Inability to replete white adipose tissue during recovery phase of sepsis is associated with increased autophagy, apoptosis, and proteasome activity

Browning of white adipose tissue may be an appropriate adaptive response to critical illness

Both the baseline amount of brown adipose tissue (BAT) and the capacity to stimulate browning of white adipose tissue (WAT) may provide a protective effect to the patient in a critical care setting. Critical illness is associated with reduced mitochondrial volume and function resulting in the increased production of reactive oxygen species, greater demand for adenosine triphosphate, a switch to uncoupled fat metabolism, and hibernation of the organelle, which all contribute to multiple organ failure. Increasing insulin resistance, decreasing fatty acid oxidation, and dependence on carbohydrate metabolism result. Browning of WAT may oppose many of these adverse effects. The presence of BAT and the changes associated with browning may help dissipate oxidative stress, increase consumption and utilization of metabolites, and reduce pro-inflammatory actions. The number of mitochondria increases, and there is greater infiltration of macrophages into adipose tissue. A shift occurs in macrophage expression from the M1 to M2 phenotype, an effect which further dampens inflammation, increases insulin sensitivity, and improves tissue healing and remodeling. Any benefit from these responses may be lost in the disease states of chronic hypermetabolism (such as burns or cancer cachexia) in which the persistence of these physiologic effects may become detrimental, contributing to excessive weight loss, adipose wasting, and loss of lean body mass. This paper discusses the plasticity of adipose tissue and whether shifts in its physiology provide clinical advantages in the intensive care unit.

Purinergic P2X7 receptor expression increases in leukocytes from intra-abdominal septic patients

Inflammation is a tightly coordinated response of the host immune system to bacterial and viral infections, triggered by the production of inflammatory cytokines. Sepsis is defined as a systemic inflammatory response followed by immunosuppression of the host and organ dysfunction. This imbalance of the immune response increases the risk of mortality of patients with sepsis, making it a major problem for critical care units worldwide. The P2X7 receptor plays a crucial role in activating the immune system by inducing the activation of peripheral blood mononuclear cells. In this study, we analyzed a cohort of abdominal origin septic patients and found that the expression of the P2X7 receptor in the plasma membrane is elevated in the different subsets of lymphocytes. We observed a direct relationship between the percentage of P2X7-expressing lymphocytes and the early inflammatory response in sepsis. Additionally, in patients whose lymphocytes presented a higher percentage of P2X7 surface expression, the total lymphocytes populations proportionally decreased. Furthermore, we found a correlation between elevated soluble P2X7 receptors in plasma and inflammasome-dependent cytokine IL-18. In summary, our work demonstrates that P2X7 expression is highly induced in lymphocytes during sepsis, and this correlates with IL-18, along with other inflammatory mediators such as IL-6, IL-8, and procalcitonin.

High-fat diet increases mortality and intensifies immunometabolic changes in septic mice

Immunometabolic changes in the liver and white adipose tissue (WAT) caused by high-fat (HF) diet intake may worse metabolic adaptation and protection against pathogens in sepsis. We investigate the effect of chronic HF diet (15 weeks) on mortality and immunometabolic responses in female mice after sepsis induced by cecum ligation and perforation (CLP). At week 14, animals were divided into four groups: sham C diet (C-Sh), sepsis C diet (C-Sp), sham HF diet (HF-Sh) and sepsis HF diet (HF-Sp). The surviving animals were euthanised on the 7th day. The HF diet decreased survival rate (58.3% vs 76.2% C-Sp group), increased serum cytokine storm (IL-6 (1.41 ×; vs HF-Sh), IL-1β (1.37 ×; vs C-Sp), TNF (1.34 ×; vs C-Sp and 1.72 ×; vs HF-Sh), IL-17 (1.44 ×; vs HF-Sh), IL-10 (1.55 ×; vs C-Sp and 1.41 ×; HF-Sh), WAT inflammation (IL-6 (8.7 ×; vs C-Sp and 2.4 ×; vs HF-Sh), TNF (5 ×; vs C-Sp and 1.7 ×;vs HF-Sh), IL-17 (1.7 ×; vs C-Sp), IL-10 (7.4 ×; vs C-Sp and 1.3 ×; vs HF-Sh), and modulated lipid metabolism in septic mice. In the HF-Sp group liver's, we observed hepatomegaly, hydropic degeneration, necrosis, an increase in oxidative stress (reduction of CAT activity (-81.7%; vs HF-Sh); increase MDA levels (82.8%; vs HF-Sh), and hepatic IL-6 (1.9 ×; vs HF-Sh), and TNF (1.3 × %;vs HF-Sh) production. Furthermore, we found a decrease in the total number of inflammatory, mononuclear cells, and in the regenerative processes, and binucleated hepatocytes in a HF-Sp group liver's. Our results suggested that the organism under metabolic stress of a HF diet during sepsis may worsen the inflammatory landscape and hepatocellular injury and may harm the liver regenerative process.

