Adipocyte size is associated with NAFLD independent of obesity, fat distribution, and PNPLA3 genotype

Gestational exposure to bisphenol S induces microvesicular steatosis in male rat offspring by modulating metaflammation

Prenatal exposure to endocrine-disrupting bisphenol A (BPA) shows a long-lasting programming effect on an organ's metabolic function and predisposes it to the risk of adult metabolic diseases. Although a reduced contaminant risk due to "BPA-free" exposure is proposed, limited data on a comparative assessment of gestational exposure to BPS and BPA and their effects on metaflammation in predisposing liver metabolic disease is reported. Pregnant Wistar rats were exposed to BPS and BPA (0.0, 0.4, 4.0 μg/kg bw) via gavage from gestational day 4 to 21, and effects were assessed in the 90 d male offspring. Prenatal BPS-exposed offspring showed a more obesogenic effect than BPA, including changes in body fat distribution, feed efficiency, and leptin signalling. The BPS exposure induced the adipocyte hypertrophy of visceral adipose to a greater extent than BPA. The adipose hypertrophy was augmented by tissue inflammation, endoplasmic reticulum (ER) stress, and apoptosis due to increased expression of pro-inflammatory (IL6, IL1β, CRP, COX2) cytokines, ER stress modulator (CHOP), and apoptotic effector (Caspase 3). The enlarged, stressed, inflamed adipocytes triggered de novo lipogenesis in the bisphenol-exposed offspring liver due to increased expression of cholesterol and lipid biogenesis mediators (srebf1, fasn, acaca, PPARα) concomitant with elevated triacylglycerol (TG) and cholesterol (TC), resulted in impaired hepatic clearance of lipids. The lipogenic effects were also promoted by increased expression of HSD11β1. BPS exposure increased absolute liver weight, discoloration, altered liver lobes more than in BPA. Liver histology showed numerous lipid droplets, and hepatocyte ballooning, upregulated ADRP expression, an increased expression of pro-inflammatory mediators (IL6, CRP, IL1β, TNFα, COX2), enhanced lipid peroxidation in the BPS-exposed offspring's liver suggest altered metaflammation leads to microvesicular steatosis. Overall, gestational BPS exposure demonstrated a higher disruption in metabolic changes than BPA, involving excess adiposity, liver fat, inflammation, and predisposition to steatosis in the adult male offspring.

The association between visceral adipocyte hypertrophy and NAFLD in subjects with different degrees of adiposity

OBJECTIVE

To investigate the association between visceral adipocyte hypertrophy and the onset and development of non-alcoholic fatty liver disease (NAFLD) in subjects with different degrees of adiposity.

METHODS

Omental adipose tissue and liver biopsies were collected from obese subjects. NAFLD was defined according to the NASH Clinical Research Network scoring system. Adipocyte size was measured using pathological section analysis. Adipose tissue insulin resistance (Adipo-IR) was calculated as fasting insulin (pmol/L) × fasting free fatty acid concentration (mmol/L).

RESULTS

In total, 275 obese patients were enrolled, including 158 females and 58 males with NAFLD. In females, adipocyte size was significantly larger in NAFLD participants as compared to the controls (99.37 ± 14.18 vs. 84.14 ± 12.65 [Formula: see text]m, p < 0.001). Moreover, adipocyte size was larger in females with non-alcoholic steatohepatitis (NASH) as compared to those with non-alcoholic fatty liver (NAFL) (101.45 ± 12.77 vs. 95.79 ± 15.80 [Formula: see text]m, p = 0.015). Mediation analysis showed that adipocyte size impacted the NAFLD activity score through Adipo-IR (b = 0.007 [95% bootstrap CI 0.002, 0.013]). Furthermore, the females were divided into: Q1 (BMI < 32.5 kg/m²), Q2 (BMI 32.5-35.5 kg/m²), Q3 (BMI 35.5-38.8 kg/m²) and Q4 (BMI ≥ 38.8 kg/m²) according to BMI quartiles. Omental adipocyte size was larger in NAFLD subjects in Q1-Q3, but not in Q4. No similar results were observed in males.

