X-Message-Number: 24731
Date: Tue, 28 Sep 2004 12:56:56 -0700 (PDT)
From: Doug Skrecky <>
Subject: could lipofuscin/ceroid be the main driver of aging?

normal metabolism in cells with a low turnover
causes lipofuscin accumulation
causes inhibition of proteasomes/lysosomes
causes mitochondrial abnormalities
causes "most aging symptoms"

[mitochondrial disfunction is a key driver of "aging"]

Ann N Y Acad Sci. 2004 Jun;1019:29-32.
Decay of mitochondrial metabolic competence in the aging cerebellum.
  Cytochemically evidenced cytochrome oxidase activity was
morphometrically measured in the cerebellar cortex of adult and old rats.
The ratio (R) between the area of the precipitate due to the cytochemical
reaction and the overall area of each mitochondrion was calculated. While
in adult rats an inverse correlation between mitochondrial size and R
values (r = -.905) was envisaged, in old animals increasing values of R
were paired by increases in mitochondrial area (r =.561). Paired-quartile
comparisons of the R values from adult and old animals documented a
marked age-related impairment of the mitochondrial metabolic competence in
small (I quartile: -31.6%) and medium-sized (II quartile: -26.4; III
quartile: -16.4) mitochondria, while large organelles showed the lowest
age-related decrease (IV quartile: -3.0%). The present findings support
that a marked dysfunction of small and medium-sized mitochondria
contributes to the significant decay of energy metabolism currently
reported in physiological aging.

[association of lipofuscin with mitochondrial damage]

Ann N Y Acad Sci. 2004 Jun;1019:70-7
Aging of cardiac myocytes in culture: oxidative stress, lipofuscin
accumulation, and mitochondrial turnover.
  Oxidative stress is believed to be an important contributor to aging,
mainly affecting long-lived postmitotic cells such as cardiac myocytes
and neurons. Aging cells accumulate functionally effete, often mutant and
enlarged mitochondria, as well as an intralysosomal undegradable pigment,
lipofuscin. To provide better insight into the role of oxidative stress,
mitochondrial damage, and lipofuscinogenesis in postmitotic aging, we
studied the relationship between these parameters in cultured neonatal
rat cardiac myocytes. It was found that the content of lipofuscin, which
varied drastically between cells, positively correlated with mitochondrial
damage (evaluated by decreased innermembrane potential), as well as with
the production of reactive oxygen species. These results suggest that
both lipofuscin accumulation and mitochondrial damage have common
underlying mechanisms, likely including imperfect autophagy and ensuing
lysosomal degradation of oxidatively damaged mitochondria and other
organelles. Increased size of mitochondria (possibly resulting from
impaired fission due to oxidative damage to mitochondrial DNA, membranes,
and proteins) also may interfere with mitochondrial turnover, leading to
the appearance of so-called "giant" mitochondria. This assumption is
based on our observation that pharmacological inhibition of autophagy
with 3-methyladenine induced only moderate accumulation of large
(senescent-like) mitochondria but drastically increased numbers of small,
apparently normal mitochondria, reflecting their rapid turnover and
suggesting that enlarged mitochondria are poorly autophagocytosed.
Overall, our findings emphasize the importance of mitochondrial turnover
in postmitotic aging and provide further support for the
mitochondrial-lysosomal axis theory of aging.

[proteasome inhibition "ages" mitochondria]

J Biol Chem. 2004 May 14;279(20):20699-707. Epub 2004 Jan 22
Proteasome inhibition alters neural mitochondrial homeostasis and
mitochondria turnover.
  Inhibition of proteasome activity occurs in normal aging and in a wide
variety of neurodegenerative conditions including Alzheimer's disease and
Parkinson's disease. Although each of these conditions is also associated
with mitochondrial dysfunction potentially mediated by proteasome
inhibition, the relationship between proteasome inhibition and the loss of
mitochondrial homeostasis in each of these conditions has not been fully
elucidated. In this study, we conducted experimentation in order to begin
to develop a more complete understanding of the effects proteasome
inhibition has on neural mitochondrial homeostasis. Mitochondria within
neural SH-SY5Y cells exposed to low level proteasome inhibition possessed
similar morphological features and similar rates of electron transport
chain activity under basal conditions as compared with untreated neural
cultures of equal passage number. Despite such similarities, maximal
complex I and complex II activities were dramatically reduced in neural
cells subject to proteasome inhibition. Proteasome inhibition also
increased mitochondrial reactive oxygen species production, reduced
intramitochondrial protein translation, and increased cellular dependence
on glycolysis. Finally, whereas proteasome inhibition generated cells
that consistently possessed mitochondria located in close proximity to
lysosomes with mitochondria present in the cellular debris located within
autophagosomes, increased levels of lipofuscin suggest that
impairments in mitochondrial turnover may occur following proteasome
inhibition. Taken together, these data demonstrate that proteasome
inhibition dramatically alters specific aspects of neural mitochondrial
homeostasis and alters lysosomal-mediated degradation of mitochondria
with both of these alterations potentially contributing to aging and
age-related disease in the nervous system.

