Most Complete Human Brain Model to Date Is a ‘Brain Changer’

Once licensed, model likely to accelerate study of Alzheimer’s, autism, more

Wednesday, 19 August 2015

Scientists at The Ohio State University have developed a nearly complete human brain in a dish that equals the brain maturity of a 5-week-old foetus.

The brain organoid, engineered from adult human skin cells, is the most complete human brain model yet developed, said Rene Anand, professor of biological chemistry and pharmacology at Ohio State.

The lab-grown brain, about the size of a pencil eraser, has an identifiable structure and contains 99 percent of the genes present in the human foetal brain. Such a system will enable ethical and more rapid and accurate testing of experimental drugs before the clinical trial stage and advance studies of genetic and environmental causes of central nervous system disorders.

“It not only looks like the developing brain, its diverse cell types express nearly all genes like a brain,” Anand said.

“We’ve struggled for a long time trying to solve complex brain disease problems that cause tremendous pain and suffering. The power of this brain model bodes very well for human health because it gives us better and more relevant options to test and develop therapeutics other than rodents.”

Anand reported on his lab-grown brain Tuesday (Aug. 18) at the 2015 Military Health System Research Symposium in Ft. Lauderdale, Florida.

This image of the lab-grown brain is labelled to

show identifiable structures: the cerebral

hemisphere, the optic stalk and the cephalic

flexure, a bend in the mid-brain region, all

characteristic of the human foetal brain. Credit:

courtesy of The Ohio State University.

Anand, who studies the association between nicotinic receptors and central nervous system disorders, was inspired to pursue a model of human neural biology after encountering disappointing results in a rodent study of an experimental autism drug. Taking a chance with a shoestring budget compared to other researchers doing similar projects, he added stem-cell engineering to his research program. Four years later, he had built himself a replica of the human brain.

The main thing missing in this model is a vascular system. What is there – a spinal cord, all major regions of the brain, multiple cell types, signalling circuitry and even a retina – has the potential to dramatically accelerate the pace of neuroscience research, said Anand, also a professor of neuroscience.

“In central nervous system diseases, this will enable studies of either underlying genetic susceptibility or purely environmental influences, or a combination,” he said.

“Genomic science infers there are up to 600 genes that give rise to autism, but we are stuck there. Mathematical correlations and statistical methods are insufficient to in themselves identify causation. You need an experimental system – you need a human brain.”

Converting adult skin cells into pluripotent cells – immature stem cells that can be programmed to become any tissue in the body – is a rapidly developing area of science that earned the researcher who discovered the technique, Shinya Yamanaka, a Nobel Prize in 2012.

“Once a cell is in that pluripotent state, it can become any organ – if you know what to do to support it to become that organ,” Anand said.

“The brain has been the holy grail because of its enormous complexity compared to any other organ. Other groups are attempting to do this as well.”

Anand’s method is proprietary and he has filed an invention disclosure with the university.

He said he used techniques to differentiate pluripotent stem cells into cells that are designed to become neural tissue, components of the central nervous system or other brain regions.

“We provide the best possible environment and conditions that replicate what’s going on in utero to support the brain,” he said of the work he completed with colleague Susan McKay, a research associate in biological chemistry and pharmacology.

High-resolution imaging of the organoid identifies functioning neurons and their signal-carrying extensions – axons and dendrites – as well as astrocytes, oligodendrocytes and microglia. The model also activates markers for cells that have the classic excitatory and inhibitory functions in the brain, and that enable chemical signals to travel throughout the structure.

It takes about 15 weeks to build a model system developed to match the 5-week-old foetal human brain. Anand and McKay have let the model continue to grow to the 12-week point, observing expected maturation changes along the way.

“If we let it go to 16 or 20 weeks, that might complete it, filling in that 1 percent of missing genes. We don’t know yet,” he said.

He and McKay have already used the platform to launch their own projects, creating brain organoid models of Alzheimer’s and Parkinson’s diseases and autism in a dish. They hope that with further development and the addition of a pumping blood supply, the model could be used for stroke therapy studies. For military purposes, the system offers a new platform for the study of Gulf War illness, traumatic brain injury and post-traumatic stress disorder.

Anand hopes his brain model could be incorporated into the Microphysiological Systems program, a platform the Defense Advanced Research Projects Agency is developing by using engineered human tissue to mimic human physiological systems.

Support for the work came from the Marci and Bill Ingram Research Fund for Autism Spectrum Disorders and the Ohio State University Wexner Medical Center Research Fund.

Anand and McKay are co-founders of a Columbus-based start-up company, NeurXstem, to commercialize the brain organoid platform, and have applied for funding from the federal Small Business Technology Transfer program to accelerate its drug discovery applications.

Source: Ohio State University

Contact: Rene Anand

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Father's Age Influences Rate of Evolution

Chimpanzee.

