Long-term culture with lipopolysaccharide induces dose-dependent cytostatic and cytotoxic effects in THP-1 monocytes

Sustained exposure to high glucose induces differential expression of cellular senescence markers in murine macrophages but impairs immunosurveillance response to senescent cells secretome

The influence of chronic diseases on various facets of macrophage cellular senescence is poorly understood. This study evaluated the impact of chronic hyperglycemia on the induction of cellular senescence and subsequent immunosurveillance functions in RAW264.7 macrophages. Macrophages were cultured under normal glucose (NG; 5 mM), high glucose (HG; 20 mM), and very high glucose (VHG; 40 mM) conditions and assessed for markers of cellular senescence. Hyperglycemia induced strong upregulation of SA-β-gal activity, and loss of PCNA and Lamin B1 gene expression while markers of cell cycle arrest generally decreased. Non-significant changes in SASP-related proteins were observed while ROS levels slightly decreased and mitochondrial membrane potential increased. Protein concentration on the exosome membrane surface and their stability appeared to increase under hyperglycemic conditions. However, when macrophages were exposed to the secretory media (SM) of senescent preadipocytes, a dramatic increase in the levels of all inflammatory proteins was recorded especially in the VHG group that was also accompanied by upregulation of NF-κB and NLRP3 gene expression. SM treatment to hyperglycemic macrophages activated the TLR-2/Myd88 pathway but decreased the expression of scavenger receptors RAGE, CD36, and Olr-1 while CD44 and CXCL16 expression increased. On exposure to LPS, a strong upregulation in NO, ROS, and inflammatory cytokines was observed. Together, these results suggest that primary markers of cellular senescence are aberrantly expressed under chronic hyperglycemic conditions in macrophages with no significant SASP activation. Nonetheless, hyperglycemia strongly deregulates macrophage functions leading to impaired immunosurveillance of senescent cells and aggravation of inflamm-aging. This work provides novel insights into how hyperglycemia-induced dysfunctions can impact the potency of macrophages to manage senescent cell burden in aging tissues.

Controlled production of lipopolysaccharides increases immune activation in Salmonella treatments of cancer

Immunotherapies have revolutionized cancer treatment. These treatments rely on immune cell activation in tumours, which limits the number of patients that respond. Inflammatory molecules, like lipopolysaccharides (LPS), can activate innate immune cells, which convert tumour microenvironments from cold to hot, and increase therapeutic efficacy. However, systemic delivery of lipopolysaccharides (LPS) can induce cytokine storm. In this work, we developed immune-controlling Salmonella (ICS) that only produce LPS in tumours after colonization and systemic clearance. We tuned the expression of msbB, which controls production of immunogenic LPS, by optimizing its ribosomal binding sites and protein degradation tags. This genetic system induced a controllable inflammatory response and increased dendritic cell cross-presentation in vitro. The strong off state did not induce TNFα production and prevented adverse events when injected into mice. The accumulation of ICS in tumours after intravenous injection focused immune responses specifically to tumours. Tumour-specific expression of msbB increased infiltration of immune cells, activated monocytes and neutrophils, increased tumour levels of IL-6, and activated CD8 T cells in draining lymph nodes. These immune responses reduced tumour growth and increased mouse survival. By increasing the efficacy of bacterial anti-cancer therapy, localized production of LPS could provide increased options to patients with immune-resistant cancers.

Age-related bone diseases: Role of inflammaging

Bone aging is characterized by an imbalance in the physiological and pathological processes of osteogenesis, osteoclastogenesis, adipogenesis, and chondrogenesis, resulting in exacerbated bone loss and the development of age-related bone diseases, including osteoporosis, osteoarthritis, rheumatoid arthritis, and periodontitis. Inflammaging, a novel concept in the field of aging research, pertains to the persistent and gradual escalation of pro-inflammatory reactions during the aging process. This phenomenon is distinguished by its low intensity, systemic nature, absence of symptoms, and potential for management. The mechanisms by which inflammaging contribute to age-related chronic diseases, particularly in the context of age-related bone diseases, remain unclear. The precise manner in which systemic inflammation induces bone aging and consequently contributes to the development of age-related bone diseases has yet to be fully elucidated. This article primarily examines the mechanisms underlying inflammaging and its association with age-related bone diseases, to elucidate the potential mechanisms of inflammaging in age-related bone diseases and offer insights for developing preventive and therapeutic strategies for such conditions.

