Activation of Src family kinase ameliorates secretory trafficking in mutant prion protein cells.

Fatal familial insomnia (FFI), genetic Creutzfeldt-Jakob disease (gCJD), and Gerstmann-Sträussler-Scheinker (GSS) syndrome are neurodegenerative disorders linked to prion protein (PrP) mutations. The pathogenic mechanisms are not known, but increasing evidence points to mutant PrP misfolding and retention in the secretory pathway. We previously found that the D178N/M129 mutation associated with FFI accumulates in the Golgi of neuronal cells, impairing post-Golgi trafficking. In this study we further characterized the trafficking defect induced by the FFI mutation and tested the 178N/V129 variant linked to gCJD and a nine-octapeptide repeat insertion associated with GSS. We used transfected HeLa cells, embryonic fibroblasts and primary neurons from transgenic mice, and fibroblasts from carriers of the FFI mutation. In all these cell types, the mutant PrPs showed abnormal intracellular localizations, accumulating in the endoplasmic reticulum (ER) and Golgi. To test the efficiency of the membrane trafficking system, we monitored the intracellular transport of the temperature-sensitive vesicular stomatite virus glycoprotein (VSV-G), a well-established cargo reporter, and of endogenous procollagen I (PC-I). We observed marked alterations in secretory trafficking, with VSV-G accumulating mainly in the Golgi complex and PC-I in the ER and Golgi. A redacted version of mutant PrP with reduced propensity to misfold did not impair VSV-G trafficking, nor did artificial ER or Golgi retention of wild-type PrP; this indicates that both misfolding and intracellular retention were required to induce the transport defect. Pharmacological activation of Src family kinase (SFK) improved intracellular transport, suggesting that mutant PrP impairs secretory trafficking through corruption of SFK-mediated signaling.

Preventive pharmacological treatment in subjects at risk for fatal familial insomnia: science and public engagement.

Engaging patients as partners in biomedical research has gradually gained consensus over the last two decades. They provide a different perspective on health priorities and help to improve design and outcomes of clinical studies. This paper describes the relationship established between scientists and members of a large family at genetic risk of very rare lethal disease, fatal familial insomnia (FFI). This interaction led to a clinical trial based on the repurposing of doxycycline - an antibiotic with a known safety profile and optimal blood-brain barrier passage - which in numerous preclinical and clinical studies had given evidence of its potential therapeutic effect in neurodegenerative disorders, including prion diseases like FFI. The design of this trial posed several challenges, which were addressed jointly by the scientists and the FFI family. Potential participants excluded the possibility of being informed of their own FFI genotype; thus, the trial design had to include both carriers of the FFI mutation (10 subjects), and non-carriers (15 subjects), who were given placebo. Periodic clinical controls were performed on both groups by blinded examiners. The lack of surrogate outcome measures of treatment efficacy has required to compare the incidence of the disease in the treated group with a historical dataset during 10 years of observation. The trial is expected to end in 2023. Regardless of the clinical outcome, it will provide worthwhile knowledge on the disease. It also offers an important example of public engagement and collaboration to improve the quality of clinical science.

Autoantibodies against the prion protein in individuals with PRNP mutations.

OBJECTIVE: To determine whether naturally occurring autoantibodies against the prion protein are present in individuals with genetic prion disease mutations and controls, and if so, whether they are protective against prion disease. METHODS: In this case-control study, we collected 124 blood samples from individuals with a variety of pathogenic PRNP mutations and 78 control individuals with a positive family history of genetic prion disease but lacking disease-associated PRNP mutations. Antibody reactivity was measured using an indirect ELISA for the detection of human immunoglobulin G1-4 antibodies against wild-type human prion protein. Multivariate linear regression models were constructed to analyze differences in autoantibody reactivity between (1) PRNP mutation carriers vs controls and (2) asymptomatic vs symptomatic PRNP mutation carriers. Robustness of results was examined in matched cohorts. RESULTS: We found that antibody reactivity was present in a subset of both PRNP mutation carriers and controls. Autoantibody levels were not influenced by PRNP mutation status or clinical manifestation of prion disease. Post hoc analyses showed anti-PrPC autoantibody titers to be independent of personal history of autoimmune disease and other immunologic disorders, as well as PRNP codon 129 polymorphism. CONCLUSIONS: Pathogenic PRNP variants do not notably stimulate antibody-mediated anti-PrPC immunity. Anti-PrPC immunoglobulin G autoantibodies are not associated with the onset of prion disease. The presence of anti-PrPC autoantibodies in the general population without any disease-specific association suggests that relatively high titers of naturally occurring antibodies are well-tolerated. CLINICALTRIALSGOV IDENTIFIER: NCT02837705.

Clinical trials of prion disease therapeutics.

