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R Martini

Publications and source records attributed to R Martini.

At least 19 recordsLinked to original sources
PubMed2001

The role of macrophages in demyelinating peripheral nervous system of mice heterozygously deficient in p0.

Mice heterozygously deficient in the p0 gene (P0(+/-)) are animal models for some forms of inherited neuropathies. They display a progressive demyelinating phenotype in motor nerves, accompanied by mild infiltration of lymphocytes and increase in macrophages. We have shown previously that the T lymphocytes are instrumental in the demyelination process. This study addresses the functional role of the macrophage in this monogenic myelin disorder. In motor nerves of P0(+/)- mice, the number of macrophages in demyelinated peripheral nerves was increased by a factor of five when compared with motor nerves of wild-type mice. Immunoelectron microscopy, using a specific marker for mouse macrophages, displayed macrophages not only in the endoneurium of the myelin mutants, but also within endoneurial tubes, suggesting an active role in demyelination. To elucidate the roles of the macrophages, we crossbred the myelin mutants with a spontaneous mouse mutant deficient in macrophage colony-stimulating factor (M-CSF), hence displaying impaired macrophage activation. In the P0-deficient double mutants also deficient in M-CSF, the numbers of macrophages were not elevated in the demyelinating motor nerves and demyelination was less severe. These findings demonstrate an active role of macrophages during pathogenesis of inherited demyelination with putative impact on future treatment strategies.

Animals↗
PubMed2001

The effect of myelinating Schwann cells on axons.

Myelinating Schwann cells control the number of neurofilaments and elevate the phosphorylation state of neurofilaments in the axon, eventually leading to the typical large axon caliber. Conversely, absence of myelin leads to lower amounts of neurofilaments, reduced phosphorylation levels, and smaller axon diameters. In addition, myelinating Schwann cells mediate the spacing of Na(+) channel clusters during development of the node of Ranvier. When axons are associated with mutant Schwann cells in inherited neuropathies, their calibers are reduced and their neurofilaments are less phosphorylated and more closely spaced. Also, axonal transport is reduced and axons degenerate at the distal ends of long nerves. Myelin-associated glycoprotein may mediate some aspects of Schwann cell-axon communication, but much remains to be learned about the molecular bases of Schwann cell-axon communication.

Animals↗
PubMed2001

Bone marrow transfer from wild-type mice reverts the beneficial effect of genetically mediated immune deficiency in myelin mutants.

Inherited demyelinating neuropathies are chronically disabling human disorders caused by various genetic defects, including deletions, single site mutations, and duplications in the respective myelin genes. We have shown in a mouse model of one distinct hereditary demyelinating neuropathy (heterozygous P0-deficiency, P0+-) that an additional null mutation in the recombination activating gene-1 (RAG-1--) leads to a substantially milder disorder, indicating a disease modifying role of T-lymphocytes. In the present study, we addressed the role of lymphocytes in the mouse model by reconstituting bone marrow of P0+-/RAG-1-- mice with bone marrow from immunocompetent wild-type mice. We compared the pathology and nerve conduction in double mutant mice (P0+-/RAG-1-- on a C57BL/6 background) with that in double mutants after receiving a bone marrow transplant. We found that the milder demyelination seen in the lymphocyte-deficient P0+-/RAG-1-- mutants was reverted to the more severe pathology by reestablishing a competent immune system by bone marrow transfer. These data corroborate the concept that the immune system contributes substantially to the pathologic process in this mouse model and may open new avenues to ameliorate human hereditary neuropathies by exploiting immunosuppressive treatments.

Animals↗
PubMed2001

Miller Fisher syndrome: immunofluorescence and immunoelectron microscopic localization of IgG at the mouse neuromuscular junction.

In vitro electrophysiological experiments have demonstrated that IgG antibodies from patients with Miller Fisher syndrome (MFS) impair neuromuscular transmission by a fast and completely reversible combined pre- and postsynaptic blockade. In this study we investigated the cellular and subcellular binding sites of IgG from four MFS patients at the mouse hemidiaphragm by immunofluorescence and immunoelectron microscopy. IgG from all patients produced significant immunostaining at the neuromuscular junction, whereas sera from healthy volunteers or from patients with other neurological diseases did not stain neuromuscular junction. Immunoelectron microscopy revealed that, when living hemidiaphragms were incubated with IgG from MFS patients, labeling was found on both pre- and postsynaptic membranes of the neuromuscular junction, whereas terminal Schwann cells and the basal lamina covering the synaptic membranes were not labeled. These findings demonstrate that IgG from MFS patients binds to synaptic membranes of the neuromuscular junction where it might interfere with the function of both the pre- and postsynaptic activities.

