Changes in brain chemistry sustain obesity

With obesity reaching epidemic levels in some parts of the world, scientists have only begun to understand why it is such a persistent condition. A study in the Journal of Biological Chemistry adds substantially to the story by reporting the discovery of a molecular chain of events in the brains of obese rats that undermined their ability to suppress appetite and to increase calorie burning.

It’s a vicious cycle, involving a breakdown in how brain cells process key proteins, that allows obesity to beget further obesity. But in a finding that might prove encouraging in the long term, the researchers at Brown University and Lifespan also found that they could intervene to break that cycle by fixing the core protein-processing problem.

Before the study, scientists knew that one mechanism in which obesity perpetuates itself was by causing resistance to leptin, a hormone that signals the brain about the status of fat in the body. But years ago senior author Eduardo A. Nillni, professor of medicine at Brown University and a researcher at Rhode Island Hospital, observed that after meals obese rats had a dearth of another key hormone — alpha-MSH — compared to rats of normal weight.

Alpha-MSH has two jobs in parts of the hypothalamus region of the brain. One is to suppress the activity of food-seeking brain cells. The second is to signal other brain cells to produce the hormone TRH, which prompts the thyroid gland to spur calorie burning activity in the body.

In the obese rats alpha-MSH was low, despite an abundance of leptin and despite normal levels of gene expression both for its biochemical precursor protein called pro-opiomelanocortin (POMC) and for a key enzyme called PC2 that processes POMC in brain cells. There had to be more to the story than just leptin, and it wasn’t a problem with expressing the needed genes.

Nillni and his co-authors, including lead authors Isin Cakir and Nicole Cyr, conducted the new study to find out where the alpha-MSH deficit was coming from. Nillni said he suspected that the problem might lie in the brain cells’ mechanism for processing the POMC protein to make alpha-MSH.

Protein processing problems

To do their work, the team fed some rats a high-calorie diet and fed others a normal diet for 12 weeks. The overfed rats developed the condition of “diet-induced obesity.” The team then studied the hormone levels and brain cell physiology of the rats. They also tested their findings by experimenting with the biochemistry of key individual cells on the lab bench.

They found that in the obese rats, a key “machine” in the brain cells’ assembly line of protein-making, called the endoplasmic reticulum (ER), becomes stressed and overwhelmed. The overloaded ER apparently fumbles the proper handling of PC2, perhaps discarding it because it can’t be folded up properly. The PC2 levels they measured in obese rats, for example, were 53 percent lower than in normal rats. Alpha-MSH peptides were also barely more than half as abundant in obese rats as they were in healthy rats.

“In our study we showed that what actually prevents the production of more alpha-MSH peptide is that ER stress was decreasing the biosynthesis of POMC by affecting one key enzyme that is essential for the formation of alpha-MSH,” Nillni said. “This is so novel. Nobody ever looked at that.”

Novel as it was, the story — a stressed ER mishandles PC2, which leaves POMC unfolded, which impedes alpha-MSH production — needed experimental confirmation.

The team provided that confirmation in several ways: In obese rats they measured elevated levels of known markers of ER stress. They also purposely induced ER stress in cells using pharmacological agents and saw that both PC2 and Alpha-MSH levels dropped.

Next they conducted an experiment to see if fixing ER stress would improve alpha-MSH production. They treated lean and obese rats for two days with a chemical called TUDCA, which is known to alleviate ER stress. If ER stress is responsible for alpha-MSH production problems, the researchers would see alpha-MSH recover in obese rats treated with TUDCA. Sure enough, while TUDCA didn’t increase alpha-MSH production in normal rats, it increased it markedly in the obese rats.

Similarly on the benchtop they took mouse neurons that produce PC2 and POMC and pretreated some with a similar chemical called PBA that prevents ER stress. They left others untreated. Then they induced ER stress in all the cells. Under that ER stress, those that had been pretreated with PBA produced about twice as much PC2 as those that had not.

Nillni cautioned that although his team found ways to restore PC2 and alpha-MSH by treating ER stress in living rats and individual cells, the agents used in the study are not readily applicable as medicines for treating obesity in humans. There could well be unknown and unwanted side effects, for example, and TUDCA is not approved for human use by the U.S. Food and Drug Administration.

But by laying out the exact mechanism responsible for why the brains of the obese rats failed to curb appetite or spur greater calorie burning, Nillni said, the study points drug makers to several opportunities where they can intervene to break this new, vicious cycle that helps obesity to perpetuate itself.

