Excessive cardiac insulin signaling exacerbates systolic dysfunction induced by pressure overload in rodents.
ABSTRACT: Although many animal studies indicate insulin has cardioprotective effects, clinical studies suggest a link between insulin resistance (hyperinsulinemia) and heart failure (HF). Here we have demonstrated that excessive cardiac insulin signaling exacerbates systolic dysfunction induced by pressure overload in rodents. Chronic pressure overload induced hepatic insulin resistance and plasma insulin level elevation. In contrast, cardiac insulin signaling was upregulated by chronic pressure overload because of mechanical stretch-induced activation of cardiomyocyte insulin receptors and upregulation of insulin receptor and Irs1 expression. Chronic pressure overload increased the mismatch between cardiomyocyte size and vascularity, thereby inducing myocardial hypoxia and cardiomyocyte death. Inhibition of hyperinsulinemia substantially improved pressure overload-induced cardiac dysfunction, improving myocardial hypoxia and decreasing cardiomyocyte death. Likewise, the cardiomyocyte-specific reduction of insulin receptor expression prevented cardiac ischemia and hypertrophy and attenuated systolic dysfunction due to pressure overload. Conversely, treatment of type 1 diabetic mice with insulin improved hyperglycemia during pressure overload, but increased myocardial ischemia and cardiomyocyte death, thereby inducing HF. Promoting angiogenesis restored the cardiac dysfunction induced by insulin treatment. We therefore suggest that the use of insulin to control hyperglycemia could be harmful in the setting of pressure overload and that modulation of insulin signaling is crucial for the treatment of HF.
Project description:A close link between heart failure (HF) and systemic insulin resistance has been well documented, whereas myocardial insulin resistance and its association with HF are inadequately investigated. This study aims to determine the role of myocardial insulin resistance in ischemic HF and its underlying mechanisms. Male Sprague-Dawley rats subjected to myocardial infarction (MI) developed progressive left ventricular dilation with dysfunction and HF at 4 wk post-MI. Of note, myocardial insulin sensitivity was decreased as early as 1 wk after MI, which was accompanied by increased production of myocardial TNF-?. Overexpression of TNF-? in heart mimicked impaired insulin signaling and cardiac dysfunction leading to HF observed after MI. Treatment of rats with a specific TNF-? inhibitor improved myocardial insulin signaling post-MI. Insulin treatment given immediately following MI suppressed myocardial TNF-? production and improved cardiac insulin sensitivity and opposed cardiac dysfunction/remodeling. Moreover, tamoxifen-induced cardiomyocyte-specific insulin receptor knockout mice exhibited aggravated post-ischemic ventricular remodeling and dysfunction compared with controls. In conclusion, MI induces myocardial insulin resistance (without systemic insulin resistance) mediated partly by ischemia-induced myocardial TNF-? overproduction and promotes the development of HF. Our findings underscore the direct and essential role of myocardial insulin signaling in protection against post-ischemic HF.
Project description:Although postcapillary pulmonary hypertension (PH) is an important prognostic factor for patients with heart failure (HF), its pathogenesis remains to be fully elucidated. To elucidate the different roles of Rho-kinase isoforms, ROCK1 and ROCK2, in cardiomyocytes in response to chronic pressure overload, we performed transverse aortic constriction (TAC) in cardiac-specific ROCK1-deficient (cROCK1-/-) and ROCK2-deficient (cROCK2-/-) mice. Cardiomyocyte-specific ROCK1 deficiency promoted pressure-overload-induced cardiac dysfunction and postcapillary PH, whereas cardiomyocyte-specific ROCK2 deficiency showed opposite results. Histological analysis showed that pressure-overload-induced cardiac hypertrophy and fibrosis were enhanced in cROCK1-/- mice compared with controls, whereas cardiac hypertrophy was attenuated in cROCK2-/- mice after TAC. Consistently, the levels of oxidative stress were up-regulated in cROCK1-/- hearts and down-regulated in cROCK2-/- hearts compared with controls after TAC. Furthermore, cyclophilin A (CyPA) and basigin (Bsg), both of which augment oxidative stress, enhanced cardiac dysfunction and postcapillary PH in cROCK1-/- mice, whereas their expressions were significantly lower in cROCK2-/- mice. In clinical studies, plasma levels of CyPA were significantly increased in HF patients and were higher in patients with postcapillary PH compared with those without it. Finally, high-throughput screening demonstrated that celastrol, an antioxidant and antiinflammatory agent, reduced the expressions of CyPA and Bsg in the heart and the lung, ameliorating cardiac dysfunction and postcapillary PH induced by TAC. Thus, by differentially affecting CyPA and Bsg expressions, ROCK1 protects and ROCK2 jeopardizes the heart from pressure-overload HF with postcapillary PH, for which celastrol may be a promising agent.
