Resistin is expressed in pancreatic islets

Resistin in rheumatoid arthritis synovial tissue, synovial fluid and serum

BACKGROUND

Resistin is a newly identified adipocytokine which has demonstrated links between obesity and insulin resistance in rodents. In humans, proinflammatory properties of resistin are superior to its insulin resistance-inducing effects.

OBJECTIVES

To assess resistin expression in synovial tissues, serum and synovial fluid from patients with rheumatoid arthritis, osteoarthritis and spondylarthropathies (SpA), and to study its relationship with inflammatory status and rheumatoid arthritis disease activity.

METHODS

Resistin expression and localisation in synovial tissue was determined by immunohistochemistry and confocal microscopy. Serum and synovial fluid resistin, leptin, interleukin (IL)1beta, IL6, IL8, tumour necrosis factor alpha, and monocyte chemoattractant protein-1 levels were measured. The clinical activity of patients with rheumatoid arthritis was assessed according to the 28 joint count Disease Activity Score (DAS28).

RESULTS

Resistin was detected in the synovium in both rheumatoid arthritis and osteoarthritis. Staining in the sublining layer was more intensive in patients with rheumatoid arthritis compared with those with osteoarthritis. In rheumatoid arthritis, macrophages (CD68), B lymphocytes (CD20) and plasma cells (CD138) but not T lymphocytes (CD3) showed colocalisation with resistin. Synovial fluid resistin was higher in patients with rheumatoid arthritis than in those with SpA or osteoarthritis (both p<0.001). In patients with rheumatoid arthritis and SpA, serum resistin levels were higher than those with osteoarthritis (p<0.01). Increased serum resistin in patients with rheumatoid arthritis correlated with both CRP (r=0.53, p<0.02), and DAS28 (r=0.44, p<0.05), but not with selected (adipo) cytokines.

CONCLUSION

The upregulated resistin at local sites of inflammation and the link between serum resistin, inflammation and disease activity suggest a role for resistin in the pathogenesis of rheumatoid arthritis.

Study of Resistin gene expression in peripheral blood mononuclear cell and its gene polymorphism in a small range population

OBJECTIVE

To observe the expression of Resistin mRNA in peripheral blood mononuclear cells and its gene polymorphism in coding region in a small range population in Zhejiang Province of China.

METHODS

Eighty-three cases of type 2 diabetes mellitus and 53 healthy people were included. The expression of Resistin mRNA in peripheral blood mononuclear cells was detected by RT-PCR and semi-quantitative PCR assay. The sequencing work was done in Resistin cDNA and gene polymorphism was analyzed.

RESULTS

At the same condition, in 83 diabetes patients, Resistin mRNA was detected in 23 cases (11 males and 12 females). There was no Resistin mRNA expression in 53 healthy people. The ratio of PCR products between Resistin and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was from 0.564 to 1.238, averaging 0.804+/-0.436. The sequence of Resistin cDNA is almost identical with each other and with that in GenBank with no single nucleotide polymorphism being found.

CONCLUSION

Resistin mRNA is expressed in human peripheral blood mononuclear cells in some type 2 diabetes mellitus, but its expression is at a low level. Among the experiment population we did not find polymorphism phenomenon in Resistin coding region. The different individual's Resistin coding region is highly coincident.

Adipokine gene expression in brain and pituitary gland

The brain has been recognized as a prominent site of peptide biosynthesis for more than 30 years, and many neuropeptides are now known to be common to gut and brain. With these precedents in mind it is remarkable that adipose-derived peptides like leptin have attracted minimal attention as brain-derived putative neuromodulators of energy balance. This review outlines the evidence that several adipose-specific genes are also expressed in the central nervous system and pituitary gland. We, and others, confirmed that the genes for leptin, resistin, adiponectin, FIAF (fasting-induced adipose factor) and adiponutrin are expressed and regulated in these tissues. For example, leptin mRNA was readily detectable in human, rat, sheep and pig brain, but not in the mouse. Leptin expression in rat brain and pituitary was regulated through development, by food restriction, and following traumatic brain injury. In contrast, hypothalamic resistin mRNA was unaffected by age or by fasting, but was significantly depleted by food restriction in mouse pituitary gland. Similar results were seen in the ob/ob mouse, and we noted a marked reduction in resistin-positive hypothalamic nerve fibres. Resistin and fiaf mRNA were also upregulated in hypoxic/ischaemic mouse brain. Our studies on the regulation of neuronal adipokines were greatly aided by the availability of clonal hypothalamic neuronal cell lines. One of these, N-1, expresses both rstn and fiaf together with several other neuropeptides and receptors involved in energy homeostasis. Selective silencing of rstn revealed an autocrine/paracrine regulatory system, mediated through socs-3 expression that may influence the feedback effects of insulin and leptin in vivo. A similar convergence of signals in the pituitary gland could also influence anterior pituitary hormone secretion. In conclusion, the evidence is suggestive that brain and pituitary-derived adipokines represent a local regulatory circuit that may fine tune the feedback effects of adipose hormones in the control of energy balance.

