Title Analysis of the Putative Role of CR 1 in Alzheimer ' s Disease : Genetic Association , Expression and Function Permalink

Chronic activation of the complement system and induced inflammation are associated with neuropathology in Alzheimer’s disease (AD). Recent large genome wide association studies (GWAS) have identified single nucleotide polymorphisms (SNPs) in the C3b/C4b receptor (CR1 or CD35) that are associated with late onset AD. Here, anti-CR1 antibodies (Abs) directed against different epitopes of the receptor, were used to localize CR1 in brain, and relative binding affinities of the CR1 ligands, C1q and C3b, were assessed by ELISA. Most Abs tested stained red blood cells in blood vessels but showed no staining in brain parenchyma. However, two monoclonal anti-CR1 Abs labeled astrocytes in all of the cases tested, and this reactivity was preabsorbed by purified recombinant human CR1. Human brain-derived astrocyte cultures were also reactive with both mAbs. The amount of astrocyte staining varied among the samples, but no consistent difference was conferred by diagnosis or the GWAS-identified SNPs rs4844609 or rs6656401. Plasma levels of soluble CR1 did not correlate with diagnosis but a slight increase was observed with rs4844609 and rs6656401 SNP. There was also a modest but statistically significant increase in relative binding activity of C1q to CR1 with the rs4844609 SNP compared to CR1 without the SNP, and of C3b to CR1 in the CR1 genotypes containing the rs6656401 SNP (also associated with the larger isoform of CR1) regardless of clinical diagnosis. These results suggest that it PLOS ONE | DOI:10.1371/journal.pone.0149792 February 25, 2016 1 / 21 OPEN ACCESS Citation: Fonseca MI, Chu S, Pierce AL, Brubaker WD, Hauhart RE, Mastroeni D, et al. (2016) Analysis of the Putative Role of CR1 in Alzheimer’s Disease: Genetic Association, Expression and Function. PLoS ONE 11(2): e0149792. doi:10.1371/journal. pone.0149792 Editor: Mark D. Zabel, Colorado State University, College of Veterinary Medicine and Biomedical Sciences, UNITED STATES Received: October 29, 2015 Accepted: February 4, 2016 Published: February 25, 2016 Copyright: © 2016 Fonseca et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Funding: This work was supported by National Institutes of Health grants AG 00538 and NS35144 (AT), National Institutes of Health Grant P50 AG16573 (AIP), R01 AI041592 and P30 AR048335 (JPA), and AG039750 and AG007367 (JR). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. is unlikely that astrocyte CR1 expression levels or C1q or C3b binding activity are the cause of the GWAS identified association of CR1 variants with AD. Further careful functional studies are needed to determine if the variant-dictated number of CR1 expressed on red blood cells contributes to the role of this receptor in the progression of AD, or if another mechanism is involved.