The pro-inflammatory role of high-mobility group box 1 protein (HMGB-1) in photoreceptors and retinal explants exposed to elevated pressure

AIBP: A New Safeguard against Glaucomatous Neuroinflammation

Glaucoma is a group of ocular diseases that cause irreversible blindness. It is characterized by multifactorial degeneration of the optic nerve axons and retinal ganglion cells (RGCs), resulting in the loss of vision. Major components of glaucoma pathogenesis include glia-driven neuroinflammation and impairment of mitochondrial dynamics and bioenergetics, leading to retinal neurodegeneration. In this review article, we summarize current evidence for the emerging role of apolipoprotein A-I binding protein (AIBP) as an important anti-inflammatory and neuroprotective factor in the retina. Due to its association with toll-like receptor 4 (TLR4), extracellular AIBP selectively removes excess cholesterol from the plasma membrane of inflammatory and activated cells. This results in the reduced expression of TLR4-associated, cholesterol-rich lipid rafts and the inhibition of downstream inflammatory signaling. Intracellular AIBP is localized to mitochondria and modulates mitophagy through the ubiquitination of mitofusins 1 and 2. Importantly, elevated intraocular pressure induces AIBP deficiency in mouse models and in human glaucomatous retina. AIBP deficiency leads to the activation of TLR4 in Müller glia, triggering mitochondrial dysfunction in both RGCs and Müller glia, and compromising visual function in a mouse model. Conversely, restoring AIBP expression in the retina reduces neuroinflammation, prevents RGCs death, and protects visual function. These results provide new insight into the mechanism of AIBP function in the retina and suggest a therapeutic potential for restoring retinal AIBP expression in the treatment of glaucoma.

The Role of High Mobility Group Box 1 (HMGB1) in Neurodegeneration: A Systematic Review

BACKGROUND

High mobility group box 1 (HMGB1) protein is a damage-associated molecular pattern (DAMP) that plays an important role in the repair and regeneration of tissue injury. It also acts as a pro-inflammatory cytokine through the activation of toll-like receptor 4 (TLR4) and receptor for advanced glycation end products (RAGE), to elicit the neuroinflammatory response. HMGB1 may aggravate several cellular responses, which may lead to pathological inflammation and cellular death. Thus, there have been a considerable amount of research into the pathological role of HMGB1 in diseases. However, whether the mechanism of action of HMGB1 is similar in all neurodegenerative disease pathology remains to be determined.

OBJECTIVE

Therefore, this systematic review aimed to critically evaluate and elucidate the role of HMGB1 in the pathology of neurodegeneration based on the available literature.

METHODS

A comprehensive literature search was performed on four databases; EMBASE, PubMed, Scopus, and CINAHL Plus.

RESULTS

A total of 85 articles were selected for critical appraisal, after subjecting to the inclusion and exclusion criteria in this study. The selected articles revealed that HMGB1 levels were found elevated in most neurodegeneration except in Huntington's disease and Spinocerebellar ataxia, where the levels were found decreased. This review also showcased that HMGB1 may act on distinctive pathways to elicit its pathological response leading to the various neurodegeneration processes/ diseases.

CONCLUSION

While there have been promising findings in HMGB1 intervention research, further studies may still be required before any HMGB1 intervention may be recommended as a therapeutic target for neurodegenerative diseases.

Neuroinflammation in retinitis pigmentosa: Therapies targeting the innate immune system

Retinitis pigmentosa (RP) is an important cause of irreversible blindness worldwide and lacks effective treatment strategies. Although mutations are the primary cause of RP, research over the past decades has shown that neuroinflammation is an important cause of RP progression. Due to the abnormal activation of immunity, continuous sterile inflammation results in neuron loss and structural destruction. Therapies targeting inflammation have shown their potential to attenuate photoreceptor degeneration in preclinical models. Regardless of variations in genetic background, inflammatory modulation is emerging as an important role in the treatment of RP. We summarize the evidence for the role of inflammation in RP and mention therapeutic strategies where available, focusing on the modulation of innate immune signals, including TNFα signaling, TLR signaling, NLRP3 inflammasome activation, chemokine signaling and JAK/STAT signaling. In addition, we describe epigenetic regulation, the gut microbiome and herbal agents as prospective treatment strategies for RP in recent advances.

