Identification of telocytes in skeletal muscle interstitium: implication for muscle regeneration.
Bottom Line: The same phenotypic profile was demonstrated in cell cultures.We also described non-satellite (resident) progenitor cell niche.In culture, TCs (but not satellite cells) emerge from muscle explants and form networks suggesting a key role in muscle regeneration and repair, at least after trauma.
Affiliation: Department of Cellular and Molecular Medicine, Carol Davila University of Medicine and Pharmacy, Bucharest, Romania. LMP@jcmm.orgShow MeSH
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Mentions: Electron microscopy showed that TCs (Figs 1–7) were present in skeletal muscle interstitium in both human (Figs 1–7) and rat (Figs 2–3) specimens. TCs formed a labyrinthine system as a result of overlapping Tps (Fig. 3C and D) and were organized in a network alongside the striated muscle cells and vascular system (Figs 1, 2 and 3A). The shape of TCs was either triangular (Fig. 1) or spindle (Fig. 2A and C), depending on the number of visible Tps (embedded in the 60-nm-thick section; Fig. 3E). The Tps had a narrow emergence from the cellular body (Figs 1 and 2B) and were extremely long (45–90 μm) and sinuous (Figs 2C and 3B). The moniliform aspect of Tps was because of the uneven calibre (Figs 1–3) and the irregular alternation of podomeres, thin (40–100 nm) segments, with podoms, dilatations (150–500 nm) containing mitochondria, endoplasmic reticulum and caveolae (Figs 1, 3, 5 and 6). This typical aspect enable the recognition of segments of Tps, which appeared separated from TCs cellular body as a result of specimen sectioning (Figs 2A, 3C and E and 6). TCs often extended their Tps between small folds in the periphery of muscle-striated cells (Fig. 3C and D). Shed vesicles and exosomes were found in the vicinity of Tps (Figs 2, 3 and 5). Tps were interconnected by different types of junctions: manubria adhaerentia (Fig. 4A), puncta adhaerentia (Fig. 4B) and small electron dense structures (Fig. 4). Electron microscopy of striated muscle showed as well that TCs are often located in the close vicinity of satellite cells (Fig. 6), striated cells with regenerative features (Fig. 6, inset) or even putative progenitor cells (Figs 7 and 8). Notably, such cells were located in between adult skeletal muscle cells in contrast to satellite cells, which are enclosed by muscle fibres basal lamina (Fig. 6).
Affiliation: Department of Cellular and Molecular Medicine, Carol Davila University of Medicine and Pharmacy, Bucharest, Romania. LMP@jcmm.org