Regulation of Acetylation in High Mobility Group Protein B1 Cytosol Translocation

Confrontation with kidney inflammation through a HMGB1-targeted peptide augments anti-fibrosis therapy

Damage to the renal tubular epithelial cells (TEC) is a key cellular event in kidney inflammation and subsequent fibrosis. However, drugs targeting renal TEC (RTEC) are limited to the alleviation of kidney fibrosis. Lethal giant larvae 1 (Lgl1) plays a key role in epithelial cell polarity and proliferation. Here, we report that the renal tubule epithelial-specific deletion of Lgl1 significantly ameliorated intrarenal inflammation and kidney fibrosis. Mechanistically, Lgl1 suppressed the activity of the deacetylase sirtuin 1 (SIRT1) and augmented the acetylation of high-mobility group box 1 (HMGB1) at the lysine 90 (K90) site. Consequently, HMGB1 migrated from the nucleus to the cytoplasm, activating an inflammatory cascade. Our renoprotective strategy was to construct a mimic peptide, TAT-K90WT, that targets HMGB1 K90 acetylation. Administration of this peptide significantly ameliorated inflammation and fibrosis in the kidneys. In summary, the Lgl1-HMGB1 axis plays an important role in renal fibrosis, and targeting HMGB1 acetylation by mimicking peptides is a potential strategy to prevent fibrosis.

Virus and Cell Specific HMGB1 Secretion and Subepithelial Infiltrate Formation in Adenovirus Keratitis

A highly contagious infection caused by human adenovirus species D (HAdV-D), epidemic keratoconjunctivitis (EKC) results in corneal subepithelial infiltration (SEI) by leukocytes, the hallmark of the infection. To date, the pathogenesis of corneal SEI formation in EKC is unresolved. HMGB1 (high-mobility group box 1 protein) is an alarmin expressed in response to infection and a marker of sepsis. Earlier studies using a different adenovirus species, HAdV-C, showed retention of HMGB1 in the infected cell nucleus by adenovirus protein VII, enabling immune evasion. Here, using HAdV-D we show cell-specific HMGB1 secretion by infected cells, and provide an HAdV-D specific mechanism for SEI formation in EKC. HMGB1 was secreted only upon infection of human corneal epithelial cells, not from other cell types, and only upon infection by HAdV-D types associated with EKC. Acetylated HMGB1 translocation from the nucleus to the cytoplasm, then to the extracellular milieu, was tightly controlled by CRM1 and LAMP1, respectively. Primary stromal cells when stimulated by rHMGB1 expressed proinflammatory chemokines. In a novel 3D culture system in tune with the architecture of the cornea, HMGB1 released by infected corneal epithelial cells induced leukocytic infiltrates either directly and/or indirectly via stimulated stromal cells, which together explains SEI formation in EKC.

Quercetin alleviates neonatal hypoxic-ischaemic brain injury by rebalancing microglial M1/M2 polarization through silent information regulator 1/ high mobility group box-1 signalling

Neonatal hypoxic-ischaemic encephalopathy (HIE) remains one of the major causes of neonatal death and long-term neurological disability. Due to its complex pathogenesis, there are still many challenges in its treatment. In our previous studies, we found that quercetin can alleviate neurological dysfunction after hypoxic-ischaemic brain injury (HIBI) in neonatal mice. As demonstrated through in vitro experiments, quercetin can inhibit the activation of the TLR4/MyD88/NF-κB signalling pathway and the inflammatory response in the microglial cell line BV2 after oxygen-glucose deprivation. However, the in-depth mechanism still needs to be further elucidated. In the present study, 7 day-old neonatal ICR mice or BV2 cells were treated with quercetin with or without the SIRT1 inhibitor EX527 via neurobehavioural, histopathological and molecular methods. In vivo experiments have shown that quercetin can significantly improve the performance of HI mice in behavioural tests, such as the Morris water maze, rotarod test and pole climbing test, and reduce HI insult-induced structural brain damage, cell apoptosis and hippocampal neuron loss. Quercetin also inhibited the immunofluorescence intensity of the microglial M1 marker CD16 + 32 and significantly downregulated the expression of the M1-related proteins iNOS, IL-1β and TNF-α. Moreover, quercetin increased the immunofluorescence intensity of the microglial M2 marker CD206 and significantly increased the expression of the M2-related proteins Arg-1 and IL-10. In addition, quercetin limits the nucleocytoplasmic translocation and release of microglial HMGB1 and further suppresses the activation of the downstream TLR4/MyD88/NF-κB signalling pathway. The above effects of quercetin are partially weakened by pretreatment with EX527. Similar results were found in in vitro experiments, and the mechanism further revealed that the rebalancing effect of quercetin on microglial polarization is achieved through the SIRT1-mediated reduction in HMGB1 acetylation levels. This study provides new and complementary insights into the neuroprotective effects of quercetin and a new direction for the treatment of neonatal HIE.

Macrophages-derived high-mobility group box-1 protein induces endothelial progenitor cells pyroptosis

Endothelial dysfunction is an important factor in the progress of sepsis. Endothelial progenitor cells (EPCs) are the precursor cells of endothelial cells and play a crucial role in the prognosis and treatment of sepsis. EPCs in the peripheral blood of patients with sepsis undergo pyroptosis, but the mechanism remains much of unknown. Serum high-mobility group box-1 (HMGB1) is significantly elevated in patients with sepsis, but whether it is related to EPCs pyroptosis is unknown. We used a cell model of sepsis in vitro to isolate EPCs for better observation. By detecting the pyroptosis-related indicators of EPCs and the level of release and acetylation of HMGB1 in inflammatory macrophages, it was found that HMGB1 released by inflammatory macrophages combined with receptor for advanced glycation end products (RAGE) is a key pathway to induce pyroptosis of EPCs.

