LPS Induces mTORC1 and mTORC2 Activation During Monocyte Adhesion

Vaginal epithelial dysfunction is mediated by the microbiome, metabolome, and mTOR signaling

Bacterial vaginosis (BV) is characterized by depletion of Lactobacillus and overgrowth of anaerobic and facultative bacteria, leading to increased mucosal inflammation, epithelial disruption, and poor reproductive health outcomes. However, the molecular mediators contributing to vaginal epithelial dysfunction are poorly understood. Here we utilize proteomic, transcriptomic, and metabolomic analyses to characterize biological features underlying BV in 405 African women and explore functional mechanisms in vitro. We identify five major vaginal microbiome groups: L. crispatus (21%), L. iners (18%), Lactobacillus (9%), Gardnerella (30%), and polymicrobial (22%). Using multi-omics we show that BV-associated epithelial disruption and mucosal inflammation link to the mammalian target of rapamycin (mTOR) pathway and associate with Gardnerella, M. mulieris, and specific metabolites including imidazole propionate. Experiments in vitro confirm that type strain G. vaginalis and M. mulieris supernatants and imidazole propionate directly affect epithelial barrier function and activation of mTOR pathways. These results find that the microbiome-mTOR axis is a central feature of epithelial dysfunction in BV.

Paraoxonase-2 contributes to promoting lipid metabolism and mitochondrial function via autophagy activation

Non-alcoholic fatty liver disease (NAFLD) is an increasingly prevalent immuno-metabolic disease that can progress to hepatic cirrhosis and cancer. NAFLD pathogenesis is extremely complex and is characterized by oxidative stress, impaired mitochondrial function and lipid metabolism, and cellular inflammation. Thus, in-depth research on its underlying mechanisms and subsequent investigation into a potential drug target that has overarching effects on these features will help in the discovery of effective treatments for NAFLD. Our study examines the role of endogenous paraoxonase-2 (PON2), a membrane protein with reported antioxidant activity, in an in vitro cell model of NAFLD. We found that the hepatic loss of PON2 activity aggravated steatosis and oxidative stress under lipotoxic conditions, and our transcriptome analysis revealed that the loss of PON2 disrupts the activation of numerous functional pathways closely related to NAFLD pathogenesis, including mitochondrial respiratory capacity, lipid metabolism, and hepatic fibrosis and inflammation. We found that PON2 promoted the activation of the autophagy pathway, specifically the mitophagy cargo sequestration, which could potentially aid PON2 in alleviating oxidative stress, mitochondrial dysfunction, lipid accumulation, and inflammation. These results provide a mechanistic foundation for the prospect of PON2 as a drug target, leading to the development of novel therapeutics for NAFLD.

Lipopolysaccharides and Cellular Senescence: Involvement in Atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the vascular walls related to aging. Thus far, the roles of cellular senescence and bacterial infection in the pathogenesis of atherosclerosis have been speculated to be independent of each other. Some types of macrophages, vascular endothelial cells, and vascular smooth muscle cells are in a senescent state at the sites of atherosclerotic lesions. Likewise, bacterial infections and accumulations of lipopolysaccharide (LPS), an outer-membrane component of Gram-negative bacteria, have also been observed in the atherosclerotic lesions of patients. This review introduces the integration of these two potential pathways in atherosclerosis. Previous studies have suggested that LPS directly induces cellular senescence in cultured monocytes/macrophages and vascular cells. In addition, LPS enhances the inflammatory properties (senescence-associated secretory phenotype [SASP]) of senescent endothelial cells. Thus, LPS derived from Gram-negative bacteria could exaggerate the pathogenesis of atherosclerosis by inducing and enhancing cellular senescence and the SASP-associated inflammatory properties of specific vascular cells in atherosclerotic lesions. This proposed mechanism can provide novel approaches to preventing and treating this common age-related disease.

