Biomedical subjects

M Henseler

Publications and source records attributed to M Henseler.

10 recordsLinked to original sources

PubMed2001

Classical and quantum periodically driven scattering in one dimension.

Irregular scattering at harmonically driven one-dimensional potential wells is studied both on the classical and the quantum level. We show that an ac-driven single square well, and a smooth well with oscillating bottom, are sufficient to generate chaotic scattering. For a square well with oscillating bottom, we introduce the concept of pseudointegrable scattering. The quantum dynamics of these models is treated using Floquet scattering theory, which is exact for arbitrary amplitude and frequency of the driving. In the deep quantum regime, scattering is dominated by multiphoton exchanges with the driving field, leading to complex resonance structures in transmission and reflection. For strong and fast driving, the ac-driven square well develops an effective double-well potential that introduces coherent tunneling in the scattering. We identify signatures of classical chaotic scattering in a phase-space representation of the quantum dynamics.

Journal Article↗

PubMed2000

A non-glycosylated and functionally deficient mutant (N215H) of the sphingolipid activator protein B (SAP-B) in a novel case of metachromatic leukodystrophy (MLD).

The lysosomal degradation of sphingolipids with short oligosaccharide chains depends on small glycosylated non-enzymatic sphingolipid activator proteins (SAPs, saposins). Four of the five known SAPs, SAP-A, -B, -C and -D, are derived by proteolytic processing from a common precursor protein (SAP-precursor) that is encoded by a gene on chromosome 10 consisting of 15 exons and 14 introns. SAP-B is a non-specific glycolipid binding protein that stimulates in vitro the hydrolysis of about 20 glycolipids by different enzymes. In vivo SAP-B stimulates in particular the degradation of sulphatides by arylsulphatase A. So far, four different point mutations have been identified on the SAP-B domain of the SAP-precursor gene. The mutations result in a loss of mature SAP-B, causing the lysosomal accumulation of sulphatides and other sphingolipids, resulting in variant forms of metachromatic leukodystrophy (MLD). Here we report on a patient with SAP-B deficiency that is caused by a new homoallelic point mutation that has been identified by mRNA and DNA analysis. A 643A > C transversion results in the exchange of asparagine 215 to histidine and eliminates the single glycosylation site of SAP-B. Metabolic labelling experiments showed that the mutation had no effect on the intracellular transport of the encoded precursor to the acidic compartments and its maturation in the patient's cells. All four SAPs (SAP-A to SAP-D) were detectable by immunochemical methods. SAP-B in the patient's cells was found to be slightly less stable than the protein in normal cells and corresponded in size to the deglycosylated form of the wild-type SAP-B. Feeding studies with non-glycosylated SAP-precursor, generating non-glycosylated SAP-B, showed that the loss of the carbohydrate chain reduced the intracellular activity of the protein significantly. The additional structural change of the patient's SAP-B, caused by the change of amino acid 215 from asparagine to histidine, presumably resulted in an almost completely inactive protein.

Child, Preschool↗

PubMed1998

Nonredox 5-lipoxygenase inhibitors require glutathione peroxidase for efficient inhibition of 5-lipoxygenase activity.

Nonredox type 5-lipoxygenase (5-LO) inhibitors, such as ZM 230487, its methyl analogue ZD 2138, or the Merck compound L-739,010, suppress cellular leukotriene synthesis of ionophore stimulated granulocytes with IC50 values of about 50 nM. However, in cell homogenates or in preparations of purified enzyme, up to 150-fold higher concentrations are required for similar inhibition of 5-LO activity. This loss of 5-LO inhibition in cell homogenates was reversed by addition of glutathione or dithiothreitol, which increased the inhibitory potency of ZM 230487 or L-739,010 by about 100 to 150-fold so that 5-LO inhibition was comparable with that of intact cells. In the presence of thiols, addition of hydroperoxide [13(S)-HpODE], glutathione-peroxidase inhibition by iodacetate or selenium-deficiency lead to impaired 5-LO inhibition by ZM 230487 in cell homogenates. Moreover, addition of glutathione peroxidase was required for efficient inhibition of purified human 5-LO by ZM 230487. The data suggest that low hydroperoxide concentrations are important for efficient 5-LO inhibition by ZM 230487. The kinetic analysis revealed a noncompetitive inhibition of 5-LO by ZM 230487 at low hydroperoxide levels, whereas it acted as a competitive inhibitor with low affinity under nonreducing conditions in granulocyte homogenates. No such redox-dependent effects were observed with the 5-LO inhibitor BWA4C, the 5-LO activating protein-inhibitor MK-886 or the pentacyclic triterpene acetyl-11-keto-beta-boswellic acid. These data suggest that physiological conditions associated with oxidative stress and increased peroxide levels lead to impaired efficacy of nonredox type 5-LO inhibitors like ZM 230487 or L-739,010. This could explain the reported lack of activity of this class of 5-LO inhibitors in chronic inflammatory processes.

