Roles of PPAR delta in lipid absorption and metabolism: a new target for the treatment of type 2 diabetes

Peroxisome proliferator-activated receptors (PPARs) are lipid-activated transcription factors exerting several functions in development and metabolism. PPARα, activated by polyunsaturated fatty acids and fibrates, is implicated in regulation of lipid metabolism, lipoprotein synthesis and metabolism and inflammatory response in liver and other tissues. PPARγ plays important roles in regulation of proliferation and differentiation of several cell types, including adipose cells. Its activation by thiazolidinediones results in insulin sensibilization and antidiabetic action. Until recently, the physiological functions of PPARδ remain elusive. The utilization of specific agonists and of appropriate cellular and animal models revealed that PPARδ has an important role in metabolic adaptation of several tissues to environmental changes. Treatment of obese animals by specific PPARδ agonists results in normalization of metabolic parameters and reduction of adiposity. The nuclear receptor appeared to be implicated in the regulation of fatty acid burning capacities of skeletal muscle and adipose tissue by controlling the expression of genes involved in fatty acid uptake, β-oxidation and energy uncoupling. PPARδ is also implicated in the adaptive metabolic response of skeletal muscle to endurance exercise by controlling the number of oxidative myofibers. Given the results obtained with animal models, PPARδ agonists may have therapeutic usefulness in metabolic syndrome by increasing fatty acid consumption in skeletal muscle and adipose tissue.