Differentiation of Adipose Derived Stem cells: Unraveling the Molecular mechanisms and the need for different isolation techniques

Abstract

Adipose derived stem cells (ASCs) are adult stem cells which reside in the human adipose tissue. They are important in the field of regenerative medicine because of their accessibility, abundance, ability to self-renew and differentiate into multiple cell types including bone, fat, muscle and cartilage. Despite their use in therapeutic applications, a constraint is the use of in vitro expansion which is required to obtain a pure population with clinically useful yields. This results in a loss of differentiation potential. However, this observation is under appreciated in the literature and the molecular mechanisms underlying this loss of differentiation are unexplored. The aim of this study was to compare the adipogenic differentiation potential of uncultured ASCs isolated by flow cytometry to those cultured for a 28 day period using a quantitative method. Microarray analysis to identify the expression profiles of miRNAs in both conditions was subsequently performed. The effect of various factors contributing to the in vivo stem cell niche on their ability to maintain adipogenic differentiation potential was determined and characterisation of serially passaged ASCs was also performed. Finally, a method was developed to isolate ASCs in an immunomagnetic isolation procedure using a novel cocktail of antibodies. FACS sorted ASCs exhibited high levels of adipogenic differentiation potential and a subsequent 28 day culture period of these cells resulted in a significant loss of adipogenic potential. A complete loss of adipogenic differentiation was observed over 30 cell divisions which was accompanied by reduced cell proliferation. Specific miRNAs (notably miR-138, miR-21 and miR-148) showed differential expression over 28 days suggesting that miRNAs have a role to play in this process. The factors contributing to the stem cell niche that were tested had a moderate effect but did not prevent the loss of differentiation. Our novel isolation protocol resulted in a population of ASCs with equal purity and adipogenic differentiation potential to cells isolated by FACS with the added benefit of higher yields. Therefore, our results begin to unravel the molecular mechanisms underlying ASC differentiation potential and provide a new clinically viable method for the isolation of ASCs.