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

Resistin gene expression: Novel study in dromedary camel (Camelus dromedarius)

Resistin, an adipocyte-specific hormone involved in insulin resistance and adipocyte differentiation, was initially identified in adipose tissue and macrophages. The physiological role of this molecule in camels remains largely unexplored. This study analysed for the first time blood and tissue levels of resistin as well as expression of resistin gene by real time PCR in adipose tissue (hump, visceral & epididymal) and different muscles (gastrocnemius, heart and caecum) in dromedary camels. The results revealed that resistin concentration was significantly (P<0.01) higher in epididymal adipose tissue as compared to other tissues and the lowest concentration was detected in serum. Additionally, the differential mRNA expression levels of resistin gene showed the highest expression level in epididymal adipose tissue as compared to other tissues. In conclusion, the results demonstrated for the first time that resistin was expressed in different tissues of dromedary camels. These data underscore an important facet of the physiological role of resistin as a factor involved in insulin resistance and glucose metabolism in camels.

High Plasma Resistin Levels Portend the Insulin Resistance-Associated Susceptibility to Early Cognitive Decline in Patients with Type 2 Diabetes Mellitus

BACKGROUND

Metabolic disorders, including insulin resistance, obesity, and hyperlipidemia occur frequently prior to hyperglycemia in patients with type 2 diabetes mellitus (T2DM) and cause mild cognitive impairment (MCI).

OBJECTIVE

We investigated the involvement of resistin in these metabolic abnormalities contributes to MCI in patients with T2DM.

METHODS

A total of 138 hospitalized patients with T2DM were enrolled and categorized into MCI and non-MCI groups according to the Montreal Cognitive Assessment (MoCA) score. Metabolic indicators and cognitive state were assessed, and plasma resistin levels were determined by ELISA.

RESULTS

The resistin levels and homeostasis model assessment of insulin resistance (HOMA-IR) scores of MCI and gender-stratified subgroups were significantly higher than those of controls without MCI (all p < 0.01). Correlation analysis showed that the resistin level was negatively associated with majority of cognitive domains, e.g., MoCA (r = -0.693, p < 0.001) and Mini-Mental State Examination (r = -0.571, p < 0.001), and was related to HOMA-IR (r = 0.667, p < 0.001) but not to obesity and lipid indices. Multivariable regression analysis indicated that resistin (β= -0.675, p < 0.001) and educational level (β= 0.177, p = 0.003) were independent risk factors of MoCA in patients with T2DM.

CONCLUSIONS

High plasma resistin levels portend the insulin resistance-related susceptibility to early cognitive decline in Chinese patients with T2DM. The involvement of this adipokine in other metabolic disorders leading to diabetic MCI and its clinical value for early disease screening must be further studied.

Immunohistochemical identification of resistin in the uterus of ewes subjected to different diets: Preliminary results

Resistin is a polypeptide hormone of the adipokine-family, primarily, but not exclusively, produced by the adipose tissue. Recent studies suggested that resistin may affect the male and female reproductive activity. The study aim was to immunohistochemically evaluate the presence and distribution of resistin in the ovine uterus. Uterine samples were collected from two groups of ewes at the end of an experimental trial during which the animals of the first group (CTRL) were fed only by grazing while those of the second one (EXP) were supplemented with barley and corn. Using a monoclonal antibody against resistin, tested by Western Blot, the immunopositive reaction was identified in the cytoplasm of epithelial lining cells and uterine glands. The endogenous production of resistin seemed to be affected by different diet, as evidenced by staining differences between the CTRL and EXP groups. Our findings support the existence of a peripheral resistin system in the sheep uterus. It is possible that this system is involved in the functionality of the uterus, which is also affected by the animal’s nutritional status.

