[Show abstract][Hide abstract] ABSTRACT: BACKGROUND: Pro-inflammatory cytokine tumor necrosis factor α (TNFα) induces β-adrenergic receptor (βAR) desensitization, but mechanisms proximal to the receptor in contributing to cardiac dysfunction are not known. METHODS AND RESULTS: Two different pro-inflammatory transgenic mouse models with cardiac overexpression of Myotrophin (a pro-hypertrophic molecule) or TNFα showed that TNFα alone is sufficient to mediate βAR desensitization as measured by cardiac adenylyl cyclase activity. M-mode echocardiography in these mouse models showed cardiac dysfunction paralleling βAR desensitization independent of sympathetic overdrive. TNFα-mediated βAR desensitization that precedes cardiac dysfunction is associated with selective upregulation of G-protein coupled receptor kinase 2 (GRK2) in both the mouse models. In vitro studies in β2AR overexpressing HEK 293 cells showed significant βAR desensitization, GRK2 upregulation and recruitment to the βAR complex following TNFα. Interestingly, inhibition of PI3K abolished GRK2-mediated βAR phosphorylation and GRK2 recruitment upon TNFα. Furthermore, TNFα-mediated βAR phosphorylation was not blocked with βAR antagonist propranolol. Additionally, TNFα administration in transgenic mice with cardiac overexpression of Gβγ sequestering peptide βARK-ct could not prevent βAR desensitization or cardiac dysfunction showing that GRK2 recruitment to the βAR is Gβγ independent. siRNA knock down of GRK2 resulted in loss of TNFα-mediated βAR phosphorylation. Consistently, cardiomyocytes from mice with cardiac-specific GRK2 ablation normalized the TNFα-mediated loss in contractility showing that TNFα-induced βAR desensitization is GRK2 dependent. CONCLUSIONS: TNFα-induced βAR desensitization is mediated by GRK2 and is independent of Gβγ uncovering a hitherto unknown cross-talk between TNFα and βAR function providing the underpinnings of inflammation-mediated cardiac dysfunction.
[Show abstract][Hide abstract] ABSTRACT: Atrial and brain natriuretic peptides (ANP and BNP) regulate blood pressure and cardiac function. In patients with heart failure (HF), plasma levels of pro-ANP and pro-BNP, the precursor forms of ANP and BNP, are highly elevated, but the mechanism underlying the apparent deficiency in natriuretic peptide processing is unclear. Corin is a cardiac protease that activates natriuretic peptides. In this study, we examined corin protein expression and activity in mouse and human failing hearts. Tissue samples were obtained from a mouse model of HF induced by myotrophin overexpression and from human nonfailing, hypertrophic, and failing hearts. Corin protein levels in the membrane fraction and tissue lysate were measured by Western blotting and ELISA. Corin catalytic and biological activities were measured by fluorescent substrate and pro-ANP processing assays. In mice, corin protein levels did not change with age in normal hearts but increased significantly in failing hearts. In humans, corin protein levels were similar in the atrium from nonfailing and failing hearts but were increased in the ventricle in failing hearts compared with those in nonfailing or hypertrophic hearts. Unlike the protein level, however, corin activity did not increase in failing hearts, as measured by fluorogenic substrate and pro-ANP processing assays. Our results indicate that corin activation is a rate-limiting step in failing hearts. Insufficient corin activation is expected to prevent natriuretic peptide processing and may contribute to body fluid retention and impaired cardiac function in patients with HF.
