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Biomedical subjects

U Langel

Publications and source records attributed to U Langel.

At least 19 recordsLinked to original sources
PubMed2006

Intramembrane receptor-receptor interactions: a novel principle in molecular medicine.

In 1980/81 Agnati and Fuxe introduced the concept of intramembrane receptor-receptor interactions and presented the first experimental observations for their existence in crude membrane preparations. The second step was their introduction of the receptor mosaic hypothesis of the engram in 1982. The third step was their proposal that the existence of intramembrane receptor-receptor interactions made possible the integration of synaptic (WT) and extrasynaptic (VT) signals. With the discovery of the intramembrane receptor-receptor interactions with the likely formation of receptor aggregates of multiple receptors, so called receptor mosaics, the entire decoding process becomes a branched process already at the receptor level in the surface membrane. Recent developments indicate the relevance of cooperativity in intramembrane receptor-receptor interactions namely the presence of regulated cooperativity via receptor-receptor interactions in receptor mosaics (RM) built up of the same type of receptor (homo-oligomers) or of subtypes of the same receptor (RM type1). The receptor-receptor interactions will to a large extent determine the various conformational states of the receptors and their operation will be dependent on the receptor composition (stoichiometry), the spatial organization (topography) and order of receptor activation in the RM. The biochemical and functional integrative implications of the receptor-receptor interactions are outlined and long-lived heteromeric receptor complexes with frozen RM in various nerve cell systems may play an essential role in learning, memory and retrieval processes. Intramembrane receptor-receptor interactions in the brain have given rise to novel strategies for treatment of Parkinson's disease (A2A and mGluR5 receptor antagonists), schizophrenia (A2A and mGluR5 agonists) and depression (galanin receptor antagonists). The A2A/D2, A2A/D3 and A2A/mGluR5 heteromers and heteromeric complexes with their possible participation in different types of RM are described in detail, especially in the cortico-striatal glutamate synapse and its extrasynaptic components, together with a postulated existence of A2A/D4 heteromers. Finally, the impact of intramembrane receptor-receptor interactions in molecular medicine is discussed outside the brain with focus on the endocrine, the cardiovascular and the immune systems.

Animals↗
PubMed2006

Galanin/GALP receptors and CNS homeostatic processes.

Galanin is a 29/30 amino acid peptide neurotransmitter that is widely distributed throughout the central nervous system and periphery. There are three well-characterized G-protein coupled galanin receptors subtypes (GalR1-3). A more recently discovered 60 amino acid galanin-like peptide (GALP) shares amino acid sequence homology with galanin (1-13) in position 9-21 and has high binding affinity for GalR1-3, with highest affinity for GalR3. Considerable evidence has accumulated that implicates both galanin and GALP as playing important roles in regulating food and water intake behavior and related neuroendocrine functions. Pharmacological tools are emerging that will allow dissociation of specific roles for the peptides and their associated receptor subtypes in mediating the homeostatic processes of energy and fluid balance.

Animals↗
PubMed2004

An antioxidant tetrapeptide UPF1 in rats has a neuroprotective effect in transient global brain ischemia.

Different glutathione analogues have potential to maintain or increase tissue glutathione level and to scavenge the reactive oxygen species. We designed and synthesized a novel non-toxic glutathione analogue, named UPF1, which possessed 60-fold higher hydroxyl radical scavenger efficiency in vitro, compared with glutathione itself, and investigated the effects of UPF1 on a four-vessel occlusion model of rats. The UPF1 was administered via the jugular vein in two separate experiments at two time points: 20 min before global brain ischemia and immediately before reperfusion. In both cases the number of pyramidal cells surviving in the subfield of CA1 at the dorsal hippocampus in the UPF1-treated groups of rats was twice as high as in the vehicle group.

Animals↗
PubMed2004

Cellular delivery of a double-stranded oligonucleotide NFkappaB decoy by hybridization to complementary PNA linked to a cell-penetrating peptide.

