1686 • JID 2005:191 (15 May) • Mallon et al.
M A J O R A R T I C L E
In Vivo, Nucleoside Reverse-Transcriptase Inhibitors
Alter Expression of Both Mitochondrial and Lipid
Metabolism Genes in the Absence of Depletion
of Mitochondrial DNA
Patrick W. G. Mallon,1,2,5Patrick Unemori,1,5,aRebecca Sedwell,1,5Adrienne Morey,4Martina Rafferty,3
Kenneth Williams,3Donald Chisholm,6Katherine Samaras,6Sean Emery,1Anthony Kelleher,1,2,5
David A. Cooper,1,2,5and Andrew Carr,2,5for the SAMA Investigatorsb
1National Centre in HIV Epidemiology and Clinical Research, University of New South Wales, and
Clinical Services Unit,
Research Laboratory, Centre for Immunology, St. Vincent’s Research Campus, and
2HIV, Immunology, and Infectious Diseases
6Garvan Institute of Medical Research, Sydney, Australia
3Clinical Trials Centre, and
4Department of Anatomical Pathology, St. Vincent’s Hospital, Sydney,
ficiency virus (HIV) infection, can cause mitochondrial dysfunction and have been associated with lipoatrophy. The
effects of this mitochondrial dysfunction on lipid metabolism, at a molecular level in vivo, have not been described.
We examined early changes (by 2 weeks after initiation of therapy) in expression of mitochondri-
al and nuclear genes in adipose tissue from 20 HIV-negative subjects randomized to receive dual-NRTI therapy
(zidovudine/lamivudine or stavudine/lamivudine) for 6 weeks.
We observed decreased transcription of mitochondrial (mt) RNA without significant depletion of
mtDNA. Decreases in mtRNA coincided with simultaneous up-regulation of nuclear genes involved in transcrip-
tional regulation of mtRNA (NRF1 and TFAM) and oxidation of fatty acids (PPARA and LPL), whereas PPARG,
which is important for differentiation of adipose tissue, was down-regulated. Many nuclear changes correlated
with changes in peroxisome proliferator–activated receptor–g coactivator–1 (PGC1), suggesting a central role for
PGC1 in nuclear responses to mitochondrial dysfunction. Expression of peripheral blood monocyte mtRNA also
decreased, suggesting that monocytes may be surrogates for NRTI-induced mitochondrial dysfunction in other
Independent of HIV, NRTIs decrease transcription of mtRNA in vivo. The absence of depletion of
mtDNA suggests that NRTIs cause mitochondrial dysfunction by means other than through inhibition of DNA poly-
Nucleoside reverse-transcriptase inhibitors (NRTIs), which are used to treat human immunode-
Combinations of 2 nucleoside reverse-transcriptase in-
hibitors (NRTIs) form the backbone of antiretroviral
Received 20 October 2004; accepted 20 December 2004; electronicallypublished
12 April 2005.
Presented in part: 6th International Workshop on Adverse Drug Reactions and
Lipodystrophy in HIV, Washington, DC, 25–28 October 2004 (abstracts L759 and
L760); 16th annual conference of the Australasian Society for HIV Medicine,
Canberra, Australia, September 2004 (oral presentation); 11th Conference on
Retroviruses and Opportunistic Infections, San Francisco, California, 9–11 February
2004 (abstract 76).
aPresent affiliation: University of California, San Francisco.
bAdditional SAMA investigators are listed after the text.
Reprints or correspondence: Dr. Patrick W. G. Mallon, National Centre in HIV
Epidemiology and Clinical Research, University of New South Wales, Level 2, St.
Vincent’s Medical Centre, St. Vincent’s Hospital Sydney, Darlinghurst, NSW 2010,
The Journal of Infectious Diseases
? 2005 by the Infectious Diseases Society of America. All rights reserved.
therapy (ART) for treatment of HIV infection.Most
NRTIs, including the thymidine analogues zidovudine
peripheral neuropathy, liver steatosis, myopathy, and
Financial support: National Heart, Lung, and Blood Institute of the National
Institutes of Health (grant RO1 HL65953 and grant RO1 HL65953 to P.W.G.M. and
K.S.); National Health and Medical Research Council of the Australian Government
(support to K.S.); Australian-American Fulbright Commission (grant support to P.U.).
Potential conflicts of interest: the authors have received honoraria (including
advisory board honoraria), research grants, and lecture fees from the following: BMS,
Abbott, Merck Sharp & Dohme, Gilead, and Roche (P.W.G.M.); GlaxoSmithKline,BMS,
Pfizer, and Johnson & Johnson (D.A.C.); GlaxoSmithKline, Roche, Abbott, Boehringer-
Ingelheim, Bristol-Myers Squibb, Merck Sharp & Dohme, and Roche (A.C.); Glaxo-
SmithKline, Astra Zeneca, Eli Lilly, Novo Nordisk, Servier, and Aventis (D.C.); Roche
and Ventana (A.M.); Virax Immunotherapeutics(A.K.);Roche,GlaxoSmithKline,Abbott,
Bristol-Myers Squibb, Merck Sharp & Dohme, Boerhinger-Ingelheim, Gilead, Virax
Immunotherapeutics, and Chiron (S.E.); and Astra Zeneca and Aventis (K.S.).
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NRTI-Induced Mitochondrial Dysfunction • JID 2005:191 (15 May) • 1687
FAO, fatty acid oxidation; FAs, fatty acids; LPL, lipoprotein lipase; mtTFA, mitochondrial transcription factor a; NRF1, nuclear respiratory factor 1; PPAR,
peroxisome proliferator–activated receptor; PGC1, PPARg coactivator 1; SREBP1, sterol regulatory element–binding protein 1.
