Since neurons were first cultured outside a living organism more than a century ago, a number of experimental techniques for their in vitro maintenance have been developed. These methods have been further adapted and refined to study specific neurobiological processes under controlled experimental conditions. Despite their limitations, the simplicity and visual accessibility of 2D cultures have enabled the study of the effects of trophic factors, adhesion molecules, and biophysical stimuli on neuron function and morphology. Nevertheless, the impact of fundamental properties of the surfaces to which neurons adhere when cultured in vitro has not been sufficiently considered. Here, we used an electroactive polymer with different electric poling states leading to different surface charges to evaluate the impact of the net electric surface charge on the behavior of primary neurons. Average negative and positive surface charges promote increased metabolic activity and enhance the maturation of primary neurons, demonstrating the relevance of considering the composition and electric charge of the culture surfaces. These findings further pave the way for the development of novel therapeutic strategies for the regeneration of neural tissues, particularly based on dynamic surface charge variation that can be induced in the electroactive films through mechanical solicitation.

https://pubs.acs.org/doi/pdf/10.1021/acsami.3c04055

Electroactive Materials Surface Charge Impacts Neuron Viability and Maturation in 2D Cultures

Mammalian orthoreovirus (reovirus) is a nonenveloped virus that establishes primary infection in the intestine and disseminates to sites of secondary infection, including the CNS. Reovirus entry involves multiple engagement factors, but how the virus disseminates systemically and targets neurons remains unclear. In this study, we identified murine neuropilin 1 (mNRP1) as a receptor for reovirus. mNRP1 binds reovirus with nanomolar affinity using a unique mechanism of virus-receptor interaction, which is coordinated by multiple interactions between distinct reovirus capsid subunits and multiple NRP1 extracellular domains. By exchanging essential capsid protein-encoding gene segments, we determined that the multivalent interaction is mediated by outer-capsid protein σ3 and capsid turret protein λ2. Using capsid mutants incapable of binding NRP1, we found that NRP1 contributes to reovirus dissemination and neurovirulence in mice. Collectively, our results demonstrate that NRP1 is an entry receptor for reovirus and uncover mechanisms by which NRPs promote viral entry and pathogenesis. 

NRP1 is a receptor for mammalian orthoreovirus engaged by distinct capsid subunits.

Three-dimensional (3D) neural cell cultures inherently lend themselves to high-throughput network electrophysiology studies addressing brain function in health and disease in a more realistic architectural complexity than two-dimensional neural networks. Epilepsy is the emblem of brain network disorders, as it reflects aberrant circuit reorganization and hyper-synchronization, resulting in sudden and uncontrolled electrical discharges (seizures). Modeling the features of epilepsy has so far relied on pharmacological, ionic or genetic manipulation of cells, ex-vivo brain tissue or intact animals, failing to recapitulate most of the epilepsies, which are triggered by unknown causes. Here, we report the spontaneous emergence of epileptiform patterns in spheroids of rodent primary hippocampal cells cultured in physiological condition, i.e., in the absence of a known initiating insult, detected by microelectrode array electrophysiology. Three distinct electrical phenotypes, i.e. interictal (between seizures), ictal (seizure) or mixed, arise from DIV10 to DIV35. In particular, the tonic-clonic ictal discharges become the most prominent at DIV28-35. These patterns exhibit electrographic and spectral features that strikingly resemble those observed in the hippocampus of in vitro and in vivo rodent epilepsy models, as well as of drug-resistant epileptic humans. Remarkably, not all spheroids exhibit full-blown ictal activity, bringing parallelism with the yet unanswered question of why a brain becomes epileptic and a seizure is generated. This evidence warrants caution against hippocampal cell-based therapies for regenerative purposes, as they may initiate epileptogenesis; at the same time, hippocampal spheroids lend themselves as reductionist model supporting high-throughput pre-clinical research on epileptic syndromes involving the hippocampus.

