Lysophosphatidylserine induces necrosis in pressure overloaded male mouse hearts via G protein coupled receptor 34

Heart failure is a leading cause of mortality in developed countries. Cell death is a key player in the development of heart failure. Calcium-independent phospholipase A₂β (iPLA₂β) produces lipid mediators by catalyzing lipids and induces nuclear shrinkage in caspase-independent cell death. Here, we show that lysophosphatidylserine generated by iPLA₂β induces necrotic cardiomyocyte death, as well as contractile dysfunction mediated through its receptor, G protein-coupled receptor 34 (GPR34). Cardiomyocyte-specific iPLA₂β-deficient male mice were subjected to pressure overload. While control mice showed left ventricular systolic dysfunction with necrotic cardiomyocyte death, iPLA₂β-deficient mice preserved cardiac function. Lipidomic analysis revealed a reduction of 18:0 lysophosphatidylserine in iPLA₂β-deficient hearts. Knockdown of Gpr34 attenuated 18:0 lysophosphatidylserine-induced necrosis in neonatal male rat cardiomyocytes, while the ablation of Gpr34 in male mice reduced the development of pressure overload-induced cardiac remodeling. Thus, the iPLA₂β-lysophosphatidylserine-GPR34-necrosis signaling axis plays a detrimental role in the heart in response to pressure overload.

Rubicon-regulated beta-1 adrenergic receptor recycling protects the heart from pressure overload

Heart failure has high morbidity and mortality in the developed countries. Autophagy is important for the quality control of proteins and organelles in the heart. Rubicon (Run domain Beclin-1-interacting and cysteine-rich domain-containing protein) has been identified as a potent negative regulator of autophagy and endolysosomal trafficking. The aim of this study was to investigate the in vivo role of Rubicon-mediated autophagy and endosomal trafficking in the heart. We generated cardiomyocyte-specific Rubicon-deficient mice and subjected the mice to pressure overload by means of transverse aortic constriction. Rubicon-deficient mice showed heart failure with left ventricular dilatation, systolic dysfunction and lung congestion one week after pressure overload. While autophagic activity was unchanged, the protein amount of beta-1 adrenergic receptor was decreased in the pressure-overloaded Rubicon-deficient hearts. The increases in heart rate and systolic function by beta-1 adrenergic stimulation were significantly attenuated in pressure-overloaded Rubicon-deficient hearts. In isolated rat neonatal cardiomyocytes, the downregulation of the receptor by beta-1 adrenergic agonist was accelerated by knockdown of Rubicon through the inhibition of recycling of the receptor. Taken together, Rubicon protects the heart from pressure overload. Rubicon maintains the intracellular recycling of beta-1 adrenergic receptor, which might contribute to its cardioprotective effect.

Living alone and prediction of weight gain and overweight/obesity in university students: a retrospective cohort study

To assess the clinical impact of living alone on weight gain in university students. Participants: This retrospective cohort study included 17540 male and 8854 female university students admitted to a national university in Japan. Methods: An association between living arrangement and the incidence of weight gain ≥10% and overweight/obesity (body mass index (BMI) ≥25 kg/m²) was assessed using multivariable-adjusted Poisson regression models. Results: Weight gain was observed in 1889 (10.8%) male and 1516 (17.1%) female students during 3.0 and 2.9 years of the mean observational period, respectively. Living alone was identified as a significant predictor of weight gain (adjusted incidence rate ratio of living alone vs. living with family: 1.24 [1.13-1.36] and 1.76 [1.58-1.95] in male and female students, respectively) and was also as a predictor of overweight/obesity. Conclusions: University students living alone were at a significantly higher risk of weight gain and overweight/obesity than those living with family.

Iron derived from autophagy-mediated ferritin degradation induces cardiomyocyte death and heart failure in mice

Heart failure is a major public health problem, and abnormal iron metabolism is common in patients with heart failure. Although iron is necessary for metabolic homeostasis, it induces a programmed necrosis. Iron release from ferritin storage is through nuclear receptor coactivator 4 (NCOA4)-mediated autophagic degradation, known as ferritinophagy. However, the role of ferritinophagy in the stressed heart remains unclear. Deletion of Ncoa4 in mouse hearts reduced left ventricular chamber size and improved cardiac function along with the attenuation of the upregulation of ferritinophagy-mediated ferritin degradation 4 weeks after pressure overload. Free ferrous iron overload and increased lipid peroxidation were suppressed in NCOA4-deficient hearts. A potent inhibitor of lipid peroxidation, ferrostatin-1, significantly mitigated the development of pressure overload-induced dilated cardiomyopathy in wild-type mice. Thus, the activation of ferritinophagy results in the development of heart failure, whereas inhibition of this process protects the heart against hemodynamic stress.

Serum Klotho Levels Contribute to the Prevention of Disease Progression

BACKGROUND

Assessing the progression of a disorder from its pre-clinical state is important in the prevention of various diseases. In the present study, we evaluated the role of serum levels of αKlotho (αKl) in the progression of several pre-clinical disorders.

METHODS

This cohort study included 80 males who underwent their annual health checkup during the entry period between April 2005 and March 2008. Physical and biochemical parameters were obtained from all subjects. The associations of baseline serum levels of soluble αKl (sαKl) with the progression of the disorders were assessed in the study.