Eur J Biochem. 2002 Apr;269(8):1996-2002
The mitochondrial-lysosomal axis theory of aging: accumulation of damaged
mitochondria as a result of imperfect autophagocytosis.
  Cellular manifestations of aging are most pronounced in postmitotic
cells, such as neurons and cardiac myocytes. Alterations of these cells,
which are responsible for essential functions of brain and heart, are
particularly important contributors to the overall aging process.
Mitochondria and lysosomes of postmitotic cells suffer the most remarkable
age-related alterations of all cellular organelles. Many mitochondria
undergo enlargement and structural disorganization, while lysosomes,
which are normally responsible for mitochondrial turnover, gradually
accumulate an undegradable, polymeric, autofluorescent material called
lipofuscin, or age pigment. We believe that these changes occur not only
due to continuous oxidative stress (causing oxidation of mitochondrial
constituents and autophagocytosed material), but also because of the
inherent inability of cells to completely remove oxidatively damaged
structures (biological 'garbage'). A possible factor limiting the
effectiveness of mitochondial turnover is the enlargement of mitochondria
which may reflect their impaired fission. Non-autophagocytosed
mitochondria undergo further oxidative damage, resulting in decreasing
energy production and increasing generation of reactive oxygen species.
Damaged, enlarged and functionally disabled mitochondria gradually
displace normal ones, which cannot replicate indefinitely because of
limited cell volume. Although lipofuscin-loaded lysosomes continue to
receive newly synthesized lysosomal enzymes, the pigment is undegradable.
Therefore, advanced lipofuscin accumulation may greatly diminish
lysosomal degradative capacity by preventing lysosomal enzymes from
targeting to functional autophagosomes, further limiting mitochondrial
recycling. This interrelated mitochondrial and lysosomal damage
irreversibly leads to functional decay and death of postmitotic cells.

[The following might explain the benefit of lowered insulin in  young
animals only, as well as the failure  of caloric restriction  in old

Biochemistry (Mosc). 2003 Jul;68(7):772-5.
Lysosomal proteolysis: effects of aging and insulin.
  Age-related characteristics of the effect of insulin on the activity of
lysosomal proteolytic enzymes were studied. The relationship between the
insulin effect on protein degradation and insulin degradation was
analyzed. The effect of insulin on the activities of lysosomal enzymes
was opposite in young and old rats (inhibitory in 3-month-old and
stimulatory in 24-month-old animals). The activities of proteolytic
enzymes were regulated by insulin in a glucose-independent manner:
similar hypoglycemic effects of insulin in animals of different ages were
accompanied by opposite changes in the activities of lysosomal enzymes.
The inhibition of lysosomal enzymes by insulin in 3-month-old rats is
consistent with a notion on the inhibitory effect of insulin on protein
degradation. An opposite insulin effect in 24-month-old rats (i.e.,
stimulation of proteolytic activity by insulin) may be partly associated
with attenuation of the degradation of insulin, resulting in disturbances
in signaling that mediates the regulatory effects of insulin on protein

[lipofuscin/ceroid directly inhibits proteasomes.]

FASEB J. 2000 Aug;14(11):1490-8.
Proteasome inhibition by lipofuscin/ceroid during postmitotic aging of
  We have studied the effects of hyperoxia and of cell loading with
artificial lipofuscin or ceroid pigment on the postmitotic aging of human
lung fibroblast cell cultures. Normobaric hyperoxia (40% oxygen) caused
an irreversible senescence-like growth arrest after about 4 wk and
shortened postmitotic life span from 1-1/2 years down to 3 months. During
the first 8 wk of hyperoxia-induced 'aging', overall protein degradation
(breakdown of [(35)S]methionine metabolically radiolabeled cell proteins)
increased somewhat, but by 12 wk and thereafter overall proteolysis was
significantly depressed. In contrast, protein synthesis rates were
unaffected by 12 wk of hyperoxia. Lysosomal cathepsin-specific activity
(using the fluorogenic substrate z-FR-MCA) and cytoplasmic
proteasome-specific activity (measured with suc-LLVY-MCA) both declined
by 80% or more over 12 wk. Hyperoxia also caused a remarkable increase in
lipofuscin/ceroid formation and accumulation over 12 wk, as judged by
both fluorescence measurements and FACscan methods. To test whether the
association between lipofuscin/ceroid accumulation and decreased
proteolysis might be causal, we next exposed cells to lipofuscin/ceroid
loading under normoxic conditions. Lipofuscin/ceroid-loaded cells indeed
exhibited a gradual decrease in overall protein degradation over 4 wk of
treatment, whereas protein synthesis was unaffected. Proteasome specific
activity decreased by 25% over this period, which is important
since proteasome is normally responsible for degrading oxidized cell
proteins. In contrast, an apparent increase in lysosomal cathepsin
activity was actually caused by a large increase in the number of
lysosomes per cell. To test whether lipofuscin/ceroid could in fact
directly inhibit proteasome activity, thus causing oxidized proteins to
accumulate, we incubated purified proteasome with lipofuscin/ceroid
preparations in vitro. We found that proteasome is directly inhibited by
lipofuscin/ceroid. Our results indicate that an accumulation of oxidized
proteins (and lipids) such as lipofuscin/ceroid may actually cause further
increases in damage accumulation during aging by inhibiting the

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