[Show abstract][Hide abstract] ABSTRACT: Myocardial remodeling denotes a chronic pathological condition of dysfunctional myocardium that occurs in cardiac hypertrophy (CH) and heart failure (HF). Reactive oxygen species (ROS) are major initiators of excessive collagen and fibronectin deposition in cardiac fibrosis. Increased production of ROS and nuclear factor κB (NF-κB) activation provide a strong link between oxidative stress and extracellular matrix (ECM) remodeling in cardiac hypertrophy. The protective inhibitory actions of pyrrolidine dithiocarbamate (PDTC), a pharmacological inhibitor of NF-κB and a potent antioxidant, make this a good agent to evaluate the role of inhibition of NF-κB and prevention of excessive ECM deposition in maladaptive cardiac remodeling during HF. In this report, we used a transgenic mouse model (Myo-Tg) that has cardiac-specific overexpression of myotrophin. This overexpression of myotrophin in the Myo-Tg model directs ECM deposition and increased NF-κB activity, which result in CH and ultimately HF. Using the Myo-Tg model, our data showed upregulation of profibrotic genes (including collagen types I and III, connective tissue growth factor, and fibronectin) in Myo-Tg mice, compared to wild-type mice, during the progression of CH. Pharmacological inhibition of NF-κB by PDTC in the Myo-Tg mice resulted in a significant reduction in cardiac mass, NF-κB activity, and profibrotic gene expression and improved cardiac function. To the best of our knowledge, this is the first report of ECM regulation by inhibition of NF-κB activation by PDTC. The study highlights the importance of the NF-κB signaling pathway and therapeutic benefits of PDTC treatment in cardiac remodeling.
Free Radical Biology and Medicine 10/2010; 50(1):206-15. DOI:10.1016/j.freeradbiomed.2010.10.711 · 5.71 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cardiac-specific overexpression of myotrophin (myo) protein in transgenic (myo-Tg) mice results in hypertrophy at 4 weeks that progresses to heart failure (HF) by 36 weeks. Gene profiling showed that p53 expression increases as hypertrophy worsens to HF, suggesting that p53 may influence myo-induced HF. We aimed to define how the p53 signalling cascade affects the spectrum of cardiac hypertrophy (CH)/HF.
Immunoblot analysis showed that in myo-Tg mice (Mus musculus), upregulation of p53 occurs only when hypertrophy transitions to HF (16 weeks onward). To elucidate the role of p53, a double-Tg mouse line (p53(-/-)/myo(+/+)) was developed by crossing myo-Tg mice with p53-null mice. A significant reduction in cardiac mass with improved cardiac function was observed in p53(-/-)/myo(+/+) mice, suggesting that absence of p53 prevents hypertrophy from turning into HF. Analysis via real-time reverse-transcription PCR revealed changes in transcripts of the p53 pathway in p53(-/-)/myo(+/+) mice. Ingenuity Pathway Analysis indicated that cross-talk among several key nodal molecules (e.g. cyclin-dependent kinase inhibitor 1A, caspase-3, nuclear factor kappa-light-chain enhancer of activated B cells etc.) may play a regulatory role in the transition of CH to HF.
Our data provide evidence, for the first time, that the coherence of p53 with myo plays an active role during the transition of CH to HF in a model of HF induced by myo overexpression. Transition from CH to HF can be prevented in the absence of p53 in myo-induced hypertrophy. Therefore, deletion/inhibition of p53 could be a therapeutic strategy to prevent CH from transitioning to HF.
Cardiovascular Research 03/2010; 87(3):524-34. DOI:10.1093/cvr/cvq068 · 5.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Studies at the morphological and molecular level have found that transgenic (Tg) mice that overexpress myotrophin in the heart develop hypertrophy at the early age of 4 weeks; this condition worsens to heart failure (HF) at approximately 36 weeks. However, how the sustained effects of alteration in cytoarchitecture of the contractile machinery lead to malfunction of the normal heart remains unclear. Our data have shown that at 4 weeks, the cytoarchitecture observed in left ventricular (LV) tissue samples of Tg mice is similar to that of wild-type (WT) mice. However, as the disease progresses, cardiomyocytes show deterioration in some mitochondrial as well as myofibril features, evidenced by swelling of mitochondria, misalignment of myofibril structure, and blurring as well as breakage of Z-lines. At 36 weeks of age, Tg mice (the group in transition from hypertrophy to HF) show significant degenerative changes in cardiomyocytes, including swelling of mitochondria, disruption of the nuclear membrane, and absence of myofibril structure. Besides these, formation of myelin bodies was also observed, a feature typically found in human hearts with HF. Changes in Z-line architecture were further confirmed by alteration in the gene expression profile of desmin and tubulin, the two main cytoskeletal proteins. We thus conclude that Tg mice overexpressing myotrophin show no visible changes in the initiation phase (4 weeks); however, as the disease progresses, alterations in the cytoskeleton are found during the transition phase from hypertrophy to HF (36 weeks onward). Our data suggest that treatment for prevention/reversal of hypertrophy should start at the early stage of hypertrophy to prevent its transition to HF.
