Diseases affecting the brain compromise the function of not just nerve cells, but also that of their support staff, the glial cells. In a new study, neuroscientists at Houston Methodist have designed neural organoids, also known as “miniature brains,” to contain both mature neurons and astrocytic glial cells in relative proportions similar to that in the human brain.
The research team, led by senior author Robert Krencik, Ph.D., assistant professor of the Department of Neurosurgery at the Center for Neuroregeneration in the Houston Methodist Research Institute, genetically engineered these organoids so that the activity of both cell types can be manipulated independently and on-demand, facilitating the emulation of brain activity during healthy and disease states. These enhanced properties open doors to multiple applications, including the rapid screening of drugs for neurological diseases.
The study on this new neural organoid technology, titled “Assessing Gq GPCR-induced human astrocyte reactivity using bioengineered neural organoids,” is published online in the Journal of Cell Biology. Krencik is the corresponding author, and Caroline Cvetkovic, Ph.D., is the first author.
“The ultimate goal is to recapitulate the functionality of the nervous system using organoids, and this study describes a next generation of that technology,” Krencik said. “Our new experimental procedure to produce the mature organoids is scalable, reproducible and much faster than previous techniques, taking weeks rather than months.”
Organoids are multicellular, 3D aggregates of cells created to simulate the structure and function of organs. These artificially generated mini organs enable scientists to investigate questions that would otherwise require probing an organ within the body. The organoids provide an edge over in vivo research with model organisms since the cellular aggregates for the organoids are derived from human stem cells, thereby retaining key characteristics of human tissue.
Traditionally, brain organoids are slowly developed from human pluripotent stem cells that differentiate into many of the cell types found in the human central nervous system. Some limitations of these organoids are that they contain a large number of cell types, including different subtypes of neurons, glial cells and non-neural cells in different states of maturity. Hence, studying the specific interactions between different cells poses a challenge.
“In the brain, synaptic connections between neurons develop and mature after astrocytes are born,” Krencik said. “Currently, using traditional methods, we have to wait several months for the astrocytes to spontaneously generate in the organoids.”
He added that even after the astrocytes appear, the organoids still take extensive time to show brain-like activity that is a hallmark of neural networks.
Addressing these shortcomings, Krencik and his team incorporated bioengineering techniques to rapidly generate neural organoids with defined populations of neurons and astrocytes produced independently from human pluripotent stem cells before combining them together. The various forms of genetic manipulation they used allowed them to activate the astrocytes experimentally with a chemical rather than wait for the brain’s natural neurotransmitters to kick into gear, which is a more complicated, lengthier process.
“By using two different technologies to target each cell type, we could selectively activate either neurons or astrocytes,” Krencik said.
The researchers then combined the mature astrocyte and neuron cultures to make spherical organoids and then recorded their electrical activity. When they activated the neurons using blue light, they found they could evoke spikes from these cells to simulate electrical activity of neural networks in the brain.
The effect of stimulating the engineered astrocyte receptor with a chemical depended on whether the activation was acute or chronic. When the researchers activated the astrocytes for a few hours, the cells increased expression of a variety of genes, particularly those important for neurons to form synapses. When chronically activated, however, the astrocytes transitioned to a detrimental state reminiscent of neuroinflammation. This overactivation seems to reduce the viability of the neurons, but could be protected in more optimal conditions, indicating the external environment likely has an important role. Krencik said this could have implications for brain stimulation in the clinic, for example, where one has to be careful not to stimulate too much.
“Our all-inducible organoid system is a useful tool to not just understand interactions between neurons and astrocytes in the healthy brain, but also how these connections are altered by disease,” Krencik said. “An exciting application for this technology is drug discovery. It can be scaled up very quickly to make thousands of organoids at once that can then be used as a high-throughput testing platform for therapeutic drugs for different neurological diseases, including Parkinson’s, Alzheimer’s and cancers of the nervous system.”
This research is supported by grants from the National Institute on Aging of the National Institutes of Health (R21AG064567), the Mission Connect program of The Institute for Rehabilitation and Research Foundation (019-114), The Michael J. Fox Foundation for Parkinson’s Research (17871) and the Cancer Prevention and Research Institute of Texas (RP200655).
Other collaborators working on this study with Krencik and Cvetkovic, who is now with the University of Illinois at Urbana-Champaign, were Philip J. Horner, Matthew K. Hogan, Morgan Anderson, Nupur Basu and Arya Shetty with the Department of Neurosurgery at the Center for Neuroregeneration in the Houston Methodist Research Institute; Rajan Patel, Debosmita Sardar and Benjamin Deneen with Baylor College of Medicine; Samira Aghlara-Fotovat and Omid Veiseh with Rice University; Srivathsan Ramesh with UT Health; and Michael E. Ward with NIH’s National Institute of Neurological Disorders and Stroke.
For more information: Assessing Gq GPCR-induced human astrocyte reactivity using bioengineered neural organoids. Journal of Cell Biology. (online Feb. 10, 2022) Caroline Cvetkovic, Rajan Patel, Arya Shetty, Matthew K. Hogan, Morgan Anderson, Nupur Basu, Samira Aghlara-Fotovat, Srivathsan Ramesh, Debosmita Sardar, Omid Veiseh, Michael E. Ward, Benjamin Deneen, Philip J. Horner and Robert Krencik. DOI: https://doi.org/10.1083/jcb.202107135