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The name telocytes has been proposed for a cell type previously often referred to as interstitial cells of Cajal. Electron microscopy and cell cultures reveal that these cells are very distinct from interstitial cells of Cajal and differ from all other types of interstitial cells. Telocytes have 2-5 very thin and extremely long (tens up to hundreds of micrometers) cell body prolongations, termed telopodes, not seen in other cell types (Popescu LM and Faussone-Pellegrini MS, 2010).
Telocytes were identified first as a distinct new cell type in the myocardial interstitium but have been found subsequently in many other tissue locations. Telocytes form homocellular junctions between themselves (puncta adhaerentia and manubria adhaerentia) and heterocellular junctions (puncta adherentia, puncta adhaerentia minima) with tissue-specific cells. They also release exosomes and thus have the capability to communicate with other cells by direct cell-to-cell contact and through shed vesicles (Popescu et al, 2011).
Ardeleanu and Bussolati (2011) have suggested that telocytes may be the cell of origin of both PEComas (perivascular epithelioid cell tumours) and GISTs (gastro-intestinal and extra-gastrointestinal stromal tumours).
Cantarero et al (2011) have shown the presence of telocytes located on the extracellular matrix of blood vessels (arterioles, venules and capillaries).
Gherghiceanu et al (2008) have reported the existence of telocytes in human myocardial sleeves of pulmonary veins. The cells express c-kit and cell processes establish close spatial relationships between each other, as well as with capillaries and nerve endings.
duodenum and jenunum
Cantarero Carmona et al (2011) have described telocytes in the lamina propria of rat duodenum, immediately below mucosal crypts. Telopodes of these cells frequently establish close spatial relationships with immune cells, blood vessels, and nerve endings.
Cretoiu et al (2012) have reported telocytes in the lamina propria of rat jejunum just beneath the epithelial layer of the mucosal crypts and in between the smooth muscle cells of muscularis mucosae.
Hinescu et al (2007) have reported telocytes in the gall bladder, where they represent approximately 5.5 % of subepithelial cells. The cells express c-kit, CD34 and also alpha-smooth muscle actin, CD1a, CD62P, CD68, chromogranin A, desmin, estrogen receptors, GFAP, nestin, NK-1, NSE, PGP-9.5, progesterone receptors, S100, tau protein, vimentin.
These cells are in close association with cardiomyocytes (Zhu et al, 2010) and may act as supporting cells for myocardial tissue organization in the developing and adult heart (Bani et al, 2010). Gherghiceanu and Popescu (2011) have reported that telocyes in the heart are directly connected to cardiomyocytes by nanocontacts as well as complex and atypical junctions and might represent a functional unit.
Cismasiu et al (2011) have reported that cardiac telocytes express microRNA miR-193 but not other microRNAs that are expressed specifically in cardiomyocytes and other muscle cells.
Manole et al (2011) have reported that cardiac telocytes play a role in neoangiogenesis following myocardial infarction. Telocytes establish multiple direct nanocontacts with endothelial cells and contribute to angiogenesis also by secreting VEGF. Telocytes also contain measurable quantities of angiogenic microRNAs (e.g. let-7e, 10a, 21, 27b, 100, 126-3p, 130a, 143, 155, 503).
Gherghiceanu and Popescu (2012) have reported that cardiac telocytes form junctions with virtually all types of cells in the human heart. Telocytes have direct cell-cell nanocontacts with Schwann cells, endothelial cells and pericytes, macrophages, mast cells), fibroblasts, stem cells and progenitor cells, cardiomyocytes.
Radu et al (2005) have report telocytes in human inactive mammary gland stroma. The cells express c-kit and vimentin.
meninges and choroid plexus
Popescu et al (2012) have reported telocytes in meninges and choroid plexus in the vicinity of putative stem cells.
Nicolescu and Popescu (2012) have reported telocytes in the exocrine pancreatic stroma.
