PAC1 receptor-mediated clearance of tau in postsynaptic compartments attenuates tau pathology in mouse brain

The angiotensin (1-7) glycopeptide PNA5 improves cognition in a chronic progressive mouse model of Parkinson's disease through modulation of neuroinflammation

Cognitive decline in Parkinson's Disease (PD) is a prevalent and undertreated aspect of disease. Currently, no therapeutics adequately improve this aspect of disease. It has been previously shown that MAS receptor agonism via the glycosylated Angiotensin (1-7) peptide, PNA5, effectively reduces cognitive decline in models of vascular contributions to cognitive impairment and dementia (VCID). PNA5 has a brain/plasma ratio of 0.255 indicating good brain penetration. The goal of the present study was to determine if (1) systemic administration of PNA5 rescued cognitive decline in a mouse model of PD, and (2) if improvements in cognitive status could be correlated with changes to histopathological or blood plasma-based changes. Mice over-expressing human, wild-type α-synuclein (αSyn) under the Thy1 promoter (Thy1-αSyn mice, "line 61") were used as a model of PD with cognitive decline. Thy1-αSyn mice were treated with a systemic dose of PNA5, or saline (1 mg/kg/day) beginning at 4 months of age and underwent behavioral testing at 6 months, compared to WT. Subsequently, mice brains were analyzed for changes to brain pathology, and blood plasma was examined with a Multiplex Immunoassay for peripheral cytokine changes. Treatment with PNA5 reversed cognitive dysfunction measured by Novel Object Recognition and spontaneous alteration in a Y-maze in Thy1-αSyn mice. PNA5 treatment was specific to cognitive deficits, as fine-motor disturbances were unchanged. Enhanced cognition was associated with decreases in hippocampal inflammation and reductions in circulating levels of Macrophage Induced Protein (MIP-1β). Additionally, neuronal loss was blunted within the CA3 hippocampal region of PNA5-treated αsyn mice. These data reveal that PNA5 treatment reduces cognitive dysfunction in a mouse model of PD. These changes are associated with decreased MIP-1β levels in plasma identifying a candidate biomarker for target engagement. Thus, PNA5 treatment could potentially fill the therapeutic gap for cognitive decline in PD.

Plasmonic nanoparticle-assisted single-molecule dynamic binding for protein kinase activity digital counting

In this work, we design a new approach for digital counting-based protein kinase activity assay by using plasmonic nanoparticle-assisted single-molecule dynamic binding. This method breaks the concentration-dependent limitation in single-molecule detection and displays good selectivity and sensitivity with a detection limit as low as 0.0001 U mL-1 for the protein kinase A (PKA) assay, which would find broad applications in drug screening and medical investigations.

Systemic Administration of Neurotransmitter-Derived Lipidoids-PROTACs-DNA Nanocomplex Promotes Tau Clearance and Cognitive Recovery for Alzheimer's Disease Therapy

Alzheimer's disease (AD) poses a significant burden on the economy and healthcare systems worldwide. Although the pathophysiology of AD remains debatable, its progression is strongly correlated with the accumulation of tau aggregates. Therefore, tau clearance from brain lesions can be a promising strategy for AD therapy. To achieve this, the present study combined proteolysis-targeting chimera (PROTAC), a novel protein-degradation technique that mediates degradation of target proteins via the ubiquitin-proteasome system, and a neurotransmitter-derived lipidoid (NT-lipidoid) nanoparticle delivery system with high blood-brain barrier-penetration activity, to generate a novel nanomedicine named NPD. Peptide 1, a cationic tau-targeting PROTAC is loaded onto the positively charged nanoparticles using DNA-intercalation technology. The resulting nanomedicine displayed good encapsulation efficiency, serum stability, drug release profile, and blood-brain barrier-penetration capability. Furthermore, NPD potently induced tau clearance in both cultured neuronal cells and the brains of AD mice. Moreover, intravenous injection of NPD led to a significant improvement in the cognitive function of the AD mice, without any remarkable abnormalities, thereby supporting its clinical development. Collectively, the novel nanomedicine developed in this study may serve as an innovative strategy for AD therapy, since it effectively and specifically induces tau protein clearance in brain lesions, which in turn enhances cognition.