Father's Age Influences Rate of Evolution

Friday, 13 June 2014

The offspring of chimpanzees inherit 90% of new mutations from their father, and just 10% from their mother, a finding which demonstrates how mutation differs between humans and our closest living relatives, and emphasises the importance of father's age on evolution.

Published today in Science, researchers from the Wellcome Trust Centre for Human Genetics and the Biomedical Primate research Centre in the Netherlands looked at whether, in chimpanzees, there was a heightened risk of fathers passing on mutations to their children compared to humans.

In humans, each individual inherits, on average, about 70 new mutations from their parents. However, this number is influenced by paternal age such that older fathers tend to result in more mutations – in humans each extra year of age results in two extra mutations.

Mutation risk is linked to father's age because the sperm lineage in males keeps dividing, while females have all the eggs they are ever going to produce present at birth. Paternal age is an established risk factor in a number of disorders including schizophrenia and autism.

The study found that the number of new mutations inherited by chimpanzees from their parents is, on average, very similar to that in humans, but that the effect of the father's age is much stronger – each additional year of father's age results in three extra mutations.

The results suggest that sexual selection can influence the rate of evolution through its effect on the male mutation rate.

Professor Gil McVean, from the Wellcome Trust Centre for Human Genetics at the University of Oxford said:

"In humans, a father's age is known to affect how many new mutations he passes on to his children, and is also an established risk factor in a number of mental health disorders.”

"This study finds that in chimpanzees the father's age has a much stronger effect on mutation rate – about one and a half times that in humans. As a consequence, a greater fraction of new mutations enter the population through males, around 90 per cent, compared to humans, where fathers account for 75 per cent of new mutations."

In the study, Wellcome Trust-funded researchers sequenced the genomes of nine western chimpanzees from a three generation family living at the biomedical primate research centre in the Netherlands.

To establish the number of new mutations a child inherits researchers sequence children and their parents and compare the genetic sequence – any change in the sequence that doesn't exist in either parent genome is a new mutation. To find out which parent the mutation comes from you need to sequence members of the next generation of the family.

One explanation for this difference is that chimpanzees, as a result of their mating system, have evolved to produce many more sperm than humans – their testes are over three times the relative size of a human. This means there are likely to be more cycles of sperm production, increasing the opportunity for new mutations to emerge.

The authors suggest that more work needs to be done across other species to investigate the impact of mating behaviour on mutation rates and male mutation bias.

Source: Wellcome Trust 

Contact: Clare Ryan

Reference:

Strong male bias drives germ line mutation in chimpanzees

Oliver Venn, Isaac Turner, Iain Mathieson, Natasja de Groot, Ronald Bontrop, Gil McVean

Science 13 June 2014, Vol. 344 no. 6189 pp. 1272-1275, DOI: 10.1126/science.344.6189.1272

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Modelling Autism in a Dish

Human iPSCs derived from patients with Rett syndrome
Monday, 15 November 2010

A collaborative effort between researchers at the Salk Institute for Biological Studies and the University of California, San Diego, successfully used human induced pluripotent stem (iPS) cells derived from patients with Rett syndrome to replicate autism in the lab and study the molecular pathogenesis of the disease.

Their findings, published in the Nov. 12, 2010, issue of Cell, revealed disease-specific cellular defects, such as fewer functional connections between Rett neurons, and demonstrated that these symptoms are reversible, raising the hope that, one day, autism maybe turn into a treatable condition.


This is Alysson R. Muotri, Ph.D., of

the University of California,

San Diego. Credit: UCSD.

"Mental disease and particularly autism still carry the stigma of bad parenting," says lead author Alysson Muotri, Ph.D., an assistant professor in the Department of Molecular and Cellular Medicine at the University of California, San Diego School of Medicine.

"We show very clearly that autism is a biological disease that is caused by a developmental defect directly affecting brain cells."

"This work is important because it puts us in a translational mode," said Muotri.

"It helps expand and deepen our understanding of autism, from behavioural disorder to developmental brain disorder. We can now look for and test drugs and therapies and see what happens at a cellular and molecular level. That's something we've never been able to do with human autistic neurons before."

Rett syndrome is a neurological disorder and the most physically disabling of the autism spectrum disorders. Primarily affecting girls, the symptoms of Rett syndrome often become apparent just after they have learned to walk and say a few words. Affected newborns display normal development until six months to 1½ years of age, "after which behavioural symptoms begin to emerge," Muotri said.

"Progressively, motor functions become impaired. There may be hypotonia or low muscle tone, seizures, diminished social skills and other autistic behaviours."

Then, the seemingly normal development slows down and eventually the infants regress, loosing speech and motor skills, developing stereotypical movements and autistic characteristics.

