Of Mice and Men…and Mental Health

One in five Americans suffers a major depressive episode in their lifetime. Twenty-eight per cent will develop an anxiety disorder, such as post-traumatic stress, phobias, obsessions, or compulsions. Another 15% will fall prey to alcoholism or drug addiction. If you gather 100 people from any square mile on earth, odds are that one will have autism or schizophrenia.

Just about everything we know about drug treatments for psychiatric disorders we learned from mice.  Just how the mouse became our avatar is part tradition and part biological accident. In the past, rats were traditionally used to test experimental drugs. Rats are small enough to be affordable but big enough to make their brains easy to dissect. And they are smarter than mice. You can swiftly teach a rat to solve a maze, for instance, and then test whether your new drug has a side effect of making rats forgetful.

However, rats missed the knockout revolution of the late 1980s. Knockout technology allows researchers to silence, or knock out, individual genes.

With mice, researchers can insert altered DNA in a mouse stem cell, insert the cell in a newly fertilized egg, and insert the egg in a surrogate mother. That egg might develop as a normal mouse or a knockout. The offspring born with knocked-out genes are mated for a few generations to create a pure strain. Once the geneticists perfected these procedures, mice almost instantly assumed the lead role in modeling human mental malfunctions.

These days, you won’t find more mentally ill mice per square mile anywhere than in Bar Harbor, Maine. Mice with anxiety, depression, autism, learning disabilities, anorexia or schizophrenia – they all congregate here. Name an affliction of the human mind, and you can probably find its avatar on this sprucy, secluded island built for America’s richest and most powerful families — including the Rockefellers, the Fords, the Vanderbilts, the Carnegies, the Astors and the Morgans.

The imbalanced mice are kept under the strictest security, in locked wards at the Jackson Laboratory, a nonprofit biomedical facility internationally renowned for its specially bred deranged rodents.

There are no visiting hours, because strangers fluster the mice and might carry in contagious diseases. The animals are attended only by highly qualified caregivers.

But, accurately reproducing a human mental illness in the tiny brain of a mouse is still hugely challenging. The basic structure of a mouse brain is mostly analogous to a human brain.  They have a hippocampus, we have a hippocampus; they have a prefrontal cortex, we have a prefrontal cortex, albeit one that is much larger. We even share about 99% of their genes. But no one would mistake you for a mouse. The mouse is a nocturnal animal with poor eyesight, adapted to fear predators that strike from above. Mice are fundamentally alarmed by light, open spaces, and sudden movements. It is no surprise then, that they manifest depression and anxiety differently than humans do, if they manifest such ailments at all.

“You cannot mimic an entire human psyche in a mouse or a rat,” says 
Jacqueline Crawley, a behavioral neuroscientist at the National Institutes of Health (NIH) “Mice aren’t a one-to-one correspondence to humans. But they are better than zero.”

Disorders like depression and schizophrenia are each linked to hundreds of genes. No one gene is likely to make much difference. But genes are only one part of the story. Other clues to human mental health can be found in the neural circuits of mouse brains. By tracing the wiring that connects one brain region to the next, researchers hope to develop more precisely targeted medications.

Many vintage psychiatric drugs, such as Valium, Ritalin, and antipsychotics, were stumbled upon rather than tailor-made to solve a problem. As a result, they are too broad.  They affect more than one type of receptor, on more than one kind of nerve cell, in more than one part of the brain. Many patients decide the cure is not worth the many side effects.

Mice may be the best models we have of psychiatric disorders, but best does not mean great, or even decent. Gerald Dawson, founder and chief scientific officer of P1Vital, a pharmaceutical consulting firm in the United Kingdom, had his heart broken by the mouse mismatch. In the late 1990s, Dawson set out to eliminate the drowsiness from anxiety drugs.The class of drugs he wanted 
to modify, benzodiazepines such as Valium, Xanax, Ativan, and Klonopin, target the GABAa system.

As with most neurotransmitters, the GABAa system is so evolutionarily ancient that it has diversified to serve many purposes. Hence, the brain has six different GABAa receptor types, presumably to perform six different jobs. Dawson had a suspicion that the sleepiness side effect originated from just one of those six receptors. If he could determine which one, corporate chemists could design a molecule that would avoid activating it. He began to make mice.

One by one, he manipulated the receptor genes, breeding a new line of mice each time. With each new strain, he would administer a tiny dose of Valium. If the animals grew drowsy, he knew he had not yet knocked out the right receptor. Knocking out receptor 1 made little difference. Receptor 3 proved too hard to knock out. Receptor 5 seemed to account for the amnesia that people (and mice) experience when they take anxiety drugs. Targeting receptor 2, Dawson identified a chemical that reduced a mouse’s startle response—a measure of anxiety—without impairing its ability to balance. Success!