Project description:Backgound: Cardiac pressure overload, for example in patients with aortic stenosis, induces irreversible damage in the myocardium leading to cardiac dysfunction, cardiomyocyte hypertrophy and interstitial fibrosis. We therefore hypothesized that insufficient cardiac regeneration might contribute to the progression of pressure overload dependent disease. Here, we aimed to elucidate whether pressure overload in the regenerative stage shortly after birth could lead to a more adaptive cardiac response than in the non-regenerative stage in mice.nTAC in the non-regenerative stage induced cardiac dysfunction, myocardial fibrosis and cardiomyocyte hypertrophy. In contrast, during induction of nTAC in the regenerative stage, cardiac function remained intact and this was associated with enhanced myocardial angiogenesis and innervation as well as increased cardiomyocyte proliferation, but neither hypertrophy nor fibrosis. Mechanistically, inhibition of cardiomyocyte proliferation and angiogenesis in nTAC in the regenerative phase by rapamycin triggered mortality and myocardial fibrosis, which both also similarly occurred upon inhibition of angiogenesis by PTK787, suggesting that both processes are essential for the adaptive cardiac response to nTAC. A comparative genome-wide transcriptomic analysis between hearts after nTAC in the regenerative versus the non-regenerative stage defined differentially expressed functional gene classes, and a related bioinformatics analysis suggested the transcription factor GATA4 as master regulator of the regenerative gene-program. Indeed, cardiomyocyte specific deletion of GATA4 converted the regenerative nTAC into a non-regenerative, maladaptive response.tablished a new model of neonatal pressure-overload in mice, which when applied in the regenerative postnatal stage, triggers a purely adaptive myocardial response. Employing this model to identify new regulators might lead to novel therapeutic strategies to combat pressure overload induced myocardial disease. Overall design: We established a transverse aortic constriction protocol in neonatal mice (nTAC) that could be induced either in the regenerative (at postnatal day P1) or in the non-regenerative stage (at P7) after birth. Echocardiography was used to assess cardiac dimensions and function in neonatal mice. Myocardial histological examinations were conducted to assess interstitial fibrosis, angiogenesis, innervation and cardiomyocyte proliferation. RNA deep sequencing was employed to compare the cardiac gene-expression pattern between nTAC in the regenerative versus the non-regenerative stage.
Project description:Cardiac pressure overload (for example due to aortic stenosis) induces irreversible myocardial dysfunction, cardiomyocyte hypertrophy and interstitial fibrosis in patients. In contrast to adult, neonatal mice can efficiently regenerate the heart after injury in the first week after birth. To decipher whether insufficient cardiac regeneration contributes to the progression of pressure overload dependent disease, we established a transverse aortic constriction protocol in neonatal mice (nTAC). nTAC in the non-regenerative stage (at postnatal day P7) induced cardiac dysfunction, myocardial fibrosis and cardiomyocyte hypertrophy. In contrast, nTAC in the regenerative stage (at P1) largely prevented these maladaptive responses and was in particular associated with enhanced myocardial angiogenesis and increased cardiomyocyte proliferation, which both supported adaptation during nTAC. A comparative transcriptomic analysis between hearts after regenerative versus non-regenerative nTAC suggested the transcription factor GATA4 as master regulator of the regenerative gene-program. Indeed, cardiomyocyte specific deletion of GATA4 converted the regenerative nTAC into a non-regenerative, maladaptive response. Our new nTAC model can be used to identify mediators of adaptation during pressure overload and to discover novel potential therapeutic strategies.
