Suspect Gene Corrupts Neural Connections

'Diseases of synapses' demonstrated in a dish

Monday, 18 August 2014

Researchers have long suspected that major mental disorders are genetically-rooted diseases of synapses – the connections between neurons. Now, investigators supported in part by the National Institutes of Health have demonstrated in patients' cells how a rare mutation in a suspect gene disrupts the turning on and off of dozens of other genes underlying these connections.

Synapses – sites of intercellular communications

– are revealed in a mature iPSC cortex neuron

derived from a participant in the study. Immune-

based staining shows synapse markers (red,

green) and the cell's nucleus (blue). Credit:

Hongjun Song, Ph.D., Johns Hopkins University.

"Our results illustrate how genetic risk, abnormal brain development and synapse dysfunction can corrupt brain circuitry at the cellular level in complex psychiatric disorders," explained Hongjun Song, Ph.D., of Johns Hopkins University, Baltimore, a grantee of the NIH's National Institute of Mental Health (NIMH), a founder of the study.

Song and colleagues, from universities in the United States, China, and Japan, report on their discovery in the journal Nature, August 17, 2014.

"The approach used in this study serves as a model for linking genetic clues to brain development," said NIMH director Thomas R. Insel, M.D..

Most major mental disorders, such as schizophrenia, are thought to be caused by a complex interplay of multiple genes and environmental factors. However, studying rare cases of a single disease-linked gene that runs in a family can provide shortcuts to discovery. Decades ago, researchers traced a high prevalence of schizophrenia and other major mental disorders – which often overlap genetically – in a Scottish clan to mutations in the gene DISC1 (Disrupted In Schizophrenia-1). But until now, most of what's known about cellular effects of such DISC1 mutations has come from studies in the rodent brain.

To learn how human neurons are affected, Song's team used a disease-in-a-dish technology called induced pluripotent stem cells (iPSCs). A patient's skin cells are first induced to revert to stem cells. Stem cells play a critical role in development of the organism by transforming into the entire range of specialized cells which make up an adult. In this experiment, these particular "reverted" stem cells were coaxed to differentiate into neurons, which could be studied developing and interacting in a petri dish. This makes it possible to pinpoint, for example, how a particular patient's mutation might impair synapses. Song and colleagues studied iPSCs from four members of an American family affected by DISC1-linked schizophrenia and genetically related mental disorders.

Strikingly, iPSC-induced neurons, of a type found in front brain areas implicated in psychosis, expressed 80 percent less of the protein made by the DISC1 gene in family members with the mutation, compared to members without the mutation. These mutant neurons showed deficient cellular machinery for communicating with other neurons at synapses.

The researchers traced these deficits to errant expression of genes known to be involved in synaptic transmission, brain development, and key extensions of neurons where synapses are located. Among these abnormally expressed genes were 89 previously linked to schizophrenia, bipolar disorder, depression, and other major mental disorders. This was surprising, as DISC1's role as a hub that regulates expression of many genes implicated in mental disorders had not previously been appreciated, say the researchers.

The clincher came when researchers experimentally produced the synapse deficits by genetically engineering the DISC1 mutation into otherwise normal iPSC neurons – and, conversely, corrected the synapse deficits in DISC1 mutant iPSC neurons by genetically engineering a fully functional DISC1 gene into them. This established that the DISC1 mutation, was, indeed the cause of the deficits.

The results suggest a common disease mechanism in major mental illnesses that integrates genetic risk, aberrant neurodevelopment, and synapse dysfunction. The overall approach may hold promise for testing potential treatments to correct synaptic deficits, say the researchers.

Source: NIH/National Institute of Mental Health 

Contact: Jules Asher

Reference:

Synaptic dysregulation in a human iPS cell model of major mental disorders 

Wen Z, Nguyen HN, Guo Z, Lalli MA, Wang X, Su Y, Kim N-S, Yoon K-J, Shin J, Zhang C, Makri G, Nauen D, Yu H, Guzman E, Chiang C-H, Yoritomo N, Kaibuchi K, Zou J, Christian KM, Cheng L, Ross CA, Margolis RL, Chen G, Kosik KS, Song H, Ming G

Nature, Aug. 17, 2014, doi:10.1038/nature13716

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Stem Cells Reveal How Schizophrenia-linked Genetic Variation Affects Neurons

Stem Cells Reveal How Schizophrenia-linked Genetic Variation Affects Neurons

Monday, 18 August 2014

A genetic variation linked to schizophrenia, bipolar disorder and severe depression wreaks havoc on connections among neurons in the developing brain, a team of researchers reports. The study, led by Guo-li Ming, M.D., Ph.D., and Hongjun Song, Ph.D., of the Johns Hopkins University School of Medicine and described online Aug. 17 in the journal Nature, used stem cells generated from people with and without mental illness to observe the effects of a rare and pernicious genetic variation on young brain cells. The results add to evidence that several major mental illnesses have common roots in faulty "wiring" during early brain development.

