A little bit of learned fear is a good thing, keeping us from making risky, stupid decisions or falling over and over again into the same trap. But new research from neuroscientists and molecular biologists at USC shows that a missing brain protein may be the culprit in cases of severe over-worry, where the fear perseveres even when there’s nothing of which to be afraid. In a study, researchers examined mice without the enzymes monoamine oxidase A and B (MAO A/B), which sit next to each other in a human’s genetic code as well as on that of mice.
Prior research has found an association between deficiencies of these enzymes in humans and developmental disabilities along the autism spectrum, such as clinical perseverance, the inability to change or modulate actions along with social context. ‘These mice may serve as an interesting model to develop interventions to these neuropsychiatric disorders,’ said University Professor and senior author Jean Shih, Boyd & Elsie Welin Professor of Pharmacology and Pharmaceutical Sciences at the USC School of Pharmacy and the Keck School of Medicine of USC. ‘The severity of the changes in the MAO A/B knockout mice compared to MAO A knockout mice supports the idea that the severity of autistic-like features may be correlated to the amounts of monoamine levels, particularly at early developmental stages.’
Shih is a world leader in understanding the neurobiological and biochemical mechanisms behind such behaviours as aggression and anxiety. In this latest study, Shih and her co-investigators — including lead author Chanpreet Singh, a USC doctoral student at the time of the research who is now at the California Institute of Technology (Caltech), and Richard Thompson, USC University Professor Emeritus and Keck Professor of Psychology and Biological Sciences at the USC Dornsife College of Letters, Arts and Sciences — expanded their past research on MAO A/B, which regulates neurotransmitters known as monoamines, including serotonin, norepinephrine and dopamine. Comparing mice without MAO A/B with their wild-type littermates, the researchers found significant differences in how the mice without MAO A/B processed fear and other types of learning. Mice without MAO A/B and wild mice were put in a new, neutral environment and given a mild electric shock. All mice showed learned fear the next time they were tested in the same environment, with the MAO A/B knockout mice displaying a greater degree of fear. But while wild mice continued to explore other new environments freely after the trauma, mice without the MAO A/B enzymes generalised their phobia to other contexts — their fear spilled over onto places where they should have no reason to be afraid. ‘The neural substrates processing fear in the brain is very different in these mice,’ Singh said. ‘Enhanced learning in the wrong context is a disorder and is exemplified by these mice. Their brain is not letting them forget. In a survival issue, you need to be able to forget things.’
The mice without MAO A and MAO B also learned eye-blink conditioning much more quickly than wild mice, which has also been noted in autistic patients but not in mice missing only one of these enzymes. Importantly, the mice without MAO A/B did not display any differences in learning for spatial skills and object recognition, the researchers found, ‘but in their ability to learn an emotional event, the [MAO A/B knockout mice] are very different than wild types,’ Singh said. He continued: ‘When both enzymes are missing, it significantly increases the levels of neurotransmitters, which causes developmental changes, which leads to differential expression of receptors that are very important for synaptic plasticity — a measure of learning — and to behavior that is quite similar to what we see along the autism spectrum.’ University of Southern California

