Differential endothelial senescence elicited by AQP1 regulation of epigenetic/metabolic responses
Authors: Saeedi Saravi S S , Karsai G , Beer J H 
Published: October 2022

Abstract

Introduction
Accumulation of senescent endothelial cells with age is an important driver of vascular aging and related cardiovascular disease. However, little is known about the mechanisms and signaling pathways that underpin endothelial cell senescence. Aquaporin-1 (AQP1) has been implicated in sensing hydrogen peroxide (H2O2), which differentially modulates endothelial signal transduction. Nonetheless, the role of AQP1 in the regulation of metabolism and function in young and old vascular cells remains elusive.

Purpose
We sought to investigate whether 1) AQP1 differentially regulates vascular senescence and angiogenesis through epigenetic/metabolic response, senescence-associated secretory phenotype (SASP), and 2) AQP1 knockdown/inhibition rejuvenates senescent endothelial cells and restores angiogenesis.

Methods
We assessed the role of AQP1 in endothelial cell senescence and impaired angiogenesis through mitochondrial metabolic disorder, epigenetic alteration, and the SASP in human aortic endothelial cells and aortas from wild-type C57BL/6 mice. For these, we conducted AQP1 knockdown (with siRNA) or blockade of AQP1 (with Bacopaside-II, 10 μM) to inhibit H2O2 transport.

Results
Here we show the upregulation of AQP1 in the senescent endothelial cells (SEC, p.15) and aorta from old mice (&gt;24 months) (p&lt;0.01 and p&lt;0.0001, respectively), facilitating outside-in H2O2 transport. Interestingly, AQP1 knockdown/inhibition reverses both replicative (increased SA-β-galactosidase positive cells) and stress-induced senescence (increased cell-cycle arrest markers p16, p19, and p21; and SASP markers IL1α, IL1β, and IL6) in SEC, whereas it triggers the senescence processes in the proliferating endothelial cells (PEC, p.5) (for each, p&lt;0.05, n=6). Unlike in PEC or young aorta (3-month-old), AQP1 knockdown/inhibition restores angiogenesis in both SEC and old aortas. The interventions increased mitochondrial OXPHOS (represented by enhanced oxygen consumption rate (OCR)) in SEC, which is accompanied by marked increase in CaMKKβ-regulated AMPKT172 phosphorylation (for each, p&lt;0.05, n=6) and in histone deacetylase-4 (HDAC4) phosphorylation at Ser632 (p&lt;0.05) and further histone 3 (H3) acetylation (p&lt;0.01). The HDAC4 phosphorylation leads to significant increase in Mef2A-mediated eNOS phosphorylation at Ser1177 (p&lt;0.05). By contrast, AQP1 knockdown/inhibition induced a senescent-like state by a decrease in mitochondrial OCR and the phosphorylation of CaMKKβ-AMPK and HDAC4-Mef2A regulation of eNOS activity.

Conclusion
Our studies identify AQP1 as essential regulator of EC proliferation that differentially regulates angiogenesis via epigenetic/metabolic response and SASP modulation. Moreover, genetic or pharmacological inhibition of AQP1 reverses endothelial senescence and restores angiogenesis, representing a potential therapeutic target for vascular rejuvenation.

Funding Acknowledgement
Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Swiss National Science Foundation (SNSF)SwissLife Jubiläumsstiftung