A unique common ancestor introduced P301L mutation in MAPT gene in frontotemporal dementia patients from Barcelona (Baix Llobregat, Spain)

Association between Alzheimer's disease, MAPT gene mutation and some biochemical biomarkers

Alzheimer's Disease (AD) is a multifactorial neurodegenerative disease and there is still no definitive treatment today. Early diagnosis of the disease is important, but there are almost no biomarkers that can be used in early diagnosis. The cerebrospinal fluid used in the diagnosis of the disease is not sufficient and is very difficult to obtain. Therefore, blood biomarkers that are less costly, less invasive, easily accessible, and can be used in long-term studies would be a better alternative. The aim of this study is to determine the relationship between Alzheimer's Disease and P301L MAPT gene mutation, homocysteine, folate and uric acid. 101 Alzheimer's patients and 101 healthy individuals were included in this study. Mutation analysis was performed using the Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) method with blood samples taken from the subjects. There was no significant difference between the patient and control groups in terms of homocysteine (p = 0.771), folate (p = 0.366) and uric acid (p = 0.860). When the genotypes were compared between the patient and control groups in terms of MAPT gene mutation (P301L), no statistically significant difference was detected (p = 0.081). There are very few studies in the literature investigating the relationship between Alzheimer's disease and P301L MAPT gene mutation. Additionally, there is no study investigating the relationship between Alzheimer's disease and homocysteine, folate, uric acid and P301L MAPT mutation in the Turkish population. We believe that this study has shed light on future studies.

Pathologic tau conformer ensembles induce dynamic, liquid-liquid phase separation events at the nuclear envelope

Background

The microtubule-associated protein tau forms aggregates in different neurodegenerative diseases called tauopathies. Prior work has shown that a single P301L mutation in tau gene, MAPT, can promote alternative tau folding pathways that correlate with divergent clinical diagnoses. Using progressive chemical denaturation, some tau preparations from the brain featured complex transitions starting at low concentrations of guanidine hydrochloride (GdnHCl) denaturant, indicating an ensemble of differently folded tau species called conformers. On the other hand, brain samples with abundant, tangle-like pathology had simple GdnHCl unfolding profile resembling the profile of fibrillized recombinant tau and suggesting a unitary conformer composition. In studies here we sought to understand tau conformer progression and potential relationships with condensed liquid states, as well as associated perturbations in cell biological processes.

Results

As starting material, we used brain samples from P301L transgenic mice containing tau conformer ensembles that unfolded at low GdnHCl concentrations and with signatures resembling brain material from P301L subjects presenting with language or memory problems. We seeded reporter cells expressing a soluble form of 4 microtubule-binding repeat tau fused to GFP or YFP reporter moieties, resulting in redistribution of dispersed fluorescence signals into focal assemblies that could fuse together and move within processes between adjacent cells. Nuclear envelope fluorescent tau signals and small fluorescent inclusions behaved as a demixed liquid phase, indicative of liquid-liquid phase separation (LLPS); these droplets exhibited spherical morphology, fusion events and could recover from photobleaching. Moreover, juxtanuclear tau assemblies were associated with disrupted nuclear transport and reduced cell viability in a stable cell line. Staining for thioflavin S (ThS) became more prevalent as tau-derived inclusions attained cross-sectional area greater than 3 μm², indicating (i) a bipartite composition, (ii) in vivo progression of tau conformers, and (iii) that a mass threshold applying to demixed condensates may drive liquid-solid transitions.

Conclusions

Tau conformer ensembles characterized by denaturation at low GdnHCl concentration templated the production of condensed droplets in living cells. These species exhibit dynamic changes and develop in vivo, and the larger ThS-positive assemblies may represent a waystation to arrive at intracellular fibrillar tau inclusions seen in end-stage genetic tauopathies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01132-y.

Frequency of frontotemporal dementia-related gene variants in Turkey

Just as its clinical heterogeneity, genetic basis of Frontotemporal dementia (FTD) is also diverse and multiple molecular pathways are thought to be involved in disease pathogenesis. In the present study, FTD- related genes were evaluated in a Turkish cohort of 175 index FTD patients with a gene panel including GRN, MAPT, TARDBP, FUS, CHMP2B and VCP genes. Potential genetic associations were prospected in 16 patients (9.1%); five variants (p.(Gly35Glufs) and p.(Cys253Ter) in GRN; p.(Arg95Cys) in VCP; p.(Met405Val) in TARDBP and p.(Pro636Leu) in MAPT) were classified as pathogenic (P) or likely pathogenic (LP), in four familial and one sporadic patients. Three novel variants in MAPT, CHMP2B and FUS were also identified in familial cases. The most common pathogenic variants were observed in the GRN gene with a frequency of 1.14% (2/175) and this rate was 4.57% (8/175), including variants of uncertain significance (VUS). In this study with the largest cohort of Turkish FTD patients, GRN and MAPT variants were identified as the most common genetic associations; and rare causes like VCP, TARDBP, CHMP2B and FUS variants are recommended to be considered in patients with compatible clinical findings.

