Pathophysiology of Type 2 Diabetes Deric Morrison October 14, 2009

Objectives Discuss the Pathophysiology of T2DM including: Discuss the Pathophysiology of T2DM including: Insulin Secretion Insulin Secretion Genetic Factors Genetic Factors Monogenic Monogenic Polygenic Polygenic Environmental factors Environmental factors Insulin Resistance Insulin Resistance Genetic Factors Genetic Factors Environmental factors Environmental factors

Introduction Type 2 Diabetes Type 2 Diabetes Hyperglycemia Hyperglycemia Insulin resistance (Skeletal muscle, liver, adipose tissue) - Early Insulin resistance (Skeletal muscle, liver, adipose tissue) - Early Insufficient pancreatic β cell compensation due to irreversible loss of β cell mass – Late Insufficient pancreatic β cell compensation due to irreversible loss of β cell mass – Late Increased hepatic glucose production Increased hepatic glucose production Genetic and environmental factors Genetic and environmental factors

Abnormal glucose tolerance Hyperinsulinemia, then  -cell failure Normal IGT* Type 2 diabetes Post-prandial glucose Insulin resistance Increased insulin resistance Fasting glucose Hyperglycemia Insulin secretion *IGT = impaired glucose tolerance Adapted from Type 2 Diabetes BASICS. International Diabetes Center (IDC), Minneapolis, 2000.

Epidemiology T2DM ~90% of DM burden worldwide T2DM ~90% of DM burden worldwide ~150 million people in 2005 ~150 million people in 2005 Estimated ~300 million in 2025 Estimated ~300 million in 2025

Associated Conditions Hypertension Hypertension High LDL High LDL Low HDL Low HDL Obesity Obesity Metabolic Syndrome Metabolic Syndrome Cause? Effect? Cause? Effect?

Pathophysiology The precise way genetic, environmental, and pathophysiologic factors interact to lead to the clinical onset of T2DM is not known The precise way genetic, environmental, and pathophysiologic factors interact to lead to the clinical onset of T2DM is not known Most T2DM is polygenic Most T2DM is polygenic Some specific monogenic defects largely confined to the pathways that regulate insulin action or β cell function cause DM Some specific monogenic defects largely confined to the pathways that regulate insulin action or β cell function cause DM

Monogenic

Monogenic - IR Type A insulin resistance Type A insulin resistance insulin resistance insulin resistance acanthosis nigricans acanthosis nigricans hyperandrogenism hyperandrogenism Leprechaunism Leprechaunism intrauterine growth retardation intrauterine growth retardation fasting hypoglycemia fasting hypoglycemia death within the first 1 to 2 years of life death within the first 1 to 2 years of life Rabson-Mendenhall syndrome Rabson-Mendenhall syndrome short stature short stature protuberant abdomen protuberant abdomen abnormalities of teeth and nails abnormalities of teeth and nails

Monogenic - IR Lipoatrophic diabetes Lipoatrophic diabetes paucity of fat paucity of fat insulin resistance insulin resistance hypertriglyceridemia hypertriglyceridemia Face-sparing partial lipoatrophy (Dunnigan Syndrome) Face-sparing partial lipoatrophy (Dunnigan Syndrome) Lamin A/C gene mutation (AD) Lamin A/C gene mutation (AD) Congenital generalized lipoatrophy (the Seip- Berardinelli syndrome - AR) Congenital generalized lipoatrophy (the Seip- Berardinelli syndrome - AR)

Monogenic - IS Mutant Insulin Syndromes Mutant Insulin Syndromes Hyperinsulinemia Hyperinsulinemia Mild DM, but no resistance to exogenous insulin Mild DM, but no resistance to exogenous insulin Mitochondrial Diabetes Mitochondrial Diabetes Maternally transmitted Maternally transmitted Diabetes Diabetes Sensorineural hearing loss Sensorineural hearing loss

Maturity Onset Diabetes of the Young Gene Molecular Basis MODY-1 HNF-4α Defect in transcription → ↓insulin secretion/β-cell mass MODY-2Glucokinase ↓ Sn of β-cell to glucose/ ↓ glucose → glycogen

MODY Gene Molecular Basis MODY-3 HNF-1α Defect in transcription → ↓insulin secretion/β-cell mass MODY-4IPF-1 Defect in transcription → Abnormal β-cell development and function

MODY Gene Molecular Basis MODY-5 HNF-1β Defect in transcription → ↓insulin secretion/β-cell mass MODY-6 NeuroD1 or β2 Defect in transcription → Abnormal β-cell development and function

