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Mitochondrial dysfunction in insulin resistance: differential contributions of chronic insulin and saturated fatty acid exposure in muscle cells.

Yang C, Aye CC, Li X, Diaz Ramos A, Zorzano A, Mora S - Biosci. Rep. (2012)

Bottom Line: The expression of mitochondrial OXPHOS (oxidative phosphorylation) subunits or Mfn-2 (mitofusin 2) were not significantly altered in comparison with untreated cells, whereas expression of PGC-1α (peroxisome-proliferator-activated receptor γ co-activator-1α) and UCPs (uncoupling proteins) were reduced.In contrast, saturated fatty acid exposure caused insulin resistance, reducing PI3K (phosphoinositide 3-kinase) and ERK (extracellular-signal-regulated kinase) activation while increasing activation of stress kinases JNK (c-Jun N-terminal kinase) and p38.Palmitate-treated cells also showed a reduced glycolytic rate.

View Article: PubMed Central - PubMed

Affiliation: Department of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Liverpool, U.K.

ABSTRACT
Mitochondrial dysfunction has been associated with insulin resistance, obesity and diabetes. Hyperinsulinaemia and hyperlipidaemia are hallmarks of the insulin-resistant state. We sought to determine the contributions of high insulin and saturated fatty acid exposure to mitochondrial function and biogenesis in cultured myocytes. Differentiated C2C12 myotubes were left untreated or exposed to chronic high insulin or high palmitate. Mitochondrial function was determined assessing: oxygen consumption, mitochondrial membrane potential, ATP content and ROS (reactive oxygen species) production. We also determined the expression of several mitochondrial genes. Chronic insulin treatment of myotubes caused insulin resistance with reduced PI3K (phosphoinositide 3-kinase) and ERK (extracellular-signal-regulated kinase) signalling. Insulin treatment increased oxygen consumption but reduced mitochondrial membrane potential and ROS production. ATP cellular levels were maintained through an increased glycolytic rate. The expression of mitochondrial OXPHOS (oxidative phosphorylation) subunits or Mfn-2 (mitofusin 2) were not significantly altered in comparison with untreated cells, whereas expression of PGC-1α (peroxisome-proliferator-activated receptor γ co-activator-1α) and UCPs (uncoupling proteins) were reduced. In contrast, saturated fatty acid exposure caused insulin resistance, reducing PI3K (phosphoinositide 3-kinase) and ERK (extracellular-signal-regulated kinase) activation while increasing activation of stress kinases JNK (c-Jun N-terminal kinase) and p38. Fatty acids reduced oxygen consumption and mitochondrial membrane potential while up-regulating the expression of mitochondrial ETC (electron chain complex) protein subunits and UCP proteins. Mfn-2 expression was not modified by palmitate. Palmitate-treated cells also showed a reduced glycolytic rate. Taken together, our findings indicate that chronic insulin and fatty acid-induced insulin resistance differentially affect mitochondrial function. In both conditions, cells were able to maintain ATP levels despite the loss of membrane potential; however, different protein expression suggests different adaptation mechanisms.

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Mitochondrial gene expression in C2C12 myotubes treated with chronic insulin treatmentC2C12 myotubes were left untreated or treated with insulin for 48 h. Total mRNA was extracted and the mRNA abundance of genes coding for mitochondrial proteins examined by quantitative real-time PCR. Results were analysed by the ΔΔCT method. Data are means±S.E.M. for three independent experiments analysed by Student's t test (*P<0.05 and **P<0.01).
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Figure 3: Mitochondrial gene expression in C2C12 myotubes treated with chronic insulin treatmentC2C12 myotubes were left untreated or treated with insulin for 48 h. Total mRNA was extracted and the mRNA abundance of genes coding for mitochondrial proteins examined by quantitative real-time PCR. Results were analysed by the ΔΔCT method. Data are means±S.E.M. for three independent experiments analysed by Student's t test (*P<0.05 and **P<0.01).

Mentions: To this end we determined the mRNA levels of the transcriptional co-activators PGC-1α and PGC-1β, which have been found to regulate mitochondrial biogenesis. We found that PGC-1α mRNA levels were markedly decreased in insulin-treated cells in comparison with controls (Figure 3), but no changes were detected in PGC-1β. Despite the changes in PGC-1α, no changes were detected in the mRNA levels of the downstream transcriptional factors NRF1 (nuclear respiratory factor-1) or Tfam (mitochondrial transcription factor A) (Figure 3).


