New findings from UCLA researchers related to muscle fibrosis show potential implication for cell therapies
Extracellular matrix (ECM) should be considered in approaching other pathologies
UCLA RESEARCH BRIEF
By Nicole Wilkins
The extracellular matrix (ECM) is an intricate network composed of an array of macromolecules organized in a cell/tissue-specific manner. Components of the ECM link together to form a structurally stable composite, contributing to the mechanical properties of tissues and providing cues to resident stem cells that can facilitate or impair regeneration.
The research findings from the team of UCLA scientists demonstrated that laminin scarring is harmful to stem cell function. Laminins are a family of glycoproteins of the extracellular matrix of all animals. They are major components of the basal lamina, cells which surround muscle and fat tissue.
Researchers found that laminin disorganization led to scarring of the basement membrane in fibrotic mdx muscle, preventing cells from adhering to and remodeling the ECM, steps needed for stem-cell mediated regeneration. The team’s findings also reveal that laminin, not collagen, hinders regeneration in muscle fibrosis.
Skeletal muscle has a strong capacity for regeneration due to resident muscle stem cells. Duchenne muscular dystrophy (DMD), a progressive muscle wasting disease, is characterized by repeated contraction-induced injury of fragile myofibers resulting in asynchronous cycles of degeneration and regeneration.
In early stages of DMD, the muscle can recover following injury and maintains its regenerative capacity. However, over time, there is progressive loss of muscle function and failed regeneration, with DMD patients exhibiting muscle weakness by the age of four and loss of ambulation by age thirteen. Research into genetic modifiers of DMD have identified genes which modulate the extracellular matrix. Researches propose that there are inherent deficiencies in the extracellular matrix in DMD that develop with progression of the disease that inhibit muscle regeneration.
The objective of the current study was to investigate the effect of the skeletal muscle ECM on specific functions of stem cells that are necessary for regeneration and, reciprocally, to determine how cells interact with the ECM.
The research team tailored in vitro methods to develop on-slide decellularization of skeletal muscle yielding myoscaffolds that retain native architecture and composition. The team then populated healthy and fibrotic DMD myoscaffolds with human skeletal muscle progenitor cells (SMPCs) derived from human pluripotent stem cells (hPSCs) and investigated stem cell functions necessary for myogenesis.
Researchers then investigated whether improving the connection between the cell and ECM could reduced laminin scarring and improve the ability of cells to stick to the ECM. Not only did the team find that the remodeled ECM had reduced scarring, but it was composed of a dense collagen matrix that facilitated, rather than inhibited, myogenesis. These findings indicated that increased matrix deposition may not always be as bad for stem cell function as previously thought.
Because the analysis requires only small volumes of muscle to generate myoscaffolds, it could be utilized as an application for precision medicine. Muscle biopsies and cells could be isolated from patients and specific treatments could be analyzed in a dish before application.
Kristen Stearns-Reider, assistant professor in the Department of Orthopaedic Surgery at the David Geffen School of Medicine at UCLA, is the study’s first author. The corresponding author is Rachelle H. Crosbie, professor and chair of the Department of Integrative Biology and Physiology in the College of Life Sciences and professor in the Department of Neurology at the David Geffen School of Medicine at UCLA.
Other authors from UCLA include:
Michael Hicks, Katherine Hammond, Joseph Reynolds, Alok Maity, Yerbol Kurmangaliyev, Jesse Chin, Adam Stieg, Ken Yamauchi, Bennett Novitch, Roy Wollman, April Pyle.
WHAT THE RESEARCHERS SAID:
“One major takeaway from this work is the application of our myoscaffold platform in future studies of cell-ECM interactions and patient-specific therapies. As compared to engineered scaffolds, our use of native ECM permits analysis of ECM composition and organization in health and disease and could be applied to investigate cell-ECM interactions not only in other neuromuscular diseases, but in other tissues and organ systems.” – Kristen Stearns-Reider
This study is published online in the journal npj Regenerative Medicine.
FUNDING & RESOURCES
The study was funded by the National Institutes of Health, the UCLA Clinical and Translational Science Institute, the Muscular Dystrophy Association USA, the Broad Stem Cell Research Fellowship, Schaffer Family Foundation Fellowship, and MDA development award.
The CNSI’s Nano and Pico Characterization Laboratory, The Technology Center for Genomics and Bioinformatics, and the MCDB/Broad Stem Cell Research Center microscopy core at UCLA provided imaging equipment and support for the investigations.