Effects of Dexmedetomidine on Immune Cells: A Narrative Review

As we all know, dexmedetomidine (DEX), as a highly selective α₂ adrenergic receptor agonist, exerts sedative, anti-anxiety and hypnotic effects by inhibiting the discharge of norepinephrine neurons in locus coeruleus and GABA-related hypnotic pathways. However, the role of DEX in anti-inflammatory and immune regulation has gradually attracted the attention of researchers in recent years. The α₂ adrenergic receptor is one of the members of the adrenergic receptor family, which is widely present in a variety of immune cells and mediates the biological behavior of the inflammatory immune system. At present, there have been more and more studies on the effects of DEX on immune cells and inflammatory responses, but few studies have systematically explored the anti-inflammatory and immunomodulatory effects of DEX. Here, we comprehensively review the published human and animal studies related to DEX, summarize the effects of DEX on immune cells and its role in related diseases, and propose potential research direction.

Glutamine Regulates Skeletal Muscle Immunometabolism in Type 2 Diabetes

Dysregulation of skeletal muscle metabolism influences whole-body insulin sensitivity and glucose homeostasis. We hypothesized that type 2 diabetes-associated alterations in the plasma metabolome directly contribute to skeletal muscle immunometabolism and the subsequent development of insulin resistance. To this end, we analyzed the plasma and skeletal muscle metabolite profile and identified glutamine as a key amino acid that correlates inversely with BMI and insulin resistance index (HOMA-IR) in men with normal glucose tolerance or type 2 diabetes. Using an in vitro model of human myotubes and an in vivo model of diet-induced obesity and insulin resistance in male mice, we provide evidence that glutamine levels directly influence the inflammatory response of skeletal muscle and regulate the expression of the adaptor protein GRB10, an inhibitor of insulin signaling. Moreover, we demonstrate that a systemic increase in glutamine levels in a mouse model of obesity improves insulin sensitivity and restores glucose homeostasis. We conclude that glutamine supplementation may represent a potential therapeutic strategy to prevent or delay the onset of insulin resistance in obesity by reducing inflammatory markers and promoting skeletal muscle insulin sensitivity.

MAP kinase-dependent autophagy controls phorbol myristate acetate-induced macrophage differentiation of HL-60 leukemia cells

We investigated the mechanisms and the role of autophagy in the differentiation of HL-60 human acute myeloid leukemia cells induced by protein kinase C (PKC) activator phorbol myristate acetate (PMA). PMA-triggered differentiation of HL-60 cells into macrophage-like cells was confirmed by cell-cycle arrest accompanied by elevated expression of macrophage markers CD11b, CD13, CD14, CD45, EGR1, CSF1R, and IL-8. The induction of autophagy was demonstrated by the increase in intracellular acidification, accumulation/punctuation of autophagosome marker LC3-II, and the increase in autophagic flux. PMA also increased nuclear translocation of autophagy transcription factors TFEB, FOXO1, and FOXO3, as well as the expression of several autophagy-related (ATG) genes in HL-60 cells. PMA failed to activate autophagy inducer AMP-activated protein kinase (AMPK) and inhibit autophagy suppressor mechanistic target of rapamycin complex 1 (mTORC1). On the other hand, it readily stimulated the phosphorylation of mitogen-activated protein (MAP) kinases extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) via a protein kinase C-dependent mechanism. Pharmacological or genetic inhibition of ERK or JNK suppressed PMA-triggered nuclear translocation of TFEB and FOXO1/3, ATG expression, dissociation of pro-autophagic beclin-1 from its inhibitor BCL2, autophagy induction, and differentiation of HL-60 cells into macrophage-like cells. Pharmacological or genetic inhibition of autophagy also blocked PMA-induced macrophage differentiation of HL-60 cells. Therefore, MAP kinases ERK and JNK control PMA-induced macrophage differentiation of HL-60 leukemia cells through AMPK/mTORC1-independent, TFEB/FOXO-mediated transcriptional and beclin-1-dependent post-translational activation of autophagy.

Epigenomic and transcriptomic analyses reveal differences between low-grade inflammation and severe exhaustion in LPS-challenged murine monocytes

