Today I'll point out a pair of open access review papers in which the authors discuss mechanisms involved in the age-related declines and detrimental altered behaviors of hematopoietic stem cells. These stem cells are responsible for generating blood and immune cells, and so are of vital importance to the function of the immune system throughout life. One paper focuses on external contributions, those arising from the surrounding environment, while the other looks at damage and change arising from the stem cells themselves.

This encapsulates the divide in thinking about stem cell aging in general. At least some stem cell populations, such as those supporting skeletal muscle, appear to remain capable of function well into late life. That their output of daughter somatic cells to support tissue function declines is a matter of the cells lapsing into quiescence for ever longer periods, rather than there being too few competent cells remaining. This is probably more a matter of signals from the surrounding environment rather than inherent damage to the stem cells.

In the case of hematopoietic stem cells, evidence suggests more of a role for damage and declining numbers of competent cells than is the case for muscle stem cells, however. In this situation, rejuvenation therapies will almost certainly have to involve the delivery of new patient-matched stem cells capable of engrafting into tissue and continuing the work of their damaged predecessors. This aspect of stem cell therapy has proven to be challenging. It remains the case that most cell therapies, certainly those presently available in clinics, struggle to achieve lasting cell survival. Whatever benefits they produce result from signals released by the transplanted cells in the short time they remain viable. Still, progress has been made, and organizations like AgeX Therapeutics are working towards reliable approaches to the replacement of stem cell populations.

Microenvironmental contributions to hematopoietic stem cell aging

Understanding intrinsic hematopoietic stem cells aging