Knockout of the cellular prion protein (PrPC) in mice is tolerated, as is complete elimination of the protein’s N-terminal domain. However, deletion of select short segments between the N- and C-terminal domains is lethal. How can one reconcile this apparent paradox? Research over the last few years demonstrates that PrPC undergoes α-cleavage in the vicinity of residue 109 (mouse sequence) to release the bioactive N1 and C1 fragments. In biophysical studies, we recently characterized the action of relevant members of the ADAM (A Disintegrin And Metalloproteinase) enzyme family (ADAM8, 10, and 17) and found that they all produce α-cleavage, but at 3 distinct cleavage sites, with proteolytic efficiency modulated by the physiologic metals copper and zinc. Remarkably, the shortest lethal deletion segment in PrPC fully encompasses the three α-cleavage sites. Analysis of all reported PrPC deletion mutants suggests that elimination of α-cleavage, coupled with retention of the protein’s N-terminal residues, segments 23–31 and longer, confers the lethal phenotype. Interestingly, these N-terminal residues are implicated in the activation of several membrane proteins, including synaptic glutamate receptors. We propose that α-cleavage is a general mechanism essential for downregulating PrPC’s intrinsic activity, and that blockage of proteolysis leads to constitutively active PrPC and consequent dyshomeostasis.
ADAM enzyme; AMPA receptor; Alzheimer disease; copper; prion protein; zinc; α-cleavage
The universe of prion and prion-like phenomena has expanded significantly in the past several years. Here, we overview the challenges in classifying this data informatically, given that terms such as “prion-like”, “prion-related” or “prion-forming” do not have a stable meaning in the scientific literature. We examine the spectrum of proteins that have been described in the literature as forming prions, and discuss how “prion” can have a range of meaning, with a strict definition being for demonstration of infection with in vitro-derived recombinant prions. We suggest that although prion/prion-like phenomena can largely be apportioned into a small number of broad groups dependent on the type of transmissibility evidence for them, as new phenomena are discovered in the coming years, a detailed ontological approach might be necessary that allows for subtle definition of different “flavors” of prion / prion-like phenomena.
bioinformatics; database; classification; prion-like; prionoid; quasi-prion
We have demonstrated that prions accumulate to high levels in non-proliferative C2C12 myotubes. C2C12 cells replicate as myoblasts but can be differentiated into myotubes. Earlier studies indicated that C2C12 myoblasts are not competent for prion replication.1 We confirmed that observation and demonstrated, for the first time, that while replicative myoblasts do not accumulate PrPSc, differentiated post-mitotic myotube cultures replicate prions robustly. Here we extend our observations and describe the implication and utility of this system for replicating prions.
C2C12; PrP; Prnp; differentiation; muscle; myotube; prion; prion replication; scrapie
In several recent studies transmissible prion disease was induced in animals by inoculation with recombinant prion protein amyloid fibrils produced in vitro. Serial transmission of amyloid fibrils gave rise to a new class of prion strains of synthetic origin. Gradual transformation of disease phenotypes and PrPSc properties was observed during serial transmission of synthetic prions, a process that resembled the phenomenon of prion strain adaptation. The current article discusses the remarkable parallels between phenomena of prion strain adaptation that accompanies cross-species transmission and the evolution of synthetic prions occurring within the same host. Two alternative mechanisms underlying prion strain adaptation and synthetic strain evolution are discussed. The current article highlights the complexity of the prion transmission barrier and strain adaptation and proposes that the phenomenon of prion adaptation is more common than previously thought.
prion protein; prion diseases; synthetic prions; strain adaptation; species barrier; deformed templating mechanism; neurodegenerative diseases
Protein misfolding and aggregation underlie the pathogenesis of many neurodegenerative diseases. In addition to chaperone-mediated refolding and proteasomal degradation, the aggresome-macroautophagy pathway has emerged as another defense mechanism for sequestration and clearance of toxic protein aggregates in cells. Previously, the 14-3-3 proteins were shown to be indispensable for the formation of aggresomes induced by mutant huntingtin proteins. In a recent study, we have determined that 14-3-3 functions as a molecular adaptor to recruit chaperone-associated misfolded proteins to dynein motors for transport to aggresomes. This molecular complex involves a dimeric binding of 14-3-3 to both the dynein-intermediate chain (DIC) and an Hsp70 co-chaperone Bcl-2-associated athanogene 3 (BAG3). As 14-3-3 has been implicated in various neurodegenerative diseases, our findings may provide mechanistic insights into its role in managing misfolded protein stress during the process of neurodegeneration.