Animals↗
PubMed2000

Animal models for inherited peripheral neuropathies: chances to find treatment strategies?

Mutations in four identified genes (peripheral myelin protein 22, P(0), connexin 32, and the early growth response 2 zinc finger protein) are the cause for several forms of inherited peripheral neuropathies that are still incurable disorders. Some forms of these disorders are well mimicked by engineered or spontaneous rodent mutants that might be instrumental for developing treatment strategies. This review focusses on common pathways of pathogenesis of the disorders and emphasizes strategies that might be suitable to ameliorate disease expression.

Animals↗
PubMed2000

P(0) glycoprotein overexpression causes congenital hypomyelination of peripheral nerves.

We show that normal peripheral nerve myelination depends on strict dosage of the most abundantly expressed myelin gene, myelin protein zero (Mpz). Transgenic mice containing extra copies of Mpz manifested a dose-dependent, dysmyelinating neuropathy, ranging from transient perinatal hypomyelination to arrested myelination and impaired sorting of axons by Schwann cells. Myelination was restored by breeding the transgene into the Mpz-null background, demonstrating that dysmyelination does not result from a structural alteration or Schwann cell-extrinsic effect of the transgenic P(0) glycoprotein. Mpz mRNA overexpression ranged from 30-700%, whereas an increased level of P(0) protein was detected only in nerves of low copy-number animals. Breeding experiments placed the threshold for dysmyelination between 30 and 80% Mpz overexpression. These data reveal new points in nerve development at which Schwann cells are susceptible to increased gene dosage, and suggest a novel basis for hereditary neuropathy.

Animals↗
PubMed2000

Immune deficiency in mouse models for inherited peripheral neuropathies leads to improved myelin maintenance.

The adhesive cell surface molecule P(0) is the most abundant glycoprotein in peripheral nerve myelin and fulfills pivotal functions during myelin formation and maintenance. Mutations in the corresponding gene cause hereditary demyelinating neuropathies. In mice heterozygously deficient in P(0) (P(0)(+/-) mice), an established animal model for a subtype of hereditary neuropathies, T-lymphocytes are present in the demyelinating nerves. To monitor the possible involvement of the immune system in myelin pathology, we cross-bred P(0)(+/-) mice with null mutants for the recombination activating gene 1 (RAG-1) or with mice deficient in the T-cell receptor alpha-subunit. We found that in P(0)(+/-) mice myelin degeneration and impairment of nerve conduction properties is less severe when the immune system is deficient. Moreover, isolated T-lymphocytes from P(0)(+/-) mice show enhanced reactivity to myelin components of the peripheral nerve, such as P(0), P(2), and myelin basic protein. We hypothesize that autoreactive immune cells can significantly foster the demyelinating phenotype of mice with a primarily genetically based peripheral neuropathy.

Animals↗
PubMed2000

Neuromyotonia in mice with hereditary myelinopathies.

The purpose of this study was to further characterize neuromyotonia in mice with deletions and point mutations of myelin protein genes. Clinical observation showed irregular stretching of the hindlimbs, tremor and generalized myokymia in mice with targeted deletions of the genes encoding myelin protein zero (P0-/-) or peripheral myelin protein 22 (Pmp22-/-), and Trembler mice, which carry a point mutation of Pmp22. By electromyography (EMG), we found irregular high-frequency bursts of spontaneous motor unit activity and rhythmic doublet or multiplet discharges of motor units in these mouse models of human hereditary neuropathies. The EMG signs are typical for neuromyotonia and myokymia, respectively. The activity persisted after a proximal nerve section in many cases, localizing the generator to the peripheral nerve or the muscle. We now show that blocking neuromuscular transmission with suxamethonium abolished the spontaneous activity, ruling out a muscle origin. Phenytoin ameliorated the motor behavior. Taken together, our study shows that neuromyotonia develops in different mouse models of hereditary myelinopathies. This indicates that spontaneous motor unit activity may underlie neuromyotonia, which is occasionally observed in Charcot-Marie-Tooth disease. These animal models will be useful to study the pathogenesis of neuromyotonia.

Animals↗
PubMed2000

Varicose symptoms without varicose veins: the hypotonic phlebopathy, epidemiology and pathophysiology. The Acireale project.

