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Mitochondrial dysfunction and oxidative stress mediate the physiological impairment induced by the disruption of autophagy.

Wu JJ, Quijano C, Chen E, Liu H, Cao L, Fergusson MM, Rovira II, Gutkind S, Daniels MP, Komatsu M, Finkel T - Aging (Albany NY) (2009)

Bottom Line: Using these models we demonstrate that isolated mitochondria obtained from Atg7(-/-) skeletal muscle exhibit a significant defect in mitochondrial respiration.In this model, the simple administration of an antioxidant can significantly ameliorate the physiological impairment in glucose-stimulated insulin secretion.Taken together, these results demonstrate the potential role of mitochondrial dysfunction and oxidative stress in autophagy related pathology.

View Article: PubMed Central - PubMed

Affiliation: Translational Medicine Branch, National Heart Lung and Blood Institute, NIH, Bethesda, MD 20892, USA.

ABSTRACT
Impaired or deficient autophagy is believed to cause or contribute to aging, as well as a number of age-related pathologies. The exact mechanism through which alterations in autophagy induce these various pathologies is not well understood. Here we describe the creation of two in vivo mouse models that allow for the characterization of the alteration in mitochondrial function and the contribution of the corresponding oxidative stress following deletion of Atg7. Using these models we demonstrate that isolated mitochondria obtained from Atg7(-/-) skeletal muscle exhibit a significant defect in mitochondrial respiration. We further show that cells derived from Atg7(-/-) mice have an altered metabolic profile characterized by decreased resting mitochondrial oxygen consumption and a compensatory increase in basal glycolytic rates. Atg7(-/-)cells also exhibit evidence for increased steady state levels of reactive oxygen species. The observed mitochondrial dysfunction and oxidative stress is also evident in a mouse model where Atg7 is deleted within the pancreatic beta cell. In this model, the simple administration of an antioxidant can significantly ameliorate the physiological impairment in glucose-stimulated insulin secretion. Taken together, these results demonstrate the potential role of mitochondrial dysfunction and oxidative stress in autophagy related pathology.

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NAC treatment of Atg7 deficient mice prevents the development of a glucose intolerance phenotype. (A) Male Atg7F/+:Rip2-Cre (n=6                                            mice), Atg7F/+:Rip2-Cre (+NAC; n=6 mice), Atg7F/F:Rip2-Cre                                            (n=11 mice) or Atg7F/F:Rip2-Cre (+NAC; n=11 mice) were fasted                                            overnight and subsequently injected with 1 g/kg D-glucose. Serum glucose                                            levels were measured and the untreated β cell Atg7 deficient mice were                                            found to be statistically different at the indicated time points, while the                                            other three groups of mice were statistically indistinguishable over the 2                                            hr timecourse. (B) Insulin levels were determined by tail vein blood                                            sampling at time 0 and 15 min following glucose administration: Atg7F/+:Rip2-Cre                                            (n=6 mice), Atg7F/+:Rip2-Cre (+NAC; n=4 mice), Atg7F/F:Rip2-Cre                                            (n=8 mice) or Atg7F/F:Rip2-Cre (+NAC; n=5 mice).  Data are                                            represented as the mean +/- SEM.  * p≤0.05; ** p≤0.001.
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Figure 7: NAC treatment of Atg7 deficient mice prevents the development of a glucose intolerance phenotype. (A) Male Atg7F/+:Rip2-Cre (n=6 mice), Atg7F/+:Rip2-Cre (+NAC; n=6 mice), Atg7F/F:Rip2-Cre (n=11 mice) or Atg7F/F:Rip2-Cre (+NAC; n=11 mice) were fasted overnight and subsequently injected with 1 g/kg D-glucose. Serum glucose levels were measured and the untreated β cell Atg7 deficient mice were found to be statistically different at the indicated time points, while the other three groups of mice were statistically indistinguishable over the 2 hr timecourse. (B) Insulin levels were determined by tail vein blood sampling at time 0 and 15 min following glucose administration: Atg7F/+:Rip2-Cre (n=6 mice), Atg7F/+:Rip2-Cre (+NAC; n=4 mice), Atg7F/F:Rip2-Cre (n=8 mice) or Atg7F/F:Rip2-Cre (+NAC; n=5 mice). Data are represented as the mean +/- SEM. * p≤0.05; ** p≤0.001.

Mentions: We next asked whether reducing the levels of oxidative stress by itself was sufficient to ameliorate the physiological impairment observed with conditional deletion of Atg7. Littermates were randomized after weaning to treatment with or without NAC and subsequently assessed at age 16 weeks. Consistent with continuous oxidative stress playing a causative role in the underlying physiology, and in contrast to untreated Atg7F/F:RIP2-Cre mice, NAC treated Atg7F/F:RIP2-Cre mice had a glucose tolerance response that was indistinguishable from control mice (Figure 7A). This protection was also seen at later time points, although the overall degree of rescue appeared to be reduced as the mice aged (data not shown). The observed differences in glucose homeostasis were not a result of reduced peripheral insulin sensitivity as insulin tolerance tests were comparable for all four groups tested (data not shown). Furthermore, mice lacking Atg7 within their β cells develop a defect in glucose-stimulated insulin secretion, and this defect was not observed in conditionally ablated mice treated with an antioxidant (Figure 7B).


