Proteomic comparison of osteoarthritic and reference human menisci using data-independent acquisition mass spectrometry

OBJECTIVE

Recent research in knee osteoarthritis (OA) highlights the role of the meniscus in OA pathology. Our aim was to compare the proteomes of medial and lateral menisci from end-stage medial compartment knee OA patients, with reference menisci from knee-healthy deceased donors, using mass spectrometry.

DESIGN

Tissue plugs of Ø3 mm were obtained from the posterior horns of the lateral and medial menisci from one knee of 10 knee-healthy deceased donors and 10 patients undergoing knee replacement. Proteins were extracted and prepared for mass spectrometric analysis. Statistical analysis was conducted on abundance data that was log₂-transformed, using a linear mixed effects model and evaluated using pathway analysis.

RESULTS

We identified a total of 835 proteins in all samples, of which 331 were included in the statistical analysis. The largest differences could be seen between the medial menisci from OA patients and references, with most proteins showing higher intensities in the medial menisci from OA patients. Several matrix proteins, e.g., matrix metalloproteinase 3 (MMP3) (4.3 times higher values [95%CI 1.8, 10.6]), TIMP1 (3.5 [1.4, 8.5]), asporin (4.1 [1.7, 10.0]) and versican (4.4 [1.8, 10.9]), all showed higher abundance in medial menisci from OA patients compared to medial reference menisci. OA medial menisci also showed increased activation of several pathways involved in inflammation.

CONCLUSION

An increase in protein abundance for proteins such as MMP and TIMP1 in the medial menisci from OA patients suggests simultaneous activation of both catabolic and anabolic processes that warrants further attention.

Long-term changes in adipose tissue gene expression following bariatric surgery

OBJECTIVE

Patients undergoing bariatric surgery present long-term metabolic improvements and reduced type 2 diabetes risk, despite long-term weight regain. We hypothesized that part of these protective effects could be linked to altered gene expression in white adipose tissue (WAT).

METHODS

Transcriptomic profiling by gene microarray was performed in abdominal subcutaneous WAT from women before (n = 50) and two (n = 49) and five (n = 38) years after Roux-en-Y gastric bypass (RYGB) surgery as well as in 28 age-matched nonoperated women.

RESULTS

In the obese women, the average body weight decrease was 38 kg 2 years postsurgery followed by an 8 kg weight regain between 2 and 5 years. Most of the long-term changes in WAT gene expression occurred during the first 2 years. However, a subset of genes encoding proteins involved in inflammation displayed a continued decrease between baseline, 2 and 5 years, respectively; that is an expression pattern independent of body weight regain. Expression of 71 of these genes correlated with measurements of adipocyte morphology or serum adipokine levels.

CONCLUSION

The continuous improvement in WAT inflammatory gene expression, despite body weight relapse, may contribute to the sustained effects on adipose morphology after bariatric surgery.

Insulin action is severely impaired in adipocytes of apparently healthy overweight and obese subjects

OBJECTIVE

Many overweight/obese subjects appear metabolically healthy with normal in vivo insulin sensitivity. Still, they have increased long-term risk of developing type 2 diabetes. We hypothesized that adipose tissue dysfunction involving decreased insulin action in adipocytes is present in apparently healthy overweight/obese subjects.

DESIGN/METHODS

Subjects with normal metabolic health according to Adult Treatment Panel-III or Framingham risk score criteria were subdivided into 67 lean, 32 overweight and 37 obese according to body mass index. They were compared with 200 obese individuals with metabolic syndrome. Insulin sensitivity and maximum action on inhibition of lipolysis and stimulation of lipogenesis was determined in subcutaneous adipocytes. Gene expression was determined by micro-array and qPCR. DNA methylation was assessed by array, pyrosequencing and reporter assays.

RESULTS

Compared with lean, adipocytes in overweight/obese displayed marked reductions in insulin sensitivity in both antilipolysis and lipogenesis as well as an attenuated maximum lipogenic response. Among these, only antilipolysis sensitivity correlated with whole-body insulin sensitivity. These differences were already evident in the overweight state, were only slightly worse in the unhealthy obese state and were not related to fat cell size. Adipose tissue analyses linked this to reduced expression of the insulin signalling protein AKT2, which associated with increased methylation at regulatory sites in the AKT2 promoter.

CONCLUSIONS

Apparently healthy subjects have severely disturbed adipocyte insulin signalling already in the overweight state which involves epigenetic dysregulation of AKT2. This may constitute an early defect in insulin action that appears even upon modest increases in fat mass.

Improved metabolism and body composition beyond normal levels following gastric bypass surgery: a longitudinal study

BACKGROUND

The cardiometabolic risk profile improves following bariatric surgery. However, the degree of improvement in relation to weight-stable control subjects is unknown.

OBJECTIVES

To study the differences in cardiometabolic risk profile between formerly obese patients following Roux-en-Y gastric bypass (RYGB) surgery and control subjects.

METHODS

Subjects undergoing RYGB and reaching a BMI <30 kg m^-2 2 years postsurgery were matched with control subjects regarding age, sex and BMI. The following examinations were performed: insulin sensitivity measured by hyperinsulinaemic-euglycaemic clamp, insulin clearance, homeostatic model assessment of insulin resistance (HOMA-IR), lipid profile, inflammatory marker levels, dual-energy X-ray absorptiometry and subcutaneous adipose tissue cellularity (fat cell size and number).

RESULTS

Sixty-nine subjects undergoing RYGB were matched to a control subject. Insulin sensitivity measured by hyperinsulinaemic-euglycaemic clamp, blood pressure, inflammatory status and glucose, triglyceride and HDL cholesterol levels were comparable to values of control subjects. However, HOMA-IR (1.0 ± 0.5 vs. 1.3 ± 0.7, P = 0.005), insulin clearance (0.38 ± 0.08 vs. 0.34 ± 0.08 μL m^-2  min^-1 , P < 0.0001) and circulating levels of insulin (31 ± 15 vs. 37 ± 17 pmol L^-1 , P = 0.008), total cholesterol (4.1 ± 0.7 vs. 4.8 ± 0.9 mmol L^-1 , P < 0.0001) and LDL cholesterol (2.1 ± 0.6 vs. 2.9 ± 0.8 mmol L^-1 , P < 0.0001) were improved beyond the levels in matched control subjects. Furthermore, formerly obese subjects had higher lean and lower fat mass as well as a more benign type of adipose cellularity (hyperplasia with many small fat cells) compared to control subjects.

CONCLUSIONS

Subjects who underwent RYGB and reached a postobese state demonstrated a beneficial body composition, slightly increased insulin sensitivity as indirectly measured by HOMA-IR and higher insulin clearance, lower atherogenic lipid/lipoprotein levels and benign adipocyte morphology compared with control subjects who had never been obese. In line with previous results, our findings may in part explain why RYGB confers long-term protection against metabolic complications.

Cardiovascular risk score is linked to subcutaneous adipocyte size and lipid metabolism

OBJECTIVE

Although white adipose tissue mass and distribution correlates with cardiovascular disease, the fat cell-specific perturbations underlying this association are not known. We determined the relationship between adipocyte size and lipid metabolism with cardiovascular risk.

DESIGN/SUBJECTS

Adipocyte size as well as spontaneous (basal) and hormone-stimulated effects on adipocyte lipid metabolism (lipolysis and lipogenesis) were investigated in abdominal subcutaneous adipose tissue of 304 men and 775 women. Subjects were classified into five categories according to Adult Treatment Panel III (ATPIII) metabolic syndrome criteria.

RESULTS

Adipocyte size increased with increasing ATPIII score (P < 0.0001). For lipolysis, there was a gradual increase in basal and catecholamine-stimulated lipolysis and a decrease in insulin-mediated inhibition of stimulated lipolysis with ATPIII (P < 0.0001). In contrast, the lipolytic action of atrial natriuretic peptide was similar between ATPIII classes. Basal and insulin-stimulated lipogenesis decreased with increasing score (P < 0.0001). Circulating free fatty acid levels were 50% higher in the top risk category (4-5) compared with the lowest score (P < 0.0001). Fat cell size correlated positively with increasing ATPIII score and lipolysis but negatively with lipogenesis. All these differences were independent of age, sex and body weight status (P < 0.0001 to 0.02 after correction). When all functional measures were put together, maximum insulin-stimulated lipogenesis, insulin-antilipolytic sensitivity and basal lipolysis together explained about 20% in the variation of ATPIII in score.

CONCLUSIONS

Independently of sex, age and body weight status, a high cardiovascular risk score associates with increased circulating free fatty acid levels and hormone-specific alterations of lipolysis/lipogenesis in enlarged subcutaneous fat cells.

Impaired atrial natriuretic peptide-mediated lipolysis in obesity

BACKGROUND

Catecholamines and natriuretic peptides (NPs) are the only hormones with pronounced lipolytic effects in human white adipose tissue. Although catecholamine-induced lipolysis is well known to be impaired in obesity and insulin resistance, it is not known whether the effect of NPs is also altered.

METHODS

Catecholamine- and atrial NP (ANP)-induced lipolysis was investigated in abdominal subcutaneous adipocytes in vitro and in situ by microdialysis.