RESULTS

Baseline serum levels of sαKl were significantly lower in subjects developing a high fasting plasma glucose (FPG) level than in subjects not developing a high FPG level. Logistic multivariable analysis showed that baseline serum levels of sαKl and FPG levels significantly associated with a high FPG level progression. It is suggested that low sαKl levels are associated with the progression of hyperglycemia. Evaluation of serum levels of sαKl in subjects with multiple disorders revealed that those with more pre-clinical disorders progression tended to show lower sαKl levels.

CONCLUSION

A decrease in serum levels of sαKl could be associated with the progression of pre-clinical disorders.

Alpha-Klotho is a novel predictor of treatment responsiveness in patients with heart failure

Heart failure is a major cause of death with an increasing population of elderly individuals. Several studies have demonstrated the involvement of soluble alpha-Klotho (sαKl) in various diseases. However, the correlation between sαKl and heart failure remains to be understood. The aim of this study is to investigate the levels and role of sαKl in patients with heart failure. Twenty-eight consecutive patients with acute heart failure (19 male, 9 female), admitted to the Osaka University Hospital from 2010 to 2018, were enrolled in this study. Mean NYHA score, left ventricular ejection fraction and BNP were 3.3, 17.0% and 588 pg/mL, respectively. SαKl significantly increased in heart failure patients. SαKl on admission were significantly higher in patients with heart failure who showed improvement after intensive treatment than that in patients who did not show improvement after the treatment. SαKl levels decreased significantly in patients who showed improvement. Interestingly, sαKl levels increased in male patients with heart failure, but not in female patients. Our data suggest that soluble αKl may be a novel biomarker for the responsiveness against treatment in patients with heart failure with reduced ejection fraction. Our findings may help developing a personalized therapy for different patients with heart failure.

Occupational sedentary behavior and prediction of proteinuria in young to middle-aged adults: a retrospective cohort study

BACKGROUND

Although sedentary behavior is a risk factor of cardiometabolic diseases and mortality, little information is available about a clinical impact of occupational sedentary behavior on chronic kidney disease (CKD).

METHODS

The present retrospective cohort study included 10,212 workers of a national university in Japan who underwent annual health checkups between April 2006 and March 2013. Main exposure of interest was self-reported occupational sedentary behavior at the baseline visit. The outcome was the incidence of proteinuria defined as dipstick urinary protein of 1 + or more. The association between sedentary workers and the incidence of proteinuria was assessed using Cox proportional hazards models adjusting for clinically relevant factors, including television viewing time, the major home sedentary behavior.

RESULTS

During median 4.8 years (interquartile range 2.1-7.9) of the observational period, the incidence of proteinuria was observed in 597 (12.0%) males and 697 (13.3%) females. In males, sedentary workers were identified as a significant predictor of proteinuria (multivariable-adjusted hazard ratio of non-sedentary and sedentary workers: 1.00 [reference] and 1.35 [1.11-1.63]), along with longer television viewing time (< 30 min, 30-60 min, 1-2 h, 2-3 h, and > 3 h/day: 1.15 [0.93-1.42], 1.00 [reference], 1.24 [1.00-1.53], 1.41 [1.03-1.93], and 1.77 [1.13-2.76]), whereas not daily exercise time. In females, neither sedentary workers nor television viewing time was associated with the incidence of proteinuria.

CONCLUSIONS

In conclusion, male sedentary workers were at high risk of proteinuria. Occupational sedentary behavior may be a potentially modifiable target for the prevention of CKD.

Cytokine mRNA Degradation in Cardiomyocytes Restrains Sterile Inflammation in Pressure-Overloaded Hearts

BACKGROUND

Proinflammatory cytokines play an important role in the pathogenesis of heart failure. The mechanisms responsible for maintaining sterile inflammation within failing hearts remain poorly defined. Although transcriptional control is important for proinflammatory cytokine gene expression, the stability of mRNA also contributes to the kinetics of immune responses. Regnase-1 is an RNase involved in the degradation of a set of proinflammatory cytokine mRNAs in immune cells. The role of Regnase-1 in nonimmune cells such as cardiomyocytes remains to be elucidated.

METHODS

To examine the role of proinflammatory cytokine degradation by Regnase-1 in cardiomyocytes, cardiomyocyte-specific Regnase-1-deficient mice were generated. The mice were subjected to pressure overload by means of transverse aortic constriction to induce heart failure. Cardiac remodeling was assessed by echocardiography as well as histological and molecular analyses 4 weeks after operation. Inflammatory cell infiltration was examined by immunostaining. Interleukin-6 signaling was inhibited by administration with its receptor antibody. Overexpression of Regnase-1 in the heart was performed by adeno-associated viral vector-mediated gene transfer.

RESULTS

Cardiomyocyte-specific Regnase-1-deficient mice showed no cardiac phenotypes under baseline conditions, but exhibited severe inflammation and dilated cardiomyopathy after 4 weeks of pressure overload compared with control littermates. Four weeks after transverse aortic constriction, the Il6 mRNA level was upregulated, but not other cytokine mRNAs, including tumor necrosis factor-α, in Regnase-1-deficient hearts. Although the Il6 mRNA level increased 1 week after operation in both Regnase-1-deficient and control hearts, it showed no increase in control hearts 4 weeks after operation. Administration of anti-interleukin-6 receptor antibody attenuated the development of inflammation and cardiomyopathy in cardiomyocyte-specific Regnase-1-deficient mice. In severe pressure overloaded wild-type mouse hearts, sustained induction of Il6 mRNA was observed, even though the protein level of Regnase-1 increased. Adeno-associated virus 9-mediated cardiomyocyte-targeted gene delivery of Regnase-1 or administration of anti-interleukin-6 receptor antibody attenuated the development of cardiomyopathy induced by severe pressure overload in wild-type mice.

