Sepsis and development impede muscle protein synthesis in neonatal pigs by different ribosomal mechanisms

Tidy up - The unfolded protein response in sepsis

Pathogens, their toxic byproducts, and the subsequent immune reaction exert different forms of stress and damage to the tissue of the infected host. This stress can trigger specific transcriptional and post-transcriptional programs that have evolved to limit the pathogenesis of infectious diseases by conferring tissue damage control. If these programs fail, infectious diseases can take a severe course including organ dysfunction and damage, a phenomenon that is known as sepsis and which is associated with high mortality. One of the key adaptive mechanisms to counter infection-associated stress is the unfolded protein response (UPR), aiming to reduce endoplasmic reticulum stress and restore protein homeostasis. This is mediated via a set of diverse and complementary mechanisms, i.e. the reduction of protein translation, increase of protein folding capacity, and increase of polyubiquitination of misfolded proteins and subsequent proteasomal degradation. However, UPR is not exclusively beneficial since its enhanced or prolonged activation might lead to detrimental effects such as cell death. Thus, fine-tuning and time-restricted regulation of the UPR should diminish disease severity of infectious disease and improve the outcome of sepsis while not bearing long-term consequences. In this review, we describe the current knowledge of the UPR, its role in infectious diseases, regulation mechanisms, and further clinical implications in sepsis.

iTRAQ-Based Quantitative Proteomic Analysis of Intestines in Murine Polymicrobial Sepsis with Hydrogen Gas Treatment

Objective

Sepsis-associated intestinal injury has a higher morbidity and mortality in patients with sepsis, but there is still no effective treatment. Our research team has proven that inhaling 2% hydrogen gas (H₂) can effectively improve sepsis and related organ damage, but the specific molecular mechanism of its role is not clear. In this study, isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative proteomics analysis was used for studying the effect of H₂ on intestinal injury in sepsis.

Methods

Male C57BL/6J mice were used to prepare a sepsis model by cecal ligation and puncture (CLP). The 7-day survival rates of mice were measured. 4-kd fluorescein isothiocyanate-conjugated Dextran (FITC-dextran) blood concentration measurement, combined with hematoxylin-eosinstain (HE) staining and Western blotting, was used to study the effect of H₂ on sepsis-related intestinal damage. iTRAQ-based liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis was used for studying the proteomics associated with H₂ for the treatment of intestinal injury.

Results

H₂ can significantly improve the 7-day survival rates of sepsis mice. The load of blood and peritoneal lavage bacteria was increased, and H₂ treatment can significantly reduce it. CLP mice had significant intestinal damage, and inhalation of 2% hydrogen could significantly reduce this damage. All 4194 proteins were quantified, of which 199 differentially expressed proteins were associated with the positive effect of H₂ on sepsis. Functional enrichment analysis indicated that H₂ may reduce intestinal injury in septic mice through the effects of thyroid hormone synthesis and nitrogen metabolism signaling pathway. Western blot showed that H₂ was reduced by down-regulating the expressions of deleted in malignant brain tumors 1 protein (DMBT1), insulin receptor substrate 2 (IRS2), N-myc downregulated gene 1 (NDRG1) and serum amyloid A-1 protein (SAA1) intestinal damage in sepsis mice.

Conclusion

A total of 199 differential proteins were related with H₂ in the intestinal protection of sepsis. H₂-related differential proteins were notably enriched in the following signaling pathways, including thyroid hormone synthesis signaling pathway, nitrogen metabolism signaling pathways, digestion and absorption signaling pathways (vitamins, proteins and fats). H₂ reduced intestinal injury in septic mice by down-regulating the expressions of SAA1, NDRG1, DMBT1 and IRS2.

Bioinformatics Analysis for Multiple Gene Expression Profiles in Sepsis

Background

This work aimed to screen key biomarkers related to sepsis progression by bioinformatics analyses.

Material/Methods

The microarray datasets of blood and neutrophils from patients with sepsis or septic shock were downloaded from Gene Expression Omnibus database. Then, differentially expressed genes (DEGs) from 4 groups (sepsis versus normal blood samples; septic shock versus normal blood samples; sepsis neutrophils versus normal controls and septic shock neutrophils versus controls) were respectively identified followed by functional analyses. Subsequently, protein–protein network was constructed, and key functional sub-modules were extracted. Finally, receiver operating characteristic analysis was conducted to evaluate diagnostic values of key genes.

