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Biomedical subjects

Heikki Rauvala

Publications and source records attributed to Heikki Rauvala.

30 records · Page 2Linked to original sources
PubMed2003

AMIGO, a transmembrane protein implicated in axon tract development, defines a novel protein family with leucine-rich repeats.

Ordered differential display identified a novel sequence induced in neurons by the neurite-promoting protein amphoterin. We named this gene amphoterin-induced gene and ORF (AMIGO), and also cloned two other novel genes homologous to AMIGO (AMIGO2 and AMIGO3). Together, these three AMIGOs form a novel family of genes coding for type I transmembrane proteins which contain a signal sequence for secretion and a transmembrane domain. The deduced extracellular parts of the AMIGOs contain six leucine-rich repeats (LRRs) flanked by cysteine-rich LRR NH2- and COOH-terminal domains and by one immunoglobulin domain close to the transmembrane region. A substrate-bound form of the recombinant AMIGO ectodomain promoted prominent neurite extension in hippocampal neurons, and in solution, the same AMIGO ectodomain inhibited fasciculation of neurites. A homophilic and heterophilic binding mechanism is shown between the members of the AMIGO family. Our results suggest that the members of the AMIGO protein family are novel cell adhesion molecules among which AMIGO is specifically expressed on fiber tracts of neuronal tissues and participates in their formation.

Animals↗
PubMed2003

Activity blockade increases the number of functional synapses in the hippocampus of newborn rats.

During development neuronal circuitries are refined by activity. Here we studied the role of spontaneous electrical activity in the regulation of synapse formation in the intact newborn (Postnatal Day 3; P3) rat hippocampus in vitro. The blockade of the spontaneous network activity with TTX led to an increase in the number of functional excitatory synapses in the CA3 area of the developing hippocampus. In parallel, there was a substantial increase in the expression levels of the presynaptic markers synaptophysin, synaptotagmin, and synapsin I and of GluR1 AMPA receptor subunits. These changes were associated with an increase in the frequency and amplitude of AMPA receptor-mediated miniature excitatory postsynaptic currents (mEPSCs). Our correlated immunocytochemical, electronmicroscopical, and electrophysiological experiments indicate that in the developing hippocampus spontaneous network activity controls the number of functional synapses.

Action Potentials↗
PubMed2002

Effects of targeted overexpression of pleiotrophin on postnatal bone development.

Pleiotrophin (PTN) is an extracellular matrix-associated growth/differentiation factor that, in post-natal life, is found mainly in bone and brain. Bone development was investigated in ptn-overexpressing mice between 1 and 30 weeks. In transgenics and controls, PTN (and its receptor syndecan-3) was synthesized by osteoblasts and was present in striated muscle. ptn over-expression enhanced intramembranous bone formation and had multiple effects on long-term bone growth. The pubertal growth spurt did not take place in transgenic mice, in which the growth trajectory was steady and continuous until 25 weeks. By 30 weeks, transgenic and control mice were of the same size, but the calcium content/mg bone was approximately 10% higher in the transgenics. PTN was also localized in growth plate and articular chondrocytes, but only in transgenic mice. In these, synthesis of type I collagen by articular chondrocytes was observed, as well as an encroachment of subchondral bone into the articular cartilage. The results suggest that PTN has multiple roles during in vivo bone formation and remodeling, probably acting as a co-factor or accessory protein that modulates the effects of primary signaling molecules.

Animals↗
PubMed2002

Receptor for advanced glycation end products-binding COOH-terminal motif of amphoterin inhibits invasive migration and metastasis.

Amphoterin has been suggested to regulate invasive process extension and cell migration in tumor cells and embryonic neurons through binding to receptor for advanced glycation end products (RAGE), a multiligand transmembrane receptor belonging to the immunoglobulin superfamily. In this study, we identify a COOH-terminal motif in amphoterin (amino acids 150-183) that is responsible for RAGE binding. We show that as a surface-bound ligand, this part of amphoterin is sufficient to induce RAGE-dependent process extension, suggesting a role in the regulation of cell motility. When applied in solution, the RAGE-binding COOH-terminal motif of amphoterin efficiently inhibits process extension and transendothelial migration of tumor cells. Furthermore, in an in vivo model, the corresponding synthetic peptide significantly suppresses formation of lung metastases. Taken together, these results suggest that amphoterin binds to RAGE through a COOH-terminal motif that can be used as an efficient inhibitor to block invasive migration of tumor cells.

Amino Acid Motifs↗
PubMed2002

Receptor for advanced glycation end products (RAGE) signaling induces CREB-dependent chromogranin expression during neuronal differentiation.

