Advanced in vitro models: Microglia in action

GRAMD1B is a regulator of lipid homeostasis, autophagic flux and phosphorylated tau

Lipid dyshomeostasis and tau pathology are present in frontotemporal lobar degeneration (FTLD) and Alzheimer's disease (AD). However, the relationship between lipid dyshomeostasis and tau pathology remains unclear. We report that GRAM Domain Containing 1B (GRAMD1B), a nonvesicular cholesterol transporter, is increased in excitatory neurons of human neural organoids (HNOs) with the MAPT R406W mutation. Human FTLD, AD cases, and PS19 tau mice also have increased GRAMD1B expression. We show that overexpression of GRAMD1B increases levels of free cholesterol, lipid droplets, and impairs autophagy flux. Modulating GRAMD1B in iPSC-derived neurons also alters key autophagy-related components such as PI3K, phospho-AKT, and p62, as well as phosphorylated tau, and CDK5R1. Blocking GRAMD1B function decreases free cholesterol and lipid droplets. Knocking down GRAMD1B additionally reduces phosphorylated tau, and CDK5R1 expression. Our findings elucidate the role of GRAMD1B in the nervous system and highlight its relevance to FTLD and AD.

Emerging Insights into Brain Inflammation: Stem-Cell-Based Approaches for Regenerative Medicine

Neuroinflammation is a complex immune response triggered by brain injury or pathological stimuli, and is highly exacerbated in neurodegenerative diseases. It plays a dual role in the central nervous system, promoting repair in acute stages while aggravating disease progression by contributing to neuronal loss, synaptic dysfunction, and glial dysregulation in chronic phases. Inflammatory responses are mainly orchestrated by microglia and infiltrated monocytes, which, when dysregulated, not only harm existing neurons, but also impair the survival and differentiation of neural stem and progenitor cells in the affected brain regions. Modulating neuroinflammation is crucial for harnessing its protective functions while minimizing its detrimental effects. Current therapeutic strategies focus on fine-tuning inflammatory responses through pharmacological agents, bioactive molecules, and stem cell-based therapies. These approaches aim to restore immune homeostasis, support neuroprotection, and promote regeneration in various neurological disorders. However, animal models sometimes fail to reproduce human-specific inflammatory responses in the brain. In this context, stem-cell-derived models provide a powerful tool to study neuroinflammatory mechanisms in a patient-specific and physiologically relevant context. These models facilitate high-throughput screening, personalized medicine, and the development of targeted therapies while addressing the limitations of traditional animal models, paving the way for more targeted and effective treatments.

A Comprehensive Review on Utilizing Human Brain Organoids to Study Neuroinflammation in Neurological Disorders

Most current information about neurological disorders and diseases is derived from direct patient and animal studies. However, patient studies in many cases do not allow replication of the early stages of the disease and, therefore, offer limited opportunities to understand disease progression. On the other hand, although the use of animal models allows us to study the mechanisms of the disease, they present significant limitations in developing drugs for humans. Recently, 3D-cultured in vitro models derived from human pluripotent stem cells have surfaced as a promising system. They offer the potential to connect findings from patient studies with those from animal models. In this comprehensive review, we discuss their application in modeling neurodevelopmental conditions such as Down Syndrome or Autism, neurodegenerative diseases such as Alzheimer's or Parkinson's, and viral diseases like Zika virus or HIV. Furthermore, we will discuss the different models used to study prenatal exposure to drugs of abuse, as well as the limitations and challenges that must be met to transform the landscape of research on human brain disorders.

