Mesenchymal Stromal Cell Transplantation Ameliorates Fibrosis and microRNA Dysregulation in Skeletal Muscle Ischaemia.

Peripheral arterial disease (PAD) is associated with lower-extremity muscle wasting. Hallmark features of PAD-associated skeletal muscle pathology include loss of skeletal muscle mass, reduced strength and physical performance, increased inflammation, fibrosis, and adipocyte infiltration. At the molecular level, skeletal muscle ischaemia has also been associated with gene and microRNA (miRNA) dysregulation. Mesenchymal stromal cells (MSCs) have been shown to enhance muscle regeneration and improve muscle function in various skeletal muscle injuries. This study aimed to evaluate the effects of intramuscularly delivered human umbilical cord-derived MSCs (hUC-MSCs) on skeletal muscle ischaemia. Herein, we report an hUC-MSC-mediated amelioration of ischaemia-induced skeletal muscle atrophy and function via enhancement of myofibre regeneration, reduction of tissue inflammation, adipocyte accumulation, and tissue fibrosis. These changes were observed in the absence of cell-mediated enhancement of blood flow recovery as measured by Laser Doppler imaging. Furthermore, reduced tissue fibrosis in the hUC-MSC-treated group was associated with upregulation of miR-1, miR-133a, and miR-29b and downregulation of targeted pro-fibrotic genes such as Col1a1 and Fn1. Our results support the use of hUC-MSCs as a novel approach to reduce fibrosis and promote skeletal muscle regeneration after ischaemic injury in patients with PAD.

Continued dysfunction of capillary pericytes promotes no-reflow after experimental stroke in vivo.

Incomplete reperfusion of the microvasculature ('no-reflow') after ischaemic stroke damages salvageable brain tissue. Previous ex vivo studies suggest pericytes are vulnerable to ischaemia and may exacerbate no-reflow, but the viability of pericytes and their association with no-reflow remains under-explored in vivo. Using longitudinal in vivo two-photon single-cell imaging over 7 days, we showed that 87% of pericytes constrict during cerebral ischaemia and remain constricted post reperfusion, and 50% of the pericyte population are acutely damaged. Moreover, we revealed ischaemic pericytes to be fundamentally implicated in capillary no-reflow by limiting and arresting blood flow within the first 24 h post stroke. Despite sustaining acute membrane damage, we observed that over half of all cortical pericytes survived ischaemia and responded to vasoactive stimuli, upregulated unique transcriptomic profiles and replicated. Finally, we demonstrated the delayed recovery of capillary diameter by ischaemic pericytes after reperfusion predicted vessel reconstriction in the subacute phase of stroke. Cumulatively, these findings demonstrate that surviving cortical pericytes remain both viable and promising therapeutic targets to counteract no-reflow after ischaemic stroke.

Atherosclerosis quantification and cardiovascular risk: the ISCHEMIA trial.

BACKGROUND AND AIMS: The aim of this study was to determine the prognostic value of coronary computed tomography angiography (CCTA)-derived atherosclerotic plaque analysis in ISCHEMIA. METHODS: Atherosclerosis imaging quantitative computed tomography (AI-QCT) was performed on all available baseline CCTAs to quantify plaque volume, composition, and distribution. Multivariable Cox regression was used to examine the association between baseline risk factors (age, sex, smoking, diabetes, hypertension, ejection fraction, prior coronary disease, estimated glomerular filtration rate, and statin use), number of diseased vessels, atherosclerotic plaque characteristics determined by AI-QCT, and a composite primary outcome of cardiovascular death or myocardial infarction over a median follow-up of 3.3 (interquartile range 2.2-4.4) years. The predictive value of plaque quantification over risk factors was compared in an area under the curve (AUC) analysis. RESULTS: Analysable CCTA data were available from 3711 participants (mean age 64 years, 21% female, 79% multivessel coronary artery disease). Amongst the AI-QCT variables, total plaque volume was most strongly associated with the primary outcome (adjusted hazard ratio 1.56, 95% confidence interval 1.25-1.97 per interquartile range increase [559 mm3]; P = .001). The addition of AI-QCT plaque quantification and characterization to baseline risk factors improved the model's predictive value for the primary outcome at 6 months (AUC 0.688 vs. 0.637; P = .006), at 2 years (AUC 0.660 vs. 0.617; P = .003), and at 4 years of follow-up (AUC 0.654 vs. 0.608; P = .002). The findings were similar for the other reported outcomes. CONCLUSIONS: In ISCHEMIA, total plaque volume was associated with cardiovascular death or myocardial infarction. In this highly diseased, high-risk population, enhanced assessment of atherosclerotic burden using AI-QCT-derived measures of plaque volume and composition modestly improved event prediction.