Mitochondrial dysfunction in insulin resistance: differential contributions of chronic insulin and saturated fatty acid exposure in muscle cells.

Yang C, Aye CC, Li X, Diaz Ramos A, Zorzano A, Mora S - Biosci. Rep. (2012)

Mitochondrial gene expression in C2C12 myotubes treated with chronic insulin treatmentC2C12 myotubes were left untreated or treated with insulin for 48 h. Total mRNA was extracted and the mRNA abundance of genes coding for mitochondrial proteins examined by quantitative real-time PCR. Results were analysed by the ΔΔCT method. Data are means±S.E.M. for three independent experiments analysed by Student's t test (*P<0.05 and **P<0.01).
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3475448&req=5

Figure 3: Mitochondrial gene expression in C2C12 myotubes treated with chronic insulin treatmentC2C12 myotubes were left untreated or treated with insulin for 48 h. Total mRNA was extracted and the mRNA abundance of genes coding for mitochondrial proteins examined by quantitative real-time PCR. Results were analysed by the ΔΔCT method. Data are means±S.E.M. for three independent experiments analysed by Student's t test (*P<0.05 and **P<0.01).
Mentions: To this end we determined the mRNA levels of the transcriptional co-activators PGC-1α and PGC-1β, which have been found to regulate mitochondrial biogenesis. We found that PGC-1α mRNA levels were markedly decreased in insulin-treated cells in comparison with controls (Figure 3), but no changes were detected in PGC-1β. Despite the changes in PGC-1α, no changes were detected in the mRNA levels of the downstream transcriptional factors NRF1 (nuclear respiratory factor-1) or Tfam (mitochondrial transcription factor A) (Figure 3).

Bottom Line: The expression of mitochondrial OXPHOS (oxidative phosphorylation) subunits or Mfn-2 (mitofusin 2) were not significantly altered in comparison with untreated cells, whereas expression of PGC-1α (peroxisome-proliferator-activated receptor γ co-activator-1α) and UCPs (uncoupling proteins) were reduced.In contrast, saturated fatty acid exposure caused insulin resistance, reducing PI3K (phosphoinositide 3-kinase) and ERK (extracellular-signal-regulated kinase) activation while increasing activation of stress kinases JNK (c-Jun N-terminal kinase) and p38.Palmitate-treated cells also showed a reduced glycolytic rate.

View Article: PubMed Central - PubMed

Affiliation: Department of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Liverpool, U.K.

ABSTRACT
Mitochondrial dysfunction has been associated with insulin resistance, obesity and diabetes. Hyperinsulinaemia and hyperlipidaemia are hallmarks of the insulin-resistant state. We sought to determine the contributions of high insulin and saturated fatty acid exposure to mitochondrial function and biogenesis in cultured myocytes. Differentiated C2C12 myotubes were left untreated or exposed to chronic high insulin or high palmitate. Mitochondrial function was determined assessing: oxygen consumption, mitochondrial membrane potential, ATP content and ROS (reactive oxygen species) production. We also determined the expression of several mitochondrial genes. Chronic insulin treatment of myotubes caused insulin resistance with reduced PI3K (phosphoinositide 3-kinase) and ERK (extracellular-signal-regulated kinase) signalling. Insulin treatment increased oxygen consumption but reduced mitochondrial membrane potential and ROS production. ATP cellular levels were maintained through an increased glycolytic rate. The expression of mitochondrial OXPHOS (oxidative phosphorylation) subunits or Mfn-2 (mitofusin 2) were not significantly altered in comparison with untreated cells, whereas expression of PGC-1α (peroxisome-proliferator-activated receptor γ co-activator-1α) and UCPs (uncoupling proteins) were reduced. In contrast, saturated fatty acid exposure caused insulin resistance, reducing PI3K (phosphoinositide 3-kinase) and ERK (extracellular-signal-regulated kinase) activation while increasing activation of stress kinases JNK (c-Jun N-terminal kinase) and p38. Fatty acids reduced oxygen consumption and mitochondrial membrane potential while up-regulating the expression of mitochondrial ETC (electron chain complex) protein subunits and UCP proteins. Mfn-2 expression was not modified by palmitate. Palmitate-treated cells also showed a reduced glycolytic rate. Taken together, our findings indicate that chronic insulin and fatty acid-induced insulin resistance differentially affect mitochondrial function. In both conditions, cells were able to maintain ATP levels despite the loss of membrane potential; however, different protein expression suggests different adaptation mechanisms.

Show MeSH
Related in: MedlinePlus