Histological examination of antler regeneration in red deer (Cervus elaphus)

Reciprocal negative feedback between Prrx1 and miR-140-3p regulates rapid chondrogenesis in the regenerating antler

During growth phase, antlers exhibit a very rapid rate of chondrogenesis. The antler is formed from its growth center reserve mesenchyme (RM) cells, which have been found to be the derivatives of paired related homeobox 1 (Prrx1)-positive periosteal cells. However, the underlying mechanism that drives rapid chondrogenesis is not known. Herein, the miRNA expression profiles and chromatin states of three tissue layers (RM, precartilage, and cartilage) at different stages of differentiation within the antler growth center were analyzed by RNA-sequencing and ATAC-sequencing. We found that miR-140-3p was the miRNA that exhibited the greatest degree of upregulation in the rapidly growing antler, increasing from the RM to the cartilage layer. We also showed that Prrx1 was a key upstream regulator of miR-140-3p, which firmly confirmed by Prrx1 CUT&Tag sequencing of RM cells. Through multiple approaches (three-dimensional chondrogenic culture and xenogeneic antler model), we demonstrated that Prrx1 and miR-140-3p functioned as reciprocal negative feedback in the antler growth center, and downregulating PRRX1/upregulating miR-140-3p promoted rapid chondrogenesis of RM cells and xenogeneic antler. Thus, we conclude that the reciprocal negative feedback between Prrx1 and miR-140-3p is essential for balancing mesenchymal proliferation and chondrogenic differentiation in the regenerating antler. We further propose that the mechanism underlying chondrogenesis in the regenerating antler would provide a reference for helping understand the regulation of human cartilage regeneration and repair.

Deer antlers: the fastest growing tissue with least cancer occurrence

Deer antlers are a bony organ solely able to acquired distinct unique attributes during evolution and all these attributes are against thus far known natural rules. One of them is as the fastest animal growing tissue (2 cm/day), they are remarkably cancer-free, despite high cell division rate. Although tumor-like nodules on the long-lived castrate antlers in some deer species do occur, but they are truly benign in nature. In this review, we tried to find the answer to this seemingly contradictory phenomenon based on the currently available information and give insights into possible clinic application. The antler growth center is located in its tip; the most intensive dividing cells are resident in the inner layer of reserve mesenchyme (RM), and these cells are more adopted to osteosarcoma rather than to normal bone tissues in gene expression profiles but acquire their energy mainly through aerobic oxidative phosphorylation pathway. To counteract propensity of neoplastic transformation, antlers evolved highly efficient apoptosis exactly in the RM, unparalleled by any known tissues; and annual wholesale cast to jettison the corps. Besides, some strong cancer suppressive genes including p53 cofactor genes and p53 regulator genes are highly positively selected by deer, which would have certainly contributed to curb tumorigenesis. Thus far, antler extracts and RM cells/exosomes have been tried on different cancer models either in vitro or in vivo, and all achieved positive results. These positive experimental results together with the anecdotal folklore that regular consumption of velvet antler is living with cancer-free would encourage us to test antlers in clinic settings.

A simple method for effective cryopreservation of antlerogenic periosteum of sika deer

Antlerogenic periosteum (AP) is the unique tissue type that gives rise to antlers and their antecedents, the pedicles. Deer antlers are the only mammalian organ that can fully regenerate. Efficient investigation of the mechanism of antler formation and regeneration requires year-round availability of AP, but naturally AP can only be obtained less than two months in a year. In the present study we took the cryopreservation approach to store the sampled AP in ultra-low temperature to overcome the limited period of availability. First, we evaluated the suitability of vitrification and cell cryopreservation method for cryopreservation of AP, cell migration status of the AP tissue pieces confirmed that vitrification methods did not work as the only few AP cells migrated out, whereas migrated cell numbers in the cell-cryo group (conventional method for cryopreservation of cells) were comparable to those of the fresh AP group. To further evaluate the suitability of cell cryopreservation method for AP tissue, AP samples were allocated into three groups based on the different ratios of cryopreservation reagents (dimethyl sulfoxide [DMSO], dulbecco's modified eagle's medium [DMEM] and fetal bovine serum [FBS]): AP-Cell-1 (1:4:5), AP-Cell-2 (1:2:7) and AP-Cell-3 (1:0:9), the results showed that migrated cell number were again comparable to the fresh AP group. There was no significant difference between the cell-cryo groups (AP-Cell-1 and AP-Cell-3) and the fresh group: (1) in viability (p > 0.05) through trypan blue staining (91.2%, 90.8%, and 92.4%, respectively); (2) in the attachment day, and all on Day 5 after cell seeding; (3) in cell proliferation rate (p > 0.05) through Cell Counting kit 8 (CCK8) measurement; and (4) in number of the formed clones (Clonogenicity). In the in vivo trials, there was no visible difference in temporal differentiation sequence of the formed xenogeneic antlers between the fresh AP and cryopreserved AP (AP-Cell-1 and AP-Cell-3). Overall, we found that the AP tissue was well cryopreserved just using the conventional freezing and thawing methods for cells, and their viability and developmental potential comparable to the fresh AP both in vitro and in vivo. The long-term preservation of the AP tissue is of great significance for the study of the periosteum biology in general and the mechanism underlying xenogeneic generation and regeneration of deer antlers in specific.

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.