CONCLUSIONS

The degradation of cytokine mRNA by Regnase-1 in cardiomyocytes plays an important role in restraining sterile inflammation in failing hearts and the Regnase-1-mediated pathway might be a therapeutic target to treat patients with heart failure.

A Mammalian Mitophagy Receptor, Bcl2-L-13, Recruits the ULK1 Complex to Induce Mitophagy

Degradation of mitochondria by selective autophagy, termed mitophagy, contributes to the control of mitochondrial quality. Bcl2-L-13 is a mammalian homolog of Atg32, which is an essential mitophagy receptor in yeast. However, the molecular machinery involved in Bcl2-L-13-mediated mitophagy remains to be elucidated. Here, we show that the ULK1 (unc-51-like kinase) complex is required for Bcl2-L-13 to process mitophagy. Screening of a series of yeast Atg mutants revealed that a different set of ATG genes is used for Bcl2-L-13- and Atg32-mediated mitophagy in yeast. The components of the Atg1 complex essential for starvation-induced autophagy were indispensable in Bcl2-L-13-, but not Atg32-mediated, mitophagy. The ULK1 complex, a counterpart of the Atg1 complex, is necessary for Bcl2-L-13-mediated mitophagy in mammalian cells. We propose a model where, upon mitophagy induction, Bcl2-L-13 recruits the ULK1 complex to process mitophagy and the interaction of LC3B with ULK1, as well as Bcl2-L-13, is important for the mitophagy.

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Atg32 and Bcl2-L-13 are yeast and mammalian mitophagy receptors, respectively

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Atg1 complex is essential for Bcl2-L-13- but not Atg32-mediated yeast mitophagy

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ULK1 complex is necessary for Bcl2-L-13-mediated mitophagy in mammalian cells

Abstract 805: A Toll-like Receptor 9 Inhibitor Prevents the Development and Progression of Sterile Inflammatory Heart Failure Induced by Mitochondrial DNA Accumulation

Mitochondrial DNA contains unmethylated cytidine-phosphate-guanosine motif, and is recognized by Toll-like receptor (TLR) 9, inducing sterile inflammation. We previously reported that the accumulation of mitochondrial DNA in cardiomyocytes induces myocardial inflammation and heart failure using an animal model. (Nature 2012) In this study, to investigate the effect of inhibition of the inflammation via TLR9 induced by mitochondrial DNA accumulation on heart failure, we examined whether a TLR9 inhibitor, E6446 (6-[3-(pyrrolidin-1-yl)propoxy)-2-(4-(3-(pyrrolidin-1-yl)propoxy)phenyl]benzo[d]oxazole), prevents the development and progression of heart failure in mice. In in vitro study, isolated cardiomyocytes were stimulated by a TLR9 ligand (ODN1668) in the presence of E6446. ODN1668 significantly increased the expression levels of inflammatory cytokine mRNAs in the cells. Incubation of cardiomyocytes with E6446 significantly reduced the level of those mRNAs induced by ODN1668. CCCP increased the number of autolysosomes with DNA accumulation. Although E6446 had no effect on the number of the autolysosomes, it significantly reduced the production of inflammatory cytokine mRNAs induced by CCCP in cardiomyocytes. In in vivo study, mice orally received E6446 or saline 2 days before transverse aortic constriction (TAC) and every two days for 4 weeks thereafter. Four weeks after TAC, chamber size and fractional shortening (FS) of left ventricle (LV) and lung weight were significantly reduced in E6446 group compared to saline group. Furthermore, the infiltration of inflammatory cells including macrophages in the TAC-operated heart was inhibited by E6446. Next, mice with LV dysfunction at 2 weeks after TAC were subjected to the oral administration with E6446 or saline every two days for 4 weeks. The LV chamber size was significantly smaller and FS was higher in E6446 group than those in saline group 6 weeks after TAC. Our study showed that E6446 prevented the development of LV dilatation and dysfunction with inflammation and slowed progression of cardiac remodeling induced by pressure overload. E6446 might be a novel therapeutic to treat patients with heart failure.

Ablation of Toll-like receptor 9 attenuates myocardial ischemia/reperfusion injury in mice

In myocardial ischemia/reperfusion injury, the innate immune and subsequent inflammatory responses play a crucial role in the extension of myocardial damage. Toll-like receptor 9 (TLR9) is a critical receptor for recognizing unmethylated CpG motifs that mitochondria contain in their DNA, and induces inflammatory responses. The aim of this study was to elucidate the role of TLR9 in myocardial ischemia/reperfusion injury. Isolated hearts from TLR9-deficient and control wild-type mice were subjected to 35 min of global ischemia, followed by 60 min of reperfusion with Langendorff apparatus. Furthermore, wild-type mouse hearts were infused with DNase I and subjected to ischemia/reperfusion. Ablation of TLR9-mediated signaling pathway attenuates myocardial ischemia/reperfusion injury and inflammatory responses, and digestion of extracellular mitochondrial DNA released from the infarct heart partially improved myocardial ischemia/reperfusion injury with no effect on inflammatory responses. TLR9 could be a therapeutic target to reduce myocardial ischemia/reperfusion injury.

