Mechanisms and translational applications of regeneration in limbs: From renewable animals to humans.

BACKGROUND: The regenerative capacity of organisms declines throughout evolution, and mammals lack the ability to regenerate limbs after injury. Past approaches to achieving successful restoration through pharmacological intervention, tissue engineering, and cell therapies have faced significant challenges. OBJECTIVES: This review aims to provide an overview of the current understanding of the mechanisms behind animal limb regeneration and the successful translation of these mechanisms for human tissue regeneration. RESULTS: Particular attention was paid to the Mexican axolotl (Ambystoma mexicanum), the only adult tetrapod capable of limb regeneration. We will explore fundamental questions surrounding limb regeneration, such as how amputation initiates regeneration, how the limb knows when to stop and which parts to regenerate, and how these findings can apply to mammalian systems. CONCLUSIONS: Given the urgent need for regenerative therapies to treat conditions like diabetic foot ulcers and trauma survivors, this review provides valuable insights and ideas for researchers, clinicians, and biomedical engineers seeking to facilitate the regeneration process or elicit full regeneration from partial regeneration events.

Grand Challenges at the Interface of Engineering and Medicine.

Over the past two decades Biomedical Engineering has emerged as a major discipline that bridges societal needs of human health care with the development of novel technologies. Every medical institution is now equipped at varying degrees of sophistication with the ability to monitor human health in both non-invasive and invasive modes. The multiple scales at which human physiology can be interrogated provide a profound perspective on health and disease. We are at the nexus of creating "avatars" (herein defined as an extension of "digital twins") of human patho/physiology to serve as paradigms for interrogation and potential intervention. Motivated by the emergence of these new capabilities, the IEEE Engineering in Medicine and Biology Society, the Departments of Biomedical Engineering at Johns Hopkins University and Bioengineering at University of California at San Diego sponsored an interdisciplinary workshop to define the grand challenges that face biomedical engineering and the mechanisms to address these challenges. The Workshop identified five grand challenges with cross-cutting themes and provided a roadmap for new technologies, identified new training needs, and defined the types of interdisciplinary teams needed for addressing these challenges. The themes presented in this paper include: 1) accumedicine through creation of avatars of cells, tissues, organs and whole human; 2) development of smart and responsive devices for human function augmentation; 3) exocortical technologies to understand brain function and treat neuropathologies; 4) the development of approaches to harness the human immune system for health and wellness; and 5) new strategies to engineer genomes and cells.

Mitsugumin 53 mitigation of ischemia-reperfusion injury in a mouse model.

OBJECTIVE: Primary graft dysfunction is often attributed to ischemia-reperfusion injury, and prevention would be a therapeutic approach to mitigate injury. Mitsugumin 53, a myokine, is a component of the endogenous cell membrane repair machinery. Previously, exogenous administration of recombinant human (recombinant human mitsugumin 53) protein has been shown to mitigate acute lung injury. In this study, we aimed to quantify a therapeutic benefit of recombinant human mitsugumin 53 to mitigate a transplant-relevant model of ischemia-reperfusion injury. METHODS: C57BL/6J mice were subjected to 1 hour of ischemia (via left lung hilar clamp), followed by 24 hours of reperfusion. mg53-/- mice were administered exogenous recombinant human mitsugumin 53 or saline before reperfusion. Tissue, bronchoalveolar lavage, and blood samples were collected at death and used to quantify the extent of lung injury via histology and biochemical assays. RESULTS: Administration of recombinant human mitsugumin 53 showed a significant decrease in an established biometric profile of lung injury as measured by lactate dehydrogenase and endothelin-1 in the bronchoalveolar lavage and plasma. Biochemical markers of apoptosis and pyroptosis (interleukin-1ß and tumor necrosis factor-α) were also significantly mitigated, overall demonstrating recombinant human mitsugumin 53's ability to decrease the inflammatory response of ischemia-reperfusion injury. Exogenous recombinant human mitsugumin 53 administration showed a trend toward decreasing overall cellular infiltrate and neutrophil response. Fluorescent colocalization imaging revealed recombinant human mitsugumin 53 was effectively delivered to the endothelium. CONCLUSIONS: These data demonstrate that recombinant human mitsugumin 53 has the potential to prevent or reverse ischemia-reperfusion injury-mediated lung damage. Although additional studies are needed in wild-type mice to demonstrate efficacy, this work serves as proof-of-concept to indicate the potential therapeutic benefit of mitsugumin 53 administration to mitigate ischemia-reperfusion injury.

