Downregulation of hsa-miR-132 and hsa-miR-129: non-coding RNA molecular signatures of Alzheimer's disease.

Alzheimer's disease (AD) affects the elderly population by causing memory impairments, cognitive and behavioral abnormalities. Currently, no curative treatments exist, emphasizing the need to explore therapeutic options that modify the progression of the disease. MicroRNAs (miRNAs), as non-coding RNAs, demonstrate multifaceted targeting potential and are known to be dysregulated in AD pathology. This mini review focuses on two promising miRNAs, hsa-miR-132 and hsa-miR-129, which consistently exhibit differential regulation in AD. By employing computational predictions and referencing published RNA sequencing dataset, we elucidate the intricate miRNA-mRNA target relationships associated with hsa-miR-132 and hsa-miR-129. Our review consistently identifies the downregulation of hsa-miR-132 and hsa-miR-129 in AD brains as a non-coding RNA molecular signature across studies conducted over the past 15 years in AD research.

Alteration of gene expression and protein solubility of the PI 5-phosphatase SHIP2 are correlated with Alzheimer's disease pathology progression.

A recent large genome-wide association study has identified EGFR (encoding the epidermal growth factor EGFR) as a new genetic risk factor for late-onset AD. SHIP2, encoded by INPPL1, is taking part in the signalling and interactome of several growth factor receptors, such as the EGFR. While INPPL1 has been identified as one of the most significant genes whose RNA expression correlates with cognitive decline, the potential alteration of SHIP2 expression and localization during the progression of AD remains largely unknown. Here we report that gene expression of both EGFR and INPPL1 was upregulated in AD brains. SHIP2 immunoreactivity was predominantly detected in plaque-associated astrocytes and dystrophic neurites and its increase was correlated with amyloid load in the brain of human AD and of 5xFAD transgenic mouse model of AD. While mRNA of INPPL1 was increased in AD, SHIP2 protein undergoes a significant solubility change being depleted from the soluble fraction of AD brain homogenates and co-enriched with EGFR in the insoluble fraction. Using FRET-based flow cytometry biosensor assay for tau-tau interaction, overexpression of SHIP2 significantly increased the FRET signal while siRNA-mediated downexpression of SHIP2 significantly decreased FRET signal. Genetic association analyses suggest that some variants in INPPL1 locus are associated with the level of CSF pTau. Our data support the hypothesis that SHIP2 is an intermediate key player of EGFR and AD pathology linking amyloid and tau pathologies in human AD.

PICALM and Alzheimer's Disease: An Update and Perspectives.

Genome-wide association studies (GWAS) have identified the PICALM (Phosphatidylinositol binding clathrin-assembly protein) gene as the most significant genetic susceptibility locus after APOE and BIN1. PICALM is a clathrin-adaptor protein that plays a critical role in clathrin-mediated endocytosis and autophagy. Since the effects of genetic variants of PICALM as AD-susceptibility loci have been confirmed by independent genetic studies in several distinct cohorts, there has been a number of in vitro and in vivo studies attempting to elucidate the underlying mechanism by which PICALM modulates AD risk. While differential modulation of APP processing and Aß transcytosis by PICALM has been reported, significant effects of PICALM modulation of tau pathology progression have also been evidenced in Alzheimer's disease models. In this review, we summarize the current knowledge about PICALM, its physiological functions, genetic variants, post-translational modifications and relevance to AD pathogenesis.

Tau Pathology and Adult Hippocampal Neurogenesis: What Tau Mouse Models Tell us?

Adult hippocampal neurogenesis (AHN) has been widely confirmed in mammalian brains. A growing body of evidence points to the fact that AHN sustains hippocampal-dependent functions such as learning and memory. Impaired AHN has been reported in post-mortem human brain hippocampus of Alzheimer's disease (AD) and is considered to contribute to defects in learning and memory. Neurofibrillary tangles (NFTs) and amyloid plaques are the two key neuropathological hallmarks of AD. NFTs are composed of abnormal tau proteins accumulating in many brain areas during the progression of the disease, including in the hippocampus. The physiological role of tau and impact of tau pathology on AHN is still poorly understood. Modifications in AHN have also been reported in some tau transgenic and tau-deleted mouse models. We present here a brief review of advances in the relationship between development of tau pathology and AHN in AD and what insights have been gained from studies in tau mouse models.

Intravenous Injection of PHF-Tau Proteins From Alzheimer Brain Exacerbates Neuroinflammation, Amyloid Beta, and Tau Pathologies in 5XFAD Transgenic Mice.

