Telocytes damage in endometriosis-affected rat oviduct and potential impact on fertility

Evaluation of Telocytes in the Ovary, Oviduct and Uterus of Kyrgyz Mares According to Pregnancy Status

In the current study, we aimed to determine the distribution of telocytes in the ovary, oviduct and uterus of Kyrgyz mares depending on whether they were pregnant. We also studied the progression during the first 6 months of pregnancy. To this end, ovary, oviduct and uterus tissues from 53 Kyrgyz mares were obtained post-mortem. The mare tissue samples were divided into two groups: pregnant (n = 43) and non-pregnant (n = 10). Telocyte levels in the tissues were determined using light microscopic and immunohistochemical methods. Subsequently, the data acquired were evaluated based on whether the mare was pregnant, and if so, the month of pregnancy was also taken into account. After the study, we found a higher number of telocytes in the myometrium (5.69 ± 0.90, p < 0.001) and oviduct propria (0.14 ± 0.05, p < 0.006) of pregnant mares. We also noted an increased number of telocytes in the oviduct propria (0.04 ± 0.02, p < 0.03) of mares 4 months into the pregnancy, and in the muscle layer (1.62 ± 0.57, p < 0.01), myometrium (4.83 ± 0.78, p < 0.03) and ovarian stroma (0.14 ± 0.06, p < 0.04) of mares 6 months into pregnancy. In conclusion, we observed an increase in telocytes in the ovaries, oviducts and uterus of Kyrgyz mares during pregnancy, with this increase becoming more marked towards the sixth month of gestation. Therefore, additional research on the role of telocytes in pregnancy may prove beneficial.

Immunohistochemical and ultrastructural identification of telocytes in the infantile hemangioma

Telocytes (TCs) are a distinctive cell entity of the stromal microenvironment of multiple tumors; to date, their existence in infantile hemangioma (IH) remains almost unexplored. This study was therefore undertaken to characterize the immunophenotype, location, morphology, and ultrastructure of telocytes in the IH by means of immunohistochemistry, immunofluorescence confocal microscopy, and transmission electron microscopy. Telocytes were initially identified by CD34, PDGFR-α, Vimentin, and AQP-1 immunostaining. Analyzing the spatial relationship among telocytes, stem cells, endothelial cells, pericytes in the IH with AQP-1/CD31, AQP-1/Glut-1, AQP-1/α-SMA, AQP-1/CD146 and AQP-1/CD133 double immunofluorescence. TCs were immunonegative for CD31, Glut-1, CD146, α-SMA, CD133, and C-kit in the IH. The ultrastructural examination confirmed the presence of TCs, namely stromal cells with characteristic cytoplasmic processes (i.e. telopodes) forming labyrinthine networks around microvessels and releasing extracellular vesicles. Our study provides evidence that telocytes are present and PDGFR-α and AQP-1 are specific antigenic markers in the IH.

Histological study of telocytes in mice intrauterine adhesion model and their positive effect on mesenchymal stem cells in vitro

Intrauterine adhesions (IUA), the main cause of secondary infertility in women, result from irreversible fibrotic repair of the endometrium due to inflammation or human factors, accompanied by disruptions in the repair function of endometrial stem cells. This significantly impacts the physical and mental health of women in their childbearing years. Telocytes (TCs), a distinctive type of interstitial cells found in various tissues and organs, play diverse repair functions due to their unique spatial structure. In this study, we conduct the inaugural exploration of the changes in TCs in IUA disease and their potential impact on the function of stem cells. Our results show that in vivo, through double immunofluorescence staining (CD34+/Vimentin+; CD34+/CD31-), as endometrial fibrosis deepens, the number of TCs gradually decreases, telopodes shorten, and the three-dimensional structure becomes disrupted in the mouse IUA mode. In vitro, TCs can promote the proliferation and cycle of bone mesenchymal stem cells (BMSCs) by promoting the Wnt/β-catenin signaling pathway, which were inhibited using XAV939. TCs can promote the migrated ability of BMSCs and contribute to the repair of stem cells during endometrial injury. In addition, TCs can inhibit the apoptosis of BMSCs through the Bcl-2/Bax pathway. In conclusion, our study demonstrates, for the first time, the resistance role of TCs in IUA disease, shedding light on their potential involvement in endometrial repair through the modulation of stem cell function.

Telocytes: current methods of research, challenges and future perspectives

Telocytes (TCs) are CD34-positive interstitial cells that have long cytoplasmic projections, called telopodes; they have been identified in several organs and in various species. These cells establish a complex communication network between different stromal and epithelial cell types, and there is growing evidence that they play a key role in physiology and pathology. In many tissues, TC network impairment has been implicated in the onset and progression of pathological conditions, which makes the study of TCs of great interest for the development of novel therapies. In this review, we summarise the main methods involved in the characterisation of these cells as well as their inherent difficulties and then discuss the functional assays that are used to uncover the role of TCs in normal and pathological conditions, from the most traditional to the most recent. Furthermore, we provide future perspectives in the study of TCs, especially regarding the establishment of more precise markers, commercial lineages and means for drug delivery and genetic editing that directly target TCs.

Roles of telocytes dominated cell–cell communication in fibroproliferative acute respiratory distress syndrome

Telocytes (TCs) are a new type of interstitial cell identified in multiple tissues of mammals, including the human lung, and mediate homocellular or heterocellular cell‐cell communication. Acute respiratory distress syndrome (ARDS) is characterized by acute hypoxemia respiratory failure and combined with direct and indirect lung injury, which is induced by pneumonia, sepsis, burns, etc. Pulmonary fibrosis is a progressive lung disease that occurs due to increased fibrosis of lung tissue in response to chronic injury of the epithelium and gets more and more attention as a well‐recognized sequela of ARDS or mechanical ventilation. However, the existing intervention measures could not prevent the progression of pulmonary fibrosis. Although the protective effect of TCs in acute lung injury had been demonstrated in both cellular and animal models in previous studies by our or other researchers, the roles of TCs mediated cell‐cell communication in fibroproliferative ARDS is unclear. This review is aimed at integrating our understanding of TC‐mediated cell–cell communication in lung diseases with pulmonary fibrosis after ARDS.

Toward understanding the role of the interstitial tissue architects: Possible functions of telocytes in the male gonad

Telocytes represent a relatively recently discovered population of interstitial cells with a unique morphological structure that distinguishes them from other neighboring cells. Through their long protrusions extending from the cell body, telocytes create microenvironments via tissue compartmentalization and create homo- and hetero-cellular junctions. These establish a three-dimensional network enabling the maintenance of interstitial compartment homeostasis through regulation of extracellular matrix organization and activity, structural support, paracrine and juxtracrine communication, immunomodulation, immune surveillance, cell survival, and apoptosis. The presence of telocytes has also been confirmed in testicular interstitial tissue of many species of animals. The objective of this review is to summarize recent findings on telocytes in the male gonad, on which conclusions have been deduced that indicate the involvement of telocytes in maintaining the cytoarchitecture of the testicular interstitial tissue, in the processes of spermatogenesis and steroidogenesis, and photoperiod-mediated changes in the testes in seasonally reproductive animals.

