Functional differences between human Cx37 polymorphic hemichannels.

A polymorphism in the human Cx37 gene (C1019T), resulting in a non-conservative amino acid change in the regulatory C-terminus of the Cx37 protein (P319S), has been proposed as a prognostic marker for atherosclerosis. We have recently demonstrated that Cx37 hemichannels control the initiation of atherosclerotic plaque development by regulating ATP-dependent monocyte adhesion in atherosclerosis-susceptible apolipoprotein E-deficient mice. In this study, we have measured the electrical properties of Cx37 hemichannels (HCs) and gap junction channels (GJCs) with voltage-clamp methods. To this end, we have transfected hCx37-P319, hCx37-S319 or empty pIRES-eGFP vector cDNA into communication-deficient HeLa cells. In clones expressing similar levels of Cx37, exposure of single cells to low-Ca(2+) solution induced a voltage-sensitive HC current. The analysis yielded a bell-shaped function g(hc)=f(V(m)) (g(hc): normalized conductance at steady state; V(m): membrane potential) with a maximum around V(m)=-30 mV. The peak g(hc) of Cx37-P319 was 3-fold larger than that of Cx37-S319 HCs. Experiments on cell pairs revealed that Cx37-P319 GJCs exhibited a 1.5-fold larger unitary conductance than Cx37-S319 GJCs. Hence, the larger peak g(hc) of the former may reflect a larger conductance of their HCs. Using the same clones, we found that Cx37-P319 cells released more ATP and were less adhesive than Cx37-S319 cells. The reduction in adhesiveness of Cx37-expressing cells was prevented by extracellular apyrase. We conclude that the differences in biophysical properties between polymorphic HCs may be responsible for inequality in ATP release between Cx37-P319 and Cx37-S319 cells, which results in differential cell adhesion.

Do allelic variants of the connexin37 1019 gene polymorphism differentially predict for coronary artery disease and myocardial infarction?

A C1019T polymorphism in the human connexin37 (hCx37) gene has been associated with cardiovascular risk, but it remains debatable whether the 1019C or the 1019T allele carries this risk. Here, we investigated whether these allelic variants are differentially predictive of increased risk for coronary artery disease (CAD) and myocardial infarction (MI). A total of 781 Swiss participants, including 597 patients diagnosed with CAD, 50% who reported previous MI, and 184 control subjects were genotyped. Patients in the +CAD group had a higher frequency of the Cx37-1019C allele (70.3% versus 65.0%, p=0.004). Multivariate analysis showed that the hCx37-C1019T polymorphism is an independent predictor of CAD (odds ratio=2.13, confidence interval=1.31-3.46 and p<0.01). Moreover, this polymorphism is not associated with any of the other characteristics examined, including gender, age, body-mass-index, diabetes, total/HDL/LDL-cholesterol, triglycerides, apoA-I, apoB, hypertension and cigarette smoking. In comparison with the -CAD group, we observed an increase of the Cx37-1019C allele in the +MI +CAD subgroup (71.2% versus 65.0%, p=0.002) but not in the -MI +CAD subgroup. Allelic frequency comparisons of these three subgroups predicted that this polymorphism is also an independent risk factor for MI. In conclusion, our results reveal the importance of screening the Cx37-1019C allele for both CAD and MI risk assessments.

Connexin37 protects against atherosclerosis by regulating monocyte adhesion.

A genetic polymorphism in the human gene encoding connexin37 (CX37, encoded by GJA4, also known as CX37) has been reported as a potential prognostic marker for atherosclerosis. The expression of this gap-junction protein is altered in mouse and human atherosclerotic lesions: it disappears from the endothelium of advanced plaques but is detected in macrophages recruited to the lesions. The role of CX37 in atherogenesis, however, remains unknown. Here we have investigated the effect of deleting the mouse connexin37 (Cx37) gene (Gja4, also known as Cx37) on atherosclerosis in apolipoprotein E-deficient (Apoe(-/-)) mice, an animal model of this disease. We find that Gja4(-/-)Apoe(-/-) mice develop more aortic lesions than Gja4(+/+)Apoe(-/-) mice that express Cx37. Using in vivo adoptive transfer, we show that monocyte and macrophage recruitment is enhanced by eliminating expression of Cx37 in these leukocytes but not by eliminating its expression in the endothelium. We further show that Cx37 hemichannel activity in primary monocytes, macrophages and a macrophage cell line (H36.12j) inhibits leukocyte adhesion. This antiadhesive effect is mediated by release of ATP into the extracellular space. Thus, Cx37 hemichannels may control initiation of the development of atherosclerotic plaques by regulating monocyte adhesion. H36.12j macrophages expressing either of the two CX37 proteins encoded by a polymorphism in the human GJA4 gene show differential ATP-dependent adhesion. These results provide a potential mechanism by which a polymorphism in CX37 protects against atherosclerosis.

Connexins in leukocytes: shuttling messages?

Gap junctions, formed by the connexin (Cx) protein family, are intercellular channels that permit the cytoplasmic exchange of ions and small metabolites between neighboring cells, a process called gap junction intercellular communication (GJIC). These channels possess unique properties, including distinctive permeabilities for various signaling molecules, which depend on the connexin member(s) that form them. Importantly, GJIC must be properly controlled as its misregulation might contribute to diseases. Morphological and functional studies have revealed 'gap junction-like' structures and cell-to-cell communication involving cells of the immune system. The connexins involved in such contacts have been partially identified in recent years. This review focuses on the potential physiological roles of gap junctions in the development and recruitment of leukocytes as well as in the regulation of the immune response. Furthermore, the importance of GJIC in immuno-inflammatory pathologies is illustrated in atherosclerosis.

Dual benefit of reduced Cx43 on atherosclerosis in LDL receptor-deficient mice.

Paracrine cell-to-cell interactions are crucial events during atherogenesis, however, little is known on the role of gap junctional communication during this process. We recently demonstrated increased expression of Cx43 in intimal smooth muscle cells and in a subset of endothelial cells covering the shoulder of atherosclerotic plaques. The purpose of this study was to examine the role of Cx43 in the development of atherosclerosis in vivo. Atherosclerosis-susceptible LDL receptor-deficient (LDLR(-/-)) mice were intercrossed with mice heterozygous for Cx43 (Cx43(+/-) mice). Male mice with normal (Cx43(+/+)LDLR(-/-)) or reduced (Cx43(+/-)LDLR(-/-)) Cx43 level of 10 weeks old were fed a cholesterol-rich diet (1.25%) for 14 weeks. Both groups of mice showed similar increases in serum lipids and body weight. Interestingly, the progression of atherosclerosis was reduced by 50% (P < 0.01) in the thoraco-abdominal aorta and in the aortic roots of Cx43(+/-)LDLR(-/-) mice compared with Cx43(+/+)LDLR(-/-) littermate controls. In addition, atheroma in Cx43(+/-)LDLR(-/-) mice contained fewer inflammatory cells and exhibited thicker fibrous caps with more collagen and smooth muscle cells, important features associated, in human, with stable atherosclerotic lesions. Thus, reducing Cx43 expression in mice provides beneficial effects on both the progression and composition of the atherosclerotic lesions.