Protective Role of MAVS Signaling for Murine Lipopolysaccharide-Induced Acute Kidney Injury

Despite treatment advances, acute kidney injury (AKI)-related mortality rates are still high in hospitalized adults, often due to sepsis. Sepsis and AKI could synergistically worsen the outcomes of critically ill patients. TLR4 signaling and mitochondrial antiviral signaling protein (MAVS) signaling are innate immune responses essential in kidney diseases, but their involvement in sepsis-associated AKI (SA-AKI) remains unclear. We studied the role of MAVS in kidney injury related to the TLR4 signaling pathway using a murine LPS-induced AKI model in wild-type and MAVS-knockout mice. We confirmed the importance of M1 macrophage in SA-AKI through in vivo assessment of inflammatory responses. The TLR4 signaling pathway was upregulated in activated bone marrow-derived macrophages, in which MAVS helped maintain the LPS-suppressed TLR4 mRNA level. MAVS regulated redox homeostasis via NADPH oxidase Nox2 and mitochondrial reverse electron transport in macrophages to alleviate the TLR4 signaling response to LPS. Hypoxia-inducible factor 1α (HIF-1α) and AP-1 were key regulators of TLR4 transcription and connected MAVS-dependent reactive oxygen species signaling with the TLR4 pathway. Inhibition of succinate dehydrogenase could partly reduce inflammation in LPS-treated bone marrow-derived macrophages without MAVS. These findings highlight the renoprotective role of MAVS in LPS-induced AKI by regulating reactive oxygen species generation-related genes and maintaining redox balance. Controlling redox homeostasis through MAVS signaling may be a promising therapy for SA-AKI.

The potential use of ascorbic acid to recover the cellular senescence of lipopolysaccharide-induced human apical papilla cells: an in vitro study

OBJECTIVES

To examine the effect of lipopolysaccharide (LPS) on cellular senescence induction of human apical papilla cells (hAPCs) and evaluate the potential use of 50 μg/ml ascorbic acid to recover cellular senescence and regenerative functions.

MATERIALS AND METHODS

hAPCs were treated with LPS at 1 and 10 μg/ml either with or without 50 μg/ml ascorbic acid for 48 h. The cellular senescence biomarkers were analyzed by senescence-associated β-galactosidase (SA-β-gal) staining and senescence-related gene expression, p16 and p21. Cell migration, at 12 h and 24 h, was evaluated using a scratch wound assay. Mineralization potential was assessed at 21 days using Alizarin red S staining and dentine sialophosphoprotein (DSPP) and bone sialoprotein (BSP) gene expression.

RESULTS

1 μg/ml and 10 μg/ml LPS stimulation for 48 h induced cellular senescence, as shown by remarkable SA-β-gal staining and p16 and p21 gene expression. The percentage of wound closure and mineralized formation was reduced. The co-incubation with ascorbic acid significantly down-regulated the level of SA-β-gal staining. The reduction of senescence-associated gene expressions was observed. Ascorbic acid improved cell migration, mineralized nodule formation, and the expression of DSPP and BSP genes in LPS-treated hAPCs.

CONCLUSIONS

LPS significantly promoted cellular senescence on hAPCs and diminished the cell function capacity. Co-presence of ascorbic acid could impede cellular senescence and possibly improve the regenerative capacity of LPS-induced senescent hAPCs in vitro.

CLINICAL RELEVANCE

The data support the in vitro potential benefit of ascorbic acid on cellular senescence recovery of apical papilla cells.

