Endothelial Pannexin 3 - B Cell Lymphoma-6 Interactions Protect Against Oxidative Stress
FASEB journal : official publication of the Federation of American Societies for Experimental Biology
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Pannexin channel isoforms (Panx1-3) are thought to release nucleotides into the extracellular milieu and have been shown to effect vascular hemodynamics. For this reason, we examined their mRNA and protein expression in hypertensive humans and genetically-inbred hypertensive mice. In both mouse and humans, we found a significant reduction in Panx3 expression in resistance artery endothelium. Thus, we hypothesized Panx3 may be a regulator of vascular function. In en face endothelial preparations from 3rd order mesenteric arteries, we localized Panx3 to the Golgi Apparatus as opposed to Panx1 which localized to the plasma membrane. Next, we generated an inducible, endothelial cell Panx3 knockout mouse (Panx3ECKO ). Radiotelemetry revealed a renin-independent spontaneous hypertension, with unremarkable immune infiltration in the kidney. There was no change in cytoplasmic or released ATP. To understand how Panx3 may regulate blood pressure, we examined whether Panx3 interacted with B Cell Lymphoma 6 (BCL6), a potential binding partner. En face proximity ligation assays demonstrated an interaction between Panx3 and BCL6 in the Golgi. Panx3ECKO mice exhibited significantly decreased BCL6 protein, hinting that Panx3 may stabilize BCL6 by binding at the BCL6 ubiquitin sites. In silico "threading" of the Panx3 sequence onto the cryo-EM structure of Panx1 confirmed this site of interaction. BCL6 is a NFκB repressor, thus its degradation in Panx3ECKO mice caused an increase in NFκB activity with IκBα and p100 significantly upregulated. A novel mimetic peptide designed to block Panx3-BCL6 interactions was administered into C57Bl/6J mice, which recapitulated these results. In addition, Panx3ECKO mice had increased endothelial NOX4 (but not NOX1 or NOX2), likely due to increased NFκB activity-this correlated with a significant increase in plasma H2 O2 , nitrotyrosine (NT3), and 4-hydroxynonenal (4-HNE). In line with this observation, 3rd order mesenteric arteries from Panx3ECKO mice constricted (not dilated) to acetylcholine, which was rescued with the H2 O2 -scavenger catalase (1000U/mL), suggesting that vascular oxidative stress drives hypertension in Panx3ECKO mice. Interestingly, Panx3ECKO mice also exhibit a significant increase in IL-4 receptors on endothelium, and increased IL-4 cytokines in bone marrow lysates. Because IL-4 can drive BCL6 expression in other cell types, we suggest a possible homeostatic immune-endothelial signaling axis. These data elucidate a novel Golgi-localized oxidative signaling pathway in endothelium with a potential immune-derived negative feedback loop.