14-3-3; aggresomes; protein misfolding; protein aggregation; chaperones; inclusion bodies; neurodegeneration
One fundamental property of prions is the formation of strains—prions that have distinct biological effects, despite a common amino acid sequence. The strain phenomenon is thought to be caused by the formation of different molecular structures, each encoding for a particular biological activity. While the precise mechanism of the formation of strains is unknown, they tend to arise following environmental changes, such as passage between different species. One possible mechanism discussed here is heterogeneous seeding; the formation of a prion nucleated by a different molecular structure. While heterogeneous seeding is not the only mechanism of prion mutation, it is consistent with some observations on species adaptation and drug resistance. Heterogeneous seeding provides a useful framework to understand how prions can adapt to new environmental conditions and change biological phenotypes.
prion structure; self-propagation; amyloid; fiber diffraction; protein aggregation
Self-assembly of proteins and peptides into amyloid structures has been the subject of intense and focused research due to their association with neurodegenerative, age-related human diseases and transmissible prion diseases in humans and mammals. Of the disease associated amyloid assemblies, a diverse array of species, ranging from small oligomeric assembly intermediates to fibrillar structures, have been shown to have toxic potential. Equally, a range of species formed by the same disease associated amyloid sequences have been found to be relatively benign under comparable monomer equivalent concentrations and conditions. In recent years, an increasing number of functional amyloid systems have also been found. These developments show that not all amyloid structures are generically toxic to cells. Given these observations, it is important to understand why amyloid structures may encode such varied toxic potential despite sharing a common core molecular architecture. Here, we discuss possible links between different aspects of amyloidogenic structures and assembly mechanisms with their varied functional effects. We propose testable hypotheses for the relationship between amyloid structure and its toxic potential in the context of recent reports on amyloid sequence, structure, and toxicity relationships.
amyloid; amyloidosis; cross-β; cytotoxicity; deposition; fibril; oligomer; structure
Several neurodegenerative diseases are caused by defects in protein folding, including Alzheimer, Parkinson, Huntington, and prion diseases. Once a disease-specific protein misfolds, it can then form toxic aggregates which accumulate in the brain, leading to neuronal dysfunction, cell death, and clinical symptoms. Although significant advances have been made toward understanding the mechanisms of protein aggregation, there are no curative treatments for any of these diseases. Since protein misfolding and the accumulation of aggregates are the most upstream events in the pathological cascade, rescuing or stabilizing the native conformations of proteins is an obvious therapeutic strategy. In recent years, small molecules known as chaperones have been shown to be effective in reducing levels of misfolded proteins, thus minimizing the accumulation of aggregates and their downstream pathological consequences. Chaperones are classified as molecular, pharmacological, or chemical. In this mini-review we summarize the modes of action of different chemical chaperones and discuss evidence for their efficacy in the treatment of protein folding diseases in vitro and in vivo.
TUDCA; DCA; UDCA; PBA; osmolytes; protein folding diseases; chemical chaperones; protein misfolding
It was shown previously that truncated molecules of prion protein can be found in brains of patients with some types of transmissible spongiform encephalopathy. One such molecule, PrP226*, is a fragment of prion protein, truncated at Tyr226. It was found to be present in aggregates, from which it can be released using chaotropic salts. In this study we investigated the distribution of PrP226* in Creutzfeldt–Jakob disease affected human brain, employing the mAb V5B2, specifically recognizing this fragment. The results show that PrP226* is not evenly distributed among different regions of human brain. Among brain regions analyzed, the fragment was found most likely to be accumulated in the cerebellum. Its distribution correlates with the distribution of PrPSc.