Visfatin and resistin in gonadotroph cells: expression, regulation of LH secretion and signalling pathways

Visfatin and resistin appear to interfere with reproduction in the gonads, but their potential action at the hypothalamic-pituitary level is not yet known. The aim of the present study was to investigate the mRNA and protein expression of these adipokines in murine gonadotroph cells and to analyse the effects of different concentrations of recombinant mouse visfatin and resistin (0.01, 0.1, 1 and 10ngmL^-1) on LH secretion and signalling pathways in LβT2 cells and/or in primary female mouse pituitary cells. Both visfatin and resistin mRNA and protein were found in vivo in gonadotroph cells. In contrast with resistin, the primary tissue source of visfatin in the mouse was the skeletal muscle, and not adipose tissue. Visfatin and resistin both decreased LH secretion from LβT2 cells after 24h exposure of cells (P<0.03). These results were confirmed for resistin in primary cell culture (P<0.05). Both visfatin (1ngmL^-1) and resistin (1ngmL^-1) increased AMP-activated protein kinase α phosphorylation in LβT2 cells after 5 or 10min treatment, up to 60min (P<0.04). Extracellular signal-regulated kinase 1/2 phosphorylation was transiently increased only after 5min resistin (1ngmL^-1) treatment (P<0.01). In conclusion, visfatin and resistin are expressed in gonadotroph cells and they may affect mouse female fertility by regulating LH secretion at the level of the pituitary.

Secret talk between adipose tissue and central nervous system via secreted factors-an emerging frontier in the neurodegenerative research

First seen as a storage organ, the white adipose tissue (WAT) is now considered as an endocrine organ. WAT can produce an array of bioactive factors known as adipokines acting at physiological level and playing a vital role in energy metabolism as well as in immune response. The global effect of adipokines in metabolic activities is well established, but their impact on the physiology and the pathophysiology of the central nervous system (CNS) remains poorly defined. Adipokines are not only produced by the WAT but can also be expressed in the CNS where receptors for these factors are present. When produced in periphery and to affect the CNS, these factors may either cross the blood brain barrier (BBB) or modify the BBB physiology by acting on cells forming the BBB. Adipokines could regulate neuroinflammation and oxidative stress which are two major physiological processes involved in neurodegeneration and are associated with many chronic neurodegenerative diseases. In this review, we focus on four important adipokines (leptin, resistin, adiponectin, and TNFα) and one lipokine (lysophosphatidic acid-LPA) associated with autotaxin, its producing enzyme. Their potential effects on neurodegeneration and brain repair (neurogenesis) will be discussed. Understanding and regulating these adipokines could be an interesting lead to novel therapeutic strategy in order to counteract neurodegenerative disorders and/or promote brain repair.

Resistin decreases insulin-like growth factor I-induced steroid production and insulin-like growth factor I receptor signaling in human granulosa cells

OBJECTIVE

To identify resistin in human ovarian follicles and investigate the effect and the molecular mechanisms associated with resistin on steroidogenesis in human granulosa cells (GCs).

DESIGN

The effects of recombinant human resistin on the secretion of progesterone (P) and estradiol (E2) by cultured human GCs were investigated.

SETTING

Academic institutions.

PATIENT(S)

Twenty infertile and healthy women undergoing IVF.

INTERVENTION(S)

Primary human GC cultures stimulated with recombinant human resistin (10 ng/mL).

MAIN OUTCOME MEASURE(S)

Determination of messenger RNA (mRNA) and protein expression of resistin in fresh human GCs by reverse transcriptase-polymerase chain reaction (RT-PCR), immunoblot and immunohistochemistry, respectively; measurement of P and E2 levels in the conditioned media by radioimmunoassay; determination of cell proliferation by tritiated thymidine incorporation; and analysis of signaling pathways activation by immunoblot analysis.

