14,15-Epoxyeicosatrienoic Acid Alleviates Pathology in a Mouse Model of Alzheimer's Disease

The serum levels of polyunsaturated fatty acids contribute to the antidepressant-like effects of 18β-Glycyrrhetinic acid in mice

RATIONALE

18β-Glycyrrhetinic acid (18β-GA) exhibits antidepressant-like effects in mice, but the underlying mechanisms remain unclear.

OBJECTIVE

This study aimed to explore the role of serum polyunsaturated fatty acids in the antidepressant-like effects of 18β-GA.

RESULTS

18β-GA exerted antidepressant-like effects in mice susceptible to chronic social defeat stress (CSDS). These effects were associated with increased serum levels of docosahexaenoic acid (DHA), neuroprotectin D1 (NPD1), and N-docosahexaenoylethanolamide (DEA), alongside decreased levels of 14,15-dihydroxyeicosatrienoic acid (DHET). Additionally, 18β-GA restored the suppressed brain-derived neurotrophic factor (BDNF)-tyrosine kinase B (TrkB) signaling pathway and reduced the elevated pro-inflammatory cytokine levels in CSDS-susceptible mice.

CONCLUSIONS

This study demonstrates that the antidepressant-like effects of 18β-GA in CSDS-susceptible mice are closely associated with DHA and its metabolites.

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.

A Naturalistic Prospective Study of the Prognostic Impact of EPHX2 in Major Depressive Disorder: Impulsivity may be an Important Factor

Background: Major depressive disorder (MDD) is a leading cause of disability worldwide. The pathophysiology of MDD remains unclear, which limits the development of treatments for MDD. Recently, epoxide hydrolase 2 (EPHX2) has been found to be associated with MDD. Our previous study revealed an association between EPHX2 expression and suicide. However, the effect of EPHX2 on the prognosis of MDD and suicide remains unclear. Previous studies have found that impulsivity at baseline can be a significant predictor of clinical improvement in patients with MDD. Therefore, we inferred that EPHX2 could be associated with the treatment effect of MDD, and impulsivity could mediate the effect of EPHX2 on the treatment effect of MDD. Methods: This naturalistic prospective study included 117 participants with MDD, who were assessed, using clinical questionnaires, cognitive function, and treatment information, at baseline, 2 weeks, and 1, 2, and 3 months. A linear mixed-effects model was used to investigate longitudinal changes in the severity of symptoms, risk of suicide, and cognitive function. Results: The interactive effects of impulsivity and EPHX2 polymorphisms on the risk of suicide (measured by the Columbia-Suicide Severity Rating Scale) were significantly different for rs11288636, rs68012435, and rs11288636. The interactive effects between polymorphisms and time on depression severity (measured by the Hamilton Depression Scale-24) were significantly different and including after adjustment for the total impulsivity score. Conclusions: This study suggests that EPHX2 polymorphisms are associated with the prognosis of MDD, and impulsivity could be a critical factor for the change in suicide risk among different EPHX2 genotypes. Trial Registration: ClinicalTrials.gov identifier: NCT05575713.

A Soluble Epoxide Hydrolase Inhibitor Improves Cerebrovascular Dysfunction, Neuroinflammation, Amyloid Burden, and Cognitive Impairments in the hAPP/PS1 TgF344-AD Rat Model of Alzheimer's Disease

Alzheimer's disease (AD) is an increasing global healthcare crisis with few effective treatments. The accumulation of amyloid plaques and hyper-phosphorylated tau are thought to underlie the pathogenesis of AD. However, current studies have recognized a prominent role of cerebrovascular dysfunction in AD. We recently reported that SNPs in soluble epoxide hydrolase (sEH) are linked to AD in human genetic studies and that long-term administration of an sEH inhibitor attenuated cerebral vascular and cognitive dysfunction in a rat model of AD. However, the mechanisms linking changes in cerebral vascular function and neuroprotective actions of sEH inhibitors in AD remain to be determined. This study investigated the effects of administration of an sEH inhibitor, 1-(1-Propanoylpiperidin-4-yl)-3-[4-(trifluoromethoxy)phenyl]urea (TPPU), on neurovascular coupling, blood-brain barrier (BBB) function, neuroinflammation, and cognitive dysfunction in an hAPP/PS1 TgF344-AD rat model of AD. We observed predominant β-amyloid accumulation in the brains of 9-10-month-old AD rats and that TPPU treatment for three months reduced amyloid burden. The functional hyperemic response to whisker stimulation was attenuated in AD rats, and TPPU normalized the response. The sEH inhibitor, TPPU, mitigated capillary rarefaction, BBB leakage, and activation of astrocytes and microglia in AD rats. TPPU increased the expression of pre- and post-synaptic proteins and reduced loss of hippocampal neurons and cognitive impairments in the AD rats, which was confirmed in a transcriptome and GO analysis. These results suggest that sEH inhibitors could be a novel therapeutic strategy for AD.

Identification of potential therapeutic targets for Alzheimer's disease from the proteomes of plasma and cerebrospinal fluid in a multicenter Mendelian randomization study

BACKGROUND

Certain peripheral proteins are believed to be involved in the development of Alzheimer's disease (AD), but the roles of other new protein biomarkers are still unclear. Current treatments aim to manage symptoms, but they are not effective in stopping the progression of the disease. New drug targets are needed to prevent Alzheimer's disease.

