The glymphatic system, that is aquaporin 4 (AQP4) facilitated exchange of CSF with interstitial fluid (ISF), may provide a clearance pathway for protein species such as amyloid-β and tau, which ...accumulate in the brain in Alzheimer's disease. Further, tau protein transference via the extracellular space, the compartment that is cleared by the glymphatic pathway, allows for its neuron-to-neuron propagation, and the regional progression of tauopathy in the disorder. The glymphatic system therefore represents an exciting new target for Alzheimer's disease. Here we aim to understand the involvement of glymphatic CSF-ISF exchange in tau pathology. First, we demonstrate impaired CSF-ISF exchange and AQP4 polarization in a mouse model of tauopathy, suggesting that this clearance pathway may have the potential to exacerbate or even induce pathogenic accumulation of tau. Subsequently, we establish the central role of AQP4 in the glymphatic clearance of tau from the brain; showing marked impaired glymphatic CSF-ISF exchange and tau protein clearance using the novel AQP4 inhibitor, TGN-020. As such, we show that this system presents as a novel druggable target for the treatment of Alzheimer's disease, and possibly other neurodegenerative diseases alike.
The interneuronal propagation of aggregated tau is believed to play an important role in the pathogenesis of human tauopathies. It requires the uptake of seed-competent tau into cells, seeding of ...soluble tau in recipient neurons and release of seeded tau into the extracellular space to complete the cycle. At present, it is not known which tau species are seed-competent. Here, we have dissected the molecular characteristics of seed-competent tau species from the TgP301S tau mouse model using various biochemical techniques and assessed their seeding ability in cell and animal models. We found that sucrose gradient fractions from brain lysates seeded cellular tau aggregation only when large (>10 mer) aggregated, hyperphosphorylated (AT8- and AT100-positive) and nitrated tau was present. In contrast, there was no detectable seeding by fractions containing small, oligomeric (<6 mer) tau. Immunodepletion of the large aggregated AT8-positive tau strongly reduced seeding; moreover, fractions containing these species initiated the formation and spreading of filamentous tau pathology in vivo, whereas fractions containing tau monomers and small oligomeric assemblies did not. By electron microscopy, seed-competent sucrose gradient fractions contained aggregated tau species ranging from ring-like structures to small filaments. Together, these findings indicate that a range of filamentous tau aggregates are the major species that underlie the spreading of tau pathology in the P301S transgenic model. Significance statement: The spread of tau pathology from neuron to neuron is postulated to account for, or at least to contribute to, the overall propagation of tau pathology during the development of human tauopathies including Alzheimer's disease. It is therefore important to characterize the native tau species responsible for this process of seeding and pathology spreading. Here, we use several biochemical techniques to dissect the molecular characteristics of native tau protein conformers from TgP301S tau mice and show that seed-competent tau species comprise small fibrils capable of seeding tau pathology in cell and animal models. Characterization of seed-competent tau gives insight into disease mechanisms and therapeutic interventions.
Intracellular tau inclusions are a pathological hallmark of Alzheimer's disease, progressive supranuclear palsy, corticobasal degeneration and other sporadic neurodegenerative tauopathies. Recent in ...vitro and in vivo studies have shown that tau aggregates may spread to neighbouring cells and functionally connected brain regions, where they can seed further tau aggregation. This process is referred to as tau propagation. Here we describe an ex vivo system using organotypic hippocampal slice cultures (OHCs) which recapitulates aspects of this phenomenon. OHCs are explants of hippocampal tissue which may be maintained in culture for months. They maintain their synaptic connections and multicellular 3D architecture whilst also permitting direct control of the environment and direct access for various analysis types. We inoculated OHCs prepared from P301S mouse pups with brain homogenate from terminally ill P301S mice and then examined the slices for viability and the production and localization of insoluble phosphorylated tau. We show that following seeding, phosphorylated insoluble tau accumulate in a time and concentration dependent manner within OHCs. Furthermore, we show the ability of the conformation dependent anti-tau antibody, MC1, to compromise tau accrual in OHCs, thus showcasing the potential of this therapeutic approach and the utility of OHCs as an ex vivo model system for assessing such therapeutics.
