Thyroid hormone induces sprouting angiogenesis in adult heart of hypothyroid mice through the PDGF-Akt pathway.

Study of physiological angiogenesis and associated signalling mechanisms in adult heart has been limited by the lack of a robust animal model. We investigated thyroid hormone-induced sprouting angiogenesis and the underlying mechanism. Hypothyroidism was induced in C57BL/6J mice by feeding with propylthiouracil (PTU). One year of PTU treatment induced heart failure. Both 12 weeks- (young) and 1 year-PTU (middle age) treatment caused a remarkable capillary rarefaction observed in capillary density. Three-day Triiodothyronine (T3) treatment significantly induced cardiac capillary growth in hypothyroid mice. In cultured left ventricle (LV) tissues from PTU-treated mice, T3 also induced robust sprouting angiogenesis where pericyte-wrapped endothelial cells formed tubes. The in vitro T3 angiogenic response was similar in mice pre-treated with PTU for periods ranging from 1.5 to 12 months. Besides bFGF and VEGF(164) , PDGF-BB was the most robust angiogenic growth factor, which stimulated notable sprouting angiogenesis in cultured hypothyroid LV tissues with increasing potency, but had little effect on tissues from euthyroid mice. T3 treatment significantly increased PDGF receptor beta (PDGFR-ß) protein levels in hypothyroid heart. PDGFR inhibitors blocked the action of T3 both on sprouting angiogenesis in cultured LV tissue and on capillary growth in vivo. In addition, activation of Akt signalling mediated in T3-induced angiogenesis was blocked by PDGFR inhibitor and neutralizing antibody. Our results suggest that hypothyroidism leads to cardiac microvascular impairment and rarefaction with increased sensitivity to angiogenic growth factors. T3-induced cardiac sprouting angiogenesis in adult hypothyroid mice was associated with PDGF-BB, PDGFR-ß and downstream activation of Akt.

Omega-3 fatty acids prevent pressure overload-induced cardiac fibrosis through activation of cyclic GMP/protein kinase G signaling in cardiac fibroblasts.

BACKGROUND: Omega-3 polyunsaturated fatty acids (eicosapentaenoic acid and docosahexaenoic acid) from fish oil ameliorate cardiovascular diseases. However, little is known about the effects of ω-3 polyunsaturated fatty acids on cardiac fibrosis, a major cause of diastolic dysfunction and heart failure. The present study assessed the effects of ω-3 polyunsaturated fatty acids on cardiac fibrosis. METHODS AND RESULTS: We assessed left ventricular fibrosis and pathology in mice subjected to transverse aortic constriction after the consumption of a fish oil or a control diet. In control mice, 4 weeks of transverse aortic constriction induced significant cardiac dysfunction, cardiac fibrosis, and cardiac fibroblast activation (proliferation and transformation into myofibroblasts). Dietary supplementation with fish oil prevented transverse aortic constriction-induced cardiac dysfunction and cardiac fibrosis and blocked cardiac fibroblast activation. In heart tissue, transverse aortic constriction increased active transforming growth factor-ß1 levels and phosphorylation of Smad2. In isolated adult mouse cardiac fibroblasts, transforming growth factor-ß1 induced cardiac fibroblast transformation, proliferation, and collagen synthesis. Eicosapentaenoic acid and docosahexaenoic acid increased cyclic GMP levels and blocked cardiac fibroblast transformation, proliferation, and collagen synthesis. Eicosapentaenoic acid and docosahexaenoic acid blocked phospho-Smad2/3 nuclear translocation. DT3, a protein kinase G inhibitor, blocked the antifibrotic effects of eicosapentaenoic acid and docosahexaenoic acid. Eicosapentaenoic acid and docosahexaenoic acid increased phosphorylated endothelial nitric oxide synthase and endothelial nitric oxide synthase protein levels and nitric oxide production. CONCLUSION: Omega-3 fatty acids prevent cardiac fibrosis and cardiac dysfunction by blocking transforming growth factor-ß1-induced phospho-Smad2/3 nuclear translocation through activation of the cyclic GMP/protein kinase G pathway in cardiac fibroblasts.

Changes in left ventricular function and remodeling after myocardial infarction in hypothyroid rats.

It has been shown that hypothyroidism may lead to delayed wound healing after experimental myocardial infarction (MI) in rats and increased infarct size in dogs. However, the long-term effect of hypothyroidism on left ventricular (LV) remodeling after MI has not been determined. Adult female Sprague-Dawley rats with and without surgical thyroidectomy (TX) were used in the study. Four weeks after TX, MI or sham MI was performed on TX and non-TX rats. Rats from all groups were examined 4 wk later. Four weeks after TX, hypothyroid-induced LV dysfunction was confirmed by echocardiography. In terminal experiments 4 wk after MI, TX sham-MI rats showed smaller hearts and impaired LV function compared with non-TX sham-MI controls. TX + MI rats showed smaller hearts with bigger infarct areas, higher LV end-diastolic pressures, and greater impairment of relaxation (-dP/dt) compared with non-TX MI rats. Relative changes after MI between TX and non-TX rats for most other hemodynamic and echocardiographic indexes were similar. These results suggest that preexisting hypothyroidism exaggerates post-MI remodeling and worsens LV function, particularly diastolic function.

Low-dose exposure and immunogenicity of transgenic maize expressing the Escherichia coli heat-labile toxin B subunit.

BACKGROUND: Transgenic maize, which produces the nontoxic B subunit of the Escherichia coli heat-labile toxin (LT-B) in seed, has proven to be an effective oral immunogen in mice. Currently, there is considerable concern over accidental consumption of transgenic maize expressing LT-B by humans and domestic animals. We have yet to define nonimmunogenic levels of transgenic LT-B when ingested. OBJECTIVES: Our goal in this study was to determine the highest dose of LT-B orally administered in mice that does not result in a measurable immune response. We defined an immune response as specific serum or mucosal IgG or IgA significantly greater than background after three feedings (0.0002-20 mug) or a priming response induced by the intermittent feeding. METHODS: We fed transgenic maize pellets on days 0, 7, 21, and 49 and collected serum and fecal samples weekly. Serum was analyzed for LT-B-specific IgG and IgA, and feces was analyzed for LT-B-specific IgA. RESULTS: We observed a dose-dependent anti-LT-B antibody response with high specific antibody concentrations in groups fed high doses (0.2, 2, 20 mug) of LT-B maize. Mice fed 0.02 mug LT-B demonstrated immune priming in 62.5% of the animals. Mice that were fed