Bruce Spiegelman’s group at the Dana Farber Cancer Institute
found a hormone that is secreted from muscle cells following exercise and acts
on fat cells, turning them from white adipose tissue cells (the bad kind of fat
cell that stores fat) to brown adipose tissue cells (the good kind that burns
fat.)
They identified this hormone by looking at the effects of
PGC1-alpha, a protein produced during exercise that is known to increase
mitochondria and regulate switching between muscle fiber types. Mice
genetically engineered to express PGC1-alpha in muscles had increased
conversion of white adipose tissue to brown adipose tissue, similar to mice
that exercised. They sought to identify what could be responding to PGC1 in fat cells, reasoning there must be a factor that muscles were releasing
that affected fat cells. After narrowing their search, they checked their candidates in humans who underwent a ten-week exercise program and found increases in the mRNA
(the stuff that makes proteins) of these proteins. One protein in
particular, FNDC5, had significant effects on the expression of genes that
regulate brown fat. Cells treated with FNDC5 had increased mitochondria and
oxygen consumption (a measure of energy expenditure.) Importantly, they found that FNDC5 is
cut and part of it is released outside the cell. The secreted part is what they
called irisin, and since it travels from muscle cells to fat cells, it’s
characterized as a hormone. They named their newly identified hormone after the
Greek messenger goddess Iris (personally, I would have gone with Pheidippides
for a Greek messenger.) They found elevated levels of irisin in the blood of
mice and humans following endurance exercise (they defined this as 10 weeks of
20-35 minutes of biking 4-5 times a week.) Finally, mice injected with FNDC5
had increased irisin and browning of white adipose tissue. In obese mice, there
was also a decrease in body weight, an increase in oxygen consumption, and
reduced insulin after fasting.
The paper ends with the obligatory plug for how this finding could lead to better therapeutics for people who struggle with diabetes or
obesity. But, I have to say, I’m not convinced. Too often we hear talk about
some miracle drug that will burn fat while you lay on the couch watching reruns
of Real Housewives. Photoshopped images try to convince us that this miracle
drug leads to dropped pounds, lost inches, and happier lives. And while I
absolutely hope we can find a way to cure America’s obesity problem, I don’t think
giving people this hormone or any other drug will ever replace the benefits of
exercise. Even if irisin does promote fat conversion and increase energy
expenditure, there is a whole host of other things exercise does that one
hormone won’t be able to mimic. I predict that even if we do discover the
miracle weight loss drug, it will only be a matter of time before we realize
some benefit of exercise we missed and start trying to design new drugs. In
John J. Ratey’s book Spark: The Revolutionary New Science of Exercise and
the Brain, he describes a whole slew of
neurological and psychological disorders and details how exercise helps
alleviate symptoms in all of them. A few chapters in, it becomes a bit
repetitive (ADHD, cured by exercise! Alzheimer’s disease, cured by exercise!
Depression, cured by exercise!) but it is filled with studies proving what us
runners already know: running is the ultimate miracle cure. Dropped pounds,
lost inches, happier lives. Why are we searching for drugs when we already have
good old-fashioned exercise?
Dream big,
Teal
Runner Teal:
ReplyDeleteInformative and persuasive. What other running blog pulls together so many interesting threads?
Keep at it!