Nasal tau immunotherapy clears intracellular tau pathology and improves cognitive functions in aged tauopathy mice

Pathological tau aggregates cause cognitive decline in neurodegenerative tauopathies, including Alzheimer's disease (AD). These aggregates are prevalent within intracellular compartments. Current tau immunotherapies have shown limited efficacy in clearing intracellular tau aggregates and improving cognition in clinical trials. In this study, we developed toxic tau conformation-specific monoclonal antibody-2 (TTCM2), which selectively recognized pathological tau aggregates in brain tissues from patients with AD, dementia with Lewy bodies (DLB), and progressive supranuclear palsy (PSP). TTCM2 potently inhibited tau-seeding activity, an essential mechanism underlying tauopathy progression. To effectively target intracellular tau aggregates and ensure rapid delivery to the brain, TTCM2 was loaded in micelles (TTCM2-ms) and administered through the intranasal route. We found that intranasally administered TTCM2-ms efficiently entered the brain in hTau-tauopathy mice, targeting pathological tau in intracellular compartments. Moreover, a single intranasal dose of TTCM2-ms effectively cleared pathological tau, elevated synaptic proteins, and improved cognitive functions in aged tauopathy mice. Mechanistic studies revealed that TTCM2-ms cleared intracellular, synaptic, and seed-competent tau aggregates through tripartite motif-containing 21 (TRIM21), an intracellular antibody receptor and E3 ubiquitin ligase known to facilitate proteasomal degradation of cytosolic antibody-bound proteins. TRIM21 was found to be essential for TTCM2-ms-mediated clearance of tau pathology. Our study collectively provides evidence of the effectiveness of nasal tau immunotherapy in targeting and clearing intracellular tau pathology through TRIM21 and enhancing cognition in aged tauopathy mice. This study could be valuable in designing effective tau immunotherapies for AD and other tauopathies.

Synaptic alterations associated with disrupted sensory encoding in a mouse model of tauopathy

Synapse loss is currently the best biological correlate of cognitive decline in Alzheimer's disease and other tauopathies. Synapses seem to be highly vulnerable to tau-mediated disruption in neurodegenerative tauopathies. However, it is unclear how and when this leads to alterations in function related to the progression of tauopathy and neurodegeneration. We used the well-characterized rTg4510 mouse model of tauopathy at 5-6 months and 7-8 months of age, respectively, to study the functional impact of cortical synapse loss. The earlier age was used as a model of prodromal tauopathy, with the later age corresponding to more advanced tau pathology and presumed progression of neurodegeneration. Analysis of synaptic protein expression in the somatosensory cortex showed significant reductions in synaptic proteins and NMDA and AMPA receptor subunit expression in rTg4510 mice. Surprisingly, in vitro whole-cell patch clamp electrophysiology from putative pyramidal neurons in layer 2/3 of the somatosensory cortex suggested no functional alterations in layer 4 to layer 2/3 synaptic transmission at 5-6 months. From these same neurons, however, there were alterations in dendritic structure, with increased branching proximal to the soma in rTg4510 neurons. Therefore, in vivo whole-cell patch clamp recordings were utilized to investigate synaptic function and integration in putative pyramidal neurons in layer 2/3 of the somatosensory cortex. These recordings revealed a significant increase in the peak response to synaptically driven sensory stimulation-evoked activity and a loss of temporal fidelity of the evoked signal to the input stimulus in rTg4510 neurons. Together, these data suggest that loss of synapses, changes in receptor expression and dendritic restructuring may lead to alterations in synaptic integration at a network level. Understanding these compensatory processes could identify targets to help delay symptomatic onset of dementia.

