Quantitative comparison of adipocytokine gene expression during adipocyte maturation in non-obese and obese rats

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.

Adverse effects of metabolic disorders in childhood on adult reproductive function and fertility in the male

Over the last 50 years, there has been a steady decline in fertility rates in humans, which has occurred in parallel with an increasing incidence of obesity and metabolic disorders. The potential impact of these disorders and plausible mechanisms by which they negatively influence male reproduction are only partly understood and published data are often controversial. Obesity is one of the most important health challenges worldwide and is becoming more prevalent in children and adolescents. Obesity, the metabolic syndrome and related co-morbidities can lead to impaired male reproductive function, including adverse effects on spermatogenesis and steroidogenesis as illustrated by reduced sperm number and quality, decreased testosterone levels and elevated inflammatory markers. The incidence of diabetes mellitus type I is also dramatically increasing and may negatively impact spermatogenesis and testicular function, resulting in decreased serum testosterone and epididymal weight. In this review, we summarize and discuss the effects of metabolic diseases that typically develop during childhood and adolescence on later reproductive function and fertility. While impact on reproductive health is likely observed in both sexes, we have chosen to focus on the male in the current review. Specifically, we illustrate adverse effects of obesity, type 1 diabetes, the metabolic syndrome and insulin resistance on sperm function and testosterone metabolism. Identification of pathophysiological mechanisms during childhood may open up new avenues for early prevention and treatment resulting in better reproductive outcomes and improved fertility rates during adulthood.

Antiadipogenesis of Oroxylum indicum (L.) Kurz Extract via PPARγ2 in 3T3-L1 Adipocytes

Oroxylum indicum is regarded as a traditional food with medicinal properties and is used widely throughout Asia. It has previously been demonstrated that O. indicum extract (OIE) was able to suppress the differentiation of 3T3-L1 preadipocytes to adipocytes. However, the mechanism underlying the antiadipogenesis of this plant has not been fully investigated. The present study aimed to explore the impact of OIE at 50 to 200 μg mL⁻¹ on the molecular mechanism involved in the antiadipogenic activity in 3T3-L1 cells at day 0 of their differentiation to adipocytes. The morphology and biochemistry of the cells on day 12 were investigated and compared to the relevant controls. Adiponectin was measured using enzyme-linked immunosorbent assay (ELISA). The mRNA expression of peroxisome proliferator-activated receptor-gamma 2 (PPARγ2), sterol regulatory element-binding proteins 1c (SREBP-1c), fatty acid synthetase (FAS), glucose transporter (GLUT4), and leptin in adipocytes was determined by real-time PCR. The results demonstrated that the OIE at 200 μg mL⁻¹ exhibited strongest suppression on intracellular lipid accumulation. The levels of adiponectin were dramatically increased in the untreated adipocytes, whereas significantly decreased in the 200 μg mL⁻¹ OIE-treated adipocytes (P < 0.05). Expression of the mRNAs revealed that OIE-treated adipocytes at 200 μg mL⁻¹ significantly inhibited the expression of PPARγ2 and SREBP-1c and lowered the level of expression of GLUT4, FAS, and leptin compared to the control (P < 0.05). These findings suggest that OIE inhibits adipocyte differentiation along with the downregulation of PPARγ2, SREBP-1c, and GLUT4, leading to the decrease in the expression of FAS and adipokine (leptin and adiponectin). Thus, OIE might be developed for hyperlipidemia and obesity prevention.

Adipocytokines may delay pubertal maturation of human Sertoli cells

Reproduction is an important target of obesity complications, including adverse effects on spermatogenesis and steroidogenesis. Adipocytokines are key mediators in various complications of obesity. Our aim was to study the potential of adipocytokines to affect Sertoli cell function, which is crucial for spermatogenesis, and possibly link these findings to the observed attenuation of spermatogenesis in obese males. Testicular biopsies were obtained from healthy donors. Highly purified adult human Sertoli cells (HSCs) were isolated by fluorescence-activated cell sorting. Cells were cultured and exposed to different concentrations of adipocytokines (10-1000ngmL-1 ) for 2-7 days. Expression of selected Sertoli cell genes was quantified by quantitative polymerase chain reaction. Long-term treatment (7 days) of HSCs with higher concentrations of chemerin, irisin, nicotinamide phosphoribosyltransferase (Nampt), resistin and progranulin significantly suppressed FSH receptor expression (by 79%, 83%, 64%, 71% and 26% respectively; P P invitro , may negatively affect Sertoli cell maturation and retain these cells in a more prepubertal stage. This could negatively affect testis function and add to fertility problems in obese adults.

