Amino acids, independent of insulin, attenuate skeletal muscle autophagy in neonatal pigs during endotoxemia

Mitophagy-related genes could facilitate the development of septic shock during immune infiltration

Septic shock often occurs following critically low blood pressure in patients with sepsis, and is accompanied by a high death rate. Although mitophagy is associated with infection and immune responses, its role in septic shock remains unknown. This study screened effective mitophagy-related genes (MRGs) for medical practice and depicted immune infiltration situations in patients with septic shock. Gene expression profiles of GSE131761 from the Gene Expression Omnibus database were compiled for differential analysis, weighted gene co-expression network analysis, and immune infiltration analysis, while other GSE series were used as validation datasets. A series of validation methods were used to verify the robustness of hub genes, while a nomogram and prognosis model were established for medical practice. Six genes were screened via combinations of differentially expressed genes, weighted gene co-expression network analysis, and MRGs. From this, 3 hub genes (MAP1LC3B, ULK1, and CDC37) were chosen for subsequent analysis based on different validation methods. Gene set enrichment analysis showed that leukocyte trans-endothelial migration and the p53 signaling pathway were abnormally activated during septic shock. Immune infiltration analysis indicated that the imbalance of neutrophils and CD4 naive T cells was significantly correlated with septic shock progression. A nomogram was generated based on MAP1LC3B, ULK1, and CDC37, as well as age. The stability of our model was confirmed using a calibration plot. Importantly, patients with septic shock with the 3 highly expressed hub genes displayed worse prognosis than did patients without septic shock. MAP1LC3B, ULK1, and CDC37 are considered hub MRGs in the development of septic shock and could represent promising diagnostic and prognostic biomarkers in blood tissue. The validated hub genes and immune infiltration pattern expand our knowledge on MRG functional mechanisms, which provides guidance and direction for the development of septic shock diagnostic and therapeutic markers.

Neuregulin-1β Alleviates Sepsis-Induced Skeletal Muscle Atrophy by Inhibiting Autophagy via AKT/mTOR Signaling Pathway in Rats

BACKGROUND

Several studies have shown that excessive protein degradation is a major cause of skeletal muscle atrophy induced by sepsis, and autophagy is the main pathway participating in protein degradation. However, the role of autophagy in sepsis is still controversial. Previously, we found that neuregulin-1β (NRG-1β) alleviated sepsis-induced diaphragm atrophy through the phosphatidylinositol-3 kinase signaling pathway. Akt/mechanistic target of rapamycin (mTOR) is a classic signaling pathway to regulate autophagy, which maintains intracellular homeostasis. This study aimed to investigate whether NRG-1β could alleviate sepsis-induced skeletal muscle atrophy by regulating autophagy.

METHODS

L6 rat myoblast cells were differentiated using 2% fetal bovine serum into myotubes, which were divided into four groups: Con group treated with normal serum; Sep group treated with septic serum to form a sepsis cell model; septic serum + NRG-1β (SN) group treated with septic serum for 24 h followed by injection with NRG-1β and incubation for another 48 h; and serum+NRG-1β+LY294002 group, in which the PI3K inhibitor LY294002 was added 30 min before NRG-1β, and other treatments were similar to those in SN group. Effects of NRG-1β were also evaluated in vivo using Sprague-Dawley (SD) rats, in which sepsis was induced by cecal ligation and puncture (CLP).

RESULTS

In L6 myotubes treated with septic serum, the expression of autophagy-related proteins UNC-51 like kinase 1, p-Beclin-1, and Beclin-1, and the ratio of LC3B II/I were highly increased, while protein p62 expression was decreased, indicating that autophagy was excessively activated. Moreover, NRG-1 expression was decreased, as detected by confocal immunofluorescence and western blotting. Upon exogenous addition of NRG-1β, autophagy was inhibited by the activation of Akt/mTOR signaling pathway, and cell viability was also increased. These effects disappeared in the presence of LY294002. In SD rats, sepsis was induced by CLP. NRG-1β was shown to inhibit autophagy in these rats via the Akt/mTOR pathway, leading to increased body weight of the septic SD rats and alleviation of atrophy of the tibialis anterior muscle.

CONCLUSION

NRG-1β could alleviate sepsis-induced skeletal muscle atrophy by inhibiting autophagy via the AKT/mTOR signaling pathway.

Mechanism of Mitophagy and Its Role in Sepsis Induced Organ Dysfunction: A Review

Autophagy, an evolutionarily conserved process, plays an important role in maintaining cellular homeostasis under physiological and pathophysiological conditions. It is widely believed that mitochondria influence the development of disease by regulating cellular metabolism. When challenged by different stimuli, mitochondria may experience morphological disorders and functional abnormalities, leading to a selective form of autophagy-mitophagy, which can clear damaged mitochondria to promote mitochondrial quality control. Sepsis is a complex global problem with multiple organ dysfunction, often accompanied by manifold mitochondrial damage. Recent studies have shown that autophagy can regulate both innate and acquired immune processes to protect against organ dysfunction in sepsis. Sepsis-induced mitochondrial dysfunction may play a pathophysiological role in the initiation and progression of sepsis-induced organ failure. Mitophagy is reported to be beneficial for sepsis by eliminating disabled mitochondria and maintaining homeostasis to protect against organ failure. In this review, we summarize the recent findings and mechanisms of mitophagy and its involvement in septic organ dysfunction as a potential therapeutic target.