MODY May account for 1-5% of DM May account for 1-5% of DM Often mild (especially the most common MODY-2 Glucokinase) Often mild (especially the most common MODY-2 Glucokinase) Family Hx in successive generations Family Hx in successive generations Onset often childhood/adolescence Onset often childhood/adolescence

DM2 Genetics High risk in certain ethnic groups High risk in certain ethnic groups Pima Indians ~21% Pima Indians ~21% 3.5x risk in 1 st degree relatives 3.5x risk in 1 st degree relatives Monozygotic vs. dizygotic twins Monozygotic vs. dizygotic twins 70 vs. 10% concordance 70 vs. 10% concordance

DM2 Genetics Common variant-common disease hypothesis (i.e. not Mendelian) Common variant-common disease hypothesis (i.e. not Mendelian) Simultaneous occurrence of common DNA sequence variations in many genes that in their sum confer an increased susceptibility toward adverse environmental factors. Simultaneous occurrence of common DNA sequence variations in many genes that in their sum confer an increased susceptibility toward adverse environmental factors. At least 27 (confirmed and potential) T2DM susceptibility genes have been identified At least 27 (confirmed and potential) T2DM susceptibility genes have been identified

Genome Wide Association

Genetics and Insulin Secretion Insulin secretion is stimulated by Insulin secretion is stimulated by Glucose Glucose Incretins Incretins Glucagon Like Peptide (GLP-1) Glucagon Like Peptide (GLP-1) Gastric Inhibitory Polypeptide (GIP) Gastric Inhibitory Polypeptide (GIP)

Glucose Taken up via glucose transporters Taken up via glucose transporters Phosphorylated by glucokinase, metabolized Phosphorylated by glucokinase, metabolized ATP is generated that causes closure of the ATP sensitive potassium channel ATP is generated that causes closure of the ATP sensitive potassium channel This provokes membrane depolarization and subsequent opening of a voltage-dependent calcium channel This provokes membrane depolarization and subsequent opening of a voltage-dependent calcium channel Calcium influx raises the cytosolic calcium concentration, and promotes exocytosis of insulin granules Calcium influx raises the cytosolic calcium concentration, and promotes exocytosis of insulin granules

Incretins In the presence of glucose incretins enhance insulin secretion In the presence of glucose incretins enhance insulin secretion Binding to G protein-coupled transmembrane receptors activates adenylyl cyclase → cAMP Binding to G protein-coupled transmembrane receptors activates adenylyl cyclase → cAMP cAMP activates protein kinase A, which mediates induction of the insulin gene and exocytosis of insulin granules cAMP activates protein kinase A, which mediates induction of the insulin gene and exocytosis of insulin granules

Insulin Secretion Genetics Hypothesis: individual differences in insulin secretion capacity are predominantly determined by genetics Hypothesis: individual differences in insulin secretion capacity are predominantly determined by genetics Strengthened by the finding that 18 among those 27 genes mentioned affect β-cell function Strengthened by the finding that 18 among those 27 genes mentioned affect β-cell function CAPN10, CDC123/CAMK1D, CDKAL1, CDKN2A/B, ENPP1, FOXO1, HHEX, IGF2BP2, JAZF1, KCNJ11, KCNQ1, MTNR1B, PPARGC1A, SGK1, SLC30A8, TCF7L2, TSPAN8/LGR5 and WFS1 CAPN10, CDC123/CAMK1D, CDKAL1, CDKN2A/B, ENPP1, FOXO1, HHEX, IGF2BP2, JAZF1, KCNJ11, KCNQ1, MTNR1B, PPARGC1A, SGK1, SLC30A8, TCF7L2, TSPAN8/LGR5 and WFS1

Insulin Secretion Some Single Nucleotide Polymorphisms affect: Some Single Nucleotide Polymorphisms affect: β-cell response to GLP-1 β-cell response to GLP-1 GIP/GLP-1 levels GIP/GLP-1 levels Proinsulin conversion Proinsulin conversion Free Fatty Acid Levels Free Fatty Acid Levels Leading to decreased β-Cell function Leading to decreased β-Cell function

Chronic hyperglycemia Oversecretion of insulin to compensate for insulin resistance 1,2 High circulating free fatty acids Glucotoxicity 2 Pancreas Lipotoxicity 3  -cell dysfunction 1 Boden G & Shulman GI. Eur J Clin Invest 2002; 32:14–23. 2 Kaiser N, et al. J Pediatr Endocrinol Metab 2003; 16:5–22. 3 Finegood DT & Topp B. Diabetes Obes Metab 2001; 3 (Suppl. 1):S20–S27. β Cell Failure Genetic Mutations

