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AICAR and Metformin Exert AMPK-dependent Effects on INS-1E Pancreatic β-cell Apoptosis via Differential Downstream Mechanisms.

Dai YL, Huang SL, Leng Y - Int. J. Biol. Sci. (2015)

Bottom Line: Both AICAR and metformin protected INS-1E cells from palmitate-induced apoptosis, as reflected by decreases in both cleaved caspase 3 protein expression and caspase 3/7 activity, and these protective effects were abrogated by AMPK inhibitor compound C.The protective action of AICAR was probably mediated by the suppression of triacylglycerol accumulation, increase in Akt phosphorylation and decrease in p38 MAPK phosphorylation, while metformin might exert its protective effect on INS-1E cells by decreases in both JNK and p38 MAPK phosphorylation.Our results provided new and informative clues for better understanding of the role of AMPK in β-cell apoptosis.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Zu Chong Zhi Road 555, Shanghai 201203, China.

ABSTRACT
The role of AMP-activated protein kinase (AMPK) in pancreatic β-cell apoptosis is still controversial, and the reasons for the discrepancies have not been clarified. In the current study, we observed the effects of two well-known AMPK activators 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) and metformin, on apoptosis in rat insulinoma INS-1E cells, and further explored their possible mechanisms. Both AICAR and metformin protected INS-1E cells from palmitate-induced apoptosis, as reflected by decreases in both cleaved caspase 3 protein expression and caspase 3/7 activity, and these protective effects were abrogated by AMPK inhibitor compound C. The protective action of AICAR was probably mediated by the suppression of triacylglycerol accumulation, increase in Akt phosphorylation and decrease in p38 MAPK phosphorylation, while metformin might exert its protective effect on INS-1E cells by decreases in both JNK and p38 MAPK phosphorylation. All these regulations were dependent on AMPK activation. However, under standard culture condition, AICAR increased JNK phosphorylation and promoted INS-1E cell apoptosis in an AMPK-dependent manner, whereas metformin showed no effect on apoptosis. Our study revealed that AMPK activators AICAR and metformin exhibited different effects on INS-1E cell apoptosis under different culture conditions, which might be largely attributed to different downstream mediators. Our results provided new and informative clues for better understanding of the role of AMPK in β-cell apoptosis.

No MeSH data available.


Related in: MedlinePlus

Effects of AICAR and metformin on fatty acid oxidation and TG accumulation in INS-1E cells exposed to palmitate. (A) Fatty acid oxidation was determined after INS-1E cells were exposed to 0.25 mM palmitate with or without 1 mM AICAR or 2 mM metformin for 10 h and further incubated with [3H]-palmitate for 2 h. Fatty acid oxidation was determined by liquid scintillation counting of 3H2O released into the aqueous phase. (B) Cellular TG content was evaluated after INS-1E cells were exposed to 0.25 mM palmitate with or without 1 mM AICAR or 2 mM metformin. (C) INS-1E cells were pretreated with compound C (10 μM) for 30 min and then exposed to 0.25 mM palmitate with or without 1 mM AICAR for 10 h, followed by measurement of TG content. Three or four independent experiments were performed. **P<0.01 vs corresponding columns as indicated; ns, not significant. Palm, palmitate; Met, metformin.
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Figure 3: Effects of AICAR and metformin on fatty acid oxidation and TG accumulation in INS-1E cells exposed to palmitate. (A) Fatty acid oxidation was determined after INS-1E cells were exposed to 0.25 mM palmitate with or without 1 mM AICAR or 2 mM metformin for 10 h and further incubated with [3H]-palmitate for 2 h. Fatty acid oxidation was determined by liquid scintillation counting of 3H2O released into the aqueous phase. (B) Cellular TG content was evaluated after INS-1E cells were exposed to 0.25 mM palmitate with or without 1 mM AICAR or 2 mM metformin. (C) INS-1E cells were pretreated with compound C (10 μM) for 30 min and then exposed to 0.25 mM palmitate with or without 1 mM AICAR for 10 h, followed by measurement of TG content. Three or four independent experiments were performed. **P<0.01 vs corresponding columns as indicated; ns, not significant. Palm, palmitate; Met, metformin.

Mentions: Based on the principle of glucolipotoxicity, effects of AICAR and metformin on fatty acid oxidation and TG content were detected. Chronic exposure of INS-1E cells to 0.25 mM palmitate resulted in a ~30% reduction of fatty acid oxidation, which was not rescued by an incubation with 1 mM AICAR or 2 mM metformin (Fig. 3A). In addition, cellular TG content increased 2.7-fold with palmitate incubation for 16 h. AICAR significantly inhibited TG accumulation, whereas metformin had no effect (P<0.01 vs palmitate-exposed cells; Fig. 3B). Furthermore, the lipid-lowering effect of AICAR was completely abrogated in the presence of compound C (Fig. 3C). This indicated that AICAR might inhibit palmitate-induced TG accumulation through activation of AMPK.