Long noncoding RNA AK144717 exacerbates pathological cardiac hypertrophy through modulating the cellular distribution of HMGB1 and subsequent DNA damage response

DNA damage induced by oxidative stress during cardiac hypertrophy activates the ataxia telangiectasia mutated (ATM)-mediated DNA damage response (DDR) signaling, in turn aggravating the pathological cardiomyocyte growth. This study aims to identify the functional associations of long noncoding RNA (lncRNAs) with cardiac hypertrophy and DDR. The altered ventricular lncRNAs in the mice between sham and transverse aortic constriction (TAC) group were identified by microarray analysis, and a novel lncRNA AK144717 was found to gradually upregulate during the development of pathological cardiac hypertrophy induced by TAC surgery or angiotensin II (Ang II) stimulation. Silencing AK144717 had a similar anti-hypertrophic effect to that of ATM inhibitor KU55933 and also suppressed the activated ATM-DDR signaling induced by hypertrophic stimuli. The involvement of AK144717 in DDR and cardiac hypertrophy was closely related to its interaction with HMGB1, as silencing HMGB1 abolished the effects of AK144717 knockdown. The binding of AK144717 to HMGB1 prevented the interaction between HMGB1 and SIRT1, contributing to the increased acetylation and then cytosolic translocation of HMGB1. Overall, our study highlights the role of AK144717 in the hypertrophic response by interacting with HMGB1 and regulating DDR, hinting that AK144717 is a promising therapeutic target for pathological cardiac growth.

Upregulations of high mobility group box 1 and TLR4/NF-κB signaling pathway in hippocampus and serum of rats with febrile seizure

PURPOSE

The aim of this study was to explore the alternations regarding the HMGB1 and TLR4/NF-κB signaling pathway in juvenile rats with febrile seizure (FS).

MATERIALS AND METHODS

During the animal modeling of the FS, seizures were triggered every four days by hot water (45 °C), and repeated ten times. After forty days' modeling, rats were divided into different groups according to the degree of seizure (FS (0) - FS (V)). Reverse transcription-polymerase chain reaction (RT-PCR) was used to evaluate the mRNA expressions of the HMGB1, TLR4 and NF-κB in the hippocampus, while Western-blot (WB) and immunofluorescence (IF) were employed to assess protein expressions. The enzyme-linked immunosorbent assay (ELISA) was used for analyzing the protein expressions in peripheral blood.

RESULTS

The mRNA levels of the HMGB1, TLR4 and NF-κB in the hippocampus of both FS (V) and FS (IV) groups were significantly higher than WT, while there was no difference between FS (III) and WT. Concerning protein expressions, increased levels of the HMGB1, TLR4, and NF-κB in FS (V) were observed with a good consistency between the WB and IF, while no significant upregulation was shown in FS (IV). The ELISA results showed that the significance of the augmented proteins between the FS (V) and WT were smaller in the serum than the hippocampus.

CONCLUSIONS

Our study shows seizure degree-related upregulations of HMGB1 and TLR4/NF-κB signaling pathway both in hippocampus and serum of juvenile rats with FS, suggesting the involvement of TLR/NF-κB pathway in inflammation promoted by HMGB1 during FS.

Evaluation of SBDP145, melatonin, sLOX-1, HMGB1 and HIF-1α in preterm infants with brain injury

BACKGROUND

Prematurity-related brain injury is a common and serious complication that has long-term effects on the survival and development of affected infants. Currently, the roles of certain biomarkers such as the protein hydrolysis product SBDP145, melatonin, soluble lectin-like oxidized low-density lipoprotein receptor-1 (sLOX-1), high mobility group box 1 protein (HMGB1), and hypoxia-inducible factor 1-alpha (HIF-1α) in prematurity-related brain injury remain not fully elucidated. Our study aims to assess the significance of SBDP145, melatonin, sLOX-1, HMGB1 and HIF-1α in preterm infants with brain injury.

METHODS

135 preterm infants admitted to our hospital from January 2020 to February 2022 were selected and divided into 78 cases in a prematurity-associated brain injury group, and 57 cases in another group of preterm infants without brain injury or other diseases according to the magnetic resonance imaging results. The levels of SBDP145, melatonin, sLOX-1, HMGB1 and HIF-1α in the two groups were analyzed. The serum concentrations of SBDP145, melatonin, sLOX-1, HMGB1 and HIF-1α in newborns with different severity of ventricular hemorrhage were observed, and the levels of SBDP145, melatonin, sLOX-1, HMGB1 and HIF-1α in those with different severity of white matter brain injury were compared.

RESULTS

The levels of SBDP145, sLOX-1, HMGB1 and HIF-1α were significantly higher in the preterm combined brain injury group than in the preterm group, and melatonin levels were significantly lower than in the preterm group(P < 0.05). The levels of SBDP145, sLOX-1, HMGB1 and HIF-1α were higher in the moderate to severe group and melatonin levels were lower in the mild group of newborns with ventricular hemorrhage (P < 0.05). The levels of SBDP145, sLOX-1, HMGB1 and HIF-1α were higher in the moderate-severe group and melatonin levels were lower in the mild group in newborns with cerebral white matter injury (P < 0.05). The independent variables were SBDP145, melatonin, sLOX-1, HMGB1, HIF-1α, and the dependent variable was the prognosis of neonates with brain injury. Univariate logistic regression analysis and multivariate logistic regression analysis were performed. The results showed that the influencing factors of newborns with brain injury were SBDP145, melatonin, sLOX-1, HMGB1, HIF-1α.

CONCLUSION

The levels of SBDP145, melatonin, sLOX-1, HMGB1 and HIF-1α were highly expressed in preterm newborns with brain injury, and the levels were higher when the condition of the newborns was more severe. These findings suggest the potential clinical utility of these biomarkers in predicting and monitoring brain injury in preterm infants, which could aid in early intervention and improve long-term outcomes.

HMGB1 regulates Th17 cell differentiation and function in patients with psoriasis

BACKGROUND

Psoriasis is an immune-mediated chronic inflammatory skin disease, in which T helper 17 (Th17) cells and its effective cytokine interleukin (IL)-17A play a pivotal pathogenic role. High mobility group box 1 (HMGB1) is an important proinflammatory cytokine, which has been confirmed to be highly expressed in the peripheral circulation and epidermis tissues of psoriasis patients. The regulatory effect of HMGB1 on IL-17A expression and function has been reported in some inflammatory and autoimmune diseases by the HMGB1-Toll-like receptor 4 (TLR4)-interleukin (IL)-23-IL-17A pathway. While, in the pathological environment of psoriasis, whether HMGB1 can exert the regulatory effect on IL-17A is not clear.