Project description:Left ventricular hypertrophy (LVH) is a major contributor to the development of heart failure (HF). Alterations in cyclic adenosine monophosphate (cAMP)-dependent signaling pathways participate in cardiomyocyte hypertrophy and mitochondrial dysfunction occurring in LVH and HF. cAMP signals are received and integrated by a family of cAMP-dependent protein kinase A (PKA) anchor proteins (AKAPs), tethering PKA to discrete cellular locations. AKAPs encoded by the Akap1 gene (mitoAKAPs) promote PKA mitochondrial targeting, regulating mitochondrial structure and function, reactive oxygen species production, and cell survival. To determine the role of mitoAKAPs in LVH development, in the present investigation, mice with global genetic deletion of Akap1 (Akap1-/-), Akap1 heterozygous (Akap1+/-), and their wild-type (wt) littermates underwent transverse aortic constriction (TAC) or SHAM procedure for 1 week. In wt mice, pressure overload induced the downregulation of AKAP121, the major cardiac mitoAKAP. Compared to wt, Akap1-/- mice did not display basal alterations in cardiac structure or function and cardiomyocyte size or fibrosis. However, loss of Akap1 exacerbated LVH and cardiomyocyte hypertrophy induced by pressure overload and accelerated the progression toward HF in TAC mice, and these changes were not observed upon prevention of AKAP121 degradation in seven in absentia homolog 2 (Siah2) knockout mice (Siah2-/-). Loss of Akap1 was also associated to a significant increase in cardiac apoptosis as well as lack of activation of Akt signaling after pressure overload. Taken together, these results demonstrate that in vivo genetic deletion of Akap1 enhances LVH development and accelerates pressure overload-induced cardiac dysfunction, pointing at Akap1 as a novel repressor of pathological LVH. These results confirm and extend the important role of mitoAKAPs in cardiac response to stress.
Project description:Induction of the cell cycle is emerging as an intervention to treat heart failure. Here, we tested the hypothesis that enhanced cardiomyocyte renewal in transgenic mice expressing cyclin D2 would be beneficial during hemodynamic overload. We induced pressure overload by transthoracic aortic constriction (TAC) or volume overload by aortocaval shunt in cyclin D2-expressing and WT mice. Although cyclin D2 expression dramatically improved survival following TAC, it did not confer a survival advantage to mice following aortocaval shunt. Cardiac function decreased following TAC in WT mice, but was preserved in cyclin D2-expressing mice. On the other hand, cardiac structure and function were compromised in response to aortocaval shunt in both WT and cyclin D2-expressing mice. The preserved function and improved survival in cyclin D2-expressing mice after TAC was associated with an approximately 50% increase in cardiomyocyte number and exaggerated cardiac hypertrophy, as indicated by increased septum thickness. Aortocaval shunt did not further impact cardiomyocyte number in mice expressing cyclin D2. Following TAC, cyclin D2 expression attenuated cardiomyocyte hypertrophy, reduced cardiomyocyte apoptosis, fibrosis, calcium/calmodulin-dependent protein kinase II? phosphorylation, brain natriuretic peptide expression, and sustained capillarization. Thus, we show that cyclin D2-induced cardiomyocyte renewal reduced myocardial remodeling and dysfunction after pressure overload but not after volume overload.
Project description:Nearly 50% of patients with heart failure (HF) have preserved LV ejection fraction, with interstitial fibrosis and cardiomyocyte hypertrophy as early manifestations of pressure overload. However, methods to assess both tissue characteristics dynamically and noninvasively with therapy are lacking. We measured the effects of mineralocorticoid receptor blockade on tissue phenotypes in LV pressure overload using cardiac magnetic resonance (CMR).Mice were randomized to l-nitro-?-methyl ester (l-NAME, 3 mg/mL in water; n=22), or l-NAME with spironolactone (50 mg/kg/day in subcutaneous pellets; n=21). Myocardial extracellular volume (ECV; marker of diffuse interstitial fibrosis) and the intracellular lifetime of water (?ic; marker of cardiomyocyte hypertrophy) were determined by CMR T1 imaging at baseline and after 7 weeks of therapy alongside histological assessments. Administration of l-NAME induced hypertensive heart disease in mice, with increases in mean arterial pressure, LV mass, ECV, and ?ic compared with placebo-treated controls, while LV ejection fraction was preserved (>50%). In comparison, animals receiving both spironolactone and l-NAME ("l-NAME+S") showed less concentric remodeling, and a lower myocardial ECV and ?ic, indicating decreased interstitial fibrosis and cardiomyocyte hypertrophy (ECV: 0.43 ± 0.09 for l-NAME versus 0.25 ± 0.03 for l-NAME+S, P<0.001; ?ic: 0.42 ± 0.11 for l-NAME groups versus 0.12 ± 0.05 for l-NAME+S group). Mice treated with a combination of l-NAME and spironolactone were similar to placebo-treated controls at 7 weeks.Spironolactone attenuates interstitial fibrosis and cardiomyocyte hypertrophy in hypertensive heart disease. CMR can phenotype myocardial tissue remodeling in pressure-overload, furthering our understanding of HF progression.