5-HT4 receptor agonists treatment reduces tau pathology and behavioral deficit in the PS19 mouse model of tauopathy

Background

Accumulation of tau in synapses in the early stages of Alzheimer's disease (AD) has been shown to cause synaptic damage, synaptic loss, and the spread of tau pathology through trans-synaptically connected neurons. Moreover, synaptic loss correlates with a decline in cognitive function, providing an opportunity to investigate therapeutic strategies to target synapses and synaptic tau to rescue or prevent cognitive decline in AD. One of the promising synaptic targets is the 5-HT4 serotonergic receptor present postsynaptically in the brain structures involved in the memory processes. 5-HT4R stimulation exerts synaptogenic and pro-cognitive effects involving synapse-to-nucleus signaling essential for synaptic plasticity. However, it is not known whether 5-HT4R activation has a therapeutic effect on tau pathology.

Methods

The goal of this study was to investigate the impact of chronic stimulation of 5-HT4R by two agonists, prucalopride and RS-67333, in PS19 mice, a model of tauopathy. We utilized gradient assays to isolate pre- and post-synaptic compartments, followed by biochemical analyses for tau species and ubiquitinated proteins in the synaptic compartments and total brain tissue. Next, we performed kinetic assays to test the proteasome's hydrolysis capacity in treatment conditions. Moreover, behavioral tests such as the open field and non-maternal nest-building tests were used to evaluate anxiety-like behaviors and hippocampal-related cognitive functioning in the treatment paradigm.

Results

Our results show that 5-HT4R agonism reduced tauopathy, reduced synaptic tau, increased proteasome activity, and improved cognitive functioning in PS19 mice. Our data suggest that enhanced proteasome activity by synaptic mediated signaling leads to the enhanced turnover of tau initially within synapses where the receptors are localized, and over time, the treatment attenuated the accumulation of tau aggregation and improved cognitive functioning of the PS19 mice.

Conclusion

Therefore, stimulation of 5-HT4R offers a promising therapy to rescue synapses from the accumulation of toxic synaptic tau, evident in the early stages of AD.

Tau here, tau there, tau almost everywhere: Clarifying the distribution of tau in the adult CNS

The microtubule-associated protein tau has gained significant attention over the last several decades primarily due to its apparent role in the pathogenesis of several diseases, most notably Alzheimer's disease. While the field has focused largely on tau's potential contributions to disease mechanisms, comparably less work has focused on normal tau physiology. Moreover, as the field has grown, some misconceptions and dogmas regarding normal tau physiology have become engrained in the traditional narrative. Here, one of the most common misconceptions regarding tau, namely its normal cellular/subcellular distribution in the CNS, is discussed. The literature describing the presence of tau in neuronal somata, dendrites, axons and synapses, as well as in glial cells is described. The origins for the erroneous description of tau as an "axon-specific," "axon-enriched" and/or "neuron-specific" protein are discussed as well. The goal of this work is to help address these specific dogmatic misconceptions and provide a concise description of tau's normal cellular/subcellular localization in the adult CNS. This information can help refine our collective understanding of- and hypotheses about tau biology and pathobiology.

Synaptic proteasome is inhibited in Alzheimer's disease models and associates with memory impairment in mice

The proteasome plays key roles in synaptic plasticity and memory by regulating protein turnover, quality control, and elimination of oxidized/misfolded proteins. Here, we investigate proteasome function and localization at synapses in Alzheimer's disease (AD) post-mortem brain tissue and in experimental models. We found a marked increase in ubiquitinylated proteins in post-mortem AD hippocampi compared to controls. Using several experimental models, we show that amyloid-β oligomers (AβOs) inhibit synaptic proteasome activity and trigger a reduction in synaptic proteasome content. We further show proteasome inhibition specifically in hippocampal synaptic fractions derived from APPswePS1ΔE9 mice. Reduced synaptic proteasome activity instigated by AβOs is corrected by treatment with rolipram, a phosphodiesterase-4 inhibitor, in mice. Results further show that dynein inhibition blocks AβO-induced reduction in dendritic proteasome content in hippocampal neurons. Finally, proteasome inhibition induces AD-like pathological features, including reactive oxygen species and dendritic spine loss in hippocampal neurons, inhibition of hippocampal mRNA translation, and memory impairment in mice. Results suggest that proteasome inhibition may contribute to synaptic and memory deficits in AD.

