Role of released mitochondrial DNA in acute lung injury

Bongkrekic acid alleviates airway inflammation via breaking the mPTP/mtDAMPs/RAGE feedback loop in a steroid-insensitive asthma model

Mitochondrial dysfunction is critical in the pathogenesis of asthma. Mitochondrial permeability transition pore (mPTP) regulates the release of mitochondrial damage-associated molecular patterns (mtDAMPs) to maintain mitochondrial homeostasis. Bongkrekic acid (BKA) is a highly selective inhibitor of mPTP opening, participates the progression of various diseases. This research investigated the exact roles of BKA and mPTP in the pathogenesis of asthma and elucidated its underlying mechanisms. In the present study, cytochrome c, one of the mtDAMPs, levels were elevated in asthmatic patients, and associated to airway inflammation and airway obstruction. BKA, the inhibitor of mPTP markedly reversed TDI-induced airway hyperresponsiveness, airway inflammation, and mitochondrial dysfunction. Pretreatment with mitochondrial precipitation, to simulate the release of mtDAMPs, further increased TDI-induced airway inflammation and the expression of RAGE in mice. Administration of the inhibitor of RAGE, FPS-ZM1, alleviated the airway inflammation, the abnormal open of mPTP and mitochondrial dysfunction induced by mtDAMPs and TDI. Furthermore, stimulation with different mtDAMPs activated RAGE signaling in human bronchial epithelial cells. Accordingly, our study indicated that mPTP was important and BKA was efficient in alleviating inflammation in TDI-induced asthma. A positive feedback loop involving mPTP, mtDAMPs and RAGE was present in TDI-induced asthma, indicating that mPTP might serve as a potential therapeutic target for asthma.

Mitochondrial function in lungs of rats with different susceptibilities to hyperoxia-induced acute lung injury

Adult rats exposed to hyperoxia (>95% O2) die from respiratory failure in 60-72 h. However, rats preconditioned with >95% O2 for 48 h followed by 24 h in room air acquire tolerance of hyperoxia (H-T), whereas rats preconditioned with 60% O2 for 7 days become more susceptible (H-S). Our objective was to evaluate lung tissue mitochondrial bioenergetics in H-T and H-S rats. Bioenergetics was assessed in mitochondria isolated from lung tissue of H-T, H-S, and control rats. Expressions of complexes involved in oxidative phosphorylation (OxPhos) were measured in lung tissue homogenate. Pulmonary endothelial filtration coefficient (Kf) and tissue mitochondrial membrane potential (Δψm) were evaluated in isolated perfused lungs (IPLs). Results show that ADP-induced state 3 OxPhos capacity (Vmax) decreased in H-S mitochondria but increased in H-T. Δψm repolarization time following ADP-stimulated depolarization increased in H-S mitochondria. Complex I expression decreased in H-T (38%) and H-S (43%) lung homogenate, whereas complex V expression increased (70%) in H-T lung homogenate. Δψm is unchanged in H-S and H-T lungs, but complex II has a larger contribution to Δψm in H-S than H-T lungs. Kf increased in H-S, but not in H-T lungs. For H-T, increased complex V expression and Vmax counter the effect of the decrease in complex I expression on Δψm. A larger complex II contribution to Δψm along with decreased Vmax and increased Kf could make H-S rats more hyperoxia susceptible. Results are clinically relevant since ventilation with ≥60% O2 is often required for extended periods in patients with acute respiratory distress syndrome (ARDS).NEW & NOTEWORTHY We assessed lung tissue mitochondrial bioenergetics in rats with tolerance (H-T) or susceptibility (H-S) to hyperoxia-induced ARDS. Results from studies in isolated mitochondria, tissue homogenate, and isolated perfused lungs show that mitochondrial bioenergetics are differentially altered in H-T and H-S lungs suggesting a potential role for mitochondrial bioenergetics in hyperoxia-induced ARDS. Results are clinically relevant since hyperoxia exposure is a primary therapy for patients with ARDS, and differential sensitivity to hyperoxia surely occurs in humans.