Antibody and Protein Profiles in Glaucoma: Screening of Biomarkers and Identification of Signaling Pathways

Simple Summary

Glaucoma is a chronic eye disease that is one of the leading causes of blindness worldwide. Currently, the only therapeutic option is to lower intraocular pressure. The onset of the disease is often delayed because patients do not notice visual impairment until very late, which is why glaucoma is also known as “the silent thief of sight”. Therefore, early detection and definition of specific markers, the so-called biomarkers, are immensely important. For the methodical implementation, high-throughput methods and omic-based methods came more and more into focus. Thus, interesting targets for possible biomarkers were already suggested by clinical research and basic research, respectively. This review article aims to join the findings of the two disciplines by collecting overlaps as well as differences in various clinical studies and to shed light on promising candidates concerning findings from basic research, facilitating conclusions on possible therapy options.

Abstract

Glaucoma represents a group of chronic neurodegenerative diseases, constituting the second leading cause of blindness worldwide. To date, chronically elevated intraocular pressure has been identified as the main risk factor and the only treatable symptom. However, there is increasing evidence in the recent literature that IOP-independent molecular mechanisms also play an important role in the progression of the disease. In recent years, it has become increasingly clear that glaucoma has an autoimmune component. The main focus nowadays is elucidating glaucoma pathogenesis, finding early diagnostic options and new therapeutic approaches. This review article summarizes the impact of different antibodies and proteins associated with glaucoma that can be detected for example by microarray and mass spectrometric analyzes, which (i) provide information about expression profiles and associated molecular signaling pathways, (ii) can possibly be used as a diagnostic tool in future and, (iii) can identify possible targets for therapeutic approaches.

Expression profiles and potential corneal epithelial wound healing regulation targets of high-mobility group box 1 in diabetic mice

As a damage-associated molecular pattern molecule, high-mobility group box 1 protein (HMGB1) is involved in diabetes and its complications. However, the role of HMGB1 in diabetic keratopathy is not yet understood. The purpose of this study was to investigate the potential roles of HMGB1 in the development of diabetic keratopathy as well as potential strategies to block HMGB1 in order to prompt epithelial wound healing and nerve regeneration in diabetic corneas. The results demonstrated that diabetic keratopathy developed in mice over the duration of the diabetic condition with typical symptoms, including damaged ocular surfaces and corneal nerves. The diabetic corneas had significantly increased protein expression levels of HMGB1 and its receptors-the receptor for advanced glycation end products (RAGE) and toll-like receptor 4 (TLR4)-compared to the age-matched normal corneas (P < 0.05). Corneal HMGB1 levels significantly increased during the corneal wound healing process of the diabetic mice, peaking on the first day after the wound was created and then decreasing to the unwounded level on the seventh day. Exogenous HMGB1 peptide significantly retarded wound and nerve healing, while glycyrrhizin (an HMGB1 inhibitor) significantly prompted wound and nerve healing. Further, the western blot results confirmed that RAGE and TLR4 were also involved in corneal wound and nerve healing. In conclusion, these data showed that HMGB1 and its related receptors are highly involved in the development of diabetic keratopathy. This finding indicates that the blockage of HMGB1 might serve as a strategy to prompt diabetic corneal and nerve wound healing.

Increased Hydrostatic Pressure Promotes Primary M1 Reaction and Secondary M2 Polarization in Macrophages

