APLN and obesity due to melanocortin 4 receptor deficiency: Cell-based experiments have also shown a similar trend and found that Apelin-13 reduced lipid content and total cholesterol content (14), indicating that amidation-modified Apelin-13 might downregulate the expression of PPARγ, thereby inhibiting the differentiation of adipocytes, resulting in the regulation of PLIN1 expression to promote lipolysis in vivo, which ameliorated obesity symptoms.