The activation of nuclear factor kappaB (NFkappaB) is a key event in immune and inflammatory responses. In this study, a cell-penetrating transport peptide, transportan (TP) or its shorter analogue TP 10, was used to facilitate the cellular uptake of an NFkappaB decoy. Peptide nucleic acid (PNA) hexamer or nonamer was linked to the transport peptide by a disulfide bond. NFkappaB decoy oligonucleotide consisted of a double-stranded consensus sequence corresponding to the kappaB site localized in the IL-6 gene promoter, 5'-GGGACTTTCCC-3', with a single-stranded protruding 3'-terminal sequence complementary to the PNA sequence was hybridized to the transport peptide-PNA construct. The ability of the transport peptide-PNA-NFkappaB decoy complex to block the effect of interleukin (IL)-1beta-induced NFkappaB activation and IL-6 gene expression was analyzed by electrophoretic mobility shift assay and reverse transcriptase-polymerase chain reaction in rat Rinm5F insulinoma cells. Preincubation with transport peptide-PNA-NFkappaB decoy (1 microM, 1 h) blocked IL-1beta-induced NFkappaB-binding activity and significantly reduced the IL-6 mRNA expression. The same concentration of NFkappaB decoy in the absence of transport peptide-PNA had no effect even after longer incubations. Our results showed that binding of the oligonucleotide NFkappaB decoy to the nonamer PNA sequence resulted in a stable complex that was efficiently translocated across the plasma membrane.

Animals↗
PubMed2002

Cell membrane translocation of the N-terminal (1-28) part of the prion protein.

The N-terminal (1-28) part of the mouse prion protein (PrP) is a cell penetrating peptide, capable of transporting large hydrophilic cargoes through a cell membrane. Confocal fluorescence microscopy shows that it transports the protein avidin (67kDa) into several cell lines. The (1-28) peptide has a strong tendency for aggregation and beta-structure formation, particularly in interaction with negatively charged phospholipid membranes. The findings have implications for how prion proteins with uncleaved signal peptides in the N-termini may enter into cells, which is important for infection. The secondary structure conversion into beta-structure may be relevant as a seed for the conversion into the scrapie (PrP(Sc)) form of the protein and its amyloidic transformation.

Amino Acid Sequence↗
PubMed2002

Interaction of calcitonin-gene-related peptide with its receptors.

The receptor for calcitonin-gene-related peptide (CGRP) is a heterodimer formed by calcitonin-receptor-like receptor (CRLR), a type II (family B) G-protein-coupled receptor, and receptor-activity-modifying protein 1 (RAMP1), a single-membrane-pass protein. It is likely that the first seven or so amino acids of CGRP (which form a disulphide-bonded loop) interact with the transmembrane domain of CRLR to cause receptor activation. The rest of the CGRP molecule falls into three domains. Residues 28-37 and 8-18 are normally required for high-affinity binding, while residues 19-27 form a hinge region. The 28-37 region is almost certainly in direct contact with the receptor; 8-18 may make additional receptor contacts or may stabilize an appropriate conformation of 28-37. It is likely that these regions of CGRP interact both with CRLR and with the extracellular domain of RAMP1.

Animals↗
PubMed2002

Possible signaling by glutathione and its novel analogue through potent stimulation of fontocortical G proteins in normal aging and in Alzheimer's disease.

In the frontal cortex (FC) of the normally aging human brain, glutathione (GSH) and its novel analogue, UPF1, stimulate G proteins more than in Alzheimer's disease (AD) FC. In normal aging and in AD, UPF1 is a more efficient stimulator of G proteins than GSH. In normal FC, both GSH and UPF1 stimulate G proteins, which mediate inhibitory signals to the cAMP system; while in AD, only UPF1 exhibits the same action. Stimulation of G proteins and coupled signaling by GSH antioxidant analogues, as potential signaling molecules, may ameliorate the oxidative impairments of neuronal signaling in AD.

Adenylyl Cyclases↗
PubMed2001

Cargo delivery kinetics of cell-penetrating peptides.

