Protocatechuic Acid, a Gut-Derived Dietary Metabolite, Attenuates Endothelial Dysfunction via GPER-Mediated NO Signaling

Protocatechuic acid (PCA), a gut-derived metabolite of dietary polyphenols, exhibits endothelial protective properties, yet its underlying mechanisms remain unclear. In this study, we investigated the molecular pathways by which PCA attenuates endothelial dysfunction in human endothelial cells. PCA increased endothelial nitric oxide synthase (eNOS) expression and phosphorylation via GPER-mediated activation of CaMKKβ/AMPK and CaMKIIα signaling pathways through the Gβγ subunit. This activation promoted upregulation of the KLF2/eNOS axis through the HDAC5 and ERK5/MEF2C transcriptional network. Further, PCA inhibited TNF-α-induced activation of NF-κB and expression of adhesion molecules (ICAM-1, VCAM-1) in a nitric-oxide-dependent manner, thereby reducing the inflammatory response and monocyte adhesion. PCA also improves aortic vasorelaxation by increasing eNOS expression and activity through GPER-dependent signaling pathways. These results provide insights into the involvement of eNOS signaling in the endothelial dysfunction protective effects of PCA, highlighting its potential as a functional food ingredient for the prevention of cardiovascular diseases.