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Secrets of the lac operon: A unified mechanism for aging, diabetes, and obesity

Secrets of the lac operon: A unified mechanism for aging, diabetes, and obesity. Lac operon: Substrates induce their own metabolism, and exhibit hysteresis. The Metabolic Mystery: Aging and Disease. Obesity increases with age Obesity pre-disposes to age-related diseases (metabolic syndrome)

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Secrets of the lac operon: A unified mechanism for aging, diabetes, and obesity

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  1. Secrets of the lac operon:A unified mechanism for aging, diabetes, and obesity

  2. Lac operon: Substrates induce their own metabolism, and exhibit hysteresis

  3. The Metabolic Mystery: Aging and Disease • Obesity increases with age • Obesity pre-disposes to age-related diseases (metabolic syndrome) • Caloric restriction extends lifespan WHY??

  4. WHY?? • Does obesity increase with age? • Does protein oxidation increase with age? • Does glycolysis increase with age? • Does protein turnover decrease with age? • Are effects of aging progressive and apparently irreversible? • Are effects of diabetes progressive and apparently irreversible? • Are effects of aging and diabetes really irreversible?

  5. Caloric (glucose?) restriction Nutrient sensors (transcription factors?) And then a miracle occurs Increased lifespan

  6. How do (glucose) calories kill?Focus on brain gene expression • Diabetic complications mainly in insulin-insensitive tissues • Neurons implicated in many models of aging • Neurons regulate metabolism

  7. Dietary restriction alters characteristics of glucose fuel use.Masoro, EJ, McCarter, RJ, Katz, MS, and McMahan, C AJ. Gerontology (1992) 47(6):B202-B208

  8. Molecular hysteresis: residual effects of hormones and glucose on genes during aging.C.V. MobbsNeurobiology of Aging (1994) 15:523-534

  9. Glucose hysteresis Glucose resistance SIP down VMH neurons glucose resistant Inducedgenes Inhibitedgenes Young&Thin Old& Fat Many meals(glucoseexcursions)

  10. But is it glucose?? • Reducing glucose increases lifespan in yeast • DR (including methionine) reduces glucose • Every-other day feeding does not reduce calories, but reduces glucose and extends lifespan • Elevated glucose causes toxicity (diabetic complications)

  11. What does glucose do?

  12. BUT- Low glucose blocks glycolysis • Phosphofructokinase DOWN • Transaldolase DOWN • Ketohexokinase DOWN • Moncarboxylate transporter 1 Down • Pyruvate dehydrogenase kinase 4 UP

  13. AND- low glucose blocks NADH glycerol shuttle • Mitochondrial glycerolphosphate dehydrogenase DOWN • Cytoplasmic glycerolphosphate dehydrogenase UP

  14. Low glucose stimulates pentose pathway (makes NADPH) • Glucose-6-phosphate dehydrogenase*UP • Linked to aging and stress resistance

  15. Low glucose stimulates TCA cycle and mitochondrial NADPH • Isocitrate dehydrogenase 2*UP • Linked to aging and stress resistance

  16. Low glucose activates hypothalamic mitochondrial lipid oxidation • Carnitine palmitoyl transferase UP • Fatty acid transport protein UP • Mitochondrial Acyl-CoA thioesterase UP

  17. AND- Low glucose activates peroxisomal fatty acid oxidation • Peroxisome membrane protein UP • Peroxysomal Acyl-CoA peroxidase Up • Peroxisomal integral membrane protein UP • Peroxisome membrane protein UP • Peroxisomal integral membrane protein UP • Peroxisomal biogenesis factor UP

  18. AND- Low glucose activates protein and amino acid degradation • Multi-ubiquitin chain binding protein UP • Ubiquitin fusion degradation protein 1 Up • Proteasome delta subunit UP • Proteasome (prosome) subunit UP • Proteasome alpha subunit UP

  19. AND- Low glucose activates protein synthesis • Ribosomal protein S7 UP • Translation initiation factor eIF2 gamma Up • Ribosomal protein S5 UP

  20. Low glucose induces the highly anti-oxidant “glucose switch” profile of gene expression • Glycolysis down (blocks NADH complex I) • Complex I produces free radicals • Pentose pathway up • Makes antioxidant NADPH • Lipid oxidation up (favors FADH2 complex II) • Complex II does not produce free radicals • Amino acid oxidation up • Eliminates oxidatively damaged proteins • Favors NAD+ • Induces protective effects (e.g., SIR1)

