Exogenous administration of mitochondrial DNA promotes ischemia reperfusion injury via TLR9-p38 MAPK pathway

Advances in crosstalk among innate immune pathways activated by mitochondrial DNA

Mitochondria are not only the power plant for intracellular oxidative phosphorylation and ATP synthesis, but also involved in cell proliferation, differentiation, signaling and apoptosis. Recent studies have shown that mitochondria play an important role in other pathophysiological functions in addition to cellular energy metabolism. Mitochondria release mitochondrial DNA (mtDNA) as a damage-associated molecular pattern (DAMP) to activate Toll-like receptor 9 (TLR9), NOD-, LRR-, and pyrin domain-containing 3 (NLRP3) inflammasome and cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) innate immune signaling pathways against foreign pathogenic microorganisms. The innate immune response not only promotes antimicrobial immune defense and regulates antiviral signaling, but their overactivation also induces the onset and progression of inflammatory diseases. In this paper, we review the role of mtDNA in the activation of innate immune signaling pathways and the crosstalk among innate immune signaling pathways activated by mtDNA, providing clues for the study of inflammatory diseases caused by mtDNA cytoplasmic translocation.

Involvement of Mitochondria in Parkinson's Disease

Mitochondrial dysregulation, such as mitochondrial complex I deficiency, increased oxidative stress, perturbation of mitochondrial dynamics and mitophagy, has long been implicated in the pathogenesis of PD. Initiating from the observation that mitochondrial toxins cause PD-like symptoms and mitochondrial DNA mutations are associated with increased risk of PD, many mutated genes linked to familial forms of PD, including PRKN, PINK1, DJ-1 and SNCA, have also been found to affect the mitochondrial features. Recent research has uncovered a much more complex involvement of mitochondria in PD. Disruption of mitochondrial quality control coupled with abnormal secretion of mitochondrial contents to dispose damaged organelles may play a role in the pathogenesis of PD. Furthermore, due to its bacterial ancestry, circulating mitochondrial DNAs can function as damage-associated molecular patterns eliciting inflammatory response. In this review, we summarize and discuss the connection between mitochondrial dysfunction and PD, highlighting the molecular triggers of the disease process, the intra- and extracellular roles of mitochondria in PD as well as the therapeutic potential of mitochondrial transplantation.

Peri-Operative Kinetics of Plasma Mitochondrial DNA Levels during Living Donor Kidney Transplantation

During ischemia and reperfusion injury (IRI), mitochondria may release mitochondrial DNA (mtDNA). mtDNA can serve as a propagator of further injury but in specific settings has anti-inflammatory capacities as well. Therefore, the aim of this study was to study the perioperative dynamics of plasma mtDNA during living donor kidney transplantation (LDKT) and its potential as a marker of graft outcome. Fifty-six donor-recipient couples from the Volatile Anesthetic Protection of Renal Transplants-1 (VAPOR-1) trial were included. Systemic venous, systemic arterial, and renal venous samples were taken at multiple timepoints during and after LDKT. Levels of mtDNA genes changed over time and between vascular compartments. Several donor, recipient, and transplantation-related variables significantly explained the course of mtDNA genes over time. mtDNA genes predicted 1-month and 24-month estimated glomerular filtration rate (eGFR) and acute rejection episodes in the two-year follow-up period. To conclude, mtDNA is released in plasma during the process of LDKT, either from the kidney or from the whole body in response to transplantation. While circulating mtDNA levels positively and negatively predict post-transplantation outcomes, the exact mechanisms and difference between mtDNA genes are not yet understood and need further exploration.

