Coordinate activation of lysosomal, Ca 2+-activated and ATP-ubiquitin-dependent proteinases in the unweighted rat soleus muscle.
Nine days of hindlimb suspension resulted in atrophy (55%) and loss of protein (53%) in rat soleus muscle due to a marked elevation in protein breakdown (66%, P < 0.005). To define which proteolytic system(s) contributed to this increase, soleus muscles from unweighted rats were incubated in the presence of proteolytic inhibitors. An increase in lysosomal and Ca 2+-activated proteolysis (254%, P < 0.05) occurred in the atrophying incubated muscles. In agreement with the measurements in vitro, cathepsin B, cathepsins B + L and m-calpain enzyme activities increased by 111%, 92% and 180% (P < 0.005) respectively in the atrophying muscles. Enhanced mRNA levels for these proteinases (P < 0.05 to P < 0.001) paralleled the increased enzyme activities, suggesting a transcriptional regulation of these enzymes. However, the lysosomal and Ca 2+-dependent proteolytic pathways accounted for a minor part of total proteolysis in both control (9%) and unweighted rats (18%). Furthermore the inhibition of these pathways failed to suppress increased protein breakdown in unweighted muscle. Thus a non-lysosomal Ca 2+-independent proteolytic process essentially accounted for the increased proteolysis and subsequent muscle wasting. Increased mRNA levels for ubiquitin, the 14 kDa ubiquitin-conjugating enzyme E2 (involved in the ubiquitylation of protein substrates) and the C2 and C9 subunits of the 20 S proteasome (i.e. the proteolytic core of the 26 S proteasome that degrades ubiquitin conjugates) were observed in the atrophying muscles (P < 0.02 to P < 0.001). Analysis of C9 mRNA in polyribosomes showed equal distribution into both translationally active and inactive mRNA pools, in either unweighted or control rats. These results suggest that increased ATP-ubiquitin-dependent proteolysis is most probably responsible for muscle wasting in the unweighted soleus muscle.
Taillandier
D
D
Centre de Recherche en Nutrition Humaine, Unité d'Etude du Métabolisme Azoté, Ceyrat, France.
Aurousseau
E
E
Meynial-Denis
D
D
Bechet
D
D
Ferrara
M
M
Cottin
P
P
Ducastaing
A
A
Bigard
X
X
Guezennec
C Y
CY
Schmid
H P
HP
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001284:Atrophy; D002118:Calcium / Q000494:pharmacology*; D002154:Calpain / Q000096:biosynthesis / Q000378:metabolism*; D002401:Cathepsin B / Q000096:biosynthesis / Q000378:metabolism; D002402:Cathepsin D / Q000096:biosynthesis / Q000378:metabolism; D056668:Cathepsin L; D002403:Cathepsins / Q000096:biosynthesis / Q000378:metabolism*; D003546:Cysteine Endopeptidases; D010450:Endopeptidases; D004789:Enzyme Activation; D006614:Hindlimb; D008247:Lysosomes / Q000201:enzymology*; D008297:Male; D018482:Muscle, Skeletal / Q000201:enzymology* / Q000473:pathology / Q000502:physiology; D011132:Polyribosomes / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors; D014158:Transcription, Genetic; D014452:Ubiquitins / Q000378:metabolism*
D011480:Protease Inhibitors; D014452:Ubiquitins; D000255:Adenosine Triphosphate; D002403:Cathepsins; D010450:Endopeptidases; D002154:Calpain; D003546:Cysteine Endopeptidases; D002401:Cathepsin B; D056668:Cathepsin L; C534280:Ctsl protein, rat; D002402:Cathepsin D; D002118:Calcium