RESULTS

In a cohort of 122 women, both catecholamine- and ANP-induced lipolysis in vitro was markedly attenuated in obesity (n=87), but normalized after substantial body weight loss (n=52). The impairment of lipolysis differed between the two hormones when expressing lipolysis per lipid weight, the ratio of stimulated over basal (spontaneous) lipolysis rate or per number of adipocytes. Thus, while the response to catecholamines was lower when expressed as the former two measures, it was higher when expressed per cell number, a consequence of the significantly larger fat cell size in obesity. In contrast, although ANP-induced lipolysis was also attenuated when expressed per lipid weight or the ratio stimulated/basal, it was similar between non-obese and obese subjects when expressed per cell number suggesting that the lipolytic effect of ANP may be even more sensitive to the effects of obesity than catecholamines. Obesity was characterized by a decrease in the protein expression of the signaling NP A receptor (NPRA) and a trend toward increased levels of the clearance receptor NPRC. The impairment in ANP-induced lipolysis observed in vitro was corroborated by microdialysis experiments in situ in a smaller cohort of lean and overweight men.

CONCLUSIONS

ANP- and catecholamine-induced lipolysis is reversibly attenuated in obesity. The pro-lipolytic effects of ANP are relatively more impaired compared with that of catecholamines, which may in part be due to specific changes in NP receptor expression.

Low early B-cell factor 1 (EBF1) activity in human subcutaneous adipose tissue is linked to a pernicious metabolic profile

AIM

Recently, in both human and murine white adipose tissue (WAT), transcription factor early B-cell factor 1 (EBF1) has been shown to regulate adipocyte differentiation, adipose morphology and triglyceride hydrolysis (lipolysis). This study investigated whether EBF1 expression and biological activity in WAT is related to different metabolic parameters.

METHODS

In this cross-sectional study of abdominal subcutaneous WAT, EBF1 protein levels were examined in 18 non-obese subjects, while biological activity was determined in 56 obese and non-obese subjects. Results were assessed by anthropometric measures and blood pressure as well as by plasma lipid levels and insulin sensitivity.

RESULTS

EBF1 protein levels were negatively associated with waist circumference (r=-0.56; P=0.015), but not with body mass index (BMI) or body fat (P=0.10-0.29). Biological activity of EBF1 correlated negatively with plasma triglycerides (r=-0.46; P=0.0005) and plasma insulin (r=-0.39; P=0.0027), but positively with plasma HDL cholesterol (r=0.48; P=0.0002) and insulin sensitivity, as assessed by intravenous insulin tolerance test (r=0.64; P<0.0001). These relationships, except for plasma insulin, remained statistically significant after adjusting for BMI and adipose morphology. EBF1 activity was not associated with age, systolic/diastolic blood pressure or total plasma cholesterol (P=0.17-0.48). In contrast to EBF1 activity, after adjusting for BMI, EBF1 mRNA levels displayed only an association with plasma triglycerides.

CONCLUSION

Low EBF1 protein expression and activity in abdominal subcutaneous WAT is a BMI-independent marker for several traits associated with the metabolic syndrome. However, whether EBF1 constitutes a novel treatment target remains to be demonstrated.

Adipose tissue morphology predicts improved insulin sensitivity following moderate or pronounced weight loss

BACKGROUND

Cross-sectional studies show that white adipose tissue hypertrophy (few, large adipocytes), in contrast to hyperplasia (many, small adipocytes), associates with insulin resistance and increased risk of developing type 2 diabetes. We investigated if baseline adipose cellularity could predict improvements in insulin sensitivity following weight loss.

METHODS

Plasma samples and subcutaneous abdominal adipose biopsies were examined in 100 overweight or obese individuals before and 10 weeks after a hypocaloric diet (7±3% weight loss) and in 61 obese subjects before and 2 years after gastric by-pass surgery (33±9% weight loss). The degree of adipose tissue hypertrophy or hyperplasia (termed the morphology value) in each individual was calculated on the basis of the relationship between fat cell volume and total fat mass. Insulin sensitivity was determined by homeostasis model assessment-estimated insulin resistance (HOMAIR).

RESULTS

In both cohorts at baseline, subjects with hypertrophy displayed significantly higher fasting plasma insulin and HOMAIR values than subjects with hyperplasia (P<0.0001), despite similar total fat mass. Plasma insulin and HOMAIR were normalized in both cohorts following weight loss. The improvement (delta insulin or delta HOMAIR) was more pronounced in individuals with hypertrophy, irrespective of whether adipose morphology was used as a continuous (P=0.0002-0.027) or nominal variable (P=0.002-0.047). Absolute adipocyte size associated (although weaker than morphology) with HOMAIR improvement only in the surgery cohort. Anthropometric measures at baseline (fat mass, body mass index, waist-to-hip ratio or waist circumference) showed no significant association with delta insulin or delta HOMAIR.

CONCLUSIONS

In contrast to anthropometric variables or fat cell size, subcutaneous adipose morphology predicts improvement in insulin sensitivity following both moderate and pronounced weight loss in overweight/obese subjects.

Semaphorin 3C is a novel adipokine linked to extracellular matrix composition

AIMS/HYPOTHESIS

Alterations in white adipose tissue (WAT) function, including changes in protein (adipokine) secretion and extracellular matrix (ECM) composition, promote an insulin-resistant state. We set out to identify novel adipokines regulated by body fat mass in human subcutaneous WAT with potential roles in adipose function.

METHODS

Adipose transcriptome data and secretome profiles from conditions with increased/decreased WAT mass were combined. WAT donors were predominantly women. In vitro effects were assessed using recombinant protein. Results were confirmed by quantitative PCR/ELISA, metabolic assays and immunochemistry in human WAT and adipocytes.

RESULTS

We identified a hitherto uncharacterised adipokine, semaphorin 3C (SEMA3C), the expression of which correlated significantly with body weight, insulin resistance (HOMA of insulin resistance [HOMAIR], and the rate constant for the insulin tolerance test [KITT]) and adipose tissue morphology (hypertrophy vs hyperplasia). SEMA3C was primarily found in mature adipocytes and had no direct effect on human adipocyte differentiation, lipolysis, glucose transport or the expression of β-oxidation genes. This could in part be explained by the significant downregulation of its cognate receptors during adipogenesis. In contrast, in pre-adipocytes, SEMA3C increased the production/secretion of several ECM components (fibronectin, elastin and collagen I) and matricellular factors (connective tissue growth factor, IL6 and transforming growth factor-β1). Furthermore, the expression of SEMA3C in human WAT correlated positively with the degree of fibrosis in WAT.

CONCLUSIONS/INTERPRETATION

SEMA3C is a novel adipokine regulated by weight changes. The correlation with WAT hypertrophy and fibrosis in vivo, as well as its effects on ECM production in human pre-adipocytes in vitro, together suggest that SEMA3C constitutes an adipocyte-derived paracrine signal that influences ECM composition and may play a pathophysiological role in human WAT.

Provitamin A carotenoids are independently associated with matrix metalloproteinase-9 in plasma samples from a general population

BACKGROUND AND AIM

Carotenoids in plasma are inversely associated with cardiovascular risk. Low levels can be explained by low dietary intake but also by a number of other factors including inflammatory activity. Given that matrix metalloproteinase (MMP)-9 has an important role in inflammation and cardiovascular disease, we hypothesized that circulating MMP-9 levels would be inversely related to total or single carotenoids in a general population cohort.

METHODS

A well-characterized population-based cohort of 285 Swedish men and women (45-69 years) was used for the present study. The intake of carotenoid-rich fruits and vegetables was estimated from a food frequency questionnaire. Levels of MMP-9, C-reactive protein (CRP), interleukin (IL)-6 and six major carotenoids [β-cryptoxanthine, α-carotene, β-carotene, lutein (+zeaxanthin) and lycopene] were determined in plasma.

RESULTS

Lower plasma levels of total and single carotenoids were associated with lower dietary intake of carotenoids, older age, male sex, lower physical activity, higher alcohol consumption, higher body mass index (BMI), higher systolic and diastolic blood pressures, lower levels of total cholesterol and HDL cholesterol and higher levels of CRP, IL-6 and MMP-9. After multivariate adjustments, plasma levels of total carotenoids and provitamin A carotenoids (β-cryptoxanthine, α-carotene and β-carotene) remained independently associated with sex, dietary intake of carotenoids, BMI, HDL cholesterol and MMP-9, whilst associations with CRP and IL-6 were not maintained. Neither dietary intake of carotenoid-rich fruits and vegetables, nor vitamin supplement use was associated with MMP-9, CRP or IL-6 levels.

CONCLUSION

Plasma carotenoids were associated with a variety of factors including age, sex, dietary intake and metabolic variables. A new finding was the independent relationship in plasma between low provitamin A carotenoids and high MMP-9, suggesting a link between these carotenoids, matrix turnover and arterial remodelling.

Adipose zinc-α2-glycoprotein is a catabolic marker in cancer and noncancerous states

OBJECTIVE

Zinc-α2-glycoprotein (ZAG) has been proposed as a tumour-derived cancer cachexia factor. However, ZAG is produced by some normal tissues, including white adipose tissue (WAT), and high serum ZAG levels are present in nonmalignant conditions. We determined whether human WAT contributes to serum ZAG levels and how serum and WAT-secreted ZAG levels correlate with catabolism in patients with cancer and in obese subjects undergoing a very low-calorie diet (VLCD) for 11 days.

