Article by Peter Hutch
Adipose tissue is infiltrated with macrophages, and its content of long-chain triacylglycerols and ceramides is increased in subjects with increased LFAT compared with equally obese subjects with normal LFAT content. Ceramides or their metabolites could contribute to adverse effects of long-chain fatty acids on insulin resistance and inflammation.
Adipose tissue is specialized connective tissue that functions as the major storage site for fat in the form of triglycerides. Adipose tissue is found in mammals in two different forms: white adipose tissue and brown adipose tissue. The presence, amount, and distribution of each varies depending upon the species. Most adipose tissue is white, the focus of this review.
Adipose tissue is primarily located beneath the skin, but is also found around internal organs. In the integumentary system, which includes the skin, it accumulates in the deepest level, the subcutaneous layer, providing insulation from heat and cold.Connective tissue composed of adipocytes that stores energy in the form of fat and cushions and insulates the body.
Brown adipose tissue is sometimes mistaken for a type of gland, which it resembles more than white adipose tissue. It varies in color from dark red to tan, reflecting lipid content. Its lipid reserves are depleted when the animal is exposed to a cold environment, and the color darkens. In contrast to white fat, brown fat is richly vascularized and has numerous unmyelinated nerves which provide sympathetic stimulation to the adipocytes.
Fat also serves a structural purpose. Approximately four percent of body weight is made up of fat in the organs, skeletal muscles, and central nervous systems. This fat is sometimes referred to as “essential fat” because these organs will stop functioning if it is depleted. Having too little fat is a health hazard. The risk of premature death begins to mount when body mass index (BMI) drops below 18. (BMI is calculated by multiplying weight in pounds by 700 and dividing the product by the square of height in inches.)
Adipose tissues at the L3 vertebra were quantified by magnetic resonance imaging. With weight reduction there was a significant decrease (P < 0.05) in body mass index, waist circumference, and visceral adipose tissue. The plasma concentrations of total cholesterol, triglyceride, insulin, and lath sterol also significantly decreased.
Tissue and cellular investigations, driven by the analysis of transcriptional interactions, revealed an increased amount of interstitial fibrosis in obese WAT, associated with an infiltration of different types of inflammatory cells, and suggest that phenotypic alterations of human pre-adipocytes, induced by a pro-inflammatory environment, may lead to an excessive synthesis of ECM components.
Adipose tissue requires lipolytic enzymes. Dysfunctional lipolysis affects energy homeostasis and may contribute to the pathogenesis of obesity and insulin resistance. Until now, hormone-sensitive lipase (HSL) was the only enzyme known to hydrolyze triglycerides in mammalian adipose tissue. Here, we report that a second enzyme, adipose triglyceride lipase (ATGL), catalyzes the initial step in triglyceride hydrolysis. It is interesting that ATGL contains a “patatin domain” common to plant acyl-hydrolases. ATGL is highly expressed in adipose tissue of mice and humans.
White adipose tissue (WAT), now considered as a pivotal endocrine organ, contributes to the systemic inflammation by producing biomolecules, including pro-inflammatory mediators, whose estimated number grows constantly and whose synthesis is altered along with the expansion of the adipose tissue. These molecules are delivered into the blood stream and exert metabolic and immune functions, as illustrated by the extensively studied adipose hormones leptin and adiponectin. Their functions are essential for inter-organ cross-talk, body weight homeostasis and probably in linking adipose tissue to the downstream complications associated with obesity.
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