High Mobility Group Box-1 Promotes Inflammation-Induced Lymphangiogenesis via Toll-Like Receptor 4-Dependent Signalling Pathway

A specific gene expression program underlies antigen archiving by lymphatic endothelial cells in mammalian lymph nodes

Lymph node (LN) lymphatic endothelial cells (LEC) actively acquire and archive foreign antigens. Here, we address questions of how LECs achieve durable antigen archiving and whether LECs with high levels of antigen express unique transcriptional programs. We used single cell sequencing in dissociated LN tissue and spatial transcriptomics to quantify antigen levels in LEC subsets and dendritic cell populations at multiple time points after immunization and determined that ceiling and floor LECs archive antigen for the longest duration. We identify, using spatial transcriptomics, antigen positive LEC-dendritic cell interactions. Using a prime-boost strategy we find increased antigen levels within LECs after a second immunization demonstrating that LEC antigen acquisition and archiving capacity can be improved over multiple exposures. Using machine learning we defined a unique transcriptional program within archiving LECs that predicted LEC archiving capacity in mouse and human independent data sets. We validated this modeling, showing we could predict lower levels of LEC antigen archiving in chikungunya virus-infected mice and demonstrated in vivo the accuracy of our prediction. Collectively, our findings establish unique properties of LECs and a defining transcriptional program for antigen archiving that can predict antigen archiving capacity in different disease states and organisms.

The Peripheral Lymphatic System Is Impaired by the Loss of Neuronal Control Associated with Chronic Spinal Cord Injury

Spinal cord injury (SCI) is associated with venous vascular dysfunction below the level of injury, resulting in dysregulation of tissue fluid homeostasis in afflicted skin. The purpose of this study was to determine whether loss of neuronal control in chronic SCI also affects the skin lymphatic system. Morphology of lymphatics was characterized by immunohistochemistry and lymphatic gene expression profiles determined by DNA microarray analysis. In SCI, skin lymphatic function appeared to be impaired, because the ratio of functionally dilated versus collapsed lymphatic vessels was decreased 10-fold compared with control. Consequently, the average lumen area of lymphatic vessels was almost halved, possibly due to the known impaired connective tissue integrity of SCI skin. In fact, collagenases were found to be overexpressed in SCI skin, and dermal collagen structure was impaired. Molecular profiling also suggested an SCI-specific phenotype of increased connective tissue turnover and decreased lymphatic contractility. The total number of lymphatic vessels in SCI skin, however, was doubled, pointing to enhanced lymphangiogenesis. In conclusion, these data show, for the first time, that lymphatic function and development in human skin are under neuronal control. Because peripheral venous and lymphatic vascular defects are associated with disturbed fluid homeostasis, inappropriate wound healing reactions, and impaired skin immunity, they might contribute to the predisposition of afflicted individuals to pressure ulcer formation and wound healing disorders.

Extracellular Vesicles Derived From Hypoxia-Conditioned Adipose-Derived Mesenchymal Stem Cells Enhance Lymphangiogenesis

Extracellular vesicles from adipose-derived mesenchymal stem cells (ADSCs) play an important role in lymphangiogenesis; however, the underlying mechanisms are not fully understood. In this study, we aimed to investigate the function of extracellular vesicles secreted by hypoxia-conditioned ADSCs in lymphangiogenesis and explore the potential molecular mechanisms. Extracellular vesicles were extracted from ADSCs cultured under hypoxia or normoxia conditions. The uptake of extracellular vesicles by lymphatic endothelial cells (LECs) was detected by immunofluorescence staining. The effects of extracellular vesicles on the viability, migration, and tube formation of LECs were determined by CCK-8 assay, migration assay, and tube formation assay, respectively. Molecules and pathway involved in lymphangiogenesis mediated by ADSC-derived extracellular vesicles were analyzed by luciferase reporter assay, qRT-polymerase chain reaction (PCR), and Western blot. Hypoxia ADSC-derived extracellular vesicles (H-ADSC/evs) significantly enhanced the proliferation, migration, and tube formation of LECs. Hypoxia decreased the expression of miR-129 in ADSC-derived extracellular vesicles. Overexpression of miR-129 counteracted the promoting effect of H-ADSC/evs on lymphangiogenesis. In addition, decreased exosomal miR-129 expression resulted in upregulation of HMGB1 in LECs, which led to AKT activation and lymphangiogenesis enhancement. Our data reveal that extracellular vesicles derived from hypoxia-conditioned ADSCs induce lymphangiogenesis, and this effect is mediated by miR-129/HMGB1/AKT signaling. Our findings imply that hypoxia ADSC-isolated extracellular vesicles may represent as a valuable target for the treatment of diseases associated with lymphatic remodeling.

