Decreased circulating CD34+ cells are associated with progression of diabetic nephropathy.

AIMS: Circulating progenitor cells such as CD34+ cells play a key role in maintenance of vascular endothelial function and neovascularization, and a decrease in the number of CD34+ cells is associated with cardiovascular disease. However, the contribution of circulating progenitor cells to microvascular disease, such as diabetic nephropathy, is unclear. This study was therefore designed to clarify the association between diabetic nephropathy and circulating CD34+ cells. METHODS: We measured circulating CD34+ cell numbers in 85 Type 2 diabetic patients aged 40-70 years with normo- and microalbuminuria and determined the association with urinary albumin excretion rate (UAER). RESULTS: The number of circulating CD34+ cells significantly correlated with log UAER (r = -0.289, P = 0.008). Furthermore, in patients with low numbers of CD34+ cells (0.68 > cells/microl, lowest quartile of CD34+ cell number) UAER increased significantly after 12 months compared with baseline [from 34.3 +/- 7.0 to 53.6 +/- 10.8 mg/g creatinine (gCr), P < 0.05], whereas in patients with a high number of CD34+ cells (1.0 < cells/microl, highest quartile of CD34+ cell number) UAER did not change (from 16.7 +/- 4.8 to 20.1 +/- 3.0 mg/gCr). CONCLUSIONS: These results suggest that a decreased number of circulating CD34+ cells is involved in the progression of diabetic nephropathy and may be a predictor of the disease.

Transgenic overexpression of brain natriuretic peptide prevents the progression of diabetic nephropathy in mice.

AIMS/HYPOTHESIS: Brain natriuretic peptide (BNP) is a potent vasorelaxing and natriuretic peptide that is secreted from the heart and has cardioprotective properties. We have previously generated hypotensive transgenic mice (BNP-Tg mice) that overproduce BNP in the liver, which is released into the circulation. Using this animal model, we successfully demonstrated the amelioration of renal injury after renal ablation and in proliferative glomerulonephritis. Glomerular hyperfiltration is an early haemodynamic derangement, representing one of the key mechanisms of the pathogenesis of diabetic nephropathy. Based on the suggested involvement of increased endogenous natriuretic peptides, the aim of this study was to investigate their role in the development and progression of diabetic nephropathy. MATERIALS AND METHODS: We evaluated the progression of renal injury and fibrogenesis in BNP-Tg mice with diabetes induced by streptozotocin. We also investigated the effect of BNP on high glucose-induced signalling abnormalities in mesangial cells. RESULTS: After induction of diabetes, control mice exhibited progressively increased urinary albumin excretion with impaired renal function, whereas these changes were significantly ameliorated in BNP-Tg mice. Notably, diabetic BNP-Tg mice revealed minimal mesangial fibrogenesis with virtually no glomerular hypertrophy. Glomerular upregulation of extracellular signal-regulated kinase, TGF-beta and extracellular matrix proteins was also significantly inhibited in diabetic BNP-Tg mice. In cultured mesangial cells, activation of the above cascade under high glucose was abrogated by the addition of BNP. CONCLUSIONS/INTERPRETATION: Chronic excess of BNP prevents glomerular injury in the setting of diabetes, suggesting that renoprotective effects of natriuretic peptides may be therapeutically applicable in preventing the progression of diabetic nephropathy.

Clinical implications of leptin and its potential humoral regulators in long-term low-calorie diet therapy for obese humans.

