MAPK8 and obesity due to melanocortin 4 receptor deficiency: Existing studies show that pro-inflammatory diets increase Gram-negative bacteria in the gut, activating Toll-like receptors, elevating inflammation levels, inducing endoplasmic reticulum stress in adipocytes to activate the UPR, JNK, and NF-κB pathways, and promoting fat accumulation, thereby linking to obesity [16].