Editorial
AMPKα2 Regulates Hypoxia-Inducible Factor-1α
Stability and Neutrophil Survival to Promote Vascular
Repair After Ischemia
Kimio Satoh
C
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irculating cytokines/chemokines and growth factors regulate endothelial function1 and influence the development
of cardiovascular diseases.2 Cardiovascular diseases are characterized by endothelial dysfunction,3 vascular smooth muscle
cell (VSMC) proliferation,4 and inflammatory cell migration,
leading to obliteration or excessive enlargement of vascular
lumens.5 Endothelial dysfunction is induced by cardiovascular
risk factors, including hypertension, diabetes mellitus, dyslipidemia, and smoking, all of which trigger a variety of vascular
disorders. Recently, AMP-activated protein kinase (AMPK)
has been demonstrated as an important regulator of metabolic
functions, including the regulation of cellular energy homeostasis and metabolism.6 AMPK is an evolutionarily conserved
serine/threonine kinase that functions as an important energy sensor and plays a crucial role in vascular homeostasis.
Moreover, AMPK is a master regulator that senses cellular
energetics in part through the AMP/ATP ratio and mitochondrial reactive oxygen species production and coordinates
cell-autonomous responses to metabolic stress.7 Importantly,
AMPK has an antiapoptotic effect in endothelial cells and a
proapoptotic effect in VSMCs, which are critical for vascular remodeling.8 The interactions between endothelial cells,
VSMCs, adventitial cells, and inflammatory cells play crucial
roles in the development of vascular diseases. Both endothelial nitric oxide (NO) production and NO-mediated signaling
in endothelial cells and VSMCs are targets and effectors of
the AMPK signaling pathway.9 Furthermore, AMPK regulates
many other stimuli modulating vascular functions, including
reactive oxygen species, that promote VSMC proliferation by
auto/paracrine growth mechanisms. AMPK is a heterotrimeric
complex consisting of a catalytic subunit (α) and 2 regulatory
subunits (β and γ), each having ≥2 isoforms (α1, α2, β1, β2, γ1,
γ2, and γ3) that are differentially expressed in various tissues
and subcellular locations. In the vascular endothelium, both
α-subunits of AMPK are expressed, although AMPK-α1 is
expressed to a greater extent than AMPK-α2.10 Endotheliumdependent vasodilatation is a vital mechanism of blood
flow regulation in response to increased metabolic demand
(Figure). We have demonstrated that endothelial AMPK plays
an important role in microvascular homeostasis and regulation of systemic arterial pressure in mice in vivo.10 As a metabolic sensor, endothelial AMPK plays an important role in
the metabolic regulation of blood flow, which is regulated by
endothelial NO synthase through the activation of the AMPKα1 subunit (Figure).10 Endothelial-specific AMPK-knockout
mice and the resultant endothelial dysfunction induce increased expression of inflammatory cell adhesion molecules.1
Accumulated inflammatory cells generate an oxidizing environment, which involves abundant reactive oxygen species,
inflammatory cytokines/chemokines, and growth factors that
contribute to aortic aneurysm formation,11 which is also regulated by AMPK-α2 in VSMCs.12 Oxidative stress and a shift
in the cellular redox balance have been linked with endothelial
dysfunction at the early stages of cardiovascular diseases.9 In
contrast, AMPK can inhibit reactive oxygen species formation
through NADPH oxidase and stimulate NO production by endothelial NO synthase.9 Indeed, AMPK has been suggested to
phosphorylate the p47phox subunit and thus prevent its translocation to the plasma membrane.
Article, see p 99
Arteriogenesis and angiogenesis are determined by endothelial cells4,13 and by circulating inflammatory cells.9 It
has been suggested that AMPK-α1 and AMPK-α2 may play
different roles in endothelial function and inflammatory cell
survival during hypoxia. Therefore, it will be of great interest
to develop novel strategies targeting the inflammatory cells
migrating to the vascular tissues. In this issue of Circulation
Research, Abdel Malik et al9 assessed the role of AMPK, particularly the AMPK-α2 subunit, in the regulation of vascular
repair in vivo in a model where the outcome is largely dependent on local responses to hypoxia and the mobilization
and recruitment of monocytes and neutrophils. The authors
demonstrated that AMPK-α2 regulates α-ketoglutarate generation, hypoxia-inducible factor-1α stability, and neutrophil
survival, which in turn determines further myeloid cell recruitment and repair potential. The authors concluded that
AMPK-α2 activation in neutrophils is a decisive event in the
initiation of vascular repair after ischemia.14 Why is this article
so intriguing and important? First, to understand the specific
role of the AMPK-α2 subunit in myeloid cells in vascular repair, the authors performed an in vivo study using mice lacking the AMPK-α1 or the AMPK-α2 subunits specifically in
myeloid cells and in endothelial cells. The authors found that
the recovery of blood flow in ischemic hindlimbs was markedly attenuated in myeloid cell–specific AMPK-α2-knockout
mice compared with that in their wild-type littermates. Next,
The opinions expressed in this article are not necessarily those of the
editors or of the American Heart Association.
