Exosomal MicroRNA-21 Promotes Keloid Fibroblast Proliferation and Collagen Production by Inhibiting Smad7

In keloid fibroblasts, microRNA-21 (miR-21) enhances activation of the TGF-beta-Smad signaling pathway by down-regulating Smad7 expression, thereby promoting keloid fibroblast proliferation and collagen production. However, it is unclear whether miR-21 performs the above-mentioned functions through exosomal transport. Here, we extracted exosomes from the culture supernatants of keloid and normal skin fibroblasts and observed that both types of cells above secrete exosomes; however, keloid fibroblasts secreted significantly more exosomal miR-21 than normal skin fibroblasts (P < .001). Interestingly, we also observed that exosomal miR-21 could enter target keloid fibroblasts. In addition, inhibiting exosomal miR-21 up-regulated Smad7 protein expression and reduced Smad2 and Smad3 protein levels in target keloid fibroblasts. Furthermore, inhibiting exosomal miR-21 down-regulated collagen I and collagen III expression in target keloid fibroblasts, increased the proportion of apoptotic cells, and reduced cell proliferation. Taken together, these results show that exosomal miR-21 promoted proliferation and collagen production in keloid fibroblasts by inhibiting Smad7. Thus, we identified regulatory roles for miR-21 in promoting keloid fibroblast proliferation and participating in keloid formation and development. These findings imply that miR-21 may serve as a novel target for controlling the development of keloids.