PrP fragment; PrP226*; anchorless PrP; denaturation; immunoassay; mAb V5B2; regional distribution
Background/Objective: Recently, PrPc has been linked to AD pathogenesis. Second, a relation of PrPc plasma levels with cognitive status and decline of healthy elderly subjects has been reported. Therefore, we hypothesized baseline plasma levels of PrPc to be associated with AD progression in cognitive and functional domains.
Materials and Methods: AD patients (n = 84) were included into an observational study at time of diagnosis. Baseline plasma PrPc levels were determined. Decline was assessed annually (mean follow-up time 3 years) with the aid of different standardized tests (MMSE, iADL, bADL, GDS, UPDRSIII). Multiple regression analyses were used to uncover potential associations between decline and PrPc levels.
Results: No association of PrPc and decline could be established. Presence of diabetes mellitus was linked to slower deterioration. Intake of neuroleptic drugs or memantine was associated with faster progression.
Conclusion: Plasma PrPc at baseline could not be shown to be related to AD progression in this study. An interesting association of diabetes mellitus and decline warrants further investigation.
Alzheimer; prion protein; cognition; biomarker
Prion is a protein-conformation-based infectious agent causing fatal neurodegenerative diseases in humans and animals. Our previous studies revealed that in the presence of cofactors, infectious prions can be synthetically generated in vitro with bacterially expressed recombinant prion protein (PrP). Once initiated, the recombinant prion is able to propagate indefinitely via serial protein misfolding cyclic amplification (sPMCA). In this study, we compared 2 separately initiated recombinant prions. Our results showed that these 2 recombinant prions had distinct biochemical properties and caused different patterns of spongiosis and PrP deposition in inoculated mice. Our findings indicate that various recombinant prions can be initiated in vitro and potential reasons for this variability are discussed.
prion; sPMCA; recombinant PrP; recombinant prion; bioassay; histopathology; GuHCl denaturation assay
The conformational conversion of the cellular prion protein (PrPC) to the β-rich infectious isoform PrPSc is considered a critical and central feature in prion pathology. Although PrPSc is the critical component of the infectious agent, as proposed in the “protein-only” prion hypothesis, cellular components have been identified as important cofactors in triggering and enhancing the conversion of PrPC to proteinase K resistant PrPSc. A number of in vitro systems using various chemical and/or physical agents such as guanidine hydrochloride, urea, SDS, high temperature, and low pH, have been developed that cause PrPC conversion, their amplification, and amyloid fibril formation often under non-physiological conditions. In our ongoing efforts to look for endogenous and exogenous chemical mediators that might initiate, influence, or result in the natural conversion of PrPC to PrPSc, we discovered that lipopolysaccharide (LPS), a component of gram-negative bacterial membranes interacts with recombinant prion proteins and induces conversion to an isoform richer in β sheet at near physiological conditions as long as the LPS concentration remains above the critical micelle concentration (CMC). More significant was the LPS mediated conversion that was observed even at sub-molar ratios of LPS to recombinant ShPrP (90–232).
prion protein; protein misfolding; lipopolysaccharide; beta oligomer; fibril
Aggregation of α-synuclein plays a crucial role in the pathogenesis of synucleinopathies, a group of neurodegenerative diseases including Parkinson disease (PD), dementia with Lewy bodies (DLB), diffuse Lewy body disease (DLBD) and multiple system atrophy (MSA). The common feature of these diseases is a pathological deposition of protein aggregates, known as Lewy bodies (LBs) in the central nervous system. The major component of these aggregates is α-synuclein, a natively unfolded protein, which may undergo dramatic structural changes resulting in the formation of β-sheet rich assemblies. In vitro studies have shown that recombinant α-synuclein protein may polymerize into amyloidogenic fibrils resembling those found in LBs. These aggregates may be uptaken and propagated between cells in a prion-like manner. Here we present the mechanisms and kinetics of α-synuclein aggregation in vitro, as well as crucial factors affecting this process. We also describe how PD-linked α-synuclein mutations and some exogenous factors modulate in vitro aggregation. Furthermore, we present a current knowledge on the mechanisms by which extracellular aggregates may be internalized and propagated between cells, as well as the mechanisms of their toxicity.
