If you solve stem cell aging you don’t automatically get more muscle cells.
You might, at least if the intervention is preventative.
(Sorry in advance if this is all review...)
Muscle cells are not like most other cell types. A single muscle cell is more like a giant conglomerate of a bunch of cells, all merged within a single membrane. There’s many nuclei in each muscle cell, many full sets of chromosomes, and the cell is big enough that most proteins will never diffuse from one end to the other before turning over. Unlike normal cells, the nucleii themselves can turn over independent of the cell—and muscle stem cells (“satellite cells”, the first type of stem cell discovered IIRC) are primarily responsible for this turnover.
Now, at this point we don’t know for sure if satellite cell problems are the primary driver of age-related muscle loss, but they’re definitely one of the top candidates (mitochondria are another). And if that is the main driver, then fixing stem cell aging would indeed fix muscle loss—not necessarily retroactively, but at least preventatively.
The main takeaway here is that, while individual muscle cells are long-lived, their components still turn over. There’s probably something upstream of muscle loss which drives it.
Replenishing nucleii in established muscle cells doesn’t replace dying muscle cells. It might very well be that part of age related muscle loss is not due to lower count of muscle cells but due to other factors but sometimes muscle cells will die and that will produce muscle loss as people age when those aren’t replaced.
Cells die for many reasons. I don’t think you should expect zero muscle cells to die for any reason even if you help them replenish their nuclei.
My understanding is that muscle cells don’t just randomly die fast enough to account for age-related muscle loss. In young people post-development (i.e. people in their 20′s or early 30′s), it’s quite slow. Then with age, it accelerates. Fix whatever’s causing that accelerated loss, and muscle loss would be basically negligible.
What does “negligible” mean here? Negligible on what time scale? Because if the overarching question is “How do we stop or reverse aging to become amortal?” then any process of monotonic irreversible decline becomes important eventually.
You might, at least if the intervention is preventative.
(Sorry in advance if this is all review...)
Muscle cells are not like most other cell types. A single muscle cell is more like a giant conglomerate of a bunch of cells, all merged within a single membrane. There’s many nuclei in each muscle cell, many full sets of chromosomes, and the cell is big enough that most proteins will never diffuse from one end to the other before turning over. Unlike normal cells, the nucleii themselves can turn over independent of the cell—and muscle stem cells (“satellite cells”, the first type of stem cell discovered IIRC) are primarily responsible for this turnover.
Now, at this point we don’t know for sure if satellite cell problems are the primary driver of age-related muscle loss, but they’re definitely one of the top candidates (mitochondria are another). And if that is the main driver, then fixing stem cell aging would indeed fix muscle loss—not necessarily retroactively, but at least preventatively.
The main takeaway here is that, while individual muscle cells are long-lived, their components still turn over. There’s probably something upstream of muscle loss which drives it.
Replenishing nucleii in established muscle cells doesn’t replace dying muscle cells. It might very well be that part of age related muscle loss is not due to lower count of muscle cells but due to other factors but sometimes muscle cells will die and that will produce muscle loss as people age when those aren’t replaced.
Cells die for many reasons. I don’t think you should expect zero muscle cells to die for any reason even if you help them replenish their nuclei.
My understanding is that muscle cells don’t just randomly die fast enough to account for age-related muscle loss. In young people post-development (i.e. people in their 20′s or early 30′s), it’s quite slow. Then with age, it accelerates. Fix whatever’s causing that accelerated loss, and muscle loss would be basically negligible.
What does “negligible” mean here? Negligible on what time scale? Because if the overarching question is “How do we stop or reverse aging to become amortal?” then any process of monotonic irreversible decline becomes important eventually.