The old adage “use it or lose it” tells us: if you stop using your muscles, they’ll shrink. Until recently, scientists thought this meant that nuclei—the cell control centers that build and maintain muscle fibers—are also lost to sloth.
But according to a review published in Frontiers in Physiology, modern lab techniques now allow us to see that nuclei gained during training persist even when muscle cells shrink due to disuse or start to break down. These residual ‘myonuclei’ allow more and faster growth when muscles are retrained—suggesting that we can “bank” muscle growth potential in our teens to prevent frailty in old age. It also suggests that athletes who cheat and grow their muscles with steroids may go undetected.
Syncytium. Sounds like a neo-noir comic book series. It’s actually a special type of tissue in your body, where cells are fused together extra close—so close, that they behave a like a giant single cell.
“Heart, bone and even placenta are built on these networks of cells,” says Lawrence Schwartz, Professor of Biology at the University of Massachusetts. “But by far our biggest cells—and biggest syncytia—are our muscles.” Like the Sin City series, it appeared at first that everything was black and white with syncytia.
This assumption long seemed valid, with many researchers reporting the presence of disintegrating nuclei in muscle tissue during atrophy induced by inactivity, injury or paralysis. But modern cell-type-specific dyes and genetic markers have shown that the dying nuclei other researchers had detected were in fact inflammatory and other cells recruited to atrophic muscle.
The new evidence paints a very different picture of muscle syncytium.
This suggest that once a nucleus has been acquired by a muscle fiber, it belongs to the muscle syncytium—probably for life. But Schwartz, for one, is unsurprised by the new findings.
Since myonuclei are the synthetic engine of muscle fibers, retaining them should enable muscle size and strength to recover more quickly after one of these insults, and help to explain the phenomenon of ‘muscle memory’.
As such, the findings have important implications beyond understanding muscle biology.
The findings also support frequent drugs testing for competitive athletes, with permanent bans for proven steroid cheats since they will benefit from the steroids long after their use has ended.