Timothy P. Fitzgibbons

Similarity of mouse perivascular and brown adipose tissues and their resistance to diet-induced inflammation

Thoracic perivascular adipose tissue (PVAT) is a unique adipose depot that likely influences vascular function and susceptibility to pathogenesis in obesity and the metabolic syndrome. Surprisingly, PVAT has been reported to share characteristics of both brown and white adipose, but a detailed direct comparison to interscapular brown adipose tissue (BAT) has not been performed. Here we show by full genome DNA microarray analysis that global gene expression profiles of PVAT are virtually identical to BAT, with equally high expression of Ucp-1, Cidea, and other genes known to be uniquely or very highly expressed in BAT. PVAT and BAT also displayed nearly identical phenotypes upon immunohistochemical analysis, and electron microscopy confirmed that PVAT contained multilocular lipid droplets and abundant mitochondria. Compared with white adipose tissue (WAT), PVAT and BAT from C57BL6/J mice fed a high-fat diet for 13 wk had markedly lower expression of immune cell-enriched mRNAs, suggesting resistance to obesity-induced inflammation. Indeed, staining of BAT and PVAT for macrophage markers (F4/80 and CD68) in obese mice showed virtually no macrophage infiltration, and FACS analysis of BAT confirmed the presence of very few CD11b(+)/CD11c(+) macrophages in BAT (1.0%) compared with WAT (31%). In summary, murine PVAT from the thoracic aorta is virtually identical to interscapular BAT, is resistant to diet-induced macrophage infiltration, and thus may play an important role in protecting the vascular bed from inflammatory stress.

Epicardial and perivascular adipose tissues and their influence on cardiovascular disease: basic mechanisms and clinical associations.

It is well established that the cardiovascular (CV) risk of obesity is more strongly associated with visceral rather than subcutaneous adiposity.[1][1]–[3][2] Anthropometric variables that account for visceral adiposity, such as body mass index (BMI) and waist circumference (WC), have limited

Acquired long QT syndrome from stress cardiomyopathy is associated with ventricular arrhythmias and torsades de pointes

BACKGROUND Stress cardiomyopathy (SCM) is a syndrome of transient ventricular dysfunction triggered by severe emotional or physical stress, likely resulting from catecholamine-mediated myocardial toxicity. Repolarization abnormalities associated with other hyperadrenergic states can cause QT prolongation and lethal arrhythmia including torsades de pointes (TdP). Despite the development of repolarization abnormalities and QT prolongation in SCM, little is known about the risk of ventricular fibrillation (VF) and TdP. OBJECTIVE The aim of this study was to assess the prevalence and clinical predictors of ventricular arrhythmias in a cohort of patients with SCM. METHODS Data from a registry of consecutive patients with SCM from 2 institutions were reviewed. Patients who developed VF or TdP were identified. Clinical characteristics and outcomes were analyzed and compared with a control group of patients with SCM without VF/TdP. RESULTS Of 93 patients with SCM, 8 (8.6%) experienced VF/TdP. Of these 8 patients, 2 presented with VF and were subsequently diagnosed with SCM. Six other patients experienced pause-dependent TdP or VF after SCM diagnosis in the setting of substantial QT prolongation. Prolongation of the corrected QT interval (QTc) was significantly associated with the occurrence of ventricular arrhythmia (odds ratio 1.28 for each 10 ms increase in QTc, 95% confidence interval 1.10 to 1.50). CONCLUSION SCM can be associated with life-threatening ventricular arrhythmia in over 8% of cases. SCM should be recognized among the causes of acquired long QT syndrome and can be associated with a risk of TdP.

Endotoxin-induced inhibition of growth hormone receptor signaling in rat liver in vivo.

The bacterial lipopolysaccharide endotoxin induces a catabolic response characterized by resistance to multiple anabolic hormones. The objective of this study was to determine the effects of endotoxin on the GH signaling pathway in rat liver in vivo. After the iv injection of Escherichia coli endotoxin (1 mg/kg), there was a progressive decrease in liver STAT5 (signal transducer and activator of transcription-5) tyrosine phosphorylation in response to GH (40% decrease 6 h after endotoxin), which occurred in the absence of a change in abundance of the STAT5 protein. Endotoxin resulted in a rapid 40-fold increase in liver Janus family kinase-2 (JAK2) messenger RNA, followed by a 2-fold increase in JAK2 protein abundance. This was associated with a 50% decrease in phosphorylated/total JAK2 after GH stimulation. GH receptor abundance was unchanged, suggesting a postreceptor site of endotoxin-induced GH resistance. Rat complementary DNAs for three members of the suppressor of cytokine signaling gene family were cloned [cytokine-inducible sequence (CIS), suppressor of cytokine signaling-2 (SOCS-2), and SOCS-3] and, using these probes, messenger RNAs for SOCS-3 and CIS were shown to be increased 10- and 4-fold above control values, respectively, 2 h after endotoxin infusion. The finding of endotoxin inhibition of in vivo STAT5 tyrosine phosphorylation in response to a supramaximal dose of GH in the absence of a change in GH receptor abundance or total GH-stimulated JAK2 tyrosine phosphorylation provides the first demonstration of acquired postreceptor GH resistance. We hypothesize that this may occur through a specificity-spillover mechanism involving the induction of SOCS genes by cytokines released in response to endotoxin and subsequent SOCS inhibition of GH signaling.

