Dietary supplementation of cystinotic mice by lysine inhibits the megalin pathway and decreases kidney cystine content.

Megalin/LRP2 is a major receptor supporting apical endocytosis in kidney proximal tubular cells. We have previously reported that kidney-specific perinatal ablation of the megalin gene in cystinotic mice, a model of nephropathic cystinosis, essentially blocks renal cystine accumulation and partially preserves kidney tissue integrity. Here, we examined whether inhibition of the megalin pathway in adult cystinotic mice by dietary supplementation (5x-fold vs control regular diet) with the dibasic amino-acids (dAAs), lysine or arginine, both of which are used to treat patients with other rare metabolic disorders, could also decrease renal cystine accumulation and protect cystinotic kidneys. Using surface plasmon resonance, we first showed that both dAAs compete for protein ligand binding to immobilized megalin in a concentration-dependent manner, with identical inhibition curves by L- and D-stereoisomers. In cystinotic mice, 2-month diets with 5x-L-lysine and 5x-L-arginine were overall well tolerated, while 5x-D-lysine induced strong polyuria but no weight loss. All diets induced a marked increase of dAA urinary excretion, most prominent under 5x-D-lysine, without sign of kidney insufficiency. Renal cystine accumulation was slowed down approx. twofold by L-dAAs, and totally suppressed by D-lysine. We conclude that prolonged dietary manipulation of the megalin pathway in kidneys is feasible, tolerable and can be effective in vivo.

Contribution of Kunitz protease inhibitor and transmembrane domains to amyloid precursor protein homodimerization.

BACKGROUND: The two major isoforms of the human amyloid precursor protein (APP) are APP695 and APP751. They differ by the insertion of a Kunitz-type protease inhibitor (KPI) sequence in the extracellular domain of APP751. APP-KPI isoforms are increased in Alzheimer's disease brains, and they could be associated with disease progression. Recent studies have shown that APP processing to Aß is regulated by homodimerization, which involves both extracellular and juxtamembrane/transmembrane (JM/TM) regions. OBJECTIVE: Our aim is to understand the mechanisms controlling APP dimerization and the contribution of the ectodomain and JM/TM regions to this process. METHODS: We used bimolecular fluorescence complementation approaches coupled to fluorescence-activated cell sorting analysis to measure the dimerization level of different APP isoforms and APP C-terminal fragments (C99) mutated in their JM/TM region. RESULTS: APP751 was found to form significantly more homodimers than APP695. Mutation of dimerization motifs in the TM domain of APP or C99 did not significantly affect fluorescence complementation. CONCLUSION: These findings indicate that the KPI domain plays a major role in APP dimerization. They set the basis for further investigation of the relation between dimerization, metabolism and function of APP.

Three unrelated sphingomyelin analogs spontaneously cluster into plasma membrane micrometric domains.

Micrometric lipid compartmentation at the plasma membrane is disputed. Using live confocal imaging, we found that three unrelated fluorescent sphingomyelin (SM) analogs spontaneously clustered at the outer leaflet into micrometric domains, contrasting with homogeneous labelling by DiIC18 and TMA-DPH. In erythrocytes, these domains were round, randomly distributed, and reversibly coalesced under hypotonicity. BODIPY-SM and -glucosylceramide showed distinct temperature-dependence, in the same ranking as Tm for corresponding natural lipids, indicating phase behaviour. Scanning electron microscopy excluded micrometric surface structural features. In CHO cells, similar surface micrometric patches were produced by either direct BODIPY-SM insertion or intracellular processing from BODIPY-ceramide, ruling out aggregation artefacts. BODIPY-SM surface micrometric patches were refractory to endocytosis block or actin depolymerization and clustered upon cholesterol deprivation, indicating self-clustering at the plasma membrane. BODIPY-SM excimers further suggested clustering in ordered domains. Segregation of BODIPY-SM and -lactosylceramide micrometric domains showed coexistence of distinct phases. Consistent with micrometric domain boundaries, fluorescence recovery after photobleaching (FRAP) revealed restriction of BODIPY-SM lateral diffusion over long-range, but not short-range, contrasting with comparable high mobile fraction of BODIPY-lactosylceramide in both ranges. Controlled perturbations of endogenous SM pool similarly affected BODIPY-SM domain size by confocal imaging and its mobile fraction by FRAP. The latter evidence supports the hypothesis that, as shown for BODIPY-SM, endogenous SM spontaneously clusters at the plasmalemma outer leaflet of living cells into ordered micrometric domains, defined in shape by liquid-phase coexistence and in size by membrane tension and cholesterol. This proposal remains speculative and calls for further investigations.

