Deer antler regeneration: a stem cell-based epimorphic process

Antler stem cell-derived exosomes promote regenerative wound healing via fibroblast-to-myofibroblast transition inhibition

INTRODUCTION

The typical outcome of mammalian wound healing is scarring, a fibrotic process mediated by myofibroblast aggregation. Perfect healing in a clinical setting is relatively unexplored. Surprisingly, our previous studies have shown that the large wound (10 cm diameter or more) of the pedicle of deer naturally achieves regenerative restoration, realized through a paracrine pathway from adjacent antler stem cells (AnSCs).

METHODS

AnSC-derived exosomes (AnSC-exos) were topically injected around the full-thickness wounds in a rat model. The effects on the rate of wound healing and the quality of healing were evaluated via morphological, histological, and molecular biological techniques on days 14 and 28 after surgery.

RESULTS

The results showed that AnSC-exos significantly accelerated the rate of wound healing and improved healing quality, including regeneration of cutaneous appendages (hair follicles and sebaceous glands) and the distribution pattern of collagen (basket-weave-like) in the healed skin. These effects of AnSC-exos were comparable to those of AnSCs but were significantly more potent than those of exosomes derived from bone marrow mesenchymal stem cells (bMSC-exos). Furthermore, AnSC-exos treatment effectively inhibited fibroblast-to-myofibroblast transition (FMT), as evidenced by the reduction of full-thickness skin injury-induced FMT in vivo and TGF-β1-induced FMT in vitro.

CONCLUSION

AnSC-exos could effectively promote regenerative cutaneous wound healing, highly likely through FMT inhibition. This suggests that AnSC-exos treatment could provide the potential for a novel approach to induce regenerative wound healing in the clinical setting.

Antler stem cell exosomes alleviate pulmonary fibrosis via inhibiting recruitment of monocyte macrophage, rather than polarization of M2 macrophages in mice

Pulmonary fibrosis (PF), a chronic interstitial lung disease, is characterized by over-abundant deposition of extracellular matrix consisting mainly of collagen I. In previous studies, we demonstrated that deer antler stem cells (AnSCs), a novel type of adult stem cell, are capable of significantly down-regulating collagen formation in different organs and tissues and speculated that they could effectively treat PF via reducing collagen deposition in the lung tissue. In the present study, we found that administration of AnSCs improved the survival rate of PF mice and reduced lung fibrosis, collagen deposition and myofibroblast differentiation. The effects of AnSC treatment were significantly better than the positive control (adipose-derived stem cells). Interestingly, AnSC-Exos were almost equally effective as AnSCs in treating PF, suggesting that the effects of AnSCs on reduction of PF may be mainly through a paracrine mechanism. Further, AnSC-Exos reduced the number of M2 macrophages, a type of macrophage that secrets pro-fibrotic factors to accelerate fibrotic progression, in the lung tissues. In vitro experiments showed that the effects of AnSC-Exos on macrophage modulation were likely achieved via inhibition of the recruitment of circulating monocyte-derived macrophages (reducing the number of macrophages), rather than via inhibition of M2 polarization of macrophages. Inhibition of macrophage recruitment by AnSCs may be achieved indirectly via inhibiting CCL7 expression in fibroblasts; both let-7b and let-7a were highly enriched in AnSC-Exos and may play a critical role in the inhibition of CCL7 expression of fibroblasts. Collectively, the use of antler stem cells or their exosomes opens up a novel strategy for PF treatment in the clinical setting.

Galectin-1 promotes angiogenesis and chondrogenesis during antler regeneration

BACKGROUND

Deer antlers are the only known mammalian structure that undergoes full regeneration. In addition, it is peculiar because when growing, it contains vascularized cartilage. The differentiation of antler stem cells (ASCs) into chondrocytes while inducing endochondral extension of blood vessels is necessary to form antler vascularized cartilage. Therefore, antlers provide an unparalleled opportunity to investigate chondrogenesis, angiogenesis, and regenerative medicine. A study found that Galectin-1 (GAL-1), which can be used as a marker in some tumors, is highly expressed in ASCs. This intrigued us to investigate what role GAL-1 could play in antler regeneration.

METHODS

We measured the expression level of GAL-1 in antler tissues and cells by immunohistochemistry, WB and QPCR. We constructed antlerogenic periosteal cells (APCs, one cell type of ASCs) with the GAL-1 gene knocked out (APC^GAL-1-/-) using CRISPR-CAS9 gene editing system. The effect of GAL-1 on angiogenesis was determined by stimulating human umbilical vein endothelial cells (HUVECs) using APC^GAL-1-/- conditioned medium or adding exogenous deer GAL-1 protein. The effect of APC^GAL-1-/- on chondrogenic differentiation was evaluated compared with the APCs under micro-mass culture. The gene expression pattern of APC^GAL-1-/- was analyzed by transcriptome sequencing.

RESULTS

Immunohistochemistry revealed that GAL-1 was widely expressed in the antlerogenic periosteum (AP), pedicle periosteum (PP) and antler growth center. Western blot and qRT-PCR analysis using deer cell lines further supports this result. The proliferation, migration, and tube formation assays of human umbilical vein endothelial cells (HUVECs) showed that the proangiogenic activity of APC^GAL-1-/- medium was significantly decreased (P < 0.05) compared with the APCs medium. The proangiogenic activity of deer GAL-1 protein was further confirmed by adding exogenous deer GAL-1 protein (P < 0.05). The chondrogenic differentiation ability of APC^GAL-1-/- was impeded under micro-mass culture. The terms of GO and KEGG enrichment of the differentially expressed genes (DEGs) of APC^GAL-1-/- showed that down-regulated expression of pathways associated with deer antler angiogenesis, osteogenesis and stem cell pluripotency, such as the PI3K-AKT signaling pathway, signaling pathways regulating pluripotency of stem cells and TGF-β signaling pathway.

CONCLUSIONS

Deer GAL-1, has strong angiogenic activity, is widely and highly expressed in deer antler. The APCs can induce angiogenesis by secreting GAL-1. The knockout of GAL-1 gene of APCs damaged its ability to induce angiogenesis and differentiate into chondrocytes. This ability is crucial to the formation of deer antler vascularized cartilage. Moreover, Deer antlers offer a unique model to explore explore how angiogenesis at high levels of GAL-1 expression can be elegantly regulated without becoming cancerous.

DNA methylation pattern and mRNA expression of OPN promoter in sika deer antler tip tissues

In order to explore the biological role of OPN gene during the growth of sika deer antler, the dermis, mesenchyme, precartilage and cartilage tissues of sika deer antler tip at the early period of the antler with a saddle-like appearance (30 days), the rapid growth period of the antler with two branches (60 days), and the final period of the antler with three branches (90 days) were analyzed. Bisulfite sequencing PCR (BSP) and quantitative real-time PCR (qRT-PCR) were used to explore the DNA promoter methylation and mRNA expression of OPN in sika deer antler from the perspective of space and time. The test results showed that: 1) The methylation rates of OPN promoter at the early, middle and late periods of dermis tissue were (40.48±0.82)%, (40.00±1.43)%, and (39.05±0.82)%; The methylation rates in mesenchyme tissue were (37.62±0.82)%, (34.76±2.18)%, and (38.57±1.43)%; The methylation rates in precartilage tissue were (36.67±0.28)%, (29.52±1.65)%, (28.10±2.18)%; The methylation rates in cartilage tissue were (31.90±1.65)%, (26.67±1.65)%, (24.29±1.43)%. 2) There are 7 CpG sites in the OPN promoter region, and the 3 CpG sites of -367 bp, -245 bp and -31 bp are all methylated to different level. 3) The methylation level of OPN in the dermis, mesenchyme, precartilage and cartilage tissues decreased in sequence at the same growth period. At the middle and late periods, the methylation level of the promoter region of the precartilage tissue was significantly different from that of the dermis and mesenchyme tissues (P<0.05); At different growth periods, the methylation level of the promoter region of cartilage tissue was extremely significantly different from that of dermis and mesenchyme tissues (P<0.01); In the same tissue, the methylation level of the promoter region at the middle period was down-regulated compared with the early period, and the methylation level of the promoter region at the early period and the middle period was extremely significantly different in the precartilage and cartilage (P<0.01). 4) OPN mRNA is highly expressed in precartilage and cartilage tissues. 5) The methylation level of OPN promoter was negatively correlated with mRNA expression level. In summary, it is speculated that the OPN gene, which may be regulated by the DNA methylation level of the promoter, promotes the growth and development of deer antler mainly by regulating the growth of precartilage and cartilage tissues.

