Telocytes in pleura: two- and three-dimensional imaging by transmission electron microscopy

Telocytes in the Luminal GI Tract

Telocytes are unique mesenchymal cells characterized by multiple remarkably long cytoplasmic extensions that extend hundreds of micron away from the cell body. Through these extensions, telocytes establish a 3-dimensional network by connecting with other telocytes and various cell types within the tissue. In the intestine, telocytes have emerged as an essential component of the stem cell niche, providing Wnt proteins that are critical for the proliferation of stem and progenitor cells. However, the analysis of single-cell RNA sequencing has revealed other stromal populations and mechanisms for niche organization, raising questions about the role of telocytes as a component of the stem cell niche. This review explores the current state-of-the-art, existing controversies, and potential future directions related to telocytes in the luminal gastrointestinal tract.

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.

Telocytes promote hepatocellular carcinoma by activating the ERK signaling pathway and miR-942-3p/MMP9 axis

In China, hepatocellular carcinoma (HCC) is considered a malignant tumor with poor prognosis, frequent metastasis, and a high relapse rate. Telocytes (TCs) participate in tumorigenic, invasive, and migratory processes by secreting functional proteins and transmitting cell-to-cell information, but their functions in HCC are still unknown. TC counts and MMP9 expression in liver cancer tissues were measured using immunohistochemistry, western blotting, and RT-PCR. Primary TCs from liver para-cancer tissues were cultured in vitro. To verify the role of TCs in HCC, a metastatic cancer animal model was established using three types of liver cancer cell lines in vivo. TCs promoted HCC cell metastasis by MMP9 expression in vitro and in vivo. Platelet-derived growth factor-alpha (PDGF-α), secreted by HCC cells, activated the Ras/ERK signaling pathway in TCs, thereby increasing MMP9 expression; Moreover, miR-942-3p suppressed MMP9 expression in TCs. Our results reveal the role of TCs in HCC and the mechanisms by which they elicit their effects, and they may serve as novel prognostic markers for HCC.

Ultrastructural evidence for telocytes in equine tendon

The three-dimensional ultrastructure of the tendon is complex. Two main cell types are classically supported: elongated tenocytes and ovoid tenoblasts. The existence of resident stem/progenitor cells in human and equine tendons has been demonstrated, but their location and relationship to tenoblasts and tenocytes remain unclear. Hence, in this work, we carried out an ultrastructural study of the equine superficial digital flexor tendon. Although the fine structure of tendons has been previously studied using electron microscopy, the presence of telocytes, a specific type of interstitial cell, has not been described thus far. We show the presence of telocytes in the equine inter-fascicular tendon matrix near blood vessels. These telocytes have characteristic telopodes, which are composed of alternating dilated portions (podoms) and thin segments (podomers). Additionally, we demonstrate the presence of the primary cilium in telocytes and its ability to release exosomes. The location of telocytes is similar to that of tendon stem cells. The telocyte-blood vessel proximity, the presence of primary immotile cilia and the release of exosomes could have special significance for tendon homeostasis.

Morpho-functional changes of cardiac telocytes in isolated atrial amyloidosis in patients with atrial fibrillation

Telocytes are interstitial cells with long, thin processes by which they contact each other and form a network in the interstitium. Myocardial remodeling of adult patients with different forms of atrial fibrillation (AF) occurs with an increase in fibrosis, age-related isolated atrial amyloidosis (IAA), cardiomyocyte hypertrophy and myolysis. This study aimed to determine the ultrastructural and immunohistochemical features of cardiac telocytes in patients with AF and AF + IAA. IAA associated with accumulation of atrial natriuretic factor was detected in 4.3-25% biopsies of left (LAA) and 21.7-41.7% of right (RAA) atrial appendage myocardium. Telocytes were identified at ultrastructural level more often in AF + IAA, than in AF group and correlated with AF duration and mitral valve regurgitation. Telocytes had ultrastructural signs of synthetic, proliferative, and phagocytic activity. Telocytes corresponded to CD117+, vimentin+, CD34+, CD44+, CD68+, CD16+, S100-, CD105- immunophenotype. No significant differences in telocytes morphology and immunophenotype were found in patients with various forms of AF. CD68-positive cells were detected more often in AF + IAA than AF group. We assume that in aged AF + IAA patients remodeling of atrial myocardium provoked transformation of telocytes into "transitional forms" combining the morphological and immunohistochemical features with signs of fibroblast-, histiocyte- and endotheliocyte-like cells.

Telocytes in the hearts of Saanen goats

Telocytes, new interstitial cells that have received significant attention in recent years, have been detected in many organs, including the heart. The distinction between telocytes and other interstitial cells can only be made based on their ultrastructural characterization and immunophenotypic features. In this study, we examined the interstitial cells in the healthy heart tissues of Saanen goats to determine whether they are telocytes or not, by using a scanning electron microscope (SEM) and immunohistochemical and immunofluorescence staining methods. The SEM revealed oval and round telocytes with two to four telopodes. Some telopodes also had podoms. The staining for immunohistochemical and immunofluorescence methods used for CD34, c-kit (CD117), and vimentin antibodies. Positive cells were detected in the heart muscle and heart valves by immunohistochemical staining. As these antigens can also be expressed by other non-telocyte cells, we used double immunofluorescence staining with CD34/c-kit and CD34/vimentin antibodies to identify true telocytes. Telocytes were determined in the right atrium and aortic valve. While telocytes were CD34+/c-kit+ and CD34+/vimentin+, fibroblasts were CD34-/vimentin+. These results confirm the presence of telocytes in the hearts of Saanen goats.

Onset of Appearance and Potential Significance of Telocytes in the Developing Fetal Lung

CD34, vimentin, and vascular endothelial growth factor immunohistochemical analysis and electron microscopic tools were employed to record the initial appearance of telocytes (TCs) and stage-by-stage variations in TC localizations in the developing rabbit lung. TCs could not be identified in the primitive embryonic lung until day 18 of gestation. In the pseudoglandular lung, CD34+ TCs had been recorded under the cartilage of the main bronchus, in the wall of large-sized pulmonary vessels and large epithelial tubes. In the canalicular phase, TCs could be demonstrated in the smooth muscle layer of the bronchioles including the terminal ones. The strength of CD34 immunoreactive signals had been amplified by age until the day of parturition. Ultrastructurally, TCs consisted of a tiny body and exceptionally long telopodes (Tps). The Tp consisted of alternating thin segments (podomers) and dilated ones (podoms). The Tp sometimes branched with a dichotomous pattern. TCs interconnected in a network either by homocellular junctions with neighboring TCs or by heterocellular junctions with smooth muscle cells and alveolar cells. Collectively, early detection of TCs in pulmonary vessels suggests a potential role for TCs in their angiogenesis. For the lung tissue, TCs seem to be involved in the regulation of lung histogenesis.

