Differential effects of 1α,25-dihydroxycholecalciferol on MCP-1 and adiponectin production in human white adipocytes.

BACKGROUND/AIM: Obesity is characterized by a low-grade inflammation in white adipose tissue (WAT), which promotes insulin resistance. Low serum levels of 1α,25-dihydroxycholecalciferol (DHCC) associate with insulin resistance and higher body mass index although it is unclear whether vitamin D supplementation improves insulin sensitivity. We investigated the effects of DHCC on adipokine gene expression and secretion in adipocytes focusing on two key factors with pro-inflammatory [monocyte chemoattractant protein-1 (MCP-1/CCL2)] and anti-inflammatory [adiponectin (ADIPOQ)] effects. METHODS: Pre-adipocytes were isolated from human subcutaneous WAT and cultured until full differentiation. Differentiated adipocytes were either pre-treated with DHCC (10(-7) M) and subsequently incubated with tumor necrosis factor-α (TNFα, 100 ng/mL) or concomitantly incubated with TNFα/DHCC. MCP1 and adiponectin mRNA expression was measured by RT-PCR and protein release by ELISA. RESULTS: DHCC was not toxic and did not affect adipocyte morphology or the mRNA levels of adipocyte-specific genes. TNFα induced a significant increase in CCL2 mRNA and protein secretion, while DHCC alone reduced CCL2 mRNA expression (~25%, p < 0.05). DHCC attenuated TNFα-induced CCL2 mRNA expression in both pre-incubation (~15%, p < 0.05) and concomitant (~60%, p < 0.01) treatments. TNFα reduced ADIPOQ mRNA (~80%) and secretion (~35%). DHCC alone decreased adiponectin secretion to a similar degree (~35%, p < 0.05). Concomitant treatment with DHCC/TNFα for 48 h had an additive effect, resulting in a pronounced reduction in adiponectin secretion (~70%). CONCLUSIONS: DHCC attenuates MCP-1 and adiponectin production in human adipocytes, thereby reducing the expression of both pro- and anti-inflammatory factors. These effects may explain the difficulties so far in determining the role of DHCC in insulin sensitivity and obesity in humans.

Uraemic sera stimulate lipolysis in human adipocytes: role of perilipin.

BACKGROUND: Although chronic kidney disease (CKD) is associated with dyslipidaemia and insulin resistance, the exact cause(s) are unknown. Since adipose tissue plays an important role in the development of these complications, we investigated the effect of uraemic sera on human adipocytes in vitro. METHODS: Cultured human adipocytes were incubated for 48 h with media containing sera from eight CKD Stage 5 patients or four (matched for age, sex and body mass index) healthy controls. Glycerol release (an index of lipolysis) was determined in conditioned media. RNA was isolated from the cells and quantitative polymerase chain reaction of genes involved in lipolysis was performed. In vivo lipolysis was determined by the plasma glycerol/total fat mass (from dual energy X-ray absorptiometry) ratio in 28 CKD patients and 28 matched controls. RESULTS: Incubation with uraemic, but not control, sera resulted in a significant ∼30% increase in spontaneous (basal) lipolysis (P <0.05). Furthermore, uraemic but not control sera induced a selective ∼30% reduction of messenger RNA (mRNA) coding for the lipid-droplet-associated protein perilipin (PLIN) (P <0.05), while mRNA levels of lipases, adipokines and differentiation factors did not differ between the groups after incubation. Also, consistent with our in vitro data, in vivo plasma glycerol/fat mass ratio was significantly elevated in uraemic patients as compared to controls (5.23 ± 4.1 versus 3.41 ± 2.3 µM/kg, P < 0.05). CONCLUSIONS: Undefined circulating factors in CKD patients increase basal lipolysis in human adipocytes in vitro, probably by attenuating the expression of the lipolytic regulator PLIN. Since in vivo lipolysis is a well-established risk factor for insulin resistance and cardiovascular disease, these effects may promote increased morbidity and mortality in CKD.

Human adipose tissue cannabinoid receptor 1 gene expression is not related to fat cell function or adiponectin level.

