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MitoNews: Research Bulletin & Discussion Forum
Published by:
MitoSciences
Advancing Vital Discoveries in Mitochondrial Research
http://www.mitosciences.com
Edited & Moderated by:
Dr. Roderick Capaldi
[email protected]
Volume 01, Issue 02 - February 23, 2005
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In This Issue...
EDITOR'S COMMENTS
RECENT RESEARCH
1. Mitochondrial dysfunction in Type 2 Diabetes
2. The bifunctionality of aconitase; Krebs cycle enzyme and
mtDNA maintenance element.
3. A relationship between Complex I activity and ethanol
consumption?
4. Kinase signaling within the mitochondria is extensive;
a comprehensive review.
5. BRCA1 in the mitochondrion.
6. Prion disease; mitochondrial localization of prion protein,
increased oxidative stress and apoptosis.
7. Picogreen staining can be used to measure mtDNA levels
in living human cells.
8. The ATP Synthase of Mycobacterium tuberculosis, a target
for a new class of TB drugs.
9. Mitochondria get the flu.
10. A mitochondrial poly(A) polymerase revealed.
11. Ameloid beta protein enters mitochondria and inhibits
cytochrome c oxidase activity.
12. ATP driven stepwise rotation of F0F1-ATP Synthase.
13. Complex I involvement in tumor cell response to hypoxia.
14. The facts and fancies of cytochrome c oxidase reviewed.
15. Quantum dots targeted to mitochondria.
-> DISCUSSION FORUM <-
1. Are you lacking antibodies against a mitochondrial protein?
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EDITOR'S COMMENTS
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This monthly review is not intended as a comprehensive
coverage of new literature on mitochondrial research.
Rather it tries to provide a sampling of the diversity of topics
in basic research in which mitochondrial function is central to
any key cellular mechanism, as well as in medicine when
mitochondrial dysfunction is associated with human disease.
Dr. Roderick Capaldi
....................................................................................................
RECENT RESEARCH
....................................................................................................
1. Mitochondrial dysfunction in Type 2 Diabetes
Type 2 diabetes is the most common metabolic disease in the
world with as many as 300 million sufferers projected in the
next 20 years. Typically, patients with type 2 diabetes are
insulin resistant for 1 or 2 decades before the onset of disease
and so understanding the progression to this resistance is
paramount to understanding and treating the disease. In the
review below, the authors review the emerging evidence that
mitochondrial dysfunction is the key to insulin resistance. The
critical role of mitochondria is clearly evident from studies of
mtDNA mutations that case pancreatic beta cell dysfunction
and reduced insulin secretion. Here the authors cover links
between other mitochondrial proteins and diabetes including
uncoupler binding proteins and OXPHOS chain proteins and
tie these to the free radical damage that is thought to lead to
beta cell dysfunction.
LOWELL.BB AND SHULMAN. GI. Science 307. 384-7 (2005).
2. The bifunctionality of aconitase; Krebs cycle enzyme and
mtDNA maintenance element.
In recent years Butow and colleagues have made important
strides toward understanding the structure and regulation of
mitochondrial nucleoids, multiprotein complexes which bundle
mtDNA. In the study below these workers describe a novel
role of the Krebs cycle enzyme aconitase in mtDNA
maintenance which is distinct from its catalytic function. This
finding has important implication for many human diseases
because of the susceptibility of aconitase to oxidative stress.
XIN.JC, WANG.X, KAUFMAN.BA AND BUTOW.RA.
Science 307 714-717
3. A relationship between Complex I activity and ethanol
consumption?
High alcohol consumption is a multifactorial disease including
a linkage to mitochondrial aldehyde dehydrogenase activity.
In the studies below, almost all (97%) of Wistar-derived rats
selectively bred for their voluntary low ethanol consumption
had a mutated allele of aldehyde dehydrogenase (Aldh2(2)
that encodes an enzyme with low affinity for NAD+. Rats
bred for high ethanol consumption did not have this allele.
To investigate any possible link between Aldh2 alleles and
maternally inherited genes in alcoholism the authors created
F2 homozygous Aldh2(2)/Aldh2(2) animals from high drinker
F0 females and low drinker F0 males and vice versa.
The high drinker female/low male drinker crosses showed
markedly higher ethanol consumption (3.9 c.f. 1.8 g/kg(-1)
day(-1)) than their low drinker female/high drinker male
counterparts. Mitochondria of these F2 rats derived from
high alcohol consuming females were found to be more active
in oxidizing substrates that generate NADH for Complex I
activity than were the mitochondria derived from low alcohol
consuming rats. This can be expected to lead to higher rates
of acetaldehyde metabolism and thereby to reduced aversion
to alcohol in the former. The results clearly show a maternal
(mitochondrial) inherited component to alcoholism which the
authors conclude is though complex I.
QUINTANILLA. ME,TAMPIER.L,VALLE-PRIETO.A, SAPAG.A
& ISRAEL.Y. FASEB J. 19. 36-42 (2005)
4. Kinase signaling within the mitochondria is extensive;
a comprehensive review.