Exosomes derived from cardiac progenitor cells attenuate CVB3-induced apoptosis via abrogating the proliferation of CVB3 and modulating the mTOR signaling pathways

Viral myocarditis is potentially fatal and lacking a specific treatment. Exosomes secreted by cardiac progenitor cells (CPCs) have emerged as a promising tool for cardioprotection and repair. In this study, we investigated whether CPCs-derived exosomes (CPCs-Ex) could utilize the mTOR signal pathway to reduce the apoptosis in viral myocarditis. In vitro, exosomes were, respectively, added to H9C2 cells after CVB3 infection to detect the anti-apoptosis effect of CPCs-Ex. Compared with the controls, the apoptosis rate was reduced, accompanied with the depressed expression of viral capsid protein 1 (VP1) and pro-apoptosis factors of Bim/caspase families. Meanwhile, the phosphorylation of Akt, mTOR, and p70S6K were promoted, but that of 4EBP1 was suppressed. In vivo, the results of apoptosis, expression of CVB3 and pro-apoptosis factors, and phosphorylation of Akt/mTOR factors of CVB3-infected cardiomyocytes were consistent with that of vitro. Following that, we use Rapamycin and MK-2206 to inhibit the Akt/mTOR signaling pathway, meanwhile, Rattus 4EBP1, p70S6K, Akt1 and Akt2 were transfected to H9C2 cells to establish the stably transfected cell lines. In the group with Rapamycin or MK-2206 pretreatment, CPCs-Ex also could decrease the apoptosis of H9C2 cells and expression of CVB3 mRNA, followed by decreased expression of apoptosis factors. In Akt2, p70S6K and 4EBP1 overexpression groups, CPCs-Ex promoted CVB3-induced apoptosis, VP1 expression and cleavage of caspase-3. Our results therefore identify CPCs-Ex exerts an anti-apoptosis effect in CVB3-infected cells by abrogating the proliferation of CVB3 and modulating the mTOR signaling pathways as well as the expression of Bcl-2 and caspase families. Viral myocarditis, mainly caused by CVB3 infection, is lacking a specific treatment. Our study identified an anti-apoptosis role of CPCs-Ex in CVB3-infected cells and rats, which shown that CPCs-Ex may be an effective tool to treat viral myocarditis. We believe that with more in-depth research on the functionality of CPCs-Ex, there will be a breakthrough in the treatment of viral myocarditis.

Critical Review: What Cell Types Are the Lung Telocytes?

Telocytes (TCs) are stromal cells defined by peculiar long, thin, moniliform prolongations known as telopodes. When isolated, their morphology often lacks the specificity for the proper definition of a particular cell type. Recent studies have linked TCs with different functions and different cell lineages. Although some authors have studied pulmonary TCs, their research has important limitations that we will attempt to summarize in this article. We will focus our analysis on the following: the culture methods used to study them, the lack of proper discrimination of TCs from lymphatic endothelial cells (LECs), whose ultrastructures are very similar, and the immune phenotype of TCs, which may appear in other cell types such as those related to the endothelial lineage or stem/progenitor cells. In conclusion, the cellular diagnosis of lung TCs should be considered with caution until properly designed studies can positively identify these cells and differentiate them from other cell types such as LECs and stem/progenitor cells. Anat Rec, 303:1280-1292, 2020. © 2019 American Association for Anatomy.

Expression of toll-like receptors and their regulatory roles in murine cardiac telocytes

Telocytes, newly discovered in the last decade, are interstitial cells found in numerous organs, with multiple proposed potential biological functions. Toll-like receptors (TLRs) play an important role in innate and adaptive immunity by recognizing pathogen-associated molecular patterns (PAMPs). However, it is still unknown whether telocytes express these innate receptors. We sought to determine the expression and role of TLRs in telocytes. In our study, we primarily detected TLR1-9 expression in telocytes. The proliferation, apoptosis and immunoregulatory activity of telocytes activated with or without TLR ligands were determined. Our results showed that purified telocytes expressed TLR2, TLR3 and TLR5. In particular, telocytes expressed high levels of TLR2 as observed using flow cytometry. When we stimulated telocytes with TLR2 or TLR3 agonists (Pam3CSK4, PolyI:C), iNOS expression was greatly increased after Pam3CSK4 treatment. Additionally, telocyte proliferation was reduced and cell apoptosis was increased after TLR agonist stimulation. A co-culture experiment showed that supernatant from telocytes pretreated with Pam3CSK4 inhibited T cell activation much more than that from untreated telocytes and this effect was mediated by iNOS. Overall, our results demonstrated TLR expression on telocytes for the first time and provided evidence of an immunoregulatory role of telocytes, indicating their clinical potential.

Telocytes in the mouse testicular interstitium: implications of G-protein-coupled estrogen receptor (GPER) and estrogen-related receptor (ERR) in the regulation of mouse testicular interstitial cells