Alzheimer’s disease has proven to be a difficult enemy to defeat. After all, ageing is the No. 1 risk factor for the disorder, and there’s no stopping that. Most researchers believe the disease is caused by one of two proteins, one called tau, the other beta-amyloid. As we age, most scientists say, these proteins either disrupt signalling between neurons or simply kill them.
Now, a new UCLA study suggests a third possible cause: iron accumulation. Dr. George Bartzokis, a professor of psychiatry at the Semel Institute for Neuroscience and Human Behavior at UCLA and senior author of the study, and his colleagues looked at two areas of the brain in patients with Alzheimer’s. They compared the hippocampus, which is known to be damaged early in the disease, and the thalamus, an area that is generally not affected until the late stages. Using sophisticated brain-imaging techniques, they found that iron is increased in the hippocampus and is associated with tissue damage in that area. But increased iron was not found in the thalamus.
While most Alzheimer’s researchers focus on the build-up of tau or beta-amyloid that results in the signature plaques associated with the disease, Bartzokis has long argued that the breakdown begins much further ‘upstream.’ The destruction of myelin, the fatty tissue that coats nerve fibres in the brain, he says, disrupts communication between neurons and promotes the build-up of the plaques. These amyloid plaques in turn destroy more and more myelin, disrupting brain signalling and leading to cell death and the classic clinical signs of Alzheimer’s.
Myelin is produced by cells called oligodendrocytes. These cells, along with myelin, have the highest levels of iron of any cells in the brain, Bartzokis says, and circumstantial evidence has long supported the possibility that brain iron levels might be a risk factor for age-related diseases like Alzheimer’s. Although iron is essential for cell function, too much of it can promote oxidative damage, to which the brain is especially vulnerable.
In the current study, Bartzokis and his colleagues tested their hypothesis that elevated tissue iron caused the tissue breakdown associated with Alzheimer’s disease. They targeted the vulnerable hippocampus, a key area of the brain involved in the formation of memories, and compared it to the thalamus, which is relatively spared by Alzheimer’s until the very late stages of disease.
The researchers used an MRI technique that can measure the amount of brain iron in ferritin, a protein that stores iron, in 31 patients with Alzheimer’s and 68 healthy control subjects.
In the presence of diseases like Alzheimer’s, as the structure of cells breaks down, the amount of water increases in the brain, which can mask the detection of iron, according to Bartzokis.
‘It is difficult to measure iron in tissue when the tissue is already damaged,’ he said. ‘But the MRI technology we used in this study allowed us to determine that the increase in iron is occurring together with the tissue damage. We found that the amount of iron is increased in the hippocampus and is associated with tissue damage in patients with Alzheimer’s but not in the healthy older individuals — or in the thalamus. So the results suggest that iron accumulation may indeed contribute to the cause of Alzheimer’s disease.’
But it’s not all bad news from this study, Bartzokis noted.
‘The accumulation of iron in the brain may be influenced by modifying environmental factors, such as how much red meat and iron dietary supplements we consume and, in women, having hysterectomies before menopause,’ he said.
In addition, he noted, medications that chelate and remove iron from tissue are being developed by several pharmaceutical companies as treatments for the disorder. This MRI technology may allow doctors to determine who is most in need of such treatments. University of California – Los Angeles

Scientists at the European Molecular Biology Laboratory (EMBL) in Heidelberg and Regensburg University, both in Germany, and the University of Lisboa, in Portugal, have discovered a promising potential drug target for cystic fibrosis. Their work also uncovers a large set of genes not previously linked to the disease, demonstrating how a new screening technique can help identify new drug targets.

Cystic fibrosis is a hereditary disease caused by mutations in a single gene called CFTR. These mutations cause problems in various organs, most notably making the lining of the lungs secrete unusually thick mucus. This leads to recurrent life-threatening lung infections, which make it increasingly hard for patients to breathe. The disease is estimated to affect 1 in every 2500-6000 new-borns in Europe.

In patients with cystic fibrosis, the mutations to CFTR render it unable to carry out its normal tasks. Among other things, this means CFTR loses the ability to control a protein called the epithelial sodium channel (ENaC). Released from CFTR’s control, ENaC becomes hyperactive, cells in the lungs absorb too much sodium and – as water follows the sodium – the mucus in patients’ airways becomes thicker and the lining of the lungs becomes dehydrated. The only drug currently available that directly counteracts a cystic fibrosis-related mutation only works on the three percent of patients that carry one specific mutation out of the almost 2000 CFTR mutations scientists have found so far.

Thus, if you were looking for a more efficient way to fight cystic fibrosis, finding a therapy that would act upon ENaC instead of trying to correct that multitude of CFTR mutations would seem like a good option. But unfortunately, the drugs that inhibit ENaC, mostly developed to treat hypertension, don’t transfer well to cystic fibrosis, where their effects don’t last very long. So scientists at EMBL, Regensburg University and University of Lisboa set out to find alternatives.

