Articles in PresS. Am J Physiol Heart Circ Physiol (May 6, 2016). doi:10.1152/ajpheart.00699.2015
1
Original article
2
Selective downregulation of mitochondrial electron transport chain activity and increased oxidative stress in human atrial fibrillation
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
Larisa Emelyanova,1 Zain Ashary,1 Milanka Cosic,1 Ulugbek Negmadjanov,1 Gracious Ross,1 Farhan Rizvi,1 Susan Olet,2 David Kress,3 Jasbir Sra,3 A. Jamil Tajik,3 Ekhson L. Holmuhamedov,1 Yang Shi,1 Arshad Jahangir1,2,3 1
Sheikh Khalifa bin Hamad Al Thani Center for Integrative Research on Cardiovascular Aging, Aurora Sinai/Aurora St. Luke’s Medical Centers, Milwaukee, Wisconsin, USA; 2Patient-Centered Research, Aurora Research Institute, Aurora Health Care, Milwaukee, Wisconsin, USA; and 3Aurora Cardiovascular Services, Aurora Sinai/Aurora St. Luke’s Medical Centers, Milwaukee, Wisconsin, USA
Short Title: Complex I is downregulated in human atrial fibrillation Word Count: Abstract: 240; Text: 5,050; Table 1; Figures 7 Conflicts of Interest: None. Funding: This work was supported by the National Institutes of Health grants (NIH R01 HL101240 and R01 HL089542); and intramural Cardiac Research Award (AHC 505-3657) from the Aurora Health Care Foundation. Author contributions: Conception and design of research: L.E., A.J. Performed experiments: L.E., Z.A., M.C., G.R. Analyzed data: L.E., S.O. Interpreted results of experiments: L.E., A.J. Prepared figures: L.E., U.N. Drafted manuscript: L.E. Edited/revised manuscript: Y.S., F.R., D.K., J.S., A.J.T., E.L.H., A.J. Approved final version: L.E., Z.A., S.O., M.C., U.N., G.R., F.R., D.K., J.S., A.J.T., L.H., Y.S., A.J. Address for reprint requests and other correspondence: Arshad Jahangir, MD Aurora St. Luke’s Medical Center 2801 W. Kinnickinnic River Parkway, Ste. 840 Milwaukee, WI 53215 USA Phone: +1 414 649 3909 Fax: +1 414 649 3578 E-mail:
[email protected]
1 Copyright © 2016 by the American Physiological Society.
41
ABSTRACT
42
Mitochondria are critical for maintaining normal cardiac function and a
43
deficit in mitochondrial energetics can lead to the development of the substrate that promotes
44
atrial fibrillation (AF) and its progression. The link, however, between mitochondrial
45
dysfunction and AF in humans is still not fully defined. The aim of this study was to elucidate
46
differences in the functional activity of mitochondrial oxidative phosphorylation (OXPHOS)
47
complexes and oxidative stress in right atrial tissue from patients without (non-AF) and with AF
48
(AF) who were undergoing open-heart surgery and were not significantly different for age,
49
gender, major comorbidities and medications. The overall functional activity of the electron
50
transport chain (ETC), NADH:O2 oxidoreductase activity, was reduced by 30% in atrial tissue
51
from AF compared to non-AF patients. This was predominantly due to a selective reduction in
52
complex I (0.06±0.007 vs. 0.09±0.006 nmol/min/citrate synthase activity, p=0.02) and II
53
(0.11±0.012 vs. 0.16±0.012 nmol/min/citrate synthase activity, p=0.003) functional activity in
54
AF patients. Conversely, complex V activity was significantly increased in AF patients
55
(0.21±0.027 in AF vs. 0.12±0.01 in non-AF nmol/min/CS activity, p=0.005). In addition, AF
56
patients exhibited a higher oxidative stress with increased production of mitochondrial
57
superoxide (73±17 in AF vs. 11±2 a.u. in non-AF, p=0.03) and 4-hydroxynonenal (4-HNE) level
58
(77.64±30.2 vs. 9.83±2.83 ng/mg protein, p=0.048). Our findings suggest that AF is associated
59
with selective downregulation of ETC activity and increased oxidative stress that can contribute
60
to the progression of the substrate for AF.
