Expansion and accumulation of Myeloid-Derived Suppressor Cells (MDSCs) during sepsis contribute to post-sepsis immunosuppression, as these cells suppress innate and adaptive immunity. We have shown that the proinflammatory S100A9 protein accumulates in the nucleus of MDSCs during late sepsis in both mice and humans. In this context, nuclear S100A9 acts as a transcription co-factor to induce the expression of two potent immunosuppressive cytokines, Interleukin-10 (IL-10) and Transforming Growth Factor-β (TGF-β). S100A9 knockdown in MDSCs from late septic mice and late septic patients significantly reduced IL-10 and TGF-β production upon ex vivo stimulation with bacterial lipopolysaccharide. In contrast, ectopic expression of S100A9 in MDSCs from S100A9-deficient mice significantly increased IL-10 and TGF-β production. Chromatin immunoprecipitation revealed that S100A9 protein binds at the IL-10 and TGF-β promoters. Moreover, co-transfection of S100A9 expression plasmid with a luciferase reporter gene under the control of IL-10 or TGF-β promoter induced the luciferase gene expression in MDSCs from S100A9-deficient mice. Notably, in vivo depletion of long noncoding Ribonucleic Acid (RNA) Hotairm1, which induces S100A9 protein accumulation in MDSCs during late sepsis, reduced IL-10 and TGF-β production ex vivo. Since IL-10 and TGF-β enhance sepsis immunosuppression and are associated with worse outcomes, our findings suggest that targeting S100A9 may mitigate the immunosuppressive effects of MDSCs in late sepsis.

BACKGROUND:Cardiomyopathy is a common complication of sepsis that contributes to increased morbidity and mortality. However, the molecular mechanisms underlying septic cardiomyopathy are poorly understood. Dichloroacetate (DCA) improves mitochondrial respiration and survival in a mouse model of sepsis by inhibiting pyruvate dehydrogenase kinase, which inactivates pyruvate dehydrogenase (PDH) through phosphorylation of its subunits. In this study, we explore the role of DCA in septic cardiac dysfunction using a murine sepsis model. METHODS:Cecal ligation and puncture (CLP) was performed in mice to investigate molecular and echocardiographic response to sepsis. DCA was administered to test the effects of PDH activation on cardiac performance during early and late sepsis and myocardial metabolic substrate production. Matrix-assisted laser desorption/ionization imaging mass spectrometry was used to reveal spatial alterations in metabolism. RESULTS:CLP significantly increased phosphorylation of the PDH E1α subunit (PDH inactivation), and DCA treatment reduced PDH E1α phosphorylation (PDH activation) to baseline without affecting total PDH E1α levels. Administration of DCA at the time of CLP improved cardiac preload and stroke volume without affecting cardiac contractility at 12 h after CLP. However, there was a significant increase in cardiac contractility at 30 h after DCA administration independent of cardiac loading conditions. This improved cardiac function after DCA administration was associated with a trend toward decreased production of metabolic intermediates such as ketogenic amino acids, succinate, and palmitoyl carnitine. Imaging mass spectrometry revealed an increase in itaconate expression upon CLP that was mitigated by DCA administration. CONCLUSION:Our findings revealed that sepsis decreased PDH activity in cardiac tissue. Rebalancing PDH activity with DCA improved cardiac performance after CLP. While imaging mass spectrometry identified changes in itaconate concentration and enabled detection of tricarboxylic acid cycle metabolites, further investigation is necessary to determine whether DCA is an effective therapeutic agent for septic cardiomyopathy.

Previous research suggests that group IIA-secreted phospholipase A(2) (sPLA(2)-IIA) plays a role in and predicts lethal COVID-19 disease. The current study reanalyzed a longitudinal proteomic data set to determine the temporal relationship between levels of several members of a family of sPLA(2) isoforms and the severity of COVID-19 in 214 ICU patients. The levels of six secreted PLA(2) isoforms, sPLA(2)-IIA, sPLA(2)-V, sPLA(2)-X, sPLA(2)-IB, sPLA(2)-IIC, and sPLA(2)-XVI, increased over the first 7 ICU days in those who succumbed to the disease but attenuated over the same time period in survivors. In contrast, a reversed pattern in sPLA(2)-IID and sPLA(2)-XIIB levels over 7 days suggests a protective role of these two isoforms. Furthermore, decision tree models demonstrated that sPLA(2)-IIA outperformed top-ranked cytokines and chemokines as a predictor of patient outcome. Taken together, proteomic analysis revealed temporal sPLA(2) patterns that reflect the critical roles of sPLA(2) isoforms in severe COVID-19 disease.

