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Unformatted text preview: Chapter 7
Robert Arking Biology of Aging, 3e Oxford University Press Wayne State University Life Span = Health Span
Longevity Determinant Mechanisms Operative + Transition + Senescent Span
Stochasticdependent Degradation of Gene/ Protein Interaction Networks Cell’s Regulatory Ability Decreases, Tissue/Systemic Functions Deteriorate Feedback Cascades Ruin Homeostatic Ability, Critical Thresholds Passed
from Arking 2006 pathwaydependent Eventdependent Altered Balance of Cell’s Defenses due to Accumulated Damage&/or Loss of Signal Abnormal Proteins Aggregate, Exceed Chaperone Capacity; Positive Feedback =>Lowered Cell Function Damaged Cells Survive, Apoptosis Homeostatic Ability Sensitive & Reliable Low ISP Levels High Stress Resistance High Repair Levels
= Table 7-1 Topical Organization of This Chapter Yeast Nematode Fly Mouse Background Metabolic Control: CR Metabolic Control: ISP Metabolic Control: NMI Stress Resistance Genomic Stability Reproductive Effects Patterns of Senescence Summary pp. 6 - 7 7 - 13 --13 -15 15 -18 18 - 20 20 - 21 --21 - 22 pp. 21 --21 - 27 27 - 30 30 - 32 32 - 33 33 - 35 35 - 36 36 pp. 36 - 38 39 - 43 43 - 46 46 - 47 47 - 54 55 - 57 57 - 60 60 60-61 pp. 61 - 64 64 - 68 68 - 73 73 73 - 80 80 - 81 82 - 84 84 - 85 85 - 86 Table 7-12 Reducing effective glucose intake, by whatever means, results in an extended longevity. This is the basis of Caloric Restriction (CR) or Dietary Restriction (DR) Does this data imply that aging is a cell level phenomenon? Sir2 is necessary for CR to occur Sir2 is responsible for the magnitude of the CR effect, but not for its presence. sir2 mtuants accumulate lots of rDNA circles in nucelolus in some but not all strains. May involve mitochondria in mammals – see text Yeast without mitochondria live longer that do yeast with active mitochondria 1. 2. Absence of mitochondria increases longevity in petites. This extended longevity is dependent on ras2 activity, which implies stress resistant. This retrograde regulation cycle is specific to yeast. Most animals cannot use acetate directly. But this nutrient shift alters mitochondrial function, which then signals the nucleus to alter nuclear gene expression in an appropriate manner. This may be the important conserved message of these yeast experiments. activated by chronic SR Note that mitochondrial DNA repair systems are simpler and less redundant. This likely underlies the greater sensitivity of mitochondria to Ox Stress Damage Reproductive Effects of Aging in Yeast: asymmetric mitotic divisions Patterns of Senescence in Yeast mother cell undergoes senescence but daughter cell stays young. ? The clock mutants of C. elegans yield a slow rate of living & extended longevity, but do it by different mechanisms which might, however, have a common theme of altering nuclear-mitochondrial interactions. GENOTYPE 2 5oC
wild type clk-1 clk-2 clk-3 gro-1 clk-1 clk-2 clk-3 clk-1 clk-3 clk-2 clk-3 gro-1 15oC
22.0 + 0.3 29.3 + 0.5 24.6 + 0.8 25.7 + 0.7 26.0 + 0.7 34.5 + 0.9 36.7 + 1.4 33.8 + 0.9 24.4 + 0.6 18oC
14.9 + 0.3 18.4 + 0.4 18.7 + 0.5 20.4 + 0.4 19.2 + 0.6 28.2 + 0.9 22.7 + 0.6 22.3 + 0.8 15.9 + 0.8 16.1 + 0.2 17.3 + 0.4 18.0 + 0.5 19.9 + 0.6 19.7 + 0.6 23.1 + 0.7 17.8 + 0.5 20.6 + 0.6 14.6 + 0.4 20 oC
9.2 + 0.3 11.6 + 0.5 11.7 + 0.7 13.0 + 0.8 15.6 + 0.5 No data 17.4 + 1.4 12.7 + 0.5 No data Stress Resistance in C. elegans ISP-dependent long lived animals are: oxidative stress resistant (CuZnSOD, MnSOD, GSTs, etc. synthetic anti-ox mimics extend LS of normal worms & rescue mutant worms heat-stress resistant implicates heat shock proteins/chaperones cross-resistant to different stressors The daf16 (forkhead family) TFs activate these various stressresistant genes. Thus one activating stimulus can result in the activation/repression of a large number of downstream target genes Genomic Stability of C. elegans 1. Not well studied but what is known is consistent with idea that genomic stability is essential to normal & extended longevity. 2. 3. Worm has a conserved type of DNA repair system Mutant p53 animals are sensitive to various stressors & live shorter lives. REPRODUCTIVE EFFECTS: Laser Ablation of Gonad Cells Leads to Different Longevity Outcomes