Acute ligand-independent Src activation mimics low EGF-induced EGFR surface signalling and redistribution into recycling endosomes.

Src, a non-receptor tyrosine kinase, is a key signal transduction partner of epidermal growth factor (EGF) receptor (EGFR). In human breast cancer, EGFR and Src are frequently over-expressed and/or over-activated. Although reciprocal activation is documented, mechanisms underlying Src:EGFR interactions are incompletely understood. We here exploited ts/v-Src thermo-activation in MDCK monolayers to test whether acute Src activation impacts on signalling and trafficking of non-liganded EGFR. We found that thermo-activation caused rapid Src recruitment to the plasma membrane, concomitant association with EGFR, and its phosphorylation at Y845 and Y1173 predominantly at the cell surface. Like low EGF concentrations, activated Src (i) decreased EGF surface binding without affecting the total EGFR pool; (ii) triggered EGFR endocytosis via clathrin-coated vesicles; (iii) and led to its sequestration in perinuclear/recycling endosomes with avoidance of multivesicular bodies and lysosomal degradation. Combined Src activation and EGF were synergistic for EGFR-Y845 and -Y1173 phosphorylation at some endosomes. We conclude that acute effects of Src in MDCK cells may mimic those of low EGF on EGFR activation and redistribution. Src:EGFR interactions may be sufficient to trigger EGFR activation and might contribute to its local signalling, without requiring either soluble extracellular signal or receptor over-expression.

Pathways followed by membrane recovered from the surface of plasma cells and myeloma cells.

Evidence for recovery of surface membrane and its fusion with Golgi cisternae has been obtained previously in several glandular cells. This study was conducted to determine whether or not membrane is similarly retrieved from the surfaces of plasma cells from lymph nodes (of rats immunized with horseradish peroxidase [HRP]) and mouse myeloma cells (RPC 5.4 and X63 Ag 8 cell lines). Electron-dense tracers (cationic and anionic ferritin, HRP) were used to trace the pathways followed by surface membrane recovered by endocytosis, and immunocytochemistry was used to identify the secretory compartments. When plasma cells or myeloma cells were incubated with cationized ferritin (CF), it bound to the cell surfaces and was taken up in endocytic vesicles, for the most part bound to the vesicle membrane. After 30-60 min, it was found increasingly within lysosomes and in several secretory compartments- notably in multiple stacked Golgi cisternae and secretory vacuoles. By immunocytochemistry the secretory product (immunoglobulins) and CF could be demonstrated in the same Golgi components. When myeloma cells were incubated with native (anionic) ferritin or in HRP, these tracers were taken up in much smaller amounts, primarily within the contents of endocytic vesicles. With continued incubation, they appeared only in lysosomes. When cells were doubly incubated, first in CF and then in HRP, both tracers were taken up (often within the same endocytic vesicle), but they maintained their same destinations as when incubated in a single tracer alone: the content marker, HRP, was localized exclusively within the lysosomal system, whereas the membrane marker, CF, was found within elements along the secretory pathway as well as within lysosomes. The findings demonstrate the existence of considerable membrane traffic between the cell membrane and the Golgi cisternae and lysosomes in both normal plasma cells and myeloma cells. Because myeloma cells behave like the glandular cells studied previously with regard to pathways of retrieved surface membrane, they represent a suitable and promising system for further studies of mechanisms and pathways of membrane retrieval and recycling in secretory cells.