The Surviving Sepsis Campaign: Basic/Translational Science Research Priorities

Objectives:

Expound upon priorities for basic/translational science identified in a recent paper by a group of experts assigned by the Society of Critical Care Medicine and the European Society of Intensive Care Medicine.

Data Sources:

Original paper, search of the literature.

Study Selection:

By several members of the original task force with specific expertise in basic/translational science.

Data Extraction:

None.

Data Synthesis:

None.

Conclusions:

In the first of a series of follow-up reports to the original paper, several members of the original task force with specific expertise provided a more in-depth analysis of the five identified priorities directly related to basic/translational science. This analysis expounds on what is known about the question and what was identified as priorities for ongoing research. It is hoped that this analysis will aid the development of future research initiatives.

Polydatin Alleviates Septic Myocardial Injury by Promoting SIRT6-Mediated Autophagy

Sepsis is a life-threatening condition. Polydatin (PD), a small natural compound from Polygonum cuspidatum, possesses antioxidant and anti-inflammatory properties. However, the protective mechanism of PD on sepsis-induced acute myocardial damage is still unclear. The aim of this study was to investigate the effect and mechanism of action of PD on lipopolysaccharide (LPS)-induced H9c2 cells and in a rat model of sepsis, and explored the role of PD-upregulated sirtuin (SIRT)6. LPS-induced H9c2 cells were used to simulate sepsis. Cecal ligation and puncture (CLP)-induced sepsis in rats were used to verify the protective effect of PD. ELISA, western blotting, immunofluorescence, immunohistochemistry, and flow cytometry were used to study the protective mechanism of PD against septic myocardial injury. PD pretreatment suppressed LPS-induced H9c2 cell apoptosis by promotion of SIRT6-mediated autophagy. Downregulation of SIRT6 or inhibition of autophagy reversed the protective effect of PD on LPS-induced apoptosis. PD pretreatment also suppressed LPS-induced inflammatory factor expression. CLP-induced sepsis in rats showed that PD pretreatment decreased CLP-induced myocardial apoptosis and serum tumor necrosis factor-α, interleukin (IL)-1β, and IL-6 expression. 3-Methyladenine (autophagy inhibitor) pretreatment prevented the protective effect of PD on septic cardiomyopathy. SIRT6 expression was increased with PD treatment, which confirmed that PD attenuates septic cardiomyopathy by promotion of SIRT6-mediated autophagy. All these results indicate that PD has potential therapeutic effects that alleviate septic myocardial injury by promotion of SIRT6-mediated autophagy.

White adipose tissue browning in critical illness: A review of the evidence, mechanisms and future perspectives

Observational studies suggest better clinical outcomes following critical illness in patients with overweight and obesity (obesity paradox). An understanding of the morphologic, physiologic and metabolic changes in adipose tissue in critical illness may provide an explanation. Recent studies have demonstrated the transformation of white to brown-like adipocytes due to the "browning process," which has been of interest as a potential novel therapy in obesity during the last decade. The characteristics of the browning of white adipose tissue (WAT) include the appearance of smaller, multilocular adipocytes, increased UCP1 mRNA expression, mitochondrial density and respiratory capacity. These changes have been identified in some critical illnesses, which specifically refers to burns, sepsis and cancer cachexia in this study. The pathophysiological nature of WAT browning, underlying mechanisms, main regulators and potential benefits and harms of this process are interesting new areas that warrants further investigations. In this review, we discuss emerging scientific discipline of adipose tissue physiology in metabolic stress, available data, gaps of knowledge and future perspectives. Future investigations in this field may provide insights into the underlying mechanisms and clinical aspects of browning that may further our understanding of the proposed obesity paradox following critical illness, which may in turn open up opportunities for novel therapies to save lives and improve recovery.

