Multiple symmetric lipomatosis. Ultrastructural investigation of the tissue and preadipocytes in primary culture

Multiple symmetric lipomatosis (MSL) is characterized by enlarging, painless fat deposits in the neck and upper trunk. The pathogenesis of MSL is unknown. Owing to localization of MSL fat deposits in the neck and interscapular region, it has been suggested that they could originate from brown fat. However, the histological appearance of MSL adipose tissue is that of white fat, with prevailing monovacuolar adipocytes. Nevertheless, MSL adipocytes are smaller than adipocytes of the common white adipose tissue and show peculiar metabolic features. The ultrastructure of MSL lesions has been not described. The present work investigated the ultrastructural morphology of MSL adipose tissue and lipomatous adipocyte precursors maintained in long-term culture. Samples of lipomatous tissue were obtained from patients affected with MSL undergoing surgical lipectomy. Portion of the tissue was processed for electron microscopy; the rest was digested with collagenase, and isolated preadipocytes from the stromal-vascular fraction were cultured up to 15 days. Cultured cells were prepared for electron microscopy in situ and their morphology compared with human white adipose tissue preadipocytes and rat brown preadipocytes cultured in parallel. Results show the following. 1) Adipocytes of MSL are not monovacuolar and resemble the largest adipocytes that can be found in rat and human brown fat. 2) Some morphological features of MSL adipocyte precursors resemble brown adipocyte more than white: cultured MSL preadipocytes transiently develop large mitochondria with parallel cristae resembling those of the brown fat cell and maintain a multivacuolar lipid deposit in culture, i.e. a typical feature of brown preadipocytes. 3) Some morphological features suggest a neoplastic nature of MSL adipocytes. Taken together, these findings suggest that MSL is a neoplastic disease which could originate in brown fat.     

The pre- and postnatal development and ageing of interscapular brown adipose tissue in the rat

Summary Developmental and ageing changes in interscapular brown adipose tissue have been studied in white Wistar rats by light, fluorescence and electron microscopy.Cellular aggregation was noted in the fetal interscapular area on the 15th day of gestation and vascularised primitive lobules of brown adipose tissue became unequivocally identifiable on the 17th day in utero. Brown adipocyte precursors appeared to be derived directly from mesenchymal cells and were uniquely characterised by larger (0.8–1.7 m diameter) mitochondria. Numbers of these precursor cells (pre-adipocytes) were seen in mitosis during intrauterine life. Pericapillary cells similar in appearance to embryonic pre-adipocytes were regularly observed within brown fat lobules throughout later life.Cardinal features noted in mature brown adipose tissue were parenchymal cells with a multilocular lipid distribution and numerous large mitochondria with distinctive inparallel cristae, as well as an extensive vascular network and a dense catecholaminergic vasomotor and parenchymal innervation.Brown adipocytes generally retained a multilocular lipid distribution into old age, and although the catecholaminergic fluorescence of the nerves supplying the tissue was reduced, a widespread distribution of noradrenergic vasomotor and parenchymal nerves and of nexuses between brown adipocytes continued to be demonstrable by electron microscopy in the brown adipose tissue of senile rats.     

Oxygenation of adipose tissue: A human perspective

Obesity is a complex disorder of excessive adiposity, and is associated with adverse health effects such as cardiometabolic complications, which are to a large extent attributable to dysfunctional white adipose tissue. Adipose tissue dysfunction is characterized by adipocyte hypertrophy, impaired adipokine secretion, a chronic low‐grade inflammatory status, hormonal resistance and altered metabolic responses, together contributing to insulin resistance and related chronic diseases. Adipose tissue hypoxia, defined as a relative oxygen deficit, in obesity has been proposed as a potential contributor to adipose tissue dysfunction, but studies in humans have yielded conflicting results. Here, we will review the role of adipose tissue oxygenation in the pathophysiology of obesity‐related complications, with a specific focus on human studies. We will provide an overview of the determinants of adipose tissue oxygenation, as well as the role of adipose tissue oxygenation in glucose homeostasis, lipid metabolism and inflammation. Finally, we will discuss the putative effects of physiological and experimental hypoxia on adipose tissue biology and whole‐body metabolism in humans. We conclude that several lines of evidence suggest that alteration of adipose tissue oxygenation may impact metabolic homeostasis, thereby providing a novel strategy to combat chronic metabolic diseases in obese humans.     

