Isolation and Characterization of a Novel Rat Factor H-related Protein That Is Up-regulated in Glomeruli under Complement Attack

Abstract

The factor H family in humans is composed of seven distinct proteins, including factor H-related proteins (FHR) 1-5. All members contain tandemly arranged short consensus repeats (SCR) typical of the regulators of complement activation gene family. FHR-5 is unusual for this group of proteins, as it was initially identified as a component of immune deposits in glomerular diseases. During our cloning of the cDNA for rat factor H from glomerular epithelial cells (GEC), we identified an alternative 2729-bp cDNA transcript. The translated sequence encoded a protein containing 11 SCRs, most similar to SCRs 7-15 and 19 -20 in native rat factor H, which is the same basic structure of human FHR-5. As such, this rat protein was termed FHR. Recombinant rat FHR produced in a eukaryotic expression system had a molecular mass of 78 kDa. In functional studies, recombinant FHR bound C3b and inhibited the complement alternative pathway in a dose-dependent fashion. Given the prominent expression of FHR-5 in human membranous nephropathy, a disease in which complement activation occurs in the vicinity of GEC, the expression of FHR in a rat model of this disease was evaluated. In both in vitro and in vivo models of complement activation on the GEC, FHR mRNA was up-regulated by a factor of 3-6-fold compared with controls in which complement could not be activated. Thus, we have identified a novel factor H family member in rats. This FHR protein is analogous to human FHR-5, both in structure and in potential involvement in glomerular immune complex diseases.

Mouse Podocyte Complement Factor H

“…Bound antibodies were detected with enhanced chemiluminescence (Pierce Biotechnology, Rockford, IL). On the basis of our previous studies, this anti-human Cfh antibody cross-reacts with both rat and mouse Cfh (11,18,29), as well as rat factor H-related protein (30), consistent with the relatedness of the various proteins within and between species (31,32).…”

“…WT kidneys in a Cfh Ϫ/Ϫ host had faintly detectable Cfh ( Figure 2B), which is consistent with localized renal production of Cfh (addressed in the next section). Also of importance from these studies using anti-Cfh antibodies are the absence of alternative forms of Cfh in Cfh Ϫ/Ϫ serum or kidneys, such as Cfh-like or related proteins that can have complement regulatory activity (30,32,39,40). WT kidneys that were transplanted into Cfh Ϫ/Ϫ mice and followed by induction of CSS uniformly developed diffuse proliferative GN ( Figure 3B), with features identical to those that were seen in previous studies in Cfh Ϫ/Ϫ mice with this model (18,19).…”

Binding of Human Factor H–Related Protein 1 to Serum‐ResistantBorrelia burgdorferiIs Mediated by Borrelial Complement Regulator–Acquiring Surface Proteins

“…The precise function(s) of the FHR proteins is currently under investigation. FHR genes are conserved in evolution and have been identified in humans, chimpanzees, rats, mice, and the bony fish barred sand bass [12,13].…”

LfhA, a Novel Factor H-Binding Protein of Leptospira interrogans

“…Mammals also produce several factor H-related proteins (FHRs), from distinct genes, which share sequence similarity with the carboxy terminus of factor H (45,62). The FHRs are not yet well characterized but appear to also possess complement-regulatory functions (20,39,49,62). Terminal sialic acid moieties on vertebrate cell glycoproteins serve as receptors to bind factor H and related proteins to cell surfaces, where they serve to protect those cells against the deleterious effects of C3 activation (23,61).…”