Alzheimer's disease (AD) is characterized by the accumulation in the brain of intraneuronal aggregates of abnormally and hyperphosphorylated tau proteins and of extracellular deposits of amyloid-ß surrounded by dystrophic neurites. Numerous experimental models have shown that tau pathology develops in the brain after intracerebral injection of brain homogenates or pathological tau [paired helical filaments (PHF)-tau)] from AD brains. Further investigations are however necessary to identify or exclude potential extracerebral routes of tau pathology transmission, e.g., through the intravascular route. In this study, we have analyzed the effect of intravenous injection of PHF-tau proteins from AD brains on the formation of tau and amyloid pathologies in the brain of wild-type (WT) mice and of 5XFAD mice (an amyloid model). We observed that 5XFAD mice with a disrupted blood-brain barrier showed increased plaque-associated astrogliosis, microgliosis, and increased deposits of Aß40 and Aß42 after intravenous injection of PHF-tau proteins. In addition, an increased phosphotau immunoreactivity was observed in plaque-associated dystrophic neurites. These results suggest that blood products contaminated by PHF-tau proteins could potentially induce an exacerbation of neuroinflammation and AD pathologies.

The lipid phosphatase Synaptojanin 1 undergoes a significant alteration in expression and solubility and is associated with brain lesions in Alzheimer's disease.

Synaptojanin 1 (SYNJ1) is a brain-enriched lipid phosphatase critically involved in autophagosomal/endosomal trafficking, synaptic vesicle recycling and metabolism of phosphoinositides. Previous studies suggest that SYNJ1 polymorphisms have significant impact on the age of onset of Alzheimer's disease (AD) and that SYNJ1 is involved in amyloid-induced toxicity. Yet SYNJ1 protein level and cellular localization in post-mortem human AD brain tissues have remained elusive. This study aimed to examine whether SYNJ1 localization and expression are altered in post-mortem AD brains. We found that SYNJ1 is accumulated in Hirano bodies, plaque-associated dystrophic neurites and some neurofibrillary tangles (NFTs). SYNJ1 immunoreactivity was higher in neurons and in the senile plaques in AD patients carrying one or two ApolipoproteinE (APOE) ε4 allele(s). In two large cohorts of APOE-genotyped controls and AD patients, SYNJ1 transcripts were significantly increased in AD temporal isocortex compared to control. There was a significant increase in SYNJ1 transcript in APOEε4 carriers compared to non-carriers in AD cohort. SYNJ1 was systematically co-enriched with PHF-tau in the sarkosyl-insoluble fraction of AD brain. In the RIPA-insoluble fraction containing protein aggregates, SYNJ1 proteins were significantly increased and observed as a smear containing full-length and cleaved fragments in AD brains. In vitro cleavage assay showed that SYNJ1 is a substrate of calpain, which is highly activated in AD brains. Our study provides evidence of alterations in SYNJ1 mRNA level and SYNJ1 protein degradation, solubility and localization in AD brains.

Picalm reduction exacerbates tau pathology in a murine tauopathy model.

Genome-wide association studies (GWAS) have identified PICALM as one of the most significant susceptibility loci for late-onset Alzheimer's disease (AD) after APOE and BIN1. PICALM is a clathrin-adaptor protein and plays critical roles in clathrin-mediated endocytosis and in autophagy. PICALM modulates brain amyloid ß (Aß) pathology and tau accumulation. We have previously reported that soluble PICALM protein level is reduced in correlation with abnormalities of autophagy markers in the affected brain areas of neurodegenerative diseases including AD, sporadic tauopathies and familial cases of frontotemporal lobar degeneration with tau-immunoreactive inclusions (FTLD-tau) with mutations in the microtubule-associated protein tau (MAPT) gene. It remains unclarified whether in vivo PICALM reduction could either trigger or influence tau pathology progression in the brain. In this study, we confirmed a significant reduction of soluble PICALM protein and autophagy deficits in the post-mortem human brains of FTLD-tau-MAPT (P301L, S364S and L266V). We generated a novel transgenic mouse line named Tg30xPicalm+/- by crossing Tg30 tau transgenic mice with Picalm-haploinsufficient mice to test whether Picalm reduction may modulate tau pathology. While Picalm haploinsufficiency did not lead to any motor phenotype or detectable tau pathology in mouse brains, Tg30xPicalm+/- mice developed markedly more severe motor deficits than Tg30 by the age of 9 months. Tg30xPicalm+/- had significantly higher pathological tau levels in the brain, an increased density of neurofibrillary tangles compared to Tg30 mice and increased abnormalities of autophagy markers. Our results demonstrate that Picalm haploinsufficiency in transgenic Tg30 mice significantly aggravated tau pathologies and tau-mediated neurodegeneration, supporting a role for changes in Picalm expression as a risk/sensitizing factor for development of tau pathology and as a mechanism underlying the AD risk associated to PICALM.

