Microglia Gravitate toward Amyloid Plaques Surrounded by Externalized Phosphatidylserine via TREM2.

Microglia play a crucial role in synaptic elimination by engulfing dystrophic neurons via triggering receptors expressed on myeloid cells 2 (TREM2). They are also involved in the clearance of beta-amyloid (Aß) plaques in Alzheimer's disease (AD); nonetheless, the driving force behind TREM2-mediated phagocytosis of beta-amyloid (Aß) plaques remains unknown. Here, using advanced 2D/3D/4D co-culture systems with loss-of-function mutations in TREM2 (a frameshift mutation engineered in exon 2) brain organoids/microglia/assembloids, it is identified that the clearance of Aß via TREM2 is accelerated by externalized phosphatidylserine (ePtdSer) generated from dystrophic neurons surrounding the Aß plaques. Moreover, it is investigated whether microglia from both sporadic (CRISPR-Cas9-based APOE4 lines) and familial (APPNL-G-F/MAPT double knock-in mice) AD models show reduced levels of TREM2 and lack of phagocytic activity toward ePtdSer-positive Aß plaques. Herein new insight is provided into TREM2-dependent microglial phagocytosis of Aß plaques in the context of the presence of ePtdSer during AD progression.

Neurotoxic Microglial Activation via IFNγ-Induced Nrf2 Reduction Exacerbating Alzheimer's Disease.

Microglial neuroinflammation appears to be neuroprotective in the early pathological stage, yet neurotoxic, which often precedes neurodegeneration in Alzheimer's disease (AD). However, it remains unclear how the microglial activities transit to the neurotoxic state during AD progression, due to complex neuron-glia interactions. Here, the mechanism of detrimental microgliosis in AD by employing 3D human AD mini-brains, brain tissues of AD patients, and 5XFAD mice is explored. In the human and animal AD models, amyloid-beta (Aß)-overexpressing neurons and reactive astrocytes produce interferon-gamma (IFNγ) and excessive oxidative stress. IFNγ results in the downregulation of mitogen-activated protein kinase (MAPK) and the upregulation of Kelch-like ECH-associated Protein 1 (Keap1) in microglia, which inactivate nuclear factor erythroid-2-related factor 2 (Nrf2) and sensitize microglia to the oxidative stress and induces a proinflammatory microglia via nuclear factor kappa B (NFκB)-axis. The proinflammatory microglia in turn produce neurotoxic nitric oxide and proinflammatory mediators exacerbating synaptic impairment, phosphorylated-tau accumulation, and discernable neuronal loss. Interestingly, recovering Nrf2 in the microglia prevents the activation of proinflammatory microglia and significantly blocks the tauopathy in AD minibrains. Taken together, it is envisioned that IFNγ-driven Nrf2 downregulation in microglia as a key target to ameliorate AD pathology.

Environmental aluminum oxide inducing neurodegeneration in human neurovascular unit with immunity.

Aluminum oxide nanoparticle (AlNP), a ubiquitous neurotoxin highly enriched in air pollution, is often produced as an inevitable byproduct in the manufacturing of industrial products such as cosmetics and metal materials. Meanwhile, ALNP has emerged as a significant public health concern due to its potential association with neurological diseases. However, the studies about the neurotoxic effects of AlNP are limited, partially due to the lack of physiologically relevant human neurovascular unit with innate immunity (hNVUI). Here, we employed our AlNP-treated hNVUI model to investigate the underlying mechanism of AlNP-driven neurodegeneration. First, we validated the penetration of AlNP across a blood-brain barrier (BBB) compartment and found AlNP-derived endothelial cellular senescence through the p16 and p53/p21 pathways. Our study showed that BBB-penetrating AlNP promoted reactive astrocytes, which produced a significant level of reactive oxygen species (ROS). The astrocytic neurotoxic factors caused neuronal damage, including the synaptic impairment, the accumulation of phosphoric-tau proteins, and even neuronal death. Our study suggests that AlNP could be a potential environmental risk factor of neurological disorders mediated by neuroinflammation.

Three-dimensional human neural culture on a chip recapitulating neuroinflammation and neurodegeneration.

Neuroinflammation has either beneficial or detrimental effects, depending on risk factors and neuron-glia interactions in neurological disorders. However, studying neuroinflammation has been challenging due to the complexity of cell-cell interactions and lack of physio-pathologically relevant neuroinflammatory models. Here, we describe our three-dimensional microfluidic multicellular human neural culture model, referred to as a 'brain-on-a-chip' (BoC). This elucidates neuron-glia interactions in a controlled manner and recapitulates pathological signatures of the major neurological disorders: dementia, brain tumor and brain edema. This platform includes a chemotaxis module offering a week-long, stable chemo-gradient compared with the few hours in other chemotaxis models. Additionally, compared with conventional brain models cultured with mixed phenotypes of microglia, our BoC can separate the disease-associated microglia out of heterogeneous population and allow selective neuro-glial engagement in three dimensions. This provides benefits of interpreting the neuro-glia interactions while revealing that the prominent activation of innate immune cells is the risk factor leading to synaptic impairment and neuronal loss, validated in our BoC models of disorders. This protocol describes how to fabricate and implement our human BoC, manipulate in real time and perform end-point analyses. It takes 2 d to set up the device and cell preparations, 1-9 weeks to develop brain models under disease conditions and 2-3 d to carry out analyses. This protocol requires at least 1 month training for researchers with basic molecular biology techniques. Taken together, our human BoCs serve as reliable and valuable platforms to investigate pathological mechanisms involving neuroinflammation and to assess therapeutic strategies modulating neuroinflammation in neurological disorders.

Astrocytic scar restricting glioblastoma via glutamate-MAO-B activity in glioblastoma-microglia assembloid.

