Biomedical subjects

Alexei Terman

Publications and source records attributed to Alexei Terman.

At least 19 recordsLinked to original sources

PubMed2006

Mitochondrial damage and intralysosomal degradation in cellular aging.

Normal mitochondrial respiration is associated with a continuous production of superoxide and hydrogen peroxide, inevitably resulting in minor macromolecular damage. Damaged cellular components are not completely turned over by autophagy and other cellular repair systems, leading to a progressive age-related accumulation of biological "garbage" material, such as defective mitochondria, cytoplasmic protein aggregates and an intralysosomal undegradable material, lipofuscin. These changes primarily affect neurons, cardiac myocytes and other long-lived postmitotic cells that neither dilute this "garbage" by mitotic activity, nor are replaced by newly differentiated cells. Defective mitochondria are insufficient in ATP production and often generate increased amounts of reactive oxygen species, further enhancing oxidative stress. Lipofuscin-loaded lysosomes, in turn, poorly turn over mitochondria that gradually leads to the overload of long-lived postmitotic cells with "garbage" material, decreased adaptability and eventual cell death.

Animals↗

PubMed2006

The lysosomal-mitochondrial axis theory of postmitotic aging and cell death.

Aging (senescence) is characterized by a progressive accumulation of macromolecular damage, supposedly due to a continuous minor oxidative stress associated with mitochondrial respiration. Aging mainly affects long-lived postmitotic cells, such as neurons and cardiac myocytes, which neither divide and dilute damaged structures, nor are replaced by newly differentiated cells. Because of inherent imperfect lysosomal degradation (autophagy) and other self-repair mechanisms, damaged structures (biological "garbage") progressively accumulate within such cells, both extra- and intralysosomally. Defective mitochondria and aggregated proteins are the most typical forms of extralysosomal "garbage", while lipofuscin that forms due to iron-catalyzed oxidation of autophagocytosed or heterophagocytosed material, represents intralysosomal "garbage". Based on findings that autophagy is diminished in lipofuscin-loaded cells and that cellular lipofuscin content positively correlates with oxidative stress and mitochondrial damage, we have proposed the mitochondrial-lysosomal axis theory of aging, according to which mitochondrial turnover progressively declines with age, resulting in decreased ATP production and increased oxidative damage. Due to autophagy of ferruginous material, lysosomes contain a pool of redox-active iron, which makes these organelles particularly susceptible to oxidative damage. Oxidant-mediated destabilization of lysosomal membranes releases hydrolytic enzymes to the cytosol, eventuating in cell death (either apoptotic or necrotic depending on the magnitude of the insult), while chelation of the intralysosomal pool of redox-active iron prevents these effects. In relation to the onset of oxidant-induced apoptosis, but after the initiating lysosomal rupture, cytochrome c is released from mitochondria and caspases are activated. Mitochondrial damage follows the release of lysosomal hydrolases, which may act either directly or indirectly, through activation of phospholipases or pro-apoptotic proteins such as Bid. Additional lysosomal rupture seems to be a consequence of a transient oxidative stress of mitochondrial origin that follows the attack by lysosomal hydrolases and/or phospholipases, creating an amplifying loop system.

Aging↗

PubMed2006

Oxidative stress and Alzheimer disease: the autophagy connection?

Intraneuronal accumulation of amyloid beta-protein (Abeta) is believed to be responsible for degeneration and apoptosis of neurons and consequent senile plaque formation in Alzheimer disease (AD), the main cause of senile dementia. Oxidative stress, an early determinant of AD, has been recently found to induce intralysosomal Abeta accumulation in cultured differentiated neuroblastoma cells through activation of macroautophagy. Because Abeta is known to destabilize lysosomal membranes, potentially resulting in apoptotic cell death, this finding suggests the involvement of oxidative stress-induced macroautophagy in the pathogenesis of AD.

Alzheimer Disease↗

PubMed2006

Catabolic insufficiency and aging.

