News & views: anti-amyloid antibodies and novel emerging approaches to Alzheimer's disease in 2023

Inhibition of soluble epoxide hydrolase confers neuroprotection and restores microglial homeostasis in a tauopathy mouse model

BACKGROUND

The epoxyeicosatrienoic acids (EETs) are derivatives of the arachidonic acid metabolism with anti-inflammatory activities. However, their efficacy is limited due to the rapid hydrolysis by soluble epoxide hydrolase (sEH). Inhibition of sEH has been shown to stabilize the EETs and reduce neuroinflammation in Aβ mouse models of Alzheimer's disease (AD). However, the role of the sEH-EET signaling pathway in other CNS cell types and neurodegenerative conditions are less understood.

METHODS

Here we investigated the mechanisms and functional role of the sEH-EET axis in tauopathy by treating PS19 mice with a small molecule sEH inhibitor TPPU and by crossing the PS19 mice with Ephx2 (gene encoding sEH) knockout mice. This was followed by single-nucleus RNA-sequencing (snRNA-seq), biochemical and immunohistochemical analysis, and behavioral assessments. Additionally, we examined the effects of the sEH-EET pathway in primary microglia cultures and human induced pluripotent stem cell (iPSC)-derived neurons exhibiting seeding-induced Tau inclusions.

RESULTS

sEH inhibition improved cognitive function, rescued neuronal cell loss, and reduced Tau pathology and microglial reactivity. snRNA-seq revealed that TPPU treatment upregulated genes involved in actin cytoskeleton and excitatory synaptic pathways. Treatment of human iPSC-derived neurons with TPPU enhanced synaptic density without affecting Tau accumulation, suggesting a cell-autonomous neuroprotective effect of sEH blockade. Furthermore, sEH inhibition reversed disease-associated and interferon-responsive microglial states in PS19 mice, while EET supplementation promoted Tau phagocytosis and clearance in primary microglia cultures.

CONCLUSION

These findings demonstrate that sEH blockade or EET augmentation confers therapeutic benefit in neurodegenerative tauopathies by simultaneously targeting neuronal and microglial pathways.

Rock inhibitors in Alzheimer's disease

Alzheimer's disease (AD) is the most common age-related neurodegenerative disease and cause of dementia. AD pathology primarily involves the formation of amyloid β (Aβ) plaques and neurofibrillary tangles containing hyperphosphorylated tau (p-tau). While Aβ targeted treatments have shown clinical promise, other aspects of AD pathology such as microgliosis, astrocytosis, synaptic loss, and hypometabolism may be viable targets for treatment. Among notable novel therapeutic approaches, the Ras homolog (Rho)-associated kinases (ROCKs) are being investigated as targets for AD treatment, based on the observations that ROCK1/2 levels are elevated in AD, and activation or inhibition of ROCKs changes dendritic/synaptic structures, protein aggregate accumulation, inflammation, and gliosis. This review will highlight key findings on the effects of ROCK inhibition in Aβ and ptau pathologies, as well as its effects on neuroinflammation, synaptic density, and potentially metabolism and bioenergetics.

Inhibition of Soluble Epoxide Hydrolase Confers Neuroprotection and Restores Microglial Homeostasis in a Tauopathy Mouse Model

Background

The epoxyeicosatrienoic acids (EETs) are derivatives of the arachidonic acid metabolism with anti-inflammatory activities. However, their efficacy is limited due to the rapid hydrolasis by the soluble epoxide hydrolase (sEH). Accordingly, inhibition of sEH has been shown to stabilize the EETs and dampen neuroinflammation in Aβ mouse models of Alzheimer's disease (AD). However, the role of the sEH-EET signaling pathway in other cell types of the CNS and in other neurodegenerative conditions are less understood.

Methods

Here we examined the mechanisms and the functional role of the sEH-EET axis in tauopathy by treating the PS19 mice with a small molecule sEH inhibitor TPPU and by crossing the PS19 mice with Ephx2 (gene encoding sEH) knockout mice, followed by single-nucleus RNA-sequencing (snRNA-seq), biochemical and immunohistochemical characterization, and behavioral analysis. We also tested the effect of the sEH-EET pathway in primary microglia cultures and human induced pluripotent stem cell (iPSC)-derived neurons that develop seeding-induced Tau inclusions.