Alternative splicing is a post-transcriptional regulatory mechanism producing distinct mRNA molecules from a single pre-mRNA with a prominent role in the development and function of the central ...nervous system. We used long-read isoform sequencing to generate full-length transcript sequences in the human and mouse cortex. We identify novel transcripts not present in existing genome annotations, including transcripts mapping to putative novel (unannotated) genes and fusion transcripts incorporating exons from multiple genes. Global patterns of transcript diversity are similar between human and mouse cortex, although certain genes are characterized by striking differences between species. We also identify developmental changes in alternative splicing, with differential transcript usage between human fetal and adult cortex. Our data confirm the importance of alternative splicing in the cortex, dramatically increasing transcriptional diversity and representing an important mechanism underpinning gene regulation in the brain. We provide transcript-level data for human and mouse cortex as a resource to the scientific community.
Display omitted
•There is widespread transcript diversity in the cortex and many novel transcripts•Some genes display big differences in isoform number between human and mouse cortex•There is evidence of differential transcript usage between human fetal and adult cortex•There are many novel isoforms of genes associated with human brain disease
Leung et al. use long-read sequencing to annotate RNA isoforms in the human and mouse cortex. They identify novel transcripts and evidence for differential transcript usage between the fetal and adult cortex. Their data confirm the importance of alternative splicing as a mechanism underpinning gene regulation in the brain.
Neurodegenerative tauopathies, of which progressive supranuclear palsy (PSP) is one of the most common, are clinically heterogeneous, reflecting differences in distribution and biochemical ...composition of tau pathology. This review highlights the range of clinical and pathologic presentations of PSP and its variants.
Progressive supranuclear palsy is a 4R tauopathy with neuronal and glial tau-immunoreactive lesions in neuroanatomically specific nuclei in the basal ganglia, diencephalon, brainstem and cerebellum, with restricted involvement of the neocortex. Hierarchical cluster analyses of clinical and pathologic features of PSP indicate that there are distinct clinicopathologic variants of PSP. In variants of PSP presenting with focal cortical syndromes, such as frontotemporal dementia, corticobasal syndrome and apraxia of speech, there is greater cortical pathology than in typical PSP. In variants of PSP presenting with levodopa-responsive Parkinsonism, as well as pure akinesia and gait failure, there is less cortical pathology and more severe degeneration in the cardinal nuclei - globus pallidus, subthalamic nucleus and substantia nigra - than in typical PSP.
Clinical variants in PSP reflect varying anatomical distribution of tau pathology, but they share histopathologic, biochemical and genetic features with typical PSP. The basis for anatomical selective vulnerability in PSP and its variants remains to be determined.
Objective
This study aimed to determine the frequency of frontotemporal lobar degeneration with ubiquitinated inclusions (FTLD‐U) in the setting of hippocampal sclerosis (HpScl) and Alzheimer's ...disease (AD) using immunohistochemistry for TAR DNA binding protein 43 (TDP‐43), a putative marker for FTLD‐U.
Methods
Initially, 21 cases of HpScl associated with a variety of other pathological processes and 74 cases of AD were screened for FTLD‐U with TDP‐43 immunohistochemistry. A confirmation study was performed on 93 additional AD cases. Specificity of TDP‐43 antibodies was assessed using double‐immunolabeling confocal microscopy, immunoelectron microscopy, and biochemistry.
Results
TDP‐43 immunoreactivity was detected in 71% of HpScl and 23% of AD cases. Double immunostaining of AD cases for TDP‐43 and phospho‐tau showed that the TDP‐43–immunoreactive inclusions were usually distinct from neurofibrillary tangles. At the ultrastructural level, TDP‐43 immunoreactivity in AD was associated with granular and filamentous cytosolic material and only occasionally associated with tau filaments. Western blots of AD cases showed a band that migrated at a higher molecular weight than normal TDP‐43 that was not present in AD cases without TDP‐43 immunoreactivity.
