Biomedical subjects

B Malgrange

Publications and source records attributed to B Malgrange.

At least 19 recordsLinked to original sources

PubMed2005

Molecular pathways involved in apoptotic cell death in the injured cochlea: cues to novel therapeutic strategies.

Most hearing loss results from lesions of the sensory cells and/or neurons of the auditory portion of the inner ear. To date, only the cochlear implantation offers long-term hearing-aid benefit, but still with limited performance and expensive cost. While the underlying causes of deafness are not clear, the death or hair cells and/or neurons and the loss of neuronal contacts are key pathological features. Pinpointing molecular events that control cell death in the cochlea is critical for the development of new strategies to prevent and treat deafness, whether in combination or not with cochlear implant therapy.

Apoptosis↗

PubMed2005

[Differentiation, protection and regeneration of hair cells and auditory neurons in mammals].

Perception deafness, as opposed to transmission deafness, results from a lesion of the sensory cells and/or of the neurons of the auditory part of inner ear. There is currently no treatment able to stop the progression of a hearing loss or to restore a lost auditory function. We review here the progress which has been made with respect to the regeneration and the protection of neurosensory structures in the inner ear. A spontaneous post-lesional regeneration of hair cells in the sensory epithelium has been observed in amphibians and birds as well as in the vestibular part of the mammalian inner ear. In contrast, hair cells regeneration in the auditory portion of the inner ear of mammals appears to be limited to the developmental stages. The objective of this first part of our work is to try to identify progenitor cells in the cochlea and to characterize factors that are able to induce their proliferation and differentiation. Otoprotection of the sensory epithelium is another therapeutical strategy aimed at preventing further degradation of the auditory function. The prevention of the deleterious effect on hair cells of several drugs such as aminoglycosides and platin derivatives has been obtained using free radical scavengers or growth factors. Studies of the development of the innervation of the inner ear suggest the potential therapeutic interest of various growth factors, mostly the neurotrophins, to maintain the innervation of the adult Corti's organ.

Animals↗

PubMed2004

Caspases, the enemy within, and their role in oxidative stress-induced apoptosis of inner ear sensory cells.

This review covers the general roles of members of the cysteine protease family of caspases in the process of apoptosis (programmed cell death) looking at their participation in both the "extrinsic" cell death receptor and the "intrinsic" mitochondrial cell death pathways. It defines the difference between initiator and effector caspases and shows the progression of caspase activations that ends up in the apoptotic cell death and elimination of a damaged cell. The review then presents what is currently know about the participation of caspases in the programmed cell death of inner ear sensory cells during the process of normal development and maturation of the inner ear and their importance in this process as illustrated by the results of caspase-3 gene knockout experiments. The participation of specific caspases and the sequence of their activation in the elimination (apoptosis) of damaged sensory cells from adult inner ears after an injury that generates oxidative stress are reviewed. Both the possibility and the potential efficacy of caspase inhibition with a broad-spectrum pancaspase inhibitor as an interventional therapy to treat and rescue oxidative stress-damaged inner ear sensory cells from apoptosis are presented and discussed.

Adult↗

PubMed2003

Substance P protects spiral ganglion neurons from apoptosis via PKC-Ca2+-MAPK/ERK pathways.