DESIGN/SUBJECTS

ZAG levels in serum and in conditioned medium from WAT/adipocytes were determined by enzyme-linked immunosorbent assay. ZAG release from WAT in vivo was determined in 10 healthy subjects. The correlation between ZAG and cachexia was studied in 34 patients with newly diagnosed gastrointestinal cancer. The impact of a VLCD on ZAG release and serum levels was assessed in 10 obese women.

RESULTS

ZAG was released from abdominal WAT and adipocytes in vitro. However, the arteriovenous differences in vivo showed that there was no significant contribution of WAT to the circulating levels. WAT-secreted but not serum ZAG correlated positively with poor nutritional status but not with fat mass (or body mass index) in patients with gastrointestinal cancer. In obese subjects on a VLCD, ZAG secretion from WAT increased significantly whereas serum levels remained unaltered.

CONCLUSIONS

 ZAG is released from human WAT, but this tissue does not contribute significantly to the circulating levels. WAT-secreted ZAG correlates with nutritional status but not with fat mass in both cancer and nonmalignant conditions. Adipose ZAG is therefore a local factor activated primarily by the catabolic state per se.

Effects of simvastatin on carotenoid status in plasma

BACKGROUND AND AIMS

Carotenoids are potent antioxidants mainly transported in the low density lipoprotein (LDL) fraction. They may also influence the immune response and inverse associations with inflammatory markers have been reported. We investigated whether simvastatin, by exerting both lipid-lowering and anti-inflammatory effects, altered the carotenoid status in plasma.

METHODS AND RESULTS

A randomized, double-blind, placebo-controlled study design was applied. Eighty volunteers with mild to moderate hypercholesterolemia received either simvastatin 40 mg or placebo for 6 weeks. Lipids, oxidized LDL (ox-LDL), C-reactive protein (CRP), interleukin (IL)-6, oxygenated carotenoids (lutein, zeaxanthin, β-cryptoxanthin) and hydrocarbon carotenoids (α-carotene, β-carotene, lycopene) were measured in plasma. Simvastatin use was associated with significant reductions in total cholesterol, LDL, ox-LDL and CRP. Simvastatin therapy also resulted in reduced plasma levels of both oxygenated and hydrocarbon carotenoids. However, when adjusted for lipids, all carotenoids except β-cryptoxanthin showed significant increases after simvastatin therapy. Both crude and lipid-adjusted carotenoids were inversely correlated with CRP and IL-6 in plasma but the change in carotenoid status during simvastatin therapy was not specifically related to any changes in inflammatory markers.

CONCLUSIONS

To summarize, the change in carotenoid status during simvastatin therapy was mainly attributed to the lowering of cholesterol and not to the suppression of inflammatory activity. After adjustment for lipids, the levels of lutein, lycopene, α-carotene and β-carotene were significantly increased by simvastatin suggesting an increased ratio of carotenoids per particle.

Enhanced ZAG production by subcutaneous adipose tissue is linked to weight loss in gastrointestinal cancer patients

Background:

Profound loss of adipose tissue is a hallmark of cancer cachexia. Zinc-α2-glycoprotein (ZAG), a recently identified adipokine, is suggested as a candidate in lipid catabolism.

Methods:

In the first study, eight weight-stable and 17 cachectic cancer patients (weight loss ⩾5% in previous 6 months) were recruited. Zinc-α2-glycoprotein mRNA and protein expression were assessed in subcutaneous adipose tissue (SAT), subcutaneous adipose tissue morphology was examined and serum ZAG concentrations were quantified. In the second cohort, ZAG release by SAT was determined in 18 weight-stable and 15 cachectic cancer patients. The effect of ZAG on lipolysis was evaluated in vitro.

Results:

Subcutaneous adipose tissue remodelling in cancer cachexia was evident through shrunken adipocytes with increased fibrosis. In cachectic cancer patients, ZAG mRNA was upregulated (2.7-fold, P=0.028) while leptin mRNA decreased (2.2-fold, P=0.018); serum ZAG levels were found to be unaffected. Zinc-α2-glycoprotein mRNA correlated positively with weight loss (r=0.51, P=0.01) and serum glycerol levels (r=0.57, P=0.003). Zinc-α2-glycoprotein release by SAT was also elevated in cachectic patients (1.5-fold, P=0.024) and correlated with weight loss (r=0.50, P=0.003). Recombinant ZAG stimulated lipolysis in human adipocytes.

Conclusions:

Zinc-α2-glycoprotein expression and secretion by adipose tissue is enhanced in cachectic cancer patients. Given its lipid-mobilising effect, ZAG may contribute to adipose atrophy associated with cancer cachexia in human beings.

Regional impact of adipose tissue morphology on the metabolic profile in morbid obesity

AIMS/HYPOTHESIS

The aim of this study was to determine whether the mean size of fat cells in either visceral or subcutaneous adipose tissue has an impact on the metabolic and inflammatory profiles in morbid obesity.

METHODS

In 80 morbidly obese women, mean visceral (omental) and subcutaneous fat cell sizes were related to in vivo markers of inflammation, glucose metabolism and lipid metabolism.

RESULTS

Visceral, but not subcutaneous, adipocyte size was significantly associated with plasma apolipoprotein B, total cholesterol, LDL-cholesterol and triacylglycerols (p ranging from 0.002 to 0.015, partial r ranging from 0.3 to 0.4). Subcutaneous, but not visceral, adipocyte size was significantly associated with plasma insulin and glucose, insulin-induced glucose disposal and insulin sensitivity (p ranging from 0.002 to 0.005, partial r ranging from -0.34 to 0.35). The associations were independent of age, BMI, body fat mass or body fat distribution. Adipose tissue hyperplasia (i.e. many small adipocytes) in both regions was significantly associated with better glucose, insulin and lipid profiles compared with adipose hypertrophy (i.e. few large adipocytes) in any or both regions (p ranging from <0.0001 to 0.04). Circulating inflammatory markers were not associated with fat cell size or corresponding gene expression in the fat cell regions examined.

CONCLUSIONS/INTERPRETATION

In morbidly obese women region-specific variations in mean adipocyte size are associated with metabolic complications but not systemic or adipose inflammation. Large fat cells in the visceral region are linked to dyslipidaemia, whereas large subcutaneous adipocytes are important for glucose and insulin abnormalities. Hyperplasia (many small adipocytes) in both adipose regions may be protective against lipid as well as glucose/insulin abnormalities in obesity.

Adipose tissue pathways involved in weight loss of cancer cachexia

Background:

The regulatory gene pathways that accompany loss of adipose tissue in cancer cachexia are unknown and were explored using pangenomic transcriptome profiling.

Methods:

Global gene expression profiles of abdominal subcutaneous adipose tissue were studied in gastrointestinal cancer patients with (n=13) or without (n=14) cachexia.

Results:

Cachexia was accompanied by preferential loss of adipose tissue and decreased fat cell volume, but not number. Adipose tissue pathways regulating energy turnover were upregulated, whereas genes in pathways related to cell and tissue structure (cellular adhesion, extracellular matrix and actin cytoskeleton) were downregulated in cachectic patients. Transcriptional response elements for hepatic nuclear factor-4 (HNF4) were overrepresented in the promoters of extracellular matrix and adhesion molecule genes, and adipose HNF4 mRNA was downregulated in cachexia.

Conclusions:

Cancer cachexia is characterised by preferential loss of adipose tissue; muscle mass is less affected. Loss of adipose tissue is secondary to a decrease in adipocyte lipid content and associates with changes in the expression of genes that regulate energy turnover, cytoskeleton and extracellular matrix, which suggest high tissue remodelling. Changes in gene expression in cachexia are reciprocal to those observed in obesity, suggesting that regulation of fat mass at least partly corresponds to two sides of the same coin.

Primary differences in lipolysis between human omental and subcutaneous adipose tissue observed using in vitro differentiated adipocytes

Catecholamine-induced lipolysis is elevated in omental as compared to subcutaneous adipocytes due to primary differences between the two cell types (i.e., they have different progenitor cells). Whether there is regional variation in atrial natriuretic peptide (ANP)-induced lipolysis is unknown. We studied whether beta-adrenoceptor signaling to lipolysis and ANP-induced lipolysis are involved in the primary differences in lipolysis. In vitro experiments on differentiated preadipocytes from human subcutaneous and omental adipose tissue were performed. The cells were kept in culture for a relative long duration, so any influence of local environment and circulation in the various adipose tissue depots could be excluded. Using beta1-, beta2-, and beta3-adenoceptor agonists, lipolysis was found to be significantly higher in omental as compared to subcutaneous differentiated preadipocytes. Forskolin and dibutyryl cAMP, which act at post-adrenoceptor levels, did not show any regional difference. There was no regional difference in ANP-induced lipolysis. Gene expression of beta1- and beta3-adrenoceptors was higher and beta2-adrenoceptor expression was lower in the omental cells. Omental fat cells have an increased beta-adrenoceptor-mediated lipolysis principally due to primary differences in the early event that couples beta-adrenoceptor subtypes to G-proteins. ANP-induced lipolysis is not subject to primary regional variation.

