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The level of the intracellular cholesterol rather than the method of cholesterol release functions as a repressor or activator of the genes that regulate cholesterol in cells. The rate of change in mRNA levels, protein content and the activity of regulatory proteins is the same when rat ovary granulosa cells are cultured with lipoproteins, hLDL or hHDL3. The pretreatment with either of the lipoproteins results in down-regulation of B/E-receptor and HMG CoA reductase proteins and an increase in acyl-CoA:cholesterol acyltransferase activity.

A study was conducted on the reconstitution of the lipoprotein cholesteryl ester transfer process using a purified plasma preparation extracted from rat luteinized ovaries. The results showed that all the lipoproteins examined were capable of acting as cholesteryl ester donors. Furthermore, the transfer process was found to be specific for cholesteryl ethers and ethers and independent of lipoprotein core lipids. The results suggest that a reconstituted lipoprotein-plasma membrane system can reenact the cholesteryl extraction process.

Abstract Background The plasma membrane scavenger receptor, SR-BI, mediates the 'selective uptake' process by which cholesteryl esters (CE) from exogenously supplied HDL are taken up by target cells. Recent work suggests that dimer and higher order oligomeric forms of the SR-BI protein are important to this process. SR-BI has been shown to be particularly associated with microvilli and microvillar channels found at the cell surface of steroidogenic cells, and a study with the hormone stimulated adrenal gland has shown impressive changes in the size and complexity of the microvillar compartment as the mass of CE uptake (and accompanying steroidogenesis) fluctuates. In the present study, we examine a cell line in which we overexpress the SR-BI protein to determine if morphological, biochemical and functional events associated with SR-BI in a controlled cell system are similar to those observed in the intact mammalian adrenal which is responsive to systemic factors. Methods Y1-BS1 mouse adrenocortical cells were transiently transfected using rat SR-BI-pcDNA6-V5-His, rat SR-BI-pcDNA6-cMyc-His or control pcDNA6-V5-His vector construct using a CaPO4 precipitation technique. Twenty four hours after transfection, cells were treated with, or without, Bt2cAMP, and SR-BI expression, CE uptake, and steroidogenesis was measured. SR-BI dimerization and cell surface architectural changes were assessed using immunoelectron microscopic techniques. Results Overexpression of the scavenger receptor protein, SR-BI, in Y1-BS1 cells results in major alterations in cell surface architecture designed to increase uptake of HDL supplied-CEs. Changes include 1 the formation of crater-like erosions of the surface with multiple double membraned channel structures lining the craters, and 2 dimerized formations of SR-BI lining the newly formed craters and associated double membraned channels. Conclusion These data show that overexpression of the scavenger receptor protein, SR-BI (accompanied by suitable hormone treatment and lipoproteins) in susceptible mammalian cells – is associated with increased cholesterol uptake and SR-BI dimerization within a much enlarged and architecturally complex microvillar compartment. These changes duplicate the structural, biochemical and functional changes related to the uptake of HDL CEs normally signaled by the action of ACTH on intact adrenal tissue.

Hormone-sensitive lipase (HSL) hydrolyzes triglyceride (TG) in adipose tissue. HSL is also expressed in heart. To explore the actions of cardiac HSL, heart-specific, tetracycline (Tc)-controlled HSL-overexpressing mice were generated. Tc-responsive element-HSL transgenic (Tg) mice were generated and crossed with myosin heavy chain (MHC) [Alpha]-tTA Tg mice, which express the Tc-responsive transactivator (tTA) in the heart. The double-Tg mice (MHC-HSL) were maintained with doxycycline (Dox) to suppress Tg HSL. Upon removal of Dox, cardiac HSL activity and protein increased 12- and 8-fold, respectively, and the expression was heart specific. Although cardiac TG content increased twofold in control mice after an overnight fast, it did not increase in HSL-induced mice. Electron microscopy showed numerous lipid droplets in the myocardium of fasted control mice, whereas fasted HSL-induced mice showed virtually no droplets. Microarray analysis showed altered expression of cardiac genes for fatty acid oxidation, transcription factors, signaling molecules, cytoskeletal proteins, and histocompatibility antigens in HSL-induced mice. Thus cardiac HSL plays a role in controlling accumulation of triglyceride droplets and can affect the expression of a number of cardiac genes. hormone-sensitive lipase; gene expression; microarray analysis

The purpose of this study was to determine if exercise training of 12-month-old Sprague-Dawley rats could reverse the resistance to insulin-induced glucose uptake that has been shown to occur in these animals. Twelve-month-old rats were trained to run 1½ miles/day in motorized exercise wheel cages, and the ability of insulin to stimulate glucose uptake in these rats was compared with values observed in two groups of similar aged sedentary rats — one fed rat chow ad libitum and the other a calorie-restricted diet for 4 months. Body weight increased and insulin-stimulated glucose uptake decreased as rats fed chow ad libitum grew from 12 to 16 months of age. In contrast, 4 months of either exercise training or calorie restriction prevented weight gain and loss of insulin-stimulated glucose uptake. Thus, the intensity of exercise training attained in this study did not result in an improvement in insulin action in older rats above and beyond that related to the reduction in rate of body weight gain [ABSTRACT FROM PUBLISHER]

We have previously shown that aging is associated with a marked decrease in glucose-stimulated insulin release by the β-cell. To determine whether this age-related defect occurs with other insulin secretagogues, we have investigated leucine-stimulated insulin release. Islets of langerhans were isolated from 2-and 12-month-old rats, and incubated with 5-20 mM leucine or with 16.7 mM glucose. Islets from 12-month-old rats showed a decline in rate of leucine-induced insulin secretion as compared to islets of 2-month-old donors (i.e., mean (± SEM) insulin secretion at 20 mM leucine was 0.79 (± 0.06) and 1.17 (± 0.09) μU/min/islet), respectively for 12-and 2-month-old rats. β-cell number is increased in islets from 12-month-old donors, and when this increase is taken into account, the average β3-cell from 12-month-old donors secretes only one-half the rate of β-cells from 2-month-old donors. These findings are comparable to those seen after glucose-stimulation, and emphasize the potential global nature of the age-related defect in β-cell function. [ABSTRACT FROM PUBLISHER]