The potential role of telocytes in Tissue Engineering and Regenerative Medicine

Telocytes in Cutaneous Biology: A Reappraisal

The telocytes (TCs) are novel interstitial cells that have been overlooked for a long time due to their histologic similarity to other stromal cells. TCs can be separated from the stromal cells based on their distinct immunohistochemical, ultrastructural, and molecular features. Functionally, TCs are involved in the tissue renewal, mechanical support, and immune modulation. These cells are also involved in the signal transduction either through their direct interactions with the neighboring cells or through the paracrine signaling via extracellular vesicles. TCs are damaged in several inflammatory and fibrotic conditions such as ulcerative colitis, Crohn's disease, hepatic fibrosis, psoriasis, and systemic sclerosis. The transplantation of TCs in the damaged tissue can promote tissue regeneration. Therefore, enhancing tissue TCs either by their transplantation or by promoting their survival and growth using novel medications represents novel therapeutic strategy in the future. In this review, we addressed several aspects of TCs including their origin, distribution, morphologic features, and functions. We also discussed their involvement of the cutaneous TCs in the development various pathologic conditions.

Telocytes in Cutaneous Biology: A Reappraisal

The telocytes (TCs) are novel interstitial cells that have been overlooked for a long time due to their histologic similarity to other stromal cells. TCs can be separated from the stromal cells based on their distinct immunohistochemical, ultrastructural, and molecular features. Functionally, TCs are involved in the tissue renewal, mechanical support, and immune modulation. These cells are also involved in the signal transduction either through their direct interactions with the neighboring cells or through the paracrine signaling via extracellular vesicles. TCs are damaged in several inflammatory and fibrotic conditions such as ulcerative colitis, Crohn's disease, hepatic fibrosis, psoriasis, and systemic sclerosis. The transplantation of TCs in the damaged tissue can promote tissue regeneration. Therefore, enhancing tissue TCs either by their transplantation or by promoting their survival and growth using novel medications represents novel therapeutic strategy in the future. In this review, we addressed several aspects of TCs including their origin, distribution, morphologic features, and functions. We also discussed their involvement of the cutaneous TCs in the development various pathologic conditions.

Modulation of Telocytes in Women with Preeclampsia: A Prospective Comparative Study

Background

Telocytes (TCs) are networking cells with enigmatic functions. Placenta is a noninnervated organ with the TCs could have function of signal transmission to placental myofibroblasts, being likely a regulator for maternal blood flow. Preeclampsia (PE) is a disease complicating the second half of pregnancy associated with hypoxia probably due to failure of vascular remodeling of spiral arteries resulting in poor placental perfusion. We hypothesized that disturbance in the morphology of TCs may have a role in the pathogenesis of PE.

Materials and Methods

Women with normal or physiological pregnancy (Group I; 15 women) and with PE (Group II; 15 women) participated in this study. Specimens were obtained from the central cotyledons and the superficial myometrium beneath the implantation sites processed for light microscopy and stained with Hematoxylin and Eosin, toluidine blue, masson trichrome, and CD117.

Results

The villi of group II has thick-walled blood vessels with increased peri-villous fibrinoid deposition, reduced areas of vasculosyncytial membrane and apparent increase in connective tissue density. Morphometric study and statistical analysis revealed a significant increase in the mean number of syncytial knots and significant decrease in placental (villous and decidual) and myometrial TCs and extravillous trophoblasts (EVTs) beneath the placental implantation site in Group II (P < 0.011) in comparison with group I.

Conclusions

PE is associated with significantly low number of placental TCs interestingly with low number of EVTs. Further studies are needed to support our findings.