Implication of alpha-Klotho as the predictive factor of stress

Stress is known as a risk factor for both mental and physical health problems. While stress is known as one of the major health problems in modern society, a biomarker of stress has not yet been well established. In the present study, we focused on the serum levels of α-Klotho (αKl) as a possible objective biomarker of stress. Subjects included apparently healthy individuals who underwent a health examination in the Osaka University Health and Counseling Center. Physical and biochemical parameters were obtained from all subjects. Information regarding the lifestyle of each individual was obtained via questionnaires. Among male subjects, serum levels of soluble αKl (sαKl) were significantly elevated in subjects who had poor stress management and unsatisfactory sleep, suggesting that stress management and sleeping conditions influenced the serum levels of sαKl. The total Kessler Screening Scale for Psychological Distress (K6) score was significantly increased in subjects who reported experiencing considerable stress, had poor stress management and unsatisfactory sleep. Since serum levels of sαKl showed the same tendency as the K6 score in terms of the relationship between stress management and sleeping conditions in male subjects, increased sαKl levels could be associated with considerable psychological stress in healthy men.

Administration of a TLR9 Inhibitor Attenuates the Development and Progression of Heart Failure in Mice

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Under pressure overload, mitochondrial deoxyribonucleic acid containing the unmethylated cytidine-phosphate-guanosine motif is accumulated in cardiomyocytes and stimulates Toll-like receptor 9, resulting in inflammation and heart failure.

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Treatment with E6446, (6-[3-(pyrrolidin-1-yl)propoxy)-2-(4-(3-(pyrrolidin-1-yl)propoxy)phenyl]benzo[d]oxazole), a specific Toll-like receptor 9 inhibitor, prevented the development and slowed the progression of left ventricular dilatation and cardiac dysfunction in mice after pressure overload.

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E6446 attenuated the inflammatory responses in the pressure-overloaded mouse heart, even though the accumulation of mitochondrial deoxyribonucleic acid in cardiomyocytes was observed.

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E6446 could be a new therapeutic agent against heart failure.

Mitochondrial deoxyribonucleic acid, containing the unmethylated cytidine-phosphate-guanosine motif, stimulates Toll-like receptor 9 to induce inflammation and heart failure. A small chemical, E6446 [(6-[3-(pyrrolidin-1-yl)propoxy)-2-(4-(3-(pyrrolidin-1-yl)propoxy)phenyl]benzo[d]oxazole)], is a specific Toll-like receptor 9 inhibitor in cardiomyocytes. In this study, we showed that E6446 exerts beneficial effects for the prevention and treatment of pressure overload–induced heart failure in mice. When administered before the operation and chronically thereafter, E6446 prevented the development of left ventricular dilatation as well as cardiac dysfunction, fibrosis, and inflammation. Furthermore, when administered after the manifestation of cardiac dysfunction, E6446 slowed progression of cardiac remodeling. Thus, the inhibitor may be a novel therapeutic agent for treating patients with heart failure.

FKBP8 protects the heart from hemodynamic stress by preventing the accumulation of misfolded proteins and endoplasmic reticulum-associated apoptosis in mice

Protein quality control in cardiomyocytes is crucial to maintain cellular homeostasis. The accumulation of damaged organelles, such as mitochondria and misfolded proteins in the heart is associated with heart failure. During the process to identify novel mitochondria-specific autophagy (mitophagy) receptors, we found FK506-binding protein 8 (FKBP8), also known as FKBP38, shares similar structural characteristics with a yeast mitophagy receptor, autophagy-related 32 protein. However, knockdown of FKBP8 had no effect on mitophagy in HEK293 cells or H9c2 myocytes. Since the role of FKBP8 in the heart has not been fully elucidated, the aim of this study is to determine the functional role of FKBP8 in the heart. Cardiac-specific FKBP8-deficient (Fkbp8^-/-) mice were generated. Fkbp8^-/- mice showed no cardiac phenotypes under baseline conditions. The Fkbp8^-/- and control wild type littermates (Fkbp8^+/+) mice were subjected to pressure overload by means of transverse aortic constriction (TAC). Fkbp8^-/- mice showed left ventricular dysfunction and chamber dilatation with lung congestion 1week after TAC. The number of apoptotic cardiomyocytes was dramatically elevated in TAC-operated Fkbp8^-/- hearts, accompanied with an increase in protein levels of cleaved caspase-12 and endoplasmic reticulum (ER) stress markers. Caspase-12 inhibition resulted in the attenuation of hydrogen peroxide-induced apoptotic cell death in FKBP8 knockdown H9c2 myocytes. Immunocytological and immunoprecipitation analyses indicate that FKBP8 is localized to the ER and mitochondria in the isolated cardiomyocytes, interacting with heat shock protein 90. Furthermore, there was accumulation of misfolded protein aggregates in FKBP8 knockdown H9c2 myocytes and electron dense deposits in perinuclear region in TAC-operated Fkbp8^-/- hearts. The data suggest that FKBP8 plays a protective role against hemodynamic stress in the heart mediated via inhibition of the accumulation of misfolded proteins and ER-associated apoptosis.

