Telocytes within the Ligamentum Arteriosum: An Ultrastructural Evidence
Authors: Mensah Benedicta Q. 
Published: May 2022

Introduction

Telocytes (TC) are distinct interstitial cell types discovered several decades ago but officially named by Popescu group about a decade ago. Ultra‐structurally, they are usually characterized by their small but morphologically varied cell bodies (9–15 μm) and a variable number (1‐5) of cytoplasmic processes (telopodes) extending from these cell bodies. Structurally, telopodes are moniliform with alternating regions of podoms (250–300 nm) and podomers (80 nm) and are pivotal in the characterization of TC. Telopodes are also a typical feature distinguishing TC from neuronal dendrites, fibroblasts, and other interstitial cells. Numerous studies have reported their role in cell proliferation, cellular mechanical support provision, inter‐cellular signaling as well as neuromodulation. Their existence in the ligamentum arteriosum (LA) has not yet been reported though they have been reported in various organs.

Method

LA of wild type mice (n = 8) and pigs (n = 6) were fixed overnight in a fixative mixture consisting of 1.5% glutaraldehyde and 1.5% paraformaldehyde in 0.1 M phosphate buffer. After fixation, tissues were washed in 0.15 M HEPES buffer, osmicated in aqueous 1% osmium tetroxide and washed in distilled water. Specimens were contrasted in aqueous 1% uranyl acetate overnight. Tissues were washed in distilled water and dehydrated with increasing concentration of ethanol. Then dehydrated in 100% ethanol, then in 100% ethanol + propylene oxide, then in propylene oxide + epon and embedded in epon overnight. The next day, samples were put in desiccators and put in fresh epon and left in 37℃. Resulting sample blocks were trimmed. Further‐on, semi‐thin sections of were cut and stained with ready to use methylene blue solution in 1% tri‐potassium phosphate. This was followed by cutting ultra‐thin sections, which were viewed using transmission electron microscope (TEM).

Results

Results from TEM revealed interstitial cells with varied morphological cell bodies (8‐13 μm) with several caveolae present on its plasma membrane widely distributed within connective tissue of LA. The nucleus had no obvious nucleolus. Projecting from the cell bodies were dichotomously branched moniliform telopodes of varying lengths and alternating regions of podoms and podomers. Cellular organelles like mitochondria and endoplasmic reticulum were accomodated within podoms. Extra‐cellular vesicles of varying shape and sizes, sometimes in proximity (0.2 μm) to telopodes were also observed. Generally, telopodes were observe either making adherens junctions contact with other telopodes or located between fibroblasts, myocytes, or nerve endings. Conclusion: The results confirm the existence of TC within the LA. Shed extra‐cellular vesicles are perhaps indicative of short‐ and long‐distance inter‐cellular communication regulation within the LA through paracrine signaling. Additionally, functional units such as caveolae present within podoms may be involved in calcium uptake/release within the LA. Finally, the telocytes within the LA may play a role in the regulation of cell proliferation and differentiation.

Experiments were conducted at the Institute of Anatomy and Cell Biology (Justus Liebig University). I acknowledge the scientific suggestions made by the head of AG Kummer group.