CONCLUSION

For the first time, we reported that visceral adipocyte hypertrophy was associated with the onset and progression of NAFLD in mild to moderate adiposity but not in severe obesity, which may be mediated by adipose tissue insulin resistance.

Associations between subcutaneous adipocyte hypertrophy and nonalcoholic fatty liver disease

Adipocyte hypertrophy and expression of adipokines in subcutaneous adipose tissue (SAT) have been linked to steatosis, nonalcoholic steatohepatitis (NASH) and fibrosis in morbidly obese (BMI ≥ 40 kg/m²) subjects. It is unknown if this is also true for subjects with NAFLD with lesser degrees of obesity (BMI < 35 kg/m²). Thirty-two subjects with biopsy-proven NAFLD and 15 non-diabetic controls matched for BMI underwent fine-needle biopsies of SAT. Adipocyte volume was calculated. RNA-sequencing of SAT was performed in a subset of 20 NAFLD patients. Adipocyte volume and gene expression levels were correlated to the presence of NASH or significant fibrosis. Subjects with NAFLD had larger adipocyte volume compared with controls, (1939 pL, 95% CI 1130-1662 vs. 854 pL, 95% CI 781-926, p < 0.001). There was no association between adipocyte volume and the presence of NASH. Gene expression of adipokines previously described to correlate with NASH in morbid obesity, was not associated with NASH or fibrosis. Our results suggest that persons with NAFLD have larger SAT adipocytes compared with controls and that adipocytes are involved in the pathophysiology of hepatic steatosis in NAFLD. However, adipocyte volume was not associated with NASH or fibrosis in NAFLD subjects with varying degrees of obesity.

Fat Cell Size: Measurement Methods, Pathophysiological Origins, and Relationships With Metabolic Dysregulations

The obesity pandemic increasingly causes morbidity and mortality from type 2 diabetes, cardiovascular diseases and many other chronic diseases. Fat cell size (FCS) predicts numerous obesity-related complications such as lipid dysmetabolism, ectopic fat accumulation, insulin resistance, and cardiovascular disorders. Nevertheless, the scarcity of systematic literature reviews on this subject is compounded by the use of different methods by which FCS measurements are determined and reported. In this paper, we provide a systematic review of the current literature on the relationship between adipocyte hypertrophy and obesity-related glucose and lipid dysmetabolism, ectopic fat accumulation, and cardiovascular disorders. We also review the numerous mechanistic origins of adipocyte hypertrophy and its relationship with metabolic dysregulation, including changes in adipogenesis, cell senescence, collagen deposition, systemic inflammation, adipokine secretion, and energy balance. To quantify the effect of different FCS measurement methods, we performed statistical analyses across published data while controlling for body mass index, age, and sex.

Assessing Obesity-Related Adipose Tissue Disease (OrAD) to Improve Precision Medicine for Patients Living With Obesity

Obesity is a heterogenous condition that affects the life and health of patients to different degrees and in different ways. Yet, most approaches to treat obesity are not currently prescribed, at least in a systematic manner, based on individual obesity sub-phenotypes or specifically-predicted health risks. Adipose tissue is one of the most evidently affected tissues in obesity. The degree of adipose tissue changes - "adiposopathy", or as we propose to relate to herein as Obesity-related Adipose tissue Disease (OrAD), correspond, at least cross-sectionally, to the extent of obesity-related complications inflicted on an individual patient. This potentially provides an opportunity to better personalize anti-obesity management by utilizing the information that can be retrieved by assessing OrAD. This review article will summarize current knowledge on histopathological OrAD features which, beyond cross-sectional analyses, had been shown to predict future obesity-related endpoints and/or the response to specific anti-obesity interventions. In particular, the review explores adipocyte cell size, adipose tissue inflammation, and fibrosis. Rather than highly-specialized methods, we emphasize standard pathology laboratory approaches to assess OrAD, which are readily-available in most clinical settings. We then discuss how OrAD assessment can be streamlined in the obesity/weight-management clinic. We propose that current studies provide sufficient evidence to inspire concerted efforts to better explore the possibility of predicting obesity related clinical endpoints and response to interventions by histological OrAD assessment, in the quest to improve precision medicine in obesity.

