound closure of a full-thickness incision injury in corneal stroma. Peak of appearance of Sox10 (Schwann cell marker)-positive and Sox2- or p75- (both repair-type Schwann cell markers) expressing cells, in the healing stroma was at day 2 post-incision injury in a WT mouse, that was delayed in a TRPA1-knockout (KO) mouse during the healing process. Expression of TGFβ1 mRNA was suppressed, in association with reduction of p-Smad3 expression in stromal cells, by TRPA1 gene deletion. We also observed that the loss of TRPA1 suppressed the appearance of myofibroblasts and expression of collagen Ia1 and fibronectin in the healing stroma. In vitro gel culture study showed that chemical TRPA1 inhibition attenuated TGFβ-induced fibroblast contractility. These results indicate that TRPA1 is involved in the process of corneal stromal wound healing in response to tissue laceration in mice. The phenotype was associated with attenuation of generation of repair Schwann cells, of TGFβ signaling in stromal cells, keratocyte-myofibroblast transformation, and collagen type I expression. (241 words).

Neural regulation of H3K27me3 during the induction of patterning competency in regenerating Axolotl limb cells

Limb regeneration in the Mexican axolotl relies on the dedifferentiation of mature limb cells into blastema cells, which gain the ability to respond to patterning signals that guide tissue regeneration. While limb nerves are essential to make the blastema cells competent to pattern, the mechanisms remain unclear due to the complex and overlapping signals in amputated limbs. To overcome this challenge, we developed the Competency Accessory Limb Model (CALM), a simplified limb regeneration assay to study the induction and maintenance of patterning competency. Using CALM, here we show specific temporal windows during which cells acquire competency and associate this state with distinct H3K27me3 chromatin signatures. Furthermore, a combination of FGF and BMP signaling is sufficient to induce patterning competency in limb wound cells, and the ErBB signaling pathway is a downstream epigenetic target of these signals. These findings offer new insights into the molecular regulation of regenerative patterning.

Development of a VEGF-activated scaffold with enhanced angiogenic and neurogenic properties for chronic wound healing applications

Chronic wounds remain in a state of disrupted healing, impeding neurite outgrowth from injured nerves and poor development of new blood vessels by angiogenesis. Current therapeutic approaches primarily focus on the restoration of vascularization and overlook the need of nerve regeneration for complete healing. Vascular endothelial growth factor (VEGF) is a critical growth factor supporting angiogenesis in wound healing, promoting vascularization and has also demonstrated neuro-protective capabilities in both central and peripheral nervous system. While the delivery of pro-regenerative recombinant growth factors has shown promise, gene delivery offers greater stability, reduced off-target side effects, diminished cytotoxicity, and lower production costs. In this context, the overarching goal of this study was to develop a VEGF-activated scaffold with the potential to provide a multifaceted response that enhances both angiogenesis and nerve repair in wound healing through the localized delivery of plasmid encoding VEGF (pVEGF) encapsulated within the GET peptide system. Initially, delivery of pVEGF/GET nanoparticles to dermal fibroblasts led to higher VEGF protein expression without a compromise in cell viability. Transfection of dermal fibroblasts and endothelial cells on the VEGF-activated scaffolds resulted in enhanced VEGF expression, improved endothelial cell migration and organization into vascular-like structures. Finally, the VEGF-activated scaffolds consistently displayed enhanced neurogenic ability through improved neurite outgrowth from neural cells in in vitro and ex vivo models. Taken together, the VEGF-activated scaffold demonstrates multifaceted outcomes through the induction of pro-angiogenic and neurogenic responses from dermal, vascular and neural cells, illustrating the potential of this platform for the healing of chronic wounds.

Glial-immune interactions in barrier organs

Neuro-immune interactions within barrier organs, such as lung, gut, and skin, are crucial in regulating tissue homeostasis, inflammatory responses, and host defence. Our rapidly advancing understanding of peripheral neuroimmunology is transforming the field of barrier tissue immunology, offering a fresh perspective for developing therapies for complex chronic inflammatory disorders affecting barrier organs. However, most studies have primarily examined interactions between the peripheral nervous system and the immune system from a neuron-focused perspective, while glial cells, the nonneuronal cells of the nervous system, have received less attention. Glial cells were long considered as mere bystanders, only supporting their neuronal neighbours, but recent discoveries mainly on enteric glial cells in the intestine have implicated these cells in immune-regulation and inflammatory disease pathogenesis. In this review, we will highlight the bi-directional interactions between peripheral glial cells and the immune system and discuss the emerging immune regulatory functions of glial cells in barrier organs.

Schwann Cell-Secreted S100B Promotes Wound Healing via Paracrine Modulation

As the supply source for gingival grafts, the palatal tissue possesses marked regenerative ability after repeated wounding over the buccal attached gingiva and skin. However, the intrinsic mechanisms are poorly understood. Schwann cells reportedly participate in wound repair of many tissues. Here, we investigate whether Schwann cells play an essential role in the wound healing of palatal mucosa. We performed multiomics analysis in nonhuman primates, integrating scRNA-seq and proteomics analysis, and built wound-healing models in the palatal mucosa and buccal attached gingiva and skin to compare the regeneration among different sites and explore the paracrine role of Schwann cells in the healing of palatal mucosa. With regard to in vivo validation, GelMA hydrogels loaded with conditional medium or exogenous protein were applied in rat and monkey skin. We revealed greater distributions and a lower differentiation state of Schwann cells in the palatal mucosa at baseline. Moreover, S100B levels were significantly greater in the wound healing of palatal mucosa than in the buccal attached gingiva, and Schwann cell-secreted S100B can promote the healing-related capabilities of fibroblasts via paracrine modulation with receptor of advanced glycation end products (RAGE), which activates the crosstalk between NF-κB and Notch signaling, leading to expedited wound closure in vivo. Our work shows that Schwann cells play a crucial role in the wound healing of the palatal mucosa through the S100B/RAGE/NF-κB/Notch paracrine axis. In addition, our data provide novel insights into the therapeutic effects of S100B protein on wound healing.

Schwann cells in regeneration and cancer: an epithelial-mesenchymal transition perspective

In the peripheral nervous system, glial cells, known as Schwann cells (SCs), are responsible for supporting and maintaining nerves. One of the most important characteristics of SCs is their remarkable plasticity. In various injury contexts, SCs undergo a reprogramming process that generates specialized cells to promote tissue regeneration and repair. However, in pathological conditions, this same plasticity and regenerative potential can be hijacked. Different studies highlight the activation of the epithelial-mesenchymal transition (EMT) as a driver of SC phenotypic plasticity. Although SCs are not epithelial, their neural crest origin makes EMT activation crucial for their ability to adopt repair phenotypes, mirroring the plasticity observed during development. These adaptive processes are essential for regeneration. However, EMT activation in SCs-derived tumours enhances cancer progression and aggressiveness. Furthermore, in the tumour microenvironment (TME), SCs also acquire activated phenotypes that contribute to tumour migration and invasion by activating EMT in cancer cells. In this review, we will discuss how EMT impacts SC plasticity and function from development and tissue regeneration to pathological conditions, such as cancer.