Cardiac Remodeling in Obesity

Obesity has generated much interest within the cardiovascular community within the past 2 decades.1 It is now recognized that obesity is an important contributor to cardiac and all-cause mortality,1,2 independent of its association with other cardiovascular risk factors and increases the risk for cardiovascular morbidity, including heart failure (Figure 1).2–4 The malefic consequences of obesity are due both to the associated structural and functional cardiac alterations as well as the high prevalence of coexisting conditions, such as coronary artery disease, hypertension, sleep–disordered breathing (SDB), and diabetes mellitus.1–7 To better understand the relationship between obesity and heart failure, we will review what is known about cardiac structural remodeling in obesity as well as the evidence for preclinical abnormalities in left-ventricular (LV) systolic and diastolic functions. We will place particular emphasis on newer concepts and findings suggested by contemporary imaging methods. Figure 1. The population attributable risk of heart failure because of overweight is 14% in women and 8.8% in men. In obesity, the corresponding population attributable risks in women and men are 13.9 and 10.9%, respectively. From Kenchaiah et al,4 used with permission. By National Institutes of Health criteria, obesity is defined as a body mass index (BMI) ≥30 kg/m2 and severe obesity as a BMI≥40 kg/m2.8 Obesity involves the growth of both lean body mass and adipose tissue and is characterized by a disproportionate growth of adipose tissue in relationship to lean body mass.9 It is now recognized that adipose tissue is not a homogeneous organ, but is differentiated in relation to its metabolic activity. Whereas fat accumulating in the subcutaneous region does not require substantial blood supply,10 fat surrounding organs (abdominal, epicardial) is metabolically active, requires energy, and produces a number of compounds …

Systolic and Diastolic Mechanics in Stress Cardiomyopathy

Background— Stress cardiomyopathy (SCM) is a peculiar form of reversible left ventricular dysfunction seen predominantly in women and occurs in response to emotional or physical stress. Because dysfunction in SCM is reversible and that of acute myocardial infarction (MI) is not, we hypothesized that these fundamental mechanistic differences between SCM and MI would be associated with different systolic and diastolic properties. Methods and Results— We examined 3 groups, all women: patients with SCM (n=24; mean age, 63±12 years), those with left anterior (LAD) ST-segment–elevation MI (n=36; mean age, 63±10 years), and referent control subjects (n=30; mean age, 62±8 years). All underwent angiography, ventriculography, and pressure measurements within 48 hours of presentation. Left ventricular volumes, diastolic pressures, and diastolic stiffness were higher in SCM and LAD MI patients than in control subjects but no different from each other. Similarly, left ventricular diastolic pressures and diastolic stiffness were elevated in the SCM and LAD MI groups compared with the control group. Left ventricular ejection fraction in SCM and LAD MI were 40.8±12.3% and 49.6±5.6%, respectively, versus 70.4±9.4% in control subjects (P<0.001), and stroke work less than half the value of control subjects. Indexes of contractility and ventricular-arterial coupling were similarly abnormal in SCM and LAD MI. Conclusions— SCM and LAD MI show severe diastolic dysfunction. At similar left ventricular volumes, their diastolic pressures are more than twice as high as in control subjects, and systolic dysfunction is equally reduced in SCM and LAD MI. Despite a completely different pathophysiology in terms of systolic and diastolic function, SCM is indistinguishable from acute LAD-territory MI.

Endothelial NADPH oxidase 4 protects ApoE-/- mice from atherosclerotic lesions

Vascular reactive oxygen species (ROS) are known to be involved in atherosclerosis development and progression. NADPH oxidase 4 (Nox4) is a constitutively active ROS-producing enzyme that is highly expressed in the vascular endothelium. Nox4 is unique in its biology and has been implicated in vascular repair, however, the role of Nox4 in atherosclerosis is unknown. Therefore, to determine the effect of endothelial Nox4 on development of atherosclerosis, Apoe E-/- mice +/- endothelial Nox4 (ApoE-/- + EC Nox4) were fed a high cholesterol/high fat (Western) diet for 24 weeks. Significantly fewer atherosclerotic lesions were observed in the ApoE-/- + EC Nox4 mice as compared to the ApoE-/- littermates, which was most striking in the abdominal region of the aorta. In addition, markers of T cell populations were markedly different between the groups; T regulatory cell marker (FoxP3) was increased whereas T effector cell marker (T-bet) was decreased in aorta from ApoE-/- + EC Nox4 mice compared to ApoE-/- alone. We also observed decreased monokine induced by gamma interferon (MIG; CXCL9), a cytokine known to recruit and activate T cells, in plasma and tissue from ApoE-/- + EC Nox4 mice. To further investigate the link between endothelial Nox4 and MIG expression, we utilized cultured endothelial cells from our EC Nox4 transgenic mice and human cells with adenoviral overexpression of Nox4. In these cultured cells, upregulation of Nox4 attenuated endothelial cell MIG expression in response to interferon-gamma. Together these data suggest that endothelial Nox4 expression reduces MIG production and promotes a T cell distribution that favors repair over inflammation, leading to protection from atherosclerosis.