METHODS

We used Mendelian randomization (MR) to study drug targets for Alzheimer's disease. We analyzed data from the European Alzheimer's and Dementia Biobank consortium and replicated our findings in GWAS data from IGAP and FinnGen cohorts. We identified genetic instruments for plasma and cerebrospinal fluid (CSF) proteins and conducted sensitivity analyses using various methods. Additionally, a comparison and analysis of protein-protein interactions (PPI) were conducted to identify potential causal proteins. The implications of these findings were further explored through an examination of existing AD drugs and their respective targets.

RESULTS

Through MR analysis, 10 protein AD pairs were identified as statistically significant at the Bonferroni level (P < 6.35 × 10-5). The specific findings indicate that elevated levels of plasma cathepsin H (CTSH) (OR = 1.06, 95%CI: 1.03-1.08, p = 6.12 × 10-6), plasma signal regulatory protein alpha (SIRPA) (OR = 1.03, 95%CI: 1.02-1.05, p = 1.37 × 10-5), plasma TMEM106B (OR = 1.16, 95%CI: 1.09-1.23, p = 1.92 × 10-6), and CSF bone sialoprotein (BSP) (OR = 1.33, 95%CI: 1.17-1.51, p = 9.34 × 10-6), CSF Interleukin-34 (IL-34) (OR = 2.13, 95%CI: 1.51-3.01, p = 1.85 × 10-5), CSF immunoglobulin-like transcript 2 (ILT-2) (OR = 1.33, 95%CI: 1.17-1.51, p = 9.34 × 10-6) are associated with an increased risk of AD, while increased levels of plasma progranulin gene (GRN) (OR = 0.79, 95%CI: 0.74-0.84, p = 2.19 × 10-12), plasma triggering receptor expressed on myeloid cells 2 (TREM2) (OR = 0.67, 95%CI: 0.58-0.78, p = 6.95 × 10-8), plasma sialic acid-bind immunoglobulin-like lectins (SIGLEC)-9 (OR = 0.67, 95%CI: 0.58-0.78, p = 6.95 × 10-8), and CSF SIGLEC7 (OR = 0.42, 95%CI: 0.28-0.64, p = 4.30 × 10-5) are associated with a decreased risk of AD. Bayesian colocalization found that the above protein-related genes shared the same mutation as AD.

CONCLUSION

Increased levels of plasma CTSH, SIRPA, TMEM106B, CSF BSP, CSF IL-34, and CSF ILT-2 have been found to be correlated with an elevated risk of AD, whereas elevated levels of plasma GRN, TREM2, SIGLEC9, and CSF SIGLEC7 are associated with a decreased risk of developing AD. Further investigation through clinical trials is needed.

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.

Dual-target inhibitors based on acetylcholinesterase: Novel agents for Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia among the elderly, accounting for 60 %-70 % of cases. At present, the pathogenesis of this condition remains unclear, but the hydrolysis of acetylcholine (ACh) is thought to play a role. Acetylcholinesterase (AChE) can break down ACh transmission from the presynaptic membrane and stop neurotransmitters' excitatory effect on the postsynaptic membrane, which plays a key role in nerve conduction. Acetylcholinesterase inhibitors (AChEIs) can delay the hydrolysis of acetylcholine (ACh), which represents a key strategy for treating AD. Due to its complex etiology, AD has proven challenging to treat. Various inhibitors and antagonists targeting key enzymes and proteins implicated in the disease's pathogenesis have been explored as potential therapeutic agents. These include Glycogen Synthase Kinase 3β (GSK-3β) inhibitors, β-site APP Cleaving Enzyme (BACE-1) inhibitors, Monoamine Oxidase (MAO) inhibitors, Phosphodiesterase inhibitors (PDEs), N-methyl--aspartic Acid (NMDA) antagonists, Histamine 3 receptor antagonists (H3R), Serotonin receptor subtype 4 (5-HT4R) antagonists, Sigma1 receptor antagonists (S1R) and soluble Epoxide Hydrolase (sEH) inhibitors. The drug development strategy of multi-target-directed ligands (MTDLs) offers unique advantages in the treatment of complex diseases. On the one hand, it can synergistically enhance the therapeutic efficacy of single-target drugs. On the other hand, it can also reduce the side effects. In this review, we discuss the design strategy of dual inhibitors based on acetylcholinesterase and the structure-activity relationship of these drugs.

Shared genetics and causal association between plasma levels of SARS-CoV-2 entry receptor ACE2 and Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is the highest risk of COVID-19 infection, hospitalization, and mortality. However, it remains largely unclear about the link between AD and COVID-19 outcomes. ACE2 is an entry receptor for SARS-CoV-2. Circulating ACE2 is a novel biomarker of death and associated with COVID-19 outcomes.

METHODS

Here, we explored the shared genetics and causal association between AD and plasma ACE2 levels using large-scale genome-wide association study, gene expression, expression quantitative trait loci, and high-throughput plasma proteomic profiling datasets.

RESULTS

We found a significant causal effect of genetically increased circulating ACE2 on increased risk of AD. Cross-trait association analysis identified 19 shared genetic variants, and three variants rs3104412, rs2395166, and rs3135344 at chromosome 6p21.32 were associated with COVID-19 infection, hospitalization, and severity. We mapped 19 variants to 117 genes, which were significantly upregulated in lung, spleen, and small intestine, downregulated in brain tissues, and involved in immune system, immune disease, and infectious disease pathways. The plasma proteins corresponding to LST1, AGER, TNXB, and APOC1 were predominantly associated with COVID-19 infection, ventilation, and death.