OBJECTIVE: To address the clinical implications of leptin and to re-examine the relationship between leptin and its potential humoral regulators such as insulin, nonesterified fatty acids (NEFA) and triiodothyronine (T3) in low-calorie diet (LCD) for obese humans. DESIGN: Longitudinal study. SETTING: University and foundation hospitals. SUBJECTS: Ten obese men and 10 premenopausal obese women. INTERVENTIONS: Five men and five women took 800 kcal/day LCD and another five men and five women took 1400 kcal/day balanced deficit diet (BDD) during 4 weeks. RESULTS: Plasma leptin levels in the LCD group decreased more markedly (46.2+/-14.6 to 13.2+/-3.6 ng/ml) than that expected for the decrement in percentage fat (39.0+/-1.7 to 35.9+/-1.7%) and body mass index (BMI; 35.4+/-2.4 to 33.1+/-2.2 kg/m(2)), while that in the BDD group did not decrease significantly (14.9+/-3.5 to 13.4+/-2.8 ng/ml). The ratio of the decrease in leptin levels to that of BMI during the first week was significantly greater than that during the following 3 weeks (39.5+/-2.7 vs 29.3+/-2.1%, P=0.017). The plasma insulin and T3 levels also fell substantially in the first week and continued to decrease during the entire course. Plasma leptin levels measured weekly in each subject were correlated well with insulin (r=0.586, P=0.0003) and T3 (r=0.785, P=0.0004). Multiple regression analyses after adjustment for the time course and BMI revealed that serum levels of T3 were independently correlated with plasma leptin levels (r=0.928, P<0.0001). The plasma NEFA level was markedly elevated during the first 2 weeks and decreased thereafter. CONCLUSIONS: A rapid fall in leptin during the first week of LCD, coordinated by insulin, T3 and NEFA, should be beneficial for responding to decreased energy intake. Inversely, in view of the powerful effect of leptin on energy dissipation, the present findings suggest the potential usefulness of leptin in combination with caloric restriction for the treatment of obesity. SPONSORSHIP: The Ministry of Education, Culture, Sports, Science and Technology of Japan and the Ministry of Health, Labour and Welfare of Japan.

[A role of the PPAR gamma activation in insulin resistance].

PPAR gamma is a major determinants of adipocyte differentiation and its activation by ligands including thiazolidinedione(TZDs) and the endogenous ligands induces transcription of the genes involving glucose and lipid metabolism. By the experiments using animal models with obesity-related phenotypes and PPAR gamma knockout mouse and the results of genetics study regarding on the mutations and SNPs in human, it is postulated that the PPAR gamma activation determines and modifies insulin sensitivity by the relationship between the degree of the activation and potency of ligands(agonists/antagonists). The modulation of the PPAR gamma activation by synthetic agonist/antagonists will be beneficial in the prevention and treatment of type 2 diabetes and obesity-related phenotypes.

Up-regulation of uncoupling protein 3 gene expression by fatty acids and agonists for PPARs in L6 myotubes.

Uncoupling protein 3 (UCP3), which uncouples electron transport from ATP synthesis, is expressed at high levels in the skeletal muscle, an important organ in glucose and lipid metabolism. Because several reports proposed that fatty acids induced UCP3 gene expression in skeletal muscle in vivo, in the present study we examined the regulation of UCP3 gene expression by various fatty acids using L6 myotubes. UCP3 gene expression was increased in L6 myotubes by various fatty acids or by alpha-bromopalmitate, a nonmetabolized derivative of palmitic acid. Because fatty acids are also known as agonists for PPARs, we examined the involvement of PPARs in the regulation of the UCP3 gene expression. L-165041, a PPAR delta agonist, increased UCP3 gene expression in L6 myotubes, whereas neither Wy 14,643, a PPAR alpha agonist, nor Pioglitazone, a PPAR gamma agonist, increased it. Therefore, we conclude that UCP3 gene expression is increased by the activation of PPAR delta in L6 myotubes and postulate that PPAR delta mediates at least some part of the increased UCP3 gene expression by fatty acids in skeletal muscle in vivo.

Simultaneous onset of type 1 diabetes mellitus and painless thyroiditis following acute pancreatitis.

A 24-year-old female suffered from acute pancreatitis, followed by simultaneous onset of painless goiter, elevation of thyroid hormones and diabetic ketoacidosis. Two months later, her insulin secreting function was severely decreased and positive for anti-GAD and anti-islet cell antibodies, whereas the serum glucagon level was normal, suggesting an autoimmune-related destruction specifically of beta cells. In addition, the initial hyperthyroid state was followed by a hypothyroid phase which later recovered to an euthyroid state, suggesting an initial destruction of thyroid cells. Because anti-thyroidal antibodies were positive, it is likely that the thyroidal destruction was also autoimmune-related. This case implies common pathogenic mechanisms in the autoimmunity related destruction of beta cells and thyroid cells.

