Prion protein and prion disease at a glance

Suspecting Non-Alzheimer's Pathologies and Mixed Pathologies: A Comparative Study Between Brain Metabolism and Tau Images

BACKGROUND

Alzheimer's disease (AD) pathology can be disclosed in vivo using amyloid and tau imaging, unlike non-AD neuropathologies for which no specific markers exist.

OBJECTIVE

We aimed to compare brain hypometabolism and tauopathy to unveil non-AD pathologies.

METHODS

Sixty-one patients presenting cognitive complaints (age 48-90), including 32 with positive AD biomarkers (52%), performed [18F]-Fluorodeoxyglucose (FDG)-PET (brain metabolism) and [18F]-MK-6240-PET (tau). We normalized these images using data from clinically normal individuals (n = 30), resulting in comparable FDG and tau z-scores. We computed between-patients correlations to evaluate regional associations. For each patient, a predominant biomarker (i.e., Hypometabolism > Tauopathy or Hypometabolism≤Tauopathy) was determined in the temporal and frontoparietal lobes. We computed within-patient correlations between tau and metabolism and investigated their associations with demographics, cognition, cardiovascular risk factors (CVRF), CSF biomarkers, and white matter hypointensities (WMH).

RESULTS

We observed negative associations between tau and FDG in 37 of the 68 cortical regions-of-interest (average Pearson's r = -0.25), mainly in the temporal lobe. Thirteen patients (21%) had Hypometabolism > Tauopathy whereas twenty-five patients (41%) had Hypometabolism≤Tauopathy. Tau-predominant patients were more frequently females and had greater amyloid burden. Twenty-three patients (38%) had Hypometabolism≤Tauopathy in the temporal lobe, but Hypometabolism > Tauopathy in the frontoparietal lobe. This group was older and had higher CVRF than Tau-predominant patients. Patients with more negative associations between tau and metabolism were younger, had worse cognition, and greater amyloid and WMH burdens.

CONCLUSIONS

Tau-FDG comparison can help suspect non-AD pathologies in patients presenting cognitive complaints. Stronger Tau-FDG correlations are associated with younger age, worse cognition, and greater amyloid and WMH burdens.

Increased Gal-3 Mediates Microglia Activation and Neuroinflammation via the TREM2 Signaling Pathway in Prion Infection

Galectin 3 (Gal-3) is one of the major elements for activating microglia and mediating neuroinflammation in some types of neurodegenerative diseases. However, its role in the pathogenesis of prion disease is seldom addressed. In this study, markedly increased brain Gal-3 was identified in three scrapie-infected rodent models at the terminal stage. The increased Gal-3 was mainly colocalized with the activated microglia. Coincidental with the increased brain Gal-3 in prion-infected animals, the expression of brain trigger receptor expressed in myeloid cell 2 (TREM2), one of the Gal-3 receptors, and some components in the downstream pathway also significantly increased, whereas Toll-like receptor 4 (TLR4), another Gal-3 receptor, and the main components in its downstream signaling were less changed. The increased Gal-3 signals were distributed at the areas with PrPSc deposit but looked not to colocalize directly with PrPSc/PrP signals. Similar changing profiles of Gal-3, the receptors TREM2 and TLR4, as well as the proteins in the downstream pathways were also observed in prion-infected cell line SMB-S15. Removal of PrPSc replication in SMB-S15 cells reversed the upregulation of cellular Gal-3, TREM2, and the relevant proteins. Moreover, we presented data for interactions of Gal-3 with TREM2 and with TLR4 morphologically and molecularly in the cultured cells. Stimulation of prion-infected cells or their normal partner cells with recombinant mouse Gal-3 in vitro induced obvious responses for activation of TREM2 signaling and TLR4 signaling. Our data here strongly indicate that prion infection or PrPSc deposit induces remarkably upregulated brain Gal-3, which is actively involved in the microglia activation and neuroinflammation mainly via TREM2 signaling.

How Big Is the Yeast Prion Universe?

The number of yeast prions and prion-like proteins described since 1994 has grown from two to nearly twenty. If in the early years most scientists working with the classic mammalian prion, PrP^Sc, were skeptical about the possibility of using the term prion to refer to yeast cytoplasmic elements with unusual properties, it is now clear that prion-like phenomena are widespread and that yeast can serve as a convenient model for studying them. Here we give a brief overview of the yeast prions discovered so far and focus our attention to the various approaches used to identify them. The prospects for the discovery of new yeast prions are also discussed.

Human prion diseases and the prion protein - what is the current state of knowledge?