Telocytes (TCs), a novel type of interstitial cells, are involved in tissue homeostasis maintenance. This study aimed to investigate TC presence in the interstitium of mouse testis. Additionally, inactivation of the G-coupled membrane estrogen receptor (GPER) in the testis was performed to obtain insight into TC function, regulation, and interaction with other interstitial cells. Mice were injected with a GPER antagonist (G-15; 50 μg/kg bw), and the GPER-signaling effect on TC distribution, ultrastructure, and function, as well as the interstitial tissue interaction of GPER with estrogen-related receptors (ERRs), was examined. Microscopic observations of TC morphology were performed with the use of scanning and transmission electron microscopes. Telocyte functional markers (CD34; c-kit; platelet-derived growth factor receptors α and β, PDGFRα and β; vascular endothelial growth factor, VEGF; and vimentin) were analyzed by immunohistochemistry/immunofluorescence and Western blot. mRNA expression of CD34 as well as ERR α, β, and γ was measured by qRT-PCR. Relaxin and Ca2+ concentrations were analyzed by immunoenzymatic and colorimetric assays, respectively. For the first time, we reveal the presence of TCs in the interstitium together with the peritubular area of mouse testis. Telocytes were characterized by specific features such as a small cell body and extremely long prolongations, constituting a three-dimensional network mainly around the interstitial cells. Expression of all TC protein markers was confirmed. Based on scanning electron microscopic observation in GPER-blocked testis, groups of TCs were frequently seen. No changes were found in TC ultrastructure in GPER-blocked testis when compared to the control. However, tendency to TC number change (increase) after the blockage was observed. Concomitantly, no changes in mRNA CD34 expression and increase in ERR expression were detected in GPER-blocked testes. In addition, Ca2+ was unchanged; however, an increase in relaxin concentration was observed. Telocytes are an important component of the mouse testicular interstitium, possibly taking part in maintaining its microenvironment as well as contractile and secretory functions (via themselves or via controlling of other interstitial cells). These cells should be considered a unique and useful target cell type for the prevention and treatment of testicular interstitial tissue disorders based on estrogen-signaling disturbances.

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 are the physiological counterpart of inflammatory fibroid polyps and PDGFRA-mutant GISTs

PDGFRA mutations in the gastrointestinal (GI) tract can cause GI stromal tumour (GIST) and inflammatory fibroid polyp (IFP). Hitherto no cell type has been identified as a physiological counterpart of the latter, while interstitial Cajal cells (ICC) are considered the precursor of the former. However, ICC hyperplasia (ICCH), which strongly supports the ICC role in GIST pathogenesis, has been identified in germline KIT-mutant settings but not in PDGFRA-mutant ones, challenging the precursor role of ICC for PDGFRA-driven GISTs. Telocytes are a recently described interstitial cell type, CD34+/PDGFRA+. Formerly considered fibroblasts, they are found in many organs, including the GI tract where they are thought to be involved in neurotransmission. Alongside IFPs and gastric GISTs, GI wall "fibrosis" has been reported in germline PDGFRA-mutants. Taking the opportunity offered by its presence in a germline PDGFRA-mutant individual, we demonstrate that this lesion is sustained by hyperplastic telocytes, constituting the PDGFRA-mutant counterpart of germline KIT mutation-associated ICCH. Moreover, our findings support a pathogenetic relationship between telocyte hyperplasia and both IFPs and PDGFRA-mutant GISTs. We propose the term "telocytoma" for defining IFP, as it conveys both the pathogenetic (neoplastic) and histotypic ("telocytary") essence of this tumour, unlike IFP, which rather evokes an inflammatory-hyperplastic lesion.

Cardiac progenitor cell‑derived exosomes promote H9C2 cell growth via Akt/mTOR activation

Exosomes are cell-derived vesicles released from a variety of mammalian cells that are involved in cell-to-cell signalling. It has been reported that cardiac progenitor cells (CPCs) derived from an adult heart are one of the most promising stem cell types for cardioprotection and repair. The mammalian target of rapamycin (mTOR) signalling pathway is a pivotal regulator in CPCs, therefore, CPC-derived exosomes were used in the present study to investigate whether it can promote H9C2 cell growth through the protein kinase B (PKB, or Akt)/mTOR signalling pathway. The CPCs were isolated from Sprague-Dawley hearts. Following treatment with a specific medium, the exosomes were purified and identified by electron micrograph and western blot assays, using CD63 and CD81 as markers. The methyl-thiazolyl-tetrazolium and 5-ethynyl-2′-deoxyuridine methods were used to detect H9C2 cell growth. The expression of Akt and mTOR were detected by western blot analysis following treatment with 200 or 400 µg/ml of exosomes for 24 or 48 h, respectively. It was found that, compared with higher concentrations of exosomes, prolonging the duration of exposure promoted cell growth. Accordingly, CPC-derived exosomes stimulated the expression of Akt to a marked degree; groups treated with exosomes for 48 h showed higher expression of Akt than those treated for 24 h at the same concentration. mTOR was also stimulated by CPC-derived exosomes. The activation of mTOR increased in accordance with the treatment time at an exosome concentration of 200 µg/ml and decreased with treatment time at an exosome concentration of 400 µg/ml. In conclusion, the present study demonstrated that CPC-derived exosomes promoted H9C2 cell growth via the activation of Akt/mTOR in a time-dependent manner at a relatively low exosome concentration, which may provide a novel therapy for cardiovascular disease.

Identification of telocytes in the porcine heart

Recently, a new interstitial cell type called telocyte has been identified. Telocytes are found in many organs including the heart, where they are especially well described. However, their presence in the porcine heart has not yet been proven. The pig is a valuable animal model in research because of its resemblance with man, making it interesting to determine whether telocytes can be found in pigs as well. The focus of this study is the identification and ultrastructural description of telocytes in the heart tissue of pig. Using transmission electron microscopy, telocytes were found in both left and right atrium and ventricle, usually close to cardiomyocytes and/or blood vessels. Their most important characteristic is the long cytoplasmic processes called telopodes, which have a moniliform aspect, measure tens of μm and usually have a thickness below 0.2 μm. This unique morphological feature enables telocytes to be recognized from other interstitial cells such as fibroblasts. Additional observations include the ability to release extracellular vesicles and to make contacts with other structures such as endothelial cells, suggesting a role in intercellular communication.

