Insulin stimulation of muscle protein synthesis in obese Zucker rats is not via a rapamycin-sensitive pathway

The obese Zucker rat is resistant to insulin for glucose disposal, but it is unknown whether this insulin resistance is accompanied by alterations of insulin-mediated muscle protein synthesis. We examined rates of muscle protein synthesis either with or without insulin in lean and obese Zucker rats with the use of a bilateral hindlimb preparation. Additional experiments examined insulin's effect on protein synthesis with or without rapamycin, an inhibitor of protein synthesis. Protein synthesis in red and white gastrocnemius was stimulated by insulin compared with control (no insulin) in obese ( n = 10, P < 0.05) but not in lean ( n = 10, P > 0.05) Zucker rats. In white gastrocnemius, rapamycin significantly reduced rates of protein synthesis compared with control in lean ( n = 6) and obese ( n = 6) rats; however, in red gastrocnemius, the attenuating effect of rapamycin occurred only in obese rats. The addition of insulin to rapamycin resulted in rates of synthesis that were similar to those for rapamycin alone for lean rats and to those for insulin alone (augmented) for obese rats in both tissues. Our results demonstrate that insulin enhances protein synthesis in muscle that is otherwise characterized as insulin resistant. Furthermore, rapamycin inhibits protein synthesis in muscle of obese Zucker rats; however, stimulation of protein synthesis by insulin is not via a rapamycin-sensitive pathway.

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Active involvement of PKC for insulin-mediated rates of muscle protein synthesis in Zucker rats

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00155.2003 ◽

2004 ◽

Vol 286 (5) ◽

pp. E753-E758 ◽

Cited By ~ 8

Author(s):

James D. Fluckey ◽

Ronald N. Cortright ◽

Edward Tapscott ◽

Timothy Koves ◽

Latasha Smith ◽

...

Keyword(s):

Protein Synthesis ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Mrna Translation ◽

Zucker Rats ◽

Insulin Signal Transduction ◽

Active Involvement ◽

Obese Rats ◽

Gf 109203X ◽

Obese Zucker Rats

A recent report from our group demonstrated that insulin facilitates muscle protein synthesis in obese Zucker rats. The purpose of this study was to determine whether PKC, a probable modulator of insulin signal transduction and/or mRNA translation, has a role in this insulin-mediated anabolic response. In the first portion of the study, gastrocnemius muscles of lean and obese Zucker rats ( n = 5–7 for each phenotype) were bilaterally perfused with or without insulin to assess cytosolic and membrane PKC activity. Limbs perfused with insulin demonstrated greater PKC activity in both lean and obese Zucker rats ( P < 0.05) compared with no insulin, but overall activity was greater in obese animals (by ∼27% compared with lean, P < 0.05). To determine whether PKC plays a role in muscle protein synthesis, hindlimbs ( n = 6–8 for each phenotype) were bilaterally perfused with or without insulin and/or GF-109203X (GF; a PKC inhibitor). The presence of GF did not influence the rates of insulin-mediated protein synthesis in gastrocnemius muscle of lean Zucker rats. However, when obese rats were perfused with GF ( P < 0.05), the effect of insulin on elevating rates of protein synthesis was not observed. We also used phorbol 12-myristate 13-acetate (TPA, a PKC activator; n = 5–7 for each phenotype) with and without insulin to determine the effect of PKC activation on muscle protein synthesis. TPA alone did not elevate muscle protein synthesis in lean or obese rats. However, TPA plus insulin resulted in elevated rates of protein synthesis in both phenotypes that were similar to rates of insulin alone of obese rats. These results suggest that PKC is a modulator and is necessary, but not sufficient, for insulin-mediated protein anabolic responses in skeletal muscle.

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Effects of Prolonged Energy Restriction and Dietary Protein on Muscle Protein Synthesis and Proteome Dynamics in Obese Zucker Rats

Current Developments in Nutrition ◽

10.1093/cdn/nzaa049_063 ◽

2020 ◽

Vol 4 (Supplement_2) ◽

pp. 670-670

Author(s):

Alyssa Varanoske ◽

Stephen Hennigar ◽

Lee Margolis ◽

Claire Berryman ◽

Mahalakshmi Shankaran ◽

...

