A Case of Early-Onset Alzheimer's Disease with MAPT P301L Mutation and Literature Review

Background: Early-onset Alzheimer's disease is defined as Parkinson's disease that begins at an age of 65 or younger. Currently, among the reports on early-onset Alzheimer's disease related genes, mutations of APP, PSEN1 and PSEN2 genes are relatively common, However, the mutation of MAPT P301L causes early-onset Alzheimer's disease, which has not been reported so far. Case report: We have found a clinical case of a 30-year-old male who suddenly developed cognitive impairment and progressed rapidly within 2 years, leaving him unable to take care of himself. The patient underwent examinations of blood and cerebrospinal fluid routine, biochemistry and immunoassay, as well as imaging examinations of MRI, FDGPET and PIBPET. PIB-PET indicated diffuse heterogeneous radionuclivity in cerebral cortex, and positive PIB imaging was considered. Sequencing results suggested that there was a heterozygous mutation in the MAPT gene of the patient, which was located in Chr17-44087755, and c.902C>T. Conclusion: We speculated that EOAD of this patient may be related to the P301L mutation on MAPT.

Tau Modulates mRNA Transcription, Alternative Polyadenylation Profiles of hnRNPs, Chromatin Remodeling and Spliceosome Complexes

Tau protein is a known contributor in several neurodegenerative diseases, including Alzheimer’s disease (AD) and frontotemporal dementia (FTD). It is well-established that tau forms pathological aggregates and fibrils in these diseases. Tau has been observed within the nuclei of neurons, but there is a gap in understanding regarding the mechanism by which tau modulates transcription. We are interested in the P301L mutation of tau, which has been associated with FTD and increased tau aggregation. Our study utilized tau-inducible HEK (iHEK) cells to reveal that WT and P301L tau distinctively alter the transcription and alternative polyadenylation (APA) profiles of numerous nuclear precursors mRNAs, which then translate to form proteins involved in chromatin remodeling and splicing. We isolated total mRNA before and after over-expressing tau and then performed Poly(A)-ClickSeq (PAC-Seq) to characterize mRNA expression and APA profiles. We characterized changes in Gene Ontology (GO) pathways using EnrichR and Gene Set Enrichment Analysis (GSEA). We observed that P301L tau up-regulates genes associated with reactive oxygen species responsiveness as well as genes involved in dendrite, microtubule, and nuclear body/speckle formation. The number of genes regulated by WT tau is greater than the mutant form, which indicates that the P301L mutation causes loss-of-function at the transcriptional level. WT tau up-regulates genes contributing to cytoskeleton-dependent intracellular transport, microglial activation, microtubule and nuclear chromatin organization, formation of nuclear bodies and speckles. Interestingly, both WT and P301L tau commonly down-regulate genes responsible for ubiquitin-proteosome system. In addition, WT tau significantly down-regulates several genes implicated in chromatin remodeling and nucleosome organization. Although there are limitations inherent to the model systems used, this study will improve understanding regarding the nuclear impact of tau at the transcriptional and post-transcriptional level. This study also illustrates the potential impact of P301L tau on the human brain genome during early phases of pathogenesis.

Tau modulates mRNA transcription, alternative polyadenylation profiles of hnRNPs, chromatin remodeling and spliceosome complexes