Transgenic overexpression of leptin rescues insulin resistance and diabetes in a mouse model of lipoatrophic diabetes.

Lipoatrophic diabetes is caused by a deficiency of adipose tissue and is characterized by severe insulin resistance, hypoleptinemia, and hyperphagia. The A-ZIP/F-1 mouse (A-ZIPTg/+) is a model of severe lipoatrophic diabetes and is insulin resistant, hypoleptinemic, hyperphagic, and shows severe hepatic steatosis. We have also produced transgenic "skinny" mice that have hepatic overexpression of leptin (LepTg/+) and no adipocyte triglyceride stores, and are hypophagic and show increased insulin sensitivity. To explore the pathophysiological and therapeutic roles of leptin in lipoatrophic diabetes, we crossed LepTg/+ and A-ZIPTg/+ mice, producing doubly transgenic mice (LepTg/+:A-ZIPTg/+) virtually lacking adipose tissue but having greatly elevated leptin levels. The LepTg/+:A-ZIPTg/+ mice were hypophagic and showed improved hepatic steatosis. Glucose and insulin tolerance tests revealed increased insulin sensitivity, comparable to LepTg/+ mice. These effects were stable over at least 6 months of age. Pair-feeding the A-ZIPTg/+ mice to the amount of food consumed by LepTg/+:A-ZIPTg/+ mice did not improve their insulin resistance, diabetes, or hepatic steatosis, demonstrating that the beneficial effects of leptin were not due to the decreased food intake. Continuous leptin administration that elevates plasma leptin concentrations to those of LepTg/+:A-ZIPTg/+ mice also effectively improved hepatic steatosis and the disorder of glucose and lipid metabolism in A-ZIP/F-1 mice. These data demonstrate that leptin can improve the insulin resistance and diabetes of a mouse model of severe lipoatrophic diabetes, suggesting that leptin may be therapeutically useful in the long-term treatment of lipoatrophic diabetes.

Multiple signal transduction pathways through two prostaglandin E receptor EP3 subtype isoforms expressed in human uterus.

PGE2 is known to induce uterine contraction by increasing intracellular Ca2+. In the present study, to investigate other functions of PGE2 in human uterus, two EP3 isoforms were isolated by the RT-PCR method using human uterus polyadenylated ribonucleic acid (RNA). These EP3 isoforms, named EP3-V and EP3-VI, are composed of 402 and 393 amino acid residues, respectively, which are unique compared with EP3 isoforms of other species. Their N-terminal 359 amino acid residues are identical to those of previously reported human EP3 isoforms, whereas the two isoforms contained a novel amino acid sequence in their C-terminal tails. The dissociation constant values of EP3-V and EP3-VI for PGE2 were 3.9 and 1.4 nmol/L, respectively, which were consistent with those of previously reported EP3 isoforms. Signaling experiments revealed that M&B28767, an EP3 agonist, not only inhibited forskolin-induced cAMP concentrations, but also activated mitogen-activated protein kinase in Chinese hamster ovary cells stably expressing EP3-V and EP3-VI. These responses were abolished by treatment with pertussis toxin. In addition, M&B28767 increased cAMP concentrations in EP3-VI-expressing cells, whereas it did not in EP3-V-expressing cells. M&B28767 did not stimulate phosphoinositide turnover in EP3-V or EP3-VI-expressing cells. EP3-V and EP3-VI messenger RNAs (mRNAs) were detected abundantly in human uterus, whereas weak, but substantial, bands were detected in the lung and kidney in RT-PCR specific for each mRNA. In situ hybridization revealed EP3-V and EP3-VI mRNAs in the human myometrium, but not in the endometrium. The present study suggests that EP3-V and EP3-VI are possibly involved in the proliferation of cells in human myometrium.

Constitutively active mitogen-activated protein kinase kinase increases GLUT1 expression and recruits both GLUT1 and GLUT4 at the cell surface in 3T3-L1 adipocytes.

