Sepsis stimulates nonlysosomal, energy-dependent proteolysis and increases ubiquitin mRNA levels in rat skeletal muscle.

Abstract

We tested the role of different intracellular proteolytic pathways in sepsis-induced muscle proteolysis. Sepsis was induced in rats by cecal ligation and puncture; controls were sham operated. Total and myofibrillar proteolysis was determined in incubated extensor digitorum longus muscles as release of tyrosine and 3-methylhistidine, respectively. Lysosomal proteolysis was assessed by using the lysosomotropic agents NH4Cl, chloroquine, leupeptin, and methylamine. Ca2"-dependent proteolysis was determined in the absence or presence of Ca2" or by blocking the Ca2+-dependent proteases calpain I and II. Energy-dependent proteolysis was determined in muscles depleted of ATP by 2-deoxyglucose and 2.4-dinitrophenol. Muscle ubiquitin mRNA and the concentrations of free and conjugated ubiquitin were determined by Northern and Western blots, respectively, to assess the role of the ATP-ubiquitin-dependent proteolytic pathway. Total and myofibrillar protein breakdown was increased during sepsis by 50 and 440%, respectively. Lysosomal and Ca2"-dependent proteolysis was similar in control and septic rats. In contrast, energy-dependent total and myofibrillar protein breakdown was increased by 172% and more than fourfold, respectively, in septic muscle. Ubiquitin mRNA was increased severalfold in septic muscle. The results suggest that the increase in muscle proteolysis during sepsis is due to an increase in nonlysosomal energy-dependent protein breakdown, which may involve the ubiquitin system. (J. Clin. Invest. 1994. 94:2255-2264

NF-κB mediates proteolysis-inducing factor induced protein degradation and expression of the ubiquitin–proteasome system in skeletal muscle

“…However, this mechanism is opposite to that induced by glucocorticoids, which have been shown (Du et al, 2000), at least in L6 muscle cells, to induce expression of the C3 proteasome subunit by antagonising interaction of NF-kB with the response element in the promoter region. Studies on protein degradation during sepsis, which is also mediated through the ubiquitin -proteasome pathway (Tiao et al, 1994), showed that NF-kB is increased at early time points (4 h), but decreased at later time points (16 h) (Penner et al, 2001). Which of these changes in NF-kB expression are responsible for the increased muscle protein degradation is not known, but the glucocorticoid receptor antagonist RU38486 increases NF-kB, suggesting that the decreased expression is due to glucocorticoids.…”

Relevância e tratamento das lesões características da insuficiência cardíaca na musculatura esquelética

“…Dentre as E3 ligases, destacam-se a Atrogin-1/ MAFbx, MuRF1 e E3a, que são altamente expressas na musculatura esquelética e aumentam consideravelmente sua expressão em estados de atrofia, como jejum, sepsis, câncer, diabetes e AIDS. [36][37][38][39] Schulze e colaboradores recentemente (2005) demonstraram que a E3 ligase Atrogin-1/MAFbx está com sua expressão aumentada no tecido muscular esquelético de camundongos com disfunção ventricular decorrente de infarto do miocárdio.…”

Ubiquitin-proteasome-dependent proteolysis in skeletal muscle

“…Unfortunately, very little is known about E3s in skeletal muscle, although thel4-kDa E2 is one of the major mammalian E2s that best supports E3-dependent conjugate formation and protein breakdown [20]. Gonen et al [16] [40,41]. In contrast, a decrease in ubiquitin-conjugates was observed during corticosterone treatment [4].…”

“…The reasons for such discrepancies are unclear, although it is conceivable that in some cases the changes in the levels of ubiquitin-conjugates may result from alteration in their rates of degradation. It has been observed that ubiquitylated proteins accumulate preferentially in the myofibrillar fraction [50], although others report conflicting findings [41]. Therefore, the proteins that are preferentially ubiquitylated in skeletal muscle remain to be identified.…”

“…In recent years, it has become apparent that both lysosomal and Ca 2+ -activated proteases (i.e. cathepsins and calpains, respectively) do not play a major role in this tissue: they contribute less than 15-20 % of total protein breakdown in muscles from control and cachectic animals, and are not responsible for the breakdown of myofibrillar proteins [15,25,41]. Furthermore, a systematic activation of either cathepsins or calpains has not been observed in several instances of muscle atrophy (see Attaix and Taillandier [1] for detailed information).…”