Background— Adipose tissue inflammation may play a critical role in the pathogenesis of insulin resistance (IR). The present study examined the role of lymphocytes in adipose tissue inflammation and IR. Methods and Results— In a mouse model of obesity-mediated IR, high-fat diet (HFD) induced IR already after 5 weeks, which was associated with a marked T-lymphocyte infiltration in visceral adipose tissue. In contrast, recruitment of macrophages was delayed with an increase of MAC3-positive staining and F4/80 mRNA expression after 10 weeks of HFD, suggesting a dissociation of macrophage invasion into adipose tissue and IR initiation. In patients with type 2 diabetes, lymphocyte content in adipose tissue biopsies significantly correlated with waist circumference, a marker of IR. Immunohistochemical staining of human adipose tissue revealed the presence of mainly CD4-positive lymphocytes as well as macrophage infiltration. Most macrophages were HLA-DR–positive, reflecting activation through IFNγ, a cytokine released from CD4-positive lymphocytes. Conclusions— Proinflammatory T-lymphocytes are present in visceral adipose tissue and may contribute to local inflammatory cell activation before the appearance of macrophages, suggesting that these cells could play an important role in the initiation and perpetuation of adipose tissue inflammation as well as the development of IR.

Estrogen receptors (ER) are important regulators of metabolic diseases such as obesity and insulin resistance (IR). While ERα seems to have a protective role in such diseases, the function of ERβ is not clear. To characterize the metabolic function of ERβ, we investigated its molecular interaction with a master regulator of insulin signaling/glucose metabolism, the PPARγ, in vitro and in high-fat diet (HFD)-fed ERβ -/- mice (βERKO) mice. Our in vitro experiments showed that ERβ inhibits ligand-mediated PPARγ-transcriptional activity. That resulted in a blockade of PPARγ-induced adipocytic gene expression and in decreased adipogenesis. Overexpression of nuclear coactivators such as SRC1 and TIF2 prevented the ERβ-mediated inhibition of PPARγ activity. Consistent with the in vitro data, we observed increased PPARγ activity in gonadal fat from HFD-fed βERKO mice. In consonance with enhanced PPARγ activation, HFD-fed βERKO mice showed increased body weight gain and fat mass in the presence of improved insulin sensitivity. To directly demonstrate the role of PPARγ in HFD-fed βERKO mice, PPARγ signaling was disrupted by PPARγ antisense oligonucleotide (ASO). Blockade of adipose PPARγ by ASO reversed the phenotype of βERKO mice with an impairment of insulin sensitization and glucose tolerance. Finally, binding of SRC1 and TIF2 to the PPARγ-regulated adiponectin promoter was enhanced in gonadal fat from βERKO mice indicating that the absence of ERβ in adipose tissue results in exaggerated coactivator binding to a PPARγ target promoter. Collectively, our data provide the first evidence that ERβ-deficiency protects against diet-induced IR and glucose intolerance which involves an augmented PPARγ signaling in adipose tissue. Moreover, our data suggest that the coactivators SRC1 and TIF2 are involved in this interaction. Impairment of insulin and glucose metabolism by ERβ may have significant implications for our understanding of hormone receptor-dependent pathophysiology of metabolic diseases, and may be essential for the development of new ERβ-selective agonists.

The endothelium releases multiple mediators, not only regulators of vasomotor function but also important physiological and pathophysiological inflammatory mediators. Endothelial dysfunction is caused by chronic exposure to various stressors such as oxidative stress and modified low-density lipoprotein (LDL) cholesterol, resulting in impaired nitric oxide (NO) production and chronic inflammation. Biomechanical forces on the endothelium, including low shear stress from disturbed blood flow and hypertension, are also important causes of endothelial dysfunction. These processes seem to be augmented in patients with diabetes. In states of insulin resistance and in type 2 diabetes insulin signalling is impaired. Increased vascular inflammation, including enhanced expression of interleukin- 6 (IL-6), vascular cellular adhesion molecule-1 (VCAM-1) and monocyte chemoattractant protein (MCP- 1) are observed, as is a marked decrease in NO bioavailability. Furthermore, hyperglycaemia leads to increased formation of advanced glycation end products (AGE), which quench NO and impair endothelial function. In summary, during the development of diabetes a number of biochemical and mechanical factors converge on the endothelium, resulting in endothelial dysfunction and vascular inflammation. In the presence of insulin resistance, these processes are potentiated and they provide a basis for the macrovascular disease seen in diabetes.

OBJECTIVE-The angiotensin type 1 receptor blocker (ARB) and peroxisome proliferator-activated receptor (PPAR) ␥ modulator telmisartan has been recently demonstrated to reduce plasma triglycerides in nondiabetic and diabetic hypertensive patients. The present study investigates the molecular mechanisms of telmisartans hypolipidemic actions, in particular its effect on the PPAR␣ pathway.RESEARCH DESIGN AND METHODS-Regulation of PPAR␣ target genes by telmisartan was studied by real-time PCR and Western immunoblotting in vitro and in vivo in liver/skeletal muscle of mice with diet-induced obesity. Activation of the PPAR␣ ligand binding domain (LBD) was investigated using transactivation assays.RESULTS-Telmisartan significantly induced the PPAR␣ target genes carnitine palmitoyl transferase 1A (CPT1A) in human HepG2 cells and acyl-CoA synthetase long-chain family member 1 (ACSL1) in murine AML12 cells in the micromolar range. Telmisartan-induced CPT1A stimulation was markedly reduced after small interfering RNA-mediated knockdown of PPAR␣. Telmisartan consistently activated the PPAR␣-LBD as a partial PPAR␣ agonist. Despite high in vitro concentrations required for PPAR␣ activation, telmisartan (3 mg ⅐ kg Ϫ1 ⅐ day Ϫ1 ) potently increased ACSL1 and CPT1A expression in liver from dietinduced obese mice associated with a marked decrease of hepatic and serum triglycerides. Muscular CPT1B expression was not affected. Tissue specificity of telmisartan-induced PPAR␣ target gene induction may be the result of previously reported high hepatic concentrations of telmisartan.CONCLUSIONS-The present study identifies the ARB/PPAR␥ modulator telmisartan as a partial PPAR␣ agonist. As a result of its particular pharmacokinetic profile, PPAR␣ activation by telmisartan seems to be restricted to the liver. Hepatic PPAR␣ activation may provide an explanation for telmisartan's antidyslipidemic actions observed in recent clinical trials.

