NT1-Tau Is Increased in CSF and Plasma of CJD Patients, and Correlates with Disease Progression

Tau and Amyloid β Protein in Patient-Derived Aqueous Brain Extracts Act Concomitantly to Disrupt Long-Term Potentiation in Vivo

Amyloid β protein (Aβ) and tau, the two main proteins implicated in causing Alzheimer's disease (AD), are posited to trigger synaptic dysfunction long before significant synaptic loss occurs in vulnerable circuits. Whereas soluble Aβ aggregates from AD brain are well recognized potent synaptotoxins, less is known about the synaptotoxicity of soluble tau from AD or other tauopathy patient brains. Minimally manipulated patient-derived aqueous brain extracts contain the more diffusible native forms of these proteins. Here, we explore how intracerebral injection of Aβ and tau present in such aqueous extracts of patient brain contribute to disruption of synaptic plasticity in the CA1 area of the male rat hippocampus. Aqueous extracts of certain AD brains acutely inhibited long-term potentiation (LTP) of synaptic transmission in a manner that required both Aβ and tau. Tau-containing aqueous extracts of a brain from a patient with Pick's disease (PiD) also impaired LTP, and diffusible tau from either AD or PiD brain lowered the threshold for AD brain Aβ to inhibit LTP. Remarkably, the disruption of LTP persisted for at least 2 weeks after a single injection. These findings support a critical role for diffusible tau in causing rapid onset, persistent synaptic plasticity deficits, and promoting Aβ-mediated synaptic dysfunction.SIGNIFICANCE STATEMENT The microtubule-associated protein tau forms relatively insoluble fibrillar deposits in the brains of people with neurodegenerative diseases including Alzheimer's and Pick's diseases. More soluble aggregates of disease-associated tau may diffuse between cells and could cause damage to synapses in vulnerable circuits. We prepared aqueous extracts of diseased cerebral cortex and tested their ability to interfere with synaptic function in the brains of live rats. Tau in these extracts rapidly and persistently disrupted synaptic plasticity and facilitated impairments caused by amyloid β protein, the other major pathologic protein in Alzheimer's disease. These findings show that certain diffusible forms of tau can mediate synaptic dysfunction and may be a target for therapy.

All the Tau We Cannot See

Alzheimer's disease (AD) was described in 1906 as a dementing disease marked by the presence of two types of fibrillar aggregates in the brain: neurofibrillary tangles and senile plaques. The process of aggregation and formation of the aggregates has been a major focus of investigation ever since the discoveries that the tau protein is the predominant protein in tangles and amyloid β is the predominant protein in plaques. The idea that smaller, oligomeric species of amyloid may also be bioactive has now been clearly established. This review examines the possibility that soluble, nonfibrillar, bioactive forms of tau-the "tau we cannot see"-comprise a dominant driver of neurodegeneration in AD.

Enzyme-based digital bioassay technology - key strategies and future perspectives

Digital bioassays based on single-molecule enzyme reactions represent a new class of bioanalytical methods that enable the highly sensitive detection of biomolecules in a quantitative manner. Since the first reports of these methods in the 2000s, there has been significant growth in this new bioanalytical strategy. The principal strategy of this method is to compartmentalize target molecules in micron-sized reactors at the single-molecule level and count the number of microreactors showing positive signals originating from the target molecule. A representative application of digital bioassay is the digital enzyme-linked immunosorbent assay (ELISA). Owing to their versatility, various types of digital ELISAs have been actively developed. In addition, some disease markers and viruses possess catalytic activity, and digital bioassays for such enzymes and viruses have, thus, been developed. Currently, with the emergence of new microreactor technologies, the targets of this methodology are expanding from simple enzymes to more complex systems, such as membrane transporters and cell-free gene expression. In addition, multiplex or multiparametric digital bioassays have been developed to assess precisely the heterogeneities in sample molecules/systems that are obscured by ensemble measurements. In this review, we first introduce the basic concepts of digital bioassays and introduce a range of digital bioassays. Finally, we discuss the perspectives of new classes of digital bioassays and emerging fields based on digital bioassay technology.

Analysis of Clinical Features, Diagnostic Tests, and Biomarkers in Patients With Suspected Creutzfeldt-Jakob Disease, 2014-2021

IMPORTANCE

Detection of prion proteins in cerebrospinal fluid (CSF) using real-time quaking-induced conversion (RT-QuIC) assays has transformed the diagnostic approach to sporadic Creutzfeldt-Jakob disease (CJD), facilitating earlier and more complete recognition of affected patients. It is unclear how expanded recognition of affected patients may affect the diagnostic and prognostic relevance of clinical features and diagnostic tests historically associated with CJD.

OBJECTIVE

To evaluate clinical features and diagnostic testing in patients presenting with CJD and determine the associations of these features with prognosis.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study incorporated data from electronic medical records of patients with CJD treated at Mayo Clinic Enterprise tertiary care centers in Rochester, Minnesota; Jacksonville, Florida; and Scottsdale, Arizona. Participants included patients with definite or probable CJD assessed from 2014 to 2021. Data were analyzed October 2021 to January 2022.

EXPOSURES

Dominant presentation, clinical features, and diagnostic tests associated with CJD.

MAIN OUTCOMES AND MEASURES

The outcomes of interest were the sensitivity and prognostic value of clinical features and accessible diagnostic tests at presentation with possible CJD.

RESULTS

A total of 115 patients were identified, including 40 patients (35%) with definite CJD. Mean (SD) age at symptom onset was 64.8 (9.4) years, and 68 patients were women (59%). The sensitivity of clinical markers (myoclonus) and tests historically considered in patients with suspected CJD was poor (eg, stereotyped electroencephalography anomalies: 17 of 105 patients [16%]; elevated CSF protein 14-3-3 levels: 54 of 90 patients [60%]). By comparison, biomarkers with good diagnostic sensitivity at presentation included RT-QuIC (66 of 71 patients [93%]), CSF total tau (T-tau) level greater than 1149 pg/mL (81 of 92 patients [88%]), and characteristic signal anomalies on magnetic resonance imaging (88 of 115 patients [77%]). Multivariable linear regression confirmed shorter survival in patients with myoclonus (difference, -125.9 [95% CI, -236.3 to -15.5] days; P = .03), visual or cerebellar signs (difference, -180.2 [95% CI, -282.2 to -78.2] days; P < .001), elevated CSF protein 14-3-3 levels (difference, -193 [95% CI, -304.9 to -82.9] days; P < .001), and elevated T-tau level (difference for every 1000 pg/mL elevation, -9.1 [95% CI, -17.7 to -1.0] days; P = .04).

CONCLUSIONS AND RELEVANCE

These findings suggest that CSF RT-QuIC, elevated CSF T-tau level, and stereotyped magnetic resonance imaging anomalies were associated with the diagnosis of CJD, while other clinical findings (eg, myoclonus), stereotyped electroencephalography anomalies, and CSF protein 14-3-3 levels offered less diagnostic value. Visual or cerebellar features, myoclonus, and CSF 14-3-3 and T-tau levels may be associated with disease duration, justifying continued inclusion in the evaluation of patients suspected to have CJD.