Telocytes and inflammation: A review

Telocytes are a new type of interstitial cell with a diverse morphology and important functions, such as mechanical support, signal transduction, immune regulation, and tissue repair. In this paper, the origin and physiological and pathological functions of telocytes as well as their role in inflammation will be discussed, and the functions and targets of telocytes in inflammation will be fully reviewed, which may contribute to a new therapeutic strategy for inflammatory diseases in the future.

Identification of telocytes in the oviduct of the mare

Telocytes (TCs), a recently discovered special type of stromal cells, have been identified in many organs of many species, including the female and male reproductive system, with proposed multiple potential bio-functions such as homeostasis, immunomodulation, tissue remodeling and regeneration, embryogenesis, angiogenesis and even tumorigenesis. The aim of this study was to investigate the existence, and characteristics of telocytes in normal equine oviduct. To identify them, we used routine light microscopy, non-conventional light microscopy (NCLM), transmission electron microscopy (TEM), and immunohistochemistry. We found that telocytes of the equine oviduct can be recognized in fixed specimens by light microscopy (methylene blue staining), with more details on Epon semi-thin sections (toluidine blue staining) by NCLM, and that they showed positive immunostaining for CD34. The telocytes, with their typical long and moniliform prolongations, formed networks in the stromal space of the submucosa, muscular and serosa layers, particularly in the lamina propia where they were observed in greater quantity. By TEM we have also confirmed the presence of cells ultrastructurally identifiable as telocytes (cells with telopodes alternating podomers and podoms) in the aforementioned locations. Direct intercellular contacts between epithelial cells and neighboring telocytes were evidenced. EIn conclusion, we demonstrated that telocytes are present in the equine oviduct as previously reported in other species. The potential implication of telocytes in multiple potential functions of physiological and pathological processes deserves further investigation.

Telocytes and endometriosis

Endometriosis involving the presence and growth of glands and stroma outside the uterine cavity is a common, inflammatory, benign gynecologic disease. Nevertheless, no single theory can exactly account for the pathogenesis of endometriosis. Telocytes, a kind of novel mesenchymal cells, have been suggested to be crucial in promoting angiogenesis and increasing the activity of endometrial interstitial cells and inflammatory cells. Given above roles, telocytes may be considered as the possible pathogenesis of endometriosis. We reviewed the current literature on telocytes. The following aspects were considered: (A) the telocytes' typical characteristics, function, and morphological changes in endometriosis; (B) the potential role of telocytes in endometriosis by impacting the inflammation, invasion, and angiogenesis; (C) telocytes as the potential treatment options for endometriosis.

Telocyte-Derived Exosomes Provide an Important Source of Wnts That Inhibits Fibrosis and Supports Regeneration and Repair of Endometrium

Intrauterine adhesions (IUAs) often occurred after common obstetrical and gynecological procedures or infections in women of reproductive age. It was characterized by the formation of endometrial fibrosis and prevention of endometrial regeneration, usually with devastating fertility consequences and poor treatment outcomes so far. Telocytes (TCs), as a novel interstitial cell type, present in female uterus with in vitro therapeutic potential in decidualization-defective gynecologic diseases. This study aims to further investigate the role of TC-derived Wnt ligands carried by exosomes (Exo) in reversal of fibrosis and enhancement of regeneration repair in endometrium. IUA cellular and animal models were established from endometrial stromal cells (ESCs) and mice, followed with treatment of TC-conditioned medium (TCM) or TC-derived Exo. In cellular model, fibrosis markers (collagen type 1 alpha 1 [COL1A1], fibronectin [FN], and α-smooth muscle actin [α-SMA]), angiogenesis (vascular endothelial growth factor [VEGF]), and pathway protein (β-catenin) were determined by quantitative reverse transcription polymerase chain reaction (qRT-PCR), Western blotting (WB), and immunofluorescence. Results showed that, TCs (either TCM or TC-derived Exo) provide a source of Wnts that inhibit cellular fibrosis, as evidenced by significantly elevated VEGF and β-catenin with decreased fibrotic markers, whereas TCs lost salvage on fibrosis after being blocked with Wnt/β-catenin inhibitors (XAV939 or ETC-159). Further in mouse model, regeneration repair (endometrial thickness, number of glands, and fibrosis area ratio), fibrosis markers (fibronectin [FN]), mesenchymal-epithelial transition (MET) (E-cadherin, N-cadherin), and angiogenesis (VEGF, microvessel density [MVD]) were studied by hematoxylin-eosin (HE), Masson staining, and immunohistochemistry. Results demonstrated that TC-Exo treatment effectively promotes regeneration repair of endometrium by relieving fibrosis, enhancing MET, and angiogenesis. These results confirmed new evidence for therapeutic perspective of TC-derived Exo in IUAs.

Evaluation of the Plasticity of Novel Regulatory Cells-Telocytes-in the Gonad of the Male Chinese Soft-Shelled Turtle (Pelodiscus sinensis) Associated with Seasonal Reproductive Activity

Telocyte (TC)—a new type of interstitial cell with long telopodes, can form cellular junctions with various tissues or cells to participate in the regulation of multitudes of physiological activities and diseases. This study aimed to characterize the morphology, molecular features, and potential functions of hormone regulation in Chinese soft-shelled turtle (Pelodiscus sinensis) testis TCs at different reproductive stages by histological evaluation, immunohistochemistry (IHC), immunofluorescence (IF), and transmission electron microscopy. During hibernation, TCs were widely distributed in the interstitial tissue. In contrast, during reproductive activity, TCs were noted to be in close proximity with peritubular myoid cells surrounding the seminiferous tubule. Moreover, formed cell–cell junctions were observed between TCs and PTMs. The results of IHC and IF showed that the immunophenotype of testicular TCs in hibernating Chinese soft-shelled turtles is CD34+Vimentin−, while the reproductive telopodes (Tps) show low expression of vimentin. The androgen receptor is expressed in Tps of TCs of testis during hibernation. Our results showed also that TCs in seasonal breeding animals regulate the activity of neighboring cells by releasing extracellular microvesicles (EXMVs), thus influencing the activity of spermatogenesis and steroidogenesis. Consideration of our novel and interesting results indicate that the whole area warrants further research.