A Novel Bongkrekic Acid Analog-Mediated Modulation of the Size of Lipid Droplets: Evidence for the Appearance of Smaller Adipocytes

Thiazolidinediones (TZDs) are known as peroxisome proliferator-activated receptor γ (PPARγ) activators, and are used in the treatment of diabetes. Although the usefulness of TZDs has been demonstrated, some of their side effects are becoming an obstacle to their clinical applicability; edema is known to be evoked by the "structural characteristics" of TZD, but not by the PPARγ activation. Thus, novel therapeutic modalities (i.e., non-TZD-type PPARγ activators) having different structures to those of TZDs are desired. We previously identified bongkrekic acid (BKA) as a PPARγ activator using the human breast cancer MCF-7 cell line as a model system. In the present study, we newly synthesized BKA analogs and examined the usefulness of BKA and its analogs as PPARγ activators in differentiated adipocyte cells. Among the chemicals investigated, one of the BKA analogs (BKA-#2) strongly stimulated PPARγ and the differentiation of 3T3-L1 cells similar to pioglitazone, a positive control. Furthermore, BKA-#2 reduced the size of lipid droplets in the mature adipocyte cells. The possible modulation mechanism by BKA-#2 is discussed.

Effects of Rosuvastatin Alone or in Combination with Omega-3 Fatty Acid on Adiponectin Levels and Cardiometabolic Profile

BACKGROUND

Adiponectin is an important adipocyte-related protein that has been postulated to participate in prevention of the development of metabolic syndrome. The relationship between adiponectin serum levels and risk of coronary artery disease (CAD) has been widely investigated and remains controversial. The aim of the present study was to evaluate the effects of rosuvastatin and/or omega-3 fatty acid on adiponectin serum levels in patients with insulin resistance (IR) and CAD.

PATIENTS AND METHODS

This study involved 87 patients with CADs and IR of different etiology, the patients were divided into three groups; 24 patients on treatment with rosuvastatin, 22 patients on treatment with omega-3 fatty acid, 23 patients on treatment with omega-3 fatty acid and rosuvastatin, 18 patients were not previously or currently treated with either rosuvastatin or omega-3 fatty acid, those regarded as control patients. Anthropometric measures, adiponectin serum levels, and other biochemical parameters were assessed in each treated group.

RESULTS

Rosuvastatin therapy leads to a significant elevation in adiponectin serum levels from 4.1 ± 0.99 ng/mL to 6.76 ± 1.03 ng/mL compared to control P < 0.01. Omega-3 fatty acid therapy leads to a significant elevation in adiponectin serum levels from 4.1 ± 0.99 ng/mL to 6.11 ± 1.29 ng/mL compared to control P < 0.01. Rosuvastatin plus omega-3 fatty acid therapy lead to a significant elevation in adiponectin serum levels from 4.1 ± 0.99 ng/mL to 7.99 ± 1.76 ng/mL compared to control P < 0.01.

CONCLUSIONS

Rosuvastatin and/or omega-3 fatty acid lead to significant cardiometabolic protection through an increment in adiponectin serum levels.

Browning of white adipose tissue uncouples glucose uptake from insulin signaling

Presence of thermogenically active adipose tissue in adult humans has been inversely associated with obesity and type 2 diabetes. While it had been shown that insulin is crucial for the development of classical brown fat, its role in development and function of inducible brown-in-white (brite) adipose tissue is less clear. Here we show that insulin deficiency impaired differentiation of brite adipocytes. However, adrenergic stimulation almost fully induced the thermogenic program under these settings. Although brite differentiation of adipocytes as well as browning of white adipose tissue entailed substantially elevated glucose uptake by adipose tissue, the capacity of insulin to stimulate glucose uptake surprisingly was not higher in the brite state. Notably, in line with the insulin-independent stimulation of glucose uptake, our data revealed that brite recruitment results in induction of solute carrier family 2 (GLUT-1) expression in adipocytes and inguinal WAT. These results for the first time demonstrate that insulin signaling is neither essential for brite recruitment, nor is it improved in cells or tissues upon browning.

