Modeling late-onset Alzheimer's disease neuropathology via direct neuronal reprogramming.

Late-onset Alzheimer's disease (LOAD) is the most common form of Alzheimer's disease (AD). However, modeling sporadic LOAD that endogenously captures hallmark neuronal pathologies such as amyloid-ß (Aß) deposition, tau tangles, and neuronal loss remains an unmet need. We demonstrate that neurons generated by microRNA (miRNA)-based direct reprogramming of fibroblasts from individuals affected by autosomal dominant AD (ADAD) and LOAD in a three-dimensional environment effectively recapitulate key neuropathological features of AD. Reprogrammed LOAD neurons exhibit Aß-dependent neurodegeneration, and treatment with ß- or γ-secretase inhibitors before (but not subsequent to) Aß deposit formation mitigated neuronal death. Moreover inhibiting age-associated retrotransposable elements in LOAD neurons reduced both Aß deposition and neurodegeneration. Our study underscores the efficacy of modeling late-onset neuropathology of LOAD through high-efficiency miRNA-based neuronal reprogramming.

Enhanced microglial dynamics and a paucity of tau seeding in the amyloid plaque microenvironment contribute to cognitive resilience in Alzheimer's disease.

Asymptomatic Alzheimer's disease (AsymAD) describes the status of individuals with preserved cognition but identifiable Alzheimer's disease (AD) brain pathology (i.e., beta-amyloid (Aß) deposits, neuritic plaques, and neurofibrillary tangles) at autopsy. In this study, we investigated the postmortem brains of a cohort of AsymAD subjects to gain insight into the mechanisms underlying resilience to AD pathology and cognitive decline. Our results showed that AsymAD cases exhibit enrichment in core plaques, decreased filamentous plaque accumulation, and increased plaque-surrounding microglia. Less pathological tau aggregation in dystrophic neurites was found in AsymAD brains than in AD brains, and tau seeding activity was comparable to that in healthy brains. We used spatial transcriptomics to characterize the plaque niche further and revealed autophagy, endocytosis, and phagocytosis as the pathways associated with the genes upregulated in the AsymAD plaque niche. Furthermore, the levels of ARP2 and CAP1, which are actin-based motility proteins that participate in the dynamics of actin filaments to allow cell motility, were increased in the microglia surrounding amyloid plaques in AsymAD cases. Our findings suggest that the amyloid-plaque microenvironment in AsymAD cases is characterized by the presence of microglia with highly efficient actin-based cell motility mechanisms and decreased tau seeding compared with that in AD brains. These two mechanisms can potentially protect against the toxic cascade initiated by Aß, preserving brain health, and slowing AD pathology progression.

Effects of SPI1-mediated transcriptome remodeling on Alzheimer's disease-related phenotypes in mouse models of Aß amyloidosis.

SPI1 was recently reported as a genetic risk factor for Alzheimer's disease (AD) in large-scale genome-wide association studies. However, it is unknown whether SPI1 should be downregulated or increased to have therapeutic benefits. To investigate the effect of modulating SPI1 levels on AD pathogenesis, we performed extensive biochemical, histological, and transcriptomic analyses using both Spi1-knockdown and Spi1-overexpression mouse models. Here, we show that the knockdown of Spi1 expression significantly exacerbates insoluble amyloid-ß (Aß) levels, amyloid plaque deposition, and gliosis. Conversely, overexpression of Spi1 significantly ameliorates these phenotypes and dystrophic neurites. Further mechanistic studies using targeted and single-cell transcriptomics approaches demonstrate that altered Spi1 expression modulates several pathways, such as immune response pathways and complement system. Our data suggest that transcriptional reprogramming by targeting transcription factors, like Spi1, might hold promise as a therapeutic strategy. This approach could potentially expand the current landscape of druggable targets for AD.

APOE loss of function: A genetic shield against Alzheimer's disease.

In this issue of Neuron, Chemparathy et al.1 provide human genetics data suggesting that APOE loss-of-function mutations may confer resistance to Alzheimer's disease (AD) without compromising longevity. These data strongly support the APOE toxic gain-of-function hypothesis for AD.

Enhanced microglial dynamics and paucity of tau seeding in the amyloid plaque microenvironment contributes to cognitive resilience in Alzheimer's disease.

