Interleukin-18 knockout mice display maladaptive cardiac hypertrophy in response to pressure overload.

Interleukin (IL)-18 is a cardiotropic proinflammatory cytokine chronically elevated in the serum of patients with cardiac hypertrophy (LVH). The purpose of this study was to examine the role of IL-18 in pressure-overload hypertrophy using wild type (WT) and IL-18 -/- (null) mice. Adult male C57Bl/6 mice underwent transaortic constriction (TAC) for 7days or sham surgery. Heart weight/body weight ratios showed blunted hypertrophy in IL-18 null TAC mice compared to WT TAC animals. Microarray analyses indicated differential expression of hypertrophy-related genes in WT versus IL-18 nulls. Northern, Western, and EMSA analyses showed Akt and GATA4 were increased in WT but unchanged in IL-18 null mice. Our results demonstrate blunted hypertrophy with reduced expression of contractile-, hypertrophy-, and remodeling-associated genes following pressure overload in IL-18 null mice, and suggest that IL-18 plays a critical role in the hypertrophic response.

Development of a synthetic promoter for macrophage gene therapy.

Macrophages have the potential to deliver therapeutic genes to many target tissues. Macrophage-specific synthetic promoters (SPs) generated by random ligation of myeloid/macrophage cis elements had activity up to 100-fold that of a native macrophage promoter in macrophage cell lines, but were minimally active in nonmyeloid cells. Mouse bone marrow cells (BMCs) transduced ex vivo with lentivectors expressing green fluorescent protein (GFP) driven either by an SP (SP-GFP) or a cytomegalovirus (CMV) promoter (CMV-GFP) were used for syngeneic transplantation of lethally irradiated mice. Blood leukocytes showed stable GFP expression for up to 15 months after transplantation. SP-GFP expression was selective for CD11b+ macrophages, whereas CMV-GFP expression was observed in erythrocytes, as well as in both CD11b+ and CD11b- leukocytes. Furthermore, SP-GFP expression was much stronger than CMV-GFP expression in CD11b+ macrophages. apoE-/- BMCs transduced with the lentiviral vector encoding human apoE were used to transplant apoE-/- mice. Macrophage expression of apoE from 10 to 26 weeks of age significantly reduced atherosclerotic lesions in recipient apoE-/- mice. Thus, the novel SPs, especially when combined with lentivectors, are useful for macrophage-specific delivery of therapeutic genes.

Interleukin-18 induces human cardiac endothelial cell death via a novel signaling pathway involving NF-kappaB-dependent PTEN activation.

The tumor suppressor gene PTEN (phosphatase and tensin homologue deleted on chromosome 10) antagonizes the pro-survival signaling of Akt and promotes cell death. Previously, we demonstrated that IL-18 induced apoptosis in human cardiac microvascular endothelial cells (HCMEC). Here we have investigated the role of PTEN in this response. Our results demonstrate that IL-18 reduced phospho-Akt and bcl-2 levels, stimulated NF-kappaB activation, and induced PTEN-promoter-reporter activity, mRNA expression, and protein levels in HCMEC. IL-18-mediated PTEN transcription was enhanced by ectopic expression of wild type p65, but inhibited by dominant negative (dn) IkappaB-alpha, dnp65, and dnIKKbeta. Furthermore, overexpression of constitutively active Akt and wild type bcl-2 blocked IL-18-mediated cell death. While forced expression of PTEN potentiated, expression of catalytically inactive PTEN attenuated IL-18-mediated cell death. IL-18-induced activation of NF-kappaB and PTEN upregulation were mediated by p38MAPK. Together, these studies demonstrate a novel signal transduction pathway involving p38MAPK-NF-kappaB-PTEN in IL-18-mediated HCMEC death, and identify IL-18 as potential therapeutic target to inhibit or reduce myocardial inflammation and injury.

Relative contribution of cardiovascular risk factors and rheumatoid arthritis clinical manifestations to atherosclerosis.