Results

We show that sEH inhibition improved cognitive function, rescued neuronal cell loss, and reduced Tau pathology and microglia reactivity. snRNA-seq revealed that TPPU treatment resulted in the upregulation of actin cytoskeleton and excitatory synaptic pathway genes. Treating the human iPSC-derived neurons with TPPU led to enhanced synaptic density without affecting Tau accumulation, indicating a cell-autonomous effect of sEH blockade in neuroprotection. Further, sEH inhibition reversed disease-associated and interferon-response microglia states in PS19 mice and EET supplementation enhanced Tau phagocytosis and clearance in primary microglia cultures.

Conclusion

These findings demonstrate that sEH blockade or EET augmentation confer therapeutic benefit against neurodegenerative tauopathies through parallel targeting of neuronal and microglial pathways.

Andrographolide mitigates neurotoxicity induced by lipopolysaccharide or amyloid-β through modulation of miR-222-mediated p62 and NF-κBp65 expression

MicroRNA-222 (miR-222) plays a crucial role in neurodegeneration and is up-regulated in Alzheimer's disease (AD) patients. Andrographolide (Andro) has been reported to have anti-inflammatory and neuroprotective effects, showing potential for treating AD. The relationship between Andro's anti-AD mechanism and the regulation of miR-222 was discussed in this study. Andro protected against cytotoxicity induced by lipopolysaccharide (LPS) or amyloid-β, accompanied by upregulating p62 and Nrf2 mRNA and protein, downregulating TLR4 and NF-κBp65 mRNA and protein, and increasing LC3Ⅱ protein in vitro. miRNA and mRNA sequencing results showed that Andro downregulated miR-222 and upregulated sqstm1/p62. Andro was observed to inhibit the expression of miR-222 and the phosphorylation of NF-κBp65, while simultaneously enhancing the levels of p62 and LC3Ⅱ proteins, decreasing Aβ levels, and attenuating the release of inflammatory factors in the 3xTg-AD mice. MiR-222 mimic increased NF-κBp65 mRNA and protein levels in LPS-induced cells, while miR-222 inhibitors increased p62 mRNA and protein levels as well as Nrf2 and LC3Ⅱ protein, and decreased p-NF-κBp65 protein level in LPS-induced cells. Furthermore, miR-222 mimic reversed the increase in p62 and LC3Ⅱ protein and the decrease in NF-κBp65 mRNA and protein, as well as the decrease in Tau protein levels induced by Andro in LPS-induced cells. These findings suggest that Andro plays a neuroprotective role through downregulation of miR-222 to promote p62 expression while inhibiting NF-kB p65 expression, providing new insights into the mechanism of action of Andro for treating AD.

Alzheimer's disease approaches - Focusing on pathology, biomarkers and clinical trial candidates

The strategy for the development of new drugs for Alzheimer's disease (AD) recognizes that an effective therapy requires early therapeutic intervention and a multifactorial approach that considers the individual initiators of AD development. Current knowledge of AD includes the understanding of pathophysiology, risk factors, biomarkers, and the evolving patterns of biomarker abnormalities. This knowledge is essential in identifying potential molecular targets for new drug development. This review summarizes promising AD drug candidates, many of which are currently in phase 2 or 3 clinical trials. New agents are classified according to the Common Alzheimer's Disease Research Ontology (CADRO). The main targets of new drugs for AD are processes related to amyloid beta and tau neurotoxicity, neurotransmission, inflammation, metabolism and bioenergetics, synaptic plasticity, and oxidative stress. These interventions are aimed at preventing disease onset and slowing or eliminating disease progression. The efficacy of pharmacotherapy may be enhanced by combining these drugs with other treatments, antioxidants, and dietary supplements. Ongoing research into AD pathophysiology, risk factors, biomarkers, and the dynamics of biomarker abnormalities may contribute to the understanding of AD and offer hope for effective therapeutic strategies in the near future.

