This blog is the final installment in our #MonthofCIRM series. Be sure to check out our other blogs highlighting important advances in CIRM-funded research and initiatives.
Neural stem cells from the brain have promising potential as cell-based therapies for treating neurological disorders such as Alzheimer’s disease, Parkinson’s, and spinal cord injury. A limiting factor preventing these brain stem cells from reaching the clinic is quantity. Scientists have a difficult time growing large populations of brain stem cells in an efficient, cost-effective manner while also maintaining the cells in a stem cell state (a condition referred to as “stemness”).
CIRM-funded scientists from Stanford University are working on a solution to this problem. Dr. Sarah Heilshorn, an associate professor of Materials Science and Engineering at Stanford, and her team are engineering 3D hydrogel technologies to make it easier and cheaper to expand high-quality neural stem cells (NSCs) for clinical applications. Their research was published yesterday in the journal Nature Materials.
Stem Cells in 3D
Similar to how moviegoers prefer to watch the latest Star Wars installment in 3D, compared to the regular screen, scientists are turning to 3D materials called hydrogels to grow large numbers of stem cells. Such an environment offers more space for the stem cells to proliferate and expand their numbers while keeping them happy in their stem cell state.
To find the ideal conditions to grow NSCs in 3D, Heilshorn’s team tested two important properties of hydrogels: stiffness and degradability (or how easy it is to remodel the structure of the hydrogel material). They designed a range of hydrogels, made from proteins with elastic qualities, that varied in these two properties. Interestingly, they found that the stiffness of the material did not have a profound effect on the “stemness” of NSCs. This result contrasts with other types of adult stem cells like muscle stem cells, which quickly differentiate into mature muscle cells when exposed to stiffer materials.
On the other hand, the researchers found that it was crucial for the NSCs to be able to remodel their 3D environment. NSCs maintained their stemness by secreting enzymes that broke down and rearranged the molecules in the hydrogels. If this enzymatic activity was blocked, or if the cells were grown in hydrogels that couldn’t be remodeled easily, NSCs lost their stemness and stopped proliferating. The team tested two other hydrogel materials and found the same results. As long as the NSCs were in a 3D environment they could remodel, they were able to maintain their stemness.
Caption: NSCs maintain their stemness in hydrogels that can be remodeled easily. Nestin (green) and Sox2 (red) are markers that indicate “high-quality” NSCs. (Images courtesy of Chris Madl)
Christopher Madl, a PhD student in the Heilshorn lab and the first author on the study, explained how remodeling their 3D environment allows NSCs to grow robustly in an interview with the Stem Cellar:
“In this study, we identified that the ability of the neural stem cells to dynamically remodel the material was critical to maintaining the correct stem cell state. Being able to remodel (or rearrange) the material permitted the cells to contact each other. This cell-cell contact is responsible for maintaining signals that allow the stem cells to stay in a stem-like state. Our findings allow expansion of neural stem cells from relatively low-density cultures (aiding scale-up) without the use of expensive chemicals that would otherwise be required to maintain the correct stem cell behavior (potentially decreasing cost).”
To 3D and Beyond
When asked what’s next on the research horizon, Heilshorn said two things:
“First, we want to see if other stem cell types – for example, pluripotent stem cells – are also sensitive to the “remodel-ability” of materials. Second, we plan to use our discovery to create a low-cost, reproducible material for efficient expansion of stem cells for clinical applications. In particular, we’d like to explore the use of a single material platform that is injectable, so that the same material could be used to expand the stem cells and then transplant them.”
Heilshorn is planning to apply the latter idea to advance another study that her team is currently working on. The research, which is funded by a CIRM Tools and Technologies grant, aims to develop injectable hydrogels containing NSCs derived from human induced pluripotent stem cells to treat mice, and hopefully one day humans, with spinal cord injury. Heilshorn explained,
“In our CIRM-funded studies, we learned a lot about how neural stem cells interact with materials. This lead us to realize that there’s another critical bottleneck that occurs even before the stage of transplantation: being able to generate a large enough number of high-quality stem cells for transplantation. We are developing materials to improve the transplantation of stem cell-derived therapies to patients with spinal cord injuries. Unfortunately, during the transplantation process, a lot of cells can get damaged. We are now creating injectable materials that prevent this cell damage during transplantation and improve the survival and engraftment of NSCs.”
An injectable material that promotes the expansion of large populations of clinical grade stem cells that can also differentiate into mature cells is highly desired by scientists pursuing the development of cell replacement therapies. Heilshorn and her team at Stanford have made significant progress on this front and are hoping that in time, this technology will prove effective enough to reach the clinic.