Ablation of AMP-activated protein kinase α1 and α2 from mouse pancreatic beta cells and RIP2.Cre neurons suppresses insulin release in vivo

Abstract

Aims/Hypothesis AMP-activated protein kinase (AMPK) is an evolutionarily-conserved enzyme and a target of antihyperglycemic agents including metformin. However, the precise role(s) of the enzyme in controlling insulin secretion remains uncertain. Methods The catalytic α1 and α2 subunits of AMPK were ablated selectively in pancreatic beta cells and hypothalamic neurons by breeding AMPKα1 null mice, bearing flox’d AMPKα2 alleles, with animals expressing Cre recombinase under the rat insulin promoter. The latter promoter was used to express constitutively-activated AMPK selectively in beta cells in transgenic mice. Food intake, body weight and urinary catecholamines were measured using metabolic cages. Glucose and insulin tolerance were determined after intraperitoneal injection. Beta cell mass and morphology were analysed by optical projection tomography and confocal immunofluorescence microscopy, respectively. Granule docking, insulin secretion, membrane potential, and intracellular free Ca2+ were measured with standard techniques. Results Trigenic βAMPKdKO mice, lacking both AMPK α subunits in the beta cell, displayed normal body weight and increased insulin sensitivity, but were profoundly insulin deficient. Secreted catecholamine levels were unchanged. Total beta cell mass was unaltered whilst mean islet and beta cell volume were reduced. AMPK-deficient beta cells displayed normal glucose-induced changes in membrane potential and intracellular free Ca2+ whilst granule docking and insulin secretion were enhanced. Conversely, βAMPK transgenic mice were glucose-intolerant and displayed defective insulin secretion. Conclusions/Interpretation Inhibition of AMPK activity within the beta cell is necessary, but not sufficient, for the stimulation of insulin secretion by glucose. AMPK activation in extrapancreatic RIP.Cre-expressing cells might also influence insulin secretion in vivo

Endurance Training Activates Pancreatic Islets Amp-Activated Kinase-Uncoupling Protein 2 Pathway and Reduces Insulin Secretion

“…Activated AMPK pathway blocks secretory granules transit (Tsuboi et al 2003, Sun et al 2010b. Furthermore, AMPK activation increases UCP2 content in several tissues such as liver, skeletal muscle, and hypothalamus (Pedersen et al 2001, Foretz et al 2005, Figure 3 Effect of endurance training on isolated pancreatic islets GIIS.…”

“…It has been argued that type 2 diabetes treatment would be associated with insulin-sensitive tissues and AMPK activation, whereas in pancreatic islets, this pathway might be inhibited, raising insulin secretion and sensitivity (Viollet et al 2009). It was recently reported that AMPK is involved with glucose sensing and insulin secretion, probably by increased expression of uncoupling protein 2 (UCP2) and granule docking control (Beall et al 2010, Sun et al 2010b. Indeed, it was also demonstrated that AMPK activation by metformin was able to reduce insulin secretion in human islets and MIN6 cells (Leclerc et al 2004).…”

Protein Kinases and Pancreatic Islet Function

“…In support of the above findings, it was recently demonstrated that transgenic mice overexpressing constitutively active AMPK specifically in pancreatic cells were glucose intolerant and displayed defective insulin secretion (26). Mice in which expression of both AMPK catalytic subunits was ablated selectively in pancreatic cells displayed defective glucose homeostasis due to defective insulin secretion in response to hyperglycaemia in vivo (26).…”

“…The second phase involves the activation of amplification pathways, also called K ATP channel independent mechanisms (18;21), whereby the increase in intracellular calcium concentrations following K ATP channel closure leads to changes in the sensitivity of the secretory machinery (18;22). Protein kinase A and C (21), AMP activated protein kinase (AMPK; (23)(24)(25)(26)(27), and insulin sensitive protein kinases such as protein kinase B and p70S6 kinase (28)(29)(30)(31)(32)(33), are involved in regulating the amplifying pathways. The phosphoinositide 3 kinases (PI3Ks) are also thought to be important in the regulation of insulin secretion and synthesis (34)(35)(36)(37)(38)(39)(40).…”

“…Mice in which expression of both AMPK catalytic subunits was ablated selectively in pancreatic cells displayed defective glucose homeostasis due to defective insulin secretion in response to hyperglycaemia in vivo (26). Ablation of the expression of AMPK catalytic subunits in the cell was protective against the deleterious effects of exposure to a high fat diet on insulin secretion (26).…”