Oviductal Oxygen Homeostasis in Patients with Uterine Myoma: Correlation between Hypoxia and Telocytes

Oxygen balance is crucial for angiogenesis, immunity, and tissue repair. The human oviduct is essential for reproductive function, and any imbalance in homeostasis leads to fertility disturbances and might be a reason for ectopic pregnancy development. Uterine myoma is a widespread benign tumour, which is often accompanied by infertility. Telocytes have been discussed in the contexts of motility, fibrosis development, and angiogenesis. We observed the oviducts from patients with and without uterine myoma, comparing the expression of HIF-1, HO, VEGF and its receptor, NOS, oestrogen, and progesterone receptors by immunolabeling. The myometrial and oviductal telocytes were also compared in both groups. Biochemical analyses were conducted for FSH, LH, AMH, sFlt, oestrogen, and progesterone in blood samples. Patients with uterine myoma have different expressions of sex steroid receptors and an increased number of telocytes. The decreasing VEFG expression was compensated by the rise in the HIF-1 and NOS expression. Blood biochemical analyses revealed a higher progesterone level and lower AMH in patients with uterine myoma. No differences in sFlt, FSH, and LF were observed. Uterine myoma impacts oviduct oxygen homeostasis and might cause fertility disturbances (uterine and oviductal infertility factors).

Neutrophil depletion reduces interstitial cajal-like cell injury and alleviates inflammation-induced motor dysfunction in guinea-pig gallbladder during acute cholecystitis

Objectives

Gallbladder interstitial Cajal-like cells (ICLCs) are known as some of the players in the complex motility mechanisms affecting gallbladder motility. This study aims to explore the mechanism of guinea-pig gallbladder motility disorders during Acute Cholecystitis (AC), focusing on the relationships between neutrophil alterations, gallbladder ICLCs, and smooth muscle contractility.

Materials and Methods

Forty-eight guinea pigs were randomly divided into four groups: normal, sham, common bile duct ligation (CBDL), and anti-PMN (anti-polymorphonuclear antibody treated +CBDL). Hematoxylin and eosin-stained slides from each gallbladder sample were examined for inflammation, and myeloperoxidase (MPO) activity was evaluated. The contractile response of gallbladder muscle to Ach, CCK-8, and KCl was registered by a tension transducer, and ultrastructure features of ICLCs were observed.

Results

Pretreatment with anti-PMN significantly reduced the circulating neutrophils by 80% and also considerably decreased the gallbladder MPO activity by 52.9% compared with the CBDL group (P<0.05). After adding Ach, CCK-8, and KCl, the contraction ability in CBDL and anti-PMN groups was lower than those of normal and sham groups (P<0.05), and they were increased substantially in the anti-PMN group compared with the CBDL group (P<0.05). Transmission electron microscopy confirmed that the cytoplasm of the neutrophils was full of granules, and neutrophils contacted closely with ICLCs. The ultrastructure of ICLCs in the anti-PMN group was less inflamed and the endoplasmic reticulum was mildly dilated, and cell processes also increased.

Conclusion

Anti-PMN could relieve the ultrastructure injury of ICLCs and alleviate gallbladder dysmotility during AC. Neutrophils may damage gallbladder ICLCs at first followed by dysmotility.

Telocytes and Their Structural Relationships With the Sperm Storage Tube and Surrounding Cell Types in the Utero-Vaginal Junction of the Chicken

Telocytes (TCs) are a new type of mesenchymal cells that have been discovered recently in many organs and tissues. However, studies of TCs in the avian reproductive system are still at the beginning. Chickens are one of the world's most popular domesticated animals, providing inexpensive but valuable proteins and nutrients from chickens and eggs to nourish the human bodies. Chickens have important scientific value; thus, understanding the reproductive system regulations seems to be important. The utero-vaginal junction is involved in the regulation of sperm storage. The sperm storage tube (SST) in the utero-vaginal junction stores sperm. The purpose of this study was to investigate the existence of TCs in the utero-vaginal junction of the chicken, and their structural relationships with the sperm storage tube and surrounding cell types. We studied the morphology, ultrastructure, and immune characterization of TCs.

Identification of PDGFRα+ cells in uterine fibroids - link between angiogenesis and uterine telocytes

INTRODUCTION

Telocytes (TCs), also called interstitial Cajal-like cells (ICLC), CD34+ cells or PDGFRα+ cells (platelet-derived growth factor receptor α positive cells), a new type of cell of mesenchymal origin, were described over one decade ago. The unique nature of these cells still deserves attention from the scientific community. Telocytes make homo- and heterocellular contact with myocytes, immunocytes and nerves, have their own immunohistochemical and secretome profiles and thus might regulate local regenerative processes including angiogenesis and fibrosis. The aim of our study was to observe the missing link between angiogenesis and telocytes in leiomyoma, the most common benign tumors affecting women of reproductive age.

MATERIAL AND METHODS

We observed uterine tissue samples from leiomyoma, adjacent myometrium and unchanged tissue from patients with leiomyoma and control subjects using routine histology, histochemistry, immunofluorescence (CD117, CD31, CD34, PDGFRα, tryptase, sFlt-1) and image analysis methods.

RESULTS

The decline of the telocyte density in the foci of fibroids correlated with poor vascularization inside the leiomyoma. Moreover, the expression of sFlt-1 (anti-angiogenic-related factor) significantly increased inside a fibroid. In leiomyoma the decrease of telocyte and blood micro-vessel density was accompanied by prevalence of collagen deposits, unlike the unchanged myometrium.

CONCLUSIONS

Our results demonstrate TCs in human uterine fibroids and highlight their possible involvement in the pathogenesis of myometrial pathology in the context of angiogenesis.

Telocytes in Fibrosis Diseases: From Current Findings to Future Clinical Perspectives

Telocytes (TCs), a distinct type of interstitial (stromal) cells, have been discovered in many organs of human and mammal animals. TCs, which have unique morphological characteristics and abundant paracrine substance, construct a three-dimensional (3D) interstitial network within the stromal compartment by homocellular and heterocellular communications which are important for tissue homeostasis and normal development. Fibrosis-related diseases remain a common but challenging problem in the field of medicine with unclear pathogenesis and limited therapeutic options. Recently, increasing evidences suggest that where TCs are morphologically or numerically destructed, many diseases continuously develop, finally lead to irreversible interstitial fibrosis. It is not difficult to find that TCs are associated with chronic inflammation and fibrosis. This review mainly discusses relationship between TCs and the occurrence of fibrosis in various diseases. We analyzed in detail the potential roles and speculated mechanisms of TCs in onset and progression of systemic fibrosis diseases, as well as providing the most up-to-date research on the current therapeutic roles of TCs and involved related pathways. Only through continuous research and exploration in the future can we uncover its magic veil and provide strategies for treatment of fibrosis-related disease.

