ENDOCRINOLOGÍA Y NUTRICIÓN Adipose tissue: Cell heterogeneity and functional diversity (original) (raw)
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White Adipose Tissue as Endocrine Organ and Its Role in Obesity
Archives of Medical Research, 2008
Due to the public health problem represented by obesity, the study of adipose tissue, particularly of the adipocyte, is central to the understanding of metabolic abnormalities associated with the development of obesity. The concept of adipocyte as endocrine and functional cell is not totally understood and can be currently defined as the capacity of the adipocyte to sense, manage, and send signals to maintain energy equilibrium in the body. Adipocyte functionality is lost during obesity and has been related to adipocyte hypertrophy, disequilibrium between lipogenesis and lipolysis, impaired transcriptional regulation of the key factors that control adipogenesis, and lack of sensitivity to external signals, as well as a failure in the signal transduction process. Thus, dysfunctional adipocytes contribute to abnormal utilization of fatty acids causing lipotoxicity in non-adipose tissue such as liver, pancreas and heart, among others. To understand the metabolism of the adipocyte it is necessary to have an overview of the developmental process of new adipocytes, regulation of adipogenesis, lipogenesis and lipolysis, endocrine function of adipocytes and metabolic consequences of its dysfunction. Finally, the key role of adipose tissue is shown by studies in transgenic animals or in animal models of diet-induced obesity that indicate the contribution of adipose tissue during the development of metabolic syndrome. Thus, understanding of the molecular process that occurs in the adipocyte will provide new tools for the treatment of metabolic abnormalities during obesity. Ó 2008 IMSS. Published by Elsevier Inc.
ARTICLE IN PRESS +Model Adipose tissue and adipocyte dysregulation
Obesity-associated insulin resistance is a complex disorder involving a number of candidate molecules, pathways and transduction systems possessing potential causal actions. Inflammation in adipose tissue (AT) is one mechanism proposed to explain the development of insulin resistance, while identification of factors that lead to or cause AT dysfunction when it reaches its limit of expansion represents an important challenge. Pathological expansion of AT is characterized by changes in its blood flow, and the presence of enlarged and dysfunctional adipocytes that begin an inflammatory campaign of altered adipokine and cytokine secretions. Adipocyte senescence, necrosis and death are associated with increased immune cell and macrophage infiltration of AT in obesity. This can boost inflammation and reinforce fat cell dysfunction and death. In addition, pathological fat mass expansion is also related to limited recruitment of fat cell progenitors able to proliferate and differentiate into healthy small fat cells to compensate for cell death and preserve adipocyte numbers. Limiting vascular development and enhancing fibrotic processes worsen inflammation towards chronic irreversibility. The AT expandability hypothesis states that failure of AT expansion is one of the key factors linking positive energy balance and cardiometabolic risks, not obesity per se. Besides the usual treatment of obesity based on behavioral approaches (specific dietary/nutritional approaches together with increased physical activity), a number of questions remain concerning the possible recovery of metabolic health after inflammation-preventing interventions.
Adipose tissue as an endocrine organ: from theory to practice
Jornal De Pediatria, 2007
To describe the advances in research into the physiological role of white adipose tissue, with emphasis on its endocrinal role in inflammatory processes, feeding behavior, insulin sensitization and modulation of the atherogenetic process. To deal with the potential role of adipose tissue as a source of stem cells for regeneration of tissues, with special emphasis on adipogenesis and its consequences for development of obesity.