4E-BP1 regulates the differentiation of white adipose tissue

4E Binding protein 1 (4E-BP1) suppresses translation initiation. The absence of 4E-BP1 drastically reduces the amount of adipose tissue in mice. To address the role of 4E-BP1 in adipocyte differentiation, we characterized 4E-BP1^−/− mice in this study. The lack of 4E-BP1 decreased the amount of white adipose tissue and increased the amount of brown adipose tissue. In 4E-BP1^−/− MEF cells, PPARγ coactivator 1 alpha (PGC-1α) expression increased and exogenous 4E-BP1 expression suppressed PGC-1α expression. The level of 4E-BP1 expression was higher in white adipocytes than in brown adipocytes and showed significantly greater up-regulation in white adipocytes than in brown adipocytes during preadipocyte differentiation into mature adipocytes. The amount of PGC-1α was consistently higher in HB cells (a brown preadipocyte cell line) than in HW cells (a white preadipocyte cell line) during differentiation. Moreover, the ectopic over-expression of 4E-BP1 suppressed PGC-1α expression in white adipocytes, but not in brown adipocytes. Thus, the results of our study indicate that 4E-BP1 may suppress brown adipocyte differentiation and PGC-1α expression in white adipose tissues.     

Mitochondrial (Dys)function in Adipocyte (De)differentiation and Systemic Metabolic Alterations

In mammals, adipose tissue, composed of BAT and WAT, collaborates in energy partitioning and performs metabolic regulatory functions. It is the most flexible tissue in the body, because it is remodeled in size and shape by modifications in adipocyte cell size and/or number, depending on developmental status and energy fluxes. Although numerous reviews have focused on the differentiation program of both brown and white adipocytes as well as on the pathophysiological role of white adipose tissues, the importance of mitochondrial activity in the differentiation or the dedifferentiation programs of adipose cells and in systemic metabolic alterations has not been extensively reviewed previously. Here, we address the crucial role of mitochondrial functions during adipogenesis and in mature adipocytes and discuss the cellular responses of white adipocytes to mitochondrial activity impairment. In addition, we discuss the increase in scientific knowledge regarding mitochondrial functions in the last 10 years and the recent suspicion of mitochondrial dysfunction in several 21st century epidemics (ie, obesity and diabetes), as well as in lipodystrophy found in HIV-treated patients, which can contribute to the development of new therapeutic strategies targeting adipocyte mitochondria.Adipocytes and, more generally, the adipose tissues are major actors in both obesity and the emergence of a cluster of associated diseases such as insulin resistance and type 2 diabetes mellitus (T2DM), cardiovascular diseases, hypertension, dyslipidemia, and even some cancers. Obesity and diabetes are now recognized as worldwide epidemics,¹ with 1.6 billion people being overweight, of which 400 million are obese (body mass index ≥30) (World Health Organization, Geneva 2006).Attention for adipocytes has increased ever since it has been found that these differentiated cells are not only able to store and release triglycerides (TGs) but also have an important endocrine activity. Indeed, adipocytes secrete “adipokines” (specific hormones and proinflammatory cytokines) to communicate systemically with other cell types and thus, importantly, contribute to the regulation of energy homeostasis.² Adipose tissue is present in different interacting depots in the body. In addition to white adipose tissue (WAT), brown adipose tissue (BAT) can also be distinguished.³ Although BAT originates from the myogenic lineage,⁴ it shares many features of WAT that are discussed in this review. Because WAT is by far the largest depot in humans and, as a metabolically active, lipid storage and endocrine organ, its proper functioning is essential for health maintenance and is of primary importance for pharmaceutical and food industries.A better understanding of the mechanisms involved in adipocyte differentiation, dedifferentiation (defined as the acquisition of a more primitive phenotype and gain of cell proliferative ability)⁵ and even trans-differentiation (a process related to reversion of one cell phenotype into another, ie, from white to brown adipocytes,^6,7 which is still poorly experimentally documented), is required to unravel mechanisms underlying obesity and its symptomatic cohort of associated pathologies. This understanding may be used to develop new, original, and more effective therapeutic approaches that directly target intracellular pathways in adipocytes. Although the adipocyte differentiation program,⁸ as well as the activity/function and dys/malfunction of the endoplasmic reticulum (which play an important role in the adipocyte physiology) have been recently reviewed,⁹ the role of mitochondrial activity or dysfunction during preadipocyte differentiation and its consequences in mature adipocytes has hardly been addressed. Subcutaneous and visceral WATs have a different metabolic activity, depending on their anatomical position and mitochondrial content: epididymal (in the visceral depot) adipocytes are richer in mitochondria than inguinal (s.c.) adipocytes.¹⁰ In addition, mitochondria play a key role in physiological processes and are involved in the pathology of many diseases.¹¹ In compiling knowledge on mitochondria in the context of adipose tissue, we hope to stimulate thoughts in regards to the impact of mitochondrial activity in adipocyte biology, the effects of mitochondrial dysfunction/stress on adipocytes, and the subsequent alterations of systemic metabolic functions.     

