Binding and molecular weight properties of the insulin receptor from omental and subcutaneous adipocytes in human obesity

DNA-GPS: A theoretical framework for optics-free spatial genomics and synthesis of current methods

While single-cell sequencing technologies provide unprecedented insights into genomic profiles at the cellular level, they lose the spatial context of cells. Over the past decade, diverse spatial transcriptomics and multi-omics technologies have been developed to analyze molecular profiles of tissues. In this article, we categorize current spatial genomics technologies into three classes: optical imaging, positional indexing, and mathematical cartography. We discuss trade-offs in resolution and scale, identify limitations, and highlight synergies between existing single-cell and spatial genomics methods. Further, we propose DNA-GPS (global positioning system), a theoretical framework for large-scale optics-free spatial genomics that combines ideas from mathematical cartography and positional indexing. DNA-GPS has the potential to achieve scalable spatial genomics for multiple measurement modalities, and by eliminating the need for optical measurement, it has the potential to position cells in three-dimensions (3D).

Of mice and men: Pinpointing species differences in adipose tissue biology

The prevalence of obesity and metabolic diseases continues to rise, which has led to an increased interest in studying adipose tissue to elucidate underlying disease mechanisms. The use of genetic mouse models has been critical for understanding the role of specific genes for adipose tissue function and the tissue’s impact on other organs. However, mouse adipose tissue displays key differences to human fat, which has led, in some cases, to the emergence of some confounding concepts in the adipose field. Such differences include the depot-specific characteristics of visceral and subcutaneous fat, and divergences in thermogenic fat phenotype between the species. Adipose tissue characteristics may therefore not always be directly compared between species, which is important to consider when setting up new studies or interpreting results. This mini review outlines our current knowledge about the cell biological differences between human and mouse adipocytes and fat depots, highlighting some examples where inadequate knowledge of species-specific differences can lead to confounding results, and presenting plausible anatomic explanations that may underlie the differences. The article thus provides critical insights and guidance for researchers working primarily with only human or mouse fat tissue, and may contribute to new ideas or concepts in the important and evolving field of adipose biology.

Characterization of visceral and subcutaneous adipose tissue transcriptome in pregnant women with and without spontaneous labor at term: implication of alternative splicing in the metabolic adaptations of adipose tissue to parturition

OBJECTIVE

The aim of this study was to determine gene expression and splicing changes associated with parturition and regions (visceral vs. subcutaneous) of the adipose tissue of pregnant women.

STUDY DESIGN

The transcriptome of visceral and abdominal subcutaneous adipose tissue from pregnant women at term with (n=15) and without (n=25) spontaneous labor was profiled with the Affymetrix GeneChip Human Exon 1.0 ST array. Overall gene expression changes and the differential exon usage rate were compared between patient groups (unpaired analyses) and adipose tissue regions (paired analyses). Selected genes were tested by quantitative reverse transcription-polymerase chain reaction.

RESULTS

Four hundred and eighty-two genes were differentially expressed between visceral and subcutaneous fat of pregnant women with spontaneous labor at term (q-value <0.1; fold change >1.5). Biological processes enriched in this comparison included tissue and vasculature development as well as inflammatory and metabolic pathways. Differential splicing was found for 42 genes [q-value <0.1; differences in Finding Isoforms using Robust Multichip Analysis scores >2] between adipose tissue regions of women not in labor. Differential exon usage associated with parturition was found for three genes (LIMS1, HSPA5, and GSTK1) in subcutaneous tissues.

CONCLUSION

We show for the first time evidence of implication of mRNA splicing and processing machinery in the subcutaneous adipose tissue of women in labor compared to those without labor.

Characterization of Visceral and Subcutaneous Adipose Tissue Transcriptome and Biological Pathways in Pregnant and Non-Pregnant Women: Evidence for Pregnancy-Related Regional-Specific Differences in Adipose Tissue

Objective

The purpose of this study was to compare the transcriptome of visceral and subcutaneous adipose tissues between pregnant and non-pregnant women.

Study Design

The transcriptome of paired visceral and abdominal subcutaneous adipose tissues from pregnant women at term and matched non-pregnant women (n = 11) was profiled with the Affymetrix Human Exon 1.0 ST array. Differential expression of selected genes was validated with the use of quantitative reverse transcription–polymerase chain reaction.

