Conditional knockout of leptin receptor in neural stem cells leads to obesity in mice and affects neuronal differentiation in the hypothalamus early after birth.

Leptin, secreted by peripheral adipocytes, binds the leptin receptor (Lepr) in the hypothalamus, thereby contributing to the regulation of satiety and body weight. Lepr is expressed in the embryonic brain as early as embryonic day 12.5. However, the function of Lepr in neural precursor cells in the brain has not been resolved. To address this issue, we crossed the Leprflox/flox mice with each of Shh-Cre mice (Shh, sonic hedgehog) and Nestin (Nes)-Cre mice. We found that deletion of Lepr specifically in nestin-expressing cells led to extreme obesity, but the conditional null of Lepr in Shh-expressing cells had no obvious phenotype. Moreover, the level of leptin-activated pSTAT3 decreased in the anterior and central subregions of the arcuate hypothalamus of Shh-Cre; Leprflox/flox mice compared with the controls. By contrast, in Nes-Cre; Leprflox/flox mice, the level of leptin-activated pSTAT3 decreased in all subregions including the anterior, central, and posterior arcuate hypothalamus as well as the dorsomedial, ventromedial, and median eminence of the hypothalamus, revealing that the extensive lack of Lepr in the differentiated neurons of the hypothalamus in the conditional null mice. Notably, conditional deletion of Lepr in nestin-expressing cells enhanced the differentiation of neural precursor cells into neurons and oligodendroglia but inhibited differentiation into astrocytes early in postnatal development of hypothalamus. Our results suggest that Lepr expression in neural precursor cells is essential for maintaining normal body weight as well as the differentiation of neural precursor cells to the neural/glial fate in the hypothalamus shortly after birth.

Acid sphingomyelinase downregulation alleviates vascular endothelial leptin resistance in rats.

Leptin resistance in endothelial cells leads to vascular endothelial dysfunction, which is the beginning and crucial link of atherosclerosis. However, the mechanism of leptin resistance remains obscure. Acid sphingomyelinase (ASM) catalyzes the hydrolysis of sphingomyelin to produce ceramide, which plays an important role in the progression of metabolic and cardiovascular diseases. In this study, we investigated whether ASM could regulate leptin resistance in vascular endothelial cells. We induced endothelial leptin resistance in rat aortic endothelial cells through treatment with palmitic acid (0.3 mM) or knockdown of leptin receptor (Ob-Rb), which resulted in the increase of suppressor of cytokine signaling 3 expression, the decrease of Ob-Rb expression, and signal transducer and activator of transcription 3 (STAT3) phosphorylation at Tyr705. We found that these indicators of leptin resistance were reversed by knockdown of ASM or by the selective ASM inhibitors amitriptyline (AMI) and imipramine (IMI). Supplementation of ceramide inhibited Ob-Rb expression and STAT3 phosphorylation by inhibiting extracellular signal-regulated kinase 1/2 activation. Furthermore, we found that knockdown of ASM enhanced endothelial nitric oxide (NO) synthase activity and NO production, as well as the Akt phosphorylation at ser473, which was regulated by STAT3. High-fat diet (HFD) feeding-induced leptin resistance in rats in vivo; administration of AMI and IMI (10 mg· kg-1 per day, intraperitoneally, for 2 weeks) increased the release of endothelial NO to relieve the vasodilatory response and improved the endothelial leptin resistance in the aorta of HFD-fed rats. These results suggest that ASM downregulation reverses endothelial leptin resistance, and consequently improves vascular endothelial dysfunction. This study highlighted ASM as a potential therapeutic target for endothelial leptin resistance.

Microbiota Contribute to Obesity-related Increases in the Pulmonary Response to Ozone.