CONCLUSION

Together, our findings suggest the shared genetics and causal association between AD and plasma ACE2 levels, which may partially explain the link between AD and COVID-19.

Novel molecular mechanism driving neuroprotection after soluble epoxide hydrolase inhibition: Insights for Alzheimer's disease therapeutics

BACKGROUND

Neuroinflammation is widely recognized as a significant hallmark of Alzheimer's disease (AD). To combat neuroinflammation, the inhibition of the soluble epoxide hydrolase (sEH) enzyme has been demonstrated crucial. Importantly, sEH inhibition could be related to other neuroprotective pathways described in AD.

AIMS

The aim of the study was to unveil new molecular pathways driving neuroprotection through sEH, we used an optimized, potent, and selective sEH inhibitor (sEHi, UB-SCG-51).

MATERIALS AND METHODS

UB-SCG-51 was tested in neuroblastoma cell line, SH-SY5Y, in primary mouse and human astrocytes cultures challenged with proinflammatory insults and in microglia cultures treated with amyloid oligomers, as well as in mice AD model (5XFAD).

RESULTS

UB-SCG-51 (10 and 30 μM) prevented neurotoxic reactive-astrocyte conversion in primary mouse astrocytes challenged with TNF-α, IL-1α, and C1q (T/I/C) combination for 24 h. Moreover, in microglial cultures, sEHi reduced inflammation and glial activity. In addition, UB-SCG-51 rescued 5XFAD cognitive impairment, reducing the number of Amyloid-β plaques and Tau hyperphosphorylation accompanied by a reduction in neuroinflammation and apoptotic markers. Notably, a transcriptional profile analysis revealed a new pathway modulated by sEHi treatment. Specifically, the eIF2α/CHOP pathway, which promoted the endoplasmic reticulum response, was increased in the 5XFAD-treated group. These findings were confirmed in human primary astrocytes by combining sEHi and eIF2α inhibitor (eIF2αi) treatment. Besides, combining both treatments resulted in increased in C3 gene expression after T/I/C compared with the group treated with sEHi alone in cultures.

DISCUSSION

Therefore, sEHi rescued cognitive impairment and neurodegeneration in AD mice model, based on the reduction of inflammation and eIF2α/CHOP signaling pathway.

CONCLUSIONS

In whole, our results support the concept that targeting neuroinflammation through sEH inhibition is a promising therapeutic strategy to fight against Alzheimer's disease with additive and/or synergistic activities targeting neuroinflammation and cell stress.

Navigating the metabolic maze: anomalies in fatty acid and cholesterol processes in Alzheimer's astrocytes

Alzheimer's disease (AD) is the most common cause of dementia, and its underlying mechanisms have been a subject of great interest. The mainstream theory of AD pathology suggests that the disease is primarily associated with tau protein and amyloid-beta (Aβ). However, an increasing body of research has revealed that abnormalities in lipid metabolism may be an important event throughout the pathophysiology of AD. Astrocytes, as important members of the lipid metabolism network in the brain, play a significant role in this event. The study of abnormal lipid metabolism in astrocytes provides a new perspective for understanding the pathogenesis of AD. This review focuses on the abnormal metabolism of fatty acids (FAs) and cholesterol in astrocytes in AD, and discusses it from three perspectives: lipid uptake, intracellular breakdown or synthesis metabolism, and efflux transport. We found that, despite the accumulation of their own fatty acids, astrocytes cannot efficiently uptake fatty acids from neurons, leading to fatty acid accumulation within neurons and resulting in lipotoxicity. In terms of cholesterol metabolism, astrocytes exhibit a decrease in endogenous synthesis due to the accumulation of exogenous cholesterol. Through a thorough investigation of these metabolic abnormalities, we can provide new insights for future therapeutic strategies by literature review to navigate this complex metabolic maze and bring hope to patients with Alzheimer's disease.

The pan-liver network theory: From traditional chinese medicine to western medicine

In traditional Chinese medicine (TCM), the liver is the "general organ" that is responsible for governing/maintaining the free flow of qi over the entire body and storing blood. According to the classic five elements theory, zang-xiang theory, yin-yang theory, meridians and collaterals theory, and the five-viscera correlation theory, the liver has essential relationships with many extrahepatic organs or tissues, such as the mother-child relationships between the liver and the heart, and the yin-yang and exterior-interior relationships between the liver and the gallbladder. The influences of the liver to the extrahepatic organs or tissues have been well-established when treating the extrahepatic diseases from the perspective of modulating the liver by using the ancient classic prescriptions of TCM and the acupuncture and moxibustion. In modern medicine, as the largest solid organ in the human body, the liver has the typical functions of filtration and storage of blood; metabolism of carbohydrates, fats, proteins, hormones, and foreign chemicals; formation of bile; storage of vitamins and iron; and formation of coagulation factors. The liver also has essential endocrine function, and acts as an immunological organ due to containing the resident immune cells. In the perspective of modern human anatomy, physiology, and pathophysiology, the liver has the organ interactions with the extrahepatic organs or tissues, for example, the gut, pancreas, adipose, skeletal muscle, heart, lung, kidney, brain, spleen, eyes, skin, bone, and sexual organs, through the circulation (including hemodynamics, redox signals, hepatokines, metabolites, and the translocation of microbiota or its products, such as endotoxins), the neural signals, or other forms of pathogenic factors, under normal or diseases status. The organ interactions centered on the liver not only influence the homeostasis of these indicated organs or tissues, but also contribute to the pathogenesis of cardiometabolic diseases (including obesity, type 2 diabetes mellitus, metabolic [dysfunction]-associated fatty liver diseases, and cardio-cerebrovascular diseases), pulmonary diseases, hyperuricemia and gout, chronic kidney disease, and male and female sexual dysfunction. Therefore, based on TCM and modern medicine, the liver has the bidirectional interaction with the extrahepatic organ or tissue, and this established bidirectional interaction system may further interact with another one or more extrahepatic organs/tissues, thus depicting a complex "pan-hepatic network" model. The pan-hepatic network acts as one of the essential mechanisms of homeostasis and the pathogenesis of diseases.