Coenzyme Q as an antiadipogenic factor

Coenzyme Q (CoQ) is not only the single antioxidant synthesized in humans but also an obligatory element of mitochondrial functions. We have previously reported CoQ deficiency in white adipose tissue of ob/ob mice. We sought to determine (i) whether this deficit exists in all species and its relevance in human obesity and (ii) to what extent CoQ could be involved in adipocyte differentiation. Here we identified in rodents as well as in humans a specific very strong nonlinear negative correlation between CoQ content in subcutaneous adipose tissue and obesity indexes. This striking correlation reveals a threshold value similar in both species. This relative deficit in CoQ content in adipose tissue rapidly took place during the time course of high-fat-diet-induced obesity in mice. Adipocyte differentiation was assessed in vitro using the preadipocyte 3T3-F442A cell line. When CoQ synthesis was inhibited by a pharmacological approach using chlorobenzoic acid, this strongly triggered adipose differentiation. In contrast, adipogenesis was strongly inhibited when a long-term increase in CoQ content was obtained by overexpressing human 4-hydroxy benzoate acid polyprenyltransferase gene. Altogether, these data suggest that a strict level of CoQ remains essential for adipocyte differentiation, and its impairment is associated with obesity.     

Quantitative image analysis in adipose tissue using an automated image analysis system: differential effects of peroxisome proliferator-activated receptor-alpha and -gamma agonist on white and brown adipose tissue morphology in AKR obese and db/db diabetic mice

Morphometric analysis of adipocytes is widely used to demonstrate the effects of antiobesity drugs or anti-diabetic drugs on adipose tissues. However, adipocyte morphometry has been quantitatively performed by manual object extraction using conventional image analysis systems. The authors have developed an automated quantitative image analysis method for adipose tissues using an innovative object-based quantitative image analysis system (eCognition). Using this system, it has been shown quantitatively that morphological features of adipose tissues of mice treated with peroxisome proliferator-activated receptor (PPAR) agonists differ dramatically depending on the type of PPAR agonist. Marked alteration of morphological characteristics of brown adipose tissue (BAT) treated with GI259578A, a PPAR-alpha agonist, was observed in AKR/J (AKR) obese mice. Furthermore, there was a 22.8% decrease in the mean size of adipocytes in white adipose tissue (WAT) compared with vehicle. In diabetic db/db mice, the PPAR-gamma agonist GW347845X decreased the mean size of adipocytes in WAT by 15.4% compared with vehicle. In contrast to changes in WAT, GW347845X increased the mean size of adipocytes in BAT greatly by 96.1% compared with vehicle. These findings suggest that GI259578A may activate fatty acid oxidation in BAT and that GW347845X may cause adipocyte differentiation in WAT and enhancement of lipid storage in BAT.     

Evaluation of brown adipose tissue with intermolecular double-quantum coherence magnetic resonance spectroscopy at 3.0 T

In the current study, we propose a single-voxel (SV) magnetic resonance spectroscopy (MRS) pulse sequence, based on intermolecular double-quantum coherence (iDQC), for in vivo specific assessment of brown adipose tissue (BAT) at 3 T. The multilocular adipocyte, present in BAT, typically contains a large number of small lipid droplets surrounded by abundant intracellular water, while the monolocular adipocyte, present in white adipose tissue (WAT), accommodates only a single large lipid droplet with much less water content. The SV-iDQC sequence probes the spatial correlation between water and fat spins at a distance of about the size of an adipocyte, thus can be used for assessment of BAT, even when mixed with WAT and/or muscle tissues. This sequence for measurement of water-to-fat (water-fat) iDQC signals was tested on phantoms and mouse BAT and WAT tissues. It was then used to differentiate adipose tissues in the supraclavicular and subcutaneous regions of healthy youth human volunteers (n = 6). Phantom results with water-fat emulsions demonstrated enhanced water-fat iDQC signal with increased voxel size, increased energy level of emulsification, or increased distribution balance of water and fat spins. The animal tissue experiments resulted in obvious water-fat iDQC signal in mouse BAT, while this signal was almost absent in the WAT spectrum. The optimal choice of the dipolar coupling distance for the observation was approximately 100 μm, as tested on both emulsion phantom and animal tissue. The water-fat iDQC signals observed in the supraclavicular adipose tissues were higher than in the subcutaneous adipose tissues in healthy young volunteers (0.43 ± 0.36 vs. 0.10 ± 0.06, p = 0.06). It was concluded that the iDQC-based sequence has potential for assessment of mouse and human BAT at 3 T, which is of interest for clinical research and the diagnosis of obesity and associated diseases.     