SGGS HYPOTHESIS TO EXPLAIN OBSERVED REPRODUCTIVE EFFECTS Based on the Hypothesis that Darwinian Competition Occurs Within an Organism as well as Between Organisms Connects Onset of Repro with Repression of Somatic Maintenance Senescence Patterns
All tissues do not age at same rate in normal-lived animals, nor are all tissues affected uniformly in long-lived animals. Muscle << Neurons Artificial Selection Demonstrates that Life Span is Plastic & Can Be Manipulated in Both Directions. Biomarker Analysis Shows That Long-lived Animals Have A Lengthened Health Span But A Normal Senescenct Span, Relative to Normal-lived Controls: Adult life span is divided into two phases Dietary restriction alters survival by delaying the onset of an increase in the age-specific mortality rate. Could this explain the data on the previous slide? DR Alters Gene Expression Patterns CR CR CR alters very few genes, & yet changes the entire organism! Two predictions as to how ln qx might change as a function of diet. (top) AL animal reverts to DR type intercept. (bottom) AL animals reverts to DR type slope The top alternative is supported by the data as reported by one lab: DR reduces the acute (immediate) risk of death.
Partridge et al., 2005 Partridge et al., 2005 This gene pathway NOT identical to the ISP pathway from other organisms! Transporter gene dependent on genetic background HDA class I HDA class III The ISP significantly alters the age-specific mortality rate in flies with a mutated ISP. Note that females have a stronger response.
Females Males Mutating downstream components of the ISP also results in an extended longevity. Thus inactivating the system at any level has an effect. There may be other, more complex, regulatory pathways available to the animal EXTENDED LONGEVITY INDUCED BY A MULTIPATHWAY REGULATORY CASCADE Interacting Longevity Pathways May Be Common Schieke et al., JBC 281:27643, 2006 Table Table 7-4 Stress Resistance Summary of genetic interventions testing the relationship between resistance to oxidative stress and altered longevity Manipulation Selection for long life Genes Involved CuZnSOD, MnSOD Catalase no data cat cat CuZnSOD CuZnSOD Effect on Life Span Increased Increased Increased Decreased No effect Decreased Increased Increased (some strains) Effect on Stress Resistance Increased Increased Increased ox stress, also increased starvation & dessication resistance no data Increased Decreased Increased Increased (some strains) Catalase reduced Catalase increased SOD1 reduced SOD1 increased SOD1 & Cat increased CuZnSOD, cat Increased Increased -------No increase over SOD alone----Decreased Increased No No effect Decreased no data No effect SOD2 reduced SOD2 increased MnSOD MnSOD GENOMIC STABILITY 1. Genome is stable during the aging process 2. Most genes do not show significant alterations in gene expression during aging 3. Observed changes in gene expression are the result of a dynamic regulation of specific genes/gene pathways in response to the change physiological status of the organism. 4. The environment affects the genome via epigenetic regulation (e.g., use of HDA enzymes to alter acetylation status of histones in specific gene loci) a) Epigenetic regulation may be done via drugs, as in next slide… Epigenetic Regulation of Histone Acetylation Levels via Drugs Alters Lifespan Reproductive Effects Somatic cells decrease fecundity & increase longevity Germ cells increase fecundity & decrease longevity DECREASING STEROID HORMONE LEVELS IN FLIES INCREASES LIFESPAN Strong flies are those whose soma is strong enough to meet various stressors as young flies because their energy allocation to somatic repair is adequate. Weak flies have an inadequate allocation. These ‘energy’ terms reflect the relative effectiveness of germ & somatic cells to inhibit their antagonists. Demands & Supplies JNK Inbred mice & rats are the usual mammalian model organisms. Outbred strains are now becoming the norm since: 1) their genetic differences allow the identification of genes involved in aging; and 2) their outbred nature is a better approximation to humans. In addition, other sometimes exotic (e.g., bats, naked mole rat) mammals are increasingly being used for aging research since they allow specific questions to be tested. Effects Effects of CR on Gene Expression in the Mouse Liver
