NF-κB inhibition compromises cardiac fibroblast viability under hypoxia

Cellular mechanisms and molecular pathways linking bitter taste receptor signalling to cardiac inflammation, oxidative stress, arrhythmia and contractile dysfunction in heart diseases

Heart diseases and related complications constitute a leading cause of death and socioeconomic threat worldwide. Despite intense efforts and research on the pathogenetic mechanisms of these diseases, the underlying cellular and molecular mechanisms are yet to be completely understood. Several lines of evidence indicate a critical role of inflammatory and oxidative stress responses in the development and progression of heart diseases. Nevertheless, the molecular machinery that drives cardiac inflammation and oxidative stress is not completely known. Recent data suggest an important role of cardiac bitter taste receptors (TAS2Rs) in the pathogenetic mechanism of heart diseases. Independent groups of researchers have demonstrated a central role of TAS2Rs in mediating inflammatory, oxidative stress responses, autophagy, impulse generation/propagation and contractile activities in the heart, suggesting that dysfunctional TAS2R signalling may predispose to cardiac inflammatory and oxidative stress disorders, characterised by contractile dysfunction and arrhythmia. Moreover, cardiac TAS2Rs act as gateway surveillance units that monitor and detect toxigenic or pathogenic molecules, including microbial components, and initiate responses that ultimately culminate in protection of the host against the aggression. Unfortunately, however, the molecular mechanisms that link TAS2R sensing of the cardiac milieu to inflammatory and oxidative stress responses are not clearly known. Therefore, we sought to review the possible role of TAS2R signalling in the pathophysiology of cardiac inflammation, oxidative stress, arrhythmia and contractile dysfunction in heart diseases. Potential therapeutic significance of targeting TAS2R or its downstream signalling molecules in cardiac inflammation, oxidative stress, arrhythmia and contractile dysfunction is also discussed.

Protective effect and mechanistic evaluation of linalool against acute myocardial ischemia and reperfusion injury in rats

Linalool causes attenuation of IR induced cell death and apoptosis eitherin vitroorin vivo.

Combined hypoxia and sodium nitrite pretreatment for cardiomyocyte protection in vitro

Methods that increase cardiomyocyte survival upon exposure to ischemia, hypoxia and reoxygenation injuries are required to improve the efficacy of cardiac cell therapy and enhance the viability and function of engineered tissues. We investigated the effect of combined hypoxia/NaNO2 pretreatment on rat neonatal cardiomyocyte (CM), cardiac fibroblast, and human embryonic stem cell-derived CM (hESC-CM) survival upon exposure to hypoxia/reoxygenation (H/R) injury in vitro. Cells were pretreated with and without hypoxia and/or various concentrations of NaNO2 for 20 min, then incubated for 2 h under hypoxic conditions, followed by 2 h in normoxia. The control cells were maintained under normoxia for 4 h. Pretreatment with either hypoxia or NaNO2 significantly increased CM viability but had no effect on cardiac fibroblast viability. Combined hypoxia/NaNO2 pretreatment significantly increased CM viability but significantly decreased cardiac fibroblast viability. In rat neonatal CMs, cell death, as determined by lactate dehydrogenase (LDH) activity, was significantly reduced with hypoxia/NaNO2 pretreatment; and in hESC-CMs, hypoxia/NaNO2 pretreatment increased the BCL-2/BAX gene expression ratio, suggesting that hypoxia/NaNO2 pretreatment promotes cell viability by downregulating apoptosis. Additionally, we found a correlation between the prosurvival effect of hypoxia/NaNO2 pretreatment and the myoglobin content of the cells by comparing neonatal rat ventricular and atrial CMs, which express high and low myoglobin respectively. Functionally, hypoxia/NaNO2 pretreatment significantly improved the excitation threshold upon H/R injury to the level observed for uninjured cells, whereas pretreatment did not affect the maximum capture rate. Hence, hypoxia/NaNO2 pretreatment may serve as a strategy to increase CM survival in cardiac regenerative therapy applications and tissue engineering.

