APLN and Obesity: Apelin-13 is considered the most functional subtype of the Apelin family, and it actively participates in regulating bone marrow mesenchymal stem cell (BMSC) apoptosis, osteoblast differentiation, glucose and lipid metabolism, and other physiological processes (11–13), which means that it has an important role in the prevention and treatment of metabolic diseases such as obesity, diabetes and osteoporosis; however, there is still some dispute regarding its regulatory effect on metabolic diseases (14, 15).