Compensation for partial lipectomy in mice with genetic alterations of leptin and its receptor subtypes

One hypothesis for the regulation of total body fat suggests that leptin is a lipostatic feedback signal that acts at brain sites involved in regulation of energy balance. The importance of leptin in recovery from partial surgical lipectomy was tested by performing bilateral epididymal lipectomy or sham surgery on wild-type and leptin-deficient ob/ob mice. Eight weeks later, nonexcised pads of lipectomized mice were increased but total carcass fat was lower than in sham-operated ob/ob mice. In experiment 2, ob/ob mice, wild-type mice, and two db/db mutants, C57BL/6J db(Lepr)/db(Lepr) (BL/6J) mice possessing short-form and circulating leptin receptors and C57BL/6J db(3J)/db(3J) (BL/3J) mice expressing only circulating receptors, were lipectomized or sham operated. Sixteen weeks later, body mass and carcass lipid were not different between sham and lipectomized ob/ob mice, wild-type mice, or BL/6J db/db mice, whereas there was incomplete (decreased carcass fat) but suggestive recovery (increased retroperitoneal fat mass and cell number) in lipectomized BL/3J db/db mice. These data indicate that leptin is not required for the regulation of total body fat.     

Metabolic responses to leptin in obese db/db mice are strain dependent

Obese, diabetic C57BL/Ks db/db mice that lack the long-form leptin receptor exhibit no decrease in body weight or food intake when treated with leptin. Here we compared responses to leptin in two strains of db/db mice: C57BL/6J mice that are hyperglycemic and hyperinsulinemic and C57BL/Ks that are hyperglycemic and normo- or hypoinsulinemic. Chronic intraperitoneal infusion of 10 microgram leptin/day partially reversed hyperglycemia in C57BL/6J male mice but exaggerated the diabetic state of female mice. Bolus intraperitoneal injections of 40 microgram leptin/day did not effect glucose in either strain of male db/db mice, whereas chronic intraperitoneal infusion of 20 microgram leptin/day significantly reduced fasting blood glucose in male mice from both strains, especially C57BL/6J mice. Food intake, body weight, rectal temperature, and body fat did not change. Chronic intraperitoneal infusion of 10 microgram leptin/day significantly reduced body fat in lean db/+ C57BL/6J but not in C57BL/Ks mice. Thus peripherally administered leptin is active in mice that have only short-form leptin receptors, and the response is dependent on the method of leptin administration and the background strain.     

Increased pulmonary responses to acute ozone exposure in obese db/db mice

Epidemiological studies indicate the incidence of asthma is increased in obese and overweight humans. Responses to ozone (O(3)), an asthma trigger, are increased in obese (ob/ob) mice lacking the satiety hormone leptin. The long form of leptin receptor (Ob-R(b)) is required for satiety; mice lacking this receptor (db/db mice) are also substantially obese. Here, wild-type (WT) and db/db mice were exposed to air or O(3) (2 ppm) for 3 h. Airway responsiveness, measured by the forced oscillation technique, was greater in db/db than WT mice after air exposure. O(3)-induced increases in pulmonary resistance and airway responsiveness were also greater in db/db mice. BALF eotaxin, IL-6, KC, and MIP-2 increased 4 h after O(3) exposure and subsided by 24 h, whereas protein and neutrophils continued to increase through 24 h. For each outcome, the effect of O(3) was significantly greater in db/db than WT mice. Previously published results obtained in ob/ob mice were similar except for O(3)-induced neutrophils and MIP-2, which were not different from WT mice. O(3) also induced pulmonary IL-1beta and TNF-alpha mRNA expression in db/db but not ob/ob mice. Leptin was increased in serum of db/db mice, and pulmonary mRNA expression of short form of leptin receptor (Ob-R(a)) was similar in db/db and WT mice. These data confirm obese mice have innate airway hyperresponsiveness and increased pulmonary responses to O(3). Differences between ob/ob mice, which lack leptin, and db/db mice, which lack Ob-R(b) but not Ob-R(a), suggest leptin, acting through Ob-R(a), can modify some pulmonary responses to O(3).     