Neuroregulation during Bone Formation and Regeneration: Mechanisms and Strategies

The skeleton is highly innervated by numerous nerve fibers. These nerve fibers, in addition to transmitting information within the bone and mediating bone sensations, play a crucial role in regulating bone tissue formation and regeneration. Traditional bone tissue engineering (BTE) often fails to achieve satisfactory outcomes when dealing with large-scale bone defects, which is frequently related to the lack of effective reconstruction of the neurovascular network. In recent years, increasing research has revealed the critical role of nerves in bone metabolism. Nerve fibers regulate bone cells through neurotransmitters, neuropeptides, and peripheral glial cells. Furthermore, nerves also coordinate with the vascular and immune systems to jointly construct a microenvironment favorable for bone regeneration. As a signaling driver of bone formation, neuroregulation spans the entire process of bone physiological activities from the embryonic formation to postmaturity remodeling and repair. However, there is currently a lack of comprehensive summaries of these regulatory mechanisms. Therefore, this review sketches out the function of nerves during bone formation and regeneration. Then, we elaborate on the mechanisms of neurovascular coupling and neuromodulation of bone immunity. Finally, we discuss several novel strategies for neuro-bone tissue engineering (NBTE) based on neuroregulation of bone, focusing on the coordinated regeneration of nerve and bone tissue.

Schwann cells in regeneration and cancer

Schwann cells are specific peripheral glial cells with remarkable plasticity following peripheral nerve injury. Injury responses stimulate c-Jun activation in Schwann cells, drive epithelial-mesenchymal transition and cellular phenotypic changes, and induce the generation of reprogrammed repair Schwann cells to orchestrate peripheral nerve regeneration process. Schwann cells and/or Schwann cell-derived molecules are commonly used as supporting cells and/or neurotrophic factors to construct Schwann cell-based tissue-engineered nerve grafts for repairing severe peripheral nerve injury with long defects. Transplantation of Schwann cells and/or Schwann cell-derived molecules also serves as a helpful approach for the treatment of other injured tissues, such as the spinal cord, skin, digit tip, and bone. Schwann cells are not only associated with tissue regeneration but also involved in tumorigenesis and tumor progression. Schwann cells are the major cellular component of neurofibromatosis type 1 and the sole cell type in neurofibromatosis type 2 and schwannomatosis. In addition, Schwann cells also function as an important player in the tumor microenvironment and aid in the growth and invasiveness of many other solid cancers. In the present review, we outline the physiological and pathological activities of Schwann cells and discuss the functional roles of Schwann cells in homeostasis, regeneration, and cancer.

Enhancer-driven Shh signaling promotes glia-to-mesenchyme transition during bone repair

Plp1-lineage Schwann cells (SCs) of peripheral nerve play a critical role in vascular remodeling and osteogenic differentiation during the early stage of bone healing, and the abnormal plasticity of SCs would jeopardize the bone regeneration. However, how Plp1-lineage cells respond to injury and initiate the vascularized osteogenesis remains incompletely understood. Here, by employing single-cell transcriptional profiling combined with lineage-specific tracing models, we uncover that Plp1-lineage cells undergoing injury-induced glia-to-MSCs transition contributed to osteogenesis and revascularization in the initial stage of bone injury. Importantly, our data demonstrated that the Sonic hedgehog (Shh) signaling was responsible for the transition process initiation, which was strongly activated by c-Jun/SIRT6/BAF170 complex-driven Shh enhancers. Collectively, these findings depict an injury-specific niche signal-mediated Plp1-lineage cells transition towards Gli1+ MSCs and may be instructive for approaches to promote bone regeneration during aging or other bone diseases.

Isoviolanthin promotes Schwann cells activity in peripheral nerve regeneration via Fhl3-mediated epithelial-mesenchymal transition-like process: An in vitro study

Schwann cells, as crucial regenerative cells, possess the ability to facilitate axon growth following peripheral nerve injury. However, the regeneration efficiency dominated by Schwann cells is impaired by factors such as the severity of peripheral nervous injury, aging, and metabolic disease. Cause the limitations of clinical treatments, it is necessary to urgently search for new substances that could reinforce the functionality of Schwann cells and promote nerve regeneration. We represented the first evidence that isoviolanthin possesses the capability to enhance Schwann cell proliferation and migration. Then, transcriptome sequencing was employed to examine the Differential Expressed Genes (DEGs), resulting in the identification of 193 DEGs. Following this, the expression levels of the top 5 up-regulated genes were confirmed through RT-qPCR, with Fhl3 demonstrating the most significant up-regulation. Schwann cells were transduced with virus particles made in HEK-293T/17 cells by transfection with lentivirus packaging plasmids containing Fhl3. A notable enhancement in Schwann cell proliferation and migration was observed following transduction. Furthermore, the Fhl3-up group exhibited a significant upregulation of Vimentin expression compared to the control group. These results suggested that isoviolanthin plays a positive role in enhancing Schwann cells' activity via increasing Fhl3 expression, and the mechanism may be related to the EMT(epithelial-mesenchymal transition)-like process.

Innervated Coculture Device to Model Peripheral Nerve-Mediated Fibroblast Activation

Cutaneous wound healing is a complex process involving various cellular and molecular interactions, resulting in the formation of a collagen-rich scar with imperfect function and morphology. Dermal fibroblasts are crucial to successful wound healing, migrating to the wound site where they are activated to provide extracellular matrix remodeling and wound closure. Peripheral nerves have been shown to play an important role in wound healing, with loss or damage to these nerves often leading to impaired healing and the formation of chronic nonhealing wounds. Previous research has suggested that sensory nerves secrete trophic factors that can regulate wound healing, including fibroblast activation; however, the direct cell-cell interaction between nerves and fibroblasts has not been extensively studied. To address this knowledge gap, we developed an in vitro co-culture model using a device called the IFlowPlate. This model supports the long-term viability of multiple cell types while allowing for direct contact between sensory nerve cells and dermal fibroblasts. Using the IFlowPlate, we demonstrate that co-culture of dorsal root ganglia with dermal fibroblasts increases fibroblast proliferation, collagen and α-smooth muscle actin expression, and secretion of pro-wound healing factors, suggesting that nerves can promote wound healing by modulating fibroblast activation. The IFlowPlate offers a user-friendly and high-throughput platform to study the in vitro interactions between nerves and a variety of cell types that can be applied to wound healing and other important biological processes.