OBJECTIVE

We aimed to evaluate the role of HMGB1-TLR4-IL-23-IL-17A pathway in the pathogenesis of psoriasis and explore the possible regulatory mechanism of HMGB1 on Th17 cell differentiation.

METHODS

Serum levels of HMGB1, TLR4, IL-23, and IL-17A were quantified in 50 patients with moderate-to-severe plaque psoriasis and 30 healthy controls. Peripheral blood mononuclear cells  were acquired from 10 severe psoriasis patients and administrated by different concentrations of recombinant-HMGB1 (rHMGB1) to detect the Th17 cell percentage, mRNA and protein levels of TLR4, IL-23, IL-17A and retinoid-related orphan receptor γt (RORγt).

RESULTS

The serum levels of HMGB1, TLR4, IL-23, and IL-17A in psoriasis patients were significantly higher than healthy controls, especially in severe patients, and positively correlated with the severity index. There were also positive correlations between every two detected indicators of HMGB1, TLR4, IL-23, and IL-17A. In vitro study, rHMGB1 can promote the elevated expression of Th17 cell percentage as well as TLR4, IL-23, IL-17A, and RORγt in a dose-dependent manner.

CONCLUSION

HMGB1 can contribute to the pathogenesis of psoriasis by regulating Th17 cell differentiation through HMGB1-TLR4-IL-23-RORγt pathway, then promotes IL-17A production and aggravates inflammation process. Targeting HMGB1 may be a possible potential candidate for the immunotherapy of psoriasis.

Inhibition of cGAS-STING pathway by stress granules after activation of M2 macrophages by human mesenchymal stem cells against drug induced liver injury

OBJECTIVE

Cells can produce stress granules (SGs) to protect itself from damage under stress. The cGAS-STING pathway is one of the important pattern recognition pathways in the natural immune system. This study was investigated whether human mesenchymal stem cells (hMSCs) could protect the liver by inducing M2 macrophages to produce SGs during acute drug induced liver injury (DILI) induced by acetaminophen (APAP).

METHODS

After intragastric administration of APAP in vivo to induce DILI mice model, hMSCs were injected into the tail vein. The co-culture system of hMSCs and M2 macrophages was established in vitro. It was further use SGs inhibitor anisomicin to intervene M2 macrophages. The liver histopathology, liver function, reactive oxygen species (ROS) level, apoptosis pathway, endoplasmic reticulum stress (ERS) level, SGs markers (G3BP1/TIA-1), cGAS-STING pathway, TNF-α, IL-6, IL-1β mRNA levels in liver tissue and M2 macrophages were observed.

RESULTS

In vivo experiments, it showed that hMSCs could alleviate liver injury, inhibite the level of ROS, apoptosis and ERS, protect liver function in DILI mice. The mount of M2 was increased in the liver. hMSCs could also induce the production of SGs, inhibit the cGAS-STING pathway and reduce TNF-α, IL-6, IL-1β mRNA expression. The results in vitro showed that hMSCs could induce the production of SGs in macrophages, inhibit the cGAS-STING pathway, promote the secretion of IL-4 and IL-13, and reduce TNF-α, IL-6, IL-1β mRNA level in cells. In the process of IL-4 inducing M2 macrophage activation, anisomycin could inhibit the production of SGs, activate the cGAS-STING pathway, and promote the inflammatory factor TNF-α, IL-6, IL-1β mRNA expression in cells.

CONCLUSIONS

HMSCs had a protective effect on acute DILI in mice induced by APAP. Its mechanism might involve in activating M2 type macrophages, promoting the production of SGs, inhibiting the cGAS-STING pathway, and reducing the expression of pro-inflammatory factors in macrophages, to reduce hepatocytes damage.

HMGB1 and Toll-like receptors: potential therapeutic targets in autoimmune diseases

HMGB1, a nucleoprotein, is expressed in almost all eukaryotic cells. During cell activation and cell death, HMGB1 can function as an alarm protein (alarmin) or damage-associated molecular pattern (DAMP) and mediate early inflammatory and immune response when it is translocated to the extracellular space. The binding of extracellular HMGB1 to Toll-like receptors (TLRs), such as TLR2 and TLR4 transforms HMGB1 into a pro-inflammatory cytokine, contributing to the occurrence and development of autoimmune diseases. TLRs, which are members of a family of pattern recognition receptors, can bind to endogenous DAMPs and activate the innate immune response. Additionally, TLRs are key signaling molecules mediating the immune response and play a critical role in the host defense against pathogens and the maintenance of immune balance. HMGB1 and TLRs are reported to be upregulated in several autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, type 1 diabetes mellitus, and autoimmune thyroid disease. The expression levels of HMGB1 and some TLRs are upregulated in tissues of patients with autoimmune diseases and animal models of autoimmune diseases. The suppression of HMGB1 and TLRs inhibits the progression of inflammation in animal models. Thus, HMGB1 and TLRs are indispensable biomarkers and important therapeutic targets for autoimmune diseases. This review provides comprehensive strategies for treating or preventing autoimmune diseases discovered in recent years.

The Redox Protein High-Mobility Group Box 1 in Cell Death and Cancer

Significance: As a redox-sensitive protein, high-mobility group box 1 (HMGB1) is implicated in regulating stress responses to oxidative damage and cell death, which are closely related to the pathology of inflammatory diseases, including cancer. Recent Advances: HMGB1 is a nonhistone nuclear protein that acts as a deoxyribonucleic acid chaperone to control chromosomal structure and function. HMGB1 can also be released into the extracellular space and function as a damage-associated molecular pattern protein during cell death, including during apoptosis, necrosis, necroptosis, pyroptosis, ferroptosis, alkaliptosis, and cuproptosis. Once released, HMGB1 binds to membrane receptors to shape immune and metabolic responses. In addition to subcellular localization, the function and activity of HMGB1 also depend on its redox state and protein posttranslational modifications. Abnormal HMGB1 plays a dual role in tumorigenesis and anticancer therapy (e.g., chemotherapy, radiation therapy, and immunotherapy) depending on the tumor types and stages. Critical Issues: A comprehensive understanding of the role of HMGB1 in cellular redox homeostasis is important for deciphering normal cellular functions and pathological manifestations. In this review, we discuss compartmental-defined roles of HMGB1 in regulating cell death and cancer. Understanding these advances may help us develop potential HMGB1-targeting drugs or approaches to treat oxidative stress-related diseases or pathological conditions. Future Directions: Further studies are required to dissect the mechanism by which HMGB1 maintains redox homeostasis under different stress conditions. A multidisciplinary effort is also required to evaluate the potential applications of precisely targeting the HMGB1 pathway in human health and disease. Antioxid. Redox Signal. 39, 569-590.