Applicability of mouse models for induction of severe acute lung injury

Acute lung injury (ALI) is a significant clinical challenge associated with high morbidity and mortality. Worldwide, it affects approximately 200.000 individuals annually, with a staggering 40 % mortality rate in hospitalized cases and persistent complications in out-of-hospital cases. This review focuses on the key immunological pathways underlying bacterial ALI and the exploration of mouse models as tools for its induction. These models serve as indispensable platforms for unraveling the inflammatory cascades and biological responses inherent to ALI, while also facilitating the evaluation of novel therapeutic agents. However, their utility is not without challenges, mainly due to the stringent biosafety protocols required by the diverse bacterial virulence profiles. Simple and reproducible models of pulmonary bacterial infection are currently available, including intratracheal, intranasal, pleural and, intraperitoneal approaches. These models use endotoxins such as commercially available lipopolysaccharide (LPS) or live pathogens such as Pseudomonas aeruginosa, Mycobacterium tuberculosis, and Streptococcus pneumoniae, all of which are implicated in the pathogenesis of ALI. Combining murine models of bacterial lung infection with in-depth studies of the underlying immunological mechanisms is a cornerstone in advancing the therapeutic landscape for acute bacterial lung injury.

Mitochondrial dynamics in pulmonary disease: Implications for the potential therapeutics

Mitochondria are dynamic organelles that continuously undergo fusion/fission to maintain normal cell physiological activities and energy metabolism. When mitochondrial dynamics is unbalanced, mitochondrial homeostasis is broken, thus damaging mitochondrial function. Accumulating evidence demonstrates that impairment in mitochondrial dynamics leads to lung tissue injury and pulmonary disease progression in a variety of disease models, including inflammatory responses, apoptosis, and barrier breakdown, and that the role of mitochondrial dynamics varies among pulmonary diseases. These findings suggest that modulation of mitochondrial dynamics may be considered as a valid therapeutic strategy in pulmonary diseases. In this review, we discuss the current evidence on the role of mitochondrial dynamics in pulmonary diseases, with a particular focus on its underlying mechanisms in the development of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), chronic obstructive pulmonary disease (COPD), asthma, pulmonary fibrosis (PF), pulmonary arterial hypertension (PAH), lung cancer and bronchopulmonary dysplasia (BPD), and outline effective drugs targeting mitochondrial dynamics-related proteins, highlighting the great potential of targeting mitochondrial dynamics in the treatment of pulmonary disease.

The emerging role of mtDNA release in sepsis: Current evidence and potential therapeutic targets

Sepsis is a systemic inflammatory reaction caused by infection, and severe sepsis can develop into septic shock, eventually leading to multiorgan dysfunction and even death. In recent years, studies have shown that mitochondrial damage is closely related to the occurrence and development of sepsis. Recent years have seen a surge in concern over mitochondrial DNA (mtDNA), as anomalies in this material can lead to cellular dysfunction, disruption of aerobic respiration, and even death of the cell. In this review, we discuss the latest findings on the mechanisms of mitochondrial damage and the molecular mechanisms controlling mitochondrial mtDNA release. We also explored the connection between mtDNA misplacement and inflammatory activation. Additionally, we propose potential therapeutic targets of mtDNA for sepsis treatment.

Advances in nanomaterial-targeted treatment of acute lung injury after burns

Acute lung injury (ALI) is a common complication in patients with severe burns and has a complex pathogenesis and high morbidity and mortality rates. A variety of drugs have been identified in the clinic for the treatment of ALI, but they have toxic side effects caused by easy degradation in the body and distribution throughout the body. In recent years, as the understanding of the mechanism underlying ALI has improved, scholars have developed a variety of new nanomaterials that can be safely and effectively targeted for the treatment of ALI. Most of these methods involve nanomaterials such as lipids, organic polymers, peptides, extracellular vesicles or cell membranes, inorganic nanoparticles and other nanomaterials, which are targeted to reach lung tissues to perform their functions through active targeting or passive targeting, a process that involves a variety of cells or organelles. In this review, first, the mechanisms and pathophysiological features of ALI occurrence after burn injury are reviewed, potential therapeutic targets for ALI are summarized, existing nanomaterials for the targeted treatment of ALI are classified, and possible problems and challenges of nanomaterials in the targeted treatment of ALI are discussed to provide a reference for the development of nanomaterials for the targeted treatment of ALI.