To address a role of mitogen-activated protein kinase (MAPK) in the regulation of glucose transport, we made a constitutively active mutant of MAPK kinase (MAPKK) and introduced it into 3T3-L1 preadipocytes by using a retrovirus-mediated transfection procedure. The deletion of 20 amino acids (those between and including 32 and 51) in the amino terminal region of Xenopus MAPKK and the replacement of serine residues on the 218 and 222 positions by glutamic acid (dSESE-MAPKK) let Xenopus MAPKK constitutively active. The isolated cell clones differently expressing dSESE-MAPKK (clone 219 higher expression, clone 233 lower expression) efficiently differentiated to adipocytes by a standard differentiation cocktail. Accordingly, the increased expression of dSESE-MAPKK protein during differentiation resulted in the increased basal MAPK activity in clone 219 adipocytes and, to a lesser extent, in clone 233 adipocytes. In contrast to clone 233 and parental adipocytes, basal 2-deoxyglucose uptake was enhanced fourfold in clone 219 adipocytes, in accordance with increased expression of GLUT1 mRNA and protein. Whereas GLUT4 mRNA was similarly expressed in all of the adipocytes, GLUT4 protein appeared to decrease in clone 219 adipocytes. More importantly, subcellular fractionation studies showed that the localization of both GLUT1 and GLUT4 in the plasma membranes (PMs) was markedly increased in the basal state in clone 219 adipocytes compared with that in clone 233 and parental adipocytes, in which both glucose transporters were preferentially located in intracellular compartments. Consequently, insulin-induced translocation of GLUT1 was abolished in clone 219 adipocytes, although the remaining intracellular GLUT4 was still responsive to insulin stimulation, which led to the movement to the PM. As combined effects on the situation of GLUT1 and GLUT4, the foldness of insulin stimulation of glucose transport based on the basal activity was reduced in cells expressing constitutively active MAPKK. These results imply that chronic activation of MAPK could be one of the mechanisms for insulin resistance.

Pathophysiological role of leptin in obesity-related hypertension.

To explore the pathophysiological role of leptin in obesity-related hypertension, we examined cardiovascular phenotypes of transgenic skinny mice whose elevated plasma leptin concentrations are comparable to those seen in obese subjects. We also studied genetically obese KKA(y) mice with hyperleptinemia, in which hypothalamic melanocortin system is antagonized by ectopic expression of the agouti protein. Systolic blood pressure (BP) and urinary catecholamine excretion are elevated in transgenic skinny mice relative to nontransgenic littermates. The BP elevation in transgenic skinny mice is abolished by alpha(1)-adrenergic, beta-adrenergic, or ganglionic blockers at doses that do not affect BP in nontransgenic littermates. Central administration of an alpha-melanocyte-stimulating hormone antagonist causes a marked increase in cumulative food intake but no significant changes in BP. The obese KKA(y) mice develop BP elevation with increased urinary catecholamine excretion relative to control KK mice. After a 2-week caloric restriction, BP elevation is reversed in nontransgenic littermates with the A(y) allele, in parallel with a reduction in plasma leptin concentrations, but is sustained in transgenic mice overexpressing leptin with the A(y) allele, which remain hyperleptinemic. This study demonstrates BP elevation in transgenic skinny mice and obese KKA(y) mice that are both hyperleptinemic, thereby suggesting the pathophysiological role of leptin in some forms of obesity-related hypertension.

Downregulation of leptin by free fatty acids in rat adipocytes: effects of triacsin C, palmitate, and 2-bromopalmitate.

Free fatty acid (FFA) has been reported to decrease leptin mRNA levels in 3T3-L1 adipocytes. When using this cell line, it is difficult to determine the protein levels because a very small amount of leptin is secreted into the medium. The effect of FFA on leptin secretion from adipocytes has not yet been determined. In addition, in vivo studies have failed to demonstrate a FFA-induced decrease in plasma leptin levels. To clarify the effect of FFA on leptin production, we investigated the leptin protein level in the medium and the mRNA level in primary cultured rat adipocytes treated with triacsin C, which is a potent inhibitor of acyl-coenzyme A (CoA) synthetase, palmitate, and 2-bromopalmitate. Triacsin C (0 to 5 x 10(-5) mol/L) decreased leptin concentrations in the culture medium in a dose-dependent manner. Leptin mRNA levels were decreased to 10% of the control in the presence of triacsin C. The concentration of triacsin C needed to suppress leptin production was similar to the Ki value (approximately 10(-5) mol/L) for inhibition of acyl-CoA synthetase. Both palmitate and 2-bromopalmitate decreased leptin concentra-tions but did not affect the triacsin C-induced decrease in leptin additively. In conclusion, both protein and mRNA levels of leptin were decreased by triacsin C and FFA in primary cultured rat adipocytes. Our findings suggest that FFA is involved in the regulation of leptin production in adipocytes.