Obesity and colorectal cancer: Role of adipokines in tumor initiation and progression

Obesity-associated diseases account for a large portion of public health challenges. Among obesity-related disorders, a direct and independent relationship has been ascertained for colorectal cancer (CRC). The evidence that adipocyte hypertrophy and excessive adipose tissue accumulation (mainly visceral) can promote pathogenic adipocyte and adipose tissue-related diseases, has led to formulate the concept of “adiposopathy”, defined as adipocyte and adipose tissue dysfunction that contributes to metabolic syndrome. Adipose tissue can, indeed, be regarded as an important and highly active player of the innate immune response, in which cytokine/adipokine secretion is responsible for a paracrine loop between adipocytes and macrophages, thus contributing to the systemic chronic low-grade inflammation associated with visceral obesity, which represents a favorable niche for tumor development. The adipocyte itself participates as a central mediator of this inflammatory response in obese individuals by secreting hormones, growth factors and proinflammatory cytokines, which are of particular relevance for the pathogenesis of CRC. Among adipocyte-secreted hormones, the most relevant to colorectal tumorigenesis are adiponectin, leptin, resistin and ghrelin. All these molecules have been involved in cell growth and proliferation, as well as tumor angiogenesis and it has been demonstrated that their expression changes from normal colonic mucosa to adenoma and adenocarcinoma, suggesting their involvement in multistep colorectal carcinogenesis. These findings have led to the hypothesis that an unfavorable adipokine profile, with a reduction of those with an anti-inflammatory and anti-cancerous activity, might serve as a prognostic factor in CRC patients and that adipokines or their analogues/antagonists might become useful agents in the management or chemoprevention of CRC.

Resistin regulates the expression of plasminogen activator inhibitor-1 in 3T3-L1 adipocytes

Resistin and plasminogen activator inhibitor-1 (PAI-1) are adipokines, which are secreted from adipocytes. Increased plasma resistin and PAI-1 levels aggravate metabolic syndrome through exacerbation of insulin resistance and induction of chronic inflammation. However, the relationship between resistin and PAI-1 gene expression remains unclear. Previously, we found that resistin regulates lipid metabolism via carbohydrate responsive element-binding protein (ChREBP) during adipocyte maturation (Ikeda et al., 2013) [6]. In this study, to clarify the relationship between expression of resistin and PAI-1, PAI-1 expression in differentiated 3T3-L1 adipocytes was measured after transfection with anti-resistin siRNA. We found that PAI-1 gene expression and secreted PAI-1 protein were significantly decreased by resistin knockdown. Furthermore, phosphorylation of Akt, which can inhibit PAI-1 expression, was accelerated and the activity of protein phosphatase 2A (PP2A) was suppressed in resistin knockdown 3T3-L1 adipocytes. In addition, the expression of glucose transporter type 4, a ChREBP target gene, was reduced and was associated with inhibition of PP2A. The addition of culture medium collected from COS7 cells transfected with a resistin expression plasmid rescued the suppression of PAI-1 expression in resistin knockdown 3T3-L1 adipocytes. Our findings suggest that resistin regulates PAI-1 expression in 3T3-L1 adipocytes via Akt phosphorylation.

Impaired leptin gene expression and release in cultured preadipocytes isolated from individuals born with low birth weight

Low birth weight (LBW) is associated with increased risk of the development of type 2 diabetes (T2D). The appetite-regulating hormone leptin is released from mature adipocytes, and its production may be decreased in immature preadipocytes from LBW individuals. We recruited 14 men born with LBW and 13 controls born with normal birth weight (NBW). Biopsy samples were obtained from subcutaneous abdominal fat depots, and preadipocytes were isolated and cultured. Gene expression of leptin and selected differentiation markers were analyzed during preadipocyte differentiation, and cell culture media were collected to analyze leptin secretion. DNA methylation of CpG sites in the leptin promoter was measured using pyrosequencing. We found that differentiating preadipocytes from LBW individuals showed reduced leptin gene expression and a corresponding reduced leptin release compared with NBW individuals. Mean DNA methylation of the proximal LEP promoter was increased in LBW compared with NBW individuals. The notion of impaired adipocyte maturation in LBW individuals was supported by a lower mRNA expression of the differentiation markers; fatty acid binding protein 4, peroxisome proliferator-activated receptor γ, and GLUT4. Our findings are consistent with impaired preadipocyte maturation, contributing to an increased risk of the development of T2D in LBW subjects.