Results

There were 2082 DEGs between blood samples of sepsis patients and controls, 2079 DEGs between blood samples of septic shock patients and healthy individuals, 6590 DEGs between neutrophils from sepsis and controls, and 1056 DEGs between neutrophils from septic shock patients and normal controls. Functional analysis showed that numerous DEGs were significantly enriched in ribosome-related pathway, cell cycle, and neutrophil activation involved in immune response. In addition, TRIM25 and MYC acted as hub genes in protein–protein interaction (PPI) analyses of DEGs from microarray datasets of blood samples. Moreover, MYC (AUC=0.912) and TRIM25 (AUC=0.843) had great diagnostic values for discriminating septic shock blood samples and normal controls. RNF4 was a hub gene from PPI analyses based on datasets from neutrophils and RNF4 (AUC=0.909) was capable of distinguishing neutrophil samples from septic shock samples and controls.

Conclusions

Our findings identified several key genes and pathways related to sepsis development.

Prematurity blunts the feeding-induced stimulation of translation initiation signaling and protein synthesis in muscle of neonatal piglets

Postnatal growth of lean mass is commonly blunted in preterm infants and may contribute to short- and long-term morbidities. To determine whether preterm birth alters the protein anabolic response to feeding, piglets were delivered at term or preterm, and fractional protein synthesis rates (K_s) were measured at 3 days of age while fasted or after an enteral meal. Activation of signaling pathways that regulate protein synthesis and degradation were determined. Relative body weight gain was lower in preterm than in term. Gestational age at birth (GAB) did not alter fasting plasma glucose or insulin, but when fed, plasma insulin and glucose rose more slowly, and reached peak value later, in preterm than in term. Feeding increased K_s in longissimus dorsi (LD) and gastrocnemius muscles, heart, pancreas, and kidney in both GAB groups, but the response was blunted in preterm. In diaphragm, lung, jejunum, and brain, feeding increased K_s regardless of GAB. Liver K_s was greater in preterm than term and increased with feeding regardless of GAB. In all tissues, changes in 4EBP1, S6K1, and PKB phosphorylation paralleled changes in K_s. In LD, eIF4E·eIF4G complex formation, phosphorylation of TSC2, mTOR, and rpS6, and association of mammalian target of rapamycin (mTOR1) complex with RagA, RagC, and Rheb were increased by feeding and blunted by prematurity. There were no differences among groups in LD protein degradation markers. Our results demonstrate that preterm birth reduces weight gain and the protein synthetic response to feeding in muscle, pancreas, and kidney, and this is associated with blunted insulin- and/or amino acid-induced translation initiation signaling.

Acute systemic inflammatory response to lipopolysaccharide stimulation in pigs divergently selected for residual feed intake

Background

It is unclear whether improving feed efficiency by selection for low residual feed intake (RFI) compromises pigs’ immunocompetence. Here, we aimed at investigating whether pig lines divergently selected for RFI had different inflammatory responses to lipopolysaccharide (LPS) exposure, regarding to clinical presentations and transcriptomic changes in peripheral blood cells.

Results

LPS injection induced acute systemic inflammation in both the low-RFI and high-RFI line (n = 8 per line). At 4 h post injection (hpi), the low-RFI line had a significantly lower (p = 0.0075) mean rectal temperature compared to the high-RFI line. However, no significant differences in complete blood count or levels of several plasma cytokines were detected between the two lines. Profiling blood transcriptomes at 0, 2, 6, and 24 hpi by RNA-sequencing revealed that LPS induced dramatic transcriptional changes, with 6296 genes differentially expressed at at least one time point post injection relative to baseline in at least one line (n = 4 per line) (|log₂(fold change)| ≥ log₂(1.2); q < 0.05). Furthermore, applying the same cutoffs, we detected 334 genes differentially expressed between the two lines at at least one time point, including 33 genes differentially expressed between the two lines at baseline. But no significant line-by-time interaction effects were detected. Genes involved in protein translation, defense response, immune response, and signaling were enriched in different co-expression clusters of genes responsive to LPS stimulation. The two lines were largely similar in their peripheral blood transcriptomic responses to LPS stimulation at the pathway level, although the low-RFI line had a slightly lower level of inflammatory response than the high-RFI line from 2 to 6 hpi and a slightly higher level of inflammatory response than the high-RFI line at 24 hpi.

Conclusions

The pig lines divergently selected for RFI had a largely similar response to LPS stimulation. However, the low-RFI line had a relatively lower-level, but longer-lasting, inflammatory response compared to the high-RFI line. Our results suggest selection for feed efficient pigs does not significantly compromise a pig’s acute systemic inflammatory response to LPS, although slight differences in intensity and duration may occur.