PACAP-Sirtuin3 alleviates cognitive impairment through autophagy in Alzheimer's disease

BACKGROUND

Autophagy is vital in the pathogenesis of neurodegeneration. Thus far, no studies have specifically investigated the relationship between pituitary adenylate cyclase-activating polypeptide (PACAP) and autophagy, particularly in the context of Alzheimer's disease (AD). This study used in vitro and in vivo models, along with clinical samples, to explore interactions between PACAP and autophagy in AD.

METHODS

AD model mice were administered 6 μl of 0.1 mg/ml PACAP liquid intranasally for 4 weeks, then subjected to behavioral analyses to assess the benefits of PACAP treatment. The underlying mechanisms of PACAP-induced effects were investigated by methods including real-time quantitative polymerase chain reaction, RNA sequencing, immunofluorescence, and western blotting. Exosomes were extracted from human serum and subjected to enzyme-linked immunosorbent assays to examine autophagy pathways. The clinical and therapeutic implications of PACAP and autophagy were extensively investigated throughout the experiment.

RESULTS

Impaired autophagy was a critical step in amyloid β (Aβ) and Tau deposition; PACAP enhanced autophagy and attenuated cognitive impairment. RNA sequencing revealed three pathways that may be involved in AD progression: PI3K-AKT, mTOR, and AMPK. In vivo and in vitro studies showed that sirtuin3 knockdown diminished the ability of PACAP to restore normal autophagy function, resulting in phagocytosis dysregulation and the accumulation of pTau, Tau, and Aβ. Additionally, the autophagic biomarker MAP1LC3 demonstrated a positive association with PACAP in human serum.

CONCLUSIONS

PACAP reverses AD-induced cognitive impairment through autophagy, using sirtuin3 as a key mediator. MAP1LC3 has a positive relationship with PACAP in humans. These findings provide insights regarding potential uses of intranasal PACAP and sirtuin3 agonists in AD treatment.

TRIAL REGISTRATION

NCT04320368.

Multivalent Tau/PSD-95 interactions arrest in vitro condensates and clusters mimicking the postsynaptic density

Alzheimer's disease begins with mild memory loss and slowly destroys memory and thinking. Cognitive impairment in Alzheimer's disease has been associated with the localization of the microtubule-associated protein Tau at the postsynapse. However, the correlation between Tau at the postsynapse and synaptic dysfunction remains unclear. Here, we show that Tau arrests liquid-like droplets formed by the four postsynaptic density proteins PSD-95, GKAP, Shank, Homer in solution, as well as NMDA (N-methyl-D-aspartate)-receptor-associated protein clusters on synthetic membranes. Tau-mediated condensate/cluster arrest critically depends on the binding of multiple interaction motifs of Tau to a canonical GMP-binding pocket in the guanylate kinase domain of PSD-95. We further reveal that competitive binding of a high-affinity phosphorylated peptide to PSD-95 rescues the diffusional dynamics of an NMDA truncated construct, which contains the last five amino acids of the NMDA receptor subunit NR2B fused to the C-terminus of the tetrameric GCN4 coiled-coil domain, in postsynaptic density-like condensates/clusters. Taken together, our findings propose a molecular mechanism where Tau modulates the dynamic properties of the postsynaptic density.

Serum tau protein elevation in migraine: a cross-sectional case-control study

BACKGROUND

Migraine is a disorder associated with neuropeptide release, pain and inflammation. Tau protein has recently been linked to inflammatory diseases and can be influenced by neuropeptides such as CGRP, a key neurotransmitter in migraine. Here, we report serum concentrations of total-tau protein in migraine patients and healthy controls.