Systematic druggable genome-wide Mendelian randomisation identifies therapeutic targets for Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is the leading cause of dementia. Currently, there are no effective disease-modifying treatments for AD. Mendelian randomisation (MR) has been widely used to repurpose licensed drugs and discover novel therapeutic targets. Thus, we aimed to identify novel therapeutic targets for AD and analyse their pathophysiological mechanisms and potential side effects.

METHODS

A two-sample MR integrating the identified druggable genes was performed to estimate the causal effects of blood and brain druggable expression quantitative trait loci (eQTLs) on AD. A repeat study was conducted using different blood and brain eQTL data sources to validate the identified genes. Using AD markers with available genome-wide association studies data, we evaluated the causal relationship between established AD markers to explore possible mechanisms. Finally, the potential side effects of the druggable genes for AD treatment were assessed using a phenome-wide MR.

RESULTS

Overall, 5883 unique druggable genes were aggregated; 33 unique potential druggable genes for AD were identified in at least one dataset (brain or blood), and 5 were validated in a different dataset. Among them, three prior druggable genes (epoxide hydrolase 2 (EPHX2), SERPINB1 and SIGLEC11) reached significant levels in both blood and brain tissues. EPHX2 may mediate the pathogenesis of AD by affecting the entire hippocampal volume. Further phenome-wide MR analysis revealed no potential side effects of treatments targeting EPHX2, SERPINB1 or SIGLEC11.

CONCLUSIONS

This study provides genetic evidence supporting the potential therapeutic benefits of targeting the three druggable genes for AD treatment, which will be useful for prioritising AD drug development.

Prenatal THC exposure induces long-term, sex-dependent cognitive dysfunction associated with lipidomic and neuronal pathology in the prefrontal cortex-hippocampal network

With increasing maternal cannabis use, there is a need to investigate the lasting impact of prenatal exposure to Δ9-tetrahydrocannabinol (THC), the main psychotropic compound in cannabis, on cognitive/memory function. The endocannabinoid system (ECS), which relies on polyunsaturated fatty acids (PUFAs) to function, plays a crucial role in regulating prefrontal cortical (PFC) and hippocampal network-dependent behaviors essential for cognition and memory. Using a rodent model of prenatal cannabis exposure (PCE), we report that male and female offspring display long-term deficits in various cognitive domains. However, these phenotypes were associated with highly divergent, sex-dependent mechanisms. Electrophysiological recordings revealed hyperactive PFC pyramidal neuron activity in both males and females, but hypoactivity in the ventral hippocampus (vHIPP) in males, and hyperactivity in females. Further, cortical oscillatory activity states of theta, alpha, delta, beta, and gamma bandwidths were strongly sex divergent. Moreover, protein expression analyses at postnatal day (PD)21 and PD120 revealed primarily PD120 disturbances in dopamine D1R/D2 receptors, NMDA receptor 2B, synaptophysin, gephyrin, GAD67, and PPARα selectively in the PFC and vHIPP, in both regions in males, but only the vHIPP in females. Lastly, using matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS), we identified region-, age-, and sex-specific deficiencies in specific neural PUFAs, namely docosahexaenoic acid (DHA) and arachidonic acid (ARA), and related metabolites, in the PFC and hippocampus (ventral/dorsal subiculum, and CA1 regions). This study highlights several novel, long-term and sex-specific consequences of PCE on PFC-hippocampal circuit dysfunction and the potential role of specific PUFA signaling abnormalities underlying these pathological outcomes.

Hepatic soluble epoxide hydrolase activity regulates cerebral Aβ metabolism and the pathogenesis of Alzheimer's disease in mice

Alzheimer's disease (AD) is caused by a complex interaction between genetic and environmental factors. However, how the role of peripheral organ changes in response to environmental stimuli during aging in AD pathogenesis remains unknown. Hepatic soluble epoxide hydrolase (sEH) activity increases with age. Hepatic sEH manipulation bidirectionally attenuates brain amyloid-β (Aβ) burden, tauopathy, and cognitive deficits in AD mouse models. Moreover, hepatic sEH manipulation bidirectionally regulates the plasma level of 14,15-epoxyeicosatrienoic acid (-EET), which rapidly crosses the blood-brain barrier and modulates brain Aβ metabolism through multiple pathways. A balance between the brain levels of 14,15-EET and Aβ is essential for preventing Aβ deposition. In AD models, 14,15-EET infusion mimicked the neuroprotective effects of hepatic sEH ablation at biological and behavioral levels. These results highlight the liver's key role in AD pathology, and targeting the liver-brain axis in response to environmental stimuli may constitute a promising therapeutic approach for AD prevention.