Lipopolysaccharide (LPS) is a known inducer of inflammatory signaling which triggers generation of reactive oxygen species (ROS) and cell death in responsive cells like THP-1 promonocytes and freshly isolated human monocytes. A key LPS-responsive metabolic pivot point is the 9 MDa mitochondrial pyruvate dehydrogenase complex (PDC), which provides pyruvate dehydrogenase (E1), lipoamide-linked transacetylase (E2) and lipoamide dehydrogenase (E3) activities to produce acetyl-CoA from pyruvate. While phosphorylation-dependent decreases in PDC activity following LPS treatment or sepsis have been deeply investigated, redox-linked processes have received less attention. Data presented here demonstrate that LPS-induced reversible oxidation within PDC occurs in PDCE2 in both THP-1 cells and primary human monocytes. Knockout of PDCE2 by CRISPR and expression of FLAG-tagged PDCE2 in THP-1 cells demonstrated that LPS-induced glutathionylation is associated with wild type PDCE2 but not mutant protein lacking the lipoamide-linking lysine residues. Moreover, the mitochondrially-targeted electrophile MitoCDNB, which impairs both glutathione- and thioredoxin-based reductase systems, elevates ROS similar to LPS but does not cause PDCE2 glutathionylation. However, LPS and MitoCDNB together are highly synergistic for PDCE2 glutathionylation, ROS production, and cell death. Surprisingly, the two treatments together had differential effects on cytokine production; pro-inflammatory IL-1β production was enhanced by the co-treatment, while IL-10, an important anti-inflammatory cytokine, dropped precipitously compared to LPS treatment alone. This new information may expand opportunities to understand and modulate PDC redox status and activity and improve the outcomes of pathological inflammation.

Activating the macrophage NLRP3 inflammasome can promote excessive inflammation with severe cell and tissue damage and organ dysfunction. Here, we show that pharmacological or genetic inhibition of pyruvate dehydrogenase kinase (PDHK) significantly attenuates NLRP3 inflammasome activation in murine and human macrophages and septic mice by lowering caspase-1 cleavage and interleukin-1β (IL-1β) secretion. Inhibiting PDHK reverses NLRP3 inflammasome-induced metabolic reprogramming, enhances autophagy, promotes mitochondrial fusion over fission, preserves crista ultrastructure, and attenuates mitochondrial reactive oxygen species (ROS) production. The suppressive effect of PDHK inhibition on the NLRP3 inflammasome is independent of its canonical role as a pyruvate dehydrogenase regulator. Our study suggests a non-canonical role of mitochondrial PDHK in promoting mitochondrial stress and supporting NLRP3 inflammasome activation during acute inflammation.

During the acute phase of sepsis, the S100A9 proinflammatory protein resides in the cytosol in a phosphorylated form. In contrast, S100A9 relocalizes to the nucleus in an unphosphorylated form during the late/chronic sepsis state of immunometabolic paralysis. We reported that Hotairm1, a long noncoding RNA, facilitates S100A9 nuclear location in myeloid-derived suppressor cells. Here, we show that Hotairm1 promotes S100A9 nuclear location by limiting its phosphorylation by p38 MAPK. Knockdown of Hotairm1 in MDSCs from mice and humans with late sepsis increases phospho-S100A9 protein. Conversely, increasing Hotairm1 in early sepsis Gr1+CD11b+ cells by transfection decreases phospho-S100A9 protein levels. Notably, increasing S100A9 protein phosphorylation in late sepsis MDSCs via Hotairm1 knockdown decreases the production of the immunosuppressive cytokine IL-10. These results suggest that targeting Hotairm1 might reduce MDSC expansion during sepsis and thus relieve immunosuppression and improve survival.

Found in all organisms, pyruvate dehydrogenase complexes (PDC) are the keystones of prokaryotic and eukaryotic energy metabolism. In eukaryotic organisms these multi-component megacomplexes provide a crucial mechanistic link between cytoplasmic glycolysis and the mitochondrial tricarboxylic acid (TCA) cycle. As a consequence, PDCs also influence the metabolism of branched chain amino acids, lipids and, ultimately, oxidative phosphorylation (OXPHOS). PDC activity is an essential determinant of the metabolic and bioenergetic flexibility of metazoan organisms in adapting to changes in development, nutrient availability and various stresses that challenge maintenance of homeostasis. This canonical role of the PDC has been extensively probed over the past decades by multidisciplinary investigations into its causal association with diverse physiological and pathological conditions, the latter making the PDC an increasingly viable therapeutic target. Here we review the biology of the remarkable PDC and its emerging importance in the pathobiology and treatment of diverse congenital and acquired disorders of metabolic integration.