Emerging studies suggest that monocytes can be trained by bacterial endotoxin to adopt distinct memory states ranging from low-grade inflammation to immune exhaustion. While low-grade inflammation may contribute to the pathogenesis of chronic diseases, exhausted monocytes with pathogenic and immune-suppressive characteristics may underlie the pathogenesis of polymicrobial sepsis including COVID-19. However, detailed processes by which the dynamic adaption of monocytes occur remain poorly understood. Here we exposed murine bone-marrow derived monocytes to chronic lipopolysaccharide (LPS) stimulation at low-dose or high-dose, as well as a PBS control. The cells were profiled for genome-wide H3K27ac modification and gene expression. The gene expression of TRAM-deficient and IRAK-M-deficient monocytes with LPS exposure was also analyzed. We discover that low-grade inflammation preferentially utilizes the TRAM-dependent pathway of TLR4 signaling, and induces the expression of interferon response genes. In contrast, high dose LPS uniquely upregulates exhaustion signatures with metabolic and proliferative pathways. The extensive differences in the epigenomic landscape between low-dose and high-dose conditions suggest the importance of epigenetic regulations in driving differential responses. Our data provide potential targets for future mechanistic or therapeutic studies.

Cooperation of cell adhesion and autophagy in the brain: Functional roles in development and neurodegenerative disease

Cellular adhesive connections directed by the extracellular matrix (ECM) and maintenance of cellular homeostasis by autophagy are seemingly disparate functions that are molecularly intertwined, each regulating the other. This is an emerging field in the brain where the interplay between adhesion and autophagy functions at the intersection of neuroprotection and neurodegeneration. The ECM and adhesion proteins regulate autophagic responses to direct protein clearance and guide regenerative programs that go awry in brain disorders. Concomitantly, autophagic flux acts to regulate adhesion dynamics to mediate neurite outgrowth and synaptic plasticity with functional disruption contributed by neurodegenerative disease. This review highlights the cooperative exchange between cellular adhesion and autophagy in the brain during health and disease. As the mechanistic alliance between adhesion and autophagy has been leveraged therapeutically for metastatic disease, understanding overlapping molecular functions that direct the interplay between adhesion and autophagy might uncover therapeutic strategies to correct or compensate for neurodegeneration.

Modulation of the mTOR pathway plays a central role in dendritic cell functions after Echinococcus granulosus antigen recognition

Immune evasion is a hallmark of persistent echinococcal infection, comprising modulation of innate immune cells and antigen-specific T cell responses. However, recognition of Echinococcus granulosus by dendritic cells (DCs) is a key determinant of the host's response to this parasite. Given that mTOR signaling pathway has been described as a regulator linking metabolism and immune function in DCs, we reported for the first time in these cells, global translation levels, antigen uptake, phenotype, cytokine transcriptional levels, and splenocyte priming activity upon recognition of the hydatid fluid (HF) and the highly glycosylated laminar layer (LL). We found that LL induced a slight up-regulation of CD86 and MHC II in DCs and also stimulated the production of IL-6 and TNF-α. By contrast, HF did not increase the expression of any co-stimulatory molecules, but also down-modulated CD40 and stimulated the expression of the anti-inflammatory cytokine IL-10. Both parasitic antigens promoted protein synthesis through mTOR activation. The use of rapamycin decreased the expression of the cytokines tested, empowered the down-modulation of CD40 and also reduced splenocyte proliferation. Finally, we showed that E. granulosus antigens increase the amounts of LC3-positive structures in DCs which play critical roles in the presentation of these antigens to T cells.

Palmitic acid induces insulin resistance by a mechanism associated with energy metabolism and calcium entry in neuronal cells

Palmitic acid (PA) is a saturated fatty acid whose high consumption has been largely associated with the development of different metabolic alterations, such as insulin resistance, metabolic syndrome, and type 2 diabetes. Particularly in the brain, insulin signaling disruption has been linked to cognitive decline and is considered a risk factor for Alzheimer's disease. Cumulative evidence has demonstrated the participation of PA in the molecular cascade underlying cellular insulin resistance in peripheral tissues, but its role in the development of neuronal insulin resistance and the mechanisms involved are not fully understood. It has generally been accepted that the brain does not utilize fatty acids as a primary energy source, but recent evidence shows that neurons possess the machinery for fatty acid β-oxidation. However, it is still unclear under what conditions neurons use fatty acids as energy substrates and the implications of their oxidative metabolism in modifying insulin-stimulated effects. In the present work, we have found that neurons differentiated from human neuroblastoma MSN exposed to high but nontoxic concentrations of PA generate ATP through mitochondrial metabolism, which is associated with an increase in the cytosolic Ca²⁺ and diminished insulin signaling in neurons. These findings reveal a novel mechanism by which saturated fatty acids produce Ca²⁺ entry and insulin resistance that may play a causal role in increasing neuronal vulnerability associated with metabolic diseases.