The characteristics and medical applications of antler stem cells

Antlers are the only fully regenerable mammalian appendages whose annual renewal is initiated by antler stem cells (ASCs), defined as a specialized type of mesenchymal stem cells (MSCs) with embryonic stem cell properties. ASCs possess the same biological features as MSCs, including the capacity for self-renewal and multidirectional differentiation, immunomodulatory functions, and the maintenance of stem cell characteristics after multiple passages. Several preclinical studies have shown that ASCs exhibit promising potential in wound healing, bone repair, osteoarthritis, anti-tissue fibrosis, anti-aging, and hair regeneration. Medical applications based on ASCs and ASC-derived molecules provide a new source of stem cells and therapeutic modalities for regenerative medicine. This review begins with a brief description of antler regeneration and the role of ASCs. Then, the properties and advantages of ASCs are described. Finally, medical research advances regarding ASCs are summarized, and the prospects and challenges of ASCs are highlighted.

Deer antler renewal gives insights into mammalian epimorphic regeneration

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

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.

Single-cell transcriptome reveals core cell populations and androgen-RXFP2 axis involved in deer antler full regeneration

Deer antlers constitute a unique mammalian model for the study of both organ formation in postnatal life and annual full regeneration. Previous studies revealed that these events are achieved through the proliferation and differentiation of antlerogenic periosteum (AP) cells and pedicle periosteum (PP) cells, respectively. As the cells resident in the AP and the PP possess stem cell attributes, both antler generation and regeneration are stem cell-based processes. However, the cell composition of each tissue type and molecular events underlying antler development remain poorly characterized. Here, we took the approach of single-cell RNA sequencing (scRNA-Seq) and identified eight cell types (mainly THY1⁺ cells, progenitor cells, and osteochondroblasts) and three core subclusters of the THY1⁺ cells (SC2, SC3, and SC4). Endothelial and mural cells each are heterogeneous at transcriptional level. It was the proliferation of progenitor, mural, and endothelial cells in the activated antler-lineage-specific tissues that drove the rapid formation of the antler. We detected the differences in the initial differentiation process between antler generation and regeneration using pseudotime trajectory analysis. These may be due to the difference in the degree of stemness of the AP-THY1⁺ and PP-THY1⁺ cells. We further found that androgen-RXFP2 axis may be involved in triggering initial antler full regeneration. Fully deciphering the cell composition for these antler tissue types will open up new avenues for elucidating the mechanism underlying antler full renewal in specific and regenerative medicine in general.

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.

Identification and Characterization of Alternative Splicing Variants and Positive Selection Genes Related to Distinct Growth Rates of Antlers Using Comparative Transcriptome Sequencing

Simple Summary

The size of antlers varies among species; antlers of the wapiti (Cervus canadensis xanthopygus) grow much faster than those of its close relative the sika deer (Cervus nippon hortulorum) in the same growing period. This contrast provides a potential model for comparative studies for the identification of potent growth factors and unique regulatory systems. In the present study, the reference transcriptomes of the antler reserve mesenchyme (RM) tissue of wapiti and sika deer were constructed using single molecule real time sequencing data. The expression profiling, positive selection, and alternative splicing of the antler transcripts were compared, and interactive relationships and expression patterns of hub genes were identified and analysed. We identified that RNA Binding Motif Protein X-Linked (RBMX) gene was under strongly positive selection. One gene found to interact with RBMX was methyltransferase-like 3 (METTL3), an oncogene that could promote translation of cancer cell proteins. There was a contrasting relationship in expression level between RBMX and METTL3 genes in the RM tissue. We believe our study can provide a better understanding of rapid antler growth at the molecular level in particular and endochondral ossification in general.

Abstract

The molecular mechanism underlying rapid antler growth has not been elucidated. The contrast of the wapiti and sika deer antler provides a potential model for comparative studies for the identification of potent growth factors and unique regulatory systems. In the present study, reference transcriptomes of antler RM tissue of wapiti and sika deer were constructed using single molecule real time sequencing data. The expression profiling, positive selection, and alternative splicing of the antler transcripts were compared. The results showed that: a total of 44,485 reference full-length transcripts of antlers were obtained; 254 highly expressed transcripts (HETs) and 1936 differentially expressed genes (DEGs) were enriched and correlated principally with translation, endochondral ossification and ribosome; 228 genes were found to be under strong positive selection and would thus be important for the evolution of wapiti and sika deer; among the alternative splicing variants, 381 genes were annotated; and 4 genes with node degree values greater than 50 were identified through interaction network analysis. We identified a negative and a positive regulator for rapid antler growth, namely RNA Binding Motif Protein X-Linked (RBMX) and methyltransferase-like 3 (METTL3), respectively. Overall, we took advantage of this significant difference in growth rate and performed the comparative analyses of the antlers to identify key specific factors that might be candidates for the positive or negative regulation of phenomenal antler growth rate.

Progress of Noncoding RNA Regulating the Growth and Development of Antler Tissue Research

Antler is the secondary sexual characteristic of deer, which develops on the forehead at puberty. It is the only organ that can be regenerated entirely in mammals. Therefore, it is often used as a research model in the field of organ regeneration and wound repair. Many growth factors and proteins play an active role throughout the developmental process of antler regeneration. With the rapid development of sequencing technology, more and more noncoding RNAs (ncRNAs) have been discovered, and the relationship between ncRNA and antler regeneration has gradually become clear. This paper focuses on the research progress of several ncRNAs (including miRNA and lncRNA) in deer antler tissues, which are helpful to reveal the molecular mechanism of deer antler regeneration at the molecular level.