Critical limb-threatening ischaemia and microvascular transformation: clinical implications.

BACKGROUND AND AIMS: Clinical management of critical limb-threatening ischaemia (CLTI) is focused on prevention and treatment of atherosclerotic arterial occlusions. The role of microvascular pathology in disease progression is still largely unspecified and more importantly not utilized for treatment. The aim of this explorative study was to characterize the role of the microvasculature in CLTI pathology. METHODS: Clinical high-resolution imaging of CLTI patients (n = 50) and muscle samples from amputated CLTI limbs (n = 40) were used to describe microvascular pathology of CLTI at the level of resting muscle blood flow and microvascular structure, respectively. Furthermore, a chronic, low arterial driving pressure-simulating ischaemia model in rabbits (n = 24) was used together with adenoviral vascular endothelial growth factor A gene transfers to study the effect of microvascular alterations on muscle outcome. RESULTS: Resting microvascular blood flow was not depleted but displayed decreased capillary transit time (P < .01) in CLTI muscles. Critical limb-threatening ischaemia muscle microvasculature also exhibited capillary enlargement (P < .001) and further arterialization along worsening of myofibre atrophy and detaching of capillaries from myofibres. Furthermore, CLTI-like capillary transformation was shown to worsen calf muscle force production (P < .05) and tissue outcome (P < .01) under chronic ischaemia in rabbits and in healthy, normal rabbit muscle. CONCLUSIONS: These findings depict a progressive, hypoxia-driven transformation of the microvasculature in CLTI muscles, which pathologically alters blood flow dynamics and aggravates tissue damage under low arterial driving pressure. Hypoxia-driven capillary enlargement can be highly important for CLTI outcomes and should therefore be considered in further development of diagnostics and treatment of CLTI.

Coronary flow capacity and survival prediction after revascularization: physiological basis and clinical implications.

BACKGROUND AND AIMS: Coronary flow capacity (CFC) is associated with an observed 10-year survival probability for individual patients before and after actual revascularization for comparison to virtual hypothetical ideal complete revascularization. METHODS: Stress myocardial perfusion (mL/min/g) and coronary flow reserve (CFR) per pixel were quantified in 6979 coronary artery disease (CAD) subjects using Rb-82 positron emission tomography (PET) for CFC maps of artery-specific size-severity abnormalities expressed as percent left ventricle with prospective follow-up to define survival probability per-decade as fraction of 1.0. RESULTS: Severely reduced CFC in 6979 subjects predicted low survival probability that improved by 42% after revascularization compared with no revascularization for comparable severity (P = .0015). For 283 pre-and-post-procedure PET pairs, severely reduced regional CFC-associated survival probability improved heterogeneously after revascularization (P < .001), more so after bypass surgery than percutaneous coronary interventions (P < .001) but normalized in only 5.7%; non-severe baseline CFC or survival probability did not improve compared with severe CFC (P = .00001). Observed CFC-associated survival probability after actual revascularization was lower than virtual ideal hypothetical complete post-revascularization survival probability due to residual CAD or failed revascularization (P < .001) unrelated to gender or microvascular dysfunction. Severely reduced CFC in 2552 post-revascularization subjects associated with low survival probability also improved after repeat revascularization compared with no repeat procedures (P = .025). CONCLUSIONS: Severely reduced CFC and associated observed survival probability improved after first and repeat revascularization compared with no revascularization for comparable CFC severity. Non-severe CFC showed no benefit. Discordance between observed actual and virtual hypothetical post-revascularization survival probability revealed residual CAD or failed revascularization.

Vago-splenic signal transduction of cardioprotection in humans.