Obesity is a risk factor for asthma, especially nonatopic asthma, and attenuates the efficacy of standard asthma therapeutics. Obesity also augments pulmonary responses to ozone, a nonatopic asthma trigger. The purpose of this study was to determine whether obesity-related alterations in gut microbiota contribute to these augmented responses to ozone. Ozone-induced increases in airway responsiveness, a canonical feature of asthma, were greater in obese db/db mice than in lean wild-type control mice. Depletion of gut microbiota with a cocktail of antibiotics attenuated obesity-related increases in the response to ozone, indicating a role for microbiota. Moreover, ozone-induced airway hyperresponsiveness was greater in germ-free mice that had been reconstituted with colonic contents of db/db than in wild-type mice. In addition, compared with dietary supplementation with the nonfermentable fiber cellulose, dietary supplementation with the fermentable fiber pectin attenuated obesity-related increases in the pulmonary response to ozone, likely by reducing ozone-induced release of IL-17A. Our data indicate a role for microbiota in obesity-related increases in the response to an asthma trigger and suggest that microbiome-based therapies such as prebiotics may provide an alternative therapeutic strategy for obese patients with asthma.

Long-term consequences of the absence of leptin signaling in early life.

Leptin regulates energy balance and also exhibits neurotrophic effects during critical developmental periods. However, the actual role of leptin during development is not yet fully understood. To uncover the importance of leptin in early life, the present study restored leptin signaling either at the fourth or tenth week of age in mice formerly null for the leptin receptor (LepR) gene. We found that some defects previously considered irreversible due to neonatal deficiency of leptin signaling, including the poor development of arcuate nucleus neural projections, were recovered by LepR reactivation in adulthood. However, LepR deficiency in early life led to irreversible obesity via suppression of energy expenditure. LepR reactivation in adulthood also led to persistent reduction in hypothalamic Pomc, Cartpt and Prlh mRNA expression and to defects in the reproductive system and brain growth. Our findings revealed that early defects in leptin signaling cause permanent metabolic, neuroendocrine and developmental problems.

Shengmai San Alleviates Diabetic Cardiomyopathy Through Improvement of Mitochondrial Lipid Metabolic Disorder.

BACKGROUND/AIMS: Shengmai San (SMS), prepared from Panax ginseng, Ophiopogon japonicus, and Schisandra chinensisin, has been widely used to treat ischemic disease. In this study, we investigated whether SMS may exert a beneficial effect in diabetic cardiomyopathy through improvement of mitochondrial lipid metabolism. METHODS: A leptin receptor-deficient db/db mouse model was utilized, and lean age-matched C57BLKS mice served as non-diabetic controls. Glucose and lipid profiles, myocardial structure, dimension, and function, and heart weight to tibial length ratio were determined. Myocardial ultrastructural morphology was observed with transmission electron microscopy. Protein expression and activity of oxidative phosphorylation (OXPHOS) complex were assessed using western blotting and microplate assay kits. We also observed cellular viability, mitochondrial membrane potential, OXPHOS complex activity, and cellular ATP level in palmitic acid-stimulated H9C2 cardiomyocytes. Changes in the sirtuin (SIRT1)/AMP-activated protein kinase (AMPK)/peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) pathway and mitochondrial uncoupling signaling were assessed using western blotting and quantitative real-time PCR. RESULTS: Leptin receptor-deficient db/db mice exhibit obesity, hyperglycemia, and hyperlipidemia, accompanied by distinct myocardial hypertrophy and diastolic dysfunction. SMS at a dose of 3 g/kg body weight contributed to a recovery of diabetes-induced myocardial hypertrophy and diastolic dysfunction. SMS administration led to an effective restoration of mitochondrial structure and function both in vivo and in vitro. Furthermore, SMS markedly enhanced SIRT1 and p-AMPKα protein levels and decreased the expression of acetylated-PGC-1α and uncoupling protein 2 protein. SMS also restored the depletion of NRF1 and TFAM levels in diabetic hearts and H9C2 cardiomyocytes. CONCLUSION: The results indicate that SMS may alleviate diabetes-induced myocardial hypertrophy and diastolic dysfunction by improving mitochondrial lipid metabolism.

Averrhoa carambola free phenolic extract ameliorates nonalcoholic hepatic steatosis by modulating mircoRNA-34a, mircoRNA-33 and AMPK pathways in leptin receptor-deficient db/db mice.

