Shallow invasion of placental trophoblast cells into the decidua is a hallmark of the early stage of the pregnancy disorder pre-eclampsia (PE). In the latter stage of PE, the decidua generates oxidative stress products including aldehydes that damage endothelial cells. Aldehyde dehydrogenases (ALDH) detoxify aldehydes produced from oxidative stress. High level ALDH activity, particularly ALDH1A1, is characteristic of stem cells and is associated with increased stem cell survival and differentiation. We previously showed cultured decidual mesenchymal stem cells (DMSCs) express ALDH1A1 but the expression pattern of ALDH1A1 in decidua tissue is unknown. We have used the “Aldefluor” assay (Aldagen, USA) to determine the percentage of DMSCs with high ALDH activity (ALDHbr cells) and showed PE-DMSCs had significantly fewer ALDHbr cells compared with control-DMSCs. The aim was to determine the decidua tissue expression pattern of ALDH1A1 and to inactivate ALDH1A1 expression in DMSCs to model decreased ALDH1A1 activity in PE-DMSCs.
Frozen decidual tissue sections were used for immunofluorescence. DMSCs were prepared by enzymatic treatment of decidua tissue. Cultured DMSCs were characterised by differentiation assays and flow cytometry verified a typical MSC immunophenotype. Immunolocalisation of ALDH1A1 (n=3 independent tissues) revealed expression in cells around vessels in close proximity to endothelial cells. To model decreased ALDH1A1 activity in PE-DMSCs, four ALDH1A1-specific siRNAs were transfected into DMSCs. We established the optimum siRNA concentration of 20µM and a 72 hour transfection period for DMSCs seeded in 6-well plates. Successful knockdown of ALDH1A1 mRNA (p-value<0.001) and protein was verified by real-time PCR and immunofluorescence respectively. Aldefluor assays confirmed a significant reduction in the percentage of ALDHbr cells (p-value<0.001) following siRNA knockdown.
We conclude that DMSCs in the decidua are in a vascular niche and that reduced ALDH1A1 expression in PE-DMSCs in the latter stages of PE may contribute to reduced capacity of PE-DMSCs to respond to oxidative stress.