Prion-related encephalopathies or transmissible spongiform encephalopathies (TSEs) are a group of rare progressive neurodegenerative disorders that are invariably fatal with often only six months elapsing from diagnosis to patient death. This makes the development of effective therapeutic strategies challenging. Nonetheless, compounds have been identified in animal models of TSE that prolong survival and, in some instances, eradicate the disease. These have been tested in the clinic, although with modest or negative outcomes. While little progress has been made over the last decade, new findings that include the ability to identify prion aggregates at low levels in biological fluids and cells may lead to the development of early-stage biomarkers for TSE. An increased focus on immunotherapeutic approaches to TSE may result in the development of novel preventive approaches for TSE.

Asymptomatic Carriers of Presenilin-1 E318G Variant Show no Cerebrospinal Fluid Biochemical Signs Suggestive of Alzheimer's disease in a Family with Late-onset Dementia.

BACKGROUND: Presenilin-1 (PSEN-1) is a component of the γ-secretase complex involved in ß-amyloid Precursor Protein (AßPP) processing. Usually, Alzheimer's disease (AD)-linked mutations in the PSEN-1 gene lead to the early onset and increase the production of the aggregation-prone peptide Aß42. However, the PSEN-1 E318G variant has an unclear pathogenic role and is recently reported as a genetic risk factor for AD. In particular, E318G variant presence correlated with increased cerebrospinal fluid (CSF) levels of Total Tau (t-tau) and Phosphorylated Tau (p-tau). OBJECTIVE: We describe a large Italian family, which we followed from January 2003 to January 2018, with the late-onset AD and the E318G variant, with the aim of assessing E318G-associated CSF or plasma biochemical changes in biomarkers of dementia. METHOD: CSF Aß42, t-tau and p-tau, plasma Aß42 and Aß40 were assessed by ELISA tests, while CSF amyloid peptides profile was investigated by mass spectrometry. RESULTS: We did not find any changes in CSF biochemical markers (Aß42, t-tau, p-tau and amyloid peptides) of asymptomatic E318G carriers in 2010 and 2012, but plasma Aß40 was increased at the same times. From 2003 to 2018, no asymptomatic E318G carrier developed AD. CONCLUSION: Our follow-up of this family may help elucidate E318G's role in AD and globally points to a null effect of this variant.

Age at onset in genetic prion disease and the design of preventive clinical trials.

OBJECTIVE: To determine whether preventive trials in genetic prion disease could be designed to follow presymptomatic mutation carriers to onset of disease. METHODS: We assembled age at onset or death data from 1,094 individuals with high penetrance mutations in the prion protein gene (PRNP) in order to generate survival and hazard curves and test for genetic modifiers of age at onset. We used formulae and simulations to estimate statistical power for clinical trials. RESULTS: Genetic prion disease age at onset varies over several decades for the most common mutations and neither sex, parent's age at onset, nor PRNP codon 129 genotype provided additional explanatory power to stratify trials. Randomized preventive trials would require hundreds or thousands of at-risk individuals in order to be statistically powered for an endpoint of clinical onset, posing prohibitive cost and delay and likely exceeding the number of individuals available for such trials. CONCLUSION: The characterization of biomarkers suitable to serve as surrogate endpoints will be essential for the prevention of genetic prion disease. Parameters such as longer trial duration, increased enrollment, and the use of historical controls in a postmarketing study could provide opportunities for subsequent determination of clinical benefit.

An in vivo 11C-PK PET study of microglia activation in Fatal Familial Insomnia.

Objective: Postmortem studies reported significant microglia activation in association with neuronal apoptosis in Fatal Familial Insomnia (FFI), indicating a specific glial response, but negative evidence also exists. An in vivo study of local immune responses over FFI natural course may contribute to the understanding of the underlying pathogenesis. Methods: We included eight presymptomatic subjects (mean ± SD age:44.13 ± 3.83 years) carrying the pathogenic D178N-129met FFI mutation, one symptomatic patient (male, 45 yrs. old), and nine healthy controls (HC) (mean ± SD age: 44.00 ± 11.10 years.) for comparisons. 11C-(R)-PK11195 PET allowed the measurement of Translocator Protein (TSPO) overexpression, indexing microglia activation. A clustering algorithm was adopted to define subject-specific reference regions. Voxel-wise statistical analyses were performed on 11C-(R)-PK11195 binding potential (BP) images both at the group and individual level. Results: The D178N-129met/val FFI patient showed significant 11C-(R)-PK11195 BP increases in the midbrain, cerebellum, anterior thalamus, anterior cingulate cortex, orbitofrontal cortex, and anterior insula, bilaterally. Similar TSPO increases, but limited to limbic structures, were observed in four out of eight presymptomatic carriers. The only carrier with the codon 129met/val polymorphism was the only one showing an additional TSPO increase in the anterior thalamus. Interpretation: In comparison to nonprion neurodegenerative diseases, the observed lack of a diffuse brain TSPO overexpression in preclinical and the clinical FFI cases suggests the presence of a different microglia response. The involvement of limbic structures might indicate a role for microglia activation in these key pathologic regions, known to show the most significant neuronal loss and functional deafferentation in FFI.

