PT Unknown
AU Gruber, H
TI Investigation of the molecular ageing process of the long-livedbivalve Arctica islandica
PY 2013
PU Christian-Albrechts-Universität zu Kiel
WP https://macau.uni-kiel.de/receive/diss_mods_00012245
LA en
DE ageing; Arctica islandica; transcriptome; gene expression; ageing markers; Altern; Transkriptom; Genexpression; Alterungsmarker
AB The question on why we age and how ageing proceeds has occupied researchers’
minds for a long time. Demands on research of healthy ageing and geriatric diseases
rise with an older growing human population. Thus, studying the mechanisms of
ageing in animals with extraordinarily long lifespans could possibly reveal secrets to
longevity and healthy ageing.
In this study, a short-lived population of the bivalve mollusk Arctica islandica from
the Baltic Sea (with a maximum lifespan – MLSP – of 40 years) was compared to a
long-lived population from Iceland (MLSP >400 years) with respect to physiological
and molecular damage parameters and gene expression. Both populations originate
from two very distinct environments that may influence the ageing process of the
animals. Cohorts of both populations were sampled in 2010 and sexes and ages of all
animals were determined. Based on this data, ageing markers (oxidation of proteins,
lipids, and nucleotides, protein stability, telomere length, telomerase activity) from
selected individuals along sampled age ranges (10-36 years in the Baltic Sea and 6-226
years in Iceland) of the two populations were investigated. Oxidation to nucleotides
significantly accumulated over age in both populations and did so significantly
faster in the shorter-lived Baltic Sea compared to the longer-lived Iceland population
regarding their absolute chronological age. Remarkably, when looking at the results in
respect to the relative lifespan of each population, nucleotide damage accumulated at
the same pace in both populations. Additionally, a significantly higher mean level of
DNA damage was detected in the shorter-lived Baltic Sea population where frequent
hypoxic and anoxic events occur and the animals are living in a warmer environment.
Interestingly, significantly higher mean levels of lipid peroxidation were observed in
the long-lived cold-adapted Iceland population that might result from a different
lipid composition at colder temperatures. Lipid peroxidation over investigated ages,
however, stayed stable in both populations. All other investigated parameters also
stayed stable over age in the two populations, which points towards a remarkable
molecular stability, exceptional repair or regeneration capacity of A. islandica.
Parallel to the ageing-marker investigations, mRNA of selected, different old animals
was sequenced using 454 pyrosequencing to represent combined transcriptomes from post-mitotic heart and highly proliferating gill tissue of different age groups of
the two populations. This transcriptome database was used to analyze global gene
expression profiles over age of the two populations but also to identify genes of interest
for further detailed gene expression analysis via qRT-PCR. The transcriptome
analyses revealed a distinct gene expression behavior in young Iceland individuals
compared to older age groups and hence, a specific transcriptional pattern for older
age classes could not be defined. Together with findings from other A. islandica
studies and considering the shape of the observed growth curve, a different physiology
in young compared to middle and old aged animals can be revealed up to approx. 40
years of age. Since this is the lifespan of the Baltic Sea A. islandica animals, two
different life strategy of both populations could have developed that remain unclear,
but factors beneficial for a long life may only be selected for in the longer-lived
Iceland population since reproductive output in older/larger animals is much higher
than in younger ones.
Due to the accumulation with age and immense detected differences in oxidative
damage to nucleotides between the two populations, gene expression over age of
identified DNA repair genes from the RNAseq database were analyzed with qRTPCR.
Further, the expression of antioxidants playing a role in the oxidative stress
response, that have previously been observed to be differentially expressed between
A. islandica populations under stressful conditions, and that are proposed to be
relevant in ageing according to the free radical theory of ageing (Harmann, 1956), was
investigated in qRT-PCR. At last, gene expression over age in the two populations
with distinct MLSPs was also investigated in known ageing-associated genes. For all
analyzed genes a stable expression over complete sampled lifespan (10-36 years for
Baltic Sea and 6-226 years for Iceland population) was detected in both populations.
Significant differences in mean gene expression levels between the short- and long-lived
population, however, could be observed for several DNA repair, ageing-associated, and
antioxidant coding genes. Neither a better DNA repair nor oxidative stress capacity,
however, in neither of the two populations could be revealed but hints towards a
differentially evolved gene expression behavior in investigated populations. Extreme
different environmental factors may evoke epigenetic changes in the populations’
genomes that lead to differential gene expression that might further be reflected in
the populations’ specific MLSPs. Further investigation on environmentally induced
changes on the epigenome and dependent gene expression of differentially expressed
genes of interest identified in this study and further investigations on the protein
levels in these two populations may be the next step leading to identify ways for
healthy ageing.
PI Kiel
ER