MMI-0100 inhibits cardiac fibrosis in myocardial infarction by direct actions on cardiomyocytes and fibroblasts via MK2 inhibition

The cell-permeant peptide inhibitor of MAPKAP kinase 2 (MK2), MMI-0100, inhibits MK2 and downstream fibrosis and inflammation. Recent studies have demonstrated that MMI-0100 reduces intimal hyperplasia in a mouse vein graft model, pulmonary fibrosis in a murine bleomycin-induced model and development of adhesions in conjunction with abdominal surgery. MK2 is critical to the pathogenesis of ischemic heart injury as MK2(-/-) mice are resistant to ischemic remodeling. Therefore, we tested the hypothesis that inhibiting MK2 with MMI-0100 would protect the heart after acute myocardial infarction (AMI) in vivo. AMI was induced by placing a permanent LAD coronary ligation. When MMI-0100 peptide was given 30 min after permanent LAD coronary artery ligation, the resulting fibrosis was reduced/prevented ~50% at a 2 week time point, with a corresponding improvement in cardiac function and decrease in left ventricular dilation. In cultured cardiomyocytes and fibroblasts, MMI-0100 inhibited MK2 to reduce cardiomyocyte caspase 3/7 activity, while enhancing primary cardiac fibroblast caspase 3/7 activity, which may explain MMI-0100's salvage of cardiac function and anti-fibrotic effects in vivo. These findings suggest that therapeutic inhibition of MK2 after acute MI, using rationally-designed cell-permeant peptides, inhibits cardiac fibrosis and maintains cardiac function by mechanisms that involve inhibiting cardiomyocyte apoptosis, while enhancing primary cardiac fibroblast cell death.

Mechanisms in cardiac fibroblast growth: an obligate role for Skp2 and FOXO3a in ERK1/2 MAPK-dependent regulation of p27kip1

Cardiac fibroblast hyperplasia associated with enhanced matrix deposition is a major determinant of tissue remodeling in several disease states of the heart. However, mechanisms controlling cell cycle progression in cardiac fibroblasts remain unexplored. Identification of cell cycle regulatory elements in these cells is important to develop strategies to check adverse cardiac remodeling under pathological conditions. This study sought to probe the mechanisms underlying ERK1/2-mediated p27Kip1 regulation in mitogenically stimulated cardiac fibroblasts. Addition of 10% fetal calf serum to quiescent cultures of adult rat cardiac fibroblasts promoted ERK1/2 activation, as evidenced by its phosphorylation status. Reduction in [3H]thymidine incorporation into DNA increased population doubling time, flow cytometry, and Western blot analysis showing reduced levels of cyclins D and A, p27Kip1 induction, and retinoblastoma protein (Rb) hypophosphorylation in ERK1/2-inhibited cells indicated ERK1/2 dependence of G1-S transition in cardiac fibroblasts. Lack of p27Kip1 protein in serum-stimulated, ERK1/2-active cells was associated with increased levels of Skp2, an E3 ubiquitin ligase for p27Kip1, whose knockdown by RNA interference induced p27Kip1 expression. Further, forced expression of Skp2 in ERK1/2-inhibited cells downregulated p27Kip1. Transcriptional upregulation of p27Kip1 mRNA in ERK1/2-inhibited cells, demonstrated by real-time PCR, correlated with forkhead box O 3a (FOXO3a) transcription factor activation, shown by gel shift assay. FOXO3a knockdown attenuated p27Kip1 mRNA and protein expression in ERK1/2-inhibited cells. We provide evidence for the first time that, in cardiac fibroblasts, activated ERK1/2 regulates p27Kip1 expression transcriptionally and posttranslationally via FOXO3a- and Skp2-dependent mechanisms. Additionally, this study uncovers interesting interactions between critical cell cycle regulatory elements that are only beginning to be understood.

