Downregulation of Lysosomal Acid Ceramidase Mediates HMGB1-Induced Migration and Proliferation of Mouse Coronary Arterial Myocytes

Role of EZH2-mediated epigenetic modification on vascular smooth muscle in cardiovascular diseases: A mini-review

Vascular smooth muscle cells (VSMCs) are integral to the pathophysiology of cardiovascular diseases (CVDs). Enhancer of zeste homolog 2 (EZH2), a histone methyltransferase, plays a crucial role in epigenetic regulation of VSMCs gene expression. Emerging researches suggest that EZH2 has a dual role in VSMCs, contingent on the pathological context of specific CVDs. This mini-review synthesizes the current knowledge on the mechanisms by which EZH2 regulates VSMC proliferation, migration and survival in the context of CVDs. The goal is to underscore the potential of EZH2 as a therapeutic target for CVDs treatment. Modulating EZH2 and its associated epigenetic pathways in VSMCs could potentially ameliorate vascular remodeling, a key factor in the progression of many CVDs. Despite the promising outlook, further investigation is warranted to elucidate the epigenetic mechanisms mediated by EZH2 in VSMCs, which may pave the way for novel epigenetic therapies for conditions such as atherosclerosis and hypertension.

Acid Ceramidase Deficiency: Bridging Gaps between Clinical Presentation, Mouse Models, and Future Therapeutic Interventions

Farber disease (FD) and spinal muscular atrophy with progressive myoclonic epilepsy (SMA-PME) are ultra-rare, autosomal-recessive, acid ceramidase (ACDase) deficiency disorders caused by ASAH1 gene mutations. Currently, 73 different mutations in the ASAH1 gene have been described in humans. These mutations lead to reduced ACDase activity and ceramide (Cer) accumulation in many tissues. Presenting as divergent clinical phenotypes, the symptoms of FD vary depending on central nervous system (CNS) involvement and severity. Classic signs of FD include, but are not limited to, a hoarse voice, distended joints, and lipogranulomas found subcutaneously and in other tissues. Patients with SMA-PME lack the most prominent clinical signs seen in FD. Instead, they demonstrate muscle weakness, tremors, and myoclonic epilepsy. Several ACDase-deficient mouse models have been developed to help elucidate the complex consequences of Cer accumulation. In this review, we compare clinical reports on FD patients and experimental descriptions of ACDase-deficient mouse models. We also discuss clinical presentations, potential therapeutic strategies, and future directions for the study of FD and SMA-PME.

Endothelial Acid Sphingomyelinase Promotes NLRP3 Inflammasome and Neointima Formation During Hypercholesterolemia

The NOD-like receptor pyrin domain 3 (NLRP3) inflammasome is activated during atherogenesis, but how this occurs is unclear. Here, we explored the mechanisms activating and regulating NLRP3 inflammasomes via the acid sphingomyelinase (ASM)-ceramide signaling pathway. As a neointima formation model, partial left carotid ligations were performed on endothelial cell (EC)-specific ASM transgene mice (Smpd1trg/ECcre) and their control littermates (Smpd1trg/WT and WT/WT) fed on the Western diet (WD). We found neointima formation remarkably increased in Smpd1trg/ECcre mice over their control littermates. Next, we observed enhanced colocalization of NLRP3 versus adaptor protein ASC (the adaptor molecule apoptosis-associated speck-like protein containing a CARD) or caspase-1 in the carotid ECs of WD-treated Smpd1trg/ECcre mice but not in their control littermates. In addition, we used membrane raft (MR) marker flotillin-1 and found more aggregation of ASM and ceramide in the intima of Smpd1trg/ECcre mice than their control littermates. Moreover, we demonstrated by in situ dihydroethidium staining, carotid intimal superoxide levels were much higher in WD-treated Smpd1trg/ECcre mice than in their control littermates. Using ECs from Smpd1trg/ECcre and WT/WT mice, we showed ASM overexpression markedly enhanced 7-ketocholesterol (7-Ket)-induced increases in NLRP3 inflammasome formation, accompanied by enhanced caspase-1 activity and elevated interleukin-1β levels. These 7-Ket-induced increases were significantly attenuated by ASM inhibitor amitriptyline. Furthermore, we determined that increased MR clustering with NADPH oxidase subunits to produce superoxide contributes to 7-Ket-induced NLRP3 inflammasome activation via a thioredoxin-interacting protein-mediated controlling mechanism. We conclude that ceramide from ASM plays a critical role in NLRP3 inflammasome activation during hypercholesterolemia via MR redox signaling platforms to produce superoxide, which leads to TXNIP dissociation.

