The influence of dolichols on fluidity of mouse synaptic plasma membranes

A cell wall synthase accelerates plasma membrane partitioning in mycobacteria

Lateral partitioning of proteins and lipids shapes membrane function. In model membranes, partitioning can be influenced both by bilayer-intrinsic factors like molecular composition and by bilayer-extrinsic factors such as interactions with other membranes and solid supports. While cellular membranes can departition in response to bilayer-intrinsic or -extrinsic disruptions, the mechanisms by which they partition de novo are largely unknown. The plasma membrane of Mycobacterium smegmatis spatially and biochemically departitions in response to the fluidizing agent benzyl alcohol, then repartitions upon fluidizer washout. By screening for mutants that are sensitive to benzyl alcohol, we show that the bifunctional cell wall synthase PonA2 promotes membrane partitioning and cell growth during recovery from benzyl alcohol exposure. PonA2's role in membrane repartitioning and regrowth depends solely on its conserved transglycosylase domain. Active cell wall polymerization promotes de novo membrane partitioning and the completed cell wall polymer helps to maintain membrane partitioning. Our work highlights the complexity of membrane-cell wall interactions and establishes a facile model system for departitioning and repartitioning cellular membranes.

Fluorescence techniques using dehydroergosterol to study cholesterol trafficking

Cholesterol itself has very few structural/chemical features suitable for real-time imaging in living cells. Thus, the advent of dehydroergosterol [ergosta-5,7,9(11),22-tetraen-3beta-ol, DHE] the fluorescent sterol most structurally and functionally similar to cholesterol to date, has proven to be a major asset for real-time probing/elucidating the sterol environment and intracellular sterol trafficking in living organisms. DHE is a naturally occurring, fluorescent sterol analog that faithfully mimics many of the properties of cholesterol. Because these properties are very sensitive to sterol structure and degradation, such studies require the use of extremely pure (>98%) quantities of fluorescent sterol. DHE is readily bound by cholesterol-binding proteins, is incorporated into lipoproteins (from the diet of animals or by exchange in vitro), and for real-time imaging studies is easily incorporated into cultured cells where it co-distributes with endogenous sterol. Incorporation from an ethanolic stock solution to cell culture media is effective, but this process forms an aqueous dispersion of DHE crystals which can result in endocytic cellular uptake and distribution into lysosomes which is problematic in imaging DHE at the plasma membrane of living cells. In contrast, monomeric DHE can be incorporated from unilamellar vesicles by exchange/fusion with the plasma membrane or from DHE-methyl-beta-cyclodextrin (DHE-MbetaCD) complexes by exchange with the plasma membrane. Both of the latter techniques can deliver large quantities of monomeric DHE with significant distribution into the plasma membrane. The properties and behavior of DHE in protein-binding, lipoproteins, model membranes, biological membranes, lipid rafts/caveolae, and real-time imaging in living cells indicate that this naturally occurring fluorescent sterol is a useful mimic for probing the properties of cholesterol in these systems.

Biliary excretion of dolichols and beta-hexosaminidase--effect of ethanol and glucagon

Alcohol has been reported to increase the urinary excretion of dolichols, and urinary dolichols are suggested to be derived from the lysosomes of the renal cells. In the present study we examined the effects of alcohol and glucagon on the biliary excretion of dolichols in rats. Chronic ethanol treatment decreased both biliary dolichol and beta-hexosaminidase excretion. The absolute amount of dolichol excreted into the bile correlated highly significantly with the absolute amount of biliary beta-hexosaminidase. Our results indicate that biliary dolichols are--at least in part--derived from hepatic lysosomes. Decreased biliary dolichol output during chronic alcohol administration suggests that urinary and biliary dolichol excretions are regulated independently of each other.

Elevated levels of dolichol in the brains of mucopolysaccharidosis and related disorders

The contents of total dolichol were measured in the cerebral cortex of various patients with lysosomal storage disorders, including mucopolysaccharidosis. Strikingly high levels of dolichol were demonstrated in GM1-gangliosides, Sanfilippo B syndrome, and a severe type of Hunter syndrome as well as neuronal ceroid-lipofuscinosis. An increased level of dolichol in cerebral cortex in neuronal ceroid-lipofuscinosis (NCL) was once regarded as pathognomonic for NCL. Our data, however, suggest that an increased level of dolichol in cerebral cortex is a nonspecific phenomenon related to some lysosomal dysfunction secondary to various neurodegenerative disorders.

