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Metformin attenuates palmitate-induced endoplasmic reticulum stress, serine phosphorylation of IRS-1 and apoptosis in rat insulinoma cells.

Simon-Szabó L, Kokas M, Mandl J, Kéri G, Csala M - PLoS ONE (2014)

Bottom Line: The underlying endoplasmic reticulum (ER) stress response can lead to even β-cell death (lipoapoptosis).Assessment of palmitate-induced lipoapoptosis by fluorescent microscopy and by detection of caspase-3 showed a significant decrease in metformin treated cells.Our results indicate that the β-cell protective activity of metformin in lipotoxicity can be at least partly attributed to suppression of ER stress.

View Article: PubMed Central - PubMed

Affiliation: Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, Budapest, Hungary; MTA-SE Pathobiochemistry Research Group, Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, Budapest, Hungary.

ABSTRACT
Lipotoxicity refers to cellular dysfunctions caused by elevated free fatty acid levels playing a central role in the development and progression of obesity related diseases. Saturated fatty acids cause insulin resistance and reduce insulin production in the pancreatic islets, thereby generating a vicious cycle, which potentially culminates in type 2 diabetes. The underlying endoplasmic reticulum (ER) stress response can lead to even β-cell death (lipoapoptosis). Since improvement of β-cell viability is a promising anti-diabetic strategy, the protective effect of metformin, a known insulin sensitizer was studied in rat insulinoma cells. Assessment of palmitate-induced lipoapoptosis by fluorescent microscopy and by detection of caspase-3 showed a significant decrease in metformin treated cells. Attenuation of β-cell lipotoxicity was also revealed by lower induction/activation of various ER stress markers, e.g. phosphorylation of eukaryotic initiation factor 2α (eIF2α), c-Jun N-terminal kinase (JNK), insulin receptor substrate-1 (IRS-1) and induction of CCAAT/enhancer binding protein homologous protein (CHOP). Our results indicate that the β-cell protective activity of metformin in lipotoxicity can be at least partly attributed to suppression of ER stress.

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Related in: MedlinePlus

Expression of ER chaperones, GRP78/BiP and PDI.Insulinoma cells were treated with palmitate (500 µM) alone or together with metformin (10 µM, 100 µM) at 70–80% confluence. GRP78 and PDI were detected by Western blot analysis using cell lysates prepared after 8 h. Typical results of three independent experiments are shown. The results were quantified by densitometry and are shown as relative band densities normalized to β-actin as a constitutive reference protein. Data are presented as mean values ± S.D. of three experiments in arbitrary units (palmitate-treated = 100%); bP<0.01, cP<0.001 v.s. untreated control; ***P<0.001 v.s. palmitate-treated.
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pone-0097868-g003: Expression of ER chaperones, GRP78/BiP and PDI.Insulinoma cells were treated with palmitate (500 µM) alone or together with metformin (10 µM, 100 µM) at 70–80% confluence. GRP78 and PDI were detected by Western blot analysis using cell lysates prepared after 8 h. Typical results of three independent experiments are shown. The results were quantified by densitometry and are shown as relative band densities normalized to β-actin as a constitutive reference protein. Data are presented as mean values ± S.D. of three experiments in arbitrary units (palmitate-treated = 100%); bP<0.01, cP<0.001 v.s. untreated control; ***P<0.001 v.s. palmitate-treated.

Mentions: Induction of ER chaperones is a fundamental element of the UPR and a well-established marker of ER stress. The amount of two major ER chaperones was assessed by Western blot. Both glucose-regulated protein 78 (GRP78) also known as BiP and protein disulfide isomerase (PDI) were largely induced in the palmitate-treated cells compared to controls. This ER chaperone inducing effect of lipotoxicity was markedly counteracted by simultaneous addition of metformin. The expression of BiP and PDI was significantly lower than in the palmitate-treated cells, and 100 µM metformin reduced the amount of both chaperons to the control level (Fig. 3).


