Oxidative stress improves coronary endothelial function through activation of the pro-survival kinase AMPK

Abstract

Age-associated decline in cardiovascular function is believed to occur from the deleterious effects of reactive oxygen species (ROS). However, failure of recent clinical trials using antioxidants in patients with cardiovascular disease, and the recent findings showing paradoxical role for NADPH oxidase-derived ROS in endothelial function challenge this long-held notion against ROS. Here, we examine the effects of endothelium-specific conditional increase in ROS on coronary endothelial function. We have generated a novel binary (Tet-ON/OFF) conditional transgenic mouse (Tet-Nox2:VE-Cad-tTA) that induces endothelial cell (EC)-specific overexpression of Nox2/gp91 (NADPH oxidase) and 1.8±0.42-fold increase in EC-ROS upon tetracycline withdrawal (Tet-OFF). We examined ROS effects on EC signaling and function. First, we demonstrate that endothelium-dependent coronary vasodilation was significantly improved in Tet-OFF Nox2 compared to Tet-ON (control) littermates. Using EC isolated from mouse heart, we show that endogenous ROS increased eNOS activation and nitric oxide (NO) synthesis through activation of the survival kinase AMPK. Coronary vasodilation in Tet-OFF Nox2 animals was CaMKKβ-AMPK-dependent. Finally, we demonstrate that AMPK activation induced autophagy and thus, protected ECs from oxidant-induced cell death. Together, these findings suggest that increased ROS levels, often associated with cardiovascular conditions in advanced age, play a protective role in endothelial homeostasis by inducing AMPK-eNOS axis.

AMPK activation by glucagon-like peptide-1 prevents NADPH oxidase activation induced by hyperglycemia in adult cardiomyocytes

“…In certain cells, increased ROS production could result in AMPK activation. Indeed, specific NOX2 overexpression in endothelial cells activates AMPK, inducing NO synthase activation (37). Similarly, in H9C2 cardiomyoblasts, mitochondrial ROS generation in response to nitrite exposure also activates AMPK (21).…”

2-Arachidonoylglycerol enhances platelet formation from human megakaryoblasts

“…57 The dual function of 2-AG should be taken into account, especially considering that platelet hyperactivation is related to aging, inflammation and cancer. 58,59 Age-related decline in cardiovascular function (and, therefore, susceptibility to thrombotic and inflammatory disorders) is often associated to increased levels of reactive oxygen species and oxidative stress; 60,61 since aged platelets display increased NADPH oxidase expression and hydrogen peroxide generation, platelet hyperactivity may contribute to this phenomenon. 62 Aging and activated platelets also modulate lineage-specific development, as well as the senescence program itself, thus promoting cell transformation and playing a role in the early progression to malignancy; [63][64][65][66] in particular, by shedding micro-RNA-containing microvesicles, activated platelets may have clinical relevance in promoting tumor growth and spread, 67 and potentially could be used as biomarkers, as circulating micro-RNA-containing microvesicles may differ according to cancer stage.…”

Involvement of NADPH oxidase in A2A adenosine receptor-mediated increase in coronary flow in isolated mouse hearts

“…Indeed, downregulation of Nox activity by cytosolic p47phox knockdown or inhibition of Nox2 attenuated the coronary vasodilation to vascular endothelial growth factor (VEGF) [52] and bradykinin [32], respectively. In addition, Nox2 overexpression enhanced the coronary vasodilation in response to both VEGF and acetylcholine [53], further confirming that the vasodilator ROS is derived from Nox in this process. More importantly, Larsen and colleagues proposed that Nox2 is a functionally relevant source of H 2 O 2 that mediates agonist-induced coronary vasodilation [32].…”

“…This heterogeneity might be due to vasoconstrictor ROS vs. vasodilator ROS [29,31] generated from different vascular beds (coronary vs. renal artery) [34,37]. Furthermore, in the coronary vasculature, the varying effects of ROS may depend on which source ROS are generated from (NADPH vs. uncoupled NO synthase) [31,52,53] or the pathophysiological conditions [32,52,53], e.g., diabetes, and the right ventricular hypertrophy [54][55][56]. In accordance with our previous studies [37], the effect of ROS scavenging with EUK134 was comparable with the effect of Nox2 inhibition with gp91 ds-tat in WT isolated hearts (P=0.24), suggesting that the majority of ROS generated by adenosine is likely from Nox2, which leads to increases in coronary flow.…”