1
|
El K, Gray SM, Capozzi ME, Knuth ER, Jin E, Svendsen B, Clifford A, Brown JL, Encisco SE, Chazotte BM, Sloop KW, Nunez DJ, Merrins MJ, D'Alessio DA, Campbell JE. GIP mediates the incretin effect and glucose tolerance by dual actions on α cells and β cells. SCIENCE ADVANCES 2021; 7:7/11/eabf1948. [PMID: 33712466 PMCID: PMC7954443 DOI: 10.1126/sciadv.abf1948] [Citation(s) in RCA: 66] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Accepted: 01/26/2021] [Indexed: 05/23/2023]
Abstract
Glucose-dependent insulinotropic polypeptide (GIP) communicates nutrient intake from the gut to islets, enabling optimal levels of insulin secretion via the GIP receptor (GIPR) on β cells. The GIPR is also expressed in α cells, and GIP stimulates glucagon secretion; however, the role of this action in the postprandial state is unknown. Here, we demonstrate that GIP potentiates amino acid-stimulated glucagon secretion, documenting a similar nutrient-dependent action to that described in β cells. Moreover, we demonstrate that GIP activity in α cells contributes to insulin secretion by invoking paracrine α to β cell communication. Last, specific loss of GIPR activity in α cells prevents glucagon secretion in response to a meal stimulus, limiting insulin secretion and driving glucose intolerance. Together, these data uncover an important axis by which GIPR activity in α cells is necessary to coordinate the optimal level of both glucagon and insulin secretion to maintain postprandial homeostasis.
Collapse
Affiliation(s)
- K El
- Duke Molecular Physiology Institute, Duke University, Durham, NC, USA
| | - S M Gray
- Duke Molecular Physiology Institute, Duke University, Durham, NC, USA
| | - M E Capozzi
- Duke Molecular Physiology Institute, Duke University, Durham, NC, USA
| | - E R Knuth
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, University of Wisconsin-Madison, Madison, WI, USA
| | - E Jin
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, University of Wisconsin-Madison, Madison, WI, USA
| | - B Svendsen
- Duke Molecular Physiology Institute, Duke University, Durham, NC, USA
| | - A Clifford
- Duke Molecular Physiology Institute, Duke University, Durham, NC, USA
| | - J L Brown
- Duke Molecular Physiology Institute, Duke University, Durham, NC, USA
| | - S E Encisco
- Duke Molecular Physiology Institute, Duke University, Durham, NC, USA
| | - B M Chazotte
- Duke Molecular Physiology Institute, Duke University, Durham, NC, USA
| | - K W Sloop
- Diabetes and Complications, Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, IN, USA
| | - D J Nunez
- Duke Molecular Physiology Institute, Duke University, Durham, NC, USA
| | - M J Merrins
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, University of Wisconsin-Madison, Madison, WI, USA
| | - D A D'Alessio
- Duke Molecular Physiology Institute, Duke University, Durham, NC, USA
- Division of Endocrinology, Department of Medicine, Duke University, Durham, NC, USA
| | - J E Campbell
- Duke Molecular Physiology Institute, Duke University, Durham, NC, USA.
- Division of Endocrinology, Department of Medicine, Duke University, Durham, NC, USA
- Department of Pharmacology and Cancer Biology, Duke University, Durham, NC, USA
| |
Collapse
|
2
|
Sandoval D. Updating the Role of α-Cell Preproglucagon Products on GLP-1 Receptor-Mediated Insulin Secretion. Diabetes 2020; 69:2238-2245. [PMID: 33082272 PMCID: PMC7576561 DOI: 10.2337/dbi19-0027] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/08/2020] [Accepted: 08/10/2020] [Indexed: 02/06/2023]
Abstract
While the field of islet biology has historically focused its attention on understanding β-cell function and the mechanisms by which these cells become dysfunctional with diabetes, there has been a scientific shift toward greater understanding of other endocrine cells of the islet and their paracrine role in regulating the β-cell. In recent years, many questions and new data have come forward regarding the paracrine role of the α-cell and specifically preproglucagon peptides in regulating insulin secretion. The role of intestinally secreted glucagon-like peptide 1 (GLP-1) in regulation of insulin secretion has been questioned, and a physiological role of pancreatic GLP-1 in regulation of insulin secretion has been proposed. In addition, in the last 2 years, a series of studies demonstrated a physiological role for glucagon, acting via the GLP-1 receptor, in paracrine regulation of insulin secretion. Altogether, this work challenges the textbook physiology of both GLP-1 and glucagon and presents a critical paradigm shift for the field. This article addresses these new findings surrounding α-cell preproglucagon products, with a particular focus on GLP-1, in the context of their roles in insulin secretion and consequently glucose metabolism.
