Cardioprotection by the transfer of coronary effluent from ischaemic preconditioned rat hearts: identification of cardioprotective humoral factors

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.

A potent and selective activator of large-conductance Ca2+-activated K+ channels induces preservation of mitochondrial function after hypoxia and reoxygenation by handling of calcium and transmembrane potential

AIMS

Ischaemic heart disease remains a significant cause of mortality globally. A pharmacological agent that protects cardiac mitochondria against oxygen deprivation injuries is welcome in therapy against acute myocardial infarction. Here, we evaluate the effect of large-conductance Ca2+-activated K+ channels (BKCa) activator, Compound Z, in isolated mitochondria under hypoxia and reoxygenation.

METHODS

Mitochondria from mice hearts were obtained by differential centrifugation. The isolated mitochondria were incubated with a BKCa channel activator, Compound Z, and subjected to normoxia or hypoxia/reoxygenation. Mitochondrial function was evaluated by measurement of O2 consumption in the complexes I, II, and IV in the respiratory states 1, 2, 3, and by maximal uncoupled O2 uptake, ATP production, ROS production, transmembrane potential, and calcium retention capacity.

RESULTS

Incubation of isolated mitochondria with Compound Z under normoxia conditions reduced the mitochondrial functions and induced the production of a significant amount of ROS. However, under hypoxia/reoxygenation, the Compound Z prevented a profound reduction in mitochondrial functions, including reducing ROS production over the hypoxia/reoxygenation group. Furthermore, hypoxia/reoxygenation induced a large mitochondria depolarization, which Compound Z incubation prevented, but, even so, Compound Z created a small depolarization. The mitochondrial calcium uptake was prevented by the BKCa activator, extruding the mitochondrial calcium present before Compound Z incubation.

CONCLUSION

The Compound Z acts as a mitochondrial BKCa channel activator and can protect mitochondria function against hypoxia/reoxygenation injury, by handling mitochondrial calcium and transmembrane potential.

Tat-heat shock protein 10 ameliorates age-related phenotypes by facilitating neuronal plasticity and reducing age-related genes in the hippocampus

We investigated the effects of heat shock protein 10 (HSP10) protein on memory function, hippocampal neurogenesis, and other related genes/proteins in adult and aged mice. To translocate the HSP10 protein into the hippocampus, the Tat-HSP10 fusion protein was synthesized, and Tat-HSP10, not HSP10, was successfully delivered into the hippocampus based on immunohistochemistry and western blotting. Tat-HSP10 (0.5 or 2.0 mg/kg) or HSP10 (control protein, 2.0 mg/kg) was administered daily to 3- and 21-month-old mice for 3 months, and observed the senescence maker P16 was significantly increased in aged mice and the treatment with Tat-HSP10 significantly decreased P16 expression in the hippocampus of aged mice. In novel object recognition and Morris water maze tests, aged mice demonstrated decreases in exploratory preferences, exploration time, distance moved, number of object contacts, and escape latency compared to adult mice. Treatment with Tat-HSP10 significantly improved exploratory preferences, the number of object contacts, and the time spent swimming in the target quadrant in aged mice but not adults. Administration of Tat-HSP10 increased the number of proliferating cells and differentiated neuroblasts in the dentate gyrus of adult and aged mice compared to controls, as determined by immunohistochemical staining for Ki67 and doublecortin, respectively. Additionally, Tat-HSP10 treatment significantly mitigated the reduction in sirtuin 1 mRNA level, N-methyl-D-aspartate receptor 1, and postsynaptic density 95 protein levels in the hippocampus of aged mice. In contrast, Tat-HSP10 treatment significantly increased sirtuin 3 protein levels in both adult and aged mouse hippocampus. These suggest that Tat-HSP10 can potentially reduce hippocampus-related aging phenotypes.