Interpretation
These results suggest that as many as 20% of AD cases and more than 70% of HpScl cases have pathology similar to that found in FTLD‐U. Whether this represents concomitant FTLD‐U or is analogous to colocalization of α‐synuclein and tau in AD, reflecting a propensity for codeposition of abnormal protein conformers, remains to be determined. Ann Neurol 2007;61:435–445
Progranulin (PGRN) is involved in wound repair, inflammation, and tumor formation, but its function in the central nervous system is unknown. Roles in development, sexual differentiation, and ...long-term neuronal survival have been suggested. Mutations in the GRN gene resulting in partial loss of the encoded PGRN protein cause frontotemporal lobar degeneration with ubiquitin immunoreactive inclusions. We sought to understand the neuropathological consequences of loss of PGRN function throughout the lifespan of GRN -deficient (−/+ and−/− ) mice. An aged series of GRN -deficient and wild-type mice were compared by histology, immunohistochemistry, and electron microscopy. Although GRN -deficient mice were viable, GRN−/− mice were produced at lower than predicted frequency. Neuropathologically, GRN−/+ were indistinguishable from controls; however, GRN−/− mice developed age-associated, abnormal intraneuronal ubiquitin-positive autofluorescent lipofuscin. Lipofuscin was noted in aged GRN+/+ mice at levels comparable with those of young GRN−/− mice. GRN−/− mice developed microgliosis, astrogliosis, and tissue vacuolation, with focal neuronal loss and severe gliosis apparent in the oldest GRN−/− mice. Although no overt frontotemporal lobar degeneration with ubiquitin immunoreactive inclusions type- or TAR DNA binding protein-43-positive lesions were observed, robust lipofuscinosis and ubiquitination in GRN−/− mice is strikingly similar to changes associated with aging and cellular decline in humans and animal models. Our data suggests that PGRN plays a key role in maintaining neuronal function during aging and supports the notion that PGRN is a trophic factor essential for long-term neuronal survival.
Abstract Increasing evidence suggests that alternative splicing plays an important role in Alzheimer’s disease (AD) pathology. We used long-read sequencing in combination with a novel bioinformatics ...tool ( FICLE ) to profile transcript diversity in the entorhinal cortex of female transgenic (TG) mice harboring a mutant form of human tau. Our analyses revealed hundreds of novel isoforms and identified differentially expressed transcripts – including specific isoforms of Apoe , App , Cd33 , Clu , Fyn and Trem2 – associated with the development of tau pathology in TG mice. Subsequent profiling of the human cortex from AD individuals and controls revealed similar patterns of transcript diversity, including the upregulation of the dominant TREM2 isoform in AD paralleling the increased expression of the homologous transcript in TG mice. Our results highlight the importance of differential transcript usage, even in the absence of gene-level expression alterations, as a mechanism underpinning gene regulation in the development of AD neuropathology.
Progranulin (PGRN) is a pleiotropic protein that has gained the attention of the neuroscience community with recent discoveries of mutations in the gene for PGRN that cause frontotemporal lobar ...degeneration (FTLD). Pathogenic mutations in PGRN result in null alleles, and the disease is likely the result of haploinsufficiency. Little is known about the normal function of PGRN in the central nervous system apart from a role in brain development. It is expressed by microglia and neurons. In the periphery, PGRN is involved in wound repair and inflammation. High PGRN expression has been associated with more aggressive growth of various tumors. The properties of full length PGRN are distinct from those of proteolytically derived peptides, referred to as granulins (GRNs). While PGRN has trophic properties, GRNs are more akin to inflammatory mediators such as cytokines. Loss of the neurotrophic properties of PGRN may play a role in selective neuronal degeneration in FTLD, but neuroinflammation may also be important. Gene expression studies suggest that PGRN is up-regulated in a variety of neuroinflammatory conditions, and increased PGRN expression by microglia may play a pivotal role in the response to brain injury, neuroinflammation and neurodegeneration.
Alzheimer’s disease (AD) is associated with the intracellular aggregation of hyperphosphorylated tau and the accumulation of β-amyloid in the neocortex. We use transgenic mice harboring human tau ...(rTg4510) and amyloid precursor protein (J20) mutations to investigate transcriptional changes associated with the progression of tau and amyloid pathology. rTg4510 mice are characterized by widespread transcriptional differences in the entorhinal cortex with changes paralleling neuropathological burden across multiple brain regions. Differentially expressed transcripts overlap with genes identified in genetic studies of familial and sporadic AD. Systems-level analyses identify discrete co-expression networks associated with the progressive accumulation of tau that are enriched for genes and pathways previously implicated in AD pathology and overlap with co-expression networks identified in human AD cortex. Our data provide further evidence for an immune-response component in the accumulation of tau and reveal molecular pathways associated with the progression of AD neuropathology.
Display omitted
•Mice with human tau and amyloid mutations develop progressive neuropathology•We identify transcriptional changes associated with tau and amyloid pathology•Discrete co-expression networks are associated with the progression of tau pathology•These are enriched for genes and pathways implicated in the onset of human AD
Castanho et al. use transgenic mice harboring human tau and amyloid precursor protein mutations to identify transcriptional changes associated with the progression of Alzheimer’s disease (AD) pathology. Their data support an immune-response component in the accumulation of tau and reveal molecular pathways associated with AD neuropathology.
PDF
