Activation of caspase-3 is an initial step triggering accelerated muscle proteolysis in catabolic conditions

Abstract

With trauma, sepsis, cancer, or uremia, animals or patients experience accelerated degradation of muscle protein in the ATP-ubiquitin-proteasome (Ub-P’some) system. The initial step in myofibrillar proteolysis is unknown because this proteolytic system does not break down actomyosin complexes or myofibrils, even though it degrades monomeric actin or myosin. Since cytokines or insulin resistance are common in catabolic states and will activate caspases, we examined whether caspase-3 would break down actomyosin. We found that recombinant caspase-3 cleaves actomyosin, producing a characteristic, approximately 14-kDa actin fragment and other proteins that are degraded by the Ub-P’some. In fact, limited actomyosin cleavage by caspase-3 yields a 125% increase in protein degradation by the Ub-P’some system. Serum deprivation of L6 muscle cells stimulates actin cleavage and proteolysis; insulin blocks these responses by a mechanism requiring PI3K. Cleaved actin fragments are present in muscles of rats with muscle atrophy from diabetes or chronic uremia. Accumulation of actin fragments and the rate of proteolysis in muscle stimulated by diabetes are suppressed by a caspase-3 inhibitor. Thus, in catabolic conditions, an initial step resulting in loss of muscle protein is activation of caspase-3, yielding proteins that are degraded by the Ub-P’some system. Therapeutic strategies could be designed to prevent these events

Development of a Diagnostic Method for Detecting Increased Muscle Protein Degradation in Patients with Catabolic Conditions

“…A practical method is needed to detect muscle wasting and to monitor therapy that is directed at minimizing this problem (1,16,17,20). Our earlier studies showed that the 14-kD actin fragments that are released during accelerated muscle atrophy are degraded rapidly by the ATP-dependent UPP (4). Consequently, the amount of the 14-kD actin fragment in the soluble fraction of a muscle cell lysate is very low and highly variable unless a a Patient samples were assayed along with a sample of muscle from the same normal adult.…”

“…In addition, an initial, rate-limiting step in muscle protein loss is activation of caspase-3 (4). Using animal models of catabolic conditions, we found that activated caspase-3 is capable of cleaving actomyosin to create substrates that are degraded rapidly by the UPP.…”

Assessment of skeletal muscle proteolysis and the regulatory response to nutrition and exercise

“…The caspase enzymes also initiate skeletal muscle proteolysis (22). Caspase-3, a cysteine protease activated after its proenzyme is cleaved by caspase-9, initiates proteolysis by cleaving myofibrillar proteins into smaller fragments, including a characteristic 14 kDa actin fragment (22).…”

“…Caspase-3, a cysteine protease activated after its proenzyme is cleaved by caspase-9, initiates proteolysis by cleaving myofibrillar proteins into smaller fragments, including a characteristic 14 kDa actin fragment (22). We have recently shown significant increases in caspase-3 activation in human skeletal muscle following a modest, short-term energy deficit (23).…”

The effect of calcium chloride injection on shear force and caspase activities in bovine longissimus muscles during postmortem conditioning

“…Measurement of the activities of caspase-9, -8 and -3 Caspase activities were determined as described by Du et al (2004). Two hundred milligrams of frozen samples were taken from liquid nitrogen, pulverized and homogenized on ice in 0.5 ml lysis buffer comprising 100 mM 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES; pH 7.5), 10% sucrose, 0.1% nonyl phenoxypolyethoxylethanol-40, 10 mM dithiothreitol and a commercial protease inhibitor cocktail (Roche Applied Science, Indianapolis, IN, USA).…”