Toll-like receptor 9 prevents cardiac rupture after myocardial infarction in mice independently of inflammation

We have reported that the Toll-like receptor 9 (TLR9) signaling pathway plays an important role in the development of pressure overload-induced inflammatory responses and heart failure. However, its role in cardiac remodeling after myocardial infarction has not been elucidated. TLR9-deficient and control C57Bl/6 wild-type mice were subjected to left coronary artery ligation. The survival rate 14 days postoperation was significantly lower in TLR9-deficient mice than that in wild-type mice with evidence of cardiac rupture in all dead mice. Cardiac magnetic resonance imaging showed no difference in infarct size and left ventricular wall thickness and function between TLR9-deficient and wild-type mice. There were no differences in the number of infiltrating inflammatory cells and the levels of inflammatory cytokine mRNA in infarct hearts between TLR9-deficient and wild-type mice. The number of α-smooth muscle actin (αSMA)-positive myofibroblasts and αSMA/Ki67-double-positive proliferative myofibroblasts was increased in the infarct and border areas in infarct hearts compared with those in sham-operated hearts in wild-type mice, but not in TLR9-deficient mice. The class B CpG oligonucleotide increased the phosphorylation level of NF-κB and the number of αSMA-positive and αSMA/Ki67-double-positive cells and these increases were attenuated by BAY1-7082, an NF-κB inhibitor, in cardiac fibroblasts isolated from wild-type hearts. The CpG oligonucleotide showed no effect on NF-κB activation or the number of αSMA-positive and αSMA/Ki67-double-positive cells in cardiac fibroblasts from TLR9-deficient hearts. Although the TLR9 signaling pathway is not involved in the acute inflammatory response in infarct hearts, it ameliorates cardiac rupture possibly by promoting proliferation and differentiation of cardiac fibroblasts.

mTOR Hyperactivation by Ablation of Tuberous Sclerosis Complex 2 in the Mouse Heart Induces Cardiac Dysfunction with the Increased Number of Small Mitochondria Mediated through the Down-Regulation of Autophagy

Mammalian target of rapamycin complex 1 (mTORC1) is a key regulator of cell growth, proliferation and metabolism. mTORC1 regulates protein synthesis positively and autophagy negatively. Autophagy is a major system to manage bulk degradation and recycling of cytoplasmic components and organelles. Tuberous sclerosis complex (TSC) 1 and 2 form a heterodimeric complex and inactivate Ras homolog enriched in brain, resulting in inhibition of mTORC1. Here, we investigated the effects of hyperactivation of mTORC1 on cardiac function and structure using cardiac-specific TSC2-deficient (TSC2-/-) mice. TSC2-/- mice were born normally at the expected Mendelian ratio. However, the median life span of TSC2-/- mice was approximately 10 months and significantly shorter than that of control mice. TSC2-/- mice showed cardiac dysfunction and cardiomyocyte hypertrophy without considerable fibrosis, cell infiltration or apoptotic cardiomyocyte death. Ultrastructural analysis of TSC2-/- hearts revealed misalignment, aggregation and a decrease in the size and an increase in the number of mitochondria, but the mitochondrial function was maintained. Autophagic flux was inhibited, while the phosphorylation level of S6 or eukaryotic initiation factor 4E -binding protein 1, downstream of mTORC1, was increased. The upregulation of autophagic flux by trehalose treatment attenuated the cardiac phenotypes such as cardiac dysfunction and structural abnormalities of mitochondria in TSC2-/- hearts. The results suggest that autophagy via the TSC2-mTORC1 signaling pathway plays an important role in maintenance of cardiac function and mitochondrial quantity and size in the heart and could be a therapeutic target to maintain mitochondrial homeostasis in failing hearts.

Bcl-2-like protein 13 is a mammalian Atg32 homologue that mediates mitophagy and mitochondrial fragmentation

Damaged mitochondria are removed by mitophagy. Although Atg32 is essential for mitophagy in yeast, no Atg32 homologue has been identified in mammalian cells. Here, we show that Bcl-2-like protein 13 (Bcl2-L-13) induces mitochondrial fragmentation and mitophagy in mammalian cells. First, we hypothesized that unidentified mammalian mitophagy receptors would share molecular features of Atg32. By screening the public protein database for Atg32 homologues, we identify Bcl2-L-13. Bcl2-L-13 binds to LC3 through the WXXI motif and induces mitochondrial fragmentation and mitophagy in HEK293 cells. In Bcl2-L-13, the BH domains are important for the fragmentation, while the WXXI motif facilitates mitophagy. Bcl2-L-13 induces mitochondrial fragmentation in the absence of Drp1, while it induces mitophagy in Parkin-deficient cells. Knockdown of Bcl2-L-13 attenuates mitochondrial damage-induced fragmentation and mitophagy. Bcl2-L-13 induces mitophagy in Atg32-deficient yeast cells. Induction and/or phosphorylation of Bcl2-L-13 may regulate its activity. Our findings offer insights into mitochondrial quality control in mammalian cells.

Atg32 is required for mitophagy in yeast, however, a mammalian homologue of this protein has not been identified. Murakawa et al. identify Bcl-2-like protein 13 as a functional homologue of Atg32 in mammalian cells, and show that this protein can rescue mitophagy in Atg32-deficient yeast cells.