The interplay between nutrients and the adipose tissue
Proceedings of the Nutrition Society, 2007
The importance of adipose tissue in health as well as disease has been demonstrated in several studies recently, and it has become appropriate to use the term 'adipose organ' when referring to adipose tissue as a whole. The obesity epidemic, with a marked increase in the incidence of the metabolic syndrome leading to diabetes type 2 as well as cardiovascular complications, has stimulated considerable interest in adipose tissue biology. Moreover, several studies in different species have shown that limited energy intake is associated with less inflammation, improved biomarkers of health and a marked increase in longevity. In addition, there is convincing evidence that an optimal amount of adipose tissue is essential for many body functions such as immune response, reproduction and bone quality. Some nutrients and their metabolites are important as energy sources as well as ligands for many transcription factors expressed in adipose tissue, including all energy-providing nutrients both directly and indirectly as well as cholesterol, vitamin E and vitamin D. In particular, fatty acids can be effectively taken up by adipocytes and they can interact with several transcription factors crucial for growth, development and metabolic response, e.g. PPARa, -d and -g, sterol regulatory elementbinding proteins1 and 2 and liver X receptors a and b). Moreover, glucose is also readily taken up and stored as fatty acids via lipogenesis in adipocytes. It is known that some metabolic signals released as proteins from adipose tissue (adipokines) are important for normal as well as pathological responses to the amount of energy stored in the adipose organ. The future challenge will be to understand the function of adipose tissue in energy homeostasis and the interplay with nutrients in order to be able to give optimal advice for the prevention and treatment of obesity.
Human Pathology, 1970
The size of the fat depot provides a morphologic index of its metabolic activity. It may be tentatively generalized that the perirenal, epicardial, orbital, plantar, and cheek adipose tissues are metabolically less active than subcutaneous, mesenteric, omental, and eventually other internal depots. The relative number of adipocytes and of potential fat ceIl precursors is not the factor primarily responsible for differences in function or degree of function of the individual depots. In both accumulation and release of particulate material a major role is presumably played by the changeable profile of the ectoplasmic membrane of the fat cell. The rate of blood flow and volume of vascular bed are equally important, but probably the most important factor rests in the adrenergic activity of the tissue, that is to say the extent of sympathetic innervation.
Endocrinology of Adipose Tissue - An Update
Hormone and Metabolic Research, 2007
Endocrinology of Adipose Tissue-An Update ures and of specifi c drugs that may be able to restore the dysregulated endocrine system of adipose tissue. It was hoped that through prevention and intervention the deleterious sequelae of obesity and, in particular, of the visceral accumulation of body fat, might be avoided. Five years later, more than one hundred adipose tissue secretion products have been described including fatty acids, prostaglandins, and steroids, as well as complex proteins (᭹ ᭤ Fig. 1). Some of these factors primarily have local auto-or paracrine effects in adipose tissue, while others are released into the circulation and exert specifi c effects at target organs or systemic effects. In this review, we present an overview of the endocrine functions of adipose tissue with special focus on fi ndings obtained within the past 5 years. Old and new fi ndings of adipose tissue cellularity & Adipose tissue mass is determined by competing processes regulating both the volume and the number of adipocytes. For many years the dogma claimed that the number of adipocytes is fi xed during childhood, and remains constant throughout life. According to this model, changes in size of adipose tissue could only be achieved by modulation of adipocyte volume, which in turn is bal-Authors P.
European Journal of Endocrinology, 2014
In mammals, adipocytes are lipid-laden cells making up the parenchyma of the multi-depot adipose 3 organ. White adipocytes store lipids for release as free fatty acids during fasting periods; brown 4 adipocytes burn glucose and lipids to maintain thermal homeostasis. A third type of adipocyte, the 5 pink adipocyte, has recently been characterised in mouse subcutaneous fat depots during pregnancy 6 and lactation. Pink adipocytes are mammary gland alveolar epithelial cells whose role is to produce 7 and secrete milk. Emerging evidence suggests that they derive from the transdifferentiation of 8 subcutaneous white adipocytes. The functional response of the adipose organ to a range of 9 metabolic and environmental challenges highlights its extraordinary plasticity. Cold exposure 10 induces an increase in the "brown" component of the organ, to meet the increased thermal demand; 11 in states of positive energy balance the "white" component expands to store excess nutrients; 12 finally, the "pink" component develops in subcutaneous depots during pregnancy to ensure litter 13 feeding. At the cell level plasticity is provided not only by stem cell proliferation and differentiation 14 but also, distinctively, by direct transdifferentiation of fully-differentiated adipocytes by stimuli that 15 induce genetic expression reprogramming and through it a change in phenotype and, consequently, 16 function. A greater understanding of adipocyte transdifferentiation mechanisms would have the 17 potential to shed light on their biology as well as inspire novel therapeutic strategies against 18 metabolic syndrome ("browning") and breast cancer ("pinking"). 19 20 21 22