High-Mobility Group Box-1 Is Critical in the Pathogenesis of Mouse Experimental Necrotizing Enterocolitis

Although high-mobility group box-1 (HMGB1) is related to the persistent intestinal inflammation in the development of necrotizing enterocolitis (NEC), the role of HMGB1 in the regulation of the intestinal microcirculation in NEC is not well understood. Therefore, we investigated the mechanism(s) by which HMGB1 regulates the generation of the following vasodilatory signals during the development of NEC: endothelial nitric oxide synthase (eNOS) and nitric oxide (NO). Experimental NEC was induced in full-term C57BL/6 mouse pups through the formula gavage and hypoxia technique. The blockade of HMGB1 was achieved with a subcutaneous injection of anti-HMGB1 antibody. Intestinal tissues and blood samples were collected at predetermined time points for the assessment of intestinal microcirculation, lipid peroxidation levels, and evaluation of eNOS activation. We found elevations in HMGB1 expression as early as 12 h after induction of NEC stress, which preceded intestinal injury. Treatment of mouse pups with HMGB1 neutralizing antibody attenuated the intestinal microvascular features and symptoms of NEC, but this improvement was not found in the eNOS knockout mice, suggesting that HMGB1 inhibition increased intestinal microcirculatory perfusion in an eNOS-dependent manner. Moreover, HMGB1 inhibition rescued NO production and eliminated O₂^•- production in experimental NEC mice through eNOS activation. These data indicate that excessive HMGB1 signaling is associated with the pathogenesis of NEC, suggesting that HMGB1 inhibition might be a promising strategy for NEC treatment.

Cellular and molecular mediators of lymphangiogenesis in inflammatory bowel disease

Background

Recent studies reporting the intricate crosstalk between cellular and molecular mediators and the lymphatic endothelium in the development of inflammatory bowel diseases (IBD) suggest altered inflammatory cell drainage and lymphatic vasculature, implicating the lymphatic system as a player in the occurrence, development, and recurrence of intestinal diseases. This article aims to review recent data on the modulatory functions of cellular and molecular components of the IBD microenvironment on the lymphatic system, particularly lymphangiogenesis. It serves as a promising therapeutic target for IBD management and treatment. The interaction with gut microbiota is also explored.

Main text

Evidence shows that cells of the innate and adaptive immune system and certain non-immune cells participate in the complex processes of inflammatory-induced lymphangiogenesis through the secretion of a wide spectrum of molecular factors, which vary greatly among the various cells. Lymphangiogenesis enhances lymphatic fluid drainage, hence reduced infiltration of immunomodulatory cells and associated-inflammatory cytokines. Interestingly, some of the cellular mediators, including mast cells, neutrophils, basophils, monocytes, and lymphatic endothelial cells (LECs), are a source of lymphangiogenic molecules, and a target as they express specific receptors for lymphangiogenic factors.

Conclusion

The effective target of lymphangiogenesis is expected to provide novel therapeutic interventions for intestinal inflammatory conditions, including IBD, through both immune and non-immune cells and based on cellular and molecular mechanisms of lymphangiogenesis that facilitate inflammation resolution.

Diabetes, inflammation, and the adiponectin paradox: Therapeutic targets in SARS-CoV-2

Aging and pre-existing conditions in older patients increase severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) severity and its complications, although the causes remain unclear. Apart from acute pulmonary syndrome, Coronavirus 2019 (COVID-19) can increasingly induce chronic conditions. Importantly, SARS-CoV-2 triggers de novo type 2 diabetes mellitus (T2DM) linked to age-associated cardiovascular disease (CVD), cancers, and neurodegeneration. Mechanistically, SARS-CoV-2 induces inflammation, possibly through damage-associated molecular pattern (DAMP) signaling and ‘cytokine storm,’ causing insulin resistance and the adiponectin (APN) paradox, a phenomenon linking metabolic dysfunction to chronic disease. Accordingly, preventing the APN paradox by suppressing APN-related inflammatory signaling might prove beneficial. A better understanding could uncover novel therapies for SARS-CoV-2 and its chronic disorders.