Detection of prion seeding activity in the olfactory mucosa of patients with Fatal Familial Insomnia.

Fatal Familial Insomnia (FFI) is a genetic prion disease caused by a point mutation in the prion protein gene (PRNP) characterized by prominent thalamic atrophy, diffuse astrogliosis and moderate deposition of PrPSc in the brain. Here, for the first time, we demonstrate that the olfactory mucosa (OM) of patients with FFI contains trace amount of PrPSc detectable by PMCA and RT-QuIC. Quantitative PMCA analysis estimated a PrPSc concentration of about 1 × 10-14 g/ml. In contrast, PrPSc was not detected in OM samples from healthy controls and patients affected by other neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease and frontotemporal dementia. These results indicate that the detection limit of these assays is in the order of a single PrPSc oligomer/molecule with a specificity of 100%.

Preventive study in subjects at risk of fatal familial insomnia: Innovative approach to rare diseases.

The text describes a preventive clinical trial with drug treatment in a very rare neurodegenerative disease (Fatal familial Insomnia, FFI) designed with the help of individuals at genetic risk of developing the disease, asymptomatic carriers, who have agreed to be exposed over a 10-year period to doxycycline, an antibiotic with anti-prion activity. At least 10 carriers of the FFI mutation over 42 y old will be treated with doxycycline (100 mg/die) and the incidence of the disease will be compared to that of an historical dataset. For ethical reasons a randomized, double-blind, placebo-controlled trial was not feasible, however the study design and the statistical analysis ensure the scientific value of the results. This approach might represent an important breakthrough in terms of potential therapy and knowledge of rare diseases that could give some hopes to these neglected patients.

Therapy in prion diseases.

In the last two decades, knowledge of the neurobiology of prion diseases or transmissible spongiform encephalopathies (TSE) has significantly advanced, but a successful therapy to stop or delay the progression of these disorders remains one of the most challenging goals of biomedical research. Several obstacles to this achievement are in common with other neurodegenerative disorders: difficulties to move from experimental level to clinical stage; appropriate timing of intervention; correct set up of clinical trial. Also in terms of molecular bases of disease, TSE and the other neurodegenerative disorders associated with protein misfolding such as Alzheimer, Parkinson and Huntington diseases, share a central pathogenic role of soluble small aggregates, named oligomers, considered the culprit of neuronal dysfunction: accordingly, these disorders could by termed oligomeropathies. However, the rapid progression of TSE, together with their clinical and molecular heterogeneity, make the therapeutic approach particularly problematic. The main target of the antiprion strategy has been the pathological form of the cellular prion protein (PrP(C)) termed PrP(Sc), invariably associated with the diseases. Several compounds have been found to affect PrP(Sc) formation or enhance its clearance in in vitro models, and prolong survival in experimental animals. However, few of them such as quinacrine and pentosan polysulfate have reached the clinical evaluation; more recently, we have conducted a clinical trial with doxycycline in patients with Creutzfeldt-Jakob disease without satisfactory results. In experimental conditions, active and passive immunization with antibodies against PrP and mucosal vaccination have shown to protect from peripheral infection. Other studies have proposed new potentially effective molecules targeting PrP oligomers. Furthermore, the possibility to interfere with PrP(C) to PrP(Sc) conversion by an active control of PrP(C) is another interesting approach emerging from experimental studies. However, in common with the other oligomeropathies, early diagnosis allowing to treat at risk population in a preclinical stage represent the more realistic perspective for efficient TSE therapy.

Presenilin-1 mutation E318G and familial Alzheimer's disease in the Italian population.

Presenilin-1 (PSEN-1) is a component of the gamma-secretase complex involved in beta-amyloid precursor protein (betaAPP) processing. To date about 140 pathogenic mutations in the PSEN-1 gene have been identified and their main biochemical effect is to increase the production of the fibrillogenic peptide Abeta(1-42). An exception is the PSEN-1 [E318G] mutation that does not alter Abeta(1-42) generation and is generally considered a non-pathogenic polymorphism. Nevertheless, this mutation was reported to be a genetic risk factor for familial Alzheimer's disease (FAD) in the Australian population. To independently confirm this indication, we performed a case-control association study in the Italian population. We found a significant association (p<0.05, Fisher's exact test) between the presence of PSEN-1 [E318G] and FAD. In addition, on measuring the Abeta(1-42) and Abeta(1-40) concentrations in fibroblast-conditioned media cultured from PSEN-1 [E318G] carriers and PSEN-1 [wild type] controls we noted a significant decrease (p<0.05, Mann-Whitney test) in the Abeta(1-42)/Abeta(1-40) ratio in PSEN-1 [E318G] carriers, suggesting a peculiar biochemical effect of this mutation.