Hepatic soluble epoxide hydrolase: A promising target for unveiling the liver-brain axis in Alzheimer's disease

Wu and Dong et al.1 report that hepatic soluble epoxide hydrolase (sEH) manipulation impacts amyloid-β (Aβ) deposits and cognitive impairment in mouse models for Alzheimer's disease (AD), suggesting that hepatic sEH activity is a promising therapeutic target to treat AD.

Fatty acid binding proteins are novel modulators of synaptic epoxyeicosatrienoic acid signaling in the brain

Fatty acid binding proteins (FABPs) govern intracellular lipid transport to cytosolic organelles and nuclear receptors. More recently, FABP5 has emerged as a key regulator of synaptic endocannabinoid signaling, suggesting that FABPs may broadly regulate the signaling of neuroactive lipids in the brain. Herein, we demonstrate that brain-expressed FABPs (FABP3, FABP5, and FABP7) interact with epoxyeicosatrienoic acids (EETs) and the peroxisome proliferator-activated receptor gamma agonist 15-deoxy-Δ12,14-Prostaglandin J2 (15d-PGJ2). Among these lipids, EETs displayed highest affinities for FABP3 and FABP5, and 11,12-EET was identified as the preferred FABP ligand. Similarly, 15d-PGJ2 interacted with FABP3 and FABP5 while binding to FABP7 was markedly lower. Molecular modeling revealed unique binding interactions of the ligands within the FABP binding pockets and highlighted major contributions of van der Waals clashes and acyl chain solvent exposure in dictating FABP affinity and specificity. Functional studies demonstrated that endogenous EETs gate the strength of CA1 hippocampal glutamate synapses and that this function was impaired following FABP inhibition. As such, the present study reveals that FABPs control EET-mediated synaptic gating, thereby expanding the functional roles of this protein family in regulating neuronal lipid signaling.

Deletion of Transferrin Receptor 1 in Parvalbumin Interneurons Induces a Hereditary Spastic Paraplegia-Like Phenotype

Hereditary spastic paraplegia (HSP) is a severe neurodegenerative movement disorder, the underlying pathophysiology of which remains poorly understood. Mounting evidence has suggested that iron homeostasis dysregulation can lead to motor function impairment. However, whether deficits in iron homeostasis are involved in the pathophysiology of HSP remains unknown. To address this knowledge gap, we focused on parvalbumin-positive (PV+) interneurons, a large category of inhibitory neurons in the central nervous system, which play a critical role in motor regulation. The PV+ interneuron-specific deletion of the gene encoding transferrin receptor 1 (TFR1), a key component of the neuronal iron uptake machinery, induced severe progressive motor deficits in both male and female mice. In addition, we observed skeletal muscle atrophy, axon degeneration in the spinal cord dorsal column, and alterations in the expression of HSP-related proteins in male mice with Tfr1 deletion in the PV+ interneurons. These phenotypes were highly consistent with the core clinical features of HSP cases. Furthermore, the effects on motor function induced by Tfr1 ablation in PV+ interneurons were mostly concentrated in the dorsal spinal cord; however, iron repletion partly rescued the motor defects and axon loss seen in both sexes of conditional Tfr1 mutant mice. Our study describes a new mouse model for mechanistic and therapeutic studies relating to HSP and provides novel insights into iron metabolism in spinal cord PV+ interneurons and its role in the regulation of motor functions.SIGNIFICANCE STATEMENT Iron is crucial for neuronal functioning. Mounting evidence suggests that iron homeostasis dysregulation can induce motor function deficits. Transferrin receptor 1 (TFR1) is thought to be the key component in neuronal iron uptake. We found that deletion of Tfr1 in parvalbumin-positive (PV+) interneurons in mice induced severe progressive motor deficits, skeletal muscle atrophy, axon degeneration in the spinal cord dorsal column, and alterations in the expression of hereditary spastic paraplegia (HSP)-related proteins. These phenotypes were highly consistent with the core clinical features of HSP cases and partly rescued by iron repletion. This study describes a new mouse model for the study of HSP and provides novel insights into iron metabolism in spinal cord PV+ interneurons.

Enhancement of the liver's neuroprotective role ameliorates traumatic brain injury pathology

Traumatic brain injury (TBI) is a pervasive problem worldwide for which no effective treatment is currently available. Although most studies have focused on the pathology of the injured brain, we have noted that the liver plays an important role in TBI. Using two mouse models of TBI, we found that the enzymatic activity of hepatic soluble epoxide hydrolase (sEH) was rapidly decreased and then returned to normal levels following TBI, whereas such changes were not observed in the kidney, heart, spleen, or lung. Interestingly, genetic downregulation of hepatic Ephx2 (which encodes sEH) ameliorates TBI-induced neurological deficits and promotes neurological function recovery, whereas overexpression of hepatic sEH exacerbates TBI-associated neurological impairments. Furthermore, hepatic sEH ablation was found to promote the generation of A2 phenotype astrocytes and facilitate the production of various neuroprotective factors associated with astrocytes following TBI. We also observed an inverted V-shaped alteration in the plasma levels of four EET (epoxyeicosatrienoic acid) isoforms (5,6-, 8,9-,11,12-, and 14,15-EET) following TBI which were negatively correlated with hepatic sEH activity. However, hepatic sEH manipulation bidirectionally regulates the plasma levels of 14,15-EET, which rapidly crosses the blood-brain barrier. Additionally, we found that the application of 14,15-EET mimicked the neuroprotective effect of hepatic sEH ablation, while 14,15-epoxyeicosa-5(Z)-enoic acid blocked this effect, indicating that the increased plasma levels of 14,15-EET mediated the neuroprotective effect observed after hepatic sEH ablation. These results highlight the neuroprotective role of the liver in TBI and suggest that targeting hepatic EET signaling could represent a promising therapeutic strategy for treating TBI.