Insulin Resistance Subnormal response to insulin Subnormal response to insulin Genetic β-cell defects only apparent when insulin requirements > insulin production Genetic β-cell defects only apparent when insulin requirements > insulin production Insulin resistance is strongly associated with obesity Insulin resistance is strongly associated with obesity Environmental factors? Environmental factors? Calculating insulin sensitivity Calculating insulin sensitivity BG and insulin levels BG and insulin levels OGTT OGTT Euglycemic clamp Euglycemic clamp Isotope tracer methods Isotope tracer methods

Insulin Resistance There are obesity independent genetic factors of insulin resistance There are obesity independent genetic factors of insulin resistance e.g. PPAR-γ e.g. PPAR-γ 2 Isoforms 2 Isoforms PPAR-γ-1: expressed in a number of tissues and cell types at moderate levels PPAR-γ-1: expressed in a number of tissues and cell types at moderate levels PPAR-γ-2: largely restricted to adipose tissue, where it represents a master regulator of fat cell differentiation PPAR-γ-2: largely restricted to adipose tissue, where it represents a master regulator of fat cell differentiation

Insulin Resistance PPAR-γ-2 PPAR-γ-2 P12Avariant ? → ↓ adipose insulin sensitivity→ ↑ release of fatty acids→ ↓ muscle and liver insulin sensitivity P12Avariant ? → ↓ adipose insulin sensitivity→ ↑ release of fatty acids→ ↓ muscle and liver insulin sensitivity PPAR-γ is the target of TZDs → ↑ insulin sensitivity PPAR-γ is the target of TZDs → ↑ insulin sensitivity

Insulin Resistance May be best predictor of T2DM May be best predictor of T2DM ↑ with age and weight ↑ with age and weight ? Unmasking defect of β-cell function ? Unmasking defect of β-cell function Leads to Hyperglycemia Leads to Hyperglycemia Hyperglycemia has toxic effects on β-cell Hyperglycemia has toxic effects on β-cell

Obesity Causes peripheral resistance to insulin-mediated glucose uptake Causes peripheral resistance to insulin-mediated glucose uptake May ↓ sensitivity of β-cells to glucose May ↓ sensitivity of β-cells to glucose Potential Exacerbating Factors Potential Exacerbating Factors Abdominal > Peripheral fat Abdominal > Peripheral fat β-3-adrenergic receptor mutation β-3-adrenergic receptor mutation ↑ c-Jun amino-terminal kinase (JNK) activity ↑ c-Jun amino-terminal kinase (JNK) activity Inflammatory Adipokines Inflammatory Adipokines (leptin, adiponectin, TNF α, and resistin) (leptin, adiponectin, TNF α, and resistin) ↑ Free fatty acids ↑ Free fatty acids

Leptin Produced by adipocytes, secreted in proportion to adipocyte mass Produced by adipocytes, secreted in proportion to adipocyte mass Signals the hypothalamus about the quantity of stored fat Signals the hypothalamus about the quantity of stored fat Leptin deficiency and leptin resistance → obesity and insulin Leptin deficiency and leptin resistance → obesity and insulin Leptin may be important for the regulation of beta cell mass/function depending upon diet and presence of insulin resistance Leptin may be important for the regulation of beta cell mass/function depending upon diet and presence of insulin resistance

Adiponectin Reduces levels of free fatty acids and associated with Reduces levels of free fatty acids and associated with improved lipid profiles improved lipid profiles better glycemic control better glycemic control reduced inflammation in diabetic patients reduced inflammation in diabetic patients inversely associated with risk for diabetes in the non- diabetic population inversely associated with risk for diabetes in the non- diabetic population

Adiponectin Lower adiponectin levels are more closely related to the degree of insulin resistance and hyperinsulinemia than to the degree of adiposity and glucose intolerance Lower adiponectin levels are more closely related to the degree of insulin resistance and hyperinsulinemia than to the degree of adiposity and glucose intolerance Adiponectin is downregulated in obesity Adiponectin is downregulated in obesity ↓ Adiponectin → ↑ TNF-α and ↑ insulin resistance ↓ Adiponectin → ↑ TNF-α and ↑ insulin resistance