Receptor for advanced glycation end products (RAGE) mediates neurite outgrowth and cell migration upon stimulation with its ligand, amphoterin. We show here that RAGE-dependent changes in cell morphology are associated with proliferation arrest and changes in gene expression in neuroblastoma cells. Chromogranin B, a component of secretory vesicles in endocrine cells and neurons, was found to be up-regulated by RAGE signaling during differentiation of neuroblastoma cells along with the two other members of the chromogranin family, chromogranin A and secretogranin II. Ligation of RAGE by amphoterin lead to rapid phosphorylation and nuclear localization of cyclic AMP response element-binding protein (CREB), a major regulator of chromogranin expression. Furthermore, inhibition of ERK1/2-Rsk2-dependent CREB phosphorylation efficiently inhibited up-regulation of chromogranin gene expression upon RAGE activation. To further study the effects of RAGE and amphoterin on cellular differentiation, we stimulated embryonic stem cells expressing RAGE or a signaling-deficient mutant of RAGE with amphoterin. Amphoterin was found to promote RAGE-dependent neuronal differentiation of embryonic stem cells characterized by up-regulation of neuronal markers light neurofilament protein and beta-III-tubulin, activation of CREB, and increased expression of chromogranins A and B. These data suggest that RAGE signaling is capable of driving neuronal differentiation involving CREB activation and induction of chromogranin expression.

Animals↗
PubMed2002

Cognitive deficit and development of motor impairment in a mouse model of Niemann-Pick type C disease.

Niemann-Pick disease type C (NPC) is a fatal, autosomal recessive lipidosis characterized by a unique error in cellular trafficking of cholesterol. In the disease, unesterified cholesterol as well as sphingolipids accumulate in the late endosomes/lysosomes due to mutations in either of two recently isolated genes, NPC1 or NPC2. A metabolic and neurological disorder reminiscent of human NPC disease has been described in Balb/C mice, and it was recently shown that the mutation in the NPC mice resides in the orthologous murine Npc1 gene. Here we have followed the growth rate and applied behavioural methods in order to establish the onset and development of the major symptoms in the NPC mouse model. Wild type and NPC mice were studied during 28-59 days of age. Both male and female NPC mice displayed retarded growth at the age between 25 and 35 days. At the age of 35-45 days the weight was similar to controls and thereafter very rapidly decreased. The battery of coordination tests (vertical screen, beam balancing, coat hanger and rotating rod) established motor impairment of the NPC mice already at the age of 28-42 days, well before the onset of visually detectable ataxia. Decreased exploratory activity and lack of habituation was revealed in the NPC mice by open field test. The diseased mice were unable to learn and remember the location of the hidden escape platform in spatial water maze task suggesting cognitive impairment. In several tests the male NPC mice were more affected than the females. The present study represents the first behavioural analysis of the NPC mice. The battery of behavioural tests employed here should be valuable in the assessment of effective approaches to treat NPC, for which no preventive or curative measures have so far been established.

Animals↗
PubMed2002

Role of heparin-binding growth-associated molecule (HB-GAM) in hippocampal LTP and spatial learning revealed by studies on overexpressing and knockout mice.

Heparin-binding growth-associated molecule (HB-GAM) is an extracellular matrix-associated protein with neurite outgrowth-promoting activity and which is suggested to be implicated in hippocampal synaptic plasticity. To study the functions of HB-GAM in adult brain we have produced HB-GAM overexpressing mice and compared phenotypic changes in the transgenic mice to those in the HB-GAM null mice. Both mutants were viable and displayed no gross morphological abnormalities. The basal synaptic transmission was normal in the area CA1 of hippocampal slices from the genetically modified mice. However, long-term potentiation (LTP) was attenuated in the mice overexpressing HB-GAM, whereas enhanced LTP was detected in the HB-GAM-deficient mice. Changes in LTP seen in vitro were paralleled by behavioral alterations in vivo. The animals overexpressing HB-GAM displayed faster learning in water maze and decreased anxiety in elevated plus-maze, while the HB-GAM knockouts demonstrated an opposite behavioral phenotype. These results show that HB-GAM suppresses LTP in hippocampus and plays a role in regulation of learning-related behavior.

Animals↗
PubMed2002

Syndecan-3-deficient mice exhibit enhanced LTP and impaired hippocampus-dependent memory.

