Plateau effects of resistance exercise results from overexpression of eIF4EBP1

1
Plateau effects of resistance exercise results
from over-expression of eIF4E-BP1 Heath G.
Gasier1, Michael P. Wiggs1, Joshua M. Swift1,
David Oliphant1, Steven A. Riechman1 and James D.
Fluckey1 Department of Health and Kinesiology,
Texas AM University, College Station, TX
ABSTRACT
OBJECTIVES
RESULTS
Resistance exercise training (RET) may lead to a
plateau effect whereby muscle protein
synthesis is not elevated post exercise. We
observed during previous studies in our lab
(unpublished) that 15 RE (resistance exercise)
sessions over 5 weeks led to muscle hypertrophy
in rats, without an elevation of muscle protein
synthesis (PS). The purpose of this study was to
determine if this anabolic plateau after training
resulted from altered mRNA translation signaling.
Fifteen, male Sprague-Dawley rats were operantly
conditioned to engage in squat-like exercises
and assigned to either a RE (n8) or control
group (n7). Resistance was progressively
increased from 80g (50 repetitions) during
session 1 to 410g (16 repetitions) during session
15. Sixteen hours post session 15, rates of
muscle protein synthesis (mixed gastrocnemius,
plantaris and soleus) and signaling intermediates
(mixed gastrocnemius) were assessed using
flooding dose and immunoblotting, respectively.
PS was not different between RE or control rats
(pgt0.05). Protein levels of eIF2B-epsilon, a key
regulator of protein synthesis, was not different
between groups (pgt0.05). However, protein levels
of p70S6k and eIF4E-BP1 were significantly higher
in RE compared to control (plt0.05). These results
suggest that over-expression of eIF4E-BP1 may, in
part, limit levels of PS with resistance exercise
training.

• To determine if elevated rates of muscle protein
  synthesis persist with chronic resistance
  exercise training
• To examine the expression of key regulators of
  mRNA translation (p70s6k, eIF4E-BP1 and eIF2B-?)
  following a chronic resistance exercise program

Plantaris g mass to 100 g body mass ratio for RE
vs control rats
Soleus g mass to 100 g body mass ratio for RE vs
control rats
6
STUDY DESIGN METHODS
n8
n7
n8
n7
Day 1
Day 7
Day 21
Day 56
Day 57
Significantly different from NoRT (p lt 0.05)
Rates of muscle protein synthesis after 5 weeks
of resistance exercise
PS Measurement
Acclimation
RT Session 1
Operant Conditioning
RT Session 15
RATIONALE

• 15, 6 month old, male Sprague-Dawley Rats were
  randomized by body mass to either resistance
  training (RT, n8) or no resistance training
  (NoRT, n7)

• RET Skeletal Muscle (SM) hypertrophy
• Net Protein Balance (NPB) Protein Synthesis
  (PS) Protein Breakdown (PB)
• Acute RE (ARE) PS and PB increase ( NPB)
• RET PS and PB (?)
• Increased mRNA translation efficiency
  PS SM growth
• ARE increased eIF2B-epsilon (guanine nucleotide
  exchanger), S6K (pre-initiation complex
  regulatory kinase) and decreased or unchanged
  4E-BP1 (pre-initiation complex inhibition)
• RET Unknown

n5
n6
n6
n5
n5
n6
4E-BP1 expression in resistance and control rats
eIF4E-BP1/eIF4E co-expression in resistance and
control rats

• Rat RT model resulted in muscle hypertrophy
  following 5 weeks of RT
• Progressive Model
• 4-6 Operant conditioning sessions
• RT Weighted Velcro vest
• NoRT Unweighted Velcro vest
• Session 1 (80 g X 50 repetitions)
• Session 15 (410 g X 16 repetitions)
• 3 sessions per week
• NoRT matched for repetitions and electrical
  stimulation

Muscle Loading Contraction
n4
n4
n4
n4
Significantly different from NoRT (p lt 0.05)
CONCLUSIONS
eIF2B-e expression in resistance and control rats
PKB/AKT

• Although we observed skeletal muscle hypertrophy,
  elevated rates of protein synthesis that occur in
  response to acute resistance exercise did not
  persist with the chronic training.
• Resistance exercise training does not increase
  eIF2B-epsilon, suggesting a decreased need for
  skeletal muscle mRNA translation.
• Resistance exercise training increases 4E-BP1,
  suggesting a potential brake mechanism to halt
  elevated post exercise PS
• Resistance exercise training increases S6K1,
  suggesting a compensatory mechanism to maintain
  basal levels of PS

e

• Rates of Muscle Protein Synthesis and
  Hypertrophy The carotid artery and contra
  lateral jugular vein were cannulated 16 hours
  after the last RT session and a flooding dose of
  tritiated L-2,3,4,5,6-3H Phe (1mCi/rat) cold
  Phe (1 ml/100 g body weight) was injected into
  the venous catheter over a 10-15 second period.
  Three arterial blood samples were taken from the
  carotid cannula during a 12 minute period (3, 6
  and 12 minutes) for the determination of Phe
  specific radioactivity. After arterial sampling,
  the gastrocnemius, plantaris and soleus muscles
  were excised, weighed, and frozen between
  aluminum blocks in liquid nitrogen. Rates of
  muscle protein synthesis (RPS) was determined by
  the quantity of tritiated L-2,3,4,5,6-3H Phe
  incorporated (nmol/g/time) into trichloroacetic
  acid (TCA)-precipitable muscle protein extracts.
  Muscle growth was calculated from wet weights
  normalized per 100 g of body mass.
• p70s6k, eIF4E-BP1 and eIF2B-? Expression Muscle
  samples were homogenized and separated
  (cytosolic/membrane from myofibrillar). Protein
  quantification was determined by the BCA method.
  Cytosolic/membrane proteins were separated via
  SDS-PAGE, determined by immunochemistry and
  quantified by arbitrary units using an
  AlphaInnotech Imager (San Leandro, CA).

mTOR
n4
n4
S6K1
4E-BP1
p70S6K1 expression in resistance and control rats
eIF4E
S6
ACKNOWLEDGEMENTS
This research project was supported by The
Sydney and J.L. Huffines Institute for Sports
Medicine and Human Performance (HGG) and NIH
AG01025 (JDF). We extend our appreciation to
Ricky Williams and Melissa Bailey (University of
Arkansas for Medical Sciences), and Sewon Lee,
Bryan Harpster, Kelsey Jones, Alden Barnett and
Kristin Johnson (Texas AM University).
3
5 CAP
eIF4B
eIF4E
eIF4A
mRNA
eIF4G
n8
n8
Significantly different from NoRT (p lt 0.05)