PARP1 Activation Induces HMGB1 Secretion Promoting Intestinal Inflammation in Mice and Human Intestinal Organoids

Extracellular High-mobility group box 1 (HMGB1) contributes to the pathogenesis of inflammatory disorders, including inflammatory bowel diseases (IBD). Poly (ADP-ribose) polymerase 1 (PARP1) has been recently reported to promote HMGB1 acetylation and its secretion outside cells. In this study, the relationship between HMGB1 and PARP1 in controlling intestinal inflammation was explored. C57BL6/J wild type (WT) and PARP1^-/- mice were treated with DSS to induce acute colitis, or with the DSS and PARP1 inhibitor, PJ34. Human intestinal organoids, which are originated from ulcerative colitis (UC) patients, were exposed to pro-inflammatory cytokines (INFγ + TNFα) to induce intestinal inflammation, or coexposed to cytokines and PJ34. Results show that PARP1^-/- mice develop less severe colitis than WT mice, evidenced by a significant decrease in fecal and serum HMGB1, and, similarly, treating WT mice with PJ34 reduces the secreted HMGB1. The exposure of intestinal organoids to pro-inflammatory cytokines results in PARP1 activation and HMGB1 secretion; nevertheless, the co-exposure to PJ34, significantly reduces the release of HMGB1, improving inflammation and oxidative stress. Finally, HMGB1 release during inflammation is associated with its PARP1-induced PARylation in RAW264.7 cells. These findings offer novel evidence that PARP1 favors HMGB1 secretion in intestinal inflammation and suggest that impairing PARP1 might be a novel approach to manage IBD.

The redox protein HMGB1 in cell death and cancer

SIGNIFICANCE

As a redox-sensitive protein, high-mobility group box 1 (HMGB1) is implicated in regulating stress responses to oxidative damage and cell death, which are closely related to the pathology of inflammatory diseases, including cancer.

RECENT ADVANCES

HMGB1 is a non-histone nuclear protein that acts as a DNA chaperone to control chromosomal structure and function. HMGB1 can also be released into the extracellular space and function as a damage-associated molecular pattern protein during cell death, including during apoptosis, necrosis, necroptosis, pyroptosis, ferroptosis, alkaliptosis, and cuproptosis. Once released, HMGB1 binds to membrane receptors to shape immune and metabolic responses. In addition to subcellular localization, the function and activity of HMGB1 also depends on its redox state and protein posttranslational modifications. Abnormal HMGB1 plays a dual role in tumorigenesis and anticancer therapy (e.g., chemotherapy, radiation therapy, and immunotherapy) depending on tumor types and stages.

CRITICAL ISSUES

A comprehensive understanding of the role of HMGB1 in cellular redox homeostasis is important for deciphering normal cellular functions and pathological manifestations. In this review, we discuss compartmental-defined roles of HMGB1 in regulating cell death and cancer. Understanding these advances may help us develop potential HMGB1-targeting drugs or approaches to treat oxidative stress-related diseases or pathological conditions.

FUTURE DIRECTIONS

Further studies are required to dissect the mechanism by which HMGB1 maintains redox homeostasis under different stress conditions. A multidisciplinary effort is also required to evaluate the potential applications of precisely targeting the HMGB1 pathway in human health and disease.

The regulation and function of acetylated high-mobility group box 1 during implantation and decidualization

Introduction

High-mobility group box 1 (HMGB1) is a non-histone nuclear protein and can be extracellularly secreted to induce sterile inflammation. Although uterine deletion of HMGB1 causes implantation and decidualization defects, how secreted HMGB1 is involved in mouse early pregnancy is still unknown.

Methods

Mouse models, mouse primary endometrial cells and human endometrial cell lines were used in this study. Both immunofluorescence and Western blot were performed to show the localization and relative level of HMGB1 and acetylated HMGB1, respectively. Relative mRNA levels were analyzed by real time RT-PCR.

Results

The secreted HMGB1 was detected in uterine lumen fluid in mouse periimplantation uterus. There is an obvious difference for secreted HMGB1 levels in uterine fluid between day 4 of pregnancy and day 4 of pseudopregnancy, suggesting the involvement of blastocysts during HMGB1 secretion. Trypsin is clearly detected in mouse blastocyst cavity and in the supernatant of cultured blastocysts. Trypsin significantly stimulates HB-EGF production through activating PAR2 and ADAM17. Uterine injection of PAR2 inhibitor into day 4 pregnant mice significantly reduces the number of implantation sites. HB-EGF released from luminal epithelium can induce mouse in vitro decidualization. The conditioned medium collected from trypsin-treated luminal epithelium is able to induce in vitro decidualization, which is suppressed by EGFR inhibitor. Intrauterine injection of glycyrrhizin (HMGB1 inhibitor) can significantly inhibit mouse embryo implantation. We also showed that exogenous HMGB1 released from human epithelial cells are able to induce human in vitro decidualization.

Conclusion

Trypsin can induce decidualization of stromal cells via PAR2-HMGB1-ADAM17-HB-EGF from luminal epithelium.

