Effect of melatonin and melatonylvalpromide on beta-amyloid and neurofilaments in N2a cells

In the present study, we have studied the effect of melatonin (Mt) and melatonin derivative, i.e., melatonylvalpromide (Mtv), on cell viability, beta-amyloid (A beta) production, cell morphology, and expression and phosphorylation of neurofilament proteins in wild-type murine neuroblastoma N2a (N2a/wt) and N2a stably transfected with amyloid precursor protein (N2a/APP) cell lines. The study used MTT assay, Sandwich ELISA, immunocytochemistry and Western blots techniques. The results showed that both Mt and Mtv could increase cell viability, but Mtv did so more effectively. The N2a/APP showed shorter and less amount of cell processes than N2a/wt, and Mtv but not Mt slightly improved the morphological changes in N2A/APP. Both Mt and Mtv suppressed the A beta level in cell lysates, but the effect of Mtv was stronger than Mt. The immunoreaction to the non-phosphorylated neurofilament proteins probed by SMI32 and SMI33 were remarkably weaker in N2a/APP than N2a/wt, while the immunoreaction to the phosphorylated neurofilament proteins at SMI34 epitopes was slightly stronger in N2a/APP than N2a/wt, suggesting higher phosphorylation level of neurofilament proteins in N2a/APP. Treatment of the cells with Mt and Mtv increased the immunoreaction at SMI32 and SMI33 epitopes, while only Mtv but not Mt decreased the staining at SMI34 epitope, suggesting both Mt and Mtv promote dephosphorylation of neurofilament at SMI32 and SMI33 epitopes, while Mtv stimulates dephosphorylation of neurofilament at SMI34 epitope. These results suggest that Mtv may be a better candidate in arresting the intracellular accumulation of A beta and protecting the cells from A beta-related toxicity.