Thyrotropin decreases leptin production in rat adipocytes.

Leptin, which is secreted from adipocytes, has a role in the regulation of appetite and energy expenditure. The thyrotropin receptor (TSH-R) was recently found in adipocytes. We examined the effects of TSH on leptin production and lipolysis in rat epididymal adipocytes. TSH decreased the concentration of leptin in the medium time (approximately 24 hours)- and dose (approximately 10(-7) mol/L)-dependently (half-maximal inhibition [IC50] approximately 10(-9) mol/L). TSH also decreased the ob mRNA level approximately 55% in adipocytes. We confirmed the presence of TSH-R mRNA in the adipocytes by reverse transcription-polymerase chain reaction (RT-PCR). TSH stimulated glycerol release dose-dependently (IC50 approximately 10(-8) mol/L) in adipocytes. This TSH-induced glycerol release was further enhanced by adenosine deaminase (ADA). In summary, TSH reduced leptin production and stimulated lipolysis in rat epididymal adipocytes. Although the pathophysiological relevance of the regulation of leptin production and lipolysis by TSH is unknown, we speculate that TSH may affect the regulation of appetite and energy expenditure in pathophysiological states.

Involvement of agouti-related protein, an endogenous antagonist of hypothalamic melanocortin receptor, in leptin action.

To understand the role of agouti-related protein (AGRP), an endogenous antagonist of hypothalamic melanocortin receptor, in leptin action, we produced a full-length recombinant AGRP and examined its effect on the satiety effect of leptin. We also studied leptin's regulation of hypothalamic AGRP mRNA expression. A single intracerebroventricular (i.c.v.) injection of AGRP significantly increased cumulative food intake and body weight in a dose-dependent manner in rats. The leptin-induced inhibition of food intake and body weight was reversed by co-injection of AGRP in a dose-dependent manner. Hypothalamic AGRP mRNA expression was upregulated in leptin-deficient ob/ob mice and leptin receptor-deficient db/db mice and downregulated in lethal yellow agouti mice (KKAy mice) with hyperleptinemia. A single i.c.v. injection of leptin reversed the increased AGRP mRNA levels in ob/ob mice but not in db/db mice. In control mice and KKAy mice, AGRP mRNA expression was upregulated during fasting, when plasma leptin concentrations were decreased. No significant increase in AGRP mRNA expression was noted during fasting in control mice and KKAy mice treated with leptin. This study provides the first direct evidence that AGRP is a negative regulator of leptin action, and leptin downregulates hypothalamic AGRP production. Because leptin is shown to increase hypothalamic alpha-melanocyte stimulating hormone (alpha-MSH) production, our data suggest that its action via the hypothalamic melanocortin system is determined by the balance between the levels of its agonist and antagonist, alpha-MSH and AGRP.

Sympathetic activation of leptin via the ventromedial hypothalamus: leptin-induced increase in catecholamine secretion.