Adipose Morphology: a Critical Factor in Regulation of Human Metabolic Diseases and Adipose Tissue Dysfunction

Emerging evidence highlights that dysfunction of adipose tissue contributes to impaired insulin sensitivity and systemic metabolic deterioration in obese state. Of note, adipocyte hypertrophy serves as a critical event which associates closely with adipose dysfunction. An increase in cell size exacerbates hypoxia and inflammation as well as excessive collagen deposition, finally leading to metabolic dysregulation. Specific mechanisms of adipocyte hypertrophy include dysregulated differentiation and maturation of preadipocytes, enlargement of lipid droplets, and abnormal adipocyte osmolarity sensors. Also, weight loss therapies exert profound influence on adipocyte size. Here, we summarize the critical role of adipocyte hypertrophy in the development of metabolic disturbances. Future studies are required to establish a standard criterion of size measurement to better clarify the impact of adipocyte hypertrophy on changes in metabolic homeostasis.

Impaired Adipogenesis and Dysfunctional Adipose Tissue in Human Hypertrophic Obesity

The subcutaneous adipose tissue (SAT) is the largest and best storage site for excess lipids. However, it has a limited ability to expand by recruiting and/or differentiating available precursor cells. When inadequate, this leads to a hypertrophic expansion of the cells with increased inflammation, insulin resistance, and a dysfunctional prolipolytic tissue. Epi-/genetic factors regulate SAT adipogenesis and genetic predisposition for type 2 diabetes is associated with markers of an impaired SAT adipogenesis and development of hypertrophic obesity also in nonobese individuals. We here review mechanisms for the adipose precursor cells to enter adipogenesis, emphasizing the role of bone morphogenetic protein-4 (BMP-4) and its endogenous antagonist gremlin-1, which is increased in hypertrophic SAT in humans. Gremlin-1 is a secreted and a likely important mechanism for the impaired SAT adipogenesis in hypertrophic obesity. Transiently increasing BMP-4 enhances adipogenic commitment of the precursor cells while maintained BMP-4 signaling during differentiation induces a beige/brown oxidative phenotype in both human and murine adipose cells. Adipose tissue growth and development also requires increased angiogenesis, and BMP-4, as a proangiogenic molecule, may also be an important feedback regulator of this. Hypertrophic obesity is also associated with increased lipolysis. Reduced lipid storage and increased release of FFA by hypertrophic SAT are important mechanisms for the accumulation of ectopic fat in the liver and other places promoting insulin resistance. Taken together, the limited expansion and storage capacity of SAT is a major driver of the obesity-associated metabolic complications.

Developmental origins of nonalcoholic fatty liver disease as a risk factor for exaggerated metabolic and cardiovascular-renal disease

Intrauterine growth restriction (IUGR) is linked to increased risk for chronic disease. Placental ischemia and insufficiency in the mother are implicated in predisposing IUGR offspring to metabolic dysfunction, including hypertension, insulin resistance, abnormalities in glucose homeostasis, and nonalcoholic fatty liver disease (NAFLD). It is unclear whether these metabolic disturbances contribute to the developmental origins of exaggerated cardiovascular-renal disease (CVRD) risk accompanying IUGR. IUGR impacts the pancreas, adipose tissue, and liver, which are hypothesized to program for hepatic insulin resistance and subsequent NAFLD. NAFLD is projected to become the major cause of chronic liver disease and contributor to uncontrolled type 2 diabetes mellitus, which is a leading cause of chronic kidney disease. While NAFLD is increased in experimental models of IUGR, lacking is a full comprehension of the mechanisms responsible for programming of NAFLD and whether this potentiates susceptibility to liver injury. The use of well-established and clinically relevant rodent models, which mimic the clinical characteristics of IUGR, metabolic disturbances, and increased blood pressure in the offspring, will permit investigation into mechanisms linking adverse influences during early life and later chronic health. The purpose of this review is to propose mechanisms, including those proinflammatory in nature, whereby IUGR exacerbates the pathogenesis of NAFLD and how these adverse programmed outcomes contribute to exaggerated CVRD risk. Understanding the etiology of the developmental origins of chronic disease will allow investigators to uncover treatment strategies to intervene in the mother and her offspring to halt the increasing prevalence of metabolic dysfunction and CVRD.