Cellular degradative processes, which include lysosomal (autophagic) and proteasomal degradation, as well as the activity of cytosolic and mitochondrial proteases, provide for a continuous turnover of damaged and obsolete biomolecules and organelles. Inherent insufficiency of these degradative processes results in progressive accumulation within long-lived postmitotic cells of biological "garbage" ("waste" material), such as indigestible protein aggregates, defective mitochondria, and lipofuscin (age pigment), an intralysosomal, polymeric, undegradable material. Intracellular "garbage" is neither completely catabolized, nor exocytosed to any considerable extent. Heavy lipofuscin loading of lysosomes, typical of old age, seems to pronouncedly decrease autophagic potential. As postulated in the mitochondrial-lysosomal axis theory of aging, this occurs on account of the transport of newly synthesized lysosomal enzymes to lipofuscin-loaded lysosomes rather than to active lysosomes/late endosomes, making the enzyme content of autophagolysosomes insufficient for proper degradation. Consequently, the turnover of mitochondria progressively declines, resulting in decreased ATP synthesis and enhanced formation of reactive oxygen species, inducing further mitochondrial damage and additional lipofuscin formation. With advancing age, lipofuscin-loaded lysosomes and defective mitochondria occupy increasingly larger parts of long-lived postmitotic cells, leaving less and less capability for normal turnover and ATP production, finally resulting in cell death.

Aging↗

PubMed2006

Oxidative stress induces intralysosomal accumulation of Alzheimer amyloid beta-protein in cultured neuroblastoma cells.

Oxidative stress is considered important for the pathogenesis of Alzheimer's disease (AD), which is characterized by the formation of extracellular senile plaques, mainly composed of amyloid beta-protein (Abeta). Abeta also accumulates within AD neurons and is believed to exert cellular toxicity through lysosomal labilization. We report that the exposure of human neuroblastoma cells to hyperoxia (40% vs. 8% ambient oxygen) induced the accumulation of large (over 1 microM) Abeta-containing lysosomes, which were not typical of control cells, showing a distinct localization of Abeta and lysosomal markers. An inhibitor of autophagy, 3-methyladenine, suppressed the effect of hyperoxia. The results suggest a link between the involvement of oxidative stress and lysosomes in AD.

Alzheimer Disease↗

PubMed2005

Autophagy of amyloid beta-protein in differentiated neuroblastoma cells exposed to oxidative stress.

Oxidative stress is considered important for the pathogenesis of Alzheimer disease (AD), which is characterized by the formation of senile plaques rich in amyloid beta-protein (Abeta). Abeta cytotoxicity has been found dependent on lysosomes, which are abundant in AD neurons and are shown to partially co-localize with Abeta. To determine whether oxidative stress has any influence on the relationship between lysosomes and Abeta1-42 (the most toxic form of Abeta), we studied the effect of hyperoxia (40% versus 8% ambient oxygen) on the intracellular localization of Abeta1-42 (assessed by immunocytochemistry) in retinoic acid differentiated SH-SY5Y neuroblastoma cells maintained in serum-free OptiMEM medium. In control cells, Abeta1-42 was mainly localized to small non-lysosomal cytoplasmic granules. Only occasionally Abeta1-42 was found in large (over 1 microm) lysosomal-associated membrane protein 2 positive vacuoles, devoid of the early endosomal marker rab5. These large Abeta1-42 -containing lysosomes were not detectable in the presence of serum (known to suppress autophagy), while their number increased dramatically (up to 24-fold) after exposure of cells to hyperoxia during 5 days. Activation of autophagy by hyperoxia was confirmed by transmission electron microscopy. Furthermore, an inhibitor of autophagic sequestration 3-methyladenine prevented the accumulation of Abeta1-42 -positive lysosomes due to hyperoxia. In parallel experiments, intralysosomal accumulation of Abeta1-40 following oxidative stress has been found as well. The results suggest that Abeta can be autophagocytosed and its accumulation within neuronal lysosomes is enhanced by oxidative stress.

Amyloid beta-Peptides↗

PubMed2005

Autophagy and aging: the importance of maintaining "clean" cells.