Mechanism of Mitophagy and Its Role in Sepsis Induced Organ Dysfunction: A Review

Autophagy, an evolutionarily conserved process, plays an important role in maintaining cellular homeostasis under physiological and pathophysiological conditions. It is widely believed that mitochondria influence the development of disease by regulating cellular metabolism. When challenged by different stimuli, mitochondria may experience morphological disorders and functional abnormalities, leading to a selective form of autophagy-mitophagy, which can clear damaged mitochondria to promote mitochondrial quality control. Sepsis is a complex global problem with multiple organ dysfunction, often accompanied by manifold mitochondrial damage. Recent studies have shown that autophagy can regulate both innate and acquired immune processes to protect against organ dysfunction in sepsis. Sepsis-induced mitochondrial dysfunction may play a pathophysiological role in the initiation and progression of sepsis-induced organ failure. Mitophagy is reported to be beneficial for sepsis by eliminating disabled mitochondria and maintaining homeostasis to protect against organ failure. In this review, we summarize the recent findings and mechanisms of mitophagy and its involvement in septic organ dysfunction as a potential therapeutic target.

Mechanism of Mitophagy and Its Role in Sepsis Induced Organ Dysfunction: A Review

Autophagy, an evolutionarily conserved process, plays an important role in maintaining cellular homeostasis under physiological and pathophysiological conditions. It is widely believed that mitochondria influence the development of disease by regulating cellular metabolism. When challenged by different stimuli, mitochondria may experience morphological disorders and functional abnormalities, leading to a selective form of autophagy-mitophagy, which can clear damaged mitochondria to promote mitochondrial quality control. Sepsis is a complex global problem with multiple organ dysfunction, often accompanied by manifold mitochondrial damage. Recent studies have shown that autophagy can regulate both innate and acquired immune processes to protect against organ dysfunction in sepsis. Sepsis-induced mitochondrial dysfunction may play a pathophysiological role in the initiation and progression of sepsis-induced organ failure. Mitophagy is reported to be beneficial for sepsis by eliminating disabled mitochondria and maintaining homeostasis to protect against organ failure. In this review, we summarize the recent findings and mechanisms of mitophagy and its involvement in septic organ dysfunction as a potential therapeutic target.

The effect of continuous digital hypothermia on lamellar energy metabolism and perfusion during laminitis development in two experimental models

BACKGROUND

Continuous digital hypothermia (CDH) prevents lamellar failure in the euglycaemic hyperinsulinaemic clamp (EHC) and oligofructose (OF) laminitis models, but the mechanisms remain unclear.

OBJECTIVES

To evaluate the effects of CDH on lamellar energy metabolism and perfusion in healthy horses and during EHC and OF laminitis models.

STUDY DESIGN

In vivo experiment.

METHODS

Archived samples were used from Standardbred geldings that received no treatment (CON) (n = 8) or underwent EHC (n = 8) or OF (n = 6) laminitis models. Both forelimbs were instrumented with a lamellar microdialysis system, and one forelimb was cooled (CDH) with the other maintained at ambient temperature (AMB). Microdialysate was collected every 6 hours and analysed for glucose, lactate and pyruvate concentrations and lactate to pyruvate ratio (L:P). Microdialysis urea clearance was used to estimate lamellar tissue perfusion. Data were analysed using a mixed-effects linear regression model.

RESULTS

Glucose did not change in CDH limbs relative to AMB in CON (P = .3), EHC (P = .3) or OF (P = .6) groups. There was a decrease in lactate (P < .001) and pyruvate (P < .01) in CDH limbs relative to AMB in all groups. L:P decreased in CON CDH relative to CON AMB (P < .001) but was not different in EHC (P = .6) and OF (P = .07) groups. Urea clearance decreased in CDH limbs relative to AMB in CON (P = .002) and EHC (P < .001), but not in OF (P = .4).

MAIN LIMITATIONS

The EHC model may not mimic natural endocrinopathic laminitis.

CONCLUSIONS

CDH caused a marked decrease in lamellar glucose metabolism (CON, EHC and OF) and perfusion (CON and EHC) without affecting lamellar glucose concentration. Although cellular energy failure is not a primary pathophysiological event in EHC and OF laminitis models, CDH may act by limiting energy supply to pathologic cellular processes whilst preserving those critical to lamellar homoeostasis.