Effects of Intermittent Hypoxia on Cytokine Expression Involved in Insulin Resistance

Sleep apnea syndrome (SAS) is a prevalent disorder characterized by recurrent apnea or hypoxia episodes leading to intermittent hypoxia (IH) and arousals during sleep. Currently, the relationship between SAS and metabolic diseases is being actively analyzed, and SAS is considered to be an independent risk factor for the development and progression of insulin resistance/type 2 diabetes (T2DM). Accumulating evidence suggests that the short cycles of decreased oxygen saturation and rapid reoxygenation, a typical feature of SAS, contribute to the development of glucose intolerance and insulin resistance. In addition to IH, several pathological conditions may also contribute to insulin resistance, including sympathetic nervous system hyperactivity, oxidative stress, vascular endothelial dysfunction, and the activation of inflammatory cytokines. However, the detailed mechanism by which IH induces insulin resistance in SAS patients has not been fully revealed. We have previously reported that IH stress may exacerbate insulin resistance/T2DM, especially in hepatocytes, adipocytes, and skeletal muscle cells, by causing abnormal cytokine expression/secretion from each cell. Adipose tissues, skeletal muscle, and the liver are the main endocrine organs producing hepatokines, adipokines, and myokines, respectively. In this review, we focus on the effect of IH on hepatokine, adipokine, and myokine expression.

Remote ischemic preconditioning improves tissue oxygenation in a porcine model of controlled hemorrhage without fluid resuscitation

Remote ischemic preconditioning (RIPC) involves deliberate, brief interruptions of blood flow to increase the tolerance of distant critical organs to ischemia. This study tests the effects of limb RIPC in a porcine model of controlled hemorrhage without replacement therapy simulating an extreme field situation of delayed evacuation to definitive care. Twenty-eight pigs (47 ± 6 kg) were assigned to: (1) control, no procedure (n = 7); (2) HS = hemorrhagic shock (n = 13); and (3) RIPC + HS = remote ischemic preconditioning followed by hemorrhage (n = 8). The animals were observed for 7 h after bleeding without fluid replacement. Survival rate between animals of the RIPC + HS group and those of the HS group were similar (HS, 6 of 13[46%]-vs-RIPC + HS, 4 of 8[50%], p = 0.86 by Chi-square). Animals of the RIPC + HS group had faster recovery of mean arterial pressure and developed higher heart rates without complications. They also had less decrease in pH and bicarbonate, and the increase in lactate began later. Global oxygen delivery was higher, and tissue oxygen extraction ratio lower, in RIPC + HS animals. These improvements after RIPC in hemodynamic and metabolic status provide essential substrates for improved cellular response after hemorrhage and reduction of the likelihood of potentially catastrophic consequences of the accompanying ischemia.

Small Heat Shock Proteins HSP10 and HSP27 in the Left Ventricular Myocardium in Rats with Arterial Hypertension and Insulin-Dependent Diabetes Mellitus

We studied the expression of small heat shock proteins HSP10 and HSP27 in left ventricular cardiomyocytes in animals with arterial hypertension, insulin-dependent diabetes mellitus, and their combination. The experiment was performed on 38-week-old male Wistar-Kyoto and 38-57-week-old SHR (spontaneously hypertensive) rats. Insulin-dependent diabetes mellitus was modeled by single parenteral injection of streptozotocin (65 mg/kg). Expression of HSP10 and HSP27 in left ventricular cardiomyocytes was evaluated by immunohistochemical assay. It was found that the content of HSP10 in the left ventricular cardiomyocytes decreased in comparison with the control in case of isolated diabetes mellitus and, on the contrary, increased in case of arterial hypertension combined with diabetes mellitus. The intensity of HSP27 expression decreased in case of 38-week arterial hypertension and a combination of arterial hypertension with diabetes mellitus. However, in case of 57-week arterial hypertension we observed an increase in the content of HSP27 in cardiomyocytes.

New Cardiomyokine Reduces Myocardial Ischemia/Reperfusion Injury by PI3K-AKT Pathway Via a Putative KDEL-Receptor Binding

Background CDNF (cerebral dopamine neurotrophic factor) belongs to a new family of neurotrophic factors that exert systemic beneficial effects beyond the brain. Little is known about the role of CDNF in the cardiac context. Herein we investigated the effects of CDNF under endoplasmic reticulum-stress conditions using cardiomyocytes (humans and mice) and isolated rat hearts, as well as in rats subjected to ischemia/reperfusion (I/R). Methods and Results We showed that CDNF is secreted by cardiomyocytes stressed by thapsigargin and by isolated hearts subjected to I/R. Recombinant CDNF (exoCDNF) protected human and mouse cardiomyocytes against endoplasmic reticulum stress and restored the calcium transient. In isolated hearts subjected to I/R, exoCDNF avoided mitochondrial impairment and reduced the infarct area to 19% when administered before ischemia and to 25% when administered at the beginning of reperfusion, compared with an infarct area of 42% in the untreated I/R group. This protection was completely abrogated by AKT (protein kinase B) inhibitor. Heptapeptides containing the KDEL sequence, which binds to the KDEL-R (KDEL receptor), abolished exoCDNF beneficial effects, suggesting the participation of KDEL-R in this cardioprotection. CDNF administered intraperitoneally to rats decreased the infarct area in an in vivo model of I/R (from an infarct area of ≈44% in the I/R group to an infarct area of ≈27%). Moreover, a shorter version of CDNF, which lacks the last 4 residues (CDNF-ΔKTEL) and thus allows CDNF binding to KDEL-R, presented no cardioprotective activity in isolated hearts. Conclusions This is the first study to propose CDNF as a new cardiomyokine that induces cardioprotection via KDEL receptor binding and PI3K/AKT activation.

