Hemoglobin expression at the myoendothelial junction regulates nitric oxide scavenging and vasomotor tone

Abstract

Endothelial nitric oxide synthase (eNOS) localizes to the myoendothelial (MEJ), a discreet location where the endothelial cells (EC) and smooth muscle cells (SMC) make contact, however the regulation of eNOS‐derived NO at the MEJ remains unknown. Using a vascular cell co‐culture (VCCC) model, we isolated EC, MEJ, and SMC protein fractions and subjected them to isobaric tag for relative and absolute quantitation analysis coupled to mass spectrometry. From this analysis, we identified enriched expression of hemoglobin subunit alpha (Hbα) at the MEJ compared to EC or SMC fractions and show mRNA expression predominately in ECs. In multiple small arteries and arterioles (i.e. thoracodorsal artery (TD), mesentery), we found enriched expression of Hbα at the MEJ. Since Hbα has the capacity to scavenge NO, we performed a NO consumption assay and found that TD arteries or isolated MEJ fractions consumed a majority of the NO. Consistent with this data, EC‐specific knockdown of HBα using siRNA showed enhanced NO diffusion in TD arteries or in VCCCs compared to control or scrambled siRNA. EC‐specific knockdown of Hbα in pressurized TD arteries attenuated phenylephrine‐mediated constriction. Lastly, in isolated TD arteries or MEJ fractions, we found that Hbα co‐immunoprecipitates with eNOS. Collectively, these results suggest that Hbα at the MEJ is critical for NO signaling and regulation of vasomotor tone.