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).     

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.     

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.     

Estrogen receptor alpha is necessary in thymic development and estradiol-induced thymic alterations.

Estrogens affect the development, maturation, and function of multiple organ systems, including the immune system. One of the main targets of estrogens in the immune system is the thymus, which undergoes atrophy and phenotypic alterations when exposed to elevated levels of estrogen. To determine how estrogens influence the thymus and affect T cell development, estrogen receptor alpha (ERalpha) knockout (ERKO) mice were examined. ERKO mice have significantly smaller thymi than their wild-type (WT) littermates. Construction of ER radiation bone marrow chimeras indicated that the smaller thymi were due to a lack of ERalpha in radiation-resistant tissues rather than hemopoietic elements. ERKO mice were also susceptible to estradiol-induced thymic atrophy, but the extent of their atrophy was less than what was seen in WT mice. The estradiol-treated ERKO mice failed, however, to manifest alterations in their thymic CD4/CD8 phenotypes compared with WT mice. Therefore, ERalpha is essential in nonhemopoietic cells to obtain a full-sized thymus, and ERalpha also mediates some of the response of the thymus to elevated estrogen levels. Finally, these results suggest that in addition to ERalpha, another receptor pathway is involved in estradiol-induced thymic atrophy.     

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.     

Prevention of fasting-mediated bone marrow atrophy by leptin administration

Leptin is an adipokine that regulates body weight. In the current study, we demonstrate that continuous injection of leptin prevents the lymphocyte reduction observed in fasted mice, especially the immature B cell populations in the bone marrow. Although leptin administration reduced apoptotic cells in the bone marrow of fasted mice, it did not prevent glucocorticoid-mediated apoptosis in vitro. Bone marrow atrophy has also been shown in the leptin receptor-deficient db/db mice. In order to investigate the mechanisms underlying these processes, we transplanted bone marrow cells from db/db or control (+m/+m) mice into C.B-17/lcr-scid/scid mice. We found that the spleen and bone marrow B cell populations were completely reconstituted when db/db and +m/+m cells were transplanted into scid mice. Our findings suggest that direct interactions between leptin and bone marrow cells are not essential for the development of B cells in a metabologically normal environment.     

Expression of the leptin receptor outside of bone marrow-derived cells regulates tuberculosis control and lung macrophage MHC expression

Leptin is a pleiotropic hormone proposed to link nutritional status to the development of strong Th1 immunity. Because Mycobacterium tuberculosis control is affected by starvation and diabetes, we studied the role of the leptin receptor in regulating distinct immune cells during chronic infection. Infected db/db mice, bearing a natural mutation in the leptin receptor, have a markedly increased bacterial load in their lungs when compared with that of their wild-type counterparts. In response to M. tuberculosis infection, db/db mice exhibited disorganized granulomas, neutrophilia, and reduced B cell migration to the lungs, correlating with dysfunctional lung chemokine responses that include XCL1, CCL2, CXCL1, CXCL2, and CXCL13. In a db/db lung, myeloid cells were delayed in their production of inducible NO synthase and had reduced expression of MHC I and II. Although the Th1 cell response developed normally in the absence of leptin signaling, production of pulmonary IFN-γ was delayed and ineffective. Surprisingly, a proper immune response took place in bone marrow (BM) chimeras lacking leptin receptor exclusively in BM-derived cells, indicating that leptin acts indirectly on immune cells to modulate the antituberculosis response and bacterial control. Together, these findings suggest that the pulmonary response to M. tuberculosis is affected by the host's nutritional status via the regulation of non-BM-derived cells, not through direct action of leptin on Th1 immunity.     