A potential new pathway for heparin treatment of sepsis-induced lung injury: inhibition of pulmonary endothelial cell pyroptosis by blocking hMGB1-LPS-induced caspase-11 activation

Sepsis is a significant cause of mortality in critically ill patients. Acute lung injury (ALI) is a leading cause of death in these patients. Endothelial cells exposed to the bacterial endotoxin lipopolysaccharide (LPS) can progress into pyroptosis, a programmed lysis of cell death triggered by inflammatory caspases. It is characterized by lytic cell death induced by the binding of intracellular LPS to caspases 4/5 in human cells and caspase-11 in mouse cells. In mice,caspase-11-dependent pyroptosis plays an important role in endotoxemia. HMGB1 released into the plasma binds to LPS and is internalized into lysosomes in endothelial cells via the advanced glycation end product receptor. In the acidic lysosomal environment, HMGB1 permeates the phospholipid bilayer, which is followed by the leakage of LPS into the cytoplasm and the activation of caspase-11. Heparin is an anticoagulant widely applied in the treatment of thrombotic disease. Previous studies have found that heparin could block caspase-11-dependent inflammatory reactions, decrease sepsis-related mortality, and reduce ALI, independent of its anticoagulant activity. Heparin or modified heparin with no anticoagulant property could inhibit the alarmin HMGB1-LPS interactions, minimize LPS entry into the cytoplasm, and thus blocking caspase-11 activation. Heparin has been studied in septic ALI, but the regulatory mechanism of pulmonary endothelial cell pyroptosis is still unclear. In this paper, we discuss the potential novel role of heparin in the treatment of septic ALI from the unique mechanism of pulmonary endothelial cell pyroptosis.

Cell Senescence and Central Regulators of Immune Response

Pathways regulating cell senescence and cell cycle underlie many processes associated with ageing and age-related pathologies, and they also mediate cellular responses to exposure to stressors. Meanwhile, there are central mechanisms of the regulation of stress responses that induce/enhance or weaken the response of the whole organism, such as hormones of the hypothalamic-pituitary-adrenal (HPA) axis, sympathetic and parasympathetic systems, thymic hormones, and the pineal hormone melatonin. Although there are many analyses considering relationships between the HPA axis and organism ageing, we found no systematic analyses of relationships between the neuroendocrine regulators of stress and inflammation and intracellular mechanisms controlling cell cycle, senescence, and apoptosis. Here, we provide a review of the effects of neuroendocrine regulators on these mechanisms. Our analysis allowed us to postulate a multilevel system of central regulators involving neurotransmitters, glucocorticoids, melatonin, and the thymic hormones. This system finely regulates the cell cycle and metabolic/catabolic processes depending on the level of systemic stress, stage of stress response, and energy capabilities of the body, shifting the balance between cell cycle progression, cell cycle stopping, senescence, and apoptosis. These processes and levels of regulation should be considered when studying the mechanisms of ageing and the proliferation on the level of the whole organism.

Endothelial contribution to COVID-19: an update on mechanisms and therapeutic implications

The global propagation of SARS-CoV-2 leads to an unprecedented public health emergency. Despite that the lungs are the primary organ targeted by COVID-19, systemic endothelial inflammation and dysfunction is observed particularly in patients with severe COVID-19, manifested by elevated endothelial injury markers, endotheliitis, and coagulopathy. Here, we review the clinical characteristics of COVID-19 associated endothelial dysfunction; and the likely pathological mechanisms underlying the disease including direct cell entry or indirect immune overreactions after SARS-CoV-2 infection. In addition, we discuss potential biomarkers that might indicate the disease severity, particularly related to the abnormal development of thrombosis that is a fatal vascular complication of severe COVID-19. Furthermore, we summarize clinical trials targeting the direct and indirect pathological pathways after SARS-CoV-2 infection to prevent or inhibit the virus induced endothelial disorders.

