title: In vivo measurements of the contributions of protein synthesis and protein degradation in regulating cardiac pressure overload hypertrophy in the mouse.
abstract: Cardiac hypertrophy is generated in response to hemodynamic overload by altering steady-state protein metabolism such that the rate of protein synthesis exceeds the rate of protein degradation. To determine the relative contributions of protein synthesis and degradation in regulating cardiac hypertrophy in mice, a continuous infusion strategy was developed to measure myocardial protein synthesis rates in vivo. Osmotic mini-pumps were implanted in the abdominal cavity to infuse radiolabeled leucine in mice that are conscious and ambulatory. Protein synthesis rates were calculated by measuring incorporation of leucine into myocardial protein over 24 h prior to each time point and dividing by the specific radioactivity of plasma leucine. Compared to sham-operated controls, fractional rates of protein synthesis (K(s)) increased significantly at days 1 and 3 of TAC, but was lower on day 7 and returned to control values by day 14. These changes coincided with the curvilinear increase in LV mass that characterizes the hypertrophic response. Fractional rates of protein degradation (K(d)) were calculated by subtracting the rate of myocardial growth from the corresponding K(s) value. K(d) fell at days 1 and 3 of TAC, increased at day 7 and returned to control on day 14. Thus, the increase in LV mass generated in response to pressure overload is caused by acceleration of K(s) and suppression of K(d). As the growth rate slows, a new steady-state is achieved once the hypertrophic response is completed.
authors.affiliation: Department of Medicine, Medical University of South Carolina, Charleston, SC 29403, USA. mcdermp@musc.edu
authors.forename: Paul J
authors.initials: PJ
authors.lastname: McDermott
authors.forename: Catalin F
authors.initials: CF
authors.lastname: Baicu
authors.forename: Shaun R
authors.initials: SR
authors.lastname: Wahl
authors.forename: An O
authors.initials: AO
authors.lastname: Van Laer
authors.forename: Michael R
authors.initials: MR
authors.lastname: Zile
mesh_terms: D000818:Animals; D006352:Heart Ventricles / Q000378:metabolism / Q000473:pathology; D017379:Hypertrophy, Left Ventricular / Q000000981:diagnostic imaging / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D009124:Muscle Proteins / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D018995:Myosin Heavy Chains / Q000378:metabolism; D009929:Organ Size; D014176:Protein Biosynthesis; D059748:Proteolysis; D013312:Stress, Physiological; D014463:Ultrasonography; D017725:Ventricular Pressure
chemical_list: D009124:Muscle Proteins; D018995:Myosin Heavy Chains