“Understanding the central control of energy-regulating neuropeptides during diet-induced obesity is important for the identification of therapeutic targets to prevent and or mitigate obesity pathology,” the authors wrote.

Research Reveals Possible Reason for Cholesterol-Drug Side Effects

The U.S. Food and Drug Administration and physicians continue to document that some patients experience fuzzy thinking and memory loss while taking statins, a class of global top-selling cholesterol-lowering drugs. 

A University of Arizona research team has made a novel discovery in brain cells being treated with statin drugs: unusual swellings within neurons, which the team has termed the “beads-on-a-string” effect.

The team is not entirely sure why the beads form, said UA neuroscientist Linda L. Restifo, who leads the investigation. However, the team believes that further investigation of the beads will help inform why some people experience cognitive declines while taking statins.

"What we think we’ve found is a laboratory demonstration of a problem in the neuron that is a more severe version for what is happening in some peoples’ brains when they take statins," said Restifo, a UA professor of neuroscience, neurology and cellular and molecular medicine, and principal investigator on the project.

Restifo and her team’s co-authored study and findings recently were published in Disease Models & Mechanisms, a peer-reviewed journal. Robert Kraft, a former research associate in the department of neuroscience, is lead author on the article.

Restifo and Kraft cite clinical reports noting that statin users often are told by physicians that cognitive disturbances experienced while taking statins were likely due to aging or other effects. However, the UA team’s research offers additional evidence that the cause for such declines in cognition is likely due to a negative response to statins.

The team also has found that removing statins results in a disappearance of the beads-on-a-string, and also a restoration of normal growth.

With research continuing, the UA team intends to investigate how genetics may be involved in the bead formation and, thus, could cause hypersensitivity to the drugs in people. Team members believe that genetic differences could involve neurons directly, or the statin interaction with the blood-brain barrier.

"This is a great first step on the road toward more personalized medication and therapy," said David M. Labiner, who heads the UA department of neurology. "If we can figure out a way to identify patients who will have certain side effects, we can improve therapeutic outcomes."

For now, the UA team has multiple external grants pending, and researchers carry the hope that future research will greatly inform the medical community and patients.

"If we are able to do genetic studies, the goal will be to come up with a predictive test so that a patient with high cholesterol could be tested first to determine whether they have a sensitivity to statins," Restifo said.

Detecting, Understanding a Drugs’ Side Effects

Restifo used the analogy of traffic to explain what she and her colleagues theorize. 

The beads indicate a sort of traffic jam, she described. In the presence of statins, neurons undergo a “dramatic change in their morphology,” said Restifo, also a BIO5 Institute member.

"Those very, very dramatic and obvious swellings are inside the neurons and act like a traffic pileup that is so bad that it disrupts the function of the neurons," she said.

It was Kraft’s observations that led to team’s novel discovery.

Restifo, Kraft and their colleagues had long been investigating mutations in genes, largely for the benefit of advancing discoveries toward the improved treatment of autism and other cognitive disorders.

At the time, and using a blind-screened library of 1,040 drug compounds, the team ran tests on fruit fly neurons, investigating the reduction of defects caused by a mutation when neurons were exposed to different drugs.

The team had shown that one mutation caused the neuron branches to be curly instead of straight, but certain drugs corrected this. The research findings were published in 2006 in the Journal of Neuroscience.

Then, something serendipitous occurred: Kraft observed that one compound, then another and then two more all created the same reaction – “these bulges, which we called beads-on-a-string,’” Kraft said. “And they were the only drugs causing this effect.”

At the end of the earlier investigation, the team decoded the library and found that the four compounds that resulted in the beads-on-a-string were, in fact, statins.

"The ‘beads’ effect of the statins was like a bonus prize from the earlier experiment," Restifo said. "It was so striking, we couldn’t ignore it."

In addition to detecting the beads effect, the team came upon yet another major finding: when statins are removed, the beads-on-a-string effect disappears, offering great promise to those being treated with the drugs.

"For some patients, just as much as statins work to save their lives, they can cause impairments," said Monica Chaung, who has been part of the team and is a UA undergraduate researcher studying molecular and cellular biology and physiology.

"It’s not a one drug fits all," said Chaung, a UA junior who is also in the Honors College. "We suspect different gene mutations alter how people respond to statins."

Having been trained by Kraft in techniques to investigate cultured neurons, Chuang was testing gene mutations and found variation in sensitivity to statins. It was through the work of Chuang and Kraft that the team would later determine that, after removing the statins, the cells were able to repair themselves; the neurotoxicity was not permanent, Restifo said.