Keyword(s):

Protein Synthesis ◽

Dietary Protein ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Energy Restriction ◽

Zucker Rats ◽

Muscle Proteins ◽

Turnover Rates ◽

Obese Zucker Rats ◽

Absolute Synthesis

Abstract Objectives High protein (HP) diets during short-term energy restriction (ER) attenuate energy-mediated reductions in muscle protein synthesis (MPS). MPS-adaptive responses to HP diets during prolonged ER are not well described. This study examined the effects of prolonged ER and HP on MPS and the synthesis rates of numerous individual muscle proteins. Methods Female 6-wk-old obese Zucker (leprfa+/fa+, n = 48) rats were randomized to one of four diet groups for 10 weeks: ad libitum-standard protein (AL-SP; 14% protein), AL-HP (35% protein), ER-SP, and ER-HP (both fed 60% of intake of AL-SP). At the start of week 10, D2O was administered by intraperitoneal injection and isotopic equilibrium was maintained daily by providing D2O in drinking water. Rats were euthanized after 1 week of labeling, and mixed-MPS (gastrocnemius), absolute mixed-MPS (mixed-MPS x muscle protein content), proteome dynamics, and protein half-lives [rate/d (k) = –ln(1-f)/d, where f is mixed-MPS and t is time in days; t1/2 (days) = ln(2)/k] were quantified. Results Mixed-MPS was not altered by energy status and protein intake. Gastrocnemius mass was lower (P < 0.001) in ER-fed rats than AL-fed rats and higher (P = 0.034) for AL-HP than AL-SP. As a result, absolute mixed-MPS was lower (P < 0.005) in ER than AL, regardless of dietary protein. Absolute synthesis in 24 of 26 myofibrillar, 32 of 61 mitochondrial, and 55 of 60 cytoplasmic measured proteins were lower in ER than AL (P < 0.05), regardless of dietary protein. The difference in absolute synthesis of myofibrillar, mitochondrial, and cytoplasmic proteins due to ER compared to AL was 28%, 16%, and 27%, respectively. Comparison of HP and SP within each energy state revealed lower turnover rates and prolonged half-lives for a majority of measured muscle proteins in HP than in SP in both ER and AL conditions (P < 0.001). Conclusions Prolonged ER in obese Zucker rats exerted a strong suppressive effect on myofibrillar, mitochondrial, and cytoplasmic MPS, suggesting reduced protein accretion contributed to lower gastrocnemius mass in ER-fed rats. Lower turnover rates of most muscle proteins in HP-fed rats without reductions in protein pool size (i.e., tissue mass) suggests prolonged HP intake, independent of energy, may prolong muscle protein lifespan of in obese Zucker rats. Funding Sources Supported by USAMRDC; authors’ views not official U.S. Army or DoD policy.

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The possible involvement of prostaglandin F2α in the stimulation of muscle protein synthesis by insulin

Biochemical and Biophysical Research Communications ◽

10.1016/s0006-291x(83)80253-8 ◽

1983 ◽

Vol 116 (3) ◽

pp. 1084-1090 ◽

Cited By ~ 35

Author(s):

P.J. Reeds ◽

R.M. Palmer

Keyword(s):

Protein Synthesis ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Prostaglandin F2α ◽

Stimulation Of

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Role of insulin and IGF-I in activation of muscle protein synthesis after oral feeding

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1996.270.4.e614 ◽

1996 ◽

Vol 270 (4) ◽

pp. E614-E620 ◽

Cited By ~ 16

Author(s):

E. Svanberg ◽

H. Zachrisson ◽

C. Ohlsson ◽

B. M. Iresjo ◽

K. G. Lundholm

Keyword(s):

Protein Synthesis ◽

Skeletal Muscles ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Oral Feeding ◽

