Telocytes in human fetal skeletal muscle interstitium during early myogenesis

Immunohistochemical properties of embryonic telocytes in a myogenic microenvironment

Telocytes are a unique interstitial cell type that functions in adulthood and embryogenesis. They have characteristic immunohistochemical phenotypes while acquiring different immunohistochemical properties related to the organ microenvironment. The present study aims to investigate the immunohistochemical features of embryonic telocytes during myogenesis and describe their morphology using light microscopy and TEM. Telocytes represent a major cellular constituent in the interstitial elements. They had distinguished telopodes and podoms and formed a 3D interstitial network in the developing muscles. They formed heterocellular contact with myoblasts and nascent myotubes. Telocytes also had distinctive secretory activity. Telocytes identified by CD34. They also express CD68 and MMP-9 to facilitate the development of new tissues. Expression of CD21 by telocytes may reveal their function in immune defense. They also express VEGF, which regulates angiogenesis. In conclusion, the distribution and immunological properties of telocytes in the myogenic tissue indicate that telocytes provide biological and structural support in the development of the myogenic tissue architecture and organization.

Anti-inflammatory effects of sericin and swimming exercise in treating experimental Achilles tendinopathy in rat

The aim of this study was to assess the effectiveness of combining sericin with swimming exercise as a treatment for type-I collagenase-induced Achilles tendinopathy (AT) in rats, with a focus on inflammatory cytokines. An experimental AT model was established using type-I collagenase in male Sprague-Dawley rats, categorized into five groups: Group 1 (Control + Saline), Group 2 (AT), Group 3 (AT + exercise), Group 4 (AT + sericin), and Group 5 (AT + sericin + exercise). Intratendinous sericin administration (0.8 g/kg/mL) took place from days 3 to 6, coupled with 30 min daily swimming exercise sessions (5 days/week, 4 weeks). Serum samples were analyzed using ELISA for tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), interleukin-10 (IL-10), and total antioxidant-oxidant status (TAS-TOS), alongside histopathological and immunohistochemical assessments of Achilles tendon samples. Elevated TNF-α and IL-1β and decreased IL-10 levels were evident in Group 2; Of these, TNF-α and IL-1β were effectively reduced and IL-10 increased across all treatment groups, particularly groups 4 and 5. Serum TAS was notably lower in Group 2 and significantly increased in Group 5 compared to Group 2. Histopathologically, Group 2 displayed severe degeneration, irregular fibers, and round cell nuclei, while Group 5 exhibited decreased degeneration and spindle-shaped fibers. The Bonar score increased in Group 2 and decreased in groups 4 and 5. Collagen type-I alpha-1 (Col1A1) expression was notably lower in Group 2 (P = 0.001) and significantly increased in groups 4 and 5 compared to Group 2 (P = 0.011 and 0.028, respectively). This study underscores the potential of sericin and swimming exercises in mitigating inflammation and oxidative stress linked to AT pathogenesis, presenting a promising combined therapeutic strategy.

Ultrastructural characteristics and morphological relationships of cardiomyocytes and telocytes in the myocardium of the bullfrog (Rana catesbeiana)

Telocytes (TCs) are distinctive interstitial cells due to their characteristic structures and heterogeneity. They are suggested to participate in tissue repair/regeneration. TCs have been identified in many organs of various mammals. However, data on TCs in lower animals are still very limited. In this work, TCs were identified in the myocardium of the bullfrog (Rana catesbeiana) by light and transmission electron microscopy (TEM). The structural relationships between TCs and neighbouring cell types were measured using the ImageJ (FiJi) morphometric software. TCs with slender Tps (telepodes) were located around cardiomyocytes (CMC). TEM revealed TCs with long Tps in the stroma between CMC. The homocellular tight junctions were observed between the Tps. The Tps were also very close to the neighbouring CMC. The distance between Tps and CMC was 0.15 ± 0.08 μm. Notably, Tps were observed to adhere to the periphery of the satellite cells. The Tps and the satellite cells established heterocellular structural connections by tight junctions. Additionally, Tps were frequently observed in close proximity to mast cells (MCs). The distance between the Tps and the MCs was 0.19 ± 0.09 μm. These results confirmed that TCs are present in the myocardium of the bullfrog, and that TCs established structural relationships with neighbouring cell types, including satellite cells and MCs. These findings provide the anatomical evidence to support the note that TCs are involved in tissue regeneration.