The objective of the present study is to investigate the hepatic steatosis relieving effect of Averrhoa carambola free phenolic extract (ACF) on leptin receptor-deficient (db/db) mice and elucidate the modulation hepatic lipogenesis mechanisms. The serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) assays, accompanying hematoxylin and eosin (H&E) staining, were applied to identify the alleviation of liver histopathological changes. Serum and hepatic lipid assays, combined with oil red O staining, were used to investigate the amelioration of lipid accumulation. Further assessments by quantitative real-time PCR and western blot assays were used to elucidate the suppression of the fatty acid and triglyceride (TG) synthesis mechanisms underlying ACF protection. These results indicated that ACF treatment significantly reduced the liver TG of db/db mice (p < 0.05). The mechanisms are partly through phosphorylation of AMPK α and down-regulation of SREBP-1c expression, and further down-regulation of FAS and SCD1 (p < 0.05). In addition, the expression levels of mircoRNA-34a and mircoRNA-33, which modulate this signaling pathway, were significantly down-regulated by ACF treatment (p < 0.05). Collectively, these results revealed that ACF exhibited a potent hepatic steatosis relieving effect partly by inhibiting the signal transduction of hepatic lipogenesis.

Mango leaf extract improves central pathology and cognitive impairment in a type 2 diabetes mouse model.

Epidemiological studies reveal that metabolic disorders, and specifically type 2 diabetes (T2D), are relevant risk factors to develop Alzheimer's disease (AD) and vascular dementia (VaD), the most common causes of dementia. AD patients are in a tremendous need of new therapeutic options because of the limited success of available treatments. Natural polyphenols, and concretely Mangifera indica Linn extract (MGF), have been reported to have antiinflammatory, antioxidant and antidiabetic activities. The role of MGF in central complications associated with T2D, after long-term treatment of db/db mice with MGF was analyzed. Metabolic parameters (body weight, glucose and insulin levels) as well as central complications including brain atrophy, inflammatory processes, spontaneous bleeding, tau phosphorylation and cognitive function in db/db mice treated with MGF for 22 weeks were assessed. MGF limits body weight gain in obese db/db mice. Insulin and C-peptide levels, indicative of pancreatic function, were longer maintained in MGF-treated animals. MGF reduced central inflammation by lowering microglia burden, both in the cortex and the hippocampus. Likewise, central spontaneous bleeding was significantly reduced in db/db mice. Cortical and hippocampal atrophy was reduced in db/db mice and tau hyperphosphorylation was lower after MGF treatment, resulting in partial recovery of learning and memory disabilities. Altogether, the data suggested that MGF treatment may provide a useful tool to target different aspects of AD and VaD pathology, and could lead to more effective clinical therapies for the prevention of metabolic related central complications associated with AD and VaD.

Effects of Melatonin, Aluminum Oxide, and Polymethylsiloxane Complex on the Expression of LYVE-1 in the Liver of Mice with Obesity and Type 2 Diabetes Mellitus.

The effects of melatonin, aluminum oxide, and polymethylsiloxane complex on the expression of LYVE-1 (lymphatic vessel endothelial hyaluronan receptor) in the liver were studied in db/db mice with experimental obesity and type 2 diabetes mellitus. The complex or placebo was administered daily by gavage from week 8 to week 16 of life. The animals receiving the complex exhibited enhanced, in comparison with the placebo group, immunohistochemical LYVE-1+ staining of endothelial cells in sinusoids. Enhanced expression of LYVE-1 was associated with less pronounced dilatation of interlobular arteries, veins, and lymphatic vessels. Thee findings suggest a protective effect of the complex towards structural changes in the liver of mice with obesity and type 2 diabetes.

The Acute-Phase Protein Orosomucoid Regulates Food Intake and Energy Homeostasis via Leptin Receptor Signaling Pathway.

