ERN1 and obesity due to melanocortin 4 receptor deficiency: To investigate if the molecular mechanism of PH could be associated to the deleterious effects of obesity, we evaluated the gene expression of ER stress markers ATF6, Ire1α, CHOP, PERK, and eIF2α in the pulmonary artery of CTL and HFD animals fed for 4 months (Figures 3A–E).