Photo courtesy of NHS
New research suggests an RNA-binding protein can be used to expand hematopoietic stem cells (HSCs) derived from umbilical cord blood.
Investigators found the protein, Musashi-2 (MSI2), regulates the function and development of cord-blood derived HSCs, and overexpressing MSI2 can significantly expand both short-term and long-term repopulating HSCs.
“By expanding the stem cells as we have done, many more donated [cord blood] samples could now be used for transplants,” said Kristin Hope, PhD, of McMaster University in Hamilton, Ontario, Canada.
“Providing enhanced numbers of stem cells for transplantation could alleviate some of the current post-transplantation complications and allow for faster recoveries, in turn, reducing overall healthcare costs and wait times for newly diagnosed patients seeking treatment.”
Dr Hope and her colleagues described this exploration of HSC expansion in Nature.
The team first found that expression of MSI2 messenger RNA was elevated in primitive cord blood hematopoietic stem and progenitor cells (HSPCs), but it decreased during differentiation.
They then found that overexpressing MSI2 enhances the activity of cord blood progenitors in vitro and increases the number of short-term repopulating HSCs in vitro and in vivo.
During in vitro culture, MSI2-overexpressing cells were 2.3-fold more abundant than control cells at 7 days and 6-fold more abundant at 21 days. After 7 days, MSI2-overexpressing cells showed a cumulative 9.3-fold increase in colony-forming cells but no changes in cell cycling or death.
MSI2-overexpressing short-term repopulating cells (STRCs) yielded 1.8-fold more primitive CD34+ cells than control STRCs. And the MSI2-overexpressing STRCs prompted a 17-fold increase in functional STRCs.
Furthermore, 100% of mice transplanted with MSI2-overexpressing STRCs were engrafted at 6.5 weeks, compared to 50% of mice transplanted with control STRCs.
Additional transplant experiments showed that MSI2 overexpression also impacted long-term HSCs (LT-HSCs). Compared to control cells, MSI2-overexpressing cells increased the percentage of GFP+ HSCs in the bone marrow 4.6-fold and the frequency of LT-HSCs 3.5-fold.
The researchers said the increase in LT-HSC frequency corresponded to MSI2-overexpressing GFP+ HSCs having expanded in mice 2.4-fold over input. With control HSCs, on the other hand, there was a 1.5-fold decrease.
In ex vivo culture, MSI2 overexpression induced a cumulative 23-fold expansion of secondary LT-HSCs when compared to control LT-HSCs.
Finally, the researchers performed a global analysis of MSI2–RNA interactions and found that MSI2 mediates HSPC self-renewal and ex vivo expansion by coordinating the post-transcriptional regulation of proteins belonging to a shared self-renewal regulatory pathway.
“We’ve really shone a light on the way these stem cells work,” Dr Hope said. “We now understand how they operate at a completely new level, and that provides us with a serious advantage in determining how to maximize these stem cells in therapeutics. With this newfound ability to control the regeneration of these cells, more people will be able to get the treatment they need.”