/pdf/developing-hippocampal-spheroids-model-ictogenesis-and-n31w4g0q.pdf

Developing hippocampal spheroids model ictogenesis and epileptogenesis

(1) Background: Central nervous system (CNS) development is characterized by dynamic changes in cell proliferation and differentiation. Key regulators of these transitions are the transcription factors such as SOX2 and SOX9. SOX2 is involved in the maintenance of progenitor cell state and neural stem cell multipotency, while SOX9, expressed in neurogenic niches, plays an important role in neuron/glia switch with predominant expression in astrocytes in the adult brain. (2) Methods: To validate SOX2 and SOX9 expression patterns in developing opossum (Monodelphis domestica) cortex, we used immunohistochemistry (IHC) and the isotropic fractionator method on fixed cortical tissue from comparable postnatal ages, as well as dissociated primary neuronal cultures. (3) Results: Neurons positive for both neuronal (TUJ1 or NeuN) and stem cell (SOX2) markers were identified, and their presence was confirmed with all methods and postnatal age groups (P4-6, P6-18, and P30) analyzed. SOX9 showed exclusive staining in non-neuronal cells, and it was coexpressed with SOX2. (4) Conclusions: The persistence of SOX2 expression in developing cortical neurons of M. domestica during the first postnatal month implies the functional role of SOX2 during neuronal differentiation and maturation, which was not previously reported in opossums.

SOX2 and SOX9 Expression in Developing Postnatal Opossum (Monodelphis domestica) Cortex

Abstract The sleep-wake cycle regulates interstitial fluid and cerebrospinal fluid (CSF) tau levels in both mouse and human by mechanisms that remain unestablished. Here, we reveal a novel pathway by which wakefulness increases extracellular tau levels in mouse and humans. In mice, higher body temperature (BT) associated with wakefulness and sleep deprivation increased CSF tau. In vitro , wakefulness temperatures upregulated tau secretion via a temperature-dependent increase in activity and expression of unconventional protein secretion pathway-1 components, namely caspase-3-mediated C-terminal cleavage of tau (TauC3), and membrane expression of PIP 2 and syndecan-3. In humans, the increase in both CSF and plasma tau levels observed post-wakefulness correlated with BT increase during wakefulness. Our findings suggest sleep-wake variation in BT may contribute to regulating extracellular tau levels, highlighting the importance of thermoregulation in pathways linking sleep disturbance to neurodegeneration, and the potential for thermal intervention to prevent or delay tau-mediated neurodegeneration.

Sleep-wake body temperature regulates tau secretion in mice and correlates with CSF and plasma tau in humans

Central nervous system (CNS) diseases have been a growing threat to the health of humanity, emphasizing the urgent need of exploring the pathogenesis and therapeutic approaches of various CNS diseases. Primary neurons are directly obtained from animals or humans, which have wide applications including disease modeling, mechanism exploration and drug development. However, traditional two-dimensional (2D) monoculture cannot resemble the native microenvironment of CNS. With the increasing understanding of the complexity of the CNS and the remarkable development of novel biomaterials, in vitro models have experienced great innovation from 2D monoculture toward three-dimensional (3D) multicellular culture. The scope of this review includes the progress of various in vitro models of primary neurons in recent years to provide a holistic view of the modalities and applications of primary neuron models and how they have been connected with the revolution of biofabrication techniques. Special attention has been paid to the interaction between primary neurons and biomaterials. First, a brief introduction on the history of CNS modeling and primary neuron culture was conducted. Next, detailed progress in novel in vitro models were discussed ranging from 2D culture, ex vivo model, spheroid, scaffold-based model, 3D bioprinting model, and microfluidic chip. Modalities, applications, advantages, and limitations of the aforementioned models were described separately. Finally, we explored future prospects, providing new insights into how basic science research methodologies have advanced our understanding of the CNS, and highlighted some future directions of primary neuron culture in the next few decades.

/pdf/recent-progresses-in-novel-in-vitro-models-of-primary-3d5sxdbp.pdf

Recent progresses in novel in vitro models of primary neurons: A biomaterial perspective

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Recent progresses in novel in vitro models of primary neurons: A biomaterial perspective