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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.

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The peripheral nerve injury (PNI) affects the morphology of the whole locomotor apparatus, which can reach the myotendinous junction (MTJ) interface. In the injury condition, the skeletal muscle satellite cells (SC) are triggered, activated, and proliferated to repair their structure, and in the MTJ, the telocytes (TC) are associated to support the interface with the need for remodeling; in that way, these cells can be associated with SC. The study aimed to describe the SC and TC relationship after PNI at the MTJ. Sixteen adult Wistar rats were divided into Control Group (C, n = 8) and PNI Group (PNI, n = 8), PNI was performed by the constriction of the sciatic nerve. The samples were processed for transmission electron microscopy and immunostaining analysis. In the C group was evidenced the arrangement of sarcoplasmic evaginations and invaginations, the support collagen layer with a TC inside it, and an SC through vesicles internally and externally to then. In the PNI group were observed the disarrangement of invaginations and evaginations and sarcomeres degradation at MTJ, as the disposition of telopodes adjacent and in contact to the SC with extracellular vesicles and exosomes in a characterized paracrine activity. These findings can determine a link between the TCs and the SCs at the MTJ remodeling. RESEARCH HIGHLIGHTS: Peripheral nerve injury promotes the myotendinous junction (MTJ) remodeling. The telocytes (TC) and the satellite cells (SC) are present at the myotendinous interface. TC mediated the SC activity at MTJ.

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SUMMARY: Telocytes are a cell population described in 2011 with a multitude of functions such as tissue support, regulation of stem cell niches or intercellular signal transmission. However, there are no studies about their embryonic origin, their function in development, or their moment of appearance. The objective of this work is to try to answer these questions through histological and immunofluorescence studies with samples from the embryological collection of the Department of Anatomy of the University of Granada. In the results obtained, as demonstrated by immunofluorescence for CD34, the presence of these cells can be seen in the fourth week of embryonic development in the perinotochordal region. Its presence is evident from the sixth week of development in a multitude of organs such as the heart, skeletal muscle tissue and supporting tissue of various organs such as the kidney, brain or pericardium. Its function seems to be when the embryonic histological images are analyzed in an evolutionary way, to act as a scaffold or scaffold for the subsequent population by mature tissue elements. In conclusion, telocytes appear at a very early stage of embryonic development and would have a fundamental role in it as scaffolding and directors of organ and tissue growth.

Los telocitos son una población celular descrita en 2011 con multitud de funciones como el sostén tisular, la regulación de los nichos de células madre o la transmisión de señales intercelulares. Sin embargo, no existen estudios acerca del origen embrionario de los mismos, su función en el desarrollo ni su momento de aparición. El objetivo de este trabajo es tratar de responder a estos interrogantes mediante estudios histológicos y por inmunofluorescencia con muestras de la colección embriológica del Departamento de Anatomía de la Universidad de Granada. En los resultados se puede observar como se demuestra mediante inmunofluorescencia para CD34, la presencia de estas células en la cuarta semana del desarrollo embrionario en la región perinotocordal. Su presencia se evidencia a partir de la sexta semana del desarrollo en multitud de órganos como corazón, tejidos músculo esqueléticos y tejidos de sostén de diversos órganos como riñón, encéfalo o pericardio. Su función parece ser al ser analizadas las imágenes histológicas embrionarias de forma evolutiva, la de actuar como un andamiaje o scafold para el posterior poblamiento por elementos tisulares maduros. Como conclusión, los telocitos aparecen en un momento muy precoz del desarrollo embrionario y presentarían una función fundamental en el mismo como andamiajes y directores del crecimiento de los órganos y tejidos.