Tau protein is a known contributor in several neurodegenerative diseases, including Alzheimer ’s disease (AD) and frontotemporal dementia (FTD). It is well-established that tau forms pathological aggregates and fibrils in these diseases. Tau has been observed within the nuclei of neurons, but there is a gap in understanding regarding the mechanism by which tau modulates transcription. We are interested in the P301L mutation of tau, which has been associated with FTD and increased tau aggregation. Our study utilized tau-inducible HEK (iHEK) cells to reveal that WT and P301L tau distinctively alter the transcription and alternative polyadenylation (APA) profiles of numerous nuclear precursors mRNAs, which then translate to form proteins involved in chromatin remodeling and splicing. We isolated total mRNA before and after over-expressing tau and then performed Poly(A)-ClickSeq (PAC-Seq) to characterize mRNA expression and APA profiles. We characterized changes in Gene Ontology (GO) pathways using EnrichR and Gene Set Enrichment Analysis (GSEA). We observed that P301L tau up-regulates genes associated with reactive oxygen species responsiveness as well as genes involved in dendrite, microtubule, and nuclear body/speckle formation. The number of genes regulated by WT tau is greater than the mutant form, which indicates that the P301L mutation causes loss-of-function at the transcriptional level. WT tau up-regulates genes contributing to cytoskeleton-dependent intracellular transport, microglial activation, microtubule and nuclear chromatin organization, formation of nuclear bodies and speckles. Interestingly, both WT and P301L tau commonly down-regulate genes responsible for ubiquitin-proteosome system. In addition, WT tau significantly down-regulates several genes implicated in chromatin remodeling and nucleosome organization. Although there are limitations inherent to the model systems used, this study will improve understanding regarding the nuclear impact of tau at the transcriptional and post-transcriptional level. This study also illustrates the potential impact of P301L tau on the human brain genome during early phases of pathogenesis.

Cytoplasmic Mislocalization of RNA Polymerase II Subunit RPB1 in Alzheimer Disease Is Linked to Pathologic Tau

Abnormal protein accumulation and mislocalization is a general hallmark of Alzheimer disease. Recent data suggest nucleocytoplasmic transport may be compromised by tau in Alzheimer disease. In this context, we have examined the RNA polymerase II subunit RPB1, which is the catalytic subunit that plays a critical role in transcription. Using immunofluorescence staining in control and Alzheimer disease hippocampal tissue, we show that 2 phosphoisoforms of RPB1 mislocalize from the nucleus to the cytoplasm of neurons in Alzheimer disease. The number of neurons with this cytoplasmic mislocalization is correlated with the burden of pathologic tau (AT8-immunopositive neurons). In order to test whether there is a causal relationship between pathologic tau and cytoplasmic RPB1 accumulation, we used the rTg4510 mouse model, which expresses a regulatable pathologic human tau species harboring the P301L mutation. Using immunofluorescence staining on brain tissue from young (2.5-month-old) and aged (8.5- to 10-month-old) rTg4510 mice, we found a tau- and age-dependent increase in cytoplasmic mislocalization of Rpb1. In summary, this study provides evidence that tau induces mislocalization of RPB1 in Alzheimer disease, and since RPB1 is essential for transcription, this raises the possibility that RPB1 mislocalization could lead to fundamental alterations in neuronal health.

Early anterior cingulate involvement is seen in presymptomatic MAPT P301L mutation carriers

Background PET imaging of glucose metabolism has revealed presymptomatic abnormalities in genetic FTD but has not been explored in MAPT P301L mutation carriers. This study aimed to explore the patterns of presymptomatic hypometabolism and atrophy in MAPT P301L mutation carriers. Methods Eighteen asymptomatic members from five families with a P301L MAPT mutation were recruited to the study, six mutation carriers, and twelve mutation-negative controls. All participants underwent standard behavioural and cognitive assessment as well as [18F]FDG-PET and 3D T1-weighted MRI brain scans. Regional standardised uptake value ratios (SUVR) for the PET scan and volumes calculated from an automated segmentation for the MRI were obtained and compared between the mutation carrier and control groups. Results The mean (standard deviation) estimated years from symptom onset was 12.5 (3.6) in the mutation carrier group with a range of 7 to 18 years. No differences in cognition were seen between the groups, and all mutation carriers had a global CDR plus NACC FTLD of 0. Significant reduction in [18F] FDG uptake in the anterior cingulate was seen in mutation carriers (mean 1.25 [standard deviation 0.07]) compared to controls (1.36 [0.09]). A similar significant reduction was also seen in grey matter volume in the anterior cingulate in mutation carriers (0.60% [0.06%]) compared to controls (0.68% [0.08%]). No other group differences were seen in other regions. Conclusions Anterior cingulate hypometabolism and atrophy are both apparent presymptomatically in a cohort of P301L MAPT mutation carriers. Such a specific marker may prove to be helpful in stratification of presymptomatic mutation carriers in future trials.