Itraq-Based Quantitative Proteomic Analysis of Lungs in Murine Polymicrobial Sepsis with Hydrogen Gas Treatment

Sepsis-associated acute lung injury (ALI), which carries a high morbidity and mortality in patients, has no effective therapeutic strategies to date. Our group has already reported that hydrogen gas (H2) exerts a protective effect against sepsis in mice. However, the molecular mechanisms underlying H2 treatment are not fully understood. This study investigated the effects of H2 on lung injuries in septic mice through the isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative proteomic analysis. Male ICR mice used in this study were subjected to cecal ligation and puncture (CLP) or sham operation. And 2% H2 was inhaled for 1 h beginning at 1 and 6 h after sham or CLP operation. The iTRAQ-based liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis was preformed to investigate lung proteomics. Sepsis-challenged animals had decreased survival rate, as well as had increased bacterial burden in blood, peritoneal lavage, and lung sample, which were significantly ameliorated by H2 treatment. Moreover, a total of 4,472 proteins were quantified, and 192 differentially expressed proteins were related to the protective mechanism of H2 against sepsis. Functional enrichment analysis showed that H2-related differential proteins could be related to muscle contraction, oxygen transport, protein synthesis, collagen barrier membranes, cell adhesion, and coagulation function. These proteins were significantly enriched in four signaling pathways, and two of which are associated with coagulation. In addition, H2 alleviates ALI in septic mice through downregulating the expression of Sema 7A, OTULIN, and MAP3K1 as well as upregulating the expression of Transferrin. Thus, our findings provide an insight into the mechanism of H2 treatment in sepsis by proteomic approach, which may be helpful to the clinic application of H2 in patients with sepsis.

Ribosome biogenesis: emerging evidence for a central role in the regulation of skeletal muscle mass

The ribosome is a supramolecular ribonucleoprotein complex that functions at the heart of the translation machinery to convert mRNA into protein. Ribosome biogenesis is the primary determinant of translational capacity of the cell and accordingly has an essential role in the control of cell growth in eukaryotes. Cumulative evidence supports the hypothesis that ribosome biogenesis has an important role in the regulation of skeletal muscle mass. The purpose of this review is to, first, summarize the main mechanisms known to regulate ribosome biogenesis and, second, put forth the hypothesis that ribosome biogenesis is a central mechanism used by skeletal muscle to regulate protein synthesis and control skeletal muscle mass in response to anabolic and catabolic stimuli. The mTORC1 and Wnt/β-catenin/c-myc signaling pathways are discussed as the major pathways that work in concert with each of the three RNA polymerases (RNA Pol I, II, and III) in regulating ribosome biogenesis. Consistent with our hypothesis, activation of these two pathways has been shown to be associated with ribosome biogenesis during skeletal muscle hypertrophy. Although further study is required, the finding that ribosome biogenesis is altered under catabolic states, in particular during disuse atrophy, suggests that its activation represents a novel therapeutic target to reduce or prevent muscle atrophy. Lastly, the emerging field of ribosome specialization is discussed and its potential role in the regulation of gene expression during periods of skeletal muscle plasticity.

In utero LPS exposure impairs preterm diaphragm contractility

Preterm birth is associated with inflammation of the fetal membranes (chorioamnionitis). We aimed to establish how chorioamnionitis affects the contractile function and phenotype of the preterm diaphragm. Pregnant ewes received intra-amniotic injections of saline or 10 mg LPS, 2 days or 7 days before delivery at 121 days of gestation (term = 150 d). Diaphragm strips were dissected for the assessment of contractile function after terminal anesthesia. The inflammatory cytokine response, myosin heavy chain (MHC) fibers, proteolytic pathways, and intracellular molecular signaling were analyzed using quantitative PCR, ELISA, immunofluorescence staining, biochemical assays, and Western blotting. Diaphragm peak twitch force and maximal tetanic force were approximately 30% lower than control values in the 2-day and 7-day LPS groups. Activation of the NF-κB pathway, an inflammatory response, and increased proteasome activity were observed in the 2-day LPS group relative to the control or 7-day LPS group. No inflammatory response was evident after a 7-day LPS exposure. Seven-day LPS exposure markedly decreased p70S6K phosphorylation, but no effect on other signaling pathways was evident. The proportion of MHC IIa fibers was lower than that for control samples in the 7-day LPS group. MHC I fiber proportions did not differ between groups. These results demonstrate that intrauterine LPS impairs preterm diaphragmatic contractility after 2-day and 7-day exposures. Diaphragm dysfunction, resulting from 2-day LPS exposure, was associated with a transient activation of proinflammatory signaling, with subsequent increased atrophic gene expression and enhanced proteasome activity. Persistently impaired contractility for the 7-day LPS exposure was associated with the down-regulation of a key component of the protein synthetic signaling pathway and a reduction in the proportions of MHC IIa fibers.