High-mobility group box 1 protein participates in acute lung injury by activating protein kinase R and inducing M1 polarization

High-mobility group box 1 protein (HMGB1) is a crucial proinflammatory cytokine that contributes to acute lung injury (ALI). Macrophages are known to express the primary receptors (Toll-like receptor [TLR] 2, and TLR4) of HMGB1 for transmitting intracellular signals. Studies have revealed that double-stranded RNA activated protein kinase R (PKR), which is expressed in macrophages, participates in ALI by regulating macrophage polarization and proinflammatory cytokine release, and that PKR is normally activated by a subset of TLRs. The present study investigated whether HMGB1 engages in ALI by activating PKR in macrophages and inducing classically activated macrophage (M1) polarization via TLR2- and TLR4-mediated nuclear factor (NF)-κB signaling pathways. In an vivo mouse model of lipopolysaccharide (LPS)-induced ALI, anti-HMGB1, rHMGB1, LPS-RS (TLR2 and TLR4 antagonist), or C16 (PKR inhibitor) was administered to mice 2 h after LPS challenge or 1 h before LPS challenge. In vitro, bone marrow-derived macrophages from mice primed with LPS were stimulated with or without anti-HMGB1, rHMGB1, LPS-RS, or C16. Our studies revealed that rHMGB1 stimulation induced M1 polarization in ALI, and that anti-HMGB1 and C16 treatments had the opposite effect. Anti-HMGB1 and LPS-RS significantly inhibited LPS-induced PKR expression in macrophages; however, rHMGB1 administration increased PKR expression. These results indicate that HMGB1 participates in the pathogenesis of ALI by activating PKR in macrophages and inducing M1 polarization through TLR2- and TLR4-mediated NF-κB signaling pathways.

Ma Xing Shi Gan Decoction Attenuates PM2.5 Induced Lung Injury via Inhibiting HMGB1/TLR4/NFκB Signal Pathway in Rat

Ma Xing Shi Gan Decoction (MXD), a classical traditional Chinese medicine prescription, is widely used for the treatment of upper respiratory tract infection. However, the effect of MXD against particulate matters with diameter of less than 2.5 μm (PM2.5) induced lung injury remains to be elucidated. In this study, rats were stimulated with PM2.5 to induce lung injury. MXD was given orally once daily for five days. Lung tissues were harvested to assess pathological changes and edema. Myeloperoxidase (MPO) activity and malonaldehyde (MDA) content in lung were determined to evaluate the degree of injury. To assess the barrier disruption, the bronchoalveolar lavage fluid (BALF) was collected to determine the total protein content and count the number of neutrophils and macrophages. For evaluating the activation of macrophage in lung tissue, CD68 was detected using immunohistochemistry (IHC). The levels of inflammatory factors including tumor necrosis factor-alpha (TNF-α), interleukin-1beta (IL-1β), and interleukin-6 (IL-6) in BALF and serum were measured. In vitro, a PM2.5-activated RAW 264.7 macrophages inflammatory model was introduced. To evaluate the protective effect of MXD-medicated serum, the cell viability and the release of inflammatory factors were measured. The effects of MXD on the High mobility group box-1/Toll-like receptor 4/Nuclear factor-kappa B (HMGB1/TLR4/NFκB) pathway in lung tissue and RAW 264.7 cells were assessed by Western blot. For further confirming the protective effect of MXD was mediated by inhibiting the HMGB1/TLR4/NFκB pathway, RAW 264.7 cells were incubated with MXD-medicated serum alone or MXD-medicated serum plus recombinant HMGB1 (rHMGB1). MXD significantly ameliorated the lung injury in rats, as evidenced by decreases in the pathological score, lung edema, MPO activity, MDA content, CD68 positive macrophages number, disruption of alveolar capillary barrier and the levels of inflammatory factors. In vitro, MXD-medicated serum increased cell viability and inhibited the release of inflammatory cytokines. Furthermore, MXD treatment was found to inhibit HMGB1/TLR4/NFκB signal pathway both in vivo and in vitro. Moreover, the protection of MXD could be reversed by rHMGB1 in RAW 264.7. Taken together, these results suggest MXD protects rats from PM2.5 induced acute lung injury, possibly through the modulation of HMGB1/TLR4/NFκB pathway and inflammatory responses.

