1. Appetite Regulation Endocrinology Rounds June 1, 2011 Selina Liu PGY5 Endocrinology

2. Objectives  To review the key neuroanatomical areas involved in central appetite regulation  To provide an overview of the major signalling circuits involved in appetite regulation  To appreciate the cross-talk between central and peripheral mechanisms involved in appetite regulation  To highlight key hormones involved in central appetite regulation

3. Conceptual Levels of Appetite Regulation http://www.endotext.org/obesity/obesity7.3/obesityframe7-3.htm Psychological Events & Behavioural Operations Central Neurotransmitter & Metabolic Events Peripheral Physiology & Metabolic Events

4. 1) Hypothalamus  Medial  Lateral 2) Brainstem  Midbrain  Pons  Medulla 3) Circumventricular Organs (CVO)  Median Eminence  Subfornical Organ (SFO)  Organum Vasculosum of Lamina Terminalis (OVLT) Central Nervous System - Key Areas 1) Hypothalamus 2) Brainstem 3) Circumventricular Organs (CVO)

5. Neuroanatomy Review (tectum + tegmentum) Brainstem Forebrain Hindbrain

6. Central Nervous System – Key Areas 1) Hypothalamus  Medial  Lateral 2) Brainstem  Midbrain  Pons  Medulla 3) Circumventricular Organs (CVO)  Median Eminence  Subfornical Organ (SFO)  Organum Vasculosum of Lamina Terminalis (OVLT)

7. 1) Hypothalamus  essential, evolutionarily highly conserved region of mammalian brain  ultimate structure that allows for maintenance of homeostasis  destruction is incompatible with life  coordinates endocrine, autonomic and behavioural responses

8. 1) Hypothalamus  receives:  sensory input from external environment (i.e. light)  input from internal environment (i.e. blood glucose levels, hormones involved in food intake/energy metabolism)  provides output to:  pituitary gland  cerebral cortex  premotor & motor neurons in brainstem, spinal cord  autonomic preganglionic neurons

9. 1) Hypothalamus – Key Nuclei  Medial  Arcuate Nucleus (ARC)  Paraventricular Nucleus (PVN)  Ventromedial Nucleus (VMN)  Dorsomedial Nucleus (DMN)  Lateral  lateral hypothalamic area (LHA)  perifornical hypothalamus

10. History  rat experiments (1930s-1950s):  ablation of ventromedial nucleus (VMN)  obesity  ablation of lateral hypothalamic area (LHA)  reduced feeding

11. History  dual centre model of feeding proposed:  satiety centre: ventromedial nucleus  feeding centre: lateral hypothalamus HOWEVER – much more complex!  involves multiple nuclei and signaling pathways

13. AC – anterior commissure OC – optic chiasm Medial Hypothalamus: ARC – arcuate nucleus PVN – paraventricular nucleus VMH – ventromedial nucleus DMH – dorsomedial nucleus Lateral Hypothalamus: LH – lateral hypothalamic area Kalra SP et al. 1999. Endocr Rev. 20(1):68-100

14. 2) Brainstem  Midbrain  Pons  Medulla  Dorsal Vagus Complex (DVC)  Nucleus of the Tractus Solitarius (NTS)  Area postrema - sensory CVO  Dorsal motor nucleus of vagus

15. MEDULLA Bloom SR et al. 2008 Mol Interv 8(2):82-98

16. 2) Brainstem  sensory visceral afferents from GI tract, hepatoportal regions are stimulated by:  gastric stretch  taste, chemical stimulation  local production of gut hormones  carried via vagus and glossopharyngeal nerves  signals terminate in the NTS of DVC – integrated with parasympathetic nervous system input, and relayed to the hypothalamus

17. 3) Circumventricular Organs - CVO  areas adjacent to hypothalamus which lack the blood-brain-barrier (BBB)  contain neuronal cell bodies – “sensory”  uniquely placed to detect peripheral signals in blood and transmit to hypothalamus

