Peptides and peptide-derived molecules targeting the intracellular domains of Cx43: Gap junctions versus hemichannels

Abstract

About a decade ago, the molecular determinants controlling the opening and closing of Cx43 gap junction channels have been identified. Advanced biophysical approaches revealed a critical role for structural rearrangements in the cytoplasmic loop and dimerization of the C-terminal tail, resulting in binding of the C-terminal tail to the cytoplasmic loop and Cx43 gap junction channel closure during cellular acidosis. This has spurred the development of Cx43-mimetic peptides and peptidomimetics that interfere with these loop/tail interactions, thereby preventing the closure of Cx43 gap junctions, e.g. in the heart upon ischemia. Recently, we found that loop/tail interactions control Cx43-hemichannel activity but with an opposite effect. Binding of the C-terminal tail to the cytoplasmic loop is a requisite for the opening of Cx43 hemichannels in response to different stimuli, like decreased extracellular [Ca2+], increased intracellular [Ca2+], positive membrane potentials or ischemia. Strikingly, peptides that favor the open state of Cx43 gap junctions like the L2 peptide inhibit Cx43-hemichannel opening. These tools now provide unprecedented opportunities to selectively inhibit Cx43 hemichannels while maintaining Cx43 gap junction communication, impossible to achieve with siRNA or knockdown approaches both affecting gap junctions and hemichannels. These tools not only are very helpful to unravel the role of Cx43 hemichannels in complex biological systems, but also hold therapeutic potential to counteract excessive Cx43-hemichannel activity like in ischemia/reperfusion in the brain and the heart or to prevent Cx43 hemichannel-mediated gliotransmitter release in the basal amygdala during memory consolidation in response to emotional events. This article is part of the Special Issue Section entitled 'Current Pharmacology of Gap Junction Channels and Hemichannels'.

Connexin hemichannel inhibition reduces acetaminophen-induced liver injury in mice

“…In recent years, peptides mimicking sequences in the cytoplasmic loop region of connexins, including Gap24 and Gap19, were found to act as specific connexin hemichannel inhibitors (De Vuyst et al, 2006; Wang et al, 2013b). Gap19 has been proven to bind to a sequence in the C -terminal tail of the connexin structure, thereby interfering with the intramolecular interaction between the cytoplasmic loop and C -terminal end, which is critical for connexin hemichannel opening (Bouvier et al, 2009; Hirst-Jensen et al, 2007; Iyyathurai et al, 2013; Ponsaerts et al, 2010; Wang et al, 2013b). As the targets of both peptides are located within the cell, they were linked to a HIV-1 TAT sequence in order to improve cytosolic uptake (Lindgren et al, 2000).…”

Functional roles of connexins and pannexins in the kidney

“…Moreover, whether required communication for renal homeostasis occurs via GJs or HCs is currently poorly understood [19,36,74]. The recent development of specific HC blocking peptides will allow us to further study molecular mechanisms underlying Cx signaling in renal functions [75][76][77]. Furthermore, cell type-specific deletion or overexpression of different Cx isoforms in mice will be a valuable approach to study the role of these proteins in renal physiological processes.…”

Translating connexin biology into therapeutics

“…The advantage of cytoplasmically acting peptides is that they may again display a level of connexin isoform specificity and in the case of Gap19, has been reported to close hemichannels but maintain cell-cell communication [16]. There is mounting evidence that connexin hemichannels and gap junction channels for Cx43 at least are inversely modulated (see for example [17][18][19][20][21][22]), which has some elegance to it.…”