AICA-riboside induces apoptosis of pancreatic beta cells through stimulation of AMP-activated protein kinase

Abstract

Aims/hypothesis. Prolonged exposure of beta cells to low glucose concentrations triggers their apoptosis and is known to activate AMP-activated protein kinase (AMPK) in beta cell lines. We examined whether prolonged activation of AMPK can trigger apoptosis in rodent beta cells. Methods. Primary beta cells were FACS-purified from rats, and from wild-type and AMPK(alpha2)-deficient mice. AMPK activation in beta cells was induced by the adenosine analog AICA-riboside and detected by immunoblotting using a phosphospecific antibody. Apoptosis of rodent beta cells was monitored by FACS analysis of beta cell DNA content, by direct counting of apoptotic cells using fluorescence microscopy, or by measurement of their caspase-3 activity.Results. Dose-dependent and time-dependent apoptosis of the cells, concommittant with an activation of caspase-3, were suppressed by the caspase inhibitors zVAD-fmk and zDEVD-fmk. Apoptosis induction by AICA-riboside was also prevented by adding the MAPK-inhibitor SB203580 which blocked the AICAriboside-induced phosphorylation of AMPK. Beta cells isolated from AMPK-(alpha2)-deficient mice were resistant against AICA-riboside induced apoptosis. Conclusion/interpretation. Sustained activation of AMPK by AICA-riboside can trigger a caspasedependent apoptosis of pancreatic beta cells. [Diabetologia (2003) 46:250-254] Keywords AICA-riboside, AICAR, AMP-activated protein kinase, AMPK, knockout, apoptosis, signalling, beta cell, glucose, diabetes. nine nucleotides that express and signal the metabolic state of the cells. The rate of glucose oxidation influences cellular ATP, ADP and AMP concentrations and hence their regulatory role on beta cell functions. During glucose deprivation, the AMP over ATP ratio is expected to increase and thus to activate the AMP-activated protein kinase (AMPK). AMPK is a serinethreonine protein kinase that is composed of a catalytic subunit (α) and two regulatory subunits (β and γ) [2]. The control of its activity involves allosteric activation by AMP, as well as phosphorylation by AMPKkinase, the upstream kinase [2]. In several cell types, this enzyme has been described as a sensor for the energy state of the cells and as a metabolic master switch [2,3]. In beta cell lines, the AMPK activity is increased by culture at low glucose concentrations [4,5]. 5-aminoimidazole-4-carboxamide (AICA)-riboside Prolonged exposure of pancreatic beta cells to low glucose concentrations results in apoptosis of the cells [1]. The underlying mechanism is not known but might be initiated by altered concentrations of the ade-

Glycolytic rate and lymphomagenesis depend on PARP14, an ADP ribosyltransferase of the B aggressive lymphoma (BAL) family

“…AMPK mediates a prosurvival signal initiated by adiponectin treatment of cardiomyocytes after ischemia and reperfusion and is similarly protective against neuronal apoptosis (38,39). Conversely, sustained AMPK activation by high concentrations of an AMP analog caused apoptosis of normal and cancerous B cells and can similarly impact other cell types (40,41). These opposite outcomes were due either to cell type-specific differences or the degree of AMPK activation, its duration, and cross-talk in which AMPK inhibits signaling via mTOR or exercises ACC-independent functions (42).…”

High glucose and hydrogen peroxide increase c-Myc and haeme-oxygenase 1 mRNA levels in rat pancreatic islets without activating NF?B

“…These V-shaped glucose concentration response curves for changes in islet c-Myc and HO1 expression with a minimum at G10 are similar to that of beta cell death [29]. Whereas the stimulation of beta cell apoptosis by prolonged culture in low glucose may be due to activation of AMP-dependent protein kinase and stimulation of c-Myc expression under these conditions [23,30], it has been suggested that the deleterious effects of supraphysiological glucose concentrations on the beta cell phenotype result from NFκB activation by oxidative stress [12,[31][32][33][34] or by induction of production and autocrine actions of IL-1β [35].…”

AMP-activated protein kinase (AMPK) activating agents cause dephosphorylation of Akt and glycogen synthase kinase-3

“…Thus, AMPK promotes catabolism to enhance ATP synthesis and reduces anabolism to spare ATP utilization. Although these actions of AMPK support cell survival [8][9][10][11][12][13], activation of AMPK also has been reported to promote apoptotic cell death [14][15][16][17][18][19][20][21].…”