IKKβ stabilizes Mitofusin 2 and suppresses doxorubicin cardiomyopathy

AIMS

The mitochondrial dynamics protein Mitofusin 2 (MFN2) coordinates critical cellular processes including mitochondrial bioenergetics, quality control, and cell viability. The NF-κB kinase IKKβ suppresses mitochondrial injury in doxorubicin cardiomyopathy, but the underlying mechanism is undefined.

METHODS AND RESULTS

Herein, we identify a novel signalling axis that functionally connects IKKβ and doxorubicin cardiomyopathy to a mechanism that impinges upon the proteasomal stabilization of MFN2. In contrast to vehicle-treated cells, MFN2 was highly ubiquitinated and rapidly degraded by the proteasomal-regulated pathway in cardiac myocytes treated with doxorubicin. The loss of MFN2 activity resulted in mitochondrial perturbations, including increased reactive oxygen species (ROS) production, impaired respiration, and necrotic cell death. Interestingly, doxorubicin-induced degradation of MFN2 and mitochondrial-regulated cell death were contingent upon IKKβ kinase activity. Notably, immunoprecipitation and proximity ligation assays revealed that IKKβ interacted with MFN2 suggesting that MFN2 may be a phosphorylation target of IKKβ. To explore this possibility, mass spectrometry analysis identified a novel MFN2 phospho-acceptor site at serine 53 that was phosphorylated by wild-type IKKβ but not by a kinase-inactive mutant IKKβK-M. Based on these findings, we reasoned that IKKβ-mediated phosphorylation of serine 53 may influence MFN2 protein stability. Consistent with this view, an IKKβ-phosphomimetic MFN2 (MFN2S53D) was resistant to proteasomal degradation induced by doxorubicin whereas wild-type MFN2 and IKKβ-phosphorylation defective MFN2 mutant (MFNS53A) were readily degraded in cardiac myocytes treated with doxorubicin. Concordantly, gain of function of IKKβ or MFN2S53D suppressed doxorubicin-induced mitochondrial injury and cell death.

CONCLUSIONS

The findings of this study reveal a novel survival pathway for IKKβ that is mutually dependent upon and obligatory linked to the phosphorylation and stabilization of the mitochondrial dynamics protein MFN2.

Ellagic acid inhibits mitochondrial fission protein Drp-1 and cell proliferation in cancer

Anthracyclines such as doxorubicin (Dox) are widely used to treat a variety of adult and childhood cancers, however, a major limitation to many of these compounds is their propensity for inducing heart failure. A naturally occurring polyphenolic compound such as Ellagic acid (EA) has been shown by our laboratory to mitigate the cardiotoxic effects of Dox, however, the effects of EA on cancer cell viability have not been established. In this study, we explored the effects of EA alone and in combination with Dox on cancer cell viability and tumorigenesis. Herein, we show that EA induces cell cycle exit and reduces proliferation in colorectal cancer (HCT116) and breast adenocarcinoma cells (MCF7). We show that EA promotes cell cycle exit by a mechanism that inhibits mitochondrial dynamics protein Drp-1. EA treatment of HCT116 and MCF7 cells resulted in a hyperfused mitochondrial morphology that coincided with mitochondrial perturbations including loss of mitochondrial membrane potential, impaired respiratory capacity. Moreover, impaired mitochondrial function was accompanied by a reduction in cell cycle and proliferation markers, CDK1, Ki67, and Cyclin B. This resulted in a reduction in proliferation and widespread death of cancer cells. Furthermore, while Dox treatment alone promoted cell death in both HCT116 and MCF7 cancer cell lines, EA treatment lowered the effective dose of Dox to promote cell death. Hence, the findings of the present study reveal a previously unreported anti-tumor property of EA that impinges on mitochondrial dynamics protein, Drp-1 which is crucial for cell division and tumorigenesis. The ability of EA to lower the therapeutic threshold of Dox for inhibiting cancer cell growth may prove beneficial in reducing cardiotoxicity in cancer patients undergoing anthracycline therapy.