Organ Repair and Regeneration During Ex Situ Dynamic Preservation: The Future is Nano.

Organ preservation and assessment with machine perfusion (MP) has provided transplant physicians with the ability to evaluate and select grafts suitable for transplantation. Nevertheless, the discard of organs considered too damaged still sustains the imbalance between donor organs supply and demands. Therefore, there is the pressing clinical need for strategies to repair and/or regenerate organs before transplantation, and MP is uniquely positioned to satisfy this need. The systemic administration of mesenchymal stromal cells (MSC) was shown to reduce ischemia-reperfusion injury in pre-clinical organ transplant models but could not be reproduced in clinical transplantation, largely because of inefficient cell delivery. The administration of MSC during MP is one strategy that recently gained much attention as an alternative delivery method to target MSC directly to the donor organ. However, careful reinterpretation of preliminary results reveals that this approach is equally limited by a suboptimal delivery of short-lived MSC to the target organ. In contrast, the use of MSC secretome and/or extracellular vesicles therapy during MP seems to be more efficient in harnessing MSC properties during MP. In this mini review we speculate on the future of the novel niche of ex situ organ repair and regeneration before transplantation.

Current Status of Tissue Regenerative Engineering for the Treatment of Uterine Infertility.

With the recent developments in tissue engineering, scientists have attempted to establish seed cells from different sources, create cell sheets through various technologies, implant them on scaffolds with various spatial structures, or load scaffolds with cytokines. These research results are very optimistic, bringing hope to the treatment of patients with uterine infertility. In this article, we reviewed articles related to the treatment of uterine infertility from the aspects of experimental treatment strategy, seed cells, scaffold application, and repair criteria so as to provide a basis for future research.

TBX3 is dynamically expressed in pancreatic organogenesis and fine-tunes regeneration.

BACKGROUND: The reactivation of genetic programs from early development is a common mechanism for injury-induced organ regeneration. T-box 3 (TBX3) is a member of the T-box family of transcription factors previously shown to regulate pluripotency and subsequent lineage commitment in a number of tissues, including limb and lung. TBX3 is also involved in lung and heart organogenesis. Here, we provide a comprehensive and thorough characterization of TBX3 and its role during pancreatic organogenesis and regeneration. RESULTS: We interrogated the level and cell specificity of TBX3 in the developing and adult pancreas at mRNA and protein levels at multiple developmental stages in mouse and human pancreas. We employed conditional mutagenesis to determine its role in murine pancreatic development and in regeneration after the induction of acute pancreatitis. We found that Tbx3 is dynamically expressed in the pancreatic mesenchyme and epithelium. While Tbx3 is expressed in the developing pancreas, its absence is likely compensated by other factors after ablation from either the mesenchymal or epithelial compartments. In an adult model of acute pancreatitis, we found that a lack of Tbx3 resulted in increased proliferation and fibrosis as well as an enhanced inflammatory gene programs, indicating that Tbx3 has a role in tissue homeostasis and regeneration. CONCLUSIONS: TBX3 demonstrates dynamic expression patterns in the pancreas. Although TBX3 is dispensable for proper pancreatic development, its absence leads to altered organ regeneration after induction of acute pancreatitis.

Developmental trajectory of pluripotent stem cell establishment in Arabidopsis callus guided by a quiescent center-related gene network.

In plant tissue culture, callus formation is induced by a high auxin concentration. Among the three cell layers (the outer, middle and inner cell layers) of the callus, pluripotency acquisition in the middle cell layer is required for the potential ability of the callus to regenerate organs. Here, we reveal the developmental trajectory of middle cell layer initiation and maintenance in callus tissue originating from Arabidopsis thaliana hypocotyls. The S phase of the cell cycle is essential for the expression of quiescent center-related SCARECROW (SCR), PLETHORA1 (PLT1) and WUSCHEL-RELATED HOMEOBOX5 (WOX5) genes during the division of callus founder cells to initiate the callus primordium. After callus initiation, SHOOT-ROOT (SHR) proteins move from the inner to the middle cell layer and act together with SCR to promote the expression of PLT1 and WOX5. WOX5 represses the expression of VASCULAR-RELATED NAC-DOMAIN (VND) genes, thereby preventing callus tissue from differentiating into xylem cells. PLT1 and PLT2 directly activate JACKDAW (JKD), which is necessary for pluripotency acquisition in the middle cell layer. We hypothesize that the middle cell layer could have pluripotent stem cell activity and its establishment requires the quiescent center-related SCR-SHR-WOX5-PLT1/2-JKD gene network.