"In the clinical literature, you can read reports on fuzzy thinking, which stops when a patient stops taking statins. So, that was a very important demonstration of a parallel between the clinical reports and the laboratory phenomena," Restifo said.

The finding led the team to further investigate the neurotoxicity of statins.

"There is no question that these are very important and very useful drugs," Restifo said. Statins have been shown to lower cholesterol and prevent heart attacks and strokes.

But too much remains unknown about how the drugs’ effects may contribute to muscular, cognitive and behavioral changes.

"We don’t know the implications of the beads, but we have a number of hypotheses to test," Restifo said, adding that further studies should reveal exactly what happens when the transportation system within neurons is disrupted.

Also, given the move toward prescribing statins to children, the need to have an expanded understanding of the effects of statins on cognitive development is critical, Kraft said.

"If statins have an effect on how the nervous system matures, that could be devastating," Kraft said. "Memory loss or any sort of disruption of your memory and cognition can have quite severe effects and negative consequences."

Restifo and her colleagues have multiple grants pending that would enable the team to continue investigating several facets related to the neurotoxicity of statins. Among the major questions is, to what extent does genetics contribute to a person’s sensitivity to statins?

"We have no idea who is at risk. That makes us think that we can use this genetic laboratory assay to infer which of the genes make people susceptible," Restifo said.

"This dramatic change in the morphology of the neurons is something we can now use to ask questions and experiment in the laboratory," she said. "Our contribution is to find a way to ask about genetics and what the genetic vulnerability factors are."

The Possibility for Future Research, Advice

The team’s findings and future research could have important implications for the medical field and for patients with regard to treatment, communication and improved personalized medicine.

"It’s important to look into this to see if people may have some sort of predisposition to the beads effect, and that’s where we want to go with this research," Kraft said. "There must be more research into what effects these drugs have other than just controlling a person’s elevated cholesterol levels."

And even as additional research is ongoing, suggestions already exist for physicians, patients and families.

"Most physicians assume that if a patient doesn’t report side effects, there are no side effects," Labiner said.

"The paternalistic days of medication are hopefully behind us. They should be," Labiner said.

"We can treat lots of things, but the problem is if there are side effects that worsen the treatment, the patient is more likely to shy away from the medication. That’s a bad outcome," he said. "There’s got to be a give and take between the patient and physician."

Patients should feel empowered to ask questions, and deeper questions, about their health and treatment and physicians should be very attentive to any reports of cognitive decline for those patients on statins, she said.

For some, it starts early after starting statins; for others, it takes time. And the signs vary. People may begin losing track of dates, the time or their keys.

"These are not trivial things. This could have a significant impact on your daily life, your interpersonal relationships, your ability to hold a job," Restifo said.

"This is the part of the brain that allows us to think clearly, to plan, to hold onto memories," she said. "If people are concerned that they are having this problem, patients should ask their physicians."

Restifo said open and direct patient-physician communication is even more important for those on statins who have a family history of side effects from statins.

Also, physicians could work more closely with patients to investigate family history and determine a better dosage plan. Even placing additional questions on the family history questionnaire could be useful, she said.

"There is good clinical data that every-other-day dosing give you most of the benefits, and maybe even prevents some of the accumulation of things that result in side effects," Restifo said, suggesting that physicians should try and get a better longitudinal picture on how people react while on statins. 

"Statins have been around now for long enough and are widely prescribed to so many people," she said. "But increased awareness could be very helpful."

Experience leads to the growth of new brain cells

A new study examines how individuality develops

The DFG-Center for Regenerative Therapies Dresden - Cluster of Excellence at the TU Dresden (CRTD), the Dresden site of the German Center for Neurodegenerative Diseases (DZNE), and the Max Planck Institute for Human Development in Berlin played a pivotal role in the study.

The adult brain continues to grow with the challenges that it faces; its changes are linked to the development of personality and behavior. But what is the link between individual experience and brain structure? Why do identical twins not resemble each other perfectly even when they grew up together? To shed light on these questions, the scientists observed forty genetically identical mice that were kept in an enclosure offering a large variety of activity and exploration options.

"The animals were not only genetically identical, they were also living in the same environment," explains principal investigator Gerd Kempermann, Professor for Genomics of Regeneration, CRTD, and Site Speaker of the DZNE in Dresden. "However, this environment was so rich that each mouse gathered its own individual experiences in it. Over time, the animals therefore increasingly differed in their realm of experience and behavior."