Comparison of genome-wide DNA methylation patterns between antler precartilage and cartilage

Deer antlers are the only mammalian organs that can fully regenerate after being lost and provide a valuable model for cartilage development. As one of the best-studied epigenetic mechanisms, DNA methylation is known to engage in organ and tissue development. This study aimed to investigate the role of DNA methylation in antler chondrogenesis by comparing whole-genome DNA methylation between precartilage and cartilage. Quantitative reverse transcription PCR (RT-qPCR) showed significant differences in the expression levels of DNA methyltransferase genes (DNMT1, DNMT3A, and DNMT3B) between precartilage and cartilage. Subsequently, we obtained DNA methylation profiles of antler precartilage and cartilage tissues by whole-genome bisulfite sequencing. Although sequencing data indicated that overall methylation levels at CpG and non-CpG sites were similar between precartilage and cartilage, 140,784 differentially methylated regions (DMRs, P < 0.05) and 3,941 DMR-related genes were identified. Gene ontology (GO) analysis of DMR-related genes demonstrated some significantly enriched GO terms (P < 0.05) related to chondrogenesis, including insulin receptor binding, collage trimer, integrin binding, and extracellular matrix structural constituent. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of DMR-related genes uncovered that the PI3K/AKT, cortisol synthesis and secretion, glycosaminoglycan biosynthesis-keratan sulfate, Hippo, and NF-κB signaling pathways might play a pivotal role in the transition of precartilage to cartilage. Moreover, we found that 25 DMR-related genes, including CD44, IGF1, ITGAV, ITGB1, RUNX1, COL2A1, COMP, and TAGLN, were most likely involved in antler chondrogenesis. In conclusion, this study revealed the genome-wide DNA methylation patterns of antler precartilage and cartilage, which may contribute to understanding the epigenetic regulation of antler chondrogenesis.

A population of stem cells with strong regenerative potential discovered in deer antlers

The annual regrowth of deer antlers provides a valuable model for studying organ regeneration in mammals. We describe a single-cell atlas of antler regrowth. The earliest-stage antler initiators were mesenchymal cells that express the paired related homeobox 1 gene (PRRX1⁺ mesenchymal cells). We also identified a population of "antler blastema progenitor cells" (ABPCs) that developed from the PRRX1⁺ mesenchymal cells and directed the antler regeneration process. Cross-species comparisons identified ABPCs in several mammalian blastema. In vivo and in vitro ABPCs displayed strong self-renewal ability and could generate osteochondral lineage cells. Last, we observed a spatially well-structured pattern of cellular and gene expression in antler growth center during the peak growth stage, revealing the cellular mechanisms involved in rapid antler elongation.

MiRNA Profiling and Its Potential Roles in Rapid Growth of Velvet Antler in Gansu Red Deer (Cervus elaphus kansuensis)

A significant variety of cell growth factors are involved in the regulation of antler growth, and the fast proliferation and differentiation of various tissue cells occur during the yearly regeneration of deer antlers. The unique development process of velvet antlers has potential application value in many fields of biomedical research. Among them, the nature of cartilage tissue and the rapid growth and development process make deer antler a model for studying cartilage tissue development or rapid repair of damage. However, the molecular mechanisms underlying the rapid growth of antlers are still not well studied. MicroRNAs are ubiquitous in animals and have a wide range of biological functions. In this study, we used high-throughput sequencing technology to analyze the miRNA expression patterns of antler growth centers at three distinct growth phases, 30, 60, and 90 days following the abscission of the antler base, in order to determine the regulatory function of miRNA on the rapid growth of antlers. Then, we identified the miRNAs that were differentially expressed at various growth stages and annotated the functions of their target genes. The results showed that 4319, 4640, and 4520 miRNAs were found in antler growth centers during the three growth periods. To further identify the essential miRNAs that could regulate fast antler development, five differentially expressed miRNAs (DEMs) were screened, and the functions of their target genes were annotated. The results of KEGG pathway annotation revealed that the target genes of the five DEMs were significantly annotated to the "Wnt signaling pathway", "PI3K-Akt signaling pathway", "MAPK signaling pathway", and "TGF-β signaling pathway", which were associated with the rapid growth of velvet antlers. Therefore, the five chosen miRNAs, particularly ppy-miR-1, mmu-miR-200b-3p, and novel miR-94, may play crucial roles in rapid antler growth in summer.

Antler tine homologies and cervid systematics: A review of past and present controversies with special emphasis on Elaphurus davidianus

Antlers are the most conspicuous trait of cervids and have been used in the past to establish a classification of their fossil and living representatives. Since the availability of molecular data, morphological characters have generally become less important for phylogenetic reconstructions. In recent years, however, the appreciation of morphological characters has increased, and they are now more frequently used in addition to molecular data to reconstruct the evolutionary history of cervids. A persistent challenge when using antler traits in deer systematics is finding a consensus on the homology of structures. Here, we review early and recent attempts to homologize antler structures and objections to this approach, compare and evaluate recent advances on antler homologies, and critically discuss these different views in order to offer a basis for further scientific exchange on the topic. We further present some developmental aspects of antler branching patterns and discuss their potential for reconstructing cervid systematics. The use of heterogeneous data for reconstructing phylogenies has resulted in partly conflicting hypotheses on the systematic position of certain cervid species, on which we also elaborate here. We address current discussions on the use of different molecular markers in cervid systematics and the question whether antler morphology and molecular data can provide a consistent picture on the evolutionary history of cervids. In this context, special attention is given to the antler morphology and the systematic position of the enigmatic Pere David's deer (Elaphurus davidianus).

lncRNA Sequencing of Antler Mesenchymal Tissue Revealed that the Regulatory Network of Antler Cell Proliferation and Differentiation

Antlers have been widely studied due to their unique physiological characteristics, such as rapid growth, periodic shedding and regeneration. However, little is known about how antler growth is regulated by long non-coding RNA (lncRNA). The aim of the present study was to identify the lncRNAs expression profile and explore the function of lncRNAs during the antler growth. Herein, RNA-sequencing technology (RNA-seq) was performed on the three growth periods (early developmental period: EP, middle developmental period: MP, later developmental period: LP) of male sika deer (Cervus nippon) antler, 16 differentially expressed lncRNAs (DE lncRNAs) and 11 DE lncRNAs were identified in EP vs MP and MP vs LP related to cell proliferation and cell differentiation, respectively. Finally, lncRNAs-mRNAs co-expression networks were constructed based on the identified DE lncRNAs and their potential trans-target genes. The result reveals that lncRNAs may play diverse roles in different periods of antler growth. It provides a novel perspective for revealing the molecular mechanism of antler growth.