A decrease in the turnover of cellular components and the intracellular accumulation of altered macromolecules and organelles are features common to all aged cells. Diminished autophagic activity plays a major role in these age-related manifestations. In this work we review the molecular defects responsible for the malfunctioning of two forms of autophagy, macroautophagy and chaperone-mediated autophagy, in old mammals, and highlight general and cell-type specific consequences of dysfunction of the autophagic system with age. Dietary caloric restriction and antilipolytic agents have been proven to efficiently stimulate autophagy in old rodents. These and other possible experimental restorative efforts are discussed.

Aging↗

PubMed2005

Autophagy in cardiac myocyte homeostasis, aging, and pathology.

Autophagy, an intralysosomal degradation of cells' own constituents that includes macro-, micro-, and chaperone-mediated autophagy, plays an important role in the renewal of cardiac myocytes. This cell type is represented by long-lived postmitotic cells with very poor (if any) replacement through differentiation of stem cells. Macroautophagy, the most universal form of autophagy, is responsible for the degradation of various macromolecules and organelles including mitochondria and is activated in response to stress, promoting cell survival. This process is also involved in programmed cell death when injury is irreversible. Even under normal conditions, autophagy is somewhat imperfect, underlying gradual accumulation of defective mitochondria and lipofuscin granules within aging cardiac myocytes. Autophagy is involved in the most important cardiac pathologies including myocardial hypertrophy, cardiomyopathies, and ischemic heart disease, a fact that has led to increasing attention to this process.

Adaptation, Physiological↗

PubMed2005

Testing the "garbage" accumulation theory of ageing: mitotic activity protects cells from death induced by inhibition of autophagy.

Imperfect autophagic degradation of oxidatively damaged macromolecules and organelles (so-called biological "garbage") is considered an important contributor to ageing and consequent death of postmitotic (non-dividing) cells, such as neurons and cardiac myocytes. In contrast, proliferating cells apparently escape senescence by a continuous dilution and repair of damaged structures during division. Postmitotic ageing can be mimicked and studied in cultures of potentially dividing cells if their mitotic activity is inhibited. To test the "garbage accumulation" theory of ageing, we compared survival of density-dependent growth-arrested (confluent) and proliferating human fibroblasts and astrocytes following inhibition of autophagic sequestration with 3-methyladenine (3MA). Exposure of confluent fibroblast cultures to 3MA for two weeks resulted in a significantly increased proportion of dying cells compared to both untreated confluent cultures and dividing cells with 3MA-inhibited autophagy. Similar results were obtained when autophagic degradation was suppressed by the protease inhibitor leupeptin. In 3MA- or leupeptin-exposed cultures, dying cells were overloaded with undegraded autofluorescent material. The results support a key role of biological lysosomal "garbage" accumulation in the triggering of ageing and death of postmitotic cells, as well as the anti-ageing role of cell division.

Adenine↗

PubMed2005

Is aging the price for memory?

Aging (senescence) is apparent in animals that possess long-lived postmitotic cells but is negligible in primitive species, such as hydras and other Cnidarians, all of whose cells are constantly renewed by cell division. This repetitive mitotic activity precludes the progressive intracellular accumulation of damaged biomolecules and organelles, which are obvious concomitants of aging in neurons and other long-lived cells of higher animals. We assume that the development of long-lived postmitotic cells, now found in the overwhelming majority of species, represented a useful evolutionary change. Probably, of particular importance was the evolution of long-lived neurons, which are required for long-term memory. However, the appearance of long-lived postmitotic cells not only increased fitness, but also gave rise to the aging process.

Aging↗

PubMed2005

The aging myocardium: roles of mitochondrial damage and lysosomal degradation.

Myocardial aging, leading to circulatory dysfunction, complicates numerous pathologies and is an important contributor to overall mortality at old age. In cardiac myocytes, mitochondria and lysosomes suffer remarkable age-related alterations. Mitochondrial changes include structural disorganization and enlargement, while lysosomes, which are responsible for autophagic turnover of mitochondria, accumulate lipofuscin (age pigment), a polymeric, autofluorescent, undegradable material. These changes are caused by continuous physiological oxidative stress, and they advance with age because the cellular turnover machinery is inherently imperfect. Several mechanisms contribute to age-related accumulation of damaged mitochondria following initial oxidative injury. Such mechanisms may include clonal expansion of defective mitochondria, decreased propensity of altered mitochondria to become autophagocytosed (due to mitochondrial enlargement or decreased membrane damage associated with weakened respiration), suppressed autophagy because of heavy lipofuscin loading of lysosomes, and decreased efficiency of Lon and AAA proteases. Because lipofuscin-laden lysosomes still receive newly synthesized lysosomal enzymes, even though they fail to degrade the pigment, the cells become in short supply of lysosomal hydrolases for functional autophagy, further limiting mitochondrial turnover. This interrelated mitochondrial and lysosomal damage eventually results in functional failure and death of cardiac myocytes.