Hyperleptinemia and reduced TNF-alpha secretion cause resistance of db/db mice to endotoxin

Leptin deficiency in ob/ob mice increases susceptibility to endotoxic shock, whereas leptin pretreatment protects them against LPS-induced lethality. Lack of the long-form leptin receptor (Ob-Rb) in db/db mice causes resistance. We tested the effects of LPS in C57BL/6J db(3J)/db(3J) (BL/3J) mice, which express only the circulating leptin receptors, compared with C57BL/6J db/db (BL/6J) mice, which express all short-form and circulating isoforms of the leptin receptor. Intraperitoneal injections of LPS significantly decreased rectal temperature and increased leptin, corticosterone, and free TNF-alpha in fed and fasted BL/3J and BL/6J mice. TNF-alpha was increased three- and fourfold in BL/3J and BL/6J, respectively. LPS (100 microg) caused 50% mortality of fasted BL/6J mice but caused no mortality in fasted BL/3J mice. Pretreatment of fasted BL/3J mice with 30 microg leptin prevented the drop in rectal temperature, blunted the increase in corticosterone, but had no effect on TNF-alpha induced by 100 microg LPS. Taken together, these data provide evidence that fasted BL/3J mice are more resistant than BL/6J mice to LPS toxicity, presumably due to the absence of leptin receptors in BL/3J mice. This resistance may be due to high levels of free leptin cross-reacting with other cytokine receptors.     

Bone abnormalities in adolescent leptin-deficient mice

Ob/ob and db/db mice have different aberrations in leptin signaling that both lead to abnormalities in bone mineral density (BMD), and bone histological and histomorphometric outcomes. A few studies have directly compared bone metabolism in ob/ob and db/db mice, and biomechanical strength properties that are surrogate measures of fracture risk, have not been extensively studied. This study compared bone mineral content (BMC), BMD and biomechanical strength properties of femurs and lumbar vertebrae among 10 week old male ob/ob, db/db and C57Bl/6 wildtype (WT) mice. Femurs and lumbar vertebrae were specifically studied to determine if trabecular and cortical bone are regulated by leptin in a similar manner in ob/ob and db/db mice. Femurs of ob/ob and db/db mice had lower BMC, BMD and biomechanical strength properties, including peak load, compared to WT mice. In contrast, lumbar vertebrae BMC and BMD did not differ among genotypes, nor did the peak load from compression testing of an individual lumbar vertebra differ among groups. These findings suggest that leptin deficiency in adolescent male mice first results in changes in femurs, a representative long bone, and alterations in lumbar vertebrae may occur later in life.     

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 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.     

Transplantation of wild-type white adipose tissue normalizes metabolic, immune and inflammatory alterations in leptin-deficient ob/ob mice

Leptin-deficient ob/ob mice exhibit several metabolic and immune abnormalities, including thymus atrophy and markedly reduced inflammatory responses. We evaluated whether transplantation of wild-type (WT) white adipose tissue (WAT) into ob/ob mice could mimic the effect of recombinant leptin administration in normalizing metabolic, immune and inflammatory abnormalities. Female ob/ob mice received a subcutaneous transplantation of WAT obtained from WT littermates. A separate group of ob/ob mice was sham-operated. Despite raising leptin levels to only 15% of those observed in WT mice, WAT transplantation normalized metabolic abnormalities (glycemia, ALT, liver weight) in ob/ob mice and prevented further body weight gain. The transplanted group demonstrated normalization of thymus and spleen cellularity, thymocyte subpopulations and rates of thymocyte apoptosis. In the model of dextran sulfate sodium-induced colitis, WAT transplantation restored inflammation to levels equivalent to those of WT mice. Colonic production of IL-6 and MIP-2 was markedly reduced in the non-transplanted ob/ob group compared to transplanted ob/ob and WT mice. Our data indicate that WAT transplantation is an effective way to normalize metabolic as well as immune and inflammatory parameters in ob/ob mice. The threshold of leptin sufficient to normalize metabolic, immune and inflammatory function is significantly lower than levels present in lean WT mice. Finally, leptin derived exclusively from WAT is sufficient to normalize metabolic, immune and inflammatory parameters in ob/ob mice.     

