X-Message-Number: 30967
Date: Thu, 21 Aug 2008 09:27:23 -0700 (PDT)
From:
Subject: autophagy dramatically slows aging in mouse liver I
[Below, a decline in chaperone-mediated autophagy (CMA) was demonstrated
to be the primary driver of aging in mouse liver. Aging in humans may be
more complex, with for example, additional significant input from eroded
telomeres. 6-Aminonicotinamide, beta-hydroxybutyrate, and geldanamycin
upregulate CMA. The result with beta-hydroxybutyrate is intriguing since
levels of this ketone body can be upregulated on an extreme low carbohydrate
diet, without fasting. Unfortunately there are significant safety concerns
regarding standard saturated fat based ketogenic diets. Unsaturated fat
based ketogenic diets may eliminate most of this risk, and are actually
somewhat more effective at upregulating ketone bodies (see PMID: 15070924
below). Nonetheless, what is desired is an easier, and possibly less risky
way to upregulate CMA.]
Nat Med. 2008 Aug 10. [Epub ahead of print] Restoration of
chaperone-mediated autophagy in aging liver improves cellular maintenance
and hepatic function.
Zhang C, Cuervo AM. Department of Developmental and Molecular Biology
and Department of Anatomy and Structural Biology, Marion Bessin Liver
Research Center and Institute for Aging Research, 1300 Morris Park Avenue,
Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Chaperone-mediated autophagy (CMA), a selective mechanism for
degradation of cytosolic proteins in lysosomes, contributes to the removal
of altered proteins as part of the cellular quality-control systems. We have
previously found that CMA activity declines in aged organisms and have
proposed that this failure in cellular clearance could contribute to the
accumulation of altered proteins, the abnormal cellular homeostasis and,
eventually, the functional loss characteristic of aged organisms. To
determine whether these negative features of aging can be prevented by
maintaining efficient autophagic activity until late in life, in this work
we have corrected the CMA defect in aged rodents. We have generated a double
transgenic mouse model in which the amount of the lysosomal receptor for
CMA, previously shown to decrease in abundance with age, can be modulated.
We have analyzed in this model the consequences of preventing the
age-dependent decrease in receptor abundance in aged rodents at the cellular
and organ levels. We show here that CMA activity is maintained until
advanced ages if the decrease in the receptor abundance is prevented and
that preservation of autophagic activity is associated with lower
intracellular accumulation of damaged proteins, better ability to handle
protein damage and improved organ function.
PMID: 18690243
Autophagy. 2007 Jul-Aug;3(4):387-9. Epub 2007 Jul 9.
Comment on:
EMBO J. 2006 Sep 6;25(17):3921-33.
J Cell Sci. 2007 Mar 1;120(Pt 5):782-91.
Chaperone-mediated autophagy and aging: a novel regulatory role of lipids
revealed.
Kaushik S, Kiffin R, Cuervo AM. Department of Anatomy and Structural
Biology, Marion Bessin Liver ResearchCenter, Institute for Aging Research,
Albert Einstein College of Medicine, Bronx, New York 10461, USA.
A wide pool of cytosolic proteins is selectively degraded in lysosomes
by chaperonemediated autophagy (CMA). Binding of these proteins to a
receptor at the lysosomal membrane is the limiting step in CMA. Levels of
this receptor are tightly regulated through changes in its degradation,
multimeric organization and dynamic distribution between the lysosomal
membrane and lumen. We have now reported that subcompartmentalization of the
receptor in discrete lipid microdomains at the lysosomal membrane regulates
its engagement in each of these processes-degradation, multimerization and
membrane retrieval. Changes in the lipid composition of the membrane thus
affect the dynamics of the receptor and, consequently, CMA activity. As an
example of CMA dysfunction resulting from perturbation of the lipid
composition of the lysosomal membrane, we discuss here a second study in
which we analyzed the changes in the dynamics of the receptor during aging.