Telocytes in the Tumor Microenvironment

There are several theories explaining the communication between cells in the context of tumor development. Over the years, interactions between normal and transformed cells have been observed. Generally, all types of cells make equal contributions to the formation of the tumor microenvironment - a location of primary oncogenesis. To date, several studies have reported the role of telocytes in cancer development, and many publications have emphasized the direct and indirect involvement of telocytes in angiogenesis; signaling through the secretion of extracellular vesicles, growth factors, and bioactive molecules; fibrosis development and extracellular matrix production; tissue repair and regeneration; and immune responses. Considering the main components of the tumor microenvironment, we will discuss the features of telocytes and their possible involvement in local tissue homeostasis.

Oviductal Telocytes in Patients with Uterine Myoma

Tubal factor infertility occurs in 30–35% of infertile pairs and may be caused by impaired muscular contractility and ciliary beating as well as immunological imbalance and chronic inflammation. Newly discovered telocytes (TCs) have a wide palette of features, which play a role in oviduct physiology. We have observed tissue samples from human fallopian tubes in patients with and without uterine myoma by immunolabelling. According to the immunohistochemical co-expression of markers, it has been determined that TCs are engaged in a wide range of physiological processes, including local innervation, sensitivity to hypoxia, regulation of calcium, and sex steroid hormones balances. Due to the proximity of NOS- and ChAT-positive nerve fibers and the expression of ion channels markers, tubal TCs might be considered conductor cells. Additionally, their integration in contractions and cilia physiology in the context of fertility has been revealed. We have observed the difference in telocytes expression in the human oviduct between groups of patients and attempted to describe this population of cells specifically in the case of infertility development, a clinically relevant avenue for further studies.

Endometriosis and the Fallopian Tubes: Theories of Origin and Clinical Implications

Endometriosis is a common, oestrogen driven chronic condition, where endometrium-like epithelial and stromal cells exist in ectopic sites. At present, no curative treatments are available and the existing evidence for disease progression is conflicting. The pathogenesis is still unknown and evidently complex, as mechanisms of initiation may depend on the anatomical distribution of endometriotic lesions. However, amongst the numerous theories and plethora of mechanisms, contributions of the fallopian tubes (FT) to endometriosis are rarely discussed. The FT are implicated in all endometriosis associated symptomatology and clinical consequences; they may contribute to the origin of endometriotic tissue, determine the sites for ectopic lesion establishment and act as conduits for the spread of proinflammatory media. Here, we examine the available evidence for the contribution of the human FT to the origin, pathogenesis and symptoms/clinical consequences of endometriosis. We also examine the broader topic linking endometriosis and the FT epithelium to the genesis of ovarian epithelial cancers. Further studies elucidating the distinct functional and phenotypical characteristics of FT mucosa may allow the development of novel treatment strategies for endometriosis that are potentially curative.

Cyclooxygenase-2 in Endometriosis

Endometriosis (EMS) is the most common gynecological disease in women of reproductive age, and it is associated with chronic pelvic pain, dyspareunia and infertility. As a consequence of genetic, immune and environmental factors, endometriotic lesions have high cyclooxygenase (COX)-2 and COX-2-derived prostaglandin E₂ (PGE₂) biosynthesis compared with the normal endometrium. The transcription of the PTGS2 gene for COX-2 is associated with multiple intracellular signals, which converge to cause the activation of mitogen-activated protein kinases (MAPKs). COX-2 expression can be regulated by several factors, such as estrogen, hypoxia, proinflammatory cytokines, environmental pollutants, metabolites and metabolic enzymes, and platelets. High concentrations of COX-2 lead to high cell proliferation, a low level of apoptosis, high invasion, angiogenesis, EMS-related pain and infertility. COX-2-derived PGE₂ performs a crucial function in EMS development by binding to EP2 and EP4 receptors. These basic findings have contributed to COX-2-targeted treatment in EMS, including COX-2 inhibitors, hormone drugs and glycyrrhizin. In this review, we summarize the most recent basic research in detail and provide a short summary of COX-2-targeted treatment.

Morphological changes of telocytes in camel efferent ductules in response to seasonal variations during the reproductive cycle

Telocytes (TCs) are a distinct stromal cell type described in many organs. The present study investigated the existence of TCs within the efferent ductules in camel and the changes that occur in their morphology and activity during active and inactive reproductive seasons. TCs in the camel had a cell body and multiple telopodes (TPs), and most TCs had indented nuclei that exhibited prominent intranucleolar chromatin. TCs exhibited seasonal differences which were evaluated by histochemistry, immunohistochemistry (IHC), Transimition electron microscopy (TEM) and scanning electron microscopy (SEM). The presence of TCs in camel efferent ductules has been confirmed by CD34 positive immunostaing. In addition to the expression of the vascular endothelial growth factor (VEGF) which was stronger in the summer season. TCs exhibited stronger immunoreactivity for progesterone and oestrogen alpha receptors (ESR1) in the spring than in the summer. In addition, TCs showed strong positive immunostaining for both vimentin and androgen receptor (AR). Several ultrastructural changes were observed in TCs during the two seasons. TPs in the summer season had delicate ramifications whereas, in the spring, TPs displayed fine arborization and became more corrugated. TCs acquired signs of exaggerated secretory activities in the spring; TPs became expanded and packed with secretory vesicles. Thus, we conclude that, hormonal alterations during the reproductive cycle impact the morphology and secretory behavior of TCs.

Recently Discovered Interstitial Cell Population of Telocytes: Distinguishing Facts from Fiction Regarding Their Role in the Pathogenesis of Diverse Diseases Called "Telocytopathies"

In recent years, the interstitial cells telocytes, formerly known as interstitial Cajal-like cells, have been described in almost all organs of the human body. Although telocytes were previously thought to be localized predominantly in the organs of the digestive system, as of 2018 they have also been described in the lymphoid tissue, skin, respiratory system, urinary system, meninges and the organs of the male and female genital tracts. Since the time of eminent German pathologist Rudolf Virchow, we have known that many pathological processes originate directly from cellular changes. Even though telocytes are not widely accepted by all scientists as an individual and morphologically and functionally distinct cell population, several articles regarding telocytes have already been published in such prestigious journals as Nature and Annals of the New York Academy of Sciences. The telocyte diversity extends beyond their morphology and functions, as they have a potential role in the etiopathogenesis of different diseases. The most commonly described telocyte-associated diseases (which may be best termed "telocytopathies" in the future) are summarized in this critical review. It is difficult to imagine that a single cell population could be involved in the pathogenesis of such a wide spectrum of pathological conditions as extragastrointestinal stromal tumors ("telocytomas"), liver fibrosis, preeclampsia during pregnancy, tubal infertility, heart failure and psoriasis. In any case, future functional studies of telocytes in vivo will help to understand the mechanism by which telocytes contribute to tissue homeostasis in health and disease.

