Ultrastructure and regulation of lateralized connexin43 in the failing heart.
BACKGROUND
Gap junctions mediate cell-to-cell electric coupling of cardiomyocytes. The primary gap junction protein in the working myocardium, connexin43 (Cx43), exhibits increased localization at the lateral membranes of cardiomyocytes in a variety of heart diseases, although the precise location and function of this population is unknown.


OBJECTIVE
To define the subcellular location of lateralized gap junctions at the light and electron microscopic level, and further characterize the biochemical regulation of gap junction turnover.


RESULTS
By electron microscopy, we characterized gap junctions formed between cardiomyocyte lateral membranes in failing canine ventricular myocardium. These gap junctions were varied in structure and appeared to be extensively internalizing. Internalized gap junctions were incorporated into multilamellar membrane structures, with features characteristic of autophagosomes. Intracellular Cx43 extensively colocalized with the autophagosome marker GFP-LC3 when both proteins were exogenously expressed in HeLa cells, and endogenous Cx43 colocalized with GFP-LC3 in neonatal rat ventricular myocytes. Furthermore, a distinct phosphorylated form of Cx43, as well as the autophagosome-targeted form of LC3 (microtubule-associated protein light chain 3) targeted to lipid rafts in cardiac tissue, and both were increased in heart failure.


CONCLUSIONS
Our data demonstrate a previously unrecognized pathway of gap junction internalization and degradation in the heart and identify a cellular pathway with potential therapeutic implications.
Hesketh
Geoffrey G
GG
Johns Hopkins University School of Medicine, 720 N Rutland Ave., Baltimore, MD 21205, USA.
Shah
Manish H
MH
Halperin
Victoria L
VL
Cooke
Carol A
CA
Akar
Fadi G
FG
Yen
Timothy E
TE
Kass
David A
DA
Machamer
Carolyn E
CE
Van Eyk
Jennifer E
JE
Tomaselli
Gordon F
GF
D000818:Animals; D001343:Autophagy; D018031:Connexin 43 / Q000235:genetics / Q000378:metabolism*; D004195:Disease Models, Animal; D004285:Dogs; D017629:Gap Junctions / Q000378:metabolism* / Q000648:ultrastructure*; D006367:HeLa Cells; D006333:Heart Failure / Q000378:metabolism* / Q000473:pathology*; D006352:Heart Ventricles / Q000378:metabolism / Q000648:ultrastructure; D006801:Humans; D021962:Membrane Microdomains / Q000378:metabolism / Q000648:ultrastructure; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism* / Q000648:ultrastructure*; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014162:Transfection
D018031:Connexin 43; C500216:GJA1 protein, human; D008869:Microtubule-Associated Proteins; D011993:Recombinant Fusion Proteins