Reactive Oxygen Species (ROS) serve signaling functions in the vasculature, and hypoxia has been associated with increased ROS production. NADPH oxidase 4 (Nox4) is an ROS-producing enzyme that is highly expressed in the endothelium, yet its specific role is unknown. We sought to determine the role of Nox4 in the endothelial response to hypoxia.
Methods and Results
Hypoxia induced Nox4 expression both in vitro and in vivo and overexpression of Nox4 was sufficient to promote endothelial proliferation, migration, and tube formation. To determine the in vivo relevance of our observations, we generated transgenic mice with endothelial-specific Nox4 overexpression using the VE-cadherin promoter (VECad-Nox4 mice). In vivo, the VECad-Nox4 mice had accelerated recovery from hind limb ischemia and enhanced aortic capillary sprouting. Because endothelial nitric oxide synthase (eNOS) is involved in endothelial angiogenic responses and eNOS is activated by ROS, we probed the effect of Nox4 on eNOS. In cultured ECs overexpressing Nox4 we observed a significant increase in eNOS protein expression and activity. To causally address the link between eNOS and Nox4 we crossed our transgenic Nox4 mice with eNOS-/- mice. Aorta from these mice did not demonstrate enhanced aortic sprouting and VECad-Nox4 mice on the eNOS-/- background did not demonstrate enhanced recovery from hind limb ischemia.
Collectively, we demonstrate that augmented endothelial Nox4 expression promotes angiogenesis and recovery from hypoxia in an eNOS-dependent manner.
NADPH oxidase 4; Reactive Oxygen Species; Endothelium; Angiogenesis; Endothelial Nitric Oxide Synthase
Asthma affects an estimated 300 million people worldwide and accounts for 1 of 250 deaths and 15 million disability-adjusted life years lost annually. Plastic-adherent bone marrow–derived cell (BMC) administration holds therapeutic promise in regenerative medicine. However, given the low cell engraftment in target organs, including the lung, cell replacement cannot solely account for the reported therapeutic benefits. This suggests that BMCs may act by secreting soluble factors. BMCs also possess antiinflammatory and immunomodulatory properties and may therefore be beneficial for asthma. Our objective was to investigate the therapeutic potential of BMC-secreted factors in murine asthma. In a model of acute and chronic asthma, intranasal instillation of BMC conditioned medium (CdM) prevented airway hyperresponsiveness (AHR) and inflammation. In the chronic asthma model, CdM prevented airway smooth muscle thickening and peribronchial inflammation while restoring blunted salbutamol-induced bronchodilation. CdM reduced lung levels of the TH2 inflammatory cytokines IL-4 and IL-13 and increased levels of IL-10. CdM up-regulated an IL-10–induced and IL-10–secreting subset of T regulatory lymphocytes and promoted IL-10 expression by lung macrophages. Adiponectin (APN), an antiinflammatory adipokine found in CdM, prevented AHR, airway smooth muscle thickening, and peribronchial inflammation, whereas the effect of CdM in which APN was neutralized or from APN knock-out mice was attenuated compared with wild-type CdM. Our study provides evidence that BMC-derived soluble factors prevent murine asthma and suggests APN as one of the protective factors. Further identification of BMC-derived factors may hold promise for novel approaches in the treatment of asthma.
cellular therapy; bone marrow stromal cells; hypersensitivity; paracrine
The insulin-sensitizing agents referred to as thiazolidinediones (TZDs) possess anti-atherogenic and anti-inflammatory actions that contribute to protection against diabetic macrovascular complications. However, little is known about the effects of TZDs on retinal microvessel disorders. Here, we investigated whether TZDs modulate retinal vessel formation in a mouse model of oxygen- retinopathy.
Methods and Results
Neonatal mice were subjected to ischemia-induced retinopathy to produce pathological neovascular tuft formation. Pioglitazone (10 mg/kg/day), rosiglitazone (10 mg/kg/day) or vehicle was given by gavage once a day from postnatal day 7 (P7) to P17. Systemic treatment of wild-type (WT) mice with TZDs led to a significant decrease in pathological retinal neovascularization during ischemia compared with vehicle treatment, which was accompanied by increased plasma levels of the fat-derived hormone adiponectin. In contrast to WT mice, TZDs had no effects on ischemia-induced pathological retinal vessel formation in adiponectin-knockout (APN-KO) mice. Pioglitazone reduced tumor necrosis factor (TNF)-α expression in ischemic retina in WT mice but not in APN-KO mice. Furthermore, pioglitazone increased plasma adiponectin levels in TNF-α-KO mice but did not affect ischemia-induced pathological retinal neovascularization in this strain.