Molecular Mechanisms of Plant Regeneration from Differentiated Cells: Approaches from Historical Tissue Culture Systems.

Plants can exert remarkable capacity for cell reprogramming even from differentiated cells. This ability allows plants to regenerate tissues/organs and even individuals in nature and in vitro. In recent decades, Arabidopsis research has uncovered molecular mechanisms of plant regeneration; however, our understanding of how plant cells retain both differentiated status and developmental plasticity is still obscure. In this review, we first provide a brief outlook of the representative modes of plant regeneration and key factors revealed by Arabidopsis research. We then re-examine historical tissue culture systems that enable us to investigate the molecular details of cell reprogramming in differentiated cells and discuss the different approaches, specifically highlighting our recent progress in shoot regeneration from the epidermal cell of Torenia fournieri.

Research progress on the mechanism of Hippo signaling pathway in organ regeneration / 药学实践与服务

Hippo signal pathway is one of the main signal pathways regulating cell proliferation and apoptosis in multicellular animals, which plays a vital role in the maintenance of tissue homeostasis and the regulation of organ growth. Most mammals have limited regenerative potential, and recent studies have shown that Hippo signal pathway is critical in the regeneration of various tissues and organs. The role of Hippo signaling pathway in organ regeneration and the research progress of related targets were introduced, the mechanism of Hippo signaling pathway promoting regeneration analyzes were aralyzed in this review, which provide theoretical reference for the treatment of diseases related to organ regeneration.

Regenerative medicine technologies applied to transplant medicine. An update.

Regenerative medicine (RM) is changing how we think and practice transplant medicine. In regenerative medicine, the aim is to develop and employ methods to regenerate, restore or replace damaged/diseased tissues or organs. Regenerative medicine investigates using tools such as novel technologies or techniques, extracellular vesicles, cell-based therapies, and tissue-engineered constructs to design effective patient-specific treatments. This review illustrates current advancements in regenerative medicine that may pertain to transplant medicine. We highlight progress made and various tools designed and employed specifically for each tissue or organ, such as the kidney, heart, liver, lung, vasculature, gastrointestinal tract, and pancreas. By combing both fields of transplant and regenerative medicine, we can harbor a successful collaboration that would be beneficial and efficacious for the repair and design of de novo engineered whole organs for transplantations.

Expression of extracellular matrix components in the meibomian gland.

Purpose: Extracellular matrix (ECM) is a key component of the stem cell local microenvironment. Our study aims to explore the periglandular distribution of major components of ECM in the Meibomian gland (MG). Methods: Human eyelids and mouse eyelids were collected and processed for immunofluorescence staining. Results: Human MG tissues stained positive for collagen IV α1, collagen IV α2, collagen IV α5, and collagen IV α6 around the acini and duct, but negative for collagen IV α3 and collagen IV α4. The mouse MG were stained positive for the same collagen IV subunits as early as postnatal day 15. Laminin α2, laminin ß1 and perlecan stained the regions surrounding the acini and the acinar/ductal junction in the human MG, but not the region around the duct. Tenascin-C was found specifically located at the junctions between the acini and the central ducts. Neither agrin nor endostatin was found in the human MG tissues. Conclusion: The ECM expresses specific components in different regions around the MG, which may play a role in MG stem cell regulation, renewal, and regeneration.

MAPK/ERK Pathway as a Central Regulator in Vertebrate Organ Regeneration.

