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Smyd1 facilitates heart development by antagonizing oxidative and ER stress responses.

ABSTRACT: Smyd1/Bop is an evolutionary conserved histone methyltransferase previously shown by conventional knockout to be critical for embryonic heart development. To further explore the mechanism(s) in a cell autonomous context, we conditionally ablated Smyd1 in the first and second heart fields of mice using a knock-in (KI) Nkx2.5-cre driver. Robust deletion of floxed-Smyd1 in cardiomyocytes and the outflow tract (OFT) resulted in embryonic lethality at E9.5, truncation of the OFT and right ventricle, and additional defects consistent with impaired expansion and proliferation of the second heart field (SHF). Using a transgenic (Tg) Nkx2.5-cre driver previously shown to not delete in the SHF and OFT, early embryonic lethality was bypassed and both ventricular chambers were formed; however, reduced cardiomyocyte proliferation and other heart defects resulted in later embryonic death at E11.5-12.5. Proliferative impairment prior to both early and mid-gestational lethality was accompanied by dysregulation of transcripts critical for endoplasmic reticulum (ER) stress. Mid-gestational death was also associated with impairment of oxidative stress defense-a phenotype highly similar to the previously characterized knockout of the Smyd1-interacting transcription factor, skNAC. We describe a potential feedback mechanism in which the stress response factor Tribbles3/TRB3, when directly methylated by Smyd1, acts as a co-repressor of Smyd1-mediated transcription. Our findings suggest that Smyd1 is required for maintaining cardiomyocyte proliferation at minimally two different embryonic heart developmental stages, and its loss leads to linked stress responses that signal ensuing lethality.

SUBMITTER: Rasmussen TL

PROVIDER: S-EPMC4372598 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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Smyd1 facilitates heart development by antagonizing oxidative and ER stress responses.

Rasmussen Tara L TL Ma Yanlin Y Park Chong Yon CY Harriss June J Pierce Stephanie A SA Dekker Joseph D JD Valenzuela Nicolas N Srivastava Deepak D Schwartz Robert J RJ Stewart M David MD Tucker Haley O HO

PloS one 20150324 3

Smyd1/Bop is an evolutionary conserved histone methyltransferase previously shown by conventional knockout to be critical for embryonic heart development. To further explore the mechanism(s) in a cell autonomous context, we conditionally ablated Smyd1 in the first and second heart fields of mice using a knock-in (KI) Nkx2.5-cre driver. Robust deletion of floxed-Smyd1 in cardiomyocytes and the outflow tract (OFT) resulted in embryonic lethality at E9.5, truncation of the OFT and right ventricle, ...[more]

PMID: 25803368

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Project description:Cellular redox control is maintained by generation of reactive oxygen/nitrogen species balanced by activation of antioxidative pathways. Disruption of redox balance leads to oxidative stress, a central causative event in numerous diseases including heart failure. Redox control in the heart exposed to hemodynamic stress, however, remains to be fully elucidated. Here, we show that production of cardiomyocyte NADPH (nicotinamide adenine dinucleotide phosphate), a key factor in redox regulation, is decreased in pressure overload-induced heart failure. As a consequence, the level of reduced glutathione is downregulated, a change associated with cardiac cell death, fibrosis, and cardiomyopathy. We report that the pentose phosphate pathway (PPP) and mitochondrial serine/glycine/folate metabolic signaling, two major NADPH-generating pathways in the cytosol and mitochondria, respectively, are induced in the heart by pressure overload. We identify ATF4 (activating transcriptional factor 4) as an upstream transcription factor controlling the expression of multiple enzymes in these two pathways. Consistent with this, joint pathway analysis (JPA) of transcriptomic and metabolomic data reveals that ATF4 preferably controls oxidative stress and redox-related pathways. Overexpression of ATF4 in cardiomyocytes in culture leads to a significant increase in NADPH-producing enzymes whereas silencing of ATF4 decreases their expression. Further, stable isotope tracer experiments reveal that ATF4 overexpression in vitro strongly augments metabolic flux within these two pathways. In vivo, cardiomyocyte-specific deletion of ATF4 exacerbates cardiomyopathy in the setting of pressure overload and accelerates the development of heart failure, attributable, at least in part, to an inability to increase the expression of NADPH-generating enzymes. Taken together, our findings reveal that ATF4 plays a critical role in cardiac homeostasis under conditions of hemodynamic stress by governing both cytosolic and mitochondrial production of NADPH.

Project description:RationaleEndoplasmic reticulum (ER) stress causes the accumulation of misfolded proteins in the ER, activating the transcription factor, ATF6 (activating transcription factor 6 alpha), which induces ER stress response genes. Myocardial ischemia induces the ER stress response; however, neither the function of this response nor whether it is mediated by ATF6 is known.ObjectiveHere, we examined the effects of blocking the ATF6-mediated ER stress response on ischemia/reperfusion (I/R) in cardiac myocytes and mouse hearts.Methods and resultsKnockdown of ATF6 in cardiac myocytes subjected to I/R increased reactive oxygen species and necrotic cell death, both of which were mitigated by ATF6 overexpression. Under nonstressed conditions, wild-type and ATF6 knockout mouse hearts were similar. However, compared with wild-type, ATF6 knockout hearts showed increased damage and decreased function after I/R. Mechanistically, gene array analysis showed that ATF6, which is known to induce genes encoding ER proteins that augment ER protein folding, induced numerous oxidative stress response genes not previously known to be ATF6-inducible. Many of the proteins encoded by the ATF6-induced oxidative stress genes identified here reside outside the ER, including catalase, which is known to decrease damaging reactive oxygen species in the heart. Catalase was induced by the canonical ER stressor, tunicamycin, and by I/R in cardiac myocytes from wild-type but not in cardiac myocytes from ATF6 knockout mice. ER stress response elements were identified in the catalase gene and were shown to bind ATF6 in cardiac myocytes, which increased catalase promoter activity. Overexpression of catalase, in vivo, restored ATF6 knockout mouse heart function to wild-type levels in a mouse model of I/R, as did adeno-associated virus 9-mediated ATF6 overexpression.ConclusionsATF6 serves an important role as a previously unappreciated link between the ER stress and oxidative stress gene programs, supporting a novel mechanism by which ATF6 decreases myocardial I/R damage.

Dataset Information

Smyd1 facilitates heart development by antagonizing oxidative and ER stress responses.

Publications

Smyd1 facilitates heart development by antagonizing oxidative and ER stress responses.

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