自噬对烧伤创面愈合的影响

细胞自噬是细胞在应激状态下应用溶酶体对自身损伤细胞器等物质进行分解,将产生的大分子物质予以回收利用,从而保留细胞活性的降解过程。自噬在细胞的发育和分化进程中起着至关重要的作用。烧伤创面经历炎症期、细胞增殖期和组织重塑期3个时期完成组织愈合。细胞自噬在烧伤创面愈合过程中,具有促进病原体清除,参与新生血管增殖、肉芽组织形成,改善上皮的角质化以及瘢痕重塑的作用。调控自噬,可影响烧伤创面愈合。本文综述细胞自噬在烧伤创面愈合中的研究进展。     

Ⅱ型固有淋巴细胞在白色脂肪棕色化中的作用

正Ⅱ型固有淋巴细胞(typeⅡinnate lymphoid cells,ILC2s)于2001年被发现,由共同淋巴样祖细胞发育而来,广泛分布在血液、肠道、气管、肺脏、脾脏、肝脏、动物脂肪和皮肤等部位,经白细胞介素(interleukin,IL)-25或IL-33刺激后可产生IL-5和IL-13等2型辅助性T(type 2 helper T,Th2)细胞因子,在Th2     

Adipose tissue development: The role of precursor cells and adipogenic factors

Summary Obesity is regarded as a heterogeneous syndrome, which may appear in different forms. Various causes have been found to contribute to its pathogenesis. During recent years investigations of adipose tissue cellularity and its dynamic changes have gained growing interest. An important progress was the discovery of adipose tissue precursor cells. These cells have not yet been precisely identified by morphological and biochemical methods in intact tissue. However, due to methodological developments such precursor cells can be cultured both as primary cultures and as established cell lines. These culture systems have proven to be valuable models for the study of the processes involved in the formation of new fat cells.Abbreviations cAMP Cyclic adenosine monophosphate - cDNA Complementary desoxyribonucleic acid - DHAP Dihydroxy-acetone phosphate - GPDH Glycero-3-phosphate dehydrogenase - IGF-I Insulin-like growth factor I - MIX 1-Methyl-3-isobutylxanthine - mRNA Messenger ribonucleic acid - TNF Tumor necrosis factor Experiments carried out in the authors' laboratories and published in this review were supported by the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 43 Terms: A number of terms have been used to describe the process of adipocyte development. These are defined as follows [11]:Adipoblast: the pluripotent mesenchymal stem cell of the adipose tissue, which at present is still putative and has not been identified biochemically and morphologicallyPreadipocyte: the cell already committed or determined to become a fat cell with the ability to synthesize lipogenic enzymes and to store lipids; these cells may even contain small lipid droplets or become quickly filled with triglyceridesAdipocyte precursor cells: a precise distinction between adipoblast and preadipocyte is usually not possible and therefore this term is frequently used to describe both differentiation phases, particularly in primary cultureAdipocyte: a cell with a central large lipid vacuole, showing the characteristic signet-ring form, with high activities for enzymes of triglyceride synthesis and releaseDetermination or commitment: the irreversible recruitment of the pluripotent stem cell to a preadipocyte, which may be preceded by one or more cell divisionsAdipogenic conversion: the development of a preadipocyte to the morphological and biochemical appearance of an adipocyte by the expression of a genetic programAdipogenic (adipose) differentiation: the continuous gradual development of an adipoblast to a mature fat cell     

Tissue engineering of white adipose tissue using hyaluronic acid-based scaffolds. I: in vitro differentiation of human adipocyte precursor cells on scaffolds

BACKGROUND AND AIM OF THE STUDY: Reconstruction of soft tissue defects is a challenge in plastic surgery and there is clinical need for adequate solutions. Aim of this study was to develop a biohybrid construct consisting of hyaluronic acid-based scaffolds and human adipocyte precursor cells as a soft tissue filler. METHODS: Human adipocyte precursor cells were obtained by collagenase digestion of adipose tissue samples and seeded on hyaluronic acid-based spongy scaffolds of various degrees of esterification and pore size using different techniques. After cell attachment, adipose differentiation was induced by defined adipogenic factors under serum-free culture conditions. RESULTS: Among the five different scaffold types under investigation the highest cell attachment rate was observed for the HYAFF scaffold with 100% esterification and a mean pore size of 400microm (HYAFF 11lp). For inoculation of human adipocyte precursor cells on hyaluronic acid-based scaffolds a "drop-on" technique and low-pressure centrifugation using a Speed Vac airfuge were compared. With respect to efficacy, cell distribution and simpleness the drop-on method proved to be the method of choice. In a serum-free medium supplemented with 66nM insulin, 100nM cortisol and 1microg/ml troglitazone a substantial proportion of cells underwent adipose differentiation as assessed by lipid accumulation and emergence of glycerol-3-phosphate dehydrogenase activity, a lipogenic marker enzyme. CONCLUSION: Hyaluronic acid-based scaffolds appear to be a suitable three-dimensional carrier for the culture and in vitro differentiation of human adipocyte precursor cells.     