A diversity of cell-penetrating peptides (CPPs), is known, but so far the only common denominator for these peptides is the ability to gain cell entry in an energy-independent manner. The mechanism used by CPPs for cell entry is largely unknown, and data comparing the different peptides are lacking. In order to gain more information about the cell-penetrating process, as well as to quantitatively compare the uptake efficiency of different CPPs, we have studied the cellular uptake and cargo delivery kinetics of penetratin, transportan, Tat (48-60) and MAP (KLAL). The respective CPPs (labelled with the fluorescence quencher, 3-nitrotyrosine) are coupled to small a pentapeptide cargo (labelled with the 2-amino benzoic acid fluorophore) via a disulfide bond. The cellular uptake of the cargo is registered as an increase in fluorescence intensity when the disulfide bond of the CPP-S-S-cargo construct is reduced in the intracellular milieu. Our data show that MAP has the fastest uptake, followed by transportan, Tat(48-60) and, last, penetratin. Similarly, MAP has the highest cargo delivery efficiency, followed by transportan, Tat (48-60) and, last, penetratin. Since some CPPs have been found to be toxic at high concentration, we characterized the influence of CPPs on cellular 2-[(3)H]deoxyglucose-6-phosphate leakage. Measurements on this system show that the membrane-disturbing potential appears to be correlated with the hydrophobic moment of the peptides. In summary, the yield and kinetics of cellular cargo delivery for four different CPPs has been quantitatively characterized.

Amino Acid Sequence↗
PubMed2001

Interaction and structure induction of cell-penetrating peptides in the presence of phospholipid vesicles.

Certain short peptides, which are able to translocate across cell membranes with a low lytic activity, can be useful as carriers (vectors) for hydrophilic molecules. We have studied three such cell penetrating peptides: pAntp ('penetratin'), pIsl and transportan. pAntp and pIsl originate from the third helix of homeodomain proteins (Antennapedia and Isl-1, respectively). Transportan is a synthetic chimera (galanin and mastoparan). The peptides in the presence of various phospholipid vesicles (neutral and charged) and SDS micelles have been characterized by spectroscopic methods (fluorescence, EPR and CD). The dynamics of pAntp were monitored using an N-terminal spin label. In aqueous solution, the CD spectra of the three peptides show secondary structures dominated by random coil. With phospholipid vesicles, neutral as well as negatively charged, transportan gives up to 60% alpha-helix. pAntp and pIsl bind significantly only to negatively charged vesicles with an induction of around 60% beta-sheet-like secondary structure. With all three peptides, SDS micelles stabilize a high degree of alpha-helical structure. We conclude that the exact nature of any secondary structure induced by the membrane model systems is not directly correlated with the common transport property of these translocating peptides.

Carrier Proteins↗
PubMed2001

Secondary structure and position of the cell-penetrating peptide transportan in SDS micelles as determined by NMR.

Transportan is a 27-residue peptide (GWTLN SAGYL LGKIN LKALA ALAKK IL-amide) which has the ability to penetrate into living cells carrying a hydrophilic load. Transportan is a chimeric peptide constructed from the 12 N-terminal residues of galanin in the N-terminus with the 14-residue sequence of mastoparan in the C-terminus and a connecting lysine. Circular dichroism studies of transportan and mastoparan show that both peptides have close to random coil secondary structure in water. Sodium dodecyl sulfate (SDS) micelles induce 60% helix in transportan and 75% helix in mastoparan. The 600 MHz (1)H NMR studies of secondary structure in SDS micelles confirm the helix in mastoparan and show that in transportan the helix is localized to the mastoparan part. The less structured N-terminus of transportan has a secondary structure similar to that of the same sequence in galanin [Ohman, A., et al. (1998) Biochemistry 37, 9169-9178]. The position of mastoparan and transportan relative to the SDS micelle surface was studied by adding spin-labeled 5-doxyl- or 12-doxyl-stearic acid or Mn2+ to the peptide/micelle system. The combined results show that the peptides are for the most part buried in the SDS micelles. Only the C-terminal parts of both peptides and the central segment connecting the two parts of transportan are clearly surface exposed. For mastoparan, the secondary chemical shifts of the amide protons were found to vary periodically and display a pattern almost identical to those reported for mastoparan in phospholipid bicelles [Vold, R., et al. (1997) J. Biomol. NMR 9, 329-335], indicating similar structures and interactions in the two membrane-mimicking environments.

