Abstract
Complex regulatory mechanisms control the abundance and localization of transcription factors due to the broad impact their transcriptional activity can have on cell, tissue and organism physiology. The activity of transcriptional repressor B cell lymphoma 6 (Bcl6), which has been well studied for its roles in immune cell specification and lymphoncogenesis, is largely regulated by its targeted degradation. However, outside of tumor-related angiogenesis, a role for Bcl6 in the vasculature has yet to be defined. Bcl6 has been reported to interact with Pannexin 3 (Panx3) channels in other cell types, though the product of this interaction has yet to be described. Here, we report that Bcl6 interacts with Golgi-localized Panx3 in endothelial cells, and demonstrate that Panx3-Bcl6 interactions modulate the endothelial transcriptional landscape by shielding the transcriptional repressor from targeted degradation. We show genetic deletion of Panx3 from endothelium induced spontaneous hypertension, aligning with human data, but did not result in any tested channelopathies. When Panx3 was deleted from endothelium, there was significantly decreased Bcl6 protein, but not Bcl6 mRNA, hinting Panx3 may stabilize Bcl6. In the absence of Panx3, Bcl6-protected oxidative genes Nox4 and NFB were significantly increased. The result was H2O2-specific oxidative damage throughout the vasculature and circulation. Pharmacological inhibition of the Panx3-Bcl6 interaction recapitulated an increase in Nox4 and blood pressure. These data elucidate a channel-independent function of Panx3 wherein interactions with perinuclear Bcl6 can dictate transcriptional repression and protect against oxidative stress. Our next study aimed to determine if Panx3-Bcl6 interactions would alter communication between endothelium and inflammatory cells. Unexpectedly, we found that loss of endothelial Panx3 was associated with a significant increase in the expression of IL4 receptors on endothelium and concomitant increase in IL4 in bone marrow. Because activation of IL4 has been reported to drive expression of Bcl6 in other cell types, we considered the potential for vascular-immune signaling to contribute to blood pressure regulation. To this end, genetic deletion of endothelial Panx3 was associated with a significantly increased population of circulating basophils, a primary source of IL4. Preliminary studies involving expansion or depletion of the circulating basophil population were shown to reduce or augment systemic blood pressure, respectively. These data elucidate a novel Golgi-localized oxidative signaling pathway in endothelium with a potential basophil-derived negative feedback loop for the purpose of homeostatic blood pressure control.