The acute-phase protein orosomucoid (ORM) exhibits a variety of activities in vitro and in vivo, notably modulation of immunity and transportation of drugs. We found in this study that mice lacking ORM1 displayed aberrant energy homeostasis characterized by increased body weight and fat mass. Further investigation found that ORM, predominantly ORM1, is significantly elevated in sera, liver, and adipose tissues from the mice with high-fat diet (HFD)-induced obesity and db/db mice that develop obesity spontaneously due to mutation in the leptin receptor (LepR). Intravenous or intraperitoneal administration of exogenous ORM decreased food intake in C57BL/6, HFD, and leptin-deficient ob/ob mice, which was absent in db/db mice and was significantly reduced in mice with arcuate nucleus (ARC) LepR knockdown, whereas enforced expression of ORM1 in ARC significantly decreased food intake, body weight, and serum insulin level. Furthermore, we found that ORM is able to bind directly to LepR and activate the receptor-mediated JAK2-STAT3 signaling in hypothalamus tissue and GT1-7 cells, which was derived from hypothalamic tumor. These data indicated that ORM could function through LepR to regulate food intake and energy homeostasis in response to nutrition status. Modulating the expression of ORM is a novel strategy for the management of obesity and related metabolic disorders.

Hypothalamic obesity.

Hypothalamic obesity represents a rare diagnosis applicable to only a small subset of obese patients. It is important to identify, diagnose, and treat these patients. This article reviews the physiology of the hypothalamus, focusing on its role in regulation of hunger, feeding, and metabolism. The causes of hypothalamic obesity are discussed including genetic, anatomic, and iatrogenic etiologies. The complex hormonal environment leading to obesity is explored for each etiology and treatment strategies are discussed. Reproductive consequences are also reviewed.

Leptin receptor deficiency confers resistance to behavioral effects of fluoxetine and desipramine via separable substrates.

Depression is a complex, heterogeneous mental disorder. Currently available antidepressants are only effective in about one-third to one-half of all patients. The mechanisms underlying antidepressant response and treatment resistance are poorly understood. Recent clinical evidence implicates the involvement of leptin in treatment response to antidepressants. In this study, we determined the functional role of the leptin receptor (LepRb) in behavioral responses to the selective serotonergic antidepressant fluoxetine and the noradrenergic antidepressant desipramine. While acute and chronic treatment with fluoxetine or desipramine in wild-type mice elicited antidepressant-like effects in the forced swim test, mice null for LepRb (db/db) displayed resistance to treatment with either fluoxetine or desipramine. Fluoxetine stimulated phosphorylation of Akt(Thr308) and GSK-3ß(Ser9) in the hippocampus and prefrontal cortex (PFC) of wild-type mice but not in db/db mice. Desipramine failed to induce measurable changes in Akt, GSK-3ß or ERK1/2 phosphorylation in the hippocampus and PFC, as well as hypothalamus of either genotype of mice. Deletion of LepRb specifically from hippocampal and cortical neurons resulted in fluoxetine insensitivity in the forced swim test and tail suspension test while leaving the response to desipramine intact. These results suggest that functional LepRb is critically involved in regulating the antidepressant-like behavioral effects of both fluoxetine and desipramine. The antidepressant effects of fluoxetine but not desipramine are dependent on the presence of functional LepRb in the hippocampus and cortex.

Astrocytic leptin-receptor knockout mice show partial rescue of leptin resistance in diet-induced obesity.

To determine how astrocytic leptin signaling regulates the physiological response of mice to diet-induced obesity (DIO), we performed metabolic analyses and hypothalamic leptin signaling assays on astrocytic leptin-receptor knockout (ALKO) mice in which astrocytes lack functional leptin receptor (ObR) signaling. ALKO mice and wild-type (WT) littermate controls were studied at different stages of DIO with measurement of body wt, percent fat, metabolic activity, and biochemical parameters. When fed regular chow, the ALKO mice had similar body wt, percent fat, food intake, heat dissipation, respiratory exchange ratio, and activity as their WT littermates. There was no change in blood concentrations of triglyceride, soluble leptin receptor (sObR), mRNA for leptin and uncoupling protein 1 (UCP1) in adipose tissue, and insulin sensitivity. Unexpectedly, in response to a high-fat diet the ALKO mice had attenuated hyperleptinemia and sObR, a lower level of leptin mRNA in subcutaneous fat, and a paradoxical increase in UCP1 mRNA. Thus, ALKO mice did not show the worsening of obesity that occurs with normal WT mice and the neuronal ObR mutation that results in morbid obesity. The findings are consistent with a competing, counterregulatory model between neuronal and astrocytic leptin signaling.

