Adipocytes cells

The most immature cells remain in the adherent layer that is described as cobblestone areas, and are released to the growth media upon division and maturation. Major cell types in the cellular environment are macrophages, adipocytes cells and blanket cells. From the cobblestone areas hematopoietic cells are released into the growth media until the cultures begin to decline (8 weeks or later). Sign that the hematopoietic activity is declining is predominance of macrophages in the non-adherent cell population and decline of hematopoietic cell foci in the adherent layer (Dexter 1982). 

In an in vitro study in an adipocyte cell line (3T3L1 cells), >75% of the 2,2, 4,4, 5,5 -hexabromobiphenyl taken up by the cells was associated with subcellular fractions that contained 85% of the cellular triglyceride, with only 20% of the compound found in the microsomal plasma-membrane fraction (Kraus and Bernstein 1986). This study also found that inhibition of respiration by cyanide at a concentration that completely inhibited oxygen consumption did not affect uptake of 2,2, 4,4, 5,5 -hexabromobiphenyl, supporting the assumption that because of their lipophilic nature, PBBs penetrate membranes by passive diffusion. 

Vanadate stimulates protein kinases in the cytosol, as demonstrated in adipose cells and extracts. The activation of a membrane and cytosolic protein tyrosine kinase have been demonstrated in adipocytes, and the membranous enzyme has been postulated to be a way to involve PI-3K actions without activation of insulin receptor substrate-1 (IRS-1) in the insulin signal transduction pathway [140], It is always difficult to determine if protein kinase activation is direct or the result of stimulation of a protein phosphatase. The fact that kinase stimulation was seen in isolated extracts after cell disintegration in this adipocyte cell system supports the idea that vanadium addition to cells could directly stimulate kinases via an as-yet-undetermined mechanism. In other experiments with 3T3-L1 adipocytes bis(acetylacetonato)oxovana-dium (IV) BMOV and bis(l-N-oxide-pyridine-2thiolato)oxovanadium (TV) caused increased tyrosine phosphorylation of both the insulin receptor and IRS-1 in a synergistic way with insulin, as measured by antibodies to phosphotyrosine residues [141]. 

Recent advances in molecular and cell biology have shown that adipose tissue not only stores excess energy in the form of fat, but also secretes physiologically active substances called adipocytokines (Matsuzawa et al., 1999). In obesity, adipocytes (cells of adipose tissues) are increased and enlarged, and they secrete excessive amounts of inflammatory adipocytokines, such as tumor necrosis factor-alpha (Hotamisligil et al., 1993) and monocyte chemoattractant protein-1 (Sartipy and Loskutoff, 2003). This induces type-2 diabetes, such as... 

Chaudhry A, MacKenzie RG, Georgic LM, Granneman JG. Differential interaction of Pi - and p3-adrenergic receptors with Gj in rat adipocytes. Cell Signal 1994 6 457 165. 

Viravaidya K, Shuler ML. Prediction of naphthalene bioaccumulation using an adipocyte cell line model. Biotechnol Prog 2002 18 174-81. 

Spiegelman BM, Ginty CA (1983) Fibronectin modulation of cell shape and lipogenic gene expression in 3T3-adipocytes. Cell 35(3 Pt 2) 657-666... 

The expression of HSL protein and mRNA levels are lower in subcutaneous fat stores compared wifh internal (visceral, omental) fat depots in the rat [288], suggesting a possible basis for the differences in the rate of lipolysis among various fat depots. In contrast, subcutaneous fat in humans has a higher HSL mRNA expression and HSL activity than omental fat [293]. Human subcutaneous fat cells are larger and fhere is a positive correlation between fat cell size and HSL expression [293]. When controlled for adipocyte cell size, the amount of HSL protein and HSL mRNA levels in subcutaneous adipocytes show a strong correlation with maximum lipolytic activity [294]. 

Bensaid M, Gary-Bobo M, Esclangon A, Maffrand JP, Le Fur G, Oury-Donat F, Soubrie P (2003) The cannabinoid CBI receptor antagonist SR141716 increases Acrp30 mRNA expression in adipose tissue of obese fa/fa rats and in cultured adipocyte cells. Mol Pharmacol 63 908-914... 

A GPl-anchor may also allow a protein to be selectively released from the cell surface upon hydrolysis by a GPI-specific phospholipase (e.g., Pl-phospholipase C or GPl-phospholipase D). This has been shown to occur for certain GPI-anchored proteins in mammalian cell culture. One example is GPI-anchored membrane dipeptidase which is released from the adipocyte cell surface by a phospholipase C in response to insulin (S. Movahedi, 2000). Interestingly, other GPI-anchored proteins are not released, indicating a level of regulation in insulin-stimulated hydrolysis of GPI-anchored proteins. GPI-anchored molecules have also been shown to transfer between cells and stably insert in the external leaflet of the acceptor cell s plasma membrane (M.G. Low, 1998). The biological significance of this event is unclear however, the ability of GPI-anchored proteins to transfer between cells has implications for the expression of foreign proteins on the cell surface. 

Fig. 14.2. 2-Deoxyglucose uptake in 3-d-old differentiating 3T3-L1 adipocytes. Cells were treated with individual CLA isomers or a mixture of equal amounts of c9,tH and fl0,cl2 CLA (a prepared isomer mixture or "typical CLA/ which contains both isomers in about equal amounts) for 24 h. Insulin treatment was for 20 min. 2-Deoxyglucose uptake was measured after 10 min of incubation in buffer. Values are means SEM from two or more independent experiments performed in triplicate, normalized to untreated control., Significantly different from representative controls (P< 0.05).