Obese and diabetic db/db mice develop marked liver fibrosis in a model of nonalcoholic steatohepatitis: role of short-form leptin receptors and osteopontin

Obesity and type 2 diabetes are associated with nonalcoholic steatohepatitis (NASH), but an obese/diabetic animal model that mimics human NASH remains undefined. We examined the induction of steatohepatitis and liver fibrosis in obese and type 2 diabetic db/db mice in a nutritional model of NASH and determined the relationship of the expressions of osteopontin (OPN) and leptin receptors to the pathogenesis of NASH. db/db mice and the corresponding lean and nondiabetic db/m mice were fed a diet deficient in methionine and choline (MCD diet) or control diet for 4 wk. Leptin-deficient obese and diabetic ob/ob mice fed similar diets were used for comparison. MCD diet-fed db/db mice exhibited significantly greater histological inflammation and higher serum alanine aminotransferase levels than db/m and ob/ob mice. Trichrome staining showed marked pericellular fibrosis in MCD diet-fed db/db mice but no significant fibrosis in db/m or ob/ob mice. Collagen I mRNA expression was increased 10-fold in db/db mice, 4-fold in db/m mice, and was unchanged in ob/ob mice. mRNA expressions of OPN, TNF-alpha, TGF-beta, and short-form leptin receptors (Ob-Ra) were significantly increased in db/db mice compared with db/m or ob/ob mice. Parallel increases in OPN and Ob-Ra protein levels were observed in db/db mice. Cultured hepatocytes expressed only Ob-Ra, and leptin stimulated OPN mRNA and protein expression in these cells. In conclusion, our results demonstrate the development of an obese/diabetic experimental model for NASH in db/db mice and suggest an important role for Ob-Ra and OPN in the pathogenesis of NASH.     

Indirect effects of leptin receptor deficiency on lymphocyte populations and immune response in db/db mice

Leptin-deficient ob/ob and leptin receptor (Ob-rb)-deficient db/db mice display a marked thymic atrophy and exhibit defective immune responses. Lymphocytes express leptin receptors and leptin exerts direct effects on T cells in vitro. In addition, ob/ob and db/db mice display multiple neuroendocrine and metabolic defects, through which leptin deficiency may indirectly affect the immune system in vivo. To study the relative contributions of direct and indirect effects of leptin on the immune system in a normal environment, we generated bone marrow chimeras (BMCs) by transplantation of leptin receptor-deficient db/db, or control db/+, bone marrow cells into wild-type (WT) recipients. The size and cellularity of the thymus, as well as cellular and humoral immune responses, were similar in db/db to WT and db/+ to WT BMCs. The immune phenotype of db/db mice is thus not explained by a cell autonomous defect of db/db lymphocytes. Conversely, thymus weight and cell number were decreased in the reverse graft setting in WT to db/db BMCs, indicating that expression of the leptin receptor in the environment is important for T cell development. Finally, normal thymocyte development occurred in fetal db/db thymi transplanted into WT hosts, indicating that direct effects of leptin are not required locally in the thymic microenvironment. In conclusion, direct effects of leptin on bone marrow-derived cells and on thymic stromal cells are not necessary for T lymphocyte maturation in normal mice. In contrast, leptin receptor deficiency affects the immune system indirectly via changes in the systemic environment.     

Oleoyl-estrone lowers the body weight of both ob/ob and db/db mice.

