Exploring Biological and Geological Age-related Changes through Variations in Intra- and Intertooth Proteomes of Ancient Dentine

Proteomic
analyses are becoming more widely used in archeology
not only due to the greater preservation of proteins in ancient specimens
than DNA but also because they can offer different information, particularly
relating to compositional preservation and potentially a means to
estimate biological and geological age. However, it remains unclear
to what extent different burial environments impact these aspects
of proteome decay. Teeth have to date been much less studied than
bone but are ideal to explore how proteins decay with time due to
the negligible turnover that occurs in dentine relative to bone. We
investigated the proteome variability and deamidation levels of different
sections of molar teeth from archeological bovine mandibles as well
as their mandibular bone. We obtained a greater yield of proteins
from the crown of the teeth but did not find differences between the
different molars analyzed within each mandible. We also obtained the
best variety of protein from a well-preserved mandible that was not
the youngest one in terms of chronological age, showing the influence
of the preservation conditions on the final proteomic outcome. Intriguingly,
we also noticed an increase in abundance levels of fetuin-A in biologically
younger mandibles as reported previously, but the opposite trend in
tooth dentine. Interestingly, we observed higher glutamine deamidation
levels in teeth from the geologically oldest mandible despite it being
the biologically youngest specimen, showing that the archeological
age strongly impacts on the level of deamidations observed, much more
so than biological aging. This indicates that the glutamine deamidation
ratio of selected peptides may act as a good predictor of the relative
geochronological age of archeological specimens.