Connexin43 and immunity : macrophage phagocytosis, cardiac calcinosis and autoimmune myocarditis

Abstract

Connexin43 (Cx43) is a gap junction protein best known for coupling the cytoplasms of cardiac myocytes and allowing the efficient conduction of action potentials throughout the heart. In addition to the heart, Cx43 is also highly expressed in many immune cells and it has been attributed numerous roles in immunity. One such reported role was in macrophage phagocytosis. The first chapter in this dissertation explored the phagocytic activity of cultured and primary murine macrophages from wild type (WT) and Cx43-deleted (Cx43-/-) macrophages. No difference in phagocytic uptake was observed between the two groups using a series of target particles, indicating that Cx43 is dispensable for phagocytosis in macrophages. Given the spectrum of immune functions in which Cx43 has been ascribed a role, we set out to characterize its effect on a model of autoimmune myocarditis (EAM). Using the area of cardiac inflammatory infiltrate as a correlate of disease severity, we observed the progression of the disease to be independent of Cx43 status utilizing WT and Cx43-heterozygous (Cx43+/-) animals as well as radiation chimeric mice reconstituted with cells from donor WT, Cx43+/- and Cx43-/- mice.

Although the severity of EAM did not measurably change when induced in animals with differing levels of Cx43 expression, substantial changes to ventricular Cx43 were noted in diseased hearts. Large foci were observed that completely lacked Cx43 immunofluorescence signal. Areas surrounding these foci exhibited disrupted Cx43 patterns such as internalization and lateralization. Similar alterations to Cx43 were also observed in the BALB/cByJ strain of laboratory mice that develop a spontaneous myocarditic disease.

To investigate the electrophysiological ramifications of EAM, especially in the context of Cx43+/- mice, ECGs were recorded from animals over the course of EAM. Significant changes to the QRS interval were noted, including prolongation that was only observed in Cx43+/- animals.