Sustained Interleukin-1β overexpression exacerbates Tau pathology in a murine tauopathy model via cyclooxygenase-1

Pathologic accumulation of abnormally phosphorylated tau in neurofibrillary tangles is a hallmark feature of Alzheimer’s disease and other tauopathies. Interleukin-1β ◻◻◻ −1β◻ is a major proinflammatory cytokine in the central nervous system that has been implicated in the pathogenesis of tauopathies as well as Alzheimer’s disease. To explore the role of chronic IL-1β overexpression in tauopathies in vivo we used an inducible model of IL-1β overexpression developed in our laboratory. The IL-1β (IL-1) mice bear a transcriptional stop flanked by LoxP elements upstream of a human IL-1β gene. Upon delivery of Cre, the IL-1 transgene is locally activated by excision of the stop sequence. The IL-1 mice were bred to JNPL3 (Tau) mice, which overexpress human tau with the P301L mutation. Expression of IL-1β was induced in the dentate gyrus of 8 to 8.5 month old progeny by stereotaxic injection of FIV-Cre. One and three months later, Tau/IL-1 mice demonstrated 2-4 fold increases in phospho-tau and glial activation. To attenuate IL-1β mediated inflammation, we reduced PGE2 production via pharmacological inhibition of cyclooxygenase-1 (COX-1) with SC560 in Tau/IL-1 mice, and observed significant reductions in phospho-tau pathology and microglial activation. Further, we found upregulation in active forms of p38MAPK, which was significantly reduced in mice receiving SC560 treatment. Our results demonstrate that IL-1β has a direct exacerbating effect on tau pathology in vivo, and inhibiting COX-1 can reverse this. COX-1 inhibition can therefore serve as a valuable therapeutic strategy for tauopathies with an advanced inflammatory component.

Clusterin ameliorates tau pathology in vivo by inhibiting fibril formation

The molecular chaperone Clusterin (CLU) impacts the amyloid pathway in Alzheimer’s disease (AD) but its role in tau pathology is unknown. We observed CLU co-localization with tau aggregates in AD and primary tauopathies and CLU levels were upregulated in response to tau accumulation. To further elucidate the effect of CLU on tau pathology, we utilized a gene delivery approach in CLU knock-out (CLU KO) mice to drive expression of tau bearing the P301L mutation. We found that loss of CLU was associated with exacerbated tau pathology and anxiety-like behaviors in our mouse model of tauopathy. Additionally, we found that CLU dramatically inhibited tau fibrilization using an in vitro assay. Together, these results demonstrate that CLU plays a major role in both amyloid and tau pathologies in AD.

Impact of the Hereditary P301L Mutation on the Correlated Conformational Dynamics of Human Tau Protein Revealed by the Paramagnetic Relaxation Enhancement NMR Experiments

Tau forms intracellular insoluble aggregates as a neuropathological hallmark of Alzheimer’s disease. Tau is largely unstructured, which complicates the characterization of the tau aggregation process. Recent studies have demonstrated that tau samples two distinct conformational ensembles, each of which contains the soluble and aggregation-prone states of tau. A shift to populate the aggregation-prone ensemble may promote tau fibrillization. However, the mechanism of this ensemble transition remains elusive. In this study, we explored the conformational dynamics of a tau fragment by using paramagnetic relaxation enhancement (PRE) and interference (PRI) NMR experiments. The PRE correlation map showed that tau is composed of segments consisting of residues in correlated motions. Intriguingly, residues forming the β-structures in the heparin-induced tau filament coincide with residues in these segments, suggesting that each segment behaves as a structural unit in fibrillization. PRI data demonstrated that the P301L mutation exclusively alters the transiently formed tau structures by changing the short- and long-range correlated motions among residues. The transient conformations of P301L tau expose the amyloid motif PHF6 to promote tau self-aggregation. We propose the correlated motions among residues within tau determine the population sizes of the conformational ensembles, and perturbing the correlated motions populates the aggregation-prone form.