RESULT(S)

Human GCs and theca cells express resistin. In primary human GCs, resistin decreases P and E2 secretion in response to insulin-like growth factor I (IGF-I). This was associated with a reduction in the P450 aromatase and P450scc (cholesterol side-chain cleavage cytochromes P450) (P450scc) protein levels but not those of 3β-hydroxysteroid dehydrogenase (3β-HSD) or steroidogenic acute regulatory protein (StAR) and with a decrease in IGF-I-induced IGF-I receptor and mitogen-activated protein kinase (MAPK) extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation. Resistin treatment does not affect IGF-I-induced cell proliferation and basal steroidogenesis (there is no IGF-I or follicle-stimulating hormone stimulation). In the basal state, resistin rapidly stimulates Akt and MAPK ERK1/2 and p38 phosphorylation in primary human GCs.

CONCLUSION(S)

Resistin is present in human GCs and theca cells. It decreases P and E2 secretion, P450scc and P450 aromatase protein levels, and IGF-IR signaling in response to IGF-I in primary human GCs.

Adipokines and cardiovascular risk in Cushing's syndrome

Cushing's syndrome (CS) is associated with increased cardiovascular morbidity and mortality. Recent evidence also suggests that increased cardiovascular risk may persist even after long-term remission of CS. Increased central obesity, a typical feature of CS, is associated with altered production of adipokines, which contributes to the pathogenesis of several metabolic and cardiovascular complications observed in this condition. In vitro and in vivo studies have shown a relationship between cortisol and adipokines in several experimental settings. In patients with either active or 'cured' CS, an increase in leptin and resistin levels as well as the release of pro-inflammatory cytokines, such as tumor necrosis factor-α and interleukin-6, may be associated with increased cardiovascular risk. For other adipokines, including adiponectin, results are inconclusive. Studies are needed to further elucidate the interactions between clinical and subclinical increases in cortisol production and altered adipokine release in CS.

Expression and effect of resistin on bovine and rat granulosa cell steroidogenesis and proliferation

Resistin, initially identified in adipose tissue and macrophages, was implicated in insulin resistance. Recently, its mRNA was found in hypothalamo-pituitary axis and rat testis, leading us to hypothesize that resistin may be expressed in ovary. In this study, we determined in rats and cows 1) the characterization of resistin in ovary by RT-PCR, immunoblotting, and immunohistochemistry and 2) the effects of recombinant resistin (10, 100, 333, and 667 ng/ml) ± IGF1 (76 ng/ml) on steroidogenesis, proliferation, and signaling pathways of granulosa cells (GC) measured by enzyme immunoassay, [(3)H]thymidine incorporation, and immunoblotting respectively. We observed that resistin mRNA and protein were present in several bovine and rat ovarian cells. Nevertheless, only bovine GC abundantly expressed resistin mRNA and protein. Resistin treatment decreased basal but not IGF1-induced progesterone (P<0.05; whatever the dose) and estradiol (P<0.005; for 10 and 333 ng/ml) production by bovine GC. In rats, resistin (10 ng/ml) increased basal and IGF1-induced progesterone secretion (P<0.0001), without effect on estradiol release. We found no effect of resistin on rat GC proliferation. Conversely, in cows, resistin increased basal proliferation (P<0.0001; for 100-667 ng/ml) and decreased IGF1-induced proliferation of GC (P<0.0001; for 10-333 ng/ml) associated with a decrease in cyclin D2 protein level (P<0.0001). Finally, resistin stimulated AKT and p38-MAPK phosphorylation in both species, ERK1/2-MAPK phosphorylation in rats and had the opposite effect on the AMPK pathway (P<0.05). In conclusion, our results show that resistin is expressed in rat and bovine ovaries. Furthermore, it can modulate GC functions in basal state or in response to IGF1 in vitro.

