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Biomedical subjects

F Gasnier

Publications and source records attributed to F Gasnier.

At least 19 recordsLinked to original sources
PubMed1998

Hormone-induced changes in cardiolipin from Leydig cells: possible involvement in intramitochondrial cholesterol translocation.

The rate-limiting and hormonally regulated step in steroid hormone biosynthesis is the delivery of cholesterol from the outer to the inner mitochondrial membrane where cytochrome P450scc resides. Although the exact mechanism of intramitochondrial cholesterol translocation remains unknown, the formation of contact sites between outer and inner mitochondrial membranes appears as a necessary component for cholesterol transfer. Several pieces of evidence suggest that local formation of intermembrane contact is a consequence of a non-bilayer arrangement of polymorphic lipids which are enriched in the junctions. As a step toward clarifying mitochondrial contact sites formation and thus cholesterol translocation in steroidogenic cells, we have undertaken studies to identify the factors which might result in non-bilayer structure to be adopted by mitochondrial phospholipids on stimulation of MA-10 Leydig cells. Our results demonstrate that an increase in the unsaturation of the cardiolipin acyl groups on hormonal stimulation might favor the formation of non-bilayer adhesion points.

Animals↗
PubMed1998

Tumor necrosis factor-alpha inhibits leydig cell steroidogenesis through a decrease in steroidogenic acute regulatory protein expression.

The aim of the present study was to identify the sites of the inhibitory action of TNFalpha (tumor necrosis factor alpha) on LH/hCG-stimulated testosterone formation. By using cultured porcine Leydig cells as a model, TNFalpha was shown to inhibit testosterone secretion when testicular cells were stimulated with hCG but not when incubated with 22R-hydroxycholesterol (a cholesterol substrate derivative that readily passes through cell and mitochondrial membranes). Such an observation suggested that the cytokine may affect cholesterol transport and/or availability to cytochrome P450scc in the mitochondria. Specifically, we report here that TNFalpha reduced in a dose- and time-dependent manner hCG-induced StAR (steroidogenic acute regulatory protein) levels. The maximal and half-maximal effects were obtained with 20 ng/ml (1.2 nM) and 1.6 ng/ml (0.09 nM) of TNFalpha, respectively. Maximal inhibitory effects of TNFalpha on StAR messenger RNA and protein levels were obtained after 48 h of treatment. Additionally, the presence of TNFalpha receptors P55 in terms of protein (identified through cross-linking experiments) and messenger RNA (identified through RT-PCR analysis) suggested that the effects of the cytokine are directly exerted on the testicular steroidogenic cell type.

Animals↗
PubMed1994

Further characterization of mitochondrial outer membrane: evidence for the presence of two endogenous sialylated glycoproteins.

The distribution of sialic acid-containing glycoproteins was investigated in highly purified mitochondrial membranes using labeled Sambucus nigra agglutinin as a detection system. Two sialylated glycoproteins were shown to be true components of the mitochondrial outer membrane. Relative to monoamine oxidase activity, these glycoproteins were found to be preferentially located in the "free" outer membrane fraction. As sialic acid is thought to be involved in molecular recognition, a role for these glycoproteins in mediating the interactions between mitochondria and other sub-cellular organelles is considered.

Animals↗
PubMed1993

Involvement of mitochondrial contact sites in the subcellular compartmentalization of phospholipid biosynthetic enzymes.

The concerted synthesis of phospholipids derived from serine involving two microsomal enzymes (phosphatidylserine synthase and phosphatidylethanolamine N-methyltransferase) and a mitochondrial one (phosphatidylserine decarboxylase) occurs in reconstituted cell-free systems. Subfractionation of crude mitochondria after swelling and separating on a sucrose density gradient resulted in the isolation of two contact site-enriched fractions from total outer membranes and inner membranes, respectively. Estimation of marker enzyme activities shows a high recovery of glucose-6-phosphate phosphatase (a marker for the endoplasmic reticulum) associated with contact site-enriched fractions. Accordingly, the linked synthesis of phosphatidylserine, phosphatidylethanolamine, and at a lesser extent phosphatidylcholine can occur. This biosynthetic pathway was absent from purified contact site-enriched fractions correlative with the absence of glucose-6-phosphate phosphatase activity. Reconstitution experiments, including contact site-enriched fractions incubated with endoplasmic reticulum-rich fraction, led to the restoration of the linked synthesis of phospholipids, thereby demonstrating that a reversible association between these two fractions can occur. These functional interactions between the endoplasmic reticulum and mitochondria are confirmed at the ultrastructural level using either chemical or physical fixation before resin embedding. These results show that the interorganelle trafficking of lipids may involve only highly specialized microdomains of both membranes, thereby allowing the maintenance of a specific lipid composition and distribution within membranes.