Focus on the cGAS-STING Signaling Pathway in Sepsis and Its Inflammatory Regulatory Effects

Sepsis is a severe systemic inflammatory response commonly occurring in infectious diseases, caused by infection with virulent pathogens. In the pathogenesis of sepsis, the cyclic guanosine monophosphate (GMP)-adenosine monophosphate (AMP) synthase-stimulator of interferon genes (cGAS-STING) signaling pathway serves a crucial role as a fundamental immunoregulatory mechanism. This signaling pathway activates STING upon recognizing intracellular DNA damage and pathogen-derived DNA, subsequently inducing the production of numerous inflammatory mediators, including interferon and inflammatory cytokines, which in turn trigger an inflammatory response. The aim of this paper is to explore the activation mechanism of the cGAS-STING signaling pathway in sepsis and its impact on inflammatory regulation. By delving into the mechanism of action of the cGAS-STING signaling pathway in sepsis, we aim to identify new therapeutic strategies for the treatment and prevention of sepsis.

IL-37 ameliorates myocardial fibrosis by regulating mtDNA-enriched vesicle release in diabetic cardiomyopathy mice

BACKGROUND

Diabetic cardiomyopathy (DCM), a serious complication of diabetes, leads to structural and functional abnormalities of the heart and ultimately evolves to heart failure. IL-37 exerts a substantial influence on the regulation of inflammation and metabolism. Whether IL-37 is involved in DCM is unknown.

METHODS

The plasma samples were collected from healthy controls, diabetic patients and DCM patients, and the level of IL-37 and its relationship with heart function were observed. The changes in cardiac function, myocardial fibrosis and mitochondrial injury in DCM mice with or without IL-37 intervention were investigated in vivo. By an in vitro co-culture approach involving HG challenge of cardiomyocytes and fibroblasts, the interaction carried out by cardiomyocytes on fibroblast profibrotic activation was studied. Finally, the possible interactive mediator between cardiomyocytes and fibroblasts was explored, and the intervention role of IL-37 and its relevant molecular mechanisms.

RESULTS

We showed that the level of plasma IL-37 in DCM patients was upregulated compared to that in healthy controls and diabetic patients. Both recombinant IL-37 administration or inducing IL-37 expression alleviated cardiac dysfunction and myocardial fibrosis in DCM mice. Mechanically, hyperglycemia impaired mitochondria through SIRT1/AMPK/PGC1α signaling, resulting in significant cardiomyocyte apoptosis and the release of extracellular vesicles containing mtDNA. Fibroblasts then engulfed these mtDNA-enriched vesicles, thereby activating TLR9 signaling and the cGAS-STING pathway to initiate pro-fibrotic process and adverse remodeling. However, the presence of IL-37 ameliorated mitochondrial injury by preserving the activity of SIRT1-AMPK-PGC1α axis, resulting in a reduction in release of mtDNA-enriched vesicle and ultimately attenuating the progression of DCM.

CONCLUSIONS

Collectively, our study demonstrates a protective role of IL-37 in DCM, offering a promising therapeutic agent for this disease.

Mitochondrial (mt)DNA-cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling promotes pyroptosis of macrophages via interferon regulatory factor (IRF)7/IRF3 activation to aggravate lung injury during severe acute pancreatitis

BACKGROUND

Macrophage proinflammatory activation contributes to the pathology of severe acute pancreatitis (SAP) and, simultaneously, macrophage functional changes, and increased pyroptosis/necrosis can further exacerbate the cellular immune suppression during the process of SAP, where cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) plays an important role. However, the function and mechanism of cGAS-STING in SAP-induced lung injury (LI) remains unknown.

METHODS

Lipopolysaccharide (LPS) was combined with caerulein-induced SAP in wild type, cGAS -/- and sting -/- mice. Primary macrophages were extracted via bronchoalveolar lavage and peritoneal lavage. Ana-1 cells were pretreated with LPS and stimulated with nigericin sodium salt to induce pyroptosis in vitro.

