Is autophagy in response to ischemia and reperfusion protective or detrimental for the heart?

Autophagy is a catabolic process that degrades long-lived proteins and damaged organelles by sequestering them into double membrane structures termed "autophagosomes" and fusing them with lysosomes. Autophagy is active in the heart at baseline and further stimulated under stress conditions including starvation, ischemia/reperfusion, and heart failure. It plays an adaptive role in the heart at baseline, thereby maintaining cardiac structure and function and inhibiting age-related cardiac abnormalities. Autophagy is activated by ischemia and nutrient starvation in the heart through Sirt1-FoxO- and adenosine monophosphate (AMP)-activated protein kinase (AMPK)-dependent mechanisms, respectively. Activation of autophagy during ischemia is essential for cell survival and maintenance of cardiac function. Autophagy is strongly activated in the heart during reperfusion after ischemia. Activation of autophagy during reperfusion could be either protective or detrimental, depending on the experimental model. However, strong induction of autophagy accompanied by robust upregulation of Beclin1 could cause autophagic cell death, thereby proving to be detrimental. This review provides an overview regarding both protective and detrimental functions of autophagy in the heart and discusses possible applications of current knowledge to the treatment of heart disease.

An alternative mitophagy pathway mediated by Rab9 protects the heart against ischemia.

Energy stress, such as ischemia, induces mitochondrial damage and death in the heart. Degradation of damaged mitochondria by mitophagy is essential for the maintenance of healthy mitochondria and survival. Here, we show that mitophagy during myocardial ischemia was mediated predominantly through autophagy characterized by Rab9-associated autophagosomes, rather than the well-characterized form of autophagy that is dependent on the autophagy-related 7 (Atg) conjugation system and LC3. This form of mitophagy played an essential role in protecting the heart against ischemia and was mediated by a protein complex consisting of unc-51 like kinase 1 (Ulk1), Rab9, receptor-interacting serine/thronine protein kinase 1 (Rip1), and dynamin-related protein 1 (Drp1). This complex allowed the recruitment of trans-Golgi membranes associated with Rab9 to damaged mitochondria through S179 phosphorylation of Rab9 by Ulk1 and S616 phosphorylation of Drp1 by Rip1. Knockin of Rab9 (S179A) abolished mitophagy and exacerbated the injury in response to myocardial ischemia, without affecting conventional autophagy. Mitophagy mediated through the Ulk1/Rab9/Rip1/Drp1 pathway protected the heart against ischemia by maintaining healthy mitochondria.

Soluble TNF receptors prevent apoptosis in infiltrating cells and promote ventricular rupture and remodeling after myocardial infarction.

OBJECTIVE: Tumor necrosis factor (TNF)-alpha induced in damaged myocardium has been considered to be cardiotoxic. However, the negative results of RENEWAL and ATTACH prompt us to reconsider the role of TNF-alpha in cardiovascular diseases. The present study aimed to evaluate the effects of soluble TNF receptor treatment on myocardial infarction (MI). METHODS: An adenovirus encoding a 55-kDa TNF receptor-IgG fusion protein (AdTNFR1) was used to neutralize TNF-alpha, and an adenovirus encoding LacZ (AdLacZ) served as control. In the pre-MI treatment protocol, mice were given an intravenous injection of AdTNFR1 or AdLacZ 1 week before left coronary artery ligation to induce MI. In the post-MI treatment protocol, mice were treated with AdTNFR1 or AdLacZ 1 week after left coronary ligation. RESULTS: Treatment with AdTNFR1 neutralized bioactivity of TNF-alpha that was activated after MI and prevented apoptosis of infiltrating cells in infarct myocardium. However, pre-MI treatment with AdTNFR1 promoted ventricular rupture by reducing fibrosis with further activation of matrix metalloproteinase (MMP)-9. Post-MI treatment with AdTNFR1 exacerbated ventricular dysfunction and remodeling, with enhanced fibrosis of non-infarct myocardium with further MMP-2 activation. CONCLUSIONS: Both pre- and post-MI treatments with AdTNFR1 were deleterious in a mouse MI model. Thus, TNF-alpha may play not only toxic but also protective roles in MI.

Blockade of NF-kappaB improves cardiac function and survival without affecting inflammation in TNF-alpha-induced cardiomyopathy.

OBJECTIVE: NF-kappaB, a key transcription factor that regulates inflammatory processes, has been shown to be activated in the failing human heart with enhanced expression of proinflammatory cytokines. In the present study, we assessed the hypothesis that cardiotoxic effects of proinflammatory cytokines are mediated by the activation of NF-kappaB. METHODS: Transgenic mice with cardiac-specific overexpression of TNF-alpha were used as a model of cytokine-induced cardiomyopathy. To block the activation of NF-kappaB, transgenic mice (TG/p50(+/+)) were crossed with knockout mice in which the p50 subunit of NF-kappaB was disrupted (WT/p50(-/-)). RESULTS: The electrophoretic mobility shift assay demonstrated that NF-kappaB was activated in the myocardium of TG/p50(+/+) mice, while it was completely abolished in TG/p50(-/-) mice. Male TG mice died of congestive heart failure earlier than females, where the disruption of the p50 subunit significantly improved the survival. Compared with TG/p50(+/+) mice, TG/p50(-/-) mice showed a significant reduction of ventricular dilatation and hypertrophy with preserved fractional shortening. Although the myocardial expression of proinflammatory cytokines or infiltration of inflammatory cells was not affected, increased expression and activity of MMP-9 were significantly suppressed in TG/p50(-/-) mice. CONCLUSION: Blockade of NF-kappaB activation did not ameliorate myocardial inflammation but improved cardiac function and survival in male TNF-alpha TG mice. An inhibition of NF-kappaB may be a new therapeutic strategy for cardiac remodeling and heart failure, especially when proinflammatory cytokines are activated.