Insights into the molecular characteristics of embryonic cranial neural crest cells and their derived mesenchymal cell pools

Neural crest cells (NCCs) are central to vertebrate embryonic development, giving rise to diverse cell types with unique migratory and differentiation capacities. This study examines the molecular characteristics of cranial neural crest cell (CNCC)-derived mesenchymal cells, specifically those from teeth which in deer show continuous but limited growth, and antlers, which exhibit remarkable regenerative capabilities. Here, through single-cell RNA sequencing analysis, we uncover shared gene expression profiles between adult antlerogenic and dental mesenchymal cells, indicating common developmental pathways. We identify a striking resemblance in transcriptomic features between antlerogenic progenitor cells and dental pulp mesenchymal cells. Comparative analysis of CNCC-derived and non-CNCC-derived mesenchymal cell pools across species reveals core signature genes associated with CNCCs and their derivatives, delineating essential connections between CNCCs and CNCC-derived adult mesenchymal pools. Furthermore, whole-genome DNA methylation analysis unveils hypomethylation of CNCC derivate signature genes in regenerative antlerogenic periosteum, implying a role in maintaining multipotency. These findings offer crucial insights into the developmental biology and regenerative potential of CNCC-derived mesenchymal cells, laying a foundation for innovative therapeutic strategies in tissue regeneration.

Satellite glial cell manipulation prior to axotomy enhances developing dorsal root ganglion central branch regrowth into the spinal cord

The central and peripheral nervous systems (CNS and PNS, respectively) exhibit remarkable diversity in the capacity to regenerate following neuronal injury with PNS injuries being much more likely to regenerate than those that occur in the CNS. Glial responses to damage greatly influence the likelihood of regeneration by either promoting or inhibiting axonal regrowth over time. However, despite our understanding of how some glial lineages participate in nerve degeneration and regeneration, less is known about the contributions of peripheral satellite glial cells (SGC) to regeneration failure following central axon branch injury of dorsal root ganglia (DRG) sensory neurons. Here, using in vivo, time-lapse imaging in larval zebrafish coupled with laser axotomy, we investigate the role of SGCs in axonal regeneration. In our studies we show that SGCs respond to injury by relocating their nuclei to the injury site during the same period that DRG neurons produce new central branch neurites. Laser ablation of SGCs prior to axon injury results in more neurite growth attempts and ultimately a higher rate of successful central axon regrowth, implicating SGCs as inhibitors of regeneration. We also demonstrate that this SGC response is mediated in part by ErbB signaling, as chemical inhibition of this receptor results in reduced SGC motility and enhanced central axon regrowth. These findings provide new insights into SGC-neuron interactions under injury conditions and how these interactions influence nervous system repair.

Hallmarks of regeneration

Regeneration is a heroic biological process that restores tissue architecture and function in the face of day-to-day cell loss or the aftershock of injury. Capacities and mechanisms for regeneration can vary widely among species, organs, and injury contexts. Here, we describe "hallmarks" of regeneration found in diverse settings of the animal kingdom, including activation of a cell source, initiation of regenerative programs in the source, interplay with supporting cell types, and control of tissue size and function. We discuss these hallmarks with an eye toward major challenges and applications of regenerative biology.

Epithelial-mesenchymal transition in tissue repair and degeneration

Epithelial-mesenchymal transitions (EMTs) are the epitome of cell plasticity in embryonic development and cancer; during EMT, epithelial cells undergo dramatic phenotypic changes and become able to migrate to form different tissues or give rise to metastases, respectively. The importance of EMTs in other contexts, such as tissue repair and fibrosis in the adult, has become increasingly recognized and studied. In this Review, we discuss the function of EMT in the adult after tissue damage and compare features of embryonic and adult EMT. Whereas sustained EMT leads to adult tissue degeneration, fibrosis and organ failure, its transient activation, which confers phenotypic and functional plasticity on somatic cells, promotes tissue repair after damage. Understanding the mechanisms and temporal regulation of different EMTs provides insight into how some tissues heal and has the potential to open new therapeutic avenues to promote repair or regeneration of tissue damage that is currently irreversible. We also discuss therapeutic strategies that modulate EMT that hold clinical promise in ameliorating fibrosis, and how precise EMT activation could be harnessed to enhance tissue repair.

Neuronal regulation of bone and tendon injury repair: a focused review

Beyond the sensation of pain, peripheral nerves have been shown to play crucial roles in tissue regeneration and repair. As a highly innervated organ, bone can recover from injury without scar formation, making it an interesting model in which to study the role of nerves in tissue regeneration. As a comparison, tendon is a musculoskeletal tissue that is hypo-innervated, with repair often resulting in scar formation. Here, we reviewed the significance of innervation in 3 stages of injury repair (inflammatory, reparative, and remodeling) in 2 commonly injured musculoskeletal tissues: bone and tendon. Based on this focused review, we conclude that peripheral innervation is essential for phases of proper bone and tendon repair, and that nerves may dynamically regulate the repair process through interactions with the injury microenvironment via a variety of neuropeptides or neurotransmitters. A deeper understanding of neuronal regulation of musculoskeletal repair, and the crosstalk between nerves and the musculoskeletal system, will enable the development of future therapies for tissue healing.

Mechanisms of regeneration: to what extent do they recapitulate development?

One of the enduring debates in regeneration biology is the degree to which regeneration mirrors development. Recent technical advances, such as single-cell transcriptomics and the broad applicability of CRISPR systems, coupled with new model organisms in research, have led to the exploration of this longstanding concept from a broader perspective. In this Review, I outline the historical parallels between development and regeneration before focusing on recent research that highlights how dissecting the divergence between these processes can uncover previously unreported biological mechanisms. Finally, I discuss how these advances position regeneration as a more dynamic and variable process with expanded possibilities for morphogenesis compared with development. Collectively, these insights into mechanisms that orchestrate morphogenesis may reshape our understanding of the evolution of regeneration, reveal hidden biology activated by injury, and offer non-developmental strategies for restoring lost or damaged organs and tissues.

MEK-SHP2 inhibition prevents tibial pseudarthrosis caused by NF1 loss in Schwann cells and skeletal stem/progenitor cells

Congenital pseudarthrosis of the tibia (CPT) is a severe pathology marked by spontaneous bone fractures that fail to heal, leading to fibrous nonunion. Half of patients with CPT are affected by the multisystemic genetic disorder neurofibromatosis type 1 (NF1) caused by mutations in the NF1 tumor suppressor gene, a negative regulator of RAS-mitogen-activated protein kinase (MAPK) signaling pathway. Here, we analyzed patients with CPT and Prss56-Nf1 knockout mice to elucidate the pathogenic mechanisms of CPT-related fibrous nonunion and explored a pharmacological approach to treat CPT. We identified NF1-deficient Schwann cells and skeletal stem/progenitor cells (SSPCs) in pathological periosteum as affected cell types driving fibrosis. Whereas NF1-deficient SSPCs adopted a fibrotic fate, NF1-deficient Schwann cells produced critical paracrine factors including transforming growth factor-β and induced fibrotic differentiation of wild-type SSPCs. To counteract the elevated RAS-MAPK signaling in both NF1-deficient Schwann cells and SSPCs, we used MAPK kinase (MEK) and Src homology 2 containing protein tyrosine phosphatase 2 (SHP2) inhibitors. Combined MEK-SHP2 inhibition in vivo prevented fibrous nonunion in the Prss56-Nf1 knockout mouse model, providing a promising therapeutic strategy for the treatment of fibrous nonunion in CPT.