A Synopsis of Signaling Crosstalk of Pericytes and Endothelial Cells in Salivary Gland

The salivary gland (SG) microvasculature constitutes a dynamic cellular organization instrumental to preserving tissue stability and homeostasis. The interplay between pericytes (PCs) and endothelial cells (ECs) culminates as a key ingredient that coordinates the development, maturation, and integrity of vessel building blocks. PCs, as a variety of mesenchymal stem cells, enthrall in the field of regenerative medicine, supporting the notion of regeneration and repair. PC-EC interconnections are pivotal in the kinetic and intricate process of angiogenesis during both embryological and post-natal development. The disruption of this complex interlinkage corresponds to SG pathogenesis, including inflammation, autoimmune disorders (Sjögren’s syndrome), and tumorigenesis. Here, we provided a global portrayal of major signaling pathways between PCs and ECs that cooperate to enhance vascular steadiness through the synergistic interchange. Additionally, we delineated how the crosstalk among molecular networks affiliate to contribute to a malignant context. Additionally, within SG microarchitecture, telocytes and myoepithelial cells assemble a labyrinthine companionship, which together with PCs appear to synchronize the regenerative potential of parenchymal constituents. By underscoring the intricacy of signaling cascades within cellular latticework, this review sketched a perceptive basis for target-selective drugs to safeguard SG function.

Morphological Evidence of Telocytes in Skeletal Muscle Interstitium of Exercised and Sedentary Rodents

Skeletal muscle atrophy, resulting from states of hypokinesis or immobilization, leads to morphological, metabolic, and functional changes within the muscle tissue, a large variety of which are supported by the stromal cells populating the interstitium. Telocytes represent a recently discovered population of stromal cells, which has been increasingly identified in several human organs and appears to participate in sustaining cross-talk, promoting regenerative mechanisms and supporting differentiation of local stem cell niche. The aim of this morphologic study was to investigate the presence of Telocytes in the tibialis anterior muscle of healthy rats undergoing an endurance training protocol for either 4 weeks or 16 weeks compared to sedentary rats. Histomorphometric analysis of muscle fibers diameter revealed muscle atrophy in sedentary rats. Telocytes were identified by double-positive immunofluorescence staining for CD34/CD117 and CD34/vimentin. The results showed that Telocytes were significantly reduced in sedentary rats at 16 weeks, while rats subjected to regular exercise maintained a stable Telocytes population after 16 weeks. Understanding of the relationship between Telocytes and exercise offers new chances in the field of regenerative medicine, suggesting possible triggers for Telocytes in sarcopenia and other musculoskeletal disorders, promoting adapted physical activity and rehabilitation programmes in clinical practice.

Role of Podoplanin-Positive Cells in Cardiac Fibrosis and Angiogenesis After Ischemia

New insights into the cellular and extra-cellular composition of scar tissue after myocardial infarction (MI) have been identified. Recently, a heterogeneous podoplanin-expressing cell population has been associated with fibrogenic and inflammatory responses and lymphatic vessel growth during scar formation. Podoplanin is a mucin-like transmembrane glycoprotein that plays an important role in heart development, cell motility, tumorigenesis, and metastasis. In the adult mouse heart, podoplanin is expressed only by cardiac lymphatic endothelial cells; after MI, it is acquired with an unexpected heterogeneity by PDGFRα-, PDGFRβ-, and CD34-positive cells. Podoplanin may therefore represent a sign of activation of a cohort of progenitor cells during different phases of post-ischemic myocardial wound repair. Podoplanin binds to C-type lectin-like receptor 2 (CLEC-2) which is exclusively expressed by platelets and a variety of immune cells. CLEC-2 is upregulated in CD11b^high cells, including monocytes and macrophages, following inflammatory stimuli. We recently published that inhibition of the interaction between podoplanin-expressing cells and podoplanin-binding cells using podoplanin-neutralizing antibodies reduces but does not fully suppress inflammation post-MI while improving heart function and scar composition after ischemic injury. These data support an emerging and alternative mechanism of interactome in the heart that, when neutralized, leads to altered inflammatory response and preservation of cardiac function and structure. The overarching objective of this review is to assimilate and discuss the available evidence on the functional role of podoplanin-positive cells on cardiac fibrosis and remodeling. A detailed characterization of cell-to-cell interactions and paracrine signals between podoplanin-expressing cells and the other type of cells that compose the heart tissue is needed to open a new line of investigation extending beyond the known function of these cells. This review attempts to discuss the role and biology of podoplanin-positive cells in the context of cardiac injury, repair, and remodeling.