These data show that TZDs attenuate pathological retinal microvessel formation through adiponectin-mediated modulation of TNF-α production.
pioglitazone; adiponectin; neovascularization; ischemia; angiogenesis
Acute coronary syndrome is a leading cause of death in developed countries. Follistatin-like 1 (FSTL1) is a myocyte-derived secreted protein that is upregulated in the heart in response to ischemic insult. Here, we investigated the therapeutic impact of FSTL1 on acute cardiac injury in small and large preclinical animal models of ischemia/reperfusion and dissected its molecular mechanism.
Methods and Results
Administration of human FSTL1 protein significantly attenuated myocardial infarct size in a mouse or pig model of ischemia/reperfusion, which was associated with a reduction of apoptosis and inflammatory responses in the ischemic heart. Administration of FSTL1 enhanced the phosphorylation of AMP-activated protein kinase in the ischemia/reperfusion–injured heart. In cultured cardiac myocytes, FSTL1 suppressed apoptosis in response to hypoxia/reoxygenation and lipopolysaccharide-stimulated expression of proinflammatory genes through its ability to activate AMP-activated protein kinase. Ischemia/reperfusion led to enhancement of bone morphogenetic protein-4 expression and Smad1/5/8 phosphorylation in the heart, and FSTL1 suppressed the increased phosphorylation of Smad1/5/8 in ischemic myocardium. Treating cardiac myocytes with FSTL1 abolished the bone morphogenetic protein-4 –stimulated increase in apoptosis, Smad1/5/8 phosphorylation, and proinflammatory gene expression. In cultured macrophages, FSTL1 diminished lipopolysaccharide-stimulated expression of proinflammatory genes via activation of AMP-activated protein kinase and abolished bone morphogenetic protein-4 – dependent induction of proinflammatory mediators.
Our data indicate that FSTL1 can prevent myocardial ischemia/reperfusion injury by inhibiting apoptosis and inflammatory response through modulation of AMP-activated protein kinase– and bone morphogenetic protein-4 – dependent mechanisms, suggesting that FSTL1 could represent a novel therapeutic target for post-myocardial infarction, acute coronary syndrome.
apoptosis; inflammation; ischemia; myocytes; cardiac; reperfusion
Adiponectin (APN) is an adipose tissue-derived factor with anti-inflammatory and vascular protective properties whose levels paradoxically decrease with increasing body fat. In this study, APN’s role in the early development of ALI to lipopolysaccharide (LPS) was investigated. Intra-tracheal (i.t.) LPS elicited an exaggerated systemic inflammatory response in APN-deficient (APN−/−) mice compared to wild-type (wt) littermates. Increased lung injury and inflammation were observed in APN−/− mice as early as 4 hours after delivery of LPS. Targeted gene expression profiling performed on immune and endothelial cells isolated from lung digests 4 hours after LPS administration showed increased pro-inflammatory gene expression (e.g. IL-6) only in endothelial cells of APN−/− mice when compared to wt mice. Direct effects on lung endothelium were demonstrated by APN’s ability to inhibit LPS-induced IL-6 production in primary human endothelial cells in culture. Furthermore, T-cadherin-deficient (T-cad−/−) mice that have significantly reduced lung airspace APN but high serum APN levels had pulmonary inflammatory responses after i.t. LPS that were similar to those of wt mice. These findings indicate the importance of serum APN in modulating LPS-induced ALI and suggest that conditions leading to hypoadiponectinemia (e.g. obesity) predispose to development of ALI through exaggerated inflammatory response in pulmonary vascular endothelium.
Adiponectin; acute lung injury; endothelium; T-cadherin
Growth differentiation factor 15 (GDF15) is a stress-responsive cytokine and biomarker that is produced after myocardial infarction and that is related to prognosis in acute coronary syndrome (ACS). We hypothesized that secreted proteins that activate GDF15 production may represent new ACS biomarkers.
We expressed clones from an infarcted mouse heart cDNA library in COS1 cells and assayed for activation of a luciferase reporter gene controlled by a 642-bp fragment of the mouse growth differentiation factor 15 (GDF15) gene promoter. We measured the circulating concentrations of follistatin-like 1 (FSTL1) and GDF15 in 1369 patients with ACS.
