Vered Lavie

Tumor necrosis factor facilitates regeneration of injured central nervous system axons

The results of this study attribute to tumor necrosis factor (TNF) a role in regeneration of injured mammalian central nervous system (CNS) axons which grow into their own degenerating environment. This is the first time that a specific factor involved in axonal regeneration has been identified. The axonal environment is occupied mostly by glia cells, i.e., astrocytes and oligodendrocytes. Previous studies have shown that mature oligodendrocytes are inhibitory to axonal growth. Therefore, it seemed likely that application of a factor such as TNF, which has been shown to be cytotoxic to oligodendrocytes, would contribute to the creation of permissive conditions for axonal regeneration. In the present work, injured adult rabbit optic nerves were treated with human recombinant TNF (rhTNF). As a result, abundant newly growing axons (circa 9000, about 4% of the total estimated number of axons in an intact adult rabbit) were observed traversing the site of injury.

Dexanabinol (HU-211) effect on experimental autoimmune encephalomyelitis: implications for the treatment of acute relapses of multiple sclerosis

Dexanabinol (HU-211) is a synthetic non-psychotropic cannabinoid which suppresses TNF-alpha production in the brain and peripheral blood. The effects of dexanabinol in rat experimental autoimmune encephalomyelitis (EAE) were studied using different doses, modes of administration and time regimes. Dexanabinol, 5 mg/kg i.v. given once after disease onset (day 10), significantly reduced maximal EAE score. Increasing the dose or treatment duration resulted in further suppression of EAE. Drug administration at earlier phases during disease induction was not effective. Histological studies supported the clinical findings demonstrating reduction in the inflammatory response in the brain and spinal cord in animals treated with dexanabinol. The results suggest that dexanabinol may provide an alternative mode of treatment for acute exacerbations of multiple sclerosis (MS).

Disappearance of astrocytes and invasion of macrophages following crush injury of adult rodent optic nerves: Implications for regeneration

Injury to the mammalian central nervous system results in loss of function because of its inability to regenerate. It has been postulated that some axons in the mammalian central nervous system have the ability to regenerate but fail to do so because of the inhospitable nature of surrounding glial cells. For example, mature oligodendrocytes were shown to inhibit axonal growth, and astrocytes were shown to form scar tissue that is nonsupportive for growth. In the present study we report an additional phenomenon which might explain the failure of axons to elongate across the site of the injury, namely, the absence of astrocytes from the crush site between the glial scar and the distal stump. Astrocytes began to disappear from the injury site as early as 2 days after the injury. After 1 week the site was necrotic and contained very few glial cells and numerous macrophages. Disappearance of glial cells was demonstrated in both rabbit and rat optic nerves by light microscopy, using antibodies directed against glial fibrillary acidic protein, and by transmission electron microscopy. Results are discussed with reference to possible implications of the long-lasting absence of astrocytes from the injury site, especially in view of the differences between the present findings in rodents and our recent observations in fish.

Vitronectin overrides a negative effect of TNF-alpha on astrocyte migration.

Morphogenesis and tissue repair require appropriate cross‐talk between the cells and their surrounding milieu, which includes extracellular components and soluble factors, e. g., cytokines and growth factors. The present work deals with this communication needed for recovery after axotomy in the central nervous system (CNS). The failure of CNS axons to regenerate after axonal injury has been attributed, in part, to astrocyte failure to repopulate the injury site. The goal of this work was to provide an in vitro model to mimic the in vivo response of astrocytes to nerve injury and to find ways to modulate this response and create a milieu that favors astrocyte migration and repopulation of the injury site. In an astrocyte scratch wound model, we blocked astrocyte migration by tumor necrosis factor a (TNF‐α). This effect could not be reversed by astrocyte migration‐inducing factors such as transforming growth factor βi (TGF‐β1) or by any of the tested extracellular matrix (ECM) components (laminin and fibronectin) except for vitronectin (Vn). Vn, added together with TNF‐α, counteracted the TNF‐ α blockage and allowed a massive migration of astrocytes (not due to cell proliferation) beyond that allowed by Vn only. Heparan sulfate proteoglycans (HSPG) were shown to be involved in the migration. The results may be relevant to regeneration of CNS axons, and may also provide an example that an extracellular component (Vn) can overcome and neutralize a negative effect of a growth factor/cytokine (TNF‐α) and can act in synergy with other features of this cytokine to promote a necessary function (e. g., cell migration) that is otherwise inhibited.—Faber‐Elman, A., Lavie, V., Schvartz, I., Shaltiel, S., Schwartz, M. Vitronectin overrides a negative effect of TNF‐α on astrocyte migration. FASEB J. 9, 1605‐1613 (1995)

New surgical approach to overcome the inability of injured mammalian axons to grow within their environment.