Mapping Somatosensory Afferent Circuitry to Bone Identifies Neurotrophic Signals Required for Fracture Healing

The profound pain accompanying bone fracture is mediated by somatosensory neurons, which also appear to be required to initiate bone regeneration following fracture. Surprisingly, the precise neuroanatomical circuitry mediating skeletal nociception and regeneration remains incompletely understood. Here, we characterized somatosensory dorsal root ganglia (DRG) afferent neurons innervating murine long bones before and after experimental long bone fracture in mice. Retrograde labeling of DRG neurons by an adeno-associated virus with peripheral nerve tropism showed AAV-tdT signal. Single cell transcriptomic profiling of 6,648 DRG neurons showed highest labeling across CGRP+ neuron clusters (6.9-17.2%) belonging to unmyelinated C fibers, thinly myelinated Aδ fibers and Aβ-Field LTMR (9.2%). Gene expression profiles of retrograde labeled DRG neurons over multiple timepoints following experimental stress fracture revealed dynamic changes in gene expression corresponding to the acute inflammatory ( S100a8 , S100a9 ) and mechanical force ( Piezo2 ). Reparative phase after fracture included morphogens such as Tgfb1, Fgf9 and Fgf18 . Two methods to surgically or genetically denervate fractured bones were used in combination with scRNA-seq to implicate defective mesenchymal cell proliferation and osteodifferentiation as underlying the poor bone repair capacity in the presence of attenuated innervation. Finally, multi-tissue scRNA-seq and interactome analyses implicated neuron-derived FGF9 as a potent regulator of fracture repair, a finding compatible with in vitro assessments of neuron-to-skeletal mesenchyme interactions.

Schwann Cells as Orchestrators of Nerve Repair: Implications for Tissue Regeneration and Pathologies

Peripheral nerves exist in a stable state in adulthood providing a rapid bidirectional signaling system to control tissue structure and function. However, following injury, peripheral nerves can regenerate much more effectively than those of the central nervous system (CNS). This multicellular process is coordinated by peripheral glia, in particular Schwann cells, which have multiple roles in stimulating and nurturing the regrowth of damaged axons back to their targets. Aside from the repair of damaged nerves themselves, nerve regenerative processes have been linked to the repair of other tissues and de novo innervation appears important in establishing an environment conducive for the development and spread of tumors. In contrast, defects in these processes are linked to neuropathies, aging, and pain. In this review, we focus on the role of peripheral glia, especially Schwann cells, in multiple aspects of nerve regeneration and discuss how these findings may be relevant for pathologies associated with these processes.

Advances in magnetoelectric composites for promoting bone regeneration: a review

Repair of large bone defects is one of the clinical problems that have not yet been fully solved. The dynamic balance of bone tissue is regulated by many biological, chemical and physical environmental factors. Simulating the microenvironment of bone tissue in the physiological state through biomimetic materials is an important development direction of tissue engineering in recent years. With the deepening of research, it has been found that when bone tissue is damaged, its surrounding magnetoelectric microenvironment is subsequently destroyed, and providing a magnetoelectric microenvironment in the biomimetic state will be beneficial to promote bone repair. This review describes the piezoelectric effect of natural bone tissue with magnetoelectric stimulation for bone regeneration, provides a detailed account of the historical development of magnetoelectric composites and the current magnetoelectric composites that are most commonly utilized in the field of tissue engineering. Besides, the hypothesized mechanistic pathways through which magnetoelectric composite materials promote bone regeneration are critically examined, including the enhancement of osteogenesis, promotion of cell adhesion and angiogenesis, modulation of bone immunity, and promotion of nerve regeneration.

Regenerative loss in the animal kingdom as viewed from the mouse digit tip and heart

The myriad regenerative abilities across the animal kingdom have fascinated us for centuries. Recent advances in developmental, molecular, and cellular biology have allowed us to unearth a surprising diversity of mechanisms through which these processes occur. Developing an all-encompassing theory of animal regeneration has thus proved a complex endeavor. In this chapter, we frame the evolution and loss of animal regeneration within the broad developmental constraints that may physiologically inhibit regenerative ability across animal phylogeny. We then examine the mouse as a model of regeneration loss, specifically the experimental systems of the digit tip and heart. We discuss the digit tip and heart as a positionally-limited system of regeneration and a temporally-limited system of regeneration, respectively. We delve into the physiological processes involved in both forms of regeneration, and how each phase of the healing and regenerative process may be affected by various molecular signals, systemic changes, or microenvironmental cues. Lastly, we also discuss the various approaches and interventions used to induce or improve the regenerative response in both contexts, and the implications they have for our understanding regenerative ability more broadly.

Tissue-resident macrophages specifically express Lactotransferrin and Vegfc during ear pinna regeneration in spiny mice

The details of how macrophages control different healing trajectories (regeneration vs. scar formation) remain poorly defined. Spiny mice (Acomys spp.) can regenerate external ear pinnae tissue, whereas lab mice (Mus musculus) form scar tissue in response to an identical injury. Here, we used this dual species system to dissect macrophage phenotypes between healing modes. We identified secreted factors from activated Acomys macrophages that induce a pro-regenerative phenotype in fibroblasts from both species. Transcriptional profiling of Acomys macrophages and subsequent in vitro tests identified VEGFC, PDGFA, and Lactotransferrin (LTF) as potential pro-regenerative modulators. Examining macrophages in vivo, we found that Acomys-resident macrophages secreted VEGFC and LTF, whereas Mus macrophages do not. Lastly, we demonstrate the requirement for VEGFC during regeneration and find that interrupting lymphangiogenesis delays blastema and new tissue formation. Together, our results demonstrate that cell-autonomous mechanisms govern how macrophages react to the same stimuli to differentially produce factors that facilitate regeneration.

Neural dependency in wound healing and regeneration

In response to injury, humans and many other mammals form a fibrous scar that lacks the structure and function of the original tissue, whereas other vertebrate species can spontaneously regenerate damaged tissues and structures. Peripheral nerves have been identified as essential mediators of wound healing and regeneration in both mammalian and nonmammalian systems, interacting with the milieu of cells and biochemical signals present in the post-injury microenvironment. This review examines the diverse functions of peripheral nerves in tissue repair and regeneration, specifically during the processes of wound healing, blastema formation, and organ repair. We compare available evidence in mammalian and nonmammalian models, identifying critical nerve-mediated mechanisms for regeneration and providing future perspectives toward integrating these mechanisms into a therapeutic framework to promote regeneration.