One cDNA clone that activated the GDF15 promoter–luciferase reporter encoded the secreted protein FSTL1. Treatment with FSTL1 activated GDF15 production in cultured cardiomyocytes. Transgenic production of FSTL1 stimulated GDF15 production in the murine heart, whereas cardiomyocyte-selective deletion of FSTL1 decreased production of GDF15 in cardiomyocytes, indicating that FSTL1 is sufficient and required for GDF15 production. In ACS, FSTL1 emerged as the strongest independent correlate of GDF15 (partial R2 = 0.26). A total of 106 patients died of a cardiovascular cause during a median follow-up of 252 days. Patients with an FSTL1 concentration in the top quartile had a 3.7-fold higher risk of cardiovascular death compared with patients in the first 3 quartiles (P < 0.001). FSTL1 remained associated with cardiovascular death after adjustment for clinical, angiographic, and biochemical variables.
Our study is the first to use expression cloning for biomarker discovery upstream of a gene of interest and to identify FSTL1 as an independent prognostic biomarker in ACS.
Wnt signaling plays critical roles in development of various organs and pathogenesis of many diseases, and augmented Wnt signaling has recently been implicated in mammalian aging and aging-related phenotypes. We here report that complement C1q activates canonical Wnt signaling and promotes aging-associated decline in tissue regeneration. Serum C1q concentration is increased with aging, and Wnt signaling activity is augmented during aging in the serum and in multiple tissues of wild-type mice, but not in those of C1qa-deficient mice. C1q activates canonical Wnt signaling by binding to Frizzled receptors and subsequently inducing C1s-dependent cleavage of the ectodomain of Wnt coreceptor low-density lipoprotein receptor-related protein 6. Skeletal muscle regeneration in young mice is inhibited by exogenous C1q treatment, whereas aging-associated impairment of muscle regeneration is restored by C1s inhibition or C1qa gene disruption. Our findings therefore suggest the unexpected role of complement C1q in Wnt signal transduction and modulation of mammalian aging.
The worldwide epidemic of obesity has brought cons iderable attention to research aimed at understanding the biology of adipocytes (fat cells) and the events occurring in adipose tissue (fat) and in the bodies of obese individuals. Accumulating evidence indicates that obesity causes chronic low-grade inflammation and that this contributes to systemic metabolic dysfunction that is associated with obesity-linked disorders. Adipose tissue functions as a key endocrine organ by releasing multiple bioactive substances, known as adipose-derived secreted factors or adipokines, that have pro-inflammatory or anti-inflammatory activities. Dysregulated production or secretion of these adipokines owing to adipose tissue dysfunction can contribute to the pathogenesis of obesity-linked complications. In this Review, we focus on the role of adipokines in inflammatory responses and discuss their potential as regulators of metabolic function.
The mitofusin proteins MFN1 and MFN2 function to maintain mitochondrial networks by binding one another and initiating outer mitochondrial membrane fusion. While it has recently been recognized that vascular endothelial cells rely upon mitochondria as signaling rather than energy-producing moieties, the role of mitochondrial dynamics in endothelial cell function has not been addressed. To begin to understand what role mitochondrial dynamics play in this context, we examined the regulation of MFN1 and MFN2 and the consequences of siRNA-mediated knockdown of these proteins in cultured endothelial cells. Treatment with VEGF-A led to the upregulation of MFN2 and, to a lesser extent, MFN1. Knockdown of either MFN led to disrupted mitochondrial networks and diminished mitochondrial membrane potential. Knockdown of either MFN decreased VEGF-mediated migration and differentiation into network structures. MFN ablation also diminished endothelial cell viability and increased apoptosis under low mitogen conditions. Knockdown of MFN2 uniquely resulted in a decrease in the generation of reactive oxygen species as well as the blunting of the gene expression of components of the respiratory chain and transcription factors associated with oxidative metabolism. In contrast, ablation of MFN1 led to the selective reduction of VEGF-stimulated Akt-eNOS signaling. Taken together, our data indicate that mitochondrial dynamics, particularly those mediated by the mitofusins, play a role in endothelial cell function and viability.
mitofusins; nitric oxide; apoptosis; energy metabolism; mitochondria
Follistatin-like 1 (FSTL1) is an extracellular glycoprotein that is found in human serum. Recent work suggests that FSTL1 is secreted in response to ischemic injuries and that its overexpression is protective in the heart and vasculature.