BACKGROUND AND AIMS: The spleen serves as an important relay organ that releases cardioprotective factor(s) upon vagal activation during remote ischaemic conditioning (RIC) in rats and pigs. The translation of these findings to humans was attempted. METHODS: Remote ischaemic conditioning or electrical auricular tragus stimulation (ATS) were performed in 10 healthy young volunteers, 10 volunteers with splenectomy, and 20 matched controls. Venous blood samples were taken before and after RIC/ATS or placebo, and a plasma dialysate was infused into isolated perfused rat hearts subjected to global ischaemia/reperfusion. RESULTS: Neither left nor right RIC or ATS altered heart rate and heart rate variability in the study cohorts. With the plasma dialysate prepared before RIC or ATS, respectively, infarct size (% ventricular mass) in the recipient rat heart was 36 ± 6% (left RIC), 34 ± 3% (right RIC) or 31 ± 5% (left ATS), 35 ± 5% (right ATS), and decreased with the plasma dialysate from healthy volunteers after RIC or ATS to 20 ± 4% (left RIC), 23 ± 6% (right RIC) or to 19 ± 4% (left ATS), 26 ± 9% (right ATS); infarct size was still reduced with plasma dialysate 4 days after ATS and 9 days after RIC. In a subgroup of six healthy volunteers, such infarct size reduction was abrogated by intravenous atropine. Infarct size reduction by RIC or ATS was also abrogated in 10 volunteers with splenectomy, but not in their 20 matched controls. CONCLUSIONS: In humans, vagal innervation and the spleen as a relay organ are decisive for the cardioprotective signal transduction of RIC and ATS.

Myocardial reperfusion injury exacerbation due to ALDH2 deficiency is mediated by neutrophil extracellular traps and prevented by leukotriene C4 inhibition.

BACKGROUND AND AIMS: The Glu504Lys polymorphism in the aldehyde dehydrogenase 2 (ALDH2) gene is closely associated with myocardial ischaemia/reperfusion injury (I/RI). The effects of ALDH2 on neutrophil extracellular trap (NET) formation (i.e. NETosis) during I/RI remain unknown. This study aimed to investigate the role of ALDH2 in NETosis in the pathogenesis of myocardial I/RI. METHODS: The mouse model of myocardial I/RI was constructed on wild-type, ALDH2 knockout, peptidylarginine deiminase 4 (Pad4) knockout, and ALDH2/PAD4 double knockout mice. Overall, 308 ST-elevation myocardial infarction patients after primary percutaneous coronary intervention were enrolled in the study. RESULTS: Enhanced NETosis was observed in human neutrophils carrying the ALDH2 genetic mutation and ischaemic myocardium of ALDH2 knockout mice compared with controls. PAD4 knockout or treatment with NETosis-targeting drugs (GSK484, DNase1) substantially attenuated the extent of myocardial damage, particularly in ALDH2 knockout. Mechanistically, ALDH2 deficiency increased damage-associated molecular pattern release and susceptibility to NET-induced damage during myocardial I/RI. ALDH2 deficiency induced NOX2-dependent NETosis via upregulating the endoplasmic reticulum stress/microsomal glutathione S-transferase 2/leukotriene C4 (LTC4) pathway. The Food and Drug Administration-approved LTC4 receptor antagonist pranlukast ameliorated I/RI by inhibiting NETosis in both wild-type and ALDH2 knockout mice. Serum myeloperoxidase-DNA complex and LTC4 levels exhibited the predictive effect on adverse left ventricular remodelling at 6 months after primary percutaneous coronary intervention in ST-elevation myocardial infarction patients. CONCLUSIONS: ALDH2 deficiency exacerbates myocardial I/RI by promoting NETosis via the endoplasmic reticulum stress/microsomal glutathione S-transferase 2/LTC4/NOX2 pathway. This study hints at the role of NETosis in the pathogenesis of myocardial I/RI, and pranlukast might be a potential therapeutic option for attenuating I/RI, particularly in individuals with the ALDH2 mutation.

Novel IL-4/HB-EGF-dependent crosstalk between eosinophils and macrophages controls liver regeneration after ischaemia and reperfusion injury.