Effluent from ischemic preconditioned hearts confers cardioprotection independent of the number of preconditioning cycles

Coronary effluent collected from ischemic preconditioning (IPC) treated hearts induces myocardial protection in non-ischemic-preconditioned hearts. So far, little is known about the number of IPC cycles required for the release of cardioprotective factors into the coronary effluent to successfully induce cardioprotection. This study investigated the cardioprotective potency of effluent obtained after various IPC cycles in the rat heart. Experiments were performed on isolated hearts of male Wistar rats, mounted onto a Langendorff system and perfused with Krebs-Henseleit buffer. In a first part, effluent was taken before (Con) and after each IPC cycle (Eff 1, Eff 2, Eff 3). IPC was induced by 3 cycles of 5 min of global myocardial ischemia followed by 5 minutes of reperfusion. In a second part, hearts of male Wistar rats were randomized to four groups (each group n = 4–5) and underwent 33 min of global ischemia followed by 60 min of reperfusion. The previously obtained coronary effluent was administered for 10 minutes before ischemia as a preconditioning stimulus. Infarct size was determined at the end of reperfusion by triphenyltetrazoliumchloride (TTC) staining. Infarct size with control effluent was 54±12%. Effluent obtained after IPC confers a strong infarct size reduction independent of the number of IPC cycles (Eff 1: 27±5%; Eff 2: 35±7%; Eff 3: 35±8%, each P<0.05 vs. Con). Effluent extracted after one cycle IPC is comparably protective as after two or three cycles IPC.

Pre- and Post-Conditioning of the Heart: An Overview of Cardioprotective Signaling Pathways

Since the discovery of ischemic pre- and post-conditioning, more than 30 years ago, the knowledge about the mechanisms and signaling pathways involved in these processes has significantly increased. In clinical practice, on the other hand, such advancement has yet to be seen. This article provides an overview of ischemic pre-, post-, remote, and pharmacological conditioning related to the heart. In addition, we reviewed the cardioprotective signaling pathways and therapeutic agents involved in the above-mentioned processes, aiming to provide a comprehensive evaluation of the advancements in the field. The advancements made over the last decades cannot be ignored and with the exponential growth in techniques and applications. The future of pre- and post-conditioning is promising.

Myocardial ischaemia-reperfusion injury and cardioprotection in perspective

Despite the increasing use and success of interventional coronary reperfusion strategies, morbidity and mortality from acute myocardial infarction are still substantial. Myocardial infarct size is a major determinant of prognosis in these patients. Therefore, cardioprotective strategies aim to reduce infarct size. However, a perplexing gap exists between the many preclinical studies reporting infarct size reduction with mechanical and pharmacological interventions and the poor translation into better clinical outcomes in patients. This Review revisits the pathophysiology of myocardial ischaemia-reperfusion injury, including the role of autophagy and forms of cell death such as necrosis, apoptosis, necroptosis and pyroptosis. Other cellular compartments in addition to cardiomyocytes are addressed, notably the coronary microcirculation. Preclinical and clinical research developments in mechanical and pharmacological approaches to induce cardioprotection, and their signal transduction pathways, are discussed. Additive cardioprotective interventions are advocated. For clinical translation into treatments for patients with acute myocardial infarction, who typically are of advanced age, have comorbidities and are receiving several medications, not only infarct size reduction but also attenuation of coronary microvascular obstruction, as well as longer-term targets including infarct repair and reverse remodelling, must be considered to improve patient outcomes. Future clinical trials must focus on patients who really need adjunct cardioprotection, that is, those with severe haemodynamic alterations.

