Erythropoietin protects post-ischemic hearts by preventing extracellular matrix degradation: role of Jak2-ERK pathway

Keratoconus patients exhibit a distinct ocular surface immune cell and inflammatory profile

Inflammatory factors have been considered to contribute to keratoconus (KC) pathogenesis. This study aims to determine the immune cells subsets and soluble inflammatory factor profile on the ocular surface of KC patients. 32 KC subjects (51 eyes) across different grades of severity and 15 healthy controls (23 eyes) were included in the study. Keratometry and pachymetry measurements were recorded. Ocular surface immune cells (collected by ocular surface wash) immunophenotyped using flow cytometry include leukocytes, neutrophils, macrophages, natural killer (NK) cells, pan-T cells, gamma delta T (γδT) cells and NKT cells. Tear fluid collected using Schirmer's strip was used to measure 50 soluble factors by multiplex ELISA. Proportions of activated neutrophils, NK cells and γδT cells were significantly increased in KC patients. Significantly higher levels of tear fluid IL-1β, IL-6, LIF, IL-17A, TNFα, IFNα/β/γ, EPO, TGFβ1, PDGF-BB, sVCAM, sL-selectin, granzyme-B, perforin, MMP2, sFasL and IgE, along with significantly lower levels of IL-1α and IL-9 were observed in KC patients. Alterations observed in few of the immuno-inflammatory parameters correlated with grades of disease, allergy, eye rubbing and keratometry or pachymetry measurements. The observation implies a distinct immuno-inflammatory component in KC pathogenesis and its potential as an additional therapeutic target in KC management.

Pleiotropic effect of erythropoiesis-stimulating agents on circulating endothelial progenitor cells in dialysis patients

BACKGROUND

Recent studies have suggested that erythropoiesis-stimulating agents (ESAs) may accelerate not only angiogenesis but also vasculogenesis, beyond erythropoiesis.

METHODS

We conducted a 12-week prospective study in 51 dialysis patients; 13 were treated with recombinant human erythropoietin (EPO, 5290.4 ± 586.9 IU/week), 16 with darbepoetin (DA, 42.9 ± 4.3 µg/week), 12 with epoetin β pegol (CERA, 40.5 ± 4.1 µg/week) and 10 with no ESAs. Vascular mediators comprising endothelial progenitor cells (EPCs), vascular endothelial growth factor (VEGF), matrix metalloproteinase-2 (MMP-2), and high-sensitivity C-reactive protein (hs-CRP) were measured at 0 and 12 weeks. EPCs were measured by flow cytometry as CD45^lowCD34⁺CD133⁺ cells.

RESULTS

The EPC count increased significantly to a greater extent in the EPO group than in the other three group, and increased significantly from 0 to 12 weeks in a EPO dose-dependent manner. In both the DA and CERA groups, the EPC count did not change at 12 weeks. Serum levels of VEGF, MMP-2 and hs-CRP were not affected by ESA treatment in all groups. In the CERA group, serum ferritin decreased significantly compared to the no-ESA group and correlated with CERA dose, although use of iron was permitted if required during the prospective study period of 12 weeks.

CONCLUSIONS

When patients on dialysis were treated with clinical doses of various ESAs, only EPO induced a significant increase of circulating EPCs from bone marrow, whereas, DA and CERA had no effect.

Novel application of amino-acid buffered solution for neuroprotection against ischemia/reperfusion injury

Ischemic neuron loss contributes to brain dysfunction in patients with cardiac arrest (CA). Histidine–tryptophan–ketoglutarate (HTK) solution is a preservative used during organ transplantation. We tested the potential of HTK to protect neurons from severe hypoxia (SH) following CA. We isolated rat primary cortical neurons and induced SH with or without HTK. Changes in caspase-3, hypoxia-inducible factor 1-alpha (HIF-1α), and nicotinamide adenine dinucleotide phosphate oxidase-4 (NOX4) expression were evaluated at different time points up to 72 h. Using a rat asphyxia model, we induced CA-mediated brain damage and then completed resuscitation. HTK or sterile saline was administered into the left carotid artery. Neurological deficit scoring and mortality were evaluated for 3 days. Then the rats were sacrificed for evaluation of NOX4 and H₂O₂ levels in blood and brain. In the in vitro study, HTK attenuated SH- and H₂O₂-mediated cytotoxicity in a volume- and time-dependent manner, associated with persistent HIF-1α expression and reductions in procaspase-3 activation and NOX4 expression. The inhibition of HIF-1α abrogated HTK’s effect on NOX4. In the in vivo study, neurological scores were significantly improved by HTK. H₂O₂ level, NOX4 activity, and NOX4 gene expression were all decreased in the brain specimens of HTK-treated rats. Our results suggest that HTK acts as an effective neuroprotective solution by maintaining elevated HIF-1α level, which was associated with inhibited procaspase-3 activation and decreased NOX4 expression.

