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Attention deficit hyperactivity disorder (ADHD) has been linked to alterations in the production, release and signaling of the neurotransmitter dopamine. Genetic changes that support these alterations, however, have been difficult to associate with specific molecular insults.

Now, Randy Blakely, Allan D. Bass Chair in Pharmacology, and colleagues have identified a novel coding variant in a 13-year-old boy with ADHD that prevents the dopamine transporter, a protein involved in inactivating dopamine at synapses, from carrying out its normal function. In essence, the transporter doesn’t go to the correct location on the nerve cell surface, and therefore doesn’t respond to normal regulatory signals, the researchers reported in the April 18 issue of the Journal of Neuroscience. Although the genetic change is rare, it points to a regulatory network where changes may individually or collectively make a much larger contribution to ADHD risk.

This is the second functional dopamine transporter alteration identified by the Blakely group in subjects with ADHD, adding support to the idea that altered dopamine signaling is a key risk factor for the disorder.

The research was supported by National Institutes of Health grants from the National Institute of Mental Health, the National Heart, Lung and Blood Institute, and the National Institute on Drug Abuse, and by the National Science Foundation.

The findings, featured on the cover of the April 10 issue of Current Biology, represent a new mechanism for defending the body against gut microbes.

The surfaces of intestinal epithelial cells are covered by microvilli – specialized structures that project, like thousands of tiny fingers, into the lumen of the gut. The “textbook” view of the microvilli is that they increase the cellular surface area for absorbing and processing nutrients, said Matthew Tyska, associate professor of cell and developmental biology.

“Our studies suggest a new function for the microvilli in regulating epithelial-microbial interactions,” he said.

Matt Tyska, left, David Shifrin and colleagues are investigating how epithelial cells defend against gut microbes. (Joe Howell / Vanderbilt University)

Tyska and his colleagues had previously demonstrated that the microvilli launch vesicles – tiny bubble-like packets of cell membrane – into the lumen, and that these vesicles contain high levels of an enzyme called intestinal alkaline phosphatase (IAP). Because IAP reduces the toxicity of bacterial products and limits their pro-inflammatory signaling, the investigators suspected that the vesicles might protect against bacteria and other pro-inflammatory compounds.

They show in the current studies that IAP in vesicles isolated from rat intestines is able to detoxify bacterial products from multiple types of bacteria. Using electron microscopy, they also observed that the vesicles “pile up” on the surface of bacteria, which may facilitate their clearance from the gut.

To study how the vesicles affect bacterial function, they incubated cultures of human intestinal epithelial cells with enteropathogenic E. coli (EPEC) in the presence or absence of vesicles. EPEC is a type of “adherent pathogenic bacteria” that gets introduced to the lumen when someone eats contaminated meat, for example, Tyska said. EPEC tries to bind to the microvilli, inject its products into the cell and destroy the brush border (the layer of densely packed microvilli).

Immunofluorescent image showing enteropathogenic E. coli bacteria adhered to the surface of intestinal epithelial cells in culture. The bacteria hijack epithelial cell machinery to form actin pedestals (red) in order to maintain attachment, and they are surrounded by host cell membrane enriched in the protein intestinal alkaline phosphatase (green). The nuclei of intestinal epithelial cells are stained with a DNA dye (blue).

“Bugs that destroy the brush border are bad news; you cannot survive without microvilli,” Tyska said. “EPEC is a major human health problem, especially in developing countries.”

To the researchers’ surprise, the vesicles were able to prevent EPEC from binding to and destroying the microvilli.

“Anything that can keep adherent pathogenic bacteria off of host cells and in the lumen is pretty exciting,” Tyska said.

Not only did the vesicles act as decoys for EPEC binding, they inhibited bacterial growth and even killed bacterial cells, the investigators found. In addition, adding EPEC to the cultured cells stimulated expression of IAP and vesicle production.