CONTEXT: The cannabinoid receptor 1 gene (CNR1) is implicated in adipocyte function. OBJECTIVE: We investigated human adipose tissue CNR1 mRNA in relation to obesity, clinical and metabolic variables, adipocyte function, and adiponectin (ADIPOQ) levels. METHODS: We assessed sc fat biopsies from 96 obese and nonobese subjects and omental fat biopsies from 82 obese and nonobese subjects. RESULTS: The sc and omental adipose CNR1 gene expression were similar in obese and nonobese subjects. No association between either sc or omental adipose CNR1 mRNA levels and body mass index, waist circumference, plasma levels of glucose and insulin, lipids, or blood pressure was found. The sc and omental maximal adrenergic lipolytic activation as well as lipolytic adrenoceptor sensitivity were not related to CNR1 gene expression. Lipogenesis in sc adipocytes also showed no association with CNR1 mRNA levels. Finally, no relation was found between adipose CNR1 gene expression and ADIPOQ mRNA, adipose tissue adiponectin secretion, or circulating adiponectin. CONCLUSION: We found no association of human adipose tissue CNR1 mRNA expression with measures of body fat, metabolic parameters, fat cell function, or ADIPOQ expression. These data do not suggest a major role of human adipose CNR1 in fat cell function or metabolic disease development.

Healthy Nordic diet downregulates the expression of genes involved in inflammation in subcutaneous adipose tissue in individuals with features of the metabolic syndrome.

BACKGROUND: Previously, a healthy Nordic diet (ND) has been shown to have beneficial health effects close to those of Mediterranean diets. OBJECTIVE: The objective was to explore whether the ND has an impact on gene expression in abdominal subcutaneous adipose tissue (SAT) and whether changes in gene expression are associated with clinical and biochemical effects. DESIGN: Obese adults with features of the metabolic syndrome underwent an 18- to 24-wk randomized intervention study comparing the ND with the control diet (CD) (the SYSDIET study, carried out within Nordic Centre of Excellence of the Systems Biology in Controlled Dietary Interventions and Cohort Studies). The present study included participants from 3 Nordic SYSDIET centers [Kuopio (n = 20), Lund (n = 18), and Oulu (n = 18)] with a maximum weight change of ±4 kg, highly sensitive C-reactive protein concentration <10 mg/L at the beginning and the end of the intervention, and baseline body mass index (in kg/m²) <38. SAT biopsy specimens were obtained before and after the intervention and subjected to global transcriptome analysis with Gene 1.1 ST Arrays (Affymetrix). RESULTS: Altogether, 128 genes were differentially expressed in SAT between the ND and CD (nominal P < 0.01; false discovery rate, 25%). These genes were overrepresented in pathways related to immune response (adjusted P = 0.0076), resulting mainly from slightly decreased expression in the ND and increased expression in the CD. Immune-related pathways included leukocyte trafficking and macrophage recruitment (e.g., interferon regulatory factor 1, CD97), adaptive immune response (interleukin32, interleukin 6 receptor), and reactive oxygen species (neutrophil cytosolic factor 1). Interestingly, the regulatory region of the 128 genes was overrepresented for binding sites for the nuclear transcription factor κB. CONCLUSION: A healthy Nordic diet reduces inflammatory gene expression in SAT compared with a control diet independently of body weight change in individuals with features of the metabolic syndrome.

Adipose tissue adiponectin production and adiponectin serum concentration in human obesity and insulin resistance.

The role of adiponectin production for the circulating protein concentration in human obesity and insulin resistance is unclear. We measured serum concentration and sc adipose tissue secretion rate of adiponectin in 77 obese and 23 nonobese women with a varying degree of insulin sensitivity. The serum adiponectin concentration was similar in both groups. In obesity, adiponectin adipose tissue secretion rate per weight unit was reduced by 30% (P = 0.01), whereas total body fat secretion rate was increased by 100% (P < 0.0001). In the group being most insulin resistant (1/3), serum concentration (P < 0.001) and adipose tissue secretion rate per tissue weight (P < 0.05) were reduced, whereas total body fat secretion rate was increased (P < 0.01), by about 30%. The adipose tissue secretion rate of adiponectin was related to the serum concentration (P = 0.005) but explained only about 10% of the interindividual variation in circulating adiponectin and insulin sensitivity. The plasma adiponectin half life was long, 2.5 h. In conclusion, the role of protein secretion for the circulating concentration of adiponectin and insulin sensitivity under these conditions is minor because adiponectin turnover rate is slow. Although increased in obesity and insulin resistance, total body production of adiponectin is insufficient to raise the circulating concentration, may be due to reduced secretion rate per tissue unit.

MTCH2 in human white adipose tissue and obesity.