Generation of Leptin Receptor Bone Marrow Chimeras: Recovery From Irradiation,Immune Cellularity,Cytokine Expression,and Metabolic Parameters

Leptin regulates appetite and metabolism but also immunity and inflammation. Although functional leptin receptors (LepR) are expressed on hematopoietic cells, the role of these receptors in regulating immune function in vivo remains controversial. To clarify this issue, we performed bone marrow (BM) transplantation between obese db/db mice, lacking LepR, and wild‐type (WT) mice. Results indicate that expression of LepR on BM‐derived cells directly, though partially, regulates spleen and thymus cellularity, although the environment of db mice contributes to maintaining reduced cellularity of these organs. Selective expression of LepR on BM‐derived cells also modulates leptin and adiponectin levels, with induction of a more favorable adipokine environment in the WT→db/db group. However, LepR signaling in BM‐derived cells is not involved in regulation of body weight (BW) and composition, glycemia, hepatosteatosis or adipose tissue inflammation, although it modulates expression of interleukin (IL)‐1β in the brain. Finally, data indicate that db mice have an increased susceptibility to irradiation compared to WT mice in terms of BW loss and recovery of leukocyte counts in peripheral blood. Therefore, interpretation of results obtained using BM chimeras between WT and db mice should take into account the difference in radiation sensitivity between the two types of animals.     

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.     

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 and the immune system: how nutritional status influences the immune response

Several observations suggest the presence of an interaction between immune and the endocrine systems. Leptin is an adipocyte-derived hormone, that belongs structurally to the long-chain helical cytokine family such as interleukin-2 (IL-2), interleukin-12 (IL-12), growth hormone (GH), and signals by a class I cytokine receptor (Ob-R). This cytokine represents an important link between fat mass on the one side and the regulation of energy balance and reproductive function on the other. Indeed, obese leptin-deficient ob/ob mice display low body temperature, hyperphagia, infertility and evidence of immune defects with lymphoid organ atrophy, mainly affecting thymic size and cellularity. Acute starvation, associated with decreased leptin levels, causes thymic atrophy and reduces the delayed type hypersensitivity (DTH) reaction to antigens in normal mice, resembling that observed in ob/ob mice. Leptin replacement reverses the immunosuppressive effects of acute starvation in mice. Leptin differentially affects the in vitro proliferation and cytokine production by naive and memory T cells, increasing IL-2 secretion and proliferation of naive T cells, while inducing IFN-g production in memory T cells with little effect on their proliferation. Presence of leptin seems to be necessary for the induction and maintenance of the pro-inflammatory Th1 immune response. These findings support the hypothesis that leptin plays a key role in linking nutritional state to the T cell function. According to this view, leptin might represent an important target for immune intervention in a variety of pathophysiological conditions.     

Decreased p110α catalytic activity accompanies increased myocyte apoptosis and cardiac hypertrophy in leptin deficient ob/ob mice

Disruption of leptin signaling has been associated with both obesity and heart failure. We recently demonstrated that leptin deficiency in ob/ob mice and leptin insensitivity in db/db mice leads to increased myocyte apoptosis and left ventricular (LV) hypertrophy. We showed that LV mass, while similar among young ob/ob, db/db, and WT (WT) mice, is significantly higher in old ob/ob and db/db versus WT. Ob/ob and db/db mice developed markedly increased rates of myocyte apoptosis by TUNEL and activated caspase 3 levels. An intriguing candidate for the study of obesity-associated cardiac hypertrophy and apoptosis is PI3K, which functions to regulate not only cell size but also maintains cell integrity through protection from apoptosis. Here we further show that ob/ob mice have decreased catalytic activity of PI3K (p110α) which is reversed with leptin treatment. Leptin repletion in ob/ob mice reduced both myocyte apoptosis and LV hypertrophy to WT levels. We have therefore concluded that normal leptin signaling is necessary to prevent age-related myocyte apoptosis and LV hypertrophy and that PI3K is a critical component of the leptin signaling axis. The decrease in p110α catalytic activity could explain the development of increased myocyte apoptosis and cardiac hypertrophy in these obese mouse models.     

