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Tuesday, March 20, 2012

Scientists reveal secret of obesity

A group of U.S. scientists have discovered how a mutation in a particular gene can lead to uncontrolled eating, which can lead to obesity, Science Daily reported Sunday.

Previous studies have revealed that the brain-derived neurotrophic factor (BDNF) gene is linked to obesity, but no one could explain how it controls the impulse to eat.

Georgetown university researchers discovered in a new study that a mutation in the BDNF gene in mice does not allow brain neurons to communicate to each other. It resulted in learning and memory defects.

They also found out that the same mutation had induced the mice to become severely obese.

According to the study’s senior investigator, Baoji Xu, BDNF plays a critical role in the formation and maturation of synapses that enables neurons to send signals between them. It does it by creating long and short transcript, a complementary RNA copy of a sequence of DNA.

However, mutated BDNF makes only a short transcript, and is only synthesized in the cell body of a neuron but not in its dendrites, causing neuron to over-produce immature synapses.

This seems to have caused the defects in the mice.

Xu said it was the first time “protein synthesis in dendrites, tree-like extensions of neurons, has been found to be critical for control of weight.”

The study goes on to show that leptin and insulin stimulate synthesis of BDNF in dendrites to allow communication between neurons.

In effect, if neurons are bus stops, then synapses are roads that connect them, and chemical signals from leptin and insulin is a bus. Stimulated protein synthesis of BDNF is like the police directing traffic, allowing signals to move from one neuron toward another.

If the police officer starts making errors, the road gets jammed and the bus gets stuck, just like the mutated BDNF causing problems for neuronal communication.

In humans, leptin and insulin chemical signals need to be passed on to correct locations in the hypothalamus, which oversees how full a person is.

If this delivery is interrupted, eating continues, just like in the mice that fattened themselves with an uncontrolled appetite.

Scientists are now hoping for a way to repair such damage in transmission and possibly help the brain control body weight.

By Yoon Min-sik

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