The Cutaneous Telocytes

Telocytes (TCs) are interstitial cells found in stroma of many organs, including the skin dermis. Ultrastructurally, normal skin TCs recapitulates all the previously documented features in interstitum of other organs. Their (ultra)structural hallmark is the presence of particular shaped cellular prolongations (termed telopodes), along other features as cellular organelles representation and their distribution within cell body and its prolongations. Transmission electron microscopy (TEM) or high magnification light microscopy indicated that the particular shape of telopodes alternate characteristically thin segments (termed podomeres) and dilated segments (called podoms). A new and powerful technique, focused ion beam scanning electron microscopy (FIB-SEM), indicated that, ultrastructurally, telopodes could be either irregular ribbon-like structures, or uneven tubular-like structures. TEM images shown that podoms consists mitochondria, elements of endoplasmic reticulum and caveolae. Immunohisochemical studies on skin TCs revealed their positive expression for CD34 and PDGFRα, but for vimentin and c-kit, also. In normal dermis, TCs are involved in junctions, either homocellular (TCs-TCs), or heterocellular (TCs - other type of cells). The junctional attribute of TCs underlies their ability of forming a 3D network within dermis. Beyond the physical interactions, the connections between TCs and other cells could be also chemical, by paracrine secretion via shed vesicles as ultrastructural studies demonstrated. In normal dermis, TCs were found distributed in particular spatial relationships with other interstitial structures and/or cells: vascular structures, nerves, skin adnexa, stem cells and immune reactive cells.To date, the study of TCs was approached into two pathologic conditions: systemic sclerosis and psoriasis. In both diseases, the normal ultrastructure of TCs and also their distribution were shown to be altered. Moreover, the pattern of TCs ultrastructural changes differs in systemic sclerosis (cytoplasmic vacuolization, swollen mitochondria, lipofuscin bodies) from those appeared in psoriasis, characterized by important dystrophic changes (telopodes fragmentation, cytoplasmic disintegration, apoptotic nuclei, nuclear extrusions). Furthermore, in psoriasis, the lesional remission is (ultra)structurally displaying a recovery of dermal TCs at values similar to normal.Considering TCs ultrastructural features, their connections and spatiality in normal dermis and also their pathologic changes, TCs are credited with roles in skin homeostasis and/or pathogeny of dermatological disorders. In our opinion, further researches should be focused on identifying a specific marker for TCs and also on comprehending the pattern of their response in different dermatoses.

Telocytes in pancreas of the Chinese giant salamander (Andrias davidianus)

Telocytes (TCs), novel interstitial cells, have been identified in various organs of many mammals. However, information about TCs of lower animals remains rare. Herein, pancreatic TCs of the Chinese giant salamanders (Andrias davidianus) were identified by CD34 immunohistochemistry (IHC) and transmission electron microscopy (TEM). The IHC micrographs revealed CD34⁺TCs with long telopodes (Tps) that were located in the interstitium of the pancreas. CD34⁺TCs/Tps were frequently observed between exocrine acinar cells and were close to blood vessels. The TEM micrographs also showed the existence of TCs in the interstitium of the pancreas. TCs had distinctive ultrastructural features, such as one to three very long and thin Tps with podoms and podomers, caveolae, dichotomous branching, neighbouring exosomes and vesicles. The Tps and exosomes were found in close proximity to exocrine acinar cells and α cells. It is suggested that TCs may play a role in the regeneration of acinar cells and α cells. In conclusion, our results demonstrated the presence of TCs in the pancreas of the Chinese giant salamander. This finding will assist us in a better understanding of TCs functions in the amphibian pancreas.

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.

Cellular Evidence of Telocytes as Novel Interstitial Cells Within the Magnum of Chicken Oviduct

Telocytes are a novel type of interstitial cell that has been identified in many organs of mammals, but there is little information available on these cells in avian species. This study shows the latest findings associated with telocytes in the muscular layer and lamina propria of the magnum of chicken oviduct analyzed by transmission electron microscopy. Telocytes are characterized by telopodes, which are thin and long prolongations, and a small amount of cytoplasm rich with mitochondria. Spindle- or triangular-shaped telocytes were detected at various locations in the magnum. In the muscular layer, telocytes have direct connection with smooth muscle cells. The cell body of telocytes along with their long telopodes mainly exists in the interstitial space between the smooth muscle bundles, whereas large numbers of short telopodes are scattered in between the smooth muscle cells. In the lamina propria, extremely long telopodes are twisting around each other and are usually collagen embedded. Both in the lamina propria and muscular layer, telocytes have a close relationship with other cell types, such as immune cells and blood vessels. Telopodes appear with dichotomous branching alternating between the podom and podomer, forming a 3D network structure with complex homo- and heterocellular junctions. In addition, a distinctive size of the vesicles is visible around the telopodes and may be released from telopodes because of the close relation between the vesicle and telopode. All characteristics of telocytes in the magnum indicate that telocytes may play a potential, but important, role in the pathogenesis of oviduct diseases.

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.

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.

Potential roles of telocytes in lung diseases

Telocytes (TCs) are a unique type of interstitial cells with specific, extremely long prolongations named telopodes (Tps), as shown by immune-positive staining against CD34, c-kit and vimentin. They were found in many organs of mammals, with potential biological functions, including the trachea and lung, even though the exact function remains unclear. Here, we give a historical overview of the TCs research field and summarize the latest findings associated with TCs, with a special focus on the recent progress about TCs specific gene and protein profiles that has been made in understanding that TCs may play a potential, but important, role in the pathogenesis of lung diseases.

Telocyte's contacts

Telocytes (TC) are an interstitial cell type located in the connective tissue of many organs of humans and laboratory mammals. By means of homocellular contacts, TC build a scaffold whose meshes integrity and continuity are guaranteed by those contacts having a mechanical function; those contacts acting as sites of intercellular communication allow exchanging information and spreading signals. Heterocellular contacts between TC and a great variety of cell types give origin to mixed networks. TC, by means of all these types of contacts, their interaction with the extracellular matrix and their vicinity to nerve endings, are part of an integrated system playing tissue/organ-specific roles.

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.

Juxtacerebral Tissue Regeneration Potential: Telocytes Contribution

It is well proved already that neurogenesis does take place in mammals' brain, including human brain. However, neurogenesis by itself is not able to compensate for brain tissue loss in serious neurological diseases, such as stroke, brain trauma or neurodegenerative disorders. Recent evidences show that neural stem cell niches are present not only in classical locations, such as subventricularor subgranular zones, but in other areas as well, including tissues contiguous to the brain (meninges and choroid plexus).In this chapter we revise the relationship of neural stem cells with interstitial cells (mainly telocytes), which we think is significant, and we describe what is known about the juxtacerebral tissue neurogenesis potential.