Transcriptomic profiling in childhood H1N1/09 influenza reveals reduced expression of protein synthesis genes

We compared the blood RNA transcriptome of children hospitalized with influenza A H1N1/09, respiratory syncytial virus (RSV) or bacterial infection, and healthy controls. Compared to controls, H1N1/09 patients showed increased expression of inflammatory pathway genes and reduced expression of adaptive immune pathway genes. This was validated on an independent cohort. The most significant function distinguishing H1N1/09 patients from controls was protein synthesis, with reduced gene expression. Reduced expression of protein synthesis genes also characterized the H1N1/09 expression profile compared to children with RSV and bacterial infection, suggesting that this is a key component of the pathophysiological response in children hospitalized with H1N1/09 infection.

Development aggravates the severity of skeletal muscle catabolism induced by endotoxemia in neonatal pigs

Accretion rates of muscle protein are elevated in normal neonates, but this anabolic drive decreases with maturation. As this change occurs, it is not known whether development also influences muscle protein catabolism induced by sepsis. We hypothesize that protein degradation in skeletal muscle induced by endotoxemia becomes more severe as the neonate develops. Fasted 7- and 26-day-old pigs were infused for 8 h with LPS (0 and 10 μg·kg(-1)·h(-1)), while plasma amino acids (AA), 3-methylhistidine (3-MH), and α-actin concentrations and muscle protein degradation signal activation were determined (n = 5-7/group/age). Plasma full-length α-actin was greater in 7- than 26-day-old pigs, suggesting a higher baseline protein turnover in neonatal pigs. LPS increased plasma total AA, 3-MH, and full-length and cleaved α-actin in 26- than in 7-day-old pigs. In muscle of both age groups, LPS increased AMPK and NF-κB phosphorylation, the abundances of activated caspase 3 and E-3 ligases MuRF1 and atrogin1, as well as the abundance of cleaved α-actin, suggesting activation of muscle proteolysis by endotoxin in muscle. LPS decreased Forkhead box 01 (Fox01) and Fox04 phosphorylation and increased procaspase 3 abundance in muscle of 26-day-old pigs despite the lack of effect of LPS on PKB phosphorylation. The results suggest that skeletal muscle in healthy neonatal pigs maintains high baseline degradation signal activation that cannot be enhanced by endotoxin, but as maturation advances, the effect of LPS on muscle protein catabolism manifests its severity.

Endotoxin transiently inhibits protein synthesis through Akt and MAPK mediating pathways in C2C12 myotubes

In this study, the effect of lipopolysaccharide (LPS) on protein synthesis (PS) and intracellular signaling factors that regulate it have been investigated in C2C12 murine-derived myotubes. In particular, the role of Akt/mammalian target of rapamycin (mTOR) and the mitogen-activated protein kinases (MAPKs) [p38 and extracelluar regulated protein kinase (ERK1/2)] have been examined. The direct effect of LPS on PS was measured at 3 and 18 h. LPS significantly decreased PS at 3 h but not at the 18-h time point. This effect was preceded by decreased Akt phosphorylation at 5 and 30 min after LPS administration. The mTOR phosphorylation exhibited a long time dose-dependent increase at all the time points. Similarly, the activity-related phosphorylation of p38 and ERK1/2 significantly increased in a time- and dose-dependent manner at all the time points. Polymyxin B abolished the LPS-induced decrease in PS rate. The phosphatidylinositol 3-kinase inhibitor LY-0294002 in combination with LPS significantly decreased the rate of PS by 81% and alone by 66%, respectively, for the 3- and 18-h time points, whereas p38 and ERK inhibitors in combination with LPS significantly decreased the rate PS rate at the 18-h time point by 41% and 59%, respectively, compared with control cells. In conclusion, LPS alone transiently decreased the rate of PS by 50% at 3 h; this effect is most likely mediated via the Toll-like receptor 4 (TLR4)-Akt/mTOR pathway, and both p38 and ERK when inhibited in the presence of LPS at 3 h have a similar effect in preventing the LPS-induced reduction in PS.