Animals↗
PubMed1993

Further evidence for both functional and structural microcompartmentation within the membranes of two associated organelles, mitochondrion and endoplasmic reticulum.

We previously demonstrated that the translocation of phospholipids between the mitochondrion and the endoplasmic reticulum occurs via highly specialized membrane microdomains of both organelles that are in situ closely associated. As understanding of the interactions between both organelles requires characterization of the translocation sites organization, we first analysed the amino acid compositions of these sites. Using principal component analysis, we have shown that the translocation sites exhibit characteristic patterns when compared with the membranes from which they are derived. The results are discussed in terms of both functional and structural microcompartmentation within the membranes of mitochondria and endoplasmic reticulum.

Amino Acids↗
PubMed1993

Use of Percoll gradients for isolation of human placenta mitochondria suitable for investigating outer membrane proteins.

Human mitochondria were isolated from placenta by a combination of differential and Percoll gradient centrifugation, resulting in a highly pure and intact preparation as assessed by marker enzyme analysis and electron microscopy. The advantages over previous methods are the rapidity of the procedure and the excellent resolution of mitochondria and lysosomes. Moreover, the high extent of intactness of the mitochondria so obtained made them particularly well suited for investigating outer membrane proteins. Taking advantage of this method, we have purified human mitochondrial porin. The purified protein consists of a single unglycosylated polypeptide of molecular mass 33 kDa.

Cell Fractionation↗
PubMed1992

Mitochondrial dolichyl-phosphate mannose synthase. Purification and immunogold localization by electron microscopy.

Mitochondrial dolichyl-phosphate mannose synthase has been purified to homogeneity using an original procedure, reconstitution into specific phospholipid vesicles and sedimentation on a sucrose gradient as final step. The enzyme has an apparent molecular mass of 30 kDa on an SDS/polyacrylamide gel. Increased enzyme activity could be correlated with this polypeptide band. A specific antibody was raised in rabbits against this transferase. Specific IgG obtained from the immune serum removed enzymatic activity from a detergent extract of mitochondrial outer membrane and reacted specifically with the 30-kDa band on immunoblots. Furthermore, an immunocytochemical experiment proved the localization of dolichyl-phosphate mannose synthase on the cytosolic face of the outer membrane of mitochondria.

Animals↗
PubMed1991

Investigation of glycosylation processes in mitochondria and microsomal membranes from human skeletal muscle.

Glycoconjugates are directly involved in major skeletal muscle functions. As little is known about glycosylation processes in muscle, we investigated glycoconjugate synthesis in subcellular fractions from human skeletal muscle tissue. Mitochondria and microsomal membranes were prepared from muscle biopsies by thorough mechanical disruption and differential centrifugations. This procedure resulted in the isolation of intact mitochondria (1 mg protein/g muscle) and of a microsomal fraction (1.5 mg protein/g muscle). Glycosyltransferases were studied in both subcellular fractions using either dolichylmonophosphate as a polyprenic acceptor or chemically modified fetuin as a glycoprotein substrate. Our results provide evidence for high rates of glycosylation in muscle. The highest activities were obtained with GDP-mannose: dilichylmonophosphate mannosyltransferase, a key enzyme in glycosylation process (220 pmol/mg per h in mitochondria and 1,550 pmol/mg per h in microsomal membranes). Substantial individual variations were observed for dolichol pathway glycosyltransferases but low individual variations were found for glycosyltransferases involved in maturation of glycoproteins. The role which glycosylation defects may play in muscle dysfunction has yet to be defined.

Adolescent↗
PubMed1991

Sialylation processes in mitochondria: evidence for two distinct sialyltransferases located in the outer membrane.