Rheb (Ras homologue enriched in brain)-dependent mammalian target of rapamycin complex 1 (mTORC1) activation becomes indispensable for cardiac hypertrophic growth after early postnatal period

Cardiomyocytes proliferate during fetal life but lose their ability to proliferate soon after birth and further increases in cardiac mass are achieved through an increase in cell size or hypertrophy. Mammalian target of rapamycin complex 1 (mTORC1) is critical for cell growth and proliferation. Rheb (Ras homologue enriched in brain) is one of the most important upstream regulators of mTORC1. Here, we attempted to clarify the role of Rheb in the heart using cardiac-specific Rheb-deficient mice (Rheb(-/-)). Rheb(-/-) mice died from postnatal day 8 to 10. The heart-to-body weight ratio, an index of cardiomyocyte hypertrophy, in Rheb(-/-) was lower than that in the control (Rheb(+/+)) at postnatal day 8. The cell surface area of cardiomyocytes isolated from the mouse hearts increased from postnatal days 5 to 8 in Rheb(+/+) mice but not in Rheb(-/-) mice. Ultrastructural analysis indicated that sarcomere maturation was impaired in Rheb(-/-) hearts during the neonatal period. Rheb(-/-) hearts exhibited no difference in the phosphorylation level of S6 or 4E-BP1, downstream of mTORC1 at postnatal day 3 but showed attenuation at postnatal day 5 or 8 compared with the control. Polysome analysis revealed that the mRNA translation activity decreased in Rheb(-/-) hearts at postnatal day 8. Furthermore, ablation of eukaryotic initiation factor 4E-binding protein 1 in Rheb(-/-) mice improved mRNA translation, cardiac hypertrophic growth, sarcomere maturation, and survival. Thus, Rheb-dependent mTORC1 activation becomes essential for cardiomyocyte hypertrophic growth after early postnatal period.

Mitochondrial DNA that escapes from autophagy causes inflammation and heart failure

Heart failure is a leading cause of morbidity and mortality in industrialized countries. Although infection with microorganisms is not involved in the development of heart failure in most cases, inflammation has been implicated in the pathogenesis of heart failure¹. However, the mechanisms responsible for initiating and integrating inflammatory responses within the heart remain poorly defined. Mitochondria are evolutionary endosymbionts derived from bacteria and contain DNA similar to bacterial DNA^2,3,4. Mitochondria damaged by external hemodynamic stress are degraded by the autophagy/lysosome system in cardiomyocytes⁵. Here, we show that mitochondrial DNA that escapes from autophagy cell-autonomously leads to Toll-like receptor (TLR) 9-mediated inflammatory responses in cardiomyocytes and is capable of inducing myocarditis, and dilated cardiomyopathy. Cardiac-specific deletion of lysosomal deoxyribonuclease (DNase) II showed no cardiac phenotypes under baseline conditions, but increased mortality and caused severe myocarditis and dilated cardiomyopathy 10 days after treatment with pressure overload. Early in the pathogenesis, DNase II-deficient hearts exhibited infiltration of inflammatory cells and increased mRNA expression of inflammatory cytokines, with accumulation of mitochondrial DNA deposits in autolysosomes in the myocardium. Administration of the inhibitory oligodeoxynucleotides against TLR9, which is known to be activated by bacterial DNA⁶, or ablation of Tlr9 attenuated the development of cardiomyopathy in DNase II-deficient mice. Furthermore, Tlr9-ablation improved pressure overload-induced cardiac dysfunction and inflammation even in mice with wild-type Dnase2a alleles. These data provide new perspectives on the mechanism of genesis of chronic inflammation in failing hearts.

Abstract P126: Calpain Protects the Heart from Hemodynamic Stress

Although calpains are well-known Ca 2+ -dependent intracellular cysteine proteases, the pathophysiological function of calpains in the heart remains to be elucidated. Previous reports have suggested that calpains play detrimental roles to induce apoptotic or necrotic cell death in pathological Ca 2+ -overloaded conditions such as ischemia-reperfusion injury or myocardial infarction. Recent loss of function studies have suggested that calpains play important physiological roles in development, cell migration, organization of actin cytoskeleton, and plasma membrane repair. In the present study, we generated and analyzed cardiac-specific calpain 4-deficient mice (CKO) to answer unresolved questions as to in vivo function of calpains in the heart. Ubiquitous calpain is consisted of a common regulatory subunit (calpain 4) and a large catalytic subunit (calpain 1 for μ-calpain and calpain 2 for m-calpain). In agreement with previous reports, cardiac-specific deletion of calpain 4 markedly resulted in a simultaneous decrease in protein levels of calpain 1 and 2, indicating that calpain activity was almost absent in CKO hearts. CKO showed no cardiac phenotypes under basal conditions. Then, we subjected CKO and control mice (CTL) to pressure overload by means of transverse aortic constriction (TAC). One week after TAC, CKO showed left ventricle dilatation (LVDd, CKO 3.64 ± 0.2 mm versus CTL 2.66 ± 0.05 mm), and contractile dysfunction (FS, CKO 33.2 ± 3.9% versus CTL 47 ± 0.7%). CKO hearts took up Evans blue, a membrane-impermeant dye, within cardiomyocytes after TAC, whereas CTL hearts or sham-operated CKO hearts did not. This indicates plasma membrane was disrupted in CKO hearts in response to pressure overload. We performed membrane repair assays on isolated cardiomyocytes from CKO hearts using a two-photon laser-scanning microscope. CKO cardiomyocytes continued to take up FM1-43FX dye for at least 480 sec after disruption of a plasma membrane by laser irradiation, although CTL cardiomyocytes resealed within 250 sec. These data indicate that plasma membrane of cardiomyocytes disrupted by pressure overload failed to be resealed in CKO hearts. Thus, we conclude that calpains protect the heart from hemodynamic stresses by promoting membrane repair.

