A role of myocardial stiffness in cell-based cardiac repair: a hypothesis

Determining which time point is optimal for bone marrow-derived cell (BMC) transplantation for acute myocardial infarction (AMI) has attracted a great deal of attention. Studies have verified the interaction between cell treatment effect and transfer timing and have suggested that the optimal time frame for BMC therapy is day 4 to day 7 after AMI. However, the potential mechanism underlying the time-dependent therapeutic response remains unclear. Recently, a growing body of in vitro evidence has suggested that stem cells are able to feel and respond to the stiffness of their microenvironment to commit to a relevant lineage, indicating that soft matrices that mimic brain are neurogenic, stiffer matrices that mimic muscle are myogenic and comparatively rigid matrices that mimic collagenous bone prove osteogenic. Simultaneously, considering the fact that the myocardium post-infarction experiences a time-dependent stiffness change from flexible to rigid as a result of myocardial remodelling following tissue necrosis and massive extracellular matrix deposition, we presume that the myocardial stiffness within a certain time frame (possibly day 4-7) post-AMI might provide a more favourable physical microenvironment for the phenotypic plasticity and functional specification of engrafted BMCs committed to some cell lineages, such as endothelial cells, vascular smooth muscle cells or cardiomyocytes. The beneficial effect facilitates angiogenesis and myocardiogenesis in the infarcted heart, and subsequently leads to more amelioration of cardiac functions. If the present hypothesis were true, it would be of great help to understand the mechanism underlying the optimal timing for BMC transplantation and to establish a direction for the time selection of cell therapy.