A 4R tauopathy develops without amyloid deposits in aged cat brains.

Human tauopathies are neurodegenerative diseases with accumulation of abnormally phosphorylated and aggregated tau proteins forming neurofibrillary tangles. We investigated the development of tau pathology in aged cat brains as a model of neurofibrillary tangle formation occurring spontaneously during aging. In 4 of 6 cats aged between 18 and 21 years, we found a somatodendritic accumulation of phosphorylated and aggregated tau in neurons and oligodendrocytes. Two of these 4 cats had no amyloid immunoreactivity. These tau inclusions were mainly composed of 4R tau isoforms and straight filaments and colocalized with the active form of the glycogen synthase kinase-3 (GSK3). Cat brains with a tau pathology showed a significant cortical atrophy and neuronal loss. We demonstrate in this study the presence of a tau pathology in aged cat brains that develop independently of amyloid deposits. The colocalization of the active form of the GSK3 with tau inclusions as observed in human tauopathies suggests that this kinase could be responsible for the abnormal tau phosphorylation observed in aged cat brains, representing a mechanism of tau pathology development shared between a naturally occurring tauopathy in aged cats and human tauopathies.

Genetic ablation of tau in postnatal neurons rescues decreased adult hippocampal neurogenesis in a tauopathy model.

Impaired adult hippocampal neurogenesis has been reported as a feature of Alzheimer's disease and other tauopathies and might contribute to defects in learning and memory in these diseases. To assess the interference of tau pathology, a common key-lesion in these diseases, with adult hippocampal neurogenesis we analyzed adult neurogenesis in the hippocampal dentate gyrus in wild-type mice, Tg30 mice expressing a FTDP-17 mutant tau and the same Tg30 mice deficient for mouse tau (Tg30/tauKO). The volume of the granular layer, the number of granule cells and of neuronal precursors expressing the immature markers DCX or 3R-tau were analyzed in the dentate gyrus (DG) using unbiased stereological methods. The co-localization of neurogenic markers with the human mutant tau was also analyzed. We observed a significant reduction of the volume of the granular layer and of granule cells number in mutant tau Tg30 mice, but not in Tg30/tauKO mice. The number of neuronal precursors expressing the immature markers DCX or 3R-tau (the latter only expressed in wild-type and Tg30 mice) and the number of cells expressing the proliferation marker Ki-67 in the neurogenic subgranular zone of the DG was reduced in Tg30 but not in Tg30/tauKO mice. The density of phosphotau positive cells in the DG and the level of soluble human phosphotau was lower in Tg30/tauKO compared to Tg30 mice. The human mutant tau was expressed in mature granule cells in Tg30 and Tg30/tauKO mice but was not expressed in Sox2 positive neural stem cells and in DCX positive neuronal precursors/immature newborn neurons. These results demonstrate an impairment of adult hippocampal neurogenesis in a FTDP-17 mutant tau mice resulting from a decrease of proliferation affecting the pool of neuronal precursors. The mutant tau was not expressed in precursors cells in these mutant tau mice, suggesting that this neurogenic defect is cell non-autonomous. Interestingly, expression of endogenous wild-type tau in mature granule cells was necessary to observe this toxic effect of human mutant tau, since this impaired adult neurogenesis was rescued by lowering tau expression in Tg30/tauKO mice. These observations suggest that development of tau pathology in granule cells of the dentate gyrus is responsible for reduction of adult hippocampal neurogenesis also in human tauopathies by impairing proliferation of neuronal precursors, and that reduction of tau expression might be an approach to rescue this impairment.

Amyloid-ß pathology enhances pathological fibrillary tau seeding induced by Alzheimer PHF in vivo.