Almost all cases of the disease are caused by a single mutation in the MeCP2 gene, which is involved in the regulation of global gene expression, leading to a host of symptoms that can vary widely in their severity.

"Rett syndrome is sometimes considered a 'Rosetta Stone' that can help us to understand other developmental neurological disorders since it shares genetic links with other conditions such as autism and schizophrenia," says first author Carol Marchetto, Ph.D., a postdoctoral researcher in the Laboratory of Genetics at the Salk Institute.

Human induced pluripotent stem (iPS) cells

derived from patients with Rett syndrome

allow researchers to replicate autism in the lab

and study the molecular pathogenesis of the

disease. Credit: Illustration: Courtesy of Jamie

Simon, Salk Institute for Biological Studies.

In the past, scientists had been limited to study the brains of people with autistic spectrum disorders via imaging technologies or post mortem brain tissues. The new research goes further. Muotri and colleagues at the Salk Institute for Biological Studies and Pennsylvania State University developed a culture system using induced pluripotent stem cells (iPSCs) derived from RTT patient's skin fibroblasts – cells that typically give rise to connective tissues. Instead, the human RTT-iPSCs were reprogrammed to generate functional neurons that, compared to normal control cells, featured fewer synapses, reduced spine density, smaller soma size, altered calcium signalling and electrophysiological defects – all indications that the deleterious alterations to human RTT neurons begin early in development.

"It is quite amazing that we can recapitulate a psychiatric disease in a Petri Dish," says lead author Fred Gage, Ph.D., a professor in the Salk's Laboratory of Genetics and holder of the Vi and John Adler Chair for Research on Age-Related Neurodegenerative Diseases.

"Being able to study Rett neurons in a dish allows us to identify subtle alterations in the functionality of the neuronal circuitry that we never had access to before."

Marchetto started with skin biopsies taken from four patients carrying four different mutations in the MeCP2 gene and a healthy control. By exposing the skin cells to four reprogramming factors, she turned back the clock, triggering the cells to look and act like embryonic stem cells. Known at this point as induced pluripotent stem cells, the Rett-derived cells were indistinguishable from their normal counterparts.


Neurons generated from Rett-iPS cells

form fewer synapses, the specialized

signal transmission points between

brain cells. Synapses are shown in

red and dendrites, which function as

signal receivers, are shown in green.

Credit: Image: Courtesy of Dr. Carol

Marchetto, Salk Institute for

Biological Studies.

It was only after she had patiently coaxed the iPS cells to develop into fully functioning neurons — a process that can take up to several months — that she was able to discern differences between the two. Neurons carrying the MeCP2 mutations had smaller cell bodies, a reduced number of synapses and dendritic spines, specialized structures that enable cell-cell communication, as well as electrophysical defects, indicating that things start to go wrong early in development.

Since insulin-like growth factor 1 (IGF-1) — a hormone which, among other things, has a role in regulating cell growth and neuronal development — was able to reverse some of the symptoms of Rett syndrome in a mouse model of disease, the Salk researchers tested whether IGF-1 could restore proper function to human Rett neurons grown in culture.

"IGF-1 treatment increased the number of synapses and spines reverting the neuronal phenotype closer to normal," says Gage.

"This suggests that the autistic phenotype is not permanent and could be, at least partially, reversible."

Muotri said IGF1 appeared to rescue some RTT-iPSCs, reverting some neuronal defects, though exactly how IGF1 works remains unknown and requires further investigation.

"This suggests, however, that synaptic deficiencies in Rett syndrome, and likely other autism spectrum disorders, may not be permanent," Muotri said.

Muotri is particularly excited about the prospect of finding a drug treatment for Rett syndrome and other forms of autism:

"We now know that we can use disease-specific iPS cells to recreate mental disorders and start looking for new drugs based on measurable molecular defects."

About autism:
Autism spectrum disorder (ASD) is a range of complex, varying neurodevelopment disorders characterized by social impairments, communication difficulties and restricted, repetitive and stereotyped patterns of behavior. It is not known what causes ASD. Scientists have identified a number of genes associated with the disorder, but environmental factors likely play a role too.
Autistic disorder (sometimes called autism or classical ASD) is the most severe form. Milder conditions include Asperger syndrome, Rett syndrome, Childhood Disintegrative Disorder and Pervasive Developmental Disorder Not Otherwise Specified (usually referred to as PDD-NOS).
The Centers for Disease Control and Prevention reports the prevalence of autism to be approximately 1 in every 110 births in the United States. An estimated 1.5 million Americans live with the effects of ASD, which occurs in all ethnic and socioeconomic groups and affects every age group, though males are four times more likely to have ASD than females.


Source: Salk Institute and University of California - San Diego
Contact: Gina Kirchweger and Contact: Scott Lafee
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