Aging↗

PubMed2004

Induction of fibroblast apolipoprotein E expression during apoptosis, starvation-induced growth arrest and mitosis.

Apolipoprotein E (apoE) mediates the hepatic clearance of plasma lipoproteins, facilitates cholesterol efflux from macrophages and aids neuronal lipid transport. ApoE is expressed at high levels in hepatocytes, macrophages and astrocytes. In the present study, we identify nuclear and cytosolic pools of apoE in human fibroblasts. Fibroblast apoE mRNA and protein levels were up-regulated during staurosporine-induced apoptosis and this was correlated with increased caspase-3 activity and apoptotic morphological alterations. Because the transcription of apoE and specific pro-apoptotic genes is regulated by the nuclear receptor LXR (liver X receptor) alpha, we analysed LXRalpha mRNA expression by quantitative real-time PCR and found it to be increased before apoE mRNA induction. The expression of ABCA1 (ATP-binding cassette transporter A1) mRNA, which is also regulated by LXRalpha, was increased in parallel with apoE mRNA, indicating that LXRalpha probably promotes apoE and ABCA1 transcription during apoptosis. Fibroblast apoE levels were increased under conditions of serum-starvation-induced growth arrest and hyperoxia-induced senescence. In both cases, an increased nuclear apoE level was observed, particularly in cells that accumulated lipofuscin. Nuclear apoE was translocated to the cytosol when mitotic nuclear disassembly occurred and this was associated with an increase in total cellular apoE levels. ApoE amino acid sequence analysis indicated several potential sites for phosphorylation. In vivo studies, using 32P-labelling and immunoprecipitation, revealed that fibroblast apoE can be phosphorylated. These studies reveal novel associations and potential roles for apoE in fundamental cellular processes.

Apolipoproteins E↗

PubMed2004

Lipofuscin.

Over time, postmitotic cells accumulate a non-degradable intralysosomal substance, lipofuscin, which forms due to iron-catalyzed oxidation/polymerization of protein and lipid residues. Lipofuscin is often considered a hallmark of aging, showing an accumulation rate that inversely correlates with longevity. There is an emerging impression that lipofuscin, although still typically considered a harmless wear-and-tear product, may have multiple negative effects. By interfering with the important autophagic process, by which most worn out cellular components are degraded, it may prevent cellular renewal and advance the accumulation of damaged cellular constituents. Due to binding of transition metals, such as iron and copper, lipofuscin also seems to sensitize lysosomes and cells to oxidative stress. Of importance for the pathogenesis of age-related macular degeneration, lipofuscin deposition interferes with the phagocytic activity of retinal pigment epithelial cells and also sensitizes their lysosomes to blue light.

Aging↗

PubMed2004

Aging as a catabolic malfunction.

Cellular degradative processes, which include lysosomal (autophagic) and proteasomal degradation, as well as catabolism of proteins by cytosolic and mitochondrial proteases, provide for a continuous turnover of cellular components, such as damaged or obsolete biomolecules and organelles. Inherent insufficiency of these degradative processes results in progressive accumulation within long-lived postmitotic cells of biological 'garbage' (waste material), such as various oxidized proteins, functionally effete mitochondria, and lipofuscin (age pigment), an intralysosomal, polymeric, undegradable material. There is increasing evidence that lipofuscin hampers lysosomal degradative capacity, thus promoting the aggravation of accumulated damage at old age. Being rich in redox-active iron, lipofuscin granules also may exacerbate oxidative stress levels in senescent cells. Thus, increasing the efficiency of cellular degradative pathways and preventing involvement of iron in oxidant-induced lysosomal and cellular damage may be potential strategies for anti-aging interventions.