AICAR and Metformin Exert AMPK-dependent Effects on INS-1E Pancreatic β-cell Apoptosis via Differential Downstream Mechanisms.

Dai YL, Huang SL, Leng Y - Int. J. Biol. Sci. (2015)

Effects of AICAR and metformin on fatty acid oxidation and TG accumulation in INS-1E cells exposed to palmitate. (A) Fatty acid oxidation was determined after INS-1E cells were exposed to 0.25 mM palmitate with or without 1 mM AICAR or 2 mM metformin for 10 h and further incubated with [3H]-palmitate for 2 h. Fatty acid oxidation was determined by liquid scintillation counting of 3H2O released into the aqueous phase. (B) Cellular TG content was evaluated after INS-1E cells were exposed to 0.25 mM palmitate with or without 1 mM AICAR or 2 mM metformin. (C) INS-1E cells were pretreated with compound C (10 μM) for 30 min and then exposed to 0.25 mM palmitate with or without 1 mM AICAR for 10 h, followed by measurement of TG content. Three or four independent experiments were performed. **P<0.01 vs corresponding columns as indicated; ns, not significant. Palm, palmitate; Met, metformin.
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Related In: Results  -  Collection

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Figure 3: Effects of AICAR and metformin on fatty acid oxidation and TG accumulation in INS-1E cells exposed to palmitate. (A) Fatty acid oxidation was determined after INS-1E cells were exposed to 0.25 mM palmitate with or without 1 mM AICAR or 2 mM metformin for 10 h and further incubated with [3H]-palmitate for 2 h. Fatty acid oxidation was determined by liquid scintillation counting of 3H2O released into the aqueous phase. (B) Cellular TG content was evaluated after INS-1E cells were exposed to 0.25 mM palmitate with or without 1 mM AICAR or 2 mM metformin. (C) INS-1E cells were pretreated with compound C (10 μM) for 30 min and then exposed to 0.25 mM palmitate with or without 1 mM AICAR for 10 h, followed by measurement of TG content. Three or four independent experiments were performed. **P<0.01 vs corresponding columns as indicated; ns, not significant. Palm, palmitate; Met, metformin.
Mentions: Based on the principle of glucolipotoxicity, effects of AICAR and metformin on fatty acid oxidation and TG content were detected. Chronic exposure of INS-1E cells to 0.25 mM palmitate resulted in a ~30% reduction of fatty acid oxidation, which was not rescued by an incubation with 1 mM AICAR or 2 mM metformin (Fig. 3A). In addition, cellular TG content increased 2.7-fold with palmitate incubation for 16 h. AICAR significantly inhibited TG accumulation, whereas metformin had no effect (P<0.01 vs palmitate-exposed cells; Fig. 3B). Furthermore, the lipid-lowering effect of AICAR was completely abrogated in the presence of compound C (Fig. 3C). This indicated that AICAR might inhibit palmitate-induced TG accumulation through activation of AMPK.

Bottom Line: Both AICAR and metformin protected INS-1E cells from palmitate-induced apoptosis, as reflected by decreases in both cleaved caspase 3 protein expression and caspase 3/7 activity, and these protective effects were abrogated by AMPK inhibitor compound C.The protective action of AICAR was probably mediated by the suppression of triacylglycerol accumulation, increase in Akt phosphorylation and decrease in p38 MAPK phosphorylation, while metformin might exert its protective effect on INS-1E cells by decreases in both JNK and p38 MAPK phosphorylation.Our results provided new and informative clues for better understanding of the role of AMPK in β-cell apoptosis.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Zu Chong Zhi Road 555, Shanghai 201203, China.

ABSTRACT
The role of AMP-activated protein kinase (AMPK) in pancreatic β-cell apoptosis is still controversial, and the reasons for the discrepancies have not been clarified. In the current study, we observed the effects of two well-known AMPK activators 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) and metformin, on apoptosis in rat insulinoma INS-1E cells, and further explored their possible mechanisms. Both AICAR and metformin protected INS-1E cells from palmitate-induced apoptosis, as reflected by decreases in both cleaved caspase 3 protein expression and caspase 3/7 activity, and these protective effects were abrogated by AMPK inhibitor compound C. The protective action of AICAR was probably mediated by the suppression of triacylglycerol accumulation, increase in Akt phosphorylation and decrease in p38 MAPK phosphorylation, while metformin might exert its protective effect on INS-1E cells by decreases in both JNK and p38 MAPK phosphorylation. All these regulations were dependent on AMPK activation. However, under standard culture condition, AICAR increased JNK phosphorylation and promoted INS-1E cell apoptosis in an AMPK-dependent manner, whereas metformin showed no effect on apoptosis. Our study revealed that AMPK activators AICAR and metformin exhibited different effects on INS-1E cell apoptosis under different culture conditions, which might be largely attributed to different downstream mediators. Our results provided new and informative clues for better understanding of the role of AMPK in β-cell apoptosis.

No MeSH data available.


Related in: MedlinePlus