Previous studies have shown that purified mitochondrial outer membrane is able to catalyze the transfer of sialic acid from CMP-Neu5Ac to an exogenous asialoglycoprotein acceptor, asialofetuin. Considering the heterogeneity of the glycan chains borne by this glycoprotein, an investigation of mitochondrial sialyltransferase activities was undertaken. Our data provide evidence for the existence of two distinct sialyltransferases in purified mitochondrial outer membranes. The use of different acceptor substrates, the temperature dependence of these enzymes, and their different sensitivity towards a sulfhydryl reagent, p-CMB, allowed us to discriminate between a galactoside alpha(2-3) sialyltransferase and a galactoside alpha(2-6) sialyltransferase presumably involved in the sialylation of O- and N-glycan chains of glycoprotein, respectively. These results are discussed in terms of mitochondrial autonomy for post-translational events.

Animals↗
PubMed1989

Topological orientation of mitochondrial GDPmannose: dolichyl-monophosphate mannosyltransferase in the outer membrane.

Previous studies have shown the existence of an autonomous mitochondrial GDPmannose:dolichylmonophosphate mannosyltransferase, located in mitochondrial outer membrane of liver cells. As nothing is known about glycosylation sites in mitochondria, we have investigated the topological orientation of this enzyme in intact mitochondria, using controlled proteolysis with trypsin. Mitochondria were purified sequentially by mild ultrasonic treatment and sucrose density gradient. Purity and homogeneity of mitochondrial fraction were assessed by electron microscopy and specific marker enzymes measures. Our data provide evidence for a mitochondrial GDPmannose:dolichylmonophosphate mannosyltransferase facing the cytoplasmic side of the outer membrane. However, the exposure of this enzyme to the water phase has been shown to be dependent on the ionic strength of the environment.

Animals↗
PubMed1989

Congenital soft tissue dysplasia: a new malformation entity and concept.

We report 185 children with clinical manifestations of various conditions classically described as giant hamartoma, angiodysplasia, congenital hypertrophy, congenital trophoedema, localised gigantism (e.g. macrodactyly), etc. It is proposed to group all these conditions into a single entity: congenital soft-tissue dysplasia (CSTD). According to recent advances in fundamental embryology and cell biology, CSTD appears to be a consequence of embryonal or fetal cell biosynthetic dysregulation. The concept of the CSTD entity leads to a common protocol for clinical investigation and a common therapeutic plan, with special reference to the stability and the benign nature of the condition. Treatment should be confined to improving function rather than attempting to correct cosmetic deficits.

Adolescent↗
PubMed1989

Organization of mitochondrial UDP-glucose:dolichylmonophosphate glucosyltransferase in the outer membrane.

Previous studies have shown the existence of an autonomous mitochondrial UDP-glucose: dolichylmonophosphate glucosyltransferase, located in mitochondrial outer membrane of liver cells. To improve our knowledge about the topographical aspects of glycosylation in mitochondria, we have investigated the organization of this enzyme in intact mitochondria, using controlled proteolysis with trypsin and sensitivity towards amino-acid specific reagents. Our data provides evidence: --for a mitochondrial glucosyltransferase facing the cytoplasmic side of the outer membrane --and for the involvement of histidine and tryptophan residues as well as sulfhydryl groups in the catalytic activity of the enzyme.

Amino Acids↗
PubMed1989

Galactosyltransferase activities in mitochondria outer membrane: biosynthesis of galactosylated proteins.

1. Mitochondria outer membranes prepared from mouse livers were purified on a discontinuous sucrose gradient. Control in electron microscopy and marker enzymes assays confirmed purity and homogeneity of this fraction. 2. Purified mitochondria outer membranes exhibited significant UDP-galactose: glycoprotein galactosyltransferase activities when incubated with endogenous or exogenous glycoprotein acceptors in presence of detergent (Nonidet P40). 3. Some properties of two distinct mitochondrial galactosyltransferases, acting respectively on ovomucoid and ovine asialo-mucin were investigated. 4. Transfer of galactose on ovomucoid was maximal for a pH of 7.6 at 33 degrees C whereas asialo-mucin galactosyltransferase exhibited an optimum pH of 5.6 for an optimal temperature of 46 degrees C. 5. These two distinct membrane-bound enzymes were both inhibited by diacylglycerophospholipids whereas lysophospholipids modulated both enzymes in a different way: at 5 mM lysophosphatidylcholine, asialo-mucin galactosyltransferase was slightly stimulated while ovomucoid galactosyltransferase was markedly activated. 6. The most important activating effect on ovomucoid galactosyltransferase was obtained with a phospholipid containing a long aliphatic side chain linked by an ester bond in sn-1 of glycerol, an hydroxyl group or hydrogen atoms in sn-2 and a phosphorylcholine head group in sn-3.