In this image, cell nuclei are shown in blue and

synapses in red and green. Credit: Zhexing Wen-

Johns Hopkins Medicine.

"This was the next best thing to going back in time to see what happened while a person was in the womb to later cause mental illness," says Ming.

"We found the most convincing evidence yet that the answer lies in the synapses that connect brain cells to one another."

Previous evidence for the relationship came from autopsies and from studies suggesting that some genetic variants that affect synapses also increase the chance of mental illness. But those studies could not show a direct cause-and-effect relationship, Ming says.

One difficulty in studying the genetics of common mental illnesses is that they are generally caused by environmental factors in combination with multiple gene variants, any one of which usually could not by itself cause disease. A rare exception is the gene known as disrupted in schizophrenia 1 (DISC1), in which some mutations have a strong effect. Two families have been found in which many members with the DISC1 mutations have mental illness.

Video of human neurons firing. Credit: Zhexing

Wen-Johns Hopkins Medicine.

To find out how a DISC1 variation with a few deleted DNA "letters" affects the developing brain, the research team collected skin cells from a mother and daughter in one of these families who have neither the variation nor mental illness, as well as the father, who has the variation and severe depression, and another daughter, who carries the variation and has schizophrenia. For comparison, they also collected samples from an unrelated healthy person. Postdoctoral fellow Zhexing Wen, Ph.D., coaxed the skin cells to form five lines of stem cells and to mature into very pure populations of synapse-forming neurons.

After growing the neurons in a dish for six weeks, collaborators at Pennsylvania State University measured their electrical activity and found that neurons with the DISC1 variation had about half the number of synapses as those without the variation. To make sure that the differences were really due to the DISC1 variation and not to other genetic differences, graduate student Ha Nam Nguyen spent two years making targeted genetic changes to three of the stem cell lines.

In one of the cell lines with the variation, he swapped out the DISC1 gene for a healthy version. He also inserted the disease-causing variation into one healthy cell line from a family member, as well as the cell line from the unrelated control. Sure enough, the researchers report, the cells without the variation now grew the normal amount of synapses, while those with the inserted mutation had half as many.

"We had our definitive answer to whether this DISC1 variation is responsible for the reduced synapse growth," Ming says.

To find out how DISC1 acts on synapses, the researchers also compared the activity levels of genes in the healthy neurons to those with the variation. To their surprise, the activities of more than 100 genes were different.

"This is the first indication that DISC1 regulates the activity of a large number of genes, many of which are related to synapses," Ming says.

The research team is now looking more closely at other genes that are linked to mental disorders. By better understanding the roots of mental illness, they hope to eventually develop better treatments for it, Ming says.

Source: Johns Hopkins Medicine 

Contact: Shawna Williams

Reference:

Synaptic dysregulation in a human iPS cell model of major mental disorders 

Wen Z, Nguyen HN, Guo Z, Lalli MA, Wang X, Su Y, Kim N-S, Yoon K-J, Shin J, Zhang C, Makri G, Nauen D, Yu H, Guzman E, Chiang C-H, Yoritomo N, Kaibuchi K, Zou J, Christian KM, Cheng L, Ross CA, Margolis RL, Chen G, Kosik KS, Song H, Ming G

Nature, Aug. 17, 2014, doi:10.1038/nature13716

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For more on stem cells and cloning, go to CellNEWS at

http://cellnews-blog.blogspot.com/

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First Stem Cell Study of Bipolar Disorder Yields Promising Results

Stem cell model shows nerve cells develop, behave and respond to lithium differently – opening doors to potential new treatments

Tuesday, 25 March 2014

What makes a person bipolar, prone to manic highs and deep, depressed lows? Why does bipolar disorder run so strongly in families, even though no single gene is to blame? And why is it so hard to find new treatments for a condition that affects 200 million people worldwide?

New stem cell research published by scientists from the University of Michigan Medical School, and fuelled by the Heinz C. Prechter Bipolar Research Fund, may help scientists find answers to these questions.

These cells, grown from skin cells taken from

people with bipolar disorder, arose from stem

cells and were coaxed to become neural

progenitor cells -- the kind that can become any

sort of nervous system cell. The research showed

differences in cell behaviour compared with cells

grown from people without bipolar disorder.

Credit: University of Michigan Pluripotent Stem
Cell Research Lab. 

The team used skin from people with bipolar disorder to derive the first-ever stem cell lines specific to the condition. In a new paper in Translational Psychiatry, they report how they transformed the stem cells into neurons, similar to those found in the brain – and compared them to cells derived from people without bipolar disorder.

The comparison revealed very specific differences in how these neurons behave and communicate with each other, and identified striking differences in how the neurons respond to lithium, the most common treatment for bipolar disorder.