alpha-synuclein; aggregation; Parkinson disease; prion-like features
The prion responsible for the Bovine Spongiform Encephalopathy (BSE) shows unique features when compared with other prions. One of these features is its ability to infect almost all experimentally tested animal models. In the paper published in The Journal of Neuroscience1 we describe a series of experiments directed toward elucidating which would be the in vivo behavior of BSE if it would infect dogs and rabbits, two alleged prion resistant species. Protein misfolding cyclic amplification (PMCA) was used to generate canidae and leporidae in vitro adapted BSE prions. A characterization of their in vivo pathobiological properties showed that BSE prions were capable not only of adapting to new species but they maintained, in the case of rabbits, their ability to infect transgenic mice expressing human PrP. The remarkable adaptation ability of certain prions implies that any new host species could lead to the emergence of new infectious agents with unpredictable transmission potential. Our results suggest that caution must be taken when considering the use of any mammal-derived protein in feedstuffs.
prion; BSE; scrapie; PMCA; transmission barrier; prion resistant species
The pathogenic mechanism of prion diseases remains unknown. We recently reported that prion infection disturbs post-Golgi trafficking of certain types of membrane proteins to the cell surface, resulting in reduced surface expression of membrane proteins and abrogating the signal from the proteins. The surface expression of the membrane proteins was reduced in the brains of mice inoculated with prions, well before abnormal symptoms became evident. Prions or pathogenic prion proteins were mainly detected in endosomal compartments, being particularly abundant in recycling endosomes. Some newly synthesized membrane proteins are delivered to the surface from the Golgi apparatus through recycling endosomes, and some endocytosed membrane proteins are delivered back to the surface through recycling endosomes. These results suggest that prions might cause neuronal dysfunctions and cell loss by disturbing post-Golgi trafficking of membrane proteins via accumulation in recycling endosomes. Interestingly, it was recently shown that delivery of a calcium channel protein to the cell surface was impaired and its function was abrogated in a mouse model of hereditary prion disease. Taken together, these results suggest that impaired delivery of membrane proteins to the cell surface is a common pathogenic event in acquired and hereditary prion diseases.
Prion; prion protein; post-Golgi membrane trafficking; insulin receptor; prion disease; neurodegeneration; attractin; Golgi apparatus
The capacity to polymerize into amyloid fibrils is common to many proteins. While some proteins naturally form these fibrils to serve functional roles, amyloid is usually associated with pathogenic processes in which specific proteins aberrantly aggregate within cells or tissues. Though the contribution of amyloid fibrils to actual disease pathogenesis is not always clear, one possibility is that the titration of essential proteins from solution into aggregates contributes to the cellular degeneration common to many amyloid diseases. Using mammalian and yeast model systems, we recently showed that the common biophysical properties of amyloid aggregates—including strong resistance to dissolution—enable stringent purification and identification of both amyloid-forming and amyloid-associated proteins directly from cells. Strikingly, many proteins that were previously implicated in formation or clearance of intracellular aggregates, including several stress granule components, were found to co-aggregate with amyloid formed by a polyglutamine-expanded huntingtin fragment. This direct evaluation of proteins within aggregates can help identify new amyloid-forming proteins, as well as proteins that can indirectly contribute to disease mechanisms.
