Myofibroblasts cause heterogeneous Cx43 reduction and are unlikely to be coupled to myocytes in the healing canine infarct

Abstract

Following myocardial infarction (MI) inflammatory responses transform cardiac fibroblasts to myofibroblasts, which in vitro studies show form heterocellular gap junctions with cardiac myocytes via Connexin43 (Cx43). The ability to form heterocellular junctions in the intact heart and the impact of these junctions on propagation is unclear. We used a canine model of MI and characterized the distribution and quantity of myofibroblasts in surviving epicardial cells [epicardial border zone (EBZ)]. We found a significant increase in myofibroblasts within the EBZ and no gap junction plaques between myofibroblasts and myocytes. Because myofibroblasts produce IL-1β, which downregulates Cx43, we asked whether myofibroblast proliferation causes loss of Cx43 near myofibroblast clusters. In vitro studies showed that IL-1β caused loss of Cx43 and reduced coupling. Western blot showed a significant increase of IL-1β in the EBZ, and immunohistochemistry showed a loss of Cx43 in regions of myofibroblasts in the intact heart. Additionally, dye studies in intact heart showed no coupling between myocytes and myofibroblasts. To quantify the effect of myofibroblasts on propagation we used a two-dimensional subcellular computer model of the EBZ, which showed that heterogeneities in myofibroblast density lead to conduction abnormalities. In conclusion, an increase of myofibroblasts in the infarcted heart causes heterogeneous Cx43 levels, possibly as a result of the release of IL-1β and decreased cell-cell communication, which leads to conduction abnormalities following MI.

Quantitative Analysis of Cardiac Tissue Including Fibroblasts Using Three-Dimensional Confocal Microscopy and Image Reconstruction: Towards a Basis for Electrophysiological Modeling

“…Moreover, we did not find myofibroblasts in our tissue preparations from infarcted hearts. Those had been suggested by other studies [46], [47]. However, the development and density of myofibroblasts might change with the region in the MI heart and the age of the MI.…”

Atherosclerosis exacerbates arrhythmia following myocardial infarction: Role of myocardial inflammation

“…18 An approximate 3-fold increase in IL-1β expression was found in the ApoE+MI compared to WT+MI hearts (Figure 6D). Collectively, these data suggest a role for macrophage-secreted cytokines in post-MI Cx43 degradation and Cx43-mediated slowing of conduction in inflamed hearts following MI.…”

“…15,16 In addition to compromised pump function, elevated post-MI inflammation may also impact electrophysiological remodeling and susceptibility to arrhythmia through the actions of inflammatory cytokines and proteases, such as interleukin-1β (IL-1β) and matrix metalloproteinase-7 (MMP-7). Both of these factors have been shown to degrade connexin43 (Cx43) following MI, 17,18 leading to slowed conduction and an increased propensity to arrhythmia.…”

TGF-β1 Increases Resistance of NIH/3T3 Fibroblasts Toward Apoptosis Through Activation of Smad2/3 and Erk1/2 Pathways

“…2,9,14,[29][30][31] Briefly, cells were plated at the indicated density using complete cell culture media (10% fetal bovine serum) and incubated overnight at 95% air/5% carbon dioxide to allow attachment. Subsequently, cells were transferred into an incubation media with low serum (2.5%) for sensitization toward exogenous growth factors.…”