Myofibrillar Proteins ◽

Diabetic Mice ◽

Igf I ◽

Stimulation Of

The aim was to evaluate the role of insulin and insulin-like growth factor I (IGF-I) in activation of muscle protein synthesis after oral feeding. Synthesis rate of globular and myofibrillar proteins in muscle tissue was quantified by a flooding dose of radioactive phenylalanine. Muscle tissue expression of IGF-I mRNA was measured. Normal (C57 Bl) and diabetic mice (type I and type II) were subjected to an overnight fast (18 h) with subsequent refeeding procedures for 3 h with either oral chow intake or provision of insulin, IGF-I, glucose, and amino acids. Anti-insulin and anti-IGF-I were provided intraperitoneally before oral refeeding in some experiments. An overnight fast reduced synthesis of both globular (38 +/- 3%) and myofibrillar proteins (54 +/- 3%) in skeletal muscles, which was reversed by oral refeeding. Muscle protein synthesis, after starvation/ refeeding, was proportional and similar to changes in skeletal muscle IGF-I mRNA expression. Diabetic mice responded quantitatively similarly to starvation/refeeding in muscle protein synthesis compared with normal mice (C57 Bl). Both anti-insulin and anti-IGF-I attenuated significantly the stimulation of muscle protein synthesis in response to oral feeding, whereas exogenous provision of either insulin or IGF-I to overnight-starved and freely fed mice did not clearly stimulate protein synthesis in skeletal muscles. Our results support the suggestion that insulin and IGF-I either induce or facilitate the protein synthesis machinery in skeletal muscles rather than exerting a true stimulation of the biosynthetic process during feeding.

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Adaptation to prolonged starvation in the rat: curtailment of skeletal muscle proteolysis

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1981.241.4.e321 ◽

1981 ◽

Vol 241 (4) ◽

pp. E321-E327 ◽

Cited By ~ 10

Author(s):

M. N. Goodman ◽

M. A. McElaney ◽

N. B. Ruderman

Keyword(s):

Skeletal Muscle ◽

Protein Synthesis ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Early Event ◽

Body Protein ◽

Fed State ◽

Prolonged Starvation ◽

Obese Rats ◽

Old Rats

Previous studies have established that 16-wk-old nonobese and obese rats conserve body protein during prolonged starvation. To determine the basis for this, protein synthesis and degradation in skeletal muscle were evaluated in the isolated perfused hindquarters of these rats, in the fed state and when starved for 2, 5, 10, and 11 days. Rats aged 4 and 8 wk were used as a comparison. The results indicate that the response to starvation depends on several factors: the age of the rat, its degree of adiposity, and the duration of the fast. An early event in starvation was a decline in muscle protein synthesis. This occurred in all groups, albeit this reduction occurred more slowly in the older rats. A later response to starvation was an increase in muscle proteolysis. This occurred between 2 and 5 days in the 8-wk-old rats. In 16-wk-old rats it did not occur until between 5 and 10 days, and it was preceded by a period of decreased proteolysis. In 16-wk-old obese rats, a decrease in proteolysis persisted for upwards of 10 days and the secondary increase was not noted during the period of study. The data suggest that the ability of older and more obese rats to conserve body protein during starvation is due, in part, to a curtailment of muscle proteolysis. This adaptation seems to correlate with the availability of lipid fuels.

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Stimulation of Muscle Protein Synthesis by Prolonged Parenteral Infusion of Leucine Is Dependent on Amino Acid Availability in Neonatal Pigs

Journal of Nutrition ◽

10.3945/jn.109.113621 ◽

2009 ◽

Vol 140 (2) ◽

pp. 264-270 ◽

Cited By ~ 52

Author(s):

Fiona A. Wilson ◽

Agus Suryawan ◽

Maria C. Gazzaneo ◽

Renán A. Orellana ◽

Hanh V. Nguyen ◽

...