[Show abstract][Hide abstract] ABSTRACT: Nuclear factor-kappaB (NF-kappaB) is a ubiquitous transcription factor that regulates various kinds of genes including inflammatory molecules, macrophage infiltration factors, cell adhesion molecules, and so forth, in various disease processes including cardiac hypertrophy and heart failure. Previously, we have demonstrated that activation of NF-kappaB was required in myotrophin-induced cardiac hypertrophy, in spontaneously hypertensive rats, and in dilated cardiomyopathy human hearts. Moreover, our recent study using the myotrophin-overexpressed transgenic mouse (Myo-Tg) model showed that short hairpin RNA-mediated knockdown of NF-kappaB significantly attenuated cardiac mass associated with improved cardiac function. Although it has been shown that NF-kappaB is substantially involved in cardiovascular remodeling, it is not clear whether the continuous blockade of NF-kappaB is effective in cardiovascular remodeling. To address this question, we took a genetic approach using IkappaB alpha triple mutant mice (3M) bred with Myo-Tg mice (a progressive hypertrophy/heart failure model). The double transgenic mice (Myo-3M) displayed an attenuated cardiac hypertrophy (9.8+/-0.62 versus 5.4+/-0.34, p<0.001) and improved cardiac function associated with significant inhibition of the NF-kappaB signaling cascade, hypertrophy marker gene expression, and inflammatory and macrophage gene expression at 24 weeks of age compared to Myo-Tg mice. NF-kappaB-targeted gene array profiling displayed several important genes that were significantly downregulated in Myo-3M mice compared to Myo-Tg mice. Furthermore, Myo-3M did not show any changes of apoptotic gene expression, indicating that significant inhibition of NF-kappaB activation reduces further proinflammatory reactions without affecting susceptibility to apoptosis. Therefore, development of therapeutic strategies targeting NF-kappaB may provide an effective approach to prevent adverse cardiac pathophysiological consequences.
[Show abstract][Hide abstract] ABSTRACT: Activation of the nuclear factor (NF)-kappaB signaling pathway may be associated with the development of cardiac hypertrophy and its transition to heart failure (HF). The transgenic Myo-Tg mouse develops hypertrophy and HF as a result of overexpression of myotrophin in the heart associated with an elevated level of NF-kappaB activity. Using this mouse model and an NF-kappaB-targeted gene array, we first determined the components of NF-kappaB signaling cascade and the NF-kappaB-linked genes that are expressed during the progression to cardiac hypertrophy and HF. Second, we explored the effects of inhibition of NF-kappaB signaling events by using a gene knockdown approach: RNA interference through delivery of a short hairpin RNA against NF-kappaB p65 using a lentiviral vector (L-sh-p65). When the short hairpin RNA was delivered directly into the hearts of 10-week-old Myo-Tg mice, there was a significant regression of cardiac hypertrophy, associated with a significant reduction in NF-kappaB activation and atrial natriuretic factor expression. Our data suggest, for the first time, that inhibition of NF-kappaB using direct gene delivery of sh-p65 RNA results in regression of cardiac hypertrophy. These data validate NF-kappaB as a therapeutic target to prevent hypertrophy/HF.