It's the first time scientists have directly measured differences in brain cell formation and function between people with bipolar disorder and those without.

The researchers are from the Medical School's Department of Cell & Developmental Biology and Department of Psychiatry, and U-M's Depression Center.

Stem cells as a window on bipolar disorder

The team used a type of stem cell called induced pluripotent stem cells, or iPSCs. By taking small samples of skin cells and exposing them to carefully controlled conditions, the team coaxed them to turn into stem cells that held the potential to become any type of cell. With further coaxing, the cells became neurons.

"This gives us a model that we can use to examine how cells behave as they develop into neurons. Already, we see that cells from people with bipolar disorder are different in how often they express certain genes, how they differentiate into neurons, how they communicate, and how they respond to lithium," says Sue O'Shea, Ph.D., the experienced U-M stem cell specialist who co-led the work.

"We're very excited about these findings. But we're only just beginning to understand what we can do with these cells to help answer the many unanswered questions in bipolar disorder's origins and treatment," says Melvin McInnis, M.D., principal investigator of the Prechter Bipolar Research Fund and its programs.

"For instance, we can now envision being able to test new drug candidates in these cells, to screen possible medications proactively instead of having to discover them fortuitously."

The research was supported by donations from the Heinz C. Prechter Bipolar Research Fund, the Steven M. Schwartzberg Memorial Fund, and the Joshua Judson Stern Foundation. The A. Alfred Taubman Medical Research Institute at the U-M Medical School also supported the work, which was reviewed and approved by the U-M Human Pluripotent Stem Cell Research Oversight committee and Institutional Review Board.

O'Shea, a professor in the Department of Cell & Developmental Biology and director of the U-M Pluripotent Stem Cell Research Lab, and McInnis, the Upjohn Woodworth Professor of Bipolar Disorder and Depression in the Department of Psychiatry, are co-senior authors of the new paper.

McInnis, who sees first-hand the impact that bipolar disorder has on patients and the frustration they and their families feel about the lack of treatment options, says the new research could take treatment of bipolar disorder into the era of personalized medicine.

Not only could stem cell research help find new treatments, it may also lead to a way to target treatment to each patient based on their specific profile – and avoid the trial-and-error approach to treatment that leaves many patients with uncontrolled symptoms.

More about the findings:

The skin samples were used to derive the 42 iPSC lines. When the team measured gene expression first in the stem cells, and then re-evaluated the cells once they had become neurons, very specific differences emerged between the cells derived from bipolar disorder patients and those without the condition.

These colourful neurons, seen forming connections

to one another across synapses, were grown from

induced pluripotent stem cells -- ones that were

derived from skin cells taken from people with

bipolar disorder. New research shows they act, and

react to the bipolar drug lithium, differently from

neurons derived from people without bipolar

disorder. Credit: University of Michigan Pluripotent 
Stem Cell Research Lab.

Specifically, the bipolar neurons expressed more genes for membrane receptors and ion channels than non-bipolar cells, particularly those receptors and channels involved in the sending and receiving of calcium signals between cells.

Calcium signals are already known to be crucial to neuron development and function. So, the new findings support the idea that genetic differences expressed early during brain development may have a lot to do with the development of bipolar disorder symptoms – and other mental health conditions that arise later in life, especially in the teen and young adult years.

Meanwhile, the cells' signalling patterns changed in different ways when the researchers introduced lithium, which many bipolar patients take to regulate their moods, but which causes side effects. In general, lithium alters the way calcium signals are sent and received – and the new cell lines will make it possible to study this effect specifically in bipolar disorder-specific cells.

Like misdirected letters and packages at the post office, the neurons made from bipolar disorder patients also differed in how they were 'addressed' during development for delivery to certain areas of the brain. This may have an impact on brain development, too.

The researchers also found differences in microRNA expression in bipolar cells – tiny fragments of RNA that play key roles in the "reading" of genes. This supports the emerging concept that bipolar disorder arises from a combination of genetic vulnerabilities.

The researchers are already developing stem cell lines from other trial participants with bipolar disorder, though it takes months to derive each line and obtain mature neurons that can be studied. They will share their cell lines with other researchers via the Prechter Repository at U-M. They also hope to develop a way to use the cells to screen drugs rapidly, called an assay.

Source: University of Michigan Health System 

Contact: Kara Gavin

Reference:

Transcripts involved in calcium signaling and telencephalic neuronal fate are altered in induced pluripotent stem cells from bipolar disorder patients

H M Chen, C J DeLong, M Bame, I Rajapakse, T J Herron, M G McInnis and K S O’Shea

Translational Psychiatry (2014) 4, e375; doi:10.1038/tp.2014.12

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For more on stem cells and cloning, go to CellNEWS at

http://cellnews-blog.blogspot.com/

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