Menstrual activity of matrix metalloproteinases is decreased in endometrium regenerating after thermal ablation.

BACKGROUND: Menstruation is associated with a striking increase in matrix metalloproteinase (MMP) activity. However, it is still unknown whether the level of MMP activity correlates with the amount of menstrual bleeding. METHODS: We used histochemistry to investigate the degradation of the extracellular matrix (ECM), and immunohistochemical labelling and zymographic analysis to determine the level of expression and activity of MMP-2 and -9, and of their tissue inhibitors (TIMPs) -1, -2 and -3, in endometria sampled during menstruation in 14 women experiencing excessive menstrual bleeding and in 10 women successfully treated for menorrhagia by thermal ablation of the endometrium. RESULTS: After thermal ablation, regenerated menstrual endometria showed reduced areas of collagen fibre lysis and increased content of TIMP-1 and TIMP-2 compared with endometria from non-treated menorrhagic women. Surprisingly, treated endometria contained more latent gelatinase A (proMMP-2) but a lower proportion of the active form of gelatinase B (MMP-9) than non-treated endometria. CONCLUSIONS: These results suggest that ECM degradation is decreased at menstruation in the endometrium regenerated after thermal ablation, mostly because of an increased TIMP expression. This represents the first molecular explanation for the decreased amount of menstrual bleeding.

Shift of equilibrium density induced by 3,3'-diaminobenzidine cytochemistry: a new procedure for the analysis and purification of peroxidase-containing organelles.

Galactosylated BSA (galBSA) and its conjugate to horseradish peroxidase (galBSA-HRP) enter the galactose-specific pathway of hepatocytes. 10 min after intravenous injection, structures containing either ligand sediment mostly between 33,000 and 3 X 10(6) g X min (LP fraction) and have an equilibrium density of 1.11-1.13 g/ml in sucrose gradients (Quintart, J., P. J. Courtoy, J. N. Limet, and P. Baudhuin, 1983, Eur. J. Biochem., 131:105-112). Such low density fractions, prepared from rats given galBSA-HRP, were incubated for 30 min at 25 degrees C in 5.5 mM 3,3'-diaminobenzidine (DAB) and 11 mM H2O2 in buffered sucrose. Upon equilibration in a second sucrose gradient, the galBSA-HRP distribution shifted towards higher (approximately 1.19 g/ml) density, but the bulk of protein remained at low density. In the absence of H2O2, galBSA-HRP distribution was also found at low density. As observed by electron microscopy, particles equilibrating at higher density after DAB cytochemistry were largely made of vesicles or tubules filled with DAB reaction product. The density shift of galBSA-HRP-containing organelles after incubation with DAB and H2O2 is attributed to the trapping of HRP-oxidized DAB inside the host organelles. If the low density fractions isolated from a rat injected with [3H]galBSA-HRP were mixed in vitro with similar fractions from another rat given [14C]galBSA, the 3H distribution shifted after DAB cytochemistry, but the 14C distribution was essentially unaffected. By contrast, if both derivatives were injected simultaneously, a concomitant density shift was observed. In conclusion, the DAB-induced density shift was specific to ligand-HRP-containing organelles. The potentials of the method include the purification of HRP-containing particles and the study of their association to ligands, fluid-phase tracers, or marker enzymes.

Receptor-mediated endocytosis in rat liver: purification and enzymic characterization of low density organelles involved in uptake of galactose-exposing proteins.