OBJECTIVE: Previous studies indicate that eosinophils are recruited into the allograft following orthotopic liver transplantation and protect from ischaemia reperfusion (IR) injury. In the current studies, we aim to explore whether their protective function could outlast during liver repair. DESIGN: Eosinophil-deficient mice and adoptive transfer of bone marrow-derived eosinophils (bmEos) were employed to investigate the effects of eosinophils on tissue repair and regeneration after hepatic IR injury. Aside from exogenous cytokine or neutralising antibody treatments, mechanistic studies made use of a panel of mouse models of eosinophil-specific IL-4/IL-13-deletion, cell-specific IL-4rα-deletion in liver macrophages and hepatocytes and macrophage-specific deletion of heparin-binding epidermal growth factor-like growth factor (hb-egf). RESULT: We observed that eosinophils persisted over a week following hepatic IR injury. Their peak accumulation coincided with that of hepatocyte proliferation. Functional studies showed that eosinophil deficiency was associated with a dramatic delay in liver repair, which was normalised by the adoptive transfer of bmEos. Mechanistic studies demonstrated that eosinophil-derived IL-4, but not IL-13, was critically involved in the reparative function of these cells. The data further revealed a selective role of macrophage-dependent IL-4 signalling in liver regeneration. Eosinophil-derived IL-4 stimulated macrophages to produce HB-EGF. Moreover, macrophage-specific hb-egf deletion impaired hepatocyte regeneration after IR injury. CONCLUSION: Together, these studies uncovered an indispensable role of eosinophils in liver repair after acute injury and identified a novel crosstalk between eosinophils and macrophages through the IL-4/HB-EGF axis.

Heterotypic macrophages/microglia differentially contribute to retinal ischaemia and neovascularisation.

AIMS/HYPOTHESIS: Diabetic retinopathy is characterised by neuroinflammation that drives neuronal and vascular degenerative pathology, which in many individuals can lead to retinal ischaemia and neovascularisation. Infiltrating macrophages and activated retina-resident microglia have been implicated in the progression of diabetic retinopathy, although the distinct roles of these immune cells remain ill-defined. Our aim was to clarify the distinct roles of macrophages/microglia in the pathogenesis of proliferative ischaemic retinopathies. METHODS: Murine oxygen-induced retinopathy is commonly used as a model of ischaemia-induced proliferative diabetic retinopathy (PDR). We evaluated the phenotype macrophages/microglia by immunostaining, quantitative real-time RT-PCR (qRT-PCR), flow cytometry and scRNA-seq analysis. In clinical imaging studies of diabetic retinopathy, we used optical coherence tomography (OCT) and OCT angiography. RESULTS: Immunostaining, qRT-PCR and flow cytometry showed expression levels of M1-like macrophages/microglia markers (CD80, CD68 and nitric oxide synthase 2) and M2-like macrophages/microglia markers (CD206, CD163 and macrophage scavenger receptor 1) were upregulated in areas of retinal ischaemia and around neo-vessels, respectively. scRNA-seq analysis of the ischaemic retina revealed distinct ischaemia-related clusters of macrophages/microglia that express M1 markers as well as C-C chemokine receptor 2. Inhibition of Rho-kinase (ROCK) suppressed CCL2 expression and reduced CCR2-positive M1-like macrophages/microglia in areas of ischaemia. Furthermore, the area of retinal ischaemia was reduced by suppressing blood macrophage infiltration not only by ROCK inhibitor and monocyte chemoattractant protein-1 antibody but also by GdCl3. Clinical imaging studies of diabetic retinopathy using OCT indicated potential involvement of macrophages/microglia represented by hyperreflective foci in areas of reduced perfusion. CONCLUSIONS/INTERPRETATION: These results collectively indicated that heterotypic macrophages/microglia differentially contribute to retinal ischaemia and neovascularisation in retinal vascular diseases including diabetic retinopathy. This adds important new information that could provide a basis for a more targeted, cell-specific therapeutic approach to prevent progression to sight-threatening PDR.

Hydrogen alleviates hypoxic-ischaemic brain damage in neonatal rats by inhibiting injury of brain pericytes.