Decline in telomere length with increasing age across nonhuman vertebrates: A meta-analysis

The prediction that telomere length (TL) shortens with increasing age is a major element in considering the role of telomeres as a key player in evolution. While telomere attrition is found in humans both in vitro and in vivo, the increasing number of studies reporting diverse age-specific patterns of TL challenges the hypothesis of a universal decline of TL with increasing age. Here, we performed a meta-analysis to estimate the relationship between TL and age across 175 estimates encompassing 98 species of vertebrates. We found that, on average, TL does decline with increasing age during adulthood. However, this decline was weak and variable across vertebrate classes, and we also found evidence for a publication bias that might weaken our current evidence of decreasing TL with increasing age. We found no evidence for a faster decline in TL with increasing age when considering the juvenile stage (from birth to age at first reproduction) compared to the adult stage. Heterogeneity in TL ageing rates was explained by the method used to measure telomeres: detectable TL declines with increasing age were found only among studies using TRF with in-gel hybridisation and qFISH methods, but not in studies using qPCR and Southern blot-based TRF methods. While we confirmed that TL declines with increasing age in most adult vertebrates, our results identify an influence of telomere measurement methodology, which highlights the need to examine more thoroughly the effect of the method of measurement on TL estimates.

Bioactive constituents of animal-derived traditional Chinese medicinal materials for breast cancer: opportunities and challenges

Breast cancer is globally the most common invasive cancer in women and remains one of the leading causes of cancer-related deaths. Surgery, radiotherapy, chemotherapy, immunotherapy, and endocrine therapy are currently the main treatments for this cancer type. However, some breast cancer patients are prone to drug resistance related to chemotherapy or immunotherapy, resulting in limited treatment efficacy. Consequently, traditional Chinese medicinal materials (TCMMs) as natural products have become an attractive source of novel drugs. In this review, we summarized the current knowledge on the active components of animal-derived TCMMs, including Ophiocordycepssinensis-derived cordycepin, the aqueous and ethanolic extracts of O.sinensis, norcantharidin (NCTD), Chansu, bee venom, deer antlers, Ostreagigas, and scorpion venom, with reference to marked anti-breast cancer effects due to regulating cell cycle arrest, proliferation, apoptosis, metastasis, and drug resistance. In future studies, the underlying mechanisms for the antitumor effects of these components need to be further investigated by utilizing multi-omics technologies. Furthermore, large-scale clinical trials are necessary to validate the efficacy of bioactive constituents alone or in combination with chemotherapeutic drugs for breast cancer treatment.

Distribution, structure, and mineralization of calcified cartilage remnants in hard antlers

Antlers are paired deciduous bony cranial appendages of deer that undergo a regular cycle of growth, death and casting, and constitute the most rapidly growing bones in mammals. Antler growth occurs in an appositional mode and involves a modified form of endochondral ossification. In endochondral bones, calcified cartilage is typically a transient tissue that is eventually completely replaced by bone tissue. We studied the distribution and characteristics of calcified cartilage in hard antlers from three deer species (Capreolus capreolus, Cervus elaphus, Dama dama), i.e., in antlers from which the skin (velvet) had been shed. Remnants of calcified cartilage were regularly present as part of the trabecular framework in the late formed, distal antler portions in all three species, whereas this tissue was largely or completely missing in the more proximal antler portions. The presence of calcified cartilage remnants in the distal antler portions is attributed to the limited antler lifespan of only a few months, which is also the reason for the virtual lack of bone remodeling in antlers. The calcified cartilage matrix was more highly mineralized than the antler bone matrix. Mineralized deposits were observed in some chondrocyte lacunae and occasionally also in osteocyte lacunae, a phenomenon that has not previously been reported in antlers. Using synchrotron radiation-induced X-ray fluorescence (SR-XRF) mapping, we further demonstrated increased zinc concentrations in cement lines, along the inner borders of incompletely formed primary osteons, along the walls of partly or completely mineral-occluded chondrocyte and osteocyte lacunae, and in intralacunar mineralized deposits. The present study demonstrates that antlers are a promising model for studying the mineralization of cartilage and bone matrices and the formation of mineralized deposits in chondrocyte and osteocyte lacunae.

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Remnants of calcified cartilage are regularly present in hard antlers of deer.

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Preservation of calcified cartilage is caused by the short lifespan of antlers.

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Calcified cartilage of antlers is more highly mineralized than antler bone.

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Mineralized deposits were observed in chondrocyte and osteocyte lacunae of antlers.

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SR-XRF showed increased Zn-concentration in cement lines and intralacunar deposits.

Deer antler extracts reduce amyloid-beta toxicity in a Caenorhabditis elegans model of Alzheimer's disease

ETHNOPHARMACOLOGICAL RELEVANCE

Velvet antler extracts (VAE) are composed of a variety of active substances and growth factors, and have been reported to improve sleep quality and memory.

AIM OF THE STUDY

We aimed to explore the protective effects and mechanism of action for VAE on Alzheimer's disease (AD) using a transgenic Caenorhabditis elegans model.

MATERIALS AND METHODS

C. elegans were cultivated at 40% relative humidity on solid nematode growth medium (NGM) containing live E. coli (OP50) as the food source, with Strain N2 (normal) held at 20 °C and the CL4176s (transgenic) held at 16 °C. AD-like aggregation of Aβ peptide in the CL4176s strain is induced by lifting the temperature to 25 °C. Nematodes were treated with three types of VAEs and Resveratrol (positive control). Analyses included qRT-PCR for quantification of gene transcripts of interest; ELISA for measuring levels of amyloid-β protein; Thioflavin T fluorescent staining for localizing Aβ depositions; assays for reactive oxygen species (ROS) and superoxide dismutase activity (SOD).

RESULTS

VAEs reduced β-amyloid peptide (Aβ) toxicity in the transgenic C. elegans model. An enzymatically-digested VAE (EDVAE) was superior to both a cold-water VAE (CWVAE) and a hot-water VAE (HWVAE) from the same velvet antler. EDVAE treatment reduced the severity of the Aβ-induced paralysis phenotype and decreased the amount of Aβ deposits in the AD model nematodes, and these effects were found to be significantly better than that of the positive control Resveratrol. In addition, EDVAE treatment reduced production of ROS (induced by Aβ), enhanced SOD activity, and elevated expression levels of antioxidant-related transcription factors, although it is not known whether these effects were achieved directly or indirectly.

CONCLUSION

EDVAE had a protective role in Aβ-induced toxicity in the transgenic AD nematodes, possibly through reducing accumulation of toxic Aβ and enhancing the ability of nematodes to resist oxidative stress. Thus, EDVAE has potential to be an effective treatment to relieve the symptoms of AD.

Cross-species metabolomic analysis identifies uridine as a potent regeneration promoting factor

Regenerative capacity declines throughout evolution and with age. In this study, we asked whether metabolic programs underlying regenerative capability might be conserved across species, and if so, whether such metabolic drivers might be harnessed to promote tissue repair. To this end, we conducted metabolomic analyses in two vertebrate organ regeneration models: the axolotl limb blastema and antler stem cells. To further reveal why young individuals have higher regenerative capacity than the elderly, we also constructed metabolic profiles for primate juvenile and aged tissues, as well as young and aged human stem cells. In joint analyses, we uncovered that active pyrimidine metabolism and fatty acid metabolism correlated with higher regenerative capacity. Furthermore, we identified a set of regeneration-related metabolite effectors conserved across species. One such metabolite is uridine, a pyrimidine nucleoside, which can rejuvenate aged human stem cells and promote regeneration of various tissues in vivo. These observations will open new avenues for metabolic intervention in tissue repair and regeneration.

Velvet Antler Peptides Reduce Scarring via Inhibiting the TGF-β Signaling Pathway During Wound Healing

Aim

Scar formation generally occurs in cutaneous wound healing in mammals, mainly caused by myofibroblast aggregations, and currently with few effective treatment options. However, the pedicle wound (about 10 cm in diameter) of the deer can initiate regenerative healing, which has been found to be achieved via paracrine factors from the internal tissues of antlers.

