Abstract 2425: Cx43 Reduction by IL-1β Prevents Myofibroblasts/Myocyte Coupling in vivo and Causes Conduction Block in the Infarcted Canine Heart
Background: Inflammatory responses to Myocardial infarction (MI) initiate transformation of cardiac fibroblasts to myofibroblasts (MYOFIBs) which release the pro-inflammatory cytokine Interleukin-1β (IL-1β), a known regulator of the cardiac gap junction protein Connexin43 (Cx43). Whether MYOFIBs form functional gap junctions with cardiac myocytes and how MYOFIBs impact propagation in vivo is unclear. We hypothesize that IL-1β from MYOFIBs inhibits gap junction formation between myocytes and MYOFIBs thus causing slowed cardiac conduction.
Methods: In a canine model of MI, we examined levels of MYOFIBs by electron microscopy and immunohistochemistry (IHC). To understand the impact of IL-1β on Cx43, we incubated cultured rat neonatal cardiomyocytes with activated IL-1β and measured Cx43 levels and localization. Using IHC we examined the relationship of Cx43 to MYOFIB clusters in the post-MI heart. To quantify the effect of randomly distributed MYOFIBs (size 10um × 10um, ~ 5% of the total volume) on propagation we used a 2D subcellular computer model of the epicardial border zone (EBZ). Cell-to-cell coupling was 6.7uS.
Results: MYOFIBs were significantly increased in both the outer and central common pathways of EBZ reentrant circuits (0.64% normal to 1.88% OP and 2.27% CCP; p<0.05). IHC showed that IL-1β alone decreased Cx43 and revealed that regions of diminished Cx43 are associated with MYOFIB clusters. Importantly, no gap junctions between MYOFIBs and myocytes were observed by any method. Computer simulations showed that MYOFIBs increased spatial heterogeneity in conduction and led to block during premature stimulation.
Conclusion: In the infarcted canine heart MYOFIB clusters populate the EBZ. Computer simulations showed that MYOFIB proliferation led to areas of slow conduction and block which were unrelated to refractory period heterogeneities. IHC studies indicated that MYOFIBs do not directly couple to surviving myocytes. Thus, IL-1β from MYOFIBs likely decreases Cx43, leading to loss of cell-cell coupling, slowed conduction and development of ventricular arrhythmias following MI.
This research has received full or partial funding support from the American Heart Association, Founders Affiliate (Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Rhode Island, Vermont).