The aim of this study was to determine the role of AMP-activated protein kinase (AMPK) in lipopolysaccharide (LPS)-induced lung endothelial barrier dysfunction and lung injury in vivo. Both cultured human pulmonary artery endothelial cells (HPAECs) and experimental animals [AMPK subunit α-deficient mice and wild-type (WT) control mice (C57BL/6J)] were used. In cultured HPAECs, LPS increased endothelial permeability in parallel with a decrease in AMPK activity. Consistent with this observation, AMPK activation with the potent AMPK activator 5-aminoimidazole-4-carboxamide-1-d-ribofuranoside (AICAR) attenuated LPS-induced endothelial hyperpermeability in vitro. Intratracheal administration of LPS (1 mg/kg) in WT mice reduced AMPK phosphorylation at Thr172 in lung tissue extracts, increased protein content and cell count in bronchial alveolar lavage fluid, and increased Evans Blue dye infiltration into the lung. These same attributes were similarly enhanced in AMPKα-knockout mice, compared with WT mice. Pretreatment with AICAR reduced these lung injury indicators in LPS-treated WT mice. AMPK activation with AICAR attenuated LPS-induced endothelial hyperpermeability by activating the Rac/Cdc42/PAK pathway, with concomitant inhibition of the Rho pathway, and decreased VE-cadherin phosphorylation at Tyr658. We conclude that AMPK activity supports normal endothelial barrier function and that LPS exposure inhibits AMPK, thereby contributing to endothelial barrier dysfunction and lung injury.

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Background Liver kinase B1 (LKB1), a tumor suppressor, is a central regulator of cell polarity and energy homeostasis. The role of LKB1 in endothelial function in vivo has not been explored. Methods and Results Endothelium-specific LKB1 knockout (LKB1endo−/−) mice were generated by crossbreeding LKB1flox/flox mice with VE-Cadherin-Cre mice. LKB1endo−/− mice exhibited hypertension, cardiac hypertrophy, and impaired endothelium-dependent relaxation. LKB1endo−/− endothelial cells exhibited reduced endothelial nitric oxide synthase (eNOS) activity and adenosine monophosphate-activated protein kinase (AMPK; downstream enzyme of LKB1) phosphorylation at Thr172, compared with those of wild-type (WT) cells. In addition, the levels of caveolin-1 were higher in the endothelial cells of LKB1endo−/− mice, and knockdown of caveolin-1 by siRNA normalized eNOS activity. Human antigen R (HuR) bound with the AU-rich elements of caveolin-1 mRNA 3′ UTR, resulting in the increased stability of caveolin-1, and genetic knockdown of HuR decreased the expression of caveolin-1 in LKB1-deficient endothelial cells. Finally, adenoviral overexpression of constitutively active AMPK (CA-AMPK), but not green fluorescent protein (GFP), decreased caveolin-1, lowered blood pressure, and improved endothelial function in LKB1endo−/− mice in vivo. Conclusions Our findings indicate that endothelial LKB1 regulates eNOS activity, endothelial function, and blood pressure by modulating AMPK-mediated caveolin-1 expression.

Background: LKB1 is a serine/threonine kinase that is essential in metabolism and tumor suppression. Results: LKB1 interacts with IKK␤ and suppresses NF-B activation in response to LPS. Conclusion: LKB1 inhibits LPS-induced inflammatory responses.Significance: This work reveals a novel mechanism for regulating LPS-induced inflammation.

A rteriogenesis is a process of developing collateral circulation through the remodeling and growth of pre-existing collateral arteries after elevated shear stress induced by occlusion.1-3 Arteriogenesis takes place both during embryogenesis and in adult tissues. In the latter case, arteriogenesis, which usually occurs at sites of occlusion or physical disruption of pre-existing arterial conduits such as coronary artery occlusion or femoral artery ligation, plays a vital role in recovery from ischemic insults. 4,5 Understanding the biological factors that affect arteriogenesis will aid in the development of new treatments for patients with arterial stenosis and occlusions.There are 2 commonly considered mechanisms for arteriogenesis: expansion of pre-existing collaterals and de novo arteriogenesis. 2,6,7 Inflammation caused by mechanical hemodynamic forces, such as shear stress and circumferential wall tension, is considered a pivotal trigger and driver for arteriogenesis. 4,[8][9][10][11] Previous studies have shown that monocytes accumulated in the surrounding tissues of collateral vessels alter arterial occlusion. 7,[11][12][13] These macrophages are potent sources of cytokines and growth factors, which are required for natural adaptive arteriogenesis. In spite of a mounting number of putative arteriogenic factors, the exact mechanisms that regulate collateral remodeling are poorly characterized. Furthermore, the processes responsible for arteriogenesis, and its associated molecular signals are poorly understood.AMP-activated protein kinase (AMPK) is a serine/threonine kinase composed of α, β, and γ subunits. 14,15 The α subunit containing the α1 and α2 isoform is the catalytic subunit, whereas the β and γ are regulatory subunits that maintain the stability of the heterotrimer complex. As an energy sensor, AMPK is activated by various cellular stresses, such as hypoxia, nutrient deprivation, and oxidative stress. [16][17][18] Once activated, AMPK phosphorylates and regulates several downstream kinases that reduce energy demand and increase energy supply to maintain whole-body energy homeostasis. 19 In addition, AMPK also regulates many other cellular processes, including cell polarity, cell growth, and proliferation. [20][21][22] Emerging studies have demonstrated that AMPK is activated in response to shear or ischemic stress. 23,24 AMPK signaling is required for angiogenesis in vivo and in vitro. [25][26][27][28] However, there is no information on the consequences of AMPK deletion in arteriogenesis. In this study, we sought to examine the role © 2016 American Heart Association, Inc. Objective-AMP-activated protein kinase (AMPK), an energy and redox sensor, is activated in response to various cellular stresses, including hypoxia, nutrient deprivation, oxidative stress, and fluid shear stress at the site of vessel blockade. The activation of AMPK is involved in angiogenesis. However, it is unknown whether AMPK can influence arteriogenesis. Here, we demonstrate the contribution of macrophage AMPK to arteriogen...