Inhibition of Experimental Autoimmune Encephalomyelitis in Human C-Reactive Protein Transgenic Mice Is FcγRIIB Dependent

We showed earlier that experimental autoimmune encephalomyelitis (EAE) in human C-reactive protein (CRP) transgenic mice (CRPtg) has delayed onset and reduced severity compared to wild-type mice. Since human CRP is known to engage Fc receptors and Fc receptors are known to play a role in EAE in the mouse, we sought to determine if FcγRI, FcγRIIb, or FcγRIII was needed to manifest human CRP-mediated protection of CRPtg. We report here that in CRPtg lacking either of the two activating receptors, FcγRI and FcγRIII, the beneficial effects of human CRP are still observed. In contrast, if CRPtg lack expression of the inhibitory receptor FcγRIIB, then the beneficial effect of human CRP is abrogated. Also, subcutaneous administration of purified human CRP stalled progression of ongoing EAE in wild-type mice, but similar treatment failed to impede EAE progression in mice lacking FcγRIIB. The results reveal that a CRP → FcγRIIB axis is responsible for protection against EAE in the CRPtg model

Characterization of ubiquitin-proteasome dynamics in Caenorhabditis elegans muscle cells during protein-folding stress

In order to adapt to changing conditions and life stages, cells must remodel the composition of the proteome by specifically removing obsolete or damaged proteins. Failure to remove proteins at the appropriate time can cause a variety of cellular dysfunctions that can lead to cell death and conditions such as cancer, Huntington's, Parkinson's and Alzheimer's disease. Protein quality control is especially important during aging and stress, as the accumulating load of damaged, misfolded, and aggregated proteins can overwhelm the cell's ability to maintain the proteome. The ubiquitin-proteasome system is responsible for the specific degradation of many proteins within eukaryotic cells. The 26S proteasome degrades proteins that have been “tagged” with a chain of ubiquitin molecules. Ubiquitin is a highly-conserved 8.5 kDa protein that is conjugated post-translationally to a target protein after passing through a complex series of enzymes. Using the nematode C. elegans as a model, we sought to 1) Characterize the roles of specific ubiquitin-conjugation enzymes (UBCs) in the response to aggregation of a polyglutamine-containing protein in body wall muscle cells and 2) Examine the subcellular localization of proteasomes in these cells during normal aging and stress. Q82::GFP, a fusion protein expressed from a transgene encoding a polyglutamine tract fused to Green Fluorescent Protein (GFP), was found to aggregate rapidly (~58 minutes) in a manner that is not directly dependent on ubiquitin but dependent on the concentration of Q82::GFP protein, which was altered in response to RNA interference of several E2 ubiquitin-conjugating enzymes. In a separate transgenic worm strain, a fluorescently-labeled proteasome subunit, RPT-1, was observed in live animals to localize to the nucleus and cytoplasm during the adult stage. Within the nucleus, RPT-1::GFP localizes diffusely and to foci, and was excluded from heterochromatin. Within the muscle contractile apparatus, RPT-1::GFP localizes to I-bands, regions of thin actin filaments, and is excluded from dense bodies. After a prolonged heat stress, RPT-1::GFP in adult worms relocalizes to dense bodies. After starvation, these foci are associated with high proteolytic activity. These studies demonstrate some of the spatial dynamics of the ubiquitin-proteasome system in response to development, aging, and stress

Exaggerated Neointima Formation in Human C-Reactive Protein Transgenic Mice Is IgG Fc Receptor Type I (FcγRI)-Dependent

