Benoit John Jenny

PSA-NCAM in postnatally generated immature neurons of the olfactory bulb: a crucial role in regulating p75 expression and cell survival

In the mammalian brain, ongoing neurogenesis via the rostral migratory stream (RMS) maintains neuronal replacement in the olfactory bulb throughout life. Mechanisms that regulate the final number of new neurons in this system include proliferation, migration and apoptosis. Here we show that the polysialylated isoforms of the neural cell adhesion molecule (PSA-NCAM) act as a pro-survival molecule in immature newborn neurons. Confocal microscopic analysis revealed a threefold increase in TUNEL-positive cells in the subventricular zone (SVZ) and the RMS of transgenic animals lacking the gene encoding NCAM (NCAM-/-), as compared with wild types. The enhanced apoptotic cell death occurred specifically in the population of mCD24-positive newborn neurons, but not in GFAP-positive astrocytes. Using in vitro cultures of purified SVZ-derived neurons, we demonstrate that the loss or inactivation of PSA on NCAM, as well as the deletion of NCAM, lead to reduced survival in response to neurotrophins including BDNF and NGF. These changes in cell survival are accompanied by an upregulation of p75 neurotrophin receptor expression in vitro as well as in vivo. Furthermore, the negative effects of PSA-NCAM inactivation on cell survival could be prevented by the pharmacological blockade of the p75 receptor-signaling pathway. We propose that PSA-NCAM may promote survival by controlling the expression of the p75 receptor in developing neurons.

GABA Regulates Dendritic Growth by Stabilizing Lamellipodia in Newly Generated Interneurons of the Olfactory Bulb

The initial formation and growth of dendrites is a critical step leading to the integration of newly generated neurons into postnatal functional networks. However, the cellular mechanisms and extracellular signals regulating this process remain mostly unknown. By directly observing newborn neurons derived from the subventricular zone in culture as well as in olfactory bulb slices, we show that ambient GABA acting through GABAA receptors is essential for the temporal stability of lamellipodial protrusions in dendritic growth cones but did not interfere with filopodia dynamics. Furthermore, we provide direct evidence that ambient GABA is required for the proper initiation and elongation of dendrites by promoting the rapid stabilization of new dendritic segments after their extension. The effects of GABA on the initial formation of dendrites depend on depolarization and Ca2+ influx and are associated with a higher stability of microtubules. Together, our results indicate that ambient GABA is a key regulator of dendritic initiation in postnatally generated olfactory interneurons and offer a mechanism by which this neurotransmitter drives early dendritic growth.

Expression and localization of VEGF‐C and VEGFR‐3 in glioblastomas and haemangioblastomas

Primary human brain tumours account for approximately 2% of all cancers. High levels of expression of vascular endothelial growth factor‐A (VEGF‐A), a potent angiogenic factor, are linked to poor prognosis. In contrast, the potential role in human brain tumour biology of newer VEGF family members, VEGF‐C and VEGF‐D, both of which are lymphangiogenic factors, is poorly understood. In the present study, the expression of all VEGFs (VEGF‐A, ‐B, ‐C, and ‐D) and their receptors (VEGFR‐1, ‐2, and ‐3) has been assessed in 39 primary human brain tumours. The well‐established findings were confirmed with VEGF‐A. Surprisingly, however, VEGF‐C and VEGF‐D, as well as VEGFR‐3, were expressed in some tumour types such as haemangioblastomas and glioblastomas, despite their lack of lymphatic vessels. VEGF‐C and VEGFR‐3 transcripts were localized to the tumour palisade around necrotic areas in glioblastomas and were evenly distributed throughout haemangioblastomas. VEGF‐C protein was localized by immunohistochemistry to the palisade layer in glioblastomas. More than 50% of VEGF‐C‐positive cells also expressed the intermediate‐stage inflammatory macrophage marker CD163; however, a significant proportion of VEGF‐C‐positive cells were CD163‐negative. These data demonstrate the presence of molecules, primarily described as regulators of lymphangiogenesis, in normal human brain and brain tumours that are devoid of lymphatics. Their localization in macrophages points to a role in tumour‐associated inflammation. Copyright

Fibroblast Growth Factor‐2 Overexpression in Transplanted Neural Progenitors Promotes Perivascular Cluster Formation with a Neurogenic Potential

Stem/progenitor cell‐based therapies hold promises for repairing the damaged nervous system. However, the efficiency of these approaches for neuronal replacement remains very limited. A major challenge is to develop pretransplant cell manipulations that may promote the survival, engraftment, and differentiation of transplanted cells. Here, we investigated whether overexpression of fibroblast growth factor‐2 (FGF‐2) in grafted neural progenitors could improve their integration in the host tissue. We show that FGF‐2‐transduced progenitors grafted in the early postnatal rat cortex have the distinct tendency to associate with the vasculature and establish multiple proliferative clusters in the perivascular environment. The contact with vessels appears to be critical for maintaining progenitor cells in an undifferentiated and proliferative phenotype in the intact cortex. Strikingly, perivascular clusters of FGF‐2 expressing cells seem to supply immature neurons in an ischemic environment. Our data provide evidence that engineering neural progenitors to overexpress FGF‐2 may be a suitable strategy to improve the integration of grafted neural progenitor cells with the host vasculature thereby generating neurovascular clusters with a neurogenic potential for brain repair. STEM CELLS 2009;27:1309–1317

Association of multiple vertebral hemangiomas and severe paraparesis in a patient with a PTEN hamartoma tumor syndrome. Case report.