Calreticulin Identified as One of the Androgen Response Genes That Trigger Full Regeneration of the Only Capable Mammalian Organ, the Deer Antler

Deer antlers are male secondary sexual characters that develop to become bone; they are unique appendages that, once lost, can fully regenerate from the permanent bony protuberances or pedicles. Pedicle periosteum (PP) is the tissue that gives rise to the regenerating antlers with three differentiation stages, namely, dormant (DoPP), potentiated (PoPP), and activated (AcPP). Thus far, the transition from the PoPP to the AcPP has not been studied. Our results showed that the AcPP cells maintained their original stem cell features by expressing mesenchymal stem cell (MSC) markers CD73, CD90, and CD105, although they had entered the proliferation mode. The differentially expressed genes (DEGs) in the AcPP compared with those of the PoPP were mainly involved in protein processing, cell cycle, and calcium signaling pathways. Calreticulin (CALR), an androgen response gene, was significantly differentially upregulated in the AcPP cells, and its expression level was negatively regulated by androgens, in contrast to the currently known model systems where all regulation is positive. The downregulation of CALR expression in the AcPP cells in vitro inhibited cell proliferation, induced apoptosis, and inhibited cell cycle progression at G1-S transition. Therefore, CALR is likely a downstream mediator of androgen hormones for triggering initiation of antler regeneration. We believe that the identification of CALR has not only discovered “one critical piece” of the “jigsaw puzzle” in the initiation of antler regeneration but also helps in revealing the mechanism underlying this unique mammalian epimorphic regeneration and has also opened a new avenue for the study of the nature of CALR regulation by androgen (putative binding partners), thus facilitating the identification of potential molecule(s) for investigation as targets for clinical evaluation.

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.

Antler stem cells and their potential in wound healing and bone regeneration

Compared to other vertebrates, the regenerative capacity of appendages in mammals is very limited. Deer antlers are an exception and can fully regenerate annually in postnatal mammals. This process is initiated by the antler stem cells (AnSCs). AnSCs can be divided into three types: (1) Antlerogenic periosteum cells (for initial pedicle and first antler formation); (2) Pedicle periosteum cells (for annual antler regeneration); and (3) Reserve mesenchyme cells (RMCs) (for rapid antler growth). Previous studies have demonstrated that AnSCs express both classic mesenchymal stem cells (MSCs) and embryonic stem cells (ESCs), and are able to differentiate into multiple cell types in vitro. Thus, AnSCs were defined as MSCs, but with partial ESC attributes. Near-perfect generative wound healing can naturally occur in deer, and wound healing can be achieved by the direct injection of AnSCs or topical application of conditioned medium of AnSCs in rats. In addition, in rabbits, the use of both implants with AnSCs and cell-free preparations derived from AnSCs can stimulate osteogenesis and repair defects of bone. A more comprehensive understanding of AnSCs will lay the foundation for developing an effective clinical therapy for wound healing and bone repair.

Substances for regenerative wound healing during antler renewal stimulated scar-less restoration of rat cutaneous wounds

Scarification is the outcome of cutaneous wound healing under normal conditions. Although considerable effort has been expended in this field, scar-less healing has not been achieved satisfactorily. The lack of a good model of scar-free healing has contributed to this undesirable situation. However, the annual regeneration of deer antlers, which starts from regenerative wound healing over the top of the pedicles (permanent bony protuberances), may provide such a model. Therefore, in this study, we investigated the process of pedicle wound healing at the organ, tissue, cell, and molecular levels. Our results convincingly demonstrate that wounds over the pedicle preceded a regenerative healing process including regeneration of skin appendages, such as hair follicles. Compared to the scar healing in rats, regenerative healing of the pedicle wound exhibited a weaker inflammatory response, lack of myofibroblast induction, and higher ratios of Col III/Col I, TGF-β3/TGF-β1, and MMP/TIMP. Importantly, our periosteal transplantation experiments in vivo revealed that this regenerative healing process was achieved through induction of antler stem cells (ASCs). Further study showed that this effect of ASCs on regenerative healing was not species-specific but more generic and could be applied to other mammalian species, as injection of ASCs stimulated regenerative healing of full-thickness excisional cutaneous wounds in rats. Overall, our findings show that ASCs may have therapeutic potential in enhancing the quality of wound healing and preventing scar formation in clinical settings.

SWATH-MS Quantitative Proteomic Analysis of Deer Antler from Two Regenerating and Mineralizing Sections

Simple Summary

Deer antler is a unique and astonishing case of annual regeneration in mammalians. Several studies have pointed out the potential for use of velvet antler extract as a nutraceutical supplement, among others, because of its anti-cancer activity. The study of antler regeneration and growth allow us to identify the main proteins and regulatory pathways involved in cell differentiation and regeneration. For this purpose, two sections of antlers (tips and middle sections) using ribs as controls were analyzed from a proteomic point of view. A total of 259 proteins mainly associated with antioxidant mechanisms and Wnt signalling pathways could be responsible for deer antler regeneration and these proteins may be linked to human health benefits. Further studies should be focused on discovering which proteins from velvet antler extracts are associated with these beneficial effects.

Abstract

Antlers are the only organ in the mammalian body that regenerates each year. They can reach growth rates of 1–3 cm/day in length and create more than 20 cm²/day of skin in the antler tips (their growth centers). Previous proteomic studies regarding antlers have focused on antler growth centers (tips) compared to the standard bone to detect the proteins involved in tissue growth. However, proteins of cell differentiation and regeneration will be more accurately detected considering more growing tissues. Thus, we set out to compare proteins expressed in antler tips (the highest metabolism rate and cell differentiation) vs. middle sections (moderate cell growth involving bone calcification), using ribs as controls. Samples were obtained in mid-June with antlers’ phenology corresponding to the middle of their growth period. Quantitative proteomic analysis identified 259 differentially abundant proteins mainly associated with antioxidant metabolic mechanisms, protein formation and Wnt signalling pathway, meanwhile, the mid antler section was linked to blood proteins. The high metabolic rate and subsequent risk of oxidative stress also seem to have resulted in strong antioxidant mechanisms. These results suggest that redox regulation of proteins is a key factor in the model of deer antler regeneration.