Keyword(s):

Protein Synthesis ◽

Amino Acid ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Neonatal Pigs ◽

Amino Acid Availability ◽

Stimulation Of

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Dexamethasone inhibits the stimulation of muscle protein synthesis and PHAS-I and p70 S6-kinase phosphorylation

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.2001.280.4.e570 ◽

2001 ◽

Vol 280 (4) ◽

pp. E570-E575 ◽

Cited By ~ 19

Author(s):

Wen Long ◽

Liping Wei ◽

Eugene J. Barrett

Keyword(s):

Protein Synthesis ◽

Amino Acid ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Initiation Factor ◽

Glucose Disposal ◽

Acid Mixture ◽

S6 Kinase ◽

P70 S6 Kinase ◽

Amino Acid Infusion

Glucocorticoids inhibit protein synthesis in muscle. In contrast, insulin and amino acids exert anabolic actions that arise in part from their ability to phosphorylate ribosomal p70 S6-kinase (p70S6k) and eukaryotic initiation factor (eIF)4E binding protein (BP)1 (PHAS-I), proteins that regulate translation initiation. Whether glucocorticoids interfere with this action was examined by giving rats either dexamethasone (DEX, 300 μg · kg−1 · day−1, n = 10) or saline ( n = 10) for 5 days. We then measured the phosphorylation of PHAS-I and p70S6kin rectus muscle biopsies taken before and at the end of a 180-min infusion of either insulin (10 mU · min−1 · kg−1 euglycemic insulin clamp, n = 5 for both DEX- and saline-treated groups) or a balanced amino acid mixture ( n = 5 for each group also). Protein synthesis was also measured during the infusion period. The results were that DEX-treated rats had higher fasting insulin, slower glucose disposal, less lean body mass, and decreased protein synthetic rates during insulin or amino acid infusion ( P < 0.05 each). DEX did not affect basal PHAS-I or p70S6k phosphorylation but blocked insulin-stimulated phosphorylation of PHAS-I- and amino acid-stimulated phosphorylation of both PHAS-I and p70S6k ( P < 0.01, for each). DEX also increased muscle PHAS-I concentration. These effects can, in part, explain glucocorticoid-induced muscle wasting.

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Mechanisms of increased lipoprotein lipase in fat cells of obese Zucker rats

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1991.261.5.e653 ◽

1991 ◽

Vol 261 (5) ◽

pp. E653-E660 ◽

Cited By ~ 2

Author(s):

S. K. Fried ◽

I. J. Turkenkopf ◽

I. J. Goldberg ◽

M. H. Doolittle ◽

T. G. Kirchgessner ◽

...

Keyword(s):

Protein Synthesis ◽

Lipoprotein Lipase ◽

Bovine Milk ◽

Zucker Rats ◽

Fat Cells ◽

Fat Cell ◽

Cell Basis ◽

Rat Adipocytes ◽

Obese Rats ◽

Obese Zucker Rats

The mechanisms underlying the increased activity of lipoprotein lipase (LPL) in adipocytes of genetically obese Zucker rats was studied. Relative rates of LPL synthesis (percent of total protein synthesis) determined by biosynthetic labeling and specific immunoprecipitation were similar in isolated fat cells from lean and obese rats, in the absence or presence of insulin. Insulin stimulated LPL synthesis as a result of a general increase in protein synthesis, and this effect was more marked in the obese fat cells. Levels of LPL mRNA, as a percent of total RNA, were also similar in fat cells from lean and obese rats. In contrast, when the data are calculated on a per fat cell basis, rates of LPL synthesis per fat cell are ninefold higher in obese compared with lean cells, accounting for the increase in LPL activity per fat cell. Fat cells from lean and obese rats showed similar rates of binding and degradation of purified bovine milk 125I-labeled LPL per unit fat cell surface area. Thus, on a per cell basis, rates of LPL turnover are increased in enlarged Zucker rat adipocytes, but there is no specific abnormality in the cellular regulation of LPL. Increases in LPL activity in obese rat adipocytes are related to an overall hyperresponsiveness to insulin effects on protein synthesis.

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