Silk protein sericin: a promising therapy for Achilles tendinopathy-evidence from an experimental rat model

OBJECTIVE

This study investigated the efficacy of sericin in treating experimental Achilles tendinopathy (AT) in rats via the transforming growth factor-beta (TGF-β)/mothers against decapentaplegic (Smad) pathway compared with diclofenac sodium (DS).

METHOD

An AT model was induced in rats using collagenase enzyme type I and divided into 5 groups: C (control), AT (diseased control), ATS (AT treated with sericin), ATN (AT treated with DS), and ATSN (AT treated with sericin and DS). Sericin injection was given on the 3rd and 6th days by intratendinous injection (0.8 g/kg/mL), and DS was administered for 14 days by oral gavage (1.1 mg/kg/day). Serum concentrations of total oxidant-antioxidant status (TOS-TAS), TGF-β1, decorin, Smad2, and connective tissue growth factor (CTGF) were measured. Histopathologic and immunohistochemical (IHC) studies were conducted on Achilles tendon samples.

RESULTS

The TOS, oxidative stress index (OSI), TGF-β1, Smad2, CTGF, and decorin serum concentrations were significantly higher in AT than in C and significantly lower in ATS than in AT (P<0.05). Histopathological examination revealed that irregular fibers, degeneration, and round cell nuclei were significantly elevated in AT. Spindle-shaped fibers were similar to those in C, and degeneration was reduced in ATS. TGF-β1 and Smad2/3 expression was increased, and collagen type I alpha-1 (Col1A1) expression was decreased in AT vs. C (P=0.001). In the ATS, TGF-β1 and Smad2/3 expression decreased, and Col1A1 expression increased. The Bonar score significantly increased in the AT group (P =0.001) and significantly decreased in the ATS group (P =0.027).

CONCLUSION

Sericin shows potential efficacy in reducing oxidative stress and modulating the TGF-β/Smad pathway in experimental AT models in rats. It may be a promising therapeutic agent for AT, warranting further clinical studies for validation. Key Points • This study revealed that sericin mitigates AT-induced damage through the TGF-β/Smad pathway in an AT rat model. • ELISA and IHC investigations corroborated the effectiveness of sericin via the pivotal TGF-β/Smad pathway in tissue repair. • Evidence indicates that sericin enhances collagen synthesis,shapes tendon fiber structure, and diminishes histopathological degeneration. • Sericin's antioxidant properties were reaffirmed in its AT treatment application.

Immunohistochemical and ultrastructural identification of telocytes in the lamina propria of human vaginal mucosa

Since their relatively recent discovery, telocytes (TCs) have been described as peculiar cells strategically positioned in the stromal tissue component of multiple organ systems of the mammalian body including female reproductive organs (i.e., ovary, uterine tube, and uterus). Nevertheless, current knowledge of TCs in the vagina is very limited. The present study was therefore undertaken to investigate the existence and characteristics of TCs in the stromal tissue of human vaginal mucosa by means of immunohistochemistry, immunofluorescence confocal microscopy, and transmission electron microscopy. In the vaginal lamina propria, TCs were first identified by CD34 immunohistochemistry that revealed the presence of CD34+ stromal cells arranged in networks, especially around blood vessels. Double immunofluorescence confocal microscopy allowed to precisely distinguish the perivascular networks of CD34+ stromal cells lacking CD31 immunoreactivity from adjacent CD31+ microvessels. All the perivascular networks of TCs/CD34+ stromal cells situated in the vaginal lamina propria coexpressed platelet-derived growth factor receptor α, which strengthened their identification as TCs. Instead, vaginal mucosal TCs were immunophenotypically negative for c-kit/CD117. The ultrastructural examination confirmed the presence of TCs, namely stromal cells with characteristic cytoplasmic processes (i.e., telopodes) forming labyrinthine networks around blood vessels and releasing extracellular vesicles. Together, our morphological findings provide the first comprehensive demonstration that TCs reside in the human vaginal lamina propria, thus paving the way for further investigation of their putative functions in vaginal mucosal homeostasis and pathophysiology.

