REGULATION OF PROTEIN TURNOVER IN SEPSIS

Project: Research project

Description

Chronic sepsis is always associated with profound muscle wasting.
The net catabolism may be due to a decreased skeletal muscle
protein synthesis, increased degradation, or combination of both.
Knowledge of which pathway is altered is fundamental to the con-
tinued development of rational and specific therapies to attenuate
the loss of skeletal muscle protein. In our chronic septic animal
model, preliminary studies in vivo have demonstrated a 50%
reduction in the rate of skeletal muscle protein synthesis.
Protein synthesis may be regulated by 1) decreased availability of
amino acids, ATP and GTP as substrates; 2) altered availability of
ribosomes, tRNA, mRNA and enzymes which catalyze peptide-bond
formation; and/or 3) altered activity of factors affecting rates
of peptide chain initiation, elongation or termination. The
proposed research will determine the physiologic significance of
the septic-induced effects on each of these mechanisms in
restricting protein synthesis. The chronic 15 days) septic rat
model will be induced by creating a stable intra-abdominal abscess
using an E. coli+B. fragilis infected sterile fecal-agar pellet as
the foreign body nidus. Rates of protein synthesis in control,
sterile inflammatory, and chronic septic rats will be determined
in vivo and in vitro perfused hemicorpus by measuring the
incorporation of (3H)-phenylalanine into protein, using the
phenylalanyl-tRNA specific radioactivity as the precursor pool for
estimating rates of protein synthesis. Tissue metabolites, amino
acids, RNA, and ribosomal subunits will be measured to determine
which mechanisms prevail in sepsis. Decreased synthetic rates in
sepsis were not due to either an energy deficit as tissue high
energy phosphate (ATP+CrP) and the ATP/ADP ratio were not altered,
or a decreased capacity for protein synthesis, as the total tissue
RNA content was not altered in sepsis. However, the translational
efficiency was significantly reduced in skeletal muscle from septic
animals. The molecular mechanisms involved in the decreased
translational efficiency in sepsis will be determined by measuring
the levels of 60s and 40s ribosomal subunits. In addition, the
rate of protein degradation will be determined in vitro by the
release of phenylalanine under conditions where the reutilization
of phenylalanine is inhibited by cycloheximide. The role of
interleukin-l in enhancing lysosomal proteases will be determined.
Pharmacological modulation of protein turnover will be assessed by
determining the role of hormones (insulin, cortisol) and amino
acids (BCAA, glutamine) in reversing septic-induced changes.
StatusFinished
Effective start/end date7/1/897/31/12

Funding

  • National Institutes of Health: $246,884.00

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Sirolimus
Sepsis
Skeletal Muscle
Muscle Proteins
Leucine
Phosphorylation
Proteins
Protein Biosynthesis
Norleucine
Glycogen Synthase Kinase 3
Glycogen Synthase Kinases
Food
Muscles
Protein-Serine-Threonine Kinases
Knockout Mice
Anti-Inflammatory Agents
Pharmacology
Inflammation
Morbidity
Mortality