Leptin is an adipocyte-derived blood-borne satiety factor that acts directly on the hypothalamus, thereby regulating food intake and energy expenditure. We have demonstrated that the hypothalamic arcuate nucleus (Arc) is a primary site of the satiety effect of leptin (Neurosci Lett 224:149-152, 1997). To explore the hypothalamic pathway of sympathetic activation of leptin, we examined the effects of a single intravenous or intracerebroventricular injection of recombinant human leptin on catecholamine secretion in rats. We also examined the effects of direct microinjection of leptin into the ventromedial hypothalamus (VMH), Arc, paraventricular nucleus (PVN), and dorsomedial hypothalamus (DMH) in rats. To further assess whether sympathetic activation of leptin is mediated via the VMH, we also examined the effects of a single intravenous injection of leptin in VMH-lesioned rats. A single injection of leptin (0.25-1.0 mg i.v./rat or 0.5-2.0 pg i.c.v./rat) increased plasma norepinephrine (NE) and epinephrine (EPI) concentrations in a dose-dependent manner. Plasma NE and EPI concentrations were increased significantly when leptin was injected directly into the VMH but were unchanged when injected into the Arc, PVN, and DMH. Plasma NE and EPI concentrations were unchanged in VMH-lesioned rats that received a single intravenous injection of leptin. The present study provides evidence that a leptin-induced increase in catecholamine secretion is mediated primarily via the VMH and suggests the presence of distinct hypothalamic pathways mediating the satiety effect and sympathetic activation of leptin.

Increased glucose metabolism and insulin sensitivity in transgenic skinny mice overexpressing leptin.

Excess of body fat, or obesity, is a major health problem and confers a higher risk of cardiovascular and metabolic disorders such as diabetes, hypertension, and coronary heart disease. Leptin is an adipocyte-derived satiety factor that plays an important role in the regulation of energy homeostasis, and its synthesis and secretion are markedly increased in obese subjects. To explore the metabolic consequences of an increased amount of leptin on a long-term basis in vivo, we generated transgenic skinny mice with elevated plasma leptin concentrations comparable to those in obese subjects. Overexpression of leptin in the liver has resulted in complete disappearance of white and brown adipose tissue for a long period of time in mice. Transgenic skinny mice exhibit increased glucose metabolism accompanied by the activation of insulin signaling in the skeletal muscle and liver. They also show small-sized livers with a marked decrease in glycogen and lipid storage. The phenotypes are in striking contrast to those of recently reported animal models of lipoatrophic diabetes and patients with lipoatrophic diabetes with reduced amount of leptin. The present study provides evidence that leptin is an adipocyte-derived antidiabetic hormone in vivo and suggests its pathophysiologic and therapeutic implications in diabetes.

Hypertension and insulin resistance: role of peroxisome proliferator-activated receptor gamma.

1. Insulin resistance has been highlighted as a common causal factor for hypertension, hyperlipidaemia, diabetes mellitus and obesity, all of which are recognized to occur simultaneously, and a distinct clinical entity is defined as 'multiple risk factor syndrome'. 2. Recently, a new class of antidiabetic agents, thiazolidinediones (TZD) has been developed and has been shown to improve insulin resistance by binding and activating a nuclear receptor, peroxisome proliferator-activated receptor (PPAR) gamma. 3. cDNA of rat PPAR gamma 1 and gamma 2 were cloned and gene regulation of PPAR gamma in rat mature adipocytes was examined. Hydrogen peroxide, an oxygen radical, which is recognized to be the common intracellular signal for multiple risk factors, potently down-regulated PPAR gamma mRNA expression in rat mature adipocytes. 4. Tumour necrosis factor (TNF)-alpha, which is considered to play a role in obesity-induced non-insulin-dependent diabetes mellitus and to augment oxidative stress, also suppressed PPAR gamma expression. 5. Thiazolidinediones dose-dependently recovered TNF-alpha-induced down-regulation of PPAR gamma mRNA expression. 6. The modulation of PPAR gamma expression by TZD can be one mechanism for the improvement of insulin resistance by TZD. 7. Vascular tone and remodelling are controlled by several vasoactive autocrine/paracrine factors produced by endothelial cells in response to several vascular injury stimuli, including hypertension. The PPAR gamma gene transcript was detected in cultured endothelial cells. 8. The administration of TZD stimulated the endothelial secretion of type-C natriuretic peptide, which is one of the natriuretic peptide family and is demonstrated by us to act as a novel endothelium-derived relaxing peptide. 9. Concomitantly, TZD significantly suppressed the secretion of endothelin, a potent endothelium-derived vasoconstricting peptide. 10. Thiazolidinediones can affect vascular tone and growth by modulating the production of endothelium-derived vasoactive substances to influence occurrence and progression of hypertension and atherosclerosis.

