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Glucose metabolism inhibits apoptosis in neurons and cancer cells by redox inactivation of cytochrome c.

Vaughn AE, Deshmukh M - Nat. Cell Biol. (2008)

Bottom Line: These two seemingly disparate cell types also show an increased regulation of the apoptotic pathway, which allows for their long-term survival.We report that the pro-apoptotic activity of cytochrome c is influenced by its redox state and that increases in reactive oxygen species (ROS) following an apoptotic insult lead to the oxidation and activation of cytochrome c.In healthy neurons and cancer cells, however, cytochrome c is reduced and held inactive by intracellular glutathione (GSH), generated as a result of glucose metabolism by the pentose phosphate pathway.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell & Developmental Biology, Box 7250, 115 Mason Farm Road, Chapel Hill, North Carolina 27599, USA.

ABSTRACT
Neurons and cancer cells use glucose extensively, yet the precise advantage of this adaptation remains unclear. These two seemingly disparate cell types also show an increased regulation of the apoptotic pathway, which allows for their long-term survival. Here we show that both neurons and cancer cells strictly inhibit cytochrome c-mediated apoptosis by a mechanism dependent on glucose metabolism. We report that the pro-apoptotic activity of cytochrome c is influenced by its redox state and that increases in reactive oxygen species (ROS) following an apoptotic insult lead to the oxidation and activation of cytochrome c. In healthy neurons and cancer cells, however, cytochrome c is reduced and held inactive by intracellular glutathione (GSH), generated as a result of glucose metabolism by the pentose phosphate pathway. These results uncover a striking similarity in apoptosis regulation between neurons and cancer cells and provide insight into an adaptive advantage offered by the Warburg effect for cancer cell evasion of apoptosis and for long-term neuronal survival.

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Role of the pentose phosphate shunt in cytochrome c-mediated apoptosisa) Average ROS levels in sympathetic neurons were observed by fluorescence intensity of the redox-sensitive dye CM-H2DCFDA following 30 min of GSH depletion with 0.1 mM DEM. b) XIAP -/- sympathetic neurons (NGF-maintained) were treated with 0.1 mM DEM for 30 min followed by injection of cytochrome c and rhodamine, or rhodamine dye alone. Cell survival was assessed at various timepoints. c) Average ROS levels were observed as in (a) following inhibition of the Pentose Phosphate Pathway with 200 μM DHEA for 24 hrs. d) XIAP -/- sympathetic neurons (NGF-maintained) were treated with 200 μM DHEA for 6 hrs, 0.1 mM 6-AN for 24 hrs, or left untreated, followed by injection with tBid-GFP or EGFP constructs. Cell survival was expressed as a percentage of healthy green cells at 16 hrs compared to 5 hrs post-injection. Error bars represent ±SEM of n≥3.
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Figure 3: Role of the pentose phosphate shunt in cytochrome c-mediated apoptosisa) Average ROS levels in sympathetic neurons were observed by fluorescence intensity of the redox-sensitive dye CM-H2DCFDA following 30 min of GSH depletion with 0.1 mM DEM. b) XIAP -/- sympathetic neurons (NGF-maintained) were treated with 0.1 mM DEM for 30 min followed by injection of cytochrome c and rhodamine, or rhodamine dye alone. Cell survival was assessed at various timepoints. c) Average ROS levels were observed as in (a) following inhibition of the Pentose Phosphate Pathway with 200 μM DHEA for 24 hrs. d) XIAP -/- sympathetic neurons (NGF-maintained) were treated with 200 μM DHEA for 6 hrs, 0.1 mM 6-AN for 24 hrs, or left untreated, followed by injection with tBid-GFP or EGFP constructs. Cell survival was expressed as a percentage of healthy green cells at 16 hrs compared to 5 hrs post-injection. Error bars represent ±SEM of n≥3.

Mentions: GSH is one of the most prevalent intracellular reducing agents and maintains redox homeostasis by scavenging ROS. We found that endogenous GSH is necessary for maintaining cytochrome c in an inactive state in NGF-maintained neurons, as removal of GSH with Diethyl Maleate (DEM) or inhibition of GSH synthesis by Buthioninesulfoximine (BSO) leads to an increase in ROS22 and sensitizes cells to cytosolic cytochrome c (Fig. 3a,b, Supplementary Information, Fig. S8a). Levels of GSH are maintained in cells by reduced nicotinamide adenine dinucleotide phosphate (NADPH), which is generated when glucose is metabolized via the pentose phosphate pathway24. We examined whether the pentose phosphate pathway was important for regulating the redox status of neurons, and thus cytochrome c-mediated apoptosis. Neurons treated with the pentose phosphate pathway inhibitors, dehydroepiandrosterone (DHEA) or 6-anicotinamide (6-AN), accumulated high levels of ROS and became sensitive to endogenous cytochrome c release with tBid (Fig. 3c,d, Supplementary Information, Fig. S8b). This effect was not unique to neurons derived from the superior cervical ganglia as sensory neurons from the Dorsal Root Ganglia (DRGs) were also resistant to cytochrome c release by tBid, but became sensitive after DHEA treatment (Supplementary Information, Fig. S9). Together, these data show that glucose metabolism via the pentose phosphate pathway promotes neuronal survival by maintaining GSH levels and directly restricting cytochrome c-mediated apoptosis.