Endothelin-1 stimulates human adipocyte lipolysis through the ET A receptor

OBJECTIVE

Levels of the vascular peptide endothelin-1 (ET-1) are significantly elevated in obesity. Adipose tissue-derived ET-1 attenuates insulin-mediated antilipolysis in human visceral adipocytes through the activation of the ET receptor B (ET(B)R), thereby linking ET-1 to insulin resistance. Whether ET-1 has direct effects on lipolysis in human adipocytes is not known.

RESEARCH DESIGN AND SUBJECTS

Endothelin-1 receptor (ETR) mRNA expression was determined by quantitative PCR in 130 non-obese and obese subjects. ET-1 mRNA in different adipose tissue regions was also assessed. ETR protein expression was analyzed by western blotting in 37 subjects. The effect of ET-1 on lipolysis was assessed in freshly isolated adipocytes and in vitro differentiated adipocytes from human donors.

RESULTS

Freshly isolated human adipocytes incubated with different concentrations of ET-1 showed no acute effect on lipolysis. In contrast, a 24 h incubation in primary cultures of human adipocytes resulted in a significant 50% increase in lipolysis. This effect was concentration dependent and could be mimicked by an agonist of the ET(A) receptor but not with a selective ET(B)R agonist. Adipocyte differentiation was not affected by any of the agonists. In subcutaneous (s.c.) adipose tissue from 19 non-obese and 18 obese subjects, the protein expression of ET(A)R was significantly higher in obese subjects whereas there was no difference in ET(B)R expression. Interestingly, the differences in protein expression were not observed at the mRNA level as ET(A)R expression was similar between lean and obese subjects.

CONCLUSION

Long-term but not acute incubation of human adipocytes with ET-1 results in a significant increase in lipolysis. This appears to be mediated through the activation of ET(A)R, demonstrating a yet another receptor-specific effect of ET-1. In addition, the protein expression of ET(A)R is increased in s.c. adipose tissue in obesity, possibly through post-transcriptional mechanisms. An increased effect of ET-1 could be a mechanism that contributes to increased basal lipolysis in human obesity.

Optimising islet engraftment is critical for successful clinical islet transplantation

Clinical islet transplantation is currently being explored as a treatment for persons with type 1 diabetes and hypoglycaemia unawareness. Although 'proof-of-principle' has been established in recent clinical studies, the procedure suffers from low efficacy. At the time of transplantation, the isolated islets are allowed to embolise the liver after injection in the portal vein, a procedure that is unique in the area of transplantation. A novel view on the engraftment of intraportally transplanted islets is presented that could explain the low efficacy of the procedure.

Intramuscular autotransplantation of pancreatic islets in a 7-year-old child: a 2-year follow-up

A 7-year-old girl with severe hereditary pancreatitis underwent total pancreatectomy. A total of 160,000 islet equivalents (6400 islet/kg) were transplanted to the brachioradialis muscle of the right forearm. Her plasma C-peptide level was undetectable after pancreatectomy but increased to 1.37 ng/mL after 17 days; at this time point, her insulin requirement was 0.75 units of insulin/kg/day. At 5- and 27-months, her hemoglobin A1c (HbA1c) and insulin requirements were 4.5 and 5.3% and 0.3 and 0.18 units/kg/day, respectively. Basal and stimulated C-peptide levels were 0.67 +/- 0.07 and 3.36 +/- 1.37 ng/mL, respectively. Stimulated insulin levels were 30% higher in the islet-bearing arm compared to the contralateral arm after glucagon stimulation. After surgery and islet transplantation, the quality of life improved dramatically and she gained 8 kg of weight. In summary, a normal HbA1c, a low insulin requirement and the absence of recurrent hypoglycemia and the gradient of insulin between the arms indicate that the intramuscularly transplanted islets contribute to a long-term clinically significant metabolic control.

Tumour necrosis factor-alpha in human adipose tissue -- from signalling mechanisms to clinical implications

From its initial implication in the development of cachexia in the early 1980s, it is now almost 15 years ago that tumour necrosis factor-alpha (TNF-alpha) was first shown to be involved in the development of insulin resistance in obesity. Since the original findings in mice, a wealth of data has been obtained in a variety of settings and species. This intensive research has demonstrated both similarities and differences between rodents and humans regarding the molecular mechanisms and metabolic consequences of TNF-alpha overexpression. This review will focus on the role of TNF-alpha in human white adipose tissue with particular emphasis on its regulation of lipolysis - an important pathway in adipocytes which is linked to insulin-resistant phenotypes in obesity and the metabolic syndrome.

Oestrogen receptor alpha gene expression levels are reduced in obese compared to normal weight females

OBJECTIVE

To determine whether oestrogen receptor (ER)alpha messenger RNA (mRNA) levels or single nucleotide polymorphisms (SNPs) are associated with obesity in Swedish women.

DESIGN

ERalpha mRNA expression levels were measured by real-time qPCR in subcutaneous adipose tissue from non-obese (N=16, BMI<30) and obese (N=17, BMI>or=30) women. In addition, ERalpha mRNA expression levels were determined in isolated adipocytes. ERalpha promoter usage was characterized by 5' RACE and by real-time qPCR in subcutaneous adipose tissue from the same non-obese and obese women. Two ERalpha SNPs were scored in 509 non-obese and 489 obese females.

RESULTS

ERalpha mRNA expression levels were lower in obese compared to non-obese women in both subcutaneous adipose tissue and in adipocytes. We show that two ERalpha promoters are differentially utilized in obese and non-obese individuals. We did not find any significant association between obesity and the ERalpha SNPs or haplotypes assayed.

CONCLUSION

The reduced ERalpha mRNA levels observed in adipose tissue from obese compared to non-obese women support a role for oestrogen signaling via ERalpha, in control of body weight. Mechanistic studies of the role of ERalpha in adipocytes and how its expression is regulated in relation to fat mass should be performed. The latter studies should focus on the two promoters that are used differently in obese and non-obese individuals.

Differential function of the alpha2A-adrenoceptor and Phosphodiesterase-3B in human adipocytes of different origin

OBJECTIVE

Human adipocytes can be obtained in vitro by differentiation of human preadipocytes or mesenchymal stem cells (hMSC). Although functionally similar to freshly isolated cells, no detailed comparison of the different cell types has been performed. The antilipolytic alpha2A-adrenoceptor (AR) and the cAMP-degrading enzyme Phosphodiesterase-3B (PDE3B) have been implicated in the fine-tuning of lipolysis but little is known regarding their role in human adipocytes nor whether their expression and/or function differs in fat cells from different precursors.

METHODS

The effects of alpha2A-AR and PDE3B inhibition in mature adipocytes was determined and compared to that in differentiated preadipocytes and hMSC-derived fat cells. Gene expression was determined by real-time PCR and protein expression by Western blot.

RESULTS

Noradrenaline (NA) stimulated lipolysis in preadipocytes and mature adipocytes but markedly reduced lipolysis in differentiated hMSC derived-adipocytes. This was due to a potent stimulation of alpha2A-AR since co-incubation with NA and the alpha2-AR-inhibitor yohimbine restored NA-induced lipolysis. The order of Yohimbine response was hMSC>preadipocytes>mature adipocytes. Although alpha2-AR mRNA expression was highest in mature adipocytes there was no difference in alpha2A-AR protein levels between the cell types. In contrast, Galphai2 mRNA and protein expression was significantly higher in MSC-derived adipocytes, suggesting that differences in the response to alpha2A-AR inhibition reside at the postreceptor level. Incubation with the cAMP-analog 8-bromo(8b) cAMP increased lipolysis in hMSC-derived fat cells while co-incubation with the PDE3-specific inhibitor OPC3911 did not alter the lipolytic effect. In contrast, OPC3911 increased 8bcAMP-induced lipolysis significantly in preadipocytes and mature adipocytes. The response to PDE3B inhibition was; mature adipocytes>preadipocytes>hMSC a finding that correlated significantly with both PDE3B mRNA expression and enzymatic activity.

CONCLUSION

Although differentiated adipocytes of different origins display similar functional characteristics there are important differences in the regulation of lipolysis with a marked alpha2A-AR and less pronounced PDE3B effect in fat cells from MSCs.

ALOX5AP expression, but not gene haplotypes, is associated with obesity and insulin resistance

OBJECTIVE

Inflammation in adipose tissue may link obesity to insulin resistance and atherosclerosis. Arachidonate 5-lipoxygenase activating protein (ALOX5AP) gene is involved in the pathogenesis of atherosclerotic cardiovascular disease (CVD). We investigated ALOX5AP expression in adipose tissue, and association of gene polymorphisms with obesity and insulin resistance.

DESIGN

For gene expression analysis in adipose tissue, we studied 12 lean and 36 obese women, eight lean and 13 obese men, and nine women before and 2-4 years after gastric banding surgery. For genetic analysis, we studied 231 nonobese and 350 obese men.

