Fig. 7
From: A positive feedback loop bi-stably activates fibroblasts
High TNC is essential for activating the irreversible PFL. a In the fibrotic nodule generated by exogenous TNC, we observed a TNC concentration gradient (top). In-depth analysis of this nodule using multiplex IHC showed that Twist1 and Prrx1 were strongly positive and coexpressed in most fibroblasts within strongly TNC-positive zone1, and this pattern disappeared as the TNC concentration decreased (bottom left) (Twist1-green, Prrx1-red, TNC-yellow and hematoxylin-blue). We measured each integrated density per zone representing the expression level of each gene using ImageJ Fiji (bottom right). Data are presented as the mean ± SEM; N = 3 independent measurements (two-tailed t test: *p<0.05, **p<0.001, ***p<0.0001). b We treated mouse dermal fibroblasts isolated from fresh Balb/c mouse tissue with TNC at different concentrations (0, 0.1, 1, 2, and 5 μg) and then evaluated Twist1 and TNC expression by western blotting (top). We estimated the kinetic parameter values of the mathematical model based on this western blotting data on the Twist1 and TNC fold changes along with the increase of exogenous TNC (bottom). Discrete data marked with squares indicate experimental measurements of the corresponding genes (N = 3, error bars indicate s.d.). c Phase diagram illustrating the irreversibility of TNC (represented by color intensity) with respect to the feedback strength (V) and the TNC level for feedback activation (Km1, the Michaelis−Menten constant) (top left). The hysteretic responses of TNC to the TNC injection in the irreversible ((Km1, V) = (5, 30)) and reversible ((Km1, V) = (10, 15)) states are shown in the top right and bottom left figures, respectively. Given that the stimulus increases from zero to TNCmax and then decreases back to zero, we compared the irreversibility of TNC, ∆TNC, with that of the reversible state (bottom right). The inlet shows examples of obtaining ∆TNC for the TNCmax