Glucose metabolism and insulin sensitivity in transgenic mice overexpressing leptin with lethal yellow agouti mutation: usefulness of leptin for the treatment of obesity-associated diabetes.

Leptin acts as an adipocyte-derived blood-borne satiety factor that can increase glucose metabolism. To elucidate the therapeutic implications of leptin for obesity-associated diabetes, we crossed transgenic skinny mice overexpressing leptin (Tg/+), which we have developed recently, and lethal yellow KKAy mice (Ay/+), a genetic model for obesity-diabetes syndrome, and examined the metabolic phenotypes of F1 animals. At 6 weeks of age, plasma leptin concentrations in Tg/+ mice with the Ay allele (Tg/+:Ay/+) were significantly higher than those in Ay/+ mice. Although no significant differences in body weight were noted among Tg/+:Ay/+ mice, Ay/+ mice, and their wild-type lean littermates (+/+), glucose and insulin tolerance tests revealed increased glucose tolerance and insulin sensitivity in Tg/+:Ay/+ compared with Ay/+ mice. However, at 12 weeks of age, when plasma leptin concentrations in Ay/+ mice were comparable to those in Tg/+:Ay/+ mice, Tg/+:Ay/+ mice developed obesity-diabetes syndrome similar to that of Ay/+ mice. Body weights of 12-week-old Tg/+:Ay/+ and Ay/+ mice were reduced to those of +/+ mice by a 3-week food restriction; when plasma leptin concentrations remained high in Tg/+:Ay/+ mice but were markedly reduced in Ay/+ and +/+ mice, glucose tolerance and insulin sensitivity in Tg/+:Ay/+ mice were markedly improved as compared with Ay/+ and +/+ mice. The present study demonstrates that hyperleptinemia can delay the onset of impaired glucose metabolism and accelerate the recovery from diabetes during caloric restriction in Tg/+:Ay/+ mice, thereby suggesting the potential usefulness of leptin in combination with a long-term caloric restriction for the treatment of obesity-associated diabetes.

Down regulation of peroxisome proliferator-activated receptorgamma expression by inflammatory cytokines and its reversal by thiazolidinediones.

AIMS/HYPOTHESIS: Previous studies show that inflammatory cytokines play a part in the development of insulin resistance. Thiazolidinediones were developed as insulin-sensitizing drugs and are ligands for the peroxisome proliferator-activated receptory (PPARgamma). We hypothesized that the anti-diabetic mechanism of thiazolidinediones depends on the quantity of PPARgamma in the insulin resistant state in which inflammatory cytokines play a part. METHODS: We isolated rat PPARgamma1 and gamma2 cDNAs and examined effects of various cytokines and thiazolidinediones on PPARgamma mRNA expression in rat mature adipocytes. RESULTS: Various inflammatory cytokines, such as tumour necrosis factor-alpha (TNF-alpha), interleukin-1alpha (IL-1alpha), IL-1beta, IL-6 and leukaemia inhibitory factor decreased PPARgamma mRNA expression. In addition, hydrogen peroxide, lysophosphatidylcholine or phorbol 12-myristate 13-acetate also decreased the expression of PPARgamma. The suppression of PPARgamma mRNA expression caused by 10 nmol/l of TNF-alpha was reversed 60% and 55% by treatment with 10(-4) mol/l of troglitazone and 10(-4) mol/l of pioglitazone, respectively. The suppression of glucose transporter 4 mRNA expression caused by TNF-alpha was also reversed by thiazolidinediones. Associated with the change of PPARgamma mRNA expression, troglitazone improved glucose uptake suppressed by TNF-alpha. CONCLUSION/INTERPRETATION: Our study suggests that inflammatory cytokines could be factors that regulate PPARgamma expression for possible modulation of insulin resistance. In addition, we speculate that the regulation of PPARgamma mRNA expression may contribute to the anti-diabetic mechanism of thiazolidinediones.

Increased adipose expression of the uncoupling protein-3 gene by thiazolidinediones in Wistar fatty rats and in cultured adipocytes.