Aging↗

PubMed2004

Myocyte aging and mitochondrial turnover.

Cardiac myocytes, skeletal muscle fibers, and other long-lived postmitotic cells show dramatic age-related alterations that mainly affect mitochondria and the lysosomal compartment. Mitochondria are primary sites of reactive oxygen species formation that causes progressive damage to mitochondrial DNA and proteins in parallel to intralysosomal lipofuscin accumulation. There is amassing evidence that several various mechanisms may contribute to age-related accumulation of damaged mitochondria following initial oxidative injury. Such mechanisms may include clonal expansion of defective mitochondria, decreased propensity of altered mitochondria to become autophagocytosed (due to mitochondrial enlargement or decreased membrane damage associated with weakened respiration), suppressed autophagy because of heavy lipofuscin loading of lysosomes, and decreased efficiency of Lon protease.

Aged↗

PubMed2004

Inhibition of autophagy with 3-methyladenine results in impaired turnover of lysosomes and accumulation of lipofuscin-like material.

Autophagy (which includes macro-, micro-, and chaperone-mediated autophagy) is an important biological mechanism for degradation of damaged/obsolete macromolecules and organelles. Ageing non-dividing cells, however, progressively accumulate oxidised proteins, defective organelles and intralysosomal lipofuscin inclusions, suggesting inherent insufficiency of autophagy. To learn more about the role of macroautophagy in the turnover of organelles and lipofuscin formation, we inhibited autophagic sequestration with 3-methyladenine (3 MA) in growth-arrested human fibroblasts, a classical model of cellular ageing. Such treatment resulted in a dramatic accumulation of altered lysosomes, displaying lipofuscin-like autofluorescence, as well as in a moderate increase of mitochondria with lowered membrane potential. The size of the late endosomal compartment appeared not to be significantly altered following 3 MA exposure. The accumulation of lipofuscin-like material was enhanced when 3 MA administration was combined with hyperoxia. The findings suggest that macroautophagy is essential for normal turnover of lysosomes. This notion is supported by reports in the literature of lysosomal membrane proteins inside lysosomes and/or late endosomes, as well as lysosomes with active hydrolases within autophagosomes following vinblastine-induced block of fusion between lysosomes and autophagosomes. The data also suggest that specific components of lysosomes, such as membranes and proteins, may be direct sources of lipofuscin.

Adenine↗

PubMed2004

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.

Adenine↗

PubMed2003

Mitochondria play a central role in apoptosis induced by alpha-tocopheryl succinate, an agent with antineoplastic activity: comparison with receptor-mediated pro-apoptotic signaling.

alpha-Tocopheryl succinate (alpha-TOS) is a semisynthetic vitamin E analogue with high pro-apoptotic and anti-neoplastic activity [Weber, T et al. (2002) Clin. Cancer Res. 8, 863-869]. Previous studies suggested that it acts through destabilization of subcellular organelles, including mitochondria, but compelling evidence is missing. Cells treated with alpha-TOS showed altered mitochondrial structure, generation of free radicals, activation of the sphingomyelin cycle, relocalization of cytochrome c and Smac/Diablo, and activation of multiple caspases. A pan-caspase inhibitor suppressed caspase-3 and -6 activation and phosphatidyl serine externalization, but not decrease of mitochondrial membrane potential or generation of radicals. For alpha-TOS, but not Fas or TRAIL, apoptosis was suppressed by caspase-9 inhibition, while TRAIL- and Fas-resistant cells overexpressing cFLIP or CrmA were susceptible to alpha-TOS. The central role of mitochondria was confirmed by resistance of mtDNA-deficient cells to alpha-TOS, by regulation of alpha-TOS apoptosis by Bcl-2 family members, and by anti-apoptotic activity of mitochondrially targeted radical scavengers. Co-treatment with alpha-TOS and anti-Fas IgM showed their cooperative effect, probably by signaling via different, convergent pathways. These data provide an insight into the molecular mechanism, by which alpha-TOS kills malignant cells, and advocate its testing as a potential anticancer agent or adjuvant.

Antineoplastic Agents↗