Journal of molecular and cellular cardiology plus最新文献

Protein phosphatase 2A (PP2A) plays a central role in myocardial ischemia-reperfusion (I/R) injury. Several studies showed a detrimental function of PP2A by using either overexpression models of the catalytic subunit (PP2Ac) or exogenous inhibitors of PP2Ac. However, all of these approaches underestimate the contribution of regulatory B subunits in modulating the PP2A holoenzyme. To better understand the influence of B subunits on a “controlled” regulation of PP2A, we tested a mouse model overexpressing PP2A-B56α (TG) in the heart under the conditions of I/R in comparison to wild-type littermates (WT). Contractility was increased after reperfusion in isolated TG hearts that were initially subjected to a 20-min no-flow ischemia. This was associated with lower phosphorylation levels of myosin-binding protein C and the ryanodine receptor 2 in TG compared to WT. The application of okadaic acid abolished the contractile and biochemical effects in TG hearts. Moreover, reperfusion resulted in the detection of higher PP2A-B56α levels in mitochondrial preparations of TG hearts. The phosphorylation of ERK1 was increased in the early reperfusion phase in TG compared to WT hearts corresponding to a transient attenuation of PP2A activity. Ischemia led to a prolonged contracture time in TG hearts and a lower acidification in isolated TG cardiomyocytes. The formation of interstitial fibrosis by transient ligation of the left anterior descending (LAD) artery was reduced in TG compared to WT hearts. Taken together, these findings indicate that overexpression of PP2A-B56α is protective against I/R injury and that B56α merits further investigation as a potential therapeutic target.

Autophagy is a highly conserved cellular process in which cytoplasmic materials are internalized into an autophagosome that later fuses with a lysosome for their degradation and recycling. MicroRNAs (miRNAs) are integral regulators in various cellular processes including autophagy and endothelial function. Accordingly, we hypothesize that miRNA, miR-378-3p, is an essential regulator of endothelial autophagy and endothelial function. MiR-378-3p expression was measured following inhibition and activation of autophagy in endothelial cells. A gain- or loss-of function approach was employed to either overexpress or inhibit the expression of miR-378-3p, respectively, in cultured endothelial cells, and markers of autophagy and indices of endothelial function, such as proliferation, migration and tube forming potential were measured. Inhibition and activation of autophagy up- and down-regulated the expression of miR-378-3p, respectively. Furthermore, miR-378a-3p overexpression was associated with impaired autophagy indicated by a reduced LC3-II/LC3-I ratio, and endothelial function indicated by increased proliferation associated with reduced p21 expression, reduced angiogenic potential and increased migration, which were associated with reduced expression of endothelial nitric oxide synthase (eNOS), an essential regulator of endothelial function. Accordingly, miR-378a-3p inhibition was associated with reduced cell proliferation, migration and increased eNOS in endothelial cells. Apoptosis was not affected in cells transfected with antagomir. Using in silico approach, Protein Disulfide Isomerase Family A Member 4 (PDIA-4) was identified and confirmed as a target of miR-378-3p. PDIA-4 expression was significantly reduced or enhanced in miR-378-3p-overexpressing or -silenced endothelial cells, respectively. Our findings show an inverse relationship between miR-378-3p and endothelial autophagy and function, providing a novel insight about the epigenetic regulation of these processes.

Angiotensin-converting enzyme (ACE) hydrolyzes N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) into inactive fragments through its N-terminal site (ACEN). We previously showed that Ac-SDKP mediates ACE inhibitors' cardiac effects. Whether increased bioavailability of endogenous Ac-SDKP caused by knocking out ACE-N also improves cardiac function in myocardial infarction (MI)-induced heart failure (HF) is unknown. Wild-type (WT) and ACE-N knockout (ACE-NKO) mice were subjected to MI by ligating the left anterior descending artery and treated with vehicle or Ac-SDKP (1.6 mg/kg/day, s.c.) for 5 weeks, after which echocardiography was performed and left ventricles (LV) were harvested for histology and molecular biology studies. ACE-NKO mice showed increased plasma Ac-SDKP concentrations in both sham and MI group compared to WT. Exogenous Ac-SDKP further increased its circulating concentrations in WT and ACE-NKO. Shortening (SF) and ejection (EF) fractions were significantly decreased in both WT and ACE-NKO mice post-MI, but ACE-NKO mice exhibited significantly lesser decrease. Exogenous Ac-SDKP ameliorated cardiac function post-MI only in WT but failed to show any additive improvement in ACE-NKO mice. Sarcoendoplasmic reticulum calcium transport ATPase (SERCA2), a marker of cardiac function and calcium homeostasis, was significantly decreased in WT post-MI but rescued with Ac-SDKP, whereas ACE-NKO mice displayed less loss of SERCA2 expression. Our study demonstrates that gene deletion of ACE-N resulted in improved LV cardiac function in mice post-MI, which is likely mediated by increased circulating Ac-SDKP and minimally reduced expression of SERCA2. Thus, future development of specific and selective inhibitors for ACE-N could represent a novel approach to increase endogenous Ac-SDKP toward protecting the heart from post-MI remodeling.

Background

Septic cardiomyopathy is a common complication of septic shock and organ dysfunction. ITCH is a HECT (homologous to the E6-AP carboxyl-terminus)-type ubiquitin E3 ligase that plays a critical role in inflammatory suppression. Herein, we focused on the interaction between ITCH and key regulators of nuclear factor-κB (NF-κB), such as tumor necrosis factor receptor-associated factor 6 (TRAF6) and transforming growth factor-β activated kinase 1 (TAK1), and examined the impact of ITCH on the development of septic cardiomyopathy.

Methods and results

In H9C2 cardiomyocytes, ITCH protein expression decreased in response to lipopolysaccharide (LPS) and tumor necrosis factor alpha (TNFα). The protein interactions of ITCH with TRAF6 and TAK1 were confirmed by immunoprecipitation in vitro and in vivo. Based on overexpression and knockdown studies of ITCH in H9C2 cardiomyocytes, ITCH regulates the phosphorylation of NF-κB and subsequent interleukin 6 (IL-6) expression in response to LPS and TNFα stimulation. LPS was intraperitoneally injected into transgenic mice with cardiac-specific overexpression of ITCH (ITCH-Tg) and wild-type (WT) mice. Compared with WT mice, phosphorylation of NF-κB and subsequent IL-6 expression were inhibited in ITCH-Tg mice. Cardiac systolic dysfunction after LPS administration was ameliorated in ITCH-Tg mice, and the survival rate was higher in ITCH-Tg mice than in WT mice.

Conclusion

ITCH interacts with TRAF6 and TAK1 in cardiomyocytes and improves cardiac function and survival rates in septic cardiomyopathy by suppressing the NF-κB pathway.