Complement Protein C1q Forms a Complex with Cytotoxic Prion Protein Oligomers

Abstract

A growing number of studies have investigated the interaction between C1q and PrP, but the oligomeric form of PrP involved in this interaction remains to be determined. Aggregation of recombinant full-length murine PrP in the presence of 100 mM NaCl allowed us to isolate three different types of oligomers by size-exclusion chromatography. In contrast to PrP monomers and fibrils, these oligomers activate the classical complement pathway, the smallest species containing 8 -15 PrP protomers being the most efficient. We used Thioflavine T fluorescence to monitor PrP aggregation and showed that, when added to the reaction, C1q has a cooperative effect on PrP aggregation and leads to the formation of C1q-PrP complexes. In these complexes, C1q interacts through its globular domains preferentially with the smallest oligomers, as shown by electron microscopy, and retains the ability to activate the classical complement pathway. Using two cell lines, we also provide evidence that C1q inhibits the cytotoxicity induced by the smallest PrP oligomers. The cooperative interaction between C1q and PrP could represent an early step in the disease, where it prevents elimination of the prion seed, leading to further aggregation.Prion diseases represent a group of singular transmissible neurodegenerative disorders that affect mammals and occur when the cellular prion protein (PrP c ) 2 is converted into an abnormal aggregated isoform called PrP Sc (1). The host PrP c is an ␣-helix-rich 30 -35-kDa glycoprotein expressed mainly in neuronal tissues in humans and other animals (2). Its expression and membrane attachment through a glycosylphosphatidyl anchor are crucial for transmissible spongiform encephalopathy susceptibility (3). The widely supported protein-only hypothesis stipulates that the infectious agent can replicate by converting the natively folded prion protein (PrP c ). During the disease, changes occur in the secondary and tertiary structure of PrP c , resulting in an increased content of the ␤-sheet, which leads to the formation of aggregates that display a dramatic shift in their physicochemical properties compared with those of the original protein (4). These ␤-sheet-rich aggregates are resistant to degradation by proteases and tend to form oligomers that can further assemble into amyloid fibrils. Recent investigations support the hypothesis that in protein misfolding and aggregation pathologies like Alzheimer disease, smaller subfibrillar particles may be much more pathological than larger amyloid fibrils or plaques (5). In line with this hypothesis, Silveira and colleagues have reported that the smallest aggregate able to initiate transmissible spongiform encephalopathies pathology is equivalent to ϳ14 -28 PrP molecules (6). In the past, several in vitro recombinant models have been used to investigate the biochemical and biophysical properties of such oligomeric intermediates (7-10). C1q is the first component of the classical complement pathway. C1q binds to many non-self and altered-self-materials. These include mi...

Emerging and Novel Functions of Complement Protein C1q

“…C1q has been found to enhance formation of PrP oligomers and form complexes with these PrP oligomers via its gC1q domain. This complex has the ability to activate classical pathway, and this is considered to prevent neuronal cell death caused by these oligomers of PrP ( 51 ). However, this interaction is considered to prevent the elimination of prion seed, thereby increasing its aggregation.…”

The role of genetics in chronic wasting disease of North American cervids

“…53,54 Several studies have evaluated the interaction between prion disease and the immune complement system, presumably because circulating or cell-associated β-sheet rich PrP oligomers fix components of the classical cascade. 55 However, both rodent TSE models 56 and studies of the C1q gene in white-tailed deer 57 found no association between complement genetics and CWD. Although, one study found that microsatellite markers linked to the neurofibromin 1 gene were associated with CWD status in mule deer, indicating that there may be genomic interactions beyond the Prnp gene.…”

Reaction of complement factors varies with prion strains in vitro and in vivo

“…However, some previous studies have reported that complement factors C1q and C3 have anti-apoptotic and neuroprotective effects as well (Rus et al, 1996; Dashiell et al, 2000; Benoit and Tenner, 2011). Interestingly, Erlich et al (2010) suggested that C1q binds small oligomers derived from murine recombinant PrP and inhibits cytotoxic effects of PrP oligomers. It is possible that complement factors have both neurotoxic and neuroprotective effects and that the role of the complement factors may be different depending on the stage of the disease.…”

“…Flores-Langarica et al (2009) demonstrated that C1q is involved in PrP Sc uptake into conventional dendritic cells, which have an important role in the prion propagation from the peripheral tissue to the CNS. Direct binding of C1q to amyloid fibrils, beta-oligomers prepared from human or mouse recombinant PrP and purified PrP Sc , resulting in activation of the classical complement pathway, has been demonstrated in vitro, suggesting that prion infection induces complement activation (Blanquet-Grossard et al, 2005; Dumestre-Perard et al, 2007; Mitchell et al, 2007; Sim et al, 2007; Sjoberg et al, 2008; Erlich et al, 2010). …”