Peroxisome proliferator-activated receptor-alpha enhances lipid metabolism in a skin equivalent model

Peroxisome proliferator-activated receptors are involved in certain cell types such as adipocytes and hepatocytes, in the control of several pathways of lipid synthesis or catabolism by regulating the gene expression level of key lipid metabolizing enzymes. As the epidermis exhibits an extensive lipid metabolism necessary for the establishment of the barrier function, we have examined the role of peroxisome proliferator-activated receptor-alpha activation in this process. Living skin equivalents were treated with Wy 14,643, a selective peroxisome proliferator- activated receptor-alpha ligand, which enhanced greatly the synthesis of membrane coating granules, the organelles specialized in the processing of stratum corneum lipids. Also, the overall stratum corneum neutral lipid content assessed by Oil red O staining was increased. A detailed analysis of the lipid species present in the reconstructed epidermis showed that peroxisome proliferator-activated receptor-alpha activation increased the synthesis of ceramides and cholesterol derivatives, thought to be essential structural components of the permeability barrier. A synergistic effect was observed on lipid synthesis when peroxisome proliferator-activated receptor-alpha and retinoid X receptor were simultaneously activated by selective ligands. Furthermore, activation of peroxisome proliferator-activated receptor-alpha led to increased mRNA expression of several key enzymes of ceramide and cholesterol metabolism. An increase of serine-palmitoyl transferase and of beta-glucocerebrosidase enzymatic activity was also demonstrated. Altogether, these results show that peroxisome proliferator-activated receptor-alpha is a key transcription factor involved in the control of the epidermal lipid barrier.