RESULTS

The ALOX5AP protein, 5-lipoxygenase activating protein (FLAP), as well as 5-lipoxygenase (5LO) itself, were detected in adipocytes. The mRNA expression of ALOX5AP in subcutaneous adipose tissue was increased in obesity and normalized following weight reduction. High adipose tissue mRNA expression of ALOX5AP is associated with insulin resistance as measured by homeostasis model assessment (HOMA(IR)). ALOX5AP haplotypes that associate with CVD are not associated with obesity or insulin resistance.

CONCLUSION

ALOX5AP is present in adipose tissue, where its expression is associated with body weight and HOMA(IR), and may provide a link between adipose tissue, inflammation and insulin resistance. Investigated ALOX5AP haplotypes are not major primary risk factors for obesity and insulin resistance.

Depot-specific differences in perilipin mRNA but not protein expression in obesity

BACKGROUND

Perilipin (PLIN) is a lipid droplet-associated protein, which regulates lipolysis in rodent adipocytes by modulating the access of hormone-sensitive lipase to the lipid surface. Little is known regarding the expression and function of PLIN in man. Subcutaneous (s.c.) and omental fat tissue display marked differences in both basal and stimulated lipolysis.

OBJECTIVE AND SUBJECTS

In order to assess whether this can be caused by differences in PLIN expression, we investigated the expression of PLIN mRNA and protein in s.c. and omental fat tissue samples from 16 obese women (n = 8) and men (n = 8).

METHODS

For mRNA detection a quantitative real-time PCR was used. Protein was analysed by Western blot.

RESULTS

PLIN mRNA was significantly reduced in omental versus s.c. tissue (P = 0.022). In contrast, although PLIN protein levels were highly variable between the two depots when related to the reference protein beta-actin, no significant difference in PLIN protein expression was observed between the fat depots (P = 0.61). There were no gender-specific differences in PLIN mRNA or protein.

CONCLUSION

Our results suggest that post-transcriptional mechanisms may influence PLIN protein expression and that PLIN expression per se is probably not a major factor in determining the lipolytic differences between the s.c. and omental fat depots.

Effect of testosterone on lipolysis in human pre-adipocytes from different fat depots

AIM/HYPOTHESIS

Regional differences in lipolysis, with higher lipolytic activity in visceral than subcutaneous fat, are important for the development of insulin resistance and might be influenced by testosterone.

METHODS

We studied testosterone-regulated lipolysis and protein expression (by western blot) in fully differentiated pre-adipocytes from visceral (omental) and abdominal subcutaneous adipose tissue from 52 human subjects. These cells were isolated and cultured in a serum-free medium.

RESULTS

Testosterone caused a specific, time- and concentration-dependent 50% reduction of catecholamine-stimulated lipolysis in the subcutaneous depot. Half of the maximum effect occurred at 10 nmol/l. The inhibitory effect was due to the inability of beta-adrenoceptors and cyclic AMP to stimulate the protein kinase A, hormone-sensitive lipase complex. Testosterone caused a depot-specific 50% reduction of the protein expression of hormone-sensitive lipase and beta(2)-adrenoceptors in differentiated subcutaneous pre-adipocytes, but no change in beta(1)-adrenoceptors, protein kinase A subunits or perilipin expression. In contrast, testosterone had no effect on lipolysis or protein expression in the visceral depot. However, testosterone receptors were present in both depots, and the hormone inhibited adipocyte leptin secretion. Similar effects on lipolysis were observed with dihydrotestosterone.

CONCLUSIONS/INTERPRETATION

Testosterone in physiological concentrations causes a depot-specific reduction of catecholamine-stimulated lipolysis in subcutaneous fat cells, probably due to reduced protein expression of beta(2)-adrenoceptors and hormone-sensitive lipase. This could be an important pathogenic factor underlying regional differences in lipolysis and development of insulin resistance and hyperandrogenic polycystic ovary syndrome.

Relationship between β-2 adrenoceptor gene haplotypes and adipocyte lipolysis in women

BACKGROUND AND AIMS

The beta(2)-adrenergic receptors are important for adipocyte lipolysis regulation by catecholamines in humans. The beta(2)-adrenoceptor gene is highly polymorphic. The role of these genetic variations for adipocyte lipolysis was investigated.

DESIGN AND METHODS

Six single-nucleotide polymorphisms (SNPs) in the promotor region and four SNPs in the coding region (leading to amino-acid substitution) of the beta(2)-adrenoceptor gene were determined in 141 overweight or obese, but otherwise healthy women. Lipolysis experiments were performed on isolated subcutaneous adipocytes.

RESULTS

Three homozygous haplotypes (6/6, 4/4 and 2/2) were found that differed about 500-fold in noradrenaline sensitivity or beta(2)-adrenoceptor sensitivity (6/6>2/2>4/4, P=0.01). The haplotypes also differed by 100% in maximum noradrenaline-induced lipolysis rates (6/6>2/2>4/4). However, there was no influence on beta(1)-, beta(3)- or alpha(2)A-adrenoceptor sensitivity. Heterozygosity at one or several SNPs in the haplotypes influenced the beta(2)-adrenoceptor sensitivity significantly.

CONCLUSION

Multiple SNPs in the beta(2)-adrenoceptor gene form several haplotypes that markedly influence beta(2)-receptor function- and catecholamine-induced lipolysis in fat cells. These haplotypes may be important genetic factors behind impaired lipolysis in obesity.

Evidence for an important role of perilipin in the regulation of human adipocyte lipolysis

AIMS/HYPOTHESIS

We investigated the role of the adipocyte-specific protein perilipin for lipolysis in humans.

METHODS

Perilipin protein content and lipolysis rates were measured in human subcutaneous fat cells of non-obese (n=10) and obese (n=117) women. Single nucleotide polymorphisms in the perilipin gene were examined in obese subjects.

RESULTS

Basal and noradrenaline-induced rates of lipolysis were two to fourfold increased (p<0.01) and perilipin protein content decreased 50% (p=0.005) in adipocytes of the obese women. In subjects matched for body mass index and fat-cell volume, a high rate of lipolysis was associated with a low adipocyte content of perilipin (p=0.01). Adipocyte content of perilipin was inversely correlated with the circulating concentrations of glycerol (r=0.62) and non-esterified fatty acids (n=0.49). A gene polymorphism (rs891460 A/G) in intron 6 was common. In AA subjects basal and noradrenaline induced lipolysis were 50 to 100% times more rapid (p</=0.01) and the adipocyte perilipin content was about 80% reduced (p=0.005) as compared to GG carriers. Intermediate values were found in AG carriers.

CONCLUSIONS/INTERPRETATION

Perilipin seems important for the regulation of lipolysis in human fat cells. Obesity and a polymorphism in the perilipin gene associate with decreased protein content of perilipin and increased basal (unstrained) and noradrenaline-induced lipolysis. Low perilipin content also associate with high in vivo lipolytic activity. Perilipin could be a factor behind impaired lipolysis in insulin-resistant conditions.

The hormone-sensitive lipase i6 gene polymorphism and body fat accumulation

BACKGROUND

The hormone sensitive lipase (HSL) catalyses the breakdown of adipose tissue triglycerides into free fatty acids. The objective of this study was to determine whether HSLi6 microsatellite allele 5 (A5) and/or homozygosity for this allele is associated with body fat in Swedes.

DESIGN

A large case-control study on gender-specific association for several body fat-related clinical parameters to HSLi6 A5, and to HSLi6 A5 homozygosity, comparing A5 with the other alleles in group. The subjects were 323 obese patients (85 males, 238 females) without other metabolic complication, and 301 nonobese healthy individuals (134 males, 167 females). They were analyzed for various body fat-related clinical parameters, and HSLi6 genotype.

RESULTS

Homozygosity for HSLi6 A5 was a risk factor for obesity, BMI > or = 30 kg m-2 (Odds ratio = 1.75, 95% CI 1.58-1.93) and body fat mass > 39.6% (Odds ratio = 1.89, 95% CI 1.60-2.23) in women. This genotype was also associated with increased diastolic blood pressure and triglyceride level among nonobese women, and with increased body fat mass and waist/hip ratio among nonobese men.

CONCLUSION

HSLi6 A5 homozygosity is a risk factor for body fat accumulation.

Effects of obesity and weight loss on the expression of proteins involved in fatty acid metabolism in human adipose tissue

OBJECTIVE

Disturbances in adipocyte lipolysis in obesity may contribute to elevated circulating non-esterified fatty acid (NEFA) concentrations and insulin resistance. In experimental models, NEFA metabolism is influenced by adipocyte proteins such as adipocyte and keratinocyte lipid binding proteins (aP2/ALBP and mal1/KLBP) and fatty acid translocase (CD36). We investigated the effect of obesity and weight loss on the expression of these proteins in human subcutaneous adipose tissue.

STUDY DESIGN AND SUBJECTS

Subcutaneous adipose tissue was obtained from 12 obese (body mass index (BMI) 42.4+/-1.6 kg/m(2)) and 12 lean (23.4+/-0.6 kg/m(2)) subjects. The obese subjects underwent gastric banding and biopsies were taken again after 2 y following a significant weight reduction (BMI 32.8+/-1.4 kg/m(2)). Adipose tissue proteins were quantified by Western blotting.