Leucine Reconstitutes Phagocytosis-Induced Cell Death in E. coli-Infected Neonatal Monocytes-Effects on Energy Metabolism and mTOR Signaling

MΦ differentiate from circulating monocytes (Mo). The reduced ability of neonatal Mo to undergo apoptosis after E. coli infection (phagocytosis-induced cell death (PICD)) could contribute to sustained inflammatory processes. The objective of our study was to investigate whether immune metabolism in Mo can be modified to gain access to pro-apoptotic signaling. To this end, we supplemented Mo from neonates and from adults with the branched amino acid leucine. In neonatal Mo, we observed increased energy production via oxidative phosphorylation (Oxphos) after E. coli infection via Seahorse assay. Leucine did not change phagocytic properties. In neonatal Mo, we detected temporal activation of the AKT and mTOR pathways, accompanied with subsequent activation of downstream targets S6 Kinase (S6K) and S6. FACS analyses showed that once mTOR activation was terminated, the level of anti-apoptotic BCL-2 family proteins (BCL-2; BCL-X_L) decreased. Release of cytochrome C and cleavage of caspase-3 indicated involvement of the intrinsic apoptotic pathway. Concomitantly, the PICD of neonatal Mo was initiated, as detected by hypodiploid DNA. This process was sensitive to rapamycin and metformin, suggesting a functional link between AKT, mTOR and the control of intrinsic apoptotic signaling. These features were unique to neonatal Mo and could not be observed in adult Mo. Supplementation with leucine therefore could be beneficial to reduce sustained inflammation in septic neonates.

IL-10 Enhances Human Natural Killer Cell Effector Functions via Metabolic Reprogramming Regulated by mTORC1 Signaling

Cell metabolism plays a pivotal role in regulating the effector functions of immune cells. Stimulatory cytokines, such as interleukin (IL)-2 or IL-12 and IL-15, activate glycolysis and oxidative phosphorylation in natural killer (NK) cells to support their enhanced effector functions. IL-10, a pleiotropic cytokine, is known to suppress macrophage activation but stimulate NK cells. However, it remains unclear if IL-10 has an effect on the metabolism of human NK cells and if so, what metabolic mechanisms are affected, and how these metabolic changes are regulated and contribute to the effector functions of NK cells. In this study, we demonstrate that IL-10 upregulates both glycolysis and oxidative phosphorylation in human NK cells, and these metabolic changes are crucial for the enhanced effector functions of NK cells. Mechanistically, we unravel that IL-10 activates the mammalian target of rapamycin complex 1 (mTORC1) to regulate metabolic reprogramming in human NK cells.

Dexmedetomidine Attenuates LPS-Induced Monocyte-Endothelial Adherence via Inhibiting Cx43/PKC-α/NOX2/ROS Signaling Pathway in Monocytes

Dexmedetomidine is widely used for sedating patients in operation rooms or intensive care units. Its protective functions against oxidative stress, inflammation reaction, and apoptosis have been widely reported. In present study, we explored the effects of dexmedetomidine on monocyte-endothelial adherence. We built lipopolysaccharide- (LPS-) induced monocyte-endothelial adherence models with U937 monocytes and human umbilical vein endothelial cells (HUVECs) and observed the effects of dexmedetomidine on U937-HUVEC adhesion. Specific siRNA was designed to knock-down Connexin43 (Cx43) expression in U937 monocytes. Gö6976, GSK2795039, and NAC were used to inhibit PKC-α, NOX2, and ROS, respectively. Then, we detected whether dexmedetomidine could downregulate Cx43 expression and its downstream PKC-α/NOX2/ROS signaling pathway activation and ultimately result in the decrease of U937-HUVEC adhesion. The results showed that dexmedetomidine, at its clinically relevant concentrations (0.1 nM and 1 nM), could inhibit adhesion of molecule expression (VLA-4 and LFA-1) and U937-HUVEC adhesion. Simultaneously, it also attenuated Cx43 expression in U937 monocytes. With the downregulation of Cx43 expression, the activity of PKC-α and its related NOX2/ROS signaling pathway were reduced. Inhibiting PKC-α/NOX2/ROS signaling pathway with Gö6976, GSK2795039, and NAC, respectively, VLA-4, LFA-1 expression, and U937-HUVEC adhesion were all decreased. In summary, we concluded that dexmedetomidine, at its clinically relevant concentrations (0.1 nM and 1 nM), decreased Cx43 expression in U937 monocytes and PKC-α associated with carboxyl-terminal domain of Cx43 protein. With the downregulation of PKC-α, the NOX2/ROS signaling pathway was inhibited, resulting in the decrease of VLA-4 and LFA-1 expression. Ultimately, U937-HUVEC adhesion was reduced.