[Show abstract][Hide abstract] ABSTRACT: The transcription factor nuclear factor (NF)-kappaB plays a leading role in cardiac hypertrophy associated with heart failure, but whether it is involved in cardiac mass reduction is not known. We evaluated whether inhibiting the NF-kappaB cascade with pyrrolidine dithiocarbamate (PDTC) in spontaneously hypertensive rats (SHRs) and age-matched Wistar-Kyoto rats (WKYs) affected hypertrophy. We measured NF-kappaB signaling components [NF-kappaB translocation, IkappaBalpha, p65, mRNA and protein levels, and IkappaB kinase-beta (IKKbeta) activity] at 12 and 36 wk in WKYs and SHRs and at 10 wk in PDTC-treated rats (n = 9). NF-kappaB activation was also evaluated in rats treated for 10 wk with captopril or hydralazine alone or with either drug plus PDTC. All components were increased in SHRs compared with WKYs. After PDTC treatment, NF-kappaB activity was inhibited, and heart weight-to-body weight ratio in SHRs was significantly attenuated (3.52 +/- 0.04 to 3.32 +/- 0.05 mg/kg). Captopril treatment significantly reduced cardiac mass (3.5 vs. 3.05 mg/kg; n = 9) and inhibited NF-kappaB activity (169.71 +/- 5.70 to 106.7 +/- 12.44). Hydralazine had no effect on cardiac mass (3.5 vs. 3.42 mg/kg) or NF-kappaB activity (169.71 +/- 5.70 to 155.52 +/- 6.11). Hydralazine plus PDTC reduced blood pressure (191.16 +/- 1.7 to 158.5 +/- 2.36 mmHg) and inhibited NF-kappaB activity (169.71 +/- 5.70 to 97.29 +/- 3.65). Our data suggest that 1) cardiac hypertrophy in SHRs is partly due to NF-kappaB activation, 2) inhibition of NF-kappaB activity by PDTC parallels regression of hypertrophy, and 3) regression of hypertrophy is partly due to inhibition of NF-kappaB activity, independent of hypertension. The relationship between NF-kappaB activity and cardiac remodeling is causal, not coincidental.
[Show abstract][Hide abstract] ABSTRACT: Cardiac hypertrophy and ensuing heart failure are among the most common causes of mortality worldwide, yet the triggering mechanisms for progression of hypertrophy to failure are not fully understood. Tissue homeostasis depends on proper relationships between cell proliferation, differentiation, and death and any imbalance between them results in compromised cardiac function. Recently, we developed a transgenic (Tg) mouse model that overexpress myotrophin (a 12-kDa protein that stimulates myocyte growth) in heart resulting in hypertrophy that progresses to heart failure. This provided us an appropriate model to study the disease process at any point from initiation of hypertrophy end-stage heart failure. We studied detailed apoptotic signaling and regenerative pathways and found that the Tg mouse heart undergoes myocyte loss and regeneration, but only at a late stage (during transition to heart failure). Several apoptotic genes were up-regulated in 9-month-old Tg hearts compared with age-matched wild type or 4-week-old Tg hearts. Cardiac cell death during heart failure involved activation of Fas, tumor necrosis factor-alpha, and caspases 9, 8, and 3 and poly(ADP-ribose) polymerase cleavage. Tg mice with hypertrophy associated with compromised function showed significant up-regulation of cyclins,cyclin-dependent kinases (Cdks), and cell regeneration markers in myocytes. Furthermore, in human failing and nonfailing hearts, similar observations were documented including induction of active caspase 3 and Ki-67 proteins in dilated cardiomyopathic myocytes. Taken together, our data suggest that the stress of extensive myocardial damage from longstanding hypertrophy may cause myocytes to reenter the cell cycle. We demonstrate, for the first time in an animal model, that cell death and regeneration occur simultaneously in myocytes during end-stage heart failure, a phenomenon not observed at the onset of the disease process.
