Staphylococcus aureus‐derived peptidoglycan induces Cx43 expression and functional gap junction intercellular communication in microglia

Abstract

Gap junctions serve as intercellular conduits that allow the exchange of small molecular weight molecules (up to 1 kDa) including ions, metabolic precursors and second messengers. Microglia are capable of recognizing peptidoglycan (PGN) derived from the outer cell wall of Staphylococcus aureus, a prevalent CNS pathogen, and respond with the robust elaboration of numerous pro-inflammatory mediators. Based on recent reports demonstrating the ability of tumor necrosis factor-a and interferon-c to induce gap junction coupling in macrophages and microglia, it is possible that pro-inflammatory mediators released from PGN-activated microglia are capable of inducing microglial gap junction communication. In this study, we examined the effects of S. aureus-derived PGN on Cx43, the major connexin in microglial gap junction channels, and functional gap junction communication using singlecell microinjections of Lucifer yellow (LY). Exposure of primary mouse microglia to PGN led to a significant increase in Cx43 mRNA and protein expression. LY microinjection studies revealed that PGN-treated microglia were functionally coupled via gap junctions, the specificity of which was confirmed by the reversal of activation-induced dye coupling by the gap junction blocker 18-a-glycyrrhetinic acid. In contrast to PGN-activated microglia, unstimulated cells consistently failed to exhibit LY dye coupling. These results indicate that PGN stimulation can induce the formation of a functional microglial syncytium, suggesting that these cells may be capable of influencing neuroinflammatory responses in the context of CNS bacterial infections through gap junction intercellular communication.

Inflammatory conditions induce gap junctional communication between rat Kupffer cells both in vivo and in vitro

“…LPS plus IFN-γ treatment induced intercellular dye transfer in ~30% KCs and induced ~45% incidence of dye coupling in macrophages/monocytes and microglia (14,15). Similarly, peptidoglycan, another proinflammatory agent, induces dye coupling in ~45% microglia (33). In KCs, the percentage of intercellular coupling was not affected by a second addition of LPS plus IFN-γ, suggesting that maximal response was achieved.…”

“…The presence of GJ channels in immune cells has been associated with activation and coordination of specific events, such as transmigration, protease secretion, antigen presentation and cell differentiation (14,15,33,(35)(36)(37)(38). All these functions require cell specific activation that is driven by the indirect action of soluble inflammatory factors.…”

Protective effects of carbenoxolone are associated with attenuation of oxidative stress in ischemic brain injury

“…is localized in the cell membranes of activated astrocytes and microglia [51,52] . Accumulation and diffusion of ROS may activate microglia and astrocytes, and these effects may be amplified by gap-junction communication [53] .…”

Modulation of connexin signaling by bacterial pathogens and their toxins

“…Such contradictory actions are also found at the gap junctional platform. Thus, S. aureus-derived peptidoglycan was reported to induce GJIC in cultures of primary mouse microglia, which was linked to enhanced Cx43 gene transcription and translation [168]. In cultures of primary mouse astrocytes, though, both S. aureus and its peptidoglycan silence gap junction activity, a process that involves the p38 MAPK signaling cascade.…”