A new cellular type in invertebrates: first evidence of telocytes in leech Hirudo medicinalis

Abstract

Telocytes, a peculiar cell type, were recently found in vertebrates. Hence this cell system has been reported as ubiquitous in the bodies of mammals and interpreted as an important player in innate immunity and tissue regeneration, it is reasonable to look for it also in invertebrates, that rely their integrity solely by innate immunity. Here we describe, at morphological and functional level, invertebrate telocytes from the body of leech Hirudo medicinalis (Annelida), suggesting how these cells, forming a resident stromal 3D network, can influence or participate in different events. These findings support the concepts that leech telocytes: i) are organized in a cellular dynamic and versatile 3D network likewise the vertebrate counterpart; ii) are an evolutionarily conserved immune-neuroendocrine system; iii) form an immuno-surveillance system of resident cells responding faster than migrating immunocytes recruited in stimulated area; iv) communicate with neighbouring cells directly and indirectly, via cell-cell contacts and soluble molecules secreted by multivesicular bodies; v) present within neo-vessels, share with immunocytes the mesodermal lineage; vi) are involved in regenerative processes. In conclusion, we propose that HmTCs, integrating so different functions, might explain the innate immune memory and can be associated with several aged related diseases.

Cardiac telocytes exist in the adult Xenopus tropicalis heart

“…Based on the observations of the representative dimensions of the upper region, middle region and base of the ventricle of the X tropicalis heart, we found that CTs were mainly twined around the surface of cardiomyocyte trabeculae and were linked together via the ends of the telopodes, producing a three‐dimensional network of CTs in the X tropicalis myocardium. This distribution pattern was quite similar among the upper region, middle region and base region and was similar to that in other species, such as the leech, rodent and human . This spatial distribution of CTs suggests that CTs and their networks play an important role as structural supports to maintain and promote the integrity of the X tropicalis myocardium under physiopathological conditions.…”

“…These distributive characteristics are different from those of the mammalian heart, such as the hearts of humans and rodents (rats and mice). As in mammals, CTs show a distribution mainly in the gaps between cardiomyocytes . It is believed that this pattern fits the course of evolutionary development, as in the mammalian myocardium, cardiomyocytes do not have a trabecular structure like that in the amphibian X tropicalis myocardium .…”

“…In the present study, we first showed that cardiac telocytes exist in the adult X tropicalis heart using TEM according to the presence and was similar to that in other species, such as the leech, rodent and human. 5,6,25,37 This spatial distribution of CTs suggests that CTs and their networks play an important role as structural supports to maintain and promote the integrity of the X tropicalis myocardium under physiopathological conditions. In support of this hypothesis, our TEM observations revealed that even though the cell body and long telopodes of CTs do not make direct contact, the nanometerrange gap between the CT cell body or telopodes and cardiomyocytes is spanned with microfilaments.…”

“…[8][9][10] One important discovery is the identification of a novel type of stromal cell named telocytes, which are found in humans and rodents in the interstitium of the heart, 7,[11][12][13][14][15][16][17] skeletal muscle, 18 trachea and lung, 19,20 intestine, 21 uterus and fallopian tubes, 22 placenta 23 and mammary glands 24 and in the interstitium of the leech Hirudo medicinalis. 25 CTs were found to be niche supporting cells that nurse cardiac stem cells and other cardiac cells in the myocardium and play an important role in regeneration following MI. 26 Recently, we reported that the death of CTs is an important mechanism that contributes to the structural damage and poor healing and regeneration observed in MI.…”

“…During development and under physiopathological conditions, cardiac stromal cells and endothelial cells control the proliferation, growth and differentiation of cardiomyocytes in the myocardium . One important discovery is the identification of a novel type of stromal cell named telocytes, which are found in humans and rodents in the interstitium of the heart, skeletal muscle, trachea and lung, intestine, uterus and fallopian tubes, placenta and mammary glands and in the interstitium of the leech Hirudo medicinalis . CTs were found to be niche supporting cells that nurse cardiac stem cells and other cardiac cells in the myocardium and play an important role in regeneration following MI .…”