Peripheral leptin regulates bone formation.

Substantial evidence does not support the prevailing view that leptin, acting through a hypothalamic relay, decreases bone accrual by inhibiting bone formation. To clarify the mechanisms underlying regulation of bone architecture by leptin, we evaluated bone growth and turnover in wild-type (WT) mice, leptin receptor-deficient db/db mice, leptin-deficient ob/ob mice, and ob/ob mice treated with leptin. We also performed hypothalamic leptin gene therapy to determine the effect of elevated hypothalamic leptin levels on osteoblasts. Finally, to determine the effects of loss of peripheral leptin signaling on bone formation and energy metabolism, we used bone marrow (BM) from WT or db/db donor mice to reconstitute the hematopoietic and mesenchymal stem cell compartments in lethally irradiated WT recipient mice. Decreases in bone growth, osteoblast-lined bone perimeter and bone formation rate were observed in ob/ob mice and greatly increased in ob/ob mice following subcutaneous administration of leptin. Similarly, hypothalamic leptin gene therapy increased osteoblast-lined bone perimeter in ob/ob mice. In spite of normal osteoclast-lined bone perimeter, db/db mice exhibited a mild but generalized osteopetrotic-like (calcified cartilage encased by bone) skeletal phenotype and greatly reduced serum markers of bone turnover. Tracking studies and histology revealed quantitative replacement of BM cells following BM transplantation. WT mice engrafted with db/db BM did not differ in energy homeostasis from untreated WT mice or WT mice engrafted with WT BM. Bone formation in WT mice engrafted with WT BM did not differ from WT mice, whereas bone formation in WT mice engrafted with db/db cells did not differ from the low rates observed in untreated db/db mice. In summary, our results indicate that leptin, acting primarily through peripheral pathways, increases osteoblast number and activity.

Neuroprotective effect of silibinin in diabetic mice.

Diabetes mellitus is associated with a higher oxidative stress and reduced activity of the antioxidant defense system in different brain regions. Results from numerous studies reported impaired cognitive and neurochemical function in diabetic patients and streptozotocin induced diabetic rodents. It is well established that polyphenols exert potent antioxidant and protective functions. Based on recent findings, one potential target for the antioxidant/antinflammatory properties of polyphenols is the heme oxygenase (HO)-1 pathway. Among various compounds tested silibinin, the main component of silymarin, has been shown to possess a strong antioxidant effect in various experimental models; however a study on the possible neuroprotective effect of this compound on the brain of diabetic animals is currently lacking. Therefore, we studied and measured in lean mice (db/m) and knock out mice for the leptin receptors mice (db/db) the effect of silibinin on HO-1 protein levels, non proteic thiol groups, isoprostanes and 8-OH deoxyguanosine (markers of lipid peroxidation and DNA damage, respectively) in different brain regions. Our results showed that HO-1 is differently expressed in various brain regions in db/db mice when compared to lean animals. Furthermore, silibinin provides DNA protection and reduces oxidative stress in a brain specific area, in part via the activation of the HO system. Silibinin may provide a valid tool to counteract oxidative stress in the diabetic status in the central nervous system under diabetic condition.

Sixteen years and counting: an update on leptin in energy balance.

Cloned in 1994, the ob gene encodes the protein hormone leptin, which is produced and secreted by white adipose tissue. Since its discovery, leptin has been found to have profound effects on behavior, metabolic rate, endocrine axes, and glucose fluxes. Leptin deficiency in mice and humans causes morbid obesity, diabetes, and various neuroendocrine anomalies, and replacement leads to decreased food intake, normalized glucose homeostasis, and increased energy expenditure. Here, we provide an update on the most current understanding of leptin-sensitive neural pathways in terms of both anatomical organization and physiological roles.

Leptin's effect on puberty in mice is relayed by the ventral premammillary nucleus and does not require signaling in Kiss1 neurons.

