Injury of skeletal muscle and specific cytokines induce the expression of gap junction channels in mouse dendritic cells

Abstract

Dendritic cells (DCs) in culture express at least connexin43, a protein subunit of gap junctions, and form gap junction channels, which could be important for T-cells activation. Here, we evaluated whether DCs express connexins in vivo and also to identify components of their microenvironment that regulate the functional expression of gap junctions. In vivo studies were performed in lymph nodes of mice under control conditions or after skeletal muscle damage. In double immunolabeling studies, connexin45 was frequently detected in DEC205(+) DCs in lymph nodes of control animals, whereas connexin43 was rarely found in DCs. However, connexin43 was upregulated in DCs after skeletal muscle damage. Upregulation of connexin43 gene expression by tissue damage was also confirmed in mice carrying a beta-galactosidase reporter gene in a connexin43 allele. The effect of several cytokines on the expression of functional gap junctions between cultured DCs was also tested. Under control conditions, cultured DCs did not communicate via gap junctions. However, after treatment with keratinocyte-conditioned medium or cytokine mixtures containing at least TNF-alpha and IL-1beta, they became transiently coupled through a pathway sensitive to octanol, a gap junction blocker. Cellular coupling induced by effective cytokine mixtures was prevented by IL-6. Single cytokines (TNF-alpha, IL-1beta, IFN-gamma, or IL-6) or other mixtures than the described above did not induce coupling via gap junctions. Increased levels of connexin43 and connexin45 protein and mRNA accompanied the appearance of cellular coupling. These studies provide demonstration of connexin expression and regulation by specific danger signals in DCs.

Gap Junctions at the Dendritic Cell-T Cell Interface Are Key Elements for Antigen-Dependent T Cell Activation

“…In the present study, we provide evidence supporting the notion that gap junctions are indeed formed between Ag-presenting DCs and T cells and these structures are required for efficient T cell activation by DCs. It was recently reported that TNF-␣ plus IL-1␤, as well as IFN-␥ induce transient gap junctional communication between monocytes/macrophages or primary DCs and DC-derived cell lines (10,12,13). In contrast, in the experiments reported here, no additional cytokine stimuli were required, in addition to the specific Ag, to observe dye coupling between DCs and T cells.…”

“…Ly (5% weight to volume Ly dissolved in 150 mM LiCl) was microinjected into DCs through glass microelectrodes by brief overcompensation of the negative capacitance circuit in the amplifier until the impaled cell was brightly fluorescent. Gap junctional communication was tested by observing whether dye transfer occurred to T cells during the first minutes after dye injection, as described previously (13). The incidence of dye coupling was calculated by dividing the number of injected cells showing dye transfer to more than one neighboring cell by the total number of cells injected in each experiment multiplied by 100.…”

“…Gap junctional communication has been detected in independent homocellular cultures of either activated DCs or T cells (11)(12)(13)21). Also, formation of heterocellular gap junctions between allogeneic DCs and T cells in cocultures has been suggested using morphological techniques (8,22).…”

“…Although the formation of gap junctions between DCs have been documented with morphological and functional evidences (12,13), the presence of this membrane specialization between APCs (Langerhans cells) and T cells has been only described at the light microscope level using an immunocytological method (14) and suggested as gap-junction-like structures at the ultrastructural level (14). Cx43 and functional gap junctions have also been detected at cell-cell contacts between a cell line of immortalized DCs and immortalized T cells (13). However, the existence of functional gap junctions between primary DCs and T cells and the role these structures may play in T cells physiology remains unknown.…”

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

“…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.…”