OBJECTIVE: To estimate the contribution of cardiovascular (CV) risk factors and rheumatoid arthritis (RA) disease manifestations to atherosclerosis in RA. METHODS: We used high-resolution carotid ultrasound to measure the carotid intima-media thickness (IMT) and plaque in 631 RA patients. Using R(2) measures from multivariable models, we estimated the contribution of demographic characteristics (age, sex, and ethnic group), CV risk factors (diabetes mellitus, hypercholesterolemia, cigarette smoking, hypertension, and body mass index, and RA manifestations (joint tenderness, swelling, and deformity, nodules, erythrocyte sedimentation rate [ESR], C-reactive protein, rheumatoid factor, the HLA-DRB1 shared epitope, and cumulative glucocorticoid dose) to each of the outcomes. Estimates were obtained in the full sample, and within strata defined by age, sex, and ethnic group. We tested for interaction between CV risk factors and RA manifestations. RESULTS: The contribution of demographic factors, CV risk factors, and RA manifestations to IMT and plaque R(2) varied depending on the patients' age stratum. Demographic features explained 11-16% of IMT variance, CV risk factors explained 4%-12%, and RA manifestations explained 1-6%. The greatest contribution of RA manifestations occurred in the youngest age group, while that of CV risk factors occurred in the older age groups. Results for carotid plaque were similar. There was a significant interaction between the number of CV risk factors present and the ESR, suggesting that the ESR's effect on IMT varied according to the number of CV risk factors. CONCLUSION: Both established CV risk factors and manifestations of RA inflammation contribute significantly to carotid atherosclerosis in RA, and may modify one another's effects. These findings may have implications regarding the prevention of atherosclerosis in RA.

The pro-atherogenic cytokine interleukin-18 induces CXCL16 expression in rat aortic smooth muscle cells via MyD88, interleukin-1 receptor-associated kinase, tumor necrosis factor receptor-associated factor 6, c-Src, phosphatidylinositol 3-kinase, Akt, c-Jun N-terminal kinase, and activator protein-1 signaling.

We recently demonstrated that the chemokine CXCL16 is expressed in aortic smooth muscle cells (ASMC) and induces ASMC adhesion and proliferation (Chandrasekar, B., Bysani, S., and Mummidi, S. (2004) J. Biol. Chem. 279, 3188-3196). Here we reort that interleukin (IL)-18 positively regulates CXCL16 transcription in rat ASMC. We characterized the cis-regulatory region of CXCL16 and identified a functional activator protein-1 (AP-1) binding motif. Deletion or mutation of this site attenuated IL-18-mediated CXCL16 promoter activity. Gel shift, supershift, and chromatin immunoprecipitation assays confirmed AP-1-dependent CXCL16 expression. CXCL16 promoter-reporter activity was increased by constitutively active c-Fos and c-Jun and decreased by dominant negative or antisense c-Fos and c-Jun. Src kinase inhibitors PP1 and PP2, phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin and LY294002, Akt inhibitor, the c-Jun N-terminal kinase (JNK) inhibitor SP600125, antisense JNK and dominant negative MyD88, interleukin-1 receptor-associated kinase (IRAK)-1, IRAK4, and phosphatidylinositol 3-kinase expression all attenuated IL-18-mediated AP-1 binding and reporter activity, CXCL16 promoter-reporter activity, and CXCL16 expression. Thus IL-18 induced CXCL16 expression via a MyD88 --> IRAK1-IRAK4-TRAF6 (tumor necrosis factor receptor-associated factor 6) --> c-Src--> PI3K --> Akt --> JNK --> AP-1 pathway. Importantly, IL-18 stimulated ASMC proliferation in a CXCL16-dependent manner. These data provide for the first time a mechanism of IL-18-mediated CXCL16 gene transcription and CXCL16-dependent ASMC proliferation and suggest a role for IL-18-CXCL16 cross-talk in atherogenesis and restenosis following angioplasty.

TNF-alpha and H2O2 induce IL-18 and IL-18R beta expression in cardiomyocytes via NF-kappa B activation.

Myocardial ischemia/reperfusion is characterized by oxidative stress and induction of proinflammatory cytokines. Interleukin (IL)-18, a member of the IL-1 family, acts as a proinflammatory cytokine, and is induced during various immune and inflammatory disorders. Therefore, in the present study we investigated whether IL-18 expression is regulated by cytokines and oxidative stress in cardiomyocytes. TNF-alpha induced rapid and sustained activation of NF-kappaB whereas H(2)O(2) induced delayed and transient activation. Both TNF-alpha and H(2)O(2) induced IL-18 mRNA and precursor protein in cardiomyocytes, and IL-18 release into culture supernatants. However, only TNF-alpha led to sustained expression. Expression of IL-18Rbeta, but not alpha, was induced by both agonists. TNF-alpha and H(2)O(2) induced delayed expression of IL-18 BP. Pretreatment with PDTC attenuated TNF-alpha and H(2)O(2) induced IL-18 and IL-18Rbeta, but not basal expression of IL-18Ralpha. These results indicate that adult cardiomyocytes express IL-18 and its receptors, and proinflammatory cytokines and oxidative stress regulate their expression via activation of NF-kappaB. Presence of both ligand and receptors suggests IL-18 impacts myocardial biology through an autocrine pathway.