Results

Six hundred forty-four transcripts from 633 known genes were differentially expressed (false discovery rate (FDR) <0.1; fold-change >1.5), while 42 exons from 36 genes showed differential usage (difference in FIRMA scores >2 and FDR<0.1) between the visceral and subcutaneous fat of pregnant women. Fifty-six known genes were differentially expressed between pregnant and non-pregnant subcutaneous fat and three genes in the visceral fat. Enriched biological processes in the subcutaneous adipose tissue of pregnant women were mostly related to inflammation.

Conclusion

The transcriptome of visceral and subcutaneous fat depots reveals pregnancy-related gene expression and splicing differences in both visceral and subcutaneous adipose tissue. Furthermore, for the first time, alternative splicing in adipose tissue has been associated with regional differences and human parturition.

Insulin metabolism in human adipocytes from subcutaneous and visceral depots

Subjects with the metabolic syndrome (insulin resistance, glucose intolerance, dyslipidemia, hypertension, etc.) have a relative increase in abdominal fat tissue compared to normal individuals and obesity has also been shown to be associated with a decrease in insulin clearance. The majority of the clearance of insulin is due to the action of insulin-degrading enzyme (IDE) and IDE is present throughout all tissues. Since abdominal fat is increased in obesity we hypothesized that IDE may be altered in the different fat depots. Adipocytes were isolated from fat samples obtained from subjects during elective abdominal surgery. Fat samples were taken from subcutaneous (SQ) and visceral (VIS) sites. Insulin metabolism was compared in adipocytes isolated from SQ and VIS fat tissue. Adipocytes from the VIS site degraded more insulin that those from SQ fat tissue. Inhibitors of cathepsins B and D has no effect on the degradation of insulin, while bacitracin, an inhibitor of IDE, inhibited degradation by approx. 33% in both SQ and VIS adipocytes. These data show that insulin metabolism is relatively greater in VIS than in SQ fat tissue and potentially due to IDE.

Role of antilipolytic mechanisms in adipose tissue distribution and function in man

Regional differences have been found in the hormone regulation of adipose tissue lipolysis. Lipolytic activity is greater in omental than in subcutaneous adipocytes owing, in part, to a less marked insulin action and lower alpha 2-adrenoceptor antilipolytic activity in the omental region. In the subcutaneous region catecholamines are less lipolytic in gluteal/femoral than in subcutaneous abdominal adipocytes, which is partly due to enhanced alpha 2-adrenoceptor responsiveness in the gluteal/femoral cells. Insulin action also differs in the two subcutaneous adipose regions in a complex way that is influenced by the degree of obesity and nutritional factors. The regional differences in the antilipolytic effects of hormones seem to be caused by site variations in the receptors as well as in the signals from the receptors. The site variations may be involved in the development of regional forms of obesity, such as android or gynoid obesity and may raise the free fatty acid levels in the portal system and therefore impair metabolism of glucose and insulin by the liver.

Vascular peptide endothelin-1 links fat accumulation with alterations of visceral adipocyte lipolysis

OBJECTIVE

Visceral obesity increases risk of insulin resistance and type 2 diabetes. This may partly be due to a region-specific resistance to insulin's antilipolytic effect in visceral adipocytes. We investigated whether adipose tissue releases the vascular peptide endothelin-1 (ET-1) and whether ET-1 could account for regional differences in lipolysis.

RESEARCH DESIGN AND METHODS

One group consisted of eleven obese and eleven nonobese subjects in whom ET-1 levels were compared between abdominal subcutaneous and arterialized blood samples. A second group included subjects undergoing anti-obesity surgery. Abdominal subcutaneous and visceral adipose tissues were obtained to study the effect of ET-1 on differentiated adipocytes regarding lipolysis and gene and protein expression.

RESULTS

Adipose tissue had a marked net release of ET-1 in vivo, which was 2.5-fold increased in obesity. In adipocytes treated with ET-1, the antilipolytic effect of insulin was attenuated in visceral but not in subcutaneous adipocytes, which could not be explained by effects of ET-1 on adipocyte differentiation. ET-1 decreased the expression of insulin receptor, insulin receptor substrate-1 and phosphodiesterase-3B and increased the expression of endothelin receptor-B (ET(B)R) in visceral but not in subcutaneous adipocytes. These effects were mediated via ET(B)R with signals through protein kinase C and calmodulin pathways. The effect of ET-1 could be mimicked by knockdown of IRS-1.

CONCLUSIONS

ET-1 is released from human adipose tissue and links fat accumulation to insulin resistance. It selectively counteracts insulin inhibition of visceral adipocyte lipolysis via ET(B)R signaling pathways, which affect multiple steps in insulin signaling.

