Current Biology: Exercise inhibits insulin production!

Insulin is an essential hormone
for humans and many other living things.
Its best-known task is regulating glucose metabolism
.
It is already clear how it does this work
.
Little is known about the activity of insulin-producing cells and how insulin secretion is controlled
.

A team from the Würzburg Biological Center in Julius-Maximilians-Universit (JMU) in Bavaria, Germany, solved the puzzle about this question, and Dr.
Jan Ache's team used fruit flies as their research subjects
.
Interestingly, this fruit fly also secretes insulin
after eating.
In fruit flies, however, the hormone does not come from the pancreas as in humans, but is released
by nerve cells in the brain.

Electrophysiological measurements of active fruit flies

The JMU team found that the flies' physical activity had a strong effect on
the cells that produce insulin.
This is the first time researchers have measured the electrophysiological activity of these cells while walking and flying in fruit flies.

The result: When the fruit fly starts walking or flying, its insulin-producing cells are immediately inhibited
.
When it stops moving, the cell's activity increases rapidly again and quickly rises above normal levels
.

Dr Sander Liessem, first author of the paper, said: "We hypothesized that the low activity of insulin-producing cells during walking and flight helps provide sugar to meet increased energy needs
.
We suspect that increased activity after exercise helps replenish energy stores in fruit flies, such as those in
muscles.
”

Blood sugar does not play a role in regulation

The JMU team was also able to demonstrate that rapid, behavior-dependent inhibition in insulin-producing cells was actively controlled
by neural pathways.
"This is largely unrelated to changes in sugar concentrations in the blood of fruit flies.
"

It makes sense
for organisms to predict an increase in energy demand in this way to prevent extreme fluctuations in blood sugar levels.

Insulin has hardly changed over the course of evolution

Can these results be concluded for humans? Possibly
.

Jan Ache said: "Although the release of insulin in fruit flies is mediated by different cells, the insulin molecule and its function have hardly changed
during evolution.
" Over the past 20 years, using fruit flies as model organisms, many fundamental questions have been answered that have also contributed to a better understanding of metabolic defects and related diseases in humans, such as diabetes or obesity
.

Less insulin means longevity

Sander Liessem told us: "The exciting thing is that reduced insulin activity contributes to healthy aging and longevity
.
" This has been confirmed
in fruit flies, mice, humans and other species.
The same applies to an active lifestyle
.
"Our study shows a possible link explaining how physical activity positively affects insulin regulation through neuronal signaling pathways
.
"

Further steps of the study

Next, Jan Ache's team plans to investigate which neurotransmitters and neuronal circuits are responsible
for changes in cellular activity in Drosophila insulin.
This can be a challenge: too many messenger substances and hormones are involved in neuromodulation processes, and individual substances may have opposite or complementary effects
when combined.

The team is currently analyzing the multiple ways
in which insulin-producing cells process outside inputs.
They are also studying other factors that may affect the activity of these cells, such as the age of the flies or their nutritional status
.

"At the same time, we are studying neuronal control of walking and flying behavior," Jan Ache explains
.
His team's long-term goal, he says, is to combine these two research questions: How does the brain control walking and other behaviors, and how does the nervous system ensure that energy balance is regulated accordingly?