Effect of lipoproteins on cholesterol synthesis in rat Sertoli cells

1995 ◽  
Vol 73 (1-2) ◽  
pp. 67-72 ◽  
Author(s):  
Jean-Claude Maboundou ◽  
Mohamed Fofana ◽  
Jacqueline Fresnel ◽  
Jean Bocquet ◽  
Dominique Le Goff
Keyword(s):  
Sertoli Cells ◽  
Free Cholesterol ◽  
Low Density Lipoproteins ◽  
High Density ◽  
High Density Lipoproteins ◽  
Low Density ◽  
Coated Pits ◽  
Apo B ◽  
Blood Capillaries ◽  
Apo E

Lipoprotein metabolism has been investigated in cultured rat Sertoli cells. Cells incubated with low-density lipoproteins (LDLs) or high-density lipoproteins (HDLs) showed a concentration-dependent decrease of sterol synthesis, indicating a net cholesterol delivery to the Sertoli cells. At 50 μg/mL, lipoproteins inhibited the incorporation of [14C]acetate into free cholesterol by 83% for the LDL and 47% for the HDL. Electron microscopic examinations of the Sertoli cells provide evidence of the internalization of gold-labelled HDL into coated pits and coated vesicles. Competitive studies between human LDL and rat HDL indicate that Sertoli cells take up cholesterol from LDL and HDL containing apolipoprotein (apo) E by common pathways. These results suggest that Sertoli cells possess apo B and E receptors for the uptake and degradation of LDL and HDL, although the basement membrane excludes the passage of LDL from blood capillaries to the Sertoli cells. At 50 μg/mL, apo-E-depleted HDL inhibited the incorporation of [14C]acetate into free cholesterol by 34%. Thus, this study shows that Sertoli cells are capable of taking up apo-E-depleted HDL cholesterol for cell metabolism.Key words: high-density lipoproteins, low-density lipoproteins, rat Sertoli cell.

Variations in the composition of low- and high-density lipoproteins during the acute phase of myocardial infarction.

1988 ◽  
Vol 34 (1) ◽  
pp. 139-140 ◽  
Author(s):  
F Mainard ◽  
Y Madec ◽  
N Robinet
Keyword(s):  
Myocardial Infarction ◽  
Acute Phase ◽  
Apolipoprotein B ◽  
Low Density Lipoproteins ◽  
High Density ◽  
Apolipoprotein A1 ◽  
High Density Lipoproteins ◽  
Low Density ◽  
Apo B ◽  
B Values

Abstract We analyzed correlations between apolipoprotein B (apo B), cholesterol and phospholipids (preponderant lipids) in low-density lipoproteins (LDL) as well as between apolipoprotein A1 (apo A1) and these same lipids in high-density lipoproteins (HDL), during the acute phase of myocardial infarction. In LDL, a very elevated and stable correlation (r) was observed between these parameters, and the coefficients of regression (b) did not differ significantly during the period studied. In HDL, there was a decrease in r and b values from day 1 to day 2, then an increase after day 2. We hypothesize that these disturbances in HDL composition may be due to a greater endocytosis of LDL at day 2, leading to intracellular increase in cholesterol and phospholipids. Part of these lipids could be taken up by HDL molecules, causing a transient overload.

Intestinal lipoprotein assembly in apobec-1–/– mice reveals subtle alterations in triglyceride secretion coupled with a shift to larger lipoproteins

2003 ◽  
Vol 285 (4) ◽  
pp. G735-G746 ◽  
Author(s):  
Yan Xie ◽  
Fatiha Nassir ◽  
Jianyang Luo ◽  
Kimberly Buhman ◽  
Nicholas O. Davidson
Keyword(s):  
Low Density Lipoproteins ◽  
High Density ◽  
High Density Lipoproteins ◽  
Low Density ◽  
Wild Type ◽  
Very Low Density Lipoproteins ◽  
Apo B ◽  
Mixed Genetic Background ◽  
Triglyceride Secretion ◽  
Lipoprotein Assembly