TNF-α ? major role in insulin action impairment ? major role in insulin action impairment A preliminary study found a strong correlation between the degree of obesity, hyperinsulinemia, and TNF-α mRNA in adipose tissue. A preliminary study found a strong correlation between the degree of obesity, hyperinsulinemia, and TNF-α mRNA in adipose tissue. In a study of a homogeneous Native Canadian population plasma TNF-α concentrations were positively correlated with insulin resistance In a study of a homogeneous Native Canadian population plasma TNF-α concentrations were positively correlated with insulin resistance

Plasminogen activator inhibitor An inhibitor of fibrinolysis, is another protein related to adipocytes. An inhibitor of fibrinolysis, is another protein related to adipocytes. It is also secreted from endothelial cells, mononuclear cells, hepatocytes, and fibroblasts It is also secreted from endothelial cells, mononuclear cells, hepatocytes, and fibroblasts May be associated with an increased risk for T2DM May be associated with an increased risk for T2DM

Resistin In obese mice adipocytes secrete resistin In obese mice adipocytes secrete resistin Administration of resistin decreases insulin- mediated glucose uptake by adipocytes Administration of resistin decreases insulin- mediated glucose uptake by adipocytes Neutralization of resistin increases insulin- mediated glucose uptake by adipocytes Neutralization of resistin increases insulin- mediated glucose uptake by adipocytes Hypothalamic administration of resistin enhances glucose production, independent of changes in glucoregulatory hormones Hypothalamic administration of resistin enhances glucose production, independent of changes in glucoregulatory hormones

Retinol-binding protein 4 Released from adipocytes Released from adipocytes Correlates with the degree of insulin resistance in mice, ? humans Correlates with the degree of insulin resistance in mice, ? humans

Intrauterine Development Low birth weight “Thrifty" genotype hypothesis Low birth weight “Thrifty" genotype hypothesis Insulin resistance might improve survival during states of caloric deprivation but would lead to diabetes in states of caloric excess or adequacy. Insulin resistance might improve survival during states of caloric deprivation but would lead to diabetes in states of caloric excess or adequacy.

Intrauterine Development Thrifty genotype might be induced by IUGR Thrifty genotype might be induced by IUGR Inverse relationship between birth weight and DM in Nurses' Health Study (69,000 women) Inverse relationship between birth weight and DM in Nurses' Health Study (69,000 women) Relative risk of T2DM by ascending birth weight categories decreased progressively Relative risk of T2DM by ascending birth weight categories decreased progressively Thinness at birth vs. in adult life have opposing effects on insulin resistance Thinness at birth vs. in adult life have opposing effects on insulin resistance

Adult, kg/m 2

Intrauterine Development Higher birth weight (>4.0 kg) may also be associated with an increased risk of diabetes Higher birth weight (>4.0 kg) may also be associated with an increased risk of diabetes A meta-analysis of 14 studies (132,180 babies) of birth weight and risk of T2DM A meta-analysis of 14 studies (132,180 babies) of birth weight and risk of T2DM U-shaped relationship between birth weight and diabetes risk U-shaped relationship between birth weight and diabetes risk High birth weight was associated with increased risk of diabetes in later life to the same extent as low birth weight High birth weight was associated with increased risk of diabetes in later life to the same extent as low birth weight Prematurity independent of birth weight may also be a risk factor for insulin resistance Prematurity independent of birth weight may also be a risk factor for insulin resistance

Summary Type 2 Diabetes Type 2 Diabetes Hyperglycemia Hyperglycemia Insulin resistance (Skeletal muscle, liver, adipose tissue) - Early Insulin resistance (Skeletal muscle, liver, adipose tissue) - Early Insufficient pancreatic β cell compensation due to irreversible loss of β cell mass – Late Insufficient pancreatic β cell compensation due to irreversible loss of β cell mass – Late Increased hepatic glucose production Increased hepatic glucose production Genetic and environmental factors Genetic and environmental factors

Summary Insulin Resistance Insulin Resistance Intrauterine Intrauterine Low/High birth weight Low/High birth weight Prematurity Prematurity Obesity/Inflammation Obesity/Inflammation Central, JNK, FFA, adipokines Central, JNK, FFA, adipokines Genetic Genetic PPAR-γ PPAR-γ Others Others

Summary Insulin Secretion/β-cell Function Insulin Secretion/β-cell Function Monogenic Monogenic MODY MODY Polygenic Polygenic SNPs afffecting SNPs afffecting Response to glucose Response to glucose Response to incretins Response to incretins

Selected References Williams Williams UpToDate UpToDate