HMGB1 participates in LPS‑induced acute lung injury by activating the AIM2 inflammasome in macrophages and inducing polarization of M1 macrophages via TLR2, TLR4, and RAGE/NF‑κB signaling pathways

High mobility group box 1 (HMGB1), a crucial proinflammatory cytokine, was reported to activate the absent in melanoma 2 (AIM2) inflammasome, which are both essential in acute lung injury (ALI). However, their interaction mechanism has remained elusive. Macrophages are known to express the AIM2 inflammasome and the main receptors [receptor for advanced glycation end products (RAGE), Toll‑like receptor 2/4 (TLR‑2/TLR‑4)] of HMGB1 to transmit intracellular signals. The present study aimed to indicate whether HMGB1 participates in the process of lipopolysaccharides (LPS)‑induced ALI through activating the AIM2 inflammasome in macrophages, as well as inducing polarization of M1 macrophages via TLR2, TLR4 and RAGE/ nuclear factor‑κB (NF‑κB) signaling pathways. In an in vivo mouse model of LPS‑induced ALI, anti‑HMGB1, recombinant (r)HMGB1, LPS from Rhodobacter sphaeroides (LPS‑RS, TLR2/4 antagonist) or FPS‑ZM1 (RAGE antagonist) were administrated. In in vitro studies, bone marrow‑derived macrophages from mice primed with LPS were stimulated with or without anti‑HMGB1, rHMGB1, LPS‑RS, or FPS‑ZM1. The findings revealed that anti‑HMGB1, LPS‑RS and FPS‑ZM1 significantly decreased infiltration of inflammatory cells, wet‑to‑dry ratio, myeloperoxidase activity in the lung, the levels of cytokines, as well as macrophages and neutrophil infiltration in the bronchoalveolar lavage fluid. However, rHMGB1 aggravated the inflammatory response in ALI. Mechanistically, anti‑HMGB1, LPS‑RS and FPS‑ZM1 attenuated activation of TLR2, TLR4, and RAGE/NF‑κB signaling pathways and expression of the AIM2 inflammasome in macrophages. However, rHMGB1 enhanced their expression levels and induced polarization of M1 macrophages. These results indicated that HMGB1 could participate in the pathogenesis of ALI by activating the AIM2 inflammasome in macrophages, as well as inducing polarization of M1 macrophages through TLR2, TLR4 and RAGE/NF‑κB signaling pathways.

HMGB1 Antagonist, Box A, Reduces TLR4, RAGE, and Inflammatory Cytokines in the Cornea of P. aeruginosa-Infected Mice

PURPOSE

High mobility group box 1 (HMGB1) contributes to adverse disease outcome in Pseudomonas aeruginosa keratitis. This study tests Box A, an HMGB1 antagonist, in a model of the disease.

METHODS

C57BL/6 mice (B6) were injected subconjunctivally (1 day before infection) with Box A or phosphate-buffered saline (PBS), infected with P. aeruginosa strain ATCC 19660, and injected intraperitoneally with Box A or PBS at 1 and 3 days postinfection (p.i.). Clinical scores, photographs with a slit lamp camera, real-time polymerase chain reaction (RT-PCR), western blot, immunohistochemistry, enzyme-linked immunosorbent assay (ELISA), myeloperoxidase (MPO), and bacterial plate count were used to assess disease outcome. In separate experiments, the therapeutic potential of Box A was tested as described above, but with treatment begun at 6 h p.i.

RESULTS

Box A versus PBS prophylactic treatment significantly reduced clinical scores, MPO activity, bacterial load, and expression of TLR4, RAGE, IL-1β, CXCL2, and TNF-α in the infected cornea. Box A blocked co-localization of HMGB1/TLR4 in infiltrated cells in the stroma at 3 and 5 days p.i., but only at 5 days p.i. for HMGB1/RAGE. Box A versus PBS therapeutic treatment significantly reduced clinical scores, MPO activity, bacterial load, and protein levels of IL-1β, CXCL2, and IL-6 in the infected cornea.

CONCLUSION

Overall, Box A lessens the severity of Pseudomonas keratitis in mice by decreasing expression of TLR4, RAGE (their interaction with HMGB1), IL-1β, CXCL2 (decreasing neutrophil infiltrate), and bacterial plate count when given prophylactically. Therapeutic treatment was not as effective at reducing opacity (disease), but shared similar features with pretreatment of the mice.