Mammalian enterocytes express apolipoprotein (apo)B-48, which is produced after posttranscriptional RNA editing of the nuclear apoB-100 transcript by the catalytic deaminase apobec-1. Earlier studies in apobec-1–/– mice revealed an apoB-100-only lipoprotein profile but no gross defects in triglyceride absorption. However, subtle defects may have been obscured by the mixed genetic background. In addition, the intrinsic susceptibility to proteolytic degradation of intestinal apoB-100 and apoB-48 has been questioned. Accordingly, we examined triglyceride absorption, intestinal apoB expression, and lipoprotein secretion in apobec-1–/– mice backcrossed into a C57BL/6 background. Inbred apobec-1–/– mice absorb triglyceride normally, yet secrete triglyceride-rich lipoproteins more slowly than wild-type congenic controls. There was comparable induction of apoB synthesis in response to fat feeding in both genotypes, but apoB-100 was preferentially retained and more extensively degraded than apoB-48. By contrast, synthesis, secretion, and content of apo A-IV were indistinguishable in apobec-1–/– and wild-type mice with 100% recovery, suggesting no degradation of this apoprotein in either genotype. Newly secreted lipoproteins from isolated enterocytes of wild-type mice revealed apoB-48 in both high-density lipoproteins and very low-density lipoproteins. By contrast, apobec-1–/– mice secreted apoB-100-containing particles that were almost exclusively in the low and very low-density lipoproteins range with no apoB-100-containing high-density lipoproteins. These studies establish the existence of preferential degradation of intestinal apoB-100 and subtle defects in triglyceride secretion in apobec-1–/– mice, coupled with a shift to the production of larger particles, findings that suggest an important divergence in intestinal lipoprotein assembly pathways with the different isoforms of apoB.

A comparison of some immunological characteristics of very low density lipoproteins of normal and hypercholesterolemic rat sera

1978 ◽  
Vol 56 (6) ◽  
pp. 673-683 ◽  
Author(s):  
Peter J. Dolphin ◽  
Laurence Wong ◽  
David Rubinstein
Keyword(s):  
Polyacrylamide Gel Electrophoresis ◽  
Normal Serum ◽  
Low Density Lipoproteins ◽  
High Density Lipoproteins ◽  
Low Density ◽  
Very Low Density Lipoproteins ◽  
Rat Serum ◽  
Apo B ◽  
Apo E

The immunological characteristics of very low density lipoproteins (VLDL) from normal and hypercholesterolemic rat sera were compared using polyspecific antisera to VLDL and high density lipoproteins (HDL) and monospecific antisera to apo-B, apo-C, apo-A-I, and apo-E. Ultracentrifugally isolated VLDL from normal serum were studied by immunodiffusion and found to contain both discrete and associated (with apo-B) apo-C and apo-E, probably in the form of lipid-containing lipoproteins. However, immunoelectrophoresis of whole serum revealed only an associated form of the lipoprotein having pre-β mobility (i.e., VLDL), suggesting that the presence of discrete lipoproteins in isolated VLDL, each containing a single apoprotein family, may represent ultracentrifugal artifacts. Ultracentrifugally isolated VLDL from diet-induced hypercholesterolemic rat serum contained only trace amounts of apo-C and large quantities of apo-E, both of which were totally associated with apo-B. VLDL isolated by ultracentrifugation from perfusate of normal and hypercholesterolemic livers contained only associated lipoprotein complexes made up of apo-B, apo-C, and apo-E in the former but only apo-B and apo-E in the latter. These data suggest that normal VLDL are secreted as lipoprotein complexes containing apo-B, apo-C, and apo-E which may become destabilized in the circulation. However, VLDL from hypercholesterolemic serum show a marked diminution in the quantity of apo-C as indicated by the relative incorporation of [3H]leucine in vivo and by polyacrylamide gel electrophoresis of apo-VLDL.

scholarly journals Stimulation of apolipoprotein secretion in very-low-density and high-density lipoproteins from cultured rat hepatocytes by dexamethasone

1990 ◽  
Vol 271 (3) ◽  
pp. 575-583 ◽  
Author(s):  
P Martin-Sanz ◽  
J E Vance ◽  
D N Brindley
Keyword(s):  
Low Density Lipoprotein ◽  
Lipoprotein Metabolism ◽  
Density Lipoprotein ◽  
Rat Hepatocytes ◽  
High Density ◽  
High Density Lipoproteins ◽  
Low Density ◽  
Apo B ◽  
Apo E ◽  
The Masses

