Electrical Stimulation Of Lv Fibroblasts Causes Frequency-Dependent Modulation Of Matrix Metalloproteinase Release And Increase In Tissue Inhibitors Of Metalloproteinases

LV fibroblasts (LVMFs), which form a cellular netwrork throughout the myocardium including electrical connectivity to myocytes, are a primary cell type that contributes to remodfeling of the extracellular matrix through the synthesis of matrix metalloproteinases (MMP) and tissue inhibitors of the MMPs (TIMPs). While cytokines and other signaling molecules can induce MMP and TIMP synthesis and release from LVMFs, whether and to what degree LVMFs respond to changes in electrical stimulation with respect to modulation of MMP/TIMP release remains unknown. Porcine LVMFs were grown to confluence, serum deprived for 24 hours, and then randomized to electrical stimulation (6x10 5 cells/well, 130V 5ms pulses) for 24 hours at 1, 2, and 4 Hz (n=6 wells/frequency). Unstimulated cells (0 Hz) served as controls. Electrical stimulation had no effect on LVMF morphology. Cell media and pellets were collected for levels of MMP-2, MMP-9 (zymography), MT1-MMP, and TIMP-4 (immunoblotting). Changes in MMP and TIMP levels with stimulation are reported as a percentage of unstimulated values (TABLE ). MMP-2, MMP-9, and TIMP-1 levels were higher than unstimulated levels at 2 and 4 Hz. MT1-MMP levels were lower than unstimulated levels at 1 and 2 Hz. Ratios for each of the MMPs to TIMP-1 were computed (TABLE ). While the MMP-2/TIMP-1 and MMP-9/TIMP-1 ratios remained similar to unstimulated values, the MT1-MMP/TIMP-1 ratio was lower than unstimulated values at 1 and 2 Hz. The unique findings of this study are two-fold. First, in vitro electrical stimulation of LVMFs, which are generally considered to be electrically inert, resulted in demonstrable changes in the release of specific MMP and TIMP species. Second, the reduced MT1-MMP to TIMP-1 ratio suggests electrical stimulation of LVMFs caused a shift in the stoichiometric balance between MMPs and TIMPs that may favor accumulation of extracellular matrix components.