‘In our screen, we attempted to mimic a drug treatment,’ says Rainer Pepperkok, whose team at EMBL developed the technique, ‘we’d knock down a gene and see if ENaC became inhibited.’

Starting with a list of around 7000 genes, the scientists systematically silenced each one, using a combination of genetics and automated microscopy, and analysed how this affected ENaC. They found over 700 genes which, when inhibited, brought down ENaC activity, including a number of genes no-one knew were involved in the process. Among their findings was a gene called DGKi. When they tested chemicals that inhibit DGKi in lung cells from cystic fibrosis patients, the scientists discovered that it appears to be a very promising drug target.

‘Inhibiting DGKi seems to reverse the effects of cystic fibrosis, but not block ENaC completely,’ says Margarida Amaral from the University of Lisboa, ‘indeed, inhibiting DGKi reduces ENaC activity enough for cells to go back to normal, but not so much that they cause other problems, like pulmonary oedema.’

These promising results have already raised the interest of the pharmaceutical industry and led the researchers to patent DGKi as a drug target, as they are keen to explore the issue further, searching for molecules that strongly inhibit DGKi without causing side-effects.

‘Our results are encouraging, but these are still early days,’ says Karl Kunzelmann from Regensburg University. ‘We have DGKi in our cells because it is needed, so we need to be sure that these drugs are not going to cause problems in the rest of the body.’ EMBL

French scientists have discovered that supposedly rare mutations in the mitochondria, the ‘power plants’ of human cells responsible for creating energy, account for more than 7% of patients with a mitochondrial disease manifesting itself as a respiratory deficiency. Their data emphasise the need for comprehensive analysis of all the mitochondrial DNA (mtDNA) in patients suspected as having a mitochondrial disease, and this should include children, a researcher will tell the annual conference of the European Society of Human Genetics.
Dr. Sylvie Bannwarth and Professor Véronique Paquis, from the Hôpital Archet 2, Nice, France, together with colleagues from the ten diagnostic centres that make up the French Mitochondrial Disease Network, investigated 743 patients who were suspected of having a respiratory chain disorder caused by defective mitochondria, but who did not carry a common mtDNA mutation. Mitochondrial diseases, which can be very severe, are estimated to affect one child in every 5000, and are usually untreatable. However, prompt diagnosis can help clinicians to prescribe treatment to alleviate secondary symptoms.

‘We examined the relationship between clinical presentation of disease, age at onset, and the localisations of mutations. Our results showed that, in the French population, clinical presentations that are not associated with common mtDA mutations begin mainly before adulthood, and that neuromuscular problems are the most common manifestation of such mutations’, says Dr. Bannwarth.

‘We found that early onset disease was significantly associated with mutations in genes that code for proteins, while late onset disorder were associated with mutations in tRNA genes, and that two genes represent ‘hotspots’ for disease-causing mutations. Knowing the prevalence of these rare mutations is essential if we are to be able to improve the diagnosis of these diseases.’

There are very many mitochondrial diseases, and they manifest themselves in a large number of different ways. They can involve muscle weakness, neurological disease, respiratory, gastrointestinal and cardiac problems, and strokes. Many are degenerative, while some are relatively static.

One of the two techniques used for screening the entirety of an individual’s mtDNA was developed by Dr. Bannwarth. The use of such techniques can aid not just in diagnosis, but also in genetic counselling and prenatal diagnosis for mitochondrial disease. Up to now the study of mtDNA mutations has usually been restricted to the detection of deletions and a few common mutations, but without any data about the prevalence of rare mutations and their associated phenotypes (characteristics or traits).

‘With the advent of Next Generation Sequencing techniques, screening all mtDNA is now feasible, and this means that we can detect both common and rare mutations as well as deletions. For example, in the patients we studied we found that Leigh syndrome – a rare disorder that affects the central nervous system – was found in 41% of patients with rare mtDNA mutations. Had we not screened all of the mtDNA, including the rare mutations, we would not have known this’, says Dr. Bannwarth. ‘This is clearly a big aid to accurate diagnosis and we hope that our results will underline the importance of comprehensive mtDNA screening.’ EurekAlert