Abstract
Telocytes (TCs) are distinctive cells widely localized in the stromal compartment of several human organs, including the skin. By means of their peculiar prolongations named telopodes, skin TCs are organized in networks interconnected with a variety of adjacent cells, being thus supposed to take part in skin homeostasis through both cell-to-cell contacts and the release of extracellular vesicles. A disarrangement/loss of the TC network was shown in human fibrotic skin as well as in the murine model of bleomycin-induced cutaneous fibrosis, but whether such TC alterations may represent just a consequence or a trigger of the fibrotic process still remains to be clarified. Thus, we investigated the effects of skin TC secretome as conditioned medium (TC-CM) on the transition of skin fibroblasts into myofibroblasts promoted by the master profibrotic cytokine transforming growth factor β1 (TGFβ1). Primary cultures of both adult human skin TCs and fibroblasts were obtained by means of immunomagnetic cell separation. Nanoparticle tracking analysis was carried out to measure extracellular vesicles in TC-CM. The combination of multiple morphological, gene/protein expression, and functional assessments demonstrated that TC-CM was able to significantly prevent TGFβ1-induced fibroblast-to-myofibroblast transition. TC-CM did not influence cell viability, while it effectively inhibited TGFβ1-induced fibroblast proliferation, migration, and morphological changes. Indeed, TC-CM was able to reduce TGFβ1-mediated skin fibroblast phenotypic and functional differentiation into myofibroblasts, as shown by a significant decrease in FAP, ACTA2, COL1A1, COL1A2, FN1, and CTGF gene expression, α-smooth muscle actin, N-cadherin, COL1A1, and FN-EDA protein levels, and collagen gel matrix contraction. Furthermore, TC-CM significantly lowered TGFβ1-mediated ERK1/2 signaling pathway activation. This in vitro study proves for the first time that TCs may play an important role in skin homeostasis through the prevention of fibroblast-to-myofibroblast transition via paracrine mechanisms and affords the necessary basis to investigate in the future the feasibility of TC secretome as an innovative antifibrotic therapeutic tool.