Amino Acid Sequence↗
PubMed2001

Different domains in the third intracellular loop of the GLP-1 receptor are responsible for Galpha(s) and Galpha(i)/Galpha(o) activation.

It has previously been shown that the GLP-1 receptor is primarily coupled to the adenylate cyclase pathway via activation of Galpha(s) proteins. Recent studies have shown that the third intracellular loop of the receptor is important in the stimulation of cAMP production. We have studied the effect of three synthetic peptide sequences derived from the third intracellular loop of the GLP-1 receptor on signal transduction in Rin m5F cell membranes. The whole third intracellular loop strongly stimulates both pertussis toxin and cholera toxin-sensitive G proteins, while the N-terminal half exclusively stimulates cholera toxin-sensitive G proteins and the C-terminal half only stimulates pertussis toxin-sensitive G-proteins as demonstrated by measurements of GTPase activity. These data confirm that the principal stimulatory G-protein interaction site resides in the third intracellular loop, but also suggest that the GLP-1 receptor is not only coupled to the Galpha(s) but also to the Galpha(i)/Galpha(o) type of G proteins and that distinct domains within the third intracellular loop are responsible for the activation of the different G-protein subfamilies.

Adenylate Cyclase Toxin↗
PubMed2001

p53 Latency. C-terminal domain prevents binding of p53 core to target but not to nonspecific DNA sequences.

The p53 transcription factor is either latent or activated through multi-site phosphorylation and acetylation of the negative regulatory region in its C-terminal domain (CTD). How CTD modifications activate p53 binding to target DNA sequences via its core domain is still unknown. It has been proposed that nonmodified CTD interacts either with the core domain or with DNA preventing binding of the core domain to DNA and that the fragments of the CTD regulatory region activate p53 by interfering with these interactions. We here characterized the sequence and target specificity of p53 activation by CTD fragments, interaction of activating peptides with p53 and target DNA, and interactions of "latent" p53 with DNA by a band shift assay and by fluorescence correlation spectroscopy. In addition to CTD fragments, several long basic peptides activated p53 and also transcription factor YY1. These peptides and CTD aggregated target DNA but apparently did not interact with p53. The potency to aggregate DNA correlated with the ability to activate p53, suggesting that p53 binds to target sequences upon interactions with tightly packed DNA in aggregates. Latent full-length p53 dissociated DNA aggregates via its core and CTD, and this effect was potentiated by GTP. Latent p53 also formed complexes via both its core and CTD with long nontarget DNA molecules. Such p53-DNA interactions may occur if latent p53 binding to DNA via CTD prevents the interaction of the core domain with target DNA sites but not with nonspecific DNA sequences.

Amino Acid Sequence↗
PubMed2001

Intrathecal administration of PNA targeting galanin receptor reduces galanin-mediated inhibitory effect in the rat spinal cord.

Peptide nucleic acids (PNA) are nucleic acid analogues containing neutral amide backbone, forming stable and tight complexes with complementary DNA/RNA. However, it is unclear whether unmodified PNA can efficiently penetrate neuronal tissue in order to act as antisense reagent. Here we show that intrathecal (i.t.) injection of an unmodified antisense PNA complementary to the rat galanin receptor type 1 (GalR1) mRNA is able to block the inhibitory effect of i.t. administered galanin on spinal nociceptive transmission. Autoradiographic ligand binding studies using [125I]galanin show that the unmodified PNA is able to reduce the density of galanin binding sites in the dorsal horn. Thus, unmodified PNA applied i.t. appears to function as an effective antisense reagent in rat spinal cord in vivo.

Animals↗
PubMed2001

Synthesis of of beta-amyloid precursor peptide and presenilin segments.