Mitochondria-derived cell-to-cell communication

In addition to their intracellular mobility, mitochondria and their components can exist outside the cells from which they originate. As a result, they are capable of acting on non-parental distant cells and mediate intercellular communication in physiological conditions and in a variety of pathologies. It has recently been demonstrated that this horizontal transfer governs a wide range of biological processes, such as tissue homeostasis, the rescue of injured recipient cells, and tumorigenesis. In addition, due to mitochondria's bacterial ancestry, they and their components can be recognized as damage-associated molecular patterns (DAMPs) by the immune cells, leading to inflammation. Here, we provide an overview of the most current and significant findings concerning the different structures of extracellular mitochondria and their by-products and their functions in the physiological and pathological context. This account illustrates the ongoing expansion of our understanding of mitochondria's biological role and functions in mammalian organisms.

Role of released mitochondrial DNA in acute lung injury

Acute lung injury(ALI)/acute respiratory distress syndrome(ARDS) is a form of acute-onset hypoxemic respiratory failure characterised by an acute, diffuse, inflammatory lung injury, and increased alveolar-capillary permeability, which is caused by a variety of pulmonary or nonpulmonary insults. Recently, aberrant mitochondria and mitochondrial DNA(mtDNA) level are associated with the development of ALI/ARDS, and plasma mtDNA level shows the potential to be a promising biomarker for clinical diagnosis and evaluation of lung injury severity. In mechanism, the mtDNA and its oxidised form, which are released from impaired mitochondria, play a crucial role in the inflammatory response and histopathological changes in the lung. In this review, we discuss mitochondrial outer membrane permeabilisation (MOMP), mitochondrial permeability transition pore(mPTP), extracellular vesicles (EVs), extracellular traps (ETs), and passive release as the principal mechanisms for the release of mitochondrial DNA into the cytoplasm and extracellular compartments respectively. Further, we explain how the released mtDNA and its oxidised form can induce inflammatory cytokine production and aggravate lung injury through the Toll-like receptor 9(TLR9) signalling, cytosolic cGAS-stimulator of interferon genes (STING) signalling (cGAS-STING) pathway, and inflammasomes activation. Additionally, we propose targeting mtDNA-mediated inflammatory pathways as a novel therapeutic approach for treating ALI/ARDS.

Mitochondrial DNA Is a Vital Driving Force in Ischemia-Reperfusion Injury in Cardiovascular Diseases

According to the latest Global Burden of Disease Study, cardiovascular disease (CVD) is the leading cause of death, and ischemic heart disease and stroke are the cause of death in approximately half of CVD patients. In CVD, mitochondrial dysfunction following ischemia-reperfusion (I/R) injury results in heart failure. The proper functioning of oxidative phosphorylation (OXPHOS) and the mitochondrial life cycle in cardiac mitochondria are closely related to mitochondrial DNA (mtDNA). Following myocardial I/R injury, mitochondria activate multiple repair and clearance mechanisms to repair damaged mtDNA. When these repair mechanisms are insufficient to restore the structure and function of mtDNA, irreversible mtDNA damage occurs, leading to mtDNA mutations. Since mtDNA mutations aggravate OXPHOS dysfunction and affect mitophagy, mtDNA mutation accumulation leads to leakage of mtDNA and proteins outside the mitochondria, inducing an innate immune response, aggravating cardiovascular injury, and leading to the need for external interventions to stop or slow the disease course. On the other hand, mtDNA released into the circulation after cardiac injury can serve as a biomarker for CVD diagnosis and prognosis. This article reviews the pathogenic basis and related research findings of mtDNA oxidative damage and mtDNA leak-triggered innate immune response associated with I/R injury in CVD and summarizes therapeutic options that target mtDNA.

Effects of acute endurance exercise and exhaustive exercise on innate immune signals induced by mtDNA

Objective: Numerous studies have shown that mitochondrial DNA (mtDNA) can trigger innate immune signaling, and exercise can induce mitochondrial stress. Therefore, this study is aimed at investigating the influence of different types of acute exercise on the innate immune signaling triggered by mtDNA.

Methods: Male C57BL/6 mice ( n = 18) were randomly and equally divided into three groups. They were control group, acute moderate-intensity endurance exercise group (AMIE), and 3-day exhaustive exercise group (EE) respectively. Mice were sacrificed immediately after exercise. The spleen, liver, and blood were taken for analysis.

