A Critical Role for Muscle Ring Finger-1 in Acute Lung Injury–associated Skeletal Muscle Wasting

Abstract

Rationale: Acute lung injury (ALI) is a debilitating condition associated with severe skeletal muscle weakness that persists in humans long after lung injury has resolved. The molecular mechanisms underlying this condition are unknown. Objectives: To identify the muscle-specific molecular mechanisms responsible for muscle wasting in a mouse model of ALI. Methods: Changes in skeletal muscle weight, fiber size, in vivo contractile performance, and expression of mRNAs and proteins encoding muscle atrophy-associated genes for muscle ring finger-1 (MuRF1) and atrogin1 were measured. Genetic inactivation of MuRF1 or electroporationmediated transduction of miRNA-based short hairpin RNAs targeting either MuRF1 or atrogin1 were used to identify their role in ALIassociated skeletal muscle wasting. Measurements and Main Results: Mice with ALI developed profound muscle atrophy and preferential loss of muscle contractile proteins associated with reduced muscle function in vivo. Although mRNA expression of the muscle-specific ubiquitin ligases, MuRF1 and atrogin1, was increased in ALI mice, only MuRF1 protein levels were up-regulated. Consistent with these changes, suppression of MuRF1 by genetic or biochemical approaches prevented muscle fiber atrophy, whereas suppression of atrogin1 expression was without effect. Despite resolution of lung injury and down-regulation of MuRF1 and atrogin1, force generation in ALI mice remained suppressed. Conclusions: These data show that MuRF1 is responsible for mediating muscle atrophy that occurs during the period of active lung injury in ALI mice and that, as in humans, skeletal muscle dysfunction persists despite resolution of lung injury.Keywords: skeletal muscle atrophy; intensive care unit-acquired weakness; critical illness myopathy; muscle atrophy genes; proteasomal-mediated protein degradation Acute lung injury (ALI) is a syndrome characterized by the acute onset of pulmonary infiltrates and respiratory failure often leading to the need for mechanical ventilation (1). Approximately 200,000 people per year develop ALI in the United States, with mortality high at 30-40% (2). A common complication associated with ALI is skeletal muscle weakness. Weakness in these patients results in decreased long-term mobility and functional status. Skeletal muscle weakness is initiated early in the course of ALI, and has been shown to persist in a large percentage of patients for up to 5 years after resolution of lung injury and hospital discharge (3-6). Although multiple factors may contribute to ALI-induced muscle atrophy including reduced nutrition, inactivity caused by bed rest, and systemic inflammation, the etiology of ALI-associated skeletal muscle atrophy remains incompletely understood.Skeletal muscle weakness is a common finding not only among patients with ALI, but also in patients with other critical illnesses. Clinically apparent weakness is present in 20-50% of patients with critical illness and has been shown to be an independent risk factor for mortality in these patients (3,5,7,8)....

High CO2 Levels Cause Skeletal Muscle Atrophy via AMP-activated Kinase (AMPK), FoxO3a Protein, and Muscle-specific Ring Finger Protein 1 (MuRF1)

“…The UPS has been described to regulate skeletal muscle atrophy in patients with chronic lung diseases (43)(44)(45)(46). In addition, there have been reports of skeletal muscle atrophy via the UPS during acute lung injury and in patients with pulmonary vascular disease (47)(48)(49). Our data suggest a direct link between hypercapnia and muscle atrophy via the UPS in this process.…”

“…A recent study showed that acute lung injury associated muscle atrophy requires the activation of the NF-B for MuRF1 to be induced, whereas our findings suggest that high CO 2 triggers muscle catabolism through FoxO3a and MuRF1 regulation (49). FoxO regulation in response to external stimuli is mostly determined by changes in its phosphorylation state and subcellular localization, which modulates its access to nuclear DNA (58).…”

Cardiac troponin T and fast skeletal muscle denervation in ageing

“…We have used the latter strain previously as a model of ageing skeletal muscle. C57B16 mice were used for intramuscular plasmid injection and electroporation according to the techniques described by Files et al 17 Briefly, skeletal muscle electroporation was carried out with a Grass stimulator (Grass S48; West Warwick, RI, USA) using platinum‐coated paddles (Harvard Apparatus, Holliston, MA, USA). After removal of the animal's hair from the hindlimb and sedation with controlled isoflurane, 40 μL of bovine hyaluronic acid (0.3 U/μL in 0.9% NaCl; H3631‐3KU Sigma‐Aldrich, St Louis, MO, USA) was injected in 10 μL‐aliquots up the length of the tibialis anterior (TA) muscle using a 26 gauge needle and syringe.…”

Calpain inhibition rescues troponin T3 fragmentation, increases Cav1.1 , and enhances skeletal muscle force in aging sedentary mice

“…Resting tension, muscle length, and stimulation current were iteratively adjusted for each muscle to obtain optimal twitch force. The nerve was then stimulated to obtain force–frequency curves as described (Files et al ., 2012). …”