“Our findings are consistent with the production of these vesicles being a regulated host defense process,” Tyska said. “When cells sense the accumulation of bacteria or bacterial toxins in their environment, they respond by cranking up alkaline phosphatase levels and vesicle production.

“Because trillions of microvilli extend into the lumen, this is going to be a very effective way of quickly conditioning the lumen against bacterial pathogens,” he said.

The investigators are currently studying the process in mice that have deficiencies in vesicle production. They expect to see chronic inflammation, changes in the microbiome (the bacterial species that normally inhabit the gut), and “other changes that push them away from normal physiology,” Tyska said. They also plan to use live tissue imaging to follow where the vesicles go in the gut lumen.

The study was featured on the journal cover. (Shifrin et al., Current Biology 22(7))

The research, which began with Tyska’s interest in a motor protein that is enriched in microvilli, “is, I think, a great example of how doing fundamental research on molecules can lead to new insights about physiology and pathophysiology,” he said.

Contributors to the current studies include first author David Shifrin, Russell McConnell, Ph.D., Rajalakshmi Nambiar, Ph.D., James Higginbotham, Ph.D., and Robert Coffey, M.D. The research was supported by National Institutes of Health grants from the National Institute of Diabetes and Digestive and Kidney Diseases and the National Cancer Institute, by grants from the American Heart Association and by a Vanderbilt University Innovation and Discovery in Engineering and Science Award.

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Previously, medical student Albert Powers III, Mark Wallace, professor of hearing and speech sciences, and colleagues showed that the window could be significantly narrowed by a computer-based perceptual training program.

In the May 2 Journal of Neuroscience, the investigators provide the first look at the brain regions involved in these changes. They found that the posterior superior temporal sulcus (where visual and auditory information comes together) and parts of auditory and visual cortex showed decreased activity on fMRI after training. Additionally, the perceptual training program enhanced the coupling among these regions.

Because abnormalities in multisensory processing may contribute to disorders such as autism, dyslexia and schizophrenia, this information could inform diagnostic strategies and interventions for these disabilities.

The research was supported by the Vanderbilt Kennedy Center and grants from National Institute for Child Health and Development and the National Institute for Deafness and Communication Disorders of the National Institutes of Health.

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The mutation – in the gamma-2 subunit of the GABA-A receptor – was identified in an Australian family with childhood absence epilepsy and febrile seizures. The researchers expressed normal or mutated gamma-2 subunits in cultured cells and transgenic mice. They report in the April 25 Journal of Neuroscience that the mutation altered how the gamma subunit was spliced, resulting in a mutant mRNA that was either degraded or translated into a stable, but shortened, form of the protein.

The study suggests that the mutation reduces surface GABA-A receptor levels, which would reduce the receptor’s ability to “quiet” excited neuronal chatter and make the brain more susceptible to epilepsy. The findings could offer new directions for targeted epilepsy therapies.

This research was supported by a National Institutes of Health grant from the National Institute of Neurological Disorders and Stroke and by a fellowship from the Epilepsy Foundation.

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The researchers identified patients who underwent an upper GI scope because of gastroesophageal reflux (GERD) or functional dyspepsia (indigestion) between five and 15 years ago. About 100 of the former pediatric patients along with 143 healthy controls were asked to self-report on current stomach troubles, anxiety, quality of life and depression.

Adolescents and adults who had stomach problems in childhood had about double the rate of anxiety as those who did not, indicating an association between pediatric dyspepsia and anxiety the researchers characterize as “strong.” Increased risk of anxiety applied equally to those with normal esophageal histology and those with histologic esophagitis in childhood.

The results, published in the April issue of Gastroenterology, suggest that evaluation of psychological functioning should be considered as an integral part of the medical evaluation for dyspeptic symptoms.

The research was supported by grants from the National Institute of Child Health and Human Development, the National Institute of Diabetes and Digestive and Kidney Diseases and the National Center for Research Resources of the National Institutes of Health.

