Magistère de Génétique Genetic and Epigenetic basis of multifactorial disease To eat or not to eat: the worldwide epidemic obesity Christophe Magnan Université Paris 7-CNRS EAC 4413 Equipe HERGE

More than 700 millions of obese in the world in 2015 billions (OMS, 2005)

1997: 8,5% 2009: 14,5% Source: étude Obépi +70% France: % of obese (adult population)

Economic cost: about 130 billions of $/year

Economic cost of obesity in France Source : IRDES, Enquête ESPS Graphique tiré d’un article intitulé « Evaluation du coût associé à l’obésité en France » paru dans la revue « La presse médicale », 2007/06, tome 36, n° 6, cahier 1, pp

Why such pandemia ? 3 millions d’années200 ans

What is obesity ? a deregulation of energy balance More energy intake/storage than energy expenditure

Gene–Environment Interactions in Common Obesity The complex interactions underlying polygenic obesity demonstrate that genetic, social, behavioral, and environmental factors are all capable of influencing the obese phenotype (Mutch and Klement, PLoS Genet. 2006)

= 1 pain au chocolat ~ 200 Kcal 25 min running

Obesity increases risk of diseases such as… x 5

Is disorder of the brain (and deregulation of energy balance) a key factor in onset of obesity ?

Signals regulating food intake/storage and energy expenditure

Ob/Ob mice: 1950: expériences de parabiose 1994: Identification du produit du gène ob: la leptine 1995: Identification du récepteur de la leptine: ObR : Identification d’individus ayant uen mutation dans le gène Ob

Leptin effect is to reduce body weight…

Ghrelin…

Ghrelin is a stimulator of food intake… and induced overweight when continuously infused in rats

Where do these signals act ?

Hypothalamus Mainly in hypothalamus (and brainstem) Brainstem

Hypothalamus is subdivided in « nuclei » Main nuclei Arcuate (arc) Ventromedian (VMN) Paraventricular (PVN)

Two neuronal populations within arcuate nucleus are sensitive to insulin, leptin and ghrelin

AgRP immunostaining in mouse brain…. Only arcuate nucleus is positive

To summarize…

Some models…

Neuron insulin-receptor KO mice: NIRKO mice Jens C. Bruning et al, Science 2000 KO WT

Farooqi et al, JCI, 2002 Leptin deficiency in mice and human After 2 years of leptin treatment Ob/ob Mouse: leptin deficient mouse

4 wks HFD (intraperitoneal leptin injection 100 µg) El-Haschimi et al JCI 2000 Genetic mutations are not the -only- key: importance of environment: effects of high fat diet (HFD) on leptin signaling in normal mice 15 wks HFD (ip injection leptin 100 µg)

Melanocortin pathway…

MC4R KO mice MC4R-deficient human subject Melanocortin receptor mutation

Brain fatty acid sensing and nervous control of energy homeostasis

Fatty acids sensitive neurons are present in arcuate nucleus in rats (Migrenne et al, Diabetes, 2006) Fragments of in vivo recording of neuronal activity

FA sensitive neurons are present in arcuate nucleus 2,5 mM G 2,5 mM G + 2µM OA 2,5 mM G In vivo multiunit recording of OA excited neurons in rat (Wang et al, J Neurophysiol, 2006) Collab Vanessa Routh (Medical School of New Jersey) : In vitro recording of neuron « excited » by oleic acid (OA) in rat

Calcium imaging: « glucose inhibited /OA excited » neuron from VMH (ventromedian hypothalamus) 2.5G = 2.5 mM glucose 0.5G = 0.5 mM glucose 50 nM OA = 50 nM Oleic Acid (Le Foll et al, Am J Physiol, 2009) Collab: Barry E Levin (Veterans Medical Center, East Orange, NJ) 2,5G0,5G2,5 mM G2,5G + 50nM OA

The concept: daily variations of plasma nutrients could be detected by hypothalamic neurons Ruge et al, JCEM, 2009 meals NEFA: Non esterified fatty acids

(Diabetes 2003) Oléate + Bloquant canaux potassiques Oléate Saline Oléate Saline

(Diabetes, 2010)

Insulin Insulin receptor Autonomic nervous system May fatty acid overload induce hypothalamic insulin resistance ? FA X X FA ? X

PKB/AKT FA Acyl-CoA Insulin FATP1 MARCKS MARCKS: Myristoylated Alanine Rich C Kinase Substrate + P X P PKC  Debbie Clegg (University of Southwestern medical center, Dallas) Stephen Benoit (University of Cincinnati, Ohio) FA sensitive neuron

Measurements (from hypothalamus) -PKCΘ plasma membrane vs cytosol -pMARCKS -pAKT in response to acute insulin injection Rats infused with palmitate, saline or oleate during 72h Osmotic minipump Palmitate Oleate NaCl

PKB/AKT Insulin FATP1 MARCKS + P X P PKC  PKC  is increased in plasma membrane fraction of hypothalamus from palmitate infused rats (Benoit et al, J Clin Invest, 2009)

PKB/AKT Insulin FATP1 MARCKS + P X P PKC  pMARCKS is increased in cytosolic fraction of hypothalamus from palmitate infused rats (Benoit et al, J Clin Invest, 2009)

PKB/AKT Insulin FATP1 MARCKS + P X P PKC  Decreased pAKT in response to insulin in palmitate infused ratd (Benoit et al, J Clin Invest, 2009)

Insulin Insulin receptor Autonomic nervous system Fatty acid overload may induce hypothalamic insulin resistance FA X X X

A role for brain LPL in lipid/FA sensing ? Ruge et al, JCEM, 2009 meals NEFA: Non esterified fatty acids

Decreased LPL activity in hypothalamus (arcuate nucleus) increases food intake in rat (unpublished data) Pharmacological approach (intracarotid infusion of tylox: LPL inhibitor) shRNA approach (injection in arcuate) tyloxapol