Irisin limits amyloid-β buildup in Alzheimer's disease

Mounting evidence suggests that physical exercise protects the brain against neurodegenerative disease. In a recent paper in Neuron, Kim et al. reported that the exercise-induced hormone irisin curbs amyloid-β buildup by promoting secretion of astrocyte-derived neprilysin. These findings may help explain the neuroprotection by irisin and exercise in Alzheimer's disease.

A Strategy for Allowing Earlier Diagnosis and Rigorous Evaluation of BACE1 Inhibitors in Preclinical Alzheimer's Disease

Given continued failure of BACE1 inhibitor programs at symptomatic and prodromal stages of Alzheimer's disease (AD), clinical trials need to target the earlier preclinical stage. However, trial design is complex in this population with negative diagnosis of classical hippocampal amnesia on standard memory tests. Besides recent advances in brain imaging, electroencephalogram, and fluid-based biomarkers, new cognitive markers should be established for earlier diagnosis that can optimize recruitment to BACE1 inhibitor trials in presymptomatic AD. Notably, accelerated long-term forgetting (ALF) is emerging as a sensitive cognitive measure that can discriminate between asymptomatic individuals with high risks for developing AD and healthy controls. ALF is a form of declarative memory impairment characterized by increased forgetting rates over longer delays (days to months) despite normal storage within the standard delays of testing (20-60 min). Therefore, ALF may represent a harbinger of preclinical dementia and the impairment of systems memory consolidation, during which memory traces temporarily stored in the hippocampus become gradually integrated into cortical networks. This review provides an overview of the utility of ALF in a rational design of next-generation BACE1 inhibitor trials in preclinical AD. I explore potential mechanisms underlying ALF and relevant early-stage biomarkers useful for BACE1 inhibitor evaluation, including synaptic protein alterations, astrocytic dysregulation and neuron hyperactivity in the hippocampal-cortical network. Furthermore, given the physiological role of the isoform BACE2 as an AD-suppressor gene, I also discuss the possible association between the poor selectivity of BACE1 inhibitors and their side effects (e.g., cognitive worsening) in prior clinical trials.

Loss of TREM2 exacerbates parenchymal amyloid pathology but diminishes CAA in Tg-SwDI mice

Alzheimer's disease (AD) is a progressive neurodegenerative disease, and it is the most common cause of dementia worldwide. Recent genome-wide association studies (GWAS) identified TREM2 (triggering receptor expressed on myeloid cells 2) as one of the major risk factors for AD. TREM2 is a surface receptor expressed on microglia and largely mediates microglial functions and immune homeostasis in the brain. The functions of TREM2 in AD pathogenesis, including in the formation of the key pathology parenchymal amyloid-β (Aβ) plaques, have been investigated by introducing Trem2 deficiency in AD mouse models. However, the role of TREM2 in cerebrovascular amyloidosis, in particular cerebral amyloid angiopathy (CAA) remains unexplored. CAA features Aβ deposition along the cerebral vessels, signifying an intersection between AD and vascular dysfunction. Using a well-characterized CAA-prone, transgenic mouse model of AD, Tg-SwDI (SwDI), we found that loss of TREM2 led to a marked increase in overall Aβ load in the brain, but a dramatic decrease in CAA in microvessel-rich regions, along with reduced microglial association with CAA. Transcriptomic analysis revealed that in the absence of Trem2 , microglia were activated but trapped in transition to the fully reactive state. Like microglia, perivascular macrophages were activated with upregulation of cell junction related pathways in Trem2 -deficient SwDI mice. In addition, vascular mural cells and astrocytes exhibited distinct responses to Trem2 deficiency, contributing to the pathological changes in the brain of Trem2 -null SwDI mice. Our study provides the first evidence that TREM2 differentially modulates parenchymal and vascular Aβ pathologies, which may have significant implications for both TREM2- and Aβ-targeting therapies for AD.