Regulatory pathways involved in expression of mitochondrial and lipid metabolism genes. COX, cytochrome c oxidase; Cyt b, cytochrome b;
perinatal encephalopathy [2–8]. Approximately 50% of HIV-in-
fected adults treated with ART develop HIV-associated lipodys-
trophy (HIVLD), which is characterized by selectivesubcutaneous
(sc) lipoatrophy, relative gain of central fat, dyslipidemia, and in-
sulin resistance [2–3, 9]. These metabolic complications are as-
sociated with increased incidence of myocardial infarction .
Both HIV protease inhibitors (PIs) and NRTIs contribute to
HIVLD —NRTIs possibly by affecting mitochondrial func-
tion and PIs by inhibiting sterolregulatoryelement–bindingpro-
tein–1 (SREBP1) and peroxisome proliferator–activatedreceptor
(PPAR) g [12–14]. SREBP1 and PPARg, together with PPARa,
regulate transcription of lipid metabolism genes. This regulation
1 (PGC1). PGC1 not only interacts with PPARa and PPARg to
affect transcription of lipid metabolism genes [15–16] but also
regulates transcription of mitochondrial genes through nuclear
respiratory factor (NRF) 1 and 2, which regulate mitochondrial
transcription factor A (mtTFA) [16–18] (figure 1).
Through these mechanisms, PGC1 can influence production
of ATP in cells that use lipid as an energy substrate [15–17,
19]. Although changes in expression of PGC1 can affect tran-
scription of mtRNA, it is unclear whether the reverse is true.
In particular, mechanisms whereby NRTI-induced mitochon-
drial toxicity affects lipid metabolism, leading to lipoatrophy,
are poorly understood.
NRTIs undergo intracellular and intramitochondrial phos-
phorylation to active triphosphates capable of inhibiting HIV
reverse transcriptase (RT). In vitro, some NRTIs inhibit DNA
polymerase-g (DNA pol-g), a nuclear-encoded polymeraseim-
portant for replication of mtDNA . Since mitochondria are
central to cellular energy production through oxidative phos-
phorylation (OXPHOS) and the mitochondrial electron trans-
port chain (mtETC), it is thought that depletion of mtDNA,
induced by inhibition of DNA pol-g, may decrease cellu-
lar OXPHOS capacity . Although direct inhibition of DNA
pol-g by NRTIs has not been demonstrated in vivo, mtDNA
quantity is commonly used as a surrogate for NRTI toxicity .
The mtETC comprises 5 complexes (I–V) encoded by both
nuclear and mitochondrial genes. Mitochondrial-encodedsub-
units—including cytochrome b (Cyt b) of complex III and
cytochrome c oxidase subunits I, II, and III (COX1, -2, and
-3) of complex IV—play important functional roles ,
whereas nuclear-encoded components, such as COX4, play
roles that are more regulatory than functional . Through
a process called “mitochondrial fine tuning,” mitochondriacan
adapt transcription of mtRNA to meet altered OXPHOS re-
quirements independent of regulation by nuclear factors or
changes in mtDNA level [18, 23]. To test the hypothesis that
NRTI-induced mitochondrial dysfunction affects lipid metab-
olism, we examined the early effects of commonly used NRTI
combinations on adipose tissue expression of genes and mtDNA
in HIV-negative subjects.
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1696 • JID 2005:191 (15 May) • Mallon et al.
macrophage differentiation and cholesterol uptake. Nat Med 2001;7:
26. Zechner R, Strauss J, Frank S, et al. The role of lipoprotein lipase in
adipose tissue development and metabolism. Int J Obes Relat Metab
Disord 2000;24(Suppl 4):S53–6.
27. Williams RS, Salmons S, Newsholme EA, Kaufman RE, Mellor J. Reg-
ulation of nuclear and mitochondrial gene expression by contractile
activity in skeletal muscle. J Biol Chem 1986;261:376–80.
28. McComsey G, Tan DJ, Lederman M, Wilson E, Wong LJ. Analysis of the
mitochondrial DNA genome in the peripheral blood leukocytes of HIV-
infected patients with or without lipoatrophy. AIDS 2002;16:513–8.
29. Miura T, Goto M, Hosoya N, et al. Depletion of mitochondrial DNA
in HIV-1-infected patients and its amelioration by antiretroviral ther-
apy. J Med Virol 2003;70:497–505.
30. Moraes CT, Kenyon L, Hao H. Mechanisms of human mitochondri-
al DNA maintenance: the determining role of primary sequence and
length over function. Mol Biol Cell 1999;10:3345–56.
31. Davis AF, Ropp PA, Clayton DA, Copeland WC. Mitochondrial DNA
polymerase gamma is expressed and translated in the absence of mi-
32. Liao X, Butlow RA. RTG1 and RTG2: two yeast genes required for a
novel path of communication from mitochondria to the nucleus. Cell
33. Considine RV. Regulation of leptin production. Rev Endocr Metab
34. Levy JR, Gyarmati J, Lesko JM, Adler RA, Stevens W. Dual regulation
of leptin secretion: intracellular energy and calcium dependence of reg-
ulated pathway. Am J Physiol Endocrinol Metab 2000;278:E892–901.
35. Liang J-S, Distler O, Cooper DA, et al. HIV protease inhibitors protect
apolipoprotein B from degradation by the proteasome: a potential
36. Gan SK, Samaras K, Thompson CH, et al. Altered myocellular and
abdominal fat partitioning predict disturbance in insulin action inHIV
protease inhibitor-related lipodystrophy. Diabetes 2002;51:3163–9.
37. Dalakas MC, Illa I, Pezeshkpour GH, Laukaitis JP, Cohen B, Griffin
JL. Mitochondrial myopathy caused by long-term zidovudine therapy.
N Engl J Med 1990;322:1098–105.
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