Presence of Ganglia and Telocytes in Proximity to Myocardial Sleeve Tissue in the Porcine Pulmonary Veins Wall

Ultrastructural evidence of telocytes in the embryonic chick heart

The cardiac telocyte (TC) is a novel interstitial cell type with a unique ultrastructure and great potential in therapy. The present study examined its presence in the heart of chicken embryos ageing 7-15 days old (Hamburger-Hamilton [HH] stages 31-41) using transmission electron microscopy. TCs were identified across all stages in the atrial and ventricular myocardium, close to maturing cardiomyocytes, blood vessels and lymphatics. Early-stage TCs have immature features resembling mesenchymal cells. Late-stage TCs were distinct, possessing the cytoplasmic prolongations termed telopodes (Tps), which are very long and thin, usually 1-3 in number, and display a moniliform appearance and have an average thickness below 0.2 μm. TCs residing in the epicardium and endocardium were also detected. In the subepicardium near developing coronary vessels, they were localized in the cardiac stem cell niches, coexisting with cardiac stem cells and cardiomyocyte progenitors. Electron-dense structures and the release of extracellular vesicles were observed between embryonic TCs and surrounding structures, suggesting roles in intercellular communication, cardiomyocyte differentiation and maturation, angiogenesis, and stem cell nursing and guidance.

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.

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 and Atrial Fibrillation: From Basic Research to Clinical Practice

The emergence of new research methods makes it possible to study the tissue, structural, cellular, and molecular causes of atrial fibrillation (AF). Recently, the role of interstitial telocyte cells in the pathogenesis of AF has been actively discussed. Telocytes are a special type of interstitial cells identified in many organs and tissues, including the heart. The roles of telocytes in the myocardium are diverse: they have pacemaker activity, and carry out structural and coordination communication between cells. The ability of these cells to change the speed of the electrical pulse in the atrial and ventricular myocardium has been proven. Telocytes form "atypical" connections with almost all types of cells in the human heart, which collects them in an integrated network. Using electron microscopy, it was found that interstitial cells have different types of connections in the network and can integrate "information" from the vascular and nervous systems, interstitial, immune system, stem cells, progenitor cells, and contractile cardiomyocytes. Currently, the results of studies have been obtained that prove both positive and negative effects of telocytes on the occurrence of various diseases of the cardiovascular system. The role of telocytes in AF arrhythmogenesis remains a subject of discussion. The unique properties of telocytes in providing intercellular contacts, transmitting genetic information, and their ability to regenerate heart tissue are undoubtedly the most promising areas of modern cardiology. There is evidence of both direct and indirect effects of telocytes on the electrophysiological properties of the myocardium. There is no doubt that the development of this area opens up new therapeutic targets for the prevention and treatment of AF.

Telocytes in the Myocardium of Children with Congenital Heart Disease Tetralogy of Fallot

Telocytes, a new type of interstitial stem cells with long thin processes that form a three-dimensional network around cardiomyocytes, vessels, and nerve fibers were described in the myocardium of children with tetralogy of Fallot. Two types of morphologically different telocytes, spindle-shaped and rounded, were identified. Contacts of telocytes with stem cells and interstitial macrophages were found. Telocytes were more common in the immature myocardium, where the assembly of myofibrils in cardiomyocytes was not completed and small Ki-67⁺ cardiomyocyte progenitor cells were present. Telocytes expressed immunohistochemical markers CD117, vimentin, CD34, and CD44. Localization and ultrastructural characteristics of telocytes suggested their participation in stem cell differentiation, coordination of neoangiogenesis, and paracrine regulation of all components of the interstitium.

Cardiac telocytes. From basic science to cardiac diseases. I. Atrial fibrillation

INTRODUCTION

Atrial fibrillation (AF) is nowadays considered to be one of the most important causes of heart failure, stroke, cognitive decline, vascular dementia, sudden death and overall cardiovascular morbidity. Recently were published a few articles suggesting a possible involvement of telocytes in the development of atrial fibrillation. The purpose of this article is to analyze the results obtained in the field systematically, and to see if there is enough data to support a possible involvement of telocytes in arrhythmogenesis.

MATERIALS AND METHODS

To this end, we performed a systematic review of the relevant scientific literature, indexed in PubMed, Web of Science, and Scopus.

RESULTS AND DISCUSSIONS

Our systematic review of the published data identified five articles containing original data, based on which the association between telocytes and atrial fibrillation was inferred in later studies. We analyzed the usefulness of the information contained in the original articles to support this association, showing a lack of definite proofs correlating telocytes with atrial fibrillation.

CONCLUSIONS

Even if a few articles implied a potential association between AF and telocytes, the current data is not enough to support it. Moreover, even an association between the morphology, characteristics, or density of the telocytes in the atrium/pulmonary veins and AF is potentially speculative, and more studies should be performed before implying it with a reasonable degree of certainty.

Mitochondrial DNA in Telocytes

Telocyte (TC) is a new identified interstitial cell type with a small nuclear and one or several long and thin prolongations with enlargements on them. They were found in many mammals including humans, mouse, rats, dogs, and monkeys and play vital roles in many physiological and pathological conditions. The ultrastructure of mitochondria was observed in TCs, and the alterations were found in TCs from inflammatory ureter tissue. MtDNA is associated with mitochondria normal functions and involved in physiological and pathological processes. However, mitochondria and mtDNA in TCs were not investigated deeply. This review will introduce the origin, distribution, morphology, and functions of TCs and the distribution and functions of TC mitochondria in order to improve a better understanding of the potential functions of mtDNA in TCs.