Pyrogenic and Precipitated Amorphous Silica Nanoparticles Differentially Affect Cell Responses to LPS in Human Macrophages

Previous work has demonstrated that precipitated (NM-200) and pyrogenic (NM-203) Amorphous Silica Nanoparticles (ASNPs) elicit the inflammatory activation of murine macrophages, with more pronounced effects observed with NM-203. Here, we compare the effects of low doses of NM-200 and NM-203 on human macrophage-like THP-1 cells, assessing how the pre-exposure to these nanomaterials affects the cell response to lipopolysaccharide (LPS). Cell viability was affected by NM-203, but not by NM-200, and only in the presence of LPS. While NM-203 stimulated mTORC1, neither ASNPs activated NFκB or the transcription of its target genes PTGS2 and IL1B. NM-200 and NM-203 caused a block of the autophagic flux and inhibited the LPS-dependent increase of Glutamine Synthetase (GS) expression. Both ASNPs suppressed the activation of caspase-1, delaying the LPS-dependent secretion of IL-1β. Thus, ASNPs modulate several important pathways in human macrophages, altering their response to LPS. NM-203 had larger effects on autophagy, mTORC1 activity and GS expression than NM-200, confirming the higher biological activity of pyrogenic ASNPs when compared with precipitated ASNPs.

Crosstalk between Akt and NF-κB pathway mediates inhibitory effect of gas6 on monocytes-endothelial cells interactions stimulated by P. gingivalis-LPS

Correlation between periodontitis and atherosclerosis is well established, and the inherent mechanisms responsible for this relationship remain unclear. The biological function of growth arrest‐specific 6 (gas6) has been discovered in both atherosclerosis and inflammation. Inhibitory effects of gas6 on the expression of inflammatory factors in human umbilical vein endothelial cells (HUVECs) stimulated by Porphyromonas gingivalis lipopolysaccharide (P. gingivalis‐LPS) were reported in our previous research. Herein, the effects of gas6 on monocytes‐endothelial cells interactions in vitro and their probable mechanisms were further investigated. Gas6 protein in HUVECs was knocked down with siRNA or overexpressed with plasmids. Transwell inserts and co‐culturing system were introduced to observe chemotaxis and adhering affinity between monocytes and endothelial cells in vitro. Expression of gas6 was decreased in inflammatory periodontal tissues and HUVECs challenged with P. gingivalis‐LPS. The inhibitory effect of gas6 on chemotaxis and adhesion affinity between monocytes and endothelial cells was observed, and gas6 promoted Akt phosphorylation and inhibited NF‐κB phosphorylation. To our best knowledge, we are first to report that gas6 inhibit monocytes‐endothelial cells interactions in vitro induced by P. gingivalis‐LPS via Akt/NF‐κB pathway. Additionally, inflammation‐mediated inhibition of gas6 expression is through LncRNA GAS6‐AS2, rather than GAS6‐AS1, which is also newly reported.

Actovegin® reduces PMA-induced inflammation on human cells

Purpose

The effect of Actovegin® was investigated on PMA- and LPS-induced human peripheral blood mononuclear cells (PBMCs).

Methods

PBMCs (1 × 10⁶ cells/ml) from five blood donors (2 f, 3 m; 45–55 years) were grown in medium and exposed to Actovegin® in the presence or absence of PMA or LPS. Supernatants were collected to assess the concentration of cytokines (TNF-α, IL-1beta, IL-6 and IL-10). The reactive oxygen species (ROS) were assessed by a ROS-Glo^TM H₂O₂ assay.