Remote ischemic preconditioning reduces myocardial ischemia-reperfusion injury through unacylated ghrelin-induced activation of the JAK/STAT pathway

Remote ischemic preconditioning (RIPC) offers cardioprotection against myocardial ischemia-reperfusion injury. The humoral factors involved in RIPC that are released from parasympathetically innervated organs have not been identified. Previous studies showed that ghrelin, a hormone released from the stomach, is associated with cardioprotection. However, it is unknown whether or not ghrelin is involved in the mechanism of RIPC. This study aimed to determine whether ghrelin serves as one of the humoral factors in RIPC. RIPC group rats were subjected to three cycles of ischemia and reperfusion for 5 min in two limbs before left anterior descending (LAD) coronary artery ligation. Unacylated ghrelin (UAG) group rats were given 0.5 mcg/kg UAG intravenously 30 min before LAD ligation. Plasma levels of UAG in all groups were measured before and after RIPC procedures and UAG administration. Additionally, JAK2/STAT3 pathway inhibitor (AG490) was injected in RIPC and UAG groups to investigate abolishment of the cardioprotection of RIPC and UAG. Plasma levels of UAG, infarct size and phosphorylation of STAT3 were compared in all groups. Infarct size was significantly reduced in RIPC and UAG groups, compared to the other groups. Plasma levels of UAG in RIPC and UAG groups were significantly increased after RIPC and UAG administration, respectively. The cardioprotective effects of RIPC and UAG were accompanied by an increase in phosphorylation of STAT3 and abolished by AG490. This study indicated that RIPC reduces myocardial ischemia and reperfusion injury through UAG-induced activation of JAK/STAT pathway. UAG may be one of the humoral factors involved in the cardioprotective effects of RIPC.

Cardioprotection by Humoral Factors Released After Remote Ischemic Preconditioning Depends on Anesthetic Regimen

OBJECTIVES

Remote ischemic preconditioning (RIPC) is a practicable and noninvasive method to protect the heart against ischemia reperfusion injury. Unfortunately results from clinical studies are not convincing. Propofol is suggested to be an inhibiting factor of cardioprotection by RIPC, but the underlying mechanism is still unknown. We investigated whether after RIPC the release of humoral factors and/or the direct cardioprotective effect at the myocardium is inhibited by propofol.

DESIGN

Randomized, prospective, blinded laboratory investigation.

SETTING

Experimental laboratory.

PATIENTS/SUBJECTS

Male Wistar rats.

INTERVENTIONS

Repetitive hind limb ischemia in rats-blood plasma transfers to isolated rat heart.

MEASUREMENTS AND MAIN RESULTS

In male Wistar rats (six groups, each n = 6/group), RIPC was induced by four cycles of 5 minutes bilateral hind limb ischemia alternately with 5 minutes of reperfusion. Blood samples were taken with (RIPC) and without RIPC (Con). Rats received continuous anesthesia with pentobarbital (Pento, 40 mg/kg body weight/hr) or propofol (Prop, 12 mg/kg body weight/hr), respectively. Cardioprotective properties of the blood plasma was investigated in the rat heart in vitro (six groups, each n = 6/group) perfused with Krebs-Henseleit buffer alone or with propofol (10 µM). Plasma was administered over 10 minutes before myocardial ischemia. All hearts underwent 33 minutes of global ischemia followed by 1 hour of reperfusion. At the end of the experiments, infarct size was determined by triphenyl-tetrazolium-chloride staining. RIPC plasma from pentobarbital anesthetized rats (Pento-RIPC) reduced infarct size from 64% (62-71%) (Pento-Con) to 34% (30-39%) (p < 0.0001). Infarct size with control plasma from propofol anesthetized rats was 59% (58-64%) (Prop-Con). RIPC plasma could not induce cardioprotection (Prop-RIPC: 63% [56-70%] ns vs Prop-Con). In contrast, RIPC plasma from pentobarbital anesthetized rats induced a significant infarct size reduction under propofol perfusion (Pento-RIPC: 34% [30-42%] vs Pento-Con: 54% [53-63%]; p < 0.0001).

CONCLUSIONS

Loss of cardioprotection by RIPC during propofol anesthesia depends on inhibition of release of humoral factors.