Or, so he thought. “When these compounds went into humans, they turned out to be just as sedating as the original drugs.”

Dawson blames the mice. “There’s not enough predictability in animal research.”

But, for all Dawson’s frustration with mice, the rodents did yield a couple of interesting drug leads.

That receptor 5 implicated in the amnesia side effect?  An experimental chemical that blocked its action created temporary geniuses: Mice on it were whizzes in the Morris water maze. A drug company is testing the compound to treat people with Down syndrome. And in the process of trying to eliminate drowsiness, Dawson and his team homed in on one of the chemical switches that cause mammals to go to sleep. Ambien locks onto that switch associated with receptor 1.

So, despite the problems, mice remain the undisputed top animal for research on mental health therapies.

Which just goes to show that mice, like us, have minds of their own.

T-A T-A to A-T?

SRxA’s Word on Health is delighted to share news that could change the lives of the 500 or so children and families in the US, dealing with a rare and deadly disease.  The breakthrough, announced this week in the online edition of Nature Medicine, suggests that scientists may have found a way to prevent and possibly reverse the most debilitating symptoms of ataxia telangiectasia (A-T) a rare, progressive childhood degenerative disease that leaves children, unable to walk, and in a wheelchair before they reach adolescence.

As regular readers of this blog know, A-T is a cause close to our hearts, and the courage of these children and their families inspire us daily.

Karl Herrup, chair of the Department of Cell Biology and Neuroscience and his colleagues at Rutgers have discovered why this genetic disease attacks certain parts of the brain, including those that control movement coordination, equilibrium, muscle tone and speech.

When the team examined the brain tissue of young adults who died from A-T, they found a protein (HDAC4) in the nucleus of the nerve cell instead of in the cytoplasm where it belongs. When HDAC4 is in the cytoplasm it helps to prevent nerve cell degeneration; however, when it gets into the nucleus it attacks histones – the small proteins that coat and protect the DNA.

“What we found is a double-edged sword,” said Herrup. “While the HDAC4 protein protected a neuron’s function when it was in the cytoplasm, it was lethal in the nucleus.”

To prove this point, Rutgers’ scientists analyzed mice, genetically engineered with the defective protein found in children with A-T, as well as wild mice. The animals were tested on a rotating rod to measure their motor coordination. While the normal mice were able to stay on the rod without any problems for five to six minutes, the mutant mice fell off within 15 to 20 seconds.

However, after being treated with trichostation A (TSA), a chemical compound that inhibits the ability of HDAC4 to modify proteins, they found that the mutant mice were able to stay on the rotating rod without falling off – almost as long as the normal mice.

Although the behavioral symptoms and brain cell loss in the engineered mice are not as severe as in humans, all of the biochemical signs of cell stress were reversed and the motor skills improved dramatically in the mice treated with TSA. This outcome proves that brain cell function could be restored.

Neurological degeneration is not the only life-threatening effect associated with A-T. The disease, which occurs in an estimated 1 in 40,000 births, causes the immune system to break down and leaves children extremely susceptible to cancers such as leukemia or lymphoma. There is no known cure and most die in their teens or early 20s.

Herrup says although this discovery does not address all of the related medical conditions associated with the disease, saving existing brain cells and restoring life-altering neurological functions would make a tremendous improvement in the lives of these children.

 “We can never replace cells that are lost,” said Herrup. “But what these mouse studies indicate is that we can take the cells that remain in the brains of these children and make them work better. This could improve the quality of life for these kids by unimaginable amounts.”

A-T families are cautiously excited by the news. The A-T Children’s Project facebook page notes “This is certainly hopeful news, and we look forward to the results from further studies.”

We certainly do. A cure cannot come soon enough.

Be Still My Beating Heart! – Monty Python and the Holy Grail

Look up the term myocardial infarction (MI) in any medical dictionary and the definition will be something along the lines of –  the changes to the myocardium (heart muscle) that occur due to the sudden deprivation of circulating blood. The main change being necrosis, or death of myocardial tissue. Death of myocardial tissue.  As in dead, as in non-viable, as in beyond repair. Kind of reminds me of the infamous Monty Python Dead Parrot sketch… “Passed on! No more! Ceased to be! Expired and gone to meet ‘is maker!”….but I digress.

Fast forward from the British humor of December 1969 to an astonishing paper presented in Britain in April 2012  at the Frontiers in CardioVascular Biology meeting. In a keynote lecture, Dr Deepak Srivastava outlined results that have been described as a “game changer” with the potential to revolutionize the treatment of MI.   Srivastava used viral vectors to deliver genes directly into the hearts of adult mice that had experienced an MI. In his original “proof of principle” study, Srivastava was able to show that all that was needed for the direct  reprogramming of fibroblasts (a major component of scar tissue) into myocytes (the heart muscle cells responsible for  beating)  was the delivery of three genes.  The work , which took place in a Petri dish, was considered groundbreaking since it showed for the first time that unrelated adult cells could be reprogrammed from one cell type to another without having to go all the way back to a stem cell state. “Our ultimate hope is that, during the acute period following MI, patients will be able to receive direct injections of factors that transform the existing fibroblast cells in the “scar” into new myocytes. The resulting increase in muscle mass should help MI survivors to live more normal lives,” explained Srivastava.