Reid Thompson talks with Lola Chambless in the neurosurgery OR. (Anne Rayner/VUMC)

The May program for My Health Chat will be the fascinating field of neuroscience.

Panelists will be Reid Thompson, chair of neurosurgery and director of the Vanderbilt Brain Tumor Center, and Jeff Conn, who directs the Vanderbilt Center for Neuroscience Drug Discovery.

Jeffrey Conn (Vanderbilt)

Topics will range from the latest innovative approaches in neurosurgery to the development of new targeted drugs and the promise of personalized medicine for such diseases as brain cancer, schizophrenia, Parkinson’s disease, Alzheimer’s and depression.

Jim Jirjis (Vanderbilt)

Hosted by Vanderbilt University Medical Center and moderated by Jim Jirjis, these 30-minute live interactive video chats offer the public a chance to hear from and ask questions of scientists and physicians on the leading edge of advances in medicine.

The event will be streamed live from 2 to 2:30 p.m. CST May 16 on Facebook and at MyHealthChat.com. Visit MyHealthChat.com to register.

Questions may be submitted live during the chat or in advance by:

• Posting them on Vanderbilt Health’s Facebook page
• Sending them on Twitter to @VUMCHealth or with #MyHealthChat
• Emailing them to connect@vanderbilt.edu.

The chats are archived at MyHealthChat.com for future viewing. Past topics include advances in heart disease, cancer, pediatrics and developmental disabilities; autism; the future of personalized medicine; and cancer drug discovery. June’s topic will be “Advances in Diabetes Research.”

Contact: Cynthia Manley, (615) 936-5711
cynthia.manley@vanderbilt.edu

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Nancy Brown, Hugh J. Morgan Chair in Medicine, and colleagues compared the effects of nebivolol, a third-generation beta-blocker, and metoprolol on glucose balance and markers of fibrinolysis in 46 subjects with metabolic syndrome. They found that the two medicines equivalently reduced blood pressure and heart rate. Metoprolol decreased insulin sensitivity and increased oxidative stress and markers of impaired fibrinolysis, whereas nebivolol lacked these detrimental metabolic effects.

The findings, reported in the April issue of Hypertension, suggest that nebivolol may be preferable for treating hypertension in obese patients with metabolic syndrome. Large-scale clinical trials are needed to fully compare the effects of nebivolol and metoprolol on clinical outcomes in such patients.

This research was supported by a grant from Forest Laboratories, Inc. and by funding through National Institutes of Health grants from the National Heart, Lung and Blood Institute (HL060906) and the National Center for Research Resources (RR024975).

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The investigators discovered that human antibodies reacted in a much weaker way than expected against proteins isolated from the virus (often used as a “subunit vaccine”) compared with the reaction to a whole virus particle. The human antibodies seemed to need the whole virus to work well. Using mapping techniques, the researchers found that a key binding site the best human antibodies use to neutralize dengue virus is a complex, bridged combination of two proteins on the virus’s envelope.

This information, published recently in the Proceedings of the National Academy of Sciences, may help speed development of an effective vaccine or treatment for dengue fever.

The research was supported by a grant from the National Institute of Allergy and Infectious Diseases (AI057157) of the National Institutes of Health.

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Therapies targeted to a specific mutation in the BRAF gene can significantly reduce tumor burden in metastatic melanoma. But these therapies are not suitable for melanomas lacking the mutation, and even tumors carrying the BRAF mutation eventually become resistant to those therapies.

Using human melanoma tumors implanted into mice, Ann Richmond, professor of cancer biology and medicine, and colleagues assessed the effectiveness of an experimental drug (RAF265) that inhibits a broader set of cellular enzymes than the BRAF-targeted drugs.

They found that 71 percent of tumors responding to the drug had the “normal” (wild-type) BRAF; only 29 percent of responding tumors carried the BRAF mutation. Additionally, responsive tumors showed increased expression of genes involved with a number of cellular pathways involving cell growth and cancer development.

