APLN and obesity due to melanocortin 4 receptor deficiency: In the obese and insulin-resistant high-fat diet female mice, the plasma apelin-12 concentration was not altered, but the level of apelin gene-expression was elevated in white-adipose tissue and reduced in brown-adipose tissue, liver, and kidneys, suggesting that the apelinergic system could be implicated in several dysfunctions in these tissues under obesity (Butruille et al., 2013).