Inhibition of inflammatory liver injury by the HMGB1-A box through HMGB1/TLR-4/NF-κB signaling in an acute liver failure mouse model

We aimed to investigate the preventive effect of high mobility group box 1 (HMGB1)-A box and the mechanism by which it alleviates inflammatory injury in acute liver failure (ALF) by inhibiting the extracellular release of HMGB1. BALB/c mice were intraperitoneally (i.p.) administered LPS/D-GalN to establish an ALF mouse model. HMGB1-A box was administered (i.p.) 1 h before establishing the ALF mouse model. The levels of extracellularly released HMGB1, TLR-4/NF-κB signaling molecules, the proinflammatory cytokines TNF-α, IL-1β, and IL-6 and COX-2 were measured in the liver tissue and/or serum by Immunohistochemistry, Western blotting and Enzyme-linked immunosorbent assay (ELISA). The levels of extracellularly released HMGB1, TLR-4/NF-κB signaling molecules and proinflammatory cytokines were measured in Huh7 cells as well as LPS- and/or HMGB1-A box treatment by confocal microscopy, Western blotting and ELISA. In the ALF mouse model, the levels of HMGB1 were significantly increased both in the liver and serum, TLR-4/NF-κB signaling molecules and proinflammatory cytokines also was upregulated. Notably, HMGB1-A box could reverse these changes. HMGB1-A box could also cause these changes in LPS-induced Huh7 cells. HMGB1-A box played a protective role by inhibiting inflammatory liver injury via the regulation of HMGB1/TLR-4/NF-κB signaling in the LPS/D-GaIN-induced ALF mouse model, which may be related to inhibiting the extracellular release of HMGB1.

New insights into ischemia-reperfusion injury signaling pathways in organ transplantation

PURPOSE OF REVIEW

Ischemia-reperfusion injury (IRI) leading to allograft rejection in solid organ transplant recipients is a devastating event that compromises graft and patient survival. As our clinical knowledge regarding its definition and presentation has significantly improved over the last years, adequate biomarkers translating to important therapeutic intervention remains a challenge. This review will summarize recent findings in this area.

RECENT FINDINGS

In the past 18 months, our understanding of organ transplantation IRI has improved. IRI involves a positive amplification feedback loop encompassing damaged cells at the graft site, the activity of redox-sensitive damage-associated molecular patterns, and local sequestration of recipient-derived monocytes, lymphocytes and polymorphonuclear leukocytes, like neutrophils, to sustain the immunological cascade and to enhance the destruction of the foreign tissue. Recent studies have identified critical components leading to IRI, including the oxidation state of high mobility group box 1, a classic danger signal, its role in the Toll-like receptor 4-interleukin (IL)-23-IL-17A signaling axis, and the role of neutrophils and CD321, a marker for transmigration of circulating leukocytes into the inflamed tissue. In addition, recent findings imply that the protective functions mediated by autophagy activation counterbalance the detrimental nucleotide-binding domain-like receptor family, pyrin domain containing 3 inflammasome pathway. Finally, clinical studies reveal the posttransplant variables associated with early allograft dysfunction and IRI.

SUMMARY

The future challenge will be understanding how crosstalk at the molecular and cellular levels integrate prospectively to predict which peri-transplant signals are essential for long-term clinical outcomes.

PRRSV Induces HMGB1 Phosphorylation at Threonine-51 Residue to Enhance Its Secretion

Porcine reproductive and respiratory syndrome virus (PRRSV) induces secretion of high mobility group box 1 (HMGB1) to mediate inflammatory response that is involved in the pulmonary injury of infected pigs. Our previous study indicates that protein kinase C-delta (PKC-delta) is essential for HMGB1 secretion in PRRSV-infected cells. However, the underlying mechanism in HMGB1 secretion induced by PRRSV infection is still unclear. Here, we discovered that the phosphorylation level of HMGB1 in threonine residues increased in PRRSV-infected cells. A site-directed mutagenesis study showed that HMGB1 phosphorylation at threonine-51 was associated with HMGB1 secretion induced by PRRSV infection. Co-immunoprecipitation (co-IP) of HMGB1 failed to precipitate PKC-delta, but interestingly, mass spectrometry analysis of the HMGB1 co-IP product showed that PRRSV infection enhanced HMGB1 binding to ribosomal protein S3 (RPS3), which has various extra-ribosomal functions. The silencing of RPS3 by siRNA blocked HMGB1 secretion induced by PRRSV infection. Moreover, the phosphorylation of HMGB1 at threonine-51 was correlated with the interaction between HMGB1 and RPS3. In vivo, PRRSV infection also increased RPS3 levels and nuclear accumulation in pulmonary alveolar macrophages. These results demonstrate that PRRSV may induce HMGB1 phosphorylation at threonine-51 and increase its interaction with RPS3 to enhance HMGB1 secretion. This finding provides insights into the pathogenesis of PRRSV infection.

Chlorogenic acid alleviated liver fibrosis in methionine and choline deficient diet-induced nonalcoholic steatohepatitis in mice and its mechanism

Nonalcoholic steatohepatitis (NASH), one of the most common chronic liver diseases, is a progressive form of nonalcoholic fatty liver disease (NAFLD) accompanied by the development of liver fibrosis. Chlorogenic acid (CGA) is a natural polyphenolic compound. This study aims to observe the CGA-provided alleviation on liver fibrosis in methionine and choline deficient (MCD) diet-induced NASH in mice and to elucidate its engaged mechanism. CGA attenuated hepatocellular injury, decreased the elevated hepatic lipids accumulation and attenuated liver fibrosis by reducing hepatic collagen deposition in mice fed with MCD diet. CGA abrogated the activation of hepatic stellate cells (HSCs) and promoted mitochondrial biogenesis both in vivo and in vitro. Moreover, the CGA-provided inhibition on HSCs activation in vitro was obviously disappeared after the application of peroxisome proliferator-activated receptor gamma, coactivator 1alpha (PGC1α) siRNA. CGA reduced the enhanced hepatic extracellular matrix (ECM) expression and the elevated serum high-mobility group box 1 (HMGB1) content in mice fed with MCD diet. CGA decreased the HMGB1-induced ECM production in both human liver sinusoidal endothelial cells (LSECs) and human umbilical vein endothelial cells (HUVECs). CGA also weakly promoted mitochondrial biogenesis in both LSECs and HUVECs incubated with HMGB1. Hence, CGA ameliorated hepatic fibrosis in mice fed with MCD diet through inhibiting HSCs activation via promoting mitochondrial biogenesis and reducing the HMGB1-initiated ECM production in hepatic vascular endothelial cells.