Telocytes enhanced the proliferation, adhesion and motility of endometrial stromal cells as mediated by the ERK pathway in vitro

Telocytes (TCs) is special interstitial cell that have recently been identified in the female reproductive system. Endometriosis (EMs) is a benign gynecological disease whose etiology is still not fully clear. Implantation and proliferation of endometrial stromal cells (ESCs) out of the uterus are essential processes in the development of EMs. Herein, we investigate the in vitro changes of ESCs when cocultured with TCs, and the potential mechanisms involved. The current results demonstrated that, vimentin-positive/pan cytokeratin-negative ESCs, and TCs with a characteristic structure and immunophenotype (CD34/vimentin double-positive) were successfully isolated and harvested. Morphologically, direct cell-to-cell contacts were observed between TCs and ESCs. Quantitatively, TCs treatment clearly promotes the viability of ESCs, enhances cell cycle progression at G2/M phase and upregulates p-ERK1/2 and cyclin-D3 (all P < 0.05). Functionally, ESCs educated by TCs displayed significantly enhanced adhesion ability and accelerated invasion and migration capacity (all P < 0.05). However, no significant changes were found in the rate of apoptosis and in the expression of AKT signaling pathway proteins in TCs-educated ESCs (both P > 0.05). Therefore, TCs treatment obviously enhanced the in vitro motile and invasive capacity of ESCs, which were mediated by the ERK-cyclin-D3 signaling pathway, likely through direct intercellular contacts and/or juxta-paracrine effects; signaling through this axis therefore increased the likelihood of EMs. The enhanced functions of TCs-educated ESCs not only contribute to a deeper understanding of TCs, but also highlight a new concept regarding the physiopathology and therapy of EMs and associated impaired reproductive function.

Immunophenotypic characterization of telocyte-like cells in pterygium

Purpose

Telocytes (TCs) are peculiar interstitial cells, characterized by their typical elongated and interconnected processes called telopodes. TCs are supposed to contribute to maintain tissue homeostasis but also to be involved in the pathophysiology of many disorders. The aim of the study was to identify TCs in pterygium, a chronic condition of bulbar conjunctiva, and to examine possible differences in TCs in terms of immunophenotype and/or localization between pterygium and normal conjunctiva, to evaluate the possible involvement of TCs in pathogenesis of pterygium.

Methods

The analysis of the immunophenotype of TCs was performed on a group of 40 formalin-fixed and paraffin-embedded primary pterygium and ten bulbar conjunctiva samples. We examined with immunohistochemistry the expression of 11 commercially available antibodies (PDGFRα, CD34, c-kit, nestin, vimentin, α-SMA, laminin, S100, VEGF, CD133, and CD31) and with double immunofluorescence the concomitant expression of PDGFRα and CD34, and PDGFRα and nestin. In addition, we performed an ultrastructural study with transmission electron microscopy (TEM) on a group of five pterygium and three conjunctiva biopsy specimens.

Results

TCs, ultrastructurally identified according to their "moniliform" prolongations, were localized underneath the epithelium along the basement membrane, around the vessels, and near the nerves and scattered in the stroma. In contrast, TCs, as fibroblasts, were almost absent in the fibrotic areas. In pterygium and normal conjunctiva, the TCs shared the same distribution pattern, except a marked TC hyperplasia detected in pterygium. Moreover, in pterygium, the immunohistochemical analysis of TCs showed a strong immunoreactivity to PDGFRα, CD34, and nestin. This result was confirmed with double immunofluorescence labeling, revealing that in pterygium stromal TCs always showed a PDGFRα+/nestin+ and PDGFRα+/CD34+ immunophenotype. Furthermore, moderate staining to vimentin and VEGF was detected, but only a small number of cells were weakly immunoreactive to laminin and S100. Only adventitial TCs of the perivascular sheaths exhibited strong immunoreactivity to α-SMA. Conversely, despite showing mild immunoreactivity to PDGFRα and CD34, the TCs in normal conjunctiva did not show any immunoreactivity to nestin and VEGF. Moreover, in pterygium and conjunctiva, the TCs were always negative for c-kit.

Conclusions

Because of the distribution and immunophenotype, TCs in pterygium may represent a subpopulation of relatively immature cells with regenerative potential. In addition, the expression of nestin may suggest possible involvement of TCs as active players in the regeneration of ultraviolet-damaged stroma and vascular remodeling. The fibrotic transformation in the cicatricial area may stand for a breakdown of the regenerative process.

Neutrophils injure gallbladder interstitial Cajal-like cells in a guinea pig model of acute cholecystitis

Acute cholecystitis is a common disease with gallbladder dysmotility. Disease pathogenesis involves immune cell infiltration as well as changes in gallbladder interstitial Cajal-like cells (ICLCs). However, it remains unclear if or how the immune cells affect ICLC morphology, density, distribution, and function in gallbladder tissue during acute cholecystitis. In this study, we explored the acute cholecystitis-related alterations in gallbladder ICLCs in a guinea pig model, focusing on the effects of neighboring neutrophils. Adult guinea pigs were randomly divided into four groups (control, 24 hr common bile duct ligation [CBDL], 48-hr CBDL, and antipolymorphonuclear neutrophil [PMN] treated) and analyzed using methylene blue staining and immunofluorescence. Gallbladder contractility was also monitored. To culture gallbladder ICLCs, collagenase digestion was performed on tissue from 10- to 15-day-old guinea pigs. Neutrophils isolated from the peripheral blood of experimental animals 48-hr postsurgery were also cocultured with the gallbladder ICLCs. Intracellular calcium was detected with Fluo-4 AM dye. Our results showed that gallbladder ICLC density significantly declined during acute cholecystitis and was accompanied by shortening of the cellular processes and damage to their network-like structure. However, pretreatment with anti-PMN partially prevented these changes. Gallbladder contraction was also significantly decreased during acute cholecystitis, and this appeared to be mediated by the neutrophils. Moreover, ICLCs cocultured with neutrophils also had shortened and reduced processes and impaired network-like structure formation. Intracellular calcium transient was less sensitive to contraction agonists and inhibitors when cocultured with neutrophils. Taken together, neutrophils greatly affect gallbladder ICLCs and dysmotility during acute cholecystitis.

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.

Endometriosis Malignant Transformation: Epigenetics as a Probable Mechanism in Ovarian Tumorigenesis

Endometriosis, defined as the presence of ectopic endometrial glands and stroma outside the uterine cavity, is a chronic, hormone-dependent gynecologic disease affecting millions of women across the world, with symptoms including chronic pelvic pain, dysmenorrhea, dyspareunia, dysuria, and subfertility. In addition, there is well-established evidence that, although endometriosis is considered benign, it is associated with an increased risk of malignant transformation, with the involvement of various mechanisms of development. More and more evidence reveals an important contribution of epigenetic modification not only in endometriosis but also in mechanisms of endometriosis malignant transformation, including DNA methylation and demethylation, histone modifications, and miRNA aberrant expressions. In this present review, we mainly summarize the research progress about the current knowledge regarding the epigenetic modifications of the relations between endometriosis malignant transformation and ovarian cancer in an effort to identify some risk factors probably associated with ectopic endometrium transformation.