Methods

Enzymatically digested velvet antler peptides (EVAP) were prepared along with other types of antler extracts as the controls. The effects of EVAP on healing of full-thickness skin wounds were evaluated using rats in vivo, and on myofibroblast transdifferentiation tested using transforming growth factor-β1 (TGF-β1)-induced human dermal fibroblasts in vitro.

Results

EVAP significantly accelerated the wound healing rate, reduced scar formation, and improved the healing quality, including promoted angiogenesis, increased number of skin appendages (hair follicles and sebaceous glands) and improved the distribution pattern of collagen fibers (basket-wave like) in the healed tissue. Moreover, EVAP significantly down-regulated the expression levels of genes pro- scar formation (Col1a2 and TGF-β1), and up-regulated the expression levels of genes anti-scar formation (Col3a1 and TGF-β3), and suppressed the excessive transdifferentiation of myofibroblasts and the formation of collagen I in vivo and in vitro. Furthermore, we found these effects were highly likely achieved by inhibiting the TGF-β signaling pathway, evidenced by decreased expression levels of the related genes, including TGF-β1, Smad2, p-Smad2, α-SMA, and collagen I.

Conclusions

EVAP may be a promising candidate to be developed as a clinic drug for regenerative wound healing.

A Comprehensive Conceptual and Computational Dynamics Framework for Autonomous Regeneration Systems

Many biological organisms regenerate structure and function after damage. Despite the long history of research on molecular mechanisms, many questions remain about algorithms by which cells can cooperate towards the same invariant morphogenetic outcomes. Therefore, conceptual frameworks are needed not only for motivating hypotheses for advancing the understanding of regeneration processes in living organisms, but also for regenerative medicine and synthetic biology. Inspired by planarian regeneration, this study offers a novel generic conceptual framework that hypothesizes mechanisms and algorithms by which cell collectives may internally represent an anatomical target morphology towards which they build after damage. Further, the framework contributes a novel nature-inspired computing method for self-repair in engineering and robotics. Our framework, based on past in vivo and in silico studies on planaria, hypothesizes efficient novel mechanisms and algorithms to achieve complete and accurate regeneration of a simple in silico flatwormlike organism from any damage, much like the body-wide immortality of planaria, with minimal information and algorithmic complexity. This framework that extends our previous circular tissue repair model integrates two levels of organization: tissue and organism. In Level 1, three individual in silico tissues (head, body, and tail-each with a large number of tissue cells and a single stem cell at the centre) repair themselves through efficient local communications. Here, the contribution extends our circular tissue model to other shapes and invests them with tissue-wide immortality through an information field holding the minimum body plan. In Level 2, individual tissues combine to form a simple organism. Specifically, the three stem cells form a network that coordinates organism-wide regeneration with the help of Level 1. Here we contribute novel concepts for collective decision-making by stem cells for stem cell regeneration and large-scale recovery. Both levels (tissue cells and stem cells) represent networks that perform simple neural computations and form a feedback control system. With simple and limited cellular computations, our framework minimises computation and algorithmic complexity to achieve complete recovery. We report results from computer simulations of the framework to demonstrate its robustness in recovering the organism after any injury. This comprehensive hypothetical framework that significantly extends the existing biological regeneration models offers a new way to conceptualise the information-processing aspects of regeneration, which may also help design living and non-living self-repairing agents.

The use of a novel deer antler decellularized cartilage-derived matrix scaffold for repair of osteochondral defects

Background

The physiologic regenerative capacity of cartilage is severely limited. Current studies on the repair of osteochondral defects (OCDs) have mainly focused on the regeneration of cartilage tissues. The antler cartilage is a unique regenerative cartilage that has the potential for cartilage repair.

Methods

Antler decellularized cartilage-derived matrix scaffolds (adCDMs) were prepared by combining freezing-thawing and enzymatic degradation. Their DNA, glycosaminoglycans (GAGs), and collagen content were then detected. Biosafety and biocompatibility were evaluated by pyrogen detection, hemolysis analysis, cytotoxicity evaluation, and subcutaneous implantation experiments. adCDMs were implanted into rabbit articular cartilage defects for 2 months to evaluate their therapeutic effects.

Results

AdCDMs were observed to be rich in collagen and GAGs and devoid of cells. AdCDMs were also determined to have good biosafety and biocompatibility. Both four- and eight-week treatments of OCDs showed a flat and smooth surface of the healing cartilage at the adCDMs filled site. The international cartilage repair society scores (ICRS) of adCDMs were significantly higher than those of controls (porcine dCDMs and normal saline) (p < 0.05). The repaired tissue in the adCDM group was fibrotic with high collagen, specifically, type II collagen.

Conclusions

We concluded that adCDMs could achieve excellent cartilage regeneration repair in a rabbit knee OCDs model. Our study stresses the importance and benefits of adCDMs in bone formation and overall anatomical reconstitution, and it provides a novel source for developing cartilage-regenerating repair materials.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13036-021-00274-5.

Transplanted Antler Stem Cells Stimulated Regenerative Healing of Radiation-induced Cutaneous Wounds in Rats

Radiation-induced cutaneous injury is the main side effect of radiotherapy. The injury is difficult to cure and the pathogenesis is complex. Mesenchymal stem cells (MSCs) serve as a promising candidate for cell-based therapy for the treatment of cutaneous wounds. The aim of the present study was to investigate whether antler stem cells (AnSCs) have better therapeutic effects on radiation-induced cutaneous injury than currently available ones. In this study, a rat model of cutaneous wound injury from Sr-90 radiation was used. AnSCs (1 × 10⁶/500 μl) were injected through the tail vein on the first day of irradiation. Our results showed that compared to the control group, AnSC-treated rats exhibited a delayed onset (14 days versus 7 days), shorter recovery time (51 days versus 84 days), faster healing rate (100% versus 70% on day 71), and higher healing quality with more cutaneous appendages regenerated (21:10:7/per given area compared to those of rat and human MSCs, respectively). More importantly, AnSCs promoted much higher quality of healing compared to other types of stem cells, with negligible scar formation. AnSC lineage tracing results showed that the injected-dye-stained AnSCs were substantially engrafted in the wound healing tissue, indicating that the therapeutic effects of AnSCs on wound healing at least partially through direct participation in the wound healing. Expression profiling of the wound-healing-related genes in the healing tissue of AnSC group more resembled a fetal wound healing. Revealing the mechanism underlying this higher quality of wound healing by using AnSC treatment would help to devise more effective cell-based therapeutics for radiation-induced wound healing in clinics.

Comparisons of Chemical Composition, Flavor and Bioactive Substances between Korean and Imported Velvet Antler Extracts

The aim of this study was to compare the antioxidant activity, chemical composition, flavor and bioactive compounds between Korean and imported velvet antlers (VAs)-derived extracts. The Korean (KVA), Russian (RVA) and New Zealand (NZVA) VAs (n=24 each, dry form) purchased from a local supplier were used in the investigation. After extracting with water (750 g VA with 6,000 mL water) for 20 h at 95°C, the VA extracts (VAE) were then used for analysis of antioxidant activity, amino acids (AAs), flavor and bioactive compounds. Compared to the RVA and NZVA, the KVA extract showed significantly higher 2,2-diphenyl 1 picrylhydrazyl (DPPH) and 2,2’-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid (ABTS) radicals scavenging activities (p<0.05). Significantly higher Fe content was found in the KVA while, higher Mn, Zn and Ca contents were found in the RVA (p<0.05). Twenty AAs were detected in all three VAEs and some of them (e.g., glycine and alanine) were higher in the KVA (p<0.05). A higher diversity (quality and quantity) of flavor compounds was found in the KVA extract compared to the imported VAs-derived extracts. Over six hundred metabolic compounds were identified in the VAEs. Among them, 412 compounds were commonly found in all the VAE types while, 109, 107, and 84 biomarker compounds were only found in the KVA, NZVA, and RVA extracts, respectively. Based on the results obtained in this study, it may be concluded that the country of origin partly affected the antioxidant activity, chemical composition, flavor and bioactive compounds of the VAEs.