Ever since 1982 the authors have been interested in varicose symptoms without varicose veins. Carrying out several pilot studies with infrared photoplethysmography (PPG) and strain gauge plethysmography they suggest that the pathophysiology of this behaviour could be caused by the reduction of the venous wall tone. They propose the name of Hypotonic Phlebopathy (HP). The diagnosis criteria are focused by symptoms (heavy legs in upright position, restless leg syndrome, sub-oedema and/or evening oedema) and signs detected by PPG, s.g plethysmography and duplex scanning (reduction of the muscle-venous calf pump and increase of the venous wall compliance). Epidemiology, assessed between 1989 and 1992 (Acireale Project), showed a 15.90% morbidity, with higher prevalence in females; the most important risk factors are pregnancy and family history. HP is not rare in males; the principal risk factor is work involving standing for long periods. These behaviours have been independently confirmed by two studies carried out in France in 1992, which showed a 15% prevalence in a similar group of subjects with functional venous insufficiency. The authors suggest the introduction of the term of Hypotonic Phlebopathy, the symptoms of which are significantly improved by phlebotonic drugs, especially when they are stronger. CEAP classification: C(0-S); E(P); A(0); P(unclassifiable); Clinical score (1-2); Anatomical score (0); Disability score (1).

Adult↗
PubMed1999

P0-deficient knockout mice as tools to understand pathomechanisms in Charcot-Marie-Tooth 1B and P0-related Déjérine-Sottas syndrome.

P0 (mylin protein zero, MPZ) is one of the four identified culprit genes for hereditary peripheral neuropathies. Homo- or heterozygous null mutants for P0 share pathological features with some patients suffering from P0-related Déjérine-Sottas-Syndrome (DSS) or Charcot-Marie-Tooth (CMT) neuropathy, type 1B, respectively, and can thus be considered as appropriate animal models for the corresponding diseases. This article focuses on distinct histopathological features in these mice. Such features include dysregulation of Schwann cell genes and axonal loss in homozygous mutants and significant infiltration of T-lymphocytes and macrophages in heterozygous mutants. These histological characteristics are instrumental in understanding the pathogenesis of the disease and may help in developing treatments.

Animals↗
PubMed1999

Loss of distal axons and sensory Merkel cells and features indicative of muscle denervation in hindlimbs of P0-deficient mice.

Mice lacking the major Schwann cell myelin component P0 show a severe dysmyelination with pathological features reminiscent of the Déjérine-Sottas syndrome in humans. Previous morphological and electrophysiological studies on these mice did not only demonstrate a compromised myelination and myelin maintenance, but were suggestive of an impairment of axons as well. Here, we studied the axonal pathology in P0-deficient mice by quantitative electron microscopy. In addition, we investigated epidermal receptor end organs by immunocytochemistry and muscle pathology by histochemistry. In proximal sections of facial and femoral nerves, axon calibers were significantly reduced, whereas the number of myelin-competent axons was not diminished in 5- and 17-month-old P0-deficient mice. However, in distal branches of the femoral and sciatic nerve (digital nerves innervating the skin of the first toe) the numbers of myelin-competent axons were reduced by 70% in 6-month-old P0-deficient mice. Immunolabeling of foot pads revealed a corresponding loss of Merkel cells by 75%, suggesting that survival of these cells is dependent on the presence or maintenance of their innervating myelinated axons. In addition, quadriceps and gastrocnemius muscles showed pathological features indicative of denervation and axonal sprouting. These findings demonstrate that loss of an important myelin component can initiate degenerative mechanisms not only in the Schwann cell but also in the distal portions of myelinated axons, leading to the degeneration of specialized receptor end organs and impairment of muscle innervation.

Animals↗
PubMed1999

Effective gene transfer of lacZ and P0 into Schwann cells of P0-deficient mice.

