3D encapsulation and inflammatory licensing of mesenchymal stromal cells alter the expression of common reference genes used in real-time RT-qPCR.

Human mesenchymal stromal cells (hMSCs) hold great promise in the treatment of inflammatory and immune diseases, due to their immunomodulatory capacity. Their therapeutic activity is often assessed measuring levels of expression of immunomodulatory genes such as indoleamine 2,3-dioxygenase 1 (IDO1) and real-time RT-qPCR is most predominantly the method of choice due to its high sensitivity and relative simplicity. Currently, multiple strategies are explored to promote hMSC-mediated immunomodulation, overlooking the effects they pose in the expression of genes commonly used as internal calibrators in real-time RT-qPCR analyses. However, variations in their expression could introduce significant errors in the evaluation of the therapeutic potential of hMSCs. This work investigates, for the first time, how some of these strategies - 3D encapsulation, the mechanical properties of the 3D matrix and inflammatory licensing - influence the expression of common reference genes in hMSCs. Both 3D encapsulation and inflammatory licensing alter significantly the expression of β-actin (ACTB) and Ubiquitin C (UBC), respectively. Using them as normalization factors leads to an erroneous assessment of IDO1 mRNA levels, therefore resulting in over or underestimation of the therapeutic potential of hMSCs. In contrast, the range of mechanical properties of the matrix encapsulating the cells did not significantly affect the expression of any of the reference genes studied. Moreover, we identify RPS13 and RPL30 as reference genes of choice under these particular experimental conditions. These results demonstrate the vital importance of validating the expression of reference genes to correctly assess the therapeutic potential of hMSCs by real-time RT-qPCR.