Cellular Biology of Tau Diversity and Pathogenic Conformers

Tau accumulation is a prominent feature in a variety of neurodegenerative disorders and remarkable effort has been expended working out the biochemistry and cell biology of this cytoplasmic protein. Tau's wayward properties may derive from germline mutations in the case of frontotemporal lobar degeneration (FTLD-MAPT) but may also be prompted by less understood cues—perhaps environmental or from molecular damage as a consequence of chronological aging—in the case of idiopathic tauopathies. Tau properties are undoubtedly affected by its covalent structure and in this respect tau protein is not only subject to changes in length produced by alternative splicing and endoproteolysis, but different types of posttranslational modifications that affect different amino acid residues. Another layer of complexity concerns alternate conformations—“conformers”—of the same covalent structures; in vivo conformers can encompass soluble oligomeric species, ramified fibrillar structures evident by light and electron microscopy and other forms of the protein that have undergone liquid-liquid phase separation to make demixed liquid droplets. Biological concepts based upon conformers have been charted previously for templated replication mechanisms for prion proteins built of the PrP polypeptide; these are now providing useful explanations to feature tau pathobiology, including how this protein accumulates within cells and how it can exhibit predictable patterns of spread across different neuroanatomical regions of an affected brain. In sum, the documented, intrinsic heterogeneity of tau forms and conformers now begins to speak to a fundamental basis for diversity in clinical presentation of tauopathy sub-types. In terms of interventions, emphasis upon subclinical events may be worthwhile, noting that irrevocable cell loss and ramified protein assemblies feature at end-stage tauopathy, whereas earlier events may offer better opportunities for diverting pathogenic processes. Nonetheless, the complexity of tau sub-types, which may be present even within intermediate disease stages, likely mitigates against one-size-fits-all therapeutic strategies and may require a suite of interventions. We consider the extent to which animal models of tauopathy can be reasonably enrolled in the campaign to produce such interventions and to slow the otherwise inexorable march of disease progression.

The Rise of the GRN C157KfsX97 Mutation in Southern Italy: Going Back to the Fall of the Western Roman Empire

BACKGROUND

Frontotemporal lobar degeneration (FTLD) designates a group of neurodegenerative diseases with remarkable clinical, pathological, and genetic heterogeneity. Mutations in progranulin gene (GRN) are among the most common causes of familial FTLD. The GRN C157KfsX97 mutation is the most frequent mutation occurring in Southern Italy and has been already described in a previous work.

OBJECTIVE

In this study, we reported on additional cases carrying the same mutation and performed a genetic study on the whole cohort, aiming at demonstrating the existence of a founder effect and estimating the age of this mutation.

METHODS/RESULTS

Based on the haplotype sharing analysis, a founder effect was highly probable, while the age of the mutation, estimated by means of DMLE+ software, resulted in a range between 52 and 82 generations, with the highest frequency at about 62 generations, 1,550 years ago.

CONCLUSION

This is the first study that reports the age estimation of the most recent common ancestor for the GRN C157KfsX97 mutation recurring in Southern Italy. Mutation dating in a geographically restricted population may be useful in order to plan genetic counseling and screening programs in the field of public health.

Diverse, evolving conformer populations drive distinct phenotypes in frontotemporal lobar degeneration caused by the same MAPT-P301L mutation

Tau protein accumulation is a common denominator of major dementias, but this process is inhomogeneous, even when triggered by the same germline mutation. We considered stochastic misfolding of human tau conformers followed by templated conversion of native monomers as an underlying mechanism and derived sensitive conformational assays to test this concept. Assessments of brains from aged TgTau^P301L transgenic mice revealed a prodromal state and three distinct signatures for misfolded tau. Frontotemporal lobar degeneration (FTLD)-MAPT-P301L patients with different clinical phenotypes also displayed three signatures, two resembling those found in TgTau^P301L mice. As physicochemical and cell bioassays confirmed diverse tau strains in the mouse and human brain series, we conclude that evolution of diverse tau conformers is intrinsic to the pathogenesis of this uni-allelic form of tauopathy. In turn, effective therapeutic interventions in FTLD will need to address evolving repertoires of misfolded tau species rather than singular, static molecular targets.