Neuropathological analysis in Alzheimer's disease (AD) and experimental evidence in transgenic models overexpressing frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTDP-17) mutant tau suggest that amyloid-ß pathology enhances the development of tau pathology. In this work, we analyzed this interaction independently of the overexpression of an FTDP-17 mutant tau, by analyzing tau pathology in wild-type (WT), 5xFAD, APP-/- and tau-/- mice after stereotaxic injection in the somatosensory cortex of short-length native human AD-PHF. Gallyas and phosphotau-positive tau inclusions developed in WT, 5xFAD, and APP-/- but not in tau-/- mice. Ultrastructural analysis demonstrated their intracellular localization and that they were composed of straight filaments. These seeded tau inclusions were composed only of endogenous murine tau exhibiting a tau antigenic profile similar to tau aggregates in AD. Insoluble tau level was higher and ipsilateral anteroposterior and contralateral cortical spreading of tau inclusions was more important in AD-PHF-injected 5xFAD mice than in WT mice. The formation of large plaque-associated dystrophic neurites positive for oligomeric and phosphotau was observed in 5xFAD mice injected with AD-PHF but never in control-injected or in non-injected 5xFAD mice. An increased level of the p25 activator of CDK5 kinase was found in AD-PHF-injected 5xFAD mice. These data demonstrate in vivo that the presence of Aß pathology enhances experimentally induced tau seeding of endogenous, wild-type tau expressed at physiological level, and demonstrate the fibrillar nature of heterotopically seeded endogenous tau. These observations further support the hypothesis that Aß enhances tau pathology development in AD through increased pathological tau spreading.

Interaction between a MAPT variant causing frontotemporal dementia and mutant APP affects axonal transport.

In Alzheimer's disease, many indicators point to a central role for poor axonal transport, but the potential for stimulating axonal transport to alleviate the disease remains largely untested. Previously, we reported enhanced anterograde axonal transport of mitochondria in 8- to 11-month-old MAPTP301L knockin mice, a genetic model of frontotemporal dementia with parkinsonism-17T. In this study, we further characterized the axonal transport of mitochondria in younger MAPTP301L mice crossed with the familial Alzheimer's disease model, TgCRND8, aiming to test whether boosting axonal transport in young TgCRND8 mice can alleviate axonal swelling. We successfully replicated the enhancement of anterograde axonal transport in young MAPTP301L/P301L knockin animals. Surprisingly, we found that in the presence of the amyloid precursor protein mutations, MAPTP301L/P3101L impaired anterograde axonal transport. The numbers of plaque-associated axonal swellings or amyloid plaques in TgCRND8 brains were unaltered. These findings suggest that amyloid-ß promotes an action of mutant tau that impairs axonal transport. As amyloid-ß levels increase with age even without amyloid precursor protein mutation, we suggest that this rise could contribute to age-related decline in frontotemporal dementia.

3D imaging in the postmortem human brain with CLARITY and CUBIC.

Recent innovations in tissue clearing and imaging technologies have enabled us to analyse biological systems directly in three-dimensions using thick samples. In this review, we discuss two of these recently reported tissue-clearing technologies (CLARITY and CUBIC) that are compatible with archival formalin-fixed human brain materials that have been fixed in formalin for a long period of time. We will discuss the pros and cons of these two technologies, examples of visualisation of Alzheimer neuropathological hallmarks and the exact protocols that we regularly use in the laboratory.

Neuropathology of iatrogenic Creutzfeldt-Jakob disease and immunoassay of French cadaver-sourced growth hormone batches suggest possible transmission of tauopathy and long incubation periods for the transmission of Abeta pathology.

Abeta deposits and tau pathology were investigated in 24 French patients that died from iatrogenic Creutzfeldt-Jakob disease after exposure to cadaver-derived human growth hormone (c-hGH) in the 1980s. Abeta deposits were found only in one case that had experienced one of the longest incubation periods. Three cases had also intracellular tau accumulation. The analysis of 24 batches of c-hGH, produced between 1974 and 1988, demonstrated for the first time the presence of Abeta and tau contaminants in c-hGH (in 17 and 6 batches, respectively). The incubation of prion disease was shorter in the French patients than the incubation times reported in two previously published British series. We interpreted the low incidence of Abeta in this French series as a consequence of the shorter incubation period observed in France, as compared to that observed in the United Kingdom. This concept suggested that a mean incubation period for the development of detectable Abeta deposits would be longer than 18 years after the first exposure. Moreover, we hypothesized that tau pathology might also be transmissible in humans.

Cortical cells reveal APP as a new player in the regulation of GABAergic neurotransmission.

The amyloid precursor protein (APP) modulates synaptic activity, resulting from the fine tuning of excitatory and inhibitory neurotransmission. GABAergic inhibitory neurotransmission is affected by modifications in intracellular chloride concentrations regulated by Na+-K+-2Cl- cotransporter 1 (NKCC1) and neuronal K+-Cl- cotransporter 2 (KCC2), allowing entrance and efflux of chloride, respectively. Modifications in NKCC1 and KCC2 expression during maturation of cortical cells induce a shift in GABAergic signaling. Here, we demonstrated that APP affects this GABA shift. Expression of APP in cortical cells decreased the expression of KCC2, without modifying NKCC1, eliciting a less inhibitory GABA response. Downregulation of KCC2 expression by APP was independent of the APP intracellular domain, but correlated with decreased expression of upstream stimulating factor 1 (USF1), a potent regulator of Slc12a5 gene expression (encoding KCC2). KCC2 was also downregulated in vivo following APP expression in neonatal mouse brain. These results argue for a key role of APP in the regulation of GABAergic neurotransmission.