From the Department of Cardiovascular Medicine, Tohoku University
Graduate School of Medicine, Sendai, Japan.
Correspondence to Kimio Satoh, MD, PhD, Department of Cardio­
vascular Medicine, Tohoku University Graduate School of Medicine,
Sendai 980-8574, Japan. E-mail [email protected]
(Circ Res. 2017;120:8-10.
DOI: 10.1161/CIRCRESAHA.116.310217.)
© 2017 American Heart Association, Inc.
Circulation Research is available at http://circres.ahajournals.org
DOI: 10.1161/CIRCRESAHA.116.310217
8
Satoh Role of AMPK-α2 in Neutrophils 9
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Figure. Roles of AMP-activated protein kinase (AMPK)-α1 and AMPK-α2 in endothelial cells, vascular smooth muscle cells
(VSMCs), and inflammatory cells. The RhoA (Ras homolog gene family member A)/Rho-kinase system is activated by many
mechanisms, including signals from cytokines/chemokines and growth factors, leading to agonist-induced VSMC contraction. In
contrast, endothelial cells produce several vasodilators including nitric oxide (NO) and H2O2 through activation of the AMPK-α1 subunit
and endothelial NO synthase (eNOS). Physiological levels of H2O2 cause vasodilatation through several mechanisms. Among them,
H2O2 rapidly reaches VSMCs, stimulates 1-α isoform of cGMP-dependent protein kinase to change to the disulfide form, and opens
Ca-activated K channels (KCa) with subsequent VSMC hyperpolarization and relaxation. Isocitrate dehydrogenases (IDH) catalyze the
oxidative decarboxylation of isocitrate to α-ketoglutarate (α-KG). α-KG is required as a cofactor for prolyl hydroxylases (PHD), which
hydroxylates hypoxia-inducible factor-1α (HIF-1α). The phosphorylation and activation of AMPK-α2 by hypoxia leads to decreased IDH
expression and decreased levels of α-KG. Stabilized HIF-1α translocates to the nucleus and forms an active HIF complex that induces
the expression of proangiogenic genes that support survival and decrease mitochondrial respiration. PGH indicates prostaglandin H; PLC,
phospholipase C; PVL, von-Hippel-Lindau protein; SOD, superoxide dismutase; and VEGF, vascular endothelial growth factor.
the authors used in vitro and ex vivo approaches and showed
that AMPK-α2 is linked to an increase in early neutrophil
infiltration, the upregulation of inflammatory cytokines, and
adhesion molecule expression. Finally, the authors precisely
demonstrated the molecular mechanism by which the AMPKα2 in neutrophils is required for protection against apoptosis
under hypoxic conditions via regulating hypoxia-inducible
factor-1α hydroxylation and stabilization and hypoxia-inducible factor-1α–dependent responses (Figure). Unlike the
AMPK-α1 subunit, AMPK-α2 can translocate to the nucleus
and affect gene and protein expression by several mechanisms. Therefore, this study provides novel information about
the role of AMPK-α2 in neutrophils, which serves as an important multifunctional regulator in cardiovascular diseases.
On the basis of this study and previous reports, AMPK-α1
and AMPK-α2 modulate endothelial function, VSMC proliferation, and inflammatory cell activation through many
intracellular and extracellular mechanisms. These data will
augment the possibilities of AMPK activators in cardiovascular diseases therapy.
Clinical Significance
Several drugs and molecules activate AMPK, all of which could
be potentially protective against the development of vascular
diseases.15 AMPK activation by statins and metformin has been
proposed to contribute to the pleiotropic effects of this compound class.6 In addition, pharmacological interventions that
include aspirin, 5-aminoimidazole-4-carboxamide riboside,
thiazolidinediones, and the phytochemicals berberine, quercetin, and resveratrol have the ability to activate AMPK signaling by raising the (AMP+ADP)/ATP ratio as a consequence of
mitochondrial electron transport and glycolysis inhibition.6 In
this study, the authors have shown that AMPK-α2 activation in
neutrophils is a decisive event in the initiation of vascular repair
after ischemia.14 These findings may have great therapeutic impact, leading to the development of novel therapeutic strategies
using AMPK activators against cardiovascular diseases. Indeed,
AMPK activation by oral administration of metformin has been
shown to inhibit pulmonary VSMC proliferation and ameliorate
the development of pulmonary hypertension.1 The pathobiology of cardiovascular diseases includes endothelial dysfunction,
10 Circulation Research January 6, 2017
VSMC proliferation, and inflammatory cell migration. Thus,
AMPK may represent a novel therapeutic target against endothelial dysfunction, VSMC proliferation, inflammation, and
vascular repair after ischemia.14 The present findings also suggest that AMPK activation may represent a novel strategy to
target vascular repair and angiogenesis in response to hypoxia.
Thus, we expect that a highly selective, tissue-specific AMPK
activator will be developed in the near future.
Sources of Funding
This work was supported in part by the grants-in-aid for Scientific
Research (15H02535, 15H04816, and 15K15046), all of which
are from the Ministry of Education, Culture, Sports, Science and
Technology, Tokyo, Japan; the grants-in-aid for Scientific Research
from the Ministry of Health, Labour, and Welfare, Tokyo, Japan
(10102895); and the grants-in-aid for Scientific Research from the
Japan Agency for Medical Research and Development, Tokyo, Japan
(15ak0101035h0001 and 16ek0109176h0001).
