The global average life expectancy during the early twentieth century was 31 years; today it stands at 67.2 years. The “Big Three”: food, health and hygiene are being hailed as miracle life longevity factors; however improving overall quality of life is far more complex than simply extending it. Without actually slowing down the pace at which we age, all this proposes is potentially a greater number of years spent with age related diseases, such as Alzheimer’s. But how much do we truly understand about aging?
35 genes believed to determine lifespan have been unveiled by research at the Louisiana State University Health Centre, coding for a wide range of cellular functions they indicate aging is multifactorial. At least four physiological processes are thought to play a role in aging including metabolic control, resistance to stress, gene deregulation and gene stability. Scientists will persevere in unravelling the mystery of aging and the complexity of the process means it may be one of the hardest nuts we will ever try to crack. The very nature of aging makes it difficult to gather substantial data; long term experimentation on human beings is unfeasible due to the crippling time constraints. Nevertheless, when there is a will there is a way and this is where model organisms step in.
The nematode, Caenorhabditis elegans makes an excellent aging model organism; living 2-3 weeks, the hermaphrodites among them are able to produce around 300 genetically identical offspring, providing the advantage of allele homozygosis and its small 97 megabase genome is fully sequenced. Most importantly, the Caenorhabditis elegans shares 35% similar genes with us, that are used as candidate human longevity genes and the development stages of each somatic cell are known from zygote to adult worm. Going through the complex developmental processes of embryogenesis, morphogenesis and growth, in four stages (L1, L2, L3 and L4) there is plenty to suggest that what we learn from the Caenorhabditis elegans may be directly applicable to us. When placed in harsh conditions, the L1 and L2 larvae become dauer larvae with delayed development and dark intestines produced by storage of fat. When the harsh conditions subside they re-enter the developmental process, carrying on as normal. This may seem insignificant, however these dauer larvae live 10 times the average lifespan of a normal nematode, in human terms that means reaching the age of about 700!
A study carried out by Golden JW and Riddle DL identified pheromone, food and temperature as dauer-inducing factors. The pheromone is a measure of population density, causing dauer formation at L2 and inhibiting recovery based on pheromone dose. Lack of food causes caloric restriction, a method which has also proven to extend lifespan in rodents. The enhancement of the dauer larvae formation needs exposure to high temperature at L1 stage. Two sensory mutants defective in thermotaxis have altered sensitivity to the pheromone but the pheromone response remains temperature dependent. The ways in which the dauer respond to inducing factors was found to be age dependent, with the older larvae having a greater tendency to recover. The dauer larvae seem to able to control the pace at which that metaphorical clock ticks, no doubt the day we learn to apply this in humans will be pivotal to the very nature of science.
To date the oldest age a human being has got to is 122 years, while average lifespan has certainly increased, maximum lifespan is yet to be understood and manipulated. As technology develops, our knowledge will continue to grow and maybe soon birthday cards will go up to 700 years or more.
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