The growth and developmental of the myodural bridge and its associated structures in the human fetus

Myodural bridge (MDB) is a dense connective tissue between suboccipital muscle and dura mater. However, there are few reports on the development and maturation of the human MDB. This study aims to explore the developmental relationship between suboccipital muscle and MDB. 30 head and neck specimens from human fetuses (F) ranging from the 12th to 41st week (W) were made into histological sections. The F12W sections showed evidence that the dura mater dominated by fibroblasts, attached to the posterior atlanto-axial membrane (PAAM) which completely sealed the atlanto-axial space. In the F13W stage, myofibrils of the suboccipital muscle fibers increased significantly in number. At the F14W stage, a gap was observed at the caudal end of the PAAM. Numerous myodural bridge-like structures were observed blending into the dura mater through the gap. At the F19W stage, muscle cells mature. Starting at the F21W stage, the MDB were observed as fibroblasts that cross the atlanto-axial interspace and attach to the dura mater. Therefore, the traction generated by the suboccipital muscles seems to promote the maturity of MDB. This study will provide new morphological knowledge to support future research on the function of the human MDB and regulating the development mechanism of MDB.

Comparison of the Behavior of Perivascular Cells (Pericytes and CD34+ Stromal Cell/Telocytes) in Sprouting and Intussusceptive Angiogenesis

Perivascular cells in the pericytic microvasculature, pericytes and CD34+ stromal cells/telocytes (CD34+SCs/TCs), have an important role in angiogenesis. We compare the behavior of these cells depending on whether the growth of endothelial cells (ECs) from the pre-existing microvasculature is toward the interstitium with vascular bud and neovessel formation (sprouting angiogenesis) or toward the vascular lumen with intravascular pillar development and vessel division (intussusceptive angiogenesis). Detachment from the vascular wall, mobilization, proliferation, recruitment, and differentiation of pericytes and CD34+SCs/TCs, as well as associated changes in vessel permeability and functionality, and modifications of the extracellular matrix are more intense, longer lasting over time, and with a greater energy cost in sprouting angiogenesis than in intussusceptive angiogenesis, in which some of the aforementioned events do not occur or are compensated for by others (e.g., sparse EC and pericyte proliferation by cell elongation and thinning). The governing mechanisms involve cell-cell contacts (e.g., peg-and-socket junctions between pericytes and ECs), multiple autocrine and paracrine signaling molecules and pathways (e.g., vascular endothelial growth factor, platelet-derived growth factor, angiopoietins, transforming growth factor B, ephrins, semaphorins, and metalloproteinases), and other factors (e.g., hypoxia, vascular patency, and blood flow). Pericytes participate in vessel development, stabilization, maturation and regression in sprouting angiogenesis, and in interstitial tissue structure formation of the pillar core in intussusceptive angiogenesis. In sprouting angiogenesis, proliferating perivascular CD34+SCs/TCs are an important source of stromal cells during repair through granulation tissue formation and of cancer-associated fibroblasts (CAFs) in tumors. Conversely, CD34+SCs/TCs have less participation as precursor cells in intussusceptive angiogenesis. The dysfunction of these mechanisms is involved in several diseases, including neoplasms, with therapeutic implications.

Maternal undernutrition alters the skeletal muscle development and methylation of myogenic factors in goat offspring

Objective

The effects of maternal undernutrition during midgestation on muscle fiber histology, myosin heavy chain (MyHC) expression, methylation modification of myogenic factors, and the mammalian target of rapamycin (mTOR) signaling pathway in the skeletal muscles of prenatal and postnatal goats were examined.