Bioactive Molecular Discovery Using Deer Antlers as a Model of Mammalian Regeneration

The ability to activate and regulate stem cells during wound healing and tissue regeneration is a promising field that is resulting in innovative approaches in the field of regenerative medicine. The regenerative capacity of invertebrates has been well documented; however, in mammals, stem cells that drive organ regeneration are rare. Deer antlers are the only known mammalian structure that can annually regenerate to produce a tissue containing dermis, blood vessels, nerves, cartilage, and bone. The neural crest derived stem cells that drive this process result in antlers growing at up to 2 cm/day. Deer antlers thus provide superior attributes compared to lower-order animal models, when investigating the regulation of stem cell-based regeneration. Antler stem cells can therefore be used as a model to investigate the bioactive molecules, biological processes, and pathways involved in the maintenance of a stem cell niche, and their activation and differentiation during organ formation. This review examines stem cell-based regeneration with a focus on deer antlers, a neural crest stem cell-based mammalian regenerative structure. It then discusses the omics technical platforms highlighting the proteomics approaches used for investigating the molecular mechanisms underlying stem cell regulation in antler tissues.

Effects of Arginine Supplementation on Serum Metabolites and the Rumen Bacterial Community of Sika Deer (Cervus nippon)

Velvet antler is a regeneration organ of sika deer (Cervus nippon) and an important Chinese medicine, and nutrient metabolism affects its growth. Here, we investigated the effects of arginine supplementation on antler growth, serum biochemical indices, and the rumen bacterial community of sika deer during the antler growth period. Fifteen male sika deer (6 years old) were randomly assigned to three dietary groups, which were supplemented with 0 (n = 5, CON), 2.5 (n = 5, LArg), or 5.0 g/d (n = 5, HArg) L-arginine. The IGF-1, ALT and AST concentrations in the serum of LArg sika deer were significantly higher than those in the serum of CON (P < 0.05) and HArg deer (P < 0.05). The phyla Bacteroidetes, Firmicutes, and Proteobacteria were dominant in the rumen of sika deer among the three groups. Comparison of alpha diversities showed that the ACE and Chao1 indices significantly increased in the LArg and HArg groups compared with those in the CON group. PCoA and ANOSIM results showed that the bacterial community was significantly changed between the CON and LArg groups. Moreover, the relative abundances of Fibrobacter spp. and Prevotellaceae UCG-003 increased, but those of Clostridium sensu stricto 1 and Corynebacterium 1 decreased in the LArg and HArg groups compared with those in the CON group. Additionally, the relative abundances of 19 OTUs were significantly different between the LArg and HArg groups. These results revealed that arginine supplementation affected the sika deer rumen bacterial community and serum biochemical indices.

Making and shaping endochondral and intramembranous bones

Skeletal elements have a diverse range of shapes and sizes specialized to their various roles including protecting internal organs, locomotion, feeding, hearing, and vocalization. The precise positioning, size, and shape of skeletal elements is therefore critical for their function. During embryonic development, bone forms by endochondral or intramembranous ossification and can arise from the paraxial and lateral plate mesoderm or neural crest. This review describes inductive mechanisms to position and pattern bones within the developing embryo, compares and contrasts the intrinsic vs extrinsic mechanisms of endochondral and intramembranous skeletal development, and details known cellular processes that precisely determine skeletal shape and size. Key cellular mechanisms are employed at distinct stages of ossification, many of which occur in response to mechanical cues (eg, joint formation) or preempting future load‐bearing requirements. Rapid shape changes occur during cellular condensation and template establishment. Specialized cellular behaviors, such as chondrocyte hypertrophy in endochondral bone and secondary cartilage on intramembranous bones, also dramatically change template shape. Once ossification is complete, bone shape undergoes functional adaptation through (re)modeling. We also highlight how alterations in these cellular processes contribute to evolutionary change and how differences in the embryonic origin of bones can influence postnatal bone repair.

Compares and contrasts Endochondral and intramembranous bone development

Reviews embryonic origins of different bones

Describes the cellular and molecular mechanisms of positioning skeletal elements.

Describes mechanisms of skeletal growth with a focus on the generation of skeletal shape

New physiological insights into the phenomena of deer antler: A unique model for skeletal tissue regeneration

Generally, mammals are unable to regenerate complex tissues and organs however the deer antler provides a rare anomaly to this rule. This osseous cranial appendage which is located on the frontal bone of male deer is capable of stem cell-based organogenesis, annual casting, and cyclic de novo regeneration. A series of recent studies have classified this form of regeneration as epimorphic stem cell based. Antler renewal is initiated by the activation of neural crest derived pedicle periosteal cells (PPCs) found residing within the pedicle periosteum (PP), these PPCs have the potential to differentiate into multiple lineages. Other antler stem cells (ASCs) are the reserve mesenchymal cells (RMCs) located in the antlers tip, which develop into cartilage tissue. Antlerogenic periosteal cells (APCs) found within the antlerogenic periosteum (AP) form the tissues of both the pedicle and first set of antlers. Antler stem cells (ASCs) further appear to progress through various stages of activation, this coordinated transition is considered imperative for stem cell-based mammalian regeneration. The latest developments have shown that the rapid elongation of the main beam and antler branches are a controlled form of tumour growth, regulated by the tumour suppressing genes TP73 and ADAMTS18. Both osteoclastogenesis, as well as osteogenic and chondrogenic differentiation are also involved. While there remains much to uncover this review both summarises and comprehensively evaluates our existing knowledge of tissue regeneration in the deer antler. This will assist in achieving the goal of in vitro organ regeneration in humans by furthering the field of modern regenerative medicine.

The Translational potential of this article

As a unique stem cell-based organ regeneration process in mammals, the deer antler represents a prime model system for investigating mechanisms of regeneration in mammalian tissues. Novel ASCs could provide cell-based therapies for regenerative medicine and bone remodelling for clinical application. A greater understanding of this process and a more in-depth defining of ASCs will potentiate improved clinical outcomes.

PTN-PTPRZ signalling is involved in deer antler stem cell regulation during tissue regeneration

A growing deer antler contains a stem cell niche that can drive endochondral bone regeneration at up to 2 cm/day. Pleiotrophin (PTN), as a multifunctional growth factor, is found highly expressed at the messenger RNA level within the active antler stem cell tissues. This study aims to map the expression patterns of PTN protein and its receptors in a growing antler and investigate the effects of PTN on antler stem cells in vitro. Immunohistochemistry was employed to localise PTN/midkine (MDK) and their functional receptors, protein tyrosine phosphatase receptor type Z (PTPRZ), anaplastic lymphoma kinase (ALK), NOTCH2, and integrin α_V β_3, on serial slides of the antler growth centre. PTN was found to be the dominantly expressed growth factor in the PTN/MDK family. High expression of PTPRZ and ALK co-localised with PTN was found suggesting a potential interaction. The high levels of PTN and PTPRZ reflected the antler stem cell activation status during the regenerative process. When antler stem cells were cultured in vitro under the normoxic condition, no PTN protein was detected and exogenous PTN did not induce differentiation or proliferation but rather stem cell maintenance. Collectively, the antler stem cell niche appears to upregulate PTN and PTPRZ in vivo, and PTN-PTPRZ signalling may be involved in regulating antler stem cell behaviour during rapid antler regeneration.