Gambogic acid moderates cardiac responses to chronic hypoxia likely by acting on the proteasome and NF-κB pathway

Gambogic acid (GA) is the principal active ingredient of gamboges. GA was reported to exert anti-tumor and anti-inflammatory effects both in vitro and in vivo. Previously, we have shown that GA is a more tissue-specific proteasome inhibitor than bortezomib and it is less toxic to peripheral white blood cells compared to bortezomib. Ubiquitous proteasome inhibition was shown by some reports, but not by others, to prevent cardiac remodeling in response to pressure overload by blocking the NF-κB pathway; however, whether GA modulates the development of chronic hypoxia-induced right ventricular hypertrophy has not been investigated yet. Here we report that GA can significantly attenuate right ventricular hypertrophy induced by chronic hypoxia, reduce cardiac fibrosis, and remarkably block the reactivation of bona fide fetal genes in the cardiac tissue. Furthermore, we also investigated the potential molecular targets of GA on right ventricular hypertrophy. The results showed that GA could accumulate the IκB levels associated with decreased proteasomal activity, block the translocation of NF-κB from the cytoplasm to the nucleus, decrease NF-κB DNA-binding activity, and reduce IL-2 levels. In conclusion, GA is capable of preventing the development of chronic hypoxia-induced right ventricular hypertrophy. GA has great potential to be developed into an effective anti-hypertrophy agent.

cIAP-2 protects cardiac fibroblasts from oxidative damage: an obligate regulatory role for ERK1/2 MAPK and NF-κB

Cardiac fibroblasts are resistant to several pro-apoptotic factors that prevail in the diseased myocardium. Resistance to death signals may, in the short-term, enable these cells to play a central role in tissue repair following myocyte loss but, in the long-term, facilitate their persistence in the infarct scar, resulting in disproportionate stromal growth and pump dysfunction. Surprisingly, the molecular basis of apoptosis resistance in cardiac fibroblasts remains unclear. We explored the recruitment of anti-apoptotic mechanisms in cardiac fibroblasts subjected to oxidative stress, a major component of ischemia-reperfusion injury and heart failure. Cardiac fibroblasts exposed to H2O2 expressed enhanced levels of anti-apoptotic cIAP-2 mRNA and protein, revealed by real time PCR and western blot analysis, respectively. Pulmonary fibroblasts did not express cIAP-2 and were more susceptible than cardiac fibroblasts to H2O2. cIAP-2 knockdown by RNA interference promoted apoptosis in H2O2-treated cardiac fibroblasts. Electrophoretic mobility shift assay showed NF-κB activation in cells under oxidative stress. NF-κB inhibition in H2O2-treated cells resulted in significant attenuation of cIAP-2 mRNA and protein expression and apoptosis, indicating involvement of NF-κB in cell survival via regulation of cIAP-2. Further, pCMV promoter-driven constitutive expression of cIAP-2 reduced viability loss in NF-κB-inhibited cardiac fibroblasts exposed to oxidative stress. H2O2 also caused ERK1/2 activation, which, upon inhibition, prevented IκBα degradation and nuclear translocation of NF-κB. Moreover, ERK1/2 inhibition attenuated H2O2-induced cIAP-2 expression and compromised viability in H2O2-treated cardiac fibroblasts. We propose for the first time that ERK1/2-dependent activation of NF-κB and consequent induction of cIAP-2 protects cardiac fibroblasts from oxidative damage.

The impact of hypoxia on cell death pathways

Hypoxia is a frequently encountered feature of the cellular microenvironment in a number of pathophysiological processes in which programmed cell death (apoptosis) affects disease progression including, but not limited to, cancer, chronic inflammation, myocardial infarction, stroke and ischaemic acute kidney injury. In these diseases, the presence of hypoxia can significantly affect the rate of cell death and thus may make a significant contribution to disease progression. In the present review, we discuss the complex relationship that exists between the presence of hypoxia and the regulation of cell death pathways.