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.

The consequences of living longer-Effects of an experimentally extended velvet antler phase on the histomorphology of antler bone in fallow deer (Dama dama)

Antlers are periodically regenerated paired cranial appendages of male deer (both sexes in reindeer) that constitute the fastest‐growing bones in the animal kingdom. The annual antler cycle of male deer is linked to testicular activity and largely controlled by seasonal fluctuations of testosterone concentrations in their blood. We studied the effects of an experimental doubling (to eight months) of the velvet antler phase, during which the antlers are covered by skin (velvet), on the histomorphology of antler bone in three adult fallow bucks. Extension of the velvet antler phase in the experimental animals had been caused by administration of the antiandrogen cyproterone acetate (CPA). The distal portions of the antlers from two of the CPA‐treated bucks exhibited partial sequestration of the antler cortex, with the separation plane typically located along the border between cortex and spongiosa. It is hypothesized that this was caused by cortical necrosis due to severe ischemia during later stages of the extended velvet antler phase. In places, new cancellous bone had been deposited on the resorption surface of the spongiosa, indicating a regeneration process. Normal fallow deer antlers (“controls”) from this and a previous study, that is, antlers with a timespan of about four months between onset of new antler growth and velvet shedding, exhibited no or only minor bone remodeling and still contained remnants of calcified cartilage in their distal portions. In contrast, the antlers of the three CPA‐treated bucks showed evidence (secondary osteons and resorption cavities) of marked bone remodeling along their entire length and lacked remnants of calcified cartilage. Our results underscore that the typical histological features of antler bone reflect its short‐lived nature. Antlers are not mechanically loaded during the velvet stage, and it is presently unclear what triggered remodeling activity in the antlers whose lifespan had been experimentally extended.

Comparative antler proteome of sika deer from different developmental stages

Antler is a special bone tissue that has the ability to regenerate completely periodically. It is the fastest growing bone in the animal kingdom. Antler provides a valuable research model for bone growth and mineralization. Antler grows longitudinally by endochondral ossification with their growth center located in its tip. Many scholars have carried out detailed studies on morphology and gene expression of antler tip. However, few scholars have analyzed the protein expression patterns of antler tip at different development stages. This study used label-free proteomics approach to analyze the protein expression dynamics of the antler tip in six developmental periods (15, 25, 45, 65, 100 and 130 days after the previous antler cast) and costal cartilage. In result, 2052 proteins were confidently quantified, including 1937 antler proteins and 1044 costal cartilage proteins. Moreover, 913 antler core proteins and 132 antler-special proteins were obtained. Besides, the stages special proteins and differentially expressed proteins (DEPs) in different development stages were analyzed. A total of 875 DEPs were determined by one-way AVOVA. It is found that the growth period (15, 25, 45 and 65 days) showed more up-regulated protein including several chondrogenesis-associated proteins (collagen types II, collagen types XI, HAPLN1, PAPSS1 and PAPSS2). In ossification stages, the up-regulated proteins related with lysosome (CTSD, CTSB, MMP9, CAII) indicated that the antler has higher bone remodeling activity. Given the up-regulated expression of immune-related molecules (S100A7, CATHL7, LTF, AZU1, ELANE and MPO), we speculate that the local immune system may contribute to the ossification of antler tip. In conclusion, proteomics technology was used to deeply analyze the protein expression patterns of antler at different development stages. This provides a strong support for the research on the molecular regulation mechanism of rapid growth and ossification of velvet antler.

Residual antler periosteum holds the potential to partially regenerate lost antler tissue

Deer antlers are the only mammalian organs that can fully regenerate, which relies on pedicle periosteum (PP). Interestingly during the growing phase, antlers themselves can regenerate partially lost antler tissue. However, what tissue type in the growing antlers fulfills this role is not known. Following antler removal during the growing phase, a "second" antler regenerates from the stump. In this study, the "second" antler growing from the cut antler base (AB) was examined in both red and sika deer. The results showed that all regenerating antlers were formed from the peripheral edge of the AB, where the antler periosteum (AnP) is located. The growth center showed a clear demarcation from the AB bone in red deer. Therefore, it is highly likely that AnP is the tissue that possesses the potential. Factors that might affect this potential were explored and the main factor was found to be AB calcification, which was controlled by rising androgens. Thus, the ultimate antler regeneration potential of the AnP was assessed through castration and repeated antler removal. The results demonstrated that the regeneration potential of AnP was somewhat limited and inferior to that of the PP. The ability of AnP to achieve partial regeneration may be evolutionarily conserved, as the regeneration of partially lost antlers within the season is secured; whereas, with PP, a new set of antlers in the next season is guaranteed. This two-level mechanism may signify how evolutionarily important it is for deer to possess reasonably intact antlers.

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.

Anti-tumour activity of deer growing antlers and its potential applications in the treatment of malignant gliomas

A recent study showed that antlers have evolved a high rate of growth due to the expression of proto-oncogenes and that they have also evolved to express several tumour suppressor genes to control the risk of cancer. This may explain why deer antler velvet (DAV) extract shows anti-tumour activity. The fast growth of antler innervation through the velvet in close association to blood vessels provides a unique environment to study the fast but non-cancerous proliferation of heterogeneous cell populations. We set out to study the anti-cancer effect of DAV in glioblastoma (GB) cell lines in comparison with temozolomide, a chemotherapeutic drug used to treat high-grade brain tumours. Here we report, for the first time, that DAV extract from the tip, but not from mid-parts of the antler, exhibits an anti-tumour effect in GB cell lines (T98G and A172) while being non-toxic in non-cancerous cell lines (HEK293 and HACAT). In T98G cells, DAV treatment showed reduced proliferation (37.5%) and colony-formation capacity (84%), inhibited migration (39%), induced changes in cell cycle progression, and promoted apoptosis. The anticancer activity of DAV extract as demonstrated by these results may provide a new therapeutic strategy for GB treatment.