Inhaled [D-Ala2]-Dynorphin 1-6 Prevents Hyperacetylation and Release of High Mobility Group Box 1 in a Mouse Model of Acute Lung Injury

COVID-19 is a respiratory infection caused by the SARS-CoV-2 virus that can rapidly escalate to life-threatening pneumonia and acute respiratory distress syndrome (ARDS). Recently, extracellular high mobility group box 1 (HMGB1) has been identified as an essential component of cytokine storms that occur with COVID-19; HMGB1 levels correlate significantly with disease severity. Thus, the modulation of HMGB1 release may be vital for treating COVID-19. HMGB1 is a ubiquitous nuclear DNA-binding protein whose biological function depends on posttranslational modifications, its redox state, and its cellular localization. The acetylation of HMGB1 is a prerequisite for its translocation from the nucleus to the cytoplasm and then to the extracellular milieu. When released, HMGB1 acts as a proinflammatory cytokine that binds primarily to toll-like receptor 4 (TLR4) and RAGE, thereby stimulating immune cells, endothelial cells, and airway epithelial cells to produce cytokines, chemokines, and other inflammatory mediators. In this study, we demonstrate that inhaled [D-Ala²]-dynorphin 1-6 (leytragin), a peptide agonist of δ-opioid receptors, significantly inhibits HMGB1 secretion in mice with lipopolysaccharide- (LPS-) induced acute lung injury. The mechanism of action involves preventing HMGB1's hyperacetylation at critical lysine residues within nuclear localization sites, as well as promoting the expression of sirtuin 1 (SIRT1), an enzyme known to deacetylate HMGB1. Leytragin's effects are mediated by opioid receptors, since naloxone, an antagonist of opioid receptors, abrogates the leytragin effect on SIRT1 expression. Overall, our results identify leytragin as a promising therapeutic agent for the treatment of pulmonary inflammation associated with HMGB1 release. In a broader context, we demonstrate that the opioidergic system in the lungs may represent a promising target for the treatment of inflammatory lung diseases.

Mitochondrial proteins in heart failure: The role of deacetylation by SIRT3

Heart failure (HF) is still the leading cause of death worldwide, occurring with a variety of complex mechanisms. However, most intervention for HF do not directly target the pathological mechanisms underlying cell damage in failing cardiomyocytes. Mitochondria are involved in many physiological processes, which is an important guarantee for normal heart function. Mitochondrial dysfunction is considered to be the critical node of the development of HF. Strict modulation of the mitochondrial function can ameliorate the myocardial injury and protect cardiac function. Acetylation plays an important role in mitochondrial protein homeostasis, and SIRT3, the most important deacetylation protein in mitochondria, is involved in the maintenance of mitochondrial function. SIRT3 can delay the progression of HF by improving mitochondrial function. Herein we summarize the interaction between SIRT3 and proteins related to mitochondrial function including oxidative phosphorylation (OXPHOS), fatty acid oxidation (FAO), mitochondrial biosynthesis, mitochondrial quality control. In addition, we also sum up the effects of this interaction on HF and the research progress of treatments targeting SIRT3, so as to find potential HF therapeutic for clinical use in the future.

Glycyrrhizic acid, as an inhibitor of HMGB1, alleviates bleomycin-induced pulmonary toxicity in mice through the MAPK and Smad3 pathways

AIM

High-mobility group box 1 (HMGB1) protein has been noticed particularly for its pivotal role in several pathologies. However, the relevance between HMGB1 and pathological progress in lung toxicity still remains unclear. In the study, we evaluated the effect of glycyrrhizic acid as an HMGB1 inhibitor on the early inflammation and late fibrosis in bleomycin-induced pulmonary toxicity in mice.

METHODS

We established a bleomycin-induced pulmonary toxicity model to detect the relevance between HMGB1 and pathological changes in the early inflammatory and late fibrotic stages.

RESULTS

We found that bleomycin-induced increase in inflammatory cytokines interleukin (IL)-β1, tumor necrosis factor (TNF)-α, monocyte chemotactic protein (MCP)-1, and inflammatory lesions in lung tissue in the early stage of the model. However, markers of fibrosis such as transforming growth factor (TGF)-β1 and α-smooth muscle actin (α-SMA) were significantly elevated on day 7 after bleomycin instillation. Interestingly, HMGB1 also began to rise on day 7, rather than in the early inflammatory phase. However, early (from day 0 to 14 after bleomycin instillation) or late (from day 14 to 28) intervention with HMGB1 neutralizing antibody or glycyrrhizic acid alleviated inflammation and fibrosis through down-regulating the inflammatory signaling mitogen-activated protein kinase (MAPK) and fibrotic signaling Smad3 pathway.

CONCLUSION

Our results suggested that HMGB1 mediates both inflammation and fibrosis in this model. The development of high-potency and low-toxicity HMGB1 inhibitors may be a class of potential drugs for the treatment of pulmonary fibrosis.

HMGB1-TLR4-IL-23-IL-17A axis accelerates renal ischemia-reperfusion injury via the recruitment and migration of neutrophils

Renal ischemia-reperfusion injury (IRI) is an important cause of setting off acute kidney injury. Neutrophil-mediated immunomodulation has a pivotal role in the evolving of IRI. The HMGB1-TLR4-IL-23-IL-17A axis gives rise to neutrophil activation. Therefore, in the study, the role of the HMGB1-TLR4-IL-23-IL-17A axis in IRI was evaluated. Cell viability, inflammation, apoptosis, oxidative stress, survival, renal function and pathology, and the activation of macrophages and neutrophils were measured. Moreover, we evaluated the acetylation, translocation, and secretion of HMGB1 as well as levels of TLR-4, IL-23, IL-17A, and neutrophil chemokines (KC, LIX, and MIP-2). In vivo, anti-HMGB1 antibody decreased the acetylation, translocation, and secretion of HMGB1, reduced the expression of TLR-4, IL-23, IL-17A, KC, LIX, and MIP-2, alleviated the activation of macrophages and neutrophils, improved the survival rate and renal dysfunction, and decreased inflammation, apoptosis, oxidative stress, and pathological injury of the kidney. However, the intervention with recombinant HMGB1(R-HMGB1) significantly abolish the above effect of anti-HMGB1 in IRI. Neutralization IL-23 or IL-17A can alleviated the neutrophils mediated renal dysfunction by suppressing inflammation, apoptosis, and oxidative stress in IRI. In vitro, we confirmed that hypoxic/deoxygenation (H/R) induces the secretion of HMGB1 though acetylation on HK-2 and HMGB1 promotes the secretion of IL-23 in a HMGB1/TLR-4-dependent manner on macrophages. Together, these results implied that the HMGB1-TLR4-IL-23-IL-17A axis regulates inflammation, oxidative stress, apoptosis, and renal injury in IRI by promoting the recruitment and migration of neutrophils.