Rat liver organelles involved in receptor-mediated endocytosis were labeled with a conjugate of galactosylated BSA to horseradish peroxidase [( 3H]galBSA-HRP), injected 10 min before sacrifice. These organelles were recovered at low density (1.11-1.13 g/ml) in sucrose gradients (Quintart, J., P. J. Courtoy, J. N. Limet, and P. Baudhuin, 1983, Eur. J. Biochem., 131:105-112). Upon incubation of such low density fractions in 3,3'-diaminobenzidine (DAB) and H2O2 and equilibration in a second sucrose gradient, galBSA-HRP-containing particles selectively shifted towards heavier densities (Courtoy, P. J., J. Quintart, and P. Baudhuin, 1984, J. Cell Biol., 98:870-876, companion paper), resulting in up to 250-to 300-fold purification with respect to the homogenate. The most purified preparations, wherein DAB-stained structures represented approximately 85% of the total volume of particles, contained only trace activities of enzymes usually regarded as markers for other subcellular entities. These minor activities could reflect either contamination or true enzyme association to the ligand-containing structures. Considering the latter hypothesis, at most 1.0% of alkaline phosphodiesterase I and 2.6% of 5'-nucleotidase (markers for plasma membrane), 3.6% of N-acetyl-beta-glucosaminidase (lysosomes), and 6.0% of galactosyltransferase (Golgi complex) from the homogenate would be associated with the whole population of ligand-containing organelles. After DAB cytochemistry on liver fixed 10 min after galBSA-HRP injection, ligand-containing structures accounted for 0.78-0.89% of the fractional volume of the hepatocytes and displayed a membrane area of 2,100 cm2/cm3, compared with 6,700 cm2/cm3 for the pericellular membrane. Altogether, our data support the hypothesis that these ligand-containing organelles are structurally distinct from plasma membrane, lysosomes, and Golgi complex.

A quantitative model of traffic between plasma membrane and secondary lysosomes: evaluation of inflow, lateral diffusion, and degradation.

We present here a mathematical model that accounts for the various proportions of plasma membrane constituents occurring in the lysosomal membrane of rat fibroblasts (Draye, J.-P., J. Quintart, P. J. Courtoy, and P. Baudhuin. 1987. Eur. J. Biochem. 170: 395-403; Draye, J.-P., P. J. Courtoy, J. Quintart, and P. Baudhuin. 1987. Eur. J. Biochem. 170:405-411). It is based on contents of plasma membrane markers in purified lysosomal preparations, evaluations of their half-life in lysosomes and measurements of areas of lysosomal and plasma membranes by morphometry. In rat fibroblasts, structures labeled by a 2-h uptake of horseradish peroxidase followed by a 16-h chase (i.e., lysosomes) occupy 3% of the cellular volume and their total membrane area corresponds to 30% of the pericellular membrane area. Based on the latter values, the model predicts the rate of inflow and outflow of plasma membrane constituents into lysosomal membrane, provided their rate of degradation is known. Of the bulk of polypeptides iodinated at the cell surface, only 4% reach the lysosomes every hour, where the major part (integral of 83%) is degraded with a half-life in lysosomes of integral to 0.8 h. For specific plasma membrane constituents, this model can further account for differences in the association to the lysosomal membrane by variations in the rate either of lysosomal degradation, of inflow along the pathway from the pericellular membrane to the lysosomes, or of lateral diffusion.

Cell-mediated extracellular acidification and bone resorption: evidence for a low pH in resorbing lacunae and localization of a 100-kD lysosomal membrane protein at the osteoclast ruffled border.

The extracellular compartment where bone resorption occurs, between the osteoclast and bone matrix, is shown in this report to be actively acidified. The weak base acridine orange accumulates within this compartment but dissipates after incubation with ammonium chloride. Upon removal of ammonium chloride, the cells are able to rapidly reacidify this compartment. The highly convoluted plasma membrane of the osteoclast facing this acidic compartment (ruffled border) is shown to contain a 100-kD integral membrane protein otherwise present in limiting membranes of lysosomes and other related acidified organelles (Reggio, H., D. Bainton, E. Harms, E. Coudrier, and D. Louvard, 1984, J. Cell Biol., 99:1511-1526; Tougard, C., D. Louvard, R. Picart, and A. Tixier-Vidal, 1985, J. Cell Biol. 100:786-793). Antibodies recognizing this 100-kD lysosomal membrane protein cross-react with a proton-pump ATPase from pig gastric mucosae (Reggio, H., D. Bainton, E. Harms, E. Coudrier, and D. Louvard, 1984, J. Cell Biol., 99:1511-1526), therefore raising the possibility that it plays a role in the acidification of both intracellular organelles and extracellular compartments. Lysosomal enzymes are also directionally secreted by the osteoclast into the acidified extracellular compartment which can therefore be considered as the functional equivalent of a secondary lysosome with a low pH, acid hydrolases, the substrate, and a limiting membrane containing the 100-kD antigen.