The effects of dexamethasone (a synthetic glucocorticoid) and insulin on the secretion of very-low-density lipoprotein (VLDL) and high-density lipoprotein (HDL) were investigated. Rat hepatocytes in monolayer culture were preincubated for 15 h in the presence or absence of combinations of 100 nM-dexamethasone and 2 nM-, 10 nM- or 50 nM-insulin. Dexamethasone increased [3H]oleate incorporation into secreted triacylglycerol by 2.7-fold and the mass of triacylglycerol secreted by 1.5-fold. Insulin alone decreased these parameters and antagonized the effect of dexamethasone. Dexamethasone increased the secretion of [3H]leucine in apolipoprotein (apo) E, and in the large (BH) and small (BI) forms of apo B in VLDL by about 7.1-, 3.6- and 4.0-fold respectively. Insulin alone decreased the secretion of these 3H-labelled apolipoproteins in VLDL. However, 2 nM-insulin with dexamethasone increased the secretion of 3H-labelled apo BH and apo BL by a further 0.8- and 3.2-fold respectively; 50 nM-insulin decreased the secretions of apo E, apo BH and apo BL in VLDL. Similar effects for dexamethasone or insulin alone were also obtained for the masses of apo E and apo BL + H secreted in VLDL. Albumin secretion was not significantly altered by either dexamethasone or insulin alone, but in combination they stimulated by 2.1-2.6-fold. Insulin or dexamethasone alone had little effect on the secretion of apolipoproteins in the HDL fraction. However, dexamethasone plus 2 nM-insulin increased the incorporation of [3H]leucine into apo AI, apo AH plus apo C, apo AIV and apo E of HDL by about 1.8-, 1.6-, 1.7- and 2.0-fold respectively. The apo E in the bottom fraction represented about 69% of the total 3H-labelled apo E secreted. The responses in the total secretion of apo E from the hepatocytes resembled those seen in HDL. The interactions of insulin and dexamethasone are discussed in relation to the general regulation of lipoprotein metabolism, the development of hyperlipidaemias and the predisposition to premature atherosclerosis.

Transfer of cholesterol between high density lipoproteins and cultured rat Sertoli cells

1996 ◽  
Vol 74 (5) ◽  
pp. 681-686 ◽  
Author(s):  
Mohamed Fofana ◽  
Jean-Claude Maboundou ◽  
Jean Bocquet ◽  
Dominique Le Goff
Keyword(s):  
Sertoli Cells ◽  
Hdl Cholesterol ◽  
High Density ◽  
High Density Lipoproteins ◽  
Phospholipid Vesicle ◽  
Steroid Production ◽  
Blood Capillaries ◽  
Apo E ◽  
Net Uptake

In the testes, the Sertoli cells are separated from the blood capillaries by the basement membrane, thereby excluding the passage of low density lipoproteins (LDLs) but allowing the passage of high density lipoproteins (HDLs). The present study examines first the capacity of Sertoli cells to uptake cholesterol from HDL and secondly the role of apolipoproteins (apo) A-I and E in cholesterol flux between HDL and cultured rat Sertoli cells. In the presence of HDL in cultured medium, rat Sertoli cells accumulated few amounts of esterified cholesterol. Incubation of [14C]cholesterol–labelled Sertoli cells with [3H]cholesterol–labelled HDL showed that the amount of cholesterol influx slightly exceeded its efflux, thus resulting in a net uptake of cholesterol from HDL to rat Sertoli cells. The amount of HDL–cholesterol converted to steroids by Sertoli cells was about 32% of influx. Uptake of cholesterol by Sertoli cells was three times higher with phospholipid – apo A-I vesicles and seven times higher with phospholipid – apo E vesicles than that with phospholipid vesicles without apolipoprotein. Phospholipid – apo A-I vesicles promoted cholesterol efflux at the same rate as native HDL and twice as efficiently as phospholipid – apo E vesicles. Thus, this study shows that rat Sertoli cells have the capacity to take up HDL–cholesterol for membrane renewal and steroid production mainly by apo E dependent pathways.Key words: apolipoproteins, cholesterol flux, phospholipid vesicle, steroid, testis.

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