PPAR gamma is required for fat cell development and is the molecular target of antidiabetic thiazolidinediones (TZDs), which exert insulin-sensitizing effects in adipose tissue, skeletal muscle, and liver. Unexpectedly, we found that inactivation of PPAR gamma in macrophages results in the development of significant glucose intolerance plus skeletal muscle and hepatic insulin resistance in lean mice fed a normal diet. This phenotype was associated with increased expression of inflammatory markers and impaired insulin signaling in adipose tissue, muscle, and liver. PPAR gamma-deficient macrophages secreted elevated levels of factors that impair insulin responsiveness in muscle cells in a manner that was enhanced by exposure to FFAs. Consistent with this, the relative degree of insulin resistance became more severe in mice lacking macrophage PPAR gamma following high-fat feeding, and these mice were only partially responsive to TZD treatment. These findings reveal an essential role of PPAR gamma in macrophages for the maintenance of whole-body insulin action and in mediating the antidiabetic actions of TZDs.

Habitual aerobic exercise is associated with enhanced endothelium-dependent dilatation (EDD) in older humans, possibly by increasing nitric oxide bioavailability and reducing oxidative stress. However, the mechanisms involved are incompletely understood. EDD was measured in young (6-8 months) and old (29-32 months) cage control and voluntary wheel running (VR) B6D2F1 mice. Age-related reductions in maximal carotid artery EDD to acetylcholine (74 vs. 96%, P < 0.01) and the nitric oxide (NO) component of EDD (maximum dilatation with ACh and l-NAME minus that with ACh alone was −28% vs. −55%, P < 0.01) were restored in old VR (EDD: 96%, NO: −46%). Nitrotyrosine, a marker of oxidative stress, was increased in aorta with age, but was markedly lower in old VR (P < 0.05). Aortic superoxide dismutase (SOD) activity was greater (P < 0.01), whereas NADPH oxidase protein expression (P < 0.01) and activity (P = 0.05) were lower in old VR vs. old cage control. Increasing SOD (with 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl) and inhibition of NADPH oxidase (with apocynin) improved EDD and its NO component in old cage control, but not old VR mice. VR increased endothelial NO synthase (eNOS) protein expression (P < 0.05) and activation (Ser1177 phosphorylation) (P < 0.05) in old mice. VR did not affect EDD in young mice. Our results show that voluntary aerobic exercise restores the age-associated loss of EDD by suppression of oxidative stress via stimulation of SOD antioxidant activity and inhibition of NADPH oxidase superoxide production. Increased eNOS protein and activation also may contribute to exercise-mediated preservation of NO bioavailability and EDD with ageing.

To determine if B6D2F1 mice represent a suitable model of oxidative stress-mediated impaired endothelium-dependent dilation (EDD) with aging, mice were studied at 6.9 +/- 0.3 and 31.9 +/- 0.6 months. EDD to acetylcholine (ACh) was 26% (p < .001) and 12% (p < .001) lower, respectively, in isolated carotid (n = 10-11) and femoral (n = 10) arteries from older mice, and reductions in arterial pressure to systemic ACh infusion were smaller in older mice (n = 6-10; p < .01). Nitrotyrosine was marked in aorta of older mice (p < .05, n = 4). Superoxide production in carotid arteries was greater (p < .05), and TEMPOL restored dilation in carotid arteries and systemically in older mice. N(G)-nitro-l-arginine methyl ester (l-NAME) reduced carotid artery dilation in young more than older mice, whereas TEMPOL restored the effects of l-NAME in older mice. Carotid artery stiffness was increased in older compared with young mice (p = .04). Our results provide the first comprehensive evidence that B6D2F1 mice are a useful model for investigating mechanisms of reduced nitric oxide-dependent, oxidative stress-associated EDD and increased arterial stiffness with aging.

We tested the hypothesis that aging will exacerbate the negative vascular consequences of exposure to a common physiological stressor, i.e., consumption of a “western” (high fat/high sucrose) diet (WD) by inducing superoxide-associated reductions in nitric oxide (NO) bioavailability, and that this would be prevented by voluntary aerobic exercise. Incremental stiffness and endothelium-dependent dilation (EDD) were measured in the carotid arteries of young (5.4±0.3 mo, N=20) and old (30.4±0.2 mo, N=19) male B6D2F1 mice fed normal chow (NC: 17% fat, 0% sucrose) or a western diet (40% fat, 19% sucrose) diet and housed in either standard cages or cages equipped with running wheels for 10–14 weeks. Incremental stiffness was higher in old NC (P<0.05) and both young (P<0.01) and old (P<0.01) WD fed mice compared with young NC mice, but WD did not further increase stiffness in the old mice. In cage control mice, EDD was 17% lower in both NC fed old mice and young WD fed mice (P<0.05). Consumption of WD by old mice led to a further 20% reduction in EDD (P<0.05). Incremental stiffness was 28% lower and EDD was 38% greater in old WD fed mice with access to running wheels vs. old WD fed control mice (P<0.05) and not different from young NC fed controls. Wheel running also tended to improve EDD (+9%, P=0.11), but not incremental stiffness in young WD fed mice. Ex vivo treatment with the superoxide scavenger TEMPOL and NO inhibitor L-NAME abolished these respective effects of age, WD and voluntary running on EDD. Ingestion of a WD induces similar degrees of endothelial dysfunction in old and young adult B6D2F1 mice, and these effects are mediated by a superoxide-dependent impairment of NO bioavailability. However, the combination of old age and WD, a common occurrence in our aging society, results in a marked, additive reduction in endothelial function. Importantly, regular voluntary aerobic exercise reduces arterial stiffness and protects against the adverse influence of WD on endothelial function in old animals by preventing superoxide suppression of NO. These findings may have important implications for arterial aging and the prevention of age-associated cardiovascular diseases.

We hypothesized that I kappa B kinase (IKK)-mediated nuclear factor kappa B and forkhead BoxO3a phosphorylation will be associated with age-related endothelial dysfunction. Endothelium-dependent dilation and aortic protein expression/phosphorylation were determined in young and old male B6D2F1 mice and old mice treated with the IKK inhibitor, salicylate. IKK activation was greater in old mice and was associated with greater nitrotyrosine and cytokines. Endothelium-dependent dilation, nitric oxide (NO), and endothelial NO synthase phosphorylation were lower in old mice. Endothelium-dependent dilation and NO bioavailability were restored by a superoxide dismutase mimetic. Nuclear factor kappa B and forkhead BoxO3a phosphorylation were greater in old and were associated with increased expression/activity of nicotinamide adenine dinucleotide phosphate oxidase and lower manganese superoxide dismutase expression. Salicylate lowered IKK phosphorylation and reversed age-associated changes in nitrotyrosine, endothelium-dependent dilation, NO bioavailability, endothelial NO synthase, nuclear factor kappa B and forkhead BoxO3a phosphorylation, nicotinamide adenine dinucleotide phosphate oxidase, and manganese superoxide dismutase. Increased activation of IKK with advancing age stimulates nuclear factor kappa B and inactivates forkhead BoxO3a. This altered transcription factor activation contributes to a pro-inflammatory/pro-oxidative arterial phenotype that is characterized by increased cytokines and nicotinamide adenine dinucleotide phosphate oxidase and decreased manganese superoxide dismutase leading to oxidative stress-mediated endothelial dysfunction.