Aging

Collected information on aging, focusing on the genes shown to give extended lifespan, the genetics of aging, and the use of the worm, C. elegans, as a model organism to study aging.

Description of aging

What is aging? One way to define aging is as the increased chance of death as an animal gets older. Another common way to define aging is as the changes an animal undergoes as it ages. What is the cause of this increased chance of death?

Not all changes in an animal as it gets older may be relevant to aging. Some may not result in an increased chance of death. Some changes may be causes of aging while others may be only consequences, or markers of aging.

Aging affects most tissues of the body. In humans, the features of aging include graying and loss of hair, reduced subcutaneous fat, cadiovascular disease, decalcification fo the bones, loss of neurons, generally as well as specific populations. Every organ of teh body shows reduced functioning, including the immune system, the kidney, the heart, and the liver. The cellular phenotype includes shortening of the telomeres and auto-fluorescent deposits. Interestingly, in old individuals, stem cells make up a larger proportion of the bone marrow, and are dividing more actively than in the young. Cells from older individuals divide fewer times in culture before senescing.

In worms, features associated with aging include torpor and finally cessation of movement, cessation of reproduction, accumulation of auto-fluorescent deposits in cells. All somatic cells in the adult worm are post-mitotic, and therefore telomere shortening likely does not play a role in aging.

Genes which have been shown (or been suggested) to provide lifespan extension when mutated or overexpressed.

Aging genes

Worm Yeast Mouse Fly Human Function Etiology References
age-1; daf-23; B0334.8 Vps34p (24%); Stt4p (24%); Pik1p (27%)     PIK3CA (27%); PIK3CG (30%); Hs.198577 (27%) phosphatidylinositol-3-OH kinase Insulin receptor aging pathway description; cloning; 8601482
daf-2         Insulin receptor paralog;receptor tyrosine kinase Insulin receptor aging pathway; ligand unknown 8601482
daf-16       FKHR and AFX hepatocyte nuclear factor 3 (HNF-3)/Fork head family of transcription factors Insulin receptor aging pathway 9353126
daf-18       PTEN PIP3 phosphatase Insulin receptor aging pathway; Downstream of age-1 cloning; 10209098; 10377431
daf-28              
akt-1; akt-1a; akt-1b; C12D8.10A; C12D8.10B Pkc1p (43%); Ypk1p (44%); Ypk2p (45%) Akt1 (54%); Pkc98E (47%); Pkc53E (49%)   AKT1/Protein kinase B alpha (56%); AKT2/Protein kinase B beta (54%); PRKCB1 (49%) Serine/threonine kinase The major transducer of the signal from AGE-1 but only one of multiple transducers of the signal from DAF-2. 9716402; Protein kinase B phosphorylates AFX, a human ortholog of daf-16.; 10217147
akt-2 Pkc1p; Ypk1p; Ypk2p Akt1; Pkc98E; Pkc53E   AKT1/Protein kinase B alpha; AKT2/Protein kinase B beta; PRKCB1 Serine/threonine kinase The major transducer of the signal from AGE-1 but only one of multiple transducers of the signal from DAF-2. 9516411; 9716402; 10217147
pdk-1       PDK-1 Serine/threonine kinase Propagates AGE-1 PI3K signals to AKT-1/AKT-2 in the DAF-2 insulin receptor-like signaling pathway. 99292684 10364160
               
clk-1 Coq7/Cat5       Mitochondrial protein involved in coenzyme Q synthesis Altered biological clock characterization of lifespan effect; 10202142; cloning; description
clk-2         Not cloned Altered biological clock description
clk-3         Not cloned Altered biological clock description
gro-1         Not cloned Slow growth, heat resistance and longevity 8638122; description
               
eat-2         Not cloned Caloric restriction->life-extension  
spe-26         Sterility in males and hermaphrodites. Paralog of Drosophila kelch and invertebrate sperm protein scruin that cross-links actin filaments. Reduced fertility/life-extension description
               
tkr-1         Tyrosine kinase receptor Overexpression extends life; Pathway not known. cloning, first description
               
  SGS1, rqh1+ (S. pombe)     WRN (Werner syndrome) DNA helicase, RecQ family    
C50F7.10       human lactase (LCT) and klotho (KL), a protein with similarity to beta-glucosidase Putative glucosidase candidate by homology  
E02H9.5       human lactase (LCT) and klotho (KL), a protein with similarity to beta-glucosidase Putative glucosidase candidate by homology  
  RAS2            
T24H7.1 PHB1     prohibitin   candidate by homology  
T24H7.1 PHB2     prohibitin   candidate by homology  
        BAP37, a protein with sequence similarity to prohibitin   candidate by homology  
E03A3.2 Sgs1p (39%); Dbp3p (23%); Dbp2p (23%)     RECQL5 (46%); BLM (37%); RECQL (33%) Member of the RECQ family of helicases that includes S. cerevisiae Sgs1p, D. melanogaster Dmblm, and human BLM and WRN candidate by homology  
F18C5.2 Sgs1p (29%); Dbp2p (21%)     WRN (27%); RECQL5 (36%); RECQL (33%) Member of the RECQ family of helicases that includes S. cerevisiae Sgs1p, D. melanogaster Dmblm, and human BLM and WRN candidate by homology  
age-2         Not cloned Appears to be a non-specific effect mediated through loss of fertility. 10219000
               
