Cellular metabolic regulators: novel indicators of low-grade inflammation in humans

Clinical treatment for persistent inflammation, immunosuppression and catabolism syndrome in patients with severe acute pancreatitis (Review)

Severe acute pancreatitis (SAP) is a severe disease with a high prevalence and a 3-15% mortality worldwide, and premature activation of zymogen for any reason is the initial factor for the onset of SAP. Gallstone disease and heavy alcohol consumption are the two most common etiologies of SAP. Persistent inflammation, immunosuppression and catabolism syndrome (PICS) is a life-threatening illness, and there are no effective treatments. The relapse state of PICS mainly leads to high mortality due to septic shock or severe trauma, both of which are dangerous and challenging conditions for clinicians. Thus, it is important for medical staff to identify patients at high risk of PICS and to master the prevention and treatment of PICS in patients with SAP. The present review aims to increase the understanding of the pathogenesis of PICS, produce evidence for PICS diagnosis and highlight clinical treatment for PICS in patients with SAP. With this information, clinical workers could implement standardized and integrated measures at an early stage of SAP to stop its progression to PICS.

TLR4 counteracts BVRA signaling in human leukocytes via differential regulation of AMPK, mTORC1 and mTORC2

TLR4 is implicated in diseases associated with chronic low-grade inflammation, yet homeostatic signaling mechanisms that prevent and/or are affected by chronic TLR4 activation are largely uncharacterized. We recently reported that LPS/TLR4 activates in human leukocytes signaling intermediates (SI), abbreviated TLR4-SI, which include mTORC1-specific effectors and targets, and that leukocytes of patients with T2D or after cardiopulmonary bypass (CPB) expressed similar SI. Extending these previous findings, here we show that TLR4-SI expression post-CPB was associated with low serum bilirubin and reduced preoperative expression of biliverdin reductase A (BVRA), the enzyme that converts biliverdin to bilirubin, in patient’s leukocytes. Biliverdin inhibited TLR4 signaling in leukocytes and triggered phosphorylation of mTORC2-specific targets, including Akt, PKCζ, AMPKα-LKB1-TSC1/2, and their association with BVRA. Torin, PP242, and a PKCζ inhibitory peptide, but not rapamycin, prevented these biliverdin-induced responses and TLR4 inhibition. In contrast, LPS/TLR4 triggered decreases in BVRA, AMPKα and PKCζ expression, and an increase in haptoglobin, a heme binding protein, in leukocytes in vivo and in vitro, indicating that activated TLR4 may suppress biliverdin/BVRA signaling. Significantly, compared to non-diabetics, BVRA and PKCζ expression was low and haptoglobin was high in T2D patients leukocytes. Sustained TLR4 activation may deregulate homeostatic anti-inflammatory BVRA/mTORC2 signaling and thereby contribute to chronic inflammatory diseases.

Insulin-Dependent Regulation of mTORC2-Akt-FoxO Suppresses TLR4 Signaling in Human Leukocytes: Relevance to Type 2 Diabetes

Leukocyte signaling in patients with systemic insulin resistance is largely unexplored. We recently discovered the presence of multiple Toll-like receptor 4 (TLR4) signaling intermediates in leukocytes from patients with type 2 diabetes or acute insulin resistance associated with cardiopulmonary bypass surgery. We extend this work to show that in addition to matrix metalloproteinase 9, hypoxia-inducible factor 1α, and cleaved AMPKα, patient leukocytes also express IRS-1 phosphorylated on Ser(312), Akt phosphorylated on Thr(308), and elevated TLR4 expression. Similar signaling intermediates were detected in leukocytes and neutrophils treated with lipopolysaccharide (LPS), a ligand of TLR4, in vitro. In contrast, insulin, but not LPS, induced mammalian target of rapamycin complex 2 (mTORC2)-dependent phosphorylation of Akt on Ser(473) and FoxO1/O3a on Thr(24/32) in leukocytes and neutrophils. Insulin suppressed LPS-induced responses in a dose- and time-dependent manner. AS1842856, a FoxO1 inhibitor, also suppressed TLR4 signaling. We propose that insulin is a homeostatic regulator of leukocyte responses to LPS/TLR4 and that the signaling intermediates expressed in leukocytes of patients with type 2 diabetes indicate TLR4 signaling dominance and deficient insulin signaling. The data suggest that insulin suppresses LPS/TLR4 signals in leukocytes through the mTORC2-Akt-FoxO signaling axis. Better understanding of leukocyte signaling in patients with type 2 diabetes may shed new light on disease causation and progression.

Metabolic endotoxemia with obesity: Is it real and is it relevant?