Resistin: a hormone which induces insulin resistance is increased in normal pregnancy

AIMS

Resistin, a newly discovered adipokine, is thought to play a key role in the regulation of insulin resistance. The objectives of this study were to develop a nomogram of maternal plasma concentrations of resistin from 11 weeks of gestation to term and to determine whether resistin concentrations differ between normal and overweight pregnant women.

METHODS

In this cross-sectional study, plasma concentrations of resistin were determined in normal pregnant women of normal body mass index (BMI 18.5-24.9; n=261), overweight pregnant women (BMI > or =25; n=140), and non-pregnant women of normal BMI (n=40). Blood samples were collected once from each woman between the first trimester and term. Percentiles for resistin concentration were determined for five pre-specified windows of gestational age. Plasma resistin concentration was determined by immunoassay. Non-parametric statistics were used for analysis.

RESULTS

The median maternal plasma concentration of resistin between 11 to 14 weeks of gestation in women of normal weight was significantly higher than non-pregnant women; the plasma concentration of resistin increased with gestational age.

CONCLUSIONS

Normal pregnant women have a higher median plasma concentration of resistin than non-pregnant women and the concentration of this adipokine increases with advancing gestation. Alterations in the maternal plasma concentration of resistin during pregnancy could contribute to metabolic changes of pregnancy.

Cloning and characterization of porcine resistin gene

Resistin is a member of resistin-like molecules (RELMs) and a hormone secreted from mature adipocytes in rodents and leukocytes in human. We now report the cloning and characterization of the full-length porcine resistin cDNA and gene. Sequence analysis indicated that the pig resistin cDNA sequence had an open reading frame of 330 bp encoding a 12 kDa protein of 109 amino acids. The deduced amino acid sequence showed 75.2% identity to the human resistin. The porcine resistin gene was composed of four exons and had exactly the same exon structure as the human resistin gene. The tissue distribution of porcine resistin mRNA was assessed by semi-quantitative RT-PCR. Resistin gene expression was the highest in porcine leukocytes and low in adipose tissue. Resistin protein could be detected in porcine serum by western blotting and it circulated in serum as dimers and trimers. We provided the first evidence that resistin was abundantly expressed in porcine leukocytes and had an expression pattern similar to that in human resistin mRNA and protein. This suggests that the pig may be a suitable animal model for studying the function of resistin in human insulin resistance.

Role of resistin in obesity, insulin resistance and Type II diabetes

Resistin is a member of a class of cysteine-rich proteins collectively termed resistin-like molecules. Resistin has been implicated in the pathogenesis of obesity-mediated insulin resistance and T2DM (Type II diabetes mellitus), at least in rodent models. In addition, resistin also appears to be a pro-inflammatory cytokine. Taken together, resistin, like many other adipocytokines, may possess a dual role in contributing to disease risk. However, to date there has been considerable controversy surrounding this 12.5 kDa polypeptide in understanding its physiological relevance in both human and rodent systems. Furthermore, this has led some to question whether resistin represents an important pathogenic factor in the aetiology of T2DM and cardiovascular disease. Although researchers still remain divided as to the role of resistin, this review will place available data on resistin in the context of our current knowledge of the pathogenesis of obesity-mediated diabetes, and discuss key controversies and developments.