Glucose metabolism inhibits apoptosis in neurons and cancer cells by redox inactivation of cytochrome c.

Vaughn AE, Deshmukh M - Nat. Cell Biol. (2008)

Role of the pentose phosphate shunt in cytochrome c-mediated apoptosisa) Average ROS levels in sympathetic neurons were observed by fluorescence intensity of the redox-sensitive dye CM-H2DCFDA following 30 min of GSH depletion with 0.1 mM DEM. b) XIAP -/- sympathetic neurons (NGF-maintained) were treated with 0.1 mM DEM for 30 min followed by injection of cytochrome c and rhodamine, or rhodamine dye alone. Cell survival was assessed at various timepoints. c) Average ROS levels were observed as in (a) following inhibition of the Pentose Phosphate Pathway with 200 μM DHEA for 24 hrs. d) XIAP -/- sympathetic neurons (NGF-maintained) were treated with 200 μM DHEA for 6 hrs, 0.1 mM 6-AN for 24 hrs, or left untreated, followed by injection with tBid-GFP or EGFP constructs. Cell survival was expressed as a percentage of healthy green cells at 16 hrs compared to 5 hrs post-injection. Error bars represent ±SEM of n≥3.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2626347&req=5

Figure 3: Role of the pentose phosphate shunt in cytochrome c-mediated apoptosisa) Average ROS levels in sympathetic neurons were observed by fluorescence intensity of the redox-sensitive dye CM-H2DCFDA following 30 min of GSH depletion with 0.1 mM DEM. b) XIAP -/- sympathetic neurons (NGF-maintained) were treated with 0.1 mM DEM for 30 min followed by injection of cytochrome c and rhodamine, or rhodamine dye alone. Cell survival was assessed at various timepoints. c) Average ROS levels were observed as in (a) following inhibition of the Pentose Phosphate Pathway with 200 μM DHEA for 24 hrs. d) XIAP -/- sympathetic neurons (NGF-maintained) were treated with 200 μM DHEA for 6 hrs, 0.1 mM 6-AN for 24 hrs, or left untreated, followed by injection with tBid-GFP or EGFP constructs. Cell survival was expressed as a percentage of healthy green cells at 16 hrs compared to 5 hrs post-injection. Error bars represent ±SEM of n≥3.
Mentions: GSH is one of the most prevalent intracellular reducing agents and maintains redox homeostasis by scavenging ROS. We found that endogenous GSH is necessary for maintaining cytochrome c in an inactive state in NGF-maintained neurons, as removal of GSH with Diethyl Maleate (DEM) or inhibition of GSH synthesis by Buthioninesulfoximine (BSO) leads to an increase in ROS22 and sensitizes cells to cytosolic cytochrome c (Fig. 3a,b, Supplementary Information, Fig. S8a). Levels of GSH are maintained in cells by reduced nicotinamide adenine dinucleotide phosphate (NADPH), which is generated when glucose is metabolized via the pentose phosphate pathway24. We examined whether the pentose phosphate pathway was important for regulating the redox status of neurons, and thus cytochrome c-mediated apoptosis. Neurons treated with the pentose phosphate pathway inhibitors, dehydroepiandrosterone (DHEA) or 6-anicotinamide (6-AN), accumulated high levels of ROS and became sensitive to endogenous cytochrome c release with tBid (Fig. 3c,d, Supplementary Information, Fig. S8b). This effect was not unique to neurons derived from the superior cervical ganglia as sensory neurons from the Dorsal Root Ganglia (DRGs) were also resistant to cytochrome c release by tBid, but became sensitive after DHEA treatment (Supplementary Information, Fig. S9). Together, these data show that glucose metabolism via the pentose phosphate pathway promotes neuronal survival by maintaining GSH levels and directly restricting cytochrome c-mediated apoptosis.

Bottom Line: These two seemingly disparate cell types also show an increased regulation of the apoptotic pathway, which allows for their long-term survival.We report that the pro-apoptotic activity of cytochrome c is influenced by its redox state and that increases in reactive oxygen species (ROS) following an apoptotic insult lead to the oxidation and activation of cytochrome c.In healthy neurons and cancer cells, however, cytochrome c is reduced and held inactive by intracellular glutathione (GSH), generated as a result of glucose metabolism by the pentose phosphate pathway.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell & Developmental Biology, Box 7250, 115 Mason Farm Road, Chapel Hill, North Carolina 27599, USA.

ABSTRACT
Neurons and cancer cells use glucose extensively, yet the precise advantage of this adaptation remains unclear. These two seemingly disparate cell types also show an increased regulation of the apoptotic pathway, which allows for their long-term survival. Here we show that both neurons and cancer cells strictly inhibit cytochrome c-mediated apoptosis by a mechanism dependent on glucose metabolism. We report that the pro-apoptotic activity of cytochrome c is influenced by its redox state and that increases in reactive oxygen species (ROS) following an apoptotic insult lead to the oxidation and activation of cytochrome c. In healthy neurons and cancer cells, however, cytochrome c is reduced and held inactive by intracellular glutathione (GSH), generated as a result of glucose metabolism by the pentose phosphate pathway. These results uncover a striking similarity in apoptosis regulation between neurons and cancer cells and provide insight into an adaptive advantage offered by the Warburg effect for cancer cell evasion of apoptosis and for long-term neuronal survival.

Show MeSH
Related in: MedlinePlus