Intra-artery infusion of recombinant human erythropoietin reduces blood-brain barrier disruption in rats following cerebral ischemia and reperfusion

OBJECTIVES

Intra-artery infusion of recombinant human erythropoietin (rhEPO) has recently been reported to confer neuroprotection against cerebral ischemia-reperfusion injury in animal models; however, the molecular mechanisms are still under investigation. The present study focused on the specific mechanism involved in blood-brain barrier (BBB) disruption.

METHODS

Thirty-six male and nine female Sprague Dawley rats were subjected to middle cerebral artery (MCA) occlusion to induce focal cerebral ischemia, and administrated rhEPO at a dose of 800 U/kg through MCA infusion at the beginning of reperfusion. Neurobehavioral deficits, brain edema, and infarct volume were evaluated after 2 h of ischemia and 24 h of reperfusion. BBB permeability was assessed by quantifying the extravasation of Evans blue (EB) dye. The expression of tight junction proteins and matrix metalloproteinases (MMPs) (Claudin-5, Occludin, MMP-2, and MMP-9) in microvessels were detected by immunofluorescence and western blot. The activities of MMPs in the cerebral microvessels were determined by gelatin zymography.

RESULTS

Treatment with rhEPO through the MCA strongly alleviated infarct volume, brain edema, and improved neurobehavioral outcomes in male and female rats. In addition, rhEPO remarkably suppressed the EB extravasation induced by brain ischemia. Furthermore, rhEPO prevented degradation of Claudin-5 and Occludin, and reduced the expression and activity of MMP-2 and MMP-9 in isolated brain microvessels.

CONCLUSIONS

Treatment with rhEPO through MCA infusion prevented brain edema formation and infarction through inhibition of MMP-mediated BBB disruption in acute ischemic stroke.

Activation of α1B-adrenoceptors contributes to intermittent hypobaric hypoxia-improved postischemic myocardial performance via inhibiting MMP-2 activation

Inhibition of matrix metalloproteinases-2 (MMP-2) activation renders cardioprotection from ischemia/reperfusion (I/R) injury; however, the signaling pathways involved have not been fully understood. Intermittent hypobaric hypoxia (IHH) has been shown to enhance myocardial tolerance to I/R injury via triggering intrinsic adaptive responses. Here we investigated whether IHH protects the heart against I/R injury via the regulation of MMP-2 and how the MMP-2 is regulated. IHH (Po2 = 84 mmHg, 4-h/day, 4 wk) improved postischemic myocardial contractile performance, lactate dehydrogenase (LDH) release, and infarct size in isolated perfused rat hearts. Moreover, IHH reversed I/R-induced MMP-2 activation and release, disorders in the levels of MMP-2 regulators, peroxynitrite (ONOO(-)) and tissue inhibitor of metalloproteinase-4 (TIMP-4), and loss of the MMP-2 targets α-actinin and troponin I. This protection was mimicked, but not augmented, by a MMP inhibitor doxycycline and lost by the α1-adrenoceptor (AR) antagonist prazosin. Furthermore, IHH increased myocardial α1A-AR and α1B-AR density but not α1D-AR after I/R. Concomitantly, IHH further enhanced the translocation of PKC epsilon (PKCε) and decreased the release of mitochondrial cytochrome c due to I/R via the activation of α1B-AR but not α1A-AR or α1D-AR. IHH-conferred cardioprotection in the postischemic contractile function, LDH release, MMP-2 activation, and nitrotyrosine as well as TIMP-4 contents were mimicked but not additive by α1-AR stimulation with phenylephrine and were abolished by an α1B-AR antagonist chloroethylclonidine and a PKCε inhibitor PKCε V1-2. These findings demonstrate that IHH exerts cardioprotection through attenuating excess ONOO(-) biosynthesis and TIMP-4 loss and sequential MMP-2 activation via the activation of α1B-AR/PKCε pathway.