Microglia signaling in health and disease - Implications in sex-specific brain development and plasticity

Microglia, the intrinsic neuroimmune cells residing in the central nervous system (CNS), exert a pivotal influence on brain development, homeostasis, and functionality, encompassing critical roles during both aging and pathological states. Recent advancements in comprehending brain plasticity and functions have spotlighted conspicuous variances between male and female brains, notably in neurogenesis, neuronal myelination, axon fasciculation, and synaptogenesis. Nevertheless, the precise impact of microglia on sex-specific brain cell plasticity, sculpting diverse neural network architectures and circuits, remains largely unexplored. This article seeks to unravel the present understanding of microglial involvement in brain development, plasticity, and function, with a specific emphasis on microglial signaling in brain sex polymorphism. Commencing with an overview of microglia in the CNS and their associated signaling cascades, we subsequently probe recent revelations regarding molecular signaling by microglia in sex-dependent brain developmental plasticity, functions, and diseases. Notably, C-X3-C motif chemokine receptor 1 (CX3CR1), triggering receptors expressed on myeloid cells 2 (TREM2), calcium (Ca2+), and apolipoprotein E (APOE) emerge as molecular candidates significantly contributing to sex-dependent brain development and plasticity. In conclusion, we address burgeoning inquiries surrounding microglia's pivotal role in the functional diversity of developing and aging brains, contemplating their potential implications for gender-tailored therapeutic strategies in neurodegenerative diseases.

An Overview of Multiple Sclerosis In Vitro Models

Multiple sclerosis (MS) still poses a challenge in terms of complex etiology, not fully effective methods of treatment, and lack of healing agents. This neurodegenerative condition considerably affects the comfort of life by causing difficulties with movement and worsening cognition. Neuron, astrocyte, microglia, and oligodendrocyte activity is engaged in multiple pathogenic processes associated with MS. These cells are also utilized in creating in vitro cellular models for investigations focusing on MS. In this article, we present and discuss a summary of different in vitro models useful for MS research and describe their development. We discuss cellular models derived from animals or humans and present in the form of primary cell lines or immortalized cell lines. In addition, we characterize cell cultures developed from induced pluripotent stem cells (iPSCs). Culture conditions (2D and 3D cultures) are also discussed.

Long-term exposure to cadmium disrupts neurodevelopment in mature cerebral organoids

Cadmium (Cd) is a pervasive environmental pollutant. Increasing evidence suggests that Cd exposure during pregnancy can induce adverse neurodevelopmental outcomes. However, due to the limitations of neural cell and animal models, it is challenging to study the developmental neurotoxicity and underlying toxicity mechanism of long-term exposure to environmental pollutants during human brain development. In this study, chronic Cd exposure was performed in human mature cerebral organoids for 49 or 77 days. Our study found that prolonged exposure to Cd resulted in the inhibition of cerebral organoid growth and the disruption of neural differentiation and cortical layer organization. These potential consequences of chronic Cd exposure may include impaired GFAP expression, a reduction in SOX2+ neuronal progenitor cells, an increase in TUJ1+ immature neurons, as well as an initial increase and a subsequent decrease in both TBR2+ intermediate progenitors and CTIP2+ deep layer cortical neurons. Transcriptomic analyses revealed that long-term exposure to Cd disrupted zinc and copper ion homeostasis through excessive synthesis of metallothionein and disturbed synaptogenesis, as evidenced by inhibited postsynaptic protein. Our study employed mature cerebral organoids to evaluate the developmental neurotoxicity induced by long-term Cd exposure.

Microglia Mediate Contact-Independent Neuronal Network Remodeling via Secreted Neuraminidase-3 Associated with Extracellular Vesicles

Neurons communicate with each other through electrochemical transmission at synapses. Microglia, the resident immune cells of the central nervous system, modulate this communication through a variety of contact-dependent and -independent means. Microglial secretion of active sialidase enzymes upon exposure to inflammatory stimuli is one unexplored mechanism of modulation. Recent work from our lab showed that treatment of neurons with bacterial sialidases disrupts neuronal network connectivity. Here, we find that activated microglia secrete neuraminidase-3 (Neu3) associated with fusogenic extracellular vesicles. Furthermore, we show that Neu3 mediates contact-independent disruption of neuronal network synchronicity through neuronal glycocalyx remodeling. We observe that NEU3 is transcriptionally upregulated upon exposure to inflammatory stimuli and that a genetic knockout of NEU3 abrogates the sialidase activity of inflammatory microglial secretions. Moreover, we demonstrate that Neu3 is associated with a subpopulation of extracellular vesicles, possibly exosomes, that are secreted by microglia upon inflammatory insult. Finally, we demonstrate that Neu3 is necessary and sufficient to both desialylate neurons and decrease neuronal network connectivity. These results implicate Neu3 in remodeling of the glycocalyx leading to aberrant network-level activity of neurons, with implications in neuroinflammatory diseases such as Parkinson's disease and Alzheimer's disease.