Methods and Results
Here, we examined serum FSTL1 levels in patients with chronic heart failure with left ventricular (LV) ejection fraction <40% (n=86). The distribution of the sample, from these chronic heart failure patients, was separated into three tertiles of low, medium and high FSTL1 levels. Serum FSTL1 levels were increased 56% above age- and gender-matched, healthy controls. Diabetes mellitus, brain natriuretic peptide level, left atrial size, LV posterior wall thickness, LV end-diastolic diameter and LV mass were significant determinants of FSTL1 serum levels by bivariate analysis. After controlling for significant covariates, FSTL1 levels predicted LV hypertrophy (as measured by LV mass index) by multivariate linear regression analysis (P<0.001). Unadjusted survival analysis demonstrated increased mortality in patients with increasing FSTL1 levels (P=0.09). After adjusting for significant parameters, patients with increased FSTL1 remained at the highest risk of death [hazard ratio (95% confidence limits) 1.028, (0.98 and 1.78)]; (P=0.26). To determine whether elevated FSTL1 may be derived from the myocardium, FSTL1 protein expression was measured in samples from explanted, failing (n=18) and non-failing human hearts (n=7). LV failing hearts showed 2.5-fold higher FSTL1 protein levels than non-failing control hearts (P<0.05).
Elevated serum FSTL1 in human heart failure patients was associated with LV hypertrophy. Further studies on the role of FSTL1 as a biomarker in chronic systolic heart failure are warranted.
follistatin-like 1; systolic heart failure; left ventricular hypertrophy
Targeting gene therapy remains a challenge. The use of magnetic force to achieve this was investigated in the present study. It was hypothesized that nanoparticles with both controllable particle size and magnetic properties would enable magnetically driven gene delivery. We investigated this hypothesis by creating a family of novel biodegradable polymeric superparamagnetic nanoparticle (MNP) formulations. Polylactide MNP were formulated using a modified emulsification-solvent evaporation methodology with both the incorporation of oleate-coated iron oxide and a polyethylenimine (PEI) oleate ion-pair surface modification for DNA binding. MNP size could be controlled by varying the proportion of the tetrahydrofuran cosolvent. Magnetically driven MNP-mediated gene transfer was studied using a green fluorescent protein reporter plasmid in cultured arterial smooth muscle cells and endothelial cells. MNP-DNA internalization and trafficking were examined by confocal microscopy. Cell growth inhibition after MNP-mediated adiponectin plasmid transfection was studied as an example of a therapeutic end point. MNP-DNA complexes protected DNA from degradation and efficiently transfected quiescent cells under both low and high serum conditions after a 15 min exposure to a magnetic field (500 G). There was negligible transfection with MNP in the absence of a magnetic field. Larger sized MNP (375 nm diameter) exhibited higher transfection rates compared with 185 nm- and 240 nm-sized MNP. Internalized larger sized MNP escaped lysosomal localization and released DNA in the perinuclear zone. Adiponectin plasmid DNA delivery using MNP resulted in a dose-dependent growth inhibition of cultured arterial smooth muscle cells. It is concluded that magnetically driven plasmid DNA delivery can be achieved using biodegradable MNP containing oleate-coated magnetite and surface modified with PEI oleate ion-pair complexes that enable DNA binding.
GFP plasmid; magnetic nanoparticles; ion-pair complex; polyethylenimine; adiponectin
Duchenne muscular dystrophy, the most common form of childhood muscular dystrophy, is caused by X-linked inherited mutations in the dystrophin gene. Dystrophin deficiencies result in the loss of the dystrophin–glycoprotein complex at the plasma membrane, which leads to structural instability and muscle degeneration. Previously, we induced muscle-specific overexpression of Akt, a regulator of cellular metabolism and survival, in mdx mice at pre-necrotic (<3.5 weeks) ages and demonstrated upregulation of the utrophin–glycoprotein complex and protection against contractile-induced stress. Here, we found that delaying exogenous Akt treatment of mdx mice after the onset of peak pathology (>6 weeks) similarly increased the abundance of compensatory adhesion complexes at the extrasynaptic sarcolemma. Akt introduction after onset of pathology reverses the mdx histopathological measures, including decreases in blood serum albumin infiltration. Akt also improves muscle function in mdx mice as demonstrated through in vivo grip strength tests and in vitro contraction measurements of the extensor digitorum longus muscle. To further explore the significance of Akt in myofiber regeneration, we injured wild-type muscle with cardiotoxin and found that Akt induced a faster regenerative response relative to controls at equivalent time points. We demonstrate that Akt signaling pathways counteract mdx pathogenesis by enhancing endogenous compensatory mechanisms. These findings provide a rationale for investigating the therapeutic activation of the Akt pathway to counteract muscle wasting.