The Effect and Regulatory Mechanism of High Mobility Group Box-1 Protein on Immune Cells in Inflammatory Diseases

High mobility group box-1 protein (HMGB1), a member of the high mobility group protein superfamily, is an abundant and ubiquitously expressed nuclear protein. Intracellular HMGB1 is released by immune and necrotic cells and secreted HMGB1 activates a range of immune cells, contributing to the excessive release of inflammatory cytokines and promoting processes such as cell migration and adhesion. Moreover, HMGB1 is a typical damage-associated molecular pattern molecule that participates in various inflammatory and immune responses. In these ways, it plays a critical role in the pathophysiology of inflammatory diseases. Herein, we review the effects of HMGB1 on various immune cell types and describe the molecular mechanisms by which it contributes to the development of inflammatory disorders. Finally, we address the therapeutic potential of targeting HMGB1.

Histone Deacetylase 6 Regulates the Activation of M1 Macrophages by the Glycolytic Pathway During Acute Liver Failure

Background

The glycolysis pathway of M1 macrophages is a key factor affecting the inflammatory response. The aim of this article is to investigate the role of histone deacetylase 6 (HDAC6) in the M1 macrophage glycolysis pathway during acute liver failure (ALF).

Methodology

Targeted metabolomics for quantitative analysis of energy metabolites technology was used to detect the characteristics of energy metabolism for 8 ALF patients and 8 normal volunteers. The ALF mice model was intervened with HDAC6 inhibitor ACY-1215. iTRAQ/TMT quantitative proteomics was used to detect protein expression in livers in different mice groups. The liver function, energy metabolites, M1 macrophages, cytokines, and pathological structure, DDX3X, NLRP3 and DNMT1 in liver tissue were detected. The changes of the above molecules were verified in cell groups.

Results

ALF patients and mice have significant energy metabolism disorders, accompanied by activation of M1 macrophages. After the intervention of ACY-1215, the activated M1 macrophages and cytokines levels in the mouse liver were reduced. The levels of IDH1, MDH1, and ATP were significantly increased. The expression of DDX3X increased, while the expression of NLRP3 and DNMT1 decreased. ACY-1215 could reduce the model cell apoptosis level and inflammatory response, and improve energy metabolism. It could also promote the expression of DDX3X, and inhibit the expression of NLRP3 and DNMT1.

Conclusion

ACY-1215 could inhibit the activation of M1 macrophages by improving the glycolytic pathway through regulating DNMT1 and DDX3X/NLRP3 signals to alleviate ALF.

Oleanolic acid exerts neuroprotective effects in subarachnoid hemorrhage rats through SIRT1-mediated HMGB1 deacetylation

Anti-inflammatory therapy for early brain injury after subarachnoid hemorrhage is a promising treatment for improving the prognosis. HMGB1 is the initiator of early inflammation after subarachnoid hemorrhage. Oleanolic acid is a natural pentacyclic triterpenoid compound with strong anti-inflammatory activity. It can relieve early brain injury in subarachnoid hemorrhage rats, but its mechanism is not very clear. Here, we study the potential mechanism of Oleanolic acid in the treatment of subarachnoid hemorrhage. First, we demonstrated that oleanolic acid alleviated early brain injury after subarachnoid hemorrhage, including improvement of grading score, neurological score, brain edema and permeability of brain blood barrier. Then we found that oleanolic acid could inhibit the transfer of HMGB1 from nucleus to cytoplasm and reduce the level of serum HMGB1. Furthermore, we found that oleanolic acid decreased the acetylation level of HMGB1 by increasing SIRT1 expression rather than by inhibiting JAK/STAT3 pathway. SIRT1 inhibitor sirtinol eliminated all beneficial effects of oleanolic acid on subarachnoid hemorrhage, which indicated that oleanolic acid inhibited the acetylation of HMGB1 by up regulating SIRT1. In addition, oleanolic acid treatment also reduced the levels of TLR4 and apoptosis related factors and reduced neuronal apoptosis after subarachnoid hemorrhage. In summary, our findings suggest that oleanolic acid may activate SIRT1 by acting as an activator of SIRT1, thereby reducing the acetylation of HMGB1, thus playing an anti-inflammatory role to alleviate early brain injury after subarachnoid hemorrhage.

Histone deacetylase 2 regulates ULK1 mediated pyroptosis during acute liver failure by the K68 acetylation site

Pyroptosis is a new necrosis pattern of hepatocyte during liver inflammation in acute liver failure (ALF). Histone deacetylase 2 (HDAC2) is associated with several pathological conditions in the liver system. The aim of this study is to investigate whether knockdown or pharmacological inhibition of HDAC2 could reduce the level of pyroptosis in ALF through ULK1-NLRP3-pyroptosis pathway. The role of HDAC2 on ULK1-NLRP3-pyroptosis pathway during ALF was detected in clinical samples. The mechanism was investigated in transfected cells or in ALF mouse model. The RNA-sequencing results revealed that ULK1 was a negative target regulatory molecule by HDAC2. During the process of pyroptosis, the HDAC2 exerted the antagonistic effect with ULK1 by the K68 acetylation site in L02 cells. Then the role of HDAC2 on ULK1-NLRP3-pyroptosis pathway in ALF mouse model was also detected. Moreover, the related molecules to ULK1-NLRP3-pyroptosis pathway were verified different expression in normal health donors and clinical ALF patients. HDAC2 in hepatocytes plays a pivotal role in an ULK1-NLRP3 pathway driven auto-amplification of pyroptosis in ALF. One of the important mechanisms is that inhibition HDAC2 to reduce pyroptosis may be by modulating the K68 lysine site of ULK1.