A cDNA encoding adipophilin was identified in cultured human macrophages stimulated with oxidised LDL using mRNA differential display (Wang et al. 1999). Adipophihn is a 50 kDa protein known to be a specific marker for adipocyte cell differentiation and hpid accumulation in a variety of cells. The time-dependent induction of adipophilin mRNA in macrophages was specific to oxidised LDL but not native LDL, and not to various cytokines and serum. In human atherosclerotic lesions, adipophihn mRNA expression was locahsed in the subset of hpid-rich macrophages. 

Figure 21.5. Human pre-adipocyte (derived fromfresh human bone marrow) culture inside mineralized chitosan-coated alginate cap>sules (n=12). A) A single whole capsule containing 450,000 pre-adipocytes at 24 hours. Pre-adipocyte cells are metabolically very active and exapnd in numbers rapidly after encapsulation. B) Embedded pre-adipocytes produce rounded colonies containing dense oil droplet formations in complete (+single insulin dose) media at day 21. C) Oil droplets stained with oil red-O to indicate presence of fat inside observed droplets at day 12. D) Oil-droplet formation from same population of cells grown in 2D mono-layer culture at day 21.

Also, Yoshida et al. [67] observed that 3T3-L1 adipocytes cell culture treatment with hesperetin and naringenin analytical standards showed anti-inflammatory effect. NFkB activation through TNF-a was inhibited with a consequent reduction in the secretion of interleukin-6 (IL-6). There was also observed an inhibition of ERK (extracellular signal regulated kinase) pathway causing a decreased activation of hormone sensitive lipase (HSL) contributing to reduce the insulin resistance. 

The pathways for liberation of fatty acids from triacylglycerols, either from adipose cells or from the diet, are shown in Figures 24.2 and 24.3. Fatty acids are mobilized from adipocytes in response to hormone messengers such as adren-... 

The term adipokine refers to any protein secreted from adipocytes [1]. Collectively, the various adipokines form the adipokinome which together with the lipid moieties secreted from fat cells (e.g. fatty acids, cholesterol, retinol) constitute what can be referred to as the secretome of adipocytes. Most adipokines are also secreted from other cell types in other organs, but one in particular - adiponectin - is considered to be exclusive to adipocytes. 

The wide range of inflammatory and immune factors secreted by adipocytes has led to the view that there are many similarities between these cells and cells of the immune system. 

The thiazolidinediones have also been reported to act as inhibitors of the respiratory chain at high concentrations, and this appears to account for their ability to activate AMGPK in cultured cells. However, the primary target of the thiazolidinediones appears to be the peroxisome proliferator-activated receptor-y ( PPAR-y), a member of the nuclear receptor superfamily expressed in adipocytes. One of the major effects of stimulation of PPAR-y in adipocytes is the release ofthe... 

AQP7 is expressed in the proximal tubule of the kidney, testis, gastrointestinal tract, immature dendritic cells and ear. This glycerol channel is also highly expressed in adipocytes where it is thought to control the release of triglycerides. 

Obesity and hyperglycemia 2. 2-AG levels are elevated in mouse adipocytes and epididymal of mice with DIO. AEA and 2-AG levels are elevated in rat insulinoma p-cells, in pancreas of mice with DIO, and in obese women. Patients with obesity or hyperglycaemia caused by type 2 diabetes exhibit elevated levels of 2-AG or of both endocannabinoids in visceral fat or blood, respectively. AEA levels are elevated in the liver of DIO mice 2. CB1 antagonists... 

Fatty Acid Transporters. Figure 2 Quencher-based real-time fatty acid uptake assay with a fluorescently labeled FFA analogue (C1-Bodipy-C12). Predominantly protein-mediated fatty acid uptake by 3T3-L1 adipocytes (diamonds) was compared with diffusion-driven uptake by fibroblasts (squares) using the QBT Fatty Acid Uptake reagent (Molecular Devices Corp., CA, USA), which contains C1-Bodipy-C12 as substrate in conjunction with a cell impermeable quencher. Uptake kinetics was recorded using a Gemini fluorescence plate reader. Error bars indicate the standard deviations from 12 independent wells. RFU relative fluorescence units. 

The insulin receptor is a transmembrane receptor tyrosine kinase located in the plasma membrane of insulin-sensitive cells (e.g., adipocytes, myocytes, hepatocytes). It mediates the effect of insulin on specific cellular responses (e.g., glucose transport, glycogen synthesis, lipid synthesis, protein synthesis). 

The cytokine leptin is secreted by adipocytes (fat cells) in proportion to the size of the adipose dq>ot and circulates via the bloodstream to the brain, where it ultimately affects feeding behavior, endocrine systems including reproductive function and, at least in rodents, energy expenditure. The major effect of Lqrtin is on the hy-pothalamous, where it suppresses appetite and hence food intake. Leptin exerts its effects via binding to the leptin receptor in the brain (specifically in the hypothalamus), which activates the JAK-STAT Pathway. 

OTRs are mainly expressed in myoepithelial cells of the galactiferus channels and the myometrium. The OTRs in vascular endothelial cells, renal epithelial cells (macula densa, proximal tubule) and cardiomyocytes induce the production of NO (vasodilation), natriuresis and release of ANP, respectively. The endometrium, ovary, amnion, testis, epididymis, prostate and thymus also express the OTR supporting a paracrine role of this peptide. Osteoblasts, osteoclasts, pancreatic islets cells, adipocytes, and several types of cancer cells also express OTRs. More over, expression of the OTR... 

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