Studies in humans and rodents indicate that a minimum amount of stored energy is required for normal pubertal development. The adipocyte-derived hormone leptin is a key metabolic signal to the neuroendocrine reproductive axis. Humans and mice lacking leptin or the leptin receptor (LepR) (ob/ob and db/db mice, respectively) are infertile and fail to enter puberty. Leptin administration to leptin-deficient subjects and ob/ob mice induces puberty and restores fertility, but the exact site or sites of leptin action are unclear. Here, we found that genetic deletion of LepR selectively from hypothalamic Kiss1 neurons in mice had no effect on puberty or fertility, indicating that direct leptin signaling in Kiss1 neurons is not required for these processes. However, bilateral lesions of the ventral premammillary nucleus (PMV) of ob/ob mice blunted the ability of exogenous leptin to induce sexual maturation. Moreover, unilateral reexpression of endogenous LepR in PMV neurons was sufficient to induce puberty and improve fertility in female LepR-null mice. This LepR reexpression also normalized the increased hypothalamic GnRH content characteristic of leptin-signaling deficiency. These data suggest that the PMV is a key site for leptin's permissive action at the onset of puberty and support the hypothesis that the multiple actions of leptin to control metabolism and reproduction are anatomically dissociated.

The roles of leptin receptors on POMC neurons in the regulation of sex-specific energy homeostasis.

Leptin regulates energy homeostasis and reproduction. One key population of leptin receptors (Lepr) are found on proopiomelanocortin (POMC) neurons in the hypothalamic arcuate nucleus, and evidence links the action of gonadal estrogens to these same POMC neurons. To determine whether Lepr on POMC neurons are critical for reproductive capacity or for sex-specific energy and glucose homeostasis, we studied Cre/loxP mice lacking Lepr specifically on POMC neurons (Pomc-Cre, Lepr(flox/flox) mice) and their controls with normal Lepr (Lepr(flox/flox) mice). Pomc-Cre, Lepr(flox/flox) mice maintained normal reproductive capacity and accumulated more body fat than their same sex controls. Ovariectomy (OVX) was performed to investigate the effects of the estrogens and Lepr on POMC neurons on body fat accumulation and glucose tolerance. OVX Pomc-Cre, Lepr(flox/flox) females accumulated more fat than OVX Lepr(flox/flox) females did. Pomc-Cre, Lepr(flox/flox) males were glucose intolerant and insulin insensitive compared with control males. In contrast, control and Pomc-Cre, Lepr(flox/flox) females had similar glucose tolerance before and after OVX. Therefore leptin's action on POMC neurons reduces body fat accumulation, but is not critical for regulation of reproduction. The sex difference in leptin signaling on POMC neurons on glucose tolerance appears independent of ovarian hormones.

Insufficiency of Janus kinase 2-autonomous leptin receptor signals for most physiologic leptin actions.

OBJECTIVE: Leptin acts via its receptor (LepRb) to signal the status of body energy stores. Leptin binding to LepRb initiates signaling by activating the associated Janus kinase 2 (Jak2) tyrosine kinase, which promotes the phosphorylation of tyrosine residues on the intracellular tail of LepRb. Two previously examined LepRb phosphorylation sites mediate several, but not all, aspects of leptin action, leading us to hypothesize that Jak2 signaling might contribute to leptin action independently of LepRb phosphorylation sites. We therefore determined the potential role in leptin action for signals that are activated by Jak2 independently of LepRb phosphorylation (Jak2-autonomous signals). RESEARCH DESIGN AND METHODS: We inserted sequences encoding a truncated LepRb mutant (LepRb(Delta65c), which activates Jak2 normally, but is devoid of other LepRb intracellular sequences) into the mouse Lepr locus. We examined the leptin-regulated physiology of the resulting Delta/Delta mice relative to LepRb-deficient db/db animals. RESULTS: The Delta/Delta animals were similar to db/db animals in terms of energy homeostasis, neuroendocrine and immune function, and regulation of the hypothalamic arcuate nucleus, but demonstrated modest improvements in glucose homeostasis. CONCLUSIONS: The ability of Jak2-autonomous LepRb signals to modulate glucose homeostasis in Delta/Delta animals suggests a role for these signals in leptin action. Because Jak2-autonomous LepRb signals fail to mediate most leptin action, however, signals from other LepRb intracellular sequences predominate.

