Abstract 19772: MANF, a Structurally Unique ER Stress-Inducible Protein, Restores ER-Protein Folding in ER Stressed Cardiac Myocytes and in the Ischemic Heart
Introduction: The sarco/endoplasmic reticulum (SR/ER) of cardiomyocytes is a critical site of protein synthesis and folding where most secreted and membrane proteins, such as receptors, growth factors, and ion channels are made. Myocardial ischemia causes ER stress, during which misfolded proteins accumulate in the SR/ER and contribute to cardiomyocyte death. Myocardial ischemia also activates the ER stress response, which, in part, is mediated by activating transcription factor 6 (ATF6). ATF6 induces ER chaperones to restore protein folding in the SR/ER. Our transcriptome analyses showed that one of the 381 genes induced by ATF6 in the heart is mesencephalic astrocyte-derived neurotrophic factor (MANF), a recently identified ER-luminal protein of unknown function. Since MANF is structurally unique, its function could not be inferred by analogy to other proteins.
Hypothesis: We hypothesize that MANF is an ER chaperone that is required for viability of cardiomyocytes during ER stress.
Methods: MANF gene induction by ER stress and the effects of MANF knockdown on cell viability were characterized in neonatal rat ventricular myocytes (NRVM). The ability of recombinant MANF to restore structure and function to model misfolded proteins was also examined. Finally, the effects of MANF loss-of-function in the ischemic heart, in vivo, were determined using a new transgenic mouse model in which MANF has been knocked down by a MANF-targeted microRNA that is expressed in a cardiomyocyte-specific manner.
Results: Surprisingly, MANF induction and function phenocopied that of the ER stress-inducible chaperone, glucose-regulated protein 78 (Grp78), as follows: MANF was induced by ER stress in an ATF6-dependent manner. MANF knockdown in NRVM increased myocyte death during ER stress. MANF exhibited a robust ability to restore structure and function to model misfolded proteins, in vitro. Finally, in terms of its function in the heart, MANF knockdown in the heart, in vivo, increased damage in a mouse model of myocardial infarction.
Conclusions: These results suggest that MANF is a novel SR/ER-resident chaperone that serves as a critical contributor to the restoration of SR/ER protein folding during ischemia and, as such, decreases tissue damage in the ischemic heart.
Author Disclosures: A. Arrieta: None. E.A. Blackwood: None. W.T. Stauffer: None. A.N. Pentoney: None. D.J. Thuerauf: None. S. Doroudgar: None. C.C. Glembotski: None.
- © 2016 by American Heart Association, Inc.