Telocytes: New Players in Gallstone Disease

Cholesterol gallstone disease is highly prevalent in Western countries, particularly in women and some specific ethnic groups. The mechanisms behind the formation of gallstones are not clearly understood, but gallbladder dysmotility seems to be a key factor that triggers the precipitation of cholesterol microcrystals from supersaturated lithogenic bile.Given that newly described interstitial cells, telocytes, are present in the gallbladder and they are located in close vicinity of smooth muscle cell and neural fibers possibly interfering with gallbladder motility or contractility, authors are trying to summarize the current knowledge on the role of telocytes with respect to disturbed gallbladder function in gallstone disease.

Transmission electron microscope evidence of telocytes in canine dura mater

Telocytes (TCs) are a novel type of interstitial cells present in a wide variety of organs and tissues (www.telocytes.com). Telocytes are identified morphologically by a small cell body and specific long prolongations (telopodes) alternating thin segments (podomers) with dilations (podoms). The presence of TCs in rat meninges has been identified in previous research. We here present further evidence that TCs existed in canine dura mater, closed to capillary and surrounded by a great deal of collagen fibres under transmission electron microscope.

Telocytes heterogeneity: From cellular morphology to functional evidence

Telocytes (TCs), located ubiquitously in the internal organs of vertebrates, are a heterogeneous, recently described, cell population of the stromal space. Characterized by lengthy cytoplasmic extensions that can reach tens of microns and are called telopodes (Tps), TCs are difficult to see using conventional microscopes. It was the electron microscopy which led to their first identification and Popescu's team the first responsible for the reconstructions indicating TCs 'organization' in a three-dimensional (3D) network that is believed to be accountable for the complex roles of TCs. Gradually, it became increasingly evident that TCs are difficult to characterize in terms of immunophenotype and that their phenotype is different depending on the location and needs of the tissue at one time. This review discusses the growing body of evidence accumulated since TCs were discovered and highlights how the complex interplay between TCs and stem cells might be of importance for tissue engineering and regenerative medicine.

Telocytes as potential targets in a cyclophosphamide-induced animal model of premature ovarian failure

Premature ovarian failure (POF) refers to the presence of ovarian atrophic permanent amenorrhea in women under the age of 40. The pathogenesis of POF remains to be fully elucidated. Telocytes are a group of specialized cells with a small cell volume and very long cytoplasmic prolongations with dichotomous branching. Previous studies have indicated that telocytes function to support the trachea and serve as stem cell niches. Although it has been confirmed that telocytes are present in numerous organs in mammals, it remains to be determined whether they are present in ovarian tissues and whether they are involved in the development of POF. The present study used a cyclophosphamide-induced mouse model of POF. Hematoxylin and eosin staining and an enzyme-linked immunosorbent assay revealed that cyclophosphamide induced edema and apoptosis of ovarian stromal and granulosa cells and increased atretic follicles. In addition, cyclophosphamide induced abnormal peripheral blood FSH and E2 levels in mice. Transmission electron microscopy revealed a small number of telocyte-like cell structures in the ovarian stroma of wild-type mice. In addition, flow cytometry and immunohistochemical staining results suggested that the number of cluster of differentiation (CD)34/platelet-derived growth factor receptor (PDGFR)α, CD34/PDGFRβ and CD34/vimentin double-positive cells in the ovaries of POF mice was significantly decreased compared with wild-type mice. In conclusion, mouse ovarian tissues appear to contain telocytes, and cyclophosphamide treatment significantly reduced the number of ovarian telocytes. Therefore, telocytes may serve as a potential novel marker of POF induced by cyclophosphamide.

Ultrastructural and immunohistochemical characteristics of telocytes in the skin and skeletal muscle of newborn rats

Telocytes (TCs) are newly described interstitial cells that might play a role in normal and pathological conditions. The aim of this study was designed to investigate its existence in the skin and skeletal muscle of one day old newborn rats and to study their ultrastructure and immunohistochemical characteristics. Ten rats (one day old newborn) were used in this study. Dorsal skin and femoral skeletal muscle samples were obtained and examined by CD117, CD34, semi-thin and ultrathin sections examination. Semi-thin sections examination revealed multiple spindle shape cells with cytoplasmic extension in the skin and in between muscle fibers. Telocytes showed positive reaction for both CD117 and CD34 immunostains. By electron microscopy these cells were spindle shaped with small cell bodies and long processes. Telocytes showed homo-cellular junctions between two adjacent telocytes and hetero-cellular junctions between telocytes and other cellular and non-cellular structures. Multiple vesicles were seen either intra-cellular or budding from the cell membrane or detached from the telocytes leaving caveolae. It could be concluded that telocytes are present in the skin and skeletal muscle of one day old newborn rats. They might play a role in pathologies and regenerative medicine due to their ability to release vesicles.

The functional morphology and role of cardiac telocytes in myocardium regeneration

Key morphological discoveries in recent years have included the discovery of new cell populations inside the heart called cardiac telocytes. These newly described cells of the connective tissue have extremely long cytoplasmic processes through which they form functionally connected three-dimensional networks that connect cells of the immune system, nerve fibers, cardiac stem cells, and cardiac muscle cells. Based on their functions, telocytes are also referred to as "connecting cells" or "nurse cells" for cardiac progenitor stem cells. In this critical review, we provide a summary of the latest research on cardiac telocytes localized in all layers of the heart - from the historical background of their discovery, through ultrastructural, immunohistochemical, and functional characterizations, to the application of this knowledge to the fields of cardiology, stem cell research, and regenerative medicine.

Telocytes in female reproductive system (human and animal)

Telocytes (TCs) are a newly discovered type of cell with numerous functions. They have been found in a large variety of organs: heart (endo‐, myo‐, epi‐ and pericardium, myocardial sleeves, heart valves); digestive tract and annex glands (oesophagus, stomach, duodenum, jejunum, liver, gallbladder, salivary gland, exocrine pancreas); respiratory system (trachea and lungs); urinary system (kidney, renal pelvis, ureters, bladder, urethra); female reproductive system (uterus, Fallopian tube, placenta, mammary gland); vasculature (blood vessels, thoracic duct); serous membranes (mesentery and pleura); and other organs (skeletal muscle, meninges and choroid plexus, neuromuscular spindles, fascia lata, skin, eye, prostate, bone marrow). Likewise, TCs are widely distributed in vertebrates (fish, reptiles, birds, mammals, including human). This review summarizes particular features of TCs in the female reproductive system, emphasizing their involvement in physiological and pathophysiological processes.