Methods

Twenty-four pregnant goats were assigned to a control (100% of the nutrients requirement, n = 12) or a restricted group (60% of the nutrients requirement, n = 12) between 45 and 100 days of gestation. Descendants were harvested at day 100 of gestation and at day 90 after birth to collect the femoris muscle tissue.

Results

Maternal undernutrition increased (p<0.05) the fiber area of the vastus muscle in the fetuses and enhanced (p<0.01) the proportions of MyHCI and MyHCIIA fibers in offspring, while the proportion of MyHCIIX fibers was decreased (p<0.01). DNA methylation at the +530 cytosine-guanine dinucleotide (CpG) site of the myogenic factor 5 (MYF5) promoter in restricted fetuses was increased (p<0.05), but the methylation of the MYF5 gene at the +274,280 CpG site and of the myogenic differentiation (MYOD) gene at the +252 CpG site in restricted kids was reduced (p<0.05). mTOR protein signals were downregulated (p<0.05) in the restricted offspring.

Conclusion

Maternal undernutrition altered the muscle fiber type in offspring, but its relationship with methylation in the promoter regions of myogenic genes needs to be elucidated.

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.

Identification of the Molecular Basis of Nanocurcumin-Induced Telocyte Preservation within the Colon of Ulcerative Colitis Rat Model

Background

Telocytes (TCs) are a distinct type of interstitial cells that play a vital role in the pathogenesis of ulcerative colitis and colonic tissue hemostasis. The aim of this study was to examine the effect of nanocurcumin (NC) on the morphometric and immunohistochemical characterization of TCs in the ulcerative colitis (UC) rat model.

Methods

Forty rats were randomly divided into control, NC, UC, and UC+NC groups. At the end of the experiment, the colon was dissected and prepared for histopathological and immunohistochemical assessment. Tissue homogenates were prepared for real-time PCR assessment of interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and transforming growth factor-beta (TGF-β) gene expression. Our results revealed extensive mucosal damage with inflammatory cell infiltration, significant reduction of CD34, and vimentin immunostained TCs in the colon of the UC group with significant elevation of expression of IL-6, TNF-α, and TGF-β. The UC+NC-treated group revealed significant elevation of TC count compared to the UC group besides, a significant reduction of the three gene expression.

Conclusion

NC successfully targeted the colonic tissue, improved the mucosal lesion, preserve TCs distribution, and count through its anti-inflammatory and fibrinolytic properties.

Telocytes: An Emerging Component of Stem Cell Niche Microenvironment

Telocytes (TCs) are newly identified interstitial cells characterized by thin and long cytoplasmic processes, called telopodes, which exhibit a distinctive moniliform shape and, often, a sinuous trajectory. Telopodes typically organize in intricate networks within the stromal space of most organs, where they communicate with neighboring cells by means of specialized cell-to-cell junctions or shedding extracellular vesicles. Hence, TCs are generally regarded as supporting cells that help in the maintenance of local tissue homeostasis, with an ever-increasing number of studies trying to explore their functions both in physiological and pathological conditions. Notably, TCs appear to be part of stem cell (SC) niches in different organs, including the intestine, skeletal muscle, heart, lung, and skin. Indeed, growing evidence points toward a possible implication of TCs in the regulation of the activity of tissue-resident SCs and in shaping the SC niche microenvironment, thus contributing to tissue renewal and repair. Here, we review how the introduction of TCs into the scientific literature has deepened our knowledge of the stromal architecture focusing on the intestine and skeletal muscle, two organs in which the recently unveiled unique relationship between TCs and SCs is currently in the spotlight as potential target for tissue regenerative purposes.