Sirtuin 1-dependent regulation of high mobility box 1 in hypoxia-reoxygenated brain microvascular endothelial cells: roles in neuronal amyloidogenesis

Hypoxia-reperfusion injury is one of the major risk factors for neurodegeneration. However, it is unclear whether ischaemic damage in brain microvascular endothelial cells plays roles in neurodegeneration, particularly in the amyloidogenic changes contributing to the development of Alzheimer's disease (AD) pathologies. Therefore, we investigated the roles of hypoxia-reoxygenation (H/R)-induced release of high mobility group box protein 1 (HMGB1), a risk molecule for AD pathogenesis in the ischaemic damaged brain, from human brain microvascular endothelial cells (HBMVECs) in neuronal amyloid-beta (Aβ) production. H/R increased nuclear-cytosolic translocation and secretion of HMGB1 in HBMVECs, along with increased permeability and HMGB1-dependent p-c-Jun activation. In addition, H/R increased the expression of Sirtuin 1 (Sirt1), coincident with an increase of intracellular Sirt1-HMGB1 binding in HBMVECs. H/R increased the acetylation of HMGB1 and extracellular secretion, which was significantly inhibited by Sirt1 overexpression. Furthermore, Sirt1 contributed to autophagy-mediated endogenous HMGB1 degradation. More importantly, treatment of neuronal cells with conditioned medium from H/R-stimulated HBMVECs (H/R-CM) activated their amyloidogenic pathways. The neuronal amyloidogenic changes (i.e. increased levels of extracellular Aβ40 and Aβ42) by H/R-CM from HBMVECs were further increased by Sirt1 inhibition, which was significantly suppressed by neutralization of the HMGB1 in H/R-CM. Collectively, our results suggest that HMGB1 derived from H/R-stimulated HBMVECs contributes to amyloidogenic pathways in neurons playing roles in the pathogenesis of AD, which are regulated by endothelial Sirt1.

Characterization of Phosphorylated Proteins Using Mass Spectrometry

Phosphorylation is arguably the most important post-translational modification that occurs within proteins. Phosphorylation is used as a signal to control numerous physiological activities ranging from gene expression to metabolism. Identifying phosphorylation sites within proteins was historically a challenge as it required either radioisotope labeling or the use of phospho-specific antibodies. The advent of mass spectrometry (MS) has had a major impact on the ability to qualitatively and quantitatively characterize phosphorylated proteins. In this article, we describe MS methods for characterizing phosphorylation sites within individual proteins as well as entire proteome samples. The utility of these methods is illustrated in examples that show the information that can be gained using these MS techniques.

The performance of the alarmin HMGB1 in pediatric diseases: From lab to clinic

INTRODUCTION

The ubiquitously expressed nonhistone nuclear protein high-mobility group box protein 1 (HMGB1) has different functions related to posttranslational modifications and cellular localization. In the nucleus, HMGB1 modulates gene transcription, replication and DNA repair as well as determines chromosomal architecture. When the post-transcriptional modified HMGB1 is released into the extracellular space, it triggers several physiological and pathological responses and initiates innate immunity through interacting with its reciprocal receptors (i.e., TLR4/2 and RAGE). The effect of HMGB1-mediated inflammatory activation on different systems has received increasing attention. HMGB1 is now considered to be an alarmin and participates in multiple inflammation-related diseases. In addition, HMGB1 also affects the occurrence and progression of tumors. However, most studies involving HMGB1 have been focused on adults or mature animals. Due to differences in disease characteristics between children and adults, it is necessary to clarify the role of HMGB1 in pediatric diseases.

METHODS AND RESULTS

Through systematic database retrieval, this review aimed to first elaborate the characteristics of HMGB1 under physiological and pathological conditions and then discuss the clinical significance of HMGB1 in the pediatric diseases according to different systems.

CONCLUSIONS

HMGB1 plays an important role in a variety of pediatric diseases and may be used as a diagnostic biomarker and therapeutic target for new strategies for the prevention and treatment of pediatric diseases.

Long Noncoding RNA HNF1A-AS1 Regulates Osteosarcoma Advancement Through Modulating the miR-32-5p/HMGB1 Axis

Background: Osteosarcoma (OS) is a primary malignant tumor in children and adolescents. Long noncoding RNA HNF1A antisense RNA 1 (HNF1A-AS1) is connected with OS development. However, there are few reports on the role and mechanism of HNF1A-AS1 in OS. Materials and Methods: Quantitative real-time polymerase chain reaction (qRT-PCR) was employed to assess the expression of HNF1A-AS1, miR-32-5p, and high-mobility group protein B1 (HMGB1). Western blot analysis was performed to detect the protein level of HMGB1. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), colony formation, transwell, or flow cytometer assays were applied to determine the proliferation, migration, invasion, and apoptosis of OS cells. The interaction between HNF1A-AS1 and miR-32-5p or HMGB1 was predicted by the starBase database and confirmed by dual-luciferase reporter assay. Enzyme-linked immunosorbent assay was employed to analyze levels of HMGB1 in the OS cell supernatant. Results: HNF1A-AS1 and HMGB1 were upregulated, while miR-32-5p was downregulated, in OS tissues and cells. Functionally, HNF1A-AS1 depletion induced apoptosis and impeded proliferation, migration, and invasion of OS cells. Interestingly, HNF1A-AS1 bound to miR-32-5p to regulate the expression of HMGB1. Furthermore, miR-32-5p knockdown overturned the effects of HNF1A-AS1 knockdown on apoptosis, proliferation, migration, and invasion of OS cells. In addition, the effects of HNF1A-AS1 silencing on the malignant behaviors of OS cells were reserved by HMGB1 overexpression. In addition, HNF1A-AS1 regulated the HMGB1 level in the OS cell supernatant through the miR-32-5p/HMGB1 axis. Conclusion: Downregulation of HNF1A-AS1 blocked OS progression through the miR-32-5p/HMGB1 axis, which provides a possible target and prognostic biomarker for treatment of OS.

Role of histone acetylation and DNA methylation in hepatic inflammatory response

In recent years, many studies have confirmed that the interaction between histone acetylation and DNA methylation plays an important role in the process of hepatic inflammatory response. This article systematically introduces the role of histone acetylation and DNA methylation in the liver inflammatory response, as well as the current research status, existing problems, and corresponding solutions, with an aim to help find new potential intervention strategies for the control of hepatic inflammatory response.