Erythropoietin protects the systolic function of neonatal hearts against ischaemia/reperfusion injury

OBJECTIVES

The effect of erythropoietin (EPO) on neonatal hearts is not well understood. The current hypothesis is that EPO has protective effects against ischaemia-reperfusion when administered prior to ischaemia induction.

METHODS

Systolic and diastolic indices, as well as the Akt and extracellular-regulated kinase (Erk) signalling pathways, were studied in vivo using a neonatal pig heart model. Regional ischaemia was induced for 45 min by the ligation of the left anterior descending artery, followed by 90 min of reperfusion. The treatment groups consisted of: (i) untreated controls, (ii) treatment with EPO 3 min prior to ischaemia and (iii) treatment with EPO 24 h before ischaemia. Sophisticated myocardial contractility indices were assessed by pressure/volume loops of the left ventricle. The Akt and Erk pathways were evaluated via a western blot.

RESULTS

Elastance was found to be higher in the group receiving EPO 3 min prior to ischaemia. In addition, preload recruitable stroke work was higher for both groups receiving EPO prior to ischaemia when compared with controls. The time constant of the isovolumic relaxation and end-diastolic pressure-volume relationship did not differ between the three groups after 90 min of reperfusion. Furthermore, EPO treatment enhanced phosphorylation of Akt, but not Erk, and EPO-treated animals showed lower levels of apoptosis-related proteins.

CONCLUSIONS

EPO had a protective effect on neonatal systolic function after ischaemia/reperfusion injury, but no effect on diastolic function. This cardioprotective effect might be mediated by the activation of the Akt pathway.

Erythropoietin alleviates post-ischemic injury of rat hearts by attenuating nitrosative stress

AIMS

Nitrosative stress caused by ischemia contributes to poor functional recovery in hearts. A previous study showed that recombinant human erythropoietin (EPO) activates the Janus-tyrosine kinase 2/extracellular signal-regulated kinase (Jak2/ERK) pathway to protect myocardium against ischemia/reperfusion (IR) injury. However, it is not clear how pro-survival signals triggered by EPO affect the nitric oxide (NO) system in post-ischemic myocardial tissue.

MAIN METHODS

Isolated rat hearts were subjected to IR injury and changes in protein expression in the myocardium were evaluated by immunostaining.

KEY FINDINGS

Compared with untreated hearts, EPO-treated IR hearts showed significant improvements in contractility and reduced myocardial injury and infarction; this was associated with attenuated caspase-3 activation. Excess formation of NO metabolites and nitrotyrosine, which cause nitrosative stress, was markedly suppressed by EPO. The mechanism underlying EPO-mediated alleviation of nitrosative stress was related to an increase in arginase II expression and to the suppression of heat shock protein 90 (HSP90)-dependent upregulation of endothelial and inducible NO synthase (NOS). Myocardial EPO content was restored after EPO treatment, which in turn recruited signal transducer and activator of transcription (STAT) 3 protein and induced ERK signaling downstream of Jak2, which increased arginase II levels and suppressed HSP90 expression, respectively. Inhibition of STAT3 and ERK specifically reversed the effects of EPO on arginase II and HSP90 expression.

SIGNIFICANCE

These results indicate that EPO triggers the Jak2-STAT3/ERK pathway to restore the balance between arginase and NOS and, thus, reduces nitrosative stress. This may form the basis of myocardial protection following IR.

