Nail Telocytes: Identification, Potential Physiological Function, and Role in Pathology: A Reappraisal of the So-Called Onychofibroblasts/Onychodermis

ABSTRACT

Some authors have suggested that the fibroblasts of the nail mesenchyme (onychofibroblasts) can be distinguished from skin fibroblasts by their high expression of CD10. My 2015 study documented the presence of a relatively sparse CD34 + /CD10 + dendritic subpopulation in the dermis and hypodermis of the matrix. For some time now, my hypothesis has been that these interstitial dendritic mesenchymal cells of the matrix correspond to telocytes. Telocytes have been described as peculiar interstitial dendritic cells present in the mesenchymal tissue of numerous organs, including the skin, but their presence and characteristics in the nail unit have not been explored. This study was undertaken to more comprehensively investigate the existence and characteristics of nail telocytes. A series of 20 normal adult nail units were examined with a combination of morphological and immunohistochemical analyses. The matrix dermis contained a sparse subpopulation of CD34 + /CD10 + elongated telocytes with a higher density in the lunular region and, at this distal level, a change in their immunohistochemical profile, resulting in a progressive loss of CD34 expression. The matrix hypodermis showed CD34 + /CD10 + telocytes in their classical elongated aspect, which acquired, especially in the distal fibromyxoid area of the thumb, an oval to round morphology with multiple intracytoplasmic vacuoles. The characteristic dynamic immunophenotypic profile of the dermal telocytes with a progressive distal loss of the defining molecule CD34 was equally observed in the distal hypodermis. The nail bed dermis was thick with a dense fibrous connective tissue. A reticular network of CD34 - /CD10 + telocytes was present in the superficial dermis of the proximal nail bed. The mesenchymal cells of the deep part of the proximal nail bed dermis and the entire distal nail bed dermis were CD34 - /CD10 - . The adult nail mesenchyme is composed of 3 microanatomically distinct regions. Only the thumb has a distal hypodermis rich in mucinous material. The population of telocytes is relatively sparse compared with the fibroblastic population of the entire nail mesenchyme. The concept of onychodermis/onychofibroblasts is not valid. Nail telocytes have a dynamic immunohistochemical profile depending on whether they are located proximally or distally. The CD34 + /CD10 + profile correlates with the onychogenic epithelial region, while the CD34 - /CD10 + profile correlates with a spatial rearrangement of the nail epidermal bed.

Are telocytes related to maintenance of vascular homeostasis in normal and pathological aorta?

The telocyte (TC) is a new interstitial cell type described in a wide variety of organs and loose connective tissues around small vessels, but its presence in large arteries remains unexplored. TCs have small cell bodies and remarkably thin, long, moniliform processes called telopods (Tps). Using transmission electron microscopy and immunofluorescence, we identified TCs in normal human thoracic aortas and in those with aneurysm or acute dissection (TAAD). In normal aortas the TCs were distributed throughout the connective tissue of the adventitial layer, in its innermost portion and at the zone of transition with the medial layer, with their long axes oriented parallel to the external elastic lamellae, forming a three-dimensional network, without prevalence in the media layer. In contrast, TAAD TCs were present in the medial layer and in regions of neovascularization. The most important feature of the adventitia of diseased aortas was the presence of numerous contacts between TCs and stem cells, including vascular progenitor cells. Although the biologically functional correlations need to be elucidated, the morphological observations presented here provide strong evidence of the involvement of TCs in maintaining vascular homeostasis in pathological situations of tissue injury.

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.

Delimiting CD34+ Stromal Cells/Telocytes Are Resident Mesenchymal Cells That Participate in Neovessel Formation in Skin Kaposi Sarcoma

Kaposi sarcoma (KS) is an angioproliferative lesion in which two main KS cell sources are currently sustained: endothelial cells (ECs) and mesenchymal/stromal cells. Our objective is to establish the tissue location, characteristics and transdifferentiation steps to the KS cells of the latter. For this purpose, we studied specimens of 49 cases of cutaneous KS using immunochemistry and confocal and electron microscopy. The results showed that delimiting CD34+ stromal cells/Telocytes (CD34+SCs/TCs) in the external layer of the pre-existing blood vessels and around skin appendages form small convergent lumens, express markers for ECs of blood and lymphatic vessels, share ultrastructural characteristics with ECs and participate in the origin of two main types of neovessels, the evolution of which gives rise to lymphangiomatous or spindle-cell patterns-the substrate of the main KS histopathological variants. Intraluminal folds and pillars (papillae) are formed in the neovessels, which suggests they increase by vessel splitting (intussusceptive angiogenesis and intussusceptive lymphangiogenesis). In conclusion, delimiting CD34+SCs/TCs are mesenchymal/stromal cells that can transdifferentiate into KS ECs, participating in the formation of two types of neovessels. The subsequent growth of the latter involves intussusceptive mechanisms, originating several KS variants. These findings are of histogenic, clinical and therapeutic interest.