Glial plasticity at nervous system transition zones

The central and peripheral nervous systems (CNS and PNS, respectively) are two separate yet connected domains characterized by molecularly distinct cellular components that communicate via specialized structures called transition zones to allow information to travel from the CNS to the periphery, and vice versa. Until recently, nervous system transition zones were thought to be selectively permeable only to axons, and the establishment of the territories occupied by glial cells at these complex regions remained poorly described and not well understood. Recent work now demonstrates that transition zones are occupied by dynamic glial cells and are precisely regulated over the course of nervous system development. This review highlights recent work on glial cell migration in and out of the spinal cord, at motor exit point (MEP) and dorsal root entry zone (DREZ) transition zones, in the physiological and diseased nervous systems. These cells include myelinating glia (oligodendrocyte lineage cells, Schwann cells and motor exit point glia), exit glia, perineurial cells that form the perineurium along spinal nerves, as well as professional and non-professional phagocytes (microglia and neural crest cells).

Role of the Peripheral Nervous System in Skeletal Development and Regeneration: Controversies and Clinical Implications

PURPOSE OF REVIEW

This review examines the diverse functional relationships that exist between the peripheral nervous system (PNS) and bone, including key advances over the past century that inform our efforts to translate these discoveries for skeletal repair.

RECENT FINDINGS

The innervation of the bone during development, homeostasis, and regeneration is highly patterned. Consistent with this, there have been nearly 100 studies over the past century that have used denervation approaches to isolate the effects of the different branches of the PNS on the bone. Overall, a common theme of balance emerges whereby an orchestration of both local and systemic neural functions must align to promote optimal skeletal repair while limiting negative consequences such as pain. An improved understanding of the functional bidirectional pathways linking the PNS and bone has important implications for skeletal development and regeneration. Clinical advances over the next century will necessitate a rigorous identification of the mechanisms underlying these effects that is cautious not to oversimplify the in vivo condition in diverse states of health and disease.

Involvement of neuronal tachykinin-like receptor at 86C in Drosophila disc repair via regulation of kynurenine metabolism

Neurons contribute to the regeneration of projected tissues; however, it remains unclear whether they are involved in the non-innervated tissue regeneration. Herein, we showed that a neuronal tachykinin-like receptor at 86C (TkR86C) is required for the repair of non-innervated wing discs in Drosophila. Using a genetic tissue repair system in Drosophila larvae, we performed genetic screening for G protein-coupled receptors to search for signal mediatory systems for remote tissue repair. An evolutionarily conserved neuroinflammatory receptor, TkR86C, was identified as the candidate receptor. Neuron-specific knockdown of TkR86C impaired disc repair without affecting normal development. We investigated the humoral metabolites of the kynurenine (Kyn) pathway regulated in the fat body because of their role as tissue repair-mediating factors. Neuronal knockdown of TkR86C hampered injury-dependent changes in the expression of vermillion in the fat body and humoral Kyn metabolites. Our data indicate the involvement of TkR86C neurons upstream of Kyn metabolism in non-autonomous tissue regeneration.

Bioprinted constructs that simulate nerve-bone crosstalk to improve microenvironment for bone repair

Crosstalk between nerves and bone is essential for bone repair, for which Schwann cells (SCs) are crucial in the regulation of the microenvironment. Considering that exosomes are critical paracrine mediators for intercellular communication that exert important effects in tissue repair, the aim of this study is to confirm the function and molecular mechanisms of Schwann cell-derived exosomes (SC-exos) on bone regeneration and to propose engineered constructs that simulate SC-mediated nerve-bone crosstalk. SCs promoted the proliferation and differentiation of bone marrow mesenchymal stem cells (BMSCs) through exosomes. Subsequent molecular mechanism studies demonstrated that SC-exos promoted BMSC osteogenesis by regulating the TGF-β signaling pathway via let-7c-5p. Interestingly, SC-exos promoted the migration and tube formation performance of endothelial progenitor cells. Furthermore, the SC-exos@G/S constructs were developed by bioprinting technology that simulated SC-mediated nerve-bone crosstalk and improved the bone regeneration microenvironment by releasing SC-exos, exerting the regulatory effect of SCs in the microenvironment to promote innervation, vascularization, and osteogenesis and thus effectively improving bone repair in a cranial defect model. This study demonstrates the important role and underlying mechanism of SCs in regulating bone regeneration through SC-exos and provides a new engineered strategy for bone repair.

Single-Cell Transcriptomic Analysis Links Nonmyelinating Schwann Cells to Proinflammatory Response in the Lung

The lung is a barrier tissue with constant exposure to the inhaled environment. Therefore, innate immunity against particulates and pathogens is of critical importance to maintain tissue homeostasis. Although the lung harbors both myelinating and nonmyelinating Schwann cells (NMSCs), NMSCs represent the most abundant Schwann cell (SC) population in the lung. However, their contribution to lung physiology remains largely unknown. In this study, we used the human glial fibrillary acidic protein promoter driving tdTomato expression in mice to identify SCs in the peripheral nervous system and determine their location within the lung. Single-cell transcriptomic analysis revealed the existence of two NMSC populations (NMSC1 and NMSC2) that may participate in pathogen recognition. We demonstrated that these pulmonary SCs produce chemokines and cytokines upon LPS stimulation using in vitro conditions. Furthermore, we challenged mouse lungs with LPS and found that NMSC1 exhibits an enriched proinflammatory response among all SC subtypes. Collectively, these findings define the molecular profiles of lung SCs and suggest a potential role for NMSCs in lung inflammation.

A Novel Perspective on Neuronal Control of Anatomical Patterning, Remodeling, and Maintenance

While the nervous system may be best known as the sensory communication center of an organism, recent research has revealed a myriad of multifaceted roles for both the CNS and PNS from early development to adult regeneration and remodeling. These systems work to orchestrate tissue pattern formation during embryonic development and continue shaping pattering through transitional periods such as metamorphosis and growth. During periods of injury or wounding, the nervous system has also been shown to influence remodeling and wound healing. The neuronal mechanisms responsible for these events are largely conserved across species, suggesting this evidence may be important in understanding and resolving many human defects and diseases. By unraveling these diverse roles, this paper highlights the necessity of broadening our perspective on the nervous system beyond its conventional functions. A comprehensive understanding of the complex interactions and contributions of the nervous system throughout development and adulthood has the potential to revolutionize therapeutic strategies and open new avenues for regenerative medicine and tissue engineering. This review highlights an important role for the nervous system during the patterning and maintenance of complex tissues and provides a potential avenue for advancing biomedical applications.