No homolog by BLAST (8/99)   methuselah (mth)     GTP-binding protein-coupled seven-TM receptor    

Life extension given by genotype
C. elegans genotype Life extension (wt = 100%) Comment Citation
daf-2(e1370) clk-1(e2519) 500%   8638122
age-1 165%   7638227
age-2(yw23) 120% Appears to be a non-specific effect mediated through loss of fertility. 10219000
daf-28(sa191) 12-13%   8807293
eat genes 100-150% Caloric restriction 9789046
germline ablation     ref
sperm production mutant 165%   1448167

Life extension for other organisms
Organism Treatment/Genotype Life extension Citation
D. melanogaster Transgene Cu/Zn SOD and catalase 34% (Orr and Sohal, 1994)
D. melanogaster Transgene human SOD1 in adult motor neurons 40% Parkes et al., 1998
D. melanogaster methuselah 35% Lin et al., 1999
       

C. elegans screens producing aging mutants

Gerontol A Biol Sci Med Sci 1999 Apr;54(4):B137-42

Characterization of a life-extending mutation in age-2, a new aging gene in Caenorhabditis elegans.

Yang Y, Wilson DL

Department of Biology, University of Miami, Coral Gables, Florida 33124-0421, USA.

We have generated a life-extending mutation, yw23, in Caenorhabditis elegans. The mutation is in what appears to be a new aging gene, which we have designated age-2. When homozygous, yw23 produces an increase of mean and maximum life span of about 20% over that of the wild-type strain, N2. Strain HG23 [age-2(yw23)] was obtained by screening for longer life spans among 430 lines of nematodes two generations after exposure to the mutagen ethylmethanesulfonate. Strain HG231 [age-2(yw23)] was obtained after a single out-crossing of HG23 to N2. When compared with N2, HG231 exhibits normal motility, slightly higher swimming rates, reduced fertility (especially at higher temperatures), somewhat longer development times, and a slightly larger size at the time of first egg laying. A Gompertz analysis suggests that HG231 extends life span by reducing the initial mortality rate. In genetic crosses, yw23 complements other known aging mutants in C. elegans genes-age-1, daf-2, spe-26, clk-1, clk-2, clk-3, and gro-1. A double-mutant strain, HG284, combining mutations in age-1 and age-2, lives longer than animals with individual mutations in either age-1 or age-2, and exhibits a longer life span at 25 degrees C than at 20 degrees C. PMID: 10219000, UI: 99233384

Dev Genet 1996;18(2):144-53

Direct isolation of longevity mutants in the nematode Caenorhabditis elegans.

Duhon SA, Murakami S, Johnson TE

Institute for Behavioral Genetics, University of Colorado, Boulder 80309, USA.

We have isolated several new EMS-induced, long-lived mutants of Caenorhabditis elegans, using a novel screen that eliminates the need for replica plating. Three new alleles of age-1 (z10, z12, and z25) were identified by failure to complement age-1 (hx546) for life span extension; these alleles had life spans ranging from 18.9 to 25.9 days at 25 degrees C, with an average 46% increase in life span. After backcrossing, alleles were examined in a wild-type background for resistance to several environmental stresses: heat (35 degrees C), ultraviolet (UV) light (20 J/m2), and hydrogen peroxide (H2O2) (0.5 M). Two replicates of the test of thermotolerance were completed on each strain, giving mean survivals of 842 min (hx546), 810 min (z10), 862 min (z12), and 860 min (z25), compared to 562 min for wild type. All the age-1 alleles were significantly tolerant, compared with wild type (P < 0.001). Two replicates for UV resistance were also completed with mean survivals of 103, 118, 108, and 89 hr, respectively, compared to 72 hr for wild type. One test of hydrogen peroxide resistance has shown that z12 and N2 had a mean survival of 41 hr, while the other age-1 alleles had mean survival of 54 hr (z10), and 62 hr (z25); H2O2 resistance is the only environmental stress that differentiates among the age-1 alleles.

C. elegans strains used in aging research

Here are strain descriptions and links to search CGC for these strains.

C. elegans aging research protocols

Aging protocols.