Single-cell deconstruction of post-sepsis skeletal muscle and adipose tissue microenvironments

BACKGROUND

Persistent loss of skeletal muscle mass and function as well as altered fat metabolism are frequently observed in severe sepsis survivors. Studies examining sepsis-associated tissue dysfunction from the perspective of the tissue microenvironment are scarce. In this study, we comprehensively assessed transcriptional changes in muscle and fat at single-cell resolution following experimental sepsis induction.

METHODS

Skeletal muscle and visceral white adipose tissue from control mice or mice 1 day or 1 month following faecal slurry-induced sepsis were used. Single cells were mechanically and enzymatically prepared from whole tissue, and viable cells were further isolated by fluorescence activated cell sorting. Droplet-based single-cell RNA-sequencing (scRNA-seq; 10× Genomics) was used to generate single-cell gene expression profiles of thousands of muscle and fat-resident cells. Bioinformatics analyses were performed to identify and compare individual cell populations in both tissues.

RESULTS

In skeletal muscle, scRNA-seq analysis classified 1438 single cells into myocytes, endothelial cells, fibroblasts, mesenchymal stem cells, macrophages, neutrophils, T-cells, B-cells, and dendritic cells. In adipose tissue, scRNA-seq analysis classified 2281 single cells into adipose stem cells, preadipocytes, endothelial cells, fibroblasts, macrophages, dendritic cells, B-cells, T-cells, NK cells, and gamma delta T-cells. One day post-sepsis, the proportion of most non-immune cell populations was decreased, while immune cell populations, particularly neutrophils and macrophages, were highly enriched. Proportional changes of endothelial cells, neutrophils, and macrophages were validated using faecal slurry and cecal ligation and puncture models. At 1 month post-sepsis, we observed persistent enrichment/depletion of cell populations and further uncovered a cell-type and tissue-specific ability to return to a baseline transcriptomic state. Differential gene expression analyses revealed key genes and pathways altered in post-sepsis muscle and fat and highlighted the engagement of infection/inflammation and tissue damage signalling. Finally, regulator analysis identified gonadotropin-releasing hormone and Bay 11-7082 as targets/compounds that we show can reduce sepsis-associated loss of lean or fat mass.

CONCLUSIONS

These data demonstrate persistent post-sepsis muscle and adipose tissue disruption at the single-cell level and highlight opportunities to combat long-term post-sepsis tissue wasting using bioinformatics-guided therapeutic interventions.

The surviving sepsis campaign: basic/translational science research priorities

Objectives

Expound upon priorities for basic/translational science identified in a recent paper by a group of experts assigned by the Society of Critical Care Medicine and the European Society of Intensive Care Medicine.

Data sources

Original paper, search of the literature.

Study selection

This study is selected by several members of the original task force with specific expertise in basic/translational science. Data extraction and data synthesis are not available.

Conclusions

In the first of a series of follow-up reports to the original paper, several members of the original task force with specific expertise provided a more in-depth analysis of the five identified priorities directly related to basic/translational science. This analysis expounds on what is known about the question and what was identified as priorities for ongoing research. It is hoped that this analysis will aid the development of future research initiatives.