Mutations in the gene encoding for the myelinating Schwann cell protein P0 have been linked to inherited peripheral neuropathies, including the Charcot-Marie-Tooth type 1B disease (CMT1B) and Dejerine-Sottas syndrome (DSS). Recently generated mice deficient in the P0 gene (P0-/- mice) resemble cases of CMT1B and DSS with impaired myelin dosage (Martini et al., 1995a). Potential approaches to treat such diseases include the introduction of the normal gene in the nerves of strongly affected patients. In the present study we used P0-/- mice to evaluate the efficiency of a replication-defective, E1-deleted adenovirus vector carrying the lacZ (Ad-RSV-lacZ) or P0 (Ad-RSV-P0) gene to infect abnormally myelinating Schwann cells. The Ad-RSV-lacZ vector suspension was injected into the left sciatic nerve ofPO-/- mice and the nerves examined for beta-galactosidase activity by X-gal histochemistry. Contralateral nerves injected with vehicle solution or non-injected served as controls. Beta-galactosidase activity was detected in nerves injected with the Ad-RSV-lacZ vector up to 2 weeks post-injection. Immunosuppressing the mice with FK506 to decrease the infiltration of activated T-cells in infected nerves lengthened beta-galactosidase activity to 8 weeks, the longest time point examined. Ultrastructural analysis indicated that X-gal crystals were present mostly in abnormally myelinating Schwann cells. These findings demonstrate that an adenovirus vector can successfully infect Schwann cells in P0-/- mice and expression can be maintained for several weeks. The Ad-RSV-P0 suspension was then injected in the sciatic nerve of immunosuppressed P0-/- mice. Two and four weeks post-injection both P0 mRNA and protein could be detected by in situ hybridization and Western blotting in some of the nerves. Furthermore, P0 protein expression was observed in myelin-like structures and onion bulb-like cells by immunohistochemistry. These results indicate that Schwann cells in P0-/- mice can be induced to produce P0 protein after gene transfer. Genetic repair of abnormal Schwann cells by using adenovirus vectors might be a possible technique to treat animal models of inherited peripheral neuropathies.

Adenoviridae↗
PubMed1999

Myelin formation by Schwann cells in the absence of beta4 integrin.

The interaction of the Schwann cell with its basal lamina has been hypothesized to be an important prerequisite for the formation of a myelin sheath in the peripheral nervous system. One possible player in this interaction is beta4 integrin; it is up-regulated during myelin formation and, in association with alpha6 integrin, can interact with particular components of the Schwann cell basal lamina. In order to characterize the functional roles of beta4 integrin during myelination, we investigated myelination in the absence of beta4 integrin, i.e., in peripheral nerve tissue from beta4 integrin-deficient mice. Because the mutants die within several hours after birth, we cultured dorsal root ganglia from neonatal mutants under conditions that promote myelination, quantified the myelin segments by immunofluorescence, and investigated the ultrastructure of the cultured myelin sheaths. In another approach, we quantified the few myelin sheaths that are detectable in femoral nerves of newborn animals. Based on both approaches, we conclude that myelination by Schwann cells can occur in the absence of beta4 integrin demonstrating that this Schwann cell component is dispensable for myelin formation in peripheral nerves.

Animals↗
PubMed1999

An unexpectedly high rate of pulmonary embolism in patients with superficial thrombophlebitis of the thigh.

PURPOSE: The rate of objectively proven pulmonary embolism in patients with thrombophlebitis of the greater saphenous vein was studied. METHODS: Consecutive ambulant patients with thrombophlebitis of the greater saphenous vein, involving the above-knee segment, underwent a complete venous echo color Doppler examination of the lower limbs, perfusion lung scanning, and chest radiography. A high probability of pulmonary embolism was defined as the presence of two or more large segmental defects, one large and two or more moderate perfusion defects, or four or more moderate perfusion defects, with no corresponding abnormality found by means of chest radiography. RESULTS: Of the 21 patients included in the study, findings compatible with a high probability of pulmonary embolism were detected in seven patients (33.3%; 95% CI, 14.6 to 57. 0), although clinical symptoms of pulmonary embolism were present only in one patient. No association was found between the presence of thrombosis at the saphenofemoral junction and the risk for pulmonary embolism. CONCLUSION: The rate of pulmonary embolism in patients with thrombophlebitis of the greater saphenous vein is unexpectedly high. This risk is similarly high in patients with thrombosis at the saphenofemoral junction and in patients without thrombosis at the saphenofemoral junction. Our results are consistent with those of other recent investigations and suggest that superficial thrombophlebitis of the thigh is not as benign a disease entity as previously described.

Adult↗
PubMed1999

A large spontaneous splenorenal shunt in a patient with liver cirrhosis and uncomplicated portal hypertension.

The aim of this paper is to describe and discuss, on the basis of a thorough review of the literature, the case of a 70-year-old woman with probable cirrhosis secondary to chronic hepatitis B and C, uncomplicated portal hypertension (without ascites, encephalopathy or bleeding varices), splenomegaly and hypersplenism, and an unusual, spontaneous, large splenorenal shunt and recanalization of the umbilical vein. The tortuous and varicose splenorenal shunt was diagnosed by abdominal ultrasound and CT investigations. A duplex Doppler ultrasonography evaluation was performed to study shunt flow direction and velocity. No gastroesophageal varices were identified on endoscopic examination. The clinical relevance of spontaneous splenorenal shunt, often associated with fundic gastric varices, is discussed.

Aged↗