Exogenous 10 kDa-Heat Shock Protein Preserves Mitochondrial Function After Hypoxia/Reoxygenation

Humoral factors released during ischemic preconditioning (IPC) protect the myocardium against ischemia/reperfusion (I/R) injury. We have recently identified 10 kDa-heat shock protein (HSP10) and a fraction of small 5-10 kDa peptides (5-10-sP) in the coronary effluent of IPC-treated hearts and demonstrated their cardioprotective potential. We here used our isolated mitochondria model to characterize the impact of exogenous HSP10 and 5-10-sP on mitochondria function from myocardium subjected to I/R injury. Isolated perfused rat hearts were submitted to 30-min global ischemia and 10-min reperfusion. Before ischemia, isolated hearts were infused with saline or 5-10-sP, with or without a mitochondrial ATP-sensitive-K⁺-channel blocker (5HD 10 μmol·L^-1) or PKC inhibitor (chelerythrine 10 μmol·L^-1), before I/R. HSP10 (1 µmol·L^-1) was infused into isolated hearts before I/R without blockers. At 10-min reperfusion, the mitochondria were isolated and mitochondrial function was assessed. In a subset of experiments, freshly isolated mitochondria were directly incubated with HSP10 or 5-10-sP with or without 5HD or chelerythrine before in vitro hypoxia/reoxygenation. Infusion of 5-10-sP (n = 5) and HSP10 (n = 5) into isolated hearts before I/R improved mitochondrial ADP-stimulated respiration, ATP production and prevented mitochondrial ROS formation compared to the I/R group (n = 5); this effect was abrogated by 5HD and chelerythrine. In freshly isolated mitochondria with in vitro hypoxia/reoxygenation, HSP10 (n = 16) and 5-10-sP (n = 16) incubation prevented reductions of mitochondrial ADP-stimulated respiration (91.5 ± 5.1 nmol O2/min/mg PTN), ATP production (250.1 ± 9.3 μmol ATP/200μg PTN), and prevented mitochondrial ROS production (219.7 ± 9.0 nmol H2O2/200μg PTN) induced by hypoxia/reoxygenation (n = 12, 51.5 ± 5.0 nmol O2/min/mg PTN; 187 ± 21.7 μmol ATP/200 μg PTN; 339.0 ± 14.3 nmol H2O2/200 μg PTN, p < 0.001, respectively). 5HD reduced the ADP-stimulated respiration in the HSP10 group (65.84 ± 3.3 nmol O2/min/mg PTN), ATP production (193.7 ± 12.1 μmol ATP/200μg PTN) and increased ROS in the 5-10-sP group (274.4 ± 21.7 nmol H2O2/200 μg PTN). Mitochondria are a target of the cardioprotection induced by 5-10-sP and HSP10. This protection is dependent of PKC and mK_ATP activation. HSP10 can act directly on mitochondria and protects against hypoxia/reoxygenation injury by mK_ATP activation.

Remote Ischemic Conditioning in Acute Myocardial Infarction and Shock States

Remote ischemic conditioning is the phenomenon whereby brief, nonlethal episodes of ischemia in one organ (such as a limb) protect a remote organ from ischemic necrosis induced by a longer duration of severe ischemia followed by reperfusion. This phenomenon has been reproduced by dozens of experimental laboratories and was shown to reduce the size of myocardial infarction in many but not all clinical studies. In one recent large clinical trial, remote ischemic conditioning induced by repetitive blood pressure cuff inflations on the arm did not reduce infarct size or improve clinical outcomes. This negative result may have been related in part to the overall success of early reperfusion and current adjunctive therapies, such as antiplatelet therapy, antiremodeling therapies, and low-risk patients, that may make it difficult to show any advantage of newer adjunctive therapies on top of existing therapies. One relevant area in which current outcomes are not as positive as in the treatment of heart attack is the treatment of shock, where mortality rates remain high. Recent experimental studies show that remote ischemic conditioning may improve survival and organ function in shock states, especially hemorrhagic shock and septic shock. In this study, we review the preclinical studies that have explored the potential benefit of this therapy for shock states and describe an ongoing clinical study.