Effects of mesenchymal stem cells on matrix metalloproteinase synthesis in cardiac fibroblasts

Mesenchymal stem cell (MSC) transplantation has been known to decrease matrix metalloproteinase (MMP) synthesis in myocardium after myocardial infarction (MI) and improve ventricular remodeling; however, the underlying mechanisms are unclear. This study investigated the effects of MSC on MMP synthesis in cardiac fibroblasts (CFs) through paracrine actions. CFs were cultured under hypoxic (0.5% pO(2)) conditions for 24 h before co-culture with MSCs or hypoxia-preconditioned MSCs (H-MSCs) in transwell plates. CFs and MSCs/H-MSCs shared a medium with or without erythropoietin (EPO) neutralizing antibody (EPOAb) or EPO-soluble receptor (EPOsR). The results showed that protein expression and activity of MMP-2 and membrane type 1-MMP, but not MMP-9, in CFs were significantly increased in response to hypoxia and decreased after co-culture with MSCs or H-MSCs. Hypoxia up-regulated phosphorylation of extracellular signal-regulated kinase (ERK)1/2 of CFs which was down-regulated after CFs' co-culture with MSCs. Tissue inhibitors of metalloproteinases-1 (TIMP-1) in CFs was decreased after hypoxia and increased when co-cultured with MSCs or H-MSCs. Exogenous EPOAb or EPOsR partially inhibited MSCs' effect on MMP-2 expression and activity in CFs. The present findings suggested that MSCs influence MMP/TIMP expression in CFs via the ERK1/2 pathway and EPO acts as a key factor in the paracrine actions of MSCs.

Mechanism of cardioprotective effect of erythropoietin-induced preconditioning in rat heart

Objective:

The cardioprotective potential of human recombinant erythropoietin (alpha) (Epo) against ischemia-reperfusion-induced injury is well known. But, the underlying mechanisms are not well elucidated. The aim of this study was to characterize the mechanism involved in the cardioprotective effect of Epo-induced preconditioning in isolated rat heart.

Materials and Methods:

The heart was mounted on a Langendorff apparatus. After 10 min of stabilization, four cycles of ischemic preconditioning (IPC) were given followed by 30 min of global ischemia and 120 min of reperfusion. Epo preconditioning was induced by four cycles of 5-min perfusion of K-H solution containing Epo (1.0 U/ml) followed by 5 min perfusion with K-H solution. Myocardial infarct size was estimated macroscopically using the triphenyltetrazolium chloride staining technique. The extent of myocardial injury was measured by release of lactate dehydrogenase and creatine kinase-MB in the coronary effluent.

Results:

The present study demonstrates that Epo preconditioning was almost as effective as IPC. Administration of Wortmannin (100 nM), a PI-3K inhibitor, or Chelerythrine (1 µM), a protein kinase-C (PKC) inhibitor, or AG490 (5 µM), a JAK-2 inhibitor, significantly attenuated the cardioprotective effects of Epo-induced preconditioning.

Conclusion:

Our result suggest that the cardioprotective potential of Epo-induced preconditioning in isolated rat heart was due to an interplay of the JAK-2, PI-3K and PKC pathways. Inhibition of any one of the three pathways was sufficient to block the cardioprotective effect of Epo-induced preconditioning in isolated rat heart.

Tissue inhibitor of matrix metalloproteinase-1 mediates erythropoietin-induced neuroprotection in hypoxia ischemia

Previous studies have shown that erythropoietin (EPO) is neuroprotective in both in vivo and in vitro models of hypoxia ischemia. However these studies hold limited clinical translations because the underlying mechanism remains unclear and the key molecules involved in EPO-induced neuroprotection are still to be determined. This study investigated if tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) and its upstream regulator signaling molecule Janus kinase-2 (JAK-2) are critical in EPO-induced neuroprotection. Hypoxia ischemia (HI) was modeled in-vitro by oxygen and glucose deprivation (OGD) and in-vivo by a modified version of Rice-Vannucci model of HI in 10-day-old rat pups. EPO treated cells were exposed to AG490, an inhibitor of JAK-2 or TIMP-1 neutralizing antibody for 2h with OGD. Cell death, phosphorylation of JAK-2 and signal transducers and activators of transcription protein-3 (STAT-3), TIMP-1 expression, and matrix metalloproteinase-9 (MMP-9) activity were measured and compared with normoxic group. Hypoxic ischemic animals were treated one hour following HI and evaluated 48 h after. Our data showed that EPO significantly increased cell survival, associated with increased TIMP-1 activity, phosphorylation of JAK-2 and STAT-3, and decreased MMP-9 activity in vivo and in vitro. EPO's protective effects were reversed by inhibition of JAK-2 or TIMP-1 in both models. We concluded that JAK-2, STAT-3 and TIMP-1 are key mediators of EPO-induced neuroprotection during hypoxia ischemia injury.