Antiquity and fundamental processes of the antler cycle in Cervidae (Mammalia)

The origins of the regenerative nature of antlers, being branched and deciduous apophyseal appendages of frontal bones of cervid artiodactyls, have long been associated with permanent evolutionary precursors. In this study, we provide novel insight into growth modes of evolutionary early antlers. We analysed a total of 34 early antlers affiliated to ten species, including the oldest known, dating from the early and middle Miocene (approx. 18 to 12 million years old) of Europe. Our findings provide empirical data from the fossil record to demonstrate that growth patterns and a regular cycle of necrosis, abscission and regeneration are consistent with data from modern antlers. The diverse histological analyses indicate that primary processes and mechanisms of the modern antler cycle were not gradually acquired during evolution, but were fundamental from the earliest record of antler evolution and, hence, explanations why deer shed antlers have to be rooted in basic histogenetic mechanisms. The previous interpretation that proximal circular protuberances, burrs, are the categorical traits for ephemerality is refuted.

Comparative Metabolomics Study Revealed Difference in Central Carbon Metabolism between Sika Deer and Red Deer Antler

The antler regeneration has been well studied for the past two decades and adopted in the regenerative medicine model for studying on developmental biology. Despite our growing knowledge of functional molecules regulating antler regeneration, we still do not know whether antler from different deer species possess the exact same mechanism or not. Our previous comparative study between sika deer and red deer suggests that the metabolic pathways between them are profoundly different based on protein level. Therefore, the metabolomic technology is used to identify and quantify the metabolites in antler samples, providing interesting insights into differential metabolite profile of antlers between sika deer and red deer. The distinct metabolic characteristics of sika deer compared to red deer provide an opportunity to explain why the red deer antler with a larger size. The enrichment analysis of differential metabolites showed that three pathways including glycine and serine metabolism, methionine metabolism, and pterine biosynthesis had a significant difference between two antler groups.

Comparative transcriptome analysis of the main beam and brow tine of sika deer antler provides insights into the molecular control of rapid antler growth

Background

Deer antlers have become a valuable model for biomedical research due to the capacities of regeneration and rapid growth. However, the molecular mechanism of rapid antler growth remains to be elucidated. The aim of the present study was to compare and explore the molecular control exerted by the main beam and brow tine during rapid antler growth.

Methods

The main beams and brow tines of sika deer antlers were collected from Chinese sika deer (Cervus nippon) at the rapid growth stage. Comparative transcriptome analysis was conducted using RNA-Seq technology. Differential expression was assessed using the DEGseq package. Functional Gene Ontology (GO) enrichment analysis was accomplished using a rigorous algorithm according to the GO Term Finder tool, and KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway enrichment analysis was accomplished with the R function phyper, followed by the hypergeometric test and Bonferroni correction. Quantitative real-time polymerase chain reaction (qRT-PCR) was carried out to verify the RNA levels for differentially expressed mRNAs.

Results

The expression levels of 16 differentially expressed genes (DEGs) involved in chondrogenesis and cartilage development were identified as significantly upregulated in the main beams, including transcription factor SOX-9 (Sox9), collagen alpha-1(II) chain (Col2a1), aggrecan core protein (Acan), etc. However, the expression levels of 17 DEGs involved in endochondral ossification and bone formation were identified as significantly upregulated in the brow tines, including collagen alpha-1(X) chain (Col10a1), osteopontin (Spp1) and bone sialoprotein 2 (Ibsp), etc.

Conclusion

These results suggest that the antler main beam has stronger growth capacity involved in chondrogenesis and cartilage development compared to the brow tine during rapid antler growth, which is mainly achieved through regulation of Sox9 and its target genes, whereas the antler brow tine has stronger capacities of endochondral bone formation and resorption compared to the main beam during rapid antler growth, which is mainly achieved through the genes involved in regulating osteoblast and osteoclast activities. Thus, the current research has deeply expanded our understanding of the intrinsic molecular regulation displayed by the main beam and brow tine during rapid antler growth.

Analysis of genetic information from the antlers of Rangifer tarandus (reindeer) at the rapid growth stage

Reindeer is the only deer species in which both males and females regularly grow antlers, providing an excellent model for studying the rapid growth and annual regeneration of antlers. The study of genetic information from reindeer is the basis for revealing the unique mechanism of antler growth. In the present study, we obtained 18.86 GB of clean reads, which were assembled to obtain 94,575 unigenes (average length: 704.69). Among these reads, 30,980 sequences were identified by searching a database of known proteins and then annotated with Gene Ontology (GO) terms, Clusters of Orthologous Groups (COG) classifications and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. All 7,480 simple sequence repeats (SSRs) were detected. A total of 84,435 and 82,226 high-quality single-nucleotide polymorphisms (SNPs) were identified in male and female reindeer, respectively. We identified 31 genes that were highly expressed in reindeer antlers. These genes regulate cell activities that are closely associated with the process of rapid tissue growth. Our results provide a basis for studying reindeer antlers and for further studying the molecular genetics, population genetics, and functional genomics of reindeer.

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.

Antler stem cell-conditioned medium stimulates regenerative wound healing in rats

Background

When the deer antler is cast, it leaves a cutaneous wound that can achieve scarless healing due to the presence of antler stem cells (ASCs). This provides an opportunity to study regenerative wound healing.

