title: p27 protein protects metabolically stressed cardiomyocytes from apoptosis by promoting autophagy.
abstract: p27(Kip1) (p27), a key regulator of cell division, has been implicated in autophagy of cancer cells. However, its role in autophagy, the evolutionarily conserved catabolic process that enables cells to remove unwanted proteins and damaged organelles, had not been examined in the heart. Here we report that ectopic delivery of a p27 fusion protein (TAT-p27) was sufficient to induce autophagy in neonatal rat ventricular cardiomyocytes in vitro, under basal conditions and after glucose deprivation. Conversely, lentivirus-delivered shRNA against p27 successfully reduced p27 levels and suppressed basal and glucose-deprived levels of autophagy in cardiomyocytes in vitro. Glucose deprivation mimics myocardial ischemia and induces apoptosis in cardiomyocytes. During glucose deprivation, TAT-p27 inhibited apoptosis, whereas down-regulation of p27 decreased survival of cardiomyocytes. However, inhibition of autophagy by pharmacological (3-methyladenine, chloroquine, or bafilomycin A1) or genetic approaches (siRNA-mediated knockdown of Atg5) sensitized cardiomyocytes to glucose deprivation-induced apoptosis, even in the presence of TAT-p27. TAT-p27 was also able to provoke greater levels of autophagy in resting and fasting cardiomyocytes in vivo. Further, TAT-p27 enhanced autophagy and repressed cardiomyocytes apoptosis, improved cardiac function, and reduced infarct size following myocardial infarction. Again, these effects were lost when cardiac autophagy in vivo was blocked by chloroquine. Taken together, these data show that p27 positively regulates cardiac autophagy in vitro and in vivo, at rest and after metabolic stress, and that TAT-p27 inhibits apoptosis by promoting autophagy in glucose-deprived cardiomyocytes in vitro and in post-myocardial infarction hearts in vivo.
authors.affiliation: From the Toronto General Research Institute.
authors.forename: Xuetao
authors.initials: X
authors.lastname: Sun
authors.affiliation: From the Toronto General Research Institute.
authors.forename: Abdul
authors.initials: A
authors.lastname: Momen
authors.affiliation: From the Toronto General Research Institute.
authors.forename: Jun
authors.initials: J
authors.lastname: Wu
authors.affiliation: From the Toronto General Research Institute.
authors.forename: Hossein
authors.initials: H
authors.lastname: Noyan
authors.affiliation: From the Toronto General Research Institute, Peter Munk Cardiac Centre, and.
authors.forename: Renke
authors.initials: R
authors.lastname: Li
authors.affiliation: From the Toronto General Research Institute, Peter Munk Cardiac Centre, and McEwen Centre for Regenerative Medicine, University Health Network, Toronto, Ontario M5G 2C4, Canada, and the Department of Medicine and.
authors.forename: Rüdiger
authors.initials: R
authors.lastname: von Harsdorf
authors.affiliation: From the Toronto General Research Institute, Peter Munk Cardiac Centre, and McEwen Centre for Regenerative Medicine, University Health Network, Toronto, Ontario M5G 2C4, Canada, and the Department of Medicine and Heart and Stroke/Richard Lewar Centre of Excellence, University of Toronto, Toronto M5G 1L7, Canada mansoor.husain@utoronto.ca.
authors.forename: Mansoor
authors.initials: M
authors.lastname: Husain
mesh_terms: D000818:Animals; D017209:Apoptosis; D001343:Autophagy; D000071187:Autophagy-Related Protein 5; D002478:Cells, Cultured; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000235:genetics / Q000378:metabolism*; D005947:Glucose / Q000172:deficiency; D051379:Mice; D008810:Mice, Inbred C57BL; D009203:Myocardial Infarction / Q000378:metabolism / Q000473:pathology; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000502:physiology; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
chemical_list: C545865:Atg5 protein, rat; D000071187:Autophagy-Related Protein 5; D011506:Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D005947:Glucose
keywords: Apoptosis; Autophagy; Cardiac Metabolism; Cardiovascular Disease; Heart Failure; p27