Strenuous physical activity, aspirin and heat stress increase urinary dolichols: evidence for lysosomal origin of urinary dolichols

Strenuous physical activity, aspirin and heat stress (Finnish sauna) were all found to significantly increase urinary dolichol excretion. In contrast, serum dolichol concentration studied before and after aspirin and sauna, was not affected. A similar aspirin-induced increase, as seen in urinary dolichol concentration, was also observed in the urinary excretion of two lysosomal enzymes--beta-hexosaminidase and beta-glucuronidase. In contrast, the excretion of two non-lysosomal enzymes--lactate dehydrogenase and leucine aminopeptidase--was not affected. The lack of correlation between serum and urinary dolichols, and the parallel increase in urinary dolichols and the activities of the lysosomal enzymes suggest that urinary dolichols may be derived from the lysosomes of the renal cells. We conclude that the finding of increased urinary dolichol concentrations in some relatively common conditions limits the clinical use of urinary dolichols as a diagnostic tool in neuronal ceroid lipofuscinosis or alcoholism.

Serum dolichols in different clinical conditions

We studied the effect of seven different clinical diseases (viral infections, bacterial infections, malignant diseases, cardiovascular diseases, gastroenterological diseases, endocrinological diseases, and rheumatic diseases) as well as normal pregnancy on serum dolichol concentrations in 76 hospitalized patients and in 10 pregnant women. In contrast to urinary dolichols, serum dolichols were not significantly increased in any of these conditions, suggesting that dolichol levels in serum and urine are independently regulated. Furthermore, we found that serum dolichol concentration does not undergo diurnal variation, as in healthy volunteers time of blood sampling did not affect serum dolichols. Our results suggest that serum dolichol concentration, which has earlier been found to be exceptionally high in aspartylglucosaminuria and mannosidosis, might serve as a laboratory marker for these recessively inherited lysosomal storage diseases.

Effects of chronic ethanol administration on plasma-membrane-bound glycosyltransferase activities

Physiological and membranous modifications induced by a 4-week ethanol administration in mouse liver plasma membrane were studied. Galactosyl- and glucosyltransferase activities were stimulated in the presence of dolichylphosphate alone or with phosphatidyl-choline. The galactosyltransferase activity was inhibited by chronic ethanol administration. These enzymes were modulated by different phospholipids. The phosphatidic acid was the most efficient activator. Ethanol provoked an inhibition of the galactosyltransferase activity whatever the phospholipid used, as well as an inhibition of the glucosyltransferase activity, chiefly in presence of phosphatidyl-inositol. The preincubation of control or treated mouse liver plasma membranes with liposomes loaded by dolichylphosphate and cholesterol greatly enhanced the enzymatic activities without removing the inhibition by ethanol treatment.

Membrane properties of dolichol in different age groups of mice

Dolichol content and the effects of dolichol in vitro on synaptic plasma membrane (SPM) structure of different age groups of C57BL/6NNIA mice were examined. SPM of aged mice had higher amounts of dolichol as compared to younger animals. Age differences also were observed in dolichol isoprenologue distribution. In older animals, dolichol isoprenologue chain length was shifted towards shorter chain length values. The structure of SPM was determined by differential polarized phase fluorometry of 1,6-diphenyl-1,3,5-hexatriene (DPH). The SPM of old mice were more rigid, as indicated by higher limiting anisotropy, than those of young mice. Dolichol administered in vitro to SPM fluidized the membranes. However, dolichol administered in vitro fluidized SPM of younger mice significantly more than SPM of aged mice. The functional role of increased dolichol content in aged individuals is not known. Dolichol may act to regulate membrane fluidity of aged animals.

Dolichol alters GABA uptake and high affinity binding of agonist to rat brain synaptic plasma membranes

The effects of dolichol on high affinity [3H]muscimol binding to synaptic plasma membrane (SPM) and [3H]GABA uptake into synaptosomes from rat brain were analyzed. Membranes were enriched with dolichol, by preincubation, in the presence of bovine serum albumin (BSA) as a vehicle (40-100 micrograms of dolichol/mg protein + 5% BSA). The rate of dolichol incorporation into the membrane was determined using [1-3H]dolichol C95, and it was in the range of 5-7 nmol/mg protein/h for synaptosomes and SPM, respectively. The uptake of [3H]GABA into synaptosomes enriched with dolichol decreased significantly by about 30%. Dolichol alone added into the incubation medium produced only a negligible effect. Specific binding of [3H]muscimol, which was higher than 90% of total binding, was significantly reduced to SPM enriched with dolichol as compared to controls. The Kd of the high affinity sites was significantly elevated by about 30% in SPM enriched with dolichol (10.8 +/- 0.3 nM vs 7.3 +/- 0.2 nM in control). This difference was more pronounced for SPM isolated from cerebellum (Kd increased by about 50%). The Bmax value was not changed. Dolichol alone did not alter the agonist binding. These results indicate for the first time that the higher level of dolichol in SPM might influence the GABAergic transmission system. An increase in dolichols in membranes may be an important factor in the decline of brain function during aging.