We present a new method for creating conditions conducive to axonal growth in injured optic nerves of adult rabbits. The surgical approach consists of making a cavity in the adult rabbit optic nerve, into which a piece of nitrocellulose soaked with conditioned medium originating from regenerating fish optic nerves is implanted. In addition, daily irradiation (10 days, 5 min, 35 mW) with low energy He-Ne laser is carried out. Such a combined treatment may open a door to neurobiologists and clinicians, hoping to unravel the enigma of mammalian CNS regeneration.

Optic nerve disease and injury: Prospects for induction of regeneration

3. Optic Nerve Regeneration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 571 3.1. Macrophage Response to Axonal Injury: Implications for Regeneration . . . . . . . . . . . . . . . . 572 3.2. Glial Cell Response to Axonal Injury . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 574 3.2.1. Oligodendrocytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 574 3.2.2. Astrocytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 574 3.3. Survival of Retinal Ganglion Cells after Axotomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 576

Horseradish peroxidase labeling of growth cones and axons beyond the site of injury in injured rabbit optic nerve axons growing in their own environment

Spontaneous growth of injured axons in the mammalian central nervous system is limited. We have previously shown an apparently regenerative growth of injured optic axons in the adult rabbit, achieved by supplying them with soluble substances originating from growing axons, followed by low energy helium-neon laser irradiation. The growing unmyelinated and thinly myelinated axons were embedded in astrocytes, and some were in the process of remyelination by oligodendrocytes. They were shown to have originated from the retinal ganglion cells. The present study further supports evidence relating to the origin and nature of these axons. Light microscopic analysis of these axons labeled with anterogradely transported horseradish peroxidase revealed that many of these axons have varicosities and bear growth cone-like swellings in their tips. These axons traverse the lesion site and extend into the distal stump in a disorganized pattern.

Helium-neon laser irradiation attenuates anoxia-induced degeneration of rabbit retinal ganglion cells

The effect of low-energy laser irradiation, known to delay axonal degeneration in mechanically traumatized nerves, was investigated in rabbit retinal ganglion cells damaged by temporary anoxia. Complete retinal vascular occlusion was induced in 39 rabbits by application of pressure to the cornea, with continuous monitoring under an operating microscope. The duration of occlusion was 15, 30 or 60 minutes. Starting immediately after the cessation of vascular occlusion, half of the rabbits in each group received transcorneal irradiation with a 35-mW helium-neon laser for 5 minutes daily on 10 consecutive days. The nonirradiated rabbits served as controls. Retinal ganglion cell viability was demonstrated by retrograde labeling of their axons with horseradish peroxidase, introduced subdurally into the optic nerve at a distance of 2 mm distal to the globe, 48 hours prior to sacrifice. For labeling intensity controls we used normal, not occluded, animals labeled with horseradish peroxidase by the same method. The animals were sacrificed 2, 4 or 8 weeks after occlusion. Labeling of retinal ganglion cells and their axons was observed in 100% of the normal control animals and in 85% of the irradiated rabbits. The results suggest that low-energy helium-neon laser irradiation attenuates the damage inflicted on the retinal ganglion cells as a result of anoxia.

Glial Cell Differentiation in Regeneration and Myelination

Spontaneous growth of axons after injury is extremely limited in the mammalian central nervous system (CNS). It is now clear, however, that injured CNS axons can be induced to elongate when provided with a suitable environment.

Growth-Associated Triggering Factors and Central Nervous System Response to Injury

Mammalian central nervous system (CNS) neurons have negligible posttraumatic regenerative capacity, whereas nerves of lower vertebrates and of the peripheral nervous system of mammals regenerate spontaneously after injury.