Project description:Cardiac failure occurs when the heart fails to adapt to chronic stresses. Reactive oxygen species (ROS)-dependent signaling is implicated in cardiac stress responses, but the role of different ROS sources remains unclear. Here we report that NADPH oxidase-4 (Nox4) facilitates cardiac adaptation to chronic stress. Unlike other Nox proteins, Nox4 activity is regulated mainly by its expression level, which increases in cardiomyocytes under stresses such as pressure overload or hypoxia. To investigate the functional role of Nox4 during the cardiac response to stress, we generated mice with a genetic deletion of Nox4 or a cardiomyocyte-targeted overexpression of Nox4. Basal cardiac function was normal in both models, but Nox4-null animals developed exaggerated contractile dysfunction, hypertrophy, and cardiac dilatation during exposure to chronic overload whereas Nox4-transgenic mice were protected. Investigation of mechanisms underlying this protective effect revealed a significant Nox4-dependent preservation of myocardial capillary density after pressure overload. Nox4 enhanced stress-induced activation of cardiomyocyte hypoxia inducible factor 1 and the release of vascular endothelial growth factor, resulting in increased paracrine angiogenic activity. These data indicate that cardiomyocyte Nox4 is a unique inducible regulator of myocardial angiogenesis, a key determinant of cardiac adaptation to overload stress. Our results also have wider relevance to the use of nonspecific antioxidant approaches in cardiac disease and may provide an explanation for the failure of such strategies in many settings.
Project description:Although cardiac and splenic mononuclear phagocytes (MPs), i.e., monocytes, macrophages and dendritic cells (DCs), are key contributors to cardiac remodeling after myocardial infarction, their role in pressure-overload remodeling is unclear. We tested the hypothesis that these immune cells are required for the progression of remodeling in pressure-overload heart failure (HF), and that MP depletion would ameliorate remodeling.C57BL/6 mice were subjected to transverse aortic constriction (TAC) or sham operation, and assessed for alterations in MPs. As compared with sham, TAC mice exhibited expansion of circulating LyC6hi monocytes and pro-inflammatory CD206- cardiac macrophages early (1 w) after pressure-overload, prior to significant hypertrophy and systolic dysfunction, with subsequent resolution during chronic HF. In contrast, classical DCs were expanded in the heart in a biphasic manner, with peaks both early, analogous to macrophages, and late (8 w), during established HF. There was no significant expansion of circulating DCs, or Ly6C+ monocytes and DCs in the spleen. Periodic systemic MP depletion from 2 to 16 w after TAC in macrophage Fas-induced apoptosis (MaFIA) transgenic mice did not alter cardiac remodeling progression, nor did splenectomy in mice with established HF after TAC. Lastly, adoptive transfer of splenocytes from TAC HF mice into naïve recipients did not induce immediate or long-term cardiac dysfunction in recipient mice.Mononuclear phagocytes populations expand in a phasic manner in the heart during pressure-overload. However, they are dispensable for the progression of remodeling and failure once significant hypertrophy is evident and blood monocytosis has normalized.
Project description:The receptor for advanced glycation end products (RAGE) is involved in heart failure (HF) by mediating diverse pathologic processes, including the promotion of inflammation and autophagy. However, the role of RAGE in pressure overload-induced HF is not well understood. We found that stimulation of RAGE triggered the death of neonatal rat ventricular myocytes (NRVMs), while cell death was alleviated by ATG5 knockdown. Using transverse aortic constriction (TAC) in mice as a model of pressure overload-induced HF, we demonstrated that RAGE knockout or RAGE blockade attenuated cardiac hypertrophy and fibrosis as well as cardiac dysfunction at 8 weeks after TAC. Importantly, RAGE knockout reversed upregulation of autophagy related proteins (LC3BII/I and Beclin 1) and reduced cardiomyocyte death, indicating that excessive autophagy after TAC was inhibited. Moreover, RAGE knockout or blockade reduced the upregulation of pp65-NF?B and BNIP3, which mediate autophagy. Taken together, these results suggest that RAGE plays an important role in the progression of HF by regulating autophagy. Therefore, inhibition of the RAGE-autophagy axis could be a promising new strategy for treatment of heart failure.