Free radical/anti-oxidant genes

Worm Yeast Mouse Human Function Etiology
    Sod      
    Sod2      
      BLM (Bloom syndrome) DNA helicase, RecQ family  
      RECQL    
ctl-1; cat2          
ctl-2          
           
           
           
           
           
           
           

Mitochondrial genes

Worm Yeast Mouse Human Function Etiology Expression
    Sod   Superoxide dismutase    
    Sod2   Superoxide dismutase    
    Ant1   Adenine nucleotide translocator   heart/skeletal muscle
    Ant2   Adenine nucleotide translocator    
    Ant3   Adenine nucleotide translocator    
             
             
             
             
             
             
             
             

Lifespan examined in different strains (any animal)

Mitochondrial superoxide and hydrogen peroxide generation, protein oxidative damage, and longevity in different species of flies.

Sohal RS, Sohal BH, Orr WC.

Free Radic Biol Med 1995 Oct;19(4):499-504

Department of Biological Sciences, Southern Methodist University, Dallas, TX 75275, USA.

The objective of this study was to further elucidate the role of oxidative stress in the aging process by determining whether or not the rates of mitochondrial superoxide anion radical and hydrogen peroxide (H2O2) production, the activity of cytochrome c oxidase, and the concentration of protein carbonyls are correlated with the life span potential of different species. A comparison was made among five different species of dipteran flies, namely, Drosophila melanogaster (fruit fly), Musca domestica (house fly), Sarcophaga bullata (flesh fly), Calliphora vicina (blow fly) and Phaenecia sericata (a species of blow flies), which range more than 2-fold in their life span potentials. The average life span potential of these species was found to be inversely correlated with the rates of mitochondrial superoxide and H2O2 production and with the level of protein carbonyls, and to be directly related to the activity of cytochrome c oxidase. The significance of these findings in context of the validity of the oxidative stress hypothesis of aging is discussed. It is inferred that longer life span potential in these insect species is associated with relatively low levels of oxidant generation and oxidative molecular damage. These results accord with our previous findings on different mammalian species.

Literature on gene expression changes in long-lived strains

C. elegans

Modulation of kinase activities in dauers and in long-lived mutants of Caenorhabditis elegans.

Age-specific modulation of light production potential, and alkaline phosphatase and protein tyrosine kinase activities in various age mutants of Caenorhabditis elegans.

Other animals

Metabolic rate in C. elegans long-lived mutants

FASEB J 1995 Oct;9(13):1355-61

The gerontogenes age-1 and daf-2 determine metabolic rate potential in aging Caenorhabditis elegans.

Vanfleteren JR, De Vreese A

Department of Morphology, Systematics and Ecology, University of Ghent, Belgium.

Mutations in the genes age-1 and daf-2 extend life span of Caenorhabditis elegans by 100 and 200%, respectively, in axenic culture. Adult worms that are mutant in either of these genes have higher metabolic capacities, called metabolic rate potentials, at all ages and the extension of their life expectancies are positively correlated with the increases of metabolic rate potential. The activities of catalase, superoxide dismutase, isocitrate dehydrogenase, isocitrate lyase, and malate synthase are all higher relative to those in worms that are wild type for these genes, but acid phosphatase is down-regulated and alkaline phosphatase activity is lowered to 10% of the activity measured in age-1(+) and daf-2(+) worms. These results suggest that genes that regulate metabolic activity may play central roles in longevity and senescence.

Related Worm Breeder's Gazette articles

Worm Breeder's Gazette 1996 14:27

Psst! Wanna buy a Clock?

Lakowski B, Hekimi S

Dept. of Biology, McGill University, 1205 Dr. Penfield Ave. Montreal, Quebec, Canada, H3A 1B1

In a recent paper we reported work on the genetic analysis of life span in Clock mutants and numerous double mutants ( Lakowski and Hekimi (1996). Science 272, 1010-1013 ). This work has generated many strain requests, so we have sent the following strains to the CGC: CB4876 clk-1(e2519) III MQ130 clk-1(qm30) III MQ125 clk-2(qm37) III MQ131 clk-3(qm38) II MQ124 clk-3(qm38) II; clk-1(e2519) III MQ225 clk-3(qm38) II; clk-2(qm37) III MQ141 clk-1(e2519) clk-2(qm37)/dpy-17(e164) III MQ223 clk-3(qm38) II; gro-1(e2400)/dpy-17(e164) III MQ224 clk-3(qm38) II; clk-1(qm30)/dpy-17(e164) III MQ524 gro-1(e2400) clk-2(qm37)/ dpy-17(e164) III MQ513 daf-2(e1370) clk-1(e2519) III MQ415 age-1(hx546) fer-15(b26) II; gro-1(e2400) III Notes on using these strains

1) All Clock mutations are maternally and zygotically rescued even in the double mutant strains. 2) Strains homozygous for clk-2(qm37) and gro-1(e2400) are not viable at 25C. They can be studied at 25C if they are allowed to complete embryogenesis at 20C or below and then shifted to 25C. MQ130 clk-1 (qm30) also has difficulty at 25C, segregating many dead eggs, but can be maintained at this temperature.