RESULTS

SAP triggered NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome activation-mediated pyroptosis of alveolar and peritoneal macrophages in mouse model. Knockout of cGAS/STING could ameliorate NLRP3 activation and macrophage pyroptosis. In addition, mitochondrial (mt)DNA released from damaged mitochondria further induced macrophage STING activation in a cGAS- and dose-dependent manner. Upregulated STING signal can promote NLRP3 inflammasome-mediated macrophage pyroptosis and increase serum interleukin (IL)-6, IL-1β, and tumor necrosis factor (TNF)-α levels and, thus, exacerbate SAP-associated LI (SAP-ALI). Downstream molecules of STING, IRF7, and IRF3 connect the mtDNA-cGAS-STING axis and the NLRP3-pyroptosis axis.

CONCLUSIONS

Negative regulation of any molecule in the mtDNA-cGAS-STING-IRF7/IRF3 pathway can affect the activation of NLRP3 inflammasomes, thereby reducing macrophage pyroptosis and improving SAP-ALI in mouse model.

CPT1A as a potential therapeutic target for lipopolysaccharide-induced acute lung injury in mice

Acute lung injury (ALI) remains a high mortality rate with dramatic lung inflammation and alveolar epithelial cell death. Although fatty acid β-oxidation (FAO) impairment has been implicated in the pathogenesis of ALI, whether Carnitine palmitoyltransferase 1A (CPT1A), the rate-limiting enzyme for FAO, plays roles in lipopolysaccharide (LPS)-induced ALI remains unclear. Accordingly, we focused on exploring the effect of CPT1A in the context of ALI and the underlying mechanisms. We found that overexpression of CPT1A (AAV-CPT1A) effectively alleviated lung injury by reduction of lung wet-to-dry ratio, inflammatory cell infiltration, and protein levels in the BALF of ALI mice. Meanwhile, AAV-CPT1A significantly lessened histopathological changes and several cytokines' secretions. In contrast, blocking CPT1A with etomoxir augmented inflammatory responses and lung injury in ALI mice. Furthermore, we found that overexpression of CPT1A with lentivirus reduced the apoptosis rates of alveolar epithelial cells and the expression of apoptosis-related proteins induced by LPS in MLE12 cells, while etomoxir increased the apoptosis of MLE12 cells. Overexpression of CPT1A prevented the drop in bioenergetics, palmitate oxidation, and ATP levels. In conclusion, the results rendered CPT1A worthy of further development into a pharmaceutical drug for the treatment of ALI.

cGAS-STING, inflammasomes and pyroptosis: an overview of crosstalk mechanism of activation and regulation

BACKGROUND

Intracellular DNA-sensing pathway cGAS-STING, inflammasomes and pyroptosis act as critical natural immune signaling axes for microbial infection, chronic inflammation, cancer progression and organ degeneration, but the mechanism and regulation of the crosstalk network remain unclear. Cellular stress disrupts mitochondrial homeostasis, facilitates the opening of mitochondrial permeability transition pore and the leakage of mitochondrial DNA to cell membrane, triggers inflammatory responses by activating cGAS-STING signaling, and subsequently induces inflammasomes activation and the onset of pyroptosis. Meanwhile, the inflammasome-associated protein caspase-1, Gasdermin D, the CARD domain of ASC and the potassium channel are involved in regulating cGAS-STING pathway. Importantly, this crosstalk network has a cascade amplification effect that exacerbates the immuno-inflammatory response, worsening the pathological process of inflammatory and autoimmune diseases. Given the importance of this crosstalk network of cGAS-STING, inflammasomes and pyroptosis in the regulation of innate immunity, it is emerging as a new avenue to explore the mechanisms of multiple disease pathogenesis. Therefore, efforts to define strategies to selectively modulate cGAS-STING, inflammasomes and pyroptosis in different disease settings have been or are ongoing. In this review, we will describe how this mechanistic understanding is driving possible therapeutics targeting this crosstalk network, focusing on the interacting or regulatory proteins, pathways, and a regulatory mitochondrial hub between cGAS-STING, inflammasomes, and pyroptosis.