Uncoupling protein (UCP) 3 and UCP2, mitochondrial carrier proteins dissipating electrochemical gradient across the mitochondrial inner membrane, have been implicated in the regulation of energy metabolism. The UCP3 gene is expressed abundantly in the skeletal muscle, while the UCP2 gene is detected in the white adipose tissue (WAT) with diffuse localization throughout the body. Uncoupling of electron transport and ATP synthesis has been reported to increase glucose uptake, suggesting that UCP may be involved in glucose metabolism. Thiazolidinediones (TZDs), which are insulin-sensitizing agents for NIDDM, have been reported to increase energy expenditure. To elucidate the pathophysiologic significance of UCP3 and UCP2 in the effect of TZDs on glucose metabolism and energy expenditure, we examined their basal mRNA levels in the WAT, brown adipose tissue (BAT), and skeletal muscle from Wistar fatty rats, a rat model of NIDDM and obesity with leptin receptor defect, and investigated expression of the genes encoding UCP3 and UCP2 in Wistar fatty rats and in Wistar lean rats with 2-week oral administration of 3 mg x kg(-1) x day(-1) pioglitazone, a TZD derivative. Basal UCP3 mRNA levels were significantly lower (38 +/- 8, 45 +/- 13, and 76 +/- 6%) in the retroperitoneal WAT, BAT, and skeletal muscle from Wistar fatty rats than in those from Wistar lean rats, while basal UCP2 mRNA levels were significantly higher by 2.1-, 1.8-, and 2.5-fold in the subcutaneous WAT, retroperitoneal WAT, and BAT from Wistar fatty rats, respectively, than in those from Wistar lean rats. In pioglitazone-treated Wistar fatty rats, UCP3 mRNA levels were significantly increased by 2.1-, 2.0-, and 1.6-fold in the epididymal WAT, retroperitoneal WAT, and BAT, respectively, as compared with those in nontreated fatty rats. In pioglitazone-treated lean rats, UCP3 mRNA levels were significantly increased by 1.3-fold in the BAT as compared with those in nontreated lean rats. No significant change of UCP2 mRNA levels was observed in pioglitazone-treated fatty and lean rats. In addition, to examine the direct effect of TZDs on adipocytes, we examined the regulation of UCP3 and UCP2 gene expression using the primary culture of rat mature adipocytes from Sprague-Dawley rats. In rat cultured mature adipocytes, UCP3 mRNA levels were increased in a dose-responsive manner by 10(-5) to 10(-4) mol/l pioglitazone, while there was no significant change of UCP2 mRNA levels. These results clearly demonstrate that UCP3 gene expression is upregulated by TZDs in the WAT and BAT in Wistar fatty rats, an obese model with leptin receptor defect, and that adipose UCP3 gene expression is increased in response to TZDs in vitro. The present study suggests the involvement of UCP3 in the effects of TZDs on energy and glucose metabolism.

Satiety effect and sympathetic activation of leptin are mediated by hypothalamic melanocortin system.

Leptin is an adipocyte-derived blood-borne satiety factor that decreases food intake and increases energy expenditure, thereby leading to a substantial decrease in body weight. To explore the possible roles of the hypothalamic melanocortin system in leptin action, we examined the effects of intracerebroventricular (i.c.v.) injection of leptin with or without SHU9119, a potent antagonist of alpha-melanocyte stimulating hormone, on food intake, body weight, and mitochondrial uncoupling protein-1 (UCP-1) mRNA expression in the brown adipose tissue (BAT) in rats. A single i.c.v. injection of leptin decreased cumulative food intake and body weight gain, and increased UCP-1 mRNA expression during 3 h at the onset of the dark phase. Inhibition of food intake and body weight change with leptin was reversed by co-injection of SHU9119 in a dose-dependent manner. Co-injection of SHU9119 also inhibited completely the leptin-induced increase in UCP-1 mRNA expression in the BAT. Treatment with SHU9119 alone did not affect food intake, body weight, and UCP-1 mRNA expression in rats. The present study provides evidence that the hypothalamic melanocortin system plays a central role in both satiety effect and sympathetic activation of leptin.