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

ABSTRACT

Convalescence in humans after severe sepsis occurs over weeks to months and is associated with prolonged functional disabilities and impaired quality-adjusted survival. While much is known regarding the acute early phase of sepsis, there is a knowledge gap pertaining to restoration of muscle mass and function after elimination of the septic nidus. We used a sepsis-recovery model-where cecal-ligation-puncture (CLP) was performed in adult male mice followed 24 h later by removal of the cecum and antibiotic treatment-to assess changes in the abundance of muscle contractile proteins and function during the acute phase of sepsis (24 h post-CLP) and during the recovery phase (day 10 post-CLP). Although body weight and food consumption decreased acutely with sepsis, both had normalized by day 10; however, extensor digitorum longus mass remained decreased 10%. During acute sepsis, there were few contractile defects or significant changes in contractile proteins. In contrast, during sepsis recovery, specific maximum isometric twitch and specific maximum tetanic force were decreased ≈50%, compared with time-matched pair-fed controls, and defects were independent of the concomitant reduction in muscle mass. Force generation in sepsis-recovery mice was decreased 30% with increasing stimulus frequency. Contractile defects during sepsis-recovery were associated with 50% to 90% reductions in thin filament (troponin T, troponin I, tropomyosin, α-sarcomeric actin), thick filament (myosin heavy and myosin light chains), Z-disc (α-actinin 3), and M-band (myomesin-2) proteins, but no change in the intermediate filaments desmin and vimentin. During sepsis recovery, myofibrillar protein synthesis did not differ from control, but synthesis of sarcoplasmic proteins was increased 60%. These data suggest intrinsic defects in muscle contractile function exist during the recovery phase of sepsis and may negatively impact convalescence.

ATG7 promotes autophagy in sepsis‑induced acute kidney injury and is inhibited by miR‑526b

Sepsis is considered to be the most common contributing factor in the development of acute kidney injury (AKI). However, the mechanisms by which sepsis leads to AKI remain unclear. Autophagy is important for a number of fundamental biological activities and plays a key role in numerous different diseases. The present study demonstrated that autophagy is involved in sepsis-induced kidney injury and upregulates ATG7, LC3 and Beclin I. In addition, it was revealed that miR-526b is decreased in sepsis-induced kidney injury, and miR-526b was identified as a direct regulator of ATG7. Furthermore, the present study investigated the biological effects of ATG7 inhibited by miR-526b and demonstrated that miR-526b could promote cell viability by inhibiting autophagy, potentially through targeting ATG7. In conclusion, the present study highlights the role of autophagy in sepsis-induced AKI, and miR-526b in regulating autophagy through targeting ATG7, which suggested that miR-526b may be a molecular therapeutic target for sepsis-induced AKI.

Sepsis Induces Adipose Tissue Browning in Nonobese Mice But Not in Obese Mice

Severe sepsis and septic shock are the biggest cause of mortality in critically ill patients. Obesity today is one of the world's greatest health challenges. Little is known about the extent of involvement of the white adipose tissue (WAT) in sepsis and how it is being modified by obesity. We sought to explore the involvement of the WAT in sepsis. We hypothesize that sepsis induces browning of the WAT and that obesity alters the response of WAT to sepsis. Six-week-old C57BL/6 mice were randomized to a high-fat diet to induce obesity (obese group) or control diet (nonobese group). After 6 to 11 weeks of feeding, polymicrobial sepsis was induced by cecal ligation and puncture (CLP). Mice were sacrificed at 0, 18, and 72 h after CLP and epididymal WAT (eWAT), inguinal WAT, and brown adipose tissue (BAT) harvested. Both types of WAT were processed for light microscopy and transmission electron microscopy to assess for morphological changes in both obese and nonobese mice. Tissues were processed for immunohistochemistry, image analyses, and molecular analyses. BATs were used as a positive control. Nonobese mice have an extensive breakdown of the unilocular lipid droplet and smaller adipocytes in WAT compared with obese mice after sepsis. Neutrophil infiltration increases in eWAT in nonobese mice after sepsis but not in obese mice. Nonobese septic mice have an increase in mitochondrial density compared with obese septic mice. Furthermore, nonobese septic mice have an increase in uncoupling protein-1 expression. Although the WAT of nonobese mice have multiple changes characteristic of browning during sepsis, these changes are markedly blunted in obesity.

Temporally Distinct Regulation of Pathways Contributing to Cardiac Proteostasis During the Acute and Recovery Phases of Sepsis

BACKGROUND

Cardiac dysfunction is a common manifestation of sepsis and is associated with early increases in inflammation and decreases in myocardial protein synthesis. However, little is known regarding the molecular mechanisms regulating protein homeostasis during the recovery phase after the removal of the septic nidus. Therefore, the purpose of this study was to investigate diverse signal transduction pathways that regulate myocardial protein synthesis and degradation.

METHODS

Adult male C57BL/6 mice were used to identify potential mechanisms mediating the acute (24 h) effect of cecal ligation and puncture as well as long-term changes that manifest during the chronic (10 days) recovery phase.

