Fate of connexin43 in cardiac tissue harbouring a disease-linked connexin43 mutant.
OBJECTIVE
More than 40 mutations in the GJA1 gene encoding connexin43 (Cx43) have been linked to oculodentodigital dysplasia (ODDD), a pleiotropic, autosomal dominant disorder. We hypothesized that even with a significant reduction in the levels of Cx43 in a mutant mouse model of ODDD (Gja1(Jrt/+)) harbouring a G60S mutation (Cx43(G60S)), cardiomyocyte function may only be moderately compromised given that a majority of mutant mice typically survive.


RESULTS
Western blotting and quantitative reverse transcriptase-polymerase chain reaction in conjunction with immunofluorescence were used to assess the expression and localization of Cx43 in hearts and cultured cardiomyocytes from wild-type and Gja1(Jrt/+) mice. Dye-coupling and dual whole cell patch-clamp recordings were also used to assess the gap junction channel status in cultured cardiomyocytes from wild-type and mutant mice. Cardiac tissue from adult Gja1(Jrt/+) mice revealed a 60-80% reduction in Cx43 protein with a preferential loss of the highly phosphorylated forms of Cx43. Compensation via the up-regulation of Cx40 or Cx45 was not observed. Immunofluorescent analysis of cultured cardiomyocytes revealed a trafficking defect, with a decrease in Cx43 plaques and a large population of Cx43 being retained in the Golgi apparatus. However, cultured cardiomyocytes from mutant mice remained beating with a 50% decrease in coupling conductance.


CONCLUSIONS
These results suggest that the Cx43(G60S) mutant impairs normal trafficking and function of co-expressed Cx43 with no dramatic effect on cardiomyocyte function, suggesting that Cx43 is biosynthesized in excess of an essential need.
Manias
Janet L
JL
Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada.
Plante
Isabelle
I
Gong
Xiang-Qun
XQ
Shao
Qing
Q
Churko
Jared
J
Bai
Donglin
D
Laird
Dale W
DW
D000818:Animals; D002450:Cell Communication / Q000235:genetics / Q000502:physiology; D002478:Cells, Cultured; D000013:Congenital Abnormalities / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D018031:Connexin 43 / Q000235:genetics* / Q000378:metabolism*; D017630:Connexins / Q000378:metabolism; D004195:Disease Models, Animal; D005260:Female; D017629:Gap Junctions / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D009154:Mutation / Q000235:genetics*; D009200:Myocardial Contraction / Q000235:genetics / Q000502:physiology; D009206:Myocardium / Q000378:metabolism / Q000473:pathology; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D018408:Patch-Clamp Techniques; D000097003:Gap Junction alpha-5 Protein
D018031:Connexin 43; D017630:Connexins; D000097003:Gap Junction alpha-5 Protein; C082920:connexin 45