Tubular Human Brain Organoid - Modeling Microglial Cell-mediated Neuroinflammation

Neuroinflammation plays a key role in neurodegenerative diseases. Microglia act as resident myeloid cells in the brain and are responsible for regulating the inflammatory response in the brain. Although the importance of microglia in neuroinflammation is widely recognized, there is still an urgent need for robust human models to probe microglia-mediated neuroinflammation in depth.

Recently, studies have reported the use of tubular human brain organoids for modeling microglial cell-mediated neuroinflammation. Creative Biolabs centers around organoid studies, outlining the various mechanisms of activation of this tubular human brain organoid used for modeling neuroinflammation.

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Microglial Cell-mediated Neuroinflammation

Neuroinflammation is a common component of various neurodegenerative diseases like Alzheimer's and Parkinson's. It's frequently associated with microglia, a type of brain cell that plays a pivotal role in inflammatory processes. In response to brain injury or disease, microglia can induce inflammation, leading to neuronal damage.

• In normal state, microglia patrol the brain, participate in synaptic pruning, promote synaptic maturation and phagocytose cellular debris.
• In response to stimuli such as lipopolysaccharides, β-amyloid (Aβ) aggregates, complement factors, or opiates, microglia can shift from a homeostatic to an activated state, secrete pro- or anti-inflammatory cytokines, and influence neuronal function.

Tubular Brain Organoids

Brain organoids are three-dimensional, miniature structures derived from human pluripotent stem cells that mimic the complex, layered organization of the human brain. However, the traditional "spheroid" brain organoids also have some limitations. Due to their shape and size, nutrient and gas exchange is poor in these organoids, making the central region often necrotic, devoid of useful cells. To mitigate these issues, a cutting-edge method has been introduced – tubular brain organoids.

• Tubular organoids simulate the layering and cellular variety of the human brain more effectively due to their shape allowing better access to nutrients and oxygen, fostering healthier organoid development.
• Tubular organoids mimic the ventricular region of the brain, where cerebrospinal fluid circulates. This region is an essential area where microglial cells reside and become activated during inflammatory responses.

By replicating this region, researchers could explore how microglia mediates neuroinflammation unfolds. The use of tubular brain organoids allows scientists to experience a more substantial homology to the human brain and provides a higher degree of relevance in modeling neurodegenerative diseases.

Overview of Tubular Human Brain Organoids for Modeling Neuroinflammation

Researchers introduced microglial cells by flow and mimicked microglial cell responses in the brain microenvironment with tubular human brain organoids. The fusion of embryoid bodies (EBs) to form tubular organoids was guided through the use of 3D-printed hollow mesh scaffolds and porous tubular structures, and the growth and development of these organoids was maintained through a continuous passive flow perfusion system.

Fig. 1 How to utilize tubular human brain organoids to study microglia-mediated neuroinflammatory responses.¹

• It was found that a comparison of hypoxic core formation in conventional and tubular 3D cultures by hypoxia dye staining showed that no signs of hypoxia were detected in tubular cultures, suggesting that perfusion on both the inner and outer sides provided sufficient oxygen.
• It was found that tubular human forebrain organoids exhibited more evenly distributed, uniformly sized subventricular/subventricular zone (VZ/SVZ) regions and had more neo-dividing cells, suggesting that improved perfusion and sustained passive flow stimulation increased cell division and guided the formation of the VZ/SVZ regions more uniformly.
• It was found that tube-cultured organoids exhibited higher expression of the dorsal forebrain neural precursor cell markers PAX6 and SOX2 and the deep cortical neuronal marker TBR1 with less variability. In addition, tube-cultured organoids showed higher expression of PAX6, SOX2, and Tuj1, suggesting that the tube-culture method enhanced better neural differentiation.

These data suggest that the tubular organoid culture system improves the neurodevelopmental consistency and quality of organoids.

The researchers modeled microglial cell-mediated neuroinflammation in tubular human brain organoids, including the mechanism by which opiates trigger neuroinflammation through activation of NLRP3 inflammasomes and microglial cells. The distribution of microglial cells and inflammasomes within the engineered tubular organoids was examined by immunofluorescence staining, as well as the quantification of the number of inflammasomes within each microglial cell under different treatment conditions.

Fig. 2 Modeling microglia-mediated neuroinflammation in tubular human brain organoids.¹

• The results revealed that microglial cell interactions with neurons and astrocytes in tubular organoids resulted in higher levels of neuroinflammation and a significant increase in TNF-α.
• Treatment with the CB2 receptor agonist LY2828360 attenuated pro-inflammatory cytokine levels after opiate exposure, demonstrating that this model can be used to study opiate-induced neuroinflammation and its therapeutic effects.

In summary, this study successfully developed a tubular human brain organoid model, where a device constructed by 3D printing technology was able to generate standardized tubular organoids on porous scaffolds and mimic microglia-mediated neuroinflammation by introducing wobble flow. This innovative tubular organoid technology is expected to be widely used in research and clinical laboratory settings due to its simplicity, versatility, low cost, and compatibility with conventional laboratory settings, providing a new research tool for basic and translational applications in inflammatory diseases.

Reference

1. Ao, Zheng, et al. "Tubular human brain organoids to model microglia-mediated neuroinflammation." Lab on a Chip 21.14 (2021): 2751-2762.

For Research Use Only. Not For Clinical Use.