Healthy heart tissue is composed of a mixture of several kinds of cells, including cardiomyocytes, which provide beating muscle and cardiac fibroblasts that provide architectural support to the myocytes. “When heart muscle cells become injured and die following an MI, patients have the major problem that these cells have little or no capacity for regeneration,” says Srivastava.  Part of the process of remodelling that occurs following the injury is that fibroblast cells migrate to the site and create the scar. At first, the process can be considered beneficial since without fibroblasts adding structural support damaged hearts would rupture. But later, difficulties arise when the fibrotic scar doesn’t contract like the muscle it has replaced. “Reduced global contractility means the heart has to work much harder, and the extra stress can ultimately lead to heart failure and even death,” said Srivastava.

One of the Holy Grails of cardiovascular research has been to replace these lost myocytes and return functionality to the heart.  Some of the first approaches to be investigated were the introduction of stem or progenitor cells to the sites of injury.  But many hurdles have been encountered including getting cells to integrate with neighboring cells in the heart, and there have been concerns that residual “rogue” cells could persist with the potential to keep dividing and give rise to tumors.

Srivastava, a pediatric cardiologist, explained how he got ahead of the game by “leveraging” knowledge from his work in embryo hearts. Over the past 15 years the focus of Srivastava’s lab has been to identify genetic factors responsible for the formation of embryonic hearts. From this work, his team identified 14 key genes that they felt were the major “on/off” switches for cardiac genetic programming. In this original study they were able to whittle things down to the three factors that were indispensible. The team then injected fibroblasts that had the three genes inserted directly into the scar tissue of mice.  They were able to show the fibroblasts differentiated into cardiomyocyte-like cells. In the latest study  they were able to take the process one step further by injecting a viral vector encoding the  3 genes directly into the scar tissue of mice who had just experienced an MI. “With these studies we’ve obtained even better results showing that the fibroblasts become more like cardiomyocytes and functionally couple with their neighbors. They could beat in synchrony and improve the function of the heart,” said Srivastava.

The next step will be to test the direct injection approach in a larger animal, such as a pig, whose heart is similar in size to a human.  But a big question remains “will the same combination of genes work in human hearts?” SRxA’s Word on Health will be watching and waiting. In the meantime…it’s back to Monty Python!

Do DIY “spit kits” stress you out?

One of the fastest growing health care trends in “individualized medicine” is home genetic testing. The over-the-counter mail-in kits, with price tags as high as $2,500, use a saliva specimen to identify small variations in the human genome  associated with heightened risk for diseases such as diabetes and prostate cancer.

The U.S. Food and Drug Administration (FDA) has raised concerns about whether the tests are clinically beneficial and has advocated they be conducted under medical supervision, but few studies, to date, have investigated the emotional effects that direct-to-consumer genetic screens have on patients.

Now that’s all changed.  A group of Mayo Clinic physicians and bioethicists have analyzed whether these genetic tests cause patients to experience excessive worry about developing diseases. “We looked for evidence of increased concern about disease based solely on genetic risk, and then whether the concern resulted in changes in health habits,” said co-author Clayton Cowl, M.D.

The randomized study found patients’ worry tended to be modestly elevated one week after the genetic testing, and that people worried more about unfamiliar diseases, for instance the thyroid condition Graves’ disease than those commonly known, such as diabetes.

One year later, however, patients who had undergone testing were no more stressed than those who hadn’t. One surprising result was that men whose genetic risk for prostate cancer was found to be lower than that of the general population, and who also had normal laboratory and physical screening results for the disease, were significantly less stressed about the disease than the control group.

The researchers concluded that the tests may be useful if they prompt patients to make health-conscious changes, such as losing weight or being vigilant about cancer screening.

However, some doctors are concerned that patients who learn they have less-than-average genetic risk for a disease might skip steps to promote good health. Others just think it’s a bad idea – period.  “Genetic testing is a complex, difficult and emotionally laden medical process which requires extensive counseling, contextualization and interpretation,” says Dr. Michael Grodin, professor of bioethics, human rights, family medicine and psychiatry at Boston University.

It’s also worth noting that the current study only assessed the emotional effects of do-it-yourself genetic testing. Nobody yet knows whether a calculation of genetic risk accurately predicts disease.

Have you bought one of these kits?  How did you feel while you waited for the results. SRxA’s Word on Health would love to know.