Deletion of Nlrp3 protects from inflammation-induced skeletal muscle atrophy

BACKGROUND: Critically ill patients develop atrophic muscle failure, which increases morbidity and mortality. Interleukin-1β (IL-1β) is activated early in sepsis. Whether IL-1β acts directly on muscle cells and whether its inhibition prevents atrophy is unknown. We aimed to investigate if IL-1β activation via the Nlrp3 inflammasome is involved in inflammation-induced atrophy. METHODS: We performed an experimental study and prospective animal trial. The effect of IL-1β on differentiated C2C12 muscle cells was investigated by analyzing gene-and-protein expression, and atrophy response. Polymicrobial sepsis was induced by cecum ligation and puncture surgery in Nlrp3 knockout and wild type mice. Skeletal muscle morphology, gene and protein expression, and atrophy markers were used to analyze the atrophy response. Immunostaining and reporter-gene assays showed that IL-1β signaling is contained and active in myocytes. RESULTS: Immunostaining and reporter gene assays showed that IL-1β signaling is contained and active in myocytes. IL-1β increased Il6 and atrogene gene expression resulting in myocyte atrophy. Nlrp3 knockout mice showed reduced IL-1β serum levels in sepsis. As determined by muscle morphology, organ weights, gene expression, and protein content, muscle atrophy was attenuated in septic Nlrp3 knockout mice, compared to septic wild-type mice 96 h after surgery. CONCLUSIONS: IL-1β directly acts on myocytes to cause atrophy in sepsis. Inhibition of IL-1β activation by targeting Nlrp3 could be useful to prevent inflammation-induced muscle failure in critically ill patients

Dysregulation of Mitochondrial Dynamics and the Muscle Transcriptome in ICU Patients Suffering from Sepsis Induced Multiple Organ Failure

BACKGROUND: Septic patients treated in the intensive care unit (ICU) often develop multiple organ failure including persistent skeletal muscle dysfunction which results in the patient's protracted recovery process. We have demonstrated that muscle mitochondrial enzyme activities are impaired in septic ICU patients impairing cellular energy balance, which will interfere with muscle function and metabolism. Here we use detailed phenotyping and genomics to elucidate mechanisms leading to these impairments and the molecular consequences. METHODOLOGY/PRINCIPAL FINDINGS: Utilising biopsy material from seventeen patients and ten age-matched controls we demonstrate that neither mitochondrial in vivo protein synthesis nor expression of mitochondrial genes are compromised. Indeed, there was partial activation of the mitochondrial biogenesis pathway involving NRF2alpha/GABP and its target genes TFAM, TFB1M and TFB2M yet clearly this failed to maintain mitochondrial function. We therefore utilised transcript profiling and pathway analysis of ICU patient skeletal muscle to generate insight into the molecular defects driving loss of muscle function and metabolic homeostasis. Gene ontology analysis of Affymetrix analysis demonstrated substantial loss of muscle specific genes, a global oxidative stress response related to most probably cytokine signalling, altered insulin related signalling and a substantial overlap between patients and muscle wasting/inflammatory animal models. MicroRNA 21 processing appeared defective suggesting that post-transcriptional protein synthesis regulation is altered by disruption of tissue microRNA expression. Finally, we were able to demonstrate that the phenotype of skeletal muscle in ICU patients is not merely one of inactivity, it appears to be an actively remodelling tissue, influenced by several mediators, all of which may be open to manipulation with the aim to improve clinical outcome. CONCLUSIONS/SIGNIFICANCE: This first combined protein and transcriptome based analysis of human skeletal muscle obtained from septic patients demonstrated that losses of mitochondria and muscle mass are accompanied by sustained protein synthesis (anabolic process) while dysregulation of transcription programmes appears to fail to compensate for increased damage and proteolysis. Our analysis identified both validated and novel clinically tractable targets to manipulate these failing processes and pursuit of these could lead to new potential treatments

Long-term neuromuscular sequelae of critical illness

In this observational study, we analyzed the long-term neuromuscular deficits of survivors of critical illness. Intensive care unit-acquired muscular weakness (ICU-AW) is a very common complication of critical illness. Critical illness polyneuropathy (CIP) and critical illness myopathy (CIM) are two main contributors to ICU-AW. ICU-AW is associated with an increased mortality and leads to rehabilitation problems. However, the long-term outcome of ICU-AW and factors influencing it are not well known. We analyzed the medical records of 490 survivors of critical illness, aged 18-75 years and located in the area of the study center. Intensive care unit (ICU) survivors with comorbidities that might influence neuromuscular follow-up examinations, muscle strength, or results of nerve conduction studies, such as renal or hepatic insufficiency, diabetes mellitus, or vitamin deficiency were excluded. A total of 51 patients were finally included in the study. Six to 24 months after discharge from the ICU, we measured the Medical Research Council (MRC) sum score, the Overall Disability Sum score (ODSS), and also performed nerve conduction studies and EMG. For all ICU survivors, the median MRC sum score was 60 (range 47-60) and the median ODSS score was 0 (range 0-8). CIP was diagnosed in 21 patients (41 %). No patient was diagnosed with CIM. Patients with diagnosis of CIP showed a higher median ODSS scores 1 (range 0-8) versus 0 (range 0-5); p < 0.001 and lower median MRC sum scores 56 (range 47-60) versus 60 (range 58-60); p < 0.001. The three main outcome variables MRC sum score, ODSS score and diagnosis of CIP were not related to age, gender, or diagnosis of sepsis. The MRC sum score (r = -0.33; p = 0.02) and the ODSS score (r = 0.31; p = 0.029) were correlated with the APACHE score. There was a trend for an increased APACHE score in patients with diagnosis of CIP 19 (range 6-33) versus 16.5 (range 6-28); p = 0.065. Patients with the diagnosis of CIP had more days of ICU treatment 11 days (range 2-74) versus 4 days (range 1-61); p = 0.015, and had more days of ventilator support 8 days (range 1-59) versus 2 days (range 1-46); p = 0.006. The MRC sum score and the ODSS score were correlated with the days of ICU treatment and with the days of ventilator support. The neuromuscular long-term consequences of critical illness were not severe in our study population. As patients with concomitant diseases and old patients were excluded from this study the result of an overall favorable prognosis of ICU-acquired weakness may not be true for other patient's case-mix. Risk factors for the development of long-term critical illness neuropathy are duration of ICU treatment, duration of ventilator support, and a high APACHE score, but not diagnosis of sepsis. Although ICU-AW can be serious complication of ICU treatment, this should not influence therapeutic decisions, given its favorable long-term prognosis, at least in relatively young patients with no concomitant diseases