Results: The amount of mtDNA in the liver cytoplasm and plasma was significantly decreased after AMIE ( p < .05). However, the amount of mtDNA in plasma was increased after EE (p < .05). The mRNA expression of TFAM, and most TLR9 and cGAS/STING signaling pathway-related genes in the liver and spleen was markedly elevated, whereas the expression of those genes in leukocytes was reduced after AMIE. Furthermore, AMIE significantly decreased the protein expression of NLRP3 inflammasome in the liver ( p < .05) and STING in spleen ( p < .01). Also, AMIE and EE caused a drop in circulating IFN-β levels ( p < .05).

Conclusion: A single bout of moderate-intensity exercise reduces mtDNA-induced innate immune signaling and suppresses inflammatory responses by decreasing hepatic cytoplasmic and circulating mtDNA. However, repeated bouts of exhaustive exercise stimulate innate immune signaling by increasing levels of circulating mtDNA.

Through DNA sensors and hidden mitochondrial effects of SARS-CoV-2

The COVID-19 pandemic brought attention to studies about viral infections and their impact on the cell machinery. SARS-CoV-2, for example, invades the host cells by ACE2 interaction and possibly hijacks the mitochondria. To better understand the disease and to propose novel treatments, crucial aspects of SARS-CoV-2 enrolment with host mitochondria must be studied. The replicative process of the virus leads to consequences in mitochondrial function, and cell metabolism. The hijacking of mitochondria, on the other hand, can drive the extrusion of mitochondrial DNA (mtDNA) to the cytosol. Extracellular mtDNA evoke robust proinflammatory responses once detected, that may act in different pathways, eliciting important immune responses. However, few receptors are validated and are able to detect and respond to mtDNA. In this review, we propose that the mtDNA and its detection might be important in the immune process generated by SARS-CoV-2 and that this mechanism might be important in the lung pathogenesis seen in clinical symptoms. Therefore, investigating the mtDNA receptors and their signaling pathways might provide important clues for therapeutic interventions.

The Role of Mitochondria in Immune-Cell-Mediated Tissue Regeneration and Ageing

During tissue injury events, the innate immune system responds immediately to alarms sent from the injured cells, and the adaptive immune system subsequently joins in the inflammatory reaction. The control mechanism of each immune reaction relies on the orchestration of different types of T cells and the activators, antigen-presenting cells, co-stimulatory molecules, and cytokines. Mitochondria are an intracellular signaling organelle and energy plant, which supply the energy requirement of the immune system and maintain the system activation with the production of reactive oxygen species (ROS). Extracellular mitochondria can elicit regenerative effects or serve as an activator of the immune cells to eliminate the damaged cells. Recent clarification of the cytosolic escape of mitochondrial DNA triggering innate immunity underscores the pivotal role of mitochondria in inflammation-related diseases. Human mesenchymal stem cells could transfer mitochondria through nanotubular structures to defective mitochondrial DNA cells. In recent years, mitochondrial therapy has shown promise in treating heart ischemic events, Parkinson's disease, and fulminating hepatitis. Taken together, these results emphasize the emerging role of mitochondria in immune-cell-mediated tissue regeneration and ageing.

Cell-free mitochondrial DNA increases granulosa cell apoptosis and reduces aged oocyte blastocyst development in the mouse

Cell-free mitochondrial DNA (cf-mtDNA) released into the extracellular environment can cause cellular inflammatory responses and damage. Here, we investigated the effects of cf-mtDNA on mouse ovarian granulosa cell function and on the developmental competence of oocytes matured in vitro. Granulosa cells in the cf-mtDNA treatment group had a lower ATP content (P < 0.05), a higher apoptotic cell percentage (P < 0.01), and higher mRNA and protein levels of apoptosis-related factors than the control group (P < 0.01). TLR9, NF-кB p65 and MAPK p38 expression levels in granulosa cells were significantly increased in the cf-mtDNA treatment group (P < 0.05). The blastocyst formation rate of aged mice oocytes matured in vitro decreased significantly (P < 0.05) when cf-mtDNA was added to the media, compared with the control. However, the oocytes from young mice were not affected. Our results suggest that cf-mtDNA may impair granulosa cell function and induce granulosa cell apoptosis, subsequently decreasing blastocyst development in aged oocytes. This role of cf-mtDNA may be associated with the binding to TLR9 and the activation of NF-кB p65 and MAPK p38 signaling pathways.