Hypoxia-ischaemia (HI) can induce the death of cerebrovascular constituent cells through oxidative stress. Hydrogen is a powerful antioxidant which can activate the antioxidant system. A hypoxia-ischaemia brain damage (HIBD) model was established in 7-day-old SD rats. Rats were treated with different doses of hydrogen-rich water (HRW), and brain pericyte oxidative stress damage, cerebrovascular function and brain tissue damage were assessed. Meanwhile, in vitro-cultured pericytes were subjected to oxygen-glucose deprivation and treated with different concentrations of HRW. Oxidative injury was measured and the molecular mechanism of how HRW alleviated oxidative injury of pericytes was also examined. The results showed that HRW significantly attenuated HI-induced oxidative stress in the brain pericytes of neonatal rats, partly through the Nrf2-HO-1 pathway, further improving cerebrovascular function and reducing brain injury and dysfunction. Furthermore, HRW is superior to a single-cell death inhibitor for apoptosis, ferroptosis, parthanatos, necroptosis and autophagy and can better inhibit HI-induced pericyte death. The liver and kidney functions of rats were not affected by present used HRW dose. This study elucidates the role and mechanism of hydrogen in treating HIBD from the perspective of pericytes, providing new theoretical evidence and mechanistic references for the clinical application of hydrogen in neonatal HIE.

SENP1 reduces oxidative stress and apoptosis in renal ischaemia-reperfusion injury by deSUMOylation of HIF-1α.

Renal ischaemia-reperfusion injury (RIRI) is a primary cause of acute kidney damage, occurring frequently in situations like renal transplantation, yet the underlying mechanisms were not fully understood. Sentrin-specific protease 1 (SENP1) is an important member of the SENP family, which is widely involved in various diseases. However, the role of SENP1 in RIRI has been unclear. In our study, we discovered that SENP1 was involved in RIRI and reduced renal cell apoptosis and oxidative stress at elevated levels. Further mechanistic studies showed that hypoxia-inducible factor-1α (HIF-1α) was identified as a substrate of SENP1. Furthermore, SENP1 deSUMOylated HIF-1α, which reduced the degradation of HIF-1α, and exerted a renoprotective function. In addition, the protective function was lost after application of the HIF-1α specific inhibitor KC7F2. Briefly, our results fully demonstrated that SENP1 reduced the degradation of HIF-1α and attenuated oxidative stress and apoptosis in RIRI by regulating the deSUMOylation of HIF-1α, suggesting that SENP1 may serve as a potential therapeutic target for the treatment of RIRI.

Macrophage-derived extracellular vesicles alter cardiac recovery and metabolism in a rat heart model of donation after circulatory death.

Conditions to which the cardiac graft is exposed during transplantation with donation after circulatory death (DCD) can trigger the recruitment of macrophages that are either unpolarized (M0) or pro-inflammatory (M1) as well as the release of extracellular vesicles (EV). We aimed to characterize the effects of M0 and M1 macrophage-derived EV administration on post-ischaemic functional recovery and glucose metabolism using an isolated rat heart model of DCD. Isolated rat hearts were subjected to 20 min aerobic perfusion, followed by 27 min global, warm ischaemia or continued aerobic perfusion and 60 min reperfusion with or without intravascular administration of EV. Four experimental groups were compared: (1) no ischaemia, no EV; (2) ischaemia, no EV; (3) ischaemia with M0-macrophage-dervied EV; (4) ischaemia with M1-macrophage-derived EV. Post-ischaemic ventricular and metabolic recovery were evaluated. During reperfusion, ventricular function was decreased in untreated ischaemic and M1-EV hearts, but not in M0-EV hearts, compared to non-ischaemic hearts (p < 0.05). In parallel with the reduced functional recovery in M1-EV versus M0-EV ischaemic hearts, rates of glycolysis from exogenous glucose and oxidative metabolism tended to be lower, while rates of glycogenolysis and lactate release tended to be higher. EV from M0- and M1-macrophages differentially affect post-ischaemic cardiac recovery, potentially by altering glucose metabolism in a rat model of DCD. Targeted EV therapy may be a useful approach for modulating cardiac energy metabolism and optimizing graft quality in the setting of DCD.

The protective effect of 1400W against ischaemia and reperfusion injury is countered by transient medullary kidney endothelial dysregulation.

