Effect of culture medium and cell size on functional heterogeneity of canine adipose-derived mesenchymal stromal cells

Abstract

Background & Aim Introduction Mesenchymal stromal cells (MSCs) are being investigated in clinical trials for treatment of a variety of veterinary conditions based on their anti-inflammatory actions and potential to induce functional tissue repair. However, outcomes of clinical trials have often fallen short of pre-clinical expectations. Heterogeneity of MSC preparations and lack of adequate characterization may be partial contributors to the variability in clinical outcomes. Purpose Identification of subpopulations within heterogenous MSC cultures may improve selection of cells with the desired functionality. Therefore, the functional heterogeneity of different subpopulations of MSCs that vary in size was evaluated, as size is hypothesized to relate to function. Methods, Results & Conclusion Methods A high-throughput, biophysical, label-free microfluidic sorting approach was used to separate subpopulations of canine adipose-derived MSCs (Ad-MSCs) based on size. Size sorted MSCs were then characterized and evaluated for the impact of culture conditions on functional heterogeneity. Results We found that larger subpopulations of MSCs with a mean diameter of ∼18 μm proliferate more slowly, senesce at earlier passages, and are inclined to form adipocytes compared to smaller MSC subpopulations (mean diameter of ∼15 μm). Most importantly, size-dependent functions are affected by culture conditions as well as time in culture. Cell surface staining for MSC-specific CD44 & CD90 antigens showed different sized subpopulations of MSCs had comparable expression levels suggesting that this criterion is not relevant to defining subpopulations of MSCs. However, transcriptome analysis showed that differently sized subpopulations of canine Ad-MSCs have distinct gene expression profiles, and culture medium and time in culture further affect gene expression. Conclusion This work provides a strategy for identifying functional subpopulations of canine MSCs based on size that could facilitate the development of quality cellular therapies through a better understanding of functional heterogeneity.