Adipocytokines: leptin--the classical, resistin--the controversical, adiponectin--the promising, and more to come

With the growing prevalence of obesity, scientific interest in the biology of adipose tissue has been extended to the secretory products of adipocytes, since they are increasingly shown to affect several aspects in the pathogenesis of obesity-related diseases. The cloning of the ob gene is consistent with this concept and suggests that body fat content in adult rodents is regulated by a negative feedback loop centred in the hypothalamus. In recent years, a number of additional signalling molecules secreted by adipose tissue have been discovered, commonly referred to as 'adipocytokines'. Among these, adiponectin is perhaps the most interesting and promising compound for the clinician since it has profound protective actions in the pathogenesis of diabetes and cardiovascular disease. Adiponectin is low in obese subjects and, in particular, insulin-resistant patients. In contrast, resistin seems to be of greater relevance in relation to the immune stress response than in the regulation of glucose homeostasis. However, inflammatory processes have recently been connected with the development of atherosclerosis. Finally, little is known regarding the clinical relevance of visfatin. Recent research has revealed many functions of adipocytokines extending far beyond metabolism, such as immunity, cancer and bone formation. This report aims to review some of the recent topics of adipocytokine research that may be of particular importance.

Association between endocrine pancreas and ductal system. More than an epiphenomenon of endocrine differentiation and development?

Traditional histological descriptions of the pancreas distinguish between the exocrine and the endocrine pancreas, as if they were two functionally distinct glands. This view has been proven incorrect and can be considered obsolete. Interactions between acinar and islet tissues have been well established through numerous studies that reveal the existence of anatomical and functional relationships between these compartments of the gland. Less attention, however, has traditionally been paid to the relationships occurring between the endocrine pancreas and the ductal system. Associations between islet tissue and ducts are considered by most researchers as only a transient epiphenomenon of endocrine development. This article reviews the evidence that has emerged in the last 10 years demonstrating the existence of stable, close, and systematic relationships between these two pancreatic compartments. Functional and pathophysiological implications are considered, and the existence of an "acinar-duct-islet" axis is put forward. The pancreas appears at present to be an integrated organ composed of three functionally related components of well-orchestrated endocrine and exocrine physiological responses.

Pituitary resistin gene expression is upregulated in vitro and in vivo by dexamethasone but is unaffected by rosiglitazone

A physiological role for the adipose-derived hormone, resistin, remains unsolved and its putative involvement in insulin resistance is largely controversial. Like leptin and other adipokines, we detected resistin in the rodent hypothalamic-pituitary system. In addition, the pituitary corticotrope cell line, AtT20, is also a source of resistin. These data suggested that resistin could be involved in diverse physiological processes in non-adipose tissue. Initial studies indicated that pituitary resistin gene expression was regulated in a nutritional (fed>fasted), age- (young>old) and gender-specific manner (male>female). In the present work we hypothesized that pituitary resistin expression should be regulated through signalling pathways similar to those reported for adipose tissue. For example, dexamethasone (DEX) potently stimulates production of resistin in murine adipose tissue, whereas thiazolidinediones such as rosiglitazone (ROSI), acting via peroxisome proliferator-activated receptor (PPAR)gamma, reportedly inhibit or stimulate resistin expression. Using quantitative real-time RT-PCR we determined that injection of DEX (10 and 50 microg) yielded 7- and 9-fold increases in pituitary resistin gene expression in prepubertal, but not adult mice. In addition, adrenalectomy attenuated pituitary resistin gene expression, which was restored by DEX (10 microg). In AtT20 cells, exposure to corticosterone (10(-7) and 10(-6)M; 24 h) and DEX (10(-9)-10(-6)M) stimulated resistin mRNA more than 65% (p<0.05) and 115% (p<0.0001), respectively. In contrast, ROSI, injected (5 and 20 mg/kg s.c. for 14 days) or given orally (3 mg/kg/day to 10 mg/kg/day for up to 7 weeks), failed to alter pituitary resistin gene expression in healthy male CD1 mice. Treatment of AtT20 cells with ROSI (10(-5)-10(-10)M; 24 h or 96 h) or the PPARgamma agonist GW 1929 (10(-9) and 10(-5)M; 24 h) had no effect on resistin mRNA. The PPARgamma antagonist GW 9662 (10(-6) and 10(-5)M) was also ineffective. In conclusion, pituitary resistin mRNA levels are robustly stimulated by corticosteroids, particularly at the time of puberty. This is consistent with our previous suggestion that resistin may be involved in maturation of the hypothalamic-pituitary axis. In contrast, pituitary resistin gene expression appears to be PPARgamma-independent and therefore different from the situation in adipose tissue.