Patients with chronic anterior uveitis are at particularly high risk of developing secondary glaucoma when corticosteroids [e.g., dexamethasone (Dex)] are used or when inflammatory activity has regressed. Macrophage migration into the eye increases when secondary glaucoma develops and may play an important role in the development of secondary glaucoma. Our aim was to evaluate in vitro if increased hydrostatic pressure and corticosteroids could induce changes in macrophages phenotype. By using a pressure chamber cell culture system, we assessed the effect of increased hydrostatic pressure (HP), inflammation, and immunosuppression (Dex) on the M1/M2 phenotype of macrophages. Bone marrow-derived macrophages (BMDMs) were stimulated with medium, lipopolysaccharide (LPS, 100 ng/ml), Dex (200 ng/ml), or LPS + Dex and incubated with different HP (0, 20, or 60 mmHg) for 2 or 7 days. The numbers of CD86+/CD206- (M1 phenotype), CD86-/CD206+ (M2 phenotype), CD86+/CD206+ (intermediate phenotype), F4/80+/TNF-α+, and F4/80+/IL-10+ macrophages were determined by flow cytometry. TNF-α and IL-10 levels in cell culture supernatants were quantified by ELISA. TNF-α, IL-10, fibronectin, and collagen IV expression in BMDMs were detected by immunofluorescence microscopy. Higher HP polarizes macrophages primarily to an M1 phenotype (LPS, 60 vs. 0 mmHg, d2: p = 0.0034) with less extra cellular matrix (ECM) production and secondary to an M2 phenotype (medium, 60 vs. 0 mmHg, d7: p = 0.0089) (medium, 60 vs. 20 mmHg, d7: p = 0.0433) with enhanced ECM production. Dex induces an M2 phenotype (Dex, medium vs. Dex, d2: p < 0.0001; d7: p < 0.0001) with more ECM production. Higher HP further increased M2 polarization of Dex-treated macrophages (Dex, 60 vs. 0 mmHg, d2: p = 0.0417; d7: p = 0.0454). These changes in the M1/M2 phenotype by high HP or Dex treatment may play a role in the pathogenesis of secondary uveitic glaucoma- or glucocorticoid (GC)-induced glaucoma.

Alterations in Tight- and Adherens-Junction Proteins Related to Glaucoma Mimicked in the Organotypically Cultivated Mouse Retina Under Elevated Pressure

Purpose

To scrutinize alterations in cellular interactions and cell signaling in the glaucomatous retina, mouse retinal explants were exposed to elevated pressure.

Methods

Retinal explants were prepared from C57bl6 mice and cultivated in a pressure chamber under normotensive (atmospheric pressure + 0 mm Hg), moderately elevated (30 mm Hg), and highly elevated (60 mm Hg) pressure conditions. The expression levels of proteins involved in the formation of tight junctions (zonula occludens 1 [ZO-1], occludin, and claudin-5) and adherens junctions (VE-cadherin and β-catenin) and in cell-signaling cascades (Cdc42 and activated Cdc42 kinase 1 [ACK1]), as well as the expression levels of the growth-factor receptors platelet-derived growth factor receptor beta and vascular endothelial growth factor receptors 1 and 2 (VEGFR-1, VEGFR-2) and of diverse intracellular proteins (β-III-tubulin, glial fibrillary acidic protein transcript variant 1, α-smooth muscle actin, vimentin, and von Willebrand factor VIII), were analyzed using immunohistochemistry, western blotting, and quantitative real-time polymerase chain reactions.

Results

The retinal explants were well preserved when cultured in the pressure chambers used in this study. The responses to pressure elevation varied among diverse retinal cells. Under elevated pressure, the expression of ZO-1 increased in the large vessels, neuronal cells began to express VEGFR-1, and the Cdc42 expression in the optic nerve head was downregulated. Overall we found significant transcriptional downregulation of VE-cadherin, β-catenin, VEGFR-1, VEGFR-2, vimentin, Cdc42, and ACK1. Western blotting and immunohistochemistry indicated a loss of VE-cadherin with pressure elevation, whereas the protein levels of ZO-1, occludin, VEGFR-1, and ACK1 increased.

Conclusions

The pressure chamber used for cultivating mouse retinal explants can serve as an in vitro model system for investigating molecular alterations in glaucoma. In this system, responses of the entire retinal cells toward elevated pressure with conspicuous changes in the vasculature and the optic nerve head can be seen. In particular, our investigations indicate that changes in the blood–retina barrier and in cellular signaling are induced by pressure elevation.