Telocytes constitute a widespread interstitial meshwork in the lamina propria and underlying striated muscle of human tongue

Telocytes have recently emerged as unique interstitial cells defined by their extremely long, thin and moniliform prolongations termed telopodes. Despite growing evidence that these cells consistently reside in the stromal compartment of various organs from human beings, studies dealing with telocytes in structures of the oral cavity are scarce. Hence, the present morphologic study was undertaken to explore for the first time the presence and specific localization of telocytes within tissues of the normal human tongue, a complex muscular organ whose main functions include taste, speech, and food manipulation in the oral cavity. Telocytes were initially identified by CD34 immunostaining and confirmed by CD34/PDGFRα double immunofluorescence and transmission electron microscopy. CD34+/PDGFRα+ telocytes were organized in interstitial meshworks either in the tongue lamina propria or in the underlying striated muscle. Lingual telocytes were immunonegative for CD31, c-kit and α-SMA. Telopodes were finely distributed throughout the stromal space and concentrated beneath the lingual epithelium and around CD31+ vessels, skeletal muscle bundles/fibers, and intramuscular nerves and ganglia. They also enveloped salivary gland units outside the α-SMA+ myoepithelial cells and delimited lymphoid aggregates. These findings establish telocytes as a previously overlooked interstitial cell population worth investigating further in the setting of human tongue pathophysiology.

Reappraising the microscopic anatomy of human testis: identification of telocyte networks in the peritubular and intertubular stromal space

Telocytes are a recently described stromal cell type widely distributed in various organs including the female and male reproductive systems. This study was aimed to investigate for the first time the existence, distribution and characteristics of telocytes in normal human testis by an integrated morphological approach (immunohistochemistry, immunofluorescence and transmission electron microscopy). We found that telocytes displaying typical long and moniliform prolongations and coexpressing CD34 and PDGFRα formed networks in the outer layer of peritubular tissue and around Leydig cells and vessels in the intertubular stroma. Testicular telocytes were immunophenotypically negative for CD31, c-kit/CD117 as well as α-SMA, thus making them clearly distinguishable from myoid cells/myofibroblasts located in the inner layer of peritubular tissue. Transmission electron microscopy confirmed the presence of cells ultrastructurally identifiable as telocytes (i.e. cells with telopodes alternating podomers and podoms) in the aforementioned locations. Intercellular contacts between neighboring telocytes and telopodes were observed throughout the testicular stromal compartment. Telopodes intimately surrounded and often established close contacts with peritubular myoid cells/myofibroblasts, Leydig cells and vessels. Extracellular vesicles were also frequently detected near telopodes. In summary, we demonstrated that telocytes are a previously neglected stromal component of human testis with potential implications in tissue homeostasis deserving further investigation.

Telocytes in human fetal skeletal muscle interstitium during early myogenesis

A new peculiar stromal cell type called telocyte (TC)/CD34-positive stromal cell (i.e. cell with distinctive prolongations named telopodes) has recently been described in various tissues and organs, including the adult skeletal muscle interstitium of mammals. By forming a resident stromal three-dimensional network, TCs have been suggested to participate in different physiological processes within the skeletal muscle tissue, including homeostasis maintenance, intercellular signaling, tissue regeneration/repair and angiogenesis. Since a continuous interplay between the stromal compartment and skeletal muscle fibers seems to take place from organogenesis to aging, the present study was undertaken to investigate for the first time the presence of TCs in the human skeletal muscle during early myogenesis. In particular, we describe the morphological distribution of TCs in human fetal lower limb skeletal muscle during early stages of myogenesis (9-12 weeks of gestation). TCs were studied on tissue sections subjected to immunoperoxidase-based immunohistochemistry for CD34. Double immunofluorescence was further performed to unequivocally differentiate TCs (CD34-positive/CD31-negative) from vascular endothelial cells (CD34-positive/CD31-positive). Our findings provide evidence that stromal cells with typical morphological features and immunophenotype of TCs are present in the human skeletal muscle during early myogenesis, revealing differences in either CD34 immunopositivity or TC numbers among different gestation ages. Specifically, few TCs weakly positive for CD34 were found between 9 and 9.5 weeks. From 10 to 11.5 weeks, TCs were more numerous and strongly reactive and their telopodes formed a reticular network in close relationship with blood vessels and primary and secondary myotubes undergoing separation. On the contrary, a strong reduction in the number and immunopositivity of TCs was observed in fetal muscle sections from 12 weeks of gestation, where mature myotubes were evident. The muscle stroma showed parallel changes in amount, density and organization from 9 to 12 weeks. Moreover, blood vessels appeared particularly numerous between 10 and 11.5 weeks. Taken together, our findings suggest that TCs might play a fundamental role in the early myogenetic period, possibly guiding tissue organization and compartmentalization, as well as angiogenesis and maturation of myotubes.