Metformin attenuates palmitate-induced endoplasmic reticulum stress, serine phosphorylation of IRS-1 and apoptosis in rat insulinoma cells.

Simon-Szabó L, Kokas M, Mandl J, Kéri G, Csala M - PLoS ONE (2014)

Expression of ER chaperones, GRP78/BiP and PDI.Insulinoma cells were treated with palmitate (500 µM) alone or together with metformin (10 µM, 100 µM) at 70–80% confluence. GRP78 and PDI were detected by Western blot analysis using cell lysates prepared after 8 h. Typical results of three independent experiments are shown. The results were quantified by densitometry and are shown as relative band densities normalized to β-actin as a constitutive reference protein. Data are presented as mean values ± S.D. of three experiments in arbitrary units (palmitate-treated = 100%); bP<0.01, cP<0.001 v.s. untreated control; ***P<0.001 v.s. palmitate-treated.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4045581&req=5

pone-0097868-g003: Expression of ER chaperones, GRP78/BiP and PDI.Insulinoma cells were treated with palmitate (500 µM) alone or together with metformin (10 µM, 100 µM) at 70–80% confluence. GRP78 and PDI were detected by Western blot analysis using cell lysates prepared after 8 h. Typical results of three independent experiments are shown. The results were quantified by densitometry and are shown as relative band densities normalized to β-actin as a constitutive reference protein. Data are presented as mean values ± S.D. of three experiments in arbitrary units (palmitate-treated = 100%); bP<0.01, cP<0.001 v.s. untreated control; ***P<0.001 v.s. palmitate-treated.
Mentions: Induction of ER chaperones is a fundamental element of the UPR and a well-established marker of ER stress. The amount of two major ER chaperones was assessed by Western blot. Both glucose-regulated protein 78 (GRP78) also known as BiP and protein disulfide isomerase (PDI) were largely induced in the palmitate-treated cells compared to controls. This ER chaperone inducing effect of lipotoxicity was markedly counteracted by simultaneous addition of metformin. The expression of BiP and PDI was significantly lower than in the palmitate-treated cells, and 100 µM metformin reduced the amount of both chaperons to the control level (Fig. 3).

Bottom Line: The underlying endoplasmic reticulum (ER) stress response can lead to even β-cell death (lipoapoptosis).Assessment of palmitate-induced lipoapoptosis by fluorescent microscopy and by detection of caspase-3 showed a significant decrease in metformin treated cells.Our results indicate that the β-cell protective activity of metformin in lipotoxicity can be at least partly attributed to suppression of ER stress.

View Article: PubMed Central - PubMed

Affiliation: Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, Budapest, Hungary; MTA-SE Pathobiochemistry Research Group, Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, Budapest, Hungary.

ABSTRACT
Lipotoxicity refers to cellular dysfunctions caused by elevated free fatty acid levels playing a central role in the development and progression of obesity related diseases. Saturated fatty acids cause insulin resistance and reduce insulin production in the pancreatic islets, thereby generating a vicious cycle, which potentially culminates in type 2 diabetes. The underlying endoplasmic reticulum (ER) stress response can lead to even β-cell death (lipoapoptosis). Since improvement of β-cell viability is a promising anti-diabetic strategy, the protective effect of metformin, a known insulin sensitizer was studied in rat insulinoma cells. Assessment of palmitate-induced lipoapoptosis by fluorescent microscopy and by detection of caspase-3 showed a significant decrease in metformin treated cells. Attenuation of β-cell lipotoxicity was also revealed by lower induction/activation of various ER stress markers, e.g. phosphorylation of eukaryotic initiation factor 2α (eIF2α), c-Jun N-terminal kinase (JNK), insulin receptor substrate-1 (IRS-1) and induction of CCAAT/enhancer binding protein homologous protein (CHOP). Our results indicate that the β-cell protective activity of metformin in lipotoxicity can be at least partly attributed to suppression of ER stress.

Show MeSH
Related in: MedlinePlus