METHODS

In this cross-sectional study, interictal blood samples from n = 92 patients with episodic migraine (EM), n = 93 patients with chronic migraine (CM), and n = 42 healthy matched controls (HC) were studied. We assessed serum total-tau protein (t-tau) and for comparison neurofilament light chain protein (NfL), glial fibrillary acidic protein (GFAP), and ubiquitin carboxy-terminal hydrolase L (UCH-L1) concentrations using the Neurology 4-plex kit, on a single molecule array HD-X Analyzer (Quanterix Corp Lexington, MA). Matched serum/cerebrospinal fluid (CSF) samples were used for post-hoc evaluations of a central nervous system (CNS) source of relevant findings. We applied non-parametric tests to compare groups and assess correlations.

RESULTS

Serum t-tau concentrations were elevated in EM [0.320 (0.204 to 0.466) pg/mL] and CM [0.304 (0.158 to 0.406) pg/mL] patients compared to HC [0.200 (0.114 to 0.288) pg/mL] (p = 0.002 vs. EM; p = 0.025 vs. CM). EM with aura [0.291 (0.184 to 0.486 pg/mL); p = 0.013] and EM without aura [0.332 (0.234 to 0.449) pg/mL; p = 0.008] patients had higher t-tau levels than HC but did not differ between each other. Subgroup analysis of CM with/without preventive treatment revealed elevated t-tau levels compared to HC only in the non-prevention group [0.322 (0.181 to 0.463) pg/mL; p = 0.009]. T-tau was elevated in serum (p = 0.028) but not in cerebrospinal fluid (p = 0.760). In contrast to t-tau, all proteins associated with cell damage (NfL, GFAP, and UCH-L1), did not differ between groups.

DISCUSSION

Migraine is associated with t-tau elevation in serum but not in the CSF. Our clinical study identifies t-tau as a new target for migraine research.

Synaptic oligomeric tau in Alzheimer's disease - A potential culprit in the spread of tau pathology through the brain

In Alzheimer's disease, fibrillar tau pathology accumulates and spreads through the brain and synapses are lost. Evidence from mouse models indicates that tau spreads trans-synaptically from pre- to postsynapses and that oligomeric tau is synaptotoxic, but data on synaptic tau in human brain are scarce. Here we used sub-diffraction-limit microscopy to study synaptic tau accumulation in postmortem temporal and occipital cortices of human Alzheimer's and control donors. Oligomeric tau is present in pre- and postsynaptic terminals, even in areas without abundant fibrillar tau deposition. Furthermore, there is a higher proportion of oligomeric tau compared with phosphorylated or misfolded tau found at synaptic terminals. These data suggest that accumulation of oligomeric tau in synapses is an early event in pathogenesis and that tau pathology may progress through the brain via trans-synaptic spread in human disease. Thus, specifically reducing oligomeric tau at synapses may be a promising therapeutic strategy for Alzheimer's disease.

Disrupting pathologic phase transitions in neurodegeneration

Solid-like protein deposits found in aged and diseased human brains have revealed a relationship between insoluble protein accumulations and the resulting deficits in neurologic function. Clinically diverse neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, frontotemporal lobar degeneration, and amyotrophic lateral sclerosis, exhibit unique and disease-specific biochemical protein signatures and abnormal protein depositions that often correlate with disease pathogenesis. Recent evidence indicates that many pathologic proteins assemble into liquid-like protein phases through the highly coordinated process of liquid-liquid phase separation. Over the last decade, biomolecular phase transitions have emerged as a fundamental mechanism of cellular organization. Liquid-like condensates organize functionally related biomolecules within the cell, and many neuropathology-associated proteins reside within these dynamic structures. Thus, examining biomolecular phase transitions enhances our understanding of the molecular mechanisms mediating toxicity across diverse neurodegenerative diseases. This Review explores the known mechanisms contributing to aberrant protein phase transitions in neurodegenerative diseases, focusing on tau and TDP-43 proteinopathies and outlining potential therapeutic strategies to regulate these pathologic events.