Toxic tall fescue grazing increases susceptibility of the Angus steer fecal microbiota and plasma/urine metabolome to environmental effects

Impaired thermoregulation and lowered average daily gains (ADG) result when livestock graze toxic endophyte (Epichloë coenophialum)-infected tall fescue (E+) and are hallmark signs of fescue toxicosis (FT), a disease exacerbated by increased temperature and humidity (+temperature-humidity index; +THI). We previously reported FT is associated with metabolic and microbiota perturbations under thermoneutral conditions; here, we assessed the influence of E+ grazing and +THI on the microbiota:metabolome interactions. Using high-resolution metabolomics and 16S rRNA gene sequencing, plasma/urine metabolomes and the fecal microbiota of Angus steers grazing non-toxic or E+ tall fescue were evaluated in the context of +THI. E+ grazing affected the fecal microbiota profile; +THI conditions modulated the microbiota only in E+ steers. E+ also perturbed many metabolic pathways, namely amino acid and inflammation-related metabolism; +THI affected these pathways only in E+ steers. Integrative analyses revealed the E+ microbiota correlated and co-varied with the metabolomes in a THI-dependent manner. Operational taxonomic units in the families Peptococcaceae, Clostridiaceae, and Ruminococcaceae correlated with production parameters (e.g., ADG) and with multiple plasma/urine metabolic features, providing putative FT biomarkers and/or targets for the development of FT therapeutics. Overall, this study suggests that E+ grazing increases Angus steer susceptibility to +THI, and offers possible targets for FT interventions.

The Role of Autophagy in Sepsis: Protection and Injury to Organs

Sepsis is a systemic inflammatory disease with infection, and autophagy has been shown to play an important role in sepsis. This review summarizes the main regulatory mechanisms of autophagy in sepsis and its latest research. Recent studies have shown that autophagy can regulate innate immune processes and acquired immune processes, and the regulation of autophagy in different immune cells is different. Mitophagy can select damaged mitochondria and remove it to deal with oxidative stress damage. The process of mitophagy is regulated by other factors. Non-coding RNA is also an important factor in the regulation of autophagy. In addition, more and more studies in recent years have shown that autophagy plays different roles in different organs. It tends to be protective in the lungs, heart, kidneys, and brain, and tends to be damaging in skeletal muscle. We also mentioned that some drugs can regulate autophagy. The process of modulating autophagy through drug intervention appears to be a new potential hope for the treatment of sepsis.

Variation in Protein Origin and Utilization: Research and Clinical Application

Muscle health can be rapidly compromised in clinical environments. Modifiable strategies to preserve metabolic homeostasis in adult patient populations include physical activity and pharmacologic support; however, optimizing dietary practices, or more specifically protein intake, is a necessary prerequisite for any other treatment strategy to be fully effective. Simply increasing protein intake is a well-intentioned but often unfocused strategy to protect muscle health in an intensive care setting. Protein quality is a frequently overlooked factor with the potential to differentially influence health outcomes. Quality can be assessed by a variety of techniques, with digestible indispensable amino acid score being the current and most comprehensive technique endorsed by the Food and Agriculture Organization. In practical terms, animal-based proteins are consistently scored higher in quality compared with incomplete proteins, regardless of the assessment method. Consequently, choosing parenteral and/or enteral feeding options that contain high-quality proteins, rich in the branched-chain amino acid leucine, may help establish a dietary framework with the potential to support clinical practice and improve health outcomes in critically ill patients.

Leucine supplementation stimulates protein synthesis and reduces degradation signal activation in muscle of newborn pigs during acute endotoxemia

Sepsis disrupts skeletal muscle proteostasis and mitigates the anabolic response to leucine (Leu) in muscle of mature animals. We have shown that Leu stimulates muscle protein synthesis (PS) in healthy neonatal piglets. To determine if supplemental Leu can stimulate PS and reduce protein degradation (PD) signaling in neonatal muscle during endotoxemia, overnight-fasted neonatal pigs were infused for 8 h with LPS or saline while plasma amino acids, glucose, and insulin were maintained at fasting levels during pancreatic-substrate clamps. Leu or saline was infused during the last hour. Markers of PS and PD were determined in skeletal muscle. Compared with controls, Leu increased PS in longissimus dorsi (LD), gastrocnemius, and soleus muscles. LPS decreased PS in these three muscles by 36%, 28%, and 38%, but Leu antagonized that reduction by increasing PS by 84%, 81%, and 83%, respectively, when supplemented to LPS. Leu increased eukaryotic translation initiation factor (eIF)3b-raptor interactions, eIF4E-binding protein-1, and S6 kinase 1 phosphorylation as well as eIF4E·eIF4G complex formation in LD, gastrocnemius, and soleus muscles of control and LPS-treated pigs. In LD muscle, LPS increased the light chain (LC)3-II-to-LC3 ratio and muscle-specific RING finger (MuRF-1) abundance but not atrogin-1 abundance or AMP-activated protein kinase-α phosphorylation. Leu supplementation to LPS-treated pigs reduced the LC3-II-to-LC3 ratio, MuRF-1 abundance, and AMP-activated protein kinase-α phosphorylation compared with LPS alone. In conclusion, parenteral Leu supplementation attenuates the LPS-induced reduction in PS by stimulating mammalian target of rapamycin complex 1-dependent translation and may reduce PD by attenuating autophagy-lysosome and MuRF-1 signaling in neonatal skeletal muscle.