Starving stem cells of oxygen can help build stronger bones

Leach_Kent_BME.2012

J. Kent Leach: Photo courtesy UC Davis

We usually think that starving something of oxygen is going to make it weaker and maybe even kill it. But a new study by J. Kent Leach at UC Davis shows that instead of weakening bone defects, depriving them of oxygen might help boost their ability to create new bone or repair existing bone.

Leach says in the past the use of stem cells to repair damaged or defective bone had limited success because the stem cells often didn’t engraft in the bone or survive long if they did. That was because the cells were being placed in an environment that lacked oxygen (concentration levels in bone range from 3% to 8%) so the cells found it hard to survive.

However, studies in the lab had shown that if you preconditioned mesenchymal stem cells (MSCs), by exposing them to low oxygen levels before you placed them on the injury site, you helped prolong their viability. That was further enhanced by forming the MSCs into three dimensional clumps called spheroids.

Lightbulb goes off

In the  current study, published in Stem Cells, Leach says the earlier spheroid results  gave him an idea:

“We hypothesized that preconditioning MSCs in hypoxic (low oxygen) culture before spheroid formation would increase cell viability, proangiogenic potential (ability to create new blood vessels), and resultant bone repair compared with that of individual MSCs.”

So, the researchers placed one group of human MSCs, taken from bone marrow, in a dish with just 1% oxygen, and another identical group of MSCs in a dish with normal oxygen levels. After three days both groups were formed into spheroids and placed in an alginate hydrogel, a biopolymer derived from brown seaweed that is often used to build cellular cultures.

Seaweed

Brown seaweed

The team found that the oxygen-starved cells lasted longer than the ones left in normal oxygen, and the longer those cells were deprived of oxygen the better they did.

Theory is great, how does it work in practice?

Next was to see how those two groups did in actually repairing bones in rats. Leach says the results were encouraging:

“Once again, the oxygen-deprived, spheroid-containing gels induced significantly more bone healing than did gels containing either preconditioned individual MSCs or acellular gels.”

The team say this shows the use of these oxygen-starved cells could be an effective approach to repairing hard-to-heal bone injuries in people.

“Short‐term exposure to low oxygen primes MSCs for survival and initiates angiogenesis (the development of new blood vessels). Furthermore, these pathways are sustained through cell‐cell signaling following spheroid formation. Hypoxic (low oxygen) preconditioning of MSCs, in synergy with transplantation of cells as spheroids, should be considered for cell‐based therapies to promote cell survival, angiogenesis, and bone formation.”

CIRM & Dr. Leach

While CIRM did not fund this study we have invested more than $1.8 million in another study Dr. Leach is doing to develop a new kind of imaging technology that will help us see more clearly what is happening in bone and cartilage-targeted therapies.

In addition, back in March of 2012, Dr. Leach spoke to the CIRM Board about his work developing new approaches to growing bone.