Archive for July 2009
Scientists at Burnham Institute for Medical Research (Burnham) have discovered that specific microRNAs (non-coding RNAs that interfere with gene expression) reduce HIV replication and infectivity in human T-cells. In particular, miR29 plays a key role in controlling the HIV life cycle. The study suggests that HIV may have co-opted this cellular defense mechanism to help the virus hide from the immune system and antiviral drugs.
Tariq Rana, Ph.D., director of the Program for RNA Biology at Burnham, and colleagues, found that the microRNA miR29 suppresses translation of the HIV-1 genome by transporting the HIV mRNA to processing-bodies (P-bodies), where they are stored or destroyed. This results in a reduction of viral replication and infectivity. The study also showed that inhibition of miR29 enhances viral replication and infectivity. The scientists further demonstrated that strains of HIV-1 with mutations in the region of the genome that interact with miR29 are not inhibited by miR29.
“We think the virus may use this mechanism to modulate its own lifecycle, and we may be able to use this to our advantage in developing new drugs for HIV,” said Dr. Rana. “Retroviral therapies greatly reduce viral load but cannot entirely eliminate it. This interaction between HIV and miR29 may contribute to that inability. Perhaps, by targeting miR29, we can force HIV into a more active state and improve our ability to eliminate it.”
Rana’s team looked at miR29 expression levels in infected and uninfected cells and found that miR29 expression was enhanced by HIV-1 infection. Blocking the activity of miR29 with interfering RNA resulted in increased replication and infectivity of the virus. The scientists tested the association of miR29 and HIV-1 by mutating both miR29 and its target region on the HIV virus. When either was altered, miR29s suppression of HIV replication and infectivity was reduced or eliminated.
In addition, the team suppressed P-bodies in the cells and noted a similar effect. This suggests that HIV may use miRNAs to become dormant and escape immune response.
Molecular Cell, Volume 34, Issue 6, 686-695, 26 June 2009
Cellular MicroRNA and P Bodies Modulate Host-HIV-1 Interactions p696
Robin Nathans 1,Chia-ying Chu 1,2, Anna Kristina Serquina 1,Chih-Chung Lu 1,2, Hong Cao 1 and Tariq M. Rana 1,2, Corresponding Authors,
1 Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, 364 Plantation Street, Worcester, MA 01605, USA
2 Program for RNA Biology, Sanford Children’s Health Research Center, Burnham Institute for Medical Research, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
MicroRNAs (miRNAs), 22 nt noncoding RNAs, assemble into RNA-induced silencing complexes (RISCs) and localize to cytoplasmic substructures called P bodies. Dictated by base-pair complementarity between miRNA and a target mRNA, miRNAs specifically repress posttranscriptional expression of several mRNAs. Here we report that HIV-1 mRNA interacts with RISC proteins and that disrupting P body structures enhances viral production and infectivity. In HIV-1-infected human T lymphocytes, we identified a highly abundant miRNA, miR-29a, which specifically targets the HIV-1 3UTR region. Inhibiting miR-29a enhanced HIV-1 viral production and infectivity, whereas expressing a miR-29 mimic suppressed viral replication. We also found that specific miR-29a-HIV-1 mRNA interactions enhance viral mRNA association with RISC and P bodyproteins. Thus we provide an example of a single host miRNA regulating HIV-1 production and infectivity. These studies highlight the significance of miRNAs and P bodies in modulating host cell interactionswith HIV-1 and possibly other viruses.
Fear is a powerful emotion, and neuroscientists have for the first time located the neurons responsible for fear conditioning in the mammalian brain. Fear conditioning is a form of Pavlovian, or associative, learning and is considered to be a model system for understanding human phobias, post-traumatic stress disorder and other anxiety disorders.
Using an imaging technique that enabled them to trace the process of neural activation in the brains of rats, University of Washington researchers have pinpointed the basolateral nucleus in the region of the brain called the of amygdala as the place where fear conditioning is encoded.
Neuroscientists previously suspected that both the amygdala and another brain region, the dorsal hippocampus, were where cues get associated when fear memories are formed. But the new work indicates that the role of the hippocampus is to process and transmit information about conditioned stimuli to the amygdala, said Ilene Bernstein, corresponding author of the new study and a UW professor of psychology.
The study is being published on July 6, in PLoS One, a journal of the Public Library of Science.
Associative conditioning is a basic form of learning across the animal kingdom and is regularly used in studying how brain circuits can change as a result of experience. In earlier research, UW neuroscientists looked at taste aversion, another associative learning behavior, and found that neurons critical to how people and animals learn from experience are located in the amygdala.
The new work was designed to look for where information about conditioned and unconditioned stimuli converges in the brain as fear memories are formed. The researchers used four groups of rats and placed individual rodents inside of a chamber for 30 minutes. Three of the groups had never seen the chamber before.
When control rats were placed in the chamber, they explored it, became less active and some fell asleep. A delayed shock group also explored the chamber, became less active and after 26 minutes received an electric shock through the floor of the chamber. The third group was acclimated to the chamber by a series of 10 prior visits and then went through the same procedure as the delayed shock rats. The final group was shocked immediately upon being introduced inside the chamber.
The following day the rats were individually returned to the chamber and the researchers observed them for freezing behavior. Freezing, or not moving, is the most common behavioral measure of fear in rodents. The only rats that exhibited robust freezing were those that received the delayed shock in a chamber which was unfamiliar to them.
“We didn’t know if we could delay the shock for 26 minutes and get a fear reaction after just one trial. I thought it would be impossible to do this with fear conditioning,” said Bernstein. “This allowed us to ask where information converged in the brain.”