Telocyte implications in human pathology: An overview

Telocytes are a recently described interstitial cell population widely distributed in the stromal compartment of many organs in vertebrates, including humans. Owing to their close spatial relationship with multiple cell types, telocytes are universally considered as 'connecting cells' mostly committed to intercellular signaling by converting the interstitium into an integrated system that drives organ development and contributes to the maintenance of local tissue homeostasis. Increasing evidence indicates that telocytes may cooperate with tissue-resident stem cells to foster organ repair and regeneration, and that telocyte damage and dysfunction may occur in several disorders. The goal of this review is to provide an overview of the most recent findings concerning the implication of telocytes in a variety of pathologic conditions in humans, including heart disease, chronic inflammation and multiorgan fibrosis. Based on recent promising experimental data, there is realistic hope that by targeting telocytes alone or in tandem with stem cells, we might be able to promote organ regeneration and/or prevent irreversible end-stage organ damage in different pathologies.

The potential role of telocytes in Tissue Engineering and Regenerative Medicine

Research and ideas for potential applications in the field of Tissue Engineering (TE) and Regenerative Medicine (RM) have been constantly increasing over recent years, basically driven by the fundamental human dream of repairing and regenerating lost tissue and organ functions. The basic idea of TE is to combine cells with putative stem cell properties with extracellular matrix components, growth factors and supporting matrices to achieve independently growing tissue. As a side effect, in the past years, more insights have been gained into cell-cell interaction and how to manipulate cell behavior. However, to date the ideal cell source has still to be found. Apart from commonly known various stem cell sources, telocytes (TC) have recently attracted increasing attention because they might play a potential role for TE and RM. It becomes increasingly evident that TC provide a regenerative potential and act in cellular communication through their network-forming telopodes. While TE in vitro experiments can be the first step, the key for elucidating their regenerative role will be the investigation of the interaction of TC with the surrounding tissue. For later clinical applications further steps have to include an upscaling process of vascularization of engineered tissue. Arteriovenous loop models to vascularize such constructs provide an ideal platform for preclinical testing of future therapeutic concepts in RM. The following review article should give an overview of what is known so far about the potential role of TC in TE and RM.

Immunohistochemistry of Telocytes in the Uterus and Fallopian Tubes

The seminal work of Popescu and colleagues first demonstrated the existence of a new cell type - the telocytes. We were among the first who reported the presence of such cells in the female genital tract and performed TEM examinations, as well as immunohistochemical staining in the attempt to find a specific marker. Telocytes from rat and from the human uterus and from human fallopian tube were extensively investigated initially by comparison with interstitial cells of Cajal. Progress in telocyte research led to the identification of different subtypes suggestive for a heterogeneous telocyte population which can even coexist in the same location. As a consequence, the functions of TCs are still elusive and can be considered a versatile phenomenon that depends on a variety of conditions, including signal reception and transmission of information via extracellular vesicles or by direct intercellular contact.

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.

Telocytes in Inflammatory Gynaecologic Diseases and Infertility

Women suffered with inflammatory gynecologic diseases, such as endometriosis (EMs) and acute salpingitis (AS) often complained of sub- or infertility, even in those women without obvious macroscopic anatomical pelvic abnormalities also have unexplained infertility. Generally, besides the well-known impairment of classically described oviduct cells caused by inflammatory diseases, such as the ciliated cells, fibroblasts and myofibroblasts, the involvement of the newly identified telocytes (TCs) in disease-affected oviduct tissues and potential pathophysiological roles in fertility problems remain unknown. In this chapter, TCs was investigated in rat model of EMs- and AS-affected oviduct tissues. Results showed inflammation and ischaemia-induced extensive ultrastructural damages of TCs both in cellular body and prolongations, with obvious TCs loss and interstitial fibrotic remodelling. Such in vivo pathological alterations might contribute to structural and functional abnormalities of oviduct tissue and potentially engaged in sub- or infertility. And especially, TCs connected to various activated immunocytes in both normal and diseased tissues, thus might participate in local immunoregulation (either repression or activation) and serve a possible explanation for immune-mediated pregnancy failure. Then, in vitro cell co-culture study showed that uterine TC conditioned media (TCM) can activate mouse peritoneal macrophages and subsequently trigger its cytokine secretion, thus providepreliminary evidence that, TCs are not simply innocent bystanders, but are instead potential functional players in local immunoregulatory and immunosurveillance.

Comparison of Chromosome 4 gene expression profile between lung telocytes and other local cell types

Telocytes (TCs) are new cellular entities of mesenchymal origin described almost ubiquitously in human and mammalian organs (www.telocytes.com). Different subtypes of TCs were described, all forming networks in the interstitial space by homo- and heterocellular junctions. Previous studies analysed the gene expression profiles of chromosomes 1, 2, 3, 17 and 18 of murine pulmonary TCs. In this study, we analysed by bioinformatics tools the gene expression profiles of chromosome 4 for murine pulmonary TCs and compared it with mesenchymal stem cells (MSCs), fibroblasts (Fbs), alveolar type II cells (ATII), airway basal cells, proximal airway cells, CD8(+) T cells from bronchial lymph nodes (T-BL) and CD8(+) T cells from lungs (T-L). Key functional genes were identified with the aid of the reference library of the National Center for Biotechnology Information Gene Expression Omnibus database. Seventeen genes were up-regulated and 56 genes were down-regulated in chromosome 4 of TCs compared with other cells. Four genes (Akap2, Gpr153, Sdc3 and Tbc1d2) were up-regulated between one and fourfold and one gene, Svep1, was overexpressed over fourfold. The main functional networks were identified and analysed, pointing out to a TCs involvement in cellular signalling, regulation of tissue inflammation and cell expansion and movement.

