A role of PSA-NCAM in the survival of retinal ganglion cells (RGCs) after kainic acid damage.

BACKGROUND: Neural cell adhesion molecule (NCAM) belongs to the immunoglobulin superfamily of adhesion molecules. Polysialic acid (PSA) is attached to NCAM post-translationally. PSA residues are considered to reduce the adhesive properties of NCAM and play an important role in the regulation of cell interactions. PSA-NCAM is largely expressed in the mature retina by glial cells adjacent to retinal ganglion cells (RGCs) but its functions remain unclear. The objective of this study was to explore the role of PSA-NCAM with respect to RGC survival following kainic acid (KA)-induced excitotoxicity. METHODS: Experiments were performed on C57BL/6NTac male mice. KA was injected intravitreally to induce RGC damage. RGCs were visualized using an anti-Brn3a antibody. Endoneuraminidase N (NA) was administrated intravitreally to cleave PSA chains from NCAM. RESULTS: KA induced an 80% reduction in the density of RGCs that was accompanied by a decrease in PSA-NCAM in the RGC layer. KA treatment induced a pronounced increase in the level of matrix metalloproteinase-9 (MMP-9) in the inner layers of the retina. Inhibition of MMP-9 reduced both RGC death and PSA-NCAM shedding in the retina. PSA-NCAM cleavage induced by NA abolished the protective action of the MMP-9 inhibitor and decreased RGC survival following KA-treatment. CONCLUSIONS: A decrease in retinal PSA-NCAM levels following KA administration is due to the induction of active MMP-9, which removes extracellular PSA-NCAM from the surface of astroglial and Müller cells. The MMP-9 induced shedding of PSA-NCAM enhances KA-induced toxicity and at least in part contributes to the observed loss of RGCs following excitotoxic damage.

Alterations in the polysialylated neural cell adhesion molecule and retinal ganglion cell density in mice with diabetic retinopathy.

AIM: To investigate the impact of polysialylated neural cell adhesion molecule (PSA-NCAM) on the survival of retinal ganglion cells (RGCs) in the experimentally induced diabetes in mice. METHODS: Diabetes was induced in 2.5 months old Swiss Webster mice by intraperitoneal injection of streptozotocin (STZ, 90 mg/kg) once daily for two consecutive days. Examination of the proteins of interest in the retinas from diabetic mice at 2mo after diabetes induction was performed using immunohistochemistry and Western blot analysis. RGCs were counted in the wholemounted retinas, and Brn3a marker was used. RESULTS: Examination of retinas from diabetic mice at 2mo after diabetes induction revealed a considerable reduction in RGC density. Our experiments also demonstrated a redistribution of PSA-NCAM in the retina of diabetic animals. PSA-NCAM immunoreactivity was diminished in the inner part of the retina where RGCs were located. In contrast, an enhanced PSA-NCAM immunoreactivity was detected in the outer layers of the retina. PSA-NCAM signal was co-localized with glial fibrillary acidic protein immunoreactivity in the Müller cell branches. Previous studies have shown that matrix metalloproteinase-9 (MMP-9) is responsible for the reduction in PSA-NCAM levels in neuronal cells. The reduced levels of PSA-NCAM in inner layers (nerve fiber layer, ganglion cell layer) were accompanied by the increased expression of MMP-9. In contrast, in the outer retinal layers, the expression of MMP-9 was much less pronounced. CONCLUSION: MMP-9 induces PSA-NCAM shedding in the inner part of the retina and the decreased level of PSA-NCAM in the inner part of the retina might be, at least in part, responsible for the loss of RGCs in diabetic mice.

PSA modification of NCAM supports the survival of injured retinal ganglion cells in adulthood.

Neural cell adhesion molecule (NCAM) is known as the cell surface glycoprotein, and it belongs to the immunoglobulin superfamily of adhesion molecules. Polysialic acid (PSA) is a carbohydrate attached to NCAM via either of two specific sialyltransferases: ST8SiaII and ST8SiaIV. Polysialylated neural cell adhesion molecule (PSA-NCAM) mediates cell interactions, plays a role in axon growth, migration, synaptic plasticity during development and cell regeneration. Some evidence has shown that PSA-NCAM supports the survival of neurons. It was demonstrated that PSA-NCAM is present in abundance in the retina during development and in adulthood. The aim of this study was to investigate whether PSA-NCAM promotes retinal ganglion cell (RGC) survival in transgenic mice with deficiencies in sialyltransferases or NCAM or after the administration of endoneuraminidase (Endo-N). RGC injury was induced by intravitreal administration of kainic acid (KA). These studies showed that injection of Endo-N after 14 days enhances the toxicity of KA to RGCs in wild-type (WT) mice by 18%. In contrast, in knockout mice (ST8SiaII-/-, ST8SiaIV-/-, NCAM-/-), survival of RGCs after KA injury did not change. Deficiencies of either ST8SiaII or ST8SiaIV did not influence the level of PSA-NCAM in the adult retina, however, in neonatal animals, decreased levels of PSA-NCAM were observed. In knockout ST8SiaII-/- adults, a reduced number of RGCs was detected, whereas in contrast, increased numbers of RGCs were noted in NCAM-/- mice. In conclusion, these data demonstrate that PSA-NCAM supports the survival of injured RGCs in adulthood. However, the role of PSA-NCAM in the adult retina requires further clarification.