Identifying genetic variants for amyloid β in subcortical vascular cognitive impairment

Background

The genetic basis of amyloid β (Aβ) deposition in subcortical vascular cognitive impairment (SVCI) is still unknown. Here, we investigated genetic variants involved in Aβ deposition in patients with SVCI.

Methods

We recruited a total of 110 patients with SVCI and 424 patients with Alzheimer's disease-related cognitive impairment (ADCI), who underwent Aβ positron emission tomography and genetic testing. Using candidate AD-associated single nucleotide polymorphisms (SNPs) that were previously identified, we investigated Aβ-associated SNPs that were shared or distinct between patients with SVCI and those with ADCI. Replication analyses were performed using the Alzheimer's Disease Neuroimaging Initiative (ADNI) and Religious Orders Study and Rush Memory and Aging Project cohorts (ROS/MAP).

Results

We identified a novel SNP, rs4732728, which showed distinct associations with Aβ positivity in patients with SVCI (P interaction = 1.49 × 10-5); rs4732728 was associated with increased Aβ positivity in SVCI but decreased Aβ positivity in ADCI. This pattern was also observed in ADNI and ROS/MAP cohorts. Prediction performance for Aβ positivity in patients with SVCI increased (area under the receiver operating characteristic curve = 0.780; 95% confidence interval = 0.757-0.803) when rs4732728 was included. Cis-expression quantitative trait loci analysis demonstrated that rs4732728 was associated with EPHX2 expression in the brain (normalized effect size = -0.182, P = 0.005).

Conclusion

The novel genetic variants associated with EPHX2 showed a distinct effect on Aβ deposition between SVCI and ADCI. This finding may provide a potential pre-screening marker for Aβ positivity and a candidate therapeutic target for SVCI.

Probing changes in brain esterified oxylipin concentrations during the early stages of pathogenesis in Alzheimer's Disease transgenic rats

Despite known pathological hallmarks of Alzheimer's Disease (AD) including neuronal loss, gliosis (inflammation), beta-amyloid plaque deposition and neurofibrillary tangle accumulation in the brain, little is known about inflammation resolution in early AD pathogenesis. In the brain, inflammation and resolution pathways are mediated by free oxylipins which are mostly bound (i.e. esterified), and therefore must be released (i.e. become free) to exert bioactivity. Recently, we showed reductions in brain esterified pro-resolving oxylipins in a transgenic rat model of AD (TgF344-AD rat) at 15 months of age, suggesting deficits in the source and availability of free pro-resolving oxylipins. In the present study, we tested whether these changes are discernable earlier in the disease process, i.e., at age of 10 months. We observed significant reductions in esterified pro-resolving 8(9)-epoxyeicosatrienoic acid (8(9)-EpETrE), 13-hydroxyoctadecatrienoic acid (13-HOTrE) and 15-hydroxyeicosapentaenoic acid (15-HEPE) oxylipins, and in pro-inflammatory 13-hydroxy-octadecadienoic acid (13-HODE), 20-hydroxy-eicosatetraenoic acid (20-HETE), 15-deoxy-prostaglandin J2 (15-deoxy-PGJ2) and prostaglandin E2 (PGE2) oxylipins in male and/or female transgenic AD rats compared to wildtype controls. These findings point to a deficit in esterified pro-resolving lipid mediators in the early stages of AD, concident with. changes in esterified lipid mediators involved in promoting inflammation.

Astrocytes as a Therapeutic Target in Alzheimer's Disease-Comprehensive Review and Recent Developments

Alzheimer's disease (AD) is a frequent and disabling neurodegenerative disorder, in which astrocytes participate in several pathophysiological processes including neuroinflammation, excitotoxicity, oxidative stress and lipid metabolism (along with a critical role in apolipoprotein E function). Current evidence shows that astrocytes have both neuroprotective and neurotoxic effects depending on the disease stage and microenvironmental factors. Furthermore, astrocytes appear to be affected by the presence of amyloid-beta (Aβ), with alterations in calcium levels, gliotransmission and proinflammatory activity via RAGE-NF-κB pathway. In addition, astrocytes play an important role in the metabolism of tau and clearance of Aβ through the glymphatic system. In this review, we will discuss novel pharmacological and non-pharmacological treatments focused on astrocytes as therapeutic targets for AD. These interventions include effects on anti-inflammatory/antioxidant systems, glutamate activity, lipid metabolism, neurovascular coupling and glymphatic system, calcium dysregulation, and in the release of peptides which affects glial and neuronal function. According to the AD stage, these therapies may be of benefit in either preventing or delaying the progression of the disease.

