Brain cell signal network genes linked to schizophrenia risk in families

New genetic factors that predispose to schizophrenia have been uncovered in five families with several affected relatives. The psychiatric disorder can disrupt thinking, feeling, and acting, and blur the border between reality and imagination.

Dr. Debby W. Tsuang, professor of psychiatry and behavioral sciences, and Dr. Marshall S. Horwitz, professor of pathology, both at the University of Washington in Seattle, led the multi-institutional study. Tsuang is also a staff physician at the Puget Sound Veterans Administration Health Care System.

The results are published in the April 3 online edition of the JAMA Psychiatry.

Loss of brain nerve cell integrity occurs in schizophrenia, but scientists have not worked out the details of when and how this happens. In all five families in the present study, the researchers found rare variants in genes tied to the networking of certain signal receptors on nerve cells distributed throughout the brain. These N-methyl-D-aspartate, or NMDA, receptors are widespread molecular control towers in the brain. They regulate the release of chemical messages that influence the strength of brain cell connections and the ongoing remodeling of the networks.

These receptors respond to glutamate, one of the most common nerve-signaling chemicals in the brain, and they are also found on brain circuits that manage dopamine release. Dopamine is a nerve signal associated with reward-seeking, movement and emotions. Deficits in glutamate and dopamine function have both been implicated in schizophrenia but most of the medications that have been developed to treat schizophrenia have targeted dopamine receptors.

Tsuang and her groups’ discovery of gene variations that disturb N-methyl-D-aspartate receptor networking functions supports the hypothesis that decreased NMDA receptor-mediated nerve-signal transmissions contributes to some cases of schizophrenia.

Tsuang pointed out that several hallucinogenic drugs, such as ketamine and phencyclidine (PCP, or angel dust), block N-methyl-D-aspartate receptors and can produce symptoms similar to schizophrenia. These are the strongest evidence implicating these receptors in schizophrenia. The drugs sometimes induce psychosis and terrifying sensory detachment. Reports of such effects in recreational drug users fingered faulty NMDA receptor networks as suspects in schizophrenia.

In all five of their study families, Tsuang’s team detected rare protein-altering variants in one of three genes involved with the N-methyl-D-aspartate receptor network. One of the genes, GRM5, is directly linked with glutamate signaling. In the other two genes, the links are indirect and connected through other proteins synthesized in brain cells. One of these proteins, PPEF2, appears to affect the levels of certain brain nerve-cell signaling mediators, and the other altered protein, LRP1B, may compete with a normal protein for a binding spot on a subunit of the NMDA receptor.

These discoveries provide additional clues to the molecular disarray that might occur in the brain nerve cells of some patients with schizophrenia, and suggest new targets for therapy for certain patients. In a disease occurring in about 1 percent of the population, the picture of how and why schizophrenia arises in all these people is far from complete.

“Disorders like schizophrenia are likely to have many underlying causes,” Tsuang noted. She added that it might eventually make sense to divide schizophrenia into categories based, for example, on which biochemical pathways in the brain are disrupted. Treatments might be developed to correct the exact malfunctioning mechanisms underlying various forms of the disease.

Tsuang gave an example: Agents that stimulate N-methyl-D-aspartate receptor-mediated nerve-signal transmissions include glycine-site blockers and glycine-transport inhibitors have shown some encouraging results in pre-clinical drug trials, but mostly in adjunctive treatment in addition to standard antipsychotic therapy.

“But perhaps the data we have generated will help pharmaceutical companies target specific subunits of the NMDA receptors and pathways,” Tsuang said. She added, however, that effective treatments may lag by many years after these kinds of discoveries. Someday it may make sense to initiate such treatments in people at high genetic risk when early symptoms, such as apathy and lack of motivation, appear, and before brain dysfunction is severe.

Also, possessing the newly discovered gene mutations does not always mean that a person will become schizophrenic. In the recent family study, three of the five families had relatives with the protein-altering variants who did not have schizophrenia.

“This isn’t surprising,” Tsuang observed, “Given that schizophrenia is such a complex disorder, we would expect that not everyone who carries the variants would develop the disease.” In the future, researchers will be seeking what triggers the gene variants into causing problems, other mutations within affected individuals’ genetic profile that might promote or protect against disease, as well as non-genetic factors in the onset of the illness in genetically susceptible people.