Alzheimer’s disease as a synaptopathy: Evidence for dysfunction of synapses during disease progression

The synapse has consistently been considered a vulnerable and critical target within Alzheimer’s disease, and synapse loss is, to date, one of the main biological correlates of cognitive decline within Alzheimer’s disease. This occurs prior to neuronal loss with ample evidence that synaptic dysfunction precedes this, in support of the idea that synaptic failure is a crucial stage within disease pathogenesis. The two main pathological hallmarks of Alzheimer’s disease, abnormal aggregates of amyloid or tau proteins, have had demonstrable effects on synaptic physiology in animal and cellular models of Alzheimer’s disease. There is also growing evidence that these two proteins may have a synergistic effect on neurophysiological dysfunction. Here, we review some of the main findings of synaptic alterations in Alzheimer’s disease, and what we know from Alzheimer’s disease animal and cellular models. First, we briefly summarize some of the human evidence to suggest that synapses are altered, including how this relates to network activity. Subsequently, animal and cellular models of Alzheimer’s disease are considered, highlighting mouse models of amyloid and tau pathology and the role these proteins may play in synaptic dysfunction, either in isolation or examining how the two pathologies may interact in dysfunction. This specifically focuses on neurophysiological function and dysfunction observed within these animal models, typically measured using electrophysiology or calcium imaging. Following synaptic dysfunction and loss, it would be impossible to imagine that this would not alter oscillatory activity within the brain. Therefore, this review also discusses how this may underpin some of the aberrant oscillatory patterns seen in animal models of Alzheimer’s disease and human patients. Finally, an overview of some key directions and considerations in the field of synaptic dysfunction in Alzheimer’s disease is covered. This includes current therapeutics that are targeted specifically at synaptic dysfunction, but also methods that modulate activity to rescue aberrant oscillatory patterns. Other important future avenues of note in this field include the role of non-neuronal cell types such as astrocytes and microglia, and mechanisms of dysfunction independent of amyloid and tau in Alzheimer’s disease. The synapse will certainly continue to be an important target within Alzheimer’s disease for the foreseeable future.

OMICS Analyses Unraveling Related Gene and Protein-Driven Molecular Mechanisms Underlying PACAP 38-Induced Neurite Outgrowth in PC12 Cells

The study aimed to understand mechanism/s of neuronal outgrowth in the rat adrenal-derived pheochromocytoma cell line (PC12) under pituitary adenylate cyclase-activating polypeptide (PACAP) treatment. Neurite projection elongation was suggested to be mediated via Pac1 receptor-mediated dephosphorylation of CRMP2, where GSK-3β, CDK5, and Rho/ROCK dephosphorylated CRMP2 within 3 h after addition of PACAP, but the dephosphorylation of CRMP2 by PACAP remained unclear. Thus, we attempted to identify the early factors in PACAP-induced neurite projection elongation via omics-based transcriptomic (whole genome DNA microarray) and proteomic (TMT-labeled liquid chromatography-tandem mass spectrometry) analyses of gene and protein expression profiles from 5-120 min after PACAP addition. The results revealed a number of key regulators involved in neurite outgrowth, including known ones, called 'Initial Early Factors', e.g., genes Inhba, Fst, Nr4a1,2,3, FAT4, Axin2, and proteins Mis12, Cdk13, Bcl91, CDC42, including categories of 'serotonergic synapse, neuropeptide and neurogenesis, and axon guidance'. cAMP signaling and PI3K-Akt signaling pathways and a calcium signaling pathway might be involved in CRMP2 dephosphorylation. Cross-referencing previous research, we tried to map these molecular components onto potential pathways, and we may provide important new information on molecular mechanisms of neuronal differentiation induced by PACAP. Gene and protein expression data are publicly available at NCBI GSE223333 and ProteomeXchange, identifier PXD039992.