Prenatal THC Exposure Induces Sex-Dependent Neuropsychiatric Endophenotypes in Offspring and Long-Term Disruptions in Fatty-Acid Signaling Pathways Directly in the Mesolimbic Circuitry

Despite increased prevalence of maternal cannabis use, little is understood regarding potential long-term effects of prenatal cannabis exposure (PCE) on neurodevelopmental outcomes. While neurodevelopmental cannabis exposure increases the risk of developing affective/mood disorders in adulthood, the precise neuropathophysiological mechanisms in male and female offspring are largely unknown. Given the interconnectivity of the endocannabinoid (ECb) system and the brain's fatty acid pathways, we hypothesized that prenatal exposure to Δ⁹-tetrahydrocannabinol (THC) may dysregulate fetal neurodevelopment through alterations of fatty-acid dependent synaptic and neuronal function in the mesolimbic system. To investigate this, pregnant Wistar rats were exposed to vehicle or THC (3 mg/kg) from gestational day (GD)7 until GD22. Anxiety-like, depressive-like, and reward-seeking behavior, electrophysiology, and molecular assays were performed on adult male/female offspring. Imaging of fatty acids using matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS) was performed at prepubescence and adulthood. We report that PCE induces behavioral, neuronal, and molecular alterations in the mesolimbic system in male and female offspring, resembling neuropsychiatric endophenotypes. Additionally, PCE resulted in profound dysregulation of critical fatty acid pathways in the developing brain lipidome. Female progeny exhibited significant alterations to fatty acid levels at prepubescence but recovered from these deficits by early adulthood. In contrast, males exhibited persistent fatty acid deficits into adulthood. Moreover, both sexes maintained enduring abnormalities in glutamatergic/GABAergic function in the nucleus accumbens (NAc). These findings identify several novel long-term risks of maternal cannabis use and demonstrate for the first time, sex-related effects of maternal cannabinoid exposure directly in the developing neural lipidome.

A Combined Chronic Low-Dose Soluble Epoxide Hydrolase and Acetylcholinesterase Pharmacological Inhibition Promotes Memory Reinstatement in Alzheimer’s Disease Mice Models

Alzheimer’s disease (AD) is a progressive neurological disorder with multifactorial and heterogeneous causes. AD involves several etiopathogenic mechanisms such as aberrant protein accumulation, neurotransmitter deficits, synaptic dysfunction and neuroinflammation, which lead to cognitive decline. Unfortunately, the currently available anti-AD drugs only alleviate the symptoms temporarily and provide a limited therapeutic effect. Thus, new therapeutic strategies, including multitarget approaches, are urgently needed. It has been demonstrated that a co-treatment of acetylcholinesterase (AChE) inhibitor with other neuroprotective agents has beneficial effects on cognition. Here, we have assessed the neuroprotective effects of chronic dual treatment with a soluble epoxide hydrolase (sEH) inhibitor (TPPU) and an AChE inhibitor (6-chlorotacrine or rivastigmine) in in vivo studies. Interestingly, we have found beneficial effects after chronic low-dose co-treatment with TPPU and 6-chlorotacrine in the senescence-accelerated mouse prone 8 (SAMP8) mouse model as well as with TPPU and rivastigmine co-treatment in the 5XFAD mouse model, in comparison with the corresponding monotherapy treatments. In the SAMP8 model, no substantial improvements in synaptic plasticity markers were found, but the co-treatment of TPPU and 6-chlorotacrine led to a significantly reduced gene expression of neuroinflammatory markers, such as interleukin 6 (Il-6), triggering receptor expressed on myeloid cell 2 (Trem2) and glial fibrillary acidic protein (Gfap). In 5XFAD mice, chronic low-dose co-treatment of TPPU and rivastigmine led to enhanced protein levels of synaptic plasticity markers, such as the phospho-cAMP response element-binding protein (p-CREB) ratio, brain-derived neurotrophic factor (BDNF) and postsynaptic density protein 95 (PSD95), and also to a reduction in neuroinflammatory gene expression. Collectively, these results support the neuroprotectant role of chronic low-dose co-treatment strategy with sEH and AChE inhibitors in AD mouse models, opening new avenues for effective AD treatment.

Endothelial Cells and the Cerebral Circulation

Endothelial cells form the innermost layer of all blood vessels and are the only vascular component that remains throughout all vascular segments. The cerebral vasculature has several unique properties not found in the peripheral circulation; this requires that the cerebral endothelium be considered as a unique entity. Cerebral endothelial cells perform several functions vital for brain health. The cerebral vasculature is responsible for protecting the brain from external threats carried in the blood. The endothelial cells are central to this requirement as they form the basis of the blood-brain barrier. The endothelium also regulates fibrinolysis, thrombosis, platelet activation, vascular permeability, metabolism, catabolism, inflammation, and white cell trafficking. Endothelial cells regulate the changes in vascular structure caused by angiogenesis and artery remodeling. Further, the endothelium contributes to vascular tone, allowing proper perfusion of the brain which has high energy demands and no energy stores. In this article, we discuss the basic anatomy and physiology of the cerebral endothelium. Where appropriate, we discuss the detrimental effects of high blood pressure on the cerebral endothelium and the contribution of cerebrovascular disease endothelial dysfunction and dementia. © 2022 American Physiological Society. Compr Physiol 12:3449-3508, 2022.

Unveiling the Multitarget Anti-Alzheimer Drug Discovery Landscape: A Bibliometric Analysis

Multitarget anti-Alzheimer agents are the focus of very intensive research. Through a comprehensive bibliometric analysis of the publications in the period 1990-2020, we have identified trends and potential gaps that might guide future directions. We found that: (i) the number of publications boomed by 2011 and continued ascending in 2020; (ii) the linked-pharmacophore strategy was preferred over design approaches based on fusing or merging pharmacophores or privileged structures; (iii) a significant number of in vivo studies, mainly using the scopolamine-induced amnesia mouse model, have been performed, especially since 2017; (iv) China, Italy and Spain are the countries with the largest total number of publications on this topic, whereas Portugal, Spain and Italy are the countries in whose scientific communities this topic has generated greatest interest; (v) acetylcholinesterase, β-amyloid aggregation, oxidative stress, butyrylcholinesterase, and biometal chelation and the binary combinations thereof have been the most commonly pursued, while combinations based on other key targets, such as tau aggregation, glycogen synthase kinase-3β, NMDA receptors, and more than 70 other targets have been only marginally considered. These results might allow us to spot new design opportunities based on innovative target combinations to expand and diversify the repertoire of multitarget drug candidates and increase the likelihood of finding effective therapies for this devastating disease.