Interleukin-33 promotes inflammation-induced lymphangiogenesis via ST2/TRAF6-mediated Akt/eNOS/NO signalling pathway

The interplay between inflammation and lymphangiogenesis is mediated by various cytokines. However, most of these molecules and their associated mechanism are yet to be defined. Here, we explored the role of IL-33 in modulating inflammation-induced lymphangiogenesis (ILA) and its underlying mechanisms using an ILA mouse model and a lymphatic endothelial cell (LEC) line. Our results show that IL-33 promoted the proliferation, migration and tube formation of LECs and ILA in vivo. The pro-lymphangiogenic activity of IL-33 was abolished by ST2 blockage. In mechanisms, IL-33 induced the phosphorylation of Akt/eNOS to produce NO in LECs. The IL-33-induced Akt/eNOS activation was suppressed by the PI3K-specific-inhibitor wortmannin, and NO-production was inhibited by both wortmannin and the NO synthase-inhibitor NMA. Knock-down of ST2 or TRAF6 suppressed Akt/eNOS phosphorylation and NO production. The reduction of NO treated with wortmannin or NMA abolished the promoting effects of IL-33 on the chemotactic motility and tube formation of HDLECs. In vivo, IL-33-induced ILA was also impaired in eNOS^−/− mice. In conclusion, our study is the first to show that IL-33 promotes inflammation-induced lymphangiogenesis via a ST2/TRAF6-mediated Akt/eNOS/NO signalling pathway. This findings may provide us more opportunities to treat inflammation and lymphangiogenesis associated diseases.

Lymphatic endothelial progenitors originate from plastic myeloid cells activated by toll-like receptor-4

BACKGROUND

Myeloid-derived lymphatic endothelial cells (M-LECP) are induced by inflammation and play an important role in adult lymphangiogenesis. However, the mechanisms driving M-LECP differentiation are currently unclear. We previously showed that activation of Toll-like receptor-4 (TLR4) induces myeloid-lymphatic transition (MLT) of immortalized mouse myeloid cells. Here the goals were to assess the potential of different TLR4 ligands to induce pro-lymphatic reprogramming in human and mouse primary myeloid cells and to identify transcriptional changes regulating this process.

METHODOLOGY/PRINCIPAL FINDINGS

Human and mouse myeloid cells were reprogrammed to the lymphatic phenotype by TLR4 ligands including lipopolysaccharide (LPS), recombinant high mobility group box 1 protein (HMGB1), and paclitaxel. TLR4 induced similar MLT in cells from mice of different strains and immune status. Commonly induced genes were detected by transcriptional profiling in human and mouse myeloid cells from either immunocompetent or immunodeficient mice. Shared trends included: (1) novel expression of lymphatic-specific markers vascular endothelial growth factor receptor-3 (VEGFR-3), lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1) and podoplanin (PDPN) largely absent prior to induction; (2) lack of notable changes in blood vessel-specific markers; (3) transient expression of VEGFR-3, but sustained increase of vascular endothelial growth factor-C (VEGF-C) and a variety of inflammatory cytokines; (4) dependency of VEGFR-3 upregulation and other LEC genes on NF-κB; and (5) novel expression of lymphatic-specific (e.g., PROX1) and stem/progenitor (e.g., E2F1) transcription factors known for their roles in adult and embryonic vascular formation. M-LECP generated by TLR4 ligands in vitro were functional in vivo as demonstrated by significantly increased lymphatic vessel density and lymphatic metastasis detected in orthotopic breast cancer models.

CONCLUSIONS/SIGNIFICANCE

We established a novel TLR4-dependent protocol for in vitro production of functionally competent M-LECP from primary human or mouse myeloid cells and identified many potential regulators of this process. This information can be further exploited for research and therapeutic purposes.

High Mobility Group Box-1: A Missing Link between Diabetes and Its Complications

High mobility group box-1 (HMGB-1), a damage-associated molecular pattern, can be actively or passively released from various cells under different conditions and plays a pivotal role in the pathogenesis of inflammation and angiogenesis-dependent diseases. More and more evidence suggests that inflammation, in addition to its role in progression of diabetes, also promotes initiation and development of diabetic complications. In this review, we focus on the role of HMGB-1 in diabetes-related complications and the therapeutic strategies targeting HMGB-1 in diabetic complications.