Skin stem cells specialize into new skin by sensing neighborhood crowding
When embarking on a road trip, the GPS technology inside our smartphones helps us know where we are and how to get where we’re going. The stem cells buried in the deepest layers of our skin don’t have a GPS and yet, they do just fine determining their location, finding their correct destination and becoming the appropriate type of skin cell. And as a single organ, all the skin covering your body maintains the right density and just the right balance of skin stem cells versus mature skin cells as we grow from a newborn into adult.

Skin cells growing in a petri dish (green: cytoskeleton, red: cell-cell junction protein).
Credit: MPI for Biology of Aging

This easily overlooked but amazing feat is accomplished as skin cells are continually born and die about every 30 days over your lifetime. How does this happen? It’s an important question to answer considering the skin is our first line of defense against germs, toxins and other harmful substances.

This week, researchers at the Max Planck Institute for Biology of Aging in Cologne, Germany reported a new insight into this poorly understood topic. The team showed that it all comes down to the skin cells sensing the level of crowding in their local environment. As skin stem cells divide, it puts the squeeze on neighboring stem cells. This physical change in tension on these cells “next door” triggers signals that cause them to move upward toward the skin surface and to begin maturing into skin cells.

Lead author Yekaterina Miroshnikova explained in a press release the beauty of this mechanism:

“The fact that cells sense what their neighbors are doing and do the exact opposite provides a very efficient and simple way to maintain tissue size, architecture and function.”

The research was picked up by Phys.Org on Tuesday and was published in Nature Cell Biology.

Stem cells respond differently to aging vs. injured muscle
From aging skin, we now move on to our aging and injured muscles, two topics I know oh too well as a late-to-the-game runner. Researchers at the Sanford Burnham Prebys Medical Discovery Institute (SBP) in La Jolla report a surprising discovery that muscle stem cells respond differently to aging versus injury. This important new insight could help guide future therapeutic strategies for repairing muscle injuries or disorders.

Muscle stem cell (pink with green outline) sits along a muscle fiber.
Image: Michael Rudnicki/OIRM

Muscle stem cells, also called satellite cells, make a small, dormant population of cells in muscle tissue that springs to life when muscle is in need of repair. It turns out that these stem cells are not identical clones of each other but instead are a diverse pool of cells.  To understand how the assortment of muscle stem cells might respond differently to the normal wear and tear of aging, versus damage due to injury or disease, the research team used a technology that tracks the fate of individual muscle stem cells within living mice.

The analysis showed a clear but unexpected result. In aging muscle, the muscle stem cells maintained their diversity but their ability to divide and grow declined. However, the opposite result was observed in injured muscle: the muscle stem cell diversity became limited but the capacity to divide was not affected. In a press release, team leader Alessandra Sacco explains the implications of these findings for therapy development:

Alessandra Sacco, PhD

“This study has shown clear-cut differences in the dynamics of muscle stem cell pools during the aging process compared to a sudden injury. This means that there probably isn’t a ‘one size fits all’ approach to prevent the decline of muscle stem cells. Therapeutic strategies to maintain muscle mass and strength in seniors will most likely need to differ from those for patients with degenerative diseases.”

This report was picked up yesterday by Eureka Alert and published in Cell Stem Cell.