G protein-coupled inward rectifier K+ (GIRK) channels represent novel targets for the development of new therapeutic agents. GIRK channels are activated by a large number of G protein-coupled receptors (GPCRs) and regulate the electrical activity of neurons, cardiac myocytes, and β-pancreatic cells. Abnormalities in GIRK channel function have been implicated in the patho-physiology of neuropathic pain, drug addiction, cardiac arrhythmias, and other disorders. However, the pharmacology of these channels remains largely unexplored. In this paper we describe the development of a screening assay for identifying new modulators of neuronal and cardiac GIRK channels. Pituitary (AtT20) and cardiac (HL-1) cell lines expressing GIRK channels were cultured in 96-well plates, loaded with oxonol membrane potential-sensitive dyes and measured using a fluorescent imaging plate reader. Activation of the endogenous GPCRs in the cells caused a rapid, time-dependent decrease in the fluorescent signal; indicative of K+ efflux through the GIRK channels (GPCR stimulation versus control, Z′-factor = 0.5–0.7). As expected this signal was inhibited by addition of Ba2+ and the GIRK channel toxin tertiapin-Q. To test the utility of the assay for screening GIRK channel blockers, cells were incubated for 5 min with a compound library of Na+ and K+ channel modulators. Ion transporter inhibitors such as 5-(N,N-hexamethylene)-amiloride and SCH-28080 were identified as blockers of the GIRK channel at sub-micromolar concentrations. Thus, the screening assay will be useful for expanding the limited pharmacology of the GIRK channel and in developing new agents for the treatment of GIRK channelopathies.
GIRK channel; clonal cell lines; drug screening; neuropathic pain; atrial fibrillation
Pulmonary arterial hypertension (PAH) is a condition of unknown etiology whose pathological features include increased vascular resistance, perivascular inflammatory cell infiltration and pulmonary arteriolar remodeling. Although risk factors for PAH are poorly defined, recent studies indicate that obesity may be an important risk factor for this condition. The mechanisms leading to this association are largely unknown, but bioactive mediators secreted from adipose tissue have been implicated in this process. One of the most important mediators released from adipose tissue is the adipokine adiponectin. Adiponectin is highly abundant in the circulation of lean healthy individuals, and possesses well-described metabolic and antiinflammatory actions. Levels of adiponectin decrease with increasing body mass, and low levels are directly linked to the development of PAH in mice. Moreover, overexpression of adiponectin has been shown to protect mice from developing PAH in response to inflammation and hypoxia. Based on the findings from these studies, it is suggested that the effects of adiponectin are mediated, in part, through its antiinflammatory and antiproliferative properties. In this review, we discuss the emerging evidence demonstrating a role for adiponectin in lung vascular homeostasis and discuss how deficiency in this adipocyte-derived hormone might explain the recent association between obesity and PAH.
adipocyte; adipokine; inflammation; metabolism; treatment of pulmonary hypertension
Mitofusin-2 (Mfn-2) is a dynamin-like protein that is involved in the rearrangement of the outer mitochondrial membrane. Research using various experimental systems has shown that Mfn-2 is a mediator of mitochondrial fusion, an evolutionarily conserved process responsible for the surveillance of mitochondrial homeostasis. Here, we find that cardiac myocyte mitochondria lacking Mfn-2 are pleiomorphic and have the propensity to become enlarged. Consistent with an underlying mild mitochondrial dysfunction, Mfn-2-deficient mice display modest cardiac hypertrophy accompanied by slight functional deterioration. The absence of Mfn-2 is associated with a marked delay in mitochondrial permeability transition downstream of Ca2+ stimulation or due to local generation of reactive oxygen species (ROS). Consequently, Mfn-2-deficient adult cardiomyocytes are protected from a number of cell death-inducing stimuli and Mfn-2 knockout hearts display better recovery following reperfusion injury. We conclude that in cardiac myocytes, Mfn-2 controls mitochondrial morphogenesis and serves to predispose cells to mitochondrial permeability transition and to trigger cell death.