amyloid; prion; yeast; protein aggregation; polyglutamine
Alzheimer disease is associated with the accumulation of oligomeric amyloid β peptide (Aβ), accompanied by synaptic dysfunction and neuronal death. Polymeric form of prion protein (PrP), PrPSc, is implicated in transmissible spongiform encephalopathies (TSEs). Recently, it was shown that the monomeric cellular form of PrP (PrPC), located on the neuron surface, binds Aβ oligomers (and possibly other β-rich conformers) via the PrP23–27 and PrP90–110 segments, acting as Aβ receptor. On the other hand, PrPSc polymers efficiently bind to Aβ monomers and accelerate their oligomerization. To identify specific PrP sequences that are essential for the interaction between PrP polymers and Aβ peptide, we have co-expressed Aβ and PrP (or its shortened derivatives), fused to different fluorophores, in the yeast cell. Our data show that the 90–110 and 28–89 regions of PrP control the binding of proteinase-resistant PrP polymers to the Aβ peptide, whereas the 23–27 segment of PrP is dispensable for this interaction. This indicates that the set of PrP fragments involved in the interaction with Aβ depends on PrP conformational state.
Alzheimer Disease; amyloid; prions; yeast; protein-protein interactions; FRET
The prion protein (PrP), a GPI-anchored glycoprotein, is inefficiently secreted by mammalian microsomes, 50% being found as transmembrane (TM) proteins with the central TM1 segment spanning the membrane. TM1 hydrophobicity is marginal for lateral membrane insertion, which is primarily driven by hydrophobic interaction between the ER translocon and substrates in transit. Most inserted TM1 has its N-terminus in the ER lumen (Ntm orientation), as expected for arrest of normal secretion. However, 20% is found in inverted Ctm orientation. These are minor species in vivo, presumably a consequence of efficient quality control. PrP mutations that increase TM1 hydrophobicity result in increased Ctm insertion, both in vitro and in mouse brain, and a strong correlation is found between CtmPrP insertion and neuropathology in transgenic mice; a copper-dependent pathogenicity mechanism is suggested. PrP fusions with a C-terminal epitope tag, when expressed in yeast cells at moderate levels, appear to interact efficiently with the translocon, providing a useful model for testing the effects of PrP mutations on TM insertion and orientation. However, secretion of PrP by the mammalian translocon requires the TRAP complex, absent in yeast, where essentially all PrP ends up as TM species, 85–90% Ntm and 10–15% Ctm. Although yeast is, therefore, an incomplete mimic of mammalian PrP trafficking, effects on Ctm insertion of mutations increasing TM1 hydrophobicity closely reflect those seen in vitro. Electrostatic substrate-translocon interactions are a major determinant of TM protein insertion orientation and the yeast model was used to investigate the role of the large negative charge difference across TM1, a likely cause of translocation delay that would favor TM insertion and Ctm orientation. An increase in ΔCh from −5 to −7 caused a marked increase in Ctm insertion, while a decrease to −3 or −1 allowed 35 and about 65% secretion, respectively. Utility of the yeast model and the role of this charge difference in driving PrP membrane insertion are confirmed.
charge difference; epitope tag fusion; pathogenicity mechanism; prion; transmembrane insertion orientation; yeast
Prions are notorious for their extraordinary resistance to traditional methods of decontamination, rendering their transmission a public health risk. Iatrogenic Creutzfeldt–Jakob disease (iCJD) via contaminated surgical instruments and medical devices has been verified both experimentally and clinically. Standard methods for prion inactivation by sodium hydroxide or sodium hypochlorite have failed, in some cases, to fully remove prion infectivity, while they are often impractical for routine applications. Prion accumulation in peripheral tissues and indications of human-to-human bloodborne prion transmission, highlight the need for novel, efficient, yet user-friendly methods of prion inactivation. Here we show both in vitro and in vivo that homogenous photocatalytic oxidation, mediated by the photo-Fenton reagent, has the potential to inactivate the pathological prion isoform adsorbed on metal substrates. Photocatalytic oxidation with 224 μg mL−1 Fe3+, 500 μg mL−1 h−1 H2O2, UV-A for 480 min lead to 100% survival in golden Syrian hamsters after intracranial implantation of stainless steel wires infected with the 263K prion strain. Interestingly, photocatalytic treatment of 263K infected titanium wires, under the same experimental conditions, prolonged the survival interval significantly, but failed to eliminate infectivity, a result that we correlate with the increased adsorption of PrPSc on titanium, in comparison to stainless steel. Our findings strongly indicate that our, user- and environmentally friendly protocol can be safely applied to the decontamination of prion infected stainless steel surfaces.