61
Keywords: atrial fibrillation; human; mitochondria; electron transport chain complexes;
62
oxidative phosphorylation; oxidative stress; superoxide; 4-hydroxynonenal protein adducts
63 2
64
NEW & NOTEWORTHY
65
The study provides evidence of a selective downregulation of mitochondrial ETC functional
66
activity predominantly affecting complex I and II and associated increase in oxidative stress in
67
atrial tissue from patients with AF in a well-matched group of patients with respect to
68
comorbidities and well-preserved left ventricular function undergoing open heart surgery.
3
69
INTRODUCTION
70
Atrial fibrillation (AF), a rapid irregular rhythm of the atria, is associated with electrical,
71
functional and structural changes in the atria that promote the substrate for its recurrence and
72
progression (36, 53, 60). The incidence and prevalence of AF increases with advancing age and
73
aging-associated diseases such as hypertension, ischemic heart disease and heart failure (2, 40),
74
and contributes to increased morbidity, particularly an increased risk for stroke, heart failure and
75
death (25, 52). Although the pathophysiology of AF has been well characterized, the underlying
76
mechanisms that contribute to the progression of AF in human atria have not been fully defined
77
(33, 35, 57, 58, 60). Mitochondria, occupying 30% of cardiomyocyte volume, are critical for
78
maintaining normal energetics of the heart, a highly aerobic organ dependent on oxidative
79
phosphorylation (OXPHOS) for maintenance of its normal electrical and mechanical function (1,
80
61). Imbalance in the production of high-energy phosphate compounds and metabolic
81
oscillations with supply-demand mismatch in ATP can affect cardiac electrical activity through
82
impact on ion channels (5, 11, 15, 27), oxidative stress and regulation of cell death/survival
83
signaling (12, 17, 56, 59), which increases predisposition to arrhythmogenesis. However,
84
information pertaining to derangement in OXPHOS in human AF compared to a well-matched
85
group without AF is wanting. This is important because conditions that predispose to AF - such
86
as aging, hypertension, coronary artery disease, heart failure or ventricular or atrial dysfunction -
87
can by themselves contribute to mitochondrial dysfunction and has to be accounted for when
88
estimating the impact of AF on mitochondrial function (4, 11, 15, 17). Moreover, it is not clear if
89
reported changes in myocardial energetics and mitochondrial function (1, 27, 56) are causative or
90
the consequence of AF or associated conditions; nor is it clear whether the OXPHOS impairment
91
reported in some (32), but not all (5) animal studies also occurs in the human atria (12, 37, 51).
4
92
Increasing evidence has been accumulated that oxidative stress plays an important role in the
93
pathogenesis of AF (47, 17, 62) and elevated oxidative stress markers are present in patients with
94
AF (34, 41, 43, 50). Oxidative stress can result from mitochondrial dysfunction with impairment
95
in electron transport chain (ETC) activity (17), but this has not been systematically assessed in
96
human atria.
97
The purpose of this study was therefore to assess the functional activity of mitochondrial
98
OXPHOS complexes I-V, expression level of their representative protein subunits, and oxidative
99
stress, in patients with AF and comorbidity-matched patients without AF undergoing open heart
100
surgery.
101
METHODS
102
Patient demographics and clinical characteristics. Middle age and elderly patients with or
103
without a history of AF undergoing elective open heart surgery between July 2012 and February
104
2016 at Aurora St. Luke’s Medical Center in Milwaukee, Wisconsin, were consented and their
105
atrial appendage tissue were used for this study. Patients undergoing emergency bypass surgery,
106
requiring inotropic support and with congenital heart disease, New York Heart Association class
107
III and IV heart failure, systemic disorders such as infection or severe left ventricular (LV)
108
dysfunction (LV ejection fraction
