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

The significance of MDK growth factor in the antler development of sika deer (Cervus nippon): An in-depth analysis

Deer antlers exhibit rapid growth during the velvet phase. As a critical endogenous growth factor in animals, midkine (MDK) is likely closely associated with the growth of antlers. However, the spatio-temporal expression pattern of MDK during the velvet phase was unclear. This study explored the physiological role of MDK by analyzing its molecular characterization and spatio-temporal expression dynamics during the growth of sika deer antlers. The study cloned the coding sequences (CDS) of MDK, which spanned 429 bp and encoded 142 amino acids. The results of bioinformatics prediction analysis showed that MDK was an extracellular hydrophilic secreted protein, which was mainly composed of random coil. MDK protein was relatively conserved in evolution and MDK protein of sika deer had the closest relatives to ruminants and the furthest relatives to Aves. The tip tissues (dermis, mesenchyme, precartilage, cartilage) of antlers were collected from three important growth and development nodes (early period, EP. middle period, MP. late period, LP), and quantitative real-time polymerase chain reaction (qRT-PCR) was chosen to detect the spatio-temporal expression of the MDK. The results showed that MDK was expressed in all tissue sites of antler tip in EP, MP, LP. MDK had a consistent expression pattern under all growth periods and was strongly expressed in dermis and cartilage. The expression of MDK was consistently up-regulated in precartilage, whereas it was first up-regulated and then down-regulated in other tissues, and it was highly significant in MP compared to EP and LP (P < 0.01). This study suggested that MDK may regulate the growth of dermis and cartilage tissues mainly by participating in the process of angiogenesis and bone formation, thus promoting the rapid growth of antlers.

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.

Expression of the pleiotrophin-midkine axis in a sheep tooth socket model of bone healing

OBJECTIVE AND BACKGROUND

Resorption of alveolar bone after tooth extraction is a common problem often requiring bone grafting. The success of the grafting procedures is dependent on multiple factors including the presence of growth factors. This is the first in vivo study to investigate the role of the pleiotrophin family of cytokines in alveolar bone regeneration. This research investigated the role of the pleiotrophin-midkine (PTN-MDK) axis during osteogenesis, with and without a grafting material, after tooth extraction in a sheep model.

METHODS

Thirty Romney-cross ewes were anesthetized, and all premolar teeth on the right side were extracted. The sockets were randomized to controls sites with no treatment and test sites with Bio-Oss® graft material and Bio-Gide® membrane. Samples were harvested after sacrificing animals 4, 8, and 16 weeks post-grafting (n = 10 per time-point). Tissue for qRT² -PCR gene analysis was recovered from the socket next to the first molar using a trephine (Ø = 2 mm). Each socket was fixed, decalcified, paraffin-embedded, and sectioned. Immunohistochemistry was conducted to localize both PTN and MDK along with their receptors, protein tyrosine phosphatase receptor type Z1 (PTPRZ1), ALK receptor tyrosine kinase (ALK), and notch receptor 2 (NOTCH2).

RESULTS

Within the healing sockets, high expression of genes for PTN, MDK, NOTCH2, and ALK was found at all time-points and in both grafted and non-grafted sites, while PTPRZ1 was only expressed at low levels. The relative gene expression of the PTN family of cytokines was not statistically different at the three time-points between test and control groups (p > .05). Immunohistochemistry found PTN and MDK in association with new bone, NOTCH2 in the connective tissue, and PTPRZ1 and ALK in association with cuboidal osteoblasts involved in bone formation.

CONCLUSIONS

The PTN-MDK axis was highly expressed in both non-grafted and grafted sockets during osteogenesis in a sheep model of alveolar bone regeneration with no evidence that grafting significantly affected expression. The activation of NOTCH2 and PTPRZ1 receptors may be important during bone regeneration in vivo. The discovery of the PTN-MDK axis as important during alveolar bone regeneration is novel and opens up new avenues of research into these stably expressed highly active cytokines. Growth factor supplementation with PTN and/or MDK during healing may be an approach for enhanced regeneration or to initiate healing where delayed.

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.