A new viewpoint on antlers reveals the evolutionary history of deer (Cervidae, Mammalia)

Recent molecular phylogeny of deer revealed that the characters of antlers previously focused on are homoplasious, and antlers tend to be considered problematic for classification. However, we think antlers are important tools and reconsidered and analysed the characters and structures to use them for classification. This study developed a method to describe the branching structure of antlers by using antler grooves, which are formed on the antlers by growth, and then projecting the position of the branching directions of tines on the burr circumference. By making diagrams, comparing the branching structure interspecifically, homologous elements (tines, beams, and processes) of the antlers of 25 species of 16 genera were determined. Subsequently, ancestral state reconstruction was performed on the fixed molecular phylogenetic tree. It was revealed that Capreolinae and Cervini gained respective three-pointed antlers independently, and their subclades gained synapomorphous tines. We found new homologous and synapomorphous characters, as the antler of Eld’s deer, which has been classified in Rucervus, is structurally close to that of Elaphurus rather than that of Rucervus, consistent with molecular phylogeny. The methods of this study will contribute to the understanding of the branching structure and phylogeny of fossil species and uncover the evolutionary history of Cervidae.

Deer antlers: traditional Chinese medicine use and recent pharmaceuticals

Deer velvet antlers (VA) have been used as a type of traditional Chinese medicine for over 2000 years, mainly for treating yang-deficiency syndromes. However, VA still largely remain a traditional remedy with scant science, although getting more attention as time goes. In recent years, our group has been trying to develop some efficacious drugs/functional food based on unique biological phenomena of VA, such as, for example, dead tissue (hard antler base) being attached to living tissue (pedicle) for over half a year without causing inflammation, a large-size wound (up to 10 cm in diameter) being left on top of a pedicle stump after previous antler casting healing within a week only with a negligible scar, and severely osteoporotic skeleton caused by intensive antler calcification fully reversing after the completion of antler calcification. Successful translation of these unique phenomena to clinical use would greatly benefit human health.

Antlers - Evolution, development, structure, composition, and biomechanics of an outstanding type of bone

Antlers are bony appendages of deer that undergo periodic regeneration from the top of permanent outgrowths (the pedicles) of the frontal bones. Of the "less familiar" bone types whose study was advocated by John Currey to gain a better understanding of structure-function relationships of mineralized tissues and organs, antlers were of special interest to him. The present review summarizes our current knowledge about the evolution, development, structure, mineralization, and biomechanics of antlers and how their formation is affected by environmental factors like nutrition. Furthermore, the potential role of antlers as a model in bone biology and several fields of biomedicine as well as their use as a monitoring tool in environmental studies are discussed.

Bone growth as the main determinant of mouse digit tip regeneration after amputation

Regeneration is classically demonstrated in mammals using mice digit tip. In this study, we compared different amputation plans and show that distally amputated digits regrow with morphology close to normal but fail to regrow the fat pad. Proximally amputated digits do not regrow the phalangeal bone, but the remaining structures (nail, skin and connective tissue), all with intrinsic regenerative capacity, re-establishing integrity indistinguishably in distally and proximally amputated digits. Thus, we suggest that the bone growth promoted by signals and progenitor cells not removed by distal amputations is responsible for the re-establishment of a drastically different final morphology after distal or proximal digit tip amputations. Despite challenging the use of mouse digit tip as a model system for limb regeneration in mammals, these findings evidence a main role of bone growth in digit tip regeneration and suggest that mechanisms that promote joint structures formation should be the main goal of regenerative medicine for limb and digit regrowth.

Post-transcriptional regulation of miRNA-15a and miRNA-15b on VEGFR gene and deer antler cell proliferation

Background

Deer antler is the only regenerative organ in mammals, the regeneration of antler is not only the regeneration of bone tissue, but also accompanied by the regeneration of nerves, blood vessels and so on. The purpose of the current study was to explore the effect of miRNA-15a and miRNA-15b on the regulation of sika deer vascular endothelial growth factor receptor (VEGFR) during rapid antler growth.

Materials and methods

The VEGFR 3′-UTR was analyzed by bioinformatics software to identify the highly matched miRNAs. After transfected with miRNA mimics, the expression of selected miRNAs were measured by RT-qPCR and the relative expression level of VEGFR protein was detected by Western Blot. Dual-luciferase activity assay was used to determine the target relationship between VEGFR and miRNAs. The cartilage cell proliferation and telomerase activity were measured by MTT kit and TRAP assay, respectively.

Results

The VEGFR 3′-UTR contains a binding site for miRNA-15a and miRNA-15b. Over-expression of miRNA-15a and miRNA-15b, which significantly reduced the expression level of VEGFR protein, inhibited the proliferation of cartilage cells, and decreased the telomerase activity of cartilage cells in vitro.

Conclusion

miRNA-15a and miRNA-15b represent novel regulatory factors of VEGFR expression in deer antler.

The effects of CRISPR-Cas9 knockout of the TGF-β1 gene on antler cartilage cells in vitro

Background

Deer antler is the only mammalian organ that can be completely regenerated every year. Its periodic regeneration is regulated by multiple factors, including transforming growth factor β (TGF-β). This widely distributed multi-functional growth factor can control the proliferation and differentiation of many types of cell, and it may play a crucial regulatory role in antler regeneration. This study explored the role of TGF-β1 during the rapid growth of sika deer antler.

Methods

Three CRISPR-Cas9 knockout vectors targeting the TGF-β1 gene of sika deer were constructed and packaged with a lentiviral system. The expression level of TGF-β1 protein in the knockout cell line was determined using western blot, the proliferation and migration of cartilage cells in vitro were respectively determined using EdU and the cell scratch test, and the expression levels of TGF-β pathway-related genes were determined using a PCR array.

Results

Of the three gRNAs designed, pBOBI-gRNA2 had the best knockout effect. Knockout of TGF-β1 gene inhibits the proliferation of cartilage cells and enhances their migration in vitro. TGF-β signaling pathway-related genes undergo significant changes, so we speculate that when the TGF-β pathway is blocked, the BMP signaling pathway mediated by BMP4 may play a key role.

Conclusions

TGF-β1 is a newly identified regulatory factor of rapid growth in sika deer antler.

Common themes in tetrapod appendage regeneration: a cellular perspective

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

A brief history of circannual time

Innate circannual timing is an ancestral trait that first evolved in free-living eukaryotic cells some 2000 million years ago, with marine algae of the genus Allexandrium providing a living unicellular model. This species shows the primitive trait of 'alternation of generations', where the organism alternates between fast replicating vegetative cells in the summer and a dormant cystic cell over the winter. The resistant cysts sink into the cold ocean sediments. Remarkably, excystment in spring is governed by an endogenous circannual timing mechanism. Thus, a tiny, short-lived unicell can utilise a circannual clock as part of the life-history programme of the species. Innate timing allows for major adjustments in physiology and behaviour in anticipation of the seasons, and provides an internalised sense of seasonal time for the many species where standard environmental cues are weak or ambiguous. This is a highly adaptive strategy irrespective of the size and longevity of an organism. Circannual rhythms are expressed by a diverse range of organisms, from flowering plants to mammals, interwoven into the life-history programme of each species, being a consequence of forever living in a periodic world. In complex vertebrates, the early division of the zygote potentially carries circannual timer genes into all progeny cells and tissues. This supports the concept of a 'clock-shop' where cell-autonomous long-term rhythms are generated in each tissue, orchestrated by a central circannual pacemaker system. This is analogous to the organisation of the circadian timing system. For the circannual time-scale, specialised thyrotroph cells located in the pars tuberalis of the pituitary gland and adjacent tanycyte cells located in the ependymal wall of the third cerebral ventricle of the brain act as putative central circannual pacemakers. At a molecular level, epigenetically regulated, cyclical remodelling of chromatin, which determines whether specific circannual timer genes are transcriptionally active, or not, is considered to drive the oscillation between the summer and winter phenotypes.

