GHRL and obesity due to melanocortin 4 receptor deficiency: Therefore, acyl ghrelin might exert proinflammatory effect, especially in our high fat diet system, which is consistent with the reports that ghrelin signaling has an important role in macrophage polarization and adipose tissue inflammation during aging [32] or feeding with high fructose corn syrup [35], in which the concurrences of obesity and insulin resistance are significantly greater.