Mitochondrial dysfunction and oxidative stress mediate the physiological impairment induced by the disruption of autophagy.

Wu JJ, Quijano C, Chen E, Liu H, Cao L, Fergusson MM, Rovira II, Gutkind S, Daniels MP, Komatsu M, Finkel T - Aging (Albany NY) (2009)

NAC treatment of Atg7 deficient mice prevents the development of a glucose intolerance phenotype. (A) Male Atg7F/+:Rip2-Cre (n=6                                            mice), Atg7F/+:Rip2-Cre (+NAC; n=6 mice), Atg7F/F:Rip2-Cre                                            (n=11 mice) or Atg7F/F:Rip2-Cre (+NAC; n=11 mice) were fasted                                            overnight and subsequently injected with 1 g/kg D-glucose. Serum glucose                                            levels were measured and the untreated β cell Atg7 deficient mice were                                            found to be statistically different at the indicated time points, while the                                            other three groups of mice were statistically indistinguishable over the 2                                            hr timecourse. (B) Insulin levels were determined by tail vein blood                                            sampling at time 0 and 15 min following glucose administration: Atg7F/+:Rip2-Cre                                            (n=6 mice), Atg7F/+:Rip2-Cre (+NAC; n=4 mice), Atg7F/F:Rip2-Cre                                            (n=8 mice) or Atg7F/F:Rip2-Cre (+NAC; n=5 mice).  Data are                                            represented as the mean +/- SEM.  * p≤0.05; ** p≤0.001.
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Figure 7: NAC treatment of Atg7 deficient mice prevents the development of a glucose intolerance phenotype. (A) Male Atg7F/+:Rip2-Cre (n=6 mice), Atg7F/+:Rip2-Cre (+NAC; n=6 mice), Atg7F/F:Rip2-Cre (n=11 mice) or Atg7F/F:Rip2-Cre (+NAC; n=11 mice) were fasted overnight and subsequently injected with 1 g/kg D-glucose. Serum glucose levels were measured and the untreated β cell Atg7 deficient mice were found to be statistically different at the indicated time points, while the other three groups of mice were statistically indistinguishable over the 2 hr timecourse. (B) Insulin levels were determined by tail vein blood sampling at time 0 and 15 min following glucose administration: Atg7F/+:Rip2-Cre (n=6 mice), Atg7F/+:Rip2-Cre (+NAC; n=4 mice), Atg7F/F:Rip2-Cre (n=8 mice) or Atg7F/F:Rip2-Cre (+NAC; n=5 mice). Data are represented as the mean +/- SEM. * p≤0.05; ** p≤0.001.
Mentions: We next asked whether reducing the levels of oxidative stress by itself was sufficient to ameliorate the physiological impairment observed with conditional deletion of Atg7. Littermates were randomized after weaning to treatment with or without NAC and subsequently assessed at age 16 weeks. Consistent with continuous oxidative stress playing a causative role in the underlying physiology, and in contrast to untreated Atg7F/F:RIP2-Cre mice, NAC treated Atg7F/F:RIP2-Cre mice had a glucose tolerance response that was indistinguishable from control mice (Figure 7A). This protection was also seen at later time points, although the overall degree of rescue appeared to be reduced as the mice aged (data not shown). The observed differences in glucose homeostasis were not a result of reduced peripheral insulin sensitivity as insulin tolerance tests were comparable for all four groups tested (data not shown). Furthermore, mice lacking Atg7 within their β cells develop a defect in glucose-stimulated insulin secretion, and this defect was not observed in conditionally ablated mice treated with an antioxidant (Figure 7B).

Bottom Line: Using these models we demonstrate that isolated mitochondria obtained from Atg7(-/-) skeletal muscle exhibit a significant defect in mitochondrial respiration.In this model, the simple administration of an antioxidant can significantly ameliorate the physiological impairment in glucose-stimulated insulin secretion.Taken together, these results demonstrate the potential role of mitochondrial dysfunction and oxidative stress in autophagy related pathology.

View Article: PubMed Central - PubMed

Affiliation: Translational Medicine Branch, National Heart Lung and Blood Institute, NIH, Bethesda, MD 20892, USA.

ABSTRACT
Impaired or deficient autophagy is believed to cause or contribute to aging, as well as a number of age-related pathologies. The exact mechanism through which alterations in autophagy induce these various pathologies is not well understood. Here we describe the creation of two in vivo mouse models that allow for the characterization of the alteration in mitochondrial function and the contribution of the corresponding oxidative stress following deletion of Atg7. Using these models we demonstrate that isolated mitochondria obtained from Atg7(-/-) skeletal muscle exhibit a significant defect in mitochondrial respiration. We further show that cells derived from Atg7(-/-) mice have an altered metabolic profile characterized by decreased resting mitochondrial oxygen consumption and a compensatory increase in basal glycolytic rates. Atg7(-/-)cells also exhibit evidence for increased steady state levels of reactive oxygen species. The observed mitochondrial dysfunction and oxidative stress is also evident in a mouse model where Atg7 is deleted within the pancreatic beta cell. In this model, the simple administration of an antioxidant can significantly ameliorate the physiological impairment in glucose-stimulated insulin secretion. Taken together, these results demonstrate the potential role of mitochondrial dysfunction and oxidative stress in autophagy related pathology.

Show MeSH
Related in: MedlinePlus