Co-Incubation With Ppar Beta/Delta Agonists And Antagonists Modeled Using Computational Chemistry: Effect On Lps Induced Inflammatory Markers In Pulmonary Artery

Peroxisome proliferator activated receptor beta/delta (PPAR beta/delta) is a nuclear receptor ubiquitously expressed in cells, whose signaling controls inflammation. There are large discrepancies in understanding the complex role of PPAR beta/delta in disease, having both anti- and pro-effects on inflammation. After ligand activation, PPAR beta/delta regulates genes by two different mechanisms; induction and transrepression, the effects of which are difficult to differentiate directly. We studied the PPAR beta/delta-regulation of lipopolysaccharide (LPS) induced inflammation (indicated by release of nitrite and IL-6) of rat pulmonary artery, using different combinations of agonists (GW0742 or L-165402) and antagonists (GSK3787 or GSK0660). LPS induced release of NO and IL-6 is not significantly reduced by incubation with PPAR beta/delta ligands (either agonist or antagonist), however, co-incubation with an agonist and antagonist significantly reduces LPS-induced nitrite production and Nos2 mRNA expression. In contrast, incubation with LPS and PPAR beta/delta agonists leads to a significant increase in Pdk-4 and Angptl-4 mRNA expression, which is significantly decreased in the presence of PPAR beta/delta antagonists. Docking using computational chemistry methods indicates that PPAR beta/delta agonists form polar bonds with His287, His413 and Tyr437, while antagonists are more promiscuous about which amino acids they bind to, although they are very prone to bind Thr252 and Asn307. Dual binding in the PPAR beta/delta binding pocket indicates the ligands retain similar binding energies, which suggests that co-incubation with both agonist and antagonist does not prevent the specific binding of each other to the large PPAR beta/delta binding pocket. To our knowledge, this is the first time that the possibility of binding two ligands simultaneously into the PPAR beta/delta binding pocket has been explored. Agonist binding followed by antagonist simultaneously switches the PPAR beta/delta mode of action from induction to transrepression, which is linked with an increase in Nos2 mRNA expression and nitrite production.