Mesenchymal stem cells promote lymphangiogenic properties of lymphatic endothelial cells

Lymphatic metastasis is one of the main prognostic factors concerning long-term survival of cancer patients. In this regard, the molecular mechanisms of lymphangiogenesis are still rarely explored. Also, the interactions between stem cells and lymphatic endothelial cells (LEC) in humans have not been well examined. Therefore, the main objective of this study was to assess the interactions between mesenchymal stem cells (MSC) and LEC using in vitro angiogenesis assays. Juvenile LEC were stimulated with VEGF-C, bFGF, MSC-conditioned medium (MSC-CM) or by co-culture with MSC. LEC proliferation was assessed using a MTT assay. Migration of the cells was determined with a wound healing assay and a transmigration assay. To measure the formation of lymphatic sprouts, LEC spheroids were embedded in collagen or fibrin gels. The LEC's capacity to form capillary-like structures was assessed by a tube formation assay on Matrigel^® . The proliferation, migration and tube formation of LEC could be significantly enhanced by MSC-CM and by co-culture with MSC. The effect of stimulation with MSC-CM was stronger compared to stimulation with the growth factors VEGF-C and bFGF in proliferation and transmigration assays. Sprouting was stimulated by VEGF-C, bFGF and by MSC-CM. With this study, we demonstrate the potent stimulating effect of the MSC secretome on proliferation, migration and tube formation of LEC. This indicates an important role of MSC in lymphangiogenesis in pathological as well as physiological processes.

An in vitro investigation of telocytes-educated macrophages: morphology, heterocellular junctions, apoptosis and invasion analysis

BACKGROUND

Telocytes (TCs), a recently discovered novel type of interstitial cells, were also found in a wide variety of human and mammalian reproductive organs/tissues, including uterus, oviduct and placenta. Previously, we demonstrated that TCs-conditioned media was capable of activating peritoneal macrophages (pMACs) through paracrine effects. This study investigates the hypothesis that direct interaction of TCs with pMACs will also play a significant role in immunoregulation of pMACs.

METHODS

TCs and pMACs were derived from the uterus and intraperitoneal cavity of female BALB/c mice, respectively. TCs were identified by immunofluorescence and then co-cultured directly with pMACs for 24 h without added cytokines, to observe the in vitro biological behavior of pMACs. We used histochemical staining to study morphology and mitochondrial metabolism of pMACs, scanning electron microscopy to study heterocellular junctions, flow cytometry to investigate mitochondrial membrane potential (ΔΨm) and apoptosis, and transwell chambers to study invasion ability. Student-t test was used accordingly.

RESULTS

Presently, TCs with typical structure and immunophenotype of double CD-34-positive/vimentin-positive were successfully isolated. pMACs co-cultured with TCs showed obviously morphological activation, with enhanced energy metabolism (P < 0.05). Meanwhile, direct physical cell-to-cell interaction promoted the development of heterocellular junctions between TCs and pMACs. Furthermore, TCs treatment markedly reduced the depletion of ΔΨm in co-cultured pMACs (all P < 0.05), and inhibited their apoptosis (P < 0.05). Functionally, pMACs co-cultured with TCs showed enhanced invasion ability (P < 0.05).

CONCLUSIONS

Direct physical cell-to-cell interaction promoted the development of heterocellular junctions between TCs and pMACs, presumably responsible for the observed novel efficient way of pMACs activation via mitochondrial signaling pathway. TCs-educated pMACs might be a promising way to restore the defective immunosurveillance in endometriosis (EMs), led to the enhanced treatment efficacy of EMs in a simple and clinically feasible fashion.