Asymptomatic Alzheimer's disease (AsymAD) describes the status of subjects with preserved cognition but with identifiable Alzheimer's disease (AD) brain pathology (i.e. Aß-amyloid deposits, neuritic plaques, and neurofibrillary tangles) at autopsy. In this study, we investigated the postmortem brains of a cohort of AsymAD cases to gain insight into the underlying mechanisms of resilience to AD pathology and cognitive decline. Our results showed that AsymAD cases exhibit an enrichment of core plaques and decreased filamentous plaque accumulation, as well as an increase in microglia surrounding this last type. In AsymAD cases we found less pathological tau aggregation in dystrophic neurites compared to AD and tau seeding activity comparable to healthy control subjects. We used spatial transcriptomics to further characterize the plaque niche and found autophagy, endocytosis, and phagocytosis within the top upregulated pathways in the AsymAD plaque niche, but not in AD. Furthermore, we found ARP2, an actin-based motility protein crucial to initiate the formation of new actin filaments, increased within microglia in the proximity of amyloid plaques in AsymAD. Our findings support that the amyloid-plaque microenvironment in AsymAD cases is characterized by microglia with highly efficient actin-based cell motility mechanisms and decreased tau seeding compared to AD. These two mechanisms can potentially provide protection against the toxic cascade initiated by Aß that preserves brain health and slows down the progression of AD pathology.

Network analysis identifies strain-dependent response to tau and tau seeding-associated genes.

Previous research demonstrated that genetic heterogeneity is a critical factor in modeling amyloid accumulation and other Alzheimer's disease phenotypes. However, it is unknown what mechanisms underlie these effects of genetic background on modeling tau aggregate-driven pathogenicity. In this study, we induced tau aggregation in wild-derived mice by expressing MAPT. To investigate the effect of genetic background on the action of tau aggregates, we performed RNA sequencing with brains of C57BL/6J, CAST/EiJ, PWK/PhJ, and WSB/EiJ mice (n = 64) and determined core transcriptional signature conserved in all genetic backgrounds and signature unique to wild-derived backgrounds. By measuring tau seeding activity using the cortex, we identified 19 key genes associated with tau seeding and amyloid response. Interestingly, microglial pathways were strongly associated with tau seeding activity in CAST/EiJ and PWK/PhJ backgrounds. Collectively, our study demonstrates that mouse genetic context affects tau-mediated alteration of transcriptome and tau seeding. The gene modules associated with tau seeding provide an important resource to better model tauopathy.

Endogenous recapitulation of Alzheimer's disease neuropathology through human 3D direct neuronal reprogramming.

Alzheimer's disease (AD) is a neurodegenerative disorder that primarily affects elderly individuals, and is characterized by hallmark neuronal pathologies including extracellular amyloid-ß (Aß) plaque deposition, intracellular tau tangles, and neuronal death. However, recapitulating these age-associated neuronal pathologies in patient-derived neurons has remained a significant challenge, especially for late-onset AD (LOAD), the most common form of the disorder. Here, we applied the high efficiency microRNA-mediated direct neuronal reprogramming of fibroblasts from AD patients to generate cortical neurons in three-dimensional (3D) Matrigel and self-assembled neuronal spheroids. Our findings indicate that neurons and spheroids reprogrammed from both autosomal dominant AD (ADAD) and LOAD patients exhibited AD-like phenotypes linked to neurons, including extracellular Aß deposition, dystrophic neurites with hyperphosphorylated, K63-ubiquitin-positive, seed-competent tau, and spontaneous neuronal death in culture. Moreover, treatment with ß- or γ-secretase inhibitors in LOAD patient-derived neurons and spheroids before Aß deposit formation significantly lowered Aß deposition, as well as tauopathy and neurodegeneration. However, the same treatment after the cells already formed Aß deposits only had a mild effect. Additionally, inhibiting the synthesis of age-associated retrotransposable elements (RTEs) by treating LOAD neurons and spheroids with the reverse transcriptase inhibitor, lamivudine, alleviated AD neuropathology. Overall, our results demonstrate that direct neuronal reprogramming of AD patient fibroblasts in a 3D environment can capture age-related neuropathology and reflect the interplay between Aß accumulation, tau dysregulation, and neuronal death. Moreover, miRNA-based 3D neuronal conversion provides a human-relevant AD model that can be used to identify compounds that can potentially ameliorate AD-associated pathologies and neurodegeneration.

The effect of Abi3 locus deletion on the progression of Alzheimer's disease-related pathologies.

