METABOLIC REGULATION: THE ROLE OF INSULIN/GLUCAGON IN DIABETES

Transcription

1 METABOLIC REGULATION: THE ROLE OF INSULIN/GLUCAGON IN DIABETES Helena Caria Biomedical Sciences Department, School of Health, Polytechnic Institute of Setubal 8/12/2016

2 Glucose is the main source of ATP in human body

3 Glicose uptake is regulated by pancreatic hormones Glucagon Insulin Peptide homones

4 Liver and pancreas are two major organ for the regulation of the level of glucose in the blood: Insulin and glucagon ensure the regulation of glucose blood level (Glicemia)

5 Peptide Hormones are indirect hormones AVILA, 1995 Insulin Receptor

6 Synthesis of Insuline : INS gene INS gene IDDM2 locus Chr 11 Klemens Raile et al. Eur J Endocrinol 2011;165: IDDM2 locus contributes to about 10% toward type 1 diabetes susceptibility. VNTR (variable number tandem repeats) and SNPs of the INS gene may play a role in susceptibility to type 1 and type 2 diabetes. There are three classes of VNTR in the INS gene: Class I ± repeat units (Caucasians: 70% of alleles being in the range of repeats). Class II ± 80 repeat units. Class III ± repeat units (Caucasians ±30% with alleles longer than 110 repeat). VNTR of INS gene affects the transcription of the insulin gene in some way: the class III alleles are associated with 15-30% lower INS mrna in pancreas and higher rate of expression in thymus, and have a

7 From Genes to protein 1 gene 1 peptide

8 Synthesis of Insuline - occurs in the β cells 1. Synthesis primarily beigins with the formation of preproinsulin 2. Preproinsulin is then cleaved by protease activity into proinsulin 3. Proinsulin is then packaged into vesicles in the Golgi apparatus 4. Proinsulin is then converted by enzymes into insulin and connecting peptide (C-peptide) Adapted from

9 Insulin synthesis and secretion process 1. After preproinsulin mrna transcription, preproinsulin is synthesized in the ER and converted into proinsulin. 2. Proinsulin is transported through the Golgi apparatus and packaged into immature clathrin-coated granules, where proinsulin is processed into insulin and c- peptide. 3. The immature granules can then become mature granules containing cystalized insulin. After glucose stimulation insulin granules joint in a pool of granules and are ready for immediate release and most remaining granules (> 95%) belong to a reserve pool responsible for the secondphase of insulin secretion

10 Insulin secretion: the role of glucose controlling the insulin gene transcription (1) Glucose metabolism in β-cells generates upstream signals that are responsible for the activation of factors involved in insulin transcription: a) Glucose metabolism causes a shift of transcription factor PDX-1 from the cytoplasm to the nucleus, increases its activation domain and binding to A3 element b) Stimulatory concentrations of glucose can activate ERK1/2, which promotes BETA2 and E47 heterodimerization and binding to E-box sites c) Glucose affects MafA at the mrna level. Stimulatory glucose levels increase MafA transcription and result in increased MafA protein responsible for gene activation

11 Insulin secretion: the role of glucose in insulin translation (2) Glucose stimulates insulin synthesis by promoting insulin translation initiation. Glucose: a) promotes the phosphorylation of eif- 4EBP and activates eif-4e; eif-4e, eif-4a and eif-4g form eif-4f, a complex whose functions include recognition of preproinsulin mrna and recruiting 40S ribosome to mrna. b) causes the dephosphorylation of eif2α, and induces an increase in the availability of the translational ternary complex c) activate eif-2b thus leading to GTP-bound eif-2, a critical factor regulating protein biosynthesis. d) leading to the formation of eif2-gtp MettRNAi translational ternary complex, which binds 40S ribosome and is indispensable for protein translation.

12 Insulin secretion: the stimulation by glucose (3) Glucose-stimulates insulin secretion by increasing the ATP/ADP ratio, which inhibits the ATP-sensitive KATP-channels, leading to membrane depolarization and opening of voltage-dependent calcium channels (VDCC), with a resultant major increase in cytosolic calcium, which, in turn, triggers exocytosis. SNARE proteins (plasma membrane proteins syntaxin and SNAP-25, vesicle protein VAMP- 2/synaptobrevin-2) play a critical role in insulin granule secretion, causing the docking of the vesicle, bringing insulin granules in close contact with the plasma membrane and calcium channels. After opening of calcium channels, the readily releasable pool insulin granules located nearby are exposed to high level of Ca 2+, resulting in granule exocytosis. Ren et al. Pancreatic islet cell therapy for type I diabetes: understanding the effects of glucose stimulation on islets in order to produce better islets for transplantation. J Transl Med (2007).

13 Synthesis of Glucagon: GCG gene The protein encoded by this gene is actually a preproprotein that is cleaved into four distinct mature peptides: One of these, glucagon (29 a.a.), is a pancreatic hormone that counteracts the glucose-lowering action of insulin by stimulating glycogenolysis and gluconeogenesis with a very short half-life in the blood. Glucagon is a ligand for a specific G-protein linked receptor whose signalling pathway controls cell proliferation. Two of the other peptides are secreted from gut endocrine cells and promote nutrient absorption through distinct mechanisms. GCG gene

14 Antagonic Effects of Insulin and Glucagon Glucose Glycogen Low blood glucose High blood glucose Insulin Glucagon Raises blood glucose Lowers blood glucose Fatty acids and glycerol Fat a.a. Protein Adapted from McKee and McKee, 2003.

