Enhancement of the aquaporin adipose gene expression by a peroxisome proliferator-activated receptor gamma

The current study demonstrates that aquaporin adipose (AQPap), an adipose-specific glycerol channel (Kishida, K., Kuriyama, H., Funahashi, T., Shimomura, I., Kihara, S., Ouchi, N., Nishida, M., Nishizawa, H., Matsuda, M., Takahashi, M., Hotta, K., Nakamura, T., Yamashita, S., Tochino, Y., and Matsuzawa, Y. (2000) J. Biol. Chem. 275, 20896-20902), is a target gene of peroxisome proliferator-activated receptor (PPAR) gamma. The AQPap mRNA amounts increased following the induction of PPARgamma in the differentiation of 3T3-L1 adipocytes. The AQPap mRNA in the adipose tissue increased when mice were treated with pioglitazone (PGZ), a synthetic PPARgamma ligand, and decreased in PPARgamma(+/-) heterozygous knockout mice. In 3T3-L1 adipocytes, PGZ augmented the AQPap mRNA expression and its promoter activity. Serial deletion of the promoter revealed the putative peroxisome proliferator-activated receptor response element (PPRE) at -93/-77. In 3T3-L1 preadipocytes, the expression of PPARgamma by transfection and PGZ activated the luciferase activity of the promoter containing the PPRE, whereas the PPRE-deleted mutant was not affected. The gel mobility shift assay showed the direct binding of PPARgamma-retinoid X receptor alpha complex to the PPRE. DeltaPPARgamma, which we generated as the dominant negative PPARgamma lacking the activation function-2 domain, suppressed the promoter activity in 3T3-L1 cells, dose-dependently. We conclude that AQPap is a novel adipose-specific target gene of PPARgamma through the binding of PPARgamma-retinoid X receptor complex to the PPRE region in its promoter.

Visceral fat is a major contributor for multiple risk factor clustering in Japanese men with impaired glucose tolerance

OBJECTIVE

The significance of abdominal visceral fat accumulation was evaluated in Japanese men with impaired glucose tolerance (IGT).

RESEARCH DESIGN AND METHODS

The IGT subjects (n = 123) were aged 55 +/- 9 years with a BMI of 24 +/- 3 kg/m(2). The 148 control subjects with normal glucose tolerance (NGT) were matched for age and BMI. IGT and NGT were classified according to the 1985 World Health Organization criteria. Abdominal fat distribution was analyzed by computed tomography at umbilical level. Plasma lipid, glucose, and insulin concentrations and blood pressure (BP) were measured.

RESULTS

In subjects with IGT, the average visceral fat area (VFA) was significantly greater than in subjects with NGT. Fasting insulin, the sum of insulin concentrations during an oral glucose tolerance test, insulin resistance according to a homeostasis model assessment for insulin resistance (HOMA-IR), systolic BP, and serum triglyceride were significantly higher, whereas the DeltaI(30-0)/DeltaG(30-0) was significantly lower, in subjects with IGT. Subjects with IGT and NGT were then divided into three subgroups according to the number of risk factors they possessed (dyslipidemia, hypertension, neither, or both). In both IGT and NGT subjects, BMI, VFA, subcutaneous fat area, fasting insulin, HOMA-IR, and insulin secretion of the homeostasis model assessment were significantly higher in the double-risk factor subgroup than in the no-risk factor subgroup, and VFA was a potent and independent variable in association with the presence of a double risk factor.

CONCLUSIONS

Visceral fat accumulation is a major contributor for multiple risk factor clustering in Japanese men with IGT and NGT.

PPARgamma ligands increase expression and plasma concentrations of adiponectin, an adipose-derived protein

Insulin resistance and its dreaded consequence, type 2 diabetes, are major causes of atherosclerosis. Adiponectin is an adipose-specific plasma protein that possesses anti-atherogenic properties, such as the suppression of adhesion molecule expression in vascular endothelial cells and cytokine production from macrophages. Plasma adiponectin concentrations are decreased in obese and type 2 diabetic subjects with insulin resistance. A regimen that normalizes or increases the plasma adiponectin might prevent atherosclerosis in patients with insulin resistance. In this study, we demonstrate the inducing effects of thiazolidinediones (TZDs), which are synthetic PPARgamma ligands, on the expression and secretion of adiponectin in humans and rodents in vivo and in vitro. The administration of TZDs significantly increased the plasma adiponectin concentrations in insulin resistant humans and rodents without affecting their body weight. Adiponectin mRNA expression was normalized or increased by TZDs in the adipose tissues of obese mice. In cultured 3T3-L1 adipocytes, TZD derivatives enhanced the mRNA expression and secretion of adiponectin in a dose- and time-dependent manner. Furthermore, these effects were mediated through the activation of the promoter by the TZDs. On the other hand, TNF-alpha, which is produced more in an insulin-resistant condition, dose-dependently reduced the expression of adiponectin in adipocytes by suppressing its promoter activity. TZDs restored this inhibitory effect by TNF-alpha. TZDs might prevent atherosclerotic vascular disease in insulin-resistant patients by inducing the production of adiponectin through direct effect on its promoter and antagonizing the effect of TNF-alpha on the adiponectin promoter.