TLR9 deficiency alleviates doxorubicin-induced cardiotoxicity via the regulation of autophagy

Doxorubicin is a commonly used anthracycline chemotherapeutic drug. Its application for treatment has been impeded by its cardiotoxicity as it is detrimental and fatal. DNA damage, cardiac inflammation, oxidative stress and cell death are the critical links in DOX-induced myocardial injury. Previous studies found that TLR9-related signalling pathways are associated with the inflammatory response of cardiac myocytes, mitochondrial dysfunction and cardiomyocyte death, but it remains unclear whether TLR9 could influence DOX-induced heart injury. Our current data imply that DOX-induced cardiotoxicity is ameliorated by TLR9 deficiency both in vivo and in vitro, manifested as improved cardiac function and reduced cardiomyocyte apoptosis and oxidative stress. Furthermore, the deletion of TLR9 rescued DOX-induced abnormal autophagy flux in vivo and in vitro. However, the inhibition of autophagy by 3-MA abolished the protective effects of TLR9 deletion on DOX-induced cardiotoxicity. Moreover, TLR9 ablation suppressed the activation of p38 MAPK during DOX administration and may promote autophagy via the TLR9-p38 MAPK signalling pathway. Our study suggests that the deletion of TLR9 exhibits a protective effect on doxorubicin-induced cardiotoxicity by enhancing p38-dependent autophagy. This finding could be used as a basis for the development of a prospective therapy against DOX-induced cardiotoxicity.

Innate immunity as a target for acute cardioprotection

Acute obstruction of a coronary artery causes myocardial ischaemia and if prolonged, may result in an ST-segment elevation myocardial infarction (STEMI). First-line treatment involves rapid reperfusion. However, a highly dynamic and co-ordinated inflammatory response is rapidly mounted to repair and remove the injured cells which, paradoxically, can further exacerbate myocardial injury. Furthermore, although cardiac remodelling may initially preserve some function to the heart, it can lead over time to adverse remodelling and eventually heart failure. Since the size of the infarct corresponds to the subsequent risk of developing heart failure, it is important to find ways to limit initial infarct development. In this review, we focus on the role of the innate immune system in the acute response to ischaemia-reperfusion (IR) and specifically its contribution to cell death and myocardial infarction. Numerous danger-associated molecular patterns are released from dying cells in the myocardium, which can stimulate pattern recognition receptors including toll like receptors and NOD-like receptors (NLRs) in resident cardiac and immune cells. Activation of the NLRP3 inflammasome, caspase 1, and pyroptosis may ensue, particularly when the myocardium has been previously aggravated by the presence of comorbidities. Evidence will be discussed that suggests agents targeting innate immunity may be a promising means of protecting the hearts of STEMI patients against acute IR injury. However, the dosing and timing of such agents should be carefully determined because innate immunity pathways may also be involved in cardioprotection. This article is part of a Cardiovascular Research Spotlight Issue entitled 'Cardioprotection Beyond the Cardiomyocyte', and emerged as part of the discussions of the European Union (EU)-CARDIOPROTECTION Cooperation in Science and Technology (COST) Action, CA16225.

