Can eye lens proteins be used to determine birth year?
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Transcript of Can eye lens proteins be used to determine birth year?
Can eye lens proteins be used to determine birth
year?Radiocarbon Dating of the human eye lens crystallines reveal
proteins without carbon turnover throughout life
Jace James & Lauren Erland
Lens Crystalline Proteins
Long lived proteins found in the lens of the eye
Maintains transparency of the lensPrevent protein aggregation
Elongation of compact fibres of crystalline proteins results in lens formation
14C Dating of Lens Crystalline Proteins
Large accumulation of 14C in the atmosphere after development and testing of nuclear bombs during and after World War II
Levels are much lower in marine environments
Assumptions
Lens crystallines formed as a single event in the year of birth and do not degrade with ageZero turnover
Primarily terrestrial dietGlobally everyone has approximately the same diet
Lens Crystallines formed as a single event and show zero turnover
Cataracts
Deamidation
Solubility
Vitamin C
Cataracts
Age-related, protein aggregation disease Denaturation & insolubilization of lens proteins
Factors promoting cataract formation UV light & ionizing radiation Diabetes, hypertension and advanced age Heavy smoking
Change from a reducing to an oxidizing environment environment results in protein unfolding Addition of oxygen atoms due to hydroxide radicals
Majority of the proteins in the nuclei of advanced ARN cataract lenses undergoing are due to extensive modification and protein unfolding
Deamidation Modifications that disrupt the order of crystallines
Deamidation Truncation Methylation Oxidation Disulfide bond formation Glycation Racemization
Modification significantly decreases the amount of intact crystallines even in young adults
Deamidation is the most abundant modification
>60% Amide group removed Leads to protein instability
Solubility
Amount of insoluble protein increases almost linearly with age
In ARN cataract, insoluble even in 8 M urea increases progressively~ 50% total nuclear protein.
It has been estimated that all people will suffer from cataract if they live long enough
Proteins do change!
Vitamin C
Vitamin C and its degradation products induce protein modifications in vivo via non-enzymatic glycation
Vitamin C levels are particularly high in the lens
Degradation products damage proteins via formation of advanced glycation end products.
Primarily terrestrial diet
“Consumption of fish would have a significant effect on the 14C content of the lenses because the 14C content is smaller than that in the atmosphere”
Humans use organic carbon as their carbon sourceAll carbon in our bodies is derived from the food we eatDiet completely determines the 14C content in our
tissues
Seafood accounts for 14-16% animal protein consumed globally
>1 billion rely on fish as their primary source of animal protein
Data Collection & Analysis
13 people of varying ages
All from Denmark
Small sample size, limited population
Cannot accurately predict age of those born before nuclear testing caused atmospheric build up of 14C 1950’sWWII
Other problems…
“It was our experience that the lens could be removed up to three days post-mortem. After this period, post-mortem degradation and putrefaction made it impossible to extract the lens, as it became more and more fluid and not intact in its capsule”
Cannot be used on corpses more than 3 days old
Often months or years before a body is discoveredPracticality for forensic use?
Other Methods of Age Determination
TeethDentineAspartic acid racemizationRadiocarbon dating
SkeletonPartial or whole Can optimize techniques based on suspected age
Ie child, adult
In both cases age can be determined from a whole or partial skeleton or a (partially) decomposed body