A Method to Induce Brown/Beige Adipocyte Differentiation from Murine Preadipocytes

Background

Obesity is characterized by excess body fat and represents a risk factor for several chronic non-transmissible diseases (World Health Organization, 2015). The activation of brown adipose tissue (BAT) and the recruitment of newly formed beige adipocytes in white adipose tissue (WAT) leads to increased thermogenesis and higher energy expenditure, thus representing a promising intervention to treat obesity and its complications. Brown adipocytes contain multiple lipid droplets in their cytoplasm. They are also filled with mitochondria that promote energy dissipation in the form of heat, by leaking protons across the inner mitochondrial membrane, thus uncoupling oxidative phosphorylation from ATP synthesis. This mechanism is mediated by uncoupling protein 1 (UCP1), in a process called non-shivering thermogenesis (Nedergaard et al., 2001; Cannon and Nedergaard, 2004). White adipocytes have a single and large lipid droplet, few mitochondria, and produce many types of adipokines (Rosen and Spiegelman, 2014). Adipocytes with increased thermogenic capacity also appear in WAT depots, under states such as cold exposure, exercise, and caloric restriction (Cinti et al., 2005; Wu et al., 2012; Fabbiano et al., 2016), and are called beige adipocytes. Although beige adipocytes are functionally similar to brown adipocytes, these two types of thermogenic cells differ in their developmental origin (Ikeda et al., 2018). In fact, beige adipocytes share common progenitor cells with white adipocytes (Ikeda et al., 2018). The process of beige adipogenesis is often called browning, and normally occurs in subcutaneous fat depots. Together, these observations suggest that cell extrinsic and intrinsic factors contribute to determine the fate of adipocyte differentiation. Understanding these factors may help elucidating adipogenesis and lead to the identification of new therapeutic targets (Vegiopoulos et al., 2017). Here, we used murine preadipocyte cell lines isolated from different fat depots to characterize and compare protocols to promote brown, beige, or white adipocyte differentiation. These protocols were based on previous studies (Morrison and Farmer, 1999; Fasshauer et al., 2001; Tseng et al., 2004), although they have been slightly modified in our laboratory, where they have been replicated and optimized to apply basic procedures, budget-friendly reagents, and minimal infrastructure.