Human amniotic mesenchymal stem cell-conditioned medium inhibited LPS-induced cell injury and inflammation by modulating CD14/TLR4-mediated signaling pathway in monocytes

Human amniotic mesenchymal stem cells (hAMSCs) have attracted considerable attention as a promising regenerative therapy. Many studies reported that the conditioned medium of hAMSCs (AM-CM) exerted anti-inflammatory and immunomodulatory functions, while its underlying mechanism is poorly understood. In this study, we first confirmed that AM-CM (25%, 50%, 100%) was optimal for anti-inflammation at 24 h. Lipopolysaccharide (LPS)-induced alteration of cell morphology, the decrease of cell proliferation, and the upregulation of cell apoptosis were significantly reversed in AM-CM-treated THP-1 cells. 25% and 50% AM-CM significantly decreased LPS-induced intracellular reactive oxygen species (ROS) production and proinflammatory cytokines secretion. Mechanistically, we found that AM-CM treatment suppressed LPS-induced activation of MAPK and NF-κB pathways by inhibiting CD14/TLR4 in THP-1 cells. Meanwhile, activation of NLRP3 inflammasome was also dose-dependently attenuated by AM-CM treatment. Thus, AM-CM may exert positive influences on the inflammation microenvironment and provide a novel strategy for improving tissue regeneration.

Cytotoxicity and genotoxicity of low-dose vanadium dioxide nanoparticles to lung cells following long-term exposure

Vanadium dioxide nanoparticles (VO₂ NPs) have been massively produced and widely applied due to their excellent metal-insulator transition property, making it extremely urgent to evaluate their safety, especially for low-dose long-term respiratory occupational exposure. Here, we report a comprehensive cytotoxicity and genotoxicity study on VO₂ NPs to lung cell lines A549 and BEAS-2B following a long-term exposure. A commercial VO₂ NP, S-VO₂, was used to treat BEAS-2B (0.15-0.6 μg/mL) and A549 (0.3-1.2 μg/mL) cells for four exposure cycles, and each exposure cycle lasted for 4 consecutive days; then various bioassays were performed after each cycle. Significant proliferation inhibition was observed in both cell lines after long-term exposure of S-VO₂ at low doses that did not cause apparent acute cytotoxicity; however, the genotoxicity of S-VO₂, characterized by DNA damage and micronuclei, was only observed in A549 cells. These adverse effects of S-VO₂ were exposure time-, dose- and cell-dependent, and closely related to the solubility of S-VO₂. The oxidative stress in cells, i.e., enhanced reactive oxygen species (ROS) generation and suppressed reduced glutathione, was the main toxicity mechanism of S-VO₂. The ROS-associated mitochondrial damage and DNA damage led to the genotoxicity, and cell proliferation retard, resulting in the cellular viability loss. Our results highlight the importance and urgent necessity of the investigation on the long-term toxicity of VO₂ NPs.

Rutin-protected BisGMA-induced cytotoxicity, genotoxicity, and apoptosis in macrophages through the reduction of the mitochondrial apoptotic pathway and induction of antioxidant enzymes

Bisphenol-A-glycidyldimethacrylate (BisGMA) is a resin monomer frequently used in dentin restorative treatments. The leakage of BisGMA monomer from BisGMA-based polymeric resins can lead to cytotoxicity in macrophages. Rutin has various beneficial bioeffects, including antioxidation and antiinflammation. In this study, we found that pretreatment of RAW264.7 macrophages with rutin-inhibited cytotoxicity induced by BisGMA in a concentration-dependent manner. BisGMA-induced apoptosis, which was detected by levels of phosphatidylserine from the internal to the external membrane and formation of sub-G1, and genotoxicity, which was detected by cytokinesis-blocked micronucleus and single-cell gel electrophoresis assays, were inhibited by rutin in a concentration-dependent manner. Rutin suppressed the BisGMA-induced activation of caspase-3 and -9 rather than caspase-8. Rutin inhibited the activation of the mitochondrial apoptotic pathway, including cytochrome C release and mitochondria disruption, after macrophages were treated with BisGMA. Finally, BisGMA-induced reactive oxygen species (ROS) generation and antioxidant enzyme (AOE) deactivation could be reversed by rutin. Parallel trends were observed in the elevation of AOE activation and inhibition of ROS generation, caspase-3 activity, mitochondrial apoptotic pathway activation, and genotoxicity. These results suggested that rutin suppressed BisGMA-induced cytotoxicity through genotoxicity, the mitochondrial apoptotic pathway, and relatively upstream factors, including reduction of ROS generation and induction of AOE.

