Generation and analysis of spheroids from human primary skin myofibroblasts: an experimental system to study myofibroblasts deactivation

Myofibroblasts are activated fibroblasts involved in tissue repair and cancer. They are characterized by de novo expression of a-smooth muscle actin (alpha-SMA), immunoregulatory phenotype and paracrine interaction with normal and tumorigenic cells leading to cell proliferation. At the end of wound-healing myofibroblasts undergo apoptotic cell death, whereas in vitro-activated fibroblasts are also subjected to a programmed necrosis-like cell death, termed nemosis, associated with cyclooxygenase-2 (COX-2) expression induction and inflammatory response. Furthermore, myofibroblasts form clusters during wound healing, fibrotic states and tumorigenesis. In this study, we generated and analysed clusters such as spheroids from human primary cutaneous myofibroblasts, which represent a part of stromal microenvironment better than established cell lines. Therefore, we evaluated apoptotic or necrotic cell death, inflammation and activation markers during myofibroblasts clustering. The spheroids formation did not trigger apoptosis, necrotic cell death and COX-2 protein induction. The significant decrease of alpha-SMA in protein extracts of spheroids, the cytostatic effect exerted by spheroids conditioned medium on both normal and cancer cell lines and the absence of proliferation marker Ki-67 after 72 h of three-dimensional culture indicated that myofibroblasts have undergone a deactivation process within spheroids. The cells of spheroids reverted to adhesion growth preserved their proliferation capability and can reacquire a myofibroblastic phenotype. Moreover, the spontaneous formation of clusters on plastic and glass substrates suggests that aggregates formation could be a physiological feature of cutaneous myofibroblasts. This study represents an experimental model to analyse myofibroblasts deactivation and suggests that fibroblast clusters could be a cell reservoir regulating tissues turnover.