Vascular endothelial dysfunction resulting from L-arginine deficiency in a patient with lysinuric protein intolerance

Although L-arginine is the only substrate for nitric oxide (NO) production, no studies have yet been reported on the effect of an L-arginine deficiency on vascular function in humans. Lysinuric protein intolerance (LPI) is a rare autosomal recessive defect of dibasic amino acid transport caused by mutations in the SLC7A7 gene, resulting in an L-arginine deficiency. Vascular endothelial function was examined in an LPI patient who was shown to be a compound heterozygote for two mutations in the gene (5.3-kbp Alu-mediated deletion, IVS3+1G-->A). The lumen diameter of the brachial artery was measured in this patient and in healthy controls at rest, during reactive hyperemia (endothelium-dependent vasodilation [EDV]), and after sublingual nitroglycerin administration (endothelium-independent vasodilation [EIV]) using ultrasonography. Both EDV and NO(x) concentrations were markedly reduced in the patient compared with those for the controls. They became normal after an L-arginine infusion. EIV was not significantly different between the patient and controls. Positron emission tomography of the heart and a treadmill test revealed ischemic changes in the patient, which were improved by the L-arginine infusion. Thus, in the LPI patient, L-arginine deficiency caused vascular endothelial dysfunction via a decrease in NO production.

The expression of SPARC in adipose tissue and its increased plasma concentration in patients with coronary artery disease

OBJECTIVE

Adipocytes secrete various cytokines and matrix proteins. Several of them precipitate in obesity-associated diseases, including atherosclerosis. In the current study, we have examined the expression of secreted protein, acidic and rich in cysteine (SPARC) in adipose tissue and its significance in obesity and coronary artery disease (CAD).

RESEARCH METHODS AND PROCEDURES

The SPARC mRNA expressions both in vivo and in vitro were detected by Northern blot analysis. Plasma SPARC concentrations were measured by enzyme immunosorbent assay. First, we investigated the plasma SPARC levels of 88 unrelated adult Japanese subjects (62 men and 26 women; average age: [+/- SD] 50 +/- 12 years; body mass index [BMI]: 16 to 46 kg/m(2)). Additionally 31 subjects with CAD diagnosed by coronary angiography (20 men and 11 women) were also investigated.

RESULTS

Human adipose tissues expressed abundant SPARC mRNA. SPARC expression in adipose tissues was upregulated in obese db/db mice. Markedly enhanced expression of SPARC mRNA was observed in 3T3-L1 fibroblasts during adipocyte differentiation. Consistent with these results, plasma SPARC levels proved a positive correlation with BMI in humans (r = 0.27; p < 0.01). Interestingly, plasma SPARC concentrations were significantly elevated in age- and BMI-matched subjects with CAD (p < 0.05).

DISCUSSION

SPARC was expressed in adipose tissues and its expression was enhanced in obese mice. In human, plasma SPARC levels were elevated in obesity and CAD patients. This elevated SPARC may be involved in the progression of CAD.

Localization of CD36 and scavenger receptor class A in human coronary arteries--a possible difference in the contribution of both receptors to plaque formation

CD36 and scavenger receptor class A types I and II (SR-AI/II) are major receptors for oxidized low density lipoproteins (OxLDL) expressed on macrophages. To elucidate the role of these two macrophage scavenger receptors in the development of coronary atherosclerosis, we examined the localization of CD36 and SR-AI/II in human coronary atherosclerotic lesions. Serial cryostat sections of 49 coronary arteries obtained from 43 autopsied cases were examined immunohistochemically. Regarding the relationship between the severity of atherosclerosis and immunoreactivities to CD36, there was almost no immunoreactivity to CD36 in regions with diffuse intimal thickening, while the expression of CD36 was accelerated in parallel with the progression of atherosclerosis. In contrast, SR-AI/II was expressed persistently from regions with diffuse intimal thickening to atherosclerotic plaques. We also clarified the differential distribution of CD36 and SR-AI/II in atheromatous plaques. Close to the luminal surface of the intima, macrophages were relatively small in size, contained lesser lipids, and expressed SR-AI/II more abundantly than CD36. In contrast, macrophages in the core region were larger in size, contained more lipids, were strongly positive for CD36 and showed a weaker immunoreactivity to SR-AI/II than those in the luminal surface of the intima. In conclusion, the expression of CD36 and SR-AI/II on macrophages may be regulated differently in the process of coronary atherogenesis.