Why do myofibroblasts preferentially accumulate on the convex surface of the remodeling lung after pneumonectomy?

Myofibroblasts preferentially accumulate on the convex and not on the concave surfaces of the murine cardiac lobe during lung remodeling after pneumonectomy. This clear difference in function due to the organ shape is most likely mediated by the various mechanical forces generated on the lung's surface. For breathing, the lobe cyclically change its configuration. The cyclic deformation requires energy, depending on the local configuration of the lobe (e.g., convex vs. concave). Considering mechanical contributions to the internal energy of the system and according to the second law of thermodynamics, the system seeks the lowest energy state for equilibrium. Although additional energy for remodeling is required, the system chooses such remodeling sites that minimize the total energy of the new equilibrium state. To test this idea, an idealized, concave-convex configuration of the lobe is assumed. The lobe is made of two homogeneous and isotropic materials of different mechanical properties, the bulk parenchyma and the pleura, a thin, mesothelial cell layer surrounding it. While the whole system cyclically changes shape during breathing, we calculated the amount of mechanical energy per unit volume at the parenchyma-pleural interface where, we believe, myofibroblasts preferentially accumulate. Comparison between convex and concave surfaces indicates that convex surfaces store a lower amount of mechanical energy than the concave ones. We also show that any additional energy for remodeling is preferably done at the convex surface where the lowest new energy equilibrium state is achieved.