Wednesday, June 10,
2009
Are the cognitively superior brains of humans, in part, responsible
for our higher rates of cancer? That's a question that has nagged
at John McDonald, chair of Georgia Tech's School of Biology and
chief research scientist at the Ovarian Cancer Institute, for a
while. Now, after an initial study, it seems that McDonald is on to
something. The new study is available online in the journal Medical
Hypothesis and will appear in the forthcoming issue of the
journal.
"I was always intrigued by the fact that chimpanzees appear to have
lower rates of cancer than humans," said McDonald. "So we went back
and reanalyzed some previously reported gene expression studies
including data that were not used in the original analyses."
McDonald and his graduate students, Gaurav Arora and Nalini
Polivarapu, compared chimp-human gene expression patterns in five
tissues: brain, testes, liver, kidneys and heart. They found
distinct differences in the way apoptosis — or programmed cell
death — operates, suggesting that humans do not "self-destroy"
cells as effectively as chimpanzees do. Apoptosis is one of the
primary mechanisms by which our bodies destroy cancer cells.
"The results from our analysis suggest that humans aren't as
efficient as chimpanzees in carrying out programmed cell death. We
believe this difference may have evolved as a way to increase brain
size and associated cognitive ability in humans, but the cost could
be an increased propensity for cancer," said McDonald.
Like all evolutionary hypotheses, this can't be proven absolutely,
according to McDonald. However, his lab has recently obtained
additional direct experimental evidence consistent with the
hypothesis that apoptotic function is more efficient in chimps than
in humans.