The History of Telocyte Discovery and Understanding

Telocytes (TCs) are identified as a peculiar cell type of interstitial cells in various organs. The typical features of TCs from the other cells are the extending cellular process as telopodes with alternation of podomeres and podoms. Before the year of 2010, TCs were considered as interstitial Cajal-like cells because of the similar morphology and immunohistochemical features with interstitial cells of Cajal which were found more than 100 years ago and considered to be pacemakers for gut motility. Subsequently, it demonstrated that TCs were not Cajal-like cells, and thus the new name "telocyte" was proposed in 2010. With the help of different techniques, e.g., transmission electron microscopy, immunohistochemistry, or omics science, TCs have been detected in various tissues and organs from different species. The pathological role of TCs in different diseases was also studied. According to observation in situ or in vitro, TCs played a vital role in mechanical support, signaling transduction, tissue renewal or repair, immune surveillance, and mechanical sensor via establishing homo- or heterogenous junctions with neighboring cells to form 3D network or release extracellular vesicles to form juxtacrine and paracrine. This review will introduce the origin, distribution, morphology, functions, omics science, methods, and interaction of TCs with other cells and provide a better understanding of the new cell type.

Telocytes of Fascial Structures

Currently, the exact role of telocytes within fascial structures is unknown. The morphology, distribution and behaviour of fascial telocytes as well as the mutual relationship between telocytes and other cellular fascia constituents should be definitely a subject of further studies. It will contribute to better understanding of the role of the fascial system in health and diseases, may shed light on the regeneration potential of these tissues and may help to find targets for future treatments for locomotor disorders, including fascial diseases. Last but not least, confirmation of the presence of telocytes within fascia may contribute to optimise the use of fascia as a graft material.

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.

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.

Upregulation of ULK1 expression in PC-3 cells following tumor protein P53 transfection by sonoporation

The aim of the present study was to investigate whether ultrasound combined with microbubbles was able to enhance liposome-mediated transfection of genes into human prostate cancer cells, and to examine the association between autophagy and tumor protein P53 (P53). An MTT assay was used to evaluate cell viability, while flow cytometry and fluorescence microscopy were used to measure gene transfection efficiency. Autophagy was observed using transmission electron microscopy. Reverse transcription-polymerase chain reaction (RT-PCR) and western blot analysis were used to assess the expression of autophagy-associated genes. The results of the present study revealed that cell viability was significantly reduced following successfully enhanced transfection of P53 by ultrasound combined with microbubbles. In addition, serine/threonine-protein kinase ULK1 levels were simultaneously upregulated. Castration-resistant prostate cancer is difficult to treat and is investigated in the present study. P53 has a significant role in a number of key biological functions, including DNA repair, apoptosis, cell cycle, autophagy, senescence and angiogenesis. Prior to the present study, to the best of our knowledge, increased transfection efficiency and reduced side effects have been difficult to achieve. Ultrasound is considered to be a 'gentle' technique that may be able to achieve increased transfection efficiency and reduced side effects. The results of the present study highlight a potential novel therapeutic strategy for the treatment of prostate cancer.

Global comparison of chromosome X genes of pulmonary telocytes with mesenchymal stem cells, fibroblasts, alveolar type II cells, airway epithelial cells, and lymphocytes

Background

Telocytes (TCs) are suggested as a new type of interstitial cells with specific telopodes. Our previous study evidenced that TCs differed from fibroblasts and stem cells at the aspect of gene expression profiles. The present study aims to search the characters and patterns of chromosome X genes of TC-specific or TC-dominated gene profiles and fingerprints, investigate the network of principle genes, and explore potential functional association.

Methods

We compared gene expression profiles in chromosome X of pulmonary TCs with mesenchymal stem cells (MSC), fibroblasts (Fb), alveolar type II cells (ATII), airway basal cells (ABC), proximal airway cells (PAC), CD8⁺ T cells come from bronchial lymph nodes (T-BL), or CD8⁺ T cells from lungs (T-L) by global analyses, and selected the genes which were consistently up or down regulated (>1 fold) in TCs compared to other cells as TC-specific genes. The functional and characteristic networks were identified and compared by bioinformatics tools.

Results

We selected 31 chromosome X genes as the TC-specific or dominated genes, among which 8 up-regulated (Flna, Msn, Cfp, Col4a5, Mum1l1, Rnf128, Syn1, and Srpx2) and 23 down-regulated (Abcb7, Atf1, Ddx26b, Drp2, Fam122b, Gyk, Irak1, Lamp2, Mecp2, Ndufb11, Ogt, Pdha1, Pola1, Rab9, Rbmx2, Rhox9, Thoc2, Vbp1, Dkc1, Nkrf, Piga, Tmlhe and Tsr2), as compared with other cells.

Conclusions

Our data suggested that gene expressions of chromosome X in TCs are different with those in other cells in the lung tissue. According to the selected TC-specific genes, we infer that pulmonary TCs function as modulators which may enhance cellular growth and migration, resist senescence, protect cells from external stress, regulate immune responses, participate in tissue remodeling and repair, regulate neural function, and promote vessel formation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0669-8) contains supplementary material, which is available to authorized users.

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.

Protein profiling of human lung telocytes and microvascular endothelial cells using iTRAQ quantitative proteomics

Telocytes (TCs) are described as a particular type of cells of the interstitial space (www.telocytes.com). Their main characteristics are the very long telopodes with alternating podoms and podomers. Recently, we performed a comparative proteomic analysis of human lung TCs with fibroblasts, demonstrating that TCs are clearly a distinct cell type. Therefore, the present study aims to reinforce this idea by comparing lung TCs with endothelial cells (ECs), since TCs and ECs share immunopositivity for CD34. We applied isobaric tag for relative and absolute quantification (iTRAQ) combined with automated 2-D nano-ESI LC-MS/MS to analyse proteins extracted from TCs and ECs in primary cell cultures. In total, 1609 proteins were identified in cell cultures. 98 proteins (the 5th day), and 82 proteins (10th day) were confidently quantified (screened by two-sample t-test, P < 0.05) as up- or down-regulated (fold change >2). We found that in TCs there are 38 up-regulated proteins at the 5th day and 26 up-regulated proteins at the 10th day. Bioinformatics analysis using Panther revealed that the 38 proteins associated with TCs represented cellular functions such as intercellular communication (via vesicle mediated transport) and structure morphogenesis, being mainly cytoskeletal proteins and oxidoreductases. In addition, we found 60 up-regulated proteins in ECs e.g.: cell surface glycoprotein MUC18 (15.54-fold) and von Willebrand factor (5.74-fold). The 26 up-regulated proteins in TCs at 10th day, were also analysed and confirmed the same major cellular functions, while the 56 down-regulated proteins confirmed again their specificity for ECs. In conclusion, we report here the first extensive comparison of proteins from TCs and ECs using a quantitative proteomics approach. Our data show that TCs are completely different from ECs. Protein expression profile showed that TCs play specific roles in intercellular communication and intercellular signalling. Moreover, they might inhibit the oxidative stress and cellular ageing and may have pro-proliferative effects through the inhibition of apoptosis. The group of proteins identified in this study needs to be explored further for the role in pathogenesis of lung disease.