18. http://www.nibb.ac.jp/annual_report/2001/html/ann501.html

19. Peptide Hormones  thus 2 main mechanisms of peptide hormone communication between periphery and brain:  via stimulation of vagal afferents  transfer between NTS (in DVC in medulla of brainstem) and ARC (in hypothalamus)  via CVO to the hypothalamic nuclei

20. Hypothalamus & Appetite Regulation  the hypothalamus regulates appetite and metabolism by detecting peripheral signals i.e. nutrients within blood hormones from gut, adipose tissue  integrates all signals together to maintain homeostatic balance between energy intake and energy expenditure

21. Hypothalamus & Appetite Regulation Arcuate nucleus (ARC) – at base of hypothalamus  2 distinct neuronal populations:  neurons that express OREXIGENIC neuropeptides  neurons that express ANORECTIC neuropeptides  relays signals to downstream effector neurons  also expresses insulin and leptin receptors

23. Arcuate Nucleus  ANORECTIC neuropeptides – appetite suppressing  Pro-Opiomelanocortin (POMC)  Cocaine & Amphetamine Regulated Transcript (CART)  OREXIGENIC neuropeptides – appetite stimulating  Neuropeptide Y (NPY)  Agouti Related Peptide (AgRP)

24. Pro-Opiomelanocortin (POMC)  Precursor peptide of Melanocortin system Kronenberg HM et al. Williams Textbook of Endocrinology. 11th edition. 2008 Saunders Elsevier.

25. Melanocortin System POMC (pro-opiomelanocortin) PC1 PC2  -melanocyte stimulating hormone (  -MSH) PC1 and PC2 = prohormone convertase 1 and 2  -MSH  agonist at melanocortin receptors MC3R, MC4R  inhibition of food intake – ANORECTIC effect  MC3R, MC4R abundant in ARC, PVN, VMN  MC4R mutation – most common single gene cause of human obesity

26. Cocaine & Amphetamine Regulated Transcript  CART neurons expressed throughout CNS  abundant in hypothalamus, almost exclusively co-expressed with POMC  first sequenced in 1980 (? function), then found to be upregulated after cocaine and amphetamine administration  intracerebral CART administration – either inhibits or stimulates feeding depending on location  role not totally elucidated

27. Neuropeptide Y (NPY)  most abundant peptide in CNS  most orexigenic peptide within hypothalamus  induces food intake – especially CHO-rich foods  also:  energy expenditure  thermogenesis  sedation anticonvulsant effect on mood/memory stimulates LH release  hypothalamic NPY levels correlate with food intake  expression increases with fasting, decreases with food intake  leptin, insulin have negative feedback on NPY expression

28. Neuropeptide Y (NPY)  endogenous ligand for 4 known receptors (GPCRs) in humans:  Y1R  Y5R  Y2R  predominant NPY receptor in brain  Y4R  these receptors also bind PP, PYY Y1R - autoinhibitory presynaptic receptor Y4R Y2R mediate orexigenic actions mediate anorectic actions Y5R

29. Agouti-Related Peptide  related to agouti protein  agouti – in mice, expressed in skin & hair follicles  endogenous melanocortin receptor antagonist (MC1R, MC4R)  induces pheomelanin production (yellow pigment)  Agouti A Y mice – model of obesity - ectopic expression of agouti - MC1R antagonism  yellow colour - MC4R antagonism  obesity

30. Barsh GS & Schwartz MW. 2002. Nat Rev Genet. 3;589-600

31. www.chem.ufl.edu/~richards/members.htm

32. Agouti-Related Peptide  endogenous melanocortin receptor (MC4R) antagonist  recall: melanocortin neurons within ARC have inhibitory effect on feeding  therefore, MC4R antagonism:  inhibits inhibition of food intake  stimulates food intake i.e. OREXIGENIC effects