The findings, reported in the April 15 Clinical Cancer Research, suggest that RAF265 may be beneficial for patients not eligible for BRAF-targeted therapies and that gene expression profiling may be useful for selecting patients for RAF265 therapy.

The research was supported by grants from the National Cancer Institute (CA68485) of the National Institutes of Health and the T.J. Martell Foundation.

(Wellcome Images)

Smith-Lemli-Opitz syndrome (SLOS) is a developmental disorder caused by mutations in the gene encoding the last enzyme in the cholesterol biosynthetic pathway. The mutations result in reduced levels of cholesterol and accumulation of the precursor 7-DHC, which can be oxidized in free radical-mediated reactions to oxysterols such as DHCEO.

Zeljka Korade, Ph.D., Ned Porter, Ph.D., and colleagues explored the consequences of 7-DHC and DHCEO accumulation in the brain tissue of a mouse model for SLOS. They found that cholesterol, 7-DHC and DHCEO have region-specific distributions in the brain, suggesting that the midbrain and cortex are the primary sites of vulnerability. They also showed that an oxysterol mixture is toxic to neurons and that DHCEO alone accelerates differentiation and changes the growth pattern of cortical neurons.

The findings, reported in the March issue of Neurobiology of Disease, suggest that 7-DHC oxidative metabolites contribute to altered neural development in SLOS. The results imply that using antioxidants to reduce oxidative stress may be a beneficial treatment for SLOS.

This research was supported by grants from the National Institute of Mental Health, the National Institute of Environmental Health Sciences, and the National Institute of Child Health and Human Development of the National Institutes of Health.

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Delirium – incoherence of thought and inattention – in intensive care unit (ICU) patients is associated with increased length of hospital stay, mortality and long-term cognitive impairment. Despite its high prevalence, the pathophysiology is unclear.

Pratik Pandharipande, M.D., Jessica Adams Wilson, M.D., and colleagues previously demonstrated that plasma tryptophan levels were associated with delirium in ICU patients. Tryptophan – a precursor for the neurotransmitter serotonin – can be metabolized through an alternate kynurenine pathway, and an imbalance in beneficial and neurotoxic kynurenine metabolites was hypothesized to be associated with delirium. The investigators studied plasma kynurenine and tryptophan levels in 84 ICU patients. They report in the March issue of Critical Care Medicine that elevated plasma kynurenine and kynurenine/tryptophan ratios were both associated with fewer days free of delirium/coma, after adjusting for sedative exposure, age and severity of illness.

The findings demonstrate that increased kynurenine pathway activation is associated with longer duration of acute brain dysfunction. The kynurenine pathway could be a therapeutic target for reducing delirium/coma in ICU patients.

This research was supported by the National Institute on Aging of the National Institutes of Health, by the Veterans Affairs Clinical Science Research and Development Service, and by the Veterans Affairs Tennessee Valley Geriatric Research, Education and Clinical Center.

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Diseases that are treatable in developed nations are often lethal in developing countries. For Wilms’ tumor, the most common childhood kidney cancer, survival rates in developed countries exceed 90 percent – but in developing nations, survival can be as low as 35 percent.

Lack of adequate health care resources is largely responsible for this survival disparity, but Andrew Murphy, M.D., Jason Axt, M.D., and colleagues suspected that biological factors may also contribute. The researchers assessed various cellular and molecular features in tumor samples from 15 Kenyan children and compared the results to those from North American Wilms’ tumor samples.

They report in the International Journal of Cancer that Kenyan Wilms’ tumors exhibit a predominance of immature cells (a feature of aggressiveness), cellular features of treatment resistance, and a molecular signature distinct from that of North American tumors.

The results suggest that these biological features may contribute to the poor outcomes in developing countries and that such tumors may require different treatment approaches than those of developed nations.

The research was funded by grants from the National Center for Research Resources and the National Cancer Institute of the National Institutes of Health, and the Department of Defense.