SHORT CONCLUSION

This review aims to provide insight into the critical roles and regulatory mechanisms of the crosstalk network of cGAS-STING, inflammasomes and pyroptosis, and to highlight some promising directions for future research and intervention.

Procyanidin B2: A promising multi-functional food-derived pigment for human diseases

Natural edible pigments play a paramount part in the food industry. Procyanidin B2 (PB2), one of the most representative naturally occurring edible pigments, is usually isolated from the seeds, fruits, and leaves of lots of common plants, such as grapes, Hawthorn, black soybean, as well as blueberry, and functions as a food additive in daily life. Notably, PB2 has numerous bioactivities and possesses the potential to treat/prevent a wide range of human diseases, such as diabetes mellitus, diabetic complications, atherosclerosis, and non-alcoholic fatty liver disease, and the underlying mechanisms were partially elucidated, including mediating signaling pathways like NF-κB, MAPK, PI3K/Akt, apoptotic axis, and Nrf-2/HO-1. This paper presents a review of the natural sources, bioactivities, and the therapeutic/preventive potential of PB2 and the possible mechanisms, with the aim of promoting the development of PB2 as a functional food and providing references for its clinical application in the treatment of diseases.

Mitochondrial DNA Release in Innate Immune Signaling

According to the endosymbiotic theory, most of the DNA of the original bacterial endosymbiont has been lost or transferred to the nucleus, leaving a much smaller (∼16 kb in mammals), circular molecule that is the present-day mitochondrial DNA (mtDNA). The ability of mtDNA to escape mitochondria and integrate into the nuclear genome was discovered in budding yeast, along with genes that regulate this process. Mitochondria have emerged as key regulators of innate immunity, and it is now recognized that mtDNA released into the cytoplasm, outside of the cell, or into circulation activates multiple innate immune signaling pathways. Here, we first review the mechanisms through which mtDNA is released into the cytoplasm, including several inducible mitochondrial pores and defective mitophagy or autophagy. Next, we cover how the different forms of released mtDNA activate specific innate immune nucleic acid sensors and inflammasomes. Finally, we discuss how intracellular and extracellular mtDNA release, including circulating cell-free mtDNA that promotes systemic inflammation, are implicated in human diseases, bacterial and viral infections, senescence and aging.

Bovine pulmonary surfactant alleviates inflammation and epithelial cell apoptosis in the early phase of lipopolysaccharide-induced acute lung injury in rats

We investigate the impact of bovine pulmonary surfactant (PS) on LPS-induced ALI in vitro and in vivo to improve recognition and prevent mortality in sepsis-induced ALI. Primary alveolar type II (AT2) cells were treated with LPS alone or in combination with PS. Cell morphology observation, CCK-8 proliferation assay, flow cytometry apoptosis assay, and ELISA for inflammatory cytokine levels were performed at different time points after treatment. An LPS-induced ALI rat model was established and treated with vehicle or PS. Lung wet/dry weight ratio, histopathological changes, lung function parameters, and serum inflammatory cytokine levels were examined 6 h after PS treatment. Survival analysis by Kaplan-Meier method. RNA sequencing was conducted to identify LPS-induced differentially expressed genes in rat lungs. Proapoptotic gene expression in rat lungs was determined by Western blot. LPS significantly inhibited cell proliferation while promoting apoptosis of AT2 cells starting 2 h after treatment, accompanied by a significant increase in inflammatory cytokine production; PS reversed these effects. PS decreased the lung wet/dry ratio in septic rats, histological abnormalities, alterations in lung function parameters, and inflammatory cytokines production; while improving the overall survival of rats. LPS-induced differentially expressed genes were closely associated with apoptosis. PS attenuated LPS-induced upregulation of proapoptotic gene expression starting 2 h after treatment in AT2 cells while restoring lung ATPase activity in vivo. Bovine PS alleviates LPS-induced ALI in the early phase, possibly by suppressing inflammation and AT2 cell apoptosis, as a preemptive therapeutic agent for managing sepsis-induced ALI.

