Endothelial cell-specific knockout of connexin 43 causes hypotension and bradycardia in mice

Abstract

Connexin 43 (Cx43) is a protein expressed in a variety of mammalian tissues. However, the lack of specific blockers and the absence of known genetic mutants have hampered the investigation of the function of this protein. Cx43-null mice die shortly after birth, thus preventing functional studies in vivo. Here, we report the generation and characterization of a vascular endothelial cell-specific deletion of the Cx43 gene (VEC Cx43 KO) in mice by using the loxP͞Cre system. Using homologous recombination, a mouse line was created carrying loxP sites flanking exon 2 of the Cx43 gene (''floxed'' mice). To produce cell specific deletion of the Cx43 gene, these mice were crossed with animals from a line carrying the Tie 2-Cre transgene. The homozygous VEC Cx43 KO mice survived to maturity. However, they were hypotensive and bradycardic when compared with heterozygous VEC Cx43 KO mice, or to the floxed Cx43 gene mice. The hypotension was associated with marked elevation of plasma nitric oxide (NO) levels as well as elevated plasma angiotensin (Ang) I and II. We hypothesize that endothelial cell Cx43 plays a key role in the formation and͞or action of NO, and that the elevation of Ang II is a secondary event. The specific cellular basis for the hypotension remains to be established, but our findings support the idea that endothelial Cx43 gap junctions are involved in maintaining normal vascular function; moreover, these animals provide the opportunity to determine more clearly the role of endothelial Cx43 in vascular development and homeostasis.

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

“…In all groups studied, the relative heart weight was found to be higher in Cx40-deficient mice. In contrast to Cx40 deficiency, targeted endothelial deletion of Cx43 was without effect on arterial pressure (26) or was associated with hypotension and bradycardia (19). Why alterations of cellular coupling by either the ubiquitous deletion of Cx40 or endothelial deletion of Cx43 lead to such different effects is interesting, but remains unexplained.…”

Characterization of astrocyte‐specific conditional knockouts

“…The ROSA locus is expressed in neurons and oligodendrocytes and thus will report if the inducible construct causes recombination in these cell types versus an astrocytic restricted recombination. Finally, transgenic lines were crossed to a line carrying a floxed Connexin43 locus (Cx43) (Liao et al, 2001) to analyze recombination of an endogenous floxed gene. Since astrocytes are the main cell type expressing Cx43 in the brain (Nagy and Rash, 2000;Rash et al, 2001;Theis et al, 2003), the level of Cx43 remaining following Cre induction was measured by Western blotting and utilized as a measure of the extent of recombination.…”

GJA1mutations, variants, and connexin 43 dysfunction as it relates to the oculodentodigital dysplasia phenotype

“…Subsequent studies delineate the abnormal cardiac morphogenetic process and changes in blood pressure and heart rate [Guerrero et al, 1997;Ya et al, 1998;Liao et al, 2001]. Mice with a homozygous lack of the carboxyl-terminal portion of Cx43 (K258X) [Maass et al, 2004] die shortly after birth (o3% survival to adulthood) due to a defect of the epidermal barrier resulting from lack of terminal keratinocyte differentiation brought about by the prolonged half life of mutant Cx43 gap junction channels in the upper layers of the epidermis.…”