Pregnancy in women with diabetes is associated with a higher risk of perinatal complications. In particular, infants of diabetic mothers frequently suffer from respiratory distress syndrome (RDS), which is a leading cause of death in preterm infants and is considered to be primarily due to hyperinsulinemia in infants in response to maternal hyperglycemia. To elucidate the mechanism of how insulin signaling induces RDS, bronchoalveolar epithelium-specific Akt1 transgenic (TG) mice were generated. Akt1 overexpression in fetal lung epithelium resulted in RDS in preterm infants born by Caesarean section at embryonic day 18.5 (E18.5). The expression levels of hypoxia-inducible factor 2α (HIF-2α) and its target vascular endothelial growth factor (VEGF) were downregulated in the lung of Akt1 TG mice. Inhibition of the Akt-mammalian target of rapamycin (mTOR) signaling axis by rapamycin restored the expression of VEGF and improved the lung pathology of Akt1 TG pups. Rapamycin also attenuated the RDS phenotype in wild-type mice delivered preterm at E17.5. In cultured lung epithelial cells, insulin reduced VEGF expression and transcriptional activity of HIF-2 on VEGF promoter in an mTOR-dependent manner. Thus, aberrant activation of the Akt-mTOR pathway in lung epithelium plays a causal role in the pathogenesis of infant RDS, presumably through downregulation of HIF-2-dependent VEGF expression in the lung.
Although increasing evidence indicates that an adipokine adiponectin exerts protective actions on heart, its effects on coronary angiogenesis following pressure overload have not been examined previously. Because disruption of angiogenesis during heart growth leads to contractile dysfunction and heart failure, we hypothesized that adiponectin modulates cardiac remodeling in response to pressure overload through its ability to regulate adaptive angiogenesis.
Methods and Results
Adiponectin-knockout (APN-KO) and wild-type (WT) mice were subjected to pressure overload caused by transverse aortic constriction (TAC). APN-KO mice exhibited greater cardiac hypertrophy, pulmonary congestion, left ventricular (LV) interstitial fibrosis and LV systolic dysfunction after TAC surgery compared with WT mice. APN-KO mice also displayed reduced capillary density in the myocardium after TAC, which was accompanied by a significant decrease in expression of vascular endothelial growth factor (VEGF) and phosphorylation of AMP-activated protein kinase (AMPK). Inhibition of AMPK in WT mice resulted in aggravated LV systolic function, attenuated myocardial capillary density and decreased VEGF expression in response to TAC. The adverse effects of AMPK inhibition on cardiac function and angiogenic response following TAC were diminished in APN-KO mice relative to WT mice. Moreover, adenovirus-mediated VEGF delivery reversed the TAC-induced deficiencies in cardiac microvessel formation and ventricular function observed in the APN-KO mice. In cultured cardiac myocytes, adiponectin treatment stimulated VEGF production, which was inhibited by inactivation of AMPK signaling pathway.
Adiponectin deficiency can accelerate the transition from cardiac hypertrophy to heart failure during pressure overload through disruption of AMPK-dependent angiogenic regulatory axis.
adiponectin; AMPK; cardiac angiogenesis; pressure overload; heart failure
Cyclooxygenase-1 and -2 are rate-limiting enzymes in the formation of a wide array of bioactive lipid mediators collectively known as prostanoids (prostaglandins, prostacyclins, thromboxanes). Evidence from clinical trials shows that selective inhibition of the second isoenzyme (cyclooxygenase-2, or Cox-2) is associated with increased risk for serious cardiovascular events and findings from animal-based studies have suggested protective roles of Cox-2 for the heart. To further characterize the function of Cox-2 in the heart, mice with loxP sites flanking exons 4 and 5 of Cox-2 were rendered knockout specifically in cardiac myocytes (Cox-2 CKO mice) via cre-mediated recombination. Baseline cardiac performance of CKO mice remained unchanged and closely resembled that of control mice. Furthermore, myocardial infarct size induced after in vivo ischemia/reperfusion (I/R) injury was comparable between CKO and control mice. In addition, cardiac hypertrophy and function four weeks after transverse aortic constriction (TAC) was found to be similar between the two groups. Assessment of Cox-2 expression in purified adult cardiac cells isolated after I/R and TAC suggests that the dominant source of Cox-2 is found in the non-myocyte fraction. In conclusion, our animal-based analyses together with the cell-based observations portray a limited role of cardiomyocyte-produced Cox-2 at baseline and in the context of ischemic or hemodynamic challenge.
