Fighting obesity: When muscle meets fat.

The prevalence of obesity has risen to an unprecedented level. According to World Health Organization, over 500 million adults, equivalent to 10%-14% of the world population, were obese with a body mass index (BMI) of 30 kg/m(2) or greater in 2008.(1) This rising prevalence and earlier onset of obesity is believed to be resulted from an interplay of genetic factors, over-nutrition and physical inactivity in modern lifestyles. Obesity also increases the susceptibility to metabolic syndromes, hypertension, cardiovascular diseases, Type 2 diabetes mellitus (T2DM) and cancer.(2-4) The global obesity epidemic has sparked substantial interests in the biology of adipose tissue (fat). In addition, the skeletal muscle and its secretive factors (myokines) have also been shown to play a critical role in controlling body energy balance, adipose homeostasis and inflammation status.(5) Interestingly, skeletal muscle cells share a common developmental origin with brown adipocytes,(6,7) which breaks down lipids to generate heat - thus reducing obesity. Here, we provide a brief overview of the basics and recent progress in muscle-fat crosstalk in the context of body energy metabolism, obesity, and diabetes. We summarize the different types of adipocytes, their developmental origins and implications in body composition. We highlight the role of several novel myokines in regulating fat mass and systemic energy balance, and evaluate the potential of skeletal muscles as a therapeutic target to treat obesity.