Proteasomal Degradation of TRAF2 Mediates Mitochondrial Dysfunction in Doxorubicin-Cardiomyopathy

BACKGROUND

Cytokines such as tumor necrosis factor-α (TNFα) have been implicated in cardiac dysfunction and toxicity associated with doxorubicin (DOX). Although TNFα can elicit different cellular responses, including survival or death, the mechanisms underlying these divergent outcomes in the heart remain cryptic. The E3 ubiquitin ligase TRAF2 (TNF receptor associated factor 2) provides a critical signaling platform for K63-linked polyubiquitination of RIPK1 (receptor interacting protein 1), crucial for nuclear factor-κB (NF-κB) activation by TNFα and survival. Here, we investigate alterations in TNFα-TRAF2-NF-κB signaling in the pathogenesis of DOX cardiotoxicity.

METHODS

Using a combination of in vivo (4 weekly injections of DOX 5 mg·kg-1·wk-1) in C57/BL6J mice and in vitro approaches (rat, mouse, and human inducible pluripotent stem cell-derived cardiac myocytes), we monitored TNFα levels, lactate dehydrogenase, cardiac ultrastructure and function, mitochondrial bioenergetics, and cardiac cell viability.

RESULTS

In contrast to vehicle-treated mice, ultrastructural defects, including cytoplasmic swelling, mitochondrial perturbations, and elevated TNFα levels, were observed in the hearts of mice treated with DOX. While investigating the involvement of TNFα in DOX cardiotoxicity, we discovered that NF-κB was readily activated by TNFα. However, TNFα-mediated NF-κB activation was impaired in cardiac myocytes treated with DOX. This coincided with loss of K63- linked polyubiquitination of RIPK1 from the proteasomal degradation of TRAF2. Furthermore, TRAF2 protein abundance was markedly reduced in hearts of patients with cancer treated with DOX. We further established that the reciprocal actions of the ubiquitinating and deubiquitinating enzymes cellular inhibitors of apoptosis 1 and USP19 (ubiquitin-specific peptidase 19), respectively, regulated the proteasomal degradation of TRAF2 in DOX-treated cardiac myocytes. An E3-ligase mutant of cellular inhibitors of apoptosis 1 (H588A) or gain of function of USP19 prevented proteasomal degradation of TRAF2 and DOX-induced cell death. Furthermore, wild-type TRAF2, but not a RING finger mutant defective for K63-linked polyubiquitination of RIPK1, restored NF-κB signaling and suppressed DOX-induced cardiac cell death. Last, cardiomyocyte-restricted expression of TRAF2 (cardiac troponin T-adeno-associated virus 9-TRAF2) in vivo protected against mitochondrial defects and cardiac dysfunction induced by DOX.

CONCLUSIONS

Our findings reveal a novel signaling axis that functionally connects the cardiotoxic effects of DOX to proteasomal degradation of TRAF2. Disruption of the critical TRAF2 survival pathway by DOX sensitizes cardiac myocytes to TNFα-mediated necrotic cell death and DOX cardiotoxicity.

NF-κB p65 Attenuates Cardiomyocyte PGC-1α Expression in Hypoxia

Hypoxia exerts broad effects on cardiomyocyte function and viability, ranging from altered metabolism and mitochondrial physiology to apoptotic or necrotic cell death. The transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) is a key regulator of cardiomyocyte metabolism and mitochondrial function and is down-regulated in hypoxia; however, the underlying mechanism is incompletely resolved. Using primary rat cardiomyocytes coupled with electrophoretic mobility shift and luciferase assays, we report that hypoxia impaired mitochondrial energetics and resulted in an increase in nuclear localization of the Nuclear Factor-κB (NF-κB) p65 subunit, and the association of p65 with the PGC-1α proximal promoter. Tumor necrosis factor α (TNFα), an activator of NF-κB signaling, similarly reduced PGC-1α expression and p65 binding to the PGC-1α promoter in a dose-dependent manner, and TNFα-mediated down-regulation of PGC-1α expression could be reversed by the NF-κB inhibitor parthenolide. RNA-seq analysis revealed that cardiomyocytes isolated from p65 knockout mice exhibited alterations in genes associated with chromatin remodeling. Decreased PGC-1α promoter transactivation by p65 could be partially reversed by the histone deacetylase inhibitor trichostatin A. These results implicate NF-κB signaling, and specifically p65, as a potent inhibitor of PGC-1α expression in cardiac myocyte hypoxia.

