Yasuhide Asaumi

Protective Role of Endogenous Erythropoietin System in Nonhematopoietic Cells Against Pressure Overload–Induced Left Ventricular Dysfunction in Mice

Background— Erythropoietin (Epo) receptors (EpoRs) are expressed in the heart. We have recently demonstrated that the endogenous Epo-EpoR system plays an important protective role in myocardial ischemia in mice and humans. In the present study, we tested our hypothesis that the endogenous Epo-EpoR system in nonhematopoietic cells also plays a protective role against pressure overload-induced cardiac dysfunction in vivo. Methods and Results— Transgene-rescued EpoR-null mutant mice (EpoR−/−rescued) that express EpoR exclusively in the hematopoietic cells were subjected to transverse aortic constriction (TAC). At 1 week after TAC, left ventricular weight and lung weight were significantly increased in EpoR−/−rescued mice compared with wild-type mice, although the fibrotic area was comparably increased after TAC in the 2 genotypes. In the EpoR−/−rescued mice with TAC, left ventricular end-diastolic diameter was significantly increased, left ventricular fractional shortening was significantly decreased, and survival rate was significantly decreased compared with wild-type mice with TAC. Phosphorylation of STAT3 at 5 hours and 1 week after TAC and that of p38 at 5 hours after TAC were significantly increased in wild-type mice but not in EpoR−/−rescued mice. Vascular endothelial growth factor protein expression and capillary density in left ventricular myocardium were significantly decreased in EpoR−/−rescued mice with TAC compared with wild-type mice with TAC. Conclusions— These results suggest that the endogenous Epo-EpoR system in the nonhematopoietic cells plays an important protective role against pressure overload-induced cardiac dysfunction in vivo.

Depressed contractile reserve and impaired calcium handling of cardiac myocytes from chronically unloaded hearts are ameliorated with the administration of physiological treatment dose of T3 in rats.

Aim:u2002 Chronic cardiac unloading causes a time‐dependent upregulation of phospholamban (PLB) and depression of myocyte contractility in normal rat hearts. As thyroid hormone is known to decrease PLB expression, we examined whether thyroid hormone restores the depressed contractile performance of myocytes from chronically unloaded hearts.

Mitsugumin 53-mediated maintenance of K+ currents in cardiac myocytes.

Mitsugumin 53 (MG53) is a muscle-specific RBCC/TRIM family member predominantly localized on small vesicles underneath the plasma membrane. Upon cell-surface lesion MG53 recruits the vesicles to the repair site in an oxidation-dependent manner and MG53-knockout mice develop progressive myopathy associated with defective membrane repair. In this report, we focus on MG53-knockout cardiomyocytes showing abnormal action potential profile and a reduced K+ current density. In cDNA expression experiments using cultured cells, KV2.1-mediated currents were remarkably increased by MG53 without affecting the total and cell-surface levels of channel expression. In imaging analysis MG53 seemed to facilitate the mobility of KV2.1-containing endocytic vesicles with acidic pH. However, similar effects on the current density and vesicular mobility were not observed in the putative dominant-negative form of MG53. Our data suggest that MG53 is involved in a constitutive cycle of certain cell-surface proteins between the plasma membrane and endosome-like vesicles in striated muscle, and also imply that the vesicular dynamics are essential for the quality control of KV2.1 in cardiomyocytes.

Identification and visualization of stimulus-specific transcriptional activity in cardiac hypertrophy in mice.

Identification of specific signaling pathways for cardiac hypertrophy in living animals is challenging because no methods have been established to directly observe sequential molecular signaling events at the transcriptional level during pathogenesis. Here, our aim was to develop a useful method for monitoring the specific signaling pathways involved in the development of cardiac hypertrophy in vivo. Expression profiling of the left ventricle by microarray was performed in 2 different mouse models of cardiac hypertrophy: mechanical pressure overload by transverse aortic constriction (TAC) and neurohumoral activation by angiotensin II (Ang II) infusion. To annotate the information on transcription factor-binding sites, we collected promoter sequences and identified significantly frequent transcription factor-binding sites in the promoter regions of coregulated genes from both models (Pxa0<xa00.05, binomial probability). Finally, we injected a firefly luciferase vector plasmid containing each transcription factor-binding site into the left ventricle in both models. In the TAC and Ang II models, we selected 379 and 12 upregulated genes, respectively. Twenty binding sites for transcription factors, including activator protein 4, were identified in the TAC model, and 4 sites for transcription factors, including ecotropic viral integration 1, were identified in the Ang II model. GATA-binding sites were noted in both models of cardiac hypertrophy. Using the firefly luciferase reporter, we demonstrated the enhancement of transcriptional activity during the progression of cardiac hypertrophy using in vivo imaging in live mice. These results suggested that our approach was useful for the identification of unique transcription factors that characterize different models of cardiac hypertrophy in vivo.