Methods

In this study, we investigated the therapeutic effects and mechanism of antler stem cell-conditioned medium (ASC-CM) on cutaneous wound healing in rats. In vitro, we investigated the effects of the ASC-CM on proliferation of HUVEC and NIH-3T3 cell lines. In vivo, we evaluated the effects of ASC-CM on cutaneous wound healing using full-thickness skin punch-cut wounds in rats.

Results

The results showed that ASC-CM significantly stimulated proliferation of the HUVEC and NIH-3T3 cells in vitro. In vivo, completion of healing of the rat wounds treated with ASC-CM was on day 16 (± 3 days), 9 days (± 2 days) earlier than the control group (DMEM); the area of the wounds treated with ASC-CM was significantly smaller (p < 0.05) than the two control groups. Further molecular characterization showed that the ratios of Col3A1/Col1A2, TGF-β3/TGF-β1, MMP1/TIMP1, and MMP3/TIMP1 significantly increased (p < 0.01) in the healed tissue in the ASC-CM group.

Conclusions

In conclusion, ASC-CM effectively accelerated the wound closure rate and enhanced the quality of healing, which might be through transforming wound dermal fibroblasts into the fetal counterparts. Therefore, the ASC-CM may have potential to be developed as a novel cell-free therapeutic for scarless wound healing.

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.

Comparative proteomics analysis reveals the difference during antler regeneration stage between red deer and sika deer

Deer antler, as the only mammalian regenerative appendage, provides an optimal model to study regenerative medicine. Antler harvested from red deer or sika deer were mainly study objects used to disclose the mechanism underlying antler regeneration over past decades. A previous study used proteomic technology to reveal the signaling pathways of antler stem cell derived from red deer. Moreover, transcriptome of antler tip from sika deer provide us with the essential genes, which regulated antler development and regeneration. However, antler comparison between red deer and sika deer has not been well studied. In our current study, proteomics were employed to analyze the biological difference of antler regeneration between sika deer and red deer. The proteomics profile was completed by searching the UniProt database, and differentially expressed proteins were identified by bioinformatic software. Thirty-six proteins were highly expressed in red deer antler, while 144 proteins were abundant in sika deer. GO and KEGG analysis revealed that differentially expressed proteins participated in the regulation of several pathways including oxidative phosphorylation, ribosome, extracellular matrix interaction, and PI3K-Akt pathway.

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.

Deer antler stem cells are a novel type of cells that sustain full regeneration of a mammalian organ-deer antler

Deer antlers are extraordinary mammalian organs that can fully regenerate annually. Antler renewal is a stem cell-based epimorphic process and antler stem (AS) cells can initiate de novo generation of antlers in postnatal mammals. However, although being called stem cells, the AS cells have not been characterized at molecular level based on the stem cell criteria. Comprehensive characterization of the AS cells would undoubtedly help to decipher the mechanism underlying the full regeneration of deer antlers, the only case of stem cell-based epimorphic regeneration in mammals. In the present study, three types of AS cells (antlerogenic periosteal cells APCs, for initial pedicle and first antler formation; pedicle periosteal cells PPC, for annual antler regeneration; and reserve mesenchyme cells RMCs, for rapid antler growth), were isolated for comprehensive molecular characterization. A horn-growth-related gene, RXFP2, was found to be expressed only in AS cells lineages but not in the facial periosteal cells (FPCs, locates geographically in the vicinity of the APCs or PPCs), suggesting the RXFP2 might be a specific marker for the AS cell lineage in deer. Our results demonstrated that AS cells expressed classic MSC markers including surface markers CD73, CD90, CD105 and Stro-1. They also expressed some of the markers including Tert, Nestin, S100A4, nucleostemin and C-Myc, suggesting that they have some attributes of the ESCs. Microinjection of male APC into deer blastocysts resulted in one female foetus (110 days gestation) recovered with obvious pedicle primordia with both male and female genotype detected in the ovary. In conclusion, the AS cells should be defined as MSCs but with partial attributes of ESCs.

Transcriptomic analysis of different tissue layers in antler growth Center in Sika Deer (Cervus nippon)

BACKGROUND

With the unprecedented rapid growth rate (up to 2.75 cm/day), velvet antler is an invaluable model for the identification of potent growth factors and signaling networks for extremely fast growing tissues, mainly cartilage. Antler growth center (AGC) locates in its tip and consists of five tissue layers: reserve mesenchyme (RM), precartilage (PC), transition zone (TZ), cartilage (CA) and mineralized cartilage (MC). The aim of this study was to investigate the transcription dynamics in the AGC using RNA-seq technology.

RESULTS

Five tissue layers in the AGC were collected from three 3-year-old male sika deer using our previously reported sampling method (morphologically distinguishable). After sequencing (15 samples; triplicates/tissue layer), we assembled a reference transcriptome de novo and used RNA-seq to measure gene expression profiles across these five layers. Nine differentially expressed genes (DEGs) were selected from our data and subsequently verified using qRT-PCR. The results showed a high consistency with the RNA-seq results (R² = 0.80). Nine modules were constructed based on co-expression network analysis, and these modules contained 370 hub genes. These genes were found to be mainly involved in mesenchymal progenitor cell proliferation, chondrogenesis, osteogenesis and angiogenesis. Combination of our own results with the previously published reports, we found that Wnt signaling likely plays a key role not only in stimulating the antler stem cells or their immediate progeny, but also in promoting chondrogenesis and osteogenesis during antler development.

CONCLUSION

We have successfully assembled a reference transcriptome, generated gene expression profiling across the five tissue layers in the AGC, and identified nine co-expressed modules that contain 370 hub genes and genes predorminantly expressed in and highly relevant to each tissue layer. We believe our findings have laid the foundation for the identification of novel genes for rapid proliferation and chondrogenic differentiation of antler cells.