Pyruvate-enriched cardioplegia suppresses cardiopulmonary bypass-induced myocardial inflammation

BACKGROUND

Cardiopulmonary bypass-induced oxidative stress initiates inflammation that can damage the myocardium. This study tested whether cardioplegia enriched with the intermediary metabolite and antioxidant pyruvate dampens postbypass myocardial inflammation.

METHODS

Pigs were maintained on cardiopulmonary bypass while their hearts were arrested for 60 minutes with 4:1 blood:crystalloid cardioplegia, in which the crystalloid contained 188 mM glucose ± 24 mM pyruvate. Pigs were weaned from bypass after 30 minutes of whole blood reperfusion and recovered for 4 hours. Glutathione (GSH) and glutathione disulfide (GSSG) were measured in coronary sinus plasma to indirectly monitor myocardial GSH redox state (GSH/GSSG). Left ventricular myocardium was sampled 4 hours after cardiopulmonary bypass for analyses of C-reactive protein, matrix metalloproteinases 2 and 9 and tissue inhibitor of metalloproteinase-2 (TIMP-2), and to assess neutrophil infiltration by histology and myeloperoxidase assay.

RESULTS

Coronary sinus GSH/GSSG fell 70% after cardiopulmonary bypass with control cardioplegia, but pyruvate cardioplegia produced a robust increase in coronary sinus GSH/GSSG that persisted for 4 hours after bypass. Myocardial C-reactive protein content increased 5.6-fold after control bypass, and neutrophil infiltration and myeloperoxidase activity also increased, but pyruvate-fortified cardioplegia prevented these inflammatory effects. Control cardioplegia lowered myocardial TIMP-2 content by 59% and increased matrix metalloproteinase-9 activity by 35% versus nonbypass sham values, but pyruvate cardioplegia increased TIMP-2 content ninefold versus control cardioplegia and prevented the increase in matrix metalloproteinase-9. Matrix metalloproteinase-2 was not affected by bypass ± pyruvate.

CONCLUSIONS

Pyruvate-enriched cardioplegia dampens cardiopulmonary bypass-induced myocardial inflammation. Increased GSH/GSSG and TIMP-2 may mediate pyruvate's effects.

Ginkgolide B preconditioning protects neurons against ischaemia-induced apoptosis

Ischaemic preconditioning (IP) has been reported to protect the brain against subsequent lethal ischaemia, but it has not been used clinically to prevent ischaemic injury because of safety concerns. The aim of the present study was to see whether Ginkgolide B (GB) is capable of preconditioning as IP to protect neurons against ischaemic injury; if so, which mechanism is involved. Cultured mouse cortical neurons at day 8 were pre-treated with GB (120 micromol/l) for 24 hrs or exposed to short-term ischaemia (1 hr) followed by 24-hr normal culture to induce IP before being treated with severe ischaemia (5 hrs). GB and IP significantly increased cell viability, expression of hypoxia-inducible factor-1 alpha (HIF-1alpha), erythropoietin (EPO), phosphorylated Bad at serine 136 (136p-Bad) and phosphorylated glycogen synthase kinase- 3beta at serine 9 (p-GSK-3beta), and decreased the percentage of apoptotic cells and the level of active caspase-3 in severely ischaemic neurons. Moreover, LY294002 that is a specific inhibitor of phosphatidylinositol 3-kinase (PI3K) significantly reduced the enhanced expression of HIF-1alpha, EPO and 136p-Bad induced by GB and IP. These results suggest that GB, like IP in neurons, is capable of preconditioning against ischaemia-induced apoptosis, the mechanism of which may involve the PI3K signalling pathway.