Homozygous obese db/db (BKS-Lepr(db) and ob/ob (B6-Lep(ob)) mice were treated for 14 days with a continuous infusion of a fat emulsion (controls) or loaded with oleoyl-estrone at doses of 12.5 and 50 nmol/g x d using surgically inserted osmotic minipumps. Treatment with oleoyl-estrone resulted in a marked decrease in body weight in both strains, compared with the unchecked growth of controls. In db/db mice, plasma urea and insulin, as well as liver lipid decreased with treatment. In ob/ob mice, the effect on insulin was more marked, in parallel with higher plasma lipids pointing to increased fat mobilisation. The results suggest that oleoyl-estrone effects on body fat reserves and insulin resistance are not mediated by leptin, since ob/ob mice lack this hormone and in the db/db it is present but cannot induce effects because of defective leptin receptors; in both cases oleoyl-estrone treatment lowers body weight.     

Leptin effect on intestinal galactose absorption in ob/ob and db/db mice

Our previous works demonstrated that leptin inhibits galactose absorption in rat and mice intestinal rings. Here, we have studied the effect of exogenous leptin on intestinal galactose absorption in the genetically obese db/db (leptin-resistant) and ob/ob (leptin-deficient) mice. Assays were performed by incubating the intestinal rings in saline solution containing 5 mM galactose in the absence or presence of 0.2 or 0.4 nM leptin. Basal galactose uptake was similar in the wild-type and the two obese groups. Contrarily to what happens in wild-type mice, leptin increased galactose uptake in db/db animals; since these mice lack the functional long leptin receptor, the measured effect may be due to the short receptor signaling. In the ob/ob mice, 0.2 nM leptin also increased galactose absorption whereas 0.4 nM did not have any effect, suggesting that in the genetically obese animals the expression and regulation of leptin receptors may be altered.     

Serotonergic activation rescues reproductive function in fasted mice: does serotonin mediate the metabolic effects of leptin on reproduction?

Negative energy balance inhibits reproduction by restraining GnRH secretion. Leptin is a permissive metabolic signal for reproduction, but GnRH neurons do not appear to express leptin receptors, suggesting that interneurons transmit leptin signals to these cells. Serotonin (5HT) has satiety effects similar to those of leptin and alters LH release, and serotonergic neurons, which have been shown to express leptin receptors, terminate on GnRH neurons. We hypothesized that serotonergic neurons convey leptin signals to the reproductive neuroendocrine axis. To test this, mice were fasted for 48 h beginning on Diestrous Day 1. While fasting, mice received saline or leptin every 12 h or the 5HT-selective reuptake-inhibitor fluoxetine once at the start of the fast. Estrous cycles of fasted mice were longer (mean +/- SEM, 10.2 +/- 0.5 days; P < 0.0001) than those of fed mice (4.5 +/- 0.2 days). As previously reported, leptin prevented fasting-induced cycle lengthening (4.6 +/- 0.7 days). Fluoxetine also rescued estrous cycles in fasted mice (4.7 +/- 0.6 days), suggesting that 5HT and leptin have similar positive effects on reproduction. Coadministration of the 5HT 1/2/7 receptor-antagonist metergoline blocked rescue of cycle length by fluoxetine and by leptin. Treating leptin-deficient ob/ob and leptin receptor-deficient db/db mice with fluoxetine did not normalize body weight or rescue fertility, perhaps due to altered serotonergic tone in these animals. Together, these data demonstrate a permissive role for serotonergic systems in the metabolic control of reproduction and are consistent with the hypothesis that serotonergic neurons convey leptin signals to GnRH neurons.     

Adrenalectomy in genetically obese ob/ob and db/db mice increases the proton conductance pathway

