PPARA and diabetes mellitus: Given the variety and anatomic distribution of endogenous PPAR ligands, and the combinations in which they occur depending on physiological (e.g., abundance and composition of food, physical activity) and pathophysiological conditions (e.g., hyperlipidemia, hypertension, diabetes, chronic inflammation, cancer, and atherosclerosis), and it is difficult to carefully evaluate the roles of each PPAR ligand in a given cell at a fixed time-point, and this remains a major challenge in the field of investigation.