The PTEN hamartoma tumor syndrome, manifestations of which include Cowden disease and Bannayan-Riley-Ruvalcaba syndrome, is caused by various mutations of the PTEN gene located at 10q23. Its major criteria are macrocephaly and a propensity to develop breast and thyroid cancers as well as endometrial carcinoma. Minor diagnostic criteria include hamartomatous intestinal polyps, lipomas, fibrocystic disease of the breasts, and fibromas. Mutations of PTEN can also be found in patients with Lhermitte-Duclos disease (dysplastic gangliocytoma of the cerebellum). The authors report the case of a 17-year-old girl who had a severe cyanotic cardiac malformation for which surgery was not advised and a heterozygous missense mutation (c.406T>C) in exon 5 of PTEN resulting in the substitution of cysteine for arginine (p.Cysl36Arg) in the protein, which was also found in her mother and sister. The patient presented in the pediatric emergency department with severe spastic paraparesis. A magnetic resonance imaging study of the spine showed vertebral hemangiomas at multiple levels, but stenosis and compression were maximal at level T5-6. An emergency T5-6 laminectomy was performed. The decompression was extremely hemorrhagic because the rapid onset of paraparesis necessitated prompt treatment, and there was no time to perform preoperative embolization. The patients postoperative course was uneventful with gradual recovery. This represents the first report of an association of a PTEN mutation and multiple vertebral angiomas. The authors did not treat the remaining angiomas because surgical treatment was contraindicated without previous embolization, which in itself would present considerable risk in this patient with congenital cyanotic heart disease.

Giant dural venous sinus ectasia in neonates.

In this report, the authors describe 4 recent cases of posterior giant dural venous sinus ectasia in neonates diagnosed during pregnancy and encountered at 3 different institutions. Posterior giant venous sinus ectasia was diagnosed in 4 patients using antenatal ultrasonography and confirmed in 2 patients using prenatal MR imaging and in 3 patients using postnatal MR angiography. In 2 children angiography was performed at the age of 6 months. The pregnancy was terminated in 1 case, and the fetus underwent an autopsy. The 3 children who were born presented with various degree of cardiac insufficiency and were admitted to the intensive care unit after birth. Signs of increased intracranial pressure were present immediately after birth, including a bulging fontanel. No endovascular treatment was used in these cases. Surgery was performed in 2 cases as an attempt to alleviate increased intracranial pressure symptoms, without any real benefit. A slow venous flow in the ectasia was shown by ultrasonography in the case in which the pregnancy was terminated. Angiography or MR angiography did not show an obvious arteriovenous malformation in any of the cases, but an arteriovenous fistula secondary or contributing to the formation of the venous ectasia is one of the physiopathological hypotheses of the cause of this condition. Interestingly, spontaneous progressive thrombosis and regression of the intravascular component of the venous sinus ectasia was observed in all cases. The clinical outcome was acceptable in 1 child (who had a moderate handicap after the surgery) and good for the other 2 children (who had normal neurological development). Stratified thrombi of different ages are found in these giant venous ectasias and develop within the leaves of the dura close to the confluence of the major posterior venous sinuses. Therefore, it appears that the formation of a progressive thrombosis represents the normal evolution of these giant dural venous sinus ectasias, which explains the favorable outcome in some cases without specific surgical treatment, except for resuscitation techniques.

Recruiting new neurons from the subventricular zone to the rat postnatal cortex: an organotypic slice culture model

The neurogenic subventricular zone (SVZ) of the lateral ventricle is a potential source for neuronal replacement in the postnatal or adult neocortex after injury. Here we present a novel model system to directly explore the cellular mechanisms of this process. In order to visualize directed migration from the SVZ towards the cortex, we transplanted green fluorescent protein‐labeled progenitor/stem cells into the SVZ of newborn rats. At 2 days after transplantation, we generated organotypic slice cultures and applied fluorescent time‐lapse imaging to explore directly the migration and integration of donor cells into the host tissue for up to 2 weeks. Our studies revealed that subventricular grafts provide a significant number of immature neurons to neocortical regions. In the cortex, immature neurons first migrate radially towards the pial surface and then differentiate into GABAergic interneurons. We conclude that our model system presents a novel and effective experimental paradigm to evaluate the recruitment of SVZ‐derived neurons into the postnatal cortex, a phenomenon that may represent a potential route for cortical repair.

