Obesity is the accumulation of white adipose tissue (WAT) which is involved in energy storage. Another type of adipose tissue is brown adipose tissue (BAT) which is involved in heat generation and increased energy expenditure. The primary focus of our lab is to understand the role of heparin-binding EGF-like growth factor (HB-EGF) in cellular reprogramming of cells into a BAT-like phenotype. BAT is a type of fat that is involved in stimulation of non-shivering thermogenesis resulting in generation of heat rather than ATP production. BAT is characterized by having an increased number of mitochondria as well as expressing PR domain 16 (PRDM16) transcriptional co-regulator, peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1?) and uncoupling protein 1 (UCP-1).
HB-EGF undergoes proteolytic processing by a disintegrase and metalloprotease (ADAM) 12S, an enzyme that processes HB-EGF yielding both soluble and intracellular domains. The soluble form of HB-EGF binds to and activates EGF receptors (EGFRs) resulting in stimulation of cell division, while the intracellular domain migrates to the nucleus and relieves transcriptional repressors involved in cell division. Co-expression of HB-EGF and ADAM 12S results in lipid accumulation, increased mitochondrial staining, up-regulation of BAT genes (PRDM16, PGC-1?, UCP-1) and down-regulation of WAT genes, including CAAT-enhancer-binding protein (C/EBP?) and lamin A/C (LMNA) further supporting the hypothesis that HB-EGF/ADAM 12S co-expression reprograms cells to a BAT-like state.
Currently, an adenoviral gene-delivery system for HB-EGF and ADAM 12S is being characterized in order to demonstrate BAT-like transdifferentiation of cells. We hypothesize that HB-EGF/ADAM 12S co-expression transdifferentiates cells to a stem-like state mediated by fibroblast growth factor 2 (FGF2) and Krüppel-like factor 3 (Klf3) and results in BAT-like cells by induction of BAT genes and down-regulation of WAT genes. Upon validation of BAT transdifferentiation in vitro, experiments are being planned to investigate BAT transdifferentiation in vivo. This research has possible therapeutic applications to combat obesity and type 2 diabetes.
aMiami University Undergraduate Student, bMiami University Graduate Student