It was performed as described earlier [22 (link), 25 (link)]. Briefly, cells plated at 50–60% confluence in 12-well plates were co-transfected with 0.25 μg of tk-PPREx3-Luc, a PPRE-dependent luciferase reporter construct, and 12.5 ng of pRL-TK (a plasmid encoding Renilla luciferase, used as transfection efficiency control; Promega) using Lipofectamine Plus (Invitrogen Life Technologies). After 24 h of transfection, cells were stimulated with different doses of gemfibrozil for 2 h. Firefly and Renilla luciferase activities were analyzed in cell extracts using the Dual Luciferase kit (Promega) in a GloMax 96 microplate luminometer (Promega) and corresponding GloMax 96 microplate luminometer software (Promega) per the manufacturer’s specifications.