Damage to organs by trauma, infection, diseases, congenital defects, aging, and other injuries causes organ malfunction and is life-threatening under serious conditions. Some of the lower order vertebrates such as zebrafish, salamanders, and chicks possess superior organ regenerative capacity over mammals. The extracellular signal-regulated kinases 1 and 2 (ERK1/2), as key members of the mitogen-activated protein kinase (MAPK) family, are serine/threonine protein kinases that are phylogenetically conserved among vertebrate taxa. MAPK/ERK signaling is an irreplaceable player participating in diverse biological activities through phosphorylating a broad variety of substrates in the cytoplasm as well as inside the nucleus. Current evidence supports a central role of the MAPK/ERK pathway during organ regeneration processes. MAPK/ERK signaling is rapidly excited in response to injury stimuli and coordinates essential pro-regenerative cellular events including cell survival, cell fate turnover, migration, proliferation, growth, and transcriptional and translational activities. In this literature review, we recapitulated the multifaceted MAPK/ERK signaling regulations, its dynamic spatio-temporal activities, and the profound roles during multiple organ regeneration, including appendages, heart, liver, eye, and peripheral/central nervous system, illuminating the possibility of MAPK/ERK signaling as a critical mechanism underlying the vastly differential regenerative capacities among vertebrate species, as well as its potential applications in tissue engineering and regenerative medicine.

A voyage from 3D to 4D printing in nanomedicine and healthcare: part II.

Recent advancements in biomedical tissue engineering are gaining wide interest. Implementing biology of living cells and organisms using technological solutions such as incorporating 4D printing and bioprinting for tissue regeneration/tissue repair, organ regeneration, early diagnosis of deadly diseases (particularly cancer, cardiac disorders and tuberculosis) has successfully opened a new generation of biomedical research. The present review primarily addresses the clinical application of 4D printing and bioprinting techniques for applications such as early detection of diseases and drug delivery. Notably, this review continues the discussion from part I regarding published informative data, in vitro and in vivo findings, commercial biosensors for early disease diagnosis, drug delivery and current challenges in 4D printing/bioprinting.

Developmental angiocrine diversification of endothelial cells for organotypic regeneration.

Adult organs are vascularized by specialized blood vessels. In addition to inter-organ vascular heterogeneity, each organ is arborized by structurally and functionally diversified populations of endothelial cells (ECs). The molecular pathways that are induced to orchestrate inter- and intra- organ vascular heterogeneity and zonation are shaped during development and fully specified postnatally. Notably, intra-organ specialization of ECs is associated with induction of angiocrine factors that guide cross-talk between ECs and parenchymal cells, establishing co-zonated vascular regions within each organ. In this review, we describe how microenvironmental tissue-specific biophysical, biochemical, immune, and inflammatory cues dictate the specialization of ECs with zonated functions. We delineate how physiological and biophysical stressors in the developing liver, lung, and kidney vasculature induce specialization of capillary beds. Deciphering mechanisms by which vascular microvasculature diversity is attained could set the stage for treating regenerative disorders and promote healing of organs without provoking fibrosis.

Comparing nerve-mediated FGF signalling in the early initiation phase of organ regeneration across mutliple amphibian species.

Amphibians have a very high capacity for regeneration among tetrapods. This superior regeneration capability in amphibians can be observed in limbs, the tail, teeth, external gills, the heart, and some internal organs. The mechanisms underlying the superior organ regeneration capability have been studied for a long time. Limb regeneration has been investigated as the representative phenomenon for organ-level regeneration. In limb regeneration, a prominent difference between regenerative and nonregenerative animals after limb amputation is blastema formation. A regeneration blastema requires the presence of nerves in the stump region. Thus, nerve regulation is responsible for blastema induction, and it has received much attention. Nerve regulation in regeneration has been investigated using the limb regeneration model and newly established alternative experimental model called the accessory limb model. Previous studies have identified some candidate genes that act as neural factors in limb regeneration, and these studies also clarified related events in early limb regeneration. Consistent with the nervous regulation and related events in limb regeneration, similar regeneration mechanisms in other organs have been discovered. This review especially focuses on the role of nerve-mediated fibroblast growth factor in the initiation phase of organ regeneration. Comparison of the initiation mechanisms for regeneration in various amphibian organs allows speculation about a fundamental regenerative process.

Rapid fabrication of gelatin-based scaffolds with prevascularized channels for organ regeneration.

