Tiny Cellular Antennae Key to Fat Formation in Muscle

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Like it or not, as we age, our muscle cells are slowly exchanged, one by one, for fat cells. This process quickens when we injure a muscle, and an extreme form of this process is also seen in muscle-wasting diseases such as Duchenne muscular dystrophy (DMD). Now, scientists at UC San Francisco have shown that cellular antennae called cilia, found on fat-forming cells interspersed in muscle, play a key role in this muscle-to-fat transformation.

The findings, revealed in experiments with mice, and published July 13, 2017 in Cell, suggest a previously unsuspected connection between cilia and tissue renewal. This fresh molecular understanding could open up new prospects for regenerative medicine, and one day enable researchers to improve muscle renewal during aging and disease.

High levels of intramuscular fat have long been associated with a loss of strength and impaired mobility, as well as more falls in elderly or obese individuals, and in patients with DMD. “The frailty of age is a huge biomedical problem,” said Jeremy Reiter, MD, PhD, a professor of biochemistry and biophysics at UCSF and senior author of the new paper. “This study helps pave the way to learn how muscles normally age, and provides a new way to possibly improve muscle repair.”

Reiter has a long-standing research interest in tiny cellular appendages called primary cilia, which look a bit like the cellular tentacles that paramecia and other single-celled critters use to move and gather food. But unlike those motile cilia, primary cilia don’t move at all. Instead, they stand stiff and solitary on the surface of nearly all of our cells, including neurons, skin cells, bone cells and certain stem cells.

For centuries, these little attachments were largely ignored, and considered a vestigial structure with no known function. But “there has been a renaissance over the past decade in figuring out what these cilia do,” Reiter said, ...

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