Abstract P111: Rheb-mTOR Signaling Pathway Regulates Cardiomyocyte Mass During Post-Neonatal Period

Rheb (Ras homologue enriched in brain) is a major activator of mTOR. Rheb-mTOR pathway is a critical mechanism for maintenance of homeostasis, cell growth and stress response by regulating both protein synthesis and degradation. In this study, we attempted to clarify the role of Rheb-mTOR pathway in the heart using cardiac-specific Rheb-deficient mice (Rheb −/− ). We generated floxed Rheb mice and crossed them with transgenic mice expressing Cre recombinase in cardiac-specific mannner to generate Rheb −/− . Rheb −/− were born in Mendelian ratio, but they started to die 8 days after birth and all of them had died until 10 days after birth. Echocardiographic analysis revealed that chamber dimension and contractile function of Rheb −/− were indistinguishable from those of control mice (Rheb +/+ ) 5 days after birth. However, Rheb −/− exhibited cardiac dilatation and reduced contractility 8 days after birth (LV end diastolic dimension, Rheb −/− : 2.5±0.2 mm vs. Rheb +/+ : 2.1±0.2 mm, p<0.01, fractional shortening, Rheb −/− : 19.7 ± 9.7 % vs. Rheb +/+ : 48.6 ± 8.8 %, p<0.01). These suggest that Rheb −/− died of cardiac dysfunction and heart failure. Heart weight and cross-sectional area of cardiomyocytes were significantly lower in Rheb −/− 8 days after birth. Electron microscopic analysis revealed that the area of sarcomere was significantly lower in Rheb −/− cardiomyocytes. Expressions of sarcomeric proteins, such as myosin heavy chain, actin or desmin, were decreased in Rheb −/− , while the mRNA expression of desmin was significantly increased in Rheb −/− . Thus impairment of cardiomyocyte growth observed in Rheb −/− could be due to either increased degradation or decreased translation. Although autophagic activity was enhanced in Rheb −/− heart, ablation of Atg5, an essential molecule for autophagy, could not prevent premature death of Rheb −/− . On the other hand, polysome analysis revealed that the mRNA translation activity had decreased in Rheb −/− heart compared with Rheb +/+ . Thus, we concluded that Rheb-mTOR pathway in the heart is essential to regulate mRNA translation activity and protein synthesis, thereby to cardiomyocyte growth in neonatal period.

Calpain protects the heart from hemodynamic stress

Calpains make up a family of Ca(2+)-dependent intracellular cysteine proteases that include ubiquitously expressed μ- and m-calpains. Both are heterodimers consisting of a distinct large catalytic subunit (calpain 1 for μ-calpain and calpain 2 for m-calpain) and a common regulatory subunit (calpain 4). The physiological roles of calpain remain unclear in the organs, including the heart, but it has been suggested that calpain is activated by Ca(2+) overload in diseased hearts, resulting in cardiac dysfunction. In this study, cardiac-specific calpain 4-deficient mice were generated to elucidate the role of calpain in the heart in response to hemodynamic stress. Cardiac-specific deletion of calpain 4 resulted in decreased protein levels of calpains 1 and 2 and showed no cardiac phenotypes under base-line conditions but caused left ventricle dilatation, contractile dysfunction, and heart failure with interstitial fibrosis 1 week after pressure overload. Pressure-overloaded calpain 4-deficient hearts took up a membrane-impermeant dye, Evans blue, indicating plasma membrane disruption. Membrane repair assays using a two-photon laser-scanning microscope revealed that calpain 4-deficient cardiomyocytes failed to reseal a plasma membrane that had been disrupted by laser irradiation. Thus, the data indicate that calpain protects the heart from hemodynamic stresses, such as pressure overload.

Inhibition of autophagy in the heart induces age-related cardiomyopathy

Constitutive autophagy is important for control of the quality of proteins and organelles to maintain cell function. Damaged proteins and organelles accumulate in aged organs. We have previously reported that cardiac-specific Atg5 (autophagy-related gene 5)-deficient mice, in which the gene was floxed out early in embryogenesis, were born normally, and showed normal cardiac function and structure up to 10 weeks old. In the present study, to determine the longer-term consequences of Atg5-deficiency in the heart, we monitored cardiac-specific Atg5-deficient mice for further 12 months. First, we examined the age-associated changes of autophagy in the wild-type mouse heart. The level of autophagy, as indicated by decreased LC3-II (microtubule-associated protein 1 light chain 3-II) levels, in the hearts of 6-, 14- or 26-month-old mice was lower than that of 10-week-old mice. Next, we investigated the cardiac function and life-span in cardiac-specific Atg5-deficient mice. The Atg5-deficient mice began to die after the age of 6 months. Atg5-deficient mice exhibited a significant increase in left ventricular dimension and decrease in fractional shortening of the left ventricle at the age of 10 months, compared to control mice, while they showed similar chamber size and contractile function at the age of 3 months. Ultrastructural analysis revealed a disorganized sarcomere structure and collapsed mitochondria in 3- and 10-month-old Atg5-deficient mice, with decreased mitochondrial respiratory functions. These results suggest that continuous constitutive autophagy has a crucial role in maintaining cardiac structure and function.