photocatalytic; photo-Fenton; prion; inactivation; decontamination; stainless steel
A sample of purified Syrian hamster PrP27–30 prion fibers was analyzed by synchrotron small-angle X-ray scattering (SAXS). The SAXS pattern obtained was fitted to a model based on infinitely long cylinders with a log-normal intensity distribution, a hard-sphere structure factor and a general Porod term for larger aggregates. The diameter calculated for the cylinders determined from the fit was 11.0 ± 0.2 nm. This measurement offers an estimation of the diameter of PrPSc fibers in suspension, i.e., free of errors derived from estimations based on 2D projections in transmission electron microscopy images, subjected to further possible distortions from the negative stain. This diameter, which corresponds to a maximum diameter of approximately 5.5 nm for each of the two intertwined protofilaments making up the fibers, rules out the possibility that PrPSc conforms to a stack of in-register, single-rung flat PrPSc monomers; rather, PrPSc subunits must necessarily coil, most likely several times, into themselves.
PrPSc structure; SAXS; synchrotron radiation; amyloid; prion; TEM
A minority of inherited prion diseases (IPD) are caused by four to 12 extra octapeptide repeat insertions (OPRI) in the prion protein gene (PRNP). Only four families affected by IPD with 8-OPRI have been reported, one of them was a three-generation Swedish kindred in which four of seven affected subjects had chorea which was initially attributed to Huntington’s disease (HD). Following the exclusion of HD, this phenotype was labeled Huntington disease-like 1 (HDL1). Here, we provide an update on the Swedish 8-OPRI family, describe the clinical features of one of its affected members with video-recordings, compare the four 8-OPRI families and study the effect of PRNP polymorphic codon 129 and gender on phenotype. Surprisingly, the Swedish kindred displayed the longest survival of all of the 8-OPRI families with a mean of 15.1 years from onset of symptoms. Subjects with PRNP polymorphic codon 129M in the mutated allele had significantly earlier age of onset, longer survival and earlier age of death than 129V subjects. Homozygous 129MM had earlier age of onset than 129VV. Females had a significantly earlier age of onset and earlier age of death than males. Up to 50% of variability in age of onset was conferred by the combined effect of PRNP polymorphic codon 129 and gender. An inverse correlation between early age of onset and long survival was found for this mutation.
Huntington disease-like 1; Huntington’s disease; PRNP; PRNP polymorphic codon 129; base pair insertions (BPI); inherited prion disease (IPD); octapeptide repeat insertions (OPRI)
Species, as well as individuals within species, have unique susceptibilities to prion infection that are likely based on sequence differences in cellular prion protein (PrPC). Species barriers to transmission also reflect PrPC sequence differences. Defining the structure-activity relationship of PrPC/PrPSc with respect to infectivity/susceptibility will benefit disease understanding and assessment of transmission risks. Here, nanopore analysis is employed to investigate genotypes of sheep PrPC corresponding to differential susceptibilities to scrapie infection. Under non-denaturing conditions scrapie resistant (ARR) and susceptible (VRQ) genotypes display similar, type I (bumping) predominant event profiles, suggesting a conserved folding pattern. Under increasingly denaturing conditions both proteins shift to type II (intercalation/translocation) events but with different sensitivities to unfolding. Specifically, when pre-incubated in 2M Gdn-HCl, the VRQ variant had more of type II events as compared with the ARR protein, suggesting a more flexible unfolding pattern. Addition of PrPSc-specific polyclonal antibody (YML) to the ARR variant, pre-incubated in 2M Gdn-HCl, reduced the number of type II events with no clear intercalation/translocation peak, whereas for VRQ, type II events above blockades of 90 pA bound YML. A second PrPSc-specific antibody (SN6b) to a different cryptic epitope reduced type II events for VRQ but not the ARR variant. Collectively, the event patterns associated with sequential denaturation, as well as interactions with PrPSc-specific antibodies, support unique patterns and/or propensities of misfolding between the genotypes. Overall, nanopore analysis identifies intermediate conformations that occur during the unfolding pathways of ARR and VRQ genotypes and may help to understand the correlation of structural properties that induce protein misfolding.