ULK1 mediated mitophagy prevents pathological cardiac remodelling and heart failure

The defects in mitochondrial clearance mechanisms can trigger adverse cardiac remodeling and severely impair cardiac performance. A new study identifies Ulk1/Rab9 mediated alternative mitophagy to be important for mitochondrial clearance in heart under pressure overload conditions. Moreover, the defects in ULK1 mediated alternative mitophagy resulted in accumulation of damaged mitochondria, severe hypertrophy, fibrosis, and cardiac dysfunction in response to TAC induced pressure overload. The findings highlight Ulk1/Rab9 mediated alternative mitophagy as a prominent mode of mitophagy and quality control in response to pressure overload hypertrophy.

Mitochondrial autophagy and cell survival is regulated by the circadian Clock gene in cardiac myocytes during ischemic stress

Cardiac function is highly reliant on mitochondrial oxidative metabolism and quality control. The circadian Clock gene is critically linked to vital physiological processes including mitochondrial fission, fusion and bioenergetics; however, little is known of how the Clock gene regulates these vital processes in the heart. Herein, we identified a putative circadian CLOCK-mitochondrial interactome that gates an adaptive survival response during myocardial ischemia. We show by transcriptome and gene ontology mapping in CLOCK Δ19/Δ19 mouse that Clock transcriptionally coordinates the efficient removal of damaged mitochondria during myocardial ischemia by directly controlling transcription of genes required for mitochondrial fission, fusion and macroautophagy/autophagy. Loss of Clock gene activity impaired mitochondrial turnover resulting in the accumulation of damaged reactive oxygen species (ROS)-producing mitochondria from impaired mitophagy. This coincided with ultrastructural defects to mitochondria and impaired cardiac function. Interestingly, wild type CLOCK but not mutations of CLOCK defective for E-Box binding or interaction with its cognate partner ARNTL/BMAL-1 suppressed mitochondrial damage and cell death during acute hypoxia. Interestingly, the autophagy defect and accumulation of damaged mitochondria in CLOCK-deficient cardiac myocytes were abrogated by restoring autophagy/mitophagy. Inhibition of autophagy by ATG7 knockdown abrogated the cytoprotective effects of CLOCK. Collectively, our results demonstrate that CLOCK regulates an adaptive stress response critical for cell survival by transcriptionally coordinating mitochondrial quality control mechanisms in cardiac myocytes. Interdictions that restore CLOCK activity may prove beneficial in reducing cardiac injury in individuals with disrupted circadian CLOCK.Abbreviations: ARNTL/BMAL1: aryl hydrocarbon receptor nuclear translocator-like; ATG14: autophagy related 14; ATG7: autophagy related 7; ATP: adenosine triphosphate; BCA: bovine serum albumin; BECN1: beclin 1, autophagy related; bHLH: basic helix- loop-helix; CLOCK: circadian locomotor output cycles kaput; CMV: cytomegalovirus; COQ5: coenzyme Q5 methyltransferase; CQ: chloroquine; CRY1: cryptochrome 1 (photolyase-like); DNM1L/DRP1: dynamin 1-like; EF: ejection fraction; EM: electron microscopy; FS: fractional shortening; GFP: green fluorescent protein; HPX: hypoxia; i.p.: intraperitoneal; I-R: ischemia-reperfusion; LAD: left anterior descending; LVIDd: left ventricular internal diameter diastolic; LVIDs: left ventricular internal diameter systolic; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MFN2: mitofusin 2; MI: myocardial infarction; mPTP: mitochondrial permeability transition pore; NDUFA4: Ndufa4, mitochondrial complex associated; NDUFA8: NADH: ubiquinone oxidoreductase subunit A8; NMX: normoxia; OCR: oxygen consumption rate; OPA1: OPA1, mitochondrial dynamin like GTPase; OXPHOS: oxidative phosphorylation; PBS: phosphate-buffered saline; PER1: period circadian clock 1; PPARGC1A/PGC-1α: peroxisome proliferative activated receptor, gamma, coactivator 1 alpha; qPCR: quantitative real-time PCR; RAB7A: RAB7, member RAS oncogene family; ROS: reactive oxygen species; RT: room temperature; shRNA: short hairpin RNA; siRNA: small interfering RNA; TFAM: transcription factor A, mitochondrial; TFEB: transcription factor EB; TMRM: tetra-methylrhodamine methyl ester perchlorate; WT: wild -type; ZT: zeitgeber time.