Notes about telocytes and immunity

The interstitial cells known as telocytes have been described in various organs. Their role in the normal physiology and pathogenesis of numerous diseases is well known. They have been described in the context of various diseases (gallstone disease, endometriosis, uterine myoma, hydronephrosis, myocardial infraction, psoriasis, etc.), while their impact on inflammation, involvement in angiogenesis, and repair highlights their part in local homeostasis. What is known about their relationship with the immune system? Their secretomes, genome, immune profiles, contacts with surrounding cells, and specific localization allow us to give a possible explanation for their involvement in pathological pathways. This review aims to present the roles and features of telocytes in the context of intestinal immunity (the largest in our body), in the spleen, their interactions with immunocytes, and their place in stem cell niches.

Cd34+ Stromal Cells/Telocytes in Normal and Pathological Skin

We studied CD34+ stromal cells/telocytes (CD34+SCs/TCs) in pathologic skin, after briefly examining them in normal conditions. We confirm previous studies by other authors in the normal dermis regarding CD34+SC/TC characteristics and distribution around vessels, nerves and cutaneous annexes, highlighting their practical absence in the papillary dermis and presence in the bulge region of perifollicular groups of very small CD34+ stromal cells. In non-tumoral skin pathology, we studied examples of the principal histologic patterns in which CD34+SCs/TCs have (1) a fundamental pathophysiological role, including (a) fibrosing/sclerosing diseases, such as systemic sclerosis, with loss of CD34+SCs/TCs and presence of stromal cells co-expressing CD34 and αSMA, and (b) metabolic degenerative processes, including basophilic degeneration of collagen, with stromal cells/telocytes in close association with degenerative fibrils, and cutaneous myxoid cysts with spindle-shaped, stellate and bulky vacuolated CD34+ stromal cells, and (2) a secondary reactive role, encompassing dermatitis—e.g., interface (erythema multiforme), acantholytic (pemphigus, Hailey–Hailey disease), lichenoid (lichen planus), subepidermal vesicular (bullous pemphigoid), psoriasiform (psoriasis), granulomatous (granuloma annulare)—vasculitis (leukocytoclastic and lymphocytic vasculitis), folliculitis, perifolliculitis and inflammation of the sweat and sebaceous glands (perifolliculitis and rosacea) and infectious dermatitis (verruca vulgaris). In skin tumor and tumor-like conditions, we studied examples of those in which CD34+ stromal cells are (1) the neoplastic component (dermatofibrosarcoma protuberans, sclerotic fibroma and solitary fibrous tumor), (2) a neoplastic component with varying presentation (fibroepithelial polyp and superficial myxofibrosarcoma) and (3) a reactive component in other tumor/tumor-like cell lines, such as those deriving from vessel periendothelial cells (myopericytoma), epithelial cells (trichoepithelioma, nevus sebaceous of Jadassohn and seborrheic keratosis), Merkel cells (Merkel cell carcinoma), melanocytes (dermal melanocytic nevi) and Schwann cells (neurofibroma and granular cell tumor).

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/CD34+ Stromal Cells in Pathologically Affected White Adipose Tissue