Polarized secretion of lysosomal enzymes: co-distribution of cation-independent mannose-6-phosphate receptors and lysosomal enzymes along the osteoclast exocytic pathway.

The osteoclast is a polarized cell which secretes large amounts of newly synthesized lysosomal enzymes into an apical extracellular lacuna where bone resorption takes place. Using immunocytochemical techniques, we have localized the cation-independent mannose-6-phosphate (Man6P) receptor and lysosomal enzymes in this cell type in order to determine the expression and distribution of this receptor and its ligands. The results demonstrate that the osteoclast expresses large amounts of immunoreactive cation-independent Man6P receptors, despite the fact that most of the lysosomal enzymes it synthesizes are secreted. The lysosomal enzymes and the receptors are co-distributed along the exocytic pathway, i.e., the endoplasmic reticulum, including the perinuclear envelope, the Golgi stacks as well as numerous small transport vesicles that appear to fuse with the ruffled border membrane. Within the Golgi complex, the receptors and lysosomal enzymes were found distributed in two predominant patterns; (a) in all the cisternae, from cis to trans, or (b) predominantly in cis- and trans-Golgi cisternae, with the middle Golgi cisternae being unstained or depleted in antigen. This pattern suggests that enzymes and receptors traverse the Golgi from cis to trans and preferentially accumulate in cis- and in trans-cisternae. This study therefore suggests that, in the osteoclast, Man6P receptors are involved in the vectorial transport and targeting of newly synthesized lysosomal enzymes, presumably via a constitutive pathway, to the apical membrane where they are secreted into the bone-resorbing compartment. This mechanism could insure polarized secretion of lysosomal enzymes into the bone-resorbing lacuna.

Fibronectin localization in the rat glomerulus.

Fibronectin (FN) has been localized in the rat glomerulus using indirect immunolabeling. It was demonstrated in frozen sections by immunofluorescence, in sections of fixed kidneys by both peroxidase and ferritin-labeled antibodies, and in isolated glomerular basement membranes (GBM) with ferritin-labeled antibodies. Complementary and convergent results were obtained with these approaches. FN was most abundant in the mesangial matrix where it was especially concentrated at the interface between the endothelial and mesangial cells. In the peripheral capillary loop, FN was also detected in the laminae rarae (interna and externa) of the GBM--i.e., between the endothelial and epithelial cells, respectively, and the GBM. These findings indicate that FN is an important constituent of the glomerulus, and they are compatible with the assumption that, in the glomerulus, as in cultured cells, FN is involved in cell-to-cell (mesangial-mesangial, mesangial-endothelial) and cell-to-substrate (mesangial cell-mesangial matrix, epithelium-GBM, endothelium-GBM) attachment.

Clathrin polymerization is not required for bulk-phase endocytosis in rat fetal fibroblasts.

