Testosterone levels dropping in men can lead to muscle loss, especially in the limbs. But why does this happen? Scientists have been digging into this question. They found that when testosterone levels drop, the body's internal clocks in muscles get messed up. This mess-up is linked to higher levels of two proteins called Period 1 and Period 2.

These proteins, Per1 and Per2, act like brakes on the body's clock. When they pile up, they might be telling muscles to shrink. Scientists did some experiments. They made muscles in a dish grow bigger, then added extra Per2. The muscles shrank. But when they took away Per2 in mice, the muscles stayed bigger even after testosterone was removed.

Per1 does the same thing. When scientists added extra Per1 to muscles in a dish, the muscles shrank too. It seems like these proteins might be causing muscles to shrink by starting a chain reaction. This chain reaction might involve inflammation. When Per1 and Per2 pile up, they seem to turn on genes that cause inflammation. This inflammation might be telling muscles to shrink.

Scientists also found that when testosterone levels drop in real life, these same inflammatory genes get turned on in muscles. So, it seems like Per1 and Per2 might be a big part of why muscles shrink when testosterone levels drop. This is a new discovery. It might help scientists find new ways to help men keep their muscle when testosterone levels drop.

MOLECULAR CLOCK

How Body Clocks Might Be Behind Muscle Loss in Low Testosterone

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