Dual effect of erythropoietin on liver protection and regeneration after subtotal hepatectomy in rats

The only currently offered curative option for many patients with primary or secondary liver tumors is the resection of hepatic tumors. The aim of this study was to evaluate the role of recombinant human erythropoietin (rhEPO) in liver protection and regeneration after subtotal hepatectomy in rats. Rats undergoing 70% hepatectomy received an intraperitoneal injection of saline (control) or rhEPO (4 U/g) 30 minutes prior to resection. Liver function was assessed by the measurement of the international normalized ratio (INR) levels, and hepatic injury was assessed by serum alanine aminotransferase and aspartate aminotransferase levels. Hepatic apoptosis was assessed by intrahepatic caspase-3 activity and morphological criteria. The regeneration capacity of remnant livers was assessed over 7 days with the regenerated liver/body weight ratio, immunohistochemistry markers of cell proliferation (Ki-67) and angiogenesis (von Willebrand factor), and phosphorylated extracellular signal-regulated kinase signaling. Two and 4 days after subtotal hepatectomy, the regenerated liver/body weight ratio was significantly higher in animals treated with rhEPO versus the control group (P < 0.005). Serum liver enzymes and INR levels on days 2 and 4 post-hepatectomy were significantly lower in animals pretreated with rhEPO in comparison with the control group (P < 0.005). No statistically significant difference was noted in intrahepatic hepatic caspase-3 activity, immunohistochemistry for caspase-3, or a terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assay between the hepatectomized groups. In the rhEPO-pretreated group, the mitotic index, Ki-67 and von Willebrand factor expression, and extracellular signal-regulated kinase activity were significantly higher on day 2 post-hepatectomy (P < 0.05) in comparison with the control group. In conclusion, rhEPO treatment may offer a unique beneficial dual-function strategy for hepatic protection and regeneration immediately after subtotal hepatectomy in rats.

Myocardial reperfusion injury management: erythropoietin compared with postconditioning

Ischemic postconditioning (IPost) and erythropoietin (EPO) have been shown to attenuate myocardial reperfusion injury using similar signaling pathways. The aim of this study was to examine whether EPO is as effective as IPost in decreasing postischemic myocardial injury in both Langendorff-isolated-heart and in vivo ischemia-reperfusion rat models. Rat hearts were subjected to 25 min ischemia, followed by 30 min or 2 h of reperfusion in the isolated-heart study. Rats underwent 45 min ischemia, followed by 24 h of reperfusion in the in vivo study. In both studies, the control group ( n = 12; ischemia-reperfusion only) was compared with IPost ( n = 16; 3 cycles of 10 s reperfusion/10 s ischemia) and EPO ( n = 12; 1,000 IU/kg) at the onset of reperfusion. The following resulted. First, in the isolated hearts, IPost or EPO significantly improved postischemic recovery of left ventricular developed pressure. EPO induced better left ventricular developed pressure than IPost at 30 min of reperfusion (73.18 ± 10.23 vs. 48.11 ± 7.92 mmHg, P < 0.05). After 2 h of reperfusion, the infarct size was significantly lower in EPO-treated hearts compared with IPost and control hearts (14.36 ± 0.60%, 19.11 ± 0.84%, and 36.21 ± 4.20% of the left ventricle, respectively; P < 0.05). GSK-3β phosphorylation, at 30 min of reperfusion, was significantly higher with EPO compared with IPost hearts. Phosphatidylinositol 3-kinase and ERK1/2 inhibitors abolished both EPO- and IPost-mediated cardioprotection. Second, in vivo, IPost and EPO induced an infarct size reduction compared with control (40.5 ± 3.6% and 28.9 ± 3.1%, respectively, vs. 53.7 ± 4.3% of the area at risk; P < 0.05). Again, EPO decreased significantly more infarct size and transmurality than IPost ( P < 0.05). In conclusion, with the use of our protocols, EPO showed better protective effects than IPost against reperfusion injury through higher phosphorylation of GSK-3β.

Erythropoietin to augment myocardial salvage induced by coronary thrombolysis in patients with ST segment elevation acute myocardial infarction

To determine whether the administration of erythropoietin (EPO) early after the onset of ischemia could enhance the preservation of jeopardized myocardium by reperfusion, 236 patients admitted <6 hours after the onset of chest pain indicative of acute coronary syndromes confirmed to be ST-segment elevation acute myocardial infarctions who were treated with tenecteplase to induce coronary thrombolysis were studied. Patients were randomized to standard care or standard care plus the administration of a single dose of EPO 30,000 IU intravenously immediately before the onset of treatment with tenecteplase. The primary end point was enzymatically estimated infarct size. The results indicated that infarct size index was virtually identical in the 2 groups, with a mean +/- SE of 13.2 +/- 0.1 creatine kinase-MB gram equivalents in controls and 12.4 +/- 0.9 creatine kinase-MB gram equivalents in patients treated with EPO. In conclusion, although the early administration of EPO was apparently safe, it did not enhance the preservation of jeopardized ischemic myocardium.