Hypothalamic resistin immunoreactivity is reduced by obesity in the mouse: co-localization with alpha-melanostimulating hormone

Resistin is a new adipokine expressed in mouse, rat and human adipose tissue. Resistin may be an important link between obesity and insulin resistance, though this controversial view is complicated by the discovery of multiple sites of resistin expression, including human macrophages, placenta and pancreas. In previous studies we demonstrated that the mouse hypothalamo-pituitary system was also a site of resistin production. Pituitary resistin is developmentally regulated, reduced in the ob/ob mouse and severely down-regulated by food deprivation (24 h). An unexpected finding was that hypothalamic resistin mRNA remained unaffected by fasting. The present experiments examined the localization and possible regulation of hypothalamic resistin protein. Using immunohistochemistry we observed a complex network of resistin+ fibres extending rostrally from the arcuate nucleus of the hypothalamus (ARC) to the preoptic area. Labelled cell bodies occurred only in the ARC and in a periventricular region of the dorsal hypothalamus. Hypothalamic resistin immunoreactivity (ir) was unaffected by fasting (48 h) or by a high fat diet, but the periventricular staining was greatly increased in the lactating mouse. Marked reductions in resistin+ fibres were seen in brain tissue from: (a) ob/ob mice, (b) young mice made underweight for their age by raising them in large litters (20 pups per litter) and (c) mice with hypothalamic lesions induced by monosodium glutamate (MSG) or gold thioglucose (GTG). We speculate that the resistin-ir deficit in genetically obese mice, and in severely underweight mice, could be due to low or absent leptin. In contrast, though MSG- and GTG-treated mice have high levels of circulating leptin, in the presence of excessive visceral fat deposits, we hypothesize that damage to the ARC destroys the resistin+ cell bodies. This latter supposition led us to an additional hypothesis, that resistin-ir would be contained in neurons expressing the proopiomelanocortin (POMC) gene. This proved to be correct. Double label immunofluorescence histochemistry revealed that alpha-MSH-ir, a marker for POMC neurons, was co-localized with resistin-ir. In conclusion, our data reveal a second example of an adipocytokine co-localized with a hypothalamic neuropeptide. We reported previously that leptin was co-localized with oxytocin and vasopressin. RT-PCR analysis confirmed that resistin mRNA is readily detectable in ARC, but further work is required to determine whether the resistin gene is expressed in POMC neurons or if resistin is specifically accumulated by these cells. Nonetheless, our data suggest that the hypothalamus is a target tissue for resistin.

Role of glucocorticoids in the physiopathology of excessive fat deposition and insulin resistance

Glucocorticoids are important hormones in the regulation of metabolic homeostasis. We infused normal rats with dexamethasone given intracerebroventricularly (i.c.v.) for 3 days. This resulted in hyperphagia, hyperinsulinemia, and marked insulin resistance. Similar metabolic defects were observed following i.c.v. infusion of neuropeptide Y (NPY) in normal rats. As central dexamethasone infusion enhanced NPY content in the arcuate nucleus, it suggested that its metabolic effects are mediated by NPY. Moreover, due to the lack of effects observed in vagotomized animals, activation of the parasympathetic nervous system by central dexamethasone infusion is proposed. Glucocorticoid action is known to involve prereceptor metabolism by enzymes such as 11beta-HSD-1 that converts inactive into active glucocorticoids. Mice overexpressing 11beta-HSD-1 in adipose tissue were shown to be obese and insulin resistant. We recently observed that adipose tissue 11beta-HSD-1 mRNA expression is increased at the onset of high-fat diet-induced obesity and positively correlated with the degree of hyperglycemia. In human obesity, increased adipose tissue 11beta-HSD-1 expression and activity were also reported. Resistin is a new adipose tissue-secreted hormone shown to play a role in glucose homeostasis by increasing hepatic glucose production and inhibiting muscle and adipose tissue glucose utilization. We observed increased adipose tissue resistin expression in the early phase of high-fat diet-induced obesity as well as decreased resistin expression in response to leptin. A positive correlation between glycemia and adipose tissue resistin expression further suggested a role of this hormone in the development of insulin resistance. The melanocortin system is another important player in the regulation of energy balance. Peripheral administration of a melanocortin agonist decreased food intake and body weight and favored lipid oxidation, effects that were more marked in obese than in lean rats. It is proposed that both resistin and melanocortin agonists may influence adipose tissue 11beta-HSD-1, thereby decreasing or enhancing glucose metabolism.