The researchers also utilized a strategy and selected more distant relatives of affected individuals for genetic sequencing. Distant kin share, a smaller proportion of genes compared to closely related family members. For example,siblings typically on the average share about 50 percent of their genes whereas cousins on the average share 12.5 percent of their genes. The researhers also hypothesized that the causative mutation within each family would be the same variant.

This strategy helped the researchers decrease the number of genetic variants that were detected by sequencing and thereby concentrate only on the remaining strongest candidates. The researchers also filtered their results against the many publicly available sequencing databases. This allowed them to pick out genetic variants not seen in individuals without psychiatric illness.

According to Tsuang, the research team was excited by recent advances in technology enabled them to uncover unknown, rare genetic variants not previously found in large populations without psychiatric condition. The ability to rapidly sequence only those portions of the genome that code for proteins made this experiment possible.

The next step for the researchers will be to screen for the newly discovered genetic variants in a large sample of unrelated cases of schizophrenia compared to controls. They want to determine if the variants are statistically associated with the disease.

Peptides helping researchers in search for Parkinson’s disease treatment

Australian researchers have taken the first step in using bioactive peptides as the building blocks to help ‘build a new brain’ to treat degenerative brain disease.

Deakin University biomedical scientist Dr Richard Williams is working in a team with Dr David Nisbet from the Australian National University and Dr Clare Parish at the Florey Neuroscience Institute to develop a way to repair the damaged parts of the brain that cause Parkinson’s disease.

Parkinson’s disease develops when the brain cells (or neurons) that produce the chemical dopamine die or are damaged. Dopamine neurons produce a lubricant that helps the brain transmit signals to the body that control muscles and movement. When these cells die or are damaged the result is the shaking and muscle stiffness that are among the common symptoms of the disease.

"We are looking at a way of helping the brain to regenerate the dead or damaged cells that transport dopamine throughout the body," Dr Williams said. "Peptides help the body heal itself, providing many positive benefits for health, particularly in regenerative medicine; this is why the sports people were using them to recover more quickly in the current doping scandal."

Peptides are both the building blocks and the messengers of the body; the team has used them to mimic the normal brain environment and provide the chemical signals needed to help the brain function.

"Peptides stick together like Lego blocks, so in the first stage of the project we have been able to make a three dimensional material or tissue scaffold that provides the networks cells need to grow; but the peptides also carry instructions in the form of chemical signals which tell the cells to grow into new neurons," Dr Williams explained.

"Importantly, this material has the same consistency as the brain, does not cause chronic inflammation and is non-toxic to the body.

"Our aim is to use this scaffold material to support the patient’s own stem cells that could be turned into dopamine neurons and implanted back into the brain. We expect that when implanted the material and stem cells would be accepted by the brain as normal tissue and grow to replace the damaged or dead cells."

While the research is not yet complete, Dr Williams is excited by the possibilities this work offers to the treatment of degenerative conditions.

"It is no secret that we are living longer, and with this we are seeing an increase in many conditions that come about because of ageing such Parkinson’s. By developing biomaterials, like the ones we are working on, it could be possible to help the body to regenerate and provide an improved quality of life to the older members of our community," he said.

"This work can also be adapted to other parts of the body which struggle to repair themselves, such as new cartilage for joints, muscle and heart cells, bones and teeth. Ultimately, it will be like taking your car to the garage to have new parts fitted to replace the worn out ones."

The results of the first stage of this Australian Research Council funded project will be published in the international journal Soft Matter.

Breaking down the Parkinson’s pathway

The key hallmark of Parkinson’s disease is a slowdown of movement caused by a cutoff in the supply of dopamine to the brain region responsible for coordinating movement. While scientists have understood this general process for many years, the exact details of how this happens are still murky.

“We know the neurotransmitter, we know roughly the pathways in the brain that are being affected, but when you come right down to it and ask what exactly is the sequence of events that occurs in the brain, that gets a little tougher,” says Ann Graybiel, an MIT Institute Professor and member of MIT’s McGovern Institute for Brain Research.

A new study from Graybiel’s lab offers insight into some of the precise impairments caused by the loss of dopamine in brain cells affected by Parkinson’s disease. The findings, which appear in the March 12 online edition of the Journal of Neuroscience, could help researchers not only better understand the disease, but also develop more targeted treatments.