[Show abstract][Hide abstract] ABSTRACT: Hemodynamic load is a major determinant of cardiac mass and its phenotype, but very little is known about how mechanical load is converted into intracellular signals of gene expression and regulation. We have shown earlier that factors other than blood pressure control play a role in the mechanism involved in the development or regression of myocardial hypertrophy. We have identified a soluble factor, myotrophin, from the hearts of spontaneously hypertensive rats and dilated cardiomyopathic humans, which stimulates protein synthesis both in neonatal and adult rat cardiac myocytes. Myotrophin gene has been mapped and shown to be a novel gene localized in human chromosome 7q-33. The present study was conducted to evaluate the mechanism by which myotrophin is released and in turn initiates myocardial hypertrophy. We used an in vitro model, where neonatal cardiac myocytes were grown on stretchable plates and examined the effect of stretch on myotrophin gene expression (to mimic pressure overload), an in vivo model using beating non-working hearts exposed to high pressure and three different models of hypertensive rats. Our data showed that both cyclic stretch and exposure to high pressure caused significant increase in the transcript levels of myotrophin followed by expression of beta-myosin heavy chain and atrial natriuretic factor associated with an increase in myocardial protein synthesis. All three models of hypertensive rats also showed a significant increase in myotrophin transcripts. Altogether, our data strongly suggest that stretching of the cells by pressure or volume turns on the myotrophin, which in turn is responsible for the initiation process of myocardial hypertrophy in response to pressure or volume overload.
[Show abstract][Hide abstract] ABSTRACT: Abnormal stiffness and altered cardiac function arising from abnormal collagen deposition occur in hypertrophy and heart failure. ANG II has been shown to play a role in this process. To evaluate the mechanism, we developed an in vitro model by subjecting fibroblasts to ANG II treatment in the presence or absence of myocytes in coculture (25). Employing this model, we demonstrated that ANG II-induced collagen gene transcription in cardiac fibroblasts was potentiated by myocyte-derived factors. In attempting to identify mechanisms of collagen upregulation and to define the role of myocytes, we found that interleukin (IL)-6, tumor necrosis factor (TNF)-alpha, and the transforming growth factor (TGF)-beta superfamily were also involved in collagen upregulation. Collagen transcripts were increased after fibroblasts were treated with IL-6 (20-50 ng/ml) and TNF-alpha (0.1-0.5 ng/ml). In this study, we show that cardiomyocytes induce secretion of active TGF-beta in the presence of ANG II and that a paracrine action of TGF-beta subsequently induces different cytokines (IL-6) in fibroblasts, thereby promoting collagen synthesis. The cross-talk between myocytes and fibroblasts and involvement of these cytokines in the upregulation of collagen transcript levels are novel findings that may explain their possible roles in the upregulation of collagen.
[Show abstract][Hide abstract] ABSTRACT: Cardiac hypertrophy and heart failure remain leading causes of death in the United States. Many studies have suggested that, under stress, myocardium releases factors triggering protein synthesis and stimulating myocyte growth. We identified and cloned myotrophin, a 12-kDa protein from hypertrophied human and rat hearts. Myotrophin (whose gene is localized on human chromosome 7q33) stimulates myocyte growth and participates in cellular interaction that initiates cardiac hypertrophy in vitro. In this report, we present data on the pathophysiological significance of myotrophin in vivo, showing the effects of overexpression of cardio-specific myotrophin in transgenic mice in which cardiac hypertrophy occurred by 4 weeks of age and progressed to heart failure by 9-12 months. This hypertrophy was associated with increased expression of proto-oncogenes, hypertrophy marker genes, growth factors, and cytokines, with symptoms that mimicked those of human cardiomyopathy, functionally and morphologically. This model provided a unique opportunity to analyze gene clusters that are differentially up-regulated during initiation of hypertrophy versus transition of hypertrophy to heart failure. Importantly, changes in gene expression observed during initiation of hypertrophy were significantly different from those seen during its transition to heart failure. Our data show that overexpression of myotrophin results in initiation of cardiac hypertrophy that progresses to heart failure, similar to changes in human heart failure. Knowledge of the changes that take place as a result of overexpression of myotrophin at both the cellular and molecular levels will suggest novel strategies for treatment to prevent hypertrophy and its progression to heart failure.