Site-specific differences of insulin action in adipose tissue derived from normal prepubertal children

Body fat distribution determines obesity-related morbidity in adults but little is known of the aetiology or pathophysiology in children. This study investigates differences in insulin-mediated metabolism in primary cell cultures of subcutaneous and visceral preadipocytes derived from prepubertal children. The impact of differentiation and responses to TNFalpha exposure was also investigated. Proliferation rates were greater in subcutaneous versus visceral preadipocytes (41 h3 versus 69 h4; P=0.008). Insulin caused a dose-dependent increase in GSK-3 phosphorylation and an increase in MAPK phosphorylation over time, with increased sensitivity in subcutaneous preadipocytes. Post-differentiation, dose-dependent increases in GSK-3 phosphorylation were maintained, while MAPK phosphorylation was identical in both subtypes. No changes were observed in insulin receptor abundance pre-/post-differentiation. GLUT4 abundance was significantly increased in visceral versus subcutaneous adipocytes by 76(4)%; P=0.03), coincidental with increased insulin-stimulated 2-deoxy-glucose transport (+150(26)% versus +79(10)%; P=0.014) and further elevated by acute exposure to TNFalpha (+230(52)%; P=0.019 versus +123(24)%; P=0.025, respectively). TNFalpha also significantly increased basal glucose transport rates (+44(14)%; P=0.006 versus +34(11)%; P=0.007) and GLUT1 localisation to the plasma membrane. These data establish site-specific differences in subcutaneous and visceral fat cells from children. Responses to insulin varied with differentiation and TNFalpha exposure in the two depots, consistent with parallel changes in GLUT1/4 abundance and localisation.

Glucose transport is equally sensitive to insulin stimulation, but basal and insulin-stimulated transport is higher, in human omental compared with subcutaneous adipocytes

Excess visceral fat has been found to correlate more closely with morbidity than subcutaneous fat. We found that isolated adipocytes from omental fat of nondiabetic women expressed significantly more of the insulin-regulated glucose transporter glucose transporter 4 protein and exhibited a higher basal and insulin-stimulated rate of glucose transport, at all concentrations of insulin, than subcutaneous adipocytes from the same individuals. In contrast, dose-response relationships for insulin stimulation of glucose transport demonstrated identical sensitivity to insulin in adipocytes from the 2 locations. The results demonstrate that there is no relative insulin resistance to stimulate glucose uptake in visceral compared with subcutaneous fat cells.

Insulin secretion, peripheral insulin sensitivity and insulin-receptor binding in subjects with different degrees of obesity

OBJECTIVES

The aim of the present study was to investigate insulin secretion, insulin-receptor binding and peripheral insulin sensitivity in subjects with different degrees of obesity.

METHODS

36 obese subjects with normal glucose tolerance and different degrees of obesity and 40 healthy normal-weight subjects participated in the study. Peripheral insulin sensitivity was measured by using the euglycaemic hyperinsulinaemic clamp technique, and insulin-receptor binding-on circulating mononuclear blood cells. Insulin secretion was studied during intravenous tolbutamide test.

RESULTS

The subjects with I degree of obesity demonstrated a significant decrease in the number of total (p<0.0001) and high-affinity (p<0.01) insulin receptors per cell, as well as significantly higher insulin receptor affinity (p<0.01) as compared to the normal-weight subjects. The subjects with II degree of obesity also demonstrated a significant decrease in the number of total (p<0.0001) and high-affinity receptors (p<0.001) per cell as well as an increase (p<0.001) in insulin-receptor affinity as compared to the controls. The significantly decreased receptor number in the subjects with I and II degree of obesity was accompanied by an increase in insulin receptor affinity; thus their insulin-receptor binding being maintained similar to the controls. The subjects with III degree obesity presented a significant decrease (p<0.0001) in the number of both the total and high-affinity insulin receptors as well as a reduction in insulin receptor affinity as compared to the controls. Therefore the percentage of specifically bound insulin was significantly lower (p<0.01) as compared to that of the control group. Insulin resistance in the obese subjects is associated with secondary hyperinsulinaemia, which is present in subjects with I and II degree of obesity; while in severely obese subjects exhaustion of beta-cell secretory capacity is observed.

CONCLUSION

We consider that III degree of obesity appears to be a risk factor for type 2 diabetes mellitus as the alterations in insulin sensitivity, insulin-receptor binding and beta-cell secretion are quite similar to the reported in diabetic patients.

