Contractility and Myofibrillar Content in Skeletal Muscle are Decreased During Post-Sepsis Recovery, But Not During the Acute Phase of Sepsis

A scoping review of preclinical intensive care unit-acquired weakness models

Background

Animal models focusing on neuromuscular outcomes are crucial for understanding the mechanisms of intensive care unit-acquired weakness (ICU-AW) and exploring potential innovative prevention and treatment strategies.

Aim

To analyse and evaluate preclinical ICU-AW models.

Methods

We manually searched five English and four Chinese databases from 1 January 2002, to 1 February 2024, and reviewed related study references. Full-text publications describing animal models of muscle weakness and atrophy in critical illness were included. Detailed information about model types, animal species, sex, age, induction methods, outcome measures, drawbacks and strengths was extracted from each included study.

Results

A total of 3,451 citations were initially retrieved, with 84 studies included in the final analysis. The most frequently studied animal model included rodents (86.9%), 64.3% of which were male animals. ICU-AW animal models were mostly induced by comprehensive intensive care unit (ICU) interventions (38.1%) and sepsis (51.2%). Most studies focused on limb muscles (66.7%), diaphragm muscles (21.4%) or both (9.5%). Reported outcomes primarily included muscular pathological changes (83.3%), electrophysiological examinations of muscles (57.1%) and animal grip strength (16.6%). However, details such as animal age, mortality data, experimental design, randomisation, blinding, sample size and interventions for the experimental group and/or control group were inadequately reported.

Conclusion

Many preclinical models are used to study ICU-AW, but the reporting of methodological details is often incomplete. Although current ICU animal models can mimic the characteristics of human ICU-AW, there is no standard model. Future preclinical studies should develop a standard ICU-AW animal model to enhance reproducibility and improve scientific rigor in exploring the mechanisms and potential treatment of ICU-AW.

Identification and verification of disulfidptosis-related genes in sepsis-induced acute lung injury

Background

Sepsis-induced acute lung injury (ALI) is a common and serious complication of sepsis that eventually progresses to life-threatening hypoxemia. Disulfidptosis is a newly discovered type of cell death associated with the pathogenesis of different diseases. This study investigated the potential association between sepsis-induced acute lung injury and disulfidptosis by bioinformatics analysis.

Methods

In order to identify differentially expressed genes (DEGs) linked to sepsis, we screened appropriate data sets from the GEO database and carried out differential analysis. The key genes shared by DEGs and 39 disulfidptosis-related genes were identified: ACSL4 and MYL6 mRNA levels of key genes were detected in different datasets. We then used a series of bioinformatics analysis techniques, such as immune cell infiltration analysis, protein-protein interaction (PPI) network, genetic regulatory network, and receiver operating characteristic (ROC), to investigate the possible relationship between key genes and sepsis. Then, experimental verification was obtained for changes in key genes in sepsis-induced acute lung injury. Finally, to investigate the relationship between genetic variants of MYL6 or ACSL4 and sepsis, Mendelian randomization (MR) analysis was applied.

Results

Two key genes were found in this investigation: myosin light chain 6 (MYL6) and Acyl-CoA synthetase long-chain family member 4 (ACSL4). We verified increased mRNA levels of key genes in training datasets. Immune cell infiltration analysis showed that key genes were associated with multiple immune cell levels. Building the PPI network between MYL6 and ACSL4 allowed us to determine that their related genes had distinct biological functions. The co-expression genes of key genes were involved in different genetic regulatory networks. In addition, both the training and validation datasets confirmed the diagnostic capabilities of key genes by using ROC curves. Additionally, both in vivo and in vitro experiments confirmed that the mRNA levels of ACSL4 and MYL6 in sepsis-induced acute lung injury were consistent with the results of bioinformatics analysis. Finally, MR analysis revealed a causal relationship between MYL6 and sepsis.

Conclusion

We have discovered and confirmed that the key genes ACSL4 and MYL6, which are linked to disulfidptosis in sepsis-induced acute lung injury, may be useful in the diagnosis and management of septic acute lung injury.

Glutamine and leucine administration attenuates muscle atrophy in sepsis

AIMS

This study investigated whether l-glutamine (Gln) and/or l-leucine (Leu) administration could attenuate muscle atrophy in a mouse model of cecal ligation and puncture (CLP)-induced sepsis.

MATERIALS AND METHODS

Septic mice were given a daily intraperitoneal injection of Gln, Leu, or Gln plus Leu, and mice were sacrificed on either day 1 or 4 after CLP. Blood and muscles were collected for analysis of amino acid contents and markers related to protein degradation, muscle regeneration, and protein synthesis.