5-HT4 receptor agonists treatment reduces tau pathology and behavioral deficit in the PS19 mouse model of tauopathy

Accumulation of tau in synapses in Alzheimer’s disease (AD) has been shown to cause synaptic damage, synaptic loss, and the spread of pathology through synaptically connected neurons. Synaptic loss correlates with a decline in cognition, providing an opportunity to investigate strategies to target synaptic tau to rescue or prevent cognitive decline. One of the promising synaptic targets is the 5-HT4 receptor present post-synaptically in the brain areas involved in the memory processes. 5-HT4R activation exerts synaptogenic and pro-cognitive effects involving synapse-to-nucleus signaling essential for synaptic plasticity. However, it is not known whether 5-HT4R activation has a therapeutic effect on tauopathy. The goal of this study was to investigate the impact of stimulation of 5-HT4R in tauopathy mice. Our results show that 5-HT4R agonism led to reduced tauopathy and synaptic tau and correlated with increased proteasome activity and improved cognitive functioning in PS19 mice. Thus, stimulation of 5-HT4R offers a promising therapy to rescue synapses from toxic synaptic tau.

Accumulation of pTau231 at the Postsynaptic Density in Early Alzheimer's Disease

BACKGROUND

Phosphorylated cytoplasmic tau inclusions correlate with and precede cognitive deficits in Alzheimer's disease (AD). However, pathological tau accumulation and relationships to synaptic changes remain unclear.

OBJECTIVE

To address this, we examined postmortem brain from 50 individuals with the full spectrum of AD (clinically and neuropathologically). Total tau, pTau231, and AMPA GluR1 were compared across two brain regions (entorhinal and middle frontal cortices), as well as clinically stratified groups (control, amnestic mild cognitive impairment, AD dementia), NIA-AA Alzheimer's Disease Neuropathologic Change designations (Not, Low, Intermediate, High), and Braak tangle stages (1-6). Significant co-existing pathology was excluded to isolate changes attributed to pathologic AD.

METHODS

Synaptosomal fractionation and staining were performed to measure changes in total Tau, pTau231, and AMPA GluR1. Total Tau and pTau231 were quantified in synaptosomal fractions using Quanterix Simoa HD-X.

RESULTS

Increasing pTau231 in frontal postsynaptic fractions correlated positively with increasing clinical and neuropathological AD severity. Frontal cortex is representative of early AD, as it does not become involved by tau tangles until late in AD. Entorhinal total tau was significantly higher in the amnestic mild cognitive impairment group when compared to AD, but only after accounting for AD associated synaptic changes. Alterations in AMPA GluR1 observed in the entorhinal cortex, but not middle frontal cortex, suggest that pTau231 mislocalization and aggregation in postsynaptic structures may impair glutamatergic signaling by promoting AMPA receptor dephosphorylation and internalization.

CONCLUSION

Results highlight the potential effectiveness of early pharmacological interventions targeting pTau231 accumulation at the postsynaptic density.

Targeting VIP and PACAP Receptor Signaling: New Insights into Designing Drugs for the PACAP Subfamily of Receptors

Pituitary Adenylate Cyclase-Activating Peptide (PACAP) and Vasoactive Intestinal Peptide (VIP) are neuropeptides involved in a diverse array of physiological and pathological processes through activating the PACAP subfamily of class B1 G protein-coupled receptors (GPCRs): VIP receptor 1 (VPAC1R), VIP receptor 2 (VPAC2R), and PACAP type I receptor (PAC1R). VIP and PACAP share nearly 70% amino acid sequence identity, while their receptors PAC1R, VPAC1R, and VPAC2R share 60% homology in the transmembrane regions of the receptor. PACAP binds with high affinity to all three receptors, while VIP binds with high affinity to VPAC1R and VPAC2R, and has a thousand-fold lower affinity for PAC1R compared to PACAP. Due to the wide distribution of VIP and PACAP receptors in the body, potential therapeutic applications of drugs targeting these receptors, as well as expected undesired side effects, are numerous. Designing selective therapeutics targeting these receptors remains challenging due to their structural similarities. This review discusses recent discoveries on the molecular mechanisms involved in the selectivity and signaling of the PACAP subfamily of receptors, and future considerations for therapeutic targeting.