Knockdown of PU.1 AS lncRNA inhibits adipogenesis through enhancing PU.1 mRNA translation

PU.1 is an Ets family transcription factor involved in the myelo-lymphoid differentiation. We have previously demonstrated that PU.1 is also expressed in the adipocyte lineage. However, the expression levels of PU.1 mRNA and protein in preadipocytes do not match the levels in mature adipocytes. PU.1 mRNA level is higher in preadipocytes, whereas its protein is expressed in the adipocytes but not in the preadipocytes. The underlying mechanism remains elusive. Here, we find that miR-155 knockdown or overexpression has no effect on the levels of PU.1 mRNA and protein in preadipocytes or adipocytes. MiR-155 regulates adipogenesis not through PU.1, but via C/EBPβ which is another target of miR-155. We also checked the expression levels of PU.1 mRNA and antisense long non-coding RNA (AS lncRNA). Interestingly, compared with the level of PU.1 mRNA, the level of PU.1 AS lncRNA is much higher in preadipocytes, whereas it is opposite in the adipocytes. We further discover that PU.1 AS lncRNA binds to its mRNA forming an mRNA/AS lncRNA compound. The knockdown of PU.1 AS by siRNA inhibits adipogenesis and promotes PU.1 protein expression in both preadipocytes and adipocytes. Furthermore, the repression of PU.1 AS decreases the expression and secretion of adiponectin. We also find that the effect of retroviral-mediated PU.1 AS knockdown on adipogenesis is consistent with that of PU.1 AS knockdown by siRNA. Taken together, our results suggest that PU.1 AS lncRNA promotes adipogenesis through preventing PU.1 mRNA translation via binding to PU.1 mRNA to form mRNA/AS lncRNA duplex in preadipocytes.

Resistin affects lipid metabolism during adipocyte maturation of 3T3-L1 cells

Resistin, an adipose-tissue-specific secretory factor, aggravates metabolic syndrome through impairment of glucose metabolism. Previously, we demonstrated that resistin expression was induced in both 3T3-L1 cells and primary pre-adipocytes derived from Zucker obese rats during the process of differentiation and maturation (Ikeda Y, Hama S, Kajimoto K, Okuno T, Tsuchiya H & Kogure K (2011) Biol Pharm Bull 34, 865-870). However, the biological function of resistin in adipocytes is poorly understood. In the present study, we examined the effects of resistin knockdown on the biological features of 3T3-L1 cells. We found that lipid content was significantly decreased in 3T3-L1 cells transfected with anti-resistin small interfering RNA (siRNA) after adipocyte differentiation. While expression of peroxisome proliferator activated receptor γ and CCAAT/enhancer-binding protein α was not affected, protein expression and transcriptional activity levels of carbohydrate response element binding protein (ChREBP), which upregulates transcription of lipogenic genes, decreased after anti-resistin siRNA treatment. Moreover, gene expression of fatty acid synthase and acetyl-CoA carboxylase 2, which are known to be regulated by ChREBP, were also suppressed by resistin knockdown. In contrast, activity of the fatty acid β-oxidation-regulating protein carnitine palmitoyltransferase 1 increased. These results suggest that resistin knockdown induces suppression of lipid production and activation of fatty acid β-oxidation. Consequently, resistin may affect lipid metabolism during adipocyte maturation.

Resistin gene expression in visceral adipose tissue of postmenopausal women and its association with insulin resistance

AIM

The present study evaluates resistin mRNA expression in visceral adipose tissue (VAT) and its correlation with insulin resistance (homeostatic model assessment) in postmenopausal obese women.

MATERIALS & METHODS

A total of 68 (nonobese = 34 and obese = 34) age-matched (49-70 years) postmenopausal women were recruited for the study. Fasting blood samples were collected at admission and abdominal VAT were obtained during surgery for gall bladder stones or hysterectomy. Physical parameters (age, height, weight and BMI) were measured. Biochemical parameters (plasma insulin, plasma glucose and serum resistin) were estimated by enzymatic methods. The VAT resistin mRNA expression was evaluated by real-time PCR.

RESULTS

The relative mean (± standard deviation) VAT resistin mRNA expression in postmenopausal obese women lowered significantly by 20.4% compared with postmenopausal nonobese women (0.029 ± 0.011 vs 0.023 ± 0.013; p = 0.047). Furthermore, VAT resistin mRNA expression in postmenopausal obese women was downregulated by 0.69-fold when compared with age-matched postmenopausal nonobese women. Furthermore, the relative VAT resistin mRNA expression in postmenopausal obese women showed significant inverse association with insulin resistance (r = -0.48; p < 0.01) and serum resistin (r = -0.84; p < 0.001), while in postmenopausal nonobese women it did not show any association with both insulin resistance (r = 0.03; p > 0.05) and serum resistin (r = -0.03; p > 0.05).

CONCLUSION

The VAT resistin mRNA expression in postmenopausal obese women is associated to insulin resistance.