KEY FINDINGS

Leu treatment alone increased both muscle mass and total muscle protein content on day 4 after CLP. Gln administration reduced muscular Gln contents on day 1 and enhanced plasma Gln levels on day 4. Higher plasma branched-chain amino acid (BCAA) abundances and lower muscular BCAA levels were observed in Leu-treated mice on day 4. Gln and Leu individually suppressed muscle expressions of the E3 ubiquitin ligase genes, Trim63 and Fbxo32, on day 4 after CLP. As to muscle expressions of myogenic genes, both Gln and Leu upregulated Myog expression on day 1, but Leu alone enhanced Myf5 gene expression, whereas Gln plus Leu increased MyoD and Myog expression levels on day 4. Akt/mammalian target of rapamycin (mTOR) signaling was only activated by Gln and Leu when individually administered.

SIGNIFICANCE

Gln and/or Leu administration reduces sepsis-induced muscle degradation and promotes myogenic gene expressions. Leu treatment alone had more-pronounced effects on maintaining muscle mass during sepsis. A combination of Gln and Leu failed to show synergistic effects on alleviating sepsis-induced muscle atrophy.

IMPORTANCE OF THE INNATE IMMUNE RESPONSE IN SKELETAL MUSCLE TO SEPSIS-INDUCED ALTERATIONS IN PROTEIN BALANCE

ABSTRACT

There is growing appreciation that skeletal muscle is a fully functional component of the body's innate immune system with the potential to actively participate in the host response to invading bacteria as opposed to being a passive target. In this regard, skeletal muscle in general and myocytes specifically possess an afferent limb that recognizes a wide variety of host pathogens via their interaction with multiple classes of cell membrane-bound and intracellular receptors, including toll-like receptors, cytokine receptors, NOD-like receptors, and the NLRP inflammasome. The efferent limb of the innate immune system in muscle is equally robust and with an increased synthesis and secretion of a variety of myocyte-derived cytokines (i.e., myokines), including TNF-α, IL-1, IL-6, and NO as well as multiple chemokines in response to appropriate stimulation. Herein, the current narrative review focuses primarily on the immune response of myocytes per se as opposed to other cell types within whole muscle. Moreover, because there are important differences, this review focuses specifically on systemic infection and inflammation as opposed to the response of muscle to direct injury and various types of muscular dystrophies. To date, however, there are few definitive muscle-specific studies that are necessary to directly address the relative importance of muscle-derived immune activation as a contributor to either the systemic immune response or the local immune microenvironment within muscle during sepsis and the resultant downstream metabolic disturbances.

Chronic critical illness and post-intensive care syndrome: from pathophysiology to clinical challenges

Background

Post‐intensive care syndrome (PICS) encompasses physical, cognition, and mental impairments persisting after intensive care unit (ICU) discharge. Ultimately it significantly impacts the long‐term prognosis, both in functional outcomes and survival. Thus, survivors often develop permanent disabilities, consume a lot of healthcare resources, and may experience prolonged suffering. This review aims to present the multiple facets of the PICS, decipher its underlying mechanisms, and highlight future research directions.

Main text

This review abridges the translational data underlying the multiple facets of chronic critical illness (CCI) and PICS. We focus first on ICU-acquired weakness, a syndrome characterized by impaired contractility, muscle wasting, and persisting muscle atrophy during the recovery phase, which involves anabolic resistance, impaired capacity of regeneration, mitochondrial dysfunction, and abnormalities in calcium homeostasis. Second, we discuss the clinical relevance of post-ICU cognitive impairment and neuropsychological disability, its association with delirium during the ICU stay, and the putative role of low-grade long-lasting inflammation. Third, we describe the profound and persistent qualitative and quantitative alteration of the innate and adaptive response. Fourth, we discuss the biological mechanisms of the progression from acute to chronic kidney injury, opening the field for renoprotective strategies. Fifth, we report long-lasting pulmonary consequences of ARDS and prolonged mechanical ventilation. Finally, we discuss several specificities in children, including the influence of the child’s pre-ICU condition, development, and maturation.

Conclusions

Recent understandings of the biological substratum of the PICS’ distinct features highlight the need to rethink our patient trajectories in the long term. A better knowledge of this syndrome and precipitating factors is necessary to develop protocols and strategies to alleviate the CCI and PICS and ultimately improve patient recovery.