A quantitative in vivo imaging platform for tracking pathological tau depositions and resultant neuronal death in a mouse model

PURPOSE

Depositions of tau fibrils are implicated in diverse neurodegenerative disorders, including Alzheimer's disease, and precise assessments of tau pathologies and their impacts on neuronal survival are crucial for pursuing the neurodegenerative tau pathogenesis with and without potential therapies. We aimed to establish an in vivo imaging system to quantify tau accumulations with positron emission tomography (PET) and brain atrophy with volumetric MRI in rTg4510 transgenic mice modeling neurodegenerative tauopathies.

METHODS

A total of 91 rTg4510 and non-transgenic control mice underwent PET with a tau radiotracer, ¹⁸F-PM-PBB3, and MRI at various ages (1.8-12.3 months). Using the cerebellum as reference, the radiotracer binding in target regions was estimated as standardized uptake value ratio (SUVR) and distribution volume ratio (DVR). Histopathological staining of brain sections derived from scanned animals was also conducted to investigate the imaging-neuropathology correlations.

RESULTS

¹⁸F-PM-PBB3 SUVR at 40-60 min in the neocortex, hippocampus, and striatum of rTg4510 mice agreed with DVR, became significantly different from control values around 4-5 months of age, and progressively and negatively correlated with age and local volumes, respectively. Neocortical SUVR also correlated with the abundance of tau inclusions labeled with PM-PBB3 fluorescence, Gallyas-Braak silver impregnation, and anti-phospho-tau antibodies in postmortem assays. The in vivo and ex vivo ¹⁸F-PM-PBB3 binding was blocked by non-radioactive PM-PBB3. ¹⁸F-PM-PBB3 yielded a 1.6-fold greater dynamic range for tau imaging than its ancestor, ¹¹C-PBB3.

CONCLUSION

Our imaging platform has enabled the quantification of tau depositions and consequent neuronal loss and is potentially applicable to the evaluation of candidate anti-tau and neuroprotective drugs.

Protective Effects of PACAP in a Rat Model of Diabetic Neuropathy

Pituitary adenylate cyclase-activating peptide (PACAP) is a neuropeptide with a widespread occurrence and diverse effects. PACAP has well-documented neuro- and cytoprotective effects, proven in numerous studies. Among others, PACAP is protective in models of diabetes-associated diseases, such as diabetic nephropathy and retinopathy. As the neuropeptide has strong neurotrophic and neuroprotective actions, we aimed at investigating the effects of PACAP in a rat model of streptozotocin-induced diabetic neuropathy, another common complication of diabetes. Rats were treated with PACAP1-38 every second day for 8 weeks starting simultaneously with the streptozotocin injection. Nerve fiber morphology was examined with electron microscopy, chronic neuronal activation in pain processing centers was studied with FosB immunohistochemistry, and functionality was assessed by determining the mechanical nociceptive threshold. PACAP treatment did not alter body weight or blood glucose levels during the 8-week observation period. However, PACAP attenuated the mechanical hyperalgesia, compared to vehicle-treated diabetic animals, and it markedly reduced the morphological signs characteristic for neuropathy: axon–myelin separation, mitochondrial fission, unmyelinated fiber atrophy, and basement membrane thickening of endoneurial vessels. Furthermore, PACAP attenuated the increase in FosB immunoreactivity in the dorsal spinal horn and periaqueductal grey matter. Our results show that PACAP is a promising therapeutic agent in diabetes-associated complications, including diabetic neuropathy.