MKP1 overexpression reduces TNF-α-induced cardiac injury via suppressing mitochondrial fragmentation and inhibiting the JNK-MIEF1 pathways

Mitochondrial stress has been acknowledged as the pathogenesis for tumor necrosis factor-α (TNF-α)-induced septic cardiomyopathy. Recently, MAP kinase phosphatase 1 (MKP1) downregulation and mitochondrial fragmentation modulate the mitochondrial stress via multiple molecular mechanisms. Thereby, the goal of our current work is to figure out the functional role of mitochondrial fragmentation in TNF-α-induced septic cardiomyopathy. Our results exhibited that MKP1 expression was significantly repressed in hearts treated by TNF-α. Overexpression of MKP1 sustained cardiac function and attenuated cardiomyocytes death in TNF-α-treated hearts. At the molecular levels, decreased MKP1 induced mitochondrial stress, as indicated by mitochondrial calcium overloading, mitochondrial oxidative stress, mitochondrial antioxidant downregulation, mitochondrial membrane potential reduction, mitochondrial bioenergetics suppression, mitochondrial proapoptotic factors liberation, and caspase-9 apoptotic pathway activation. To the end, we illustrated that MKP1-modulated mitochondrial stress via mitochondrial fragmentation; reactivation of mitochondrial fragmentation abolished the protective effect of MKP1 overexpression on mitochondrial function. Further, MKP1 affected mitochondrial division in a mechanism through the JNK-MIEF1 axis. Blockade of JNK pathway abolished the regulatory actions of MKP1 on mitochondrial division. Altogether, our results identify MKP1 as a novel cardioprotective factor in TNF-α-related septic cardiomyopathy via affecting mitochondrial division by the way of JNK-MIEF1 signaling pathway. Therefore, MKP1 expression, mitochondrial fragmentation modification, and JNK-MIEF1 pathway modulation may be considered as potential therapeutic targets for the treatment of cardiac injury induced by sepsis.

A Review of Humoral Factors in Remote Preconditioning of the Heart

A humoral mechanism of cardioprotection by remote ischemic preconditioning (RIP) has been clearly demonstrated in various models of ischemia-reperfusion including upper and lower extremities, liver, and the mesenteric and renal arteries. A wide range of humoral factors for RIP have been proposed including hydrophobic peptides, opioid peptides, adenosine, prostanoids, endovanilloids, endocannabinoids, calcitonin gene-related peptide, leukotrienes, noradrenaline, adrenomedullin, erythropoietin, apolipoprotein, A-I glucagon-like peptide-1, interleukin 10, stromal cell-derived factor 1, and microRNAs. Virtually, all of the components of ischemic preconditioning's signaling pathway such as nitric oxide synthase, protein kinase C, redox signaling, PI3-kinase/Akt, glycogen synthase kinase β, ERK1/2, mitoK_ATP channels, Connexin 43, and STAT were all found to play a role. The signaling pattern also depends on which remote vascular bed was subjected to ischemia and on the time between applying the rip and myocardial ischemia occurs. Because there is convincing evidence for many seemingly diverse humoral components in RIP, the most likely explanation is that the overall mechanism is complex like that seen in ischemic preconditioning where multiple components are both in series and in parallel and interact with each other. Inhibition of any single component in the right circumstance may block the resulting protective effect, and selectively activating that component may trigger the protection. Identifying the humoral factors responsible for RIP might be useful in developing drugs that confer RIP's protection in a more comfortable and reliable manner.

LATS2 overexpression attenuates the therapeutic resistance of liver cancer HepG2 cells to sorafenib-mediated death via inhibiting the AMPK-Mfn2 signaling pathway

Background

Effective therapy for hepatocellular carcinoma (HCC) is currently an imperative issue, and sorafenib is a first-line drug for the treatment of HCC. However, the clinical benefit of sorafenib is often impaired by drug resistance. Accordingly, the present study was conducted to investigate the molecular mechanisms involving sorafenib resistance, with a focus on large tumor suppressor 2 (LATS2) and mitophagy.

Methods

HepG2 liver cancer cells were treated with sorafenib and infected with adenovirus-loaded LATS2 (Ad-LATS2). Cell death, proliferation and migration were measured via western blotting analysis, immunofluorescence and qPCR. Mitochondrial function and mitophagy were determined via western blotting and immunofluorescence.

Results

Our data indicated that LATS2 expression was repressed by sorafenib treatment, and overexpression of LATS2 could further enhance sorafenib-mediated apoptosis in HepG2 liver cancer cells. At the molecular level, mitochondrial stress was triggered by sorafenib treatment, as evidenced by decreased mitochondrial membrane potential, increased mitochondrial ROS production, more cyc-c release into the nucleus, and elevated mitochondrial pro-apoptotic proteins. However, in response to mitochondrial damage, mitophagy was activated by sorafenib treatment, whereas LATS2 overexpression effectively inhibited mitophagy activity and thus augmented sorafenib-mediated mitochondrial stress. Subsequently, we also demonstrated that the AMPK–MFN2 signaling pathway was involved in mitophagy regulation after exposure to sorafenib treatment and/or LATS2 overexpression. Inhibition of the AMPK pathway interrupted mitophagy and thus enhanced the antitumor property of sorafenib, similar to the results obtained via overexpression of LATS2.