Lipopolysaccharide (LPS) stimulates adipokine and socs3 gene expression in mouse brain and pituitary gland in vivo, and in N-1 hypothalamic neurons in vitro

Adipokines that modulate metabolic and inflammatory responses, such as resistin (rstn) and fasting-induced adipose factor (fiaf), are also expressed in mouse brain and pituitary gland. Since lipopolysaccharide (LPS)-induced endotoxinemia provokes an anorectic response via a hypothalamic-dependent mechanism we hypothesized that LPS would also modify hypothalamic adipokine expression. Challenging male CD-1 mice with LPS (5 mg/kg; s.c.) significantly reduced bodyweight (24 h) and realtime RT-PCR revealed time- and tissue-dependent increases in rstn, fiaf and suppressor of cytokine signaling-3 (socs-3) mRNA in hypothalamic, pituitary, cortical and adipose tissues. Gene expression was rapidly increased (3-6 h) in the hypothalamus and pituitary, but returned to normal within 24 h. In contrast, with the exception of rstn in fat, the expression of target genes remained elevated in cortex and visceral fat at 24 h post-injection. In order to more specifically examine the hypothalamic response to LPS we investigated its effects directly on N-1 hypothalamic neurons in vitro. LPS (25 microg/mL; 3 h) had no effect on rstn mRNA, but significantly stimulated fiaf and socs-3 expression. Although various toll-like receptor 4 (TLR4) antagonists (parthenolide, PD098059, and SB202190) did not prevent the LPS-induced increases in fiaf and socs-3, they did partially attenuate its stimulatory effects. We conclude that LPS treatment increases the expression of central, and possibly neuronal, adipokine genes which may influence local tissue repair and function, but could also have downstream consequences on the hypothalamic control of appetite and energy metabolism following an inflammatory insult.

Regulation of pituitary gene expression by adrenalectomy

Excessive secretion of adrenal hormones, such as glucocorticoid and mineralocorticoid, leads to metabolic syndrome, including insulin resistance, obesity, and hypertension. These metabolic abnormalities are ameliorated by adrenalectomy (ADX). To identify pituitary mediators for ADX-induced physiological alterations, such as weight loss and hypotension, we investigated the effect of ADX on the pituitary transcriptome using serial analysis of gene expression (SAGE). SAGE method is based on isolation of short sequence tags, which usually correspond to unique mRNA species. The SAGE libraries were constructed from pituitary gland of intact (n = 51) and ADX (n = 12) mice. Thirty-one transcripts were differentially expressed between intact and ADX. Three transcripts encoding for proopiomelanocortin and three other transcripts involved in regulation of hormone secretion (neuromedin B, proprotein convertase subtilisin/kexin type 2, and IA-2) were induced by ADX. In addition, ADX increased the expression levels of genes encoding for cation extracellular matrix (matrix gamma-carboxyglutamate protein) and transport (solute carrier family 22 member 17). Conversely, ADX downregulated two transcripts involved in mitochondrial oxidative phosphorylation (nicotinamide adenine dinucleotide (NADH) dehydrogenase 3 and cytochrome c oxidase 3). Moreover, ADX significantly modulated the expression levels of one gene with uncharacterized function and 20 novel transcripts. This study reveals alterations of pituitary gene expressions that may be associated with ADX-induced physiological changes including weight loss.

Adipokine gene expression in a novel hypothalamic neuronal cell line: resistin-dependent regulation of fasting-induced adipose factor and SOCS-3

Adipokines such as leptin, resistin, and fasting-induced adipose factor (FIAF) are secreted by adipocytes, but their expression is also detectable in the brain and pituitary. The role of central adipokines remains elusive, but we speculate that they may modulate those hypothalamic signaling pathways that control energy homeostasis. Here we describe experiments to test this in which we exploited a novel hypothalamic neuronal cell line (N-1) that expresses a variety of neuropeptides and receptors that are known to be implicated in appetite regulation. Using real-time RT-PCR, we confirmed that N-1 neurons express resistin (rstn) and fiaf, as well as suppressor of cytokine signaling-3 (socs-3), a feedback inhibitor of leptin signaling. Treating N-1 cells with recombinant resistin (200 ng/ml, 30 min) reduced both fiaf (25%, p < 0.005) and socs-3 (29%, p < 0.005) mRNA levels, and similar reductions in fiaf (40%, p < 0.001) and socs-3 (25%, p < 0.001) resulted following the overexpression of resistin. Conversely, when RNA interference (RNAi) was used to reduce endogenous rstn levels (-60%, p < 0.005), fiaf and socs-3 expression was increased (46 and 65% respectively, p < 0.005). A similar reduction in rstn mRNA was achieved using RNAi in differentiated 3T3-L1 adipocytes, and this manipulation also reduced fiaf and socs-3 expression (-53, -21 and -20% respectively, p < 0.005). In contrast, although RNAi successfully reduced fiaf mRNA by 50% (p < 0.001) in N-1 cells and 40% (p < 0.001) in 3T3-L1 cells, there was no effect on rstn or socs-3 mRNA. These data suggest that resistin exerts a novel autocrine/paracrine control over fiaf and socs-3 expression in both 3T3-L1 adipocytes and N-1 neurons. Such a mechanism could be part of the central feedback system that modulates the effects of adipokines, and other adiposity signals, implicated in hypothalamic energy homeostasis. However, it remains to be determined whether these in vitro results can be translated to the control of adipokine expression in brain and adipose tissue.