c-fos expression interferes with thymus development in transgenic mice

To study the function of the proto-oncogene c-fos in hematopoietic tissues, transgenic mice were generated that express c-fos from the H2-Kb promoter in several organs. These H2-c-fos mice have enlarged spleens and hyperplastic thymuses containing an increased number of thymic epithelial cells. The exogenous c-fos expression specifically affects T cell development in the thymus, thereby increasing the fraction of mature thymocytes. Results obtained with bone marrow radiation chimeras suggest that the altered distribution of T cell subsets is not a direct effect of c-fos expression within the T cell lineage. No changes in the proportion of hematopoietic cell lineages are seen in the spleen, and these mice do not develop lymphoid malignancies. B and T cell function, however, is impaired, and H2-c-fos mice are immune deficient. It appears that c-fos specifically stimulates the proliferation of thymic epithelial cells, and may thus indirectly affect T cell development.     

Role of CC chemokine receptor 2 in bone marrow cells in the recruitment of macrophages into obese adipose tissue

The MCP-1 (monocyte chemoattractant protein-1)/CCR2 (CC motif chemokine receptor-2) pathway may play a role in macrophage infiltration into obese adipose tissue. Here we investigated the role of CCR2 in the recruitment of bone marrow-derived macrophages into obese adipose tissue in vitro and in vivo. Using the TAXIScan device, which can measure quantitatively the directionality and velocity of cell migration at time lapse intervals in vitro, we demonstrated that bone marrow cells (BMCs) from wild type mice migrate directly toward MCP-1 or culture medium conditioned by adipose tissue explants of genetically obese ob/ob mice, which are efficiently suppressed by pharmacological blockade of CCR2 signaling. The number of F4/80-positive macrophages was reduced in the adipose tissue from high fat diet-fed obese KKAy or ob/ob mice treated with a CCR2 antagonist propagermanium relative to vehicle-treated groups. We also found that the number of macrophages is reduced in the adipose tissue from ob/ob mice reconstituted with CCR2(-/-) BMCs (ob/ob + CCR2(-/-) BMCs) relative to those with CCR2+/+ BMCs (ob/ob + CCR2+/+ BMCs). Expression of mRNAs for CD11c and TLR4 (Toll-like receptor 4) markers of proinflammatory M1 macrophages was also decreased in the adipose tissue from ob/ob + CCR2(-/-) BMCs relative to ob/ob + CCR2+/+ BMCs, whereas mannose receptor and CD163, markers of anti-inflammatory M2 macrophages, were unchanged. This study provides in vivo and in vitro evidence that CCR2 in bone marrow cells plays an important role in the recruitment of macrophages into obese adipose tissue.     

Cutting edge: fasting-induced hypoleptinemia expands functional regulatory T cells in systemic lupus erythematosus

Fasting is beneficial in the prevention and amelioration of the clinical manifestations of autoimmune diseases including systemic lupus erythematosus. The mechanisms responsible for these effects are not well understood. During fasting, there is a dramatic reduction of the levels of circulating leptin, an adipokine with proinflammatory effects. Leptin also inhibits CD4(+)CD25(+)Foxp3(+) regulatory T cells, which are known to contribute significantly to the mechanisms of peripheral immune tolerance. In this study, we show that fasting-induced hypoleptinemia in (NZB × NZW)F(1) lupus-prone mice induced an expansion of functional regulatory T cells that was reversed by leptin replacement. The specificity of the findings was indicated by the lack of these effects in leptin-deficient ob/ob mice and leptin receptor-deficient db/db mice. These observations help to explain the beneficial effects of fasting in autoimmunity and could be exploited for leptin-based immune intervention in systemic lupus erythematosus.