Tracking the source of cerebellar epilepsy: Hemifacial seizures associated with cerebellar cortical dysplasia

Traditionally, subcortical structures such as the cerebellum are supposed to exert a modulatory effect on epileptic seizures, rather than being the primary seizure generator. We report a 14-month old girl presenting, since birth, with seizures symptomatic of a right cerebellar dysplasia, manifested as paroxystic contralateral hemifacial spasm and ipsilateral facial weakness. Multimodal imaging was used to investigate both anatomical landmarks related to the cerebellar lesion and mechanisms underlying seizure generation. Electric source imaging (ESI) supported the hypothesis of a right cerebellar epileptogenic generator in concordance with nuclear imaging findings; subsequently validated by intra-operative intralesional recordings. Diffusion spectrum imaging-related tractography (DSI) showed severe cerebellar structural abnormalities confirmed by histological examination. We suggest that hemispheric cerebellar lesions in cases like this are likely to cause epilepsy via an effect on the facial nuclei through ipsilateral and contralateral aberrant connections.

Pediatric epilepsy surgery: could age be a predictor of outcomes?

OBJECTIVE Like adults, many children suffering from intractable seizures benefit from surgical therapy. Although various reports indicate that early intervention may avoid severe developmental consequences often associated with intractable epilepsy, surgery is still considered a last option for many children. In this retrospective study, the authors aimed to determine whether pediatric epilepsy surgery, in particular during the first years of life, relates to measurable benefits. METHODS Data from 78 patients (age range 5 months to 17 years) who underwent epilepsy surgery at the Geneva and Lausanne University Hospitals between 1997 and 2012 were reviewed retrospectively. Patients were dichotomized into 2 groups: infants (≤ 3 years of age, n = 19), and children/adolescents (4-17 years of age, n = 59). Compared with children/adolescents, infants more often had a diagnosis of dysplasia (37% vs 10%, respectively; p < 0.05, chi-square test). RESULTS The overall seizure-free rate was 76.9%, with 89.5% in infants and 72.9% in the children/adolescents group. Infants were 2.76 times as likely to achieve seizure-free status as children/adolescents. Postoperative antiepileptic medication was reduced in 67.9% of patients. Only 11.4% of the patients were taking more than 2 antiepileptic drugs after surgery, compared with 43% before surgery (p < 0.0001). The overall complication rate was 15.1% (6.4% transient hemiparesis), and no major complications or deaths occurred. CONCLUSIONS The data show a high seizure-free rate in children ≤ 3 years of age, despite a higher occurrence of dysplastic, potentially ill-defined lesions. Pediatric patients undergoing epilepsy surgery can expect a significant reduction in their need for medication. Given the excellent results in the infant group, prospective studies are warranted to determine whether age ≤ 3 years is a predictor for excellent surgical outcome.

Management of positional plagiocephaly—helmet or no helmet?

Dear Editor: The “Back to Sleep Campaign” to prevent sudden infant death syndrome has led to a significant increase in the incidence of positional plagiocephaly. This clinical entity with an abnormal head shape is not the result of craniosynostosis, which represents a premature closure of cranial sutures, but rather a purely cosmetic problem caused by persistent occipital pressure during sleep [1]. A prospective cohort study from New Zealand showed a distinct age-dependent prevalence of 16 % at 6 weeks, 19.7 % at 4 months, 6.8 % at 12 months, and 3.3 % at 2 years [2]. Although it is generally accepted that high rates of up to 70 % improve spontaneously, several conservative treatment options have been established including regular changes of head position, physiotherapy, osteopathy, and also cranial remodeling helmets for moderate to severe asymmetry [3]. There is, however, a dearth of evidence-based recommendations in the international literature for the management of patients with positional plagiocephaly [4]. In the absence of a radiologically diagnosed craniosynostosis, parents should be advised that a positional plagiocephaly is essentially a cosmetic problem that does not cause potentially life-threatening or disabling neurological deficits. The information that the natural history, also without treatment, is mostly favorable, is equally of paramount importance. In the case of moderate or very severe skull asymmetry, where positional exercises, physiotherapy, and osteopathy do not lead to a satisfactory result, a cranial helmet might be considered [5]. The latter is a generally well-tolerated method to correct positional head deformity. Most of the rarely occurring complications are minor and self-limited [6]. Therefore, minor forms do usually not necessitate helmet treatment, whereas it is generally recommended for severe forms. Despite efforts to introduce three-dimensional analysis to clinical practice, there are no standardized well-established objective measurements of skull asymmetry from which to decide on the initiation of therapy [7–10]. Without measurements of symmetry, naturally there have been no prospective randomized studies investigating the effectiveness of helmet treatment, noting the high rates of spontaneous “self-healing”. Thus, in the face of significant socioeconomic impact on the healthcare system and distress to parents and caregivers, the use of such helmets should be guarded. Therefore, we strongly believe that further randomized controlled trials, using, e.g., the severity ratings suggested by Looman and Flannery [11], are mandatory in order to answer the question if, when, and for how long cranial remodeling helmets should be recommended.