Morphological evidence of telocytes in human synovium

A new cell type named telocyte (i.e. cell with distinctive prolongations called telopodes) has recently been identified in the stroma of various organs in humans. However, no study has yet reported the existence of telocytes in the synovial membrane of diarthrodial joints. This work was therefore undertaken to search for telocytes in the normal human synovium using transmission electron microscopy, immunohistochemistry and immunofluorescence. Ultrastructural analyses demonstrated the presence of numerous spindle-shaped telocytes in the whole synovial sublining layer. Synovial telocytes exhibited very long and thin moniliform telopodes and were particularly concentrated at the boundary between the lining and sublining layers and around blood vessels. Light microscopy confirmed the presence of CD34-positive telocytes in the aforementioned locations. Moreover, synovial telocytes coexpressed CD34 and platelet-derived growth factor receptor α. Double immunostaining further allowed to unequivocally differentiate synovial telocytes (CD34-positive/CD31-negative) from vascular endothelial cells (CD34-positive/CD31-positive). The in vitro examination of fibroblast-like synoviocyte primary cultures revealed the coexistence of different cell types, including CD34-positive telocytes projecting typical moniliform telopodes. In conclusion, our work provides the first evidence that telocytes do exist in the human synovium and lays the groundwork for future studies on synovial telocytes in a variety of degenerative and destructive joint diseases.

Telocytes in normal and keratoconic human cornea: an immunohistochemical and transmission electron microscopy study

Telocytes (TC) are typically defined as cells with telopodes by their ultrastructural features. Their presence was reported in the interstitium of various organs in vertebrates, including humans. However, no study has yet described the presence of TC in the human eye and in particular, within the stromal compartment of the cornea. To address this issue, samples of normal and pathologic (keratoconic) human corneas were tested by immunohistochemistry for CD34, platelet‐derived growth factor receptor α (PDGFRα) and c‐kit/CD117 or examined by transmission electron microscopy. We found that TC coexpressing CD34 and PDGFRα were distributed throughout the whole normal corneal stroma with different TC subtypes being distinguishable on the basis of the expression of the stemness marker c‐kit (i.e. c‐kit‐positive and c‐kit‐negative TC subpopulations). Transmission electron microscopy examination confirmed the existence of spindle‐shaped and bipolar TC typically displaying two long and thin moniliform telopodes establishing intercellular contacts formed by gap junctions. Keratoconic corneas were characterized by ultrastructural damages and patchy loss of TC with an almost complete depletion of the c‐kit‐positive TC subpopulation. We propose that TC may contribute to the maintenance of corneal stromal homoeostasis and that, in particular, the c‐kit‐positive TC subtype might have stemness capacity participating in corneal regeneration and repair processes. Further studies are needed to clarify the differential roles of corneal TC subtypes as well as the possible therapeutic applications of TC in degenerative corneal disorders such as keratoconus.

Potential applications and human biosafety of nanomaterials used in nanomedicine

With the rapid development of nanotechnology, potential applications of nanomaterials in medicine have been widely researched in recent years. Nanomaterials themselves can be used as image agents or therapeutic drugs, and for drug and gene delivery, biological devices, nanoelectronic biosensors or molecular nanotechnology. As the composition, morphology, chemical properties, implant sites as well as potential applications become more and more complex, human biosafety of nanomaterials for clinical use has become a major concern. If nanoparticles accumulate in the human body or interact with the body molecules or chemical components, health risks may also occur. Accordingly, the unique chemical and physical properties, potential applications in medical fields, as well as human biosafety in clinical trials are reviewed in this study. Finally, this article tries to give some suggestions for future work in nanomedicine research. Copyright © 2017 John Wiley & Sons, Ltd.

Therapeutic roles of telocytes in OVA-induced acute asthma in mice

Telocytes (TCs) newly discovered as the mesenchyme-derived interstitial cells were found to have supportive effects on mesenchymal stem cells (MSCs). The present study aimed at investigating effects of TCs or TCs gathered with MSCs on experimental airway inflammation and hyper-responsiveness. The TCs were isolated from the lung tissue of the female BALB/c mice. The ovalbumin (OVA)-induced asthma model was established. TCs (1 × 10⁶ /2 × 10⁶ ) and/or MSCs (1 × 10⁶ ) were injected through mice tail vein for consecutive three days before OVA excited the mice. This study at first demonstrated that the transplantation of TCs could improve allergen-induced asthma by obviously inhibiting airway inflammation and airway hyper-responsiveness preclinically, with the down-regulation of Th2-related cytokine IL-4, transcription factor GATA-3 and Th2 cell differentiation, while up-regulation of Th1-related cytokine IFN-γ, transcription factor T-bet and Th1 cells proliferation in asthma, just like MSCs. Co-transplantation of TCs with MSCs showed better therapeutic effects on experimental asthma, even though the therapeutic effects of TCs alone were similar to those of MSCs alone. TCs and the combination of TCs with MSCs could improve the airway inflammation and airway hyper-responsiveness and can be a new alternative for asthma therapy.