Heterogeneous ozone effects on the DNA methylome of bronchial cells observed in a crossover study

We used a randomized crossover experiment to estimate the effects of ozone (vs. clean air) exposure on genome-wide DNA methylation of target bronchial epithelial cells, using 17 volunteers, each randomly exposed on two separated occasions to clean air or 0.3-ppm ozone for two hours. Twenty-four hours after exposure, participants underwent bronchoscopy to collect epithelial cells whose DNA methylation was measured using the Illumina 450 K platform. We performed global and regional tests examining the ozone versus clean air effect on the DNA methylome and calculated Fisher-exact p-values for a series of univariate tests. We found little evidence of an overall effect of ozone on the DNA methylome but some suggestive changes in PLSCR1, HCAR1, and LINC00336 DNA methylation after ozone exposure relative to clean air. We observed some participant-to-participant heterogeneity in ozone responses.

Hypoxia-induced downregulation of cyclooxygenase 2 leads to the loss of immunoprivilege of allogeneic mesenchymal stem cells

Allogeneic mesenchymal stem cells (MSCs) from young and healthy donors are reported to hold the potential to treat several immunological and degenerative disorders. However, recent data from animal studies and clinical trials demonstrate that immunogenicity and poor survival of transplanted MSCs impaired the efficacy of cells for regenerative applications. It is reported that initially immunoprivileged under in vitro conditions, MSCs are targeted by the host immune system after transplantation in the ischemic tissues in vivo. We performed in vitro (in MSCs) and in vivo (in the rat model of myocardial infarction [MI]) studies to elucidate the mechanisms responsible for the change in the immunophenotype of MSCs from immunoprivileged to immunogenic under ischemic conditions. We have recently reported that a soluble factor prostaglandin E2 (PGE2) preserves the immunoprivilege of allogeneic MSCs. In the current study, we found that PGE2 levels, which were elevated during normoxia, decreased in MSCs following exposure to hypoxia. Further, we found that proteasome-mediated degradation of cyclooxygenase-2 (COX2, rate-limiting enzyme in PGE2 biosynthesis) in hypoxic MSCs is responsible for PGE2 decrease and loss of immunoprivilege of MSCs. While investigating the mechanisms of COX2 degradation in hypoxic MSCs, we found that in normoxic MSCs, COP9 signalosome subunit 5 (CSN5) binds to COX2 and prevents its degradation by the proteasome. However, exposure to hypoxia leads to a decrease in CSN5 levels and its binding to COX2, rendering COX2 protein susceptible to proteasome-mediated degradation. This subsequently causes PGE2 downregulation and loss of immunoprivilege of MSCs. Maintaining COX2 levels in MSCs preserves immunoprivilege in vitro and improves the survival of transplanted MSCs in a rat model of MI. These data provide novel mechanistic evidence that PGE2 is downregulated in hypoxic MSCs which is responsible for the post-transplantation rejection of allogeneic MSCs. Therefore, our data suggest that the new strategies that target CSN5-COX2 signaling may improve survival and utility of transplanted allogeneic MSCs in the ischemic heart.

Ageing-associated increase in SGLT2 disrupts mitochondrial/sarcoplasmic reticulum Ca2+ homeostasis and promotes cardiac dysfunction

