RSPO3 and obesity due to melanocortin 4 receptor deficiency: This observation was followed by confirmation of elevations of mRNA expressions of PPARδ and Cpt1a, but not of PPARα (Fig 3J), as well as protein expressions of PPARδ (1.99-fold, P < 0.01) and Cpt1a (2.39-fold, P < 0.05), in obese Rspo3-mice (Fig 3K), partially accounting for the amelioration of obesity-related hepatic steatosis.