The varied roles of mitochondria, that include several
metabolic functions as well as cell death signaling, need
to be under control from within and from outside the
organelle. In the review below the present understanding
of signaling cascades involving protein kinase A,
P13K/Akt/PKB, protein kinase C, Raf-MEK-ERK and
JNK/SAPK and p38MAPK are each detailed. In particular
there is extensive coverage
of what is known to date about a number of scaffold proteins
that bring specific kinases to the cytoplasmic surface of
mitochondria. Also the link between the different signaling
pathways and oxidative stress is emphasized.
HORBINSKI. C.& CHU. CT. Free Radicals in Biol & Med.
38. 2-11 (2005)
5. BRCA1 in the mitochondrion.
Immuno-electron microscopy studies of BRCA1 were
undertaken in primary breast and nasal epithelial cells
along with several cancer cell lines. BRCA1 was
found in the nucleus in these cells as expected of a
protein involved in nuclear genome repair. In addition
BRCA1 was also present in mitochondria with a punctate
distribution overlapping that of nucleoids, structures
that contain the mtDNA. BRCA1 isolated from
mitochondria was phosphorylated. Both the modified
state of the protein and its cellular redistribution are
known to occur with DNA damage. The authors
conclude that BRCA1 plays a role in maintainance
of genome integrity not only in the nucleus but also
in mitochondria.
COENE.ED, HOLLINSHEAD. MS, WAEYTENS. AA,
SCHELFHOUT. VR, EECHAUTE WP, SHAW. MK,
VAN OOSTVELDT. PM. & VAUX. DJ. Mol Biol.
Cell. 16. 997-1010 (2005)
6. Prion disease; mitochondrial localization of prion protein,
increased oxidative stress and apoptosis.
The neurotoxicity of prion proteins depends on interactions
between a disease causing isoform of prion protein (PrP(Sc))
and the normal cellular isoform of this protein (PrP(C)).
Transgenic mice with a high copy number of the normal form
of the protein show spontaneous neurological dysfunction in
an age dependent function even when the mutant isoform is
absent. Hence, the authors argue, studying such transgenic
mice can give insight into the neurotoxic properties of prion
proteins. Aged mice with overexpression of PrP(C) were
found to have an aberrant mitochondrial localization of the
prion protein while younger animals did not. This
mitochondrial relocation increased apoptosis via increased
oxidative stress.
HACHIYA.NS, YAMADA.M, WATANABE.K, JOZUKA.A,
OHKUBO.T, SANO.K, TAKEUCHI.Y, KOZIKA.Y
SAKASEGAWA.Y. & KANEKO.K. Neurosci Lett 374.
98-103. (2005)
7. Picogreen staining can be used to measure mtDNA levels
in living human cells.
Quantitating the levels of mtDNA has become increasingly
important in medicine because a wide range of human
diseases, as well as number of commonly used drugs,
cause mtDNA depletion. In the article below a simple and
rapid approach for measuring mtDNA levels is described
that uses the fluorescence stain Picogreen. Among the
useful applications of this technique described by the authors
is the efficient sorting of rho0 cells from partly depleted cells
by FACS.
ASHLEY. N, HARRIS.D & POULTON J. Exp. Cell Res.
303. 432-46 (2005)
8. The ATP Synthase of Mycobacterium tuberculosis, a target
for a new class of TB drugs.
No TB specific drugs have been discovered for more than 4
decades. In the article referenced below, scientists at
Johnson and Johnson with colleagues in Sweden and
France have now identified a new class of drug, the
diarylquinolines, as highly active against the causative
Mycobacterium bacterium while apparently well tolerated
in humans. Sequencing of strains of M tuberculosis and
M. smegmatis found to be resistant to this agent were
used to identify the site of action. Mutants conferring
resistance were all in the c subunit of the ATP synthase
and close to the residues thought to participate in proton
pumping. The authors argue that their predicted site of
reaction within the c subunit explains not only the drug
effect but also why it is not toxic to humans.
ANDRIES.K and 17 other authors.Science 307.
223-7 (2005)
9. Mitochondria get the flu.
Previous studies that found a mitochondrial location of the
influenza A virus protein PB1-F2 are supported in the article
below by studies showing that this protein is targeted to
mitochondria in several cell lines. Transfection of cells with
PB1-F2 was found to change mitochondrial morphology
from a filamentous to a punctate form while suppressing
the inner membrane potential.
YAMADA H, CHOUNAN R, HIGASHI Y, KURIHARA N &
KIDO H.,FEBS Lett.578. 331-6 (2004)
10. A mitochondrial poly(A) polymerase revealed.
Mitochondrial transcripts have been found to have a poly(A)
tail which it has been claimed stabilize human mitochondrial
transcripts. In the study below a novel human nuclear
encoded mitochondrial poly (A) polymerase has been identified
for the first time. Immunocytochemical studies confirmed that
this is a mitochondrial enzyme. Inhibition of expression of the
protein by RNA interference led to significant shortening of
the poly(A) tails of ND3, COXIII and ATP6/8 transcripts, but
even with profoundly shortened poly(A) tails, these transcripts
were relatively stable. Therefore other factors must stabilize
mitochondrial transcripts.