Feeding long-chain n-3 polyunsaturated fatty acids to obese leptin receptor-deficient JCR:LA- cp rats modifies immune function and lipid-raft fatty acid composition.

Dietary EPA and DHA modulate immunity and thereby may improve the aberrant immune function in obese states. To determine the effects of feeding fish oil (FO) containing EPA and DHA on splenocyte phospholipid (PL) and lipid-raft fatty acid composition, phenotypes and cytokine production, 14-week-old obese, leptin receptor-deficient JCR:LA-cp rats (cp/cp; n 10) were randomised to one of three nutritionally adequate diets for 3 weeks: control (Ctl, 0 % EPA+DHA); low FO (LFO, 0.8 % (w/w) EPA+DHA); high FO (HFO, 1.4 % (w/w) EPA+DHA). Lean JCR:LA-cp (+/ - or +/+) rats (n 5) were fed the Ctl diet. Obese Ctl rats had a higher proportion of n-3 PUFA in splenocyte PL than lean rats fed the same diet (P < 0.05). The lower n-6:n-3 PUFA ratio of splenocyte PL was consistent with the lower mitogen-stimulated interferon (IFN)-gamma and IL-1beta production by cells from obese rats (P < 0.05). Obese rats fed the FO diet had lower mitogen-stimulated Th1 (IFN-gamma) and Th2 (IL-4) cytokine responses, but IL-2 production (concanavalin A; ConA) did not differ (P < 0.05). The HFO diet was more effective in lowering IL-1beta and increasing IL-10 production (ConA, P < 0.05). This lower IL-1beta production was accompanied by a lower proportion of major histocompatability complex class II-positive cells and a higher incorporation of DHA into lipid rafts. This is the first study to demonstrate impaired responses to mitogen stimulation and altered fatty acid incorporation into the membrane PL of JCR:LA-cp rats. Feeding FO lowered the ex vivo inflammatory response, without altering IL-2 production from ConA-stimulated splenocytes which may occur independent of leptin signalling.

Effects of feeding fish oil on mesenteric lymph node cytokine responses in obese leptin receptor-deficient JCR:LA-cp rats.

OBJECTIVE: berrant immune responses have been identified in obesity; however, immune cells of lymph nodes residing in the inflammatory environment of visceral adipose tissue have been largely overlooked. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) can reduce inflammation and modify T-cell function and therefore may improve immune function in obesity. Thus, we determined the effects of feeding fish oil (FO) containing EPA and DHA on mesenteric lymph node (MLN) immune cell function. METHODS: In this study, 14-week-old obese, leptin receptor-deficient JCR:LA-cp rats (cp/cp) (n=10 per group) were randomized to one of three nutritionally adequate diets for 3 weeks: control (ctl, 0% EPA+DHA), low FO (LFO, 0.8% w/w EPA+DHA) or high FO (HFO, 1.4% w/w EPA+DHA). Lean JCR:LA-cp (Cp/cp or Cp/Cp) rats (n=5) were fed ctl diet. MLN cell phospholipid (PL) fatty acid composition, phenotypes and cytokine production were measured. RESULTS: Obese ctl rats produced more IL-1beta, IL-4 and IL-10, despite a higher proportion of (n-3) polyunsaturated fatty acids (PUFAs) and a lower (n-6):(n-3) PUFA ratio in MLN PL compared with lean ctl rats (P<0.05). Concanavalin A-stimulated IL-2 production did not differ from lean rats even though obese ctl rats had a lower proportion of CD4(+)CD25(+) cells (P<0.05). Feeding FO to obese rats increased the incorporation of (n-3) PUFA into MLN PL and normalized production of IL-1beta (HFO only), IL-4 and IL-10 to the levels similar to lean ctl rats (P<0.05). CONCLUSION: We demonstrate for the first time that obese JCR:LA-cp rats have impaired responses of MLN immune cells to mitogen stimulation and altered PL fatty acid composition. Feeding FO lowered the ex vivo inflammatory response (HFO only) and production of Th2 cytokines, without changing IL-2 production from ConA-stimulated splenocytes, which may occur independent of leptin signalling.