JAK redux: a second look at the regulation and role of JAKs in the heart

A number of type 1 receptor cytokine family members protect the heart from acute and chronic oxidative stress. This protection involves activation of two intracellular signaling cascades: the reperfusion injury salvage kinase (RISK) pathway, which entails activation of phosphatidylinositol 3-kinase (PI3-kinase) and ERK1/2, and JAK-STAT signaling, which involves activation of transcription factor signal transducer and activator of transcription 3 (STAT3). Obligatory for activation of both RISK and STAT3 by nearly all of these cytokines are the kinases JAK1 and JAK2. Yet surprisingly little is known about how JAK1 and JAK2 are regulated in the heart or how they couple to PI3-kinase activation. Although the JAKs are linked to antioxidative stress programs in the heart, we recently reported that these kinases are inhibited by oxidative stress in cardiac myocytes. In contrast, others have reported that cardiac JAK2 is activated by acute oxidative stress by an undefined process. Here we summarize recent insights into the regulation of JAK1 and JAK2. Besides oxidative stress, inhibitory regulation involves phosphorylation, nitration, and intramolecular restraints. Stimulatory regulation involves phosphorylation and adaptor proteins. The net effect of stress on JAK activity in the heart likely represents the sum of both inhibitory and stimulatory processes, along with their dynamic interaction. Thus the regulation of JAKs in the heart, once touted as the paragon of simplicity, is proving rather complicated indeed, requiring a second look. It is our contention that a better understanding of the regulation of this kinase family that is implicated in cardiac protection could translate into effective therapeutic strategies for preventing myocardial damage or repairing the injured heart.

Effects of recombinant human erythropoietin (rhEPO) on JAK2/STAT3 pathway and endothelial apoptosis in the rabbit basilar artery after subarachnoid hemorrhage

Previous studies have shown that recombinant human erythropoietin (rhEPO) can attenuate the degree of cerebral vasospasm following experimental subarachnoid hemorrhage (SAH). However, the mechanisms for this beneficial effect are still poorly understood. SAH-induced endothelial apoptosis may trigger, aggravate, and maintain cerebral vasospasm. We, therefore, tried to analyze whether rhEPO administration influenced the endothelial cell apoptosis in the basilar artery after SAH. Another aim of the current study was to investigate the modulation of rhEPO on the activity of Janus kinase 2 (JAK2) and signal transducer and activator of transcription 3 (STAT3), which played an important role in the signaling of apoptosis. A total of 48 rabbits were randomly divided into four groups; control group, SAH group, SAH+vehicle group, and SAH+rhEPO group. All SAH animals were subjected to injection of autologous blood into cisterna magna twice on day 0 and day 2. The rhEPO was administered i.p. starting 5 min after the induction of SAH on day 0 and repeated every 8 h for 120 h. The basilar arteries were extracted on day 5 after SAH. As a result, we found that administration of rhEPO could activate JAK2 and STAT3 in the basilar artery and decrease the apoptosis index of endothelial cells following SAH. Moreover, the anti-apoptotic genes such as bcl-2 and bcl-xL were up-regulated after the injections of rhEPO. In conclusion, the therapeutic effect of rhEPO on the subsequent vasospasm after SAH may relate to its inhibition on the endothelial apoptosis in the cerebral arteries, which may be mediated in part by JAK2/STAT3 signaling pathway.

Hypoxic preconditioning protects rat hearts against ischaemia-reperfusion injury: role of erythropoietin on progenitor cell mobilization