Treatment of standardised wounds with pure epidermal micrografts generated with an automated device

In this study, we analysed the effects of pure epidermal micrografts generated with an automated device in a standardised human wound model. Epidermal micrografts were harvested using an automated device. Micrografts were then transplanted onto split-skin donor sites. The target area was only partially covered with transplants to create an intra-individual control area. Wounds were evaluated by subjective assessment as well as measurements with combined laser and white light spectroscopy and cutometry. The epidermal graft sites remained completely stable, whereas control sites offered partially unstable and blistering areas. Statistically, no measurable difference in the speed of initial reepithelialisation could be shown. However, there was an increased pliability and softness of the treated areas that correlated with the subjective impression of both investigators and patients. There was a significantly higher relative haemoglobin concentration, measurable in treated and untreated areas at 4 weeks and 6 months. Cutometry showed no differences in skin properties between treated and untreated areas. This study shows an effect of epidermal micrografts in a standardised human wound model and supports the positive impact of keratinocytes on early wound healing as described in literature. Long-term effects of epidermal grafting deserve further studies.

Telocytes in gastric lamina propria of the Chinese giant salamander, Andrias davidianus

In this study, we attempt to identify gastric telocytes (TCs) of the Chinese giant salamander Andrias davidianus, by light microscopy, immunohistochemistry and transmission electron microscopy (TEM) methods. Toluidine blue staining showed TCs with one to two very thin and long telopodes (Tps) that were located in gastric lamina propria. Tps had characteristic structures, including podoms, podomers and dichotomous branching. Immunohistochemistry showed the existence of CD34⁺/PDGFRα⁺ TCs with moniliform Tps in stroma and were close to gastric glands and blood vessels. TEM micrographs also demonstrated the presence of TCs in interstitium between gastric glands. TCs/Tps were located in close proximity to gastric glands, blood vessels, endocrine cells and stem cells. In particular, Tps frequently surrounded stem cells. TCs and Tps, Tps and stem cells established close contacts. Moreover, the exosomes were also found near TCs/Tps. Our data confirmed the presence of TCs in gastric lamina propria of the amphibian, and suggested that TCs cooperate with resident stem cells to regulate endocrine cells and gastric glands regeneration and homeostasis.

Telocytes and Their Extracellular Vesicles-Evidence and Hypotheses

Entering the new millennium, nobody believed that there was the possibility of discovering a new cellular type. Nevertheless, telocytes (TCs) were described as a novel kind of interstitial cell. Ubiquitously distributed in the extracellular matrix of any tissue, TCs are regarded as cells with telopodes involved in intercellular communication by direct homo- and heterocellular junctions or by extracellular vesicle (EVs) release. Their discovery has aroused the interest of many research groups worldwide, and many researchers regard them as potentially regenerative cells. Given the experience of our laboratory, where these cells were first described, we review the evidence supporting the fact that TCs release EVs, and discuss alternative hypotheses about their future implications.

Decoding Telocytes

Telocytes (TCs) are a novel type of interstitial cells, with extremely long and thin cellular prolongations termed telopodes (Tps). TCs were first identified by Popescu et al. and described their finding as "cells with telopodes." The presence of TCs has been reported in the majority of tissues and organs (for details please visit www.telocytes.com ). TCs have been ignored or overlooked for a long time due to our inability to observe these cells via a light microscopy. TCs represent a distinct cell population, different from other types of interstitial cells, based on their distinct (ultra)structure, immunophenotype, microRNA profile, gene feature, proteome signature, and secretome features. As TCs have been suggested as new cellular targets for forthcoming therapies, developing specific methods to modulate TC numbers represents an important objective.