Loss of Functional Endothelial Connexin40 Results in Exercise-Induced Hypertension in Mice

Abstract

Morton et al Endothelial Cx40 and Activity-Dependent Hypertension 663over distance. 5,6 Although both connexin (Cx)37 and Cx40 are highly expressed in gap junctions within the endothelium, it is Cx40 which is essential for ascending vasodilation. 5 Because the resulting vasodilation reduces peripheral resistance and opposes the increase in blood pressure which occurs during exercise, we hypothesized that functional Cx40 in the endothelium may also be necessary for adequate blood pressure regulation during exercise. Thus, disruption of endothelial Cx40 function may lead to exercise-induced hypertension and provide a model in which to study this condition.Unfortunately, the current mouse models are not suitable to address this hypothesis. Global deletion of Cx40 (Cx40ko) or replacement of the endogenous Cx40 gene coding sequence with either Cx45 or a nonfunctional mutant Cx40A96S produces hypertension that is predominantly renal in origin. [7][8][9][10] Loss of functional Cx40 from the cardiac conduction system also results in arrhythmia.11,12 Interestingly, mice carrying an endothelial-specific deletion of Cx40 are reportedly normotensive 13 ; however, the effect of activity was not investigated. Our laboratory recently developed the Cx40T202STg mouse, which expresses an endothelial Cx40 mutant that permits electric, but not chemical transfer through gap junctions.14 As ascending vasodilation relies on electrotonic transmission of EDH, these mice were also not suitable for investigating the role of Cx40 in exercise-dependent blood pressure regulation.We have therefore developed a novel transgenic mouse expressing a mutant form of Cx40, Cx40T152A, alongside endogenous wtCx40, specifically within the vascular endothelium, a situation analogous to the heterozygous expression of mutant genes in the human population. Substitution of this highly conserved threonine has been described in Cx26, Cx37, Cx43, and Cx50, where it produces structurally sound, yet electrically impaired gap junctions that act as a dominantnegative toward their respective endogenous Cx isoforms. 15,16 The functional importance of this region is underscored by x-ray crystallography, which shows that the conserved threonine contributes to hemichannel stability by likely forming a hydrogen bond with a similarly conserved histidine, H95, in the second transmembrane domain ( Figure S1 in the online-only Data Supplement).17 Interestingly, atrial fibrillation is associated with mutation of the neighboring residue, Cx40A96S, in humans, 18,19 while mice globally expressing Cx40A96S exhibit atrial fibrillation, renal hypertension, and attenuation in ascending vasodilation without change in Cx37 expression. 10,20,21 When expressed in vitro, the Cx40A96S mutant forms electrically impaired gap junctions that act as a dominant-negative toward wtCx40. 18 We hypothesized that endothelial-specific expression of Cx40T152A would interfere with endogenous wtCx40, leading to impairment of ascending vasodilation and onset of exercise-induced hypertension, making t...

Increased myoendothelial feedback is associated with increased connexin37 and IK1 channel expression in mesenteric arteries of diet‐induced hyperhomocysteinemic mice

“…Both Cx37 mRNA and protein were greater, indicating that increased transcription is responsible for the increased expression. While it is not certain which connexins are responsible for MEJ communication in mouse mesenteric arteries, there is sufficient evidence to indicate that Cx37 is involved and may even be the dominant connexin in MEJ communication . Although our data indicate increased overall expression of Cx37, it does not distinguish whether the increase includes expression at the MEJ, which is a limitation of the study.…”

“…In the present study, we show that diet‐induced HHcy results in enhanced myoendothelial feedback, which provides further evidence for enhanced MEJ communication. This functional change occurs in tandem with increased Cx37 mRNA and protein, a connexin shown to be involved in MEJ communication, and increased IK1 protein. Upregulation of these 2 genes could contribute to the enhancement of both myoendothelial feedback and the EDH response.…”

Coronary microcirculatory pathophysiology: can we afford it to remain a black box?

“…It has been hypothesized that a compromised conduction contributes to the very heterogeneous oxygen distribution in tumour tissue. 32 While the regulation of vascular connexins in the heart is not known in detail, there are reports showing the relation of connexin expression and function to ageing, 46 to hypertension, 47 and to ischaemia/reperfusion, 48 again rendering it plausible that a compromised conductive function may contribute to CMVD.

Figure 4Conducted signals in vascular adaptation and effect of compromised conduction.

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Interaction Between ALK1 Signaling and Connexin40 in the Development of Arteriovenous Malformations

“…38,39 Genetic studies show that mice lacking Cx40 develop hypertension because of increased secretion of renin and reduced relaxation of peripheral vessels. 40 These defects have recently been shown to be at least partially dependent on endothelial Cx40 function indicating that Cx40 expression levels regulate blood pressure. How endothelial Cx40 controls blood pressure remains poorly understood but might be attributable to endothelial nitric oxide synthase activity, an important modulator of vascular tone.…”

“…How endothelial Cx40 controls blood pressure remains poorly understood but might be attributable to endothelial nitric oxide synthase activity, an important modulator of vascular tone. 40 Interestingly, both ALK1 and Cx40 interact and regulate the activity of endothelial nitric oxide synthase, 33,41 suggesting that the phenotype of the Acvrl1 +/− ; Gja5 EGFP/+ mice may be at least partially attributable to uncoupled endothelial nitric oxide synthase activity. To support this hypothesis, we have found an increase production of reactive oxygen species in the lung arteries of Acvrl1 +/− ; Gja5 EGFP/+ mice.…”