CMA activity decreases with age primarily due to a decrease in the levels of
the CMA receptor at the lysosomal membrane. Now we have found that
age-related alterations in the lipid composition of the discrete
microdomains at the lysosomal membrane are behind the reduced lysosomal
levels of the receptor and, consequently, the declined CMA activity that
occurs during aging.
PMID: 17438364
[Macroautophagy can not fully substitute for CMA.]
Proc Natl Acad Sci U S A. 2006 Apr 11;103(15):5805-10. Epub 2006 Apr 3.
Consequences of the selective blockage of chaperone-mediated autophagy.
Massey AC, Kaushik S, Sovak G, Kiffin R, Cuervo AM. Department of
Anatomy and Structural Biology, Marion Bessin Liver Research Center, Albert
Einstein College of Medicine, 1300 Morris Park Avenue, Ullmann Building,
Room 611, Bronx, NY 10461, USA.
Chaperone-mediated autophagy (CMA) is a selective pathway for the
degradation of cytosolic proteins in lysosomes. CMA declines with age
because of a decrease in the levels of lysosome-associated membrane protein
(LAMP) type 2A, a lysosomal receptor for this pathway. We have selectively
blocked the expression of LAMP-2A in mouse fibroblasts in culture and
analyzed the cellular consequences of reduced CMA activity. CMA-defective
cells maintain normal rates of long-lived protein degradation by
up-regulating macroautophagy, the major form of autophagy. Constitutive
up-regulation of macroautophagy is unable, however, to compensate for all
CMA functions. Thus, CMA-defective cells are more sensitive to stressors,
suggesting that, although protein turnover is maintained, the selectivity of
CMA is necessary as part of the cellular response to stress. Our results
also denote the existence of cross-talk among different forms of autophagy.
PMID: 16585521 PMCID: PMC1458654
snip>"6-aminonicotinamide, and heat shock protein of 90 kilodaltons
inhibitor, geldanamycin, have the ability to activate CMA."
Autophagy. 2005 Oct-Dec;1(3):141-5. Epub 2005 Oct 11.
Effects of small molecules on chaperone-mediated autophagy.
Finn PF, Mesires NT, Vine M, Dice JF. Department of Cellular and
Molecular Physiology, Tufts University School of Medicine, Boston,
Massachusetts 02111, USA.
Autophagy, including macroautophagy (MA), chaperone-mediated autophagy
(CMA), crinophagy, pexophagy and microautophagy, are processes by which
cells select internal components such as proteins, secretory vesicles,
organelles, or foreign bodies, and deliver them to lysosomes for
degradation. MA and CMA are activated during conditions of serum withdrawal
in cell culture and during short-term and prolonged starvation in organisms,
respectively. Although MA and CMA are activated under similar conditions,
they are regulated by different mechanisms. We used pulse/chase analysis
under conditions in which most intracellular proteolysis is due to CMA to
test a variety of compounds for effects on this process. We show that
inhibitors of MA such as 3-methyladenine, wortmannin, and LY294002 have no
effect on CMA. Protein degradation by MA is sensitive to microtubule
inhibitors such as colcemide and vinblastine, but protein degradation by CMA
is not. Activators of MA such as rapamycin also have no effect on CMA. We
demonstrate that CMA, like MA, is inhibited by protein synthesis inhibitors
anisomycin and cycloheximide. CMA is also partially inhibited when the p38
mitogen activated protein kinase is blocked. Finally we demonstrate that the
glucose-6-phophate dehydrogenase inhibitor, 6-aminonicotinamide, and heat
shock protein of 90 kilodaltons inhibitor, geldanamycin, have the ability to
activate CMA.
PMID: 16874031
[The ketone body beta-hydroxybutyrate upregulates CMA.]
J Biol Chem. 2005 Jul 8;280(27):25864-70. Epub 2005 May 9.
Ketone bodies stimulate chaperone-mediated autophagy.
