Blocking the hunger hormone improves muscles in old mice, but not their lifespan
Ghrelin is best known as the hormone that makes you feel hungry. But it also plays a role in how muscles age. Researchers found that suppressing ghrelin signaling significantly improves muscle function in aged mice, yet the animals did not live any longer as a result.
Muscle loss with aging, known in medical circles as sarcopenia, is one of the most underappreciated health problems of our time. When someone in their seventies or eighties struggles to rise from a chair, can no longer manage a flight of stairs, or falls without obvious cause, the underlying issue is often muscle loss that began decades earlier. Loss of muscle mass is associated with higher rates of disability, hospitalization, and death. New leads on how to address it are therefore valuable.
Mitochondria at the core of the problem
Mitochondria are the energy-generating organelles inside cells. In muscle tissue, they are especially critical: muscle cells consume enormous amounts of energy with every contraction. As we age, mitochondria function less efficiently, they produce less energy, generate more harmful byproducts, and repair themselves less effectively. This directly contributes to muscle weakness.
The new study, published via Fight Aging, showed that disabling or inhibiting the ghrelin receptor, the protein to which ghrelin binds to exert its effects, substantially improved mitochondrial function in aged mouse muscle tissue. This was achieved both through genetic knockout and through a small-molecule inverse agonist that blocks the receptor. Muscle strength in treated animals increased measurably.
What the results did not show
Here is where the findings become interesting, and somewhat puzzling. Despite the improvement in muscle function, muscle mass itself did not increase. And the animals did not live longer. That is a striking result. One would ordinarily expect improved mitochondrial function to translate into better overall health, and eventually into extended lifespan. That link was absent here.
This raises questions about the precise relationship between muscle function, muscle mass, and longevity. It suggests that strength and bulk are partly independent processes, and that living longer requires more than stronger muscles alone. Whether the ghrelin receptor represents a useful therapeutic target in humans remains to be seen. Mouse studies translate notoriously poorly to the clinic. But the underlying mechanism, regulating mitochondria in muscle through hormonal signaling, is a direction worth pursuing.