Asteroid impact: the potential of astrocytes to modulate human neural networks within organoids

Astrocytes are a vital cellular component of the central nervous system that impact neuronal function in both healthy and pathological states. This includes intercellular signals to neurons and non-neuronal cells during development, maturation, and aging that can modulate neural network formation, plasticity, and maintenance. Recently, human pluripotent stem cell-derived neural aggregate cultures, known as neurospheres or organoids, have emerged as improved experimental platforms for basic and pre-clinical neuroscience compared to traditional approaches. Here, we summarize the potential capability of using organoids to further understand the mechanistic role of astrocytes upon neural networks, including the production of extracellular matrix components and reactive signaling cues. Additionally, we discuss the application of organoid models to investigate the astrocyte-dependent aspects of neuropathological diseases and to test astrocyte-inspired technologies. We examine the shortcomings of organoid-based experimental platforms and plausible improvements made possible by cutting-edge neuroengineering technologies. These advancements are expected to enable the development of improved diagnostic strategies and high-throughput translational applications regarding neuroregeneration.

Leveraging iPSC technology to assess neuro-immune interactions in neurological and psychiatric disorders

Communication between the immune and the nervous system is essential for human brain development and homeostasis. Disruption of this intricately regulated crosstalk can lead to neurodevelopmental, psychiatric, or neurodegenerative disorders. While animal models have been essential in characterizing the role of neuroimmunity in development and disease, they come with inherent limitations due to species specific differences, particularly with regard to microglia, the major subset of brain resident immune cells. The advent of induced pluripotent stem cell (iPSC) technology now allows the development of clinically relevant models of the central nervous system that adequately reflect human genetic architecture. This article will review recent publications that have leveraged iPSC technology to assess neuro-immune interactions. First, we will discuss the role of environmental stressors such as neurotropic viruses or pro-inflammatory cytokines on neuronal and glial function. Next, we will review how iPSC models can be used to study genetic risk factors in neurological and psychiatric disorders. Lastly, we will evaluate current challenges and future potential for iPSC models in the field of neuroimmunity.

Microglia mediate contact-independent neuronal pruning via secreted Neuraminidase-3 associated with extracellular vesicles

Neurons communicate with each other through electrochemical transmission at synapses. Microglia, the resident immune cells of the central nervous system, can prune these synapses through a variety of contact-dependent and -independent means. Microglial secretion of active sialidase enzymes upon exposure to inflammatory stimuli is one unexplored mechanism of pruning. Recent work from our lab showed that treatment of neurons with bacterial sialidases disrupts neuronal network connectivity. Here, we find that activated microglia secrete Neuraminidase-3 (Neu3) associated with fusogenic extracellular vesicles. Furthermore, we show Neu3 mediates contact-independent pruning of neurons and subsequent disruption of neuronal networks through neuronal glycocalyx remodeling. We observe that NEU3 is transcriptionally upregulated upon exposure to inflammatory stimuli, and that a genetic knock-out of NEU3 abrogates the sialidase activity of inflammatory microglial secretions. Moreover, we demonstrate that Neu3 is associated with a subpopulation of extracellular vesicles, possibly exosomes, that are secreted by microglia upon inflammatory insult. Finally, we demonstrate that Neu3 is both necessary and sufficient to both desialylate neurons and decrease neuronal network connectivity. These results implicate Neu3 in remodeling of the glycocalyx leading to aberrant network-level activity of neurons, with implications in neuroinflammatory diseases such as Parkinson's disease and Alzheimer's disease.