nanopore; genotypes; polymorphisms; prion disease; antibody
A diagnostics of infectious diseases can be done by the immunologic methods or by the amplification of nucleic acid specific to contagious agent using polymerase chain reaction. However, in transmissible spongiform encephalopathies, the infectious agent, prion protein (PrPSc), has the same sequence of nucleic acids as a naturally occurring protein. The other issue with the diagnosing based on the PrPSc detection is that the pathological form of prion protein is abundant only at late stages of the disease in a brain. Therefore, the diagnostics of prion protein caused diseases represent a sort of challenges as that hosts can incubate infectious prion proteins for many months or even years. Therefore, new in vivo assays for detection of prion proteins and for diagnosis of their relation to neurodegenerative diseases are summarized. Their applicability and future prospects in this field are discussed with particular aim at using quantum dots as fluorescent labels.
imaging; label; neurodegenerative disease; prion protein; quantum dots
In the brain, apolipoprotein E (APOE) delivers cholesterol-rich lipoproteins to neurons to support synaptogenesis and maintenance of synaptic connections. Three APOE alleles exist in the human population with ε4 being an Alzheimer disease (AD) risk gene and ε2 being protective relative to the common ε3 variant. Many hypotheses have been advanced concerning allele-specific effects of APOE on neurodegeneration including effects on Aβ clearance, synaptic transmission, or neurotoxicity. Central to most proposed APOE functions is its interaction with receptors that mediate cellular uptake of this ligand. Several members of the LDL receptor gene family have been implicated as APOE receptors in the (patho)physiology of APOE in the brain, yet their specific modes of action in AD remain controversial. Recently, the pro-neurotrophin receptor sortilin has been identified as a novel APOE receptor in neurons. Ablation of sortilin expression in mice results in accumulation of APOE and Aβ in the brain. Moreover, primary neurons lacking sortilin exhibit significantly impaired uptake of APOE/Aβ complexes. Despite increased brain APOE levels, sortilin-deficient animals recapitulate anomalies in brain lipid homeostasis seen in APOE null mice, indicating functional deficiency in APOE uptake pathways. Taken together, these findings suggest a link between Aβ catabolism and pro-neurotrophin signaling converging on this receptor pathway.
Alzheimer disease; LDLR gene family; amyloid β; apolipoprotein E; neurotrophins; sortilin
Creutzfeldt-Jakob disease (CJD) is a heterogenic neurodegenerative disorder associated with abnormal post-translational processing of cellular prion protein (PrPc). CJD displays distinctive clinical and pathological features which correlate with the genotype at the codon 129 (methionine or valine: M or V respectively) in the prion protein gene and with size of the protease-resistant core of the abnormal prion protein PrPsc (type 1: 20/21 kDa and type 2: 19 kDa). MM1 and VV2 are the most common sporadic CJD (sCJD) subtypes. PrP mRNA expression levels in the frontal cortex and cerebellum are reduced in sCJD in a form subtype-dependent. Total PrP protein levels and PrPsc levels in the frontal cortex and cerebellum accumulate differentially in sCJD MM1 and sCJD VV2 with no relation between PrPsc deposition and spongiform degeneration and neuron loss, but with microgliosis, and IL6 and TNF-α response. In the CSF, reduced PrPc, the only form present in this compartment, occurs in sCJD MM1 and VV2. PrP mRNA expression is also reduced in the frontal cortex in advanced stages of Alzheimer disease, Lewy body disease, progressive supranuclear palsy, and frontotemporal lobe degeneration, but PrPc levels in brain varies from one disease to another. Reduced PrPc levels in CSF correlate with PrP mRNA expression in brain, which in turn reflects severity of degeneration in sCJD.
prion protein; Creutzfeldt-Jakob disease; cerebrospinal fluid; brain; mRNA; neurodegenerative diseases