Adrenalectomy (ADX) prevents the excessive weight gain in the genetically obese ob/ob and db/db mice. To test the possibility that this results from increased energy expenditure due to increased thermogenesis in brown adipose tissue (BAT), we measured GDP binding to mitochondria from interscapular brown adipose tissue (BAT) in db/db and ob/ob mice and their lean controls after adrenalectomy, with and without corticosterone replacement. Both the vehicle treated and corticosterone treated db/db and ob/ob mice had lower body weights than the sham-operated mice GDP binding to mitochondria from IBAT was significantly lower in both the db/db and ob/ob mice than in their lean controls. Adrenalectomy significantly increased GDP binding in all mice compared to the respective sham-operated mice, but, the percentage increase was always greater in the db/db and ob/ob mice. Corticosterone treatment of adrenalectomized db/db, ob/ob or lean mice lowered GDP binding to sham levels. Our data confirm previous findings that adrenalectomy results in increased GDP binding to mitochondria from IBAT. Injections of corticosterone into adrenalectomized mice results in a decrease in GDP binding to values which are similar to values in sham-operated mice. Thus adrenalectomy may inhibit the development of obesity by increasing the thermic activity in IBAT.     

Evidence for an interaction between leptin, T cell costimulatory antigens CD28, CTLA-4 and CD26 (dipeptidyl peptidase IV) in BCG-induced immune responses of leptin- and leptin receptor-deficient mice

We assessed changes of the enzyme dipeptidyl peptidase IV (DPP IV, CD26) in the context of leptin or leptin receptor deficiency. C57BL/6 mice, Leptin-deficient mice (ob/ob mice, B6.V-Lep) and Leptin-receptor-deficient mice (db/db mice, B6.Cg-m+/+Lepr) were infected with B. Calmette-Guerin (BCG) and sacrificed three days later. DPP IV activity in serum was higher in ob/ob mice and in db/db mice than in wild-type mice. The expression of DPP IV/CD26 on splenocytes was higher in ob/ob mice than in wild-type animals, and lower in db/db mice, and decreased upon stimulation with BCG in ob/ob mice only. Several T cell antigens including CTLA-4 were expressed aberrantly in ob/ob and in db/db mice. Our observations provide evidence for a relationship between DPP IV and leptin.     

Leptin and insulin down-regulate angiopoietin-like protein 3, a plasma triglyceride-increasing factor

We reported previously that angiopoietin-like protein3 (ANGPTL3), a liver-specific secretory factor, increased plasma triglyceride (TG) via inhibition of lipoprotein lipase and free fatty acid (FFA) by activating adipose-lipolysis. The current study examined the regulation of Angptl3 by leptin and insulin, both of which are key players in the metabolic syndrome. Angptl3 expression and plasma ANGPTL3 levels were increased in leptin-resistant C57BL/6J(db/db) and -deficient C57BL/6J(ob/ob) mice, relative to the control. Leptin supplements decreased Angptl3 gene expression and plasma ANGPTL3 in C57BL/6J(ob/ob) mice. The changes of Angptl3 were associated with alterations of plasma TG and FFA levels. Leptin treatment directly suppressed Angptl3 gene expression in hepatocytes. Angptl3 gene expression and plasma protein levels were also increased in insulin-deficient streptozotocin-treated mice. Insulin treatment of hepatocytes decreased Angptl3 gene expression and protein secretion. Our results suggest that elevated ANGPTL3 by leptin- or insulin-resistance is attributed to increased plasma TG and FFA concentrations in obesity.     

Both leptin and leptin-receptor are essential for apolipoprotein M expression in vivo

It was previously shown that circulating levels of leptin and apolipoprotein M (apoM) correlate to each other. In this study, we examined whether plasma leptin and leptin-receptors are of importance for apoM expression in vivo. It was found that in both liver and kidney, expression of apoM was significantly lower in leptin deficient ob/ob mice and in leptin-receptor deficient db/db mice than in control mice. Furthermore, leptin administration (0.5 or 1.5 microg/g body weight) significantly increased plasma apoM levels and apoM mRNA levels in liver and in kidney in ob/ob mice. We conclude that both leptin and leptin-receptor are essential for the apoM expression, indicating that leptin is physiologically regulating apoM synthesis in vivo.     