Syndecan-3 (N-syndecan) is a transmembrane heparan sulfate proteoglycan expressed predominantly in the nervous system in a developmentally regulated manner. Syndecan-3 has been suggested to play a role in the development and plasticity of neuronal connections by linking extracellular signals to the regulation of the cytoskeleton. To study its physiological functions, we produced mice deficient in syndecan-3 by gene targeting. The mutant animals are healthy, are fertile, and have no apparent defects in the structure of the brain. We focused on characterizing the functions of the hippocampus, a brain area where expression of syndecan-3 is prominent in adults. Mice lacking syndecan-3 exhibited an enhanced level of long-term potentiation (LTP) in area CA1, while basal synaptic transmission and short-term plasticity were similar to those in wild-type animals. Further, the mutant mice were not responsive to the syndecan-3 ligand heparin-binding growth-associated molecule, which inhibits LTP in area CA1 in wild-type animals. Behavioral testing of the syndecan-3-deficient mice revealed impaired performance in tasks assessing hippocampal functioning. We suggest that syndecan-3 acts as an important modulator of synaptic plasticity that influences hippocampus-dependent memory.

Animals↗
PubMed2002

N -Glycans on the receptor for advanced glycation end products influence amphoterin binding and neurite outgrowth.

In this study we show that embryonic neurite growth-promoting protein amphoterin binds to carboxylated N -glycans previously identified on mammalian endothelial cells. Since amphoterin is a ligand for the receptor for advanced glycation end products (RAGE), and the ligand-binding V-domain of the receptor contains two potential N -glycosylation sites, we hypothesized that N -glycans on RAGE may mediate its interactions with amphoterin. In support of this, anti-carboxylate antibody mAbGB3.1 immunoprecipitates bovine RAGE, and PNGase F treatment reduces its molecular mass by 4.5 kDa, suggesting that the native receptor is a glycoprotein. The binding potential of amphoterin to RAGE decreases significantly in presence of soluble carboxylated glycans or when the receptor is deglycosylated. Oligosaccharide analysis shows that RAGE contains complex type anionic N -glycans with non-sialic acid carboxylate groups, but not the HNK-1 (3-sulfoglucuronyl beta1-3 galactoside) epitope. Consistent with the functional localization of RAGE and amphoterin at the leading edges of developing neurons, mAbGB3.1 stains axons and growth cones of mouse embryonic cortical neurons, and inhibits neurite outgrowth on amphoterin matrix. The carboxylated glycans themselves promote neurite outgrowth in embryonic neurons and RAGE-transfected neuroblastoma cells. This outgrowth requires full-length, signalling-competent RAGE, as cells expressing cytoplasmic domain-deleted RAGE are unresponsive. These results indicate that carboxylated N -glycans on RAGE play an important functional role in amphoterin-RAGE-mediated signalling.

Animals↗
PubMed2001

Receptor for advanced glycation end products plays a more important role in cellular survival than in neurite outgrowth during retinoic acid-induced differentiation of neuroblastoma cells.

The receptor for advanced glycation end products (RAGE), a member of the immunoglobulin superfamily, is known to interact with amphoterin. This interaction has been proposed to play a role in neurite outgrowth and process elongation during neurodifferentiation. However, there is as yet no direct evidence of the relevance of this pathway to neurodifferentiation under physiological conditions. In this study we have investigated a possible role of RAGE and amphoterin in the retinoic acid-induced differentiation of neuroblastoma cells. The functional inactivation of RAGE by dominant negative and antisense strategies showed that RAGE is not required for process outgrowth or differentiation, although overexpression of RAGE accelerates the elongation of neuritic processes. Using the antisense strategy, amphoterin was shown to be essential for process outgrowth and differentiation, suggesting that amphoterin may interact with other molecules to exert its effect in this context. Interestingly, the survival of the neuroblastoma cells treated with retinoic acid was partly dependent on the expression of RAGE, and inhibition of RAGE function partially blocked the increase in anti-apoptotic protein Bcl-2 following retinoic acid treatment. Based on these results we propose that a combination therapy using RAGE blockers and retinoic acid may prove as a useful approach for chemotherapy for the treatment of neuroblastoma.

Animals↗
PubMedDate not supplied

HB-GAM/Pleiotrophin and Midkine are differently expressed and distributed during retinoic acid-induced neural differentiation of P19 cells.

HB-GAM/Pleiotrophin and Midkine (MK) are developmentally-regulated proteins with putative functions during cell growth and differentiation. Using the P19 cell which is a model to study the events associated with early development, we examined the expression and cellular localization of HB-GAM and MK during neural differentiation of P19 cells induced by retinoic acid (RA). The temporal expressions of HB-GAM and MK transcripts and both the levels and cellular localizations of the corresponding proteins appeared dramatically different. MK mRNA, already expressed in untreated P19 cells, was transiently increased by exposure to RA and then largely down regulated. More interestingly, HB-GAM which was not detected in untreated P19 cells was strongly expressed after 2 days of RA treatment and this expression persists throughout the duration of the culture suggesting that it could be involved in different aspects of this differentiation process.

Animals↗