A. Detailed Results Not many genes are involved….?
CR Effects Genes Decreased with Age CR Effects Genes Unaffected with Age CR Effects Genes Increased with Age Normal AL Sub-Categories Inflammation Stress/hsps Apoptosis Other 20 a 14a, 6NE 26a 13a, 13 NE 33 11a , 22a 8 5 3 4 6a 3a 2a 3a Cell cycle/DNA rep 6 Xenobiotic metab Urinary proteins Other 5 4 11 2a 3a 4a 4a Energy Metab 11 2a, 9a 4a, 3a 3a, 2a 4a 2a 2a, 2a Apoptosis/cell growth 7 Xenobiotic metab Intracellular SD Stress/hsps Other 5 4 2 4 N = 79 genes Table 7.6B B. Summary Total Genes Alterd by CR = 79 (0.007%) Apoptosis/cell survival Energy metabolism Xenobiotic metabolism Inflammation Stress/hsps Urinary proteins Intracellular signaling 4 Other 16 11 10 8 7 4 19 Table Table 7-7 …and they get activated rather quickly! Temporal Effects of CR on Gene Expression in Mouse Liver
Age at CR Start CR Period Temporal Response CR Effect: % of Total Effect on Mortality Genes Reversed by AL % of CR ~33 months 2-4 weeks Early Genes 15a , 22a 57.7 --- 11, 5 43 ~32 months 8 weeks Intermediate Genes 7a , 10a 71.5 42%a 5, 10. 88 7 months 27 months Late Genes 14a , 21a 100.0 ~40%a 14, 21 100 ~33 months 2 weeks Oscillating Genes 16a , 18a --- --- 11, 16 --- Notes: CR effect = number of genes increased or decreased as noted; % reversed by AL = number of CR genes cumulatively induced in the indicated time periods relative to the total number (N=123) of all CR genes induced by long term CR; % of CR= % of CR effect genes for that time period reversed by 8 weeks of AL control diet. After Dhahbi et al., 2004 SO WHAT DO THESE GENES DO? Ad libitum Aging yields… • gluconeogenesis protein turnover Caloric Restricted Aging yields… • gluconeogenesis protein turnover Food Intake Insulin/glucagon Chaperone levels Protein folding Survival of tumorigenic cells BUT NOTE THAT THE GENES AFFECTED BY DR ARE NOT THE GENES IDENTIFIED AS BEING PART OF THE ISP. IN OTHER WORDS, THE EXTENDED LONGEVITY MECHANISMS ACTIVATED BY A DIETARY RESTRICTION IS DIFFERENT FROM THE EXTENDED LONGEVITY MECHANISMS ACTIVATED BY THE ISP-MEDIATED ENVIRONMENTAL EFFECTS. ISP = STRESS RESISTANCE; DR = METABOLIC ALTERATIONS WE HAVE MULTIPLE EXTENDED LONGEVITY MECHANISMS. 1. DR 2. ILP 3. Pituitary Mutants 4. p66shc 5. Signaling Enhancements TABLE 7-8 Effect of GHR-KO on Life Span Gender Males Genotype +/+ +/-/Lifespan (days) 629 + 72 668 + 51 975 + 106 a55% Females +/+ +/-/- 749 + 41 701 + 36 1031 + 4 a38% From Coschigano et al 2000 Growth Hormone Regulates the Synthesis of IGF-1, and thus the activity of the ISP It is therefore NOT true that taking GH supplements will make you live long. Quite the opposite – it will likely increase ISP activity, inhibit FOXO activity, repress your somatic maintenance gene expression, and shorten your life span. COMPARISON OF ISP OF MODEL ORGANISMS Table 7-10 Comparison of Characteristics of Long-lived Dwarf and GHR-KO Mice with the Characteristics of Wild Type Animals Subjected to
Caloric Restriction f Characteristic WT-CR Dwarf df dw (Prop1df & Pitdw ) GHR-KO Glucose Regulation: Plasma insulin Plasma glucose Insulin sensitivity Somatropic Axis Plasma GH Plasma IGF-1 Body size Thyroid Function & Metabolism Plasma thyroid hormones Body core temperature Reproduction Sexual maturation Fertility Reduced Reduced Increased Reduced Reduced Increased Greatly reduced Modestly reduced Increased Reduced a Reduced Reduced Absent Greatly reduced Reduced Elevated b Greatly reduced Reduced Reduced Reduced Delayed Reduced Greatly reduced Reduced Delayed Severely suppressed c Reduced Slightly reduced Delayed Reduced Glucocorticoids & adiposity Plasma corticosterone Elevated Percent body fat Reduced Notes: all data after Bartke and Turyn, 2001. a . Pulsatile GH secretion is preserved in long term CR rats