The Role of Mitochondrial DNA in the Development of Ischemia Reperfusion Injury

Ischemia/reperfusion (I/R) injury is a common occurrence resulting from acute mesenteric ischemia, traumatic or septic shock, burns, and surgical procedures that can lead to multiple organ failure and high mortality in critically ill patients. Mitochondria are often considered the cellular power factory via their capacity for ATP generation. Recently, mitochondria have been further identified as vital regulators of cell death, inflammation, and oxidative stress, all of which can aggravate I/R injury. Studies have indicated that mitochondrial DNA (mtDNA) damage leads to mitochondrial dysfunction and aggravates I/R injury. mtDNA is emerging as an agonist of the innate immune system that influences inflammatory pathology during I/R injury. In addition, when mtDNA is released into the cytoplasm, extracellular milieu, or circulation, it can activate multiple pattern-recognition receptors to trigger type I interferon and pro-inflammatory responses. Here, we review the emerging role of mtDNA in I/R injury to highlight novel mechanistic insights and discuss the pathophysiological relevance of mitochondrial biology.

Mechanisms and therapeutic targets of ischemic acute kidney injury

Acute kidney injury (AKI) due to renal ischemia reperfusion (IR) is a major clinical problem without effective therapy and is a significant and frequent cause of morbidity and mortality during the perioperative period. Although the pathophysiology of ischemic AKI is not completely understood, several important mechanisms of renal IR-induced AKI have been studied. Renal ischemia and subsequent reperfusion injury initiates signaling cascades mediating renal cell necrosis, apoptosis, and inflammation, leading to AKI. Better understanding of the molecular and cellular pathophysiological mechanisms underlying ischemic AKI will provide more targeted approach to prevent and treat renal IR injury. In this review, we summarize important mechanisms of ischemic AKI, including renal cell death pathways and the contribution of endothelial cells, epithelial cells, and leukocytes to the inflammatory response during ischemic AKI. Additionally, we provide some updated potential therapeutic targets for the prevention or treatment of ischemic AKI, including Toll-like receptors, adenosine receptors, and peptidylarginine deiminase 4. Finally, we propose mechanisms of ischemic AKI-induced liver, intestine, and kidney dysfunction and systemic inflammation mainly mediated by Paneth cell degranulation as a potential explanation for the high mortality observed with AKI.

Effects of Changes in the Levels of Damage-Associated Molecular Patterns Following Continuous Veno-Venous Hemofiltration Therapy on Outcomes in Acute Kidney Injury Patients With Sepsis

Background: We investigated the association of damage-associated molecular pattern (DAMP) removal with mortality in sepsis patients undergoing continuous veno–venous hemofiltration (CVVH).

Methods: Circulating levels of DAMPs [mitochondrial DNA (mtDNA); nuclear DNA (nDNA); heat shock protein 70 (HSP70); and high mobility group box 1 (HMGB1)] and cytokines were measured at baseline, 6 and 12 h after initiation of CVVH. Urinary DNA levels were analyzed at baseline and end of CVVH. The expression of human leukocyte antigen (HLA)-DR was assayed at 0, 3, and 7 days after initiation of CVVH. Moreover, the effects of HSP70 and HMGB1 clearance on survival were analyzed.

Results: We evaluated 43 patients with acute kidney injury (AKI) (33 sepsis patients). Twenty-two sepsis patients (67%) and three non-sepsis patients (30%) expired (P = 0.046). Significant reductions in the levels of circulating interleukin-6 (P = 0.046) and tumor necrosis factor-α (P = 0.008) were found in the sepsis group. The levels of mtDNA were increased (ND2, P = 0.035; D-loop, P = 0.003), whereas that of HSP70 was reduced (P = 0.000) in all patients during the first 12 h. The levels of DAMPs in the plasma were markedly increased after blood passage from the inlet through the dialyzer in survivor sepsis patients. The clearance rates of HSP70 and HMGB1 were good predictors of mortality [area under the curve (AUC) = 0.937, P = 0.000; AUC = 0.90, P = 0.001, respectively]. The level of HLA-DR was increased in response to higher HSP70 clearance (P = 0.006). Survival was significantly worse in groups with higher clearance rates of HSP70 and HMGB1 than the cut-off value (log-rank test: P = 0.000 for both). Higher HSP70 clearance was a significant independent predictor of mortality (odds ratio = 1.025, 95% confidence interval [CI]: 1.012–1.039, P = 0.000). The urinary nDNA (β-globin) level before CVVH was an independent risk factor for the duration of CVVH in patients with sepsis (sRE = 0.460, 95% CI: 1.720–8.857, P = 0.005).