Mitochondria-derived vesicles and their potential roles in kidney stone disease

Recent evidence has shown significant roles of mitochondria-derived vesicles (MDVs) in mitochondrial quality control (MQC) system. Under mild stress condition, MDVs are formed to carry the malfunctioned mitochondrial components, such as mitochondrial DNA (mtDNA), peptides, proteins and lipids, to be eliminated to restore normal mitochondrial structure and functions. Under severe oxidative stress condition, mitochondrial dynamics (fission/fusion) and mitophagy are predominantly activated to rescue mitochondrial structure and functions. Additionally, MDVs generation can be also triggered as the major MQC machinery to cope with unhealthy mitochondria when mitophagy is unsuccessful for eliminating the damaged mitochondria or mitochondrial fission/fusion fail to recover the mitochondrial structure and functions. This review summarizes the current knowledge on MDVs and discuss their roles in physiologic and pathophysiologic conditions. In addition, the potential clinical relevance of MDVs in therapeutics and diagnostics of kidney stone disease (KSD) are emphasized.

Mechanisms behind therapeutic potentials of mesenchymal stem cell mitochondria transfer/delivery

Mesenchymal stromal/stem cells (MSCs) perform their therapeutic effects through various mechanisms, including their ability to differentiate, producing different growth factors, immunomodulatory factors, and extracellular vesicles (EVs). In addition to the mentioned mechanisms, a new aspect of the therapeutic potential of MSCs has recently been noticed, which occurs through mitochondrial transfer. Various methods of MSCs mitochondria transfer have been used in studies to benefit from their therapeutic potential. Among these methods, mitochondrial transfer after MSCs transplantation in cell-to-cell contact, EVs-mediated transfer of mitochondria, and the use of MSCs isolated mitochondria (MSCs-mt) are well studied. Pathological conditions can affect the cells in the damaged microenvironment and lead to cells mitochondrial damage. Since the defect in the mitochondrial function of the cell leads to a decrease in ATP production and the subsequent cell death, restoring the mitochondrial content, functions, and hemostasis can affect the functions of the damaged cell. Various studies show that the transfer of MSCs mitochondria to other cells can affect vital processes such as proliferation, differentiation, cell metabolism, inflammatory responses, cell senescence, cell stress, and cell migration. These changes in cell attributes and behavior are very important for therapeutic purposes. For this reason, their investigation can play a significant role in the direction of the researchers'.

Peak Plasma Levels of mtDNA Serve as a Predictive Biomarker for COVID-19 in-Hospital Mortality

Several predictive biomarkers for coronavirus disease (COVID-19)-associated mortality in critically ill patients have been described. Although mitochondrial DNA (mtDNA) is elevated in patients with COVID-19, the association with coagulation function and its predictive power for mortality is unclear. Accordingly, this study investigates the predictive power of mtDNA for in-hospital mortality in critically ill patients with COVID-19, and whether combining it with thromboelastographic parameters can increase its predictive performance. This prospective explorative study included 29 patients with COVID-19 and 29 healthy matched controls. mtDNA encoding for NADH dehydrogenase 1 (ND1) was quantified using a quantitative polymerase chain reaction analysis, while coagulation function was evaluated using thromboelastometry and impedance aggregometry. Receiver operating characteristic (ROC) curves were used for the prediction of in-hospital mortality. Within the first 24 h, the plasma levels of mtDNA peaked significantly (controls: 65 (28-119) copies/µL; patients: 281 (110-805) at t₀, 403 (168-1937) at t₂₄, and 467 (188-952) copies/µL at t₇₂; controls vs. patients: p = 0.02 at t₀, p = 0.03 at t₂₄, and p = 0.44 at t₇₂). The mtDNA levels at t₂₄ showed an excellent predictive performance for in-hospital mortality (area under the ROC curve: 0.90 (0.75-0.90)), which could not be improved by the combination with thromboelastometric or aggregometric parameters. Critically ill patients with COVID-19 present an early increase in the plasma levels of ND1 mtDNA, lasting over 24 h. They also show impairments in platelet function and fibrinolysis, as well as hypercoagulability, but these do not correlate with the plasma levels of fibrinogen. The peak plasma levels of mtDNA can be used as a predictive biomarker for in-hospital mortality; however, the combination with coagulation parameters does not improve the predictive validity.