The prevalence of death from cardiovascular disease is significantly higher in elderly populations; the underlying factors that contribute to the age‐associated decline in cardiac performance are poorly understood. Herein, we identify the involvement of sodium/glucose co‐transporter gene (SGLT2) in disrupted cellular Ca²⁺‐homeostasis, and mitochondrial dysfunction in age‐associated cardiac dysfunction. In contrast to younger rats (6‐month of age), older rats (24‐month of age) exhibited severe cardiac ultrastructural defects, including deformed, fragmented mitochondria with high electron densities. Cardiomyocytes isolated from aged rats demonstrated increased reactive oxygen species (ROS), loss of mitochondrial membrane potential and altered mitochondrial dynamics, compared with younger controls. Moreover, mitochondrial defects were accompanied by mitochondrial and cytosolic Ca²⁺ ([Ca²⁺]_i) overload, indicative of disrupted cellular Ca²⁺‐homeostasis. Interestingly, increased [Ca²⁺]_i coincided with decreased phosphorylation of phospholamban (PLB) and contractility. Aged‐cardiomyocytes also displayed high Na⁺/Ca²⁺‐exchanger (NCX) activity and blood glucose levels compared with young‐controls. Interestingly, the protein level of SGLT2 was dramatically increased in the aged cardiomyocytes. Moreover, SGLT2 inhibition was sufficient to restore age‐associated defects in [Ca²⁺]_i‐homeostasis, PLB phosphorylation, NCX activity and mitochondrial Ca²⁺‐loading. Hence, the present data suggest that deregulated SGLT2 during ageing disrupts mitochondrial function and cardiac contractility through a mechanism that impinges upon [Ca²⁺]_i‐homeostasis. Our studies support the notion that interventions that modulate SGLT2‐activity can provide benefits in maintaining [Ca²⁺]_i and cardiac function with advanced age.

Impaired NF-κB signalling underlies cyclophilin D-mediated mitochondrial permeability transition pore opening in doxorubicin cardiomyopathy

AIMS

The chemotherapy drug doxorubicin (Dox) is commonly used for treating a variety of human cancers; however, it is highly cardiotoxic and induces heart failure. We previously reported that the Bcl-2 mitochondrial death protein Bcl-2/19kDa interaction protein 3 (Bnip3), is critical for provoking mitochondrial perturbations and necrotic cell death in response to Dox; however, the underlying mechanisms had not been elucidated. Herein, we investigated mechanism that drives Bnip3 gene activation and downstream effectors of Bnip3-mediated mitochondrial perturbations and cell death in cardiac myocytes treated with Dox.

METHODS AND RESULTS

Nuclear factor-κB (NF-κB) signalling, which transcriptionally silences Bnip3 activation under basal states in cardiac myocytes was dramatically reduced following Dox treatment. This was accompanied by Bnip3 gene activation, mitochondrial injury including calcium influx, permeability transition pore (mPTP) opening, loss of nuclear high mobility group protein 1, reactive oxygen species production, and cell death. Interestingly, impaired NF-κB signalling in cells treated with Dox was accompanied by protein complexes between Bnip3 and cyclophilin D (CypD). Notably, Bnip3-mediated mPTP opening was suppressed by inhibition of CypD-demonstrating that CypD functionally operates downstream of Bnip3. Moreover, restoring IKKβ-NF-κB activity in cardiac myocytes treated with Dox suppressed Bnip3 expression, mitochondrial perturbations, and necrotic cell death.

CONCLUSIONS

The findings of the present study reveal a novel signalling pathway that functionally couples NF-κB and Dox cardiomyopathy to a mechanism that is mutually dependent upon and obligatorily linked to the transcriptional control of Bnip3. Our findings further demonstrate that mitochondrial injury and necrotic cell death induced by Bnip3 is contingent upon CypD. Hence, maintaining NF-κB signalling may prove beneficial in reducing mitochondrial dysfunction and heart failure in cancer patients undergoing Dox chemotherapy.

Abstract 734: NF-kB Signaling Regulates Mitochondrial Permeability Transition Pore Opening of Cardiac Myocytes via Cyclophilin D (CypD) Modulation

Nuclear Factor-κB (NF-κB) is ubiquitously present transcription factor that regulates a variety of cellular functions including cell survival. Herein, we show a critical role for NF-κB signaling in regulation of mitochondrial permeability transition pore opening (mPTP) of cardiac myocytes that involves cyclophilin D (CypD). Cardiac myocytes expressing a kinase defective form of IKKβ (IKK K-M ), the principle IKK required for NF-κB activation, displayed impaired NF-κB gene activity. Defects in NF-κB signaling coincided with an increase in mPTP opening and cell death. Interestingly, mPTP opening and cell death observed in the NF-κB defective cardiomyocytes was supressed by inhibition of mPTP modulator CypD, with cyclosporin A (CSA) or by siRNA knock down (CypDsiRNA), suggesting a link between mPTP regulation and NF-κB signaling. Earlier, we reported that doxorubicin (Dox) treatment resulted in severe ultra-structural defects including disrupted mitochondrial cristae and impaired respiration, increased mitochondrial calcium overload, mPTP opening and a widespread cell death. Interestingly, we observed a dramatic reduction in NF-κB signaling in cardiac myocytes treated with doxorubicin (18 Hrs), coupled with mitochondrial dysfunction including impaired respiration. Inhibition of CyPD suppressed doxorubicin induced cell death of cardiac myocytes. Finally restoration of NF-κB signaling in cardiac myocytes treated with doxorubicin by IKKβ, active kinase, suppressed mitochondrial calcium overload, mitochondrial perturbations, respiration and cell death. The data herein, provides the first direct evidence that impaired NF-κB signaling predispose Dox treated cardiac myocytes to cell death. Hence, interventions that preserve NF-κB survival signaling pathways in the heart may prove beneficial in reducing cardiac dysfunction and heart failure in cancer patients undergoing doxorubicin chemotherapy.

