In vivo imaging reveals selective PPAR activity in the skin of peroxisome proliferator-activated receptor responsive element-luciferase reporter mice

Peroxisome proliferator-activated receptors (PPARs) have been revealed as key regulators of several skin disorders. This has led to a growing interest in the development of drugs targeting PPARs as therapeutics for skin diseases. To evaluate skin PPAR activity, we developed peroxisome proliferator responsive element-luciferase (PPRE-Luc) mice, a mouse model in which the luciferase gene expression is under the control of a PPAR-inducible promoter in all organs. Our aim was to define and validate experimental conditions to establish PPRE-Luc mice as a valuable tool for in vivo non-invasive evaluation of PPARs activation in the skin. We demonstrated by optical imaging that topical application of 40 mm of Luciferin for 10 min was enough to reveal the optimal luciferase activity in mice skin. The treatment of mice skin with the PPARγ and PPARα agonists, pioglitazone and WY14643, was associated with significant increase in photons emission reaching maximal signalling at 6 h. We have performed dose response studies by testing a large range of pioglitazone and WY14643 concentrations on mouse skin. The specificity of bioluminescence signal induced by pioglitazone and WY14643 was assessed using PPARγ and PPARα antagonists, GW9662 and GW6471, respectively. This approach revealed that the isoform specificity of PPARs agonists decreased when high ligand concentrations were applied on mouse skin. These results were further confirmed by in vitro measurement of luciferase activity in skin extracts. Overall, our results demonstrated that PPRE-Luc mice represent a valuable reporter mouse model for the in vivo pharmacological profiling of drugs targeting PPARs in the skin.