Bone Marrow-Mesenchymal Stromal Cell Secretome as Conditioned Medium Relieves Experimental Skeletal Muscle Damage Induced by Ex Vivo Eccentric Contraction

Bone marrow-mesenchymal stem/stromal cells (MSCs) may offer promise for skeletal muscle repair/regeneration. Growing evidence suggests that the mechanisms underpinning the beneficial effects of such cells in muscle tissue reside in their ability to secrete bioactive molecules (secretome) with multiple actions. Hence, we examined the effects of MSC secretome as conditioned medium (MSC-CM) on ex vivo murine extensor digitorum longus muscle injured by forced eccentric contraction (EC). By combining morphological (light and confocal laser scanning microscopies) and electrophysiological analyses we demonstrated the capability of MSC-CM to attenuate EC-induced tissue structural damages and sarcolemnic functional properties’ modifications. MSC-CM was effective in protecting myofibers from apoptosis, as suggested by a reduced expression of pro-apoptotic markers, cytochrome c and activated caspase-3, along with an increase in the expression of pro-survival AKT factor. Notably, MSC-CM also reduced the EC-induced tissue redistribution and extension of telocytes/CD34⁺ stromal cells, distinctive cells proposed to play a “nursing” role for the muscle resident myogenic satellite cells (SCs), regarded as the main players of regeneration. Moreover, it affected SC functionality likely contributing to replenishment of the SC reservoir. This study provides the necessary groundwork for further investigation of the effects of MSC secretome in the setting of skeletal muscle injury and regenerative medicine.

Developmental events and cellular changes occurred during esophageal development of quail embryos

The current study focused on the histogenesis of the esophagus in quail embryos. Formation of the gut tube occurred on the 4th day of incubation. Development of the muscular layers occurred in a sequential manner; the inner circular layer on the 7th day, the outer longitudinal layer on the 8th day and the muscularis mucosae on the 9th day. Glandular development began on the 13th day of incubation. The epithelium was pseudostratified columnar that consisted of mucous cells, dendritic cells, and keratinocyte precursors. Epithelial stratification occurred on the 15th day of incubation. We used Mallory trichrome, Weigert-Van Gieson, and Gomori silver stains to visualize fibrous components. Scanned samples showed formation of endoderm and mesoderm on the 5th day of incubation. A layer of myoblasts developed on the 8th day of incubation. Formation of mucosal folds, which contained glandular openings, occurred on the 14th to 17th days of incubation. On the 5th to 8th days of incubation, CD34 and vascular endothelial growth factor (VEGF) positive-mesodermal cells, and telocytes (TCs) were detected. On the 15th day of incubation, CD34 and VEGF positive-telocytes, and fibroblasts, were identified. The current study described the correlations between functional morphology and evolutionary biology.

Structural Investigation of Epididymal Microvasculature and Its Relation to Telocytes and Immune Cells in Camel

The vascular and perivascular cells, including telocytes (TCs) and immune cells, play an important role in male fertility. The current study intended to describe in detail the microvascular structures harboring special regulatory devices in addition to the interstitial cellular components of the one-humped camel epididymis. The samples were collected from 10 clinically healthy mature camels (Camelus dromedarius). The distribution and characteristics of TCs, peripheral blood vessels of the epididymis, and immune cells were investigated using the light, immunohistochemistry, immunofluorescence, and transmission electron microscopy analyses. Frequent occlusive or throttle arterioles were demonstrated in the epididymal interstitium and their tunica media consisted of glomus cells. In addition, some vein walls consisted of one or two layers of glomus cells. TCs, fibroblasts, muscle cells, and tunica media of the blood vessels, that present in the loose connective tissue surrounding the intertubular interstitium of camel epididymis, showed a positive reaction with vimentin. The endothelium of blood vessels and veins showed positive immunoreactivity for CD34 and vascular endothelial growth factor (VEGF). Furthermore, VEGF, CD34, and S100 proteins were expressed in dendritic cells (DCs) as well as TCs. The current data suggest the involvement of DCs and TCs in angiogenesis and a possible role for the interstitial components in creating an appropriate milieu for the full maturation of sperms.