Human genetics studies of Alzheimer's disease (AD) have identified the ABI3 gene as a candidate risk gene for AD. Because ABI3 is highly expressed in microglia, the brain's immune cells, it was suggested that ABI3 might impact AD pathogenesis by regulating the immune response. Recent studies suggest that microglia have multifaceted roles in AD. Their immune response and phagocytosis functions can have beneficial effects in the early stages of AD by clearing up amyloid-beta (Aß) plaques. However, they can be harmful at later stages due to their continuous inflammatory response. Therefore, it is important to understand the role of genes in microglia functions and their impact on AD pathologies along the progression of the disease. To determine the role of ABI3 at the early stage of amyloid pathology, we crossed Abi3 knock-out mice with the 5XFAD Aß-amyloidosis mouse model and aged them until 4.5-month-old. Here, we demonstrate that deletion of the Abi3 locus increased Aß plaque deposition, while there was no significant change in microgliosis and astrogliosis. Transcriptomic analysis indicates alterations in the expression of immune genes, such as Tyrobp, Fcer1g, and C1qa. In addition to the transcriptomic changes, we found elevated cytokine protein levels in Abi3 knock-out mouse brains, strengthening the role of ABI3 in neuroinflammation. These findings suggest that loss of ABI3 function may exacerbate AD progression by increasing Aß accumulation and inflammation starting from earlier stages of the pathology.

Network analysis reveals strain-dependent response to misfolded tau aggregates.

Mouse genetic backgrounds have been shown to modulate amyloid accumulation and propagation of tau aggregates. Previous research into these effects has highlighted the importance of studying the impact of genetic heterogeneity on modeling Alzheimer's disease. However, it is unknown what mechanisms underly these effects of genetic background on modeling Alzheimer's disease, specifically tau aggregate-driven pathogenicity. In this study, we induced tau aggregation in wild-derived mice by expressing MAPT (P301L). To investigate the effect of genetic background on the action of tau aggregates, we performed RNA sequencing with brains of 6-month-old C57BL/6J, CAST/EiJ, PWK/PhJ, and WSB/EiJ mice (n=64). We also measured tau seeding activity in the cortex of these mice. We identified three gene signatures: core transcriptional signature, unique signature for each wild-derived genetic background, and tau seeding-associated signature. Our data suggest that microglial response to tau seeds is elevated in CAST/EiJ and PWK/PhJ mice. Together, our study provides the first evidence that mouse genetic context influences the seeding of tau. SUMMARY: Seeding of tau predates the phosphorylation and spreading of tau aggregates. Acri and colleagues report transcriptomic responses to tau and elevated tau seeds in wild-derived mice. This paper creates a rich resource by combining genetics, tau biosensor assays, and transcriptomics.

Deletion of the Alzheimer's disease risk gene Abi3 locus results in obesity and systemic metabolic disruption in mice.

Alzheimer's disease (AD) genetics studies have identified a coding variant within ABI3 gene that increases the risk of developing AD. Recently, we demonstrated that deletion of the Abi3 gene locus dramatically exacerbates AD neuropathology in a transgenic mouse model of amyloidosis. In the course of this AD project, we unexpectedly found that deletion of the Abi3 gene locus resulted in a dramatic obese phenotype in non-transgenic mice. Here, we report our investigation into this serendipitous metabolic finding. Specifically, we demonstrate that mice with deletion of the Abi3 gene locus (Abi3-/- ) have dramatically increased body weight and body fat. Further, we determined that Abi3-/- mice have impaired energy expenditure. Additionally, we found that deletion of the Abi3 gene locus altered gene expression within the hypothalamus, particularly within immune-related pathways. Subsequent immunohistological analysis of the central nervous system (CNS) revealed that microglia number and area were decreased specifically within the mediobasal hypothalamus of Abi3-/- mice. Altogether, this investigation establishes the functional importance of the Abi3 gene locus in the regulation of systemic metabolism and maintenance of healthy body weight. While our previous findings indicated the importance of Abi3 in neurodegeneration, this study indicates that Abi3 related functions are also essential for metabolic regulation.

Deletion of Abi3 gene locus exacerbates neuropathological features of Alzheimer's disease in a mouse model of Aß amyloidosis.

Recently, large-scale human genetics studies identified a rare coding variant in the ABI3 gene that is associated with an increased risk of Alzheimer's disease (AD). However, pathways by which ABI3 contributes to the pathogenesis of AD are unknown. To address this question, we determined whether loss of ABI3 function affects pathological features of AD in the 5XFAD mouse model. We demonstrate that the deletion of Abi3 locus significantly increases amyloid ß (Aß) accumulation and decreases microglia clustering around the plaques. Furthermore, long-term potentiation is impaired in 5XFAD;Abi3 knockout ("Abi3−/−") mice. Moreover, we identified marked changes in the proportion of microglia subpopulations in Abi3−/− mice using a single-cell RNA sequencing approach. Mechanistic studies demonstrate that Abi3 knockdown in microglia impairs migration and phagocytosis. Together, our study provides the first in vivo functional evidence that loss of ABI3 function may increase the risk of developing AD by affecting Aß accumulation and neuroinflammation.

