A Lipoprotein Receptor Cluster IV Mutant Preferentially Binds Amyloid-β and Regulates Its Clearance from the Mouse Brain

Soluble low density lipoprotein receptor-related protein-1 (sLRP1) binds similar to 70% of amyloid beta-peptide (A beta) in human plasma. In Alzheimer disease (AD) and individuals with mild cognitive impairment converting to AD, plasma sLRP1 levels are reduced and sLRP1 is oxidized, which results in diminished A beta peripheral binding and higher levels of free A beta in plasma. Experimental studies have shown that free circulating A beta re-enters the brain and that sLRP1 and/or its recombinant wild type cluster IV (WT-LRPIV) prevent A beta from entering the brain. Treatment of Alzheimer APPsw(+/0) mice with WT-LRPIV has been shown to reduce brain A beta pathology. In addition to A beta, LRPIV binds multiple ligands. To enhance LRPIV binding for A beta relative to other LRP1 ligands, we generated a library of LRPIV-derived fragments and full-length LRPIV variants with glycine replacing aspartic acid residues 3394, 3556, and 3674 in the calcium binding sites. Compared with WT-LRPIV, a lead LRPIV-D3674G mutant had 1.6- and 2.7-fold higher binding affinity for A beta 40 and A beta 42 in vitro, respectively, and a lower binding affinity for other LRP1 ligands (e.g. apolipoprotein E2, E3, and E4 (1.3-1.8-fold), tissue plasminogen activator (2.7-fold), matrix metalloproteinase-9 (4.1-fold), and Factor Xa (3.8-fold)). LRPIV-D3674G cleared mouse endogenous brain A beta 40 and A beta 42 25-27% better than WT-LRPIV. A 3-month subcutaneous treatment of APPsw(+/0) mice with LRPIV-D3674G (40 mu g/kg/day) reduced A beta 40 and A beta 42 levels in the hippocampus, cortex, and cerebrospinal fluid by 60-80% and improved cerebral blood flow responses and hippocampal function at 9 months of age. Thus, LRPIV-D3674G is an efficient new A beta clearance therapy.