Alcohol-dependent pulmonary inflammation: A role for HMGB-1

Previous studies have demonstrated that acute alcohol intoxication significantly impairs lung immune responses, which can lead to the tissue being undefended from microbial infection and resulting disease. Data suggest that acute intoxication presents an axis where simultaneously suppressing early pro-inflammatory cytokines while inducing anti-inflammatory signals contributes to alcohol-dependent immune suppression in the lung, and thus undeterred microbial replication. Interestingly, alcoholics and those with alcohol use disorder present with increased pneumonia and acute respiratory diseases (ARDs), suggesting a more active priming of inflammatory responses in the lungs. There is current research evaluating the acute effects of binge ethanol consumption on adolescents, which is of grave concern, though long-term effects of adolescent ethanol binge exposure are less studied. We hypothesize that adolescent binge drinking may prime the individual to severe pulmonary distress, when later challenged by a microbial pathogen. Herein, we evaluate a model of adolescent intermittent ethanol (AIE) exposure to investigate pulmonary pathology after microbial challenge. Ethanol was administered to adolescent mice using a binge exposure schedule, and mice were then rested to early adulthood. These mice were then challenged with a sub-lethal intranasal inoculation of Klebsiella pneumoniae and evaluated for severity of disease. We find that AIE exposure initially activates inflammatory mediators within the lung, which resolves over time. However, when challenged with a microbial pathogen after this resolution period, these animals present with more severity of inflammation, pulmonary tissue damage, and mortality when challenged with a pulmonary microbial infection. Interestingly, our data suggest a role for alcohol-dependent release of the protein HMGB-1 from host cells, for both morbidity and mortality in our model of microbial-dependent pulmonary inflammation.

miR-34a alleviates spinal cord injury via TLR4 signaling by inhibiting HMGB-1

The aim of the present study was to investigate the effect of microRNA (miR)-34a on spinal cord injury (SCI)-induced inflammation and the possible underlying mechanisms. The results indicated that miR-34a expression was downregulated in a rat model of SCI compared with the control group. Furthermore, miR-34a knockdown was demonstrated to aggravate inflammation, inhibit cell proliferation and enhance apoptosis in an in vitro model of SCI. MiR-34a inhibition was demonstrated to upregulate the expression of inducible nitric oxide synthase and nitric oxide, as well as inducing the expression of toll-like receptor 4 (TLR4) and high mobility group box-1 (HMGB-1) in an in vitro model of SCI. TLR4 inhibitor reduced the effects of miR-34a downregulation on inflammation and cell growth in SCI. Together, these results suggest that miR-34a is able to alleviate SCI via inhibiting HMGB-1 expression in TLR4 signaling.

Porphyromonas Gingivalis Elevated High-Mobility Group Box 1 Levels After Myocardial Infarction in Mice

High mobility group box 1 (HMGB1) is a nuclear protein released from necrotic cells, inducing inflammatory responses. Epidemiological studies suggested a possible association between periodontitis and cardiovascular diseases (CVDs). Due to tissue damage and necrosis of cardiac cells following myocardial infarction (MI), HMGB1 is released, activating an inflammatory reaction. However, it remains unclear whether periodontitis is also involved in myocardial damage. The purpose of this study was to determine the effect of the periodontal pathogen Porphyromonas gingivalis (P.g.) after MI in mice.C57BL/6J wild type mice in post-MI were inoculated with P.g. in the infected group (P.g.-inoculated MI group) and with phosphate buffer saline (PBS) in the control group (PBS-injected MI group). Plasma samples and twelve tissue samples from mice hearts after MI were obtained. We determined the expression of HMGB1 by ELISA and immunohistochemistry.The level of HMGB1 protein in the P.g.-inoculated MI group was significantly higher than in the PBS-injected MI group on day 5, but not on day 14. Immunohistochemistry analysis revealed that HMGB1 was mainly expressed in cardiomyocytes, immune cells, and vascular endothelial cells in the PBS-injected MI group, while HMGB1 was seen broadly in degenerated cardiomyocytes, extracellular fields, immune cells, and vascular endothelial cells in the P.g.-inoculated MI group. A significant increase in the number of HMGB1 positive cells was observed in the P.g.-inoculated MI group compared to the PBS-injected MI group.Infection with P.g. after MI enhanced myocardial HMGB1 expression. There is a possible relationship between periodontitis and post-infarction myocardial inflammation through HMGB-1.