Renal ischaemia and reperfusion (I/R) is caused by a sudden temporary impairment of the blood flow. I/R is a prevalent cause of acute kidney injury. As nitric oxide generated by inducible nitric oxide synthase (iNOS) has detrimental effects during I/R, the pharmacological blockade of iNOS has been proposed as a potential strategy to prevent I/R injury. The aim of this study was to improve the understanding of 1400W (an iNOS inhibitor) on renal I/R as a pharmacological strategy against kidney disease. BALB/c mice received 30 min of bilateral ischaemia, followed by 48 h or 28 days of reperfusion. Vehicle or 1400W (10 mg/kg) was administered 30 min before inducing ischaemia. We found that after 48 h of reperfusion 1400W decreased the serum creatinine, blood urea nitrogen, neutrophil gelatinase-associated lipocalin and proliferating cell nuclear antigen 3 in the I/R animals. Unexpectedly, we observed mRNA upregulation of genes involved in kidney injury, cell-cycle arrest, inflammation, mesenchymal transition and endothelial activation in the renal medulla of sham animals treated with 1400W. We also explored if 1400W promoted chronic kidney dysfunction 28 days after I/R and did not find significant alterations in renal function, fibrosis, blood pressure or mortality. The results provide evidence that 1400W may have adverse effects in the renal medulla. Importantly, our data point to 1400W-induced endothelial dysfunction, establishing therapeutic limitations for its use. KEY POINTS: Acute kidney injury is a global health problem associated with high morbidity and mortality. The pharmacological blockade of inducible nitric oxide synthase (iNOS) has been proposed as a potential strategy to prevent AKI induced by ischaemia and reperfusion (I/R). Our main finding is that 1400W, a selective and irreversible iNOS inhibitor with low toxicity that is proposed as a therapeutic strategy to prevent kidney I/R injury, produces aberrant gene expression in the medulla associated to tissue injury, cell cycle arrest, inflammation, mesenchymal transition and endothelial activation. The negative effect of 1400W observed in the renal medulla at 48 h from drug administration, is transient as it did not translate into a chronic kidney disease condition.

Cathodal bilateral transcranial direct-current stimulation regulates selenium to confer neuroprotection after rat cerebral ischaemia-reperfusion injury.

Non-invasive transcranial direct-current stimulation (tDCS) is a safe ischaemic stroke therapy. Cathodal bilateral tDCS (BtDCS) is a modified tDCS approach established by us recently. Because selenium (Se) plays a crucial role in cerebral ischaemic injury, we investigated whether cathodal BtDCS conferred neuroprotection via regulating Se-dependent signalling in rat cerebral ischaemia-reperfusion (I/R) injury. We first showed that the levels of Se and its transport protein selenoprotein P (SEPP1) were reduced in the rat cortical penumbra following I/R, whereas cathodal BtDCS prevented the reduction of Se and SEPP1. Interestingly, direct-current stimulation (DCS) increased SEPP1 level in cultured astrocytes subjected to oxygen-glucose deprivation reoxygenation (OGD/R) but had no effect on SEPP1 level in OGD/R-insulted neurons, indicating that DCS may increase Se in ischaemic neurons by enhancing the synthesis and secretion of SEPP1 in astrocytes. We then revealed that DCS reduced the number of injured mitochondria in OGD/R-insulted neurons cocultured with astrocytes. DCS and BtDCS prevented the reduction of the mitochondrial quality-control signalling, vesicle-associated membrane protein 2 (VAMP2) and syntaxin-4 (STX4), in OGD/R-insulted neurons cocultured with astrocytes and the ischaemic brain respectively. Under the same experimental conditions, downregulation of SEPP1 blocked DCS- and BtDCS-induced upregulation of VAMP2 and STX4. Finally, we demonstrated that cathodal BtDCS increased Se to reduce infract volume following I/R. Together, the present study uncovered a molecular mechanism by which cathodal BtDCS confers neuroprotection through increasing SEPP1 in astrocytes and subsequent upregulation of SEPP1/VAMP2/STX4 signalling in ischaemic neurons after rat cerebral I/R injury. KEY POINTS: Cathodal bilateral transcranial direct-current stimulation (BtDCS) prevents the reduction of selenium (Se) and selenoprotein P in the ischaemic penumbra. Se plays a crucial role in cerebral ischaemia injury. Direct-current stimulation reduces mitochondria injury and blocks the reduction of vesicle-associated membrane protein 2 (VAMP2) and syntaxin-4 (STX4) in oxygen-glucose deprivation reoxygenation-insulted neurons following coculturing with astrocytes. Cathodal BtDCS regulates Se/VAMP2/STX4 signalling to confer neuroprotection after ischaemia.

