ATP Is Required and Advances Cytokine-Induced Gap Junction Formation in Microglia In Vitro

Abstract

Microglia are the immune cells in the central nervous system. After injury microglia release bioactive molecules, including cytokines and ATP, which modify the functional state of hemichannels (HCs) and gap junction channels (GJCs), affecting the intercellular communication via extracellular and intracellular compartments, respectively. Here, we studied the role of extracellular ATP and several cytokines as modulators of the functional state of microglial HCs and GJCs using dye uptake and dye coupling techniques, respectively. In microglia and the microglia cell line EOC20, ATP advanced the TNF-α/IFN-γ-induced dye coupling, probably through the induction of IL-1β release. Moreover, TNF-α/IFN-γ, but not TNF-α plus ATP, increased dye uptake in EOC20 cells. Blockade of Cx43 and Panx1 HCs prevented dye coupling induced by TNF-α/IFN-γ, but not TNF-α plus ATP. In addition, IL-6 prevented the induction of dye coupling and HC activity induced by TNF-α/IFN-γ in EOC20 cells. Our data support the notion that extracellular ATP affects the cellular communication between microglia through autocrine and paracrine mechanisms, which might affect the timing of immune response under neuroinflammatory conditions.

Regulation of Hemichannels and Gap Junction Channels by Cytokines in Antigen-Presenting Cells

“…As observed in DCs by Corvalán et al [86], IL-6 prevents the induction of GJCs in microglia by preventing upregulation of Cx43 and Panx1, as well as by increasing free intracellular Ca 2+ levels [96]. Furthermore, it is possible that IL-6 might disrupt cell adhesion between microglia as shown in other cells [198], and consequently it might also prevent the formation of GJCs.…”

“…In addition, TNF-α/IFN- γ increases Panx1 HC activity, leading to ATP release [96]. Moreover, microglial Panx1 HCs present an increased activity after exposure to high concentrations of ATP, which favor microglial migration [96, 190, 191].…”

Glioma-associated microglia and macrophages/monocytes display distinct electrophysiological properties and do not communicate via gap junctions

“…GJs are comprised of a family of integral membrane proteins known as connexins (Cxs) that are named according to their predicted molecular mass, among them Cx43 [28]. A number of in vitro reports indicate that microglia express connexins and show gap junctional coupling (GJC) in vitro [3, 4, 6, 16, 23]. Although GJC could not be verified in dye- transfer experiments in brain slices in situ , neither in direct brain injury nor in an Aß pathology [27], microglia/macrophages in the tumor context might use the GJ pathway for communication with cells of the tumor microenvironment.…”

TLR-Activated Gap Junction Channels Protect Mice against Bacterial Infection through Extracellular UDP Release

“…Among them, gap junction channels (GJCs) play important roles in cell-cell communications through the direct transfer of ions, second messengers, and other molecules including Ag peptides (13,14). Generally, each GJC contains a serial docking of two hemichannels, which are composed of six protein subunits called connexins and pannexins (15). Although connexin 43 was first uncovered in heart muscle cells and plays important roles in heart development (16,17), connexin 43 is expressed ubiquitously, in contrast to most connexin isoforms, which are restrictively expressed and their malfunction results in disorders such as deafness, skin diseases, fertility problems, and lens cataracts (18).…”