Metformin represses glucose starvation induced autophagic response in microvascular endothelial cells and promotes cell death

Samson Mathews Samuel, Suparna Ghosh, Yasser Majeed, Gnanapragasam Arunachalam, Mohamed Emara, Hong Ding, Christopher Triggle

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13 Citations (Scopus)

Abstract

Metformin, the most frequently administered drug for the treatment of type 2 diabetes, is being investigated for its potential in the treatment of various types of cancer; however, the cellular basis for this putative anti-cancer action remains controversial. In the current study we examined the effect of metformin on endoplasmic reticulum (ER) stress and autophagy in glucose-starved micro-vascular endothelial cells (MECs). The rationale for our experimental protocol is that in a growing tumor MECs are subjected to hypoxia and nutrient/glucose starvation that results from the reduced supply and relatively high consumption of glucose. Mouse MECs (MMECs) were glucose-starved for up to 48 h in the absence or presence of metformin (50 μM and 2 mM) and the status of ER stress, autophagic, cell survival and apoptotic markers were assessed. Activation of ER stress and autophagy was observed in glucose starved MECs as evidenced by the significant increase in the levels of ER stress and autophagic markers while accumulation of LC3B stained punctae in the MECs confirmed autophagic activation. Treatment with 2 mM metformin, independent of AMPK, significantly reversed glucose starvation induced ER stress and autophagy in MECs, but, at 24 h, did not decrease cell viability; however, at 48 h, persistent ER stress and metformin associated inhibition of autophagy decreased cell viability, caused cell cycle arrest in G2/M and increased the number of cells in the sub-G0/G1 phase of cell cycle. Treatment with metformin reduced phosphorylation of Akt and mTOR and inhibited downstream targets of mTOR. Our findings support the argument that treatment with metformin when used in combination with glycolytic inhibitors will inhibit pro-survival autophagy and promote cell death and potentially prove to be the basis for an effective anti-cancer strategy.

Original languageEnglish
Pages (from-to)118-132
Number of pages15
JournalBiochemical Pharmacology
Volume132
DOIs
Publication statusPublished - 15 May 2017

Fingerprint

Metformin
Endothelial cells
Cell death
Endoplasmic Reticulum Stress
Starvation
Cell Death
Autophagy
Endothelial Cells
Glucose
Cells
Cell Survival
Neoplasms
Chemical activation
G2 Phase Cell Cycle Checkpoints
Cell Cycle Resting Phase
Phosphorylation
AMP-Activated Protein Kinases
G1 Phase
Medical problems
Type 2 Diabetes Mellitus

Keywords

  • Autophagy
  • Cancer
  • Endothelium
  • ER stress
  • Metformin

ASJC Scopus subject areas

  • Biochemistry
  • Pharmacology

Cite this

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title = "Metformin represses glucose starvation induced autophagic response in microvascular endothelial cells and promotes cell death",
abstract = "Metformin, the most frequently administered drug for the treatment of type 2 diabetes, is being investigated for its potential in the treatment of various types of cancer; however, the cellular basis for this putative anti-cancer action remains controversial. In the current study we examined the effect of metformin on endoplasmic reticulum (ER) stress and autophagy in glucose-starved micro-vascular endothelial cells (MECs). The rationale for our experimental protocol is that in a growing tumor MECs are subjected to hypoxia and nutrient/glucose starvation that results from the reduced supply and relatively high consumption of glucose. Mouse MECs (MMECs) were glucose-starved for up to 48 h in the absence or presence of metformin (50 μM and 2 mM) and the status of ER stress, autophagic, cell survival and apoptotic markers were assessed. Activation of ER stress and autophagy was observed in glucose starved MECs as evidenced by the significant increase in the levels of ER stress and autophagic markers while accumulation of LC3B stained punctae in the MECs confirmed autophagic activation. Treatment with 2 mM metformin, independent of AMPK, significantly reversed glucose starvation induced ER stress and autophagy in MECs, but, at 24 h, did not decrease cell viability; however, at 48 h, persistent ER stress and metformin associated inhibition of autophagy decreased cell viability, caused cell cycle arrest in G2/M and increased the number of cells in the sub-G0/G1 phase of cell cycle. Treatment with metformin reduced phosphorylation of Akt and mTOR and inhibited downstream targets of mTOR. Our findings support the argument that treatment with metformin when used in combination with glycolytic inhibitors will inhibit pro-survival autophagy and promote cell death and potentially prove to be the basis for an effective anti-cancer strategy.",
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T1 - Metformin represses glucose starvation induced autophagic response in microvascular endothelial cells and promotes cell death