Nicolescu et al (2012) have reported telocytes in the stroma of parotid glands in close contact or vicinity of both secretory (acini and ducts) and regulatory (nerves and blood vessels) apparatuses.
Hinescu et al (2011) have reported telocytes in the sub-mesothelial layer in mouse and human pleura where they appear to form an interstitial network beneath the mesothelium, covering about two-thirds of the abluminal mesothelial layer.
respiratory tract (lungs and trachea)
Zheng et al (2011) have reported telocytes in trachea and lungs in close relationships with nerve endings and blood capillaries. These cells express c-kit, vimentin and CD34.
Popescu et al (2011) have reported telocytes in the human and mouse respiratory tree (terminal and respiratory bronchioles, as well as alveolar ducts). At bronchoalveolar junctions, telocytes appear in close association with putative stem cells in the subepithelial stroma. Telocytes surround these stem cells and are connected to stem cells by bridging nanostructures.
Rusu et al (2012) have found telocytes in all stromal compartments of the tracheal wall. Telocytes with long prolongations are lining longitudinally the collagen bundles, and are arranged in an end-to-end fashion. Telocaytes frequently establish stromal synapses with mast cells.
Popescu et al (2011) and Bojin et al (2011) have identified telocytes in the skeletal muscle interstitium of rat, mouse and human skeletal muscle. These telocytes are in close vicinity with nerve endings, capillaries, satellite cells and myocytes. The cells have been shown to express c-kit, caveolin-1 and to secrete VEGF. Bojin et al (2011) have reported that cells with telocyte morphology express c-kit and VEGF. Cultured cells show high proliferation capacity and also exhibit pluripotent capacity.
Suciu et al (2012) have reported that telocytes in human skeletal muscle are constantly located around intermediate and small blood vessels and endomysial capillaries in the perivascular or pericapillary space. The cells express c-kit, PDGF receptors, and VEGF and may be involved in the process of mural cell recruitment during angiogenesis and vascular remodelling.
Rusu et al (2012) have localized telocytes in human skin dermis in close proximity or connecting to fibroblasts, mast cells, adipocytes, and connective fiber bundles.
Ceafalan et al (2012) have reported that human dermal telocytes. are found in the reticular dermis, around blood vessels, in the perifollicular sheath, outside the glassy membrane and surrounding sebaceous glands, arrector pili muscles and both the secretory and excretory portions of eccrine sweat glands. The cells are connected to each other by homocellular junctions, and form an interstitial 3D network. Telocytes are also observed adjoined to stem cells in the bulge region of hair follicles. They also establish junctions with stem cells. The authors have suggested that, based on the distribution and intercellular connections of telocytes, these cells may be involved in skin homeostasis, skin remodelling, skin regeneration and skin repair.
uterus and fallopian tube, placenta, endometrium
Telocytes have been located also in the uterus and fallopian tube (Popescu et al, 2007). Cretoiu et al (2009) have reported that these cells express c-kit and also estrogen receptors and progesterone receptors.
Hatta et al (2012) have reported the presence of telocytes in the human and rat endometrium. Cultured cells express CD34 and stain positive for vimentin and connexin 43. Telopodes connect cell colonies and distant cells.
Suciu et al (2010) have reported telocytes in human placenta in close contacts with perivascular smooth muscle cells in stem villi. The cells express c-kit, CD34, vimentin, caveolin-1, VEGF, and inducible nitric oxide synathase (iNOS). The c-kit-positive cells inconsistently co-express CD34, CD44, alpha-smooth muscle actin, S100, neuron-specific enolase, and nestin.
Gevaert et al (2012) have identified telocytes in the upper lamina propria of the urinary tract (human renal pelvis, ureter and urethra) directly underneath the urothelium The cells show variable expression of estrogen receptor and progesterone receptor.
For related information of interest see also: Cell types.
Copyright © 2012 by H IBELGAUFTS. All rights reserved.
ENTRY LAST MODIFIED: August 2012
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