Proteomic Analysis of Plasma Membrane Proteins of Antler Stem Cells Using Label-Free LC⁻MS/MS

Deer antlers are unusual mammalian organs that can fully regenerate after annual shedding. Stem cells resident in the pedicle periosteum (PPCs) provide the main cell source for antler regeneration. Central to various cellular processes are plasma membrane proteins, but the expression of these proteins has not been well documented in antler regeneration. In the present study, plasma membrane proteins of PPCs and facial periosteal cells (FPCs) were analyzed using label-free liquid chromatography⁻mass spetrometry (LC⁻MS/MS). A total of 1739 proteins were identified. Of these proteins, 53 were found solely in the PPCs, 100 solely in the FPCs, and 1576 co-existed in both PPCs and FPCs; and 39 were significantly up-regulated in PPCs and 49 up-regulated in FPCs. In total, 226 gene ontology (GO) terms were significantly enriched from the differentially expressed proteins (DEPs). Five clusters of biological processes from these GO terms comprised responses to external stimuli, signal transduction, membrane transport, regulation of tissue regeneration, and protein modification processes. Further studies are required to demonstrate the relevancy of these DEPs in antler stem cell biology and antler regeneration.

Deer thymosin beta 10 functions as a novel factor for angiogenesis and chondrogenesis during antler growth and regeneration

BACKGROUND

Deer antlers are the only known mammalian organ with vascularized cartilage that can completely regenerate. Antlers are of real significance as a model of mammalian stem cell-based regeneration with particular relevance to the fields of chondrogenesis, angiogenesis, and regenerative medicine. Recent research found that thymosin beta 10 (TMSB10) is highly expressed in the growth centers of growing antlers. The present study reports here the expression, functions, and molecular interactions of deer TMSB10.

METHODS

The TMSB10 expression level in both tissue and cells in the antler growth center was measured. The effects of both exogenous (synthetic protein) and endogenous deer TMSB10 (lentivirus-based overexpression) on antlerogenic periosteal cells (APCs; nonactivated antler stem cells with no basal expression of TMSB10) and human umbilical vein endothelial cells (HUVECs; endothelial cells with no basal expression of TMSB10) were evaluated to determine whether TMSB10 functions on chondrogenesis and angiogenesis. Differences in deer and human TMSB10 in angiogenesis and molecular structure were determined using animal models and molecular dynamics simulation, respectively. The molecular mechanisms underlying deer TMSB10 in promoting angiogenesis were also explored.

RESULTS

Deer TMSB10 was identified as a novel proangiogenic factor both in vitro and in vivo. Immunohistochemistry revealed that TMSB10 was widely expressed in the antler growth center in situ, with the highest expression in the reserve mesenchyme, precartilage, and transitional zones. Western blot analysis using deer cell lines further supports this result. Both exogenous and endogenous deer TMSB10 significantly decreased proliferation of APCs (P < 0.05), while increasing the proliferation of HUVECs (P < 0.05). Moreover, deer TMSB10 enhanced chondrogenesis in micromass cultures and nerve growth as assessed using a dorsal root ganglion model (P < 0.05). Deer TMSB10 was proangiogenic using models of chicken chorioallantoic membrane, tube formation, and aortic arch assay. At the molecular level, endogenous deer TMSB10 elevated the expression of vascular endothelial growth factor (VEGF), VEGF-B, VEGF-C, and VEGF-D, and VEGFR2 and VEGFR3 in HUVECs (P < 0.05).

CONCLUSIONS

Deer TMSB10, in contrast to its human counterpart, was identified as a novel stimulating factor for angiogenesis, cartilage formation, and nerve growth, which is understandable given that deer antlers (as the arguably fastest mammalian growing tissue) may require this extra boost during a period of rapid growth and regeneration.

A Novel Secretory Vesicle from Deer Antlerogenic Mesenchymal Stem Cell-Conditioned Media (DaMSC-CM) Promotes Tissue Regeneration

Multipotent stem cells have the capacity to generate terminally differentiated cell types of each lineage; thus, they have great therapeutic potential for a wide variety of diseases. The most widely available stem cells are derived from human tissues, and their use for therapeutic application is limited by their high cost and low productivity. Herein, we report that conditioned media of mesenchymal stem cells (MSCs) isolated from deer antlers enhanced tissue regeneration through paracrine action via a combination of secreted growth factors and cytokines. Notably, DaMSC-conditioned media (DaMSC-CM) enhanced hair regeneration by activating the Wnt signaling pathway. In addition, DaMSC-CM had regenerative potential in damaged skin tissue through induction of skin regeneration-related genes. Remarkably, we identified round vesicles derived from DaMSC-CM, with an average diameter of ~120 nm that were associated with hair follicle formation, suggesting that secretory vesicles may act as paracrine mediators for modulation of local cellular responses. In addition, these secretory vesicles could regulate the expression of Wnt-3a, Wnt-10b, and lymphoid enhancer-binding factor-1 (LEF-1), which are related to tissue renewal. Thus, our findings demonstrate that the use of DaMSC-CM as a unique natural model for rapid and complete tissue regeneration has possible application for therapeutic development.

The blastema and epimorphic regeneration in mammals

Studying regeneration in animals where and when it occurs is inherently interesting and a challenging research topic within developmental biology. Historically, vertebrate regeneration has been investigated in animals that display enhanced regenerative abilities and we have learned much from studying organ regeneration in amphibians and fish. From an applied perspective, while regeneration biologists will undoubtedly continue to study poikilothermic animals (i.e., amphibians and fish), studies focused on homeotherms (i.e., mammals and birds) are also necessary to advance regeneration biology. Emerging mammalian models of epimorphic regeneration are poised to help link regenerative biology and regenerative medicine. The regenerating rodent digit tip, which parallels human fingertip regeneration, and the regeneration of large circular defects through the ear pinna in spiny mice and rabbits, provide tractable, experimental systems where complex tissue structures are regrown through blastema formation and morphogenesis. Using these models as examples, we detail similarities and differences between the mammalian blastema and its classical counterpart to arrive at a broad working definition of a vertebrate regeneration blastema. This comparison leads us to conclude that regenerative failure is not related to the availability of regeneration-competent progenitor cells, but is most likely a function of the cellular response to the microenvironment that forms following traumatic injury. Recent studies demonstrating that targeted modification of this microenvironment can restrict or enhance regenerative capabilities in mammals helps provide a roadmap for eventually pushing the limits of human regeneration.

Antlerogenic stem cells: molecular features and potential in rabbit bone regeneration

AIM

(i) To assess the expression profiles of stem cell-associated markers including Oct4, Sox2, Klf4, Nanog, C-myc, Stat3 and Cd9, (ii) analyze the nanotopography of the MIC-1 stem cells and (iii) evaluate the efficiency of live stem cell implants and stem cell culture derivatives on the regeneration of bone deficiencies in rabbit mandibles.

MATERIALS AND METHODS

The expression profiles of stem cell-associated genes, including Oct4, Sox2, Klf4, Nanog, C-myc, Stat3 and CD9 were assessed using reverse transcription polymerase chain reaction and flow cytometry. Nanotopography of the antlerogenic MIC-1 cell lineage was analyzed using atomic force microscopy. The effect of MIC-1 stem cells, their homogenate and supernatant on the regeneration of bone deficiencies in rabbit mandibles was evaluated using histological analysis. The effect of MIC-1 stem cells and stem cell-based derivatives on the immune responses of the animals was assessed by analyses of acute phase protein levels (haptoglobin and fibrinogen).

RESULTS

We found that the MIC-1 cells isolated from the apical regions of growing antlers exhibited molecular features that were characteristics of pluripotent stem cells. Using atomic force microscopy, we determined the details of the cell surface morphologies with a particular emphasis on the patterns of formation of plasma extensions for interlinking adjacent cells. We also demonstrated that not only implanted stem cells but also cell homogenates and cell post-culture supernatants have potential in the regeneration of bone deficiencies in the rabbit mandible.

CONCLUSIONS

Our findings indicate that the use of both antlerogenic stem cell implants and the preparations derived from the cells offer alternative approaches to those based on autologous stem cells in the biological stimulation of osteogenesis and in bone regeneration.