Malignant pleural mesothelioma: history, controversy and future of a manmade epidemic

Asbestos is the term for a family of naturally occurring minerals that have been used on a small scale since ancient times. Industrialisation demanded increased mining and refining in the 20th century, and in 1960, Wagner, Sleggs and Marchand from South Africa linked asbestos to mesothelioma, paving the way to the current knowledge of the aetiology, epidemiology and biology of malignant pleural mesothelioma. Pleural mesothelioma is one of the most lethal cancers, with increasing incidence worldwide. This review will give some snapshots of the history of pleural mesothelioma discovery, and the body of epidemiological and biological research, including some of the controversies and unresolved questions. Translational research is currently unravelling novel circulating biomarkers for earlier diagnosis and novel treatment targets. Current breakthrough discoveries of clinically promising noninvasive biomarkers, such as the 13-protein signature, microRNAs and the BAP1 mesothelioma/cancer syndrome, are highlighted. The asbestos history is a lesson to not be repeated, but here we also review recent in vivo and in vitro studies showing that manmade carbon nanofibres could pose a similar danger to human health. This should be taken seriously by regulatory bodies to ensure thorough testing of novel materials before release in the society.

Malignant pleural mesothelioma is a cancer with increasing death tolls due to the past and present use of asbestoshttp://ow.ly/DhA2y

Cardiac telocytes and fibroblasts in primary culture: different morphologies and immunophenotypes

Telocytes (TCs) are a peculiar type of interstitial cells with very long prolongations termed telopodes. TCs have previously been identified in different anatomic structures of the heart, and have also been isolated and cultured from heart tissues in vitro. TCs and fibroblasts, both located in the interstitial spaces of the heart, have different morphologies and functionality. However, other than microscopic observation, a reliable means to make differential diagnosis of cardiac TCs from fibroblasts remains unclear. In the present study, we isolated and cultured cardiac TCs and fibroblasts from heart tissues, and observed their different morphological features and immunophenotypes in primary culture. Morphologically, TCs had extremely long and thin telopodes with moniliform aspect, stretched away from cell bodies, while cell processes of fibroblasts were short, thick and cone shaped. Furthermore, cardiac TCs were positive for CD34/c-kit, CD34/vimentin, and CD34/PDGFR-β, while fibroblasts were only vimentin and PDGFR-β positive. In addition, TCs were also different from pericytes as TCs were CD34 positive and α-SMA weak positive while pericytes were CD34 negative but α-SMA positive. Besides that, we also showed cardiac TCs were homogenously positive for mesenchymal marker CD29 but negative for hematopoietic marker CD45, indicating that TCs could be a source of cardiac mesenchymal cells. The differences in morphological features and immunophenotypes between TCs and fibroblasts will provide more compelling evidence to differentiate cardiac TCs from fibroblasts.

Uterine Telocytes: A Review of Current Knowledge

Telocytes (TCs), a novel cell type, are briefly defined as interstitial cells with telopodes (Tps). However, a specific immunocytochemical marker has not yet been found; therefore, electron microscopy is currently the only accurate method for identifying TCs. TCs are considered to have a mesenchymal origin. Recently proteomic analysis, microarray-based gene expression analysis, and the micro-RNA signature clearly showed that TCs are different from fibroblasts, mesenchymal stem cells, and endothelial cells. The dynamics of Tps were also revealed, and some electrophysiological properties of TCs were described (such as membrane capacitance, input resistance, membrane resting potential, and absence of action potentials correlated with different ionic currents characteristics), which can be used to distinguish uterine TCs from smooth muscle cells (SMCs). Here, we briefly present the most recent findings on the characteristics of TCs and their functions in human pregnant and nonpregnant uteri.

Telocytes and putative stem cells in ageing human heart

Tradition considers that mammalian heart consists of about 70% non-myocytes (interstitial cells) and 30% cardiomyocytes (CMs). Anyway, the presence of telocytes (TCs) has been overlooked, since they were described in 2010 (visit http://www.telocytes.com). Also, the number of cardiac stem cells (CSCs) has not accurately estimated in humans during ageing. We used electron microscopy to identify and estimate the number of cells in human atrial myocardium (appendages). Three age-related groups were studied: newborns (17 days–1 year), children (6–17 years) and adults (34–60 years). Morphometry was performed on low-magnification electron microscope images using computer-assisted technology. We found that interstitial area gradually increases with age from 31.3 ± 4.9% in newborns to 41 ± 5.2% in adults. Also, the number of blood capillaries (per mm²) increased with several hundreds in children and adults versus newborns. CMs are the most numerous cells, representing 76% in newborns, 88% in children and 86% in adults. Images of CMs mitoses were seen in the 17-day newborns. Interestingly, no lipofuscin granules were found in CMs of human newborns and children. The percentage of cells that occupy interstitium were (depending on age): endothelial cells 52–62%; vascular smooth muscle cells and pericytes 22–28%, Schwann cells with nerve endings 6–7%, fibroblasts 3–10%, macrophages 1–8%, TCs about 1% and stem cells less than 1%. We cannot confirm the popular belief that cardiac fibroblasts are the most prevalent cell type in the heart and account for about 20% of myocardial volume. Numerically, TCs represent a small fraction of human cardiac interstitial cells, but because of their extensive telopodes, they achieve a 3D network that, for instance, supports CSCs. The myocardial (very) low capability to regenerate may be explained by the number of CSCs, which decreases fivefold by age (from 0.5% to 0.1% in newborns versus adults).