RESULTS

Differential expression of ALBP, KLBP and CD36 was observed in lean and weight-reduced subjects compared with obese individuals. This resulted in a significantly lower ALBP/KLBP ratio in lean and weight-reduced individuals compared to obese subjects. Furthermore there was a significant influence of gender on this ratio. Moreover, the commonly used internal standard protein actin was expressed significantly higher in lean compared to obese individuals.

CONCLUSION

The relative content of ALBP and KLBP in human adipose tissue changes with obesity, weight loss and gender indicating differential regulation. Differing responses in the expression patterns of adipose tissue proteins capable of binding NEFAs in response to weight changes suggest a potential importance in the development of obesity-associated complications.

Polymorphism in the Calpain 10 gene influences glucose metabolism in human fat cells

AIMS/HYPOTHESIS

A common G to A polymorphism ( UCSNP-43) in the Calpain 10 gene was recently found to be associated with Type II (non-insulin-dependent) diabetes mellitus and variations in post-absorptive and insulin stimulated glucose metabolism in vivo. We aimed to study the influence of Calpain 10 polymorphism on insulin action in fat cells.

METHODS

Calpain 10 polymorphism ( UCSNP-19, -43 or -63) were set in relation to lipolysis and lipogenesis in isolated subcutaneous adipocytes of 46 apparently healthy non-obese subjects.

RESULTS

For UCSNP-43 the G/G genotype had twofold higher basal and insulin stimulated rates as compared with AA/AG genotypes. However, there was no genotype effect on basal or insulin inhibited lipolysis rates in fat cells. The protein amount of GLUT 4 in adipocytes was not influenced by the polymorphism. Fat cells expressed mRNA for the Calpain 10 gene at a relatively high concentration, about 4 amol/microg RNA, which is similar to that of uncoupling protein-2. Neither a UCSNP-19 nor a UCSNP-63 polymorphism in the Calpain 10 gene was found to be associated with basal or insulin-induced adipocyte lipolysis and lipogenesis. None of the polymorphisms influenced body mass index or fasting plasma concentrations of insulin and glucose in 693 non-obese healthy subjects.

CONCLUSIONS/INTERPRETATION

The Calpain 10 gene could be involved in the regulation of glucose metabolism but not lipolysis in human fat cells, although it does not involve adipocyte GLUT-4 protein content. It is possible that the Calpain 10 gene predisposes to diabetes by influencing the glucose metabolism.

The Arg 389 Gly beta1-adrenergic receptor gene polymorphism and human fat cell lipolysis

BACKGROUND

The beta1-adrenoceptor is a candidate gene for obesity because of its role in catecholamine-induced energy homeostasis. A common Arg 389 Gly variant polymorphism has been shown in recombinant cells to influence its-coupling properties.

OBJECTIVE

To investigate the effect of the Arg 389 Gly beta1-adrenoceptor polymorphism on catecholamine-induced lipolysis in native human fat cells obtained by subcutaneous biopsy.

SUBJECTS

Two-hundred and ninety-eight apparently healthy male and female subjects with a wide variation in body mass index (BMI, 18-60 kg/m2).

MEASURES

The lipolytic sensitivities and maximum lipolytic action of noradrenaline and the selective adrenoceptor agonists dobutamine (beta1), terbutaline (beta2) and CGP 12177 (beta3) were determined in isolated subcutaneous adipocytes and related to beta-adrenoceptor radioligand binding parameters.

RESULTS

No differences in the sensitivity or maximum lipolytic capacity of the agonists were found between the genotypes. This was true both when all subjects were analyzed together and when subgroups (lean, obese, men, women) were analyzed separately. Radioligand binding to beta1- or beta2-adrenoceptors was also similar between genotypes. The polymorphism had no important influence on either BMI or the distribution of obese and non-obese subjects between the genotypes.

CONCLUSION

The distribution of the Arg 389 Gly polymorphism is similar in lean and obese subjects and has no apparent effect on the lipolytic response to beta-adrenergic stimulation in native human adipocytes. This suggests, despite the altered coupling properties reported in recombinant cells, that the Arg 386 Gly polymorphism has no important influence on human obesity.

Fatty acid binding protein expression in different adipose tissue depots from lean and obese individuals

AIMS/HYPOTHESIS

This study investigated the expression of adipose tissue fatty acid binding proteins (FABPs) in subcutaneous and visceral human adipose tissue depots from lean and obese individuals.

METHODS

Adipocyte lipid binding protein (ALBP) and keratinocyte lipid binding protein (KLBP) expression was quantified by western blot in subcutaneous and omental adipose tissue from 20 obese and 9 lean individuals. RNA expression was quantified by Northern blot in the obese subjects.

RESULTS

In the obese subjects, ALBP protein and RNA expression was higher in subcutaneous compared with omental adipose tissue (increases of 31 +/- 14 % and 40 +/- 13 % respectively, both p < 0.05), whereas in the lean group, KLBP protein levels were 32 +/- 9 % lower in subcutaneous fat (p < 0.03). However, the ALBP/KLBP ratio was greater in subcutaneous compared to omental adipose tissue from both lean and obese subjects: increases of 187 +/- 71 % (p = 0.01) and 52 +/- 23 % (p = 0.17) respectively for the protein ratio, and 21 +/- 6 % for RNA (p = 0.01, obese individuals). In lean subjects, insulin concentrations correlated positively with the ALBP/KLBP protein ratio in both depots (both p < or = 0.03).

CONCLUSION/INTERPRETATION

There are regional differences in adipose tissue FABP expression, which could be influenced by obesity. However, the ALBP/KLBP ratio is greater in subcutaneous than visceral adipose tissue in lean as well as in obese subjects. Investigation of adipose tissue FABPs could further our understanding of the role of fatty acids in the insulin resistance syndrome.

Increased expression of eNOS protein in omental versus subcutaneous adipose tissue in obese human subjects

OBJECTIVE

To investigate the expression of eNOS and iNOS mRNA and protein in adipose tissue from subcutaneous (s.c.) and omental adipose tissue of obese subjects.

DESIGN

Subcutaneous and omental adipose tissue was obtained from subjects undergoing weight reduction surgery. Messenger RNA and protein levels were measured in tissue extracts and related to basal lipolysis, which was measured in isolated adipocytes from the same subjects.

SUBJECTS

Eight overweight but otherwise healthy male subjects (age 43.4+/-10.3 y, BMI 39+/-3.5 kg/m(2), mean+/-s.e.m.).

MEASUREMENTS

For mRNA detection a competitive reverse transcription polymerase chain reaction method was used while protein was detected by Western blot. Glycerol release was determined in isolated adipocytes using a standard luminometric assay.

RESULTS

Tissue mRNA levels for eNOS in s.c. tissue were 6098+/-1969 amol/mg RNA and in omental tissue 6987+/-2914 amol/mg RNA (mean+/-s.e.m., P=0.75). iNOS mRNA levels were substantially lower; in s.c. tissue 227+/-127 amol/mg RNA and in omental tissue 245+/-162 amol/mg RNA (P=0.8). In Western blot, eNOS protein levels in s.c. and omental tissue were 1.88+/-2.0 and 7.47+/-4.11 (OD/mm(2) 100 microg total protein, P=0.0063), respectively. iNOS protein was expressed at significantly lower levels and barely detectable in both s.c. and omental tissue. Basal rate of lipolysis was two times higher in s.c. compared to omental fat cells (P=0.028).

CONCLUSIONS

eNOS protein is markedly increased in omental compared to s.c. adipose tissue in human obese subjects, probably due to post-transcriptional mechanisms. Since basal lipolysis is much lower in omental vs s.c. adipose tissue it is possible that regionally increased NO production, primarily by eNOS, may be involved in the site difference of basal lipolysis in obese subjects.

Expression of nitric oxide synthases in subcutaneous adipose tissue of nonobese and obese humans

Studies have shown evidence of production of nitric oxide (NO) in adipose tissue, as well as inhibition of lipolysis by NO. We have analyzed nitric oxide synthase (NOS) expression in subcutaneous adipose tissue from 13 nonobese and 18 obese male subjects. Using a competitive reverse transcription polymerase chain reaction method, endothelial (eNOS) and inducible (iNOS), but not neuronal (nNOS), nitric oxide synthase mRNA expression was detected in isolated fat cells and pieces of adipose tissue. Tissue mRNA levels for eNOS were 3,814 +/- 825 and 5,956 +/- 476 amol/mg RNA (P = 0.043), and for iNOS 306 +/- 38 and 332 +/- 48 amol/mg RNA, for nonobese and obese individuals, respectively. Western blotting revealed similar eNOS protein levels in isolated fat cells and adipose tissue pieces. Protein levels for eNOS in nonobese and obese individuals, respectively, were (in optical density [OD] units per mm(2) per 100 microgram of total protein) 0.11 +/- 0.08 and 2.80 +/- 1.30 (P = 0.043). iNOS protein was detectable, but not measurable, at low levels in a subset of obese patients (3 of 10). iNOS protein levels could not be detected in nonobese individuals. Hormone-sensitive lipase (HSL), the key regulating enzyme in lipolysis, is reduced in obesity. The expression of HSL protein in subcutaneous adipose tissue was studied in the same subset of patients; in agreement with previous results, HSL levels were reduced in obese subjects: 4.64 +/- 1.10 and 1.27 +/- 0.35 (P = 0.012) in nonobese and obese subjects, respectively. In conclusion, this study shows that eNOS and iNOS, but not nNOS, are present in human subcutaneous adipose tissue. Gene expression and protein levels of eNOS are increased, whereas HSL protein levels are decreased in obesity. It is speculated that increased NO production, preferably by eNOS, and decreased HSL levels may cause decreased subcutaneous adipose tissue lipolysis in obesity. synthases in subcutaneous adipose tissue of nonobese and obese humans.