In the current study, we have investigated the ability of substance P (SP) to protect 3-day-old (P3) rat spiral ganglion neurons (SGNs) from trophic factor deprivation (TFD)-induced cell death. The presence of SP high affinity neurokinin-1 receptor (NK1) transcripts was detected in the spiral ganglion and the NK1 protein localized to SGNs both ex vivo and in vitro. Treatment with SP increased cytoplasmic Ca2+ in SGNs, further arguing for the presence of functional NK1 on these neurons. Both SP and the agonist [Sar9,Met(O2)11]-SP significantly decreased SGN cell death induced by TFD, with no effect on neurite outgrowth. The survival promoting effect of SP was blocked by the NK1 antagonist, WIN51708. Both pan-caspase inhibitor BOC-D-FMK and SP treatments markedly reduced activation of caspases and DNA fragmentation in trophic factor deprived-neurons. The neuroprotective action of SP was antagonised by specific inhibitors of second messengers, including 1.2-bis-(O-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM) to chelate cytosolic Ca2+, the protein kinase C (PKC) inhibitors bisindolylmaleimide I, Gö6976 and LY333531 and the MAPK/ERK inhibitor U0126. In contrast, nifedipine, a specific inhibitor of l-type Ca2+ channel, and LY294002, a phosphatidylinositol-3-OH kinase (PI3K) inhibitor, had no effect on SP trophic support of SGNs. Moreover, activation of endogenous PKC by 4 beta-phorbol 12-myristate 13-acetate (PMA) also reduced the loss of trophic factor-deprived SGNs. Thus, NK1 expressed by SGNs transmit a survival-promoting regulatory signal during TFD-induced SGN cell death via pathways involving PKC activation, Ca2+ signalling and MAPK/ERK activation, which can be accounted for by an inhibition of caspase activation.

Animals↗

PubMed2002

AAV2 vectors mediate efficient and sustained transduction of rat embryonic ventral mesencephalon.

The success of transplantation of human embryonic mesencephalic tissue to treat parkinsonian patients is limited by the poor survival of the transplant. We show that an AAV2 vector mediates efficient expression of the egfp reporter gene in organotypic cultures of freshly explanted solid fragments of rat embryonic ventral mesencephalon (VM). We observed early and sustained transgene expression (4 days to > or = 6 weeks). Furthermore, rAAV-infected rat embryonic VM transplanted in the adult striatum continued to express EGFP for > or = 3 months. More than 95% of the transduced cells were neurons. Dopaminergic neurons were transduced at low frequency at earlier time points. This method of gene delivery could prove useful to achieve local, continuous secretion of neurotrophic factors at physiologically relevant doses to treat Parkinson's disease.

Animals↗

PubMed2002

Epithelial supporting cells can differentiate into outer hair cells and Deiters' cells in the cultured organ of Corti.

The organ of Corti is a complex structure containing a single row of inner hair cells (IHCs) and three rows of outer hair cells (OHCs), supported respectively by one row of inner phalangeal cells and three rows of Deiters' cells. When fetal rat organ of Corti explants are cultured, supernumerary OHCs and supernumerary Deiters' cells are produced, without any additional cell proliferation. Analysis of semi- and ultrathin sections revealed that supernumerary OHCs are produced at the distal edge of the organ of Corti. Quantitative analysis of cell types present in the organ of Corti demonstrates that when the number of OHCs increases: (i) the total number of cells remains constant; (ii) the number of Deiters' cells increases; (iii) the number of tectal cells decreases and of Hensen's cells decreases. Using specific HC markers, i.e. jagged2 (Jag2) and Math1, we showed that in addition to existing OHCs, supernumerary OHCs, tectal cells and Hensen's cells expressed these markers in embryonic day 19 organ of Corti explants after 5 days in vitro. The results of this study suggest that Hensen's cells retain the capacity to differentiate into either tectal cells, which differentiate into OHCs, or into undertectal cells which differentiate into Deiters' cells.

Animals↗

PubMed2002

The anti-epileptic drug levetiracetam reverses the inhibition by negative allosteric modulators of neuronal GABA- and glycine-gated currents.