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Disclosures
None.
References
1.Omura J, Satoh K, Kikuchi N, et al. Protective roles of endothelial AMP-activated protein kinase against hypoxia-induced pulmonary
hypertension in mice. Circ Res. 2016;119:197–209. doi: 10.1161/
CIRCRESAHA.115.308178.
2. Satoh K, Satoh T, Kikuchi N, et al. Basigin mediates pulmonary hypertension by promoting inflammation and vascular smooth muscle cell proliferation. Circ Res. 2014;115:738–750. doi: 10.1161/
CIRCRESAHA.115.304563.
3.Shimokawa H, Sunamura S, Satoh K. RhoA/Rho-Kinase in the cardiovascular system. Circ Res. 2016;118:352–366. doi: 10.1161/
CIRCRESAHA.115.306532.
4. Satoh K, Kagaya Y, Nakano M, et al. Important role of endogenous
erythropoietin system in recruitment of endothelial progenitor cells
in hypoxia-induced pulmonary hypertension in mice. Circulation.
2006;113:1442–1450. doi: 10.1161/CIRCULATIONAHA.105.583732.
5.Satoh K, Kikuchi N, Kurosawa R, Shimokawa H. PDE1C negatively regulates growth factor receptor degradation and promotes
VSMC proliferation. Circ Res. 2015;116:1098–1100. doi: 10.1161/
CIRCRESAHA.115.306139.
6. Alfaras I, Di Germanio C, Bernier M, Csiszar A, Ungvari Z, Lakatta EG,
de Cabo R. Pharmacological strategies to retard cardiovascular aging. Circ
Res. 2016;118:1626–1642. doi: 10.1161/CIRCRESAHA.116.307475.
7. Towler DA. AMPKα1: SUMO Wrestling Runx2 as a strategy to inhibit
arteriosclerotic calcification. Circ Res. 2016;119:398–400. doi: 10.1161/
CIRCRESAHA.116.309237.
8.Shah MS, Brownlee M. Molecular and cellular mechanisms of cardiovascular disorders in diabetes. Circ Res. 2016;118:1808–1829. doi:
10.1161/CIRCRESAHA.116.306923.
9. Fisslthaler B, Fleming I. Activation and signaling by the AMP-activated
protein kinase in endothelial cells. Circ Res. 2009;105:114–127. doi:
10.1161/CIRCRESAHA.109.201590.
10. Enkhjargal B, Godo S, Sawada A, Suvd N, Saito H, Noda K, Satoh
K, Shimokawa H. Endothelial AMP-activated protein kinase regulates
blood pressure and coronary flow responses through hyperpolarization
mechanism in mice. Arterioscler Thromb Vasc Biol. 2014;34:1505–
1513. doi: 10.1161/ATVBAHA.114.303735.
11. Satoh K, Nigro P, Matoba T, O’Dell MR, Cui Z, Shi X, Mohan A, Yan
C, Abe J, Illig KA, Berk BC. Cyclophilin A enhances vascular oxidative
stress and the development of angiotensin II-induced aortic aneurysms.
Nat Med. 2009;15:649–656. doi: 10.1038/nm.1958.
12. Sugamura K, Keaney JF Jr. Nicotine: linking smoking to abdominal aneurysms. Nat Med. 2012;18:856–858. doi: 10.1038/nm.2714.
13. Nakano M, Satoh K, Fukumoto Y, Ito Y, Kagaya Y, Ishii N, Sugamura
K, Shimokawa H. Important role of erythropoietin receptor to promote
VEGF expression and angiogenesis in peripheral ischemia in mice. Circ
Res. 2007;100:662–669. doi: 10.1161/01.RES.0000260179.43672.fe.
14. Abdel Malik R, Zippel N, Frömel T, Heidler J, Zukunft S, Walzog B,
Ansari N, Pampaloni F, Wingert S, Rieger MA, Wittig I, Fisslthaler B,
Fleming I. AMP-activated protein kinase α2 in neutrophils regulates vascular repair via hypoxia-inducible factor-1α and a network of proteins
affecting metabolism and apoptosis. Circ Res. 2017;120:99–109. doi:
10.1161/CIRCRESAHA.116.309937.
15. Cameron AR, Morrison VL, Levin D, et al. Anti-inflammatory effects of
metformin irrespective of diabetes status. Circ Res. 2016;119:652–665.
doi: 10.1161/CIRCRESAHA.116.308445.
Key Words: Editorials
neutrophils
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apoptosis
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chemokines
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cytokines
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hypertension
AMPKα2 Regulates Hypoxia-Inducible Factor-1α Stability and Neutrophil Survival to
Promote Vascular Repair After Ischemia
Kimio Satoh
Downloaded from http://circres.ahajournals.org/ by guest on June 14, 2017
Circ Res. 2017;120:8-10
doi: 10.1161/CIRCRESAHA.116.310217
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