Obesity is associated with metabolic derangements in multiple tissues, which contribute to the progression of insulin resistance and the metabolic syndrome. The underlying stimulus for these metabolic derangements in obesity are not fully elucidated, however recent evidence in rodents and humans suggests that systemic, low level elevations of gut derived endotoxin (lipopolysaccharide, LPS) may play an important role in obesity related, whole-body and tissue specific metabolic perturbations. LPS initiates a well-characterized signaling cascade that elicits many pro- and anti-inflammatory pathways when bound to its receptor, Toll-Like Receptor 4 (TLR4). Low-grade elevation in plasma LPS has been termed "metabolic endotoxemia" and this state is associated with a heightened pro-inflammatory and oxidant environment often observed in obesity. Given the role of inflammatory and oxidative stress in the etiology of obesity related cardio-metabolic disease risk, it has been suggested that metabolic endotoxemia may serve a key mediator of metabolic derangements observed in obesity. This review provides supporting evidence of mechanistic associations with cell and animal models, and provides complimentary evidence of the clinical relevance of metabolic endotoxemia in obesity as it relates to inflammation and metabolic derangements in humans. Discrepancies with endotoxin detection are considered, and an alternate method of reporting metabolic endotoxemia is recommended until a standardized measurement protocol is set forth.

Proteolytic Cleavage of AMPKα and Intracellular MMP9 Expression Are Both Required for TLR4-Mediated mTORC1 Activation and HIF-1α Expression in Leukocytes

LPS-induced TLR4 activation alters cellular bioenergetics and triggers proteolytic cleavage of AMPKα and HIF-1α expression in leukocytes. In human leukocytes, and more specifically neutrophils, AMPKα cleavage yields 55- and 35-kDa protein fragments. In this study, we address the mechanism by which AMPKα is cleaved and its relevance to human health. Our data indicate that AMPKα cleavage is linked to MMP9 expression and that both are required for mammalian target of rapamycin complex-1 and S6K1 activation and HIF-1α expression in LPS-stimulated human and mice leukocytes. Three key observations support this conclusion. First, no changes in AMPKα and TLR4 signaling intermediates (mammalian target of rapamycin complex-1/S6 kinase 1/HIF-1α) were detected in LPS-stimulated MMP9-deficient mice leukocytes. Second, rMMP9 cleaved human AMPKα ex vivo, producing degradation products similar in size to those detected following LPS stimulation. Third, MMP9 inhibitors prevented AMPKα degradation and HIF-1α expression in LPS-activated human leukocytes, whereas AMPK activators blocked MMP9 and HIF-1α expression. Significantly, AMPKα degradation, MMP9, and TLR4 signaling intermediates were all detected in leukocytes from patients with type 2 diabetes mellitus and patients following cardiopulmonary bypass surgery. Plasma from these two patient cohorts induced AMPKα cleavage and TLR4 signaling intermediates in healthy donor leukocytes and either a TLR4 inhibitor or polymyxin prevented these outcomes. Detection of AMPKα degradation, MMP9 expression, and TLR4 signaling intermediates described in this study in leukocytes, the most readily available human cells for clinical investigation, may provide a powerful tool for further exploring the role of TLR4 signaling in human diseases and lead to identification of new, context-specific therapeutic modalities for precision medicine.

Tissue-specific RNA-Seq in human evoked inflammation identifies blood and adipose LincRNA signatures of cardiometabolic diseases

OBJECTIVE

Inappropriate transcriptional activation of innate immunity is a pathological feature of several cardiometabolic disorders, but little is known about inflammatory modulation of long intergenic noncoding RNAs (lincRNAs) in disease-relevant human tissues.

APPROACH AND RESULTS

We applied deep RNA sequencing (>500 million filtered reads per sample) to blood and adipose during low-dose experimental endotoxemia (lipopolysaccharide) in a healthy human, with targeted replication in separate individuals undergoing endotoxemia (n=6), to identify inflammatory lincRNAs. A subset of these lincRNAs was examined for expression in adipocytes and monocytes, modulation in adipose of obese humans, and overlap with genome-wide association study signals for inflammatory and cardiometabolic traits. Of a stringent set of 4284 lincRNAs, ≈11% to 22% were expressed with 201 and 56 lincRNAs modulated by lipopolysaccharide in blood or adipose, respectively. Tissue-specific expression of a subset of 6 lipopolysaccharide-lincRNAs was replicated with lipopolysaccharide modulation confirmed for all 3 expressed in blood and 2 of 4 expressed in adipose. The broader generalizability of findings in blood of subject A was confirmed by RNA sequencing in 7 additional subjects. We confirmed adipocytes and monocytes as potential cell-sources of selective lipopolysaccharide-regulated lincRNAs, and 2 of these, linc-DMRT2 (P=0.002) and linc-TP53I13 (P=0.01), were suppressed in adipose of obese humans. Finally, we provide examples of lipopolysaccharide-modulated lincRNAs that overlap single nucleotide polymorphisms that are associated with cardiometabolic traits.

CONCLUSIONS

Our findings provide novel insights into tissue-level, inflammatory transcriptome regulation in cardiometabolic diseases. These are complementary to more usual approaches limited to interrogation of DNA variations.