To assess the role of clathrin in the bulk endocytic flow of rat foetal fibroblasts, the rate of internalization of fluid-phase and membrane-lipid tracers were compared, under control conditions and after inhibition of endocytic clathrin-coated pit formation. After intracellular potassium depletion or upon cell transfer into 0.35 M NaCl, the rate of internalization of receptor-bound transferrin and the residual membrane area of plasmalemmal clathrin-coated pits and vesicles were similarly decreased by approximately 90%. In contrast, the initial rate (< 5 min) of intracellular accumulation of the fluid-phase tracer HRP was not affected. Both in control and treated cells, the rate of HRP accumulation declined after approximately 5 min, and was twofold lower in treated cells, due to enhanced regurgitation. After correction for regurgitation, the endocytic rate constant was similar to measurements at shorter intervals and identical in control and treated cells. Similarly, the rate of internalization and the steady-state level of intracellular accumulation of two fluorescent lipid derivatives, 6-[N-(7-nitro-2,1,3-benzoxadiazol-4-yl)amino]hexanoylglucosylsp hingosine (C6-NBD-GlcCer) and 1-[4-(trimethylamino)phenyl]-6-phenylhexa-1,3,5-triene (TMA-DPH), were not affected by potassium depletion, indicating that the endocytic membrane traffic was equally preserved. Finally, the size distribution of primary endocytic particles that were accessible to HRP within 15 s before glutaraldehyde fixation was also indistinguishable in control and potassium-depleted cells. The simplest explanation is that clathrin polymerization is necessary to concentrate receptor-bound ligands in primary endocytic vesicles, but superfluous to the basic endocytic machinery in rat foetal fibroblasts.

Decrease of elastic moduli of DOPC bilayers induced by a macrolide antibiotic, azithromycin.

The elastic properties of membrane bilayers are key parameters that control its deformation and can be affected by pharmacological agents. Our previous atomic force microscopy studies revealed that the macrolide antibiotic, azithromycin, leads to erosion of DPPC domains in a fluid DOPC matrix [A. Berquand, M. P. Mingeot-Leclercq, Y. F. Dufrene, Real-time imaging of drug-membrane interactions by atomic force microscopy, Biochim. Biophys. Acta 1664 (2004) 198-205.]. Since this observation could be due to an effect on DOPC cohesion, we investigated the effect of azithromycin on elastic properties of DOPC giant unilamellar vesicles (GUVs). Microcinematographic and morphometric analyses revealed that azithromycin addition enhanced lipid membranes fluctuations, leading to eventual disruption of the largest GUVs. These effects were related to change of elastic moduli of DOPC, quantified by the micropipette aspiration technique. Azithromycin decreased both the bending modulus (k(c), from 23.1+/-3.5 to 10.6+/-4.5 k(B)T) and the apparent area compressibility modulus (K(app), from 176+/-35 to 113+/-25 mN/m). These data suggested that insertion of azithromycin into the DOPC bilayer reduced the requirement level of both the energy for thermal fluctuations and the stress to stretch the bilayer. Computer modeling of azithromycin interaction with DOPC bilayer, based on minimal energy, independently predicted that azithromycin (i) inserts at the interface of phospholipid bilayers, (ii) decreases the energy of interaction between DOPC molecules, and (iii) increases the mean surface occupied by each phospholipid molecule. We conclude that azithromycin inserts into the DOPC lipid bilayer, so as to decrease its cohesion and to facilitate the merging of DPPC into the DOPC fluid matrix, as observed by atomic force microscopy. These investigations, based on three complementary approaches, provide the first biophysical evidence for the ability of an amphiphilic antibiotic to alter lipid elastic moduli. This may be an important determinant for drug: lipid interactions and cellular pharmacology.

A novel renal carbonic anhydrase type III plays a role in proximal tubule dysfunction.

Dysfunction of the proximal tubule (PT) is associated with variable degrees of solute wasting and low-molecular-weight proteinuria. We measured metabolic consequences and adaptation mechanisms in a model of inherited PT disorders using PT cells of ClC-5-deficient (Clcn5Y/-) mice, a well-established model of Dent's disease. Compared to cells taken from control mice, those from the mutant mice had increased expression of markers of proliferation (Ki67, proliferative cell nuclear antigen (PCNA), and cyclin E) and oxidative scavengers (superoxide dismutase I and thioredoxin). Transcriptome and protein analyses showed fourfold induction of type III carbonic anhydrase in a kidney-specific manner in the knockout mice located in scattered PT cells. Kidney-specific carbonic anhydrase type III (CAIII) upregulation was confirmed in other mice lacking the multiligand receptor megalin and in a patient with Dent's disease due to an inactivating CLCN5 mutation. The type III enzyme was specifically detected in the urine of mice lacking ClC-5 or megalin, patients with Dent's disease, and in PT cell lines exposed to oxidative stress. Our study shows that lack of PT ClC-5 in mice and men is associated with CAIII induction, increased cell proliferation, and oxidative stress.