Collapse
|
3
|
El K, Campbell JE. The role of GIP in α-cells and glucagon secretion. Peptides 2020; 125:170213. [PMID: 31785304 PMCID: PMC7580028 DOI: 10.1016/j.peptides.2019.170213] [Citation(s) in RCA: 48] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/10/2019] [Revised: 11/22/2019] [Accepted: 11/25/2019] [Indexed: 02/07/2023]
Abstract
Glucose-dependent insulinotropic polypeptide (GIP) is an intestinally derived peptide that is secreted in response to feeding. The GIP receptor (GIPR) is expressed in many cell types involved in the regulation of metabolism, including α- and β-cells. Glucagon and insulin exert tremendous control over glucose metabolism. Thus, GIP action in islets strongly dictates metabolic control in the postprandial state. Loss of GIPR activity in β-cells is a characteristic of type 2 diabetes (T2D) which associates with reduced postprandial insulin secretion and hyperglycemia. Less is known about GIPR activity in α-cells or the control of glucagon secretion. GIP stimulates glucagon secretion in a glucose-dependent manner in healthy people, with enhanced activity at lower glycemia. However, GIP stimulates glucagon secretion even at hyperglycemia in people with T2D, suggesting that inappropriate GIPR activity in α-cells contributes to the pathogenesis of T2D. Here, we review the literature describing GIP action and GIPR activity in the α-cell, detailing the basic science that has shaped the view of how GIP regulates glucagon secretion. We also contrast the effects of GIP on glucagon secretion in healthy and T2D people. Finally, we contextualize these observations in light of recent work that redefines the role of glucagon in glucose homeostasis, suggesting that hyperglucagonemia per se does not drive hyperglycemia. As new medications for T2D that incorporate GIPR activity are being developed, it is clear that a better understanding of GIPR activity beyond the β-cell is necessary. This work highlights the importance of focusing on the GIPR in α-cells.
Collapse
Affiliation(s)
| | - Jonathan E Campbell
- Duke Molecular Physiology Institute, USA; Department of Medicine, Division of Endocrinology, Duke University, Durham, NC, USA; Department of Pharmacology and Cancer Biology, Duke University, Durham, NC, USA.
| |
Collapse
|
4
|
Karlsson S, Scheurink AJW, Ahrén B. Gender difference in the glucagon response to glucopenic stress in mice. Am J Physiol Regul Integr Comp Physiol 2002; 282:R281-8. [PMID: 11742849 DOI: 10.1152/ajpregu.2002.282.1.r281] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A gender difference in the glucagon response to insulin-induced hypoglycemia was previously demonstrated in humans. Whether this reflects a gender difference in autonomic activation or in pancreatic alpha-cell regulation is not known. We investigated the glucagon, epinephrine, and norepinephrine responses to neuroglycopenic stress induced by 2-deoxy-D-glucose (2-DG) or insulin in female and male mice. 2-DG increased plasma glucagon levels by 559 +/- 68% in females versus 281 +/- 46% in males (P < 0.01). Plasma levels of epinephrine or norepinephrine after 2-DG administration did not differ between genders. During insulin-induced hypoglycemia, the glucagon response was similarly higher in females (P < 0.001), whereas the plasma catecholamine response was higher in males (P < 0.05). In vivo, the glucagon response to carbachol or clonidine was higher in females (P < 0.05). In isolated islets, the glucagon response to carbachol (100 microM; P = 0.003) but not to clonidine (1 microM) was larger in females. We conclude that in addition to a larger alpha-cell mass (previously described in female mice), an increased sensitivity of the glucagon-producing alpha-cell to cholinergic activation contributes to the larger glucagon response to glucopenic stress in female mice.
