Acute catabolism of leukocyte lipid bodies: Characterization of a nordihydroguaiaretic acid (NDGA)-induced proteasomal-dependent model.

Cytoplasmic availability of leukocyte lipid bodies is controlled by a highly regulated cycle of opposing biogenesis- and catabolism-related events. While leukocyte biogenic machinery is well-characterized, lipid body catabolic mechanisms are yet mostly unknown. Here, we demonstrated that nordihydroguaiaretic acid (NDGA) very rapidly decreases the numbers of pre-formed lipid bodies within lipid body-enriched cytoplasm of mouse leukocytes - macrophages, neutrophils and eosinophils.

Inhibitors of the 5-lipoxygenase pathway activate pannexin1 channels in macrophages via the thromboxane receptor.

A multitude of environmental signaling molecules influence monocyte and macrophage innate and adaptive immune responses, including ATP and prostanoids. Interestingly, purinergic (P2) and eicosanoid receptor signaling interact such that the activation of P2 receptors leads to prostanoid production, which can then interfere with P2Y-mediated macrophage migration. Recent studies suggest that blockade of 5-lipoxygenase (5-LOX) in macrophages can activate a permeation pathway involved in the influx of dye and the release of ATP.

Inhibitors of the 5-lipoxygenase arachidonic acid pathway induce ATP release and ATP-dependent organic cation transport in macrophages.

We have previously described that arachidonic acid (AA)-5-lipoxygenase (5-LO) metabolism inhibitors such as NDGA and MK886, inhibit cell death by apoptosis, but not by necrosis, induced by extracellular ATP (ATPe) binding to P2X7 receptors in macrophages. ATPe binding to P2X7 also induces large cationic and anionic organic molecules uptake in these cells, a process that involves at least two distinct transport mechanisms: one for cations and another for anions. Here we show that inhibitors of the AA-5-LO pathway do not inhibit P2X7 receptors, as judged by the maintenance of the ATPe-induced uptake of fluorescent anionic dyes.

ATP-induced P2X7-associated uptake of large molecules involves distinct mechanisms for cations and anions in macrophages.

Macrophages express the P2X(7) receptor and other nucleotide (P2) receptors, and display the phenomenon of extracellular ATP (ATP(e))-induced P2X(7)-dependent membrane permeabilization, which occurs through a poorly understood mechanism. We used patch-clamp recordings, cytoplasmic Ca(2+) measurements and fluorescent dye uptake assays to compare P2X(7)-associated transport phenomena of macrophages and HEK-293 cells transfected with P2X(7) receptors (HEK-P2X(7) cells). Both cell types showed inward currents, increase of free cytoplasmic Ca(2+) concentration and the uptake of cationic dyes upon exposure to ATP(e), as previously described.

Activation of ERK1/2 by extracellular nucleotides in macrophages is mediated by multiple P2 receptors independently of P2X7-associated pore or channel formation.

Macrophages express several P2X and P2Y nucleotide receptors and display the phenomenon of ATP-induced P2X7-dependent membrane permeabilization, which occurs through a poorly understood mechanism. Several P2 receptors are known to be coupled to the activation of mitogen-activated protein kinases (MAPKs) and Ca2+ signaling. Here, we use macrophages to investigate the phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) by nucleotides and the involvement of MAPKs and intracellular Ca2+ concentration in ATP-induced membrane permeabilization.