Secretion of tumor necrosis factor-alpha shows a strong relationship to insulin-stimulated glucose transport in human adipose tissue

Some animal models suggest that tumor necrosis factor (TNF)-alpha is a key component in obesity-linked insulin resistance because it inhibits insulin receptor signaling and glucose transport in insulin-sensitive tissues. However, in vivo data in humans have given conflicting results regarding the relationship between circulating TNF-alpha levels and insulin sensitivity. In the present study, the potential local role of TNF-alpha on insulin action in human subcutaneous adipose tissue was studied in 42 obese women (BMI 39+/-10 kg/m2). We found a strong inverse correlation between adipose TNF-alpha secretion and maximum insulin-stimulated glucose transport in adipocytes that was independent of fat cell volume, age, and BMI (P < 0.001, r = 0.58). As much as one-third of the variation in insulin-stimulated glucose transport could be accounted for by variations in TNF-alpha secretion. There was no significant correlation (r = 0.11) between secretion of adipose plasminogen activator inhibitor 1 and glucose transport. Furthermore, subcutaneous adipose tissue of 4 obese women (BMI 40+/-4) incubated with TNF-A for 24 h showed a one-third concentration-dependent inhibition of insulin-stimulated glucose transport (P < 0.01). In conclusion, adipose TNF-alpha may be an important specific and local factor in adipose tissue that influences the ability of insulin to stimulate glucose transport in human fat cells, at least in obese women.

Excessive fat accumulation is associated with the TNF alpha-308 G/A promoter polymorphism in women but not in men

AIMS/HYPOTHESIS

Tumour necrosis factor alpha (TNF alpha) is a candidate gene for the development of obesity, which in turn is a major risk factor for diabetes mellitus. The aim of our study was to investigate whether a previously known NcoI-sensitive polymorphism (-308 G/A) in the promoter region of the TNF alpha gene was related to body weight.

METHODS

Genotyping was done in 239 male and 342 female non-diabetic subjects with a marked variation in body mass index (BMI).

RESULTS

We found three genotypes; AA (n = 13), AG (n = 158) and GG (n = 410). When the material was divided according to sex, allele specific phenotypic differences were confined to women. The female subjects carrying the AA genotype were markedly more obese than both the AG and GG carriers (mean BMI = 41.4 vs 32.3 and 31.7 kg/m2, respectively, p = 0.02). The body fat content of female AA carriers was increased by one-third compared with AG/GG carriers (p = 0.02). We found no differences between genotypes with respect to waist-to-hip ratio, blood pressure or metabolic variables. Among obese female subjects (BMI > 27 kg/m2), we also found that the BMI and body fat content of AA carriers (n = 7) were also higher than for AG/GG carriers.

CONCLUSION/INTERPRETATION

The AA-variant at position -308 in the promoter region of the TNF alpha gene could be an important genetic factor behind excessive fat accumulation in women.

A second determinant of binding to the p75 neurotrophin receptor revealed by alanine-scanning mutagenesis of a conserved loop in nerve growth factor

In the neurotrophin family, variable regions contain solvent-accessible residues important for receptor binding specificity, whereas many of the conserved residues are buried in hydrophobic cores or in the dimer interface. A stretch of six amino acids (from Asp-72 to Asn-77) in nerve growth factor (NGF) represents an exception to this general rule. These residues are highly conserved and yet form an exposed hydrophilic loop region away from other known determinants of receptor binding. We have investigated the functional importance of this region in NGF using alanine-scanning mutagenesis. Individual mutation of Asp-72, Lys-74, or His-75 to alanine (mutants D72A, K74A, and H75A, respectively) reduced the binding affinity for the p75 neurotrophin receptor by 4-10-fold. Only the D72A mutant showed an additional impairment in binding to the TrkA receptor, which was accompanied by reduced biological activity in PC12 cells, indicating a structural and/or conformational effect of this mutation. Replacement of Ser-73 or Asn-77 with alanine (mutants S73A and N77A, respectively) had no measurable effects on receptor binding. The triple mutant K74A/H75A/N77A exhibited properties that were consistent with the combined effects of the individual mutations, namely impaired binding to p75 without deficits in its interaction with TrkA. In contrast, in the triple mutant D72A/S73A/K74A, the simultaneous replacement of Asp-72 and Lys-74 with alanine had a compensatory effect such that binding to both p75 and TrkA was comparable to that of wild-type NGF, despite the deficits seen in the individual replacements. This molecule, however, was produced at low levels, and its biological activity in sympathetic ganglion explants was reduced, which, together with results from TrkA phosphorylation assays, indicated a reduced stability during prolonged culture conditions. Taken together, these data reveal a second region of interaction with the p75 receptor in NGF with the positively charged residues Lys-74 and His-75 as candidate points of contact. In addition, Asp-72 appears to be a structurally important side chain for stabilizing the conformation of the loop through interactions with neighboring residues.

Coexpression of mRNA for the full-length neurotrophin receptor trk-C and trk-A in favourable neuroblastoma

Neuroblastoma, a childhood tumour of the sympathetic nervous system, may sometimes regress spontaneously in infants, or progress to a poor clinical outcome despite intensive therapy. Neuroblastomas express neurotrophin receptors and high levels of mRNA for trk-A correlates with favourable outcome, whereas trk-B mRNA is expressed by more unfavourable tumours. Using a sensitive RNase protection assay, mRNA expression for the neurotrophin receptor trk-C was investigated in 50 tumour samples from 45 children at different stages including metastatic and relapsing tumour tissue, out of which 22 were also investigated for trk-A mRNA. Thirty-seven of 43 primary tumours (86%) showed trk-C mRNA with more than 300-fold difference between the highest and the lowest values. A higher trk-C index (trk-C mRNA/GAPDH mRNA) was associated with favourable features such as younger age (P = 0.009-0.003), favourable tumour stage (1, 2 or 4S; P < 0.001) and favourable prognosis (P = 0.044). Better survival probability was shown in children with intermediate or high trk-C index compared with patients with low or undetectable levels (P = 0.031). All localised tumours co-expressed mRNA for trk-A and trk-C receptors. RT-PCR analysis detected mRNA encoding the cytoplasmic trk-C tyrosine kinase region only in favourable neuroblastomas. We conclude that favourable neuroblastoma may express the full-length trk-C receptor while unfavourable tumours, especially those with MYCN amplification, seem to either express no trk-C or truncated trk-C receptors with unknown biological function. Trk-C and possibly its preferred ligand NT-3 may be involved in the biology of favourable neuroblastomas showing apoptosis or differentiation.

Differential modulation of neuron survival during development by nerve growth factor binding to the p75 neurotrophin receptor

Nerve growth factor (NGF) supports the survival and differentiation of distinct populations of peripheral and central neurons. NGF binds to two classes of cell-surface receptors, the protein tyrosine kinase TrkA and the smaller p75 receptor lacking intrinsic catalytic activity. It has been suggested that both receptors are required for NGF high affinity binding, although TrkA appears to be sufficient for transducing most of the biological effects of NGF. Some evidence suggests that p75 could play a modulatory role on TrkA activation by an as yet unknown mechanism. In this study, we have investigated functional roles of p75 using a purified triple mutant NGF (triNGF) deficient in p75 binding but retaining significant TrkA binding and activation. The mutant was found to be as potent as wild type NGF at promoting survival of serum-deprived TrkA-expressing fibroblasts. On developing chick sensory neurons, survival responses to mutant and native NGF were indistinguishable when assayed at nanomolar concentrations. However, triNGF was 3- to 4-fold less potent than wild type NGF at lower concentrations (i.e. 10(-11) M). Interestingly, in PC12 cells coexpressing TrkA and p75, no high affinity binding sites for triNGF could be detected. The reduced responsiveness to triNGF in sensory neurons was increasingly evident at later developmental stages; late embryonic neurons did not respond at all to concentrations of triNGF that were saturating at earlier developmental stages. Likewise, although no difference could be seen between wild type and mutant NGF on the survival responses of embryonic rat superior cervical ganglion sympathetic neurons, the mutant was much less potent than native NGF on postnatal sympathetic neurons. In sensory neurons, the decrease in responsiveness to triNGF correlated with a developmental reduction in the expression of both p75 and TrkA. Thus, NGF binding to p75 enhances responsiveness to ligand, particularly when this is present at limiting concentrations. During development, p75 modulates responsiveness to NGF so that binding to p75 becomes increasingly important in neurons undergoing a down-regulation of NGF receptors. These results support a ligand-dependent modulatory role for p75 in NGF-mediated neuron survival consistent with p75 functioning as a TrkA regulator and/or signaling receptor.