One of the biggest hindrances in tissue engineering in recent decades has been the complexity of the prevascularized channels of the engineered scaffold, which was still lower than that of human tissues. Another relative difficulty was the lack of precision molding capability, which restricted the clinical applications of the huge engineered scaffold. In this study, a promising approach was proposed to prepare hydrogel scaffold with prevascularized channels by liquid bath printing, in which chitosan/ß-sodium glycerophosphate served as the ink hydrogel, and gelation/nanoscale bacterial cellulose acted as the supporting hydrogel. Here, the ink hydrogel was printed by a versatile nozzle and embedded in the supporting hydrogel. The ink hydrogel transformed into liquid effluent at low temperature after the cross-linking of gelatin by microbial transglutaminase (mTG). No residual template was seen on the channel surface after template removal. This preparation had a high degree of freedom in the geometry of the channel, which was demonstrated by making various prevascularized channels including circular, branched, and tree-shaped networks. The molding accuracy of the channel was assessed by studying the roundness of the cross section of the molded hollow channel, and the effect of the mechanical properties by adding bacterial cellulose to the supporting hydrogel was analyzed. Human umbilical vein endothelial cells were injected into the aforementioned channels which formed a confluent and homogeneous distribution on the surface of the channels. Altogether, these results showed that this approach can construct hydrogel scaffolds with complex and accurate molding prevascularized channels, and hs great potential to resolve the urgent vascularization issue of bulk tissue-engineering scaffold.

Ex-vivo Kidney Machine Perfusion: Therapeutic Potential.

Kidney transplantation remains the gold standard treatment for patients suffering from end-stage kidney disease. To meet the constantly growing organ demands grafts donated after circulatory death (DCD) or retrieved from extended criteria donors (ECD) are increasingly utilized. Not surprisingly, usage of those organs is challenging due to their susceptibility to ischemia-reperfusion injury, high immunogenicity, and demanding immune regulation after implantation. Lately, a lot of effort has been put into improvement of kidney preservation strategies. After demonstrating a definite advantage over static cold storage in reduction of delayed graft function rates in randomized-controlled clinical trials, hypothermic machine perfusion has already found its place in clinical practice of kidney transplantation. Nevertheless, an active investigation of perfusion variables, such as temperature (normothermic or subnormothermic), oxygen supply and perfusate composition, is already bringing evidence that ex-vivo machine perfusion has a potential not only to maintain kidney viability, but also serve as a platform for organ conditioning, targeted treatment and even improve its quality. Many different therapies, including pharmacological agents, gene therapy, mesenchymal stromal cells, or nanoparticles (NPs), have been successfully delivered directly to the kidney during ex-vivo machine perfusion in experimental models, making a big step toward achievement of two main goals in transplant surgery: minimization of graft ischemia-reperfusion injury and reduction of immunogenicity (or even reaching tolerance). In this comprehensive review current state of evidence regarding ex-vivo kidney machine perfusion and its capacity in kidney graft treatment is presented. Moreover, challenges in application of these novel techniques in clinical practice are discussed.

Recruited CD68+CD206+ macrophages orchestrate graft immune tolerance to prompt xenogeneic-dentin matrix-based tooth root regeneration.

Successful regenerative medicine strategies of xenogeneic extracellular matrix need a synergistic balance among inflammation, fibrosis, and remodeling process. Adaptive macrophage subsets have been identified to modulate inflammation and orchestrate the repair of neighboring parenchymal tissues. This study fabricated PPARγ-primed CD68+CD206+ M2 phenotype (M2γ), and firstly verified their anti-inflammatory and tissue-regenerating roles in xenogeneic bioengineered organ regeneration. Our results showed that Th1-type CD3+CD8+ T cell response to xenogeneic-dentin matrix-based bioengineered root complex (xeno-complex) was significantly inhibited by M2γ macrophage in vitro. PPARγ activation also timely recruited CD68+CD206+ tissue macrophage polarization to xeno-complex in vivo. These subsets alleviated proinflammatory cytokines (TNF-α, IFN-γ) at the inflammation site and decreased CD3+CD8+ T lymphocytes in the periphery system. When translated to an orthotopic nonhuman primate model, PPARγ-primed M2 macrophages immunosuppressed IL-1ß, IL-6, TNF-α, MMPs to enable xeno-complex to effectively escape immune-mediated rejection and initiate graft-host synergistic integrity. These collective activities promoted the differentiation of odontoblast-like and periodontal-like cells to guide pulp-dentin and cementum-PDLs-bone regeneration and rescued partially injured odontogenesis such as DSPP and periostin expression. Finally, the regenerated root showed structure-biomechanical and functional equivalency to the native tooth. The timely conversion of M1-to-M2 macrophage mainly orchestrated odontogenesis, fibrogenesis, and osteogenesis, which represents a potential modulator for intact parenchymal-stromal tissue regeneration of targeted organs.