It seems likely that the beta-amyloid precursor protein (APP) and the presenilins (PS-1/2) play important roles in the development of Alzheimer's disease (AD). Attempts to mimic the biochemical actions of these proteins are often made by the application of fragments of these proteins. However, the synthesis of these segments by conventional methods of peptide synthesis is problematic. We have synthesized several C-terminal fragments of APP and PS-1/2 by solid-phase synthesis through combination of automatic and manual methods of synthesis. This permits solution of the 'difficult sequences' in the solid-phase synthesis of these peptides. Some details of the syntheses of nine segments are presented in this paper.

Amino Acid Sequence↗
PubMed2001

PNA oligomers as tools for specific modulation of gene expression.

Small synthetic molecules that can specifically inhibit translation and/or transcription have shown great promise as potential antisense/antigene drugs. Peptide nucleic acid (PNA), an oligonucleotide mimic, has a non-charged achiral polyamide backbone to which the nucleobases are attached. PNA oligomers are extremely stable in biological fluids and they specifically hybridise to DNA or RNA in a complementary manner, forming very strong heteroduplexes. Some of the mRNAs have yet undetermined and possibly long half-lives, successful down regulation of gene expression by antisense oligonucleotides (ON) requires that the antisense agent is long lived. PNA fulfils this requirement better than phosphodiester or phosphorothioate ONs. PNA can inhibit transcription and translation of respective genes by tight binding to DNA or mRNA. First in vitro experiments to specifically down regulate protein expression by PNA have been followed by successful antisense and antigene application of PNA oligomers in vivo. This review discusses the principles of the in vitro and in vivo use of PNA oligonucleotides.

Animals↗
PubMed2001

Galanin: an endogenous anticonvulsant?

Galanin is a neuroendocrine peptide involved in the regulation of feeding, pain, sexual behavior, learning, and memory. The recent discovery, that galanin antagonized excitatory glutamatergic neurotransmission in the hippocampus, provided a rationale for its possible antiepileptic effects. Here we summarize the data on the effects of galanin on seizure activity in several animal models of epilepsy. Pharmacological and molecular biological evidence suggest potent anticonvulsant effects of galanin. Exogenous administration of galanin receptor agonists attenuated seizures, whereas application of galanin receptor antagonists potentiated seizure expression. Genetically engineered mice, with either deletion or overexpression of galanin gene, showed altered resistance to seizures, which was in direct correlation with galanin gene expression. Possible mechanisms of the anticonvulsant action of galanin include its effects on synaptic potentiation in hippocampal circuits and inhibition of the release of the excitatory neurotransmitter glutamate from principal hippocampal neurons.

Animals↗
PubMed2001

Increased gene expression of interleukin-1alpha and interleukin-6 in rat primary glial cells induced by beta-amyloid fragment.

One of the pathological hallmarks of Alzheimer's disease (AD) is the presence of amyloid plaques. The main constituent of the amyloid plaques is the amyloid beta-peptide (A beta) shown to activate glial cells in vitro. A growing body of evidence suggests that these cells contribute to neurotoxicity through production of inflammatory cytokines, chemokines, and neurotoxic substances, such as reactive oxygen species (ROS). In this study, mRNA levels of the inflammatory cytokines interleukin (IL)-1alpha and beta, and IL-6 were analysed by reverse transcriptase-polymerase chain reaction (RT-PCR) in rat primary mixed glial cells after treatment with A beta(25-35), a biologically active fragment of A beta peptide with neurotoxic properties. Clear morphological changes of the astrocytes, as well as proliferation and clustering of microglial cells were observed by light and immunofluorescence microscopy after 24 h treatment. Significant increases in IL-1alpha and IL-6 mRNA levels were detected after 24 and 72 h, whereas significantly increased levels of IL-1beta mRNA could only be detected after 4 h treatment. The most pronounced effect was seen on IL-6 mRNA expression, which increased approx two- to threefold after treatment. In addition, increased secretion of IL-6 was detected after 96 h exposure. Recently, association of IL-1alpha and IL-6 gene polymorphism with AD was reported, suggesting that these cytokines may play an important role in the development of the disease. The increased mRNA levels of IL-1alpha and IL-6 in parallel with the morphological changes in the mixed glial-cell cultures support that these cytokines may be involved in A beta-induced gliosis and in the pathogenesis of AD.

Amyloid beta-Peptides↗