AU - Mathews Samuel, Samson

AU - Ghosh, Suparna

AU - Majeed, Yasser

AU - Arunachalam, Gnanapragasam

AU - Emara, Mohamed

AU - Ding, Hong

AU - Triggle, Christopher

PY - 2017/5/15

Y1 - 2017/5/15

N2 - Metformin, the most frequently administered drug for the treatment of type 2 diabetes, is being investigated for its potential in the treatment of various types of cancer; however, the cellular basis for this putative anti-cancer action remains controversial. In the current study we examined the effect of metformin on endoplasmic reticulum (ER) stress and autophagy in glucose-starved micro-vascular endothelial cells (MECs). The rationale for our experimental protocol is that in a growing tumor MECs are subjected to hypoxia and nutrient/glucose starvation that results from the reduced supply and relatively high consumption of glucose. Mouse MECs (MMECs) were glucose-starved for up to 48 h in the absence or presence of metformin (50 μM and 2 mM) and the status of ER stress, autophagic, cell survival and apoptotic markers were assessed. Activation of ER stress and autophagy was observed in glucose starved MECs as evidenced by the significant increase in the levels of ER stress and autophagic markers while accumulation of LC3B stained punctae in the MECs confirmed autophagic activation. Treatment with 2 mM metformin, independent of AMPK, significantly reversed glucose starvation induced ER stress and autophagy in MECs, but, at 24 h, did not decrease cell viability; however, at 48 h, persistent ER stress and metformin associated inhibition of autophagy decreased cell viability, caused cell cycle arrest in G2/M and increased the number of cells in the sub-G0/G1 phase of cell cycle. Treatment with metformin reduced phosphorylation of Akt and mTOR and inhibited downstream targets of mTOR. Our findings support the argument that treatment with metformin when used in combination with glycolytic inhibitors will inhibit pro-survival autophagy and promote cell death and potentially prove to be the basis for an effective anti-cancer strategy.

AB - Metformin, the most frequently administered drug for the treatment of type 2 diabetes, is being investigated for its potential in the treatment of various types of cancer; however, the cellular basis for this putative anti-cancer action remains controversial. In the current study we examined the effect of metformin on endoplasmic reticulum (ER) stress and autophagy in glucose-starved micro-vascular endothelial cells (MECs). The rationale for our experimental protocol is that in a growing tumor MECs are subjected to hypoxia and nutrient/glucose starvation that results from the reduced supply and relatively high consumption of glucose. Mouse MECs (MMECs) were glucose-starved for up to 48 h in the absence or presence of metformin (50 μM and 2 mM) and the status of ER stress, autophagic, cell survival and apoptotic markers were assessed. Activation of ER stress and autophagy was observed in glucose starved MECs as evidenced by the significant increase in the levels of ER stress and autophagic markers while accumulation of LC3B stained punctae in the MECs confirmed autophagic activation. Treatment with 2 mM metformin, independent of AMPK, significantly reversed glucose starvation induced ER stress and autophagy in MECs, but, at 24 h, did not decrease cell viability; however, at 48 h, persistent ER stress and metformin associated inhibition of autophagy decreased cell viability, caused cell cycle arrest in G2/M and increased the number of cells in the sub-G0/G1 phase of cell cycle. Treatment with metformin reduced phosphorylation of Akt and mTOR and inhibited downstream targets of mTOR. Our findings support the argument that treatment with metformin when used in combination with glycolytic inhibitors will inhibit pro-survival autophagy and promote cell death and potentially prove to be the basis for an effective anti-cancer strategy.

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KW - Metformin

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