Ulk1/Rab9-mediated alternative mitophagy confers cardioprotection during energy stress

The heart relies on mitochondria-derived energy production for continuous contraction and relaxation; therefore, the maintenance of a pool of healthy mitochondria is essential for sustaining normal cardiac performance. Mitophagy serves as a critical process for maintaining mitochondrial quality control and involves the PTEN-induced kinase 1/Parkin (Pink1/Parkin) pathway and autophagosomes labeled with the autophagy proteins autophagy-related 7 (ATG) and light chain 3 (LC3). In this issue of the JCI, Saito and colleagues identify an alternative pathway for mitophagy that utilizes the serine/threonine protein kinase Unc-51-like kinase 1 (Ulk1) and the small GTPase Rab9 to clear damaged mitochondria independently of conventional autophagy proteins. Together, the results of this study reveal that Ulk1 phosphorylation of Rab9 at serine 179 is critical for alternative mitophagy and cardioprotection under energy stress conditions.

Assessment of safety and efficacy of an indigenous self-expandable fully covered esophageal metal stent for palliation of esophageal cancer

BACKGROUND

Patients with unresectable esophageal cancer require palliation for dysphagia. Placement of a self-expandable metal stent (SEMS) is the procedure of choice for palliation of dysphagia.

OBJECTIVE

To evaluate the safety and efficacy of an indigenous fully-covered SEMS in patients with esophageal cancer.

METHODS

Eligible patients with unresectable esophageal cancer requiring palliation for dysphagia were included in the study. An indigenous fully covered SEMS of appropriate length was placed under endoscopic and fluoroscopic guidance. Outcome measures assessed were adverse events and improvement in dysphagia.

RESULTS

Twenty one patients (mean age 57.71±13.14 years; 17 males) were included. After stenting, dysphagia score decreased from 3.2+0.4 to 0.35+0.74 at 4 weeks. Adverse events included retrosternal pain, respiratory distress and aspiration pneumonia in 12, 2 and 1 patients respectively. Five patients required repeat stenting due to stent migration in 4 (following radiotherapy in 3) and tumour ingrowth in 1. There was primary stent malfunction in one patient. The median survival of patients was 140 (76-199) days, which was higher in those who received radiotherapy.

CONCLUSION

The stent was reasonably safe and effective to relieve dysphagia due to unresectable esophageal cancer.

Ellagic acid antagonizes Bnip3-mediated mitochondrial injury and necrotic cell death of cardiac myocytes

The Bcl-2 protein Bnip3 is crucial for provoking oxidative injury to mitochondria following anthracycline treatment or ischemia-reperfusion injury. Herein, we investigate the effects of the polyphenolic compound ellagic acid (EA) on Bnip3 mediated mitochondrial injury and necrotic cell death in cardiac myocytes. In contrast to vehicle treated cardiomyocytes, Bnip3 was highly enriched in mitochondrial fractions of cardiac myocytes treated with the anthracycline doxorubicin or in cells subjected to hypoxia (HPX). Mitochondrial associated Bnip3 was accompanied by mPTP opening and loss of ∆Ψm. The dynamin related fission protein Drp-1 was phosphorylated (Drp1⁶¹⁶) and coincided with excessive mitochondrial fragmentation, mitophagy and necrosis in cardiac myocytes treated with doxorubicin or subjected to hypoxia. Moreover, knock-down of Bnip3 was sufficient to prevent mitochondrial fission and doxorubicin-induced cell death supporting the involvement of Bnip3 in doxorubicin cardiotoxity. Interestingly, mitochondrial associated Bnip3 in cells treated with doxorubicin was markedly reduced by EA. This resulted in significantly less mitochondrial fission and cell death. Notably, EA similarly suppressed mitochondrial injury and cell death induced by hypoxia or Bnip3 over-expression. Herein, we identify a novel signaling axis that operationally links EA and Bnip3 for suppression of cardiac cell death. We provide compelling new evidence that EA suppresses mitochondrial injury and necrotic cell death of cardiac myocytes by functionally abrogating Bnip3 activity. Hence, by suppressing mitochondrial injury induced by Bnip3, EA may provide a therapeutic advantage in reducing oxidative injury and cardiac dysfunction in cancer patients undergoing anthracycline treatment or individuals with ischemic cardiac stress.

