Biological Activity of Asp-hemolysin as a Regulation Factor to Atherogenic Effect by Oxidized Low-Density Lipoprotein

Abstract

Oxidatively modified low-density lipoprotein (OxLDL) is present in atherosclerotic lesions and has been proposed to play an important role in atherogenesis. Asp-hemolysin, a hemolytic toxin from Aspergillus fumigatus, is a binding protein for OxLDL. This study was undertaken to clarify the biological activity of OxLDL and the potentially of Asp-hemolysin as a regulation factor to atherogenic effect by OxLDL. We first analyzed the interaction between OxLDL and blood coagulation factors, which are involved in the blood coagulation pathway. OxLDL caused prolongation of activated partial thromboplastin time (APTT) as a parameter of the intrinsic pathway of blood coagulation in a dose- and oxidation time-dependent manner. In addition, OxLDL significantly inhibited blood coagulation factor VIII, IX, and XI activity. Furthermore, we demonstrated that factor VIII binds to OxLDL. These results indicate that the binding of factor VIII to OxLDL affects the intrinsic pathway of the blood coagulation cascade. Next, to clarify the structure-function relationship of Asp-hemolysin, we expressed Asp-hemolysin in Escherichia coli as a fusion protein with a maltose-binding protein (MBP) and purified it by affinity chromatography. The purified recombinant Asp-hemolysin showed an immunoreactivity with the anti-Asp-hemolysin antibody. In addition, MBP-Asp-hemolysin fusion protein exhibited binding activity to Ox-LDL as did native Asp-hemolysin. Furthermore, to investigate the effect of the Asp-hemolysin-related peptide (P-21), a synthetic peptide derived from a region of Asp-hemolysin that is rich in positive charges, on macrophage proliferation induced by OxLDL. P-21 inhibited OxLDL-induced macrophage proliferation in a dose-dependent manner. In addition, the binding analysis of P-21 to OxLDL indicated that P-21 binds to OxLDL. These results indicate that P-21 inhibits the OxLDL-induced macrophage proliferation through binding of P-21 to OxLDL. In conclusion, we have shown that OxLDL affects the intrinsic pathway of blood coagulation, and its mechanism is dependent on the binding of factor VIII to OxLDL. Furthermore, we indicate the possibility that Asp-hemolysin is a useful tool to investigate the pathophysiological significance of OxLDL. In particular, since the P-21, an Asp-hemolysin-related peptide, inhibits the OxLDL-induced macrophage proliferation through binding of P-21 to OxLDL, further study on the binding mechanism between Asp-hemolysin-related peptide and OxLDL may provide important information on the prevention and treatment of atherosclerosis.