BackgroundInflammation of adipose tissue (AT) has been recently accepted as a first step towards obesity-mediated insulin resistance. We could previously show that mice fed with high fat diet (HFD) develop systemic insulin resistance (IR) and glucose intolerance (GI) associated with CD4-positive T-lymphocyte infiltration into visceral AT. These T-lymphocytes, when enriched in AT, participate in the development of fat tissue inflammation and subsequent recruitment of proinflammatory macrophages. The aim of this work was to elucidate the action of the insulin sensitizing PPARgamma on T-lymphocyte infiltration during development of IR, and comparison of the PPARgamma-mediated anti-inflammatory effects of rosiglitazone and telmisartan in diet-induced obesity model (DIO-model) in mice.MethodsIn order to investigate the molecular mechanisms underlying early development of systemic insulin resistance and glucose intolerance male C57BL/6J mice were fed with high fat diet (HFD) for 10-weeks in parallel to the pharmacological intervention with rosiglitazone, telmisartan, or vehicle.ResultsBoth rosiglitazone and telmisartan were able to reduce T-lymphocyte infiltration into AT analyzed by quantitative analysis of the T-cell marker CD3gamma and the chemokine SDF1alpha. Subsequently, both PPARgamma agonists were able to attenuate macrophage infiltration into AT, measured by the reduction of MCP1 and F4/80 expression. In parallel to the reduction of AT-inflammation, ligand-activated PPARgamma improved diet-induced IR and GI.ConclusionTogether the present study demonstrates a close connection between PPARgamma-mediated anti-inflammation in AT and systemic improvement of glucose metabolism identifying T-lymphocytes as one cellular mediator of PPARgamma´s action.

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Abstract-Migration of CD4-positive lymphocytes into the vessel wall represents an important step in early atherogenesis.Telmisartan is an angiotensin type 1 receptor (AT1R) blocker with peroxisome proliferator-activated receptor (PPAR)-␥-activating properties. The present study examined the effect of telmisartan on CD4-positive cell migration and the role of PPAR␥ in this context. CD4-positive lymphocytes express both the AT1R and PPAR␥. Stimulation of CD4-positive lymphocytes with stromal cell-derived factor (SDF)-1 leads to a 4.1Ϯ3.1-fold increase in cell migration. Pretreatment of cells with telmisartan reduces this effect in a concentration-dependent manner to a maximal 1.6Ϯ0.7-fold induction at 10 mol/L of telmisartan (PϽ0.01 compared with SDF-1-treated cells; nϭ22). Three different PPAR␥ activators, rosiglitazone, pioglitazone, and GW1929, had similar effects, whereas eprosartan, a non-PPAR␥-activating AT1R blocker, did not affect chemokine-induced lymphocyte migration. Telmisartan's effect on CD4-positive lymphocyte migration was mediated through an early inhibition of chemokine-induced phosphatidylinositol 3-kinase activity. Downstream, telmisartan inhibited F-actin formation, as well as intercellular adhesion molecule-3 translocation. Transfection of CD4-positive lymphocytes with PPAR␥ small interfering RNA abolished telmisartan's effect on migration, whereas blockade of the AT1R had no such effect. Telmisartan inhibits chemokine-induced CD4-positive cell migration independent of the AT1R via PPAR␥. These data provide a novel mechanism to explain how telmisartan modulates lymphocyte activation by its PPAR␥-activating properties. Key Words: telmisartan Ⅲ PPAR␥ Ⅲ angiotensin type 1 receptor blocker Ⅲ CD4-positive lymphocytes Ⅲ migration A therogenesis is an inflammatory process in the vessel wall involving inflammatory cells like monocytes, macrophages, and CD4-positive lymphocytes. 1 In early atherogenesis, CD4-positive lymphocytes are attracted by chemotactic proteins, such as regulated upon activation, normal T-cell expressed, and secreted (RANTES) and stromal cellderived factor (SDF)-1 and enter the vessel wall as naïve T-helper 0 cells. In the subendothelium, these cells then encounter antigens like oxidized low-density lipoprotein and differentiate into T-helper 1 cells, subsequently releasing proinflammatory mediators like tumor necrosis factor-␣ and interferon-␥. These cytokines then govern the inflammatory response in the vessel wall by activating other cells, such as endothelial cells, macrophages, and vascular smooth muscle cells, thus promoting the inflammatory process in atherogenesis. It is unclear whether an inhibition of cell migration itself modulates vascular disease, but various experimental studies have shown that a reduction in CD4-positive lymphocyte recruitment hampers lesion development and plaque formation. 2,3 Still, most of these studies targeted the effect of T-cell-specific chemokines, but hitherto little is known about modulatory effects on CD4-positive lymphocyte migration.T...

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