Johns Hopkins University School of Medicine, 720 N Rutland Ave., Baltimore, MD 21205, USA.
Circ Res. 2010 Apr 2;106(6):1153-63. doi: 10.1161/CIRCRESAHA.108.182147. Epub 2010 Feb 18.
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.
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.
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.
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.
缝隙连接介导心肌细胞间的电耦联。工作心肌中的主要缝隙连接蛋白连接蛋白 43（Cx43）在多种心脏病中，虽然这种群体的确切位置和功能尚不清楚，但在心肌细胞的侧膜上呈现出增加的定位。
在光镜和电镜水平上定义侧向缝隙连接的亚细胞定位，并进一步描述缝隙连接周转率的生化调节。
通过电子显微镜，我们描述了衰竭犬心室心肌细胞侧膜之间形成的缝隙连接。这些缝隙连接在结构上各不相同，似乎广泛内化。内化的缝隙连接被纳入多层膜结构，具有自噬体的特征。当这两种蛋白质在 HeLa 细胞中外源表达时，细胞内的 Cx43 与自噬体标记 GFP-LC3 广泛共定位，内源性 Cx43 在新生大鼠心室肌细胞中与 GFP-LC3 共定位。此外，Cx43 的一种独特磷酸化形式以及靶向心脏组织脂筏的自噬体靶向形式 LC3（微管相关蛋白轻链 3）在心力衰竭中增加。
我们的数据表明，心脏中存在以前未被识别的缝隙连接内化和降解途径，并确定了具有潜在治疗意义的细胞途径。