Myeloid-derived suppressor cells (MDSCs) prolong sepsis by promoting immunosuppression. We reported that sepsis MDSC development requires long non-coding RNA Hotairm1 interactions with S100A9. Using a mouse model that simulates the immunobiology of sepsis, we find that histone demethylase KDM6A promotes Hotairm1 transcription by demethylating transcription repression H3K27me3 histone mark. We show that chemical targeting of KDM6A by GSK-J4 represses Hotairm1 transcription, which coincides with decreases in transcription activation H3K4me3 histone mark and transcription factor PU.1 binding to the Hotairm1 promoter. We further show that immunosuppressive IL-10 cytokine promotes KDM6A binding at the Hotairm1 promoter. IL-10 knockdown repletes H3K27me3 and reduces Hotairm1 transcription. GSK-J4 treatment also relocalizes nuclear S100A9 protein to the cytosol. To support translation to human sepsis, we demonstrate that inhibiting H3K27me3 demethylation by KDM6A ex vivo in MDSCs from patients with protracted sepsis decreases Hotairm1 transcription. These findings suggest that epigenetic targeting of MDSCs in human sepsis might resolve post-sepsis immunosuppression and improve sepsis survival.

EDITORIAL article Front. Immunol., 16 May 2022Sec. Inflammation Volume 13 - 2022 | https://doi.org/10.3389/fimmu.2022.914639

Sepsis is a life-threatening organ dysfunction caused by dysregulated host response to an infection. The metabolic aberrations associated with sepsis underly an acute and organism-wide hyperinflammatory response and multiple organ dysfunction; however, crosstalk between systemic metabolomic alterations and metabolic reprogramming at organ levels remains unknown. We analyzed substrate utilization by the respiratory exchange ratio, energy expenditure, metabolomic screening, and transcriptional profiling in a cecal ligation and puncture model to show that sepsis increases circulating free fatty acids and acylcarnitines but decreases levels of amino acids and carbohydrates, leading to a drastic shift in systemic fuel preference. Comparative analysis of previously published metabolomics from septic liver indicated a positive correlation with hepatic and plasma metabolites during sepsis. In particular, glycine deficiency was a common abnormality of the plasma and liver during sepsis. Interrogation of the hepatic transcriptome in septic mice suggested that the septic liver may contribute to systemic glycine deficiency by downregulating genes involved in glycine synthesis. Interestingly, intraperitoneal injection of the pyruvate dehydrogenase kinase (PDK) inhibitor dichloroacetate reversed sepsis-induced anorexia, energy imbalance, inflammation, dyslipidemia, hypoglycemia, and glycine deficiency. Collectively, our data indicated that PDK inhibition rescued systemic energy imbalance and metabolic dysfunction in sepsis partly through restoration of hepatic fuel metabolism.

The Modern Western Diet has been associated with the rise in metabolic and inflammatory diseases, including obesity, diabetes, and cardiovascular disease. This has been attributed, in part, to the increase in dietary omega-6 polyunsaturated fatty acid (PUFA) consumption, specifically linoleic acid (LA), arachidonic acid (ARA), and their subsequent metabolism to pro-inflammatory metabolites which may be driving human disease. Conversion of dietary LA to ARA is regulated by genetic variants near and within the fatty acid desaturase (FADS) haplotype block, most notably single nucleotide polymorphism rs174537 is strongly associated with FADS1 activity and expression. This variant and others within high linkage disequilibrium may potentially explain the diversity in both diet and inflammatory mediators that drive chronic inflammatory disease in human populations. Mechanistic exploration into this phenomenon using human hepatocytes is limited by current two-dimensional culture models that poorly replicate in vivo functionality. Therefore, we aimed to develop and characterize a three-dimensional hepatic construct for the study of human PUFA metabolism. Primary human hepatocytes cultured in 3D hydrogels were characterized for their capacity to represent basic lipid processing functions, including lipid esterification, de novo lipogenesis, and cholesterol efflux. They were then exposed to control and LA-enriched media and reproducibly displayed allele-specific metabolic activity of FADS1, based on genotype at rs174537. Hepatocytes derived from individuals homozygous with the minor allele at rs174537 (i.e., TT) displayed the slowest metabolic conversion of LA to ARA and significantly reduced FADS1 and FADS2 expression. These results support the feasibility of using 3D human hepatic cultures for the study of human PUFA and lipid metabolism and relevant gene-diet interactions, thereby enabling future nutrition targets in humans.