Discovery and In Vivo Proof of Concept of a Highly Potent Dual Inhibitor of Soluble Epoxide Hydrolase and Acetylcholinesterase for the Treatment of Alzheimer's Disease

With innumerable clinical failures of target-specific drug candidates for multifactorial diseases, such as Alzheimer's disease (AD), which remains inefficiently treated, the advent of multitarget drug discovery has brought a new breath of hope. Here, we disclose a class of 6-chlorotacrine (huprine)-TPPU hybrids as dual inhibitors of the enzymes soluble epoxide hydrolase (sEH) and acetylcholinesterase (AChE), a multitarget profile to provide cumulative effects against neuroinflammation and memory impairment. Computational studies confirmed the gorge-wide occupancy of both enzymes, from the main site to a secondary site, including a so far non-described AChE cryptic pocket. The lead compound displayed in vitro dual nanomolar potencies, adequate brain permeability, aqueous solubility, human microsomal stability, lack of neurotoxicity, and it rescued memory, synaptic plasticity, and neuroinflammation in an AD mouse model, after low dose chronic oral administration.

Identification of novel drug targets for Alzheimer's disease by integrating genetics and proteomes from brain and blood

Genome-wide association studies (GWASs) have discovered numerous risk genes for Alzheimer's disease (AD), but how these genes confer AD risk is challenging to decipher. To efficiently transform genetic associations into drug targets for AD, we employed an integrative analytical pipeline using proteomes in the brain and blood by systematically applying proteome-wide association study (PWAS), Mendelian randomization (MR) and Bayesian colocalization. Collectively, we identified the brain protein abundance of 7 genes (ACE, ICA1L, TOM1L2, SNX32, EPHX2, CTSH, and RTFDC1) are causal in AD (P < 0.05/proteins identified for PWAS and MR; PPH4 >80% for Bayesian colocalization). The proteins encoded by these genes were mainly expressed on the surface of glutamatergic neurons and astrocytes. Of them, ACE with its protein abundance was also identified in significant association with AD on the blood-based studies and showed significance at the transcriptomic level. SNX32 was also found to be associated with AD at the blood transcriptomic level. Collectively, our current study results on genetic, proteomic, and transcriptomic approaches has identified compelling genes, which may provide important leads to design future functional studies and potential drug targets for AD.

14,15-EET Reduced Brain Injury from Cerebral Ischemia and Reperfusion via Suppressing Neuronal Parthanatos

To investigate the effect of 14,15-EET on the parthanatos in neurons induced by cerebral ischemia and reperfusion, middle cerebral artery occlusion and reperfusion (MCAO/R) and oxygen glucose deprivation/reoxygenation (OGD/R) were used to simulate cerebral ischemia reperfusion in vivo and in vitro, respectively. TTC staining and the Tunel method were used to detect cerebral infarct volume and neuronal apoptosis. Western blot and immunofluorescence were used to detect poly (ADP-ribose) polymerase-1 (PARP-1) activation and AIF nuclear translocation. The production of reactive oxygen species (ROS) and the expression of antioxidant genes were detected by Mito SOX, DCFH-DA and qPCR methods. MCAO/R increased cerebral infarct volume and neuronal apoptosis in mice, while 14,15-EET pretreatment increased cerebral infarct volume and neuronal apoptosis. OGD/R induced reactive oxygen species generation, PARP-1 cleavage, and AIF nuclear translocation in cortical neurons. 14,15-EET pretreatment could enhance the antioxidant gene expression of glutathione peroxidase (GSH-Px), heme oxygenase-1 (HO-1) and superoxide dismutase (SOD) in cortical neurons after ischemia and reperfusion. 14,15-EET inhibits the neuronal parthanatos induced by MCAO/R through upregulation of the expression of antioxidant genes and by reducing the generation of reactive oxygen species. This study advances the EET neuroprotection theory and provides a scientific basis for targeted clinical drugs that reduce neuronal parthanatos following cerebral ischemia and reperfusion.

Alzheimer's Disease Animal Models: Elucidation of Biomarkers and Therapeutic Approaches for Cognitive Impairment

Alzheimer's disease (AD) is an age-related and progressive neurodegenerative disorder. It is widely accepted that AD is mainly caused by the accumulation of extracellular amyloid β (Aβ) and intracellular neurofibrillary tau tangles. Aβ begins to accumulate years before the onset of cognitive impairment, suggesting that the benefit of currently available interventions would be greater if they were initiated in the early phases of AD. To understand the mechanisms of AD pathogenesis, various transgenic mouse models with an accelerated accumulation of Aβ and tau tangles have been developed. However, none of these models exhibit all pathologies present in human AD. To overcome these undesirable phenotypes, APP knock-in mice, which were presented with touchscreen-based tasks, were developed to better evaluate the efficacy of candidate therapeutics in mouse models of early-stage AD. This review assesses several AD mouse models from the aspect of biomarkers and cognitive impairment and discusses their potential as tools to provide novel AD therapeutic approaches.