3) MQ124 clk-3(qm38) II; clk-1(e2519) III is a strain which is just barely viable and can not be maintained at 25C. This strain produces a lot of dead eggs and sporadically becomes sterile during culture.

4) The strains MQ141, 223, 224 and 524 have LGIII Clock mutations balanced over dpy-17(e164) because these Clock double mutant combinations are not viable as homozygotes, dying out over a few generations. dpy-17 was chosen because it lies about 0.2 cM to the left of clk-1 and gro-1 and only about 1 cM to the left of clk-2. dpy-17 is also convenient because it has a strong phenotype as an L1 larva. Homozygous double mutants should be identifiable because their progeny take so long to hatch and to develop.

Cross references

Genes: age-1, clk-1, clk-2, clk-3, daf-2, dpy-17, fer-15, gro-1 Alleles: b26, e164, e1370, e2400, e2519, hx546, qm30, qm37, qm38 Strains: MQ415, MQ141, MQ524, MQ223, MQ224, MQ513, CB4876, MQ124, MQ130, MQ125, MQ225, MQ131

Interaction between sex/germline and aging in C. elegans

Nature 1992 Dec 3;360(6403):456-8

Production of sperm reduces nematode lifespan.

Van Voorhies WA

Department of Ecology and Evolutionary Biology, University of Arizona, Tucson 85721.

Sex and death are two fundamental but poorly understood aspects of life. They are often thought to be linked because reproduction requires the diversion of limited resources from somatic growth and maintenance. This diversion of resources in mated animals, often called a cost of reproduction, is usually expressed as a reduction of lifespan in mated animals, although some debate exists on the best way to measure this cost. I report here that in the soil nematode, Caenorhabiditis elegans, sex significantly decreases male lifespan without reducing hermaphrodite lifespan. The reduction of mated male lifespan seems to be caused by additional sperm production and not by the physical activity of mating. This conclusion is supported by observations that a mutation reducing sperm production increased mean lifespan by about 65% in both mated males and hermaphrodites. This suggests that spermatogenesis, rather than oogenesis or the physical act of mating, is a major factor reducing lifespan in C. elegans. This contradicts the traditional biological assumption that large oocytes are much costlier to produce than small sperm.

Nature 1996 Feb 22;379(6567):723-5

Longevity in Caenorhabditis elegans reduced by mating but not gamete production.

Gems D, Riddle DL

Molecular Biology Program and Division of Biological Sciences, University of Missouri, Columbia, 65211, USA.

Theories of life-history evolution propose that trade-offs occur between fitness components, including longevity and maximal reproduction. In Drosophila, female lifespan is shortened by increased egg production, receipt of male accessory fluid and courting. Male lifespan is also reduced by courting and/or mating. Here we show that in the nematode Caenorhabditis elegans, mating with males reduces the lifespan of hermaphrodites by a mechanism independent of egg production or receipt of sperm. Conversely, males appear unaffected by mating. Thus, in C. elegans there is no apparent trade-off between longevity and increased egg or sperm production, but there is a substantial cost to hermaphrodites associated with copulation.

Theories of aging

There is a body of evidence that aging is caused by free radical damage. The primary source of free radicals is oxygen spun off the oxidative phosphorylation complex in the mitochondria, that is, the oxygen animals breathe. The dangers of oxygen were noted in 1956 by Chemical & Engineering News:

Oxygen is a very toxic gas and an extreme fire hazard. It is fatal in concentrations of as little as 0.000001 p.p.m. Humans exposed to the oxygen concentrations die within a few minutes. Symptoms resemble very much those of cyanide poisoning (blue face, etc.). In higher concentrations, e.g. 20%, the toxic effect is somewhat delayed and it takes about 2.5 billion inhalations before death takes place. The reason for the delay is the difference in the mechanism of the toxic effect of oxygen in 20% concentration. It apparently contributes to a complex process called aging, of which very little is known, except that it is always fatal. However, the main disadvantage of the 20% oxygen concentration is in the fact it is habit forming. The first inhalation (occurring at birth) is sufficient to make oxygen addiction permanent. After that, any considerable decrease in the daily oxygen doses results in death with symptoms resembling those of cyanide poisoning. Oxygen is an extreme fire hazard. All of the fires that were reported in the continental U.S. for the period of the past 25 years were found to be due to the presence of this gas in the atmosphere surrounding the buildings in question. Oxygen is especially dangerous because it is odorless, colorless and tasteless, so that its presence can not be readily detected until it is too late. -- Chemical & Engineering News February 6, 1956