RNA isolation
Total RNA was isolated from placental tissue with the use of Gene MATRIX Universal RNA Purification Kit (EurX, Gdansk, Poland) supplemented with TRI-reagent (phenol equilibrated, stabilized: chloroform: isoamyl alcohol 25:24:1) (AppliChem GmbH, Darmstadt, Germany) and β-mercaptoethanol (Acros Organics, New Jersey, USA). The procedure was conducted according to the manufacturer’s protocol. 3 mg of each sample were homogenized using gentleMACS Tubes (Miltenyi Biotec GmbH, Bergisch Gladbach, Germany) and gentleMACS Dissociator (Miltenyi Biotec GmbH, Bergisch Gladbach, Germany). Total RNA quantity and concentration were measured by Nanodrop 2000 spectrophotometer (Thermofisher Scientific, Massachusetts, USA) and stored at -80°C.