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.

Biomechanical characteristics of immediately loaded and osseointegration dental implants inserted into Sika deer antler

This study aimed to compare biomechanical characteristics of immediately loaded (IL) and osseointegrated (OS) dental implants inserted into Sika deer antler and lay a foundation for developing an alternative animal model for dental implants studies. Two implants per antler were inserted. One implant was loaded immediately via a self-developed loading device; the other was submerged and unloaded as control. IL implants were harvested after different loading periods. The unloaded implants were collected after OS and the shedding of antler. Specimens were scanned by µCT scanner and finite element models were generated. A vertical force of 10 N was applied on the implant. The mean values of maximum displacements, stresses and strains were compared. The results showed that the density of antler tissue around the implants dramatically increased as the loading time increased. After shedding the antler, 3 pairs of antlers were collected and the density of antler tissue remained in a similar value in all specimens. The maximum values of displacement and stresses in implant and stresses and strains in antler tissue were significantly different among OS models. In one antler, all the biomechanical parameters of IL model were significantly higher than those of OS model of the same animal (P < 0.05) and wider distributions were obtained from IL model. It can be concluded that implants inserted into Sika deer antler might not disturb the growth and calcification process of antler and the use of Sika deer antler model is a promising alternative for implant studies that does not require animal sacrifice.

Expression and Functional Analysis of Tumor-Related Factor S100A4 in Antler Stem Cells

Annual antler renewal is a stem cell-based epimorphic process driven by antler stem cells (ASCs) resident in antlerogenic periosteum (AP). Antlerogenic periosteal cells express a high level of S100A4, a metastasis-associated protein, which intrigued us to explore what role S100A4 could play in antler regeneration. The present study set out to investigate expression and effects of S100A4 in the ASCs and their progeny. The results showed that not only did cells from the AP express a high level of S100A4, but also the pedicle periosteum and the antler growth center. In the antler growth center, we found S100A4-positive cells were specifically located in blood vessel walls and in vascularized areas. In vitro, recombinant deer S100A4 protein stimulated the proliferation of the AP cells, promoted proliferation, migration and tube formation of human vascular endothelial cells, and enhanced migration of Hela cells, but not AP cells. These findings demonstrated that S100A4 in the ASCs may play a significant role in stimulating angiogenesis, proliferation, but not motility, of ASCs. Deer antlers offer a unique model to explore how rapid cell proliferation with a high level of S100A4 expression is elegantly regulated without becoming cancerous.

Distribution of BDNF and TrkB isoforms in growing antler tissues of red deer

Antlers are the cranial appendages of deer that regenerate each year. This renewal provides a model to explore molecules involved in mammalian organ regeneration. The cellular distributions of the brain-derived neurotrophic factor (BDNF) and the isoforms of its cognate receptor Trk tyrosine kinase receptor (TrkB) were localized by immunohistochemistry in sections of growing red deer antler. BDNF and TrkB full length were widely expressed in the integument, perichondrium, periosteum and bone. The truncated isoform receptor was particularly evidenced in integument and vascular inner dermis, but very light reaction was observed in cartilage and bone, both at the site of endochondral and intramembranous ossification. These observations were also assessed at transcriptional level by RT-PCR analyses. The highest expression of all genes significantly occurred in chondroprogenitor cells; however the full-length TrkB receptor was down regulated in osteocartilaginous compartments, in which the truncated isoform was up regulated. The truncated isoform is a dominant-negative receptor that inhibits the full length receptor signalling, even if the truncated isoform not only has this function. This study establishes the presence of BDNF and its receptor in the different cellular compartments of growing antler. Their transcripts assessed by RT-PCR indicate a local synthesis of these molecules that may contribute to the modulation of antler growth, acting as autocrine and/or paracrine factors independently of nerve supply. Among the plethora of other molecular signals and growth factors affecting the antler growth, the local production of BDNF and its cognate receptor could be of interest in understanding their role in antler renewal and to delineate the different involvement of the receptor isoforms.

Regeneration and Regrowth Potentials of Digit Tips in Amphibians and Mammals

Tissue regeneration and repair have received much attention in the medical field over the years. The study of amphibians, such as newts and salamanders, has uncovered many of the processes that occur in these animals during full-limb/digit regeneration, a process that is highly limited in mammals. Understanding these processes in amphibians could shed light on how to develop and improve this process in mammals. Amputation injuries in mammals usually result in the formation of scar tissue with limited regrowth of the limb/digit; however, it has been observed that the very tips of digits (fingers and toes) can partially regrow in humans and mice under certain conditions. This review will summarize and compare the processes involved in salamander limb regeneration, mammalian wound healing, and digit regeneration in mice and humans.

iTRAQ-Based Quantitative Proteomic Analysis of the Potentiated and Dormant Antler Stem Cells

As the only known organ that can completely regenerate in mammals, deer antler is of real significance in the field of regenerative medicine. Recent studies have shown that the regenerative capacity of the antlers comes from the pedicle periosteum and the cells resident in the periosteum possess the attributes of stem cells. Currently, the molecular mechanism of antler regeneration remains unclear. In the present study, we compared the potentiated and dormant antler stem cells using isobaric tags for the relative and absolute quantification (iTRAQ) labeling of the peptides, coupled with two-dimensional liquid chromatography-tandem mass spectrometry (LC-MS/MS) to compare the proteome profiles. Proteins were identified by searching against the NCBI nr database and our own Cervine transcriptome database, and bioinformatics analysis was conducted to identify the differentially expressed proteins. Based on this searching strategy, we identified 169 differentially expressed proteins in total, consisting of 70 up- and 99 down-regulated in the potentiated vs. dormant antler stem cells. Reliability of the iTRAQ was confirmed via quantitative real-time polymerase chain reaction (qRT-PCR) to measure the expression of selected genes. We identified transduction pathways through the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, such as HIF-1 and PI3K-AKT signaling pathways that play important roles in regulating the regeneration of antlers. In summary, the initiation stage of antler regeneration, a process from dormant to potentiated states in antler stem cells, is regulated by multiple proteins and complicated signal networks.