Cloning and Characterization of a Nanog Pseudogene in Sika Deer (Cervus nippon)

Nanog plays a crucial role in the maintenance of stem cell pluripotency. Annual full regeneration of deer antlers has been shown to be a stem cell-based process, and antler stem cells (ASCs) reportedly express Nanog. In the present study, we found that Nanog RNA expressed by ASCs was a pseudogene (Nanog-ps). The coding sequence of Nanog-ps was 93.1% homologous to that of bovine Nanog, but with two missing nucleotides after position 391. Deletion of the two nucleotides in Nanog-ps resulted in a frame-shift mutation, suggesting that Nanog-ps would not encode a normal Nanog protein. Overexpression of Nanog-ps failed to affect downstream genes of Nanog or to enhance cell proliferation in the ASCs. However, this pseudogene was transcribed in the ASCs and encoded a nuclear protein; the expression levels of Nanog-ps were also related to the degree of stemness in antler cells. Here, we reported this pseudogene, because it could serve as a useful marker for identifying ASCs and evaluating the degree of their stemness.

Target morphology and cell memory: a model of regenerative pattern formation

Despite the growing body of work on molecular components required for regenerative repair, we still lack a deep understanding of the ability of some animal species to regenerate their appropriate complex anatomical structure following damage. A key question is how regenerating systems know when to stop growth and remodeling – what mechanisms implement recognition of correct morphology that signals a stop condition? In this work, we review two conceptual models of pattern regeneration that implement a kind of pattern memory. In the first one, all cells communicate with each other and keep the value of the total signal received from the other cells. If a part of the pattern is amputated, the signal distribution changes. The difference fromthe original signal distribution stimulates cell proliferation and leads to pattern regeneration, in effect implementing an error minimization process that uses signaling memory to achieve pattern correction. In the second model, we consider a more complex pattern organization with different cell types. Each tissue contains a central (coordinator) cell that controls the tissue and communicates with the other central cells. Each of them keeps memory about the signals received from other central cells. The values of these signals depend on the mutual cell location, and the memory allows regeneration of the structure when it is modified. The purpose of these models is to suggest possible mechanisms of pattern regeneration operating on the basis of cell memory which are compatible with diverse molecular implementation mechanisms within specific organisms.

A conceptual model of morphogenesis and regeneration

This paper is devoted to computer modelling of the development and regeneration of multicellular biological structures. Some species (e.g. planaria and salamanders) are able to regenerate parts of their body after amputation damage, but the global rules governing cooperative cell behaviour during morphogenesis are not known. Here, we consider a simplified model organism, which consists of tissues formed around special cells that can be interpreted as stem cells. We assume that stem cells communicate with each other by a set of signals, and that the values of these signals depend on the distance between cells. Thus the signal distribution characterizes location of stem cells. If the signal distribution is changed, then the difference between the initial and the current signal distribution affects the behaviour of stem cells-e.g. as a result of an amputation of a part of tissue the signal distribution changes which stimulates stem cells to migrate to new locations, appropriate for regeneration of the proper pattern. Moreover, as stem cells divide and form tissues around them, they control the form and the size of regenerating tissues. This two-level organization of the model organism, with global regulation of stem cells and local regulation of tissues, allows its reproducible development and regeneration.

Effects of p21 Gene Down-Regulation through RNAi on Antler Stem Cells In Vitro

Cell cycle is an integral part of cell proliferation, and consists mainly of four phases, G1, S, G2 and M. The p21 protein, a cyclin dependent kinase inhibitor, plays a key role in regulating cell cyclevia G1 phase control. Cells capable of epimorphic regeneration have G2/M accumulation as their distinctive feature, whilst the majority of somatic cells rest at G1 phase. To investigate the role played byp21 in antler regeneration, we studied the cell cycle distribution of antler stem cells (ASCs), via down-regulation of p21 in vitro using RNAi. The results showed that ASCs had high levels of p21 mRNA expression and rested at G1 phase, which was comparable to the control somatic cells. Down-regulation of p21 did not result in ASC cell cycle re-distribution toward G2/M accumulation, but DNA damage and apoptosis of the ASCs significantly increased and the process of cell aging was slowed. These findings suggest that the ASCs may have evolved to use an alternative, p21-independent cell cycle regulation mechanism. Also a unique p21-dependent inhibitory effect may control DNA damage as a protective mechanism to ensure the fast proliferating ASCs do not become dysplastic/cancerous. Understanding of the mechanism underlying the role played by p21 in the ASCs could give insight into a mammalian system where epimorphic regeneration is initiated whilst the genome stability is effectively maintained.

Element concentrations and element ratios in antler and pedicle bone of yearling red deer (Cervus elaphus) stags-a quantitative X-ray fluorescence study

The present study compared the concentrations of different elements (Ca, P, Mg, Sr, Ba, K, S, Zn, Mn) as well as Ca/P, Ca/Mg, Sr/Ca, and Ba/Ca ratios in hard antler and pedicle bone of yearling red deer stags (n = 11). Pedicles showed higher concentrations of calcium and phosphorus and a higher Ca/Mg ratio than antlers, while antlers exhibited higher concentrations of potassium, sulfur, and manganese as well as higher Ca/P, Sr/Ca, and Ba/Ca ratios. The findings indicate that antlers are less mineralized and show less maturation of their bone mineral than pedicles. Antlers also showed a higher intrasample variation of mineralization than pedicles, which can be related to the shorter life span of the (deciduous) antlers compared to the (permanent) pedicles. It is suggested that antler bone formation is stopped before the theoretically possible degree of mineralization and mineral maturation is reached, resulting in antler biomechanical properties (high bending strength and work to fracture) that are well suited for their role in intraspecific fighting. It is further suggested that the differences in Sr/Ca and Ba/Ca ratios of antlers and pedicles are related to the dietary shift from milk to vegetation in combination with an increasing intestinal discrimination against Sr and Ba with age, resulting in a less marked difference in these ratios than would be expected based on the dietary shift alone. The findings of our study underscore the suitability of antlers and pedicles as models of bone mineralization and the influence of different animal-related and/or external factors on this process.

Deer antler--a novel model for studying organ regeneration in mammals

Deer antler is the only mammalian organ that can fully grow back once lost from its pedicle - the base from which it grows. Therefore, antlers probably offer the most pertinent model for studying organ regeneration in mammals. This paper reviews our current understanding of the mechanisms underlying regeneration of antlers, and provides insights into the possible use for human regenerative medicine. Based on the definition, antler renewal belongs to a special type of regeneration termed epimorphic. However, histological examination failed to detect dedifferentiation of any cell type on the pedicle stump and the formation of a blastema, which are hallmark features of classic epimorphic regeneration. Instead, antler regeneration is achieved through the recruitment, proliferation and differentiation of the single cell type in the pedicle periosteum (PP). The PP cells are the direct derivatives of cells resident in the antlerogenic periosteum (AP), a tissue that exists in prepubertal deer calves and can induce ectopic antler formation when transplanted elsewhere on the deer body. Both the AP and PP cells express key embryonic stem cell markers and can be induced to differentiate into multiple cell lineages in vitro and, therefore, they are termed antler stem cells, and antler regeneration is a stem cell-based epimorphic regeneration. Comparisons between the healing process on the stumps from an amputated mouse limb and early regeneration of antlers suggest that the stump of a mouse limb cannot regenerate because of the limited potential of periosteal cells in long bones to proliferate. If we can impart a greater potential of these periosteal cells to proliferate, we might at least be able to partially regenerate limbs lost from humans. Taken together, a greater understanding of the mechanisms that regulate the regeneration of antlers may provide a valuable insight to aid the field of regenerative medicine. This article is part of a Directed Issue entitled: Regenerative Medicine: the challenge of translation.