CONNEXIN37 PARTICIPATES IN ATHEROSCLEROSIS BY REGULATING LEUKOCYTE RECRUITMENT.

C. W. Wong (1), T. Christen (1), B.F. Foglia (1), I. Roth (1), D.A. Goodenough (2), and B.R. Kwak (1).

(1) Division of Cardiology, University Hospital of Geneva, Switzerland and (2)Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.  

Members of the connexin protein family form intercellular channels that permit the direct cytoplasmic exchange of ions and small metabolites between cells, a process called gap junction intercellular communication. There are presently over 20 connexins, each of which can create functional channels with unique properties including a distinctive permeability for various signaling molecules. A genetic polymorphism in the human connexin37 (Cx37) gene has been reported as a potential prognostic marker for atherosclerosis, a progressive immuno-inflammatory disease that is presently the leading cause of illness and death in developed countries. Furthermore, the expression pattern of Cx37 is altered in mouse and human atherosclerotic lesions. In particular, Cx37 disappears from the dysfunctional endothelium of advanced atherosclerotic plaques and becomes expressed in macrophages in the atherosclerotic lesions. These findings prompted us to investigate the participation of Cx37 in the development of atherosclerosis in vivo. To begin this study, Cx37-deficient (Cx37-/-) and atherosclerosis-susceptible apolipoprotein E-deficient (ApoE-/-) mice were interbred to generate double knockout mice (Cx37-/-ApoE-/-). Male Cx37-/-ApoE-/- and Cx37+/+ApoE-/- mice (n=10 per group) were fed an atherogenic diet and then sacrificed. Development of atherosclerosis in these mice was evaluated by quantifying the sudanophilic lesions located in their thoracic-abdominal aortas and aortic roots. We found that lipid deposition was 1.5 fold (thoracic-abdominal aortas) and 1.6 fold (aortic roots) higher in the Cx37-/-ApoE-/- than in the Cx37+/+ApoE-/- mice (p<0.05). This implies that the progression of atherosclerosis was significantly enhanced in the Cx37-/-ApoE-/- mice. Knowing that recruitment of leukocytes is a prerequisite for the development of atherosclerosis, we asked whether the increased atherosclerosis observed in Cx37-/-ApoE-/- mice was caused by accelerated monocyte/macrophage migration across the dysfunctional endothelium. To address this question, mouse peritoneal macrophages were isolated and used for transendothelial migration assays. As speculated, Cx37-/-ApoE-/- macrophages transmigrated 1.5 fold faster (p<0.05) across mouse endothelial cells. Taken together, our results demonstrate that Cx37 plays an important role in atherogenesis, possibly by regulating the recruitment of leukocytes to inflammatory sites.