New neurons for individualized brains

Each of the mice was equipped with a special micro-chip emitting electromagnetic signals. This allowed the scientists to construct the mice’s movement profiles and to quantify their exploratory behavior. The result: Despite a common environment and identical genes the mice showed highly individualized behavioral patterns. They reacted to their environment differently. In the course of the three-month experiment these differences increased in size.

"Though the animals shared the same life space, they increasingly differed in their activity levels. These differences were associated with differences in the generation of new neurons in the hippocampus, a region of the brain that supports learning and memory," says Kempermann. "Animals that explored the environment to a greater degree also grew more new neurons than animals that were more passive."

Adult neurogenesis, that is, the generation of new neurons in the hippocampus, allows the brain to react to new information flexibly. With this study, the authors show for the first time that personal experiences and ensuing behavior contribute to the „individualization of the brain.” The individualization they observed cannot be reduced to differences in environment or genetic makeup.

"Adult neurogenesis also occurs in the hippocampus of humans," says Kempermann. "Hence we assume that we have tracked down a neurobiological foundation for individuality that also applies to humans."

Impulses for discussion across disciplines

"The finding that behavior and experience contribute to differences between individuals has implications for debates in psychology, education science, biology, and medicine," states Prof. Ulman Lindenberger, Director of the Center for Lifespan Psychology at the Max Planck Institute for Human Development (MPIB) in Berlin. "Our findings show that development itself contributes to differences in adult behavior. This is what many have assumed, but now there is direct neurobiological evidence in support of this claim. Our results suggest that experience influences the aging of the human mind."

In the study, a control group of animals housed in a relatively unattractive enclosure was also examined; on average, neurogenesis in these animals was lower than in the experimental mice. „When viewed from educational and psychological perspectives, the results of our experiment suggest that an enriched environment fosters the development of individuality,” comments Lindenberger.

Interdisciplinary teamwork

The study is also an example of multidisciplinary cooperation — it was made possible because neuroscientists, ethologists, computer scientists, and developmental psychologists collaborated closely in designing the experimental set-up and applying new data analysis methods. Biologist Julia Freund from the CRTD Dresden and computer scientist Dr. Andreas Brandmaier from the MPIB in Berlin share first authorship on the article. In addition to the DZNE, CRTD, and the MPIB, the German Research Center for Artificial Intelligence in Saarbrücken and the Institute for Geoinformatics and the Department of Behavioural Biology at the University of Münster were also involved in this project.

Original publication

"Emergence of Individuality in Genetically Identical Mice", Julia Freund, Andreas M. Brandmaier, Lars Lewejohann, Imke Kirste, Mareike Kritzler, Antonio Krüger, Norbert Sachser, Ulman Lindenberger, Gerd Kempermann, Science

(Image: Dr Jonathan Clarke, Wellcome Images)

Study shows that individual brain cells track where we are and how we move

Leaving the house in the morning may seem simple, but with every move we make, our brains are working feverishly to create maps of the outside world that allow us to navigate and to remember where we are.

Take one step out the front door, and an individual brain cell fires. Pass by your rose bush on the way to the car, another specific neuron fires. And so it goes. Ultimately, the brain constructs its own pinpoint geographical chart that is far more precise than anything you’d find on Google Maps.

But just how neurons make these maps of space has fascinated scientists for decades. It is known that several types of stimuli influence the creation of neuronal maps, including visual cues in the physical environment — that rose bush, for instance — the body’s innate knowledge of how fast it is moving, and other inputs, like smell. Yet the mechanisms by which groups of neurons combine these various stimuli to make precise maps are unknown.

To solve this puzzle, UCLA neurophysicists built a virtual-reality environment that allowed them to manipulate these cues while measuring the activity of map-making neurons in rats. Surprisingly, they found that when certain cues were removed, the neurons that typically fire each time a rat passes a fixed point or landmark in the real world instead began to compute the rat’s relative position, firing, for example, each time the rodent walked five paces forward, then five paces back, regardless of landmarks. And many other mapping cells shut down altogether, suggesting that different sensory cues strongly influence these neurons.

Finally, the researchers found that in this virtual world, the rhythmic firing of neurons that normally speeds up or slows down depending on the rate at which an animal moves, was profoundly altered. The rats’ brains maintained a single, steady rhythmic pattern.

The findings, reported in the May 2 online edition of the journal Science, provide further clues to how the brain learns and makes memories.

