ERN1 and obesity due to melanocortin 4 receptor deficiency: Mice with diet-induced obesity (DIO) have increased expression of hypothalamic ER stress markers, including phospho-PERK (p-PERK), phospho-eukaryotic initiation factor-2α (p-eIF2α), and phospho-IRE1 (p-IRE1) (Won et al., 2009; Cakir et al., 2013).