Age-associated changes in dolichol and dolichyl phosphate metabolism in the kidneys and liver of mice

The total amounts of cholesterol, dolichol and dolichyl phosphate (Dol-P) in kidneys and liver from 1- and 24-month-old mice were measured after saponification of the tissues. The cholesterol content of kidneys decreased by about 4-fold per g of tissue between the two ages, while the amount of cholesterol/g liver remained constant. The dolichol content of both tissues increased by about 2-fold. The amount of Dol-P in kidneys increased by 7-fold over 23 months, while the concentration in liver decreased some 6-fold. Metabolic labelling experiments using tritiated water demonstrated that the rate of synthesis of total dolichol (dolichol + Dol-P) in the kidneys did not change as a function of age. However, the kidneys of young mice incorporated 3-fold more radioactivity into dolichol than Dol-P, whereas this distribution was reversed in old mice. In liver, the rate of dolichol synthesis decreased 2-fold over 23 months. It was not possible to compare the rates of Dol-P biosynthesis between ages as Dol-P was undetectable in liver of old mice. The relative abundance of the 19 isoprene unit homologs of both dolichol and Dol-P decreased approx. 5% while the 17 isoprene unit homologs increased by a similar amount in both tissues of the old mice.

Effect of alcohol on blood dolichol concentration

Serum dolichol levels were studied in 95 active alcoholics and 16 abstinent alcoholics (at the time of blood sampling) and compared to those of 41 social drinkers. Active alcoholics had a significantly higher mean serum dolichol concentration (182.7 +/- 5.1 ng/ml, p less than 0.001 than either abstinent alcoholics (138.7 +/- 5.4 ng/ml) or social drinkers (142.1 +/- 4.1 ng/ml). During weekend (48 hr) heavy drinking (5.5 g of alcohol per kg b.w.) no significant changes were seen in mean serum dolichol concentrations in 10 healthy, nonalcoholic volunteers. Neither did moderate drinking for 10 days (60 g of alcohol daily)--preceded and followed by a period of abstinence--produce any significant changes in serum dolichol levels in 10 nonalcoholic subjects. During detoxification treatment of 12 alcoholics, mean serum dolichol concentration stayed constant for the first 7 days; on entering treatment it was 227.7 +/- 15.0 ng/ml, on the 3rd day 238.5 +/- 15.9 ng/ml, and on the 7th day of treatment 222.6 +/- 18.6 ng/ml. Our results show that as well as increasing urinary dolichol excretion, chronic alcohol abuse also produces increased serum dolichol concentrations. However, contrary to urinary dolichols, serum dolichol levels do not react significantly to heavy drinking lasting for 48 hr in nonalcoholic volunteers. Furthermore in alcoholics increased serum dolichol concentrations do not decrease as rapidly during abstinence as urinary dolichol concentrations do.

Increased dolichol content in glucocorticoid-sensitive human T-cell leukemia line grown in the presence of dexamethasone

Two cell lines, derived from human T-cell acute leukemia, one glucocorticoid sensitive (CEM-C7) and the other glucocorticoid resistant (CEM-C1) were grown in the presence of 1 x 10-7 M dexamethasone and were analyzed for their dolichol content. After 24 hrs of incubation, dolichols became significantly elevated in the sensitive but not in the resistant line. Lovastatin, the specific inhibitor of cholesterol synthesis did not affect dolichol levels in either of the two cell lines. The results raise the possibility that dolichol accumulation might be involved in the early stages of the glucocorticoid-induced apoptosis (directed cell killing).

Characterization of a glucosyltransferase activity in liver plasma membrane: modulation by cations and lipidic effectors

1. Glucosyltransferase activity incorporating [14C]glucose from UDP-[14C]glucose onto endogenous lipidic acceptors was localized primarily in the plasma membrane of liver. 2. Incubation of plasma membrane by phosphatidyl-choline liposomes loaded with dolichyl-phosphate stimulated the enzymatic activity. 3. This enzyme required Mg2+ for maximal catalitic activity. Ca2+ could substitute Mg2+. 4. Mn2+ acted as a partial non-competitive inhibitor of the Mg2+-activated glucosyltransferase. 5. This enzyme can be modulated by neutral and acidic phospholipids; the most efficient were phosphatidyl-serine and phosphatidyl-inositol. 6. The enzymatic activity was not significantly changed by cholesterol alone but it is greatly enhanced by liposomes loaded with dolichyl-phosphate and cholesterol.