Researchers develop in vitro model of brain for research

Harvard University researchers have developed a multiregional brain-on-a-chip that models the connectivity between three distinct regions of the brain. The in vitro model was used to extensively characterize the differences between neurons from different regions of the brain and to mimic the system’s connectivity.  The research was published in the Journal of Neurophysiology.

Image of the in vitro model showing three distinct regions of the brain connected by axons.
Credit: Disease Biophysics Group/Harvard University

“The brain is so much more than individual neurons,” said Ben Maoz, co-first author of the paper and postdoctoral fellow in the Disease Biophysics Group in the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS). “It’s about the different types of cells and the connectivity between different regions of the brain. When modeling the brain, you need to be able to recapitulate that connectivity because there are many different diseases that attack those connections.”

Researchers from the Disease Biophysics Group at SEAS and the Wyss Institute modeled three regions of the brain most affected by schizophrenia the amygdala, hippocampus and prefrontal cortex. They began by characterizing the cell composition, protein expression, metabolism, and electrical activity of neurons from each region in vitro.

“It’s no surprise that neurons in distinct regions of the brain are different but it is surprising just how different they are,” said Stephanie Dauth, co-first author of the paper and former postdoctoral fellow in the Disease Biophysics Group. “We found that the cell-type ratio, the metabolism, the protein expression and the electrical activity all differ between regions in vitro. This shows that it does make a difference which brain region’s neurons you’re working with.”

Next, the team looked at how these neurons change when they’re communicating with one another. To do that, they cultured cells from each region independently and then let the cells establish connections via guided pathways embedded in the chip.

The researchers then measured cell composition and electrical activity again and found that the cells dramatically changed when they were in contact with neurons from different regions.

“When the cells are communicating with other regions, the cellular composition of the culture changes, the electrophysiology changes, all these inherent properties of the neurons change,” said Maoz. “This shows how important it is to implement different brain regions into in vitro models, especially when studying how neurological diseases impact connected regions of the brain.”

To demonstrate the chip’s efficacy in modeling disease, the team doped different regions of the brain with the drug Phencyclidine hydrochloride commonly known as PCP which simulates schizophrenia. The brain-on-a-chip allowed the researchers for the first time to look at both the drug’s impact on the individual regions as well as its downstream effect on the interconnected regions in vitro.

The brain-on-a-chip could be useful for studying any number of neurological and psychiatric diseases, including drug addiction, post-traumatic stress disorder, and traumatic brain injury.

“To date, the Connectome project has not recognized all of the networks in the brain,” said Parker. “In our studies, we are showing that the extracellular matrix network is an important part of distinguishing different brain regions and that, subsequently, physiological and pathophysiological processes in these brain regions are unique. This advance will not only enable the development of therapeutics, but fundamental insights as to how we think, feel, and survive.”

Citation: Dauth, Stephanie, Ben M. Maoz, Sean P. Sheehy, Matthew A. Hemphill, Tara Murty, Mary Kate Macedonia, Angie M. Greer, Bogdan Budnik, and Kevin Kit Parker. “Neurons derived from different brain regions are inherently different in vitro: A novel multiregional brain-on-a-chip.” Journal of Neurophysiology (2016): jn-00575.
DOI: 10.1152/jn.00575.2016
Research funding: Defense Advanced Research Projects Agency.
Adapted from press release by Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS).

New chromosomal mapping technique reveals additional genes behind Schizophrenia

UCLA scientists have made a major advance in understanding the biology of schizophrenia. Using a recently developed technology for analyzing DNA, the scientists found dozens of genes and two major biological pathways that are likely involved in the development of the disorder but had not been uncovered in previous genetic studies of schizophrenia. The work provides important new information about how schizophrenia originates and points the way to more detailed studies — and possibly better treatments in the future.The study, which is published online in the journal Nature.

Schizophrenia has long been known to be highly genetic; it often runs in families. A large genome-wide association study of people with schizophrenia, published in 2014, linked the disorder to small DNA variations at more than 100 distinct locations on the human genome, which is the complete set of DNA for humans. However, most of those locations lie outside of actual genes, so their roles in schizophrenia have been unclear. Genome-wide study analyses of other major diseases have come up with similarly puzzling results.

In some cases, the non-gene locations identified in these studies have turned out to be what are known as “regulatory regions,” which serve to enhance or repress the activity of genes lying near them on the genome. But many of these disease-linked locations have no obvious gene target nearby on the genome.

One possibility is that these mysterious disease-linked locations are also regulatory regions that target genes lying relatively far away on the genome. They could do this if they are brought physically close to those “distant” genes by the complex twisting and looping that DNA undergoes when packaged into a chromosome, just as two opposite ends of a rope can end up close together when the rope is coiled.

To investigate that possibility, Geschwind and his team used a relatively new, high-resolution version of a technology called “chromosome conformation capture,” which chemically marks and then maps the locations where loops of chromosomal DNA come into contact.

Because each cell type in the body can have subtly different 3-D chromosome structures, the researchers applied the technique to immature human brain cells from the cortex — the large region across the top of the brain that handles higher cognitive tasks. Schizophrenia is believed to be a disorder of abnormal cortical development.

The mapping revealed that most of the more than 100 schizophrenia-linked sites from the 2014 study contact known genes during brain development. Many of these are genes that already have been linked to schizophrenia in previous studies. Others had been suspected of involvement, for example because their level of activity in schizophrenics is known to be abnormal in the cortex.

The genes newly linked to schizophrenia in the study include several for brain cell receptors that are activated by the neurotransmitter acetylcholine, implying that variations in the functions of these receptors can help bring about schizophrenia.

“There’s a lot of clinical and pharmacologic data suggesting that changes in acetylcholine signaling in the brain can worsen schizophrenia symptoms, but until now there’s been no genetic evidence that it can help cause the disorder,” Geschwind said.The analysis also pointed for the first time to several genes that are involved in the early-life burst of brain cell production that gives rise to the cerebral cortex of humans.

In all, the researchers identified several hundred genes that may be abnormally regulated in schizophrenia but had not been linked to the disorder before. In further experiments and analyses of two dozen of those genes, they found additional evidence of abnormal regulation in schizophrenia.
As further studies clarify the roles of these genes in schizophrenia, scientists will get a more complete picture of how the disorder develops and persists, and should then be able to develop more effective treatments.

In principle, the 3-D chromosome mapping technology can be used to make sense of gene association data for any disease involving genetic risk. This same approach also can be used to discover relationships between genes and their regulatory regions in ordinary biological processes.
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Publication: Chromosome conformation elucidates regulatory relationships in developing human brain.
DOI: http://dx.doi.org/10.1038/nature19847
Journal: NatureNews
Research funding: National Institute of Health,  the National Science Foundation, Glenn/AFAR Postdoctoral Fellowship Program and the National Research Foundation of Korea.

Adapted from press release by UCLA