Recurrence of ventricular fibrillation in out-of-hospital cardiac arrest: Clinical evidence and underlying ionic mechanisms.

Defibrillation remains the optimal therapy for terminating ventricular fibrillation (VF) in out-of-hospital cardiac arrest (OHCA) patients, with reported shock success rates of ∼90%. A key persistent challenge, however, is the high rate of VF recurrence (∼50-80%) seen during post-shock cardiopulmonary resuscitation (CPR). Studies have shown that the incidence and time spent in recurrent VF are negatively associated with neurologically-intact survival. Recurrent VF also results in the administration of extra shocks at escalating energy levels, which can cause cardiac dysfunction. Unfortunately, the mechanisms underlying recurrent VF remain poorly understood. In particular, the role of chest-compressions (CC) administered during CPR in mediating recurrent VF remains controversial. In this review, we first summarize the available clinical evidence for refibrillation occurring during CPR in OHCA patients, including the postulated contribution of CC and non-CC related pathways. Next, we examine experimental studies highlighting how CC can re-induce VF via direct mechano-electric feedback. We postulate the ionic mechanisms involved by comparison with similar phenomena seen in commotio cordis. Subsequently, the hypothesized contribution of partial cardiac reperfusion (either as a result of CC or CC independent organized rhythm) in re-initiating VF in a globally ischaemic heart is examined. An overview of the proposed ionic mechanisms contributing to VF recurrence in OHCA during CPR from a cellular level to the whole heart is outlined. Possible therapeutic implications of the proposed mechanistic theories for VF recurrence in OHCA are briefly discussed.

Jun-activated SOCS1 enhances ubiquitination and degradation of CCAAT/enhancer-binding protein ß to ameliorate cerebral ischaemia/reperfusion injury.

This study investigates the molecular mechanisms behind ischaemia/reperfusion (I/R) injury in the brain, focusing on neuronal apoptosis. It scrutinizes the role of the Jun proto-oncogene in apoptosis, involvement of SOCS1 in neural precursor cell accumulation in ischaemic regions, and the upregulation of C-EBPß in the hippocampus following I/R. Key to the study is understanding how Jun controls C-EBPß degradation via SOCS1, potentially offering new clinical treatment avenues for I/R. Techniques such as mRNA sequencing, KEGG enrichment analysis and protein-protein interaction (PPI) in mouse models have indicated involvement of Jun (AP-1) in I/R-induced cerebral damage. The study employs middle cerebral artery occlusion in different mouse models and oxygen-glucose deprivation/reoxygenation in cortical neurons to examine the impacts of Jun and SOCS1 manipulation on cerebral I/R injury and neuronal damage. The findings reveal that I/R reduces Jun expression in the brain, but its restoration lessens cerebral I/R injury and neuron death. Jun activates SOCS1 transcriptionally, leading to C-EBPß degradation, thereby diminishing cerebral I/R injury through the SOCS1/C-EBPß pathway. These insights provide a deeper understanding of post-I/R cerebral injury mechanisms and suggest new therapeutic targets for cerebral I/R injury. KEY POINTS: Jun and SOCS1 are poorly expressed, and C-EBPß is highly expressed in ischaemia/reperfusion mouse brain tissues. Jun transcriptionally activates SOCS1. SOCS1 promotes the ubiquitination-dependent C-EBPß protein degradation. Jun blunts oxygen-glucose deprivation/reoxygenation-induced neuron apoptosis and alleviates neuronal injury. This study provides a theoretical basis for the management of post-I/R brain injury.

Left ventricular global longitudinal strain and acute myocardial injury in patients with sickle cell disease admitted to the intensive care unit for vaso-occlusive crisis.