Cytometric analysis of adipose tissue reveals increments of adipocyte progenitor cells after weight loss induced by bariatric surgery

Obesity-related comorbidities are, in large part, originated from the dysfunction of adipose tissue. Most of them revert after the normalization of body mass. Adipose tissue is essentially occupied by adipocytes. However, different populations of immunological cells and adipocyte precursor cells (AdPCs) are the main cellular components of tissue. During obesity, body fat depots acquire a low-level chronic inflammation and adipocytes increase in number and volume. Conversely, weight loss improves the inflammatory phenotype of adipose tissue immune cells and reduces the volume of adipocytes. Nevertheless, very little is known about the evolution of the human AdPCs reservoir. We have developed a flow cytometry-based methodology to simultaneously quantify the main cell populations of adipose tissue. Starting from this technical approach, we have studied human adipose tissue samples (visceral and subcutaneous) obtained at two different physiological situations: at morbid obesity and after bariatric surgery-induced weight loss. We report a considerable increase of the AdPCs reservoir after losing weight and several changes in the immune cells populations of adipose tissue (mast cells increase, neutrophils decrease and macrophages switch phenotype). No changes were observed for T-lymphocytes, which are discussed in the context of recent findings.

ASK1 (MAP3K5) is transcriptionally upregulated by E2F1 in adipose tissue in obesity, molecularly defining a human dys-metabolic obese phenotype

Objective

Obesity variably disrupts human health, but molecular-based patients' health-risk stratification is limited. Adipose tissue (AT) stresses may link obesity with metabolic dysfunction, but how they signal in humans remains poorly-characterized. We hypothesized that a transcriptional AT stress-signaling cascade involving E2F1 and ASK1 (MAP3K5) molecularly defines high-risk obese subtype.

Methods

ASK1 expression in human AT biopsies was determined by real-time PCR analysis, and chromatin immunoprecipitation (ChIP) adopted to AT explants was used to evaluate the binding of E2F1 to the ASK1 promoter. Dual luciferase assay was used to measure ASK1 promoter activity in HEK293 cells. Effects of E2F1 knockout/knockdown in adipocytes was assessed utilizing mouse-embryonal-fibroblasts (MEF)-derived adipocyte-like cells from WT and E2F1^−/− mice and by siRNA, respectively. ASK1 depletion in adipocytes was studied in MEF-derived adipocyte-like cells from WT and adipose tissue-specific ASK1 knockout mice (ASK1-ATKO).

Results

Human visceral-AT ASK1 mRNA (N = 436) was associated with parameters of obesity-related cardio-metabolic morbidity. Adjustment for E2F1 expression attenuated the association of ASK1 with fasting glucose, insulin resistance, circulating IL-6, and lipids (triglycerides, HDL-cholesterol), even after adjusting for BMI. Chromatin-immunoprecipitation in human-AT explants revealed BMI-associated increased occupancy of the ASK1 promoter by E2F1 (r² = 0.847, p < 0.01). In adipocytes, siRNA-mediated E2F1-knockdown, and MEF-derived adipocytes of E2F1-knockout mice, demonstrated decreased ASK1 expression and signaling to JNK. Mutation/truncation of an E2F1 binding site in hASK1 promoter decreased E2F1-induced ASK1 promoter activity, whereas E2F1-mediated sensitization of ASK1 promoter to further activation by TNFα was inhibited by JNK-inhibitor. Finally, MEF-derived adipocytes from adipocyte-specific ASK1-knockout mice exhibited lower leptin and higher adiponectin expression and secretion, and resistance to the effects of TNFα.

Conclusions

AT E2F1 –ASK1 molecularly defines a metabolically-detrimental obese sub-phenotype. Functionally, it may negatively affect AT endocrine function, linking AT stress to whole-body metabolic dysfunction.