The neurons responsible for coordinating movement are located in a part of the brain called the striatum, which receives information from two major sources — the neocortex and a tiny region known as the substantia nigra. The cortex relays sensory information as well as plans for future action, while the substantia nigra sends dopamine that helps to coordinate all of the cortical input.

“This dopamine somehow modulates the circuit interactions in such a way that we don’t move too much, we don’t move too little, we don’t move too fast or too slow, and we don’t get overly repetitive in the movements that we make. We’re just right,” Graybiel says.

Parkinson’s disease develops when the neurons connecting the substantia nigra to the striatum die, cutting off a critical dopamine source; in a process that is not entirely understood, too little dopamine translates to difficulty initiating movement. Most Parkinson’s patients receive L-dopa, which can substitute for the lost dopamine. However, the effects usually wear off after five to 10 years, and complications appear.

Mouse Research Links Adolescent Stress and Severe Adult Mental Illness

Working with mice, Johns Hopkins researchers have established a link between elevated levels of a stress hormone in adolescence - a critical time for brain development - and genetic changes that, in young adulthood, cause severe mental illness in those predisposed to it.

The findings, reported in the journal Science, could have wide-reaching implications in both the prevention and treatment of schizophrenia, severe depression and other mental illnesses.

"We have discovered a mechanism for how environmental factors, such as stress hormones, can affect the brain’s physiology and bring about mental illness," says study leader Akira Sawa, M.D., Ph.D., a professor of psychiatry and behavioral sciences at the Johns Hopkins University School of Medicine. "We’ve shown in mice that stress in adolescence can affect the expression of a gene that codes for a key neurotransmitter related to mental function and psychiatric illness. While many genes are believed to be involved in the development of mental illness, my gut feeling is environmental factors are critically important to the process."

Sawa, director of the Johns Hopkins Schizophrenia Center, and his team set out to simulate social isolation associated with the difficult years of adolescents in human teens. They found that isolating healthy mice from other mice for three weeks during the equivalent of rodent adolescence had no effect on their behavior. But, when mice known to have a genetic predisposition to characteristics of mental illness were similarly isolated, they exhibited behaviors associated with mental illness, such as hyperactivity. They also failed to swim when put in a pool, an indirect correlate of human depression. When the isolated mice with genetic risk factors for mental illness were returned to group housing with other mice, they continued to exhibit these abnormal behaviors, a finding that suggests the effects of isolation lasted into the equivalent of adulthood.

"Genetic risk factors in these experiments were necessary, but not sufficient, to cause behaviors associated with mental illness in mice," Sawa says. "Only the addition of the external stressor - in this case, excess cortisol related to social isolation - was enough to bring about dramatic behavior changes."

The investigators not only found that the “mentally ill” mice had elevated levels of cortisol, known as the stress hormone because it’s secreted in higher levels during the body’s fight-or-flight response. They also found that these mice had significantly lower levels of the neurotransmitter dopamine in a specific region of the brain involved in higher brain function, such as emotional control and cognition. Changes in dopamine in the brains of patients with schizophrenia, depression and mood disorders have been suggested in clinical studies, but the mechanism for the clinical impact remains elusive.

Parkinson’s Treatment Can Trigger Creativity

Parkinson’s experts across the world have been reporting a remarkable phenomenon — many patients treated with drugs to increase the activity of dopamine in the brain as a therapy for motor symptoms such as tremors and muscle rigidity are developing new creative talents, including painting, sculpting, writing, and more.

Prof. Rivka Inzelberg of Tel Aviv University’s Sackler Faculty of Medicinefirst noticed the trend in her own Sheba Medical Center clinic when the usual holiday presents from patients — typically chocolates or similar gifts — took a surprising turn. “Instead, patients starting bringing us art they had made themselves,” she says.

Inspired by the discovery, Prof. Inzelberg sought out evidence of this rise in creativity in current medical literature. Bringing together case studies from around the world, she examined the details of each patient to uncover a common underlying factor — all were being treated with either synthetic precursors of dopamine or dopamine receptor agonists, which increase the amount of dopamine activity in the brain by stimulating receptors. Her report published in the journal Behavioral Neuroscience.

Giving in to artistic impulse

Dopamine is involved in several neurological systems, explains Prof. Inzelberg. Its main purpose is to aid in the transmission of motor commands, which is why a lack of dopamine in Parkinson’s patients is associated with tremors and a difficulty in coordinating their movements.