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Telocytes are interstitial cells that are present in various tissues, have long cytoplasmic projections known as telopodes, and are classified as CD34+ cells. Telopodes form extensive networks that permeate the stroma, and there is evidence that these networks connect several stromal cell types, giving them an important role in intercellular communication and the maintenance of tissue organisation. Data have also shown that these networks can be impaired and the number of telocytes reduced in association with many pathological conditions such as cancer and fibrosis. Thus, techniques that promote telocyte proliferation have become an important therapeutic target. In this study, ex vivo and in vitro assays were conducted to evaluate the impact on prostatic telocytes of SDF-1, a factor involved in the proliferation and migration of CD34+ cells. SDF-1 caused an increase in the number of telocytes in explants, as well as morphological changes that were possibly related to the proliferation of these cells. These changes involved the fusion of telopode segments, linked to an increase in cell body volume. In vitro assays also showed that SDF-1 enriched prostate stromal cells with telocytes. Altogether, the data indicate that SDF-1 may offer promising uses in therapies that aim to increase the number of telocytes. However, further studies are needed to confirm the efficiency of this factor in different tissues/pathological conditions.

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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.

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The prostate is not an organ exclusive to the male. It is also found in females of several species, including humans, in which part of the Skene gland is homologous to the male prostate. Evidence is accumulating that changes in the stroma are central to tumorigenesis. Equally, telocytes, a recently discovered type of interstitial cell, are essential for the maintenance of stromal organization. However, it is still uncertain whether there are telocytes in the female prostate and if they play a role in tumorigenesis. The present study used ultrastructural and immunofluorescence techniques to investigate the presence of telocytes in the prostate of Mongolian gerbil females, a rodent model that often has a functional prostate in females, as well as to assess the impact of a combination of N-ethyl-N-nitrosourea, testosterone, and estradiol on telocytes. The results point to the presence of telocytes in the female prostate in the perialveolar and interalveolar regions, and reveal that these cells are absent in regions of benign and premalignant lesions in the gland, in which the perialveolar smooth muscle is altered. Additionally, telocytes are also closely associated with infiltrated immune cells in the stroma. Our data suggest that telocytes are important for both the maintenance of smooth muscle and prostatic epithelium integrity, which indicates a protective role against the advancement of tumorigenesis. But telocytes are also associated with immune cells and a proinflammatory/proangiogenic role for these cells cannot be ruled out, implying that telocytes have a complex role in prostatic tumorigenesis in females.

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The male urogenital system is composed of the reproductive system and the urinary tract; they have an interconnected embryonic development and share one of their anatomical components, the urethra. This system has a highly complex physiology deeply interconnected with the circulatory and nervous systems, as well as being capable of adapting to environmental variations; it also undergoes changes with aging and, in the case of the reproductive system, with seasonality. The stroma is an essential component in this physiological plasticity and its complexity has increased with the description in the last decade of a new cell type, the telocyte. Several studies have demonstrated the presence of telocytes in the organs of the male urogenital system and other systems; however, their exact function is not yet known. The present review addresses current knowledge about telocytes in the urogenital system in terms of their locations, interrelationships, possible functions and pathological implications. It has been found that telocytes in the urogenital system possibly have a leading role in stromal tissue organization/maintenance, in addition to participation in stem cell niches and an association with the immune system, as well as specific functions in the urogenital system, lipid synthesis in the testes, erythropoiesis in the kidneys and the micturition reflex in the bladder. There is also evidence that telocytes are involved in pathologies in the kidneys, urethra, bladder, prostate, and testes.

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The morphology of the oral cavity of mammals relates to diet, habitat, and function. The palate is an important region with adaptations for oral somatosensation and mechanical loads due to the pressure of the tongue with food. The research aimed to describe the structural and ultrastructural characteristics of the epithelium and the connective tissue cores of the guinea pig palate using macroscopic, light microscopy, scanning electron microscopy, and transmission electron microscopy analysis. The hard palate had conical and filiform papillae, and the soft palate had open salivary ducts. After the removal of the epithelium, the connective tissue cores revealed thin filaments and laminar projections in the hard palate, and opening ducts were evidenced in the soft palate. The palatine epithelium was keratinized and organized by layers, lamellated corpuscles were found in lamina propria of the hard palate. In contrast, the soft palate had glands clusters associated with nerve fibers, and in both regions were identified telocytes. We concluded that the hard palate presented conical and filiform papillae that differ from other mammals. Besides, it is a new description of the connective tissue cores morphology and the first record of the telocytes in this anatomical region for mammals.

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