We studied telocytes/CD34+ stromal cells (TCs/CD34+SCs) in pathologically affected white adipose tissue after briefly examining them in normal fat. To this aim, we reviewed pathological processes, including original contributions, in which TCs/CD34+SCs are conserved, increased, and lost, or acquire a specific arrangement. The pathologic processes in which TCs/CD34+SCs are studied in adipose tissue include inflammation and repair through granulation tissue, iatrogenic insulin-amyloid type amyloidosis, non-adipose tissue components (nerve fascicles and fibres in neuromas and hyperplastic neurogenic processes) and tumours (signet ring carcinoma with Krukenberg tumour and colon carcinoma) growing in adipose tissue, adipose tissue tumours (spindle cell lipoma, dendritic fibromyxolipoma, pleomorphic lipoma, infiltrating angiolipoma of skeletal muscle and elastofibrolipoma), lipomatous hypertrophy of the interatrial septum, nevus lipomatosus cutaneous superficialis of Hoffman–Zurhelle and irradiated adipose tissue of the perirectal and thymic regions. Two highly interesting issues emerged: (1) whether the loss of CD34 expression in TCs/CD34+SCs is by changes in marker expression or the disappearance of these cells (the findings suggest the first possibility) and (2) whether in some invasive and metastatic malignant tumours, TCs/CD34+SCs that completely surround neoplastic cells act as nurse and/or isolating cells. Further studies are required on adipose tissue TCs/CD34+SCs, mainly in lipomatosis and obesity.

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.

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.

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.

Relation between ureteral telocytes and the hydronephrosis development in children

INTRODUCTION

Hydronephrosis is an actual pediatric problem, affecting children in the ante- and neonatal periods. Intrinsic stenosis is due to external obstruction and creates a pathophysiological basis of this urological pathology. Co-localization of ureter with a renal vasculature also could not be omitted from this point of view. Mesenchymal cells, partially telocytes, are important for local fibrosis development and hydronephrosis formation as well. In the current study, we focused on identification of telocytes in the human ureters to hypothesize their role in hydronephrosis pathophysiology.

MATERIAL AND METHODS

the samples were taken from 18 surgically treated patients with hydronephrosis (due to ureteral obstruction and crossing renal vessel). The control group consisted of 10 patients suffered from a non-obstructive disease of the urinary tract - predominantly renal tumors. Tissue samples from a ureter were stained for c-kit, tryptase, CD34 and PDGFRα to identify telocytes. Routine histology was performed to analyze tissue morphology, collagen deposits and mast cell's profile.

RESULTS

Telocytes were detected in the ureteral wall. In patients with hydronephrosis we revealed decreasing density of telocytes, the prevalence of collagen, rise in mast cells amount and the ureteral wall thickening. In ureters with crossing renal vessels as a primary etiologic factor more telocytes have been observed in comparison with the obstructive hydronephrosis.

CONCLUSIONS

A declined density of telocytes accompanied hydronephrosis development. Increased number of mast cells in the ureteral wall reflects a local inflammation, while detailed observation of collagen/muscle deposits and density of telocytes reveal a difference depended on etiologic factor (obstruction or crossing vessel) in patients with hydronephrosis.

Histopathologic and immunohistochemical findings in congenital anorectal malformations

It remains controversial whether the distal rectal pouch should be either resected or used for reconstruction in anorectoplasty for the treatment of anorectal malformations (ARMs). Hence the aim of this study was to investigate whether ARMs were associated with a global neuromuscular maldevelopment of the terminal rectum specimens.There were 36 cases of ARMs (25 recto-bulbar fistula and 11 recto-prostatic fistula) and 10 healthy controls. The hematoxylin and eosin and Masson trichrome stain were used to conduct the histologic examination. The immunohistochemistry (IHC) and Western blot were conducted to analyze the neuron-specific enolase (NSE), S-100 protein, interstitial cells of Cajal marker (C-kit) within the rectal specimens in control group and ARM group.The most frequently observed histologic findings in mucosa were inflammation, congestion, eroded, and hemorrhage in the ARM cases. Submucosal inflammation and congestion were the most common submucosal findings in the ARM cases. Disrupted muscularis propria was observed in 60% of ARM cases. Mature ganglionic cells were reduced and muscularis propria showed reduced and patchy positivity for NSE, S-100, and C-kit protein in ARM group compared to that in control group according to IHC. Western blotting showed the expression levels of NSE, S-100, and C-kit were lower in the ARM group than that in the control group (P < .01).Histopathologic and IHC findings suggest that the distal rectal pouch has distinct defects in the neuromusculature. So it suggested that ARMs are abnormally developed tissue and need to be resected for better functional outcomes of the remaining gut.

Histological and immunohistochemical study of cardiac telocytes in a rat model of isoproterenol-induced myocardial infarction with a reference to the effect of grape seed extract

INTRODUCTION

Cardiac telocytes (TCs) represent a unique type of cells that make a supportive network for stem cells that contribute in cardiac renewal, but their role during myocardial infarction (MI) is not clear. Grape seed extract (GSE) is a powerful natural antioxidant.