Telocytes are associated with tissue remodeling and angiogenesis during the postlactational involution of the mammary gland in gerbils

The postlactational involution of the mammary gland is a complex process. It involves the collapse of the alveoli and the remodeling of the extracellular matrix, which in turn implies a complex set of interrelations between the epithelial, stromal, and extracellular matrix elements. The telocytes, a new type of CD34-positive stromal cell that differs from fibroblasts in morphological terms and gene expression, were detected in the stroma of several tissues, including the mammary gland; however, their function remains elusive. The present study employed three-dimensional reconstructions and immunohistochemical, ultrastructural, and immunofluorescence techniques in histological sections of the mammary gland of the Mongolian gerbil during lactation and postlactational involution to evaluate the presence of telocytes and to investigate a possible function for these cells. By means of immunofluorescence assays for CD34 and c-kit, major markers of telocytes, and also through morphological and ultrastructural evidences, telocytes were observed to surround the mammary ducts and collapsing alveoli. It was also found that these cells are associated with matrix metalloproteinase 9, which indicates that telocytes can play a role in extracellular matrix digestion, as well as vascular endothelial growth factor, a factor that promotes angiogenesis. Together, these data indicate that telocytes are a distinct cell type in the mammary gland and, for the first time, show that these cells possibly play a role in tissue remodeling and angiogenesis during the postlactional involution of the mammary gland.

Telocytes and lymphatic endothelial cells: Two immunophenotypically distinct and spatially close cell entities

Telocytes (TCs) have recently emerged as a peculiar type of stromal cells located in both perivascular and interstitial compartments of multiple anatomical sites in humans, other mammals and vertebrates. Pioneer electron microscopy studies have ultrastructurally defined TCs as "stromal cells with telopodes" (i.e. very long and thin cell processes with a moniliform morphology conferred by the irregular alternation of slender segments and small, bead-like, dilated portions), whereupon it has become apparent that TCs largely correspond to the CD34+ stromal/interstitial cells detectable by immunohistochemical assays. Besides CD34, TCs are also characterized by the expression of platelet-derived growth factor receptor (PDGFR)α. Interestingly, recent works recommended that lymphatic endothelial cell (LEC) markers should be routinely assessed to discriminate with certainty TCs from LECs, because these two cell types may exhibit similar morphological traits, especially when initial lymphatics are sectioned longitudinally and appear as vascular profiles with no obvious lumen. Furthermore, it has been argued that lymphatic microvessels immunostained for the small mucin-type transmembrane glycoprotein podoplanin (PDPN), which is widely used as lymphatic endothelial marker, can be easily misidentified as TCs. Nevertheless, surprisingly these assumptions were not based on double tissue immunostaining for TC and LEC markers. Therefore, the present morphological study was undertaken to precisely investigate the mutual spatial organization and putative relationships of TCs and lymphatic vessels in tissues from different human organs. For this purpose, we carried out a series of double immunofluorescence analyses simultaneously detecting the CD34 or PDGFRα antigen and a marker of LECs, either PDPN or lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1). In the connective tissue compartment of different organs, TCs were CD34+/PDGFRα+/PDPN-/LYVE-1- while LECs were CD34-/PDGFRα-/PDPN+/LYVE-1+, thus representing two definitely distinct, though spatially close, cell entities. The arrangement of telopodes to intimately surround the abluminal side of LECs suggests a possible role of TCs in the regulation of lymphatic capillary functionality, which is worth investigating further.

Ultrastructural and immunohistochemical characteristics of telocytes in human scalp tissue

This study was designed to characterize the location, morphology and ultrastructure of telocytes (TCs) in human scalp tissue. After obtaining approval for this study and informed consent from the patient, a scalp specimen was obtained. The distribution and morphology of TCs in human scalp tissue was assessed by immunohistochemical staining of CD34 and CD117/c-KIT, and the ultrastructure of TCs was investigated using transmission electron microscopy (TEM). Immunohistochemical staining of CD34 revealed that TCs were located in the connective tissue of human scalp, and were concentrated around hair follicles (HFs), blood vessels, sweat glands, sebaceous glands and adipose lobules. Immunohistochemical staining of CD117 revealed that TCs were mainly located in the dermis of human scalp, surrounding the HFs and sweat glands. Under TEM, TCs were seen and confirmed by their special morphological features. These cells were spindle-shaped, had small cell bodies and long thin processes, and surrounded stem cell clusters in the bulge region of HFs. These results demonstrate that TCs in human scalp were positive for CD34 and CD117, and their strategic positioning surrounding stem cells suggests their possible involvement in local regeneration, remodeling and homeostasis of the skin.

