Visualization of Annular Gap Junction Vesicle Processing: The Interplay between Annular Gap Junctions and Mitochondria

Abstract

It is becoming clear that in addition to gap junctions, playing a role in cell-cell communication, gap junction proteins, connexins, located in cytoplasmic-compartments may have other important functions. Mitochondrial connexin 43 (Cx43) is increased after ischemic preconditioning and has been suggested to play a protective role in the heart. How Cx43 traffics to the mitochondria and the interactions of mitochondria with other Cx43-containing structures are unknown. In this study, immunocytochemical, super-resolution and transmission electron microscopy were used to detect cytoplasmic Cx43-containing structure and to demonstrate their interactions with other cytoplasmic organelles. The most prominent cytoplasmic Cx43-containing structures, annular gap junctions, were demonstrated to form intimate associations with lysosomes as well as with mitochondria. Surprisingly, the frequency of associations between mitochondria and annular gap junctions was greater than that between lysosomes and annular gap junctions. The benefits of annular gap junction/mitochondrial associations are not known. However, it is tempting to suggest that the contact between annular gap junction vesicles and mitochondria facilitates Cx43 deliver to the mitochondria. Furthermore, it points to the need for investigating trafficking of Cx43 to cytoplasmic compartments and annular gap junction as more than only a vesicle destined for degradation.

Astrocytes‐derived exosomes induce neuronal recovery after traumatic brain injury via delivering gap junction alpha 1‐20 k

“…GJA1 is extremely important for maintaining mitochondrial integrity (Kim, Kwon, Im, et al, ). In the blockade of GJA1 to mitochondrial membrane transfer, myocardial hypoxia injury induced by cobalt chloride (CoCl 2 ) can be aggravated (Pecoraro, Pinto, & Popolo, ), whereas in myocardial cells pretreated with ischemia‐reperfusion injury, the expression of mitochondrial GJA1 is significantly increased (Bell, Shakespeare, Smith, et al, ). Our previous studies also showed that GJA5, which is compensated for GJA1 phosphorylation after brain injury, is closely related to the activation of oxidative stress associated with mitochondrial‐endoplasmic reticulum dysfunction (Chen et al, ).…”

Gap junction internalization and processing in vivo: a 3D immuno-electron microscopy study

“…Direct imaging of living cultured cells has shown that connexosomes are formed by internalization of entire gap junctions, and that connexosomes can undergo fission (Piehl et al, 2007;Bell et al, 2018). We examined the high pressure frozen and serial sectioned ovarian follicles for connexosome formation.…”

“…The surface areas of invaginated gap junctions are significantly larger than connexosomes based on one-way ANOVA analysis. In live imaging of Cx43-GFP expressing cells, connexosomes were observed to undergo fission (Piehl et al, 2007;Bell et al, 2018). In ovarian follicle cells, the connexosomes may also undergo fission after internalization; alternatively, they could form from a portion of a larger invaginated gap junction.…”

Gap junction internalization and processing in vivo: a 3D immuno-electron microscopy study

“…Direct imaging of living cultured cells has shown that connexosomes are formed by internalization of entire gap junctions, and that connexosomes can undergo fission (Piehl et al, 2007;Bell et al, 2018). We examined the high pressure frozen and serial sectioned ovarian follicles for connexosome formation.…”

“…Live cell imaging studies of several cultured mammalian cell lines expressing Cx43-GFP chimeras showed that either entire gap junctions are internalized, followed by fission (Piehl et al, 2007;Bell et al, 2018), or that a small portion of the gap junction center is internalized (Falk et al, 2009).…”