Insulin fails to enhance mTOR phosphorylation, mitochondrial protein synthesis, and ATP production in human skeletal muscle without amino acid replacement

Barazzoni, Rocco; Short, Kevin R.; Asmann, Yan W.; Coenen-Schimke, Jill M.; Robinson, Matthew M.; Nair, K. Sreekumaran

doi:10.1152/ajpendo.00067.2012

Cited by 44 publications

(43 citation statements)

References 28 publications

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“…These results are also supported by other studies [17, 20, Louard et al(a) 1992 [19] Fryburg et al 1995 [26] Timmerman et al (1b) 28-31, 34, 44]. In all healthy human studies where AA availability has been reduced, MPS has been reduced or remained unchanged [18,19,37,45,46], even in the presence of supraphysiological concentrations of insulin [18]. The meta-analysis of the 25 studies showed that insulin exerts its regulation of lean muscle mass principally via an anticatabolic effect in reducing MPB.…”

Section: Discussionsupporting

confidence: 81%

Role of insulin in the regulation of human skeletal muscle protein synthesis and breakdown: a systematic review and meta-analysis

et al. 2015

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Aims/hypothesis We aimed to investigate the role of insulin in regulating human skeletal muscle metabolism in health and diabetes. Methods We conducted a systematic review and metaanalysis of published data that examined changes in skeletal muscle protein synthesis (MPS) and/or muscle protein breakdown (MPB) in response to insulin infusion. Random-effects models were used to calculate weighted mean differences (WMDs), 95% CIs and corresponding p values. Both MPS and MPB are reported in units of nmol (100 ml leg vol.)Results A total of 104 articles were examined in detail. Of these, 44 and 25 studies (including a total of 173 individuals) were included in the systematic review and meta-analysis, respectively. In the overall estimate, insulin did not affect MPS 8.55], p=0.71), but significantly reduced MPB .18], p<0.001). Overall, insulin significantly increased net balance protein acquisition (WMD 20.09 [95% CI 15.93,24.26], p<0.001). Subgroup analysis of the effect of insulin on MPS according to amino acid (AA) delivery was performed using meta-regression analysis. The estimate size (WMD) was significantly different between subgroups based on AA availability (p=0.001). An increase in MPS was observed when AA availability increased (WMD 13.44 [95% CI 4.07,22.81], p<0.01), but not when AA availability was reduced or unchanged. In individuals with diabetes and in the presence of maintained delivery of AA, there was a significant reduction in MPS in response to insulin (WMD −6.67 [95% CI −12.29, −0.66], p<0.05). Conclusions/interpretation This study demonstrates the complex role of insulin in regulating skeletal muscle metabolism. Insulin appears to have a permissive role in MPS in the presence of elevated AAs, and plays a clear role in reducing MPB independent of AA availability.

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Section: Discussionsupporting

confidence: 81%

Role of insulin in the regulation of human skeletal muscle protein synthesis and breakdown: a systematic review and meta-analysis

et al. 2015

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“…Potential explanations include that degradation of damaged ribosomal proteins may have preserved the protein quality and that there is no evidence showing that protein synthesis is directly proportional to the ribosomal protein content. Previous work has shown that the availability of amino acids, which are released following protein degradation, is critical to maintain protein synthesis (2,36). However, as we have reported previously, insulin deprivation increases net protein degradation (35), and longer periods of insulin deprivation would significantly reduce the content of muscle proteins whose degradation continues to exceed synthesis.…”

Section: Discussionmentioning

confidence: 47%

Release of skeletal muscle peptide fragments identifies individual proteins degraded during insulin deprivation in type 1 diabetic humans and mice