Balancing high energy-consuming danger resistance and low energy supply of disease tolerance is a universal survival principle that often fails during sepsis. Our research supports the concept that sepsis phosphorylates and deactivates mitochondrial pyruvate dehydrogenase complex control over the tricarboxylic cycle and the electron transport chain. StimulatIng mitochondrial energetics in septic mice and human sepsis cell models can be achieved by inhibiting pyruvate dehydrogenase kinases with the pyruvate structural analog dichloroacetate. Stimulating the pyruvate dehydrogenase complex by dichloroacetate reverses a disruption in the tricarboxylic cycle that induces itaconate, a key mediator of the disease tolerance pathway. Dichloroacetate treatment increases mitochondrial respiration and ATP synthesis, decreases oxidant stress, overcomes metabolic paralysis, regenerates tissue, organ, and innate and adaptive immune cells, and doubles the survival rate in a murine model of sepsis.

Dietary changes associated with industrialization increase the prevalence of chronic diseases, such as obesity, type II diabetes, and cardiovascular disease. This relationship is often attributed to an ‘evolutionary mismatch’ between human physiology and modern nutritional environments. Western diets enriched with foods that were scarce throughout human evolutionary history (e.g. simple sugars and saturated fats) promote inflammation and disease relative to diets more akin to ancestral human hunter-gatherer diets, such as a Mediterranean diet. Peripheral blood monocytes, precursors to macrophages and important mediators of innate immunity and inflammation, are sensitive to the environment and may represent a critical intermediate in the pathway linking diet to disease. We evaluated the effects of 15 months of whole diet manipulations mimicking Western or Mediterranean diet patterns on monocyte polarization in a well-established model of human health, the cynomolgus macaque ( Macaca fascicularis ). Monocyte transcriptional profiles differed markedly between diets, with 40% of transcripts showing differential expression (FDR < 0.05). Monocytes from Western diet consumers were polarized toward a more proinflammatory phenotype. The Western diet shifted the co-expression of 445 gene pairs, including small RNAs and transcription factors associated with metabolism and adiposity in humans, and dramatically altered behavior. For example, Western-fed individuals were more anxious and less socially integrated. These behavioral changes were also associated with some of the effects of diet on gene expression, suggesting an interaction between diet, central nervous system activity, and monocyte gene expression. This study provides new molecular insights into an evolutionary mismatch and uncovers new pathways through which Western diets alter monocyte polarization toward a proinflammatory phenotype.

Sepsis-induced myeloid-derived suppressor cells (MDSCs) increase mortality risk. We previously identified that long non-coding RNA Hotairm1 supports myeloid precursor shifts to Gr1+CD11b+ MDSCs during mouse sepsis. A major unanswered question is what molecular processes control Hotairm1 expression. In this study, we found by a genetic deletion that a specific PU.1-binding site is indispensable in controlling Hotairm1 transcription. We then identified H3K4me3 and H3K27me3 at the PU.1 site on the Hotairm1 promoter. Controlling an epigenetic switch of Hotairm1 transcription by PU.1 was histone KDM6A demethylase for H3K27me3 that derepressed its transcription with possible contributions from Ezh2 methyltransferase for H3K27me3. KDM6A knockdown in MDSCs increased H3K27me3, decreased H3K4me3, and inhibited Hotairm1 transcription activation by PU.1. These results enlighten clinical translation research of PU.1 epigenetic regulation as a potential sepsis immune-checkpoint treatment site.

Macrophages play a central role in the pathogenesis of atherosclerosis. Our previous study demonstrated that solute carrier family 37 member 2 (SLC37A2), an endoplasmic reticulum-anchored phosphate-linked glucose-6-phosphate transporter, negatively regulates macrophage Toll-like receptor activation by fine-tuning glycolytic reprogramming in vitro. Whether macrophage SLC37A2 impacts in vivo macrophage inflammation and atherosclerosis under hyperlipidemic conditions is unknown. We generated hematopoietic cell-specific SLC37A2 knockout and control mice in C57Bl/6 Ldlr-/- background by bone marrow transplantation. Hematopoietic cell-specific SLC37A2 deletion in Ldlr-/- mice increased plasma lipid concentrations after 12-16 wks of Western diet induction, attenuated macrophage anti-inflammatory responses, and resulted in more atherosclerosis compared to Ldlr-/- mice transplanted with wild type bone marrow. Aortic root intimal area was inversely correlated with plasma IL-10 levels, but not total cholesterol concentrations, suggesting inflammation but not plasma cholesterol was responsible for increased atherosclerosis in bone marrow SLC37A2-deficient mice. Our in vitro study demonstrated that SLC37A2 deficiency impaired IL-4-induced macrophage activation, independently of glycolysis or mitochondrial respiration. Importantly, SLC37A2 deficiency impaired apoptotic cell-induced glycolysis, subsequently attenuating IL-10 production. Our study suggests that SLC37A2 expression is required to support alternative macrophage activation in vitro and in vivo. In vivo disruption of hematopoietic SLC37A2 accelerates atherosclerosis under hyperlipidemic pro-atherogenic conditions.