Prion diseases and the prion protein are only partially understood so far in many aspects. This explains the continued research on this topic, calling for an overview on the current state of knowledge. The main objective of the present review article is to provide a comprehensive up-to-date presentation of all major features of human prion diseases bridging the gap between basic research and clinical aspects. Starting with the prion protein, current insights concerning its physiological functions and the process of pathological conversion will be highlighted. Diagnostic, molecular, and clinical aspects of all human prion diseases will be discussed, including information concerning rare diseases like prion-associated amyloidoses and Huntington disease-like 1, as well as the question about a potential human threat due to the transmission of prions from prion diseases of other species such as chronic wasting disease. Finally, recent attempts to develop future therapeutic strategies will be addressed.

iTRAQ-Based Proteomic Analysis of APP Transgenic Mouse Urine Exosomes

Alzheimer's disease (AD) is a common dementia disease in the elderly. To get a better understanding of the pathophysiology, we performed a proteomic analysis of the urine exosomes (U-exo) in AD model mice (J20). The polymer precipitation method was used to isolate U-exo from the urine of 3-month-old J20 and wild-type (WT) mice. Neuron-derived exosome (N-exo) was isolated from U-exo by immunoprecipitation. iTRAQ-based MALDI TOF MS/MS was used for proteomic analysis. The results showed that compared to WT, the levels of 61 and 92 proteins were increased in the J20 U-exo and N-exo, respectively. Gene ontology enrichment analysis demonstrated that the sphingolipid catabolic process, ceramide catabolic process, membrane lipid catabolic process, Aβ clearance, and Aβ metabolic process were highly enriched in U-exo and N-exo. Among these, Asah1 was shown to be the key protein in lipid metabolism, and clusterin, ApoE, neprilysin, and ACE were related to Aβ metabolism and clearance. Furthermore, protein-protein interaction analysis identified four protein complexes where clusterin and ApoE participated as partner proteins. Thus, J20 U-exo and N-exo contain proteins related to lipid- and Aβ-metabolism in the early stages of AD, providing a new insight into the underlying pathological mechanism of early AD.

Redox stress and metal dys-homeostasis appear as hallmarks of early prion disease pathogenesis in mice

Neurodegenerative diseases are associated with a multitude of dysfunctional cellular pathways. One major contributory factor is a redox stress challenge during the development of several protein misfolding conditions including Alzheimer's (AD), Parkinson's disease (PD), and less common conditions such as Creutzfeldt Jakob disease (CJD). CJD is caused by misfolding of the neuronal prion protein and is characterised by a neurotoxic unfolded protein response involving chronic endoplasmic reticulum stress, reduced protein translation and spongiosis leading subsequently to synaptic and neuronal loss. Here we have characterised prion disease in mice to assess redox stress components including nitrergic and oxidative markers associated with neuroinflammatory activation. Aberrant regulation of the homeostasis of several redox metals contributes to the overall cellular redox stress and we have identified altered levels of iron, copper, zinc, and manganese in the hippocampus of prion diseased mice. Our data show that early in disease, there is evidence for oxidative stress in conjunction with reduced antioxidant superoxide dismutase mRNA and protein expression. Moreover, expression of divalent metal transporter proteins was reduced for Atp7b, Atox1, Slc11a2, Slc39a14 at 6-7 weeks but increased for Slc39a14 and Mt1 at 10 weeks of disease. Our data present evidence for a strong pro-oxidant environment and altered redox metal homeostasis in early disease pathology which both may be contributory factors to aggravating this protein misfolding disease.

Recent Advances in Our Molecular and Mechanistic Understanding of Misfolded Cellular Proteins in Alzheimer’s Disease (AD) and Prion Disease (PrD)

Naturally occurring neuron-abundant proteins including amyloid Aβ42 peptide and the microtubule-associated protein tau (MAPT) can, over time and under pathological situations, assume atypical conformations, altering their normal biological structure and function, and causing them to aggregate into insoluble and neurotoxic intracellular inclusions. These misfolded proteins ultimately contribute to the pathogenesis of several progressive, age-related and ultimately lethal human neurodegenerative disorders. The molecular mechanism of this pathological phenomenon of neuronal protein misfolding lends support to the ‘prion hypothesis’, which predicts that the aberrant folding of endogenous natural protein structures into unusual pathogenic isoforms can induce the atypical folding of other similar brain-abundant proteins, underscoring the age-related, progressive nature and potential transmissible and spreading capabilities of the aberrant protein isoforms that drive these invariably fatal neurological syndromes. The abnormal folding and aggregation of host proteins is a consistent feature of both amyloidopathies and tauopathies that encompass a continuous spectrum of brain diseases that include Alzheimer’s disease (AD), prion disorders (PrD) such as scrapie in sheep and goats (Bovidae), experimental prion infection of rodents (Muridae), Creutzfeldt–Jakob disease (CJD) and Gerstmann–Sträussler–Scheinker syndrome (GSS) in humans (Hominidae), and other fatal prion-driven neurological disorders. Because AD patients accumulate both misfolded tau and Aβ peptides, AD may be somewhat unique as the first example of a ‘double prion disorder’. This commentary will examine current research trends in this fascinating research area, with a special emphasis on AD and PrD, and the novel pathological misfolded protein processes common to both intractable neurological disorders.