The salamander blastema within the broader context of metazoan regeneration

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

The Role of Sensory Innervation in Homeostatic and Injury-Induced Corneal Epithelial Renewal

The cornea is the window through which we see the world. Corneal clarity is required for vision, and blindness occurs when the cornea becomes opaque. The cornea is covered by unique transparent epithelial cells that serve as an outermost cellular barrier bordering between the cornea and the external environment. Corneal sensory nerves protect the cornea from injury by triggering tearing and blink reflexes, and are also thought to regulate corneal epithelial renewal via unknown mechanism(s). When protective corneal sensory innervation is absent due to infection, trauma, intracranial tumors, surgery, or congenital causes, permanent blindness results from repetitive epithelial microtraumas and failure to heal. The condition is termed neurotrophic keratopathy (NK), with an incidence of 5:10,000 people worldwide. In this report, we review the currently available therapeutic solutions for NK and discuss the progress in our understanding of how the sensory nerves induce corneal epithelial renewal.

miR-140 and miR-200 regulate the migratory heterogeneity of location-specific Schwann cell population

Schwann cells are functional cells in nerve regeneration and are commonly used as seed cells in tissue engineering. Enhanced Schwann cell migration capacity improves recovery effects, and thus, the identification of Schwann cells with greater migration ability is of great importance. In the present study, we examined the biological activities of Schwann cells collected from rat sciatic nerves (SN) and dorsal root ganglia (DRG). Observations from transwell migration assay and wound healing assay demonstrate that DRG Schwann cells migrate at a faster speed as compared with SN Schwann cells. Sequencing and bioinformatics suggest that differentially expressed genes between SN and DRG Schwann cells are associated with cell motility and migration. miR-140 and miR-200, two microRNAs (miRNAs) that are highly expressed in SN Schwann cells negatively influence Schwann cell migration and thus may be key regulators of Schwann cell phenotype. Igsf10, Plxna2, and Lcp1 are screened as candidate downstream targets of miR-140 and miR-200 based on bioinformatic analysis and their expression correlation with miRNAs. Our comparative analysis displays the unique characteristics of Schwann cells in different anatomical localizations and demonstrates that DRG Schwann cells are suitable seed cells for tissue engineering and regenerative medicine.

Deer antler renewal gives insights into mammalian epimorphic regeneration

Deer antlers are the only known mammalian organ that, once lost, can fully grow back naturally. Hence, the antler offers a unique opportunity to learn how nature has solved the problem of mammalian epimorphic regeneration (EpR). Comprehensive comparisons amongst different types of EpR reveal that antler renewal is fundamentally different from that in lower vertebrates such as regeneration of the newt limb. Surprisingly, antler renewal is comparable to wound healing over a stump of regeneration-incompetent digit/limb, bone fracture repair, and to a lesser extent to digit tip regeneration in mammals. Common to all these mammalian cases of reaction to the amputation/mechanical trauma is the response of the periosteal cells at the distal end/injury site with formation of a circumferential cartilaginous callus (CCC). Interestingly, whether the CCC can proceed to the next stage to transform to a blastema fully depends on the presence of an interactive partner. The actual form of the partner can vary in different cases with the nail organ in digit tip EpR, the opposing callus in bone fracture repair, and the closely associated enveloping skin in antler regeneration. Due to absence of such an interactive partner, the CCC of a mouse/rat digit/limb stump becomes involuted gradually. Based on these discoveries, we created an interactive partner for the rat digit/limb stump through surgically removal of the interposing layers of loose connective tissue and muscle between the resultant CCC and the enveloping skin after amputation and by forcefully bonding two tissue types tightly together. In so doing partial regeneration of the limb stump occurred. In summary, if EpR in humans is to be realized, then I envisage that it would be more likely in a manner akin to antler regeneration rather to that of lower vertebrates such as newt limbs.

Toeing the line between regeneration and fibrosis

Understanding the remarkable capacity of vertebrates to naturally regenerate injured body parts has great importance for potential translation into human therapeutic applications. As compared to other vertebrates, mammals have low regenerative capacity for composite tissues like the limb. However, some primates and rodents can regenerate the distal tips of their digits following amputation, indicating that at least very distal mammalian limb tissues are competent for innate regeneration. It follows that successful digit tip regenerative outcome is highly dependent on the location of the amputation; those proximal to the position of the nail organ do not regenerate and result in fibrosis. This distal regeneration versus proximal fibrosis duality of the mouse digit tip serves as a powerful model to investigate the driving factors in determining each process. In this review, we present the current understanding of distal digit tip regeneration in the context of cellular heterogeneity and the potential for different cell types to function as progenitor cells, in pro-regenerative signaling, or in moderating fibrosis. We then go on to discuss these themes in the context of what is known about proximal digit fibrosis, towards generating hypotheses for these distinct healing processes in the distal and proximal mouse digit.

Inhibition of a signaling modality within the gp130 receptor enhances tissue regeneration and mitigates osteoarthritis

Adult mammals are incapable of multitissue regeneration, and augmentation of this potential may shift current therapeutic paradigms. We found that a common co-receptor of interleukin 6 (IL-6) cytokines, glycoprotein 130 (gp130), serves as a major nexus integrating various context-specific signaling inputs to either promote regenerative outcomes or aggravate disease progression. Via genetic and pharmacological experiments in vitro and in vivo, we demonstrated that a signaling tyrosine 814 (Y814) within gp130 serves as a major cellular stress sensor. Mice with constitutively inactivated Y814 (F814) were resistant to surgically induced osteoarthritis as reflected by reduced loss of proteoglycans, reduced synovitis, and synovial fibrosis. The F814 mice also exhibited enhanced regenerative, not reparative, responses after wounding in the skin. In addition, pharmacological modulation of gp130 Y814 upstream of the SRC and MAPK circuit by a small molecule, R805, elicited a protective effect on tissues after injury. Topical administration of R805 on mouse skin wounds resulted in enhanced hair follicle neogenesis and dermal regeneration. Intra-articular administration of R805 to rats after medial meniscal tear and to canines after arthroscopic meniscal release markedly mitigated the appearance of osteoarthritis. Single-cell sequencing data demonstrated that genetic and pharmacological modulation of Y814 resulted in attenuation of inflammatory gene signature as visualized by the anti-inflammatory macrophage and nonpathological fibroblast subpopulations in the skin and joint tissue after injury. Together, our study characterized a molecular mechanism that, if manipulated, enhances the intrinsic regenerative capacity of tissues through suppression of a proinflammatory milieu and prevents pathological outcomes in injury and disease.

Hyperdry Human Amniotic Membrane as a Protective Dressing for Open Wounds With Exposed Bowel in Mice

INTRODUCTION

An enteroatmospheric fistula forms when the exposed bowel is perforated with chronic enteric fistula formation. Currently, there is no established preventative method for this condition. Hyperdry (HD) amniotic membrane (AM) can promote early granulation tissue formation on the exposed viscera and is suitable for dressing intractable wounds as it possesses anti-inflammatory, antibacterial, and immunomodulatory properties. This study investigated whether HD-AM promotes early formation of blood vessel-containing granulation tissue for enteroatmospheric fistula treatment.