Ultrasound-targeted antisense oligonucleotide attenuates ischemia/reperfusion-induced myocardial tumor necrosis factor-alpha.

Ultrasound contrast agents are now emerging as effective vehicles for delivering therapeutic agents to target tissues. In the present study, we used ultrasound-targeted, contrast-bound antisense oligonucleotides to inhibit the expression of tumor necrosis factor-alpha (TNF-alpha), a proinflammatory cytokine with negative inotropic effects. We compared the efficacy of left ventricular vs. intravenous administration and determined the optimal time for delivery. WKY rats were treated with perfluorocarbon-exposed sonicated dextrose albumin (PESDA) microspheres incubated with 100 microg of antisense oligonucleotide directed against TNF-alpha. Contrast was infused into either the superior vena cava or the left ventricular cavity along with simultaneous application of ultrasound. Twenty-four hours later, the animals underwent 15 min of ischemia and 2 h reperfusion. Control animals underwent sham operation only, ischemia/reperfusion only, or received PESDA only. A second group received treatment just prior to, or immediately after the onset of ischemia. At the end of the experimental period, hearts were removed and analyzed for TNF-alpha by northern and western blotting. While no TNF-alpha expression was detected in sham-operated animals, robust expression of TNF-alpha mRNA and protein was seen in controls treated with ultrasound and PESDA alone. In contrast, intravenous or left ventricular administration of antisense oligonucleotides significantly inhibited ischemia/reperfusion-induced TNF-alpha expression. Direct delivery into the left ventricular cavity was more effective than intravenous administration, and delivery just prior to ischemia was most effective in attenuating TNF-alpha expression. Furthermore, attenuation of TNF-alpha expression also significantly inhibited other post-ischemic inflammatory mediators including IL-1beta and intercellular adhesion molecule-1 (ICAM-1). Thus, ultrasound-targeted antisense oligonucleotides can effectively attenuate post-ischemic cytokine expression when delivered in a clinically relevant time frame, obviating the need for pretreatment.

A novel peroxide-induced calcium transient regulates interleukin-6 expression in cardiac-derived fibroblasts.

Reperfusion of ischemic myocardium leads to a local burst of free radicals, increased [Ca(2+)](i), and the release of proinflammatory cytokines. The purpose of this study was to determine whether brief exposure of cardiac fibroblasts to H(2)O(2) is associated with transient changes in [Ca(2+)](i) levels and whether this stimulus is sufficient to induce interleukin-6 (IL-6) expression. Cardiac derived fibroblasts were isolated from adult male rats and cultured under standard conditions. Individual coverslip-attached fibroblasts were loaded with the calcium probe Fura-2/AM and exposed to a single 3-min pulse of 100 microm H(2)O(2). In addition, low passage cultures were exposed to a pulse of H(2)O(2) and assayed for IL-6 expression. A brief exposure of H(2)O(2) led to a large intracellular Ca(2+) transient with a mean transient magnitude of 318 +/- 28 nm (mean +/- S.D., n = 12). Stimulation in the absence of [Ca(2+)](o) led to a 59% reduction in mean transient magnitude (129 +/- 23 nm, n = 10, p < 0.001), whereas pretreatment with the inositol 1,4,5-trisphosphate receptor blocker xestospongin C resulted in a 37% reduction (199 +/- 25 nm, n = 10, p < 0.01). Cells treated with xestospongin C and stimulated in the absence of [Ca(2+)](o) did not exhibit a Ca(2+) transient. Time-dependent IL-6 release was significantly elevated by 4 h (368 +/- 64 pg/mg protein, p < 0.01) and increased further by 24 h (1030 +/- 76 pg/mg protein). The depletion of cellular Ca(2+) by pretreatment with thapsigargin in the absence of [Ca(2+)](o) attenuated H(2)O(2)-induced IL-6 mRNA expression while blocking protein release. These data show that the exposure of cardiac fibroblasts to a brief pulse of physiological levels of H(2)O(2) resulted in a large Ca(2+) transient with intracellular and extracellular Ca(2+) contributions. Furthermore, brief H(2)O(2) exposure led to calcium-dependent IL-6 expression.