In vitro morphology, viability and cytokine secretion of uterine telocyte-activated mouse peritoneal macrophages

Telocytes (TCs), a distinct interstitial cell population, have been identified in the uterus, oviduct and placenta, with multiple proposed potential biological functions. Their unique structure allows them to form intercellular junctions with various immunocytes, both in normal and diseased tissues, suggesting a potential functional relationship with the local immune response. It has been hypothesized that through direct heterocellular junctions or indirect paracrine effects, TCs influence the activity of local immunocytes that are involved in the inflammatory process and in immune-mediated reproductive abnormalities. However, no reliable cytological evidence for this hypothesis is currently available. In this study, we cultured primary murine uterine TCs and collected TC conditioned media (TCM). Mouse peritoneal macrophages (pMACs) were co-cultured for 48 hrs with TCM or with DMEM/F12 or lipopolysaccharide (LPS) as negative and positive controls, respectively. Normal uterine TCs with a typical structure and a CD-34-positive/vimentin-positive/c-kit-negative immunophenotype were observed during culture. Morphologically, TCM-treated pMACs displayed an obvious activation/immunoresponse, in contrast to over-stimulation and cell death after LPS treatment and no sign of activation in the presence of DMEM/F12. Accordingly, a cell counting kit 8 (CCK-8) assay indicated significant activation of pMACs by TCM and LPS compared to DMEM/F12, thus supporting the marked morphological differences among these groups of cells. Furthermore, within a panel of macrophage-derived cytokines/enzymes, interleukin-6 (IL-6) and inducible nitric oxide synthase were significantly elevated in TCM-treated pMACs; tumour necrosis factor α, IL1-R1, and IL-10 were slightly, but significantly, up-regulated; and no changes were observed for transforming growth factor-β1, IL-1β, IL-23α and IL-18. Our results indicate that TCs are not simply innocent bystanders but are rather functional players in the activation of pMACs; they trigger and maintain the immune response, likely through indirect paracrine effects. Thus, we provide preliminary in vitro evidence of immunoregulatory and immunosurveillance roles for TCs.

Skin telocytes versus fibroblasts: two distinct dermal cell populations

It is already accepted that telocytes (TCs) represent a new type of interstitial cells in human dermis. In normal skin, TCs have particular spatial relations with different dermal structures such as blood vessels, hair follicles, arrector pili muscles or segments of sebaceous and/or eccrine sweat glands. The distribution and the density of TCs is affected in various skin pathological conditions. Previous studies mentioned the particular (ultra)structure of TCs and also their immunophenotype, miR imprint or proteome, genome or secretome features. As fibroblast is the most common intersitital cell (also in human dermis), a dedicated comparison between human skin TCs and fibroblasts (Fbs) was required to be performed. In this study, using different techniques, we document several points of difference between human dermis TCs and Fbs. By transmission electron microscopy (TEM) and scanning electron microscopy (SEM), we demonstrated TCs with their hallmark cellular prolongations - telopodes. Thus, we showed their ultrastructural distinctiveness from Fbs. By RayBio Human Cytokine Antibody Array V analyses performed on the supernatant from separately cultured TCs and Fbs, we detected the cytokine profile of both cell types, individually. Two of 79 detected cytokines - epithelial-derived neutrophil-activating peptide 78 and granulocyte chemotactic protein-2 - were 1.5 times higher in the supernatant of TCs (comparing with Fbs). On the other hand, 37 cytokines were at least 1.5 higher in Fbs supernatant (comparing with TCs), and among them six cytokines - interleukin 5, monocyte chemotactic protein-3 (MCP-3), MCP-4, macrophage inflammatory protein-3, angiogenin, thrombopoietin - being 9.5 times higher (results also confirmed by ELISA testing). In summary, using different techniques, we showed that human dermal TCs and Fbs are different in terms of ultrastructure and cytokine profile.

The failing human heart is characterized by decreased numbers of telocytes as result of apoptosis and altered extracellular matrix composition

Telocytes (TCs) are a novel type of interstitial cells only recently described. This study aimed at characterizing and quantifying TCs and telopodes (Tps) in normal and diseased hearts. We have been suggested that TCs are influenced by the extracellular matrix (ECM) composition. We used transmission electron microscopy and c-kit immunolabelling to identify and quantify TCs in explanted human hearts with heart failure (HF) because of dilated, ischemic or inflammatory cardiomyopathy. LV myectomy samples from patients with aortic stenosis with preserved ejection fraction and samples from donor hearts which could not be used for transplantation served as controls. Quantitative immunoconfocal analysis revealed that 1 mm² of the normal myocardium contains 14.9 ± 3.4 TCs and 41.6 ± 5.9 Tps. As compared with the control group, the number of TCs and Tps in HF decreased more than twofold. There were no differences between HF and control in the number of Ki67-positive TCs. In contrast, terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling-positive TCs increased threefold in diseased hearts as compared to control. Significant inverse correlations were found between the amount of mature fibrillar collagen type I and the number of TCs (r = −0.84; P < 0.01) and Tps (r = −0.85; P < 0.01). The levels of degraded collagens showed a significant positive relationship with the TCs numbers. It is concluded that in HF the number of TCs are decreased because of higher rates of TCs apoptosis. Moreover, our results indicate that a close relationship exists between TCs and the ECM protein composition such that the number of TCs and Tps correlates negatively with the amount of mature fibrillar collagens and correlates positively with degraded collagens.

Telocytes in regenerative medicine

Telocytes (TCs) are a distinct type of interstitial cells characterized by a small cell body and extremely long and thin telopodes (Tps). The presence of TCs has been documented in many tissues and organs (go to http://www.telocytes.com). Functionally, TCs form a three-dimensional (3D) interstitial network by homocellular and heterocellular communication and are involved in the maintenance of tissue homeostasis. As important interstitial cells to guide or nurse putative stem and progenitor cells in stem cell niches in a spectrum of tissues and organs, TCs contribute to tissue repair and regeneration. This review focuses on the latest progresses regarding TCs in the repair and regeneration of different tissues and organs, including heart, lung, skeletal muscle, skin, meninges and choroid plexus, eye, liver, uterus and urinary system. By targeting TCs alone or in tandem with stem cells, we might promote regeneration and prevent the evolution to irreversible tissue damage. Exploring pharmacological or non-pharmacological methods to enhance the growth of TCs would be a novel therapeutic strategy besides exogenous transplantation for many diseased disorders.

Cardiac telocytes are double positive for CD34/PDGFR-α

Telocytes (TCs) are a distinct type of interstitial cells, which are featured with a small cellular body and long and thin elongations called telopodes (Tps). TCs have been widely identified in lots of tissues and organs including heart. Double staining for CD34/PDGFR-β (Platelet-derived growth factor receptor β) or CD34/Vimentin is considered to be critical for TC phenotyping. It has recently been proposed that CD34/PDGFR-α (Platelet-derived growth factor receptor α) is actually a specific marker for TCs including cardiac TCs although the direct evidence is still lacking. Here, we showed that cardiac TCs were double positive for CD34/PDGFR-α in primary culture. CD34/PDGFR-α positive cells (putative cardiac TCs) also existed in mice ventricle and human cardiac valves including mitral valve, tricuspid valve and aortic valve. Over 87% of cells in a TC-enriched culture of rat cardiac interstitial cells were positive for PDGFR-α, while CD34/PDGFR-α double positive cells accounted for 30.25% of the whole cell population. We show that cardiac TCs are double positive for CD34/PDGFR-α. Better understanding of the immunocytochemical phenotypes of cardiac TCs might help using cardiac TCs as a novel source in cardiac repair.