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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 Akt, JNK and p38 MAPK phosphorylation in palmitate-challenged INS-1E cells. (A) INS-1E cells were exposed to 0.25 mM palmitate with or without 1 mM AICAR or 2 mM metformin for 16 h, followed by immunoblotting of Akt, JNK and p38 MAPK phosphorylation. (B, C) INS-1E cells were preincubated with or without compound C (10 μM) for 30 min, and then exposed to 0.25 mM palmitate with or without 1 mM AICAR (B) or 2 mM metformin (C) for 16 h, followed by immunoblotting of Akt (only for AICAR), JNK and p38 MAPK phosphorylation. Representative immunoblots were shown and protein contents were quantified separately from three or four independent experiments. *P<0.05 and **P<0.01 vs control (cells exposed to 0.25% BSA) or corresponding columns as indicated; #P<0.05 and ##P<0.01 vs cells exposed to 0.25 mM palmitate. Palm, palmitate; Met, metformin.
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Figure 4: Effects of AICAR and metformin on Akt, JNK and p38 MAPK phosphorylation in palmitate-challenged INS-1E cells. (A) INS-1E cells were exposed to 0.25 mM palmitate with or without 1 mM AICAR or 2 mM metformin for 16 h, followed by immunoblotting of Akt, JNK and p38 MAPK phosphorylation. (B, C) INS-1E cells were preincubated with or without compound C (10 μM) for 30 min, and then exposed to 0.25 mM palmitate with or without 1 mM AICAR (B) or 2 mM metformin (C) for 16 h, followed by immunoblotting of Akt (only for AICAR), JNK and p38 MAPK phosphorylation. Representative immunoblots were shown and protein contents were quantified separately from three or four independent experiments. *P<0.05 and **P<0.01 vs control (cells exposed to 0.25% BSA) or corresponding columns as indicated; #P<0.05 and ##P<0.01 vs cells exposed to 0.25 mM palmitate. Palm, palmitate; Met, metformin.

Mentions: Since impairment of PI3K/Akt signalling pathway and activation of JNK and p38 MAPK are involved in palmitate-induced β-cell apoptosis, effects of AICAR and metformin on Akt, JNK and p38 MAPK phosphorylation were first investigated under palmitate-challenged condition. After incubation with 0.25 mM palmitate for 16 h, Akt phosphorylation decreased, JNK phosphorylation increased and p38 MAPK phosphorylation remained unchanged. Under this stress condition, AICAR could largely reverse the inhibitory effect of palmitate on Akt phosphorylation and significantly decrease p38 MAPK phosphorylation. However, an unexpected additional increase in JNK phosphorylation was observed. On the other hand, metformin scarcely affected Akt phosphorylation, but significantly decreased both JNK and p38 MAPK phosphorylation (P<0.05 and P<0.01 vs palmitate-exposed cells; Fig. 4A).


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 Akt, JNK and p38 MAPK phosphorylation in palmitate-challenged INS-1E cells. (A) INS-1E cells were exposed to 0.25 mM palmitate with or without 1 mM AICAR or 2 mM metformin for 16 h, followed by immunoblotting of Akt, JNK and p38 MAPK phosphorylation. (B, C) INS-1E cells were preincubated with or without compound C (10 μM) for 30 min, and then exposed to 0.25 mM palmitate with or without 1 mM AICAR (B) or 2 mM metformin (C) for 16 h, followed by immunoblotting of Akt (only for AICAR), JNK and p38 MAPK phosphorylation. Representative immunoblots were shown and protein contents were quantified separately from three or four independent experiments. *P<0.05 and **P<0.01 vs control (cells exposed to 0.25% BSA) or corresponding columns as indicated; #P<0.05 and ##P<0.01 vs cells exposed to 0.25 mM palmitate. Palm, palmitate; Met, metformin.
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Figure 4: Effects of AICAR and metformin on Akt, JNK and p38 MAPK phosphorylation in palmitate-challenged INS-1E cells. (A) INS-1E cells were exposed to 0.25 mM palmitate with or without 1 mM AICAR or 2 mM metformin for 16 h, followed by immunoblotting of Akt, JNK and p38 MAPK phosphorylation. (B, C) INS-1E cells were preincubated with or without compound C (10 μM) for 30 min, and then exposed to 0.25 mM palmitate with or without 1 mM AICAR (B) or 2 mM metformin (C) for 16 h, followed by immunoblotting of Akt (only for AICAR), JNK and p38 MAPK phosphorylation. Representative immunoblots were shown and protein contents were quantified separately from three or four independent experiments. *P<0.05 and **P<0.01 vs control (cells exposed to 0.25% BSA) or corresponding columns as indicated; #P<0.05 and ##P<0.01 vs cells exposed to 0.25 mM palmitate. Palm, palmitate; Met, metformin.
Mentions: Since impairment of PI3K/Akt signalling pathway and activation of JNK and p38 MAPK are involved in palmitate-induced β-cell apoptosis, effects of AICAR and metformin on Akt, JNK and p38 MAPK phosphorylation were first investigated under palmitate-challenged condition. After incubation with 0.25 mM palmitate for 16 h, Akt phosphorylation decreased, JNK phosphorylation increased and p38 MAPK phosphorylation remained unchanged. Under this stress condition, AICAR could largely reverse the inhibitory effect of palmitate on Akt phosphorylation and significantly decrease p38 MAPK phosphorylation. However, an unexpected additional increase in JNK phosphorylation was observed. On the other hand, metformin scarcely affected Akt phosphorylation, but significantly decreased both JNK and p38 MAPK phosphorylation (P<0.05 and P<0.01 vs palmitate-exposed cells; Fig. 4A).

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