Conclusion: CVVH removes inflammatory factors, reduces urinary DAMPs, and removes plasma DAMPs. However, survival decreases in response to higher HSP70 clearance.

The myocardial infarct-exacerbating effect of cell-free DNA is mediated by the high-mobility group box 1-receptor for advanced glycation end products-Toll-like receptor 9 pathway

INTRODUCTION

Damage-associated molecular patterns, such as high-mobility group box 1 (HMGB1) and cell-free DNA (cfDNA), play critical roles in mediating ischemia-reperfusion injury (IRI). HMGB1 activates RAGE to exacerbate IRI, but the mechanism underlying cfDNA-induced myocardial IRI remains unknown. We hypothesized that the infarct-exacerbating effect of cfDNA is mediated by HMGB1 and receptor for advanced glycation end products (RAGE).

METHODS

C57BL/6 wild type mice, RAGE knockout (KO), and Toll-like receptor 9 KO mice underwent 20- or 40-minute occlusions of the left coronary artery followed by up to 60 minutes of reperfusion. Cardiac coronary perfusate was acquired from ischemic hearts without reperfusion. Exogenous mitochondrial DNA was acquired from livers of normal C57BL/6 mice. Myocardial infarct size (IS) was reported as percent risk region, as measured by 2,3,5-triphenyltetrazolium chloride and Phthalo blue (Heucotech, Fairless Hill, Pa) staining. cfDNA levels were measured by Sytox Green assay (Thermo Fisher Scientific, Waltham, Mass) and/or spectrophotometer.

RESULTS

Free HMGB1 and cfDNA levels were increased in the ischemic myocardium during prolonged ischemia and subsequently in the plasma during reperfusion. In C57BL/6 mice undergoing 40'/60' IRI, deoxyribonuclease I, or anti-HMGB1 monoclonal antibody reduced IS by approximately half to 29.0% ± 5.2% and 24.3% ± 3.5% (P < .05 vs control 54.3% ± 3.4%). However, combined treatment with deoxyribonuclease I + anti-HMGB1 monoclonal antibody did not further attenuate IS (29.3% ± 4.9%). In C57BL/6 mice undergoing 20'/60' IRI, injection of 40'/5' plasma upon reperfusion increased IS by more than 3-fold (to 19.9 ± 4.3; P < .05). This IS exacerbation was abolished by pretreating the plasma with deoxyribonuclease I or by depleting the HMGB1 by immunoprecipitation, or by splenectomy. The infarct-exacerbating effect also disappeared in RAGE KO mice and Toll-like receptor 9 KO mice. Injection of 40'/0' coronary perfusate upon reperfusion similarly increased IS. The levels of HMGB1 and cfDNA were significantly elevated in the 40'/0' coronary perfusate and 40'/reperfusion (min) plasma but not in those with 10' ischemia. In C57BL/6 mice without IRI, 40'/5' plasma significantly increased the interleukin-1β protein and messenger RNA expression in the spleen by 30 minutes after injection. Intravenous bolus injection of recombinant HMGB1 (0.1 μg/g) or mitochondrial DNA (0.5 μg/g) 5 minutes before reperfusion did not exacerbate IS (P = not significant vs control). However, combined administration of recombinant HMGB1 + mitochondrial DNA significantly increased IS (P < .05 vs individual treated groups) and this infarct-exacerbating effect disappeared in RAGE KO mice and splenectomized C57BL/6 mice. The accumulation of cfDNA in the spleen after combined recombinant HMGB1 + mitochondrial DNA treatment was significantly more elevated in C57BL/6 mice than in RAGE KO mice.

