Altered Dye Diffusion and Upregulation of Connexin37 in Mouse Aortic Endothelium Deficient in Connexin40

Abstract

Connexin40 (Cx40), connexin37 (Cx37) and connexin43 (Cx43) are subunit proteins of gap junction channels in the vascular wall which are presumably involved in the propagation of vasomotor signals. In this study we have investigated in Cx40-deficient versus wild-type aortic endothelium to which extent loss of Cx40 impairs intercellular communication. We show in Cx40-deficient mice that expression of both Cx37 and Cx43 protein was increased approximately 3- and 2-fold over the level in wild-type endothelium, respectively. Furthermore, Cx37 immunosignals were distributed more homogeneously on contacting plasma membranes in Cx40-deficient versus with wild-type endothelium. Cx43 was not detected in endothelium but only in smooth muscle cells of the vessel wall. Iontophoretic injection of Lucifer Yellow or neurobiotin into aortic endothelium of Cx40-deficient mice showed extensive intercellular transfer of neurobiotin but not of Lucifer Yellow. In contrast, intercellular spreading of Lucifer Yellow was observed in endothelium of wild-type aorta. As shown by electron microscopy, gap junctions in Cx40-deficient endothelium were morphologically different from those of wild-type vessels. These results demonstrate that dye diffusibility of endothelial gap junctions is different in Cx40-deficient and wild-type mice, although Cx40-deficient mice retain the capability of intercellular communication. Apparently, Cx40-deficient endothelial cells upregulate and redistribute Cx37 as a molecular adaptation to the lack of Cx40.

Lack of vascular connexin 40 is associated with hypertension and irregular arteriolar vasomotion

“…On the other hand, alterations within the vascular system have been shown previously in these mice (7,18). Moreover, irregular vasomotion patterns were observed (Fig.…”

“…Additionally, the hypertension is unlikely to be due to an activation of the renin-angiotensin system or to an activation of the sympathetic nervous system. The data show that the specific functions of Cx40 cannot be fully compensated by another member of the connexin family expressed in vascular cells despite endothelial upregulation and redistribution of Cx37 in Cx40-deficient mice (18). We propose that Cx40-dependent cell coupling has an important role in the control of peripheral vascular resistance and that defects in cell coupling within the vascular tree should be regarded as a possible cause of hypertension in humans.…”

Decreased intercellular dye-transfer and downregulation of non-ablated connexins in aortic endothelium deficient in connexin37 or connexin40

“…Consistent with these findings, we did not detect expression of Cx43 protein in endothelium of wild-type mouse aorta, nor did we see compensatory expression of Cx43 in aortas from connexin knockout mice. Krüger et al also did not detect Cx43 in adult mouse aortic endothelium (Krüger et al, 2002). The absence of Cx43 from mouse arterial endothelium differs substantially from results obtained from rat and bovine studies (Yeh et al, 1997;Gabriels and Paul, 1998;Yeh et al, 1998;van Kempen and Jongsma, 1999).…”

“…endothelial coupling has not been fully investigated. While this work was in progress, Krüger et al investigated the effects of a deficiency of Cx40 and concluded that intercellular transfer of injected dyes was altered in Cx40-deficient aortic endothelium and that expression of endothelial Cx37 was upregulated (Krüger et al, 2002). In this report, we used intercellular dyetransfer to assess interendothelial communication in wild-type, Cx37 -/-, Cx40 -/-, Cx37 +/-Cx40 -/-and Cx37 -/-Cx40 -/-aortic segments isolated from mice of different age groups.…”

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

“…This is in contrast to connexin expression levels in EC (ie, lacking inflammatory stimuli), which have been demonstrated previously to have coregulated connexins, ie, the up or down connexin expression is dependent on the expression of other connexins. 22,28,29 How OxPAPC may decouple connexin coregulation is potentially of great interest in understanding EC response to inflammatory mediators. As the effects of OxPAPC on nuclear transcription factors become more clear (eg, Kronke et al 24 ), a more precise idea of the differential control of connexin expression will likely become more evident.…”