Results

Stimulation of cells by PMA or LPS (without Actovegin®) significantly increased the secretion of IL-1beta, IL-6, IL-10 and TNF-α from PBMCs, compared to controls. Pre-treatment of cells with Actovegin® (1, 5, 25, 125 µg/ml) plus PMA significantly decreased the secretion of IL-1beta from PBMCs, compared to controls (PMA without Actovegin®). In contrast, addition of Actovegin® (1, 5, 25, 125 and 250 µg/ml) plus LPS did not alter the IL-1beta production, compared to controls (LPS without Actovegin®). TNF-α, IL-6 and IL-10 do not contribute to the reduction of inflammatory reactions with Actovegin®.

Conclusions

Actovegin® can reduce the PMA-induced IL-1beta release and the ROS production from PBMCs. These findings may help to explain the clinically known positive effects of Actovegin® on athletic injuries with inflammatory responses (e.g., muscle injuries, tendinopathies).

IL-4 Receptor α Chain Protects the Kidney Against Tubule-Interstitial Injury Induced by Albumin Overload

Increasing evidence has highlighted the role of tubule-interstitial injury (TII) as a vital step in the pathogenesis of acute kidney injury (AKI). Incomplete repair of TII during AKI could lead to the development of chronic kidney disease. Changes in albumin endocytosis in proximal tubule epithelial cells (PTECs) is linked to the development of TII. In this context, interleukin (IL)-4 has been shown to be an important factor in modulating recovery of TII. We have studied the possible role of IL-4 in TII induced by albumin overload. A subclinical AKI model characterized by albumin overload in the proximal tubule was used, without changing glomerular function. Four groups were generated: (1) CONT, wild-type mice treated with saline; (2) BSA, wild-type mice treated with 10 g/kg/day bovine serum albumin (BSA); (3) KO, IL4Rα^–/– mice treated with saline; and (4) KO + BSA, IL4Rα^–/– mice treated with BSA. As reported previously, mice in the BSA group developed TII without changes in glomerular function. The following parameters were increased in the KO + BSA group compared with the BSA group: (1) tubular injury score; (2) urinary γ-glutamyltransferase; (3) CD4⁺ T cells, dendritic cells, macrophages, and neutrophils are associated with increases in renal IL-6, IL-17, and transforming growth factor β. A decrease in M2-subtype macrophages associated with a decrease in collagen deposition was observed. Using LLC-PK1 cells, a model of PTECs, we observed that (1) these cells express IL-4 receptor α chain associated with activation of the JAK3/STAT6 pathway; (2) IL-4 alone did not change albumin endocytosis but did reverse the inhibitory effect of higher albumin concentration. This effect was abolished by JAK3 inhibitor. A further increase in urinary protein and creatinine levels was observed in the KO + BSA group compared with the BSA group, but not compared with the CONT group. These observations indicate that IL-4 has a protective role in the development of TII induced by albumin overload that is correlated with modulation of the pro-inflammatory response. We propose that megalin-mediated albumin endocytosis in PTECs could work as a sensor, transducer, and target during the genesis of TII.

Comparison of anti-inflammatory mechanisms between doxofylline and theophylline in human monocytes

BACKGROUND

Methylxanthines are important pharmacological agents in the treatment of asthma and of chronic obstructive pulmonary diseases. The present study was designed to compare the ability of doxofylline and theophylline to modulate inflammatory pathways in human monocytes.

METHODS

Monocytes isolated from healthy anonymous human buffy coats were treated with doxofylline or theophylline in the presence of phorbol 12-myristate 13-acetate (PMA) or lipopolysaccharide (LPS), and their phenotype, the oxidative burst, cytokine expression and release, cAMP production, and protein kinase C (PKC) activity were evaluated.

RESULTS

Doxofylline and theophylline did not have overlapping effects on human monocytes. While sharing some common characteristics, they differed significantly in their selectivity. Theophylline affected LPS- above PMA-induced cellular responsivity, while doxofylline behaved in the opposite manner. Furthermore, when testing PKC activity, we found an inhibitory effect of doxofylline but not of theophylline, at equimolar doses.

CONCLUSIONS

In conclusion, our data support the growing hypothesis that doxofylline does not have a superimposable mechanism of action compared to theophylline, and this may both explain some differences in the risk/benefit ratio and may direct studies to tailor therapy for patients.