Secreted adiponectin as a marker to evaluate in vitro the adipogenic differentiation of human mesenchymal stromal cells

Background aims: Multipotency is one of the hallmarks of mesenchymal stromal cells (MSCs). Given the widespread adoption of MSC-based clinical applications, the need for rapid and reliable methods to estimate MSC multipotency is demanding. Adipogenic potential is commonly evaluated by staining cell lipid droplets with oil red O. This cytochemical assay is performed at the terminal stage of adipogenic induction (21-28 days) and necessitates the destruction of the specimen. In this study, we investigated whether it is possible to assess MSC adipogenic differentiation in a more efficient, timely and non-destructive manner, while monitoring in vitro secretion of adiponectin, a hormone specifically secreted by adipose tissue. Methods: A commercially available enzyme-linked immunosorbent assay kit was used to quantify adiponectin secreted in the culture medium of adipo-induced human bone marrow-derived MSCs. Oil red O staining was used as a reference method. Results: Adiponectin is detectable after 10 days of induction at a median concentration of 5.13 ng/mL. The secretion of adiponectin steadily increases as adipogenesis proceeds. Adiponectin is undetectable when adipogenic induction is pharmacologically blocked, inefficient or when human MSCs are induced to differentiate toward the osteogenic lineage, proving the specificity of the assay. Furthermore, the results of adiponectin secretion strongly correlate with oil red O quantification at the end of induction treatment. Conclusions: Our results demonstrate that quantification of secreted adiponectin can be used as a reliable and robust method to evaluate adipogenic potential without destroying samples. This method provides a useful tool for quality control in the laboratory and in clinical applications of human MSCs.