Method of leptin dosing,strain, and group housing influence leptin sensitivity in high-fat-fed weanling mice

High-fat diets are reported to induce resistance to peripherally administered leptin. In an attempt to develop a model of juvenile diet-induced obesity, mice were weaned onto high-fat diet. Male and female, 35-day-old, C57BL/6J high-fat (45% kcal fat) diet-fed mice housed individually on grid floors did not decrease food intake or body weight in response to intraperitoneal (30 microg), lateral ventricle (5 microg), or third ventricle (0.5 microg) injections of leptin. Body weight and fat were significantly reduced by 13-day intraperitoneal infusions of 10 microg leptin/day, which doubled circulating leptin. Leptin infusion also reduced body fat in weanling, high-fat diet-fed NIH Swiss mice. Group housing mice on bedding prevented loss of fat in high-fat diet-fed male and female NIH Swiss and female C57BL/6J mice. These results indicate that peripherally infused leptin reduces fat in part by increasing thermogenesis and that inhibition of food intake in high-fat diet-fed mice requires either chronic activation of central leptin receptors or is independent of receptors that inhibit feeding in response to an acute central injection of leptin.     

Leptin receptor-deficient MMTV-TGF-alpha/Lepr(db)Lepr(db) female mice do not develop oncogene-induced mammary tumors

Being overweight is a risk factor for postmenopausal breast cancer and is associated with an increased incidence and shortened latency of spontaneous and chemically induced mammary tumors in rodents. However, leptin-deficient obese Lep(ob)Lep(ob) female mice have reduced incidences of spontaneous and oncogene-induced mammary tumors. Of interest, leptin enhances the proliferation of human breast cancer cell lines in which leptin receptors are expressed, which suggests that leptin signaling plays a role in tumor development. We evaluated oncogene-induced mammary tumor development in obese MMTV-TGF-alpha/Lepr(db)Lepr(db) mice that exhibit a defect in OB-Rb, which is considered to be the major signaling isoform of the leptin receptor. Lepr and MMTV-TGF-alpha mice were crossed, and the offspring were genotyped for oncogene expression and the determination of Lepr status. Lean MMTV-TGF-alpha/Lepr(+)Lepr(+) (homozygous) and MMTV-TGF-alpha/Lepr(+)Lepr(db) (heterozygous) mice and obese MMTV-TGF-alpha/Lepr(db)Lepr(db) mice were monitored until age 104 weeks. Body weights of MMTV-TGF-alpha/ Lepr(db)Lepr(db) mice were significantly heavier than those of the lean groups. No mammary tumors were detected in MMTV-TGF-alpha/Lepr(db)Lepr(db) mice, whereas the incidence of mammary tumors in MMTV-TGF-alpha/Lepr(+)Lepr(+) and MMTV-TGF-alpha/ Lepr(+)Lepr(db) mice was 69% and 82%, respectively. Examination of mammary tissue whole mounts indicated an absence of duct formation and branching for MMTV-TGF-alpha/Lepr(db)Lepr(db) mice. Both age at mammary tumor detection and tumor burden (tumors/mouse and tumor weights) were similar for the lean genotypes. Serum leptin levels of MMTV-TGF-alpha/Lepr(db)Lepr(db) mice were 12-20-fold higher than levels of lean mice. Thus, despite elevated serum leptin levels, leptin receptor-deficient MMTV-TGF-alpha/Lepr(db)Lepr(db) mice do not develop mammary tumors. This study provides additional evidence that leptin and its cognate receptor may be involved in mammary tumorigenesis.     