BACKGROUND: Glial scar formation is a reactive glial response confining injured regions in a central nervous system. However, it remains challenging to identify key factors formulating glial scar in response to glioblastoma (GBM) due to complex glia-GBM crosstalk. METHODS: Here, we constructed an astrocytic scar enclosing GBM in a human assembloid and a mouse xenograft model. GBM spheroids were preformed and then co-cultured with microglia and astrocytes in 3D Matrigel. For the xenograft model, U87-MG cells were subcutaneously injected to the Balb/C nude female mice. RESULTS: Additional glutamate was released from GBM-microglia assembloid by 3.2-folds compared to GBM alone. The glutamate upregulated astrocytic monoamine oxidase-B (MAO-B) activity and chondroitin sulfate proteoglycans (CSPGs) deposition, forming the astrocytic scar and restricting GBM growth. Attenuating scar formation by the glutamate-MAO-B inhibition increased drug penetration into GBM assembloid, while reducing GBM confinement. CONCLUSIONS: Taken together, our study suggests that astrocytic scar could be a critical modulator in GBM therapeutics.

Bright-Field and Edge-Enhanced Imaging Using an Electrically Tunable Dual-Mode Metalens.

The imaging of microscopic biological samples faces numerous difficulties due to their small feature sizes and low-amplitude contrast. Metalenses have shown great promise in bioimaging as they have access to the complete complex information, which, alongside their extremely small and compact footprint and potential to integrate multiple functionalities into a single device, allow for miniaturized microscopy with exceptional features. Here, we design and experimentally realize a dual-mode metalens integrated with a liquid crystal cell that can be electrically switched between bright-field and edge-enhanced imaging on the millisecond scale. We combine the concepts of geometric and propagation phase to design the dual-mode metalens and physically encode the required phase profiles using hydrogenated amorphous silicon for operation at visible wavelengths. The two distinct metalens phase profiles include (1) a conventional hyperbolic metalens for bright-field imaging and (2) a spiral metalens with a topological charge of +1 for edge-enhanced imaging. We demonstrate the focusing and vortex generation ability of the metalens under different states of circular polarization and prove its use for biological imaging. This work proves a method for in vivo observation and monitoring of the cell response and drug screening within a compact form factor.

In Vitro Tumor Models on Chip and Integrated Microphysiological Analysis Platform (MAP) for Life Sciences and High-Throughput Drug Screening.

The evolution of preclinical in vitro cancer models has led to the emergence of human cancer-on-chip or microphysiological analysis platforms (MAPs). Although it has numerous advantages compared to other models, cancer-on-chip technology still faces several challenges such as the complexity of the tumor microenvironment and integrating multiple organs to be widely accepted in cancer research and therapeutics. In this review, we highlight the advancements in cancer-on-chip technology in recapitulating the vital biological features of various cancer types and their applications in life sciences and high-throughput drug screening. We present advances in reconstituting the tumor microenvironment and modeling cancer stages in breast, brain, and other types of cancer. We also discuss the relevance of MAPs in cancer modeling and precision medicine such as effect of flow on cancer growth and the short culture period compared to clinics. The advanced MAPs provide high-throughput platforms with integrated biosensors to monitor real-time cellular responses applied in drug development. We envision that the integrated cancer MAPs has a promising future with regard to cancer research, including cancer biology, drug discovery, and personalized medicine.

Nanomedicine for advanced cancer immunotherapy.

Immunotherapy has emerged as a powerful strategy for liquid tumors to overcome the limitations of conventional cancer therapies. The nanomedical delivery system offers the possibility of enhancing cancer immunotherapy and expanding it to solid tumors. Here, we discuss the applications of medical nanoparticles to improve the efficacy of immunotherapy. We first focus on nanomedical particles used in cancer immunotherapy to deliver peptide and mRNA vaccines to the lymph nodes; and the exosome-based therapeutic cancer vaccine. Next, we highlight the applications of nanomedicine in immune checkpoint therapy to prolong the therapeutic effects, enhance tumor-targeting ability, and overcome drug resistance. We also evaluate the roles of nanomedical particles in oncolytic viral treatment, enabling the systemic injection of viruses or oncolytic plasmids/oncotoxic proteins; and virus entry in a receptor-independency manner. Lastly, we focus on nanoparticles in chimeric antigen receptor (CAR) T cell therapy to engineer CAR T cells, enhancing T cell proliferation and infiltration. We envision the nanomedical particles enhancing the therapeutic effects of immunotherapy and revolutionizing cancer therapy in the foreseeable future.

Therapeutic Targeting Strategies for Early- to Late-Staged Alzheimer's Disease.

Alzheimer's disease (AD) is the most common cause of dementia, typically showing progressive neurodegeneration in aging brains. The key signatures of the AD progression are the deposition of amyloid-beta (Aß) peptides, the formation of tau tangles, and the induction of detrimental neuroinflammation leading to neuronal loss. However, conventional pharmacotherapeutic options are merely relying on the alleviation of symptoms that are limited to mild to moderate AD patients. Moreover, some of these medicines discontinued to use due to either the insignificant effectiveness in improving the cognitive impairment or the adverse side effects worsening essential bodily functions. One of the reasons for the failure is the lack of knowledge on the underlying mechanisms that can accurately explain the major causes of the AD progression correlating to the severity of AD. Therefore, there is an urgent need for the better understanding of AD pathogenesis and the development of the disease-modifying treatments, particularly for severe and late-onset AD, which have not been covered thoroughly. Here, we review the underlying mechanisms of AD progression, which have been employed for the currently established therapeutic strategies. We believe this will further spur the discovery of a novel disease-modifying treatment for mild to severe, as well as early- to late-onset, AD.