Reduced Expression of Endothelial Connexin37 and Connexin40 in Hyperlipidemic Mice

Abstract

Objective-We sought to clarify the response of endothelial connexins to hyperlipidemia and lipid-lowering therapy. Methods and Results-Aortic endothelial gap junctions were analyzed by en face immunoconfocal microscopy and electron microscopy in C57BL/6 mice subjected to the following regimens: (1) normal chow (NC) for 3 months (3 mo), (2) NC for 9 mo, (3) NC for 3 mo, followed by a cholesterol-enriched diet (CED) for 6 mo, (4) NC for 3 mo and CED for 6 mo, with simvastatin in the final week, and (5) (in apoprotein E [apoE]-deficient mice) NC and examined at 3 mo and 7 to 9 mo. In wild-type mice, connexin37 (Cx37) and Cx40 were markedly downregulated in the CED-fed animals compared with those fed NC (CED vs 9-mo NC, 77% reduction in Cx37 and 65% reduction in Cx40; both PϽ0.01).After simvastatin treatment, Cx40 remained depressed, but Cx37 recovered to 94% of the level found in non-cholesterol-fed animals (PϽ0.01). Electron microscopy demonstrated that gap junctions were smaller in animals fed the CED compared with those given simvastatin and with controls fed NC (PϽ0.01). Endothelial connexins were rare in the atherosclerotic plaques of apoE-deficient mice. 3,4 Studies in animal models have demonstrated that hyperlipidemia is associated with alterations to the junctions between neighboring endothelial cells, including gap junctions. 5,6 Gap junctions are cellmembrane protein channels made of connexin molecules, which belong to a multigene family. In mammals, connexin37 (Cx37), Cx40, and Cx43 are known to be variously expressed in endothelial cells of different sites within the vascular tree. 7,8 In vitro studies indicate that the properties of gap-junctional channels are determined by their connexin makeup, 9 and gene-knockout studies show that mice deficient in specific type(s) of endothelial connexins are associated with vascular functional defects or morphological changes. 10 -12 Furthermore, distinct differences in the distribution and expression between connexin types in the vascular wall have been demonstrated in processes related to atherogenesis, such as hypertension, 13,14 postinjury regeneration, 15,16 and aging, 17 raising the possibility that each connexin type might play a distinctive role. Although recent investigations of hyperlipidemia induced by different experimental approaches in animal models of different species have reported that endothelial gap junctions and connexins change in the hyperlipidemic state, 5,6 whether the change is specific to the model remained unclear. In addition, in those studies, the extent of endothelium examined was limited, and knowledge regarding the response of each endothelial connexin to lipid-lowering therapy was lacking. Conclusions-MouseIn this study, we examined the expression patterns of endothelial gap junctions and connexins in C57BL/6 mice fed a cholesterol-enriched diet (CED) and in the same strain of mice deprived of the apoprotein E (apoE) gene. In addition, the effect of statins, a class of potent, lipidlowering agents reported to decrease progressio...

Downregulation of connexin40 is associated with coronary endothelial cell dysfunction in streptozotocin-induced diabetic mice

“…A number of pathologies in which intercellular communication is disrupted are known where the gap-junction proteins Cxs are modified (11,21,27,28,31,41,53). In the present report, we first demonstrate that Cx37 and Cx40 protein expression were significantly lowered in coronary ECs isolated from diabetic mice when compared with ECs from control (Fig.…”

Abnormally low expression of connexin 37 and connexin 43 in subcutaneously transplanted cryopreserved mouse ovarian tissue

“…GV oocytes were places on slides and fixed in methanol for 30 s and in 3.7% paraformaldehyde for 10 min. After blocking with 10% (v/v) normal goat serum for 1 h at 37°C, the slides were incubated with rabbit polyclonal anti-mouse Cx37 antibody (1:50) [24] at 4°C for overnight. All slides were gently agitated in three changes of PBS containing 0.1% (v/v) Tween-20 solution for 10 min each and then treated with FITC-conjugated goat antirabbit IgG (1:3000) (Vector Laboratories, Burlingame, CA) in 10% (v/v) normal goat serum for 1 h at room temperature.…”

Oxidized Phospholipids Alter Vascular Connexin Expression, Phosphorylation, and Heterocellular Communication

“…Yeh et al 26 characterized the effect of hypercholesteremia on aortic EC and found that Cx40 and Cx37 were both decreased and that a return to normal mouse chow diet rapidly brought Cx37 expression up to normal levels, whereas Cx40 levels remained decreased. Simon et al 27 demonstrated that injections of lipopolysaccharide into mice caused significant Cx40 downregulation in aortic EC compared with Cx37.…”