To do this, the researchers repeated the procedure, but then killed the rats. They then took slices of the brains and used Arc catfish, an imaging technique, which allowed them to follow the pattern of neural activation in the animals.
Only the delayed shock group displayed evidence of converging activation from the conditioned stimulus (the chamber) and the unconditioned stimulus (the shock). The experiment showed that animals can acquire a long-term fear when a novel context is paired with a shock 26 minutes later, but not when a familiar context is matched with a shock.
“Fear learning and taste aversion learning are both examples of associative learning in which two experiences occur together. Often they are learned very rapidly because they are critical to survival, such as avoiding dangerous places or toxic foods,” said Bernstein.
“People have phobias that often are set off by cues from something bad that happened to them, such as being scared by a snake or being in a dark alley. So they develop an anxiety disorder,” she said.
“By understanding the process of fear conditioning we might learn how to treat anxiety by making the conditioning weaker or to go away. It is also a tool for learning about these brain cells and the underlying mechanism of fear conditioning.”
PLoS ONE 4(7): e6156. doi:10.1371/journal.pone.0006156
Amygdalar Neurons during Pavlovian Fear Conditioning. PLoS ONE 4(7): e6156.
Sabiha K. Barot1,2, Ain Chung2, Jeansok J. Kim1,2, Ilene L. Bernstein1,2*
1 Program in Neurobiology & Behavior, University of Washington, Seattle, Washington, United States of America, 2 Department of Psychology, University of Washington, Seattle, Washington, United States of America
Associative conditioning is a ubiquitous form of learning throughout the animal kingdom and fear conditioning is one of the most widely researched models for studying its neurobiological basis. Fear conditioning is also considered a model system for understanding phobias and anxiety disorders. A fundamental issue in fear conditioning regards the existence and location of neurons in the brain that receive convergent information about the conditioned stimulus (CS) and unconditioned stimulus (US) during the acquisition of conditioned fear memory. Convergent activation of neurons is generally viewed as a key event for fear learning, yet there has been almost no direct evidence of this critical event in the mammalian brain.
Here, we used Arc cellular compartmental analysis of temporal gene transcription by fluorescence in situ hybridization (catFISH) to identify neurons activated during single trial contextual fear conditioning in rats. To conform to temporal requirements of catFISH analysis we used a novel delayed contextual fear conditioning protocol which yields significant single- trial fear conditioning with temporal parameters amenable to catFISH analysis. Analysis yielded clear evidence that a population of BLA neurons receives convergent CS and US information at the time of the learning, that this only occurs when the CS-US arrangement is supportive of the learning, and that this process requires N-methyl-D-aspartate receptor activation. In contrast, CS-US convergence was not observed in dorsal hippocampus.
Based on the pattern of Arc activation seen in conditioning and control groups, we propose that a key requirement for CS-US convergence onto BLA neurons is the potentiation of US responding by prior exposure to a novel CS. Our results also support the view that contextual fear memories are encoded in the amygdala and that the role of dorsal hippocampus is to process and transmit contextual CS information.
In times of doubt and uncertainty, many Americans turn to self-help books in search of encouragement, guidance and self-affirmation. The positive self-statements suggested in these books, such as “I am a lovable person” or “I will succeed,” are designed to lift a person’s low self-esteem and push them into positive action.
According to a recent study in Psychological Science, however, these statements can actually have the opposite effect.
Psychologists Joanne V. Wood and John W. Lee from the University of Waterloo, and W.Q. Elaine Perunovic from the University of New Brunswick, found that individuals with low self-esteem actually felt worse about themselves after repeating positive self-statements.
The researchers asked participants with low self-esteem and high self-esteem to repeat the self-help book phrase “I am a lovable person.” The psychologists then measured the participants’ moods and their momentary feelings about themselves. As it turned out, the individuals with low self-esteem felt worse after repeating the positive self-statement compared to another low self-esteem group who did not repeat the self-statement. The individuals with high self-esteem felt better after repeating the positive self-statement–but only slightly.
In a follow-up study, the psychologists allowed the participants to list negative self-thoughts along with positive self-thoughts. They found that, paradoxically, low self-esteem participants’ moods fared better when they were allowed to have negative thoughts than when they were asked to focus exclusively on affirmative thoughts.
The psychologists suggested that, like overly positive praise, unreasonably positive self-statements, such as “I accept myself completely,” can provoke contradictory thoughts in individuals with low self-esteem. Such negative thoughts can overwhelm the positive thoughts. And, if people are instructed to focus exclusively on positive thoughts, they may find negative thoughts to be especially discouraging.
As the authors concluded, “Repeating positive self-statements may benefit certain people [such as individuals with high self-esteem] but backfire for the very people who need them the most.”
Psychological Science, 2009; DOI: 10.1111/j.1467-9280.2009.02370.x
Positive Self-Statements: Power for Some, Peril for Others.
Joanne V. Wood, W.Q. Elaine Perunovic, and John W. Lee
ABSTRACT—Positive self-statements are widely believed to boost mood and self-esteem, yet their effectiveness has not been demonstrated. We examined the contrary prediction that positive self-statements can be ineffective or even harmful. A survey study confirmed that people often use positive self-statements and believe them to be effective. Two experiments showed that among participants with low self-esteem, those who repeated a positive self-statement (“I’m a lovable person”) or who focused on how that statement was true felt worse than those who did not repeat the statement or who focused on how it was both true and not true. Among participants with high self-esteem, those who repeated the statement or focused on how it was true felt better than those who did not, but to a limited degree. Repeating positive self-statements may benefit certain people, but backfire for the very people who “need” them the most.