  21. The glucose switch: “ATP-neutral” substrate repartitioning Glucose Transport GLUT1 Pentose Shunt Cytoplasm Glycolysis PFK Glucose-6-Phosphate DH NADPH Fatty Acid Oxidation Glucose to Krebs PDHK4 CPT1 PPaRγ NAD+ Krebs Cycle NADH Complex I Complex II FADH2 Isocitrate DH2 NADPH Mitochondria/Peroxisome Respiratory Chain Shift to Complex II

  22. Conversely, high glucose blocks the “glucose switch” profile, leading to an oxidative profile • Glycolysis up (favors NADH complex I) • Complex I produces free radicals • Reduced Complex I, III, IV, and V increase lifespan • Pentose pathway down • Reducing antioxidant NADPH • Lipid oxidation down (inhibits FADH2 complex II) • Complex II does not produce free radicals • Impaired Complex II reduces lifespan • Amino acid oxidation down • Allows accumulation of oxidatively damaged proteins • Favors NAD+ • Inhibits protective mechanisms (e.g., SIR1)

  23. Mechanistic studies: Evidence that NADH mediates toxic effects of glucose a a a a % cells alive (CCK) 100 b 50 b 0 5150 150 15 Glucose Lactate Pyruvate 5 mM Glucose

  24. High-throughput screen discovers drugs protective against glucose toxicity

  25. High-throughput screen discovers drugs protective against glucose toxicity

  26. OK, high glucose can cause oxidative damage acutely, but what accounts for the progressive and (apparently) irreversible nature of age-related impairments?

  27. Hypothalamic glucose sensor: similarities to and differences from pancreatic beta-cell mechanisms.Yang, Kow, Funabashi, MobbsDiabetes 1999 Sep;48(9):1763-72 “The pancreatic, but not hepatic, form of glucokinase was expressed in the VMH..…These data suggest that glucose-responsive neurons sense glucose through glycolysis, specifically the production of NADH, not ATP”.

  28. Implication of glucose switch • Glucose activates its own metabolism (esp. NADH) • Cytoplasmic NADH is the unique signature of glucose, thus particularly suited as a signal • This implies a self-perpetuating, cumulative sensitization or priming effect: HYSTERESIS! • Could this be reversed?

  29. Multistability in the lactose utilization network of Escherichia coliOzbudak et al.Nature (2004) Feb; 427:737-740 “The phase diagram of the wild-type network shows that lac induction always takes place hysteretically, with cells increasing their expression levels discontinuously as a switching threshold is reached….”

  30. Molecular hysteresis in metabolic gene expression

  31. Implication: Aging is reversible

  32. Mechanistic studies: Evidence that NADH mediates toxic effects of glucose a a % cells alive (CCK) 100 b 50 b 0 0100 10 Glucose (mM)

  33. Obesity: What is the question?

  34. How much variability in genetically identical laboratory mice? About the same as in humans! . 20 . . . Body Wt Gain (gm) 15 . . 10 . 5 0 Coefficent of variation: 47%!

  35. Variability in caloric intake is much less than variability in weight gain . . . . . . Caloric intake (kCal) 500 0 Coefficent of variation: 8%!

  36. 20% of retired breeder C57Bl/6J mice don’t gain weight on a high-fat diet but eat each just as much

  37. Diet-induced obesity (independent of food intake) depends on genotype * 25 20 Body weight Gain on HF Diet (grams) 15 10 5 A/JC57

  38. Hypothalamus • According to glucostatic hypothesis A/J mice are resistant to diet-induced obesity because they have increased hypothalamic sensitivity to glucose. This hypothesis implies that induction of genes by hypoglycemia will be less robust in (glucose-sensitive?) A/J mice than in (glucose-insensitive?)

  39. GLUT 1

  40. Ubp41

  41. CITED-1

  42. NPY and AGRP

  43. AGRP (in vitro)

  44. Liver and Cortex Evidence of a hypothalamic defect

  45. Liver: Glut1

  46. Cortex: Glut1

  47. Humanized monoclonal antibody reverses genetic obesity

  48. Anti-obesity effect of FGF antibody is at least partially independent of feeding

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