[Tauopathies : From molecule to therapy]

Progressive Supranuclear Palsy Syndrome: An Overview

Progressive supranuclear palsy (PSP) is a neurodegenerative disease, commonly observed as a movement disorder in the group of parkinsonian diseases. The term PSP usually refers to PSP-Richardson's syndrome (PSP-RS), the most typical clinical presentation. However, the broad concept of progressive supranuclear palsy syndrome (PSP-S) applies to a set of clinical entities that share a pathophysiological origin and some symptoms. According to its clinical predominance, PSP-S is divided into subtypes. PSP-S has clinical similarities with Parkinson's disease, and both pathologies are classified in the group of parkinsonisms, but they do not share pathophysiological traits. By contrast, the pathophysiology of corticobasal syndrome (CBS) depends on tau expression and shares similarities with PSP-S in both pathophysiology and clinical picture. An involvement of the immune system has been proposed as a cause of neurodegeneration. The role of neuroinflammation in PSP-S has been studied by neuroimaging, among other methods. As it is the case in other neurodegenerative pathologies, microglial cells have been attributed a major role in PSP-S. While various studies have explored the detection and use of possible inflammatory biomarkers in PSP-S, no significant advances have been made in this regard. This review is aimed at highlighting the most relevant information on neuroinflammation and peripheral inflammation in the development and progression of PSP-S, to lay the groundwork for further research on the pathophysiology, potential biomarkers, and therapeutic strategies for PSP-S.

Potential role of Drug Repositioning Strategy (DRS) for management of tauopathy

Tauopathy is a term that has been used to represent a pathological condition in which hyperphosphorylated tau protein aggregates in neurons and glia which results in neurodegeneration, synapse loss and dysfunction and cognitive impairments. Recently, drug repositioning strategy (DRS) becomes a promising field and an alternative approach to advancing new treatments from actually developed and FDA approved drugs for an indication other than the indication it was originally intended for. This paradigm provides an advantage because the safety of the candidate compound has already been established, which abolishes the need for further preclinical safety testing and thus substantially reduces the time and cost involved in progressing of clinical trials. In the present review, we focused on correlation between tauopathy and common diseases as type 2 diabetes mellitus and the global virus COVID-19 and how tau pathology can aggravate development of these diseases in addition to how these diseases can be a risk factor for development of tauopathy. Moreover, correlation between COVID-19 and type 2 diabetes mellitus was also discussed. Therefore, repositioning of a drug in the daily clinical practice of patients to manage or prevent two or more diseases at the same time with lower side effects and drug-drug interactions is a promising idea. This review concluded the results of pre-clinical and clinical studies applied on antidiabetics, COVID-19 medications, antihypertensives, antidepressants and cholesterol lowering drugs for possible drug repositioning for management of tauopathy.

Therapeutic Application of rTMS in Atypical Parkinsonian Disorders

The terms atypical parkinsonian disorders (APDs) and Parkinson plus syndromes are mainly used to describe the four major entities of sporadic neuronal multisystem degeneration: progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), multiple system atrophy (MSA), and dementia with Lewy bodies (LBD). APDs are characterized by a variety of symptoms and a lack of disease modifying therapies; their treatment thus remains mainly symptomatic. Brain stimulation via repetitive transcranial magnetic stimulation (rTMS) is a safe and noninvasive intervention using a magnetic coil, and it is considered an alternative therapy in various neuropsychiatric pathologies. In this paper, we review the available studies that investigate the efficacy of rTMS in the treatment of these APDs and Parkinson plus syndromes. Τhe majority of the studies have shown beneficial effects on motor and nonmotor symptoms, but research is still at a preliminary phase, with large, double-blind studies lacking in the literature.

[Neuroprotective treatment of tauopathies]

Tau pathology is now considered to be the main cause of a wide spectrum of neurodegenerative diseases, which are collectively referred to as tauopathies. These include primary tauopathies, in which tau plays the main role in the pathogenesis as well as secondary tauopathies, such as Alzheimer's disease, in which amyloid beta also plays a substantial role in the disease process in addition to the tau pathology. Primary tauopathies include progressive supranuclear palsy, corticobasal degeneration, Pick's disease and rare hereditary tauopathies, which are referred to as frontotemporal lobar degeneration with microtubule-associated protein tau (MAPT) mutation. Tauopathies differ from each other pathologically by the affected brain regions and cell types as well as by the biochemical characteristics of the aggregated tau protein. Various tau-centered neuroprotective treatment approaches are currently in preclinical and clinical development. They target different mechanisms, including the reduction of tau expression, inhibition of tau aggregation, dissolution of tau aggregates, improvement of cellular mechanisms to eliminate toxic tau species, stabilization of microtubules and prevention of intercellular tau spreading. This review article gives an overview of tauopathies and the current concepts for the development of disease-modifying treatment.

Evolving concepts in progressive supranuclear palsy and other 4-repeat tauopathies

Tauopathies are classified according to whether tau deposits predominantly contain tau isoforms with three or four repeats of the microtubule-binding domain. Those in which four-repeat (4R) tau predominates are known as 4R-tauopathies, and include progressive supranuclear palsy, corticobasal degeneration, argyrophilic grain disease, globular glial tauopathies and conditions associated with specific MAPT mutations. In these diseases, 4R-tau deposits are found in various cell types and anatomical regions of the brain and the conditions share pathological, pathophysiological and clinical characteristics. Despite being considered 'prototype' tauopathies and, therefore, ideal for studying neuroprotective agents, 4R-tauopathies are still severe and untreatable diseases for which no validated biomarkers exist. However, advances in research have addressed the issues of phenotypic overlap, early clinical diagnosis, pathophysiology and identification of biomarkers, setting a road map towards development of treatments. New clinical criteria have been developed and large cohorts with early disease are being followed up in prospective studies. New clinical trial readouts are emerging and biomarker research is focused on molecular pathways that have been identified. Lessons learned from failed trials of neuroprotective drugs are being used to design new trials. In this Review, we present an overview of the latest research in 4R-tauopathies, with a focus on progressive supranuclear palsy, and discuss how current evidence dictates ongoing and future research goals.

Progressive supranuclear palsy

Progressive supranuclear palsy (PSP) is a neurodegenerative disease characterized pathologically by 4 repeat tau deposition in various cell types and anatomical regions. Richardson's syndrome (RS) is the initially described and one of the clinical phenotypes associated with PSP pathology, characterized by vertical supranuclear gaze paly in particular downwards, postural instability with early falls and subcortical frontal dementia. PSP can manifest as several other clinical phenotypes, including PSP-parkinsonism, -pure akinesia with gait freezing, -frontotemporal dementia, - corticobasal syndrome, - speech/language impairment. RS can also have a pathologic diagnosis other than PSP, including corticobasal degeneration, FTD-TDP-43 and others. New clinical diagnostic criteria take into account this phenotypic variability in an attempt to diagnose the disease earlier, given the current lack of a validated biomarker. At present, therapeutic options for PSP are symptomatic and insufficient. Recent large neuroprotective trials have failed to provide a positive clinical outcome, however, have led to the design of better studies that are ongoing and hold promise for a neuroprotective treatment for PSP.