In patients with sickle cell disease (SCD), SCD-related cardiomyopathy may be partly due to repeated ischaemic events related to sickling during vaso-occlusive crises, but few clinical studies support this hypothesis. We evaluated the incidence of acute myocardial ischaemia during vaso-occlusive crises as assessed by the left ventricular global longitudinal strain (LVGLS) and high-sensitive cardiac troponin T (hs-cTnT). We included adult patients with SCD admitted to the intensive care unit (ICU) for vaso-occlusive crisis. We collected hs-cTnT and measured LVGLS with echocardiography at admission (day 1), day 2, day 3 and ICU discharge. Among 55 patients included, considering only the first hospitalization of patients admitted several times, 3 (5%) had elevated hs-cTnT at ≥1 time point of the ICU stay. It was ≤2 times the upper limit of normal in two of these patients. LVGLS was altered at ≥1 time point of the ICU stay in 13 (24%) patients. Both hs-cTnT and LVGLS were abnormal at ≥1 time point of the hospital stay in 2 (4%) patients. Acute myocardial injury as assessed by troponin elevation and LVGLS impairment was a rare event during vaso-occlusive crises.

The impact of fingolimod on Treg function in brain ischaemia.

Fingolimod has generally shown neuroprotective effects in stroke models. Here, we tested the hypothesis that fingolimod modulates T-cell cytokine production towards a regulatory phenotype. Second, we investigated how fingolimod altered the Treg suppressive function and the sensitivity of effector T cells to regulation. Mice that had underwent the permanent electrocoagulation of the left middle cerebral artery received saline or fingolimod (0.5 mg/kg) daily for 10-days post-ischaemia. Fingolimod improved neurobehavioural recovery compared to saline control and increased Treg frequency in the periphery and brain. Tregs from fingolimod-treated animals had a higher expression of CCR8. Fingolimod increased the frequencies of CD4+ IL-10+ , CD4+ IFN-γ+ and CD4+ IL-10+ IFN-γ+ cells in spleen and blood, and CD4+ IL-17+ cells in the spleen, with only minor effects on CD8+ T-cell cytokine production. Treg from post-ischaemic mice had reduced suppressive function compared to Treg from non-ischaemic mice. Fingolimod treatment rescued this function against saline-treated but not fingolimod-treated CD4+ effector T cells. In conclusion, fingolimod seems to improve the suppressive function of Treg post-stroke while also increasing the resistance of CD4+ effector cells to this suppression. Fingolimod's capacity to increase both effector and regulatory functions may explain the lack of consistent improvement in functional recovery in experimental brain ischaemia.

Recent insights into the effect of endoplasmic reticulum stress in the pathophysiology of intestinal ischaemia‒reperfusion injury.

Intestinal ischaemia‒reperfusion (I/R) injury is a surgical emergency. This condition is associated with a high mortality rate. At present, there are limited number of efficient therapeutic measures for this injury, and the prognosis is poor. Therefore, the pathophysiological mechanisms of intestinal I/R injury must be elucidated to develop a rapid and specific diagnostic and treatment protocol. Numerous studies have indicated the involvement of endoplasmic reticulum (ER) stress in the development of intestinal I/R injury. Specifically, the levels of unfolded and misfolded proteins in the ER lumen are increased due to unfolded protein response. However, persistent ER stress promotes apoptosis of intestinal mucosal epithelial cells through three signalling pathways in the ER, impairing intestinal mucosal barrier function and leading to the dysfunction of intestinal tissues and distant organ compartments. This review summarises the mechanisms of ER stress in intestinal I/R injury, diagnostic indicators, and related treatment strategies with the objective of providing novel insights into future therapies for this condition.

The role of deubiquitinases in cardiac disease.

Deubiquitinases are a group of proteins that identify and digest monoubiquitin chains or polyubiquitin chains attached to substrate proteins, preventing the substrate protein from being degraded by the ubiquitin-proteasome system. Deubiquitinases regulate cellular autophagy, metabolism and oxidative stress by acting on different substrate proteins. Recent studies have revealed that deubiquitinases act as a critical regulator in various cardiac diseases, and control the onset and progression of cardiac disease through a board range of mechanism. This review summarizes the function of different deubiquitinases in cardiac disease, including cardiac hypertrophy, myocardial infarction and diabetes mellitus-related cardiac disease. Besides, this review briefly recapitulates the role of deubiquitinases modulators in cardiac disease, providing the potential therapeutic targets in the future.