Constitutive macropinocytosis in oncogene-transformed fibroblasts depends on sequential permanent activation of phosphoinositide 3-kinase and phospholipase C.

Macropinocytosis results from the closure of lamellipodia generated by membrane ruffling, thereby reflecting cortical actin dynamics. Both transformation of Rat-1 fibroblasts by v-Src or K-Ras and stable transfection for expression of dominant-positive, wild-type phosphoinositide 3-kinase (PI3K) regulatory subunit p85 alpha constitutively led to stress fiber disruption, cortical actin recruitment, extensive ruffling, and macropinosome formation, as measured by a selective acceleration of fluid-phase endocytosis. These alterations closely correlated with activation of PI3K and phosphatidylinositol-specific phospholipase C (PI-PLC), as assayed by 3-phosphoinositide synthesis in situ and in vitro and inositol 1, 4,5 trisphosphate steady-state levels, respectively; they were abolished by stable transfection of v-Src-transformed cells for dominant-negative truncated p85 alpha expression and by pharmacological inhibitors of PI3K and PI-PLC, indicating a requirement for both enzymes. Whereas PI3K activation resisted PI-PLC inhibition, PI-PLC activation was abolished by a PI3K inhibitor and dominant-negative transfection, thus placing PI-PLC downstream of PI3K. Together, these data suggest that permanent sequential activation of both PI3K and PI-PLC is necessary for the dramatic reorganization of the actin cytoskeleton in oncogene-transformed fibroblasts, resulting in constitutive ruffling and macropinocytosis.

Role for dynamin in late endosome dynamics and trafficking of the cation-independent mannose 6-phosphate receptor.

It is well established that dynamin is involved in clathrin-dependent endocytosis, but relatively little is known about possible intracellular functions of this GTPase. Using confocal imaging, we found that endogenous dynamin was associated with the plasma membrane, the trans-Golgi network, and a perinuclear cluster of cation-independent mannose 6-phosphate receptor (CI-MPR)-containing structures. By electron microscopy (EM), it was shown that these structures were late endosomes and that the endogenous dynamin was preferentially localized to tubulo-vesicular appendices on these late endosomes. Upon induction of the dominant-negative dynK44A mutant, confocal microscopy demonstrated a redistribution of the CI-MPR in mutant-expressing cells. Quantitative EM analysis of the ratio of CI-MPR to lysosome-associated membrane protein-1 in endosome profiles revealed a higher colocalization of the two markers in dynK44A-expressing cells than in control cells. Western blot analysis showed that dynK44A-expressing cells had an increased cellular procathepsin D content. Finally, EM revealed that in dynK44A-expressing cells, endosomal tubules containing CI-MPR were formed. These results are in contrast to recent reports that dynamin-2 is exclusively associated with endocytic structures at the plasma membrane. They suggest instead that endogenous dynamin also plays an important role in the molecular machinery behind the recycling of the CI-MPR from endosomes to the trans-Golgi network, and we propose that dynamin is required for the final scission of vesicles budding from endosome tubules.

Identification, purification and partial characterisation of an oligonucleotide receptor in membranes of HepG2 cells.