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.

Type 2 diabetes and cardiovascular disease: getting to the fat of the matterThis paper is one of a selection of papers published in this Special Issue, entitled Young Investigators' Forum

The increasing national prevalence of obesity is a major public health concern and a substantial burden on the health care resources of Canada. In addition to the direct health impact of obesity, this condition is a well-established risk factor for the development of various prevalent comorbidities including type 2 diabetes, hypertension, and cardiovascular disease. Historically, adipose tissue has been regarded primarily as an organ for energy storage. However, the discovery of leptin in the mid 1990’s revolutionized our understanding of this tissue and has focused attention on the endocrine function of adipose tissue as a source of secreted bioactive peptides. These compounds, collectively termed adipokines, regulate a number of biological functions including appetite and energy balance, insulin sensitivity, lipid metabolism, blood pressure, and inflammation. The physiological importance of adipokines has led to the hypothesis that changes in the synthesis and secretion of these compounds in the obese are a causative factor contributing to the development of obesity and obesity-related diseases in these individuals. Following from this it has been proposed that pharmacologic manipulation of adipokine levels may provide novel effective therapeutic strategies to treat and prevent obesity, type 2 diabetes, and cardiovascular disease.

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.

Increased expression of the adipokine genes resistin and fasting-induced adipose factor in hypoxic/ischaemic mouse brain

Adipose tissue is the primary source of the adipokines resistin and fasting-induced adipose factor (FIAF). We reported that the brain is also a site of adipokine expression, although their function there is unknown. Peripheral resistin and fasting-induced adipose factor are reported to be inflammatory markers, and we hypothesized that they would be induced in the brain by hypoxia/ischaemia. We show that neonatal hypoxia/ischaemia rapidly increased fiaf mRNA in the injured cortex and hippocampus at 2 and 7 days after hypoxia/ischaemia. In contrast, resistin (retn) mRNA was increased in the cortex only at 21 days after hypoxia/ischaemia. As a lipopolysaccharide-induced inflammatory response did not increase brain fiaf and retn mRNA levels, we conclude that brain injury may be responsible for the novel hypoxia/ischaemia-induced changes in adipokine gene expression. In summary, our results indicate that brain injury, or an inflammatory stimulus, regulates the central expression of two genes normally considered to be adipose tissue-specific. These observations add to our previous evidence that the brain is an important site of adipokine gene expression.

Adipokines: implications for female fertility and obesity

Obesity is associated with a diverse set of metabolic disorders, and has reproductive consequences that are complex and not well understood. The adipose tissue-produced leptin has dominated the literature with regards to female fertility complications, but it is pertinent to explore the likely role of other adipokines--adiponectin and resistin--as our understanding of their biological functions emerge. Leptin influences the developing embryo, the functioning of the ovary and the endometrium, interacts with the release and activity of gonadotrophins and the hormones that control their synthesis. In this review such biological actions and potential roles of the adipokines leptin, adiponectin and resistin are explored in relation to female fertility and the complexity of the obese metabolic state.