Bacteria-Derived Recombinant Human ANGPTL8/Betatrophin Significantly Increases the Level of Triglyceride.

ANGPTL8/Betatrophin has been implicated in the regulation of both glucose and triglyceride metabolism. However, its role in regulating glucose metabolism by promoting ß cell proliferation remains controversial, and its physiological functions and molecular targets are largely unknown. Hence, it is of great importance to make recombinant protein and test its effects on ß cell mass directly. In this study, the mature form gene of human ANGPTL8/betatrophin was obtained through chemical synthesis on to the vector pUCE, and the fusion protein was expressed in the Transetta (DE3)/pEASY-E2-betatrophin strain. The inclusion bodies were solubilized in urea and purified by Ni-NTA affinity chromatography. The yield of purified ANGPTL8/betatrophin was approximately 20 mg per liter of culture medium. In vitro studies revealed that the recombinant ANGPTL8/betatrophin had no proliferation effect on MIN6 cells but promoted TG levels in HepG2 cells. This method to generate bioactive ANGPTL8/betatrophin is a simple, practical and user-friendly protocol.

On the mechanism of angiopoietin-like protein 8 for control of lipoprotein lipase activity.

Angiopoietin-like (ANGPTL) 8 is a secreted inhibitor of LPL, a key enzyme in plasma triglyceride metabolism. It was previously reported that ANGPTL8 requires another member of the ANGPTL family, ANGPTL3, to act on LPL. ANGPTL3, much like ANGPTL4, is a physiologically relevant regulator of LPL activity, which causes irreversible inactivation of the enzyme. Here, we show that ANGPTL8 can form complexes with either ANGPTL3 or ANGPTL4 when the proteins are refolded together from their denatured states. In contrast to the augmented inhibitory effect of the ANGPTL3/ANGPTL8 complex on LPL activity, the ANGPTL4/ANGPTL8 complex is less active compared with ANGPTL4 alone. In our experiments, all three members of the ANGPTL family use the same mechanism to inactivate LPL, which involves dissociation of active dimeric LPL to monomers. This inactivation can be counteracted by the presence of glycosylphosphatidylinositol-anchored HDL binding protein 1, the endothelial LPL transport protein previously known to protect LPL from spontaneous and ANGPTL4-catalyzed inactivation. Our data demonstrate that ANGPTL8 may function as an important metabolic switch, by forming complexes with ANGPTL3, or with ANGPTL4, in order to direct the flow of energy from triglycerides in blood according to the needs of the body.