MIC-1 Antlerogenic Stem Cells Homogenate from Cervus elaphus Accelerate Corneal Burn Reepithelization in Rabbits

Deer antler is the only mammalian organ that can fully grow back once lost from its pedicle. Antler regeneration is a stem cell-based process. Therefore, antlers probably offer the most pertinent model for studying organ regeneration in mammals. Evaluation of the effect of deer antler stem cells on the healing of superficial and deep rabbit corneal wounds was performed. Thirty-six New Zealeand White rabbits were used in this study in superficial and deep denaturation models, and corneal erosion was performed with n-heptanol placed on the cornea for 30 and NaOH for 90 s. Antler stem cells in drop formulation with hyaluronate was used. As a control, sodium hyaluronate in the superficial model and protein-free calf blood dialysate (Solcoseryl) in the deep model were administered. In superficial corneal damage, a reduction in the area of the damaged cornea was observed from day 3 of the experiment to an adequate level: 45% in the test group and 52% in the control group relative to the baseline damage (100%). Between days 3 and 7, on average, a smaller lesion area was observed in the group receiving antler stem cells. The use of antler stem cells has resulted in a marked improvement in cornea clarity. According to the 5-point scale of corneal opacity evaluation, where 1 is completely clear and 5 is completely opaque, the first statistically significant changes were observed after 4 weeks of treatment: 3.0 in the study group, 4.1 in the control with Solcoseryl, and 4.4 in the control group. After 9 weeks, these values were, 2.5, 3.8, and 4.1, respectively. The present preliminary study shows the promising results of antlerogenic stem cells of Cervus elaphus topically applied for the treatment of corneal injury. A deeper understanding of the developmental mechanisms involved in antler renewal can be useful for controlling regeneration cornea processes.

Protein tyrosine phosphatase receptor zeta 1 deletion triggers defective heart morphogenesis in mice and zebrafish

Protein tyrosine phosphatase receptor-ζ1 (PTPRZ1) is a transmembrane tyrosine phosphatase receptor highly expressed in embryonic stem cells. In the present work, gene expression analyses of Ptprz1^−/− and Ptprz1^+/+ mice endothelial cells and hearts pointed to an unidentified role of PTPRZ1 in heart development through the regulation of heart-specific transcription factor genes. Echocardiography analysis in mice identified that both systolic and diastolic functions are affected in Ptprz1^−/− compared with Ptprz1^+/+ hearts, based on a dilated left ventricular (LV) cavity, decreased ejection fraction and fraction shortening, and increased angiogenesis in Ptprz1^−/− hearts, with no signs of cardiac hypertrophy. A zebrafish ptprz1^−/− knockout was also generated and exhibited misregulated expression of developmental cardiac markers, bradycardia, and defective heart morphogenesis characterized by enlarged ventricles and defected contractility. A selective PTPRZ1 tyrosine phosphatase inhibitor affected zebrafish heart development and function in a way like what is observed in the ptprz1^−/− zebrafish. The same inhibitor had no effect in the function of the adult zebrafish heart, suggesting that PTPRZ1 is not important for the adult heart function, in line with data from the human cell atlas showing very low to negligible PTPRZ1 expression in the adult human heart. However, in line with the animal models, Ptprz1 was expressed in many different cell types in the human fetal heart, such as valvar, fibroblast-like, cardiomyocytes, and endothelial cells. Collectively, these data suggest that PTPRZ1 regulates cardiac morphogenesis in a way that subsequently affects heart function and warrant further studies for the involvement of PTPRZ1 in idiopathic congenital cardiac pathologies.

NEW & NOTEWORTHY Protein tyrosine phosphatase receptor ζ1 (PTPRZ1) is expressed in fetal but not adult heart and seems to affect heart development. In both mouse and zebrafish animal models, loss of PTPRZ1 results in dilated left ventricle cavity, decreased ejection fraction, and fraction shortening, with no signs of cardiac hypertrophy. PTPRZ1 also seems to be involved in atrioventricular canal specification, outflow tract morphogenesis, and heart angiogenesis. These results suggest that PTPRZ1 plays a role in heart development and support the hypothesis that it may be involved in congenital cardiac pathologies.

The periosteum: a simple tissue with many faces, with special reference to the antler-lineage periostea

Periosteum is a thin membrane covering bone surfaces and consists of two layers: outer fibrous layer and inner cambium layer. Simple appearance of periosteum has belied its own complexity as a composite structure for physical bone protection, mechano-sensor for sensing mechanical loading, reservoir of biochemical molecules for initiating cascade signaling, niche of osteogenic cells for bone formation and repair, and "umbilical cord" for nourishing bone tissue. Periosteum-derived cells (PDCs) have stem cell attributes: self-renewal (no signs of senescence until 80 population doublings) and multipotency (differentiate into fibroblasts, osteoblasts, chondrocytes, adipocytes and skeletal myocytes). In this review, we summarized the currently available knowledge about periosteum and with special references to antler-lineage periostea, and demonstrated that although periosteum is a type of simple tissue in appearance, with multiple faces in functions; antler-lineage periostea add another dimension to the properties of somatic periostea: capable of initiation of ectopic organ formation upon transplantation and full mammalian organ regeneration when interacted with the covering skin. Very recently, we have translated this finding into other mammals, i.e. successfully induced partial regeneration of the amputated rat legs. We believe further refinement along this line would greatly benefit human health.

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.