Exploring the significance of caspase-cleaved tau in tauopathies and as a complementary pathology to phospho-tau in Alzheimer's disease: implications for biomarker development and therapeutic targeting.

Tauopathies are neurodegenerative diseases that typically require postmortem examination for a definitive diagnosis. Detecting neurotoxic tau fragments in cerebrospinal fluid (CSF) and serum provides an opportunity for in vivo diagnosis and disease monitoring. Current assays primarily focus on total tau or phospho-tau, overlooking other post-translational modifications (PTMs). Caspase-cleaved tau is a significant component of AD neuropathological lesions, and experimental studies confirm the high neurotoxicity of these tau species. Recent evidence indicates that certain caspase-cleaved tau species, such as D13 and D402, are abundant in AD brain neurons and only show a modest degree of co-occurrence with phospho-tau, meaning caspase-truncated tau pathology is partially distinct and complementary to phospho-tau pathology. Furthermore, these caspase-cleaved tau species are nearly absent in 4-repeat tauopathies. In this review, we will discuss the significance of caspase-cleaved tau in the development of tauopathies, specifically emphasizing its role in AD. In addition, we will explore the potential of caspase-cleaved tau as a biomarker and the advantages for drug development targeting caspase-6. Developing specific and sensitive assays for caspase-cleaved tau in biofluids holds promise for improving the diagnosis and monitoring of tauopathies, providing valuable insights into disease progression and treatment efficacy.

A novel 384-multiwell microelectrode array for the impedimetric monitoring of Tau protein induced neurodegenerative processes.

Over the last decades, countless bioelectronic monitoring systems were developed for the analysis of cells as well as complex tissues. Most studies addressed the sensitivity and specificity of the bioelectronic detection method in comparison to classical molecular biological assays. In contrast, the up scaling as a prerequisite for the practical application of these novel bioelectronic monitoring systems is mostly only discussed theoretically. In this context, we developed a novel 384-multiwell microelectrode array (MMEA) based measurement system for the sensitive label-free real-time monitoring of neurodegenerative processes by impedance spectroscopy. With respect to the needs of productive screening systems for robust and reproducible measurements on high numbers of plates, we focused on reducing the critical contacting of more than 400 electrodes for a 384-MMEA. Therefore, we introduced an on top array of immersive counter electrodes that are individually addressed by a multiplexer and connected all measurement electrodes on the 384-MMEA to a single contact point. More strikingly, our novel approach provided a comparable signal stability and sensitivity similar to an array with integrated counter electrodes. Next, we optimized a SH-SY5Y cell based tauopathy model by introducing a novel 5-fold Tau mutation eliminating the need of artificial tauopathy induction. In combination with our novel 384-MMEA based measurement system, the concentration and time dependent neuroregenerative effect of the kinase inhibitor SRN-003-556 could be quantitatively monitored. Thus, our novel screening system could be a useful tool to identify and develop potential novel therapeutics in the field of Tau-related neurodegenerative diseases.

[Antidementia drugs]. / Antidementiva.

The pharmacological treatment of dementias aims to improve cognitive deficits, activities of daily living and behavioural and psychiatric symptoms. The weighting of theses therapeutic aims varies with disease progression. Behavioural symptoms may dominate especially in the more severe stages of the disease and may further deteriorate global functional level of the patient. Today there is no causal therapy for Alzheimer's disease (AD). Based on preclinical disease models novel therapeutic approaches are under development that target the beta-amyloid and tau protein metabolism. Some of them aim to inhibit the formation, aggregation and toxicity of beta-amyloid peptides or promote their clearance from the brain. Others inhibit the formation of neurofibrillary tangles or have neuroprotective effects. Active or passive immunisation against beta-amyloid may be a very specific and effective approach. The efficacy of acetylcholine esterase inhibitors (AchEI) in the treatment of mild to moderate AD is well documented. They are first line therapeutics in the treatment of the disease and lead to a delay of symptomatic progression. Memantine is effective in the treatment of moderate to severe stages of AD. The evidence for the treatment of vascular dementia is comparatively weak. However, positive effects have been shown for all available AchEI and memantine. Non pharmacological therapy is an indispensable part of the treatment of dementia patients and should be adapted to the individual needs of the patient in the respective stage of the disease. The efficacy of antipsychotics in the treatment of behavioural and psychiatric symptoms of dementia is limited. These drugs are associated with increased morbidity and mortality in dementia patients. Therefore, their application should be based on a critical and individual evaluation of risks and benefits.

Development of a sensitive ELISA for quantification of three- and four-repeat tau isoforms in tauopathies.

Tau protein plays an important role in stabilising and assembling neuronal microtubules. Pathological changes in expression and aggregation of tau isoforms containing three (3R-tau) and four (4R-tau) microtubule-binding repeat domains are associated with several tauopathies. This paper describes novel sandwich ELISAs for quantification of 3R- and 4R-tau in brain. The assays are constructed using well-characterised isoform-specific antibodies (RD3 and RD4) as capture antibodies and an affinity-purified HRP-anti-tau peptide antibody and biotin-tyramide amplification for detection. For 3R-tau, we achieved a minimal detection limit in buffer of 460 pg mL(-1) and a recovery of 81.0% using 500 pg mL(-1) recombinant 3R-tau spiked in diluted brain homogenate. Mean intra- and inter-assay variation of the 3R-tau ELISA was 8.8 and 10.5%, respectively. For 4R-tau, the detection limit was 780 pg mL(-1) and the recovery of 5 ng mL(-1) spiked recombinant 4R-tau was 86.0% and the mean intra- and inter-assay variation was 10.4 and 15.6%, respectively. With these assays, we showed that in progressive supranuclear palsy (PSP) brains, 4R-tau is significantly increased in frontal cortex and caudate, the two regions that are usually associated with 4R-tau-dominant pathology. This increase was not observed in occipital lobe, a region that is spared of tau inclusions. No differences in 3R-tau levels were found between PSP and control brains in all regions tested. With this, we have for the first time developed ELISAs for quantification of 3R- and 4R-tau isoforms in pathological samples. These could prove useful in the pathological investigation and differential diagnosis of tauopathies.

Sonographic discrimination of corticobasal degeneration vs progressive supranuclear palsy.

OBJECTIVE: To study the use of brain parenchyma sonography (BPS) in discriminating between patients with corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP). METHODS: Thirteen patients with PSP and eight with CBD were studied with BPS according to a standardized protocol. RESULTS: Seven (88%) of the eight CBD patients showed marked hyperechogenicity of the substantia nigra (SN) but none of eleven PSP patients (Mann-Whitney U test, p < 0.001). This finding indicated CBD with a positive predictive value of 100%. Marked dilatation of the third ventricle (width > 10 mm) was found in 10 (83%) of 12 PSP patients, but in none of the CBD patients (p < 0.005). BPS measurements of ventricle widths closely matched MRI measurements (Pearson correlation, r = 0.90, p < 0.001). The presence of at least one of the BPS findings 1) marked SN hyperechogenicity and 2) third-ventricle width < 10 mm indicated CBD with a sensitivity of 100%, a specificity of 83%, and a positive predictive value of 80%. Other BPS findings such as echogenicity of lentiform and caudate nuclei and widths of the frontal horns did not discriminate between CBD and PSP. One PSP patient could not be assessed because of insufficient acoustic temporal bone windows. CONCLUSIONS: Substantia nigra hyperechogenicity, reported earlier as characteristic brain parenchyma sonography finding in idiopathic Parkinson disease, is also typical for corticobasal degeneration.