METHODS

An experimental animal model of an open wound with exposed bowel was developed. A 15 × 20 mm wound was prepared on the abdomen of Institute of Cancer Research mice, and the HD-AM was placed. The mice were assigned to one of the following groups: HD-AM group, in which the stromal layer of the HD-AM was placed in contact with the exposed bowel; HD-AM UD group, in which the epithelial layer of the HD-AM was placed in contact with the exposed bowel; and the HD-AM (-) or control group, in which the HD-AM was not used.

RESULTS

On postoperative days 7 and 14, granulation tissue thickness significantly increased in the HD-AM and HD-AM UD groups compared with that in the HD-AM (-) group. Macrophages accumulated in the HD-AM epithelium only in the HD-AM group. During HD-AM contact, a subset of invading macrophages switched from M1 to M2 phenotype.

CONCLUSIONS

HD-AM is a practical wound dressing with its scaffolding function, regulation of TGF β-1 and C-X-C motif chemokine 5 (CXCL-5), and ability to induce M1-to-M2 macrophage conversion.

Failure of digit tip regeneration in the absence of Lmx1b suggests Lmx1b functions disparate from dorsoventral polarity

Mammalian digit tip regeneration is linked to the presence of nail tissue, but a nail-explicit model is missing. Here, we report that nail-less double-ventral digits of ΔLARM1/2 mutants that lack limb-specific Lmx1b enhancers fail to regenerate. To separate the nail's effect from the lack of dorsoventral (DV) polarity, we also interrogate double-dorsal double-nail digits and show that they regenerate. Thus, DV polarity is not a prerequisite for regeneration, and the nail requirement is supported. Transcriptomic comparison between wild-type and non-regenerative ΔLARM1/2 mutant blastemas reveals differential upregulation of vascularization and connective tissue functional signatures in wild type versus upregulation of inflammation in the mutant. These results, together with the finding of Lmx1b expression in the postnatal dorsal dermis underneath the nail and uniformly in the regenerative blastema, open the possibility of additional Lmx1b roles in digit tip regeneration, in addition to the indirect effect of mediating the formation of the nail.

Sensory nerve niche regulates mesenchymal stem cell homeostasis via FGF/mTOR/autophagy axis

Mesenchymal stem cells (MSCs) reside in microenvironments, referred to as niches, which provide structural support and molecular signals. Sensory nerves are niche components in the homeostasis of tissues such as skin, bone marrow and hematopoietic system. However, how the sensory nerve affects the behavior of MSCs remains largely unknown. Here we show that the sensory nerve is vital for mesenchymal tissue homeostasis and maintenance of MSCs in the continuously growing adult mouse incisor. Loss of sensory innervation leads to mesenchymal disorder and a decrease in MSCs. Mechanistically, FGF1 from the sensory nerve directly acts on MSCs by binding to FGFR1 and activates the mTOR/autophagy axis to sustain MSCs. Modulation of mTOR/autophagy restores the MSCs and rescues the mesenchymal tissue disorder of Fgfr1 mutant mice. Collectively, our study provides insights into the role of sensory nerves in the regulation of MSC homeostasis and the mechanism governing it.

Hallmarks of peripheral nerve function in bone regeneration

Skeletal tissue is highly innervated. Although different types of nerves have been recently identified in the bone, the crosstalk between bone and nerves remains unclear. In this review, we outline the role of the peripheral nervous system (PNS) in bone regeneration following injury. We first introduce the conserved role of nerves in tissue regeneration in species ranging from amphibians to mammals. We then present the distribution of the PNS in the skeletal system under physiological conditions, fractures, or regeneration. Furthermore, we summarize the ways in which the PNS communicates with bone-lineage cells, the vasculature, and immune cells in the bone microenvironment. Based on this comprehensive and timely review, we conclude that the PNS regulates bone regeneration through neuropeptides or neurotransmitters and cells in the peripheral nerves. An in-depth understanding of the roles of peripheral nerves in bone regeneration will inform the development of new strategies based on bone-nerve crosstalk in promoting bone repair and regeneration.

Schwann Cells Contribute to Alveolar Bone Regeneration by Promoting Cell Proliferation

The plasticity of Schwann cells (SCs) following nerve injury is a critical feature in the regeneration of peripheral nerves as well as surrounding tissues. Here, we show a pivotal role of Schwann cell-derived cells in alveolar bone regeneration through the specific ablation of proteolipid protein 1 (Plp)-expressing cells and the transplantation of teased nerve fibers and associated cells. With inducible Plp specific genetic tracing, we observe that Plp⁺ cells migrate into wounded alveolar defect and dedifferentiate into repair SCs. Notably, these cells barely transdifferentiate into osteogenic cell lineage in both SCs tracing model and transplant model, but secret factors to enhance the proliferation of alveolar skeletal stem cells (aSSCs). As to the mechanism, this effect is associated with the upregulation of extracellular matrix (ECM) receptors and receptor tyrosine kinases (RTKs) signaling and the downstream extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) pathway and the phosphoinositide 3-kinase-protein kinase B (PI3K-Akt) pathway. Collectively, our data demonstrate that SCs dedifferentiate after neighboring alveolar bone injury and contribute to bone regeneration mainly by a paracrine function. © 2022 American Society for Bone and Mineral Research (ASBMR).

Schwann cell functions in peripheral nerve development and repair

The glial cell of the peripheral nervous system (PNS), the Schwann cell (SC), counts among the most multifaceted cells of the body. During development, SCs secure neuronal survival and participate in axonal path finding. Simultaneously, they orchestrate the architectural set up of the developing nerves, including the blood vessels and the endo-, peri- and epineurial layers. Perinatally, in rodents, SCs radially sort and subsequently myelinate individual axons larger than 1 μm in diameter, while small calibre axons become organised in non-myelinating Remak bundles. SCs have a vital role in maintaining axonal health throughout life and several specialized SC types perform essential functions at specific locations, such as terminal SC at the neuromuscular junction (NMJ) or SC within cutaneous sensory end organs. In addition, neural crest derived satellite glia maintain a tight communication with the soma of sensory, sympathetic, and parasympathetic neurons and neural crest derivatives are furthermore an indispensable part of the enteric nervous system. The remarkable plasticity of SCs becomes evident in the context of a nerve injury, where SC transdifferentiate into intriguing repair cells, which orchestrate a regenerative response that promotes nerve repair. Indeed, the multiple adaptations of SCs are captivating, but remain often ill-resolved on the molecular level. Here, we summarize and discuss the knowns and unknowns of the vast array of functions that this single cell type can cover in peripheral nervous system development, maintenance, and repair.

