IL-10 and TGF-β Increase Connexin-43 Expression and Membrane Potential of HL-1 Cardiomyocytes Coupled with RAW 264.7 Macrophages

Cardiac resident macrophages facilitate electrical conduction by interacting with cardiomyocytes via connexin-43 (Cx43) hemichannels. Cx43 is critical for impulse propagation and coordination between muscle contractions. Cardiomyocyte electrophysiology can be altered when coupled with noncardiomyocyte cell types such as M2c tissue-resident macrophages. Using cocultures of murine HL-1 cardiomyocytes and RAW 264.7 macrophages, we examined the hypothesis that cytokine signals, TGF-β1 and IL-10, upregulate Cx43 expression at points of contact between the two cell types. These cytokine signals maintain the macrophages in an M2c anti-inflammatory phenotype, mimicking cardiac resident macrophages. The electrophysiology of cardiomyocytes was examined using di-8-ANEPPS potentiometric dye, which reflects a change in membrane potential. Greater fluorescence intensity of di-8-ANEPPS occurred in areas where macrophages interacted with cardiomyocytes. Suppressor of cytokine signaling 3 (SOCS3) peptide mimetic downregulated fluorescence of this membrane potentiometric stain. Cx43 expression in cocultures was confirmed by fluorescence microscopy and flow cytometry. Confocal images of these interactions demonstrate the Cx43 hemichannel linkages between the cardiomyocytes and macrophages. These results suggest that TGF-β1 and IL-10 upregulate Cx43 hemichannels, thus enhancing macrophage–cardiomyocyte coupling, raising the cellular resting membrane potential and leading to a more excitatory cardiomyocyte