Blockade of NF-kappaB ameliorates myocardial hypertrophy in response to chronic infusion of angiotensin II.

OBJECTIVE: Nuclear factor (NF)-kappaB is a key transcription factor that regulates inflammatory processes. In the present study, we assessed the hypothesis that blockade of NF-kappaB may ameliorate ventricular hypertrophy in response to chronic infusion of angiotensin II. METHODS: Mice with targeted disruption of the p50 subunit of NF-kappaB (KO) were used to block the activation of NF-kappaB. Male KO and age-matched wild-type (WT) mice were chronically infused with angiotensin II at the rate of 0.2 (low dose) or 2 microg/kg/min (high dose) for 4 weeks. RESULTS: High- but not low-dose angiotensin II significantly increased systemic blood pressure and left ventricular weight in WT mice. In contrast, although the pressor response was slightly but significantly augmented, the hypertrophic effect of angiotensin II was significantly attenuated in KO mice. The attenuated hypertrophic responsiveness was confirmed histologically (cross-sectional area) and transcriptionally (atrial natriuretic peptide). Echocardiography revealed no evidence of cardiac dysfunction in angiotensin II-treated KO mice. Although phosphorylation of MAPKs, including ERK, JNK, or p38-MAPK, was not affected after 4 weeks of angiotensin II treatment in WT mice, phosphorylation of JNK was specifically abrogated in KO mice. Angiotensin II increased myocardial expression of proinflammatory cytokines and chemokines in WT mice, while expression of TNF-alpha and RANTES was paradoxically augmented in KO mice. CONCLUSION: Blockade of NF-kappaB activation attenuated myocardial hypertrophy without deteriorating cardiac function. NF-kappaB may play an important role in cardiac hypertrophy and remodeling besides promoting inflammation.

Tumor necrosis factor-alpha is toxic via receptor 1 and protective via receptor 2 in a murine model of myocardial infarction.

Tumor necrosis factor (TNF)-alpha induced in damaged myocardium has been considered to be cardiotoxic. TNF-alpha initiates its biological effects by binding two distinct receptors: R1 (p55) and R2 (p75). Although TNF-alpha has been shown to be cardiotoxic via R1-mediated pathways, little is known about the roles of R2-mediated pathways in myocardial infarction (MI). We created MI in R1 knockout (R1KO), R2KO, and wild-type (WT) mice by ligating the left coronary artery. Functional, histological, and biochemical analyses were performed 4 wk after ligation. Although infarct size was not different among WT, R1KO, and R2KO mice, post-MI survival was significantly improved in R1KO but not R2KO mice. R1KO significantly ameliorated contractile dysfunction after MI, whereas R2KO significantly exaggerated ventricular dilatation and dysfunction. Myocyte hypertrophy and interstitial fibrosis in noninfarct myocardium was exacerbated in R2KO but not in R1KO mice. Expression of R1, which was not affected by MI and was nullified in R1KO mice, was significantly upregulated in R2KO mice. In contrast, expression of R2, which was significantly upregulated by MI and was nullified in R2KO mice, was unaffected in R1KO mice. Meanwhile, TNF-alpha expression, which was significantly upregulated in noninfarct myocardium after MI, was not affected by R1KO or R2KO. However, transcript levels of IL-6, IL-1beta, transforming growth factor-beta, and monocyte chemotactic protein-1, which were significantly upregulated after MI, were significantly downregulated in R1KO mice. In contrast, transcript levels of IL-6 and IL-1beta were significantly further upregulated in R2KO mice. TNF-alpha is toxic via R1 and protective via R2 in a murine model of MI. Selective blockade of R1 may be a candidate therapeutic intervention for MI.

Blockade of NF-kappaB improves cardiac function and survival after myocardial infarction.

NF-kappaB is a key transcription factor that regulates inflammatory processes. In the present study, we tested the hypothesis that blockade of NF-kappaB ameliorates cardiac remodeling and failure after myocardial infarction (MI). Knockout mice with targeted disruption of the p50 subunit of NF-kappaB (KO) were used to block the activation of NF-kappaB. MI was induced by ligation of the left coronary artery in male KO and age-matched wild-type (WT) mice. NF-kappaB was activated in noninfarct as well as infarct myocardium in WT+MI mice, while the activity was completely abolished in KO mice. Blockade of NF-kappaB significantly reduced early ventricular rupture after MI and improved survival by ameliorating congestive heart failure. Echocardiographic and pressure measurements revealed that left ventricular fractional shortening and maximum rate of rise of left ventricular pressure were significantly increased and end-diastolic pressure was significantly decreased in KO+MI mice compared with WT+MI mice. Histological analysis demonstrated significant suppression of myocyte hypertrophy as well as interstitial fibrosis in the noninfarct myocardium of KO+MI mice. Blockade of NF-kappaB did not ameliorate expression of proinflammatory cytokines in infarct or noninfarct myocardium. In contrast, phosphorylation of c-Jun NH2-terminal kinase was almost completely abolished in KO+MI mice. The present study demonstrates that targeted disruption of the p50 subunit of NF-kappaB reduces ventricular rupture as well as improves cardiac function and survival after MI. Blockade of NF-kappaB might be a new therapeutic strategy to attenuate cardiac remodeling and failure after MI.