RESULTS

Sepsis acutely decreased cardiac protein synthesis that was associated with reduced phosphorylation of S6K1/S6 but not 4E-BP1. Sepsis also decreased proteasome activity, although with no change in MuRF1 and atrogin-1 mRNA expression. Sepsis acutely increased apoptosis (increased caspase-3 and PARP cleavage), autophagosome formation (increased LC3B-II), and canonical inflammasome activity (increased NLRP3, TMS1, cleaved caspase-1). In contrast, during the recovery phase, independent of a difference in food consumption, global protein synthesis was increased, the early repression in proteasome activity was restored to basal levels, whereas stimulation of apoptosis, autophagosome formation, and the canonical inflammasome pathway had abated. However, during recovery there was a selective stimulation of the noncanonical inflammasome pathway as evidenced by activation of caspase-11 with cleavage of Gasdermin D.

CONCLUSIONS

These data demonstrate a temporally distinct homeostatic shift in the cardiac proteostatic response to acute infection and recovery.

Pseudomonas aeruginosa-derived pyocyanin reduces adipocyte differentiation, body weight, and fat mass as mechanisms contributing to septic cachexia

Pseudomonas aeruginosa, a leading cause of sepsis, produces pyocyanin, a blue-pigmented virulence factor. Sepsis is associated with cachexia, but mechanisms are unknown and conventional nutrition approaches are not effective treatments. Pyocyanin has affinity for the aryl hydrocarbon receptor (AhR), which is expressed on adipocytes and regulates adipocyte differentiation. The purpose of this study was to define in vitro and in vivo effects of pyocyanin on adipocyte differentiation and body weight regulation as relates to septic cachexia. In 3T3-L1 preadipocytes, pyocyanin activated AhR and its downstream marker CYP1a1, and reduced differentiation. Administration of pyocyanin to male C57BL/6J mice acutely reduced body temperature with altered locomotion, but caused sustained weight loss. Chronic pyocyanin administration to male and female C57BL/6J mice resulted in sustained reductions in body weight and fat mass, with adipose-specific AhR activation. Pyocyanin-treated male mice had decreased energy expenditure and physical activity, and increased adipose explant lipolysis. In females, pyocyanin caused robust reductions in body weight, adipose-specific AhR activation, and increased expression of inflammatory cytokines in differentiated adipocytes. These results demonstrate that pyocyanin reduces adipocyte differentiation and decreases body weight and fat mass in male and female mice, suggesting that pyocyanin may play a role in septic cachexia.

Biological effects of autophagy in mice with sepsis-induced acute kidney injury

This study investigated whether autophagy is activated after sepsis-induced acute kidney injury (AKI) and explored its biological role. Seventy-two normal C57 mice were randomly divided into sham operation group, cecal ligation and puncture (CLP) group and CLP+3-MA (autophagy inhibitor) group; 24 mice in each group. Mice in CLP and CLP+3-MA group were treated with cecal ligation to establish sepsis, while mice in sham operation group were treated with the same surgical operations, but not cecal ligation. Blood samples were collected from 12 mice of each group and the levels of serum creatinine (Cr) and blood urea nitrogen (BUN) were measured. The pathological changes were observed. The remaining 12 mice in each group were kept and the survival rate was recorded. Changes in the expressions of autophagy-related proteins were detected by reverse transcription-semi-quantitative PCR and western blotting. The results revealed that the levels of Cr and BUN in CLP and CLP+3-MA group were significantly higher than those in sham operation group (P<0.05), and the levels of Cr and BUN in CLP+3-MA group were higher than those in CLP group (P<0.05). The pathological score of renal injury in CLP+3-MA group was significantly higher than that of CLP group (P<0.01). The expression levels of Beclin1 and LC3-II/I were significantly increased in CLP group compared to sham operation group (P<0.01), while the expression of p62 was decreased (P<0.01). After 3-MA treatment the expression levels of Beclin1 and LC3-II/I were decreased, compared with CLP group, but accumulation of p62 occurred, and the degree of renal injury was increased. In conclusion, AKI induced by sepsis in mice can induce apoptosis and activate autophagy. The activation of autophagy aggravates the renal injury in mice, which in turn inhibits AKI after sepsis.