33. Summary - Arcuate Nucleus  ANORECTIC neuropeptides – appetite suppressing  Pro-Opiomelanocortin (POMC)  Cocaine & Amphetamine Regulated Transcript (CART)  OREXIGENIC neuropeptides – appetite stimulating  Neuropeptide Y (NPY)  Agouti Related Peptide (AgRP)

34. AC – anterior commissure OC – optic chiasm Medial Hypothalamus: ARC – arcuate nucleus PVN – paraventricular nucleus VMH – ventromedial nucleus DMH – dorsomedial nucleus Lateral Hypothalamus: LH – lateral hypothalamic area Kalra SP et al. 1999. Endocr Rev. 20(1):68-100

35. Hypothalamus & Appetite Regulation Paraventricular Nucleus (PVN) – base of 3 rd ventricle  divisions:  medial parvocellular - TRH, CRH, somatostatin, VIP, enkephalin  lateral magnocellular - vasopressin, oxytocin  important in energy balance  role in thyroid and adrenal axes  site of integration with ARC and NTS

36. Hypothalamus & Appetite Regulation Dorsomedial Nucleus (DMN)  role in coordinating circadian rhythm with feeding and energy expenditure Ventromedial Nucleus (VMN)  previously “satiety centre”  contains neurons expressing brain-derived neurotrophic factor (BDNF) – ANORECTIC effects

37. Hypothalamus & Appetite Regulation Lateral Hypothalamic Area (LHA)  previously “feeding centre”  very sensitive to NPY  also contains neurons releasing:  orexin A  orexin B  melanin concentrating hormone – ↑ food intake aka “hypocretins” – OREXIGENIC ↑ appetite, ↑ arousal, may initiate food- seeking behaviour in starvation

38. Hypothalamus & Appetite Regulation Lateral Hypothalamic Area (LHA)  connections with nuccleus accumbens (reward centre)  ? enhance hedonistic value of food

39. AC – anterior commissure OC – optic chiasm Medial Hypothalamus: ARC – arcuate nucleus PVN – paraventricular nucleus VMH – ventromedial nucleus DMH – dorsomedial nucleus Lateral Hypothalamus: LH – lateral hypothalamic area Kalra SP et al. 1999. Endocr Rev. 20(1):68-100

40. Brain-Gut-Adipose Axis  cross-talk between brain, gut and adiposse tissue is essential for regulation of energy homeostasis  complex interplay of neuronal and endocrine signals

42. Hormonal Regulation of Brain-Gut- Adipose Axis Adipostatic factors  leptin  insulin  glucose Satiety & Hunger factors  ghrelin  cholecystokinin (CCK)  GLP-1  PP, PYY  amylin  oxyntomodulin

44. Leptin  product of ob gene  produced by white adipose tissue – in proportion to total body fat content  minor sites: skeletal muscle, placenta, stomach  leptin-R on hypothalamic neurons: inhibits NPY/AgRP, stimulates POMC/CART neurons  fasting decreases leptin levels  stimulates food intake and reduces energy expenditure  leptin deficiency (or leptin-R deficiency) – obesity

45. Leptin  previously thought that leptin was ANORECTIC  but in common human obesity, increased leptin levels do not suppress appetite  due to leptin resistance?  role of leptin: signal that energy stores are sufficient i.e. acts as a permissive hormone allowing energy requiring processes to occur

46. Insulin  not produced by adipose tissue, but levels correlate with body adipose tissue mass  “adipostat” hormone  contrasting role in peripheral tissues (anabolic) vs central (catabolic)  insulin-R in brain – intracerebral injection of insulin decreased food intake (baboons, rodents)  deletion of insulin-R from neurons – mild obesity (mice)  overall – central effect is ANORECTIC

47. Ghrelin  only peripheral OREXIGENIC hormone  secreted from X/A-like endocrine cells in stomach oxyntic (parietal) cell glands  endogenous ligand at the GHS-R 1a (growth hormone secretagogue receptor 1a) – hypothalamus & brainstem  increases with fasting, decreases after food intake  role in meal initiation?  stimulates NPY and AgRP neurons in ARC  ghrelin administration – stimulates feeding (rodents, humans)