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

Women with endometriosis (EMs) have unexplained infertility. The recently identified telocytes (TCs) might participate in the maintenance of structural and functional integrity of oviduct tissue, but so far the involvement of TCs in EMs-affected oviduct tissue and potential impact on fertility capacity remain unknown. By an integrated technique of haematoxylin and eosin staining, in situ immunohistochemistry and double-labelled immunofluorescence staining and electron microscopy approach, TCs were studied in the autotransplantation Sprague-Dawley rat model of EMs-affected oviduct tissue and in sham control, respectively, together with determination of iNOS, COX-2, LPO and estradiol. TCs were found in perivascular connective tissue and smooth muscle bundles in sham oviduct, with typical ultrastructural features (a slender piriform/spindle/triangular cell body, and one or more extremely long prolongations, emerged from cell bodies and extend to various directions), and specific immunophenotype of CD34-positive/vimentin-positive/c-kit-negative. However, in EMs-affected oviduct tissue (grade III), extensive ultrastructural damage (degeneration, discontinue, dissolution and destruction), significant decrease or loss of TCs and interstitial fibrosis were observed, together with elevated level of iNOS, COX-2, LPO and estradiol, thus suggestive of inflammation and ischaemia-induced TCs damage. Based on TCs distribution and intercellular connections, we proposed that such damage might be involved in structural and functional abnormalities of oviduct, such as attenuated intercellular signalling and oviduct contractility, impaired immunoregulation and stem cell-mediated tissue repair, 3-D interstitial architectural derangement and tissue fibrosis. Therefore, TCs damage might provide a new explanation and potential target for EMs-induced tubal damage and fertility disorders.

Variations of chromosomes 2 and 3 gene expression profiles among pulmonary telocytes, pneumocytes, airway cells, mesenchymal stem cells and lymphocytes

Telocytes (TCs) were identified as a distinct cellular type of the interstitial tissue and defined as cells with extremely long telopodes (Tps). Our previous data demonstrated patterns of mouse TC-specific gene profiles on chromosome 1. The present study focuses on the identification of characters and patterns of TC-specific or TC-dominated gene expression profiles in chromosome 2 and 3, the network of principle genes and potential functional association. We compared gene expression profiles of pulmonary TCs, mesenchymal stem cells, fibroblasts, alveolar type II cells, airway basal cells, proximal airway cells, CD8⁺T cells from bronchial lymph nodes (T-BL), and CD8⁺ T cells from lungs (T-LL). We identified that 26 or 80 genes of TCs in chromosome 2 and 13 or 59 genes of TCs up-or down-regulated in chromosome 3, as compared with other cells respectively. Obvious overexpression of Myl9 in chromosome 2 of TCs different from other cells, indicates that biological functions of TCs are mainly associated with tissue/organ injury and ageing, while down-expression of Pltp implies that TCs may be associated with inhibition or reduction of inflammation in the lung. Dominant overexpression of Sh3glb1, Tm4sf1 or Csf1 in chromosome 3 of TCs is mainly associated with tumour promotion in lung cancer, while most down-expression of Pde5 may be involved in the development of pulmonary fibrosis and other acute and chronic interstitial lung disease.

Extracellular vesicles release by cardiac telocytes: electron microscopy and electron tomography

Telocytes have been reported to play an important role in long-distance heterocellular communication in normal and diseased heart, both through direct contact (atypical junctions), as well as by releasing extracellular vesicles (EVs) which may act as paracrine mediators. Exosomes and ectosomes are the two main types of EVs, as classified by size and the mechanism of biogenesis. Using electron microscopy (EM) and electron tomography (ET) we have found that telocytes in culture release at least three types of EVs: exosomes (released from endosomes; 45 ± 8 nm), ectosomes (which bud directly from the plasma membrane; 128 ± 28 nm) and multivesicular cargos (MVC; 1 ± 0.4 μm), the latter containing tightly packaged endomembrane-bound vesicles (145 ± 35 nm). Electron tomography revealed that endomembrane vesicles are released into the extracellular space as a cargo enclosed by plasma membranes (estimated area of up to 3 μm(2)). This new type of EV, also released by telocytes in tissue, likely represents an essential component in the paracrine secretion of telocytes and may consequently be directly involved in heart physiology and regeneration.

Identification and characterization of telocytes in the uterus of the oviduct in the Chinese soft-shelled turtle, Pelodiscus sinensis: TEM evidence

Telocytes (Tcs) are cells with telopodes (Tps), which are very long cellular extensions with alternating thin segments (podomers) and dilated bead-like thick regions known as podoms. Tcs are a distinct category of interstitial cells and have been identified in many mammalian organs including heart, lung and kidney. The present study investigates the existence, ultrastructure, distribution and contacts of Tcs with surrounding cells in the uterus (shell gland) of the oviduct of the Chinese soft-shelled turtle, Pelodiscus sinensis. Samples from the uterine segment of the oviduct were examined by transmission electron microscopy. Tcs were mainly located in the lamina propria beneath the simple columnar epithelium of the uterus and were situated close to nerve endings, capillaries, collagen fibres and secretory glands. The complete morphology of Tcs and Tps was clearly observed and our data confirmed the existence of Tcs in the uterus of the Chinese soft-shelled turtle Pelodiscus sinensis. Our results suggest these cells contribute to the function of the secretory glands and contraction of the uterus.

Extracellular vesicles from human cardiac progenitor cells inhibit cardiomyocyte apoptosis and improve cardiac function after myocardial infarction

AIMS

Recent evidence suggests that cardiac progenitor cells (CPCs) may improve cardiac function after injury. The underlying mechanisms are indirect, but their mediators remain unidentified. Exosomes and other secreted membrane vesicles, hereafter collectively referred to as extracellular vesicles (EVs), act as paracrine signalling mediators. Here, we report that EVs secreted by human CPCs are crucial cardioprotective agents.

METHODS AND RESULTS

CPCs were derived from atrial appendage explants from patients who underwent heart valve surgery. CPC-conditioned medium (CM) inhibited apoptosis in mouse HL-1 cardiomyocytic cells, while enhancing tube formation in human umbilical vein endothelial cells. These effects were abrogated by depleting CM of EVs. They were reproduced by EVs secreted by CPCs, but not by those secreted by human dermal fibroblasts. Transmission electron microscopy and nanoparticle tracking analysis showed most EVs to be 30-90 nm in diameter, the size of exosomes, although smaller and larger vesicles were also present. MicroRNAs most highly enriched in EVs secreted by CPCs compared with fibroblasts included miR-210, miR-132, and miR-146a-3p. miR-210 down-regulated its known targets, ephrin A3 and PTP1b, inhibiting apoptosis in cardiomyocytic cells. miR-132 down-regulated its target, RasGAP-p120, enhancing tube formation in endothelial cells. Infarcted hearts injected with EVs from CPCs, but not from fibroblasts, exhibited less cardiomyocyte apoptosis, enhanced angiogenesis, and improved LV ejection fraction (0.8 ± 6.8 vs. -21.3 ± 4.5%; P < 0.05) compared with those injected with control medium.