Tubular human brain organoids to model microglia-mediated neuroinflammation.

Human brain organoids, 3D brain tissue cultures derived from human pluripotent stem cells, hold promising potential in modeling neuroinflammation for a variety of neurological diseases. However, challenges remain in generating standardized human brain organoids that can recapitulate key physiological features of a human brain. Here, we present tubular organoid-on-a-chip devices to generate better organoids and model neuroinflammation. By employing 3D printed hollow mesh scaffolds, our device can be easily incorporated into multiwell-plates for reliable, scalable, and reproducible generation of tubular organoids. By introducing rocking flows through the tubular device channel, our device can perfuse nutrients and oxygen to minimize organoid necrosis and hypoxia, and incorporate immune cells into organoids to model neuro-immune interactions. Compared with conventional protocols, our method increased neural progenitor proliferation and reduced heterogeneity of human brain organoids. As a proof-of-concept application, we applied this method to model the microglia-mediated neuroinflammation after exposure to an opioid receptor agonist. We found isogenic microglia were activated after exposure to an opioid receptor agonist (DAMGO) and transformed back to the homeostatic status with further treatment by a cannabinoid receptor 2 (CB2) agonist (LY2828360). Importantly, the activated microglia in tubular organoids had stronger cytokine responses compared to those in 2D microglial cultures. Our tubular organoid device is simple, versatile, inexpensive, easy-to-use, and compatible with multiwell-plates, so it can be widely used in common research and clinical laboratory settings. This technology can be broadly used for basic and translational applications in inflammatory diseases including substance use disorders, neural diseases, autoimmune disorders, and infectious diseases.

MicroRNAs on the move: microRNAs in astrocyte-derived ApoE particles regulate neuronal function.

In this issue of Neuron, Li et al. (2021) demonstrate that ApoE lipoprotein particles shuttle miRNAs from astrocytes to neurons, leading to inhibition of cholesterol biosynthesis and an increase in histone acetylation in neurons.

Neuroactivity of the naturally occurring aporphine alkaloid, roemerine.

Roemerine is a naturally occurring aporphine alkaloid. In this study, we screened a conformer library of Food and Drug Administration (FDA)-approved drugs to identify similar drugs that can assist in identifying the biological targets of roemerine. To assess the neuroactivity in vitro, we measured the levels of cell metabolites, Brain-Derived Neurotrophic Factor (BDNF) and serotonin (5-HT) in SH-SY5Y cell line. By means of structure-based virtual screening, we identified five drugs that are similar to roemerine; mirtazapine, atomoxetine, epinastine, diphenhydramine and orphenadrine. GC-MS metabolomics study revealed that roemerine has a high impact on alanine-aspartate-glutamate pathway in cell lysate and cultured medium. Additionally, roemerine increased intercellular 5-HT level and intracellular BDNF protein expression at 10 µM. In conclusion, roemerine - a major alkaloid in antidepressant-like effect possessing plants (P. lacerum and P. syriacum) - has a neuronal activity through increasing BDNF protein expression and affecting serotonergic and glutamatergic systems in SH-SY5Y cell line.

Effect of atorvastatin on Aß1-42 -induced alteration of SESN2, SIRT1, LC3II and TPP1 protein expressions in neuronal cell cultures.

OBJECTIVES: Sestrins (SESNs) and sirtuins (SIRTs) are antioxidant and antiapoptotic genes and crucial mediators for lysosomal autophagy regulation that play a pivotal role in the Alzheimer's disease (AD). Recently, statins have been linked to the reduced prevalence of AD in statin-prescribed populations yet molecular basis for the neuroprotective action of statins is still under debate. METHODS: This study was undertaken whether Aß-induced changes of SESN2 and SIRT1 protein expression, autophagy marker LC3II and lysosomal enzyme TPP1 affected by atorvastatin (Western blot) and its possible role in Aß neurotoxicity (ELISA). KEY FINDINGS/RESULTS: We showed that SESN2 and LC3II expressions were elevated, whereas SIRT1 and TPP1 expressions were decreased in the Aß1-42 -exposed human neuroblastoma cells (SH-SY5Y). Co-administration of atorvastatin with Aß1-42 compensates SESN2 increase and recovers SIRT1 decline by reducing oxidative stress, decreasing SESN2 expression and increasing SIRT1 expression by its neuroprotective action. Atorvastatin induced LC3II but not TPP1 level in the Aß1-42 -exposed cells suggested that atorvastatin is effective in the formation of autophagosome but not on the expression of the specific lysosomal enzyme TPP1. DISCUSSION AND CONCLUSION: Together, these results indicate that atorvastatin induced SESN2, SIRT1 and LC3II levels play a protective role against Aß1-42 neurotoxicity.