Concise review: adipocyte origins: weighing the possibilities

Adipose tissue is the primary energy reservoir in the body and an important endocrine organ that plays roles in energy homeostasis, feeding, insulin sensitivity, and inflammation. While it was tacitly assumed that fat in different anatomical locations had a common origin and homogenous function, it is now clear that regional differences exist in adipose tissue characteristics and function. This is exemplified by the link between increased deep abdominal or visceral fat, but not peripheral adipose tissue and the metabolic disturbances associated with obesity. Regional differences in fat function are due in large part to distinct adipocyte populations that comprise the different fat depots. Evidence accrued primarily in the last decade indicates that the distinct adipocyte populations are generated by a number of processes during and after development. These include the production of adipocytes from different germ cell layers, the formation of distinct preadipocyte populations from mesenchymal progenitors of mesodermal origin, and the production of adipocytes from hematopoietic stem cells from the bone marrow. This review will examine each of these process and their relevance to normal adipose tissue formation and contribution to obesity-related diseases.     

自噬在免疫及免疫相关疾病中的研究进展

自噬是细胞内溶酶体/内体参与的,涉及细胞增殖,分化及稳态平衡调节的降解过程.遗传学研究发现其在物种进化过程中较保守,从酵母到哺乳动物细胞中均有自噬相关基因的存在,提示自噬广泛参与各类生物正常的生理过程.近年来,随着研究的不断深入,人们发现自噬在许多疾病尤其在免疫相关疾病中亦扮演着重要角色,在感染,自身免疫,肿瘤免疫中所起的作用可为今后研究提供依据.     

In vivo differentiation of brown adipocytes in adult mice: An electron microscopic study

The differentiation of brown adipocyte precursor cells was studied in interscapular brown adipose tissue of adult mice by electron microscopy. Different stages of cell differentiation were characterized in situ. Previous autoradiographic studies suggested that interstitial cells represent the precursor cells of fully differentiated brown adipocytes. The present observations provide morphological evidence for a progressive differentiation of interstitial stem cells into mature brown adipocytes. Four typical stages of development were identified: (1) interstitial cells, (2) protoadipocytes, (3) preadipocytes, and (4) mature brown adipocytes. Interstitial stem cells were small spindle shaped cells, situated between brown adipocytes and characterized by a high nuclear-cytoplasmic ratio, the scarcity of organelles, and the absence of lipid inclusions. Protoadipocytes resembled interstitial cells except that they contained a few tiny lipid droplets in their cytoplasm. Preadipocytes had a larger cytoplasm enclosing many mitochondria and lipid droplets; the smooth endoplasmic reticulum was well developed surrounding the lipid droplets, and was closely associated with the mitochondria. Preadipocytes had the typical structure of growing cells, developing long cytoplasmic processes between and around blood capillaries. Mature brown adipocytes represented the final stage of differentiation. Almost all their cellular volume was occupied by lipid droplets and numerous mitochondria with very dense cristae. Brown adipocytes were also characterized by a tight association with blood capillaries, as expected from metabolically active cells requiring oxygen and substrates. These observations provide direct ultrastructural evidence for a progressive differentiation of interstitial cells into brown adipocytes with a continuum of intermediate cellular types.     

Brown adipocyte precursor cells: a morphological study

The origin of brown adipocyte precursor cells is to date unknown. Some authors believe they arise from vascular cells, others from interstitial cells. The purpose of the present ultrastructural study was to find markers in rat fetal and perinatal adipose tissue that can be used to identify brown adipose precursor cells. The study was carried out on the interscapular brown adipose tissue of fetal (fetuses of 19 and 21 days) and perinatal rats (pups of 4 and 12 hours and of 1, 3, 5, 7, 9, 11, 13, and 15 days). The analysis focused on stem cells and showed the characteristic presence of typical mitochondria which make their identification as brown adipocyte precursor cells inequivocal. These cells were frequently observed in a pericytic position. Also some endothelial cells were characterised by typical mitochondria and abundant glycogen. These data seem to support the hypothesis that brown adipocytes originate from vascular cells.