The role of MRI in understanding the underlying mechanisms in obesity associated diseases

Obesity and its possible association with diseases including diabetes and cardiovascular diseases have been studied for decades for its impact on healthcare. Recent studies clearly indicate the need for developing accurate and reproducible methodologies for assessing body fat content and distribution. Body fat distribution plays a significant role in developing an insight in the underlying mechanisms in which adipose tissue is linked with various diseases. Among imaging technologies including computerized axial tomography (CAT or CT), magnetic resonance imaging (MRI), and magnetic resonance spectroscopy (MRS), MRI and MRS seem to be the best emerging techniques and together are being considered as the gold standard for body fat content and distribution. This paper reviews studies up to the present time involving different methodologies of these two emerging technologies and presents the basic concepts of MRI and MRS with required novel image analysis techniques in accurate, quantitative, and direct assessment of body fat content and distribution. This article is part of a Special Issue entitled: Oxidative Stress and Mitochondrial Quality in Diabetes/Obesity and Critical Illness Spectrum of Diseases - edited by P. Hemachandra Reddy.

Caspase-2 promotes obesity, the metabolic syndrome and nonalcoholic fatty liver disease

Obesity and its resulting metabolic disturbances are major health threats. In response to energy surplus, overtaxed adipocytes release fatty acids and pro-inflammatory factors into the circulation, promoting organ fat accumulation (including nonalcoholic fatty liver disease), insulin resistance and the metabolic syndrome. Recently, caspase-2 was linked to lipoapoptosis, so we hypothesized that caspase-2 might be a critical determinant of metabolic syndrome pathogenesis. Caspase-2-deficient and wild-type mice were fed a Western diet (high-fat diet, enriched with saturated fatty acids and 0.2% cholesterol, supplemented with fructose and glucose in the drinking water) for 16 weeks. Metabolic and hepatic outcomes were evaluated. In vitro studies assessed the role of caspase-2 in adipose tissue proliferative properties and susceptibility for lipoapoptosis. Caspase-2-deficient mice fed a Western diet were protected from abdominal fat deposition, diabetes mellitus, dyslipidemia and hepatic steatosis. Adipose tissue in caspase-2-deficient mice was more proliferative, upregulated mitochondrial uncoupling proteins consistent with browning, and was resistant to cell hypertrophy and cell death. The liver was protected from steatohepatitis through a decrease in circulating fatty acids and more efficient hepatic fat metabolism, and from fibrosis as a consequence of reduced fibrogenic stimuli from fewer lipotoxic hepatocytes. Caspase-2 deficiency protected mice from diet-induced obesity, metabolic syndrome and nonalcoholic fatty liver disease. Further studies are necessary to assess caspase-2 as a therapeutic target for those conditions.

Central obesity as a clinical marker of adiposopathy; increased visceral adiposity as a surrogate marker for global fat dysfunction

PURPOSE OF REVIEW

Subcutaneous adipose tissue (SAT) is often described as 'protective'. Visceral adipose tissue (VAT) is often described as 'pathologic'. However, both SAT and VAT have protective and pathologic potential, with interdependent biologic functions.

RECENT FINDINGS

Most of the body's (excess) energy is stored as fat in SAT. If during positive caloric balance, SAT does not undergo adequate adipogenesis, then excess energy may result in adipocyte hypertrophy, leading to hypoxia, immunopathies, and endocrinopathies. Energy overflow may promote accumulation of pericardial fat, perivascular fat, and myocardial fat, which may directly contribute to atherosclerotic cardiovascular disease (CVD). Lipotoxic free fatty acid delivery to nonadipose body organs (e.g. liver, muscle, and pancreas) may indirectly contribute to CVD by promoting the most common metabolic disorders encountered in clinical practice (e.g. high blood sugars, high blood pressure, and dyslipidaemia), all major CVD risk factors. Finally, SAT energy overflow may increase VAT accumulation, which is also associated with increased risk of metabolic diseases and CVD.

SUMMARY

Increased VAT is a surrogate marker for SAT dysfunction which increases waist circumference, reflecting a shared pathologic process leading to the pathogenic fat accumulation of other fat depots and fatty infiltration of nonadipose body organs. Central obesity is a clinical marker for adiposopathy.