The low and unpredictable uptake and cytosolic transfer of oligonucleotides (ODN) is a major reason for their limited benefit. Improving the ODN potential for therapy and research requires a better understanding of their receptor-mediated endocytosis. We have undertaken to identify a membrane ODN receptor on HepG2 cells by ligand blotting of cell extracts with [(125)I]ODN and by photolabelling of living cells with a [(125)I]ODN-benzophenone conjugate. A major band at 66 kDa was identified by the two methods. Its labelling was saturable and competed for by unlabelled ODN of various sequences and irrespective of the presence of a phosphodiester or phosphoro-thioate backbone. This protein remained sedimentable after carbonate extraction, indicating strong membrane association. About half of the total cell amount resisted extensive surface proteolysis, suggesting a dual localisation at the plasma membrane and cytoplasmic vesicles. The protein was purified using a biotinylated ODN-benzophenone conjugate by photocrosslinking followed by streptavidin affinity purification. A sequence obtained by Edman degradation showed no homology with known proteins. Using anti-peptide antisera, labelling by western blotting revealed at 66 kDa a band with comparable properties as found by ligand blotting. Thus, a new membrane protein acting as an ODN receptor has been demonstrated.

Hematopoietic Stem Cells Transplantation Can Normalize Thyroid Function in a Cystinosis Mouse Model.

Hypothyroidism is the most frequent and earliest endocrine complication in cystinosis, a multisystemic lysosomal storage disease caused by defective transmembrane cystine transporter, cystinosin (CTNS gene). We recently demonstrated in Ctns(-/-) mice that altered thyroglobulin biosynthesis associated with endoplasmic reticulum stress, combined with defective lysosomal processing, caused hypothyroidism. In Ctns(-/-) kidney, hematopoietic stem cell (HSC) transplantation provides long-term functional and structural protection. Tissue repair involves transfer of cystinosin-bearing lysosomes from HSCs differentiated as F4/80 macrophages into deficient kidney tubular cells, via tunneling nanotubes that cross basement laminae. Here we evaluated the benefit of HSC transplantation for cystinotic thyroid and investigated the underlying mechanisms. HSC engraftment in Ctns(-/-) thyroid drastically decreased cystine accumulation, normalized the TSH level, and corrected the structure of a large fraction of thyrocytes. In the thyroid microenvironment, HSCs differentiated into a distinct, mixed macrophage/dendritic cell lineage expressing CD45 and major histocompatibility complex II but low CD11b and F4/80. Grafted HSCs closely apposed to follicles and produced tunneling nanotube-like extensions that crossed follicular basement laminae. HSCs themselves further squeezed into follicles, allowing extensive contact with thyrocytes, but did not transdifferentiate into Nkx2.1-expressing cells. Our observations revealed significant differences of basement lamina porosity between the thyroid and kidney and/or intrinsic macrophage invasive properties once in the thyroid microenvironment. The contrast between extensive thyrocyte protection and low HSC abundance at steady state suggests multiple sequential encounters and/or remanent impact. This is the first report demonstrating the potential of HSC transplantation to correct thyroid disease and supports a major multisystemic benefit of stem cell therapy for cystinosis.

Expression and role of Bcl-2 in rat blastocysts exposed to high D-glucose.

Bcl-2 mRNA expression was detected in rat blastocysts by in situ hybridization. The distribution of mRNA expression was rather heterogenous, with approximately 2% of high-expressing cells. In vitro exposure to 28 mmol/l D-glucose for 24 h resulted in a significant increase in the proportion of these cells compared with control embryos in either 6 mmol/l D-glucose or 28 mmol/l D+L-glucose. Heterogeneity in the expression of Bcl-2 was also observed at the protein level by immunocytochemistry. Exposure to 28 mmol/l D-glucose significantly increased the incidence of chromatin degradation (karyolysis) and nuclear fragmentation (karyorhexis), two nuclear markers of apoptosis in rat blastocysts. When two different antisense oligodeoxynucleotides designed to block Bcl-2 expression were added to 28 mmol/1 D-glucose, the incidence of karyolysis (but not karyorhexis) was increased compared with embryos in 28 mmol/l D-glucose alone. These data suggest that Bcl-2 is involved in the protective response against the induction of karyolysis in blastocysts on their exposure to high concentrations of D-glucose in vitro, whereas karyorhexis appears to result from the activation of an intracellular pathway that is independent of Bcl-2.