AIM OF THE WORK

Quantitative study of cardiac TCs in a rat model of Isoproterenol (ISO)-induced MI, and to evaluate the effect of GSE on TCs and MI progression.

MATERIALS AND METHODS

Seventy adult male albino rats were assigned into 4 groups; group I; control rats, group II received GSE (100mg/kg/day) dissolved in distilled water orally, group III received 2 intra-peritoneal injections of 85mg/kg ISO dissolved in saline on 14th and 15th day to induce MI, and group IV received GSE and ISO. Myocardium was obtained 1 and 14days after ISO i.e. on day 16 and day 30 respectively. Tissue was prepared for histological and immunohistochemical study of CD117 and CD34 as two markers for TCs. CD34 was used also as a marker for angiogenesis.

RESULTS

Group III showed focal areas of myocardial infarction 1day and 14days after ISO. Degenerated cardiomyocytes showed loss of striation and hypereosinophilic vacuolated cytoplasm with condensed nuclei. Mononuclear cell infiltration and a significantly increased percentage area of fibrosis 14days after ISO were observed. CD117 and CD34 positive TCs were hardly detected 1day after ISO. Their number slightly increased 14days after ISO with insignificant difference to control. There was also a significant increase in the number of CD34 positive blood vessels 14days after ISO. Group IV showed much better histological picture with a significant decrease in the percentage area of fibrosis and a significant increase in the number of CD117 and CD34 positive TCs and the number of CD34 positive blood vessels as compared to group III.

CONCLUSION

Telocytes were significantly decreased in MI. GSE reduced ISO-induced histological changes and increased the number of TCs that improved angiogenesis.

Characterization of smooth muscle, enteric nerve, interstitial cells of Cajal, and fibroblast-like cells in the gastric musculature of patients with diabetes mellitus

AIM

To investigate histologic abnormalities in the gastric smooth muscle of patients with diabetes mellitus (DM).

METHODS

Full-thickness gastric specimens were obtained from patients undergoing surgery for gastric cancer. H&E stain and Masson’s Trichrome stain were performed to assess the degree of fibrosis. Immunohistochemical staining using various antibodies was also performed [antibodies against protein gene product 9.5 (PGP9.5), neuronal nitric oxide synthase (nNOS), vasoactive intestinal peptide (VIP), neurokinin-1 (NK1) receptor, c-Kit, and platelet-derived growth factor receptor-alpha, (PDGFRα)]. Immunofluorescent staining and evaluation with confocal microscopy were also conducted.

RESULTS

Twenty-six controls and 35 diabetic patients (21 short-duration patients and 14 long-duration patients) were included. There were no significant differences in basic demographics between the two groups except in mean body mass index (BMI) (higher in the DM group). Proportions of moderate-to-severe intercellular fibrosis in the muscle layer were significantly higher in the DM group than in the control group (P < 0.01). On immunohistochemical staining, c-Kit- and PDGFRα-positive immunoreactivity were significantly decreased in the DM group compared with the control group (P < 0.05). There were no statistically significant differences in PGP9.5, nNOS, VIP, and neurokinin 1 expression. On immunofluorescent staining, cellularity of interstitial cells of Cajal (ICC) was observed to decrease with increasing duration of DM.

CONCLUSION

Our study suggests that increased intercellular fibrosis, loss of ICC, and loss of fibroblast-like cells are found in the smooth muscle of DM patients. These abnormalities may contribute to changes in gastric motor activity in patients with DM.

Tubal telocytes: factor infertility reason?

Infertility is actually widespread pathological condition, which affected one in every four couples in developing countries. Approximately one third of all cases are connected with tubal factor infertility, o en accompanies by endometriosis, acute salpingitis, urogenital infections etc. The newly identified telocytes (TCs) have multiple potential bio-functions and might participate in the fertility problems. They influence on structural and functional integrity of oviduct tissue. Despite recent discovery, TCs involvement in the majority of physiological and pathological processes is still unclear and require significant increasing of deep observations and data analysis. Focusing on female reproductive system help better understands the main reasons of infertility, while evaluation of TCs impact on Fallopian tube and uterus contractility might be a key point of its correction. The article summarizes the main features of telocytes in Fallopian tubes, emphasizing their involvement in pathophysiological processes and tubal factor infertility.