Damage to the optic nerve in mammals induces retrograde degeneration and apoptosis of the retinal ganglion cell (RGC) bodies. The mechanisms that mediate the response of the neuronal cells to the axonal injury are still unknown. We have previously shown that semaphorins, axon guidance molecules with repulsive cues, are capable of mediating apoptosis in cultured neuronal cells (Shirvan, A., Ziv, I., Fleminger, G., Shina, R., He, Z., Brudo, I., Melamed, E., and Brazilai, A. (1999) J. Neurochem. 73, 961-971). In this study, we examined the involvement of semaphorins in an in vivo experimental animal model of complete axotomy of the rat optic nerve. We demonstrate that a marked induction of type III semaphorin proteins takes place in ipsilateral retinas at early stages following axotomy, well before any morphological signs of RGC apoptosis can be detected. Time course analysis revealed that a peak of expression occurred after 2-3 days and then declined. A small conserved peptide derived from semaphorin 3A that was previously shown to induce neuronal death in culture was capable of inducing RGC loss upon its intravitreous injection into the rat eye. Moreover, we demonstrate a marked inhibition of RGC loss when axotomized eyes were co-treated by intravitreous injection of functionblocking antibodies against the semaphorin 3A-derived peptide. Marked neuronal protection from degeneration was also observed when the antibodies were applied 24 h post-injury. We therefore suggest that semaphorins are key proteins that modulate the cell fate of axotomized RGC. Neutralization of the semaphorin repulsive function may serve as a promising new approach for treatment of traumatic injury in the adult mammalian central nervous system or of ophthalmologic diseases such as glaucoma and ischemic optic neuropathy that induce apoptotic RGC death.

Abstract-The ability of the central nervous system to cope with stressful conditions was shown to be dependent on proper T-cell-mediated immune response. Because the therapeutic window for neuroprotection after acute insults such as stroke is relatively narrow, we searched for a procedure that would allow the relevant T cells to be recruited rapidly. Permanent middle cerebral artery occlusion was induced in adult rats. To facilitate a rapid poststroke T cell activity, rats were treated with poly-YE using different regimens. Control and poly-YE-treated rats were assessed for functional recovery using neurological severity score and Morris water maze. Neuroprotection, neurogenesis, growth factor expression, and microglial phenotype were assessed using histological and immunofluorescence methods. Administration of poly-YE as late as 24 hours after middle cerebral artery occlusion yielded a beneficial effect manifested by better neurological performance, reduced neuronal loss, attenuation of behavioral deficits, and increased hippocampal and cortical neurogenesis. This compound affected the subacute phase by modulating microglial response and by increasing local production of insulin-like growth factor-I, known to be a key player in neuronal survival and neurogenesis. The relative wide therapeutic window, coupled with its efficacy in attenuating further degeneration and enhancing restoration, makes poly-YE a promising immune-based candidate for stroke therapy. Key Words: neuroprotection Ⅲ neurogenesis Ⅲ reactive microglia Ⅲ stroke P reviously, we have demonstrated that central nervous system (CNS) trauma spontaneously evokes a beneficial, T-cell-mediated immune response, which reduces neuronal loss. 1 In the damaged CNS tissue, CNS-specific T cells accumulate and become reactivated on recognizing and interacting with their corresponding autoantigens presented to them by local antigen-presenting cells. 2,3 This in turn leads to the production of specific neurotrophic factors (eg, brainderived neurotrophic factor) by T cells, and to the proper activation of microglia/macrophages. 4,5 Enhancing the activity of CNS-specific T cells (by a well-regulated passive or active immunization) was found to be beneficial in various animal models of CNS injuries. 6 -8 The ability to maintain autoimmunity in healthy individuals, without developing autoimmune disease, was shown to be regulated by naturally occurring CD4 ϩ CD25 ϩ regulatory T cells. However, recovery from CNS injury can benefit from a transient elimination or decreased activity of these cells. 9 Compounds that can downregulate the constitutive suppression of regulatory T cells (Treg) were therefore considered by us as potential candidates.We found that poly-YE, a high-molecular-weight (22 to 45 kDa) copolymer that was shown to exert modulatory effects on the immune system, 10,11 is capable of downregulating the activity of the regulatory T cells, and used this copolymer to facilitate the spontaneous response of effector T cells recognizing antigens associated with a ...

Deciphering the molecular mechanisms of glaucoma-induced death and its mediators is a crucial step towards designing new therapeutic strategies to treat this incurable disease.