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Elevated levels of S100A8 and S100A9 exacerbate muscle mitochondrial fragmentation in sepsis-induced muscle atrophy

ABSTRACT: Sepsis-induced skeletal muscle atrophy is common in septic patients with the increases risk of mortality and is associated with myocellular mitochondrial dysfunction. Nevertheless, the specific mechanism of sepsis muscle atrophy remains unclear. Here we conducted a clinical retrospective analysis and observed the elevation of skeletal muscle index (ΔSMI) was an independent risk factor for 60-day mortality in septic patients. Moreover, in mouse model of sepsis, the skeletal muscle atrophy was also observed, which was associated with the upregulation of S100a8/a9-mediated mitochondrial dysfunction. Inhibition of S100a8/a9 significantly improved mitochondrial function and alleviated muscle atrophy. Conversely, administration of recombinant S100a8/a9 protein exacerbated mitochondrial energy exhaustion and myocyte atrophy. Mechanistically, S100a8/a9 binding to RAGE induced Drp1 phosphorylation and mitochondrial fragmentation, resulting in muscle atrophy. Additionally, RAGE ablation or administration of Drp1 inhibitor significantly reduced Drp1-mediated mitochondrial fission, improved mitochondrial morphology and function. Our findings indicated the pivotal role of S100a8/a9 in driving the mitochondrial fragmentation in septic muscle atrophy. Targeting S100a8/a9-RAGE-initiated mitochondrial fission might offer a promising therapeutic intervention against septic muscle atrophy. Taken together, our data provide a potential mechanism for sepsis-induced muscle atrophy.

ORGANISM(S): Mus musculus

PROVIDER: GSE285318 | GEO | 2025/01/15

REPOSITORIES: GEO

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Project description:Sepsis is the most common cause of hospitalization worldwide. Millions of people survive sepsis each year and are at risk for rehospitalization and death. Pulmonary complications such as respiratory failure due to pneumonia and exacerbation of chronic respiratory disease are among the most common reasons for rehospitalization in sepsis survivors. In order to prevent additional morbidity and death in patients surviving sepsis, we must establish biomarkers to identify patients at risk for pulmonary complications and develop treatments. Late complications in sepsis survivors, particularly nosocomial infections, are proposed to occur through persistent immune reprogramming after sepsis known as immunoparalysis. However, pro-inflammatory immune reprogramming in the form of primed or enhanced responses to secondary stimuli has also been described and could directly contribute to tissue injury and death. Primed immune responses and their contribution to long-term sepsis complications remains understudied. We hypothesize that primed immune responses to inflammatory stimuli in the lung after sepsis are associated with pulmonary complications in survivors of sepsis. To this end, we developed a model of antibiotic treated sepsis induced by cecal ligation and puncture followed three weeks later by secondary challenge with intranasal lipopolysaccharide to induce inflammatory lung injury. We find that mice surviving sepsis have enhanced lung injury responses in the setting of an exaggerated proinflammatory immune response, including primed Ly6Chi monocyte Tnf expression. Using RNA sequencing, we identified derangements in lung gene expression after CLP prior to LPS administration which may mediate enhanced lung injury in this model. One potential mediator, S100A8/A9, was also found to be elevated in the circulation of human sepsis survivors for up to 180 days after sepsis. These findings validate our model and identify S100A8/A9 as one of many potential biomarkers and therapeutic targets for patients at risk for long-term pulmonary complications after sepsis. The role of S100A8/A9, monocyte priming, and other factors predisposing to enhanced lung injury responses and pulmonary complications after sepsis warrant further investigation in humans and mice.

Project description:Septic patients treated in the intensive care unit (ICU) often develop multiple organ failure including persistent skeletal muscle dysfunction which results in the patientâs protracted recovery process. We have demonstrated that muscle mitochondrial enzyme activities are impaired in septic ICU patients resulting in decreased cellular energy which will interfere with muscle function and metabolism. Here we use detailed phenotyping and genomics to elucidate mechanisms leading to these impairments. Methodology/Principle 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 NRF2?/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. Experiment Overall Design: 13 septic samples, 8 controls

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Elevated levels of S100A8 and S100A9 exacerbate muscle mitochondrial fragmentation in sepsis-induced muscle atrophy

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