Collapse
Affiliation(s)
- Sven Karlsson
- Department of Medicine, Lund University, SE-221 84 Lund, Sweden.
| | | | | |
Collapse
|
6
|
Deacon CF, Danielsen P, Klarskov L, Olesen M, Holst JJ. Dipeptidyl peptidase IV inhibition reduces the degradation and clearance of GIP and potentiates its insulinotropic and antihyperglycemic effects in anesthetized pigs. Diabetes 2001; 50:1588-97. [PMID: 11423480 DOI: 10.2337/diabetes.50.7.1588] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Glucose-dependent insulinotropic peptide (GIP) is known to be degraded by dipeptidyl peptidase IV (DPP IV), forming an inactive metabolite, but the extent of the enzyme's role in regulating the biological activity of GIP in vivo is still largely unknown. In nonfasted anesthetized pigs given an intravenous infusion of GIP, the intact peptide (determined by a novel NH(2)-terminally directed radioimmunoassay) accounts for only 14.5 +/- 2.5% of total immunoreactivity. This is increased (to 40.9 +/- 0.9%, P < 0.0001) by coadministration of valine-pyrrolidide (a specific DPP IV inhibitor) at a dose that completely inhibits plasma DPP IV activity. The plasma t(1/2) of intact GIP is prolonged by the inhibitor (from 3.3 +/- 0.3 to 8.1 +/- 0.6 min; P < 0.001), whereas the t(1/2) for COOH-terminal immunoreactivity is unaffected (13.2 +/- 0.5 and 11.5 +/- 0.8 min, pre- and postinhibitor). Measurement of arteriovenous concentration differences revealed that the liver, kidney, and extremities are the main sites of removal of exogenous intact GIP (organ extractions, 28.0 +/- 2.2, 26.3 +/- 5.7, and 21.8 +/- 3.0%, respectively). These organ extractions are reduced (P < 0.02) but not eliminated (kidney and extremities) by valine-pyrrolidide (to 6.5 +/- 4.6, 14.1 +/- 3.1, and 13.9 +/- 2.4%, respectively). Valine-pyrrolidide potentiates the insulinotropic effect of GIP (P < 0.02), resulting in an enhanced glucose disappearance rate (k, from 8.0 +/- 0.5 to 15.5 +/- 2.2%/min; P < 0.01) and a reduction in the glucose excursion after an intravenous glucose load (area under the curve, from 133 +/- 23 to 75 +/- 9 min. mmol/l; P < 0.05). These results suggest that DPP IV plays an important role in GIP metabolism but is not the sole enzyme responsible for its NH(2)-terminal degradation. Nevertheless, DPP IV inhibition increases the proportion of intact peptide sufficiently to enhance its insulinotropic and antihyperglycemic effects.
Collapse
Affiliation(s)
- C F Deacon
- Department of Medical Physiology, The Panum Institute, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark.
| | | | | | | | | |
Collapse
|
7
|
Sherwood NM, Krueckl SL, McRory JE. The origin and function of the pituitary adenylate cyclase-activating polypeptide (PACAP)/glucagon superfamily. Endocr Rev 2000; 21:619-70. [PMID: 11133067 DOI: 10.1210/edrv.21.6.0414] [Citation(s) in RCA: 157] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The pituitary adenylate cyclase-activating polypeptide (PACAP)/ glucagon superfamily includes nine hormones in humans that are related by structure, distribution (especially the brain and gut), function (often by activation of cAMP), and receptors (a subset of seven-transmembrane receptors). The nine hormones include glucagon, glucagon-like peptide-1 (GLP-1), GLP-2, glucose-dependent insulinotropic polypeptide (GIP), GH-releasing hormone (GRF), peptide histidine-methionine (PHM), PACAP, secretin, and vasoactive intestinal polypeptide (VIP). The origin of the ancestral superfamily members is at least as old as the invertebrates; the most ancient and tightly conserved members are PACAP and glucagon. Evidence to date suggests the superfamily began with a gene or exon duplication and then continued to diverge with some gene duplications in vertebrates. The function of PACAP is considered in detail because it is newly (1989) discovered; it is tightly conserved (96% over 700 million years); and it is probably the ancestral molecule. The diverse functions of PACAP include regulation of proliferation, differentiation, and apoptosis in some cell populations. In addition, PACAP regulates metabolism and the cardiovascular, endocrine, and immune systems, although the physiological event(s) that coordinates PACAP responses remains to be identified.
Collapse
Affiliation(s)
- N M Sherwood
- Department of Biology, University of Victoria, British Columbia, Canada.
| | | | | |
Collapse
|