Homocysteine activates calcium-mediated cell signaling mechanisms targeting the cytoskeleton in rat hippocampus

Homocysteine is considered to be neurotoxic and a risk factor for neurodegenerative diseases. Despite the increasing evidences of excitotoxic mechanisms of homocysteine (Hcy), little is known about the action of Hcy on the cytoskeleton. In this context, the aim of the present work was to investigate the signaling pathways involved in the mechanism of action of Hcy on cytoskeletal phosphorylation in cerebral cortex and hippocampus of rats during development. Results showed that 100 μM Hcy increased the intermediate filament (IF) phosphorylation only in 17-day-old rat hippocampal slices without affecting the cerebral cortex from 9- to 29-day-old animals. Stimulation of ⁴⁵Ca²⁺ uptake supported the involvement of NMDA receptors and voltage-dependent channels in extracellular Ca²⁺ flux, as well as Ca²⁺ release from intracellular stores through inositol-3-phosphate and ryanodine receptors. Moreover, the mechanisms underlying the Hcy effect on hippocampus cytoskeleton involved the participation of phospholipase C, protein kinase C, mitogen-activated protein kinase, phosphoinositol-3 kinase and calcium/calmodulin-dependent protein kinase II. The Hcy-induced IF hyperphosphorylation was also related to G_i protein and inhibition of cAMP levels. These findings demonstrate that Hcy at a concentration described to induce neurototoxicity activates the IF-associated phosphorylating system during development in hippocampal slices of rats through different cell signaling mechanisms. These results probably suggest that hippocampal rather than cortical cytoskeleton is succeptible to neurotoxical concentrations of Hcy during development and this could be involved in the neural damage characteristic of mild homocystinuric patients.