Hallmarks of Alzheimer's Disease in Stem-Cell-Derived Human Neurons Transplanted into Mouse Brain.

Human pluripotent stem cells (PSCs) provide a unique entry to study species-specific aspects of human disorders such as Alzheimer's disease (AD). However, in vitro culture of neurons deprives them of their natural environment. Here we transplanted human PSC-derived cortical neuronal precursors into the brain of a murine AD model. Human neurons differentiate and integrate into the brain, express 3R/4R Tau splice forms, show abnormal phosphorylation and conformational Tau changes, and undergo neurodegeneration. Remarkably, cell death was dissociated from tangle formation in this natural 3D model of AD. Using genome-wide expression analysis, we observed upregulation of genes involved in myelination and downregulation of genes related to memory and cognition, synaptic transmission, and neuron projection. This novel chimeric model for AD displays human-specific pathological features and allows the analysis of different genetic backgrounds and mutations during the course of the disease.

Cell cycle S phase markers are expressed in cerebral neuron nuclei of cats infected by the Feline Panleukopenia Virus.

The cell cycle-associated neuronal death hypothesis, which has been proposed as a common mechanism for most neurodegenerative diseases, is notably supported by evidencing cell cycle effectors in neurons. However, in naturally occurring nervous system diseases, these markers are not expressed in neuron nuclei but in cytoplasmic compartments. In other respects, the Feline Panleukopenia Virus (FPV) is able to complete its cycle in mature brain neurons in the feline species. As a parvovirus, the FPV is strictly dependent on its host cell reaching the cell cycle S phase to start its multiplication. In this retrospective study on the whole brain of 12 cats with naturally-occurring, FPV-associated cerebellar atrophy, VP2 capsid protein expression was detected by immunostaining not only in some brain neuronal nuclei but also in neuronal cytoplasm in 2 cats, suggesting that viral mRNA translation was still occurring. In these cats, double immunostainings demonstrated the expression of cell cycle S phase markers cyclin A, cdk2 and PCNA in neuronal nuclei. Parvoviruses are able to maintain their host cells in S phase by triggering the DNA damage response. S139 phospho H2A1, a key player in the cell cycle arrest, was detected in some neuronal nuclei, supporting that infected neurons were also blocked into the S phase. PCR studies did not support a co-infection with an adeno or herpes virus. ERK1/2 nuclear accumulation was observed in some neurons suggesting that the ERK signaling pathway might be involved as a mechanism driving these neurons far into the cell cycle.

High-Molecular-Weight Paired Helical Filaments from Alzheimer Brain Induces Seeding of Wild-Type Mouse Tau into an Argyrophilic 4R Tau Pathology in Vivo.

In Alzheimer disease, the development of tau pathology follows neuroanatomically connected pathways, suggesting that abnormal tau species might recruit normal tau by passage from cell to cell. Herein, we analyzed the effect of stereotaxic brain injection of human Alzheimer high-molecular-weight paired helical filaments (PHFs) in the dentate gyrus of wild-type and mutant tau THY-Tau22 mice. After 3 months of incubation, wild-type and THY-Tau22 mice developed an atrophy of the dentate gyrus and a tau pathology characterized by Gallyas and tau-positive grain-like inclusions into granule cells that extended in the hippocampal hilus and eventually away into the alveus, and the fimbria. Gallyas-positive neuropil threads and oligodendroglial coiled bodies were also observed. These tau inclusions were composed only of mouse tau, and were immunoreactive with antibodies to 4R tau, phosphotau, misfolded tau, ubiquitin, and p62. Although local hyperphosphorylation of tau was increased in the dentate gyrus in THY-Tau22 mice, the development of neurofibrillary tangles made of mutant human tau was not accelerated in the hippocampus, indicating that wild-type human PHFs were inefficient in seeding tau aggregates made of G272V/P301S mutant human tau. Our results indicate thus that injection of human wild-type Alzheimer PHF seeded aggregation of wild-type murine tau into an argyrophilic 4R tau pathology, and constitutes an interesting model independent of expression of a mutant tau protein.