Effect of lipid composition on rat liver nuclear membrane fluidity

Abstract

Nuclear membrane fluidity is measured in rat liver by use of the fluorescence anisotropy of two probes: diphenylhexatriene and its cationic derivative trimethylammonium-diphenylhexatriene. It has been shown that, in 2-month-old rat liver cells, the bilayer surface is less fluid than the hydrophobic core. The fluidity was higher in 6-day-old rat liver nuclei, in which both the amount of cholesterol and the cholesterol/phospholipid ratio decreased. The influence of the single phospholipids, and in particular of phosphatidylcholine, has been studied by increasing the phosphatidylcholine with a choline base exchange reaction in isolated nuclear membranes. After this reaction, the fluorescence anisotropy of the bilayer surface increased, whereas at the hydrophobic core it decreased. Analysis of fatty acid composition shows an increase of phosphatidylcholine unsaturated fatty acids. The results show that the fluidity of nuclear membranes changes in relation to the lipid content and to the fatty acid composition. The role of nuclear membrane fluidity in cell function is discussed.

Membrane Fluidity Is a Key Modulator of Membrane Binding, Insertion, and Activity of 5-Lipoxygenase

“…Our results lead to a novel concept of membrane-mediated activation of 5-LO, implying that membrane fluidity supports 5-LO activity by facilitating insertion of the enzyme into the hydrocarbon region of the membrane. Considering that the nuclear membranes of various mammalian cells, including leukocytes, are enriched in AA-containing lipids more than other subcellular membranes (Neufeld et al, 1985;Capriotti et al, 1988;Albi et al, 1997;Surette and Chilton, 1998;D'Antuono et al, 2000), which results in increased fluidity of nuclear membranes (Yu et al, 1996;Albi et al, 1997;D'Antuono et al, 2000), our findings suggest that membrane fluidity may play a central role in nuclear membrane targeting and activation of 5-LO.…”

“…In rat renal papillary cells, the fraction of AA-containing lipids was 1.5 times higher, whereas the fraction of lipids with saturated chains was 1.6 times lower in nuclear than in endoplasmic reticulum membranes (D'Antuono et al, 2000). Large fractions of AA-containing lipids result in elevated fluidity of nuclear membranes (Yu et al, 1996;Albi et al, 1997;D'Antuono et al, 2000). This leads to a mechanism suggesting that increased membrane fluidity via high levels of AA-containing lipids may be an important factor for localization of 5-LO to nuclear membranes.…”

“…To study the effect of lipid acyl chain unsaturation on the membrane-binding mode and activity of 5-LO, we have used PCs that contain a saturated palmitoyl chain at the sn-1 position, whereas the acyl chain at the sn-2 position was either a palmitoyl (16:0), oleoyl (18:1), linoleoyl (18:2), arachidonoyl (20:4), or docosahexaenoyl (22:6) residue (shown in parentheses are the ratios of carbon atoms to double bonds per chain). The choice of these lipids was based on the fact that in major lipids of mammalian cell membranes the sn-1 position is usually occupied by a saturated chain, such as a palmitoyl residue, and the sn-2 position is most frequently occupied by one of the unsaturated fatty acyl chains specified above (Albi et al, 1997;Surette and Chilton, 1998;D'Antuono et al, 2000). Replacement of fully saturated DPPC membranes by membranes containing lipids with cis-unsaturated acyl chains results in an ;3-fold increase in 5-LO activity.…”

“…Nuclear membranes are enriched in AA-containing lipids more than other cellular membranes (Neufeld et al, 1985;Capriotti et al, 1988;Albi et al, 1997;Surette and Chilton, 1998;D'Antuono et al, 2000). Thus, up to 48% of the total cellular AA-containing lipids were found in the nuclear membranes of various mammalian cell lines, including leukemia cells (Surette and Chilton, 1998).…”

Common binding sites for cholesterol and neurosteroids on a pentameric ligand-gated ion channel

“…Cholesterol can affect integral membrane protein (IMP) structure and function by two mutually non-exclusive mechanisms (6,16): 1) Cholesterol affects the physical properties of lipid bilayers such as membrane fluidity (6,17,18), membrane thickness (19), and the structure of lipid microdomains (20) and; 2) cholesterol can directly modulate protein function or stability by binding to specific sites on IMPs. Multiple computational studies suggest cholesterol binds to specific sites in the TMDs of pLGICs (21,22).…”