Evidence for activation of inflammatory lipoxygenase pathways in visceral adipose tissue of obese Zucker rats.

Central obesity is associated with low-grade inflammation that promotes type 2 diabetes and cardiovascular disease in obese individuals. The 12- and 5-lipoxygenase (12-LO and 5-LO) enzymes have been linked to inflammatory changes, leading to the development of atherosclerosis. 12-LO has also been linked recently to inflammation and insulin resistance in adipocytes. We analyzed the expression of LO and proinflammatory cytokines in adipose tissue and adipocytes in obese Zucker rats, a widely studied genetic model of obesity, insulin resistance, and the metabolic syndrome. mRNA expression of 12-LO, 5-LO, and 5-LO-activating protein (FLAP) was upregulated in adipocytes and adipose tissue from obese Zucker rats compared with those from lean rats. Concomitant with increased LO gene expression, the 12-LO product 12-HETE and the 5-LO products 5-HETE and leukotriene B4 (LTB4) were also increased in adipocytes. Furthermore, upregulation of key proinflammatory markers interleukin (IL)-6, TNFα, and monocyte chemoattractant protein-1 were observed in adipocytes isolated from obese Zucker rats. Immunohistochemistry indicated that the positive 12-LO staining in adipose tissue represents cells in addition to adipocytes. This was confirmed by Western blotting in stromal vascular fractions. These changes were in part reversed by the novel anti-inflammatory drug lisofylline (LSF). LSF also reduced p-STAT4 in visceral adipose tissue from obese Zucker rats and improved the metabolic profile, reducing fasting plasma glucose and increasing insulin sensitivity in obese Zucker rats. In 3T3-L1 adipocytes, LSF abrogated the inflammatory response induced by LO products. Thus, therapeutic agents reducing LO or STAT4 activation may provide novel tools to reduce obesity-induced inflammation.

Activation of the pluripotency factor OCT4 in smooth muscle cells is atheroprotective.

Although somatic cell activation of the embryonic stem cell (ESC) pluripotency factor OCT4 has been reported, this previous work has been controversial and has not demonstrated a functional role for OCT4 in somatic cells. Here we demonstrate that smooth muscle cell (SMC)-specific conditional knockout of Oct4 in Apoe(-/-) mice resulted in increased lesion size and changes in lesion composition that are consistent with decreased plaque stability, including a thinner fibrous cap, increased necrotic core area, and increased intraplaque hemorrhage. Results of SMC-lineage-tracing studies showed that these effects were probably the result of marked reductions in SMC numbers within lesions and SMC investment within the fibrous cap, which may result from impaired SMC migration. The reactivation of Oct4 within SMCs was associated with hydroxymethylation of the Oct4 promoter and was hypoxia inducible factor-1α (HIF-1α, encoded by HIF1A) and Krüppel-like factor-4 (KLF4)-dependent. These results provide the first direct evidence that OCT4 has a functional role in somatic cells, and they highlight the potential role of OCT4 in normal and diseased somatic cells.

CD40 ligand promotes Mac-1 expression, leukocyte recruitment, and neointima formation after vascular injury.

High levels of circulating soluble CD40 ligand (sCD40L) are frequently found in patients with hypercholesterolemia, diabetes, ischemic stroke, or acute coronary syndromes, predicting an increased rate of atherosclerotic plaque rupture and restenosis after coronary/carotid interventions. Clinical restenosis is characterized in part by exaggerated neointima formation, but the underlying mechanism remains incompletely understood. This study investigated the role of elevated sCD40L in neointima formation in response to vascular injury in an atherogenic animal model and explored the molecular mechanisms involved. apoE(-/-) mice fed a Western diet developed severe hypercholesterolemia, significant hyperglycemia, and high levels of plasma sCD40L. Neointima formation after carotid denudation injury was exaggerated in the apoE(-/-) mice. In vivo, blocking CD40L with anti-CD40L monoclonal antibody attenuated the early accumulation of Ly-6G(+) neutrophils and Gr-1(+) monocytes (at 3 days) and the late accumulation of Mac-2(+) macrophages (at 28 days) in the denudated arteries; it also reduced the exaggerated neointima formation at 28 days. In vitro, recombinant CD40L stimulated platelet P-selectin and neutrophil Mac-1 expression and platelet-neutrophil co-aggregation and adhesive interaction. These effects were abrogated by anti-CD40L or anti-Mac-1 monoclonal antibody. Moreover, recombinant CD40L stimulated neutrophil oxidative burst and release of matrix metalloproteinase-9 in vitro. We conclude that elevated sCD40L promotes platelet-leukocyte activation and recruitment and neointima formation after arterial injury, potentially through enhancement of platelet P-selectin and leukocyte Mac-1 expression and oxidative activity.

12-Lipoxygenase-knockout mice are resistant to inflammatory effects of obesity induced by Western diet.

Inflammation is a key pathological process in the progression of atherosclerosis and type 2 diabetes. 12/15-lipoxygenase (12-LO), an enzyme involved in fatty acid metabolism, may contribute to inflammatory damage triggered by stressors such as obesity and insulin resistance. We hypothesized that mice lacking 12-LO are protected against inflammatory-mediated damage associated with a "western" diet. To test this hypothesis, age-matched male 12-LO knockout (12-LOKO) and wild-type C57BL/6 (B6) mice were fed either a standard chow or western diet and assessed for several inflammatory markers. Western-fed B6 mice showed expected reductions in glucose and insulin tolerance compared with chow-fed mice. In contrast, western-fed 12-LOKO mice maintained glucose and insulin tolerance similar to chow-fed mice. Circulating proinflammatory cytokines, tumor necrosis factor-alpha and interleukin-6, were increased in western B6 mice but not 12-LOKO mice, whereas the reported protective adipokine, adiponectin, was decreased only in western B6 mice. 12-LO activity was significantly elevated by western diet in islets from B6 mice. Islets from 12-LOKO mice did not show western-diet-induced islet hyperplasia or increases in caspase-3 apoptotic staining observed in western-fed B6 mice. Islets from 12-LOKO mice were also protected from reduced glucose-stimulated insulin secretion observed in islets from western-fed B6 mice. In visceral fat, macrophage numbers and monocyte chemoattractant protein-1 expression were elevated in western B6 mice but not 12-LOKO mice. These data suggest that 12-LO activation plays a role in western-diet-induced damage in visceral fat and islets. Inhibiting 12-LO may provide a new therapeutic approach to prevent inflammation-mediated metabolic consequences of excess fat intake.