1. In this study in vitro and in vivo approaches were combined in order to investigate if the anti-epileptic mechanism(s) of action of levetiracetam (LEV; Keppra) may involve modulation of inhibitory neurotransmission. 2. GABA- and glycine-gated currents were studied in vitro using whole-cell patch-clamp techniques applied on cultured cerebellar granule, hippocampal and spinal neurons. Protection against clonic convulsions was assessed in vivo in sound-susceptible mice. The effect of LEV was compared with reference anti-epileptic drugs (AEDs): carbamazepine, phenytoin, valproate, clonazepam, phenobarbital and ethosuximide. 3. LEV contrasted the reference AEDs by an absence of any direct effect on glycine-gated currents. At high concentrations, beyond therapeutic relevance, it induced a small reduction in the peak amplitude and a prolongation of the decay phase of GABA-gated currents. A similar action on GABA-elicited currents was observed with the reference AEDs, except ethosuximide. 4. These minor direct effects contrasted with a potent ability of LEV (EC(50)=1 - 10 microM) to reverse the inhibitory effects of the negative allosteric modulators zinc and beta-carbolines on both GABA(A) and glycine receptor-mediated responses. 5. Clonazepam, phenobarbital and valproate showed a similar ability to reverse the inhibition of beta-carbolines on GABA-gated currents. Blockade of zinc inhibition of GABA responses was observed with clonazepam and ethosuximide. Phenytoin was the only AED together with LEV that inhibited the antagonism of zinc on glycine-gated currents and only clonazepam and phenobarbital inhibited the action of DMCM. 6. LEV (17 mg kg(-1)) produced a potent suppression of sound-induced clonic convulsions in mice. This protective effect was significantly abolished by co-administration of the beta-carboline FG 7142, from a dose of 5 mg kg(-1). In contrast, the benzodiazepine receptor antagonist flumazenil (up to 10 mg kg(-1)) was without any effect on the protection afforded by LEV. 7. The results of the present study suggest that a novel ability to oppose the action of negative modulators on the two main inhibitory ionotropic receptors may be of relevance for the anti-epileptic mechanism(s) of action of LEV.

Allosteric Regulation↗

PubMed2002

Effect of systemic nitroglycerin on CGRP and 5-HT afferents to rat caudal spinal trigeminal nucleus and its modulation by estrogen.

Systemic administration of nitroglycerin, a nitric oxide donor, triggers in migraine patients a delayed attack of unknown mechanism. After puberty migraine is more prevalent in women. Attacks can be triggered by abrupt falls in plasma estrogen levels, which accounts in part for sexual dimorphism, but lacks an established neurobiological explanation. We studied the effect of nitroglycerin on the innervated area of calcitonin gene-related peptide (CGRP) and serotonin-immunoreactive afferents to the superficial laminae of the spinal portion of trigeminal nucleus caudalis, and its modulation by estrogen. In male rats, nitroglycerin produced after 4 h a significant decrease of the area innervated by CGRP-immunoreactive afferents and an increase of that covered by serotonin-immunoreactive fibres. These effects were not observed in the superficial laminae of thoracic dorsal horns. The effect of nitroglycerin was similar in ovariectomized females. In estradiol-treated ovariectomized females the area in the spinal portion of trigeminal nucleus caudalis laminae I-II covered by CGRP-immunoreactive fibres was lower and that of serotonin-immunoreactive fibres was higher than in males and for both transmitters not significantly changed after nitroglycerin. The bouton size of CGRP profiles was smaller in estradiol-treated ovariectomized females, whereas after nitroglycerin it decreased significantly but only in males and ovariectomized females. Nitroglycerin, i.e. nitric oxide, is thus able to differentially influence afferent fibres in the superficial laminae of rat spinal trigeminal nucleus caudalis. Estradiol modulates the basal expression of these transmitters and blocks the nitroglycerin effect. These data may contribute to understanding the mechanisms by which estrogens influence migraine severity and the triggering of attacks by nitric oxide.

Afferent Pathways↗

PubMed2002

Pharmacologic treatment of inner ear: from basic science to the patient.