Changes in the telocyte/CD34+ stromal cell and α-SMA+ myoid cell networks in human testicular seminoma

Telocytes (TCs), also known as CD34+ stromal/interstitial cells, have recently been identified within the connective tissue of a variety of organs including the normal human testis. Testicular TCs appear to constitute a widespread reticular network distributed either in the peritubular or in the intertubular stromal spaces where they have been suggested to play different roles, such as participation to testis morphogenesis, postnatal preservation of the normal tissue/organ three-dimensional structure, and regulation of spermatogenesis and androgen hormone secretion and release. Although increasing evidence indicates that TCs may be involved in the pathophysiology of various diseases, no study has yet reported possible changes in these cells within the stromal compartment of seminoma, one of the most frequent malignant testicular cancers in humans. Therefore, here we carried out the first investigation of the presence and tissue distribution of TCs/CD34+ stromal cells in human testicular seminoma in comparison with normal human testis using either CD34 immunohistochemistry or CD34/CD31 and CD34/α-smooth muscle actin (α-SMA) double immunofluorescence analyses. In seminoma tissue sections, we observed an overall loss of TCs (CD34+/CD31- stromal cells) accompanying a severe degeneration of the normal architecture of seminiferous tubules and stromal tissue associated with dense cellularity increase and presence of interstitial fibrosis. Noteworthy, in the seminoma tissue the disappearance of TCs was paralleled by an expansion of α-SMA+ myoid cells. Moreover, the CD34+/CD31+ blood vessel network was greatly expanded, while steroidogenic Leydig cells were undetectable in seminoma specimens. Since TCs are emerging as important regulators of tissue and organ homeostasis, collectively the present findings indicate that the possible pathophysiologic implications of the loss of TCs in human testicular seminoma should not be further overlooked.

Morphological evidence for telocytes as stromal cells supporting satellite cell activation in eccentric contraction-induced skeletal muscle injury

Although telocytes (TCs) have been proposed to play a “nursing” role in resident satellite cell (SC)-mediated skeletal muscle regeneration, currently there is no evidence of TC-SC morpho-functional interaction following tissue injury. Hence, we explored the presence of TCs and their relationship with SCs in an ex vivo model of eccentric contraction (EC)-induced muscle damage. EC-injured muscles showed structural/ultrastructural alterations and changes in electrophysiological sarcolemnic properties. TCs were identified in control and EC-injured muscles by either confocal immunofluorescence (i.e. CD34⁺CD31⁻ TCs) or transmission electron microscopy (TEM). In EC-injured muscles, an extended interstitial network of CD34⁺ TCs/telopodes was detected around activated SCs displaying Pax7⁺ and MyoD⁺ nuclei. TEM revealed that TCs invaded the SC niche passing with their telopodes through a fragmented basal lamina and contacting the underlying activated SCs. TC-SC interaction after injury was confirmed in vitro by culturing single endomysial sheath-covered myofibers and sprouting TCs and SCs. EC-damaged muscle-derived TCs showed increased expression of the recognized pro-myogenic vascular endothelial growth factor-A, and SCs from the same samples exhibited increased MyoD expression and greater tendency to fuse into myotubes. Here, we provide the essential groundwork for further investigation of TC-SC interactions in the setting of skeletal muscle injury and regenerative medicine.

