Each of our cells has an energy furnace（火炉，熔炉）, and it is called a mitochondrion（线粒体）. A Northwestern University-led research team now has identified a new mode of timekeeping that involves priming the cell's furnace to properly use stored fuel when we are not eating. The interdisciplinary team has identified the "match" and "flint" responsible for lighting¹ this tiny furnace. And the match is only available when the circadian clock says so, underscoring the importance of the biological timing² system to metabolism³.

 

"Circadian clocks are with us on Earth because they have everything to do with energy," said Joe Bass⁴, M.D., who led the research. "If an organism burns its energy efficiently⁵, it has a better chance of survival. Our results tell us how the circadian clock triggers the cell's energy-burning process. Cells are most capable of using fuel when the clock is working properly."

 

Bass is the Charles F. Kettering Professor and chief of the division of endocrinology, metabolism and molecular⁶ medicine at Northwestern University Feinberg School of Medicine and an endocrinologist at Northwestern Memorial Hospital.

 

Mitochondria regulate the supply of energy to cells when we are at rest, with no glucose⁷ available from food. In a study of mice, the researchers found that the circadian clock supplies the match to light the furnace and on the match tip is a critical compound called NAD+. It combines with an enzyme⁸ in mitochondria called Sirtuin 3, which acts as the flint, to light the furnace. When the clock in an animal isn't working, the animal can't metabolize stored energy and the process doesn't ignite.

 

This pathway through which the body clock controls activities within the mitochondria shows how energy generation is tied tightly to the light-dark/activity-rest cycle each day.

 

The findings, which could be useful in the development of therapies to treat metabolic⁹ disorders¹⁰ related to circadian disruption, will be published by the journal Science.

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