CONCLUSIONS

Both HMGB1 and cfDNA are released from the heart upon reperfusion after prolonged ischemia and both contribute importantly and interdependently to post-IRI by a common RAGE-Toll-like receptor 9-dependent mechanism. Depleting either of these 2 damage-associated molecular patterns suffices to significantly reduce IS by approximately 50%.

A new hypothesis for Parkinson's disease pathogenesis: GTPase-p38 MAPK signaling and autophagy as convergence points of etiology and genomics

The combination of genetics and genomics in Parkinson´s disease has recently begun to unveil molecular mechanisms possibly underlying disease onset and progression. In particular, catabolic processes such as autophagy have been increasingly gaining relevance as post-mortem evidence and experimental models suggested a participation in neurodegeneration and alpha-synuclein Lewy body pathology. In addition, familial Parkinson´s disease linked to LRRK2 and alpha-synuclein provided stronger correlation between etiology and alterations in autophagy. More detailed cellular pathways are proposed and genetic risk factors that associate with idiopathic Parkinson´s disease provide further clues in dissecting contributions of single players. Nevertheless, the fine-tuning of these processes remains elusive, as the initial stages of the pathways are not yet clarified.In this review, we collect literature evidence pointing to autophagy as the common, downstream target of Parkinsonian dysfunctions and augment current knowledge on the factors that direct the subsequent steps. Cell and molecular biology evidence indicate that p38 signaling underlies neurodegeneration and autoptic observations suggest a participation in neuropathology. Moreover, alpha-synuclein and LRRK2 also appear involved in the p38 pathway with additional roles in the regulation of GTPase signaling. Small GTPases are critical modulators of p38 activation and thus, their functional interaction with aSyn and LRRK2 could explain much of the detailed mechanics of autophagy in Parkinson´s disease.We propose a novel hypothesis for a more comprehensive working model where autophagy is controlled by upstream pathways, such as GTPase-p38, that have been so far underexplored in this context. In addition, etiological factors (LRRK2, alpha-synuclein) and risk loci might also combine in this common mechanism, providing a powerful experimental setting to dissect the cause of both familial and idiopathic disease.

The source of cell-free mitochondrial DNA in trauma and potential therapeutic strategies

Mitochondria play a key role in the pathophysiology of post-injury inflammation. Cell-free mitochondrial DNA (cf-mtDNA) is now understood to catalyse sterile inflammation after trauma. Observations in trauma cohorts have identified high cf-mtDNA in patients with systemic inflammatory response syndrome and multiple organ failure as well as following major surgery. The source of cf-mtDNA can be various cells affected by mechanical and hypoxic injury (passive mechanism) or induced by inflammatory mechanisms (active mechanism). Multiple forms of cf-mtDNA exist; mtDNA fragments, mtDNA in microparticles/vesicles and cell-free mitochondria. Trauma to cells that are rich in mitochondria are believed to release more cf-mtDNA. This review describes the current understanding of the mechanisms of cf-mtDNA release, its systemic effects and the potential therapeutic implications related to its modification. Although current understanding is insufficient to change trauma management, focussed research goals have been identified to pave the way for monitoring and manipulation of cf-mtDNA release and effects in trauma.

Pathogenesis of cardiac ischemia reperfusion injury is associated with CK2α-disturbed mitochondrial homeostasis via suppression of FUNDC1-related mitophagy

