Molecular mechanisms of progranulin as a regulator of endothelial biology and blood pressure control - ABSTRACT Endothelial cell (EC) dysfunction initiates the development of hypertension (HTN), but the mechanisms are not fully elucidated. Given that HBP is the leading cause of cardiovascular diseases, it is critical to identify new opportunities to restore EC function in HTN. In a series of supportive preliminary studies, we identified progranulin (PGRN), an anti-inflammatory protein, as a novel regulator of EC function and BP. We recently published that PGRN deficiency induces vascular dysfunction and HTN, whereas treatment with recombinant PGRN (rPGRN) restores these cardiovascular outcomes via EphrinA2 and nitric oxide (NO) production. In this proposal, we are extending our knowledge on PGRN and BP and identifying endothelial PGRN as a new regulator of endothelial function and BP. In preliminary study, we show that Angiotensin II- induced HTN selectively reduces PGRN in mesenteric EC, whereas mouse with a selective deletion of PGRN in EC (PGRNEC Cre+) displays endothelial dysfunction, reduced circulating PGRN, and are more susceptible to develop HTN. In further preliminary studies, we identified a new function of angiotensin converting enzyme (ACE), which is to degrade endothelial PGRN and limits its vasodilatory function. These data suggest that reduced endothelial PGRN, driven by ACE-mediate cleavage, is a trigger for EC dysfunction and HTN. Mechanistically, we found that mesentery EC from PGRNEC Cre+ present suppressed AMP-activated protein kinase (AMPK), while overexpressing PGRN in mesenteric EC resulted in exacerbated PGRN secretion followed by AMPK activation and NO formation, which were blunted by blocking EphrinA2, suggesting that endothelial PGRN regulates AMPK activation and NO formation via EphrinA2 in an autocrine-dependent manner. In further preliminary studies, rescuing PGRN expression in mesenteric arteries ex vivo with rPGRN restored the endothelial function in PGRNEC Cre+, but it failed to produce vasodilation in our novel double knockout mouse – global PGRN deficient mice with lack of endothelial AMPK. We also demonstrated that AMPK is in oxidized form in EC from PGRN deficient mice. Finally, Nox1-derived ROS are elevated in EC from PGRN EC Cre+, and that pharmacological inhibition of Nox1 rescues the endothelial function in PGRN EC Cre+. These findings indicate that endothelial PGRN maintains EC function and BP by restricting AMPK oxidation and Nox1 activity. These novel findings inform the central hypothesis of this proposal: Endothelial PGRN, via an autocrine mechanism, regulates endothelial function and BP and in HTN ACE degrades endothelial PGRN affecting its bioactivity and contributing to cardiovascular outcomes. This hypothesis will be tested in the following aims: AIM 1: Determine if reduced endothelial PGRN levels facilitate the genesis and progression of HTN via Nox1- derived ROS, AMPK oxidation, and EC dysfunction. AIM 2: Determine if ACE cleaves endothelial PGRN and contributes to endothelial dysfunction and HTN.