Diminished schwann cell repair responses play a role in delayed diabetes-associated wound healing

Diabetes mellitus is the most common metabolic disease associated with impaired wound healing. Recently, Schwann cells (SCs), the glia of the peripheral nervous system, have been suggested to accelerate normal skin wound healing. However, the roles of SCs in diabetic wound healing are not fully understood. In this study, Full-thickness wounds were made in the dorsal skin of C57/B6 mice and db/db (diabetic) mice. Tissue samples were collected at different time points, and immunohistochemical and immunofluorescence analyses were performed to detect markers of de-differentiated SCs, including myelin basic protein, Sox 10, p75, c-Jun, and Ki67. In addition, in vitro experiments were performed using rat SC (RSC96) and murine fibroblast (L929) cell lines to examine the effects of high glucose conditions (50 mM) on the de-differentiation of SCs and the paracrine effects of SCs on myofibroblast formation. Here, we found that, compared with that in normal mice, wound healing was delayed and SCs failed to rapidly activate a repair program after skin wound injury in diabetic mice. Furthermore, we found that SCs from diabetic mice displayed functional impairments in cell de-differentiation, cell-cycle re-entry, and cell migration. In vitro, hyperglycemia impaired RSC 96 cell de-differentiation, cell-cycle re-entry, and cell migration, as well as their paracrine effects on myofibroblast formation, including the secretion of TGF-β and Timp1. These results suggest that delayed wound healing in diabetes is due in part to a diminished SC repair response and attenuated paracrine effects on myofibroblast formation.

Nail-associated mesenchymal cells contribute to and are essential for dorsal digit tip regeneration

Here, we ask why the nail base is essential for mammalian digit tip regeneration, focusing on the inductive nail mesenchyme. We identify a transcriptional signature for these cells that includes Lmx1b and show that the Lmx1b-expressing nail mesenchyme is essential for blastema formation. We use a combination of Lmx1bCreERT2-based lineage-tracing and single-cell transcriptional analyses to show that the nail mesenchyme contributes cells for two pro-regenerative mechanisms. One group of cells maintains their identity and regenerates the new nail mesenchyme. A second group contributes specifically to the dorsal blastema, loses their nail mesenchyme phenotype, acquires a blastema transcriptional state that is highly similar to blastema cells of other origins, and ultimately contributes to regeneration of the dorsal but not ventral dermis and bone. Thus, the regenerative necessity for an intact nail base is explained, at least in part, by a requirement for the inductive nail mesenchyme.

Application and Molecular Mechanisms of Extracellular Vesicles Derived from Mesenchymal Stem Cells in Osteoporosis

Osteoporosis (OP) is a chronic bone disease characterized by decreased bone mass, destroyed bone microstructure, and increased bone fragility. Accumulative evidence shows that extracellular vesicles (EVs) derived from mesenchymal stem cells (MSCs) (MSC-EVs), especially exosomes (Exos), exhibit great potential in the treatment of OP. However, the research on MSC-EVs in the treatment of OP is still in the initial stage. The potential mechanism has not been fully clarified. Therefore, by reviewing the relevant literature of MSC-EVs and OP in recent years, we summarized the latest application of bone targeted MSC-EVs in the treatment of OP and further elaborated the potential mechanism of MSC-EVs in regulating bone formation, bone resorption, bone angiogenesis, and immune regulation through internal bioactive molecules to alleviate OP, providing a theoretical basis for the related research of MSC-EVs in the treatment of OP.

Evi5 is required for Xenopus limb and tail regeneration

Amphibians such as salamanders and the African clawed frog Xenopus are great models for regeneration studies because they can fully regenerate their lost organs. While axolotl can regenerate damaged organs throughout its lifetime, Xenopus has a limited regeneration capacity after metamorphosis. The ecotropic viral integrative factor 5 (Evi5) is of great interest because its expression is highly upregulated in the limb blastema of axolotls, but remains unchanged in the fibroblastema of post-metamorphic frogs. Yet, its role in regeneration-competent contexts in Xenopus has not been fully analyzed. Here we show that Evi5 is upregulated in Xenopus tadpoles after limb and tail amputation, as in axolotls. Down-regulation of Evi5 with morpholino antisense oligos (Mo) impairs limb development and limb blastema formation in Xenopus tadpoles. Mechanistically, we show that Evi5 knockdown significantly reduces proliferation of limb blastema cells and causes apoptosis, blocking the formation of regeneration blastema. RNA-sequencing analysis reveals that in addition to reduced PDGFα and TGFβ signaling pathways that are required for regeneration, evi5 Mo downregulates lysine demethylases Kdm6b and Kdm7a. And knockdown of Kdm6b or Kdm7a causes defective limb regeneration. Evi5 knockdown also impedes tail regeneration in Xenopus tadpoles and axolotl larvae, suggesting a conserved function of Evi5 in appendage regeneration. Thus, our results demonstrate that Evi5 plays a critical role in appendage regeneration in amphibians.

Transection injury differentially alters the proteome of the human sural nerve

Regeneration after severe peripheral nerve injury is often poor. Knowledge of human nerve regeneration and the growth microenvironment is greatly lacking. We aimed to identify the regenerative proteins in human peripheral nerve by comparing the proteome before and after a transection injury. In a unique study design, we collected closely matched samples of naïve and injured sural nerve. Naïve and injured (two weeks after injury) samples were analyzed using mass spectrometry and immunoassays. We found significantly altered levels following the nerve injury. Mass spectrometry revealed that injury samples had 568 proteins significantly upregulated and 471 significantly downregulated compared to naïve samples (q-value ≤ 0.05 and Z ≥ |2| (log2)). We used Gene Ontology (GO) pathway overrepresentation analysis to highlight groups of proteins that were significantly upregulated or downregulated with injury-induced degeneration and regeneration. Significant protein changes in key pathways were identified including growth factor levels, Schwann cell de-differentiation, myelination downregulation, epithelial-mesenchymal transition (EMT), and axonal regeneration pathways. The proteomes of the uninjured nerve compared to the degenerating/regenerating nerve may reveal biomarkers to aid in the development of repair strategies such as infusing supplemental trophic factors and in monitoring neural tissue regeneration.

Altered developmental programs and oriented cell divisions lead to bulky bones during salamander limb regeneration

There are major differences in duration and scale at which limb development and regeneration proceed, raising the question to what extent regeneration is a recapitulation of development. We address this by analyzing skeletal elements using a combination of micro-CT imaging, molecular profiling and clonal cell tracing. We find that, in contrast to development, regenerative skeletal growth is accomplished based entirely on cartilage expansion prior to ossification, not limiting the transversal cartilage expansion and resulting in bulkier skeletal parts. The oriented extension of salamander cartilage and bone appear similar to the development of basicranial synchondroses in mammals, as we found no evidence for cartilage stem cell niches or growth plate-like structures during neither development nor regeneration. Both regenerative and developmental ossification in salamanders start from the cortical bone and proceeds inwards, showing the diversity of schemes for the synchrony of cortical and endochondral ossification among vertebrates.