Preconditioning, such as by brief hypoxic exposure, has been shown to protect hearts against severe ischaemia. Here we hypothesized that hypoxic preconditioning (HPC) protects injured hearts by mobilizing the circulating progenitor cells. Ischaemia-reperfusion (IR) injury was induced by left coronary ligation and release in rats kept in room air or preconditioned with 10% oxygen for 6 weeks. To study the role of erythropoietin (EPO), another HPC + IR group was given an EPO receptor (EPOR) antibody via a subcutaneous mini-osmotic pump 3 weeks before IR induction. HPC alone gradually increased haematocrit, cardiac and plasma EPO, and cardiac vascular endothelial growth factor (VEGF) only in the first two weeks. HPC improved heart contractility, reduced ischaemic injury, and maintained EPO and EPOR levels in the infarct tissues of IR hearts, but had no significant effect on VEGF. Interestingly, the number of CD34(+)CXCR4(+) cells in the peripheral blood and their expression in HPC-treated hearts was higher than in control. Preconditioning up-regulated cardiac expression of stromal derived factor-1 (SDF-1) and prevented its IR-induced reduction. The EPOR antibody abolished HPC-mediated functional recovery, and reduced SDF-1, CXCR4 and CD34 expression in IR hearts, as well as the number of CD34(+)CXCR4(+) cells in blood. The specificity of neutralizing antibody was confirmed in an H9c2 culture system. In conclusion, exposure of rats to moderate hypoxia leads to an increase in progenitor cells in the heart and circulation. This effect is dependent on EPO, which induces cell homing by increased SDF-1/CXCR4 and reduces the heart susceptibly to IR injury.

Insulin—Blood Cardioplegia Decreases Matrix Metalloproteinase Activity in Ischaemia-reperfusion Injury during Coronary Artery Bypass Surgery

Reperfusion of myocardium during coronary bypass activates matrix metalloproteinases (MMPs) with changes occurring in the levels of tissue inhibitors of metalloproteinases (TIMPs) in the myocardium. This study investigated the effects of insulin-blood cardioplegia on MMP activity and TIMP levels during reperfusion. Non-diabetic patients undergoing coronary artery bypass graft with cardiopulmonary bypass were randomized into a control group ( n = 12) or an insulin group ( n = 12). Blood cardioplegia was used for both groups; insulin and glucose were added to the insulin group. Blood samples were obtained from the coronary sinus just before aortic cross clamping and after 1 and 30 min of reperfusion. Plasma proenzyme MMPs (proMMP-2 and −9) and TIMPs (TIMP-1 and TIMP-2) levels were measured. There were no differences between groups for MMP-2 and TIMP-2 levels. However, insulin diminished proMMP-9 activation, although some still occurred. TIMP-1 consumption lessened during reperfusion which, we conclude, was as a result of the diminished MMP activation. This is the first open heart surgery study in which diminished MMP activation was achieved via a metabolic change.

Deficiency of M2 muscarinic acetylcholine receptors increases susceptibility of ventricular function to chronic adrenergic stress

Suppressed parasympathetic nervous system (PSNS) function has been found in a variety of cardiovascular diseases, such as hypertension, heart failure, and diabetes. However, whether impaired PSNS function plays a significant role in ventricular dysfunction remains to be investigated. Cardiac regulation by the PSNS is primarily mediated by the M(2) muscarinic acetylcholine receptor (M(2)-AChR). In this study, we tested the hypothesis that lack of M(2)-AChR-mediated PSNS function may adversely impact cardiac ventricular function. Using M(2)-AChR knockout (KO) and wild-type (WT) mice, we found that the basal levels of heart rate and left ventricular function were similar in M(2)-AChR KO and WT mice. A bolus injection of isoproterenol (Iso) induced a greater increase in heart rate in M(2)-AChR KO mice than in WT mice. However, the responses of change in pressure over time (dP/dt) to Iso were similar in the two groups. After chronic infusion with Iso for 1 wk, the baseline values of left ventricular function were increased to similar extents in M(2)-AChR KO and WT mice. However, the M(2)-AChR KO mice exhibited impaired ventricular function, indicated as attenuated dP/dt and increased end-diastolic pressure, during an increase in cardiac afterload induced by a bolus injection of phenylephrine. Furthermore, chronic Iso infusion significantly increased matrix metalloproteinase (MMP) activity in the heart in M(2)-AChR KO mice. In primary culture of mixed neonatal rat cardiac fibroblast and cardiomyocytes, cotreatment with muscarinic agonist bethanechol reversed phenylephrine-induced increase in MMP-9 activation. These data suggest that M(2)-AChR may mediate an inhibitory regulation on MMP function. The overall results from this study suggest that M(2)-AChR-mediated PSNS function may provide cardiac protection. Lack of this protective mechanism will increase the susceptibility of the heart to cardiac stresses.