Low-Density Lipoprotein (LDL) Receptor/Transferrin Fusion Protein: In Vivo Production and Functional Evaluation as a Potential Therapeutic Tool for Lowering Plasma LDL Cholesterol

Abstract

A soluble form of human low-density lipoprotein receptor (LDL-R) fused in frame with rabbit transferrin (LDL-Rs_hu/Tf_rab) is assessed in vivo as a therapeutic tool for lowering plasma LDL cholesterol. The cDNA encoding LDL-Rs_hu/Tf_rab is expressed in mice, using a hydrodynamics-based gene transfer procedure. The transgene is transcribed in the liver of transduced animals and the corresponding protein is secreted into the bloodstream. Circulating LDL-Rs_hu/Tf_rab binds LDL specifically, thus indicating that it is correctly processed through the cellular compartments in vivo. More importantly, the expression of LDL-Rs_hu/Tf_rab allows the removal of injected human ¹²⁵I-labeled LDL (¹²³I-LDL) from the bloodstream of transduced CD1 mice, which show faster LDL plasma clearance, anticipating by approximately 90 min the same clearance value observed in control animals. A similar effect is observed in transduced LDL-R^-/- mice, in which the clearance of injected human LDL depends solely on the presence of circulating LDL-Rs_hu /Tf_rab. In these animals the extent of plasma LDL clearance is directly related to the concentration of LDL-Rs_hu/Tf_rab in the blood. Finally, LDL-Rs_hu/Tf_rab does not alter the pattern of LDL organ distribution: in transduced animals, as well as in control animals, liver and bladder are the predominantly labeled organs after ¹²³I-LDL injection. However, LDL-Rs_hu/Tf_rab has a quantitative effect on LDL tissue deposition: in treated animals LDL-Rs_hu/Tf_rab determines an increase in radioactivity in the liver at early times after ¹²³I-LDL injection and a progressive labeling of the bladder, starting 20 min after injection.