signal transduction pathways involved in the regulation of food intake or why does Homer Simpson loves to eat an excess of donuts

Regulation of food intake; a complex circuitry between different areas of the brainSignaltransduction

With respect to regulation, a general distinction is made between homeostatic (metabolite input) and hedonic regulation (reward input)

Remember that warm blooded animals, with highly developed brains, have two big worries; how to keep warm and how to keep the brain turning over

A simplified version of homeostatic regulation of food intake; focus on signals from the digestive system (ghrelin, CCK, PYY), adipose tissue (leptin) and the pancreas (insulin)

Nature of the different hormones and neurotransmittorCCK, cholecystokinin (P06307) (chole=bile, cysto=pouch, kinin=move the bile bladder) is a peptide hormone produced in the small intestine in response to feeding. It causes the release of digestive enzymes from the (exocrine) pancreas, bile from the galbladder and release of H+ in parietal cells of the stomach. In the central nervous system it acts as an anorexigen (hunger suppressant).PYY, peptide tyrosine-tyrosine (P10082) , released by by cells in the ileum and colon in response to feeding and acts as an anorexigenInsulin, (P01308) peptide hormone released by b-cells in the islet of Langerhans of the (endocrine) pancreas (hence its name insulin) in response to elevated levels of blood glucose. It acts as an anorexigen. Leptin, (P41159) peptide hormone released by adipose tissue in response to triglyceride loading. Mice lacking the peptide or its receptor are obese. Leptin comes from leptos, meaning thin.

Ghrelin, (Q9UBU3) is a polypeptide hormone produced by cells lining the fundus of the stomach and en by epsilon cells of the pancreas. It has an orexigenic effect (stimulates food intake. It is also produced in the arcuate nucleus where it stimulates secretion of growth hormone by the anterior pituitary gland, hence its name Ghre meaning growth

ghrelin signals hunger (orexigen, stimulates food intake), whereas leptin, insulin, CCK and PYY signal satiety (anorexigen, inhibit food intake).

Their targets are neurons in the arcuate nucleus, of which POMPC/CARTprovide an orexic signal and AgRP/NPY neurons drive the anorexic response NTS, nucleus tractus solitarius

Neuro-anatomy of homeostatic regulation of food intake; opposing actions of AgRP/NPY and POMC/CART containing neurons

Nature of neurotransmitters involved in homeostatic regulation of food intakeCART, cocaine and amphetamine regulated transcript (Q16568) , discovered as a cocaine- and amphetamine-inducible gene, propeptide, converted by prohormone convertase into at least two active peptides (CART 55-102 and CART 62-102)POMC, pro-opiomelanocortin (P01189) , precursor peptide, converted by prohormone convertases, yielding as many as 10 active peptides amongst which a- and b-MSH (melanocortin) but also b-endorphine, hence its name (voir ressource 08, partir de page 28 (section troisime transit); vers la voie de la scrtion contrle)NPY , neuropeptide Y (P01303) , short neuropeptide isolated from the hypothalamus and resembling peptide YY produced by the digestive tract, hence its name. AgRP, agouti-related protein (O00253) , sequence similarity with Agouti signalling peptide, a hormone that controls coat pigmentation in Augoutis (rodents). Acts as an antagonist of the melanocortin-3 and -4 receptor (blocks action of a-MSH)

Neuro-anatomy of hedonic regulation of food intake; reward (or pleasure) seeking areas of the brain control orexigenic neurons of LHA

Neurotransmittors involved in hedonic regulation of food intakeDopamine, tyrosine-derived neurotransmitter

endocannabinoids , -anandamide (arachidonoyl ethanolamide, AEA) (meaning bliss), binds CB1 and CB2-2-arachidonoyl glycerol (2-AG)-2-arachidonoyl glyceryl ethere (noladin ether), binds CB1 anb CB2-N-arachidonoyl dopamine (NADA), binds CB1-Virodhamine (O-arachidonoyl-ethanolamine, OEA), binds CB1 and CB2

endogenous opioids,-enkephalin short peptide cleaved from proenkephalin protein (act on m- and d-receptor)examples tyr-gly-gly-phe-leu (leu-enkephalin) or tyr-gly-gly-phe-met (met-enkephalin)-endorphins, short peptides cleaved from pro-opiomelanocortin protein (act on m-receptor-dynorphin short peptide cleaved from prodynorphin protein (act on k-receptor

GABA, g-aminobutyric acid, amino-acid derived neurotransmitter

anandamide

So whats wrong with obese people?BMI = weight (kg)/height (m)2In most cases a polygenic disorder which still has to be understood furtherIn some (severe) cases a lack of MC4-R signalling, an excess of ghrelin, a lack of leptin or a dysfunctioning of insulin signallingIn some cases a disorder associated with a syndrome such as Prader-Willi, Bardet-Biedl or Alstrm 3030BMI body mass index(IMC indice de masse corporelle)

In the following lectures we will look into more detail how insulin, leptin and ghrelin signal in the arcuate nucleusReceptor tyrosinekinase (insulin)Cytokine receptor (leptin)7 TM receptor (ghrelin)