Animals↗
PubMed1988

Galactosyltransferase activities in mitochondrial outer membrane: biosynthesis of dolichylmonophosphate-galactose.

Mitochondrial outer membranes were prepared from mouse liver homogenates by swelling purified mitochondria in phosphate buffer and were purified on a discontinuous sucrose gradient. Assays for marker enzymes and controls in electron microscopy confirmed the purity and homogeneity of this subfraction. Mitochondrial outer membranes had significant galactosyltransferase activity when incubated with UDP-[14C]galactose: 14C-labelling was found in products extractable with organic solvents and in a residual precipitate. Addition of exogenous dolichylmonophosphate loaded into phosphatidylcholine liposomes strongly enhanced the incorporation of [14C]galactose into chloroform/methanol (2:1, v/v) -extractable products. Thin-layer chromatography of these 2:1 extracts showed that the increase of [14C]galactose incorporation was attributable to the synthesis of a new galactosylated lipid, 'lipid L'. This 'lipid L' has been purified on silicic acid columns by elution with chloroform/methanol (1:1, v/v). The purified 'lipid L' was labile in acid and released [14C]galactose. It had the same chromatographic behaviour as dolichylmonophosphate-mannose in neutral, acid and alkaline solvent systems. Upon incubation in presence of [3H]dolichylmonophosphate and UDP-[14C]galactose, purified 'lipid L' contained both 3H- and 14C-labelling. 'Lipid L', synthesized by mitochondrial outer membranes, was therefore characterized as dolichylmonophosphate-galactose.

Animals↗
PubMed1987

Purification and properties of a mannosyltransferase solubilized from mitochondrial outer membranes.

The enzyme GDPmannose: dolichyl monophosphate mannosyltransferase has been solubilized and purified from mice liver mitochondrial outer membranes. The purification combines detergent extraction of purified outer membranes using Nonidet P-40, with subsequent ion-exchange chromatography on DEAE-cellulose. At this stage, a 400-fold purification is obtained. The partially purified mannosyltransferase is activated by choline-containing lipids such as phosphatidylcholine, lysophosphatidylcholine and sphingomyelin. The reaction is dependent upon the addition of exogenous dolichyl monophosphate. The sole reaction product has been identified as dolichyl phosphate-mannose. The partially purified mannosyltransferase exhibits a Km of 1.33 microM for GDPmannose. Enzyme activity, eluted from DEAE-cellulose, could be further purified after incorporation into sphingomyelin vesicles containing dolichyl monophosphate followed by a sucrose density gradient centrifugation. The mannosyltransferase activity is completely associated with the liposomes at the top of the gradient. Significant stabilization and purification (approx. 1600-fold) of enzyme activity associated with these liposomes is obtained. Furthermore, the reconstitution of this purified enzyme within specific liposomes provides a good model membrane to investigate the molecular requirement of this mitochondrial mannosyltransferase.

Animals↗
PubMed1986

Papillary meningioma. Clinicopathologic study of seven cases and review of the literature.

Seven cases of papillary meningioma are reported. The patients, 3 females and 4 males, were aged between 21 and 69 years. Five tumors were supratentorial, 1 was located in the left temporal bone, and 1 in the thoracic spinal canal. Five patients had local recurrences and died within 1.4 to 9 years of the original operation. In Case 2, one small pulmonary metastatic nodule was found at autopsy. Microscopically, these meningiomas showed foci of necrosis, numerous mitotic figures and local invasiveness. Psammoma bodies were occasional or absent. Forty-six papillary meningiomas have been identified in the literature. Certain histologic features (necrosis, high mitotic index, rich peripapillary reticulin network) and evolutive events (high rate of local recurrence, development of distant metastases) suggest that this aggressive variant of meningioma could form a histologic link between syncytial, fibroblastic, and hemangiopericytic meningiomas.

Adult↗