Most of the deafness are of sensorineural origin and are characterized by a loss of hair cells and of spiral ganglion neurons. At the present time, hearing aids are the only treatment. However, in some diseases of the inner ear, pharmacological treatment have been proposed and used successfully. In this paper, we will review some basic science aspects of the biology of the neurosensory structures of the inner ear, in particular of the auditory neurons, that lead to the rationale of some treatments for the inner ear diseases. Developmental studies, neuronal cell culture experiments, and analyses of gene knockout animals reveal a number of growth factors which are important for the rescue and repair of injured auditory neurons in the inner ear. These factors rescue the injured auditory neurons in vivo. Furthermore, perfusion of antioxydant to the cochlea prevented the hearing loss induced by cisplatin. These in vitro and in vivo experiments demonstrate that it is possible to manipulate the neurosensory structures of the inner ear and provide an effective treatment to prevent the degeneration of the neurons. The molecules or drugs can be administered locally to the inner ear through a direct perilymphatic perfusion or through the round window membrane. As an example, we will discuss the treatment of patients suffering from idiopathic sensorineural hearing loss which can be treated successfully by a perfusion through the round window membrane, improving their hearing threshold and their speech discrimination.

Animals↗

PubMed2001

Neurotransmitters as early signals for central nervous system development.

During brain ontogenesis, the temporal and spatial generation of the different types of neuronal and glial cells from precursors occurs as a sequence of successive progenitor stages whose proliferation, survival and cell-fate choice are controlled by environmental and cellular regulatory molecules. Neurotransmitters belong to the chemical microenvironment of neural cells, even at the earliest stages of brain development. It is now established that specific neurotransmitter receptors are present on progenitor cells of the developing central nervous system and could play, during neural development, a role that has remained unsuspected until recently. The present review focuses on the occurrence of neurotransmitters and their corresponding ligand-gated ion channel receptors in immature cells, including neural stem cells of specific embryonic and neonatal brain regions. We summarize in vitro and in vivo data arguing that neurotransmitters could regulate morphogenetic events such as proliferation, growth, migration, differentiation and survival of neural precursor cells. The understanding of neurotransmitter function during early neural maturation could lead to the development of pharmacological tools aimed at improving adult brain repair strategies.

Acetylcholine↗

PubMed2001

Supernumerary outer hair cells arise external to the last row of sensory cells in the organ of corti.

During the development of the mammalian inner ear, the number of hair cells produced is highly regulated and remains constant throughout life. The mechanism underlying this regulation is beginning to be understood although many aspects still remain obscure. When late embryonic or early postnatal rat organs of Corti were cultured, the production of supernumerary hair cells was observed. This overproduction of sensory cells could be modulated by the addition of several growth factors. In this study, we examined explants of rat organs of Corti that produced supernumerary hair cells. In the supernumerary hair cell region, up to two rows of inner hair cells and five rows of outer hair cells were observed. Morphological evaluation of these specimens revealed that less mature hair cells were located in the most external rows of these sensory cells. When a supernumerary hair cell was produced, a supporting cell (i.e. Deiters' cell) was also produced, strongly suggesting that the conversion of a Deiters' cell into a hair cell was not the mechanism that produced these extra hair cells. Based on these results, we propose that prosensory cells located at the external edge of the organ of Corti retain a capacity to form hair cells and that it is these prosensory cells that differentiate into supernumerary hair cells and Deiters' cells.

Animals↗

PubMed2000

Peripheral nerve regeneration using bioresorbable macroporous polylactide scaffolds.

The ability of DRG-derived neurons to survive and attach onto macroporous polylactide (PLA) foams was assessed in vitro. The foams were fabricated using a thermally induced polymer-solvent phase separation. Two types of pore structures, namely oriented or interconnected pores, can be produced, depending on the mechanism of phase separation, which in turn can be predicted by the thermodynamics of the polymer-solvent pair. Coating of the porous foams with polyvinylalcohol (PVA) considerably improved the wettability of the foams and allowed for cell culture. The in vitro biocompatibility of the PVA-coated supports was demonstrated by measuring cell viability and neuritogenesis. Microscopic observations of the cells seeded onto the polymer foams showed that the interconnected pore networks were more favorable to cell attachment than the anisotropic ones. The capacity of highly oriented foams to support in vivo peripheral nerve regeneration was studied in rats. A sciatic nerve gap of 5-mm length was bridged with a polymer implant showing macrotubes of 100 microm diameter. At 4 weeks postoperatively, the polymer implant was still present. It was well integrated and had restored an anatomic continuity. An abundant cell migration was observed at the outer surface of the polymer implant, but not within the macrotubes. This dense cellular microenvironment was found to be favorable for axogenesis.