Interactions of Aromatase and Seladin-1: A Neurosteroidogenic and Gender Perspective.

Aromatase and seladin-1 are enzymes that have major roles in estrogen synthesis and are important in both brain physiology and pathology. Aromatase is the key enzyme that catalyzes estrogen biosynthesis from androgen precursors and regulates the brain's neurosteroidogenic activity. Seladin-1 is the enzyme that catalyzes the last step in the biosynthesis of cholesterol, the precursor of all hormones, from desmosterol. Studies indicated that seladin-1 is a downstream mediator of the neuroprotective activity of estrogen. Recently, we also showed that there is an interaction between aromatase and seladin-1 in the brain. Therefore, the expression of local brain aromatase and seladin-1 is important, as they produce neuroactive steroids in the brain for the protection of neuronal damage. Increasing steroid biosynthesis specifically in the central nervous system (CNS) without affecting peripheral hormone levels may be possible by manipulating brain-specific promoters of steroidogenic enzymes. This review emphasizes that local estrogen, rather than plasma estrogen, may be responsible for estrogens' protective effects in the brain. Therefore, the roles of aromatase and seladin-1 and their interactions in neurodegenerative events such as Alzheimer's disease (AD), ischemia/reperfusion injury (stroke), and epilepsy are also discussed in this review.

Aromatase/Seladin-1 Interactions in Human Neuronal Cell Culture, the Hippocampus of Healthy Rats and Transgenic Alzheimer's Disease Mice.

BACKGROUND/AIMS: Decreasing levels of aromatase and seladin-1 could be one of the molecular mechanisms of Alzheimer's disease (AD). Aromatase is an enzyme that catalyzes estrogen biosynthesis from androgen precursors, and seladin-1 is an enzyme that converts desmosterol to cholesterol, which is the precursor of all hormones. Verifying the potential relationship between these proteins and accordingly determining new therapeutic targets constitute the aims of this study. METHODS: Changes in protein levels were compared in vitro in aromatase and seladin-1 inhibitor-administered human neuroblastoma (SH-SY5Y) cells in vivo in intracerebroventricular (icv) aromatase or seladin-1 inhibitor-administered rats, as well as in transgenic AD mice in which the genes encoding these proteins were knocked out. RESULTS AND CONCLUSIONS: In the cell cultures, we observed that seladin-1 protein levels increased after aromatase enzyme inhibition. The hippocampal aromatase protein levels decreased following chronic seladin-1 inhibition in icv inhibitor-administered rats; however, the aromatase levels in the dentate gyrus of seladin-1 knockout (SelKO) AD male mice increased. These findings indicate a partial relationship between these proteins and their roles in AD pathology.

Chronic levetiracetam decreases hippocampal and testicular aromatase expression in normal but not kainic acid-induced experimental model of acute seizures in rats.

Reproductive disorders are more common in men with epilepsy taking anticonvulsant medications. Antiseizure/anticonvulsant drugs and seizures in medial temporal lobe structures may cause gonadal dysfunction, including infertility, decreased libido, and potency. Levels of circulating bioavailable testosterone are affected by the aromatase enzyme, which converts testosterone into estrogen and may be affected by seizure medications. However, the relationship of anticonvulsant drugs with central aromatase levels is not clear. This study investigated the possible effects of the highly efficient, new-generation antiseizure/anticonvulsant drug levetiracetam on central and gonadal aromatase expression and gonadal tissue functionality at 27 and 54 mg/kg/day doses. Epileptogenesis was generated in male Wistar rats by an intraperitoneal injection of the excitotoxic agent kainic acid. Aromatase levels were 1.5 times higher in the brain cortex of the kainic acid groups after 4 weeks and the hippocampus after 4 and 8 weeks compared with the controls. Decreased basal aromatase levels were observed after 1 week of levetiracetam treatment (27 mg/kg/day). Administration of 27 mg/kg/day levetiracetam did not alter vas deferens contractions at 1, 4, or 8 weeks compared with the controls. No histological changes were observed in the vas deferens, epididymis, or testis after 8 weeks of levetiracetam administration at both doses. Administration of 27 and 54 mg/kg/day levetiracetam downregulated testis aromatase expression at 8 weeks compared with the controls. These results suggest that levetiracetam decreases aromatase levels in the testis and increases the seizure threshold by a possible decrease in systemic estradiol levels.