Leptin Hormone and Appetite Control

Appetite is controlled by the hypothalamus “appetite control center” Makes us feel full when we have eaten enough food.

When the hypothalamus receives certain hormone signals, it reduces the desire to eat Insulin from the pancreas PYY3-36 from the small intestine Leptin from adipose tissue (fat cells) “OK, time to stop eating!”

Leptin Leptin is a protein hormone. Can you see the chain of amino acids in the structure? Notice the N-C-C backbone running throughout the structure. Remember, there is a carbon at every kink in the structure.

Leptin Leptin is a protein hormone. Can you see the chain of amino acids in the structure? Notice the N-C-C backbone running throughout the structure. Remember, there is a carbon at every kink in the structure.

Leptin Leptin is secreted from adipose tissue (fat storage cells). Leptin targets cells in the hypothalamus appetite control center.

Leptin is a protein, so it is made through the transcription and translation of a gene. All cells in our body have the leptin gene, but it is only expressed in fat tissue cells. The gene that codes for leptin is called “OB.” Normal version of the gene, correctly codes for leptin = OB (dominant) Mutated version of the gene, does not correctly code for leptin = ob (recessive) Without functional leptin, no leptin signal is received by the hypothalamus and the organism will keep eating (leading to obesity) Discovery of Leptin

Discovery of Leptin The gene for leptin was discovered in 1994 by studying obese human and mice (Friedman et al) Watch this video. Actually do it.

Leptin Resistance Not all obese people have mutations of the OB gene. Most obese people produce plenty of leptin, but their bodies fail to respond to it—rather than leptin deficiency, obesity is most often due to leptin resistance. The leptin is made but the receptor proteins in the hypothalamus fail to respond to it. The leptin is there, but the brain ignores it. The organism will keep eating (leading to obesity)

Leptin as a treatment for obesity Remember, inheriting mutations of the OB gene (ob/ob; homozygous recessive) can lead to obesity because the leptin protein is not made. What happens when leptin is given a to the patients as a treatment? Weight loss occurs…. BUT...

Leptin as a treatment for obesity … BUT... … injections of leptin must occur multiple times a day … leptin injection affect the development and functioning of the reproductive systems … weight lost with leptin treatment was immediately regained when treatment stopped ...injections irritated the skin and caused swelling … and, giving leptin to people who are obese due to leptin resistance (as opposed to having the leptin mutation) has no effect on weight loss.

Appetite is controlled by a centre in the hypothalamus. D.1.U7 Appetite is controlled by a centre in the hypothalamus. Describe how hormones and the appetite control center regulate a desire to eat. 6.6.U3 Leptin is secreted by cells in adipose tissue and acts on the hypothalamus of the brain to inhibit appetite. Sate that leptin is a protein hormone. Outline the mechanism of action of leptin. Describe the role and discovery of the ob allele and obese mice. 6.6.A2 Testing of leptin on patients with clinical obesity and reasons for the failure to control the disease. Explain the double blind study that tested the effect of leptin treatment on human obesity. Outline the role of leptin resistance in human obesity.