Skeletal muscle myofibrillar and sarcoplasmic protein synthesis rates are affected differently by altitude-induced hypoxia in native lowlanders

TY - JOUR

T1 - Skeletal muscle myofibrillar and sarcoplasmic protein synthesis rates are affected differently by altitude-induced hypoxia in native lowlanders

AU - Holm, Lars

AU - Haslund, Mads Lyhne

AU - Robach, Paul

AU - van Hall, Gerrit

AU - Calbet, Jose Al

AU - Saltin, Bengt

AU - Lundby, Carsten

PY - 2010/1/1

Y1 - 2010/1/1

N2 - As a consequence to hypobaric hypoxic exposure skeletal muscle atrophy is often reported. The underlying mechanism has been suggested to involve a decrease in protein synthesis in order to conserve O2. With the aim to challenge this hypothesis, we applied a primed, constant infusion of 1-13C-leucine in nine healthy male subjects at sea level and subsequently at high-altitude (4559 m) after 7-9 days of acclimatization. Physical activity levels and food and energy intake were controlled prior to the two experimental conditions with the aim to standardize these confounding factors. Blood samples and expired breath samples were collected hourly during the 4 hour trial and vastus lateralis muscle biopsies obtained at 1 and 4 hours after tracer priming in the overnight fasted state. Myofibrillar protein synthesis rate was doubled; 0.041±0.018 at sea-level to 0.080±0.018%·hr-1 (p<0.05) when acclimatized to high altitude. The sarcoplasmic protein synthesis rate was in contrast unaffected by altitude exposure; 0.052±0.019 at sea-level to 0.059±0.010%·hr-1 (p>0.05). Trends to increments in whole body protein kinetics were seen: Degradation rate elevated from 2.51±0.21 at sea level to 2.73±0.13 μmol·kg-1·min-1 (p = 0.05) at high altitude and synthesis rate similar; 2.24±0.20 at sea level and 2.43±0.13 μmol·kg-1·min-1 (p>0.05) at altitude. We conclude that whole body amino acid flux is increased due to an elevated protein turnover rate. Resting skeletal muscle myocontractile protein synthesis rate was concomitantly elevated by high-altitude induced hypoxia, whereas the sarcoplasmic protein synthesis rate was unaffected by hypoxia. These changed responses may lead to divergent adaptation over the course of prolonged exposure.

AB - As a consequence to hypobaric hypoxic exposure skeletal muscle atrophy is often reported. The underlying mechanism has been suggested to involve a decrease in protein synthesis in order to conserve O2. With the aim to challenge this hypothesis, we applied a primed, constant infusion of 1-13C-leucine in nine healthy male subjects at sea level and subsequently at high-altitude (4559 m) after 7-9 days of acclimatization. Physical activity levels and food and energy intake were controlled prior to the two experimental conditions with the aim to standardize these confounding factors. Blood samples and expired breath samples were collected hourly during the 4 hour trial and vastus lateralis muscle biopsies obtained at 1 and 4 hours after tracer priming in the overnight fasted state. Myofibrillar protein synthesis rate was doubled; 0.041±0.018 at sea-level to 0.080±0.018%·hr-1 (p<0.05) when acclimatized to high altitude. The sarcoplasmic protein synthesis rate was in contrast unaffected by altitude exposure; 0.052±0.019 at sea-level to 0.059±0.010%·hr-1 (p>0.05). Trends to increments in whole body protein kinetics were seen: Degradation rate elevated from 2.51±0.21 at sea level to 2.73±0.13 μmol·kg-1·min-1 (p = 0.05) at high altitude and synthesis rate similar; 2.24±0.20 at sea level and 2.43±0.13 μmol·kg-1·min-1 (p>0.05) at altitude. We conclude that whole body amino acid flux is increased due to an elevated protein turnover rate. Resting skeletal muscle myocontractile protein synthesis rate was concomitantly elevated by high-altitude induced hypoxia, whereas the sarcoplasmic protein synthesis rate was unaffected by hypoxia. These changed responses may lead to divergent adaptation over the course of prolonged exposure.

U2 - 10.1371/journal.pone.0015606

DO - 10.1371/journal.pone.0015606

M3 - Journal article

C2 - 21187972

SN - 1932-6203

VL - 5

SP - e15606

JO - PLoS Computational Biology

JF - PLoS Computational Biology

IS - 12

ER -