Robinson

Dasari

Karakelides

et al. 2016

American Journal of Physiology-Endocrinology and Metabolism

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Robinson MM, Dasari S, Karakelides H, Bergen HR 3rd, Nair KS. Release of skeletal muscle peptide fragments identifies individual proteins degraded during insulin deprivation in type 1 diabetic humans and mice. Am J Physiol Endocrinol Metab 311: E628 -E637, 2016. First published July 19, 2016; doi:10.1152/ajpendo.00175.2016.-Insulin regulates skeletal muscle protein degradation, but the types of proteins being degraded in vivo remain to be determined due to methodological limitations. We present a method to assess the types of skeletal muscle proteins that are degraded by extracting their degradation products as low-molecular weight (LMW) peptides from muscle samples. High-resolution mass spectrometry was used to identify the original intact proteins that generated the LMW peptides, which we validated in rodents and then applied to humans. We deprived insulin from insulin-treated streptozotocin (STZ) diabetic mice for 6 and 96 h and for 8 h in type 1 diabetic humans (T1D) for comparison with insulin-treated conditions. Protein degradation was measured using activation of autophagy and proteasome pathways, stable isotope tracers, and LMW approaches. In mice, insulin deprivation activated proteasome pathways and autophagy in muscle homogenates and isolated mitochondria. Reproducibility analysis of LMW extracts revealed that ϳ80% of proteins were detected consistently. As expected, insulin deprivation increased whole body protein turnover in T1D. Individual protein degradation increased with insulin deprivation, including those involved in mitochondrial function, proteome homeostasis, nDNA support, and contractile/cytoskeleton. Individual mitochondrial proteins that generated more LMW fragment with insulin deprivation included ATP synthase subunit-␥ (ϩ0.5-fold, P ϭ 0.007) and cytochrome c oxidase subunit 6 (ϩ0.305-fold, P ϭ 0.03).In conclusion, identifying LMW peptide fragments offers an approach to determine the degradation of individual proteins. Insulin deprivation increases degradation of select proteins and provides insight into the regulatory role of insulin in maintaining proteome homeostasis, especially of mitochondria.peptidomics; isotope tracer; low molecular weight; method; autophagy THE ANTICATABOLIC EFFECT OF INSULIN was evident from early reports of humans with type 1 diabetes (T1D) showing dramatic atrophy of skeletal muscle without insulin and then restoration of muscle mass with insulin treatment (17). Skeletal muscle protein content represents the balance between protein synthesis and protein degradation. Previous studies demonstrated that skeletal muscle catabolism during insulin deprivation in T1D is due primarily to increased protein degradation, with little change to mixed muscle protein synthesis, representing the average of multiple protein pools (8,16,35). Separating specific muscle protein fractions revealed that insulin has a stimulatory effect on mitochondrial proteins when amino acids are provided (36,40). In contrast, the synthesis rates of contractile proteins, such as myosin heavy cha...

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“…Phosphorylation of mTOR at S2448 tended to increase following leucine treatment and mechanical stretch and decreased following insulin treatment; however, these differences were not significant. In contrast, the phosphorylation of Akt at S473 was markedly increased by the addition of insulin in both control and stretched [46] reported that sustained insulin infusion without amino acid replacement causes sustained stimulation of Akt phosphorylation, without downstream stimulatory effects on mTOR phosphorylation. These results suggest that Akt-induced upregulation of mTOR phosphorylation at S2448 may not be essential for p70S6K activation by mechanical stretch and nutrient supplementation in C2C12 cells.…”

Section: Discussionmentioning

confidence: 90%

Mechanical stretch activates mammalian target of rapamycin and AMP-activated protein kinase pathways in skeletal muscle cells

2015

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Cellular protein synthesis is believed to be antagonistically regulated by mammalian target of rapamycin (mTOR) and AMP-activated protein kinase (AMPK) signaling pathways. In the present study, we examined the relationship between mTOR/p70 S6 kinase (p70S6K) and AMPK in response to mechanical stretch. C2C12 myoblasts were grown on a silicone elastomer chamber to confluence and further cultured in differentiation medium for 4 days to form multinucleated myotubes. Cells were subjected to 15% cyclic uniaxial stretch for 4 h at a frequency of 1 Hz. Phosphorylation of p70S6K at threonine 389 and AMPK at threonine 172 of the catalytic α subunit were concomitantly increased by mechanical stretch. Stimulation of the mTOR pathway by adding leucine and insulin increased the phosphorylation of p70S6K without inactivation of AMPK. In contrast, addition of compound C, a pharmacological inhibitor of AMPK, increased the phosphorylation of p70S6K in stretched cells. Activation of AMPK by the addition of 5-amino-4-imidazolecarboxamide ribonucleoside reduced the phosphorylation of p70S6K in response to mechanical stretch. In conclusion, crosstalk between mTOR and AMPK signaling was not tightly regulated in response to physiological stimuli, such as mechanical stress and/or nutrients. However, pharmacological modulation of AMPK influenced the mTOR/p70S6K signaling pathway.

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Insulin fails to enhance mTOR phosphorylation, mitochondrial protein synthesis, and ATP production in human skeletal muscle without amino acid replacement

Abstract: Barazzoni R, Short KR, Asmann Y, Coenen-Schimke JM, Robinson MM, Nair KS. Insulin fails to enhance mTOR phosphorylation, mitochondrial protein synthesis, and ATP production in human skeletal muscle without amino acid replacement.

Cited by 44 publications

References 28 publications

Role of insulin in the regulation of human skeletal muscle protein synthesis and breakdown: a systematic review and meta-analysis

Role of insulin in the regulation of human skeletal muscle protein synthesis and breakdown: a systematic review and meta-analysis

Release of skeletal muscle peptide fragments identifies individual proteins degraded during insulin deprivation in type 1 diabetic humans and mice

Mechanical stretch activates mammalian target of rapamycin and AMP-activated protein kinase pathways in skeletal muscle cells

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