An international collaboration between UC Davis and Swedish scientists has resulted in the first comprehensive characterization of a recently discovered cell-to-cell communication system used by stem cells. The findings, posted online today in the journal Stem Cells, will help scientists develop new stem cell-based treatment options for peripheral artery disease, a condition which affects about 12 million people in the United States alone.
Proteins, RNA and other cellular contents were recently discovered to be released from stem cells in millions of small bubbles – called exosomes – and taken up by neighboring cells, influencing their behavior and activity. This latest research has characterized for the first time the proteins contained in exosomes from mesenchymal stem cells by exposing them to both normal physiological conditions and low oxygen conditions that mimic the low blood flow seen in peripheral arterial disease.
“We have provided the first comprehensive snapshot of the communication proteins’ stem cells and their exosomes use to talk to other cells,” said Johnathon Anderson, lead author of the study and a research scientist with the UC Davis Stem Cell Program. “It has enabled us to fundamentally grasp how stem cells use this newly identified communication system to heal damaged tissues that have reduced or cut off blood flow in individuals suffering from peripheral arterial disease.”
The researchers focused on mesenchymal stem cells (MSCs), which are stem cells found in the bone marrow of adults that can renew themselves and repair damaged tissue. According to Anderson, the traditional view of MSCs emphasized their ability to differentiate into different cell types. The more recent view suggests a therapeutic role for these so-called “paramedic cells” that help heal tissue by homing in on damaged tissues and encouraging more cells to help out in the revascularization process.
How MSCs influence other cells has been a source of intense research interest. Until recently, scientists believed that they primarily communicated by simply secreting individual proteins outside of themselves into the intercellular space – the area between cells.
In the last few years, a sophisticated communications system has been discovered involving exosomes – small bubbles that cells use to transport part of themselves to neighboring cells. Cells use the intricate communication system to cope with changes in their surroundings such as low oxygen or stressful conditions.
Anderson worked in collaboration with the Karolisnka Institute’s Janne Lehtio. Their research teams used a specialized mass spectrometry system known as “high-resolution isoelectric focusing coupled liquid chromatography tandem mass spectrometry” (HiRIEF LC-MS/MS), which allowed them to characterize the protein contents of MSCs and MSC-derived exosomes in a comprehensive fashion for the first time. They identified more than 6,000 different proteins in MSCs and nearly 2,000 in exosomes, and through computer algorithms were able to discern the relationships between these proteins and how they likely interact with one another.
Interestingly, out of nearly 2,000 proteins found in exosomes, nearly one-quarter were not detected in the MSCs, indicating that MSCs might be making certain proteins solely for transportation in the communication bubbles.
Investigators also found the paramedic cells (MSCs) reacted very differently when exposed to normal physiological conditions as compared to low-oxygen conditions, which mimic the low blood flow seen in peripheral artery disease.
The research revealed that MSCs exposed to low-oxygen conditions expressed several proteins in higher concentrations, especially those associated with new blood vessel formation – a process called angiogenesis. Most notable was the expression of proteins involved with nuclear factor-kappaB (NFkB) signaling, an important communication pathway that helps new blood vessels form and is a vital process in treating peripheral arterial disease.
“One of the most interesting aspects of these little exosome bubbles is the fact that we can package them with novel types of therapeutics to enhance their tissue-healing capabilities,” said Anderson. “With this fundamental understanding of how the communication system works, it really opens the floodgates for developing new therapeutics for cardiovascular and neurological diseases using MSC exosomes.”
“This research represents a significant step in the field of mesenchymal stem cell communication,” added Jan Nolta, principal investigator of the study and director of UC Davis’ Stem Cell Program and its Institute for Regenerative Cures in Sacramento. “The results help to explain how MSCs and the exosomes that they produce can be such effective mediators of angiogenesis and have the potential to further the development of new treatments for ischemic tissue-related diseases.”
The article in Stem Cells is entitled, “Comprehensive proteomic analysis of mesenchymal stem cell exosomes reveals modulation of angiogenesis via NFkB signaling.”
Other study authors from the UC Davis Stem Cell Program are Calvin Graham, Missy Pham, Charles Bramlett, Elizabeth Montgomery, Renee Bardini, Gerhard Bauer, Kyle Fink, Brian Fury, Zelenia Contreras, Madeline Hoon and Kyle Hendrix. Additional authors include Matt Mellema from the UC Davis Department of Veterinary Medicine; Frederic Chedin from the UC Davis Department of Molecular and Cellular Biology; Billie Hwang and Michael Mulligan from the University of Washington; and Henrik Johansson, Mattias Versterlund, Janne Lehtiö and Samir EL-Andaloussi from the Karolinska Institutet in Stockholm, Sweden.
The UC Davis research was funded in part by a Transformative Research Award from National Institutes of Health (NIH) Common Fund, for what the agency terms “innovative, unconventional, paradigm-shifting research projects that are inherently risky and untested” (NIH High-Risk, High-Reward Program, R01GM099688, T32-GM008799 and T32-HL086350). Additional research support came from the National Science Foundation (Graduate Research Fellowships Program 2011116000 and Graduate Research Opportunities Worldwide 201111600).