b. Normal d Normal e Normal d no data Elevated GH levels in these animals do not imply increased GH signaling since GH receptors are absent The p66shc protein regulates whether damaged cells will be repaired or die. A null gene mutant increases longevity, presumably by decreasing apoptosis (& thus increasing the risk of future cancer) Restricting the intake of only Methionine significantly increases Life span. This raises the possibility that the DR effect is really just the effect of Methionine Restriction. GENOMIC STABILITY REPRODUCTIVE EFFECTS Genomic Instability May Be A Major Factor in the Transition of Mitotically Active Tissues from Health to Senescence
Hyperplasia hOOG1; ATM, Chk2, H2Ax Phosphorylation DNA Damage (SSB, DSB) Activation of DNA Damage Checkpoint DNA Replication Stress
after Gorgulis et al Nature 434:907, 2005 after Bannerjee et al., Nature 434:612, 2005 after Bartkove et al., Nature 434:864, 2005 after Venkitaraman, Nature 434:829, 2005 Cell Senescence p53-dependent Arrest Table Table 7-10 Age Genes PQ responsive Genes Common Common genes w/altered expression Immediate early genes expressed at each age 249 55 298 55 256 55 Age Related Alterations in Inducibility of Stress Response Genes 5 mos 15 mos 25 mos a4
7 a2, a8
5 Notes: PQ=paraquat; Common=# of genes expressed in response to PQ at all ages; u = significant up- or sown-regulation of gene expression as a function of age; immediate early genes=expressed in response to PQ within one hour of treatment.
Gene pathways become less data taken from Edwards et al 2003 responsive with age. Why is that? The genes themselves seem to be OK. Could it be the signaling process is at fault? FOXO3a Downregulation Increases ROS & Accelerates Senescence in Human Fibroblasts in vitro from Kim et al., JGBS 60A:49, 2005 Reducing I-IGF &/or dFOXO Signaling Halts Cardiac Aging in Flies… heart rate heart failure rate …But Cardiac Aging Can Be Restarted by Excess JH which is itself regulated by dFOXO
from Wessels et al., Nature Genetics 36:1275, 2004 Old Animals Have Lower Levels of Signals Than Do Young Animals…But Their Cells Are Still Responsive
Pair Old or Young Animals via Common Circulatory System….. Measure Their Ability to Regenerate Damaged Muscle. Old Animals Regenerate Better When They Have Young Blood Circulating! Cells from Old Animals Put in Culture and Bathed with Sera from Young Animals Have Higher Incidence of Activated Regenerating Cells Than Do Old Cells in Old Sera. Old Cells Are Activated to Regenerate By Sera From Young Animals! Aging May Be A Software Problem & Not A Hardware Problem! from Conboy et al., Nature 433:760, 2005 Senescence May Start With the Degradation of the Gene Interaction Network
1 2 hubs & spokes
4 3 6 5 after Giot et al, 2003 Table 7-11 Signaling Signaling pathways activated by oxidative stress and their ultimate cellular outcomes Signaling pathways Enhanced survival p53 NfkB HSF1 PI3K/Akt ERK JNK p38 PLC JAK/STAT c-Abl + + +++ +++ +++ ++ + +++ +++ + Cellular outcome Cell death +++ +++ ++ +++ + +++ Note: This table summarizes the prevailing evidence regarding the activation of these major pathways and how their downstream targets either enhance cell survival or promote cell death specifically in response to oxidant injury. (-), there is minimal or no evidence that this pathway influences this outcome. (+), indicates the degree to which this outcome appears to be affected by this pathway: +, some evidence for this outcome; ++, much evidence that this pathway promotes this outcome; +++, predominant outcome for this pathway. after Martindale and Holbrook, 2002. END ...
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This note was uploaded on 08/05/2010 for the course BIO 5750 taught by Professor Arking during the Winter '09 term at Wayne State University.
- Winter '09