CONTEXT: Genome-wide association studies have identified single-nucleotide polymorphisms in approximately 40 loci associated with obesity-related traits. How these loci regulate obesity is largely unknown. One obesity-associated single-nucleotide polymorphism is close to the MTCH2 gene (mitochondrial carrier homolog 2). OBJECTIVE: The objective of the study was to assess the expression of genes in obesity-associated loci in abdominal sc white adipose tissue (scWAT) in relation to obesity. A more comprehensive expression study was performed on MTCH2. DESIGN: mRNA levels of 66 genes from 40 loci were determined by microarray in scWAT from lean and obese women (n = 30). MTCH2 mRNA was measured by quantitative RT-PCR in lean and obese before and after weight loss in intact adipose pieces and isolated adipocytes, paired samples of scWAT and omental WAT, and primary adipocyte cultures (n = 191 subjects in total). MTCH2 genotypes were compared with mRNA expression in 96 women. MTCH2 protein was examined in scWAT of 38 individuals. RESULTS: Adipose expression of eight genes was significantly associated with obesity; of these, MTCH2 displayed the highest absolute signal. MTCH2 mRNA and protein expression was significantly increased in obese women but was not affected by weight loss. MTCH2 was enriched in isolated fat cells and increased during adipocyte differentiation. There was no cis influence of MTCH2 genotypes on mRNA levels. CONCLUSION: MTCH2 is highly expressed in human WAT and adipocytes with increased levels in obese women. These results suggest that MTCH2 may play a role in cellular processes underlying obesity.

Regulation of lipolysis in small and large fat cells of the same subject.

CONTEXT: Large fat cell size is linked to type 2 diabetes risk and may involve an enhanced rate of adipocyte lipolysis causing elevated levels of fatty acids. OBJECTIVE: Our objective was to study the role of fat cell size in the regulation of lipolysis within a subject. DESIGN AND MAIN OUTCOME MEASURES: Subcutaneous adipose tissue was obtained from 16 healthy subjects. Large and small adipocytes were isolated for each sample. Hormonal regulation of lipolysis and expression of lipolysis-regulating proteins were investigated. RESULTS: No effect of cell size on the rate of lipolysis was observed when lipolysis was expressed per lipid weight of fat cells. However, when expressed per number of fat cells, the lipolysis was significantly higher in large as compared with small adipocytes. This was observed in both the unstimulated (basal) state and in the presence of the major lipolysis-regulating hormones such as catecholamines (stimulating), natriuretic peptides (stimulating), and insulin (inhibiting). The receptor properties (number, affinity, and coupling) for these hormones did not differ between large and small adipocytes. However, the expression of proteins regulating the final steps in hormone signaling to lipolysis (hormone-sensitive lipase, adipose triglyceride lipase, and perilipin) was increased in large adipocytes. CONCLUSION: Independently of the donor, sc fat cell size per se determines lipolysis rates. Large adipocytes have increased lipolytic capacity, probably due to the enrichment of regulatory proteins distal in the lipolytic cascade, to which all lipolytic signals converge (lipases and perilipin). Enhanced lipolytic capacity may link adipocyte hypertrophy to the risk of developing type 2 diabetes.

The common rs9939609 gene variant of the fat mass- and obesity-associated gene FTO is related to fat cell lipolysis.

We investigated the rs9939609 single nucleotide polymorphism of the FTO gene in relation to fat cell function and adipose tissue gene expression in 306 healthy women with a wide range in body mass index (18-53 kg/m(2)). Subcutaneous adipose tissue biopsies were taken for fat cell metabolism studies and in a subgroup (n = 90) for gene expression analyses. In homozygous carriers of the T-allele, the in vitro basal (spontaneous) adipocyte glycerol release was increased by 22% (P = 0.007) and the in vivo plasma glycerol level was increased by approximately 30% (P = 0.037) compared with carriers of the A allele. In contrast, there were no genotype effects on catecholamine-stimulated lipolysis or basal or insulin-induced lipogenesis. We found no difference between genotypes for adipose tissue mRNA levels of FTO, hormone-sensitive lipase, adipose triglyceride lipase, perilipin, or CGI-58. Finally, the adipose tissue level of FTO mRNA was increased in obesity (P = 0.002), was similar in subcutaneous and omental adipose tissue, was higher in fat cells than in fat tissue (P = 0.0007), and was induced at an early stage in the differentiation process (P = 0.004). These data suggest a role of the FTO gene in fat cell lipolysis, which may be important in explaining why the gene is implicated in body weight regulation.