Finn PF, Dice JF. Department of Molecular and Cellular Physiology, Tufts
University School of Medicine, Boston, Massachusetts 02111, USA.
Chaperone-mediated autophagy (CMA) is a selective lysosomal protein
degradative process that is activated in higher organisms under conditions
of prolonged starvation and in cell culture by the removal of serum. Ketone
bodies are comprised of three compounds (beta-hydroxybutyrate, acetoacetate,
and acetone) that circulate during starvation, especially during prolonged
starvation. Here we have investigated the hypothesis that ketone bodies
induce CMA. We found that physiological concentrations of
beta-hydroxybutyrate (BOH) induced proteolysis in cells maintained in media
with serum and without serum; however, acetoacetate only induced proteolysis
in cells maintained in media with serum. Lysosomes isolated from BOH-treated
cells displayed an increased ability to degrade both
glyceraldehyde-3-phosphate dehydrogenase and ribonuclease A, substrates for
CMA. Isolated lysosomes from cells maintained in media without serum also
demonstrated an increased ability to degrade glyceraldehyde-3-phosphate
dehydrogenase and ribonuclease A when the reaction was supplemented with
BOH. Such treatment did not affect the levels of lysosome-associated
membrane protein 2a or lysosomal heat shock cognate protein of 70 kDa, two
rate-limiting proteins in CMA. However, pretreatment of
glyceraldehyde-3-phosphate and ribonuclease A with BOH increased their rate
of degradation by isolated lysosomes. Lysosomes pretreated with BOH showed
no increase in proteolysis, suggesting that BOH acts on the substrates to
increase their rates of proteolysis. Using OxyBlot analysis to detect
carbonyl formation on proteins, one common marker of protein oxidation, we
showed that treatment of substrates with BOH increased their oxidation.
Neither glycerol, another compound that increases in circulation during
prolonged starvation, nor butanol or butanone, compounds closely related to
BOH, had an effect on CMA. The induction of CMA by ketone bodies may provide
an important physiological mechanism for the activation of CMA during
prolonged starvation.
PMID: 15883160
J Cereb Blood Flow Metab. 2008 Jul 23. [Epub ahead of print]
Neuroprotection in diet-induced ketotic rat brain after focal ischemia.
Puchowicz MA, Zechel JL, Valerio J, Emancipator DS, Xu K, Pundik S,
Lamanna JC, Lust WD. 1Department of Anatomy, School of Medicine, Case
Western Reserve University, Cleveland, Ohio, USA.
Neuroprotective properties of ketosis may be related to the upregulation
of hypoxia inducible factor (HIF)-1alpha, a primary constituent associated
with hypoxic angiogenesis and a regulator of neuroprotective responses. The
rationale that the utilization of ketones by the brain results in elevation
of intracellular succinate, a known inhibitor of prolyl hydroxylase (the
enzyme responsible for the degradation of HIF-1alpha) was deemed as a
potential mechanism of ketosis on the upregulation of HIF-1alpha. The
neuroprotective effect of diet-induced ketosis (3 weeks of feeding a
ketogenic diet), as pretreatment, on infarct volume, after reversible middle
cerebral artery occlusion (MCAO), and the upregulation of HIF-1alpha were
investigated. The effect of beta-hydroxybutyrate (BHB), as a pretreatment,
via intraventricular infusion (4 days of infusion before stroke) was also
investigated following MCAO. Levels of HIF-1alpha and Bcl-2 (anti-apoptotic
protein) proteins and succinate content were measured. A 55% or 70%
reduction in infarct volume was observed with BHB infusion or diet-induced
ketosis, respectively. The levels of HIF-1alpha and Bcl-2 proteins increased
threefold with diet-induced ketosis; BHB infusions also resulted in
increases in these proteins. As hypothesized, succinate content increased by
55% with diet-induced ketosis and fourfold with BHB infusion. In conclusion,
the biochemical link between ketosis and the stabilization of HIF-1alpha is
through the elevation of succinate, and both HIF-1alpha stabilization and
Bcl-2 upregulation play a role in ketone-induced neuroprotection in the
brain.Journal of Cerebral Blood Flow & Metabolism advance online
publication, 23 July 2008; doi:10.1038/jcbfm.2008.79.