Conclusions

Altogether, our findings revealed the importance of the LATS2/AMPK/MFN2/mitophagy axis in understanding sorafenib resistance mechanisms, with a potential application to increase the sensitivity response of sorafenib in the treatment of liver cancer.

Sepsis-related myocardial injury is associated with Mst1 upregulation, mitochondrial dysfunction and the Drp1/F-actin signaling pathway

LPS-induced septic cardiomyopathy has been found to be connected with mitochondrial stress through unknown mechanisms. Mitochondrial fission is an early event in mitochondrial dysfunction. The aim of our study was to determine the role and regulatory mechanism of mitochondrial fission in the progression of LPS-induced septic cardiomyopathy, with a particular focus on Mst1 and F-actin. Our data demonstrated that Mst1 expression was rapidly upregulated in LPS-treated hearts and that increased Mst1 promoted cardiomyocyte death by inducing mitochondrial stress. Mechanistically, elevated expression of Mst1 upregulated Drp1, and the latter initiated mitochondrial fission. Excessive mitochondrial fission caused mitochondrial oxidative injury, mitochondrial membrane potential reduction, mitochondrial proapoptotic element translocation into the cytoplasm/nucleus, mitochondrial energy dysfunction and mitochondrial apoptosis activation. Inhibition of mitochondrial fission sustained mitochondrial function and favored cardiomyocyte survival. Furthermore, we identified F-actin degradation as an apparent downstream event of mitochondrial fission activation in the context of LPS-induced septic cardiomyopathy. Stabilization of F-actin attenuated fission-mediated cardiomyocyte death. Altogether, our results define the Mst1/Drp1/mitochondrial fission/F-actin axis as a new signaling pathway that mediates LPS-related septic cardiomyopathy by inducing mitochondrial stress and cardiomyocyte death. Therefore, Mst1 expression, mitochondrial fission modification and F-actin stabilization may serve as potential therapeutic targets for sepsis-related myocardial injury.

Direct evidence that hypoxia triggers the cardioprotective response of ischemic preconditioning in a dog double-circuit cardiopulmonary bypass model

AIMS

It has been widely accepted that ischemic preconditioning (IPC) exhibits a promising and reproducible cardioprotective effect against ischemia/reperfusion (I/R) injury. However, the actual trigger that amplifies the molecular signaling and protects I/R heart is still unclear.

MAIN METHODS

To separate the factors involved in IPC, we established a dog double-circuit cardiopulmonary bypass (CPB) model, which consists of a systemic circuit and a coronary circuit. Forty-two male adult beagle dogs were randomly allocated into 7 groups: sham, I/R, IPC, hypoxia preconditioning (HPC), accumulated metabolite preconditioning (MPC), oxygenated or deoxygenated erythrocytes preconditioning (OxyEPC and DeoxyEPC). After pretreatment, dogs were subjected to 2 h-cardiac arrest and 2 h-reperfusion.

KEY FINDINGS

There were no differences in the cardiac function and hemodynamic parameters at baseline among groups. Like IPC, the hypoxia-related pretreatments HPC and DeoxyEPC improved post-arrest left ventricular systolic/diastolic performance and reduced pulmonary vascular resistance. The cardiac oxygen (O₂) utilization was also greatly elevated in these hypoxia-related pretreatment groups, as evidenced by increased cardiac O₂ consumption (VO₂) and O₂ extraction index (O₂EI) and suppressed lactate level. Besides, we did not observe improvement of these parameters in the MPC and OxyEPC groups. Further study indicated that these hypoxia-related pretreatments were associated with the attenuation of pro-inflammatory cytokines release and the elevation of complex I-supported mitochondrial respiration.

SIGNIFICANCE

With a dog double-circuit CPB model, we demonstrated that hypoxia is the actual trigger to initiate the cardioprotective effect of IPC in vivo, which was related to reduced cardiac inflammation and ameliorated complex-I supported mitochondrial function.