Neointima formation after vascular injury is exaggerated in ovariectomized (OVX) human C-reactive protein transgenic mice (CRPtg) compared to nontransgenic mice (NTG). We tested the hypothesis that this CRP-mediated exacerbation requires IgG Fc receptors (FcγRs). OVX NTG, CRPtg, and CRPtg lacking FcγRI, FcγRIIb, FcγRIII, or the common γ chain (FcRγ) had their common carotid artery ligated. Twenty-eight days later neointimal thickening in CRPtg/FcγRI−/− and CRPtg/FcRγ−/− was significantly less than in CRPtg and no worse than in NTG, whereas in CRPtg/FcγRIIb−/− and CRPtg/FcγRIII−/− neointimal thickness was equal to or greater than in CRPtg. Immunohistochemistry revealed human CRP in the neointima of CRPtg, but little or none was observed in those lacking FcγRI or FcRγ. Real-time reverse transcriptase-polymerase chain reaction demonstrated that FcγR types I to III were expressed in the CRPtg arteries, with FcγRI expression increasing by threefold after ligation injury. Levels of serum complement (C3), neointimal deposition of complement (C3d), and cellular composition (monocytes, macrophages, lymphocytes) in the neointima did not differ among the different CRPtg genotypes. However, by immunofluorescence a neointimal population of F4/80+CRP+ cells was revealed only in OVX CRPtg. The exaggerated response to vascular injury provoked by CRP in OVX CRPtg depends on FcγRI and probably requires its expression by F4/80+ cells

Spongiform Neurodegeneration-associated E3 Ligase Mahogunin Ubiquitylates TSG101 and Regulates Endosomal Trafficking

A null mutation in the gene encoding the putative E3 ubiquitin–protein ligase Mahogunin causes spongiform neurodegeneration, a recessively transmitted prion-like disease in mice. However, no substrates of Mahogunin have been identified, and the cellular role of Mahogunin is unknown. Here, we report the identification of TSG101, a key component of the endosomal sorting complex required for transport (ESCRT)-I, as a specific Mahogunin substrate. We find that Mahogunin interacts with the ubiquitin E2 variant (UEV) domain of TSG101 via its PSAP motif and that it catalyzes monoubiquitylation of TSG101 both in vivo and in vitro. Depletion of Mahogunin by small interfering RNAs in mammalian cells disrupts endosome-to-lysosome trafficking of epidermal growth factor receptor, resulting in prolonged activation of a downstream signaling cascade. Our findings support a role for Mahogunin in a proteasome-independent ubiquitylation pathway and suggest a link between dysregulation of endosomal trafficking and spongiform neurodegeneration

Sensitivity of revised diagnostic criteria for the behavioural variant of frontotemporal dementia

Based on the recent literature and collective experience, an international consortium developed revised guidelines for the diagnosis of behavioural variant frontotemporal dementia. The validation process retrospectively reviewed clinical records and compared the sensitivity of proposed and earlier criteria in a multi-site sample of patients with pathologically verified frontotemporal lobar degeneration. According to the revised criteria, 'possible' behavioural variant frontotemporal dementia requires three of six clinically discriminating features (disinhibition, apathy/inertia, loss of sympathy/empathy, perseverative/compulsive behaviours, hyperorality and dysexecutive neuropsychological profile). 'Probable' behavioural variant frontotemporal dementia adds functional disability and characteristic neuroimaging, while behavioural variant frontotemporal dementia 'with definite frontotemporal lobar degeneration' requires histopathological confirmation or a pathogenic mutation. Sixteen brain banks contributed cases meeting histopathological criteria for frontotemporal lobar degeneration and a clinical diagnosis of behavioural variant frontotemporal dementia, Alzheimer's disease, dementia with Lewy bodies or vascular dementia at presentation. Cases with predominant primary progressive aphasia or extra-pyramidal syndromes were excluded. In these autopsy-confirmed cases, an experienced neurologist or psychiatrist ascertained clinical features necessary for making a diagnosis according to previous and proposed criteria at presentation. Of 137 cases where features were available for both proposed and previously established criteria, 118 (86%) met 'possible' criteria, and 104 (76%) met criteria for 'probable' behavioural variant frontotemporal dementia. In contrast, 72 cases (53%) met previously established criteria for the syndrome (P < 0.001 for comparison with 'possible' and 'probable' criteria). Patients who failed to meet revised criteria were significantly older and most had atypical presentations with marked memory impairment. In conclusion, the revised criteria for behavioural variant frontotemporal dementia improve diagnostic accuracy compared with previously established criteria in a sample with known frontotemporal lobar degeneration. Greater sensitivity of the proposed criteria may reflect the optimized diagnostic features, less restrictive exclusion features and a flexible structure that accommodates different initial clinical presentations. Future studies will be needed to establish the reliability and specificity of these revised diagnostic guidelines