Disturbed mitochondrial homeostasis contributes to the pathogenesis of cardiac ischemia reperfusion (IR) injury, although the underlying mechanism remains elusive. Here, we demonstrated that casein kinase 2α (CK2α) was upregulated following acute cardiac IR injury. Increased CK2α was shown to be instrumental to mitochondrial damage, cardiomyocyte death, infarction area expansion and cardiac dysfunction, whereas cardiac-specific CK2α knockout (CK2α^CKO) mice were protected against IR injury and mitochondrial damage. Functional assay indicated that CK2α enhanced the phosphorylation (inactivation) of FUN14 domain containing 1 (FUNDC1) via post-transcriptional modification at Ser13, thus effectively inhibiting mitophagy. Defective mitophagy failed to remove damaged mitochondria induced by IR injury, resulting in mitochondrial genome collapse, electron transport chain complex (ETC) inhibition, mitochondrial biogenesis arrest, cardiolipin oxidation, oxidative stress, mPTP opening, mitochondrial debris accumulation and eventually mitochondrial apoptosis. In contrast, loss of CK2α reversed the FUNDC1-mediated mitophagy, providing a survival advantage to myocardial tissue following IR stress. Interestingly, mice deficient in both CK2α and FUNDC1 failed to show protection against IR injury and mitochondrial damage through a mechanism possible attributed to lack of mitophagy. Taken together, our results confirmed that CK2α serves as a negative regulator of mitochondrial homeostasis via suppression of FUNDC1-required mitophagy, favoring the development of cardiac IR injury.

Inflammatory Response During Myocardial Infarction

The occlusion of a coronary artery by a thrombus generated on a ruptured atherosclerotic plaque has been pursued in the last decades as a determining event for the clinical outcome after myocardial infarction (MI). Yet, MI causes a cell death wave front, which triggers an inflammatory response to clear cellular debris, and which in excess can double the myocardial lesion and influence the clinical prognosis in the short and long term. Accordingly, proper, timely regulated inflammatory response has now been considered a second pivotal player in cardiac recovery after MI justifying the search for pharmacological strategies to modulate inflammatory effectors. This chapter reviews the key events and the main effectors of inflammation after myocardial ischemic insult, as well as the contribution of this phenomenon to the progression of atherosclerosis.

Effects of TLR3 and TLR9 Signaling Pathway on Brain Protection in Rats Undergoing Sevoflurane Pretreatment during Cardiopulmonary Bypass

OBJECTIVE

To investigate the effects of TLR3 and TLR9 signaling pathway on brain injury during CPB in rats pretreated with sevoflurane and its possible molecular mechanism.

METHODS

SD rats were randomly assigned to sham group, CPB group, and Sev group. Brain tissue was obtained at before CPB (T0), at CPB for 30 minutes (T1), 1 hour after CPB (T3), and 3 hours after CPB (T5). ELISA was used to measure S100-β and IL-6. Western blot was utilized to determine TLR3 and TLR9 expression. TUNEL was applied to detect neuronal apoptosis.

RESULTS

Compared with CPB group, at T1, at termination after 1 hour of CPB (T2), T3, 2 hours after CPB (T4) and T5, S100-β and IL-6 decreased in Sev group. Compared with CPB group, IFN-β were increased in Sev group, except T0. Compared with CPB group, TLR3 expression increased, and TLR9 and NF-κB decreased in Sev group. The apoptotic neurons were less in Sev group than in CPB group (P < 0.05).

CONCLUSION

Sevoflurane intervention can activate TLR3 and TLR9 signaling pathway, upregulate TLR3 expression and downstream TRIF expression, decrease TLR9 expression, and downregulate downstream NF-κB expression in CPB rat models, thereby mitigating brain injury induced by inflammatory response during CPB.

Roles of Mitochondrial DNA Signaling in Immune Responses

Mitochondrial DNA (mtDNA) plays an important role in immune responses during the evolution. The present chapter systemically describes its role on immune-related diseases and its interaction on immune responses. It is important to explore the main function and mechanisms of mtDNA in immune responses by which mtDNA regulates the signaling pathways of Toll-like receptor 9, autophagy, and STING. There are potentials to discover therapeutic targets of mtDNA in immune diseases and inflammation. It will be more exciting if the CRISPR-Cas9 method can be applied for mtDNA gene editing to cure diseases and provide a novel insight of mtDNA in immune responses as well as new therapies.