Endoscopic and clinical responses to anti-tubercular therapy can differentiate intestinal tuberculosis from Crohn's disease

BACKGROUND

Differentiation between intestinal tuberculosis and Crohn's disease is difficult and may require therapeutic trial with anti-tubercular therapy in tuberculosis-endemic regions.

AIM

To evaluate the role of therapeutic trial with anti-tubercular therapy in patients with diagnostic confusion between intestinal tuberculosis and Crohn's disease.

METHODS

We performed retrospective-comparative (n = 288: 131 patients who received anti-tubercular therapy before being diagnosed as Crohn's disease and 157 intestinal tuberculosis patients) and prospective-validation study (n = 55 patients with diagnostic confusion of intestinal tuberculosis/Crohn's disease). Outcomes assessed were global symptomatic response and endoscopic mucosal healing.

RESULTS

In the derivation cohort, among those eventually diagnosed as Crohn's disease, global symptomatic response with anti-tubercular therapy was seen in 38% at 3 months and in 37% who completed 6 months of anti-tubercular therapy. Ninety-four per cent of intestinal tuberculosis patients showed global symptomatic response by 3 months. Endoscopic mucosal healing was seen in only 5% of patients with Crohn's disease compared with 100% of intestinal tuberculosis patients. In the validation cohort, all the patients with intestinal tuberculosis had symptomatic response and endoscopic mucosal healing after 6 months of anti-tubercular therapy. Among the patients with an eventual diagnosis of Crohn's disease, symptomatic response was seen in 64% at 2 months and in 31% who completed 6 months of anti-tubercular therapy, none had mucosal healing.

CONCLUSIONS

Disproportionately lower mucosal healing rate despite an overall symptom response with 6 months of anti-tubercular therapy in patients with Crohn's disease suggests a need for repeat colonoscopy for diagnosing Crohn's disease. Patients with intestinal tuberculosis showing significant symptomatic response after 2-3 months of anti-tubercular therapy, suggest that symptom persistence after a therapeutic trial of 3 months of anti-tubercular therapy may indicate the diagnosis of Crohn's disease.

PDK2-mediated alternative splicing switches Bnip3 from cell death to cell survival

Herein we describe a novel survival pathway that operationally links alternative pre-mRNA splicing of the hypoxia-inducible death protein Bcl-2 19-kD interacting protein 3 (Bnip3) to the unique glycolytic phenotype in cancer cells. While a full-length Bnip3 protein (Bnip3FL) encoded by exons 1-6 was expressed as an isoform in normal cells and promoted cell death, a truncated spliced variant of Bnip3 mRNA deleted for exon 3 (Bnip3Δex3) was preferentially expressed in several human adenocarcinomas and promoted survival. Reciprocal inhibition of the Bnip3Δex3/Bnip3FL isoform ratio by inhibiting pyruvate dehydrogenase kinase isoform 2 (PDK2) in Panc-1 cells rapidly induced mitochondrial perturbations and cell death. The findings of the present study reveal a novel survival pathway that functionally couples the unique glycolytic phenotype in cancer cells to hypoxia resistance via a PDK2-dependent mechanism that switches Bnip3 from cell death to survival. Discovery of the survival Bnip3Δex3 isoform may fundamentally explain how certain cells resist Bnip3 and avert death during hypoxia.

