Date Published: April 3, 2019
Publisher: Public Library of Science
Author(s): Deena A. Rennerfeldt, Joana S. Raminhos, Samantha M. Leff, Pristinavae Manning, Krystyn J. Van Vliet, Thomas Abraham.
Bone marrow stromal cells (BMSCs) include a subset of stem cells that are considered promising for developmental studies and therapeutic applications. While it is appreciated generally that BMSC populations can exhibit morphological and functional heterogeneity upon in vitro culture expansion, the potential for heterogeneity within a single colony forming unit–generated ostensibly from a single mother cell–is less explored but is critical to design of both fundamental studies and cell therapy production. Here we observed BMSC colony formation in real time via time lapsed optical imaging and analysis, to quantify whether and how heterogeneity emerged over multiple cell divisions spanning the duration of a typical colony formation unit assay. These analyses demonstrate that such colonies are neither homogeneous subpopulations of stem cells nor necessarily derived from single originating cells. While the mechanisms for and causes of this intracolony heterogeneity are not understood fully, we further demonstrate that extensive cell-cell contacts do not correlate with senescence, but that media exchange was concurrent with diversification in even the most uniform single-cell-derived colonies. These direct quantitative observations and visualizations of colony formation provide new insights that are motivated by significant implications for both basic research and stem cell-based therapies.
Bone marrow stromal cells (BMSCs), a subset of which are characterized as multipotent mesenchymal stem cells, are considered potential cell therapies for diverse medical conditions–from bone tissue regeneration to autism and Parkinson’s disease [1–3]. Such culture-expanded BMSC populations have been implemented in over 600 clinical trials since 1995 (http://www.clinicaltrials.gov). Despite these advances at the lab scale and in ongoing clinical trials, however, we are aware of no therapies to date that have been approved by the U.S. Food & Drug Administration for delivery of BMSCs or putative mesenchymal stem cells (http://www.clinicaltrials.gov).
Detailed methods are located following the References, for manuscript readability. These methods include: cell source, expansion, and serial dilution to attain sparsely seeded dishes for colony imaging; time-lapse image acquisition of colony growth; image analysis including extensive image preprocessing to identify and track and distinguish cells over days of continuous culture and imaging, parameter extraction and classification; construction of multivariate lineage trees; correlation analysis linking parameters to intracolony heterogeneity; processes for creating data visualizations; and statistical analysis to identify differences among and within colonies. We have also provided a detailed experimental protocol at protocols.io  and source code for image processing and analysis as a GitHub repository .