Activation of MTK1/MEKK4 induces cardiomyocyte death and heart failure

MTK1 (MEKK4) is a mitogen-activated protein kinase kinase kinase that regulates the activity of its downstream mitogen-activated kinases, p38, and c-Jun N-terminal kinase (JNK). However, the physiological function of MTK1 in the heart remains to be determined. Here, we attempted to elucidate the function of MTK1 in the heart using in vitro and in vivo models. MTK1 was activated in the hearts of mice subjected to pressure overload-induced heart failure. Overexpression of a constitutively active mutant of MTK1 (MTK1DeltaN) induced apoptosis in isolated neonatal rat cardiomyocytes, whereas a kinase domain-deleted form of MTK1 attenuated H(2)O(2)-induced apoptosis. Specific inhibitors of p38 or JNK effectively protected cardiomyocytes from MTK1DeltaN-induced cell death. In mice, cardiac-specific overexpression of MTK1DeltaN resulted in early mortality compared with the lifespan of littermate controls. Echocardiographic analysis revealed increases in end-diastolic and end-systolic left ventricular internal dimensions and a decrease in fractional shortening in MTK1DeltaN transgenic mice. In addition, the mice showed characteristic phenotypes of heart failure such as an increase in lung weight. The number of TUNEL-positive myocytes and the level of cleaved caspase 3 protein were both increased in MTK1DeltaN transgenic mice. Thus, MTK1 plays an important role in the regulation of cell death and is also involved in the pathogenesis of heart failure.

The I{kappa}B kinase {beta}/nuclear factor {kappa}B signaling pathway protects the heart from hemodynamic stress mediated by the regulation of manganese superoxide dismutase expression

Cardiomyocyte death plays an important role in the pathogenesis of heart failure. The nuclear factor (NF)-kappaB signaling pathway regulates cell death, however, the effect of NF-kappaB pathway on cell death can vary in different cells or stimuli. The purpose of the present study was to clarify the in vivo role of the NF-kappaB pathway in response to pressure overload. First, we subjected C57Bl6/J mice to pressure overload by means of transverse aortic constriction (TAC) and examined the activity of the NF-kappaB pathway in response to pressure overload. IkappaB kinase (IKK) and NF-kappaB were activated after TAC. Then, we investigated the role of the activation using cardiac-specific IKKbeta-deficient mice (CKO). CKO displayed normal global cardiac structure and function compared with control littermates. We subjected CKO and control mice to pressure overload. One week after TAC, CKO showed cardiac dilation, dysfunction, and lung congestion, which are characteristics of heart failure. The number of apoptotic cells in the hearts of CKO mice increased significantly after TAC. The levels of manganese superoxide dismutase mRNA and protein expression in CKO after TAC were significantly attenuated compared with control mice. The levels of oxidative stress and c-Jun N-terminal kinase (JNK) activation in CKO after TAC were significantly greater than those in control mice. Isoproterenol-induced cell death of isolated adult CKO cardiomyocytes was inhibited by treatment with either a manganese superoxide dismutase mimetic or a JNK inhibitor. Thus, the IKKbeta/NF-kappaB signaling pathway plays a protective role in cardiomyocytes because of the attenuation of oxidative stress and JNK activation in a setting of acute pressure overload.

Computed tomography analysis of causes of local failure in radiotherapy for cervical carcinoma

BACKGROUND

The authors analyzed the radiation dose to the periphery of the cervix and area of the cervix in relation to local failure of radiotherapy for carcinoma of the cervix using computed tomography (CT) images.

METHODS

Between 1981-1990, 127 consecutive patients were treated with definitive radiotherapy. Ninety-nine of these patients had CT images taken at the time of intracavitary therapy. Of these 99 patients, 80 were eligible for this analysis. After CT scanning, isodose curves relative to the point A dose were superimposed on the CT images. The minimum percent dose and minimum dose at the periphery of the cervix were estimated. The area of the cervix also was measured. These factors were examined in relation to the local tumor control rate.

RESULTS

Histograms of both the minimum percent dose and the cervical area showed significant differences between the local control and local failure groups (P <0.001). The local control rates were related to both the minimum percent dose and the cervical area, and differed significantly over and below the values of 60% and 18 cm2 (P <0.001 each), respectively. The local control patients, over and below the line: Y = -0.220X + 21.2, in which X (gray [Gy]) and Y (Gy) are the whole pelvis dose and the minimum dose, respectively, could be well differentiated with significance (91.7% vs. 25.0%; P <0.001).

CONCLUSIONS

Computed tomography analysis indicated that the local tumor control rate was related strongly to the minimum percent dose, the cervical area, and the pair of whole pelvis and minimum dose values. These factors were found to be more useful than the point A dose in predicting local tumor control.