Animals↗

PubMed2000

Pharmacological modulation of the bystander effect in the herpes simplex virus thymidine kinase/ganciclovir gene therapy system: effects of dibutyryl adenosine 3',5'-cyclic monophosphate, alpha-glycyrrhetinic acid, and cytosine arabinoside.

The herpes simplex virus type 1 thymidine kinase (HSV1-tk) suicide gene/ganciclovir system was first applied to the treatment of glioblastoma tumors, but was hampered by the low gene transfection yield. Fortunately, the gap junction-dependent diffusion of phosphorylated ganciclovir metabolites from transfected cells to their neighbors proved to enhance the overall benefit of this strategy. However, as tumor cells are often gap junction-deficient, we sought to restore this property pharmacologically and hence to improve the efficacy of the treatment. We demonstrated that this approach was feasible in glioblastoma cells using dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP) (100 microM) as a pharmacological inducer of gap junctions. alpha-Glycyrrhetinic acid (25 microM), on the other hand, strongly inhibited both gap junction-mediated intercellular communication and the bystander effect, thus confirming the role of gap junctions in HSV-tk-mediated bystander killing. Using cytosine arabinoside as a growth inhibitor, we underlined the role of tumor cell proliferation in the sensitivity of HSV-tk-transfected cells to ganciclovir and demonstrated its correlation with the importance of the bystander effect.

Animals↗

PubMed2000

Glycine triggers an intracellular calcium influx in oligodendrocyte progenitor cells which is mediated by the activation of both the ionotropic glycine receptor and Na+-dependent transporters.

Using fluo-3 calcium imaging, we demonstrate that glycine induces an increase in intracellular calcium concentration ([Ca2+]i) in cortical oligodendrocyte progenitor (OP) cells. This effect results from a calcium entry through voltage-gated calcium channels (VGCC), as it is observed only in OP cells expressing such channels, and it is abolished either by removal of calcium from the extracellular medium or by application of an L-type VGCC blocker. Glycine-triggered Ca2+ influx in OP cells actually results from an initial depolarization that is the consequence of the activation of both the ionotropic glycine receptor (GlyR) and Na+-dependent transporters, most probably the glycine transporters 1 (GLYT1) and/or 2 (GLYT2) which are colocalized in these cells. Through this GlyR- and transporter-mediated effect on OP intrcellular calcium concentration [Ca2+]i, glycine released by neurons may, as well as other neurotransmitters, serve as a signal between neurons and OP during development.

Amino Acid Transport Systems, Neutral↗

PubMed2000

Epidermal growth factor upregulates production of supernumerary hair cells in neonatal rat organ of corti explants.

The organ of Corti is highly ordered, with a single row of inner hair cells and three rows of outer hair cells. The number of hair cells produced was thought to be limited by the time of their terminal mitosis (i.e. E14 in the mouse). However, exogenous application of retinoic acid has been shown to stimulate the formation of supernumerary hair cells in organ of Corti explants from E13 to E16 mouse embryos. Using late embryonic and neonatal rat organ of Corti explants, we investigated the potential for production of supernumerary hair cells in more mature auditory sensory epithelia. When newborn rat organ of Corti explants were cultured under control conditions, an area of supernumerary hair cells was observed in a segment of organ of Corti that was at the junction between the basal and middle turns. In these areas of supernumerary hair cells the number of hair cells increased per unit of length, but remained constant per surface unit, further demonstrating the supernumerary character of this phenomenon. Organ of Corti explants treated with epidermal growth factor (EGF) showed a 50% increase in the length of the organ of Corti segment containing supernumerary hair cells. Upregulation of supernumerary hair cell formation by EGF was found to start and be maximal at birth (P0) and to disappear by 2 days after birth (P2). Treatment of EGF stimulated P0 explants with an antimitotic drug, cytosine arabinoside (ARAc), demonstrated that the production of supernumerary hair cells occurred independently of cell division.

