Skin telocyte secretome as conditioned medium prevents profibrotic differentiation of skin fibroblasts into myofibroblasts

Telocytes (TCs) are a distinct type of stromal cells found in different organs of the human body, including the skin. By means of their characteristic prolongations (telopodes), skin TCs are arranged in networks intermingled with a multitude of neighboring cells and, hence, they are thought to contribute to skin homeostasis through both intercellular contacts and release of extracellular vesicles. A disruption of the dermal network of TCs was reported in both human fibrotic skin lesions and mouse model of bleomycin-induced skin fibrosis [1,2], but whether TC damage/disappearance may be a mere fibrosis consequence or contribute to fibrogenesis remains unclear. Hence, we examined the in vitro effects of skin TC secretome as conditioned medium (TC-CM) on skin fibroblast-to-myofibroblast transition induced by the key profibrotic mediator transforming growth factor β1 (TGFβ1). Primary cultures of adult human skin TCs and fibroblasts were established through immunomagnetic microbead-based cell separation [3]. Extracellular vesicle measurements in TC-CM were performed with nanoparticle tracking analysis (NanoSight). By combining morphological, gene/protein expression, and functional analyses we demonstrated the capability of TC-CM to significantly prevent TGFβ1-induced fibroblast activation and transition to myofibroblasts. TC-CM did not affect fibroblast viability, while it was able to inhibit TGFβ1-induced proliferation, wound healing capacity, and changes in cell morphology. TC-CM was effective in attenuating TGFβ1-induced skin fibroblast phenotypic and functional differentiation into myofibroblasts, as demonstrated by a significant reduction in FAP, ACTA2, COL1A1, COL1A2, and FN1 gene expression, α-smooth muscle actin, N-cadherin, COL1A1, and FN-EDA protein levels, and collagen gel matrix contraction. Moreover, TC-CM significantly decreased TGFβ1-mediated activation of ERK1/2 signaling. This study demonstrates for the first time that TCs may contribute to skin homeostasis by preventing profibrotic activation of fibroblasts and provides the necessary groundwork for further investigation of the use of TC secretome as potential antifibrotic therapeutic intervention.