A novel type I receptor serine-threonine kinase predominantly expressed in the adult central nervous system

Receptor serine-threonine kinases (RSTK) mediate inhibitory as well as stimulatory signals for growth and differentiation by binding to members of the transforming growth factor-beta (TGF-beta) superfamily. Over 12 different RSTKs have been isolated so far, displaying wide expression in peripheral tissues and in the nervous system. Here we report the isolation and characterization of a novel type I RSTK termed activin receptor-like kinase-7 (ALK-7) that, unlike other members of this receptor family, is predominantly expressed in the adult central nervous system. The ALK-7 gene encodes a 55-kDa cell-surface protein that exhibits up to 78% amino acid sequence identity in the kinase domain to previously isolated type I receptors for TGF-beta and activin. In the extracellular domain, however, ALK-7 is more divergent, displaying comparable similarities with all members of the ALK subfamily. RNase protection and in situ hybridization studies demonstrated a highly specific mRNA distribution restricted to neurons in several regions of the adult rat central nervous system, including cerebellum, hippocampus, and nuclei of the brainstem. Receptor reconstitution and cross-linking experiments indicated that ALK-7 can form complexes with type II RSTKs for TGF-beta and activin in a ligand-dependent manner, although direct binding of ALK-7 to ligand in these complexes could not be demonstrated. The specific expression pattern of ALK-7, restricted to the postnatal central nervous system, indicates that this receptor may play an important role in the maturation and maintenance of several neuronal subpopulations.

Expression of mRNA for the neurotrophin receptor trkC in neuroblastomas with favourable tumour stage and good prognosis

Childhood neuroblastoma tumours of the sympathetic nervous system show a remarkable clinical heterogeneity ranging from spontaneous regression to unfavourable outcome despite intensive therapy. Favourable neuroblastomas often express high levels of trkA mRNA, encoding the tyrosine kinase receptor for nerve growth factor. We have investigated mRNA expression for the neurotrophin receptor trkC in 23 primary neuroblastomas using a sensitive RNAase protection assay. TrkC expression was detected in 19 of these tumours at highly variable levels with a 300-fold difference between the highest and lowest values. Significantly higher levels of trkC mRNA were found in tumours from patients with favourable features such as low age (P < 0.012), favourable tumour stage (P < 0.012) and favourable prognosis (P < 0.05). Children with intermediate or high trkC mRNA expression had better prognosis compared with those with low or undetectable levels (83.3% vs 20%, P = 0.005). Further characterisation of trkC mRNA expression by reverse transcriptase-polymerase chain reaction (RT-PCR) showed that mRNA encoding the full-length cytoplasmic tyrosine kinase domain of the receptor was only expressed in a subset of favourable tumours. These data show that favourable neuroblastomas may express the full trkC receptor while advanced tumours, in particular MYCN-amplified neuroblastoma, seem to either express no trkC or truncated trkC receptors of as yet unknown biological function. These data are suggestive of a role for trkC and its preferred ligand neutotrophin-3, NT-3, in neuroblastoma differentiation and/or regression.

Binding of neurotrophin-3 to p75LNGFR, TrkA, and TrkB mediated by a single functional epitope distinct from that recognized by trkC

Neurotrophins regulate differentiation and survival of vertebrate neurons through binding to members of the Trk family of receptor tyrosine kinases and to a common low affinity receptor, p75LNGFR. The specificity of neurotrophin action is determined by their selective interaction with the different members of the Trk family; TrkA, TrkB, and TrkC serve as cognate receptors for nerve growth factor, brain-derived neurotrophic factor, and neurotrophin-3 (NT-3), respectively. Unlike nerve growth factor and brain-derived neurotrophic factor, NT-3 can to some extent also bind and activate non-cognate TrkA and B receptors, although the physiological relevance of these interactions is unclear. Previous studies established that neurotrophins use an extended surface for binding to cognate Trk receptors, while binding to p75LNGFR is mediated by a localized cluster of positively charged residues. Here we show that the binding site of NT-3 to its non-preferred receptors TrkA and TrkB is dominated by two positively charged residues, Arg-31 and His-33, previously shown to constitute a main determinant of binding to p75LNGFR. Simultaneous mutation of these two residues into Ala completely abolished NT-3 binding and signaling through TrkA and greatly diminished binding and activation of TrkB. However, NT-3 binding and signaling through its cognate receptor TrkC was unaffected by the mutation. These results show that binding of NT-3 to p75LNGFR, TrkA, and TrkB is mediated by a common determinant, which is distinct from that recognized by TrkC and also different and more localized than the one recognized by TrkA and TrkB in their cognate ligands. Thus, although homologous regions in all neurotrophins are used for binding to Trk receptors, a given Trk may actually contact different residues in different neurotrophins. The mutant NT-3 described here may be of greater advantage than native NT-3 when a trophic activity needs to be specifically targeted to TrkC-expressing neurons and provides a monospecific neurotrophin for future therapeutic development.

Peripheral expression and biological activities of GDNF, a new neurotrophic factor for avian and mammalian peripheral neurons

Glial cell line-derived neurotrophic factor (GDNF) is a neurotrophic polypeptide, distantly related to transforming growth factor-beta (TGF-beta), originally isolated by virtue of its ability to induce dopamine uptake and cell survival in cultures of embryonic ventral midbrain dopaminergic neurons, and more recently shown to be a potent neurotrophic factor for motorneurons. The biological activities and distribution of this molecule outside the central nervous system are presently unknown. We report here on the mRNA expression, biological activities and initial receptor binding characterization of GDNF and a shorter spliced variant termed GDNF beta in different organs and peripheral neurons of the developing rat. Both GDNF mRNA forms were found to be most highly expressed in developing skin, whisker pad, kidney, stomach and testis. Lower expression was also detected in developing skeletal muscle, ovary, lung, and adrenal gland. Developing spinal cord, superior cervical ganglion (SCG) and dorsal root ganglion (DRG) also expressed low levels of GDNF mRNA. Two days after nerve transection, GDNF mRNA levels increased dramatically in the sciatic nerve. Overall, GDNF mRNA expression was significantly higher in peripheral organs than in neuronal tissues. Expression of either GDNF mRNA isoform in insect cells resulted in the production of indistinguishable mature GDNF polypeptides. Purified recombinant GDNF promoted neurite outgrowth and survival of embryonic chick sympathetic neurons. GDNF produced robust bundle-like, fasciculated outgrowth from chick sympathetic ganglion explants. Although GDNF displayed only low activity on survival of newborn rat SCG neurons, this protein was found to increase the expression of vasoactive intestinal peptide and preprotachykinin-A mRNAs in cultured SCG neurons. GDNF also promoted survival of about half of the neurons in embryonic chick nodose ganglion and a small subpopulation of embryonic sensory neurons in chick dorsal root and rat trigeminal ganglia. Embryonic chick sympathetic neurons expressed receptors for GDNF with Kd 1-5 x 10(-9) M, as measured by saturation and displacement binding assays. Our findings indicate GDNF is a new neurotrophic factor for developing peripheral neurons and suggest possible non-neuronal roles for GDNF in the developing reproductive system.

[Nerve growth factors in future therapies. Protein mutation broadens the range of therapeutic possibilities]

The development and maintenance of the vertebrate nervous system requires a continuous supply of a number of polypeptide hormones known as neurotrophic factors. The ability of neurotrophic factors to promote the survival of peripheral and central neurons during development and after neuronal damage has aroused interest in these molecules as potential therapeutic agents for the treatment of nervous lesions and neurodegenerative diseases. Understanding of the molecular basis of the biological specificity of neurotrophic polypeptides has provided insight into their mechanisms of action and allowed strategies to be developed for the rational design of derivatives and analogues with specific pharmacological properties.

Functional analysis of mutant neurotrophins deficient in low-affinity binding reveals a role for p75LNGFR in NT-4 signalling

The neurotrophins mediate their effects through binding to two classes of receptors, a tyrosine kinase receptor, member of the Trk family, and the low-affinity neurotrophin receptor, p75LNGFR, of as yet undefined signalling capacity. The need for a two-component receptor system in neurotrophin signalling is still not understood. Using site-directed mutagenesis, we have identified positively charged surfaces in BDNF, NT-3 and NT-4 that mediate binding to p75LNGFR. Arg31 and His33 in NT-3, and Arg34 and Arg36 in NT-4, located in an exposed hairpin loop, were found to be essential for binding to p75LNGFR. In BDNF, however, positively charged residues critical for p75LNGFR binding (Lys95, Lys96 and Arg97) were found in a spatially close but distinct loop region. Models of each neurotrophin were built using the coordinates of NGF. Analysis of their respective electrostatic surface potentials revealed similar clusters of positively charged residues in each neurotrophin but with differences in their precise spatial locations. Disruption of this positively charged interface abolished binding to p75LNGFR but not activation of cognate Trk receptors or biological activity in Trk-expressing fibroblasts. Unexpectedly, loss of low-affinity binding in NT-4, but not in BDNF or NT-3, affected receptor activation and biological activity in neuronal cells co-expressing p75LNGFR and TrkB, suggesting a role for p75LNGFR in regulating biological responsiveness to NT-4. These findings reveal a possible mechanism of ligand discrimination by p75LNGFR and suggest this receptor may selectively modulate the biological actions of specific neurotrophin family members.