IRF3 and type I interferons fuel a fatal response to myocardial infarction

Interferon regulatory factor 3 (IRF3) and type I interferons (IFNs) protect against infections and cancer, but excessive IRF3 activation and type I IFN production cause autoinflammatory conditions such as Aicardi–Goutières syndrome and STING-associated vasculopathy of infancy (SAVI). Myocardial infarction (MI) elicits inflammation, but the dominant molecular drivers of MI-associated inflammation remain unclear. Here we show that ischemic cell death and uptake of cell debris by macrophages in the heart fuel a fatal response to MI by activating IRF3 and type I IFN production. In mice, single-cell RNA-seq analysis of 4,215 leukocytes isolated from infarcted and non-infarcted hearts showed that MI provokes activation of an IRF3–interferon axis in a distinct population of interferon-inducible cells (IFNICs) that were classified as cardiac macrophages. Mice genetically deficient in cyclic GMP-AMP synthase (cGAS), its adaptor STING, IRF3, or the type I IFN receptor IFNAR exhibited impaired interferon-stimulated gene (ISG) expression and, in the case of mice deficient in IRF3 or IFNAR, improved survival after MI as compared to controls. Interruption of IRF3-dependent signaling resulted in decreased cardiac expression of inflammatory cytokines and chemokines and decreased inflammatory cell infiltration of the heart, as well as in attenuated ventricular dilation and improved cardiac function. Similarly, treatment of mice with an IFNAR-neutralizing antibody after MI ablated the interferon response and improved left ventricular dysfunction and survival. These results identify IRF3 and the type I IFN response as a potential therapeutic target for post-MI cardioprotection.

Prevalence and clinical characteristics of right ventricular dysfunction in transient stress cardiomyopathy.

Transient stress cardiomyopathy (TSC) is a cause of reversible left ventricular (LV) dysfunction that is increasingly recognized. Reports to date have focused primarily on LV involvement, with little attention paid to associated right ventricular (RV) dysfunction. With other forms of LV dysfunction, RV involvement has been shown to confer an adverse prognosis. Prevalence, clinical characteristics, and short-term prognosis of RV dysfunction in TSC remain ill-defined. Presenting echocardiograms of 40 patients with TSC were reviewed. RV function was assessed by evaluating regional wall motion and calculating a wall motion score index (WMSI). RV dysfunction was defined as a WMSI >1.0. Clinical and demographic characteristics of patients with and without RV dysfunction were compared. RV dysfunction was identified in 27% of patients (11 of 40). RV WMSI was 1.20 +/- 0.30 for the entire cohort compared with 1.72 +/- 0.30 for those with RV dysfunction (p <0.05). In each case with RV dysfunction, regional wall motion abnormalities involved the apex and spared the base. Patients with RV dysfunction had higher B-type natriuretic peptide levels, higher pulmonary artery systolic pressures, and longer hospital stays. RV dimensions, clinical characteristics, electrocardiographic findings, other biomarkers, and in-hospital complications were similar. In conclusion, RV wall motion abnormalities, predominantly involving the apex and sparing the base, occur in slightly >1/4 of cases of TSC. Although associated with higher B-type natriuretic peptide levels, higher pulmonary artery systolic pressures, and longer hospital stays, RV dysfunction was not associated with significant differences in short-term cardiac morbidity or increased early mortality.

Endothelial protein kinase MAP4K4 promotes vascular inflammation and atherosclerosis

Signalling pathways that control endothelial cell (EC) permeability, leukocyte adhesion and inflammation are pivotal for atherosclerosis initiation and progression. Here we demonstrate that the Sterile-20-like mitogen-activated protein kinase kinase kinase kinase 4 (MAP4K4), which has been implicated in inflammation, is abundantly expressed in ECs and in atherosclerotic plaques from mice and humans. On the basis of endothelial-specific MAP4K4 gene silencing and gene ablation experiments in Apoe−/− mice, we show that MAP4K4 in ECs markedly promotes Western diet-induced aortic macrophage accumulation and atherosclerotic plaque development. Treatment of Apoe−/− and Ldlr−/− mice with a selective small-molecule MAP4K4 inhibitor also markedly reduces atherosclerotic lesion area. MAP4K4 silencing in cultured ECs attenuates cell surface adhesion molecule expression while reducing nuclear localization and activity of NFκB, which is critical for promoting EC activation and atherosclerosis. Taken together, these results reveal that MAP4K4 is a key signalling node that promotes immune cell recruitment in atherosclerosis.