Analysis of Genomewide DNA Methylation Reveals Differences in DNA Methylation Levels between Dormant and Naturally as well as Artificially Potentiated Pedicle Periosteum of Sika Deer (Cervus nippon)

Deer antlers are the only mammalian appendages that can fully regenerate each year from the permanent bony protuberances of the frontal bones, called pedicles. Pedicle periosteum (PP) is the key tissue for antler regeneration and the source of antler stem cells. The distal one third of the PP has acquired the ability to regenerate antlers and is termed the potentiated PP (PPP), whereas the proximal two thirds of the PP requires further interactions within its niche to launch antler regeneration and is termed the dormant PP (DPP). However, the molecular mechanisms underlying the process of potentiation from the DPP to the PPP are unknown. In this study, we used the fluorescence-labeled methylation-sensitive amplified polymorphism method to assess the levels of DNA methylation in both cells and tissues of the PPP and the DPP. The results showed that the levels of DNA methylation were significantly lower in the PPP compared to the DPP (P < 0.05). Therefore, DNA demethylation may be involved in the process of this potentiation. This involvement was further confirmed by functional testing by artificially creating a potentiated PP (aPPP) from DPP tissue. Moreover, we identified 15 methylated fragments by the methylation sensitive amplified polymorphism method that are either unique to the PPP or the DPP, which were further confirmed by Southern blot analysis. Taken together, our data suggest that DNA demethylation is involved in the process of PP potentiation, which is a prerequisite step for the initiation of antler regeneration. These findings provide the first experimental evidence to link epigenetic regulation and mammalian appendage regeneration.

MicroRNA profiling of antler stem cells in potentiated and dormant states and their potential roles in antler regeneration

MicroRNAs (miRNAs) can effectively regulate gene expression at the post-transcriptional level and play a critical role in tissue growth, development and regeneration. Our previous studies showed that antler regeneration is a stem cell-based process and antler stem cells reside in the periosteum of a pedicle, the permanent bony protuberance, from which antler regeneration takes place. Antlers are the only mammalian organ that can fully regenerate and hence provide a unique opportunity to identify miRNAs that are involved in organ regeneration. In the present study, we used next generation sequencing technology sequenced miRNAs of the stem cells derived from either the potentiated or the dormant pedicle periosteum. A population of both conserved and 20 deer-specific miRNAs was identified. These conserved miRNAs were derived from 453 homologous hairpin precursors across 88 animal species, and were further grouped into 167 miRNA families. Among them, the miR-296 is embryonic stem cell-specific. The potentiation process resulted in the significant regulation (>±2 Fold, q value <0.05) of conserved miRNAs; 8 miRNA transcripts were down- and 6 up-regulated. Several GO biology processes and the Wnt, MAPK and TGF-beta signaling pathways were found to be up-regulated as part of antlerogenic stem cell potentiation process. This research has identified miRNAs that are associated either with the dormant or the potentiated antler stem cells and identified some target miRNAs for further research into their role played in mammalian organ regeneration.

Calcium orthophosphates (CaPO4): occurrence and properties

The present overview is intended to point the readers' attention to the important subject of calcium orthophosphates (CaPO4). This type of materials is of the special significance for the human beings because they represent the inorganic part of major normal (bones, teeth and antlers) and pathological (i.e., those appearing due to various diseases) calcified tissues of mammals. For example, atherosclerosis results in blood vessel blockage caused by a solid composite of cholesterol with CaPO4, while dental caries and osteoporosis mean a partial decalcification of teeth and bones, respectively, that results in replacement of a less soluble and harder biological apatite by more soluble and softer calcium hydrogenorthophosphates. Therefore, the processes of both normal and pathological calcifications are just an in vivo crystallization of CaPO4. Similarly, dental caries and osteoporosis might be considered as in vivo dissolution of CaPO4. In addition, natural CaPO4 are the major source of phosphorus, which is used to produce agricultural fertilizers, detergents and various phosphorus-containing chemicals. Thus, there is a great significance of CaPO4 for the humankind and, in this paper, an overview on the current knowledge on this subject is provided.

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.

Morphogenetic mechanisms in the cyclic regeneration of hair follicles and deer antlers from stem cells

We have made comparisons between hair follicles (HFs) and antler units (AUs)—two seemingly unrelated mammalian organs. HFs are tiny and concealed within skin, whereas AUs are gigantic and grown externally for visual display. However, these two organs share some striking similarities. Both consist of permanent and cyclic/temporary components and undergo stem-cell-based organogenesis and cyclic regeneration. Stem cells of both organs reside in the permanent part and the growth centres are located in the temporary part of each respective organ. Organogenesis and regeneration of both organs depend on epithelial-mesenchymal interactions. Establishment of these interactions requires stem cells and reactive/niche cells (dermal papilla cells for HFs and epidermal cells for AUs) to be juxtaposed, which is achieved through destruction of the cyclic part to bring the reactive cells into close proximity to the respective stem cell niche. Developments of HFs and AUs are regulated by similar endocrine (particularly testosterone) and paracrine (particularly IGF1) factors. Interestingly, these two organs come to interplay during antlerogenesis. In conclusion, we believe that investigators from the fields of both HF and AU biology could greatly benefit from a comprehensive comparison between these two organs.