Comparison of Gene Expression in Intra-Abdominal and Subcutaneous Fat: A Study of Men with Morbid Obesity and Nonobese Men Using Microarray and Proteomics

Extent of intra-abdominal fat had significant linear relations with six metabolic coronary risk factors: systolic and diastolic blood pressure, fasting blood concentrations of glucose, high density lipoprotein (HDL) cholesterol, triglyceride, and plasminogen activator inhibitor-1. Tumor necrosis factor-alpha and adiponectin can be biological mediators from the intra-abdominal fat to the metabolic coronary risk factors. Complementarily, we describe a new study that will analyze the gene expression in intra-abdominal and subcutaneous fat on mRNA and protein level using high throughput methods. The study will elucidate further whether intra-abdominal obesity is the common denominator for the different components of the metabolic syndrome.

Extreme insulin resistance of the central adipose depot in vivo

Despite the well-described association between obesity and insulin resistance, the physiologic mechanisms that link these two states are poorly understood. The present study was performed to elucidate the role of visceral adipose tissue in whole-body glucose homeostasis. Dogs made abdominally obese with a moderately elevated fat diet had catheters placed into the superior mesenteric artery so that the visceral adipose bed could be insulinized discretely. Omental insulin infusion was extracted at approximately 27%, such that systemic insulin levels were lower than in control (portal vein) insulin infusions. Omental infusion did not lower systemic free fatty acid levels further than control infusion, likely because of the resistance of the omental adipose tissue to insulin suppression and the confounding lower systemic insulin levels. The arteriovenous difference technique showed that local infusion of insulin did suppress omental lipolysis, but only at extremely high insulin concentrations. The median effective dose for suppression of lipolysis was almost fourfold higher in the visceral adipose bed than for whole-body suppression of lipolysis. Thus, the omental adipose bed represents a highly insulin-resistant depot that drains directly into the portal vein. Increased free fatty acid flux to the liver may account for hepatic insulin resistance in the moderately obese state.

Gene expression in visceral and subcutaneous adipose tissues

A large body of evidence demonstrates depot-specific differences in the expression of genes coding important functional proteins in adipocytes. This may contribute to the well-known specific functional properties of the adipocytes from intra-abdominal and subcutaneous regions. This review will focus on the main findings regarding the regional differences in adipocyte gene expression in humans. These genes encode proteins belonging to three different functional groups: the metabolic enzyme and related signalling proteins, the adipogenic factors, and, finally, the products of adipocytes.

Regional variation in HDL metabolism in human fat cells: effect of cell size

Abdominal obesity is related to reduced plasma high-density lipoprotein (HDL) cholesterol, and both are associated with cardiovascular disease risk. We have observed that plasma membranes from abdominal subcutaneous adipocytes have a greater HDL binding capacity than omental fat cell plasma membranes. The present study examined whether these binding characteristics could be due to differences in fat cell size or cholesterol concentration between the two adipose depots. Abdominal subcutaneous and deep omental fat were obtained from massively obese patients at surgery. Subcutaneous abdominal fat cells were significantly larger and their cellular cholesterol content greater than omental adipocytes. The uptake of HDL by collagenase-isolated fat cells was studied by incubating the cells for 2 h at 37 degrees C with 10 micrograms/ml 125I-HDL2 or 125I-HDL3. In both depots, the cellular uptake of 125I-HDL2 and 125I-HDL3 was specifically inhibited by addition of 25-fold excess unlabeled HDL and a close correlation was observed between the cellular uptake of 125I-HDL2 and 125I-HDL3. In obese patients, the uptake of 125I-HDL was higher in subcutaneous cells than in omental cells [5.85 +/- 0.53 vs. 2.74 +/- 0.30 pmol X 2 h-1. (10(6) cells)-1]. The cellular 125I-HDL uptake was significantly correlated with adipocyte size and fat cell cholesterol content but not with adipocyte cholesterol concentration. These results suggest that the higher HDL uptake observed in subcutaneous cells compared with omental cells in obesity is the result of differences in adipocyte size rather than differences in the cholesterol concentration (cholesterol-to-triglyceride ratio).(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin receptor kinase in human skeletal muscle from obese subjects with and without noninsulin dependent diabetes