Therapeutic administration of etoposide coincides with reduced systemic HMGB1 levels in macrophage activation syndrome

BACKGROUND

Macrophage activation syndrome (MAS) is a potentially fatal complication of systemic inflammation. HMGB1 is a nuclear protein released extracellularly during proinflammatory lytic cell death or secreted by activated macrophages, NK cells, and additional cell types during infection or sterile injury. Extracellular HMGB1 orchestrates central events in inflammation as a prototype alarmin. TLR4 and the receptor for advanced glycation end products operate as key HMGB1 receptors to mediate inflammation.

METHODS

Standard ELISA and cytometric bead array-based methods were used to examine the kinetic pattern for systemic release of HMGB1, ferritin, IL-18, IFN-γ, and MCP-1 before and during treatment of four children with critical MAS. Three of the patients with severe underlying systemic rheumatic diseases were treated with biologics including tocilizumab or anakinra when MAS developed. All patients required intensive care therapy due to life-threatening illness. Add-on etoposide therapy was administered due to insufficient clinical response with standard treatment. Etoposide promotes apoptotic rather than proinflammatory lytic cell death, conceivably ameliorating subsequent systemic inflammation.

RESULTS

This therapeutic intervention brought disease control coinciding with a decline of the increased systemic HMGB1, IFN-γ, IL-18, and ferritin levels whereas MCP-1 levels evolved independently.

CONCLUSION

Systemic HMGB1 levels in MAS have not been reported before. Our results suggest that the molecule is not merely a biomarker of inflammation, but most likely also contributes to the pathogenesis of MAS. These observations encourage further studies of HMGB1 antagonists. They also advocate therapeutic etoposide administration in severe MAS and provide a possible biological explanation for its mode of action.

Extracellular HMGB1: a therapeutic target in severe pulmonary inflammation including COVID-19?

BACKGROUND

The 2019 novel coronavirus disease (COVID-19) causes for unresolved reasons acute respiratory distress syndrome in vulnerable individuals. There is a need to identify key pathogenic molecules in COVID-19-associated inflammation attainable to target with existing therapeutic compounds. The endogenous damage-associated molecular pattern (DAMP) molecule HMGB1 initiates inflammation via two separate pathways. Disulfide-HMGB1 triggers TLR4 receptors generating pro-inflammatory cytokine release. Extracellular HMGB1, released from dying cells or secreted by activated innate immunity cells, forms complexes with extracellular DNA, RNA and other DAMP or pathogen-associated molecular (DAMP) molecules released after lytic cell death. These complexes are endocytosed via RAGE, constitutively expressed at high levels in the lungs only, and transported to the endolysosomal system, which is disrupted by HMGB1 at high concentrations. Danger molecules thus get access to cytosolic proinflammatory receptors instigating inflammasome activation. It is conceivable that extracellular SARS-CoV-2 RNA may reach the cellular cytosol via HMGB1-assisted transfer combined with lysosome leakage. Extracellular HMGB1 generally exists in vivo bound to other molecules, including PAMPs and DAMPs. It is plausible that these complexes are specifically removed in the lungs revealed by a 40% reduction of HMGB1 plasma levels in arterial versus venous blood. Abundant pulmonary RAGE expression enables endocytosis of danger molecules to be destroyed in the lysosomes at physiological HMGB1 levels, but causing detrimental inflammasome activation at high levels. Stress induces apoptosis in pulmonary endothelial cells from females but necrosis in cells from males.

CONCLUSION

Based on these observations we propose extracellular HMGB1 to be considered as a therapeutic target for COVID-19.