Cell Cycle Regulation in Macrophages and Susceptibility to HIV-1

Macrophages are the first line of defence against invading pathogens. They play a crucial role in immunity but also in regeneration and homeostasis. Their remarkable plasticity in their phenotypes and function provides them with the ability to quickly respond to environmental changes and infection. Recent work shows that macrophages undergo cell cycle transition from a G0/terminally differentiated state to a G1 state. This G0-to-G1 transition presents a window of opportunity for HIV-1 infection. Macrophages are an important target for HIV-1 but express high levels of the deoxynucleotide-triphosphate hydrolase SAMHD1, which restricts viral DNA synthesis by decreasing levels of dNTPs. While the G0 state is non-permissive to HIV-1 infection, a G1 state is very permissive to HIV-1 infection. This is because macrophages in a G1 state switch off the antiviral restriction factor SAMHD1 by phosphorylation, thereby allowing productive HIV-1 infection. Here, we explore the macrophage cell cycle and the interplay between its regulation and permissivity to HIV-1 infection.

TLR4-Mediated Pathway Triggers Interferon-Independent G0 Arrest and Antiviral SAMHD1 Activity in Macrophages

Macrophages exist predominantly in two distinct states, G0 and a G1-like state that is accompanied by phosphorylation of SAMHD1 at T592. Here, we demonstrate that Toll-like receptor 4 (TLR4) activation can potently induce G0 arrest and SAMHD1 antiretroviral activity by an interferon (IFN)-independent pathway. This pathway requires TLR4 engagement with TRIF, but not involvement of TBK1 or IRF3. Exclusive Myd88 activators are unable to trigger G0 arrest or SAMHD1 dephosphorylation, demonstrating this arrest is also Myd88/nuclear factor κB (NF-κB) independent. The G0 arrest is accompanied by p21 upregulation and CDK1 depletion, consistent with the observed SAMHD1 dephosphorylation at T592. Furthermore, we show by SAMHD1 knockdown that the TLR4-activated pathway potently blocks HIV-1 infection in macrophages specifically via SAMHD1. Together, these data demonstrate that macrophages can mobilize an intrinsic cell arrest and anti-viral state by activating TLR4 prior to IFN secretion, thereby highlighting the importance of cell-cycle regulation as a response to pathogen-associated danger signals in macrophages.

Towards Age-Related Anti-Inflammatory Therapy: Klotho Suppresses Activation of ER and Golgi Stress Response in Senescent Monocytes

Immunosenescence in monocytes has been shown to be associated with several biochemical and functional changes, including development of senescence-associated secretory phenotype (SASP), which may be inhibited by klotho protein. To date, it was believed that SASP activation is associated with accumulating DNA damage. However, some literature data suggest that endoplasmic reticulum and Golgi stress pathways may be involved in SASP development. Thus, the aim of this study was to investigate the role of klotho protein in the regulation of immunosenescence-associated Golgi apparatus and ER stress response induced by bacterial antigens in monocytes. We provide evidence that initiation of immunosenescent-like phenotype in monocytes is accompanied by activation of CREB34L and TFE3 Golgi stress response and ATF6 and IRE1 endoplasmic reticulum stress response, while klotho overexpression prevents these changes. Further, these changes are followed by upregulated secretion of proinflammatory cytokines, which final modification takes place exclusively in the Golgi apparatus. In conclusion, we provide for the first time evidence of klotho involvement in the crosstalk on the line ER-Golgi, which may, in turn, affect activation of SASP. This data may be useful for a novel potential target for therapy in age-related and chronic inflammatory conditions.