PMID: 18648382
Neurobiol Aging. 2004 Mar;25(3):311-4.
Effects of beta-hydroxybutyrate on cognition in memory-impaired adults.
Reger MA, Henderson ST, Hale C, Cholerton B, Baker LD, Watson GS, Hyde
K, Chapman D, Craft S. Accera, Inc., Aurora, CO 80010, USA.
Glucose is the brain's principal energy substrate. In Alzheimer's
disease (AD), there appears to be a pathological decrease in the brain's
ability to use glucose. Neurobiological evidence suggests that ketone bodies
are an effective alternative energy substrate for the brain. Elevation of
plasma ketone body levels through an oral dose of medium chain triglycerides
(MCTs) may improve cognitive functioning in older adults with memory
disorders. On separate days, 20 subjects with AD or mild cognitive
impairment consumed a drink containing emulsified MCTs or placebo.
Significant increases in levels of the ketone body beta-hydroxybutyrate
(beta-OHB) were observed 90 min after treatment (P=0.007) when cognitive
tests were administered. beta-OHB elevations were moderated by
apolipoprotein E (APOE) genotype (P=0.036). For 4+ subjects, beta-OHB levels
continued to rise between the 90 and 120 min blood draws in the treatment
condition, while the beta-OHB levels of 4- subjects held constant (P<0.009).
On cognitive testing, MCT treatment facilitated performance on the
Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-cog) for 4-
subjects, but not for 4+ subjects (P=0.04). Higher ketone values were
associated with greater improvement in paragraph recall with MCT treatment
relative to placebo across all subjects (P=0.02). Additional research is
warranted to determine the therapeutic benefits of MCTs for patients with AD
and how APOE-4 status may mediate beta-OHB efficacy.
PMID: 15123336
Brain Res. 2008 Jun 11. [Epub ahead of print]
Induction of ketosis may improve mitochondrial function and decrease
steady-state amyloid-beta precursor protein (APP) levels in the aged dog.
Studzinski CM, Mackay WA, Beckett TL, Henderson ST, Murphy MP, Sullivan
PG, Burnham WM. Department of Pharmacology, University of Toronto, Canada;
Sanders-Brown Center on Aging, University of Kentucky, USA.
Region specific declines in the cerebral glucose metabolism are an early
and progressive feature of Alzheimer's disease (AD). Such declines occur
pre-symptomatically and offer a potential point of intervention in
developing AD therapeutics. Medium chain triglycerides (MCTs), which are
rapidly converted to ketone bodies, were tested for their ability to provide
an alternate energy source to neurons suffering from compromised glucose
metabolism. The present study determined the short-term effects of ketosis
in aged dogs, a natural model of amyloidosis. The animals were administered
a 2 g/kg/day dose of MCTs for 2 months. Mitochondrial function and oxidative
damage assays were then conducted on the frontal and parietal lobes.
Amyloid-beta (Abeta), amyloid precursor protein (APP) processing and
beta-site APP cleaving enzyme (BACE1) assays were conducted on the frontal,
parietal and occipital lobes. Aged dogs receiving MCTs, as compared to
age-matched controls, showed dramatically improved mitochondrial function,
as evidenced by increased active respiration rates. This effect was most
prominent in the parietal lobe. The improved mitochondrial function may have
been due to a decrease in oxidative damage, which was limited to the
mitochondrial fraction. Steady-state APP levels were also decreased in the
parietal lobe after short-term MCT administration. Finally, there was a
trend towards a decrease in total Abeta levels in the parietal lobe. BACE1
levels remained unchanged. Combined, these findings suggest that short-term
MCT administration improves energy metabolism and decreases APP levels in
the aged dog brain.
PMID: 18582445
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