cyclooxygenase-2; cardiomyocyte; genetic; recombination; echocardiography; infarction; hypertrophy; fibrosis
Cardiac hypertrophy is associated with upregulation of vascular endothelial growth factor (VEGF) in the myocardium. Here, we evaluated the effects of a decoy VEGF receptor on heart morphology and function to a murine model of pressure overload hypertrophy. Mice were administered adenoviral vector encoding a decoy VEGF receptor (Ad-Flk), and their hearts were subjected to pressure overload by transverse aortic constriction (TAC). Treatment with Ad-Flk led to a net reduction in capillary density in hearts subjected to TAC. Ad-Flk also led to a reduction in TAC-induced cardiac hypertrophy and promoted left ventricle dilatation and a loss in contractile function. Treatment with Ad-Flk markedly increased myocardial fibrosis and collagen gene upregulation. In contrast, Ad-Flk had no effect on any of these parameters in sham-treated mice. Administration of a VEGF trap reagent diminished pressure overload cardiac hypertrophy and promoted the progression to heart failure but had no effect on sham-treated animals. These findings suggest that VEGF is required to maintain myocardial capillary density and that reductions in the vascular bed are associated with the transition from compensatory hypertrophy to failure.
heart failure; remodeling; endothelial growth factors; hypertrophy
Adipose tissue secretes proteins referred to as adipokines, many of which promote inflammation and disrupt glucose homeostasis. Here we show that secreted frizzled-related protein 5 (Sfrp5), a protein previously linked to the Wnt signaling pathway, is an anti-inflammatory adipokine whose expression is perturbed in models of obesity and type 2 diabetes. Sfrp5-deficient mice fed a high-calorie diet developed severe glucose intolerance and hepatic steatosis, and their adipose tissue showed an accumulation of activated macrophages that was associated with activation of the c-Jun N-terminal kinase signaling pathway. Adenovirus-mediated delivery of Sfrp5 to mouse models of obesity ameliorated glucose intolerance and hepatic steatosis. Thus, in the setting of obesity, Sfrp5 secretion by adipocytes exerts salutary effects on metabolic dysfunction by controlling inflammatory cells within adipose tissue.
Adiponectin, an adipocytokine, is secreted by adipocytes and mediates anti-hypertrophic and anti-inflammatory effects in the heart. Plasma concentrations of adiponectin are decreased in obesity, insulin resistance and obesity-associated conditions such as hypertension and coronary heart disease. However, a paradoxical increase in adiponectin levels is observed in human systolic heart failure (HF). We sought to investigate the determinants of adiponectin levels in patients with chronic systolic HF. Total adiponectin levels were measured in 99 patients with stable HF and left ventricular (LV) ejection fraction (EF) <40%. Determinants of adiponectin levels by univariate analysis were included in a multivariate linear regression model. At baseline patients were 62% black, 63% male, mean age of 60±13 years, LVEF of 21±9% and a body mass index (BMI) of 30.6±6.7kg/m2. Mean adiponectin levels were 15.8±15µg/ml. Beta-blocker use, BMI, and blood urea nitrogen (BUN) were significant determinants of adiponectin levels by multivariate analysis. LV mass, structure, and LVEF were not related to adiponectin levels by multivariate analysis. Interestingly, the effect of beta-blocker therapy was most marked in non-obese patients with BMI < 30kg/m2. In conclusion, in chronic systolic HF patients, beta-blocker therapy is correlated with lower adiponectin levels, especially in non-obese patients. This relation should be taken into account when studying the complex role of adiponectin in chronic systolic HF.
Adiponectin; chronic systolic heart failure; beta-blockers
The vasoactive peptide angiotensin II (AngII) is a potent cardiotoxic hormone whose actions have been well studied, yet questions remain pertaining to the downstream factors that mediate its effects in cardiomyocytes.
The in vivo role of the MEF2A target gene Xirp2 in AngII-mediated cardiac remodeling was investigated.
Methods and Results
Here we demonstrate that the MEF2A target gene Xirp2 (also known as cardiomyopathy associated gene 3; CMYA3) is an important effector of the AngII signaling pathway in the heart. Xirp2 belongs to the evolutionarily conserved, muscle-specific, actin-binding Xin gene family and is significantly induced in the heart in response to systemic administration of AngII. Initially, we characterized the Xirp2 promoter and demonstrate that AngII activates Xirp2 expression by stimulating MEF2A transcriptional activity. To further characterize the role of Xirp2 downstream of AngII signaling we generated mice harboring a hypomorphic allele of the Xirp2 gene that resulted in a marked reduction in its expression in the heart. In the absence of AngII, adult Xirp2 hypomorphic mice displayed cardiac hypertrophy and increased βMHC expression. Strikingly, Xirp2 hypomorphic mice chronically infused with AngII exhibited altered pathological cardiac remodeling including an attenuated hypertrophic response, as well as diminished fibrosis and apoptosis.
