Carette Diane, Gilleron Jérôme, Denizot Jean-Pierre, Grant Kirsty, Pointis Georges, Segretain Dominique
INSERM U 1065, Team 5 «Physiopathological control of germ cell proliferation: genomic and non-genomic mechanisms», University of Nice Sophia-Antipolis, Nice cedex 3, 06204, France.
UMR S1147, University Paris Descartes, Paris, 75006, France.
Biol Cell. 2015 Jul;107(7):218-31. doi: 10.1111/boc.201400048. Epub 2015 May 6.
Connexins (Cxs), the constitutive proteins of gap junctions, are key actors of many physiological processes. Therefore, alterations of Cx expression and degradation lead to the development of physiopathological disorders. Because of the formation of a double membrane vesicle termed annular gap junction (AGJ), gap junction degradation is a unique physiological process for which many cellular aspects remain unclear.
By using a combination of time-lapse fluorescence microscopy and high-resolution transmission electron microscopy, we evidenced new specific cellular events concerning gap junction degradation and recycling. Indeed, by time lapse video microscopy we demonstrated, for the first time to our knowledge, that an entire AGJ can be fully recycled back to the plasma membrane. Moreover, we dissected the degradative processes of gap junction by electron microscopy approaches. Interestingly, in addition to canonical autophagy and heterophagy pathways, previously described, we discovered that both pathways could sometimes intermingle. Strikingly, our results also highlighted a new lysosome-based autophagy pathway that could play a pivotal role in common autophagy degradation.
The present investigation reveals that AGJ degradation is a more complex process that it was previously thought. First, a complete recycling of the gap junction plaque after its internalisation could occur. Second, the degradation of this peculiar double membrane structure is possible through autophagy, heterophagy, hetero-autophagy or by lysosomal-based autophagy. Altogether, this work underlines novel aspects of gap junction degradation that could be extended to other cell biology processes.
连接蛋白（Cxs）是间隙连接的组成蛋白，是许多生理过程的关键参与者。因此，Cx表达和降解的改变会导致生理病理紊乱的发生。由于形成了一种称为环形间隙连接（AGJ）的双膜囊泡，间隙连接降解是一个独特的生理过程，其许多细胞层面的情况仍不清楚。
通过结合延时荧光显微镜和高分辨率透射电子显微镜，我们证明了与间隙连接降解和再循环相关的新的特定细胞事件。事实上，通过延时视频显微镜，据我们所知首次证明了整个AGJ可以完全再循环回到质膜。此外，我们通过电子显微镜方法剖析了间隙连接的降解过程。有趣的是，除了先前描述的经典自噬和异噬途径外，我们发现这两种途径有时会相互交织。引人注目的是，我们的结果还突出了一种新的基于溶酶体的自噬途径，它可能在常见的自噬降解中起关键作用。
本研究表明，AGJ降解是一个比以前认为的更复杂的过程。首先，间隙连接斑块内化后可能会发生完全再循环。其次，这种特殊的双膜结构可以通过自噬、异噬、异源自噬或基于溶酶体的自噬进行降解。总之，这项工作强调了间隙连接降解的新方面，这些方面可能会扩展到其他细胞生物学过程。