Leptin attenuates gene expression for renal 25-hydroxyvitamin D3-1alpha-hydroxylase in mice via the long form of the leptin receptor

Leptin, the ob gene product secreted by adipocytes, controls overall energy balance. We previously showed that leptin administration to leptin-deficient obese (ob/ob) mice suppressed mRNA expression and activity of renal 25-hydroxyvitamin D(3)-1alpha-hydroxylase (CYP27B1). In leptin receptor-deficient (db/db) mice, we presently examined whether leptin affects 1alpha-hydroxylase expression in renal tubules through the active form of the leptin receptor (ObRb). Elevated serum concentrations of calcium and 1,25-dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)] in untreated ob/ob mice showed sharp reduction with leptin administration (4 mg/kg, i.p. every 12h for 2 days); no such reduction of elevation occurred in db/db mice. ObRb mRNA was expressed in kidney, brain, fat, lung, and bone in wild-type and ob/ob mice, but not db/db mice. The ob/ob and db/db mice showed large increases in renal 1alpha-hydroxylase mRNA expression and activity. Leptin administration (4 mg/kg) completely abrogated these increases in ob/ob but not db/db mice. Renal 25-hydroxyvitamin D(3)-24-hydroxylase (CYP24) mRNA synthesis also was greatly elevated in ob/ob and db/db mice; excesses decreased significantly with leptin administration in ob/ob mice, but increased in db/db mice. Renal tubular cells in primary culture expressed mRNAs including proximal tubules markers (1alpha-hydroxylase and megalin), parathyroid hormone receptor, and vitamin D receptor. Calcitonin receptor mRNA, synthesized mainly in distal tubules, was scant, indicating that most cultured cells were from proximal tubules. Cells did not express ObRb mRNA. Forskolin exposure at 10(-6)M for 3 or 6h significantly increased 1alpha-hydroxylase mRNA. Leptin at 10(-6)M did not change mRNA expression in either presence or absence of forskolin. Accordingly, leptin attenuates renal 1alpha-hydroxylase gene expression through ObRb. Furthermore, leptin appears to act indirectly on renal proximal tubules to regulate 1alpha-hydroxylase gene expression.     

Leptin selectively augments thymopoiesis in leptin deficiency and lipopolysaccharide-induced thymic atrophy

The thymus is a lymphoid organ that selects T cells for release to the peripheral immune system. Unfortunately, thymopoiesis is highly susceptible to damage by physiologic stressors and can contribute to immune deficiencies that occur in a variety of clinical settings. No treatment is currently available to protect the thymus from stress-induced involution. Leptin-deficient (ob/ob) mice have severe thymic atrophy and this finding suggests that this hormone is required for normal thymopoiesis. In this study, the ability of leptin to promote thymopoiesis in wild-type C57BL/6 and BALB/c mice, as well as in leptin-deficient (ob/ob) and endotoxin-stressed (Escherichia coli LPS) mice, was determined. Leptin administration induced weight loss and stimulated thymopoiesis in ob/ob mice, but did not stimulate thymopoiesis in wild-type C57BL/6 nor BALB/c mice. In endotoxin-stressed mice, however, leptin prevented LPS-induced thymus weight loss and stimulated TCRalpha gene rearrangement. Coadministration of leptin with LPS blunted endotoxin-induced systemic corticosterone response and production of proinflammatory cytokines. Thus, leptin has a selective thymostimulatory role in settings of leptin deficiency and endotoxin administration, and may be useful for protecting the thymus from damage and augmenting T cell reconstitution in these clinical states.     

Temperature dependence of O2 consumption; opposite effects of leptin and etomoxir on respiratory quotient in mice

Objectives : The aims were to compare the temperature dependence of the metabolic rate in young ob/ob mice with that in mature ob/ob and db/db mice and to examine the effect on the metabolic substrate preference of leptin and etomoxir in ob/ob, C57BL/6J (wild‐type), and db/db mice. Research Methods and Procedures : In vivo oxygen consumption and carbon dioxide production were continuously measured by indirect calorimetry, and body temperature and total locomotor activity were measured by an implanted transponder. Leptin, etomoxir, or vehicle was administered intraperitoneally. Results : The temperature dependence of the metabolic rate of mature ob/ob and db/db mice were similar to that in wild‐type mice. In young 6‐week‐old ob/ob mice, the metabolic rate was almost doubled at 15 °C. Leptin (2 × 3 mg/kg) decreased the respiratory quotient (RQ) and carbon dioxide production but did not alter oxygen consumption, body temperature, or locomotor activity in ob/ob and C57BL/6J mice and had no effect in the db/db mice. Etomoxir (2 × 30 mg/kg) enhanced RQ and decreased oxygen consumption, carbon dioxide production, and body temperature in ob/ob, C57BL/6J, and db/db mice. Total locomotor activity was reduced in ob/ob and C57BL/6J mice. Discussion : In young ob/ob mice, the temperature sensitivity was enhanced compared with mature mice. Leptin and etomoxir had opposite effects on metabolic substrate preference. Leptin and lowered environmental temperature increased the relative fat oxidation as indicated by decreased RQ, possibly through activation of the sympathetic nervous system.     