But it’s also involved in the brain’s “reward system” — the satisfaction or happiness we experience from an accomplishment. This is the system which Prof. Inzelberg predicts is associated with increasing creativity. Dopamine and artistry have long been connected, she points out, citing the example of the Vincent Van Gogh, who suffered from psychosis. It’s possible that his creativity was the result of this psychosis, thought to be caused by a spontaneous spiking of dopamine levels in the brain.

There are seemingly no limits to the types of artistic work for which patients develop talents, observes Prof. Inzelberg. Cases include an architect who began to draw and paint human figures after treatment, and a patient who, after treatment, became a prize-winning poet though he had never been involved in the arts before.

It’s possible that these patients are expressing latent talents they never had the courage to demonstrate before, she suggests. Dopamine-inducing therapies are also connected to a loss of impulse control, and sometimes result in behaviors like excessive gambling or obsessional hobbies. An increase in artistic drive could be linked to this lowering of inhibitions, allowing patients to embrace their creativity. Some patients have even reported a connection between their artistic sensibilities and medication dose, noting that they feel they can create more freely when the dose is higher.

Therapeutic value

Prof. Inzelberg believes that such artistic expressions have promising therapeutic potential, both psychologically and physiologically. Her patients report being happier when they are busy with their art, and have noted that motor handicaps can lessen significantly. One such patient is usually wheelchair-bound or dependent on a walker, but creates intricate wooden sculptures that have been displayed in galleries. External stimuli can sometimes bypass motor issues and foster normal movement, she explains. Similar types of art therapy are already used for dementia and stroke patients to help mitigate the loss of verbal communication skills, for example.

The next step is to try to characterize those patients who become more creative through treatment through comparing them to patients who do not experience a growth in artistic output. “We want to screen patients under treatment for creativity and impulsivity to see if we can identify what is unique in those who do become more creative,” says Prof. Inzelberg. She also believes that such research could provide valuable insights into creativity in healthy populations, too.

Dopamine regulates the motivation to act

The widespread belief that dopamine regulates pleasure could go down in history with the latest research results on the role of this neurotransmitter. Researchers have proved that it regulates motivation, causing individuals to initiate and persevere to obtain something either positive or negative.

The neuroscience journal Neuron publishes an article by researchers at the Universitat Jaume I of Castellón that reviews the prevailing theory on dopamine and poses a major paradigm shift with applications in diseases related to lack of motivation and mental fatigue and depression, Parkinson’s, multiple sclerosis, fibromyalgia, etc. and diseases where there is excessive motivation and persistence as in the case of addictions.

"It was believed that dopamine regulated pleasure and reward and that we release it when we obtain something that satisfies us, but in fact the latest scientific evidence shows that this neurotransmitter acts before that, it actually encourages us to act. In other words, dopamine is released in order to achieve something good or to avoid something evil", explains Mercè Correa.

Studies had shown that dopamine is released by pleasurable sensations but also by stress, pain or loss. These research results however had been skewed to only highlight the positive influence, according to Correa. The new article is a review of the paradigm based on the data from several investigations, including those conducted over the past two decades by the Castellón group in collaboration with the John Salamone of the University of Connecticut (USA), on the role of dopamine in the motivated behaviour in animals.

The level of dopamine depends on individuals, so some people are more persistent than others to achieve a goal. “Dopamine leads to maintain the level of activity to achieve what is intended. This in principle is positive, however, it will always depend on the stimuli that are sought: whether the goal is to be a good student or to abuse of drugs” says Correa. High levels of dopamine could also explain the behaviour of the so-called sensation seekers as they are more motivated to act.

Application for depression and addiction

To know the neurobiological parameters that make people be motivated by something is important to many areas such as work, education or health. Dopamine is now seen as a core neurotransmitter to address symptoms such as the lack of energy that occurs in diseases such as depression. “Depressed people do not feel like doing anything and that’s because of low dopamine levels,” explains Correa. Lack of energy and motivation is also related to other syndromes with mental fatigue such as Parkinson’s, multiple sclerosis or fibromyalgia, among others.

In the opposite case, dopamine may be involved in addictive behaviour problems, leading to an attitude of compulsive perseverance. In this sense, Correa indicates that dopamine antagonists which have been applied so far in addiction problems probably have not worked because of inadequate treatments based on a misunderstanding of the function of dopamine.