We have studied the structure and function of the insulin receptors in obese patients with and without noninsulin dependent diabetes mellitus (NIDDM) and in nonobese controls using partially purified receptors from muscle biopsies. Insulin binding was decreased in obesity due to reduced number of binding sites but no differences were observed in insulin binding between obese subjects with or without NIDDM. The structural characteristics of the receptors, as determined by affinity labeling methods and electrophoretic mobility of the beta-subunit, were not altered in obese or NIDDM compared to normal weight subjects. Furthermore, the ability of insulin to stimulate the autophosphorylation of the beta-subunit and the phosphoamino acid composition of the phosphorylated receptor were the same in all groups. However, insulin receptor kinase activity was decreased in obesity using Glu4:Tyr1 as exogenous phosphoacceptor without any appreciable additional defect when obesity was associated with NIDDM. Thus, our data are supportive of the hypothesis that in muscle of obese humans, insulin resistance is partially due to decreased insulin receptors and insulin receptor kinase activity. In NIDDM the defect(s) in muscle is probably distal to the insulin receptor kinase.

Regional variation in high-density lipoprotein binding to human adipocyte plasma membranes of massively obese subjects

Obesity is associated with significant changes in cholesterol and lipoprotein metabolism. High density lipoprotein (HDL) cholesterol is often reduced and adipose tissue cholesterol stores are increased in obese individuals. This prompted a study on the binding of HLD fractions (HDL2 and HDL3) to adipocyte plasma membranes obtained from massively obese subjects (BMI greater than 37 kg m-2) undergoing gastroplasty. Regional variation in HDL binding to these adipocyte plasma membranes was demonstrated. Membranes derived from the abdominal subcutaneous depot exhibited similar binding affinity (Kd) but higher binding capacity (Bmax) for HDL2 and HDL3 than that from the omental depot. There was significant inter-individual variation in Bmax but the amount of HDL2 or HDL3 bound to the two depots of the same individual was positively correlated (HDL2, r = 0.66, P less than 0.05; HDL3, r = 0.88, P less than 0.01). While HDL2 binding showed a higher affinity (lower Kd) than HDL3, a significant positive correlation existed between HDL2 and HDL3 binding to the same adipocyte membranes (r = 0.89, P less than 0.01). A significant inverse correlation (P less than 0.05) was also observed between HDL2 and HDL3 binding to adipocyte membranes and plasma HDL-cholesterol concentration. These results suggest that adipose tissue is an important site of HDL metabolism and the subcutaneous fat depot may play a proportionally more significant role due to its higher HDL binding capacity. It is further suggested that increased HDL binding and metabolism by the expanded adipose tissue mass may contribute to reduced plasma HDL-cholesterol levels frequently associated with obesity.

Studies of the human liver insulin receptor in noninsulin-dependent diabetes mellitus

The insulin binding characteristics and the structural components of the insulin receptor were studied in the purified liver plasma membranes from seven patients with noninsulin-dependent diabetes (NIDDM) and seven control subjects. In comparison to the controls, diabetic subjects had a 65% reduction in plasma insulin levels in response to an oral glucose load. Specific insulin binding by liver membranes from diabetic patients was, however, twofold greater than the binding activity by membranes from control subjects. This alteration resulted largely from an increase in the number of insulin receptors and a modest increase in receptor binding affinity. Holo (nonreduced) receptor species of similar molecular weights were detected by an affinity labeling technique in the two membrane preparations and sulfhydryl reduction demonstrated an insulin binding subunit of 125,000 mol wt. Overall, these results show that the hepatic insulin resistance of NIDDM cannot be explained by a deficiency in insulin binding.

Insulin resistance: receptor and post-binding defects in human obesity and non-insulin-dependent diabetes mellitus

Insulin resistance is a prominent feature of three clinical conditions: obesity, impaired glucose tolerance, and non-insulin-dependent (type II) diabetes mellitus. Numerous studies over the past 15 years have provided a better understanding, from both a clinical and cellular standpoint, of the pathophysiology of these insulin-resistant states as well as of insulin action. In addition, it has recently been recognized that correction of glucose intolerance leads to an improvement in insulin secretion and a reduction in insulin resistance. Examination of the most recent data suggests that the basis for insulin resistance in these common clinical disorders is often multifactorial. In uncomplicated obesity, the cellular alterations responsible for insulin resistance appear to be at the level of the hepatic insulin receptor and in post-binding processes in peripheral target tissues. In type II diabetes, a post-binding defect(s) in peripheral tissues appears to be the primary lesion. In humans, many of the factors that mediate the changes leading to insulin resistance are still unknown and are the object of current investigations.