48. Ghrelin  levels are highest in cachetic subjects, reduced in lean subjects, and lowest in obese subjects  adaptive response – attempt to stimulate or suppress appetite according to energy imbalance  however – obese subjects more sensitive to effects of ghrelin  ? role of ghrelin antagonist to treat obesity  ? role of ghrelin treatment as appetite stimulant (i.e. cancer-related cachexia)

50. Cholecystokinin (CCK)  produced by GI tract – enteroendocrine I cells in duodenum, jejunum  released post-prandially in response to fat, protein  actions:  food intake  delay gastric emptying stimulates pancreatic enzyme secretion stimulates gallbladder contraction  mediated via binding to CCKA R on vagus nerve – activates neurons in NTS and AP (in dorsal vagal complex)  CCK administration – inhibits food intake  meal size,  meal duration  ANORECTIC effects

51. Glucagon Like Peptide-1 (GLP-1)  produced via post-translational modification of pre-proglucagon  incretin effects: stimulates insulin release, inhibits glucagon release  upper GI motility, gastric emptying, gastric acid secretion  central effects:  in hypothalamus not totally clear, but GLP-1 R found on POMC neurons in ARC  signal via vagus nerve to NTS and ARC  in brainstem

52. Pancreatic Polypeptide (PP)  same family as NPY, peptide tyrosine tyrosine (PYY)  secreted from pancreas, distal gut in response to meals via vagus nerve stimulation  act via Y4R – in dorsal vagus complex of medulla  ANORECTIC effects

53. Peptide Tyrosine Tyrosine (PYY)  found in pancreas and small intestine  released post-prandially  act via binding to Y2R on NPY in ARC  recall: Y2R – autoinhibitory  decrease NPY signaling  decreased appetite - ANORECTIC  also via signaling through vagus nerve to NTS to hypothalamus  reduced by fasting – likely a satiety factor  levels lower in obese subjects  PYY response to nutrient ingestion is reduced in obesity

54. Amylin  co-secreted with insulin – in response to nutrient ingestion  amylin readily enters brain  high-affinity amylin binding sites – in hypothalamus (ARC)  peripheral & intracerebral amylin infusions: (rodents)  acute – inhibit food intake  chronic – sustained weight loss

55. Oxyntomodulin (OXM)  37 a.a. peptide – contains entire sequence of glucagon and a C- terminal extension  binds to GLP-1 R (but  affinity)  released post-prandially (co-secreted with GLP-1, PYY)  shares ANORECTIC effets  OXM administration in humans over 4 weeks  weight loss  due to  energy intake and  energy expenditure

56. Hormonal Regulation of Brain-Gut- Adipose Axis Adipostatic factors  leptin  insulin  glucose Satiety & Hunger factors  ghrelin  cholecystokinin (CCK)  GLP-1  PP, PYY  amylin  oxyntomodulin

57. Objectives  To review the key neuroanatomical areas involved in central appetite regulation  To provide an overview of the major signalling circuits involved in appetite regulation  To appreciate the cross-talk between central and peripheral mechanisms involved in appetite regulation  To highlight key hormones involved in central appetite regulation

59. References  Barsh GS & Schwartz MW. 2002. Nat Rev Genet. 3:589-600  Bloom SR et al. 2008. Mol Interv. 8(2):82-98  Kalra SP et al. 1999. Endocr Rev. 20(1):68-100  Zac-Varghese S et al. 2010. Discov Med 10(55):543-52  Kronenberg HM et al. Williams Textbook of Endocrinology. 11th edition. 2008 Saunders Elsevier.  www.endotext.orgwww.endotext.org  www.medscape.comwww.medscape.com  http://www.nibb.ac.jp/annual_report/2001/html/ann501.htmlhttp://www.nibb.ac.jp/annual_report/2001/html/ann501.html  www.chem.ufl.edu/~richards/members.htmwww.chem.ufl.edu/~richards/members.htm