Lipolysis--not inflammation, cell death, or lipogenesis--is involved in adipose tissue loss in cancer cachexia.

BACKGROUND: Cancer cachexia is an important, negative prognostic marker that has been linked to systemic inflammation and cell death through unclear mechanisms. A key feature of cancer cachexia is loss of white adipose tissue (WAT) because of increased adipocyte lipolysis and possibly reduced lipid synthesis (lipogenesis). In this study, the authors investigated whether alterations in fat cell numbers, lipogenesis, or cytokine and/or leukocyte infiltration could account for some of the functional changes observed in WAT in cancer cachexia. METHODS: Blood and subcutaneous WAT samples were obtained from a 10 weight-stable patients, from 13 weight losing (cachexia) patients with cancer, and from 5 patients without cancer (noncancer patients) who initially were classified with cancer. RESULTS: Systemic inflammation (increased circulating levels of interleukin 6 [IL-6]) and enhanced lipolysis were confirmed in the cachectic patients compared with the other patients. However, the messenger RNA expression of IL-6 and other cytokine or leukocyte markers, as well as WAT secretion of IL-6, were not altered in the patients with cachexia. Thus, the elevated serum levels of IL-6 that were observed in cachexia were not derived from WAT. Insulin-induced lipogenesis in adipocytes from patients with cachexia was the same as that in adipocytes from patients with weight-stable cancer and from noncancer patients (2.5-fold maximal stimulation; half-maximum effective concentration, approximately 0.03 nmol/L). Fat cell size was decreased but adipocyte numbers were normal in cancer patients with cachexia, suggesting that there was no major fat cell death. CONCLUSIONS: The current findings indicated that subcutaneous WAT does not contribute to the systemic inflammatory reaction and does not induce adipocyte insulin resistance in cancer cachexia. Moreover, increased fat cell lipolysis, not reduced lipogenesis or adipocyte cell death, appeared to be the primary cause of fat loss in this condition.

A role of lipin in human obesity and insulin resistance: relation to adipocyte glucose transport and GLUT4 expression.

The mouse lipin gene, Lpin1, is important for adipose tissue development and is a candidate gene for insulin resistance. Here, we investigate the adipose tissue expression levels of the human LPIN1 gene in relation to various clinical variables as well as adipocyte function. LPIN1 gene expression was induced at an early step in human preadipocyte differentiation in parallel with peroxisome proliferator-activated receptor gamma. Lipin mRNA levels were higher in fat cells than in adipose tissue segments but showed no difference between subcutaneous and omental depots. Moreover, LPIN1 expression levels were reduced in obesity, improved following weight reduction in obese subjects, and were downregulated in women with the metabolic syndrome. With respect to adipocyte function, adipose LPIN1 gene expression was strongly associated with both basal and insulin-mediated subcutaneous adipocyte glucose transport as well as mRNA levels of glucose transporter 4 (GLUT4). We show that body fat accumulation is a major regulator of human adipose LPIN1 expression and suggest a role of LPIN1 in human preadipocyte as well as mature adipocyte function.

Differential lipolytic regulation in human embryonic stem cell-derived adipocytes.

OBJECTIVE: Human embryonic stem cells (hESCs) have raised great hopes for future clinical applications. Several groups have succeeded in differentiating hESCs into adipocytes, as determined by morphology, mRNA expression, and protein secretion. However, determination of lipolytic response, the most important characteristic of adipocytes, has not been performed. This work was intended to study adipogenic conversion of hESCs by functional assessment of differentiation. RESEARCH METHODS AND PROCEDURES: Single undifferentiated colonies were allowed to transform into embryonic bodies. mRNA expression for a set of adipocyte-specific genes and leptin/adiponectin secretion and lipolysis were assessed at different time-points after differentiation. RESULTS: In contrast to primary human adipocytes, hESC-derived adipocytes showed a very small response to classical beta-adrenergic agonists, although they expressed the major genes in the lipolytic cascade. In contrast, there was a significant lipolytic response to atrial natriuretic peptide. DISCUSSION: Although hESC-derived adipocytes seem to be morphologically and expressionally similar to mature adipocytes, there are important functional differences that could depend on their early developmental origin. We conclude that, in contrast to mature adipocytes, hESC-derived adipocytes display a differential response to atrial natriuretic peptide and catecholamines.