A study on fat browning effect of white adipocyte-targeted recombinant fusion protein

Abstract

Obesity causes many diseases such as cardiovascular diseases, metabolic diseases, and various cancers, and is the route of many deaths. In obese patients, the plasma transforming growth factor-β (TGF-β) level is higher than normal people, and TGF-β/ Smad3 signaling is also high in white adipose tissue (WAT). TGF-β/Smad3 signaling pathway is known to maintain WAT-associated gene expression such as Leptin and inhibit brown adipose tissue (BAT)-associated gene expression such as UCP-1 in WAT. If this signaling is reduced, the expression of WAT-associated genes will be decreased while the expression of BAT-associated genes will be increased, leading to a “fat browning effect”. The Src homology 3 (SH3), a domain of Sorting nexin 9 (SNX9), can specifically bind to phospho-Smad3 (pSmad3) phosphorylated by TGF-β and is expected to interfere with transcriptional regulation of pSmad3. To confirm the therapeutic effect of SH3 by binding to pSmad3 and inhibiting TGF-β/Smad3 signaling in WAT, prohibitin targeting sequence (PTS) and a nona-arginine (9R), a cell penetrating peptide (CPP), were expressed using a recombinant fusion protein form at the N-terminal of SH3 (PTS-9R-SH3). In this study, various in vitro kinetic studies were conducted to examine the SH3 fusion protein binding effect to pSmad3 for effective obesity treatment via fat browning effect. We conducted several in vitro experiments to demonstrate the therapeutic effect of PTS-9R-SH3 binding to the pSmad3 in mature adipocytes and concluded that targeting the nucleus-accumulated pSmad3 holds a promising therapeutic effect for browning.