15 Antagonic Effect of Insulin and Glucagon Glucagon receptor Insulin receptor Epinephrine receptor liver (+) Adenylate cyclase (-) (+) muscle ATP AMPc Phosphorylase kinase (inactive) Phosphorylase kinase (active) Phosphorylase kinase (inactive) Phosphorylase kinase (active) Glycogen (active) synthase Glycogen synthase (inactive) Phosphoprotein phosphatase Phosphoprotein phosphatase Glycogen phosphorylase (inactive) Glycogen phosphorylase (active) Glycogen Glucose-1-phosphate (+) Insulin Glycogen synthase (active) UDP-glucose UTP UDP-glucose-pyrophosphorylase PPi

16 Diabetes mellitus is a heterogeneous group of metabolic disorders characterized by persistent hyperglycemia. Insulin deficiency Increased hepatic glycogenolysis Decreased glucose utilization Increased hepatic Ketogenesis Decreased Ketone utilization Increased hepatic glycogenolysis Increased lipolysis Hyperglycemia Hyperketonemia Osmotic diuresis Dehydration Ketoacidosis Adaptaded from McKee and McKee, 2003.

17 Diabetes is the result either of insufficient production of insulin by the pancreas (Type 1, previously known as insulindependent diabetes or IDDM) or by cells in the body that do not respond properly to the insulin that is produced (Type 2, previously known as non-insulindependent diabetes or NIDDM).

18 Genetic of Diabetes: type 1 Type 1 diabetes is a polygenic autoimunedisease. There is evidence that more than 20 regions of the genome may be involved in genetic susceptibility: HLA class II genes in chr 6 (40-50% of the cases); INS gene in chr 11 (shorter class I variant predisposes to diabetes, whereas the longer class III variant appears to be dominantly protective); CTLA-4 gene in chr 2 (most common mutation is Thr17Ala)

19 Genetic of Diabetes: type 1 HLA (human leukocyte antigen) class II genes MHC (major histocompatibility complex) HLA is a gene complex encoding the major histocompatibility complex (MHC) proteins in humans. These cell-surface proteins are responsible for the regulation of the immune system in humans. Each of the class II antigens (DP, DQ, DR) is encoded by an α-chain-gene and by a β-chain-gene and codify to peptide α and β pair to form the functional HLA molecule. Expressed on B lymphocytes, activated T lymphocytes, monocytes, macrophages, Langerhans cells, dendritic cells, endothelium and epithelial cells

20 Genetic of Diabetes: type 1 CTLA-4 gene codify for the cytotoxic T-lymphocyte-associated protein 4 CTLA-4 negatively regulates T-cell function. Impaired activity of T-cell (associated with the Thr17Ala variant) due to mutations in the gene, may increase diabetes risk (~ 1.5 X), and have been associated with insulin-dependent diabetes mellitus (as other diseases: Graves disease, Hashimoto thyroiditis, celiac disease, systemic lupus erythematosus, thyroid-associated orbitopathy and other autoimmune diseases). CTLA-4, 2q31-35

21 Genetic of Diabetes: type 2 Some genes associated with type 2 diabetes risk include: TCF7L2 (Transcription factor 7L2 at 5q34-q35.2) - affects insulin secretion and glucose production ABCC8 and KCNJ11 (11p15.1) - helps regulate insulin action CALPN10 (Calcium-Activated Neutral Proteinase at 2q37.3, c.a43g) - associated with type 2 diabetes risk in Mexican-Americans GLUT2 (Glucose transporter 2 at 3q ) - helps move glucose into the pancreas GCG - glucagon gene PPAR (Peroxisome proliferator-activated receptor gamma at 3p25; Pro12Ala) - decreases insulin sensitivity and increases the risk by several fold.

22 Genetic of Diabetes: type 2 KCNJ11 gene provides instructions for making 4 subunits of the ATP-sensitive potassium (K-ATP) channel (each consists of eight subunits). The ABCC8 gene provides instructions for making the sulfonylurea receptor 1 (SUR1) protein and other 3 proteins. KCNJ11 gene ABCC8 gene Mutations in KCNJ11 gene accounts for 30% of the cases. Mutations in ABCC8 accounts for 20% of the cases. The K-ATP channels are embedded in cell membranes of the β cells. Closure of the K-ATP channels results in a process that triggers insulin secretion by β cells, which helps control blood sugar levels.

23 Insulin: resistance? Obesity is a component of the metabolic syndrome, mechanistically linked to diabetes, fatty liver disease, and cardiovascular disease

24 Insuline Resistance: INSR (insuline receptor) gene mutations INSR mutations can have either an autosomal dominant or, less commonly, an autosomal recessive pattern of inheritance. Patients with INSR mutations (Donohue syndrome, Rabson Mendenhall syndrome) exhibit major growth defects and insulin resistance so severe as to mimic untreated type 1 diabetes The E3 ubiquitin ligase MARCH1 potently inhibits cellular insulin sensitivity in multiple cell types including hepatocytes and adipocytes, and is itself transcriptionally regulated by insulin through the transcription factor FOXO1 In the insulin-sensitive state, INSR activation inhibits FOXO1, resulting in transcriptional repression of MARCH1, increasing surface INSR levels and preserved insulin signalling. In the insulin-resistant state, insulin fails to inhibit FOXO1, resulting in inappropriately increased MARCH1 expression, decreased surface INSR levels, and impaired insulin signalling.

25 Graphene patch could help patients manage diabetes A wearable, graphene-based patch could one day maintain healthy blood glucose levels in people by measuring the sugar in sweat and then delivering the necessary dose of a diabetes drug through the skin (Nat. Nanotechnol. 2016, DOI: /nnano ). Nallon et al.(2016)

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27 THANK YOU!

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