Animals↗

PubMed1999

Calpain inhibitors protect auditory sensory cells from hypoxia and neurotrophin-withdrawal induced apoptosis.

Inhibitors of calpain have been shown to protect nerve growth factor (NGF)-deprived ciliary ganglion neurons and hypoxic cortical neurons. Calpains have been identified in the cochlea and are active during ischemic injury. Since apoptosis can be initiated by loss of neurotrophic support, hypoxia, and ototoxins (e.g., cisplatin, CDDP), the role of calpain inhibitors under these conditions was examined in auditory hair cells and neurons. Dissociated spiral ganglion neuron (SGN) cell cultures and organ of Corti explants from P3 rats were used to test the efficacy of calpain inhibitors as otoprotective molecules. Our results indicate that calpain inhibitor I, calpain inhibitor II, and leupeptin all provided significant protection of SGNs against neurotrophin-withdrawal and hypoxia-induced apoptosis. The increase in neuronal survival ranged from 2.16 to 2.31 times greater than in untreated neurotrophin-withdrawn SGN cell cultures. BOC-Asp(Ome)-Fluoromethyl Ketone (B-D-FMK), a general caspase inhibitor, increased neuronal survival 2.16 times more. Neuronal survival rates were from 1.88 to 2.27 times greater than in untreated, hypoxic neurons and hair cell survival rates were from 1.98 to 2.03 times greater than untreated, hypoxic organ of Corti explants. However, protection of auditory hair cells and neurons from CDDP-induced damage (10 and 6 micrograms/ml, respectively) was limited with any of these calpain inhibitors. Apoptotic pathways initiated by neurotrophin-deprivation and ototoxic stress (e.g., CDDP) have been shown to be different. Our results agree with this finding, with neurotrophin-withdrawal and hypoxia, but not CDDP damage-induced apoptosis being calpain-dependent.

Animals↗

PubMed1999

Growth factor therapy to the damaged inner ear: clinical prospects.

Most hearing loss results from lesions of the sensory cells and/or of the neurons of the auditory part of the inner ear. There is currently no treatment able to stop the progression of a hearing loss or to restore a lost auditory function. In this paper, we review the progress which has been made with respect to the regeneration and the protection of the hair cells and of the auditory neurons in the cochlea. In particular, we emphasize the control by growth factors of the protection/repair mechanisms of the neurosensory structures within the inner ear, in the prospect of the possible clinical use of these molecules. Finally, we discuss the different approaches which can be used to deliver these therapeutic agents to the inner ear.

Animals↗

PubMed1999

Identification of PSF, the polypyrimidine tract-binding protein-associated splicing factor, as a developmentally regulated neuronal protein.

The polypyrimidine tract-binding protein-associated splicing factor (PSF), which plays an essential role in mammalian spliceosomes, has been found to be expressed by differentiating neurons in developing mouse brain. The sequence of a fragment of mouse PSF was found to be remarkably similar to that of human PSF. Both the expression of PSF mRNA in cortex and cerebellum and PSF immunoreactivity in all brain areas were high during embryonic and early postnatal life and almost disappeared in adult tissue, except in the hippocampus and olfactory bulb where various neuronal populations remained PSF-immunopositive. Double-labeling experiments with anti-PSF antibody and anti-neurofilaments or anti-glial fibrillary acidic protein antibodies on sections of cortex, hippocampus, and cerebellum indicate that PSF is expressed by differentiating neurons but not by astrocytic cells. In vitro, mouse PSF was found to be expressed by differentiating cortical and cerebellar neurons. Radial glia or astrocyte nuclei were not immunopositive; however, oligodendrocytes differentiating in vitro were found to express PSF. The restricted expression of PSF suggests that this splicing factor could be involved in the control of neuronal-specific splicing events occurring at particular stages of neuronal differentiation and maturation.

Amino Acid Sequence↗