TOMECKI.R, DMOCHOWSKI.A,GEWARTOWSKI.K,
DZIEMBOWSKI.A & STEPIEN.PP Nucleic Acid Res. 32.
6001-14 (2004)
11. Ameloid beta protein enters mitochondria and inhibits
cytochrome c oxidase activity.
Altered cytochrome c oxidase activity has been correlated
with Alzheimers disease in several studies. In the work
referenced below, a synthetically produced Abeta(1-42)
protein was shown to specifically inhibit cytochrome c oxidase
activity in a dose dependent manner, but only in the presence
of Cu(2+) and specific aging of the Abeta(1-42) solution.
This aging was linked to dimerization of Abeta(1-42) as
revealed by cross-linking studies. The authors also show
abundant Abeta protein in brain mitochondria in a mouse
model of Alzheimers disease.
CROUCH.PJ, BLAKE.R, DUCE.JA, CICCOTOSTO.GD,
LI.QX, BARNHAM.KJ, CURTAIN.CC, CHERN Y.RA,
CAPPAI.R, DYRKS.T, MASTERS.CL. & TROUNCE.IA.
J. Neuosci 25. 672-79 (2005)
12. ATP driven stepwise rotation of F0F1-ATP Synthase.
The number of Nobel Prizes for work in bioenergetics attests
to the elegance of many of the studies in this field. One of the
most revealing bodies of work in the last few years has been
the studies of Yoshida, Kinosita and their colleagues
demonstrating, and more recently quantitating, the rotating
motor function of the ATP synthase. Most of the studies to
date have used the F1 part of the enzyme. In the study
referenced below, the authors have measured rotations in
the intact F1F0 complex after attaching an 80nm bead to
the ring of c subunits of the F0 part while fixing the protein
complex to a surface through the F1 part. Quantitative
measurements of the steps in the rotation process are
provided. Importantly, these parameters are the same
in the F1F0 as in F1, indicating that friction in the F0
motor is negligible.
UENO.H, SUZUKI.T, KINOSITA.K.Jr. & YOSHIDA.M.
(Proc. Natl. Acad. Sci. USA 102. 1333-8 (2005)
13. Complex I involvement in tumor cell response to hypoxia.
Certain human cells are more tolerant of hypoxia (oxygen
starvation) than others because of an as yet poorly defined
defence mechanism that reduces oxygen consumption.
Not surprisingly, given their role in respiration, this mechanism
includes altered mitochondrial functioning. In the study below,
the authors have explored the mitochondrial connection by
comparing hypoxia-tolerant and hypoxia-intolerant human
glioma cell lines for differences in mtDNA sequence. In all,
23 mtDNA alterations were identified between the cell types,
one of which, aT14634C mutation is a previously unreported
change. This mutation/polymorphism in subunit ND6 of
complex I in one of the hypoxia-sensitive cell lines caused
increased resistance to rotenone as well as the anti-cancer
drug adriamycin. The authors conclude both that complex
I ND subunits are mutational hot spots in tumor mtDNA
and argue that complex I plays a role in a cellšs ability to
respond to oxygen deficit.
DELTAAN.C, HABIBI-NAZHAD.B, YAN.E, SALOUM.N,
PARLIAMENT.M & ALLALUNIS-TURNER.J. J. Mol. Cancer.
13. 19-28. (2004)
14. The facts and fancies of cytochrome c oxidase reviewed.
The large membrane bound complexes of OXPHOS have
largely gone from cellular black boxes to well understood
if complicated enzymes in the last decade as high resolution
structures of several have become available. A case in
point is the terminal oxidase of the respiratory chain,
cytochrome c oxidase. There are now largely agreed upon
models for electron transfer and coupled proton translocation
through this complex. However, not everything is understood
about how cytochrome c oxidase works as this review attests.
The paper critically evaluates questionable interpretations,
particularly in the area of partial reactions within the hemes
and coppers and is an excellent resource for readers wanting
an up to date review of this area.
BRUNORI. M, GUIFFRE.A & SARTI.P. J. Inorg. Biochem. 99.
324-36 (2005).
15. Quantum dots targeted to mitochondria.
Visualizing mitochondria in live cells is now accomplished
using green fluorescent protein or its kin. However, GFPs
are not always bright enough for dynamic studies to be
conducted. In the paper below the author direct quantum
dots into mitochondria via signal peptide ligands. Quantum
dots emit higher and far longer fluorescence than GFPs or
other organic probes. The authors point out that such probes
should be useful for following transit of proteins into and
through the mitochondrial protein trafficking machinery.
HOSHINO.A, FUJIOKA.K, OKU.T, NAKAMURA.S, SUGA.M,
YAMAGUCHI.Y, SUZUKI.K, YASUHARA.M & YAMAMOTO.K.
Microbiol.Immunol. 48. 985-94 (2004)
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