Regulation of muscle cathepsin B proteolytic activity in protein-depleted patients with chronic diseases.
OBJECTIVE
The lysosomal cathepsin system contributes to degrading cellular skeletal muscle proteins in many catabolic diseases. We have assessed the relationships between cathepsin B mRNA levels and the enzyme activity for this protease in the skeletal muscle of acutely ill patients with severe trauma (n=7) and in patients with a variety of chronic disease states (hemodialysis, n=3; nervous anorexia, n=1; type 2 diabetes, n=2; prolonged immobilization, n=1).


METHODS
Muscle biopsies were taken from the vastus lateralis muscle in patients and controls to assess tissue levels of cathepsin B mRNA by competitive-quantitative polymerase chain reaction, cathepsin B proteolytic activity and myofibrillar protein content as alkali-soluble protein to DNA ratio (ASP/DNA). In the trauma patients, muscle protein loss was assessed by the arteriovenous balance technique as rate of phenylalanine release from leg muscle.


RESULTS
The acute trauma patients exhibited a significant net phenylalanine release from leg muscle (33+/-4 nmol phenylalanine/min/100 ml leg volume) despite a continuous nutritional support. The muscle ASP/DNA ratio was lower (P<0.05) in the patients with chronic diseases (383+/-33) than in groups of healthy controls (554+/-41) or of uncomplicated, moderately obese subjects (525+/-26). Cathepsin B mRNA levels were 6-10 times greater (P<0.05) in the patients with acute trauma or chronic catabolic diseases than in the healthy subjects. Cathepsin B enzymatic activity were 2-3 times greater (P<0.05) in the chronic and acute patients than in the group of uncomplicated, moderately obese subjects. Regression analysis between cathepsin B mRNA and cathepsin B enzymatic activity indicates a significant direct correlation (r=0.84; P<0.05) in the chronic catabolic conditions, but not in the acute trauma patients (r=-0.05).


CONCLUSIONS
In skeletal muscle of patients with stable chronic catabolic diseases, cathepsin B activity is directly related to cathepsin B mRNA levels, suggesting that in these patients this enzyme could be mainly regulated at the level of gene transcription.
Bosutti
A
A
Department of Clinical, Morphological and Technological Sciences, Division of Internal Medicine, University of Trieste, Trieste, Italy.
Toigo
G
G
Ciocchi
B
B
Situlin
R
R
Guarnieri
G
G
Biolo
G
G
D000704:Analysis of Variance; D001707:Biopsy, Needle; D002401:Cathepsin B / Q000378:metabolism*; D002908:Chronic Disease; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology; D018529:Nutritional Support; D010649:Phenylalanine / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011502:Protein-Energy Malnutrition / Q000201:enzymology* / Q000473:pathology*; D012333:RNA, Messenger / Q000378:metabolism; D012044:Regression Analysis
D009124:Muscle Proteins; D012333:RNA, Messenger; D010649:Phenylalanine; D002401:Cathepsin B