The mystery of how cells determine place

"Place cells" are individual neurons located in the brain’s hippocampus that create maps by registering specific places in the outside environment. These cells are crucial for learning and memory. They are also known to play a role in such conditions as post-traumatic stress disorder and Alzheimer’s disease when damaged.

For some 40 years, the thinking had been that the maps made by place cells were based primarily on visual landmarks in the environment, known as distal cues — a tall tree, a building — as well on motion, or gait, cues. But, as UCLA neurophysicist and senior study author Mayank Mehta points out, other cues are present in the real world: the smell of the local pizzeria, the sound of a nearby subway tunnel, the tactile feel of one’s feet on a surface. These other cues, which Mehta likes to refer to as “stuff,” were believed to have only a small influence on place cells.

Could it be that these different sensory modalities led place cells to create individual maps, wondered Mehta, a professor with joint appointments in the departments of neurology, physics and astronomy. And if so, do these individual maps cooperate with each other, or do they compete? No one really knew for sure.

Virtual reality reveals new clues

To investigate, Mehta and his colleagues needed to separate the distal and gait cues from all the other “stuff.” They did this by crafting a virtual-reality maze for rats in which odors, sounds and all stimuli, except distal and gait cues, were removed. As video of a physical environment was projected around them, the rats, held by a harness, were placed on a ball that rotated as they moved. When they ran, the video would move along with them, giving the animals the illusion that they were navigating their way through an actual physical environment.

As a comparison, the researchers had the rats — six altogether — run a real-world maze that was visually identical to the virtual-reality version but that included the additional “stuff” cues. Using micro-electrodes 10 times thinner than a human hair, the team measured the activity of some 3,000 space-mapping neurons in the rats’ brains as they completed both mazes.

What they found intrigued them. The elimination of the “stuff” cues in the virtual-reality maze had a huge effect: Fully half of the neurons being recorded became inactive, despite the fact that the distal and gate cues were similar in the virtual and real worlds. The results, Mehta said, show that these other sensory cues, once thought to play only a minor role in activating the brain, actually have a major influence on place cells.

And while in the real world, place cells responded to fixed, absolute positions, spiking at those same positions each time rats passed them, regardless of the direction they were moving — a finding consistent with previous experiments — this was not the case in the virtual-reality maze.

"In the virtual world," Mehta said, "we found that the neurons almost never did that. Instead, the neurons spiked at the same relative distance in the two directions as the rat moved back and forth. In other words, going back to the front door-to-car analogy, in a virtual world, the cell that fires five steps away from the door when leaving your home would not fire five steps away from the door upon your return. Instead, it would fire five steps away from the car when leaving the car. Thus, these cells are keeping track of the relative distance traveled rather than absolute position. This gives us evidence for the individual place cell’s ability to represent relative distances."

Mehta thinks this is because neuronal maps are generated by three different categories of stimuli — distal cues, gait and “stuff” — and that all are competing for control of neural activity. This competition is what ultimately generates the “full” map of space.

"All the external stuff is fixed at the same absolute position and hence generates a representation of absolute space," he said. "But when all the stuff is removed, the profound contribution of gait is revealed, which enables neurons to compute relative distances traveled."

The researchers also made a new discovery about the brain’s theta rhythm. It is known that place cells use the rhythmic firing of neurons to keep track of “brain time,” the brain’s internal clock. Normally, Mehta said, the theta rhythm becomes faster as subjects run faster, and slower as running speed decreases. This speed-dependent change in brain rhythm was thought to be crucial for generating the ‘brain time’ for place cells. But the team found that in the virtual world, the theta rhythm was uninfluenced by running speed.

"That was a surprising and fascinating discovery, because the ‘brain time’ of place cells was as precise in the virtual world as in the real world, even though the speed-dependence of the theta rhythm was abolished," Mehta said. "This gives us a new insight about how the brain keeps track of space-time."

The researchers found that the firing of place cells was very precise, down to one-hundredth of a second, “so fast that we humans cannot perceive it but neurons can,” Mehta said. “We have found that this very precise spiking of neurons with respect to ‘brain-time’ is crucial for learning and making new memories.”

Mehta said the results, taken together, provide insight into how distinct sensory cues both cooperate and compete to influence the intricate network of neuronal activity. Understanding how these cells function is key to understanding how the brain makes and retains memories, which are vulnerable to such disorders as Alzheimer’s and PTSD.

"Ultimately, understanding how these intricate neuronal networks function is a key to developing therapies to prevent such disorders," he said.