Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Insulin action in the brain can lead to obesity

07.06.2011
Researchers decode an important mechanism through which insulin in the hypothalamus controls the body's energy balance

Fat-rich food makes you fat. Behind this simple equation lie complex signalling pathways, through which the neurotransmitters in the brain control the body's energy balance.


This is a visualization of how insulin affects the SF-1 neurons of the hypothalamus. After stimulation with insulin, the SF-1 cells (red) form the signaling molecule PiP3 (green). (Blue: cell nucleus) Credit: Max Planck Institute for Neurological Research

Scientists at the Cologne-based Max Planck Institute for Neurological Research and the Cluster of Excellence in Cellular Stress Responses in Ageing-associated Diseases (CECAD) at the University of Cologne have clarified an important step in this complex control circuit. They have succeeded in showing how the hormone insulin acts in the part of the brain known as the ventromedial hypothalamus.

The consumption of high-fat food causes more insulin to be released by the pancreas. This triggers a signalling cascade in special nerve cells in the brain, the SF-1 neurons, in which the enzyme P13-kinase plays an important role. Over the course of several intermediary steps, the insulin inhibits the transmission of nerve impulses in such a way that the feeling of satiety is suppressed and energy expenditure reduced. This promotes overweight and obesity.

The hypothalamus plays an important role in energy homeostasis: the regulation of the body's energy balance. Special neurons in this part of the brain, known as POMC cells, react to neurotransmitters and thus control eating behaviour and energy expenditure. The hormone insulin is an important messenger substance. Insulin causes the carbohydrate consumed in food to be transported to target cells (e.g. muscles) and is then available to these cells as an energy source. When high-fat food is consumed, more insulin is produced in the pancreas, and its concentration in the brain also increases. The interaction between the insulin and the target cells in the brain also plays a crucial role in the control of the body's energy balance. However, the precise molecular mechanisms that lie behind the control exercised by insulin remain largely unclear.

A research group led by Jens Brüning, Director of the Max Planck Institute for Neurological Research and scientific coordinator of the CECAD (Cellular Stress Responses in Aging-Associated Diseases) cluster of excellence at the University of Cologne has achieved an important step in the explanation of this complex regulatory process. As the scientists have shown, insulin in the SF-1 neurons – another group of neurons in the hypothalamus – triggers a signalling cascade. Interestingly, however, these cells appear only to be regulated by insulin when high-fat food is consumed and in the case of overweight. The enzyme P13-kinase plays a central role in this cascade of messenger substances. In the course of the intermediary steps in the process, the enzyme activates ion channels and thereby prevents the transmission of nerve impulses. The researchers suspect that the SF-1 cells communicate in this way with the POMC cells.

Kinases are enzymes that activate other molecules through phosphorylation – the addition of a phosphate group to a protein or other organic molecule. "If insulin binds to its receptor on the surface of the SF-1 cells, it triggers the activation of the PI3-kinase," explains Tim Klöckener, first author of the study. "The PI3-kinase, in turn, controls the formation of PIP3, another signalling molecule, through phosphorylation. PIP3 makes the corresponding channels in the cell wall permeable to potassium ions." Their influx causes the neuron to 'fire' more slowly and the transmission of electrical impulses is suppressed.

"Therefore, in overweight people, insulin probably indirectly inhibits the POMC neurons, which are responsible for the feeling of satiety, via the intermediary station of the SF-1 neurons," supposes the scientist. "At the same time, there is a further increase in food consumption." The direct proof that the two types of neurons communicate with each other in this way still remains to be found, however.

In order to find out how insulin acts in the brain, the Cologne-based scientists compared mice that lacked an insulin receptor on the SF-1 neurons with mice whose insulin receptors were intact. With normal food consumption, the researchers discovered no difference between the two groups. This would indicate that insulin does not exercise a key influence on the activity of these cells in slim individuals. However, when the rodents were fed high-fat food, those with the defective insulin receptor remained slim, while their counterparts with functional receptors rapidly gained weight. The weight gain was due to both an increase in appetite and reduced calorie expenditure. This effect of insulin could constitute an evolutionary adaptation by the body to an irregular food supply and extended periods of hunger: if an excess supply of high-fat food is temporarily available, the body can lay down energy reserves particularly effectively through the action of insulin.

It is not currently possible to say whether the findings of this research will eventually help to facilitate targeted intervention in the body's energy balance. "We are currently still very far away from a practical application," says Jens Brüning. "Our objective is to find out how hunger and the feeling of satiety arise. Only when we understand the entire system at work here, we will be able to start developing treatments."

Original publication:

Tim Klöckener, Simon Hess, Bengt F. Belgardt, Lars Paeger, Linda A.W. Verhagen, Andreas Husch, Jong-Woo Sohn, Brigitte Hampel, Harveen Dhillon, Jeffrey M. Zigman, Bradford B. Lowell, Kevin W. Williams, Joel K. Elmquist, Tamas L. Horvath, Peter Kloppenburg, Jens C. Brüning
High-fat Feeding Promotes Obesity via Insulin Receptor/P13k-Dependent Inhibition of SF-1 VMH Neurons

Nature Neuroscience, June 5th 2011

Professor Jens C. Brüning | EurekAlert!
Further information:
http://www.nf.mpg.de

More articles from Life Sciences:

nachricht Fingerprint' technique spots frog populations at risk from pollution
27.03.2017 | Lancaster University

nachricht Parallel computation provides deeper insight into brain function
27.03.2017 | Okinawa Institute of Science and Technology (OIST) Graduate University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Northern oceans pumped CO2 into the atmosphere

27.03.2017 | Earth Sciences

Fingerprint' technique spots frog populations at risk from pollution

27.03.2017 | Life Sciences

Big data approach to predict protein structure

27.03.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>