Alcohol dehydrogenase of Candida albicans triggers differentiation of THP-1 cells into macrophages

Candida albicans proteins located on the cell wall and in the cytoplasm have gained great attention because they are not only involved in cellular metabolism and the maintenance of integrity but also interact with host immune systems. Previous research has reported that enolase from C. albicans exhibits high immunogenicity and effectively protects mice against disseminated candidiasis. In this study, alcohol dehydrogenase (ADH) of C. albicans was cloned and purified for the first time, and this study focused on evaluating its effects on the differentiation of the human monocytic cell line THP-1. The morphological features of THP-1 cells exposed to ADH were similar to those of phorbol-12-myristate acetate-differentiated (PMA-differentiated) macrophages. Functionally, ADH enhanced the adhesion, phagocytosis, and killing capacities of THP-1 cells. A flow cytometric assay demonstrated that ADH-induced THP-1 cells significantly increased CD86 and CD11b expression. The production of IL-1β, IL-6, and TNF-α by cells increased in the presence of ADH. As expected, after pretreatment with a MEK inhibitor (U0126), ADH-induced THP-1 cells exhibited unaltered morphological features, eliminated ERK1/2 phosphorylation, prevented CD86/CD11b upregulation and inhibited pro-inflammatory cytokine increase. Collectively, these results suggest that ADH enables THP-1 cells to differentiate into macrophages via the ERK pathway, and it may play an important role in the immune response against fungal invasion.

Paracrine Anti-inflammatory Effects of Adipose Tissue-Derived Mesenchymal Stem Cells in Human Monocytes

The inflammatory process is an essential phenomenon in the induction of immune responses. Monocytes are key effector cells during the inflammatory process. A wide range of evidence indicates that mesenchymal stem cells from adipose tissue (ASC) are endowed with immunomodulatory capacity. However, the interaction between ASC and monocytes in the innate immune response is not well understood. The aim of this work was to investigate the possible paracrine anti-inflammatory effects of ASC in human monocytes. Monocytes were isolated from buffy coats and ASC from fat of non-obese patients. Conditioned medium (CM) from ASC in primary culture was used. We have assessed the effects of CM on the production of inflammatory mediators, degranulation, migration, phagocytic activity, senescence, oxidative stress, mitochondrial membrane potential and macrophage polarization. We have shown that ASC exert paracrine anti-inflammatory actions on human monocytes. CM significantly reduced the production of TNFα, NO and PGE₂ and the activation of NF-κB. In addition, we observed a significant reduction of degranulation, phagocytic activity and their migratory ability in the presence of the chemokine CCL2. The senescence process and the production of oxidative stress and mitochondrial dysfunction were inhibited by CM which also reduced the production of TNFα by M1 macrophages while enhanced TGFβ1 and IL-10 release by M2 macrophages. This study have demonstrated relevant interactions of ASC with human monocytes and macrophages which are key players of the innate immune response. Our results indicate that ASC secretome mediates the anti-inflammatory actions of these cells. This paracrine mechanism would limit the duration and amplitude of the inflammatory response.

[Effect of inflammaging on periodontitis]

Inflammaging is the chronic, systematic, and controllable upregulation of a pro-inflammation state with advancing age. Chronic low-grade inflammation accompanied by sustained stimuli is correlated with various age-related diseases (ARDs). Recent studies on ARDs have prompted further research interest in the inner mechanisms underlying inflammaging to establish prevention and treatment plans for inflammatory diseases. In this article, we discuss inflammaging and its significant role in periodontitis.