CONCLUSION

EVs are the active component of the paracrine secretion by human CPCs. As a cell-free approach, EVs could circumvent many of the limitations of cell transplantation.

Phenotypical and ultrastructural features of Oct4-positive cells in the adult mouse lung

Octamer binding trascription factor 4 (Oct4) is a transcription factor of POU family specifically expressed in embryonic stem cells (ESCs). A role for maintaining pluripotency and self-renewal of ESCs is assigned to Oct4 as a pluripotency marker. Oct4 can also be detected in adult stem cells such as bone marrow-derived mesenchymal stem cells. Several studies suggest a role for Oct4 in sustaining self-renewal capacity of adult stem cells. However, Oct4 gene ablation in adult stem cells revealed no abnormalities in tissue turnover or regenerative capacity. In the present study we have conspicuously found pulmonary Oct4-positive cells closely resembling the morphology of telocytes (TCs). These cells were found in the perivascular and peribronchial areas and their presence and location were confirmed by electron microscopy. Moreover, we have used Oct4-GFP transgenic mice which revealed a similar localization of the Oct4-GFP signal. We also found that Oct4 co-localized with several described TC markers such as vimentin, Sca-1, platelet-derived growth factor receptor-beta C-kit and VEGF. By flow cytometry analyses carried out with Oct4-GFP reporter mice, we described a population of EpCAM(neg) /CD45(neg) /Oct4-GFP(pos) that in culture displayed TC features. These results were supported by qRT-PCR with mRNA isolated from lungs by using laser capture microdissection. In addition, Oct4-positive cells were found to express Nanog and Klf4 mRNA. It is concluded for the first time that TCs in adult lung mouse tissue comprise Oct4-positive cells, which express pluripotency-related genes and represent therefore a population of adult stem cells which might contribute to lung regeneration.

Telocytes and stem cells in limbus and uvea of mouse eye

The potential of stem cell (SC) therapies for eye diseases is well-recognized. However, the results remain only encouraging as little is known about the mechanisms responsible for eye renewal, regeneration and/or repair. Therefore, it is critical to gain knowledge about the specific tissue environment (niches) where the stem/progenitor cells reside in eye. A new type of interstitial cell–telocyte (TC) (http://www.telocytes.com) was recently identified by electron microscopy (EM). TCs have very long (tens of micrometres) and thin (below 200 nm) prolongations named telopodes (Tp) that form heterocellular networks in which SCs are embedded. We found TCs by EM and electron tomography in sclera, limbus and uvea of the mouse eye. Furthermore, EM showed that SCs were present in the anterior layer of the iris and limbus. Adhaerens and gap junctions were found to connect TCs within a network in uvea and sclera. Nanocontacts (electron-dense structures) were observed between TCs and other cells: SCs, melanocytes, nerve endings and macrophages. These intercellular ‘feet’ bridged the intercellular clefts (about 10 nm wide). Moreover, exosomes (extracellular vesicles with a diameter up to 100 nm) were delivered by TCs to other cells of the iris stroma. The ultrastructural nanocontacts of TCs with SCs and the TCs paracrine influence via exosomes in the epithelial and stromal SC niches suggest an important participation of TCs in eye regeneration.

Suburothelial interstitial cells

The suburothelium has received renewed interest because of its role in sensing bladder fullness. Various studies evaluated suburothelial myofibroblasts (MFs), interstitial cells (ICs), interstitial Cajal cells (ICCs) or telocytes (TCs), which resulted in inconsistencies in terminology and difficulties in understanding the suburothelial structure. In order to elucidate these issues, the use of electron microscopy seems to be an ideal choice. It was hypothesized that the cell population of the suburothelial band is heterogeneous in an attempt to clarify the above-mentioned inconsistencies. The suburothelial ICs of the bladder were evaluated by immunohistochemistry (IHC) and transmission electron microscopy (TEM). Bladder samples from 6 Wistar rats were used for IHC and TEM studies and human bladder autopsy samples were used for IHC. Desmin labeled only the detrusor muscle, while all the myoid structures of the bladder wall were positive for α-smooth muscle actin (SMA). A distinctive α-SMA-positive suburothelial layer was identified. A layered structure of the immediate suburothelial band was detected using TEM: (1) the inner suburothelial layer consisted of fibroblasts equipped for matrix synthesis; (2) the middle suburothelial layer consisted of smooth muscle cells (SMCs) and myoid ICCs, and (3) the outer suburothelial layer consisted of ICs with TC morphology, building a distinctive network. In conclusion, the suburothelial layer consists of distinctive types of ICs but not MFs. The myoid layer, with SMCs and ICCs, which could be considered identical to the α-SMA-positive cells in the suburothelial band, seems the best-equipped layer for pacemaking and signaling. Noteworthy, the network of ICs also seems suitable for stromal signaling.

Renal telocytes contribute to the repair of ischemically injured renal tubules

Telocytes (TCs), a distinct type of interstitial cells, have been identified in many organs via electron microscopy. However, their precise function in organ regeneration remains unknown. This study investigated the paracrine effect of renal TCs on renal tubular epithelial cells (TECs) in vitro, the regenerative function of renal TCs in renal tubules after ischaemia–reperfusion injury (IRI) in vivo and the possible mechanisms involved. In a renal IRI model, transplantation of renal TCs was found to decrease serum creatinine and blood urea nitrogen (BUN) levels, while renal fibroblasts exerted no such effect. The results of histological injury assessments and the expression levels of cleaved caspase-3 were consistent with a change in kidney function. Our data suggest that the protective effect of TCs against IRI occurs via inflammation-independent mechanisms in vivo. Furthermore, we found that renal TCs could not directly promote the proliferation and anti-apoptosis properties of TECs in vitro. TCs did not display any advantage in paracrine growth factor secretion in vitro compared with renal fibroblasts. These data indicate that renal TCs protect against renal IRI via an inflammation-independent pathway and that growth factors play a significant role in this mechanism. Renal TCs may protect TECs in certain microenvironments while interacting with other cells.