Abstract
Angiopoietin-like 3 (ANGPTL3) is a secreted protein that is mainly expressed in the liver and regulates lipid metabolism by inhibiting the lipolysis of triglyceriderich lipoproteins. Using deletion mutants of human ANGPTL3, we demonstrated that the N-terminal coiled-coil domain-containing fragment-(17-207) and not the C-terminal fibrinogen-like domain-containing fragment-(207-460) increased the plasma triglyceride levels in mice. We also found that the N-terminal region 17-165 was required to increase plasma triglyceride levels in mice and that a substitution of basic amino acid residues in the region 61-66 of the fragment showed no increase in the plasma triglyceride levels and no inhibition of lipolysis by lipoprotein lipase. In addition, when we analyzed ANGPTL3 in human plasma, we detected cleaved fragments of ANGPTL3. By analyzing recombinant ANGPTL3 in mouse plasma, we found that it was cleaved at two sites, Arg221 downward arrow Ala222 and Arg224 downward arrow Thr225, which are located in the linker region between the coiled-coil domain and the fibrinogen-like domain. Furthermore, a cleavage-resistant mutant of ANGPTL3 was determined to be less active than wild-type ANGPTL3 in increasing mouse plasma triglyceride levels but not in inhibiting lipoprotein lipase activity. These findings suggest that the cleavage of ANGPTL3 is important for the activation of ANGPTL3 in vivo.
Highlights
Angiopoietin-like 3 (ANGPTL3) is a secreted protein that is mainly expressed in the liver and regulates lipid metabolism by inhibiting the lipolysis of triglyceriderich lipoproteins
By analyzing recombinant ANGPTL3 in mouse plasma, we found that it was cleaved at two sites, Arg2212Ala[222] and Arg2242Thr[225], which are located in the linker region between the coiled-coil domain and the fibrinogen-like domain
The C-terminal fibrinogen-like domain (FLD) of ANGPTL3 was reported to be involved in angiogenesis via binding to integrin ␣V3 (6), but the domain of ANGPTL3 that is involved in the regulation of lipid metabolism has not been elucidated
Summary
Angiopoietin-like 3 (ANGPTL3) is a secreted protein that is mainly expressed in the liver and regulates lipid metabolism by inhibiting the lipolysis of triglyceriderich lipoproteins. Injection of recombinant ANGPTL3 or adenoviruses encoding ANGPTL3 resulted in an increase of plasma lipid levels in mice. The recombinant proteins were detected in the plasma of mice injected with Ad/ANGPTL3-(17– 207) and Ad/ANGPTL3-(207– 460) (Fig. 1C).
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