Adrenalectomy and steroid treatment in obese (ob/ob) and diabetic (db/db) mice

Adrenalectomy in young obese (ob/ob) and the diabetic (db/db) mouse slowed body weight gain. Treatment of adrenalectomized ob/ob mice with cortisone or deoxycorticosterone acetate (DOCA) significantly increased weight gain in a dose-related manner. Cortisone had no effect on weight gain on lean mice and treatment with dehydroepiandrosterone sulfate was without effect on either ob/ob or lean mice. The increment in body weight of adrenalectomized ob/ob mice treated with corticosterone and DOCA was associated with an increase in body weight and an increase in food intake. When adrenalectomy was performed at twenty-three days of age (five days before weaning), animals carrying the (db/db) genotype remained lighter than their normal littermates. These data document the importance of the adrenal gland and its steroids for the development and maintenance of many features of the obese or diabetes mouse.     

Adrenal function and the effect of a high-fat diet on C57BL/6J and C57BL/6J-ob/ob mice.

In C57BL/6J mice and the ob/+ and ob/ob mutants total plasma corticosterone levels were found to be statistically different. In C57BL/6J mice the level was 1.9 +/- 0.2 mug/100 ml plasma, in ob/+ mice 8.6 +/- 1.6 mug/100 ml and in ob/ob mice 13.7 +/- 1.5 mug/100 ml. The percentage of protein-bound corticosterone as well as the free endogenous corticosterone levels were also different. Feeding a high-fat diet to young C57BL/6J and C57BL/6J-ob/ob mice for a period of 4 weeks had no effect upon blood glucose, plasma insulin and plasma corticosterone levels. The significantly higher increase in body weight of the high-fat diet groups of both lines of mice was mainly due to fat cell hypertrophy.     

Leptin signaling deficiency impairs humoral and cellular immune responses and attenuates experimental arthritis.

Leptin is produced almost exclusively by adipocytes and regulates body weight at the hypothalamic level. In addition, recent studies showed that leptin plays an important role in T lymphocyte responses. To examine the role of leptin in Ag-induced arthritis, the development of joint inflammation was assessed in immunized leptin-deficient mice (ob/ob), +/?, and wild-type mice (+/+) following the administration of methylated BSA into the knees. The results showed that ob/ob mice developed less severe arthritis compared with control mice. The levels of IL-1beta and TNF-alpha mRNA in the synovium of arthritic knees were lower in ob/ob than in +/? mice. In vitro Ag-specific T cell proliferative responses were significantly decreased in ob/ob mice with lower IFN-gamma and higher IL-10 production, suggesting a shift toward a Th2-type response in ob/ob mice. The serum levels of anti-methylated BSA Abs of any isotype were significantly decreased in arthritic ob/ob mice compared with controls. Essentially identical results were obtained in db/db mice, which lack the expression of the long isoform of leptin receptor. By RT-PCR, we observed that B lymphocytes express leptin receptor mRNA, indicating that in addition to its effect on the cellular response, leptin may exert a direct effect on B cell function. In conclusion, leptin contributes to the mechanisms of joint inflammation in Ag-induced arthritis by regulating both humoral and cell-mediated immune responses.