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

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

"Prostate telocytes change their phenotype in response to castration or testosterone replacement"

Telocytes are CD34-positive cells with a fusiform cell body and long, thin cytoplasmic projections called telopodes. These cells were detected in the stroma of various organs, including the prostate. The prostate is a complex gland capable of undergoing involution due to low testosterone levels; and this condition can be reversed with testosterone replacement. Telocyte function in the mature prostate remains to be dermined, and it is not known whether telocytes can take place in tissue remodeling during prostate involution and regrowth. The present study employed structural, ultrastructural and immunohistochemical methods to investigate the telocyte's phenotypes in the ventral prostate (VP) from control (CT), castrated (CS) and testosterone replacement (TR) groups of adult male Wistar rats. Telocytes were found in the subepithelial, perimuscular and interstitical regions around glandular acini. Telocytes from CT animals have condensed chromatin and long and thin telopodes. In CS group, telocytes appeared quiescent and exhibited layers of folded up telopodes. After TR, telocytes presented loose chromatin, abundant rough endoplasmic reticulum and enlarged telopodes, closely associated with bundles of collagen fibrils. We called these cells "telocytes with a synthetic phenotype". As testosterone levels and glandular morphology returned toward to the CT group parameters, after 10 days of TR, these telocytes progressively switched to the normal phenotype. Our results demonstrate that telocytes exhibit phenotypic plasticity upon androgen manipulation and interact with fibroblast and smooth muscle cells to maintain glandular architecture in control animals and during tissue remodeling after hormonal manipulation.

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.

Immunolocalization of VEGF/VEGFR system in human fetal vomeronasal organ during early development

The vomeronasal system (VNS) is an accessory olfactory structure present in most mammals adhibited to the detection of specific chemosignals implied in social and reproductive behavior. The VNS comprises the vomeronasal organ (VNO), vomeronasal nerve and accessory olfactory bulb. VNO is characterized by a neuroepithelium constituted by bipolar neurons and supporting and stem/progenitor cells. In humans, VNO is present during fetal life and is supposed to possess chemoreceptor activity and participate in gonadotropin-releasing hormone neuronal precursor migration toward the hypothalamus. Instead, the existence and functions of VNO in postnatal life is debated. Vascular endothelial growth factor (VEGF) and its receptors (VEGFRs) have been demonstrated to play fundamental roles in various neurogenic events. However, there are no data regarding the localization and possible function of VEGF/VEGFRs in human fetal VNO. Therefore, this study was conceived to investigate the expression of VEGF/VEGFRs in human VNO in an early developmental period (9-12 weeks of gestation), when this organ appears well structured. Coronal sections of maxillofacial specimens were subjected to peroxidase-based immunohistochemistry for VEGF, VEGFR-1 and VEGFR-2. Double immunofluorescence for VEGF, VEGFR-1 or VEGFR-2 and the neuronal marker protein gene product 9.5 (PGP 9.5) was also performed. VEGF expression was evident in the entire VNO epithelium, with particularly strong reactivity in the middle layer. Strongly VEGF-immunostained cells with aspect similar to bipolar neurons and/or their presumable precursors were detected in the middle and basal layers. Cells detaching from the basal epithelial layer and detached cell groups in the surrounding lamina propria showed moderate/strong VEGF expression. The strongest VEGFR-1 and VEGFR-2 expression was detected in the apical epithelial layer. Cells with aspect similar to bipolar neurons and/or their presumable precursors located in the middle and basal layers and the detaching/detached cells displayed a VEGFR-1 and VEGFR-2 reactivity similar to that of VEGF. The basal epithelial layer exhibited stronger staining for VEGFRs than for VEGF. Cells with morphology and VEGF/VEGFR expression similar to those of the detaching/detached cells were also detected in the middle and basal VNO epithelial layers. Double immunofluorescence using anti-PGP 9.5 antibodies demonstrated that most of the VEGF/VEGFR-immunoreactive cells were neuronal cells. Collectively, our findings suggest that during early fetal development the VEGF/VEGFR system might be involved in the presumptive VNO chemoreceptor activity and neuronal precursor migration.

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

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