Tiny Brain Organoids Show Promise in Alzheimer’s Research

These organoids express genes much like natural brains.

by Arkadi Mazin
October 21, 2025

Scientists have developed a new tool to study neurological diseases, incorporating all six major brain cell types derived from patient-specific induced pluripotent stem cells (iPSCs) [1].

What Are Brain Organoids?

• Brain organoids are made from reprogrammed cells derived from patients.
• The environment that these cells grow in is similar to natural brains, including the blood-brain barrier.
• These organoids can be used to study diseases such as Alzheimer’s and may be used as tissue replacements in the future.

Organoids, tiny lab-grown patches of tissue, are a promising tool for accelerating medical research [2]. They are a step above cultured cells, being able to mimic the workings of a specific organ, such as the liver. Organoids can often replace animal models as a cheaper and more humane alternative.

Making a Piece of Brain

Creating brain organoids, however, has been a challenge. In a new study published in the Proceedings of the National Academy of Science, MIT scientists have reported a breakthrough: they have created brain organoids called miBrains that contain all the essential brain cell types and even the blood-brain barrier.

The scientists reprogrammed patient-derived iPSCs into the required cell types, including neurons, astrocytes, oligodendrocytes, microvascular endothelial cells, pericytes, and microglia. They validated the transformation by measuring gene expression and cellular function, with iPSC-derived neurons demonstrating robust expression of neuron-associated proteins and forming healthy networks.

Research Validation

The cells were mixed with a hydrogel environment called Neuromatrix, which closely matches the natural extracellular matrix (ECM). The researchers experimented with several matrix variants to find one suitable for cell growth.

Vascularizing organoids presents a particular challenge. The brain relies on the blood-brain barrier, formed by endothelial cells that permit only selective molecule entry. The team observed the self-assembly of microvessels and the formation of tight junctions—both crucial features of the blood-brain barrier.

Interestingly, miBrain cells exhibited more “lifelike” properties compared to their monocultured counterparts. For instance, astrocytes in miBrains displayed enhanced identity and functional gene expression.

A Research Platform and More

The researchers conducted a significant experiment to demonstrate their model’s research value. The APOE4 allele of the gene APOE is the strongest common genetic risk factor for late-onset Alzheimer’s disease [3]. Astrocytes produce a lot of the APOE protein, but the extent to which astrocytic APOE4 drives pathology is unclear.

Using miBrain, the researchers easily swapped genotypes cell-by-cell to investigate whether APOE4 astrocytes impact neuronal pathways adversely. They discovered that miBrains where all cell lineages carried APOE4 exhibited increased amyloid aggregation and tau phosphorylation compared to controls with APOE3.

Research Findings

Further experimentation revealed that removing microglia from the system significantly reduced neuronal tau phosphorylation levels, indicating the essential role of astrocyte-to-microglia signaling in pathology development.

Upon constructing APOE3 miBrains, where only the astrocytes were substituted with APOE4 astrocytes via CRISPR, the same tau phosphorylation increase was observed, confirming that astrocytes can independently drive neuronal changes.

Future Possibilities

Li-Huei Tsai, director of The Picower Institute of Learning and Memory, emphasizes that “the miBrain is the only in vitro system that contains all six major cell types present in the human brain.” The potential applications range from discovering interaction mechanisms that trigger pathology to creating individualized miBrains for personalized medicine.

Alice Stanton, assistant professor at Harvard Medical School, noted the modularity of the miBrain, offering precise control over cellular inputs and potential applications in disease modeling and drug testing.

Long-Term Vision

Beyond their immediate use in analyzing neurodegenerative diseases, miBrain technologies may later contribute to gradual brain tissue replacement in longevity contexts.

Literature

• [1] Stanton, A. E., et al. (2025). Engineered 3D immuno-glial-neurovascular human miBrain model. Proceedings of the National Academy of Sciences, 122(42), e2511596122.
• [2] Yao, Q., et al. (2024). Organoids: development and applications in disease models, drug discovery, precision medicine, and regenerative medicine. MedComm, 5(10), e735.
• [3] Belloy, M. E., et al. (2023). APOE genotype and Alzheimer disease risk across age, sex, and population ancestry. JAMA Neurology, 80(12), 1284-1294.

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