Arachidonate 5-Lipoxygenase↗

PubMed1996

Expression of the three alternative forms of the sphingolipid activator protein precursor in baby hamster kidney cells and functional assays in a cell culture system.

Sphingolipid activator proteins (SAPs) are non-enzymatic glycoproteins required for lysosomal degradation of various sphingolipids with short oligosaccharide chains by their respective exohydrolases. Four of these (SAP-A to SAP-D or saposins A to D) are derived from a common precursor by proteolytic processing. Alternative splicing of the SAP-precursor gene results in insertion of additional 6 or 9 bases of exon 8' or 8, respectively, into the SAP-B coding region of the transcribed mRNAs. To examine the features of the three different SAP-precursor proteins (prosaposins), the respective cDNAs were stably expressed in baby hamster kidney cells. Pulse-chase experiments with transfected cells and endocytosis studies on human fibroblasts showed that synthesis, transport, and maturation of all SAP-precursor led to formation of the four mature SAPs (SAP-A to SAP-D). In order to determine the biological function of the three different SAP-B isoforms, SAP-precursor-deficient human fibroblasts were loaded with recombinant SAP-precursor proteins with or without 2- and 3-amino acid insertions, respectively, purified from the medium of the baby hamster kidney cells. They were found to stimulate at nanomolar concentrations the turnover of biosynthetically labeled ceramide, glucosylceramide, and lactosylceramide. Since the physiological function of SAP-B is to stimulate the degradation of sulfatide by arylsulfatase A (EC 3.1.6.1) and globotriaosylceramide by beta-galactosidase (EC 3.2.1.23) loading studies with the respective exogenously labeled lipids on SAP-precursor-deficient fibroblasts were performed. Addition of different purified SAP-precursors to the medium of the lipid-loaded fibroblasts showed positive stimulation of the lipid degradation by all three SAP-B isoforms derived from the SAP-precursors. These findings establish that all three forms of the SAP-B can function as sulfatide/globotriaosylceramide activator.

Alternative Splicing↗

PubMed1996

Targeted disruption of the mouse sphingolipid activator protein gene: a complex phenotype, including severe leukodystrophy and wide-spread storage of multiple sphingolipids.

The four established or putative sphingolipid activator proteins derive from a large precursor protein encoded by a single gene. In addition to generating the four sphingolipid activator proteins, the precursor protein is suspected of having functions of its own, as, for example, a lipid binding/transport protein or a neurotrophic factor. The gene also appears to encode the Sertoli cell major sulfated glycoprotein. Sequence similarities have been noted with many other proteins of diverse functions. One patient and a fetus in a single family with a complete defect of this gene due to a mutation in the initiation codon exhibited complex pathological and biochemical abnormalities. Mutant mice homozygous for an inactivated gene of the sphingolipid activator protein precursor exhibit two distinct clinical phenotypes-neonatally fatal and later-onset. The latter develop rapidly progressive neurological signs around 20 days and die by 35-38 days. At 30 days, severe hypomyelination and periodic acid-Schiff-positive materials throughout the nervous system and in abnormal cells in the liver and spleen are the main pathology. Most prominently lactosylceramide, and additionally ceramide, glucosylceramide, galactosylceramide, sulfatide, and globotriaosylceramide are abnormally increased in the brain, liver, kidney, and their catabolism abnormally slow in cultured fibroblasts. Brain gangliosides are generally increased, particularly the monosialogangliosides. The clinical, pathological and biochemical phenotype closely resembles that of the human disease. This model not only allows further clarification of the physiological functions of the four individual sphingolipid activator proteins but also should be useful to explore putative functions of the precursor protein.

Animals↗

PubMed1996

Analysis of a splice-site mutation in the sap-precursor gene of a patient with metachromatic leukodystrophy.

Sphingolipid activator proteins (SAPs) are small, nonenzymatic glycoproteins required for the lysosomal degradation of various sphingolipids with a short oligosaccharide chain by their exohydrolases. Four of the five known activator proteins (sap-A-sap-D), also called "saposins," are derived from a common precursor by proteolytic processing. sap-B stimulates hydrolysis of sulfatides by arylsulfatase A in vivo. Its recessively inherited deficiency results in a metabolic disorder similar to classical metachromatic leukodystrophy, which is caused by a defect of arylsulfatase A. Here we report on a patient with sap-B deficiency. Reverse-transcription-PCR studies on the patient's mRNA revealed the occurrence of two distinct mutant species: one with an in-frame deletion of the first 21 bases of exon 6, the other with a complete in-frame deletion of this exon. The patient was homozygous for the underlying mutation, which was found to be a G-->T transversion within the acceptor splice site between intron e and exon 6, abolishing normal RNA splicing. Allele-specific oligonucleotide hybridization revealed that the parents and both grandfathers of the patient were carriers of this mutation. In order to analyze the fate of the mutant precursor proteins, both abnormal cDNAs were stably expressed in baby hamster kidney cells. Pulse-chase experiments showed that the deletion of 21 bp had no effect on the transport and the maturation of the encoded precursor. All sap forms except sap-B were detectable by immunochemical methods. The cDNA bearing a complete deletion of exon 6 encoded a shortened precursor of only 60 kD, and no mature SAPs were detectable. The carbohydrate chains of this polypeptide were of the high-mannose and hybrid type, indicating no transport of the mutant precursor beyond early Golgi apparatus. An endoplasmic-reticulum localization of this polypeptide was supported by indirect immunofluorescence analysis.

