Hormonal Functions of Cthrc1 Figure 8. Pharmacokinetic properties of Cthrc1. (A) Clearance curve of 125I-Cthrc1 injected intra-arterially into Cthrc1 mice. The half-life of the protein was calculated to be 146 min. (B) SDS-PAGE and autoradiographic analysis of plasma 30 min after 125I-Cthrc1 injection. Monomeric, dimeric and higher molecular weight forms of Cthrc1 were detectable. (C) 125I-Cthrc1 content in various tissues 6 h after injection. doi:10.1371/journal.pone.0047142.g008 Discussion We originally discovered Cthrc1 in a screen for genes upregulated in balloon-injured arteries, where it was highly induced in activated adventitial cells. Database searches and sequence alignments revealed that Cthrc1 is a highly conserved and unique gene in chordates with no homologues found in lower species such as flies or worms [1]. With adiponectin and other members of the C1q/TNF-related protein (CTRP) family Cthrc1 shares the presence of a short N terminal collagen domain but it lacks the characteristic C1q domain that defines the CTRP family of proteins [9]. Cthrc1 and adiponectin are similar in molecular mass, 243 and 244 amino acids, respectively. Like adiponectin, we demonstrate here that Cthrc1 is a circulating hormone that forms high molecular weight complexes [10,11], although the signifi- cance of the different Cthrc1 molecular weight complexes needs to be determined. Yamamoto et al. [2] reported an interaction of Cthrc1 with the planar cell polarity pathway (PCP) of non-canonical WNT signaling. The authors’ reasoning for investigating an involvement of Cthrc1 in the PCP pathway was based on the fact that the Figure 9. Cthrc1 detection in human plasma. A pull-down assay with monoclonal Cthrc1 antibody coupled to magnetic beads was performed on human plasma samples (#1–#4). (A) The eluate was analyzed by Western blotting with HRP-conjugated anti-Cthrc1 antibody, conditioned medium from hCthrc1 expressing CHO-K1 cells was used as a positive control. No Cthrc1 was detectable in the unbound plasma fraction (note absence of non-specific bands). (B) The eluates from plasma samples #2–#4 were immunoblotted with biotin-conjugated anti-Cthrc1 antibody followed by HRP-conjugated streptavidin. doi:10.1371/journal.pone.0047142.g009 PLOS ONE | www.plosone.org 9 October 2012 | Volume 7 | Issue 10 | e47142