Cell depletion is the loss of cells without equivalent replacement. It happens in some of our most important tissues as we age. The brain and heart are particularly affected but it can also affect our skeletal muscles.
The gaps in our long-lived tissues left behind by unreplaced cell loss are dealt with in different ways:
Cell depletion can be fixed in two main ways: by stimulating the division of existing cells, or by directly introducing new ones. Cell division is naturally stimulated in some muscles by exercise (although most of the increased tissue volume and strength is a result of the increased size of the exercised cells rather than increased number), and can be artificially stimulated through the introduction (e.g. by injection) of growth factors that stimulate cell division; this works well in muscle, and animal studies suggest that it may also work in the thymus, an organ with an important role in the immune system that progressively shrinks with age.
However, both natural and artificial stimulation of cell division have their limitations. This is partly because, as a defence against cancer, cells have a variety of blocks against dividing excessively. So, for example, there is evidence that stem cells in continuously renewing tissues like the blood tend to get depleted late in life in some mouse strains. Therefore, it will be preferable in most cases to introduce entirely new cells that are both free of any defects (such as mutations or other aging damage) present in the native cells, and that in some cases have been engineered into a state where they will divide to fix the tissue even though cells already present within the body were not doing so. For more details, see the section on cell therapy.
We need more work in all these areas, even though they are all progressing very encouragingly. However, the current fashion for stem cell research in the international scientific community means that SENS Foundation does not currently intend to allocate resources to projects in this area.
Talks on exercise at IABG 10: Ji, Powers, Tidball, Goto
Talks on growth factors at IABG 10: Rosenthal, Aspinall, Brockes, Goldspink
Talks on growth factors at SENS2: Conner
Talks on stem cells at IABG 10: West, Svendsen, Sefton, Kirkwood, Van Zant, Haseltine
Talks on stem cells at SENS2: West, Sharpe, Song, Hwang, Cibelli, Schatten, Holm, Schiller, Stelzner
Talks on RepleniSENS topics at SENS3: Conboy, Emsley (abstract only), Gardiner, Lee, Mason, Minger, Stojkovic, Stolzing, Wernig
