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Genetic age determination through the use of telomere length and single joint T-cell receptor excision circles

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Genetic age determination through the use of telomere length and single joint T-cell receptor excision circles

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Samenvatting

The LifeLines investigation is a project that started in the year 2006 in order to investigate healthy aging. The project will ultimately cover a total of 165000 individuals from the provinces Groningen, Friesland and Drenthe. These individuals are observed for a period of 30 years during which information is gathered using for instance questionnaires blood samples and stool samples. During my graduation project at the Universitary Medical Centre Groningen (UMCG) I have tested and optimized multiple biological age estimation methods in order to enable their use on the LifeLines deep samples (a fraction of about 1500 LifeLines samples).
The age estimation methods that have been tested can be divided in two groups with each group taking advantage of a different biological process. The first group of methods makes use of the fact that the telomere length is reduced as you age. Telomere length is mainly reduced through the end replication problem during cell division meaning that each cell division around 20 basepairs are lost due to imperfect replication. Other reasons for telomere length reduction are disease and oxidative stress. Only an estimation of aging process can be made using methods based on telomere length since the speed at which the telomere repeats are lost varies from person to person. The second group of methods uses single joint T-cel receptor excision circles (sjTRECS), these sjTRECS are a byproduct of T-cel formation by the thymus. Since the thymus slowly degrades over the years the sjTREC concentration will slowly decrease allowing the use of sjTREC concentration as an age estimation method. A problem with the sjTREC concentration is that it can be altered by sickness which will lead to an increase in T-cells and therefore its byproduct the sjTRECS.
The Cawthon (2002), Cawthon (2009) and O’Callaghan (2008) methods were used in order to determine the correlation between biological age and telomere length in an individual. In addition the correlation between sjTREC concentration and biological age was also determined using the method of Zubakov et al.. Besides setting up the sjTREC age estimation with healthy volunteers the method was also tested on rheumatoid arthritis and celiac disease patients in order to determine the effects of disease on sjTREC concentration. Since disease should increase the amount of T-cells and therefore sjTREC’s present, patients are expected to have a lower biological age when compared to the biological age of same aged healthy individuals.
After testing and optimizing the aforementioned telomere length methods reproducible results were determined. A correlation of 0.411 between age and telomere length was found for the Cawthon (2002) method and a correlation of 0.17 for the O’Callaghan (2008) method. The Cawthon (2009) multiplex method could not be properly optimized on the VIIA 7 PCR because of the technical limitations of this specific PCR leading to irreproducible results, the Cawthon (2009) method was therefore omitted. After testing and optimizing the sjTREC concentration method reproducible results for this method were also collected resulting in a correlation of 0.70 between age and sjTREC concentration in healthy volunteers and a correlation rate of 0.61 and 0.51 in patients suffering from celiac disease and Rheumatoid arthritis.
Except for the Cawthon (2009) method all methods could be used for the analysis of the LifeLines deep samples. Which method should be used depends on the goal of subsequent experiments. In experiments where variation between chronological age and biological age is investigated a method with a lower correlation should be used, therefore the use of one of the telomere length estimations would be preferable.
In cases like forensics where a high correlation between chronological and biological age is wanted the use of the sjTREC age estimation method is preferred. This is because the correlation between sjTREC concentration and age is higher than the correlation between telomere length and age. Furthermore no primer dimer sensitive primer pairs are needed when measuring the sjTREC concentration, the lack of primer dimer sensitive primer pairs leads to more accurate PCR results. This is because primer dimer formation leads to the presence of excess fluorescent signaling by a product formed of the forward and the reverse primer. The use of telomere length or sjTREC concentration in order to determine age should only be used to make a rough estimate since age estimation that are off by 20 years or more are occasionally measured.
No definitive conclusions can be taken when comparing the sjTREC concentration and age correlation in samples from healthy volunteers against rheumatoid arthritis and celiac disease patients. This inability to take definitive conclusions was mainly comprised of a lack of age related samples in each group since only the age range of 31 to 62 is represented in each of the groups.

Toon meer
OrganisatieAvans Hogeschool
OpleidingBiologie en Medisch Laboratoriumonderzoek-Breda
AfdelingATGM Academie voor de technologie van Gezondheid en Milieu
PartnersUniversitair Medisch Centrum Groningen
Datum2013-03-07
TypeBachelor
TaalEngels

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