These findings reveal a novel MEF2A-Xirp2 pathway that functions downstream of AngII signaling to modulate its pathological effects in the heart.
Myocyte enhancer factor 2; Angiotensin II; Xirp2; myomaxin; cardiac hypertrophy; hypomorphic mice
The circulating, adipocyte-secreted hormone adiponectin (APN) exerts protective effects on the heart under stress conditions. The receptors binding APN to cardiac tissue, however, have remained elusive. Here, we report that the glycosyl phosphatidylinositol–anchored cell surface glycoprotein T-cadherin (encoded by Cdh13) protects against cardiac stress through its association with APN in mice. We observed extensive colocalization of T-cadherin and APN on cardiomyocytes in vivo. In T-cadherin–deficient mice, APN failed to associate with cardiac tissue, and its levels dramatically increased in the circulation. Pressure overload stress resulted in exacerbated cardiac hypertrophy in T-cadherin–null mice and paralleled corresponding defects in mice lacking APN. During ischemia-reperfusion injury, the absence of T-cadherin increased infarct size similar to that in APN-null mice. Myocardial AMPK is a major downstream protective signaling target of APN. In both cardiac hypertrophy and ischemia-reperfusion models, T-cadherin was necessary for APN-dependent AMPK phosphorylation. In APN-null mice, recombinant adenovirus-expressed APN reduced exaggerated hypertrophy and infarct size and restored AMPK phosphorylation as previously reported. In contrast, rescue was ineffective in mice lacking T-cadherin in addition to APN. These data suggest that T-cadherin protects from stress-induced pathological cardiac remodeling by binding APN and activating its cardioprotective functions.
TGF-β family cytokines have diverse actions in the maintenance of cardiac homeostasis. Activin A is a member of this family whose regulation and function in heart is not well understood at a molecular level. Follistatin-like 3 (Fstl3) is an extracellular regulator of Activin A protein, and its function in the heart is also unknown.
Methods and Results
We analyzed the expression of various TGF-β superfamily cytokines and their binding partners in mouse heart. Activin βA and Follistatin-like 3 (Fstl3) were upregulated in models of myocardial injury. Overexpression of Activin A with an adenoviral vector (Ad-actβA) or treatment with recombinant Activin A protein protected cultured myocytes from hypoxia/reoxygenation- induced apoptosis. Systemic overexpression of Activin A in mice, by intravenous injection of Ad-actβA, protected hearts from ischemia/reperfusion injury. Activin A induced the expression of Bcl-2, and ablation of Bcl-2 by siRNA abrogated its protective action in myocytes. The protective effect of Activin A on cultured myocytes was abolished by treatment with Fstl3 or by a pharmacological Activin receptor-Like Kinase (ALK) inhibitor. Cardiac specific Fstl3 knock-out mice showed significantly smaller infarcts after ischemia/reperfusion injury that was accompanied by reduced apoptosis.
Activin A and Fstl3 are induced in heart by myocardial stress. Activin A protects myocytes from death and this activity is antagonized by Fstl3. Thus, the relative expression levels of these factors following injury is a determinant of cell survival in the heart.
myocytes; apoptosis; reperfusion; Activin A; Follistatin-like 3
Pathological left ventricular (LV) hypertrophy frequently progresses to dilated heart failure with suppressed mitochondrial oxidative capacity. Dietary marine ω-3 polyunsaturated fatty acids (ω-3 PUFA) up-regulate adiponectin and prevent LV dilation in rats subjected to pressure overload. This study 1) assessed the effects of ω-3 PUFA on LV dilation and down-regulation of mitochondrial enzymes in response to pressure overload; and 2) evaluated the role of adiponectin in mediating the effects of ω-3 PUFA in heart.
Wild type (WT) and adiponectin-/- mice underwent transverse aortic constriction (TAC) and were fed standard chow ± ω-3 PUFA for 6 weeks. At 6 weeks, echocardiography was performed to assess LV function, mice were terminated, and mitochondrial enzyme activities were evaluated.
TAC induced similar pathological LV hypertrophy compared to sham mice in both strains on both diets. In WT mice TAC increased LV systolic and diastolic volumes and reduced mitochondrial enzyme activities, which were attenuated by ω-3 PUFA without increasing adiponectin. In contrast, adiponectin-/- mice displayed no increase in LV end diastolic and systolic volumes or decrease in mitochondrial enzymes with TAC, and did not respond to ω-3 PUFA.
These findings suggest ω-3 PUFA attenuates cardiac pathology in response to pressure overload independent of an elevation in adiponectin.