Abstract 24: Bnip3 Provokes ROS Production and Maladaptive Autophagy by Displacing Uncoupling Protein3 (UCP3) From Cytochrome c Oxidase of Respiration Chain Complex in Cardiotoxicity

Doxorubicin is known for its cardiotoxic effects and inducing cardiac failure, however, the underlying mechanisms remain cryptic. Earlier we established the inducible - death protein, Bcl-2-like Nineteen- Kilodalton- Interacting - Protein 3 (Bnip3) to be crucial for disrupting mitochondrial function and inducing cell death of cardiac myocytes. Whether Bnip3 underlies cardiotoxic effects of doxorubicin toxicity is unknown. Herein we demonstrate a novel signaling pathway that functionally links activation and preferential mitochondrial targeting of Bnip3 to the cardiotoxic properties of doxorubicin. Perturbations to mitochondria including increased calcium loading, ROS, loss of αΨm and mPTP opening were observed in cardiac myocytes treated with doxorubicin. In mitochondria, Bnip3 forms strong association with Cytochrome c oxidase subunit1 (COX1) of respiratory chain and displaces uncoupling protein 3 (UCP3) resulting in increased ROS production, decline in maximal and reserved respiration capacity and cell viability. Impaired mitochondrial function was accompanied by an accumulated increase in autophagosomes and necrosis demonstrated by increase release of LDH, cTnT and loss of nuclear High Mobility Group Protein 1 (HMGB-1) immunoreactivity. Interestingly, pharmacological or genetic inhibition of autophagy with 3-methyl adenine (3-MA), or Atg7 knock-down suppressed necrotic cell death induced by doxorubicin. Loss of function of Bnip3 restored UCP3-COX complexes, mitochondrial respiratory integrity and abrogated necrotic cell death induced by doxorubicin. Mice germ-line deficient for Bnip3 were resistant to doxorubicin cardiotoxicity displaying normal mitochondrial morphology, cardiac function and survival rates comparable to vehicle treated mice. The findings of the present study demonstrate that doxorubicin provokes maladaptive autophagy and necrotic cell death of ventricular myocytes that is mutually dependent and obligatorily linked to Bnip3.

Abstract 23: Disruption of TRAF2-TAK1-NF-κB Signaling Axis Triggers K-48 Linked Poly-Ubiquitylation of RIP1 and Necrotic Cell Death in Doxorubicin Cardiotoxicity

The anthracycline doxorubicin (Dox) is a highly effective anti-tumour agent, however, its use is limited by its severe cardiotoxic effects that manifests as heart failure. The decline in cardiac performance induced by doxorubicin remains poorly defined. A critical survival role for the canonical IKKβ -mTOR-NF-κB signaling pathway has been demonstrated in ventricular myocytes. In this report, we demonstrate that, Dox impairs IKKβ-mTOR- NF-κB signaling in ventricular myocytes accompanied by mitochondrial perturbations including mPTP, loss of mitochondrial membrane potential and ROS production. IKKβ- NF-κB signaling involves TRAF 2 mediated ligation of K63- ubiquitin chains to RIP1 (Receptor Interacting Protein 1) which serves as scaffold for recruitment of ubiquitylated Tak1 complexes and phosphorylation-dependent activation of IKKβ -NF-kB signaling. Interestingly, ventricular myocytes treated with dox demonstrated reduction in expression levels of TRAF2 and TAK1, in vivo and in vitro. This was accompanied by a decline in K63- and concomitant increase in K-48 linked polyubiquitination on RIP1, impaired NF-kB activation and necrotic cell death of cardiac myocytes. Interestingly, inhibiting the kinase activity of RIP1 with Necrostatin-1, (Nec1) suppressed necrotic cell injury induced by dox but not NF-kB activation. Concordant with these findings was a marked increase in necrotic cell death in cardiac myocytes defective for IKKB signaling or MEF cells deficient for p65 treated with dox. Notably, mitochondrial perturbations, including PT-pore opening , ROS production, calcium uptake, LDH, Tn(T) and HMGB-1 release and necrotic cell injury induced by dox were completely abrogated by restoring NF-kB signaling in cardiac myocytes or Nec-1. Herein, we provide novel evidence that K-48 linked poly ubiquitylation of RIP1 provides a functional switch that impairs NF-kB activation and signals necrosis in cells treated with dox. Interventions that modulate NF-kB activity may prove beneficial in mitigating the cardiotoxic effects of dox.