Animals↗

PubMed1995

Sphingolipid activator proteins (SAPs) are stored together with glycosphingolipids in the infantile neuronal ceroid-lipofuscinosis (INCL).

The storage material isolated from the brains of patients with infantile neuronal ceroid-lipofuscinosis (INCL) contains, on average, 43% protein and 35% lipids on a dry weight basis. Recently we identified the major storage proteins as sphingolipid activator proteins (SAPs) A and D by direct sequencing. In the present study we used monospecific anti-sap-B-, anti-sap-C, and anti-sap-D-antisera in immunohistochemical and Western analyses to show that sap-D is, indeed, an integral component of the storage bodies. In contrast, no (or little) immunoreactivity for sap-B or sap-C was detected in the INCL storage granules. This observation is of interest for an understanding of the pathogenesis because the four SAPs are produced from a single precursor protein by proteolytic cleavage. Furthermore, we analysed the stored lipids on high performance thin layer chromatography combined with different staining techniques. In this preliminary analysis we found two glycosphingolipids, yet to be identified, to be common for all INCL patients.

Adolescent↗

PubMed1995

Sphingolipid activator proteins in the neuronal ceroid-lipofuscinoses: an immunological study.

The molecular defects underlying neuronal ceroid-lipofuscinoses (NCL) are still unknown. However, more data exist on the composition of the hydrophobic storage material characteristic of NCL. Accumulation of subunit c of the mitochondrial ATP synthase has been shown in most forms of human NCL with the exception of the infantile NCL (INCL) for which we have recently demonstrated storage of sphingolipid activator proteins (SAP). In the present study we raised an antiserum against storage cytosomes purified from INCL brain. Using the anti-INCL antiserum and monospecific SAP antisera, we studied storage material isolated from the brains of patients affected with NCL by Western analysis, and found a 12-kDa protein showing a SAP-like immunoreactivity not only in INCL, but also in all the childhood forms of NCL. Furthermore, using the anti-sap-D antiserum for immunohistochemistry, we observed strong immunoreactivity of the storage cytosomes in all major forms of NCL, and also in tissues of non-neuroectodermal origin. From these data we conclude that the presence of SAP within the storage bodies is a phenomenon common to all major forms of human NCL.

Adolescent↗

PubMed1995

Immunological studies on sphingolipid activator proteins in the neuronal ceroid-lipofuscinoses.

The neuronal ceroid-lipofuscinoses constitute an important group of progressive encephalopathies leading to severe psychomotor retardation, blindness, and early death. They are characterized by accumulation of autofluorescent, electron-dense storage bodies within the cytoplasm of neurons and many other cell types. We have recently identified sphingolipid activator proteins A and D as major components of the storage cytosomes in the infantile form of NCL. Using an immunological approach we have shown that sphingolipid activator proteins also constitute an integral component of the storage bodies in the other major forms of the disease.

Blotting, Western↗

PubMed1994

Sphingolipid activator protein D (sap-D) stimulates the lysosomal degradation of ceramide in vivo.

Glycosphingolipids of cultured fibroblasts from patients with total sphingolipid activator proteins (SAPs) deficiency (Schnabel et al. J. Biol. Chem. 267:3312-3315, 1992) were labeled biosynthetically with [14C]serine. After a chase period of 120h the patients' fibroblasts showed increased labeling of ceramide, glucosylceramide, lactosylceramide and ganglioside GM3 in comparison to normal control cells. Addition of sap-D to the chase-media of the patients' fibroblasts led to the degradation of the accumulated ceramide down to nearly normal levels, whereas the levels of other labeled sphingolipids remained unaffected. In contrast, addition of sap-B to the chase-media of the patients' fibroblasts did not reduce the increased ceramide levels but resulted, as expected from in vitro experiments, in a specific decrease of levels of lactosylceramide and ganglioside GM3. Therefore, we conclude that sap-D stimulates in vivo the lysosomal degradation of ceramide.

Cells, Cultured↗