NEUROTOXIC EFFECT OF SALSOLINOL ON NE-4C NEURAL STEM CELL MEDIATED THROUGH MTOR PATHWAY

Abstract

Parkinson’s disease is a common neurological disease characterised by motor and non-motor symptoms. Parkinson’s disease is associated with the loss of dopamine in the substantia nigra pars compacta neurons. Current treatment for Parkinson’s disease is ingestion of levodopa (dopamine precursor) complemented with the administration of dopamine agonists and inhibitors of dopamine degrading enzymes. However as the syndrome advances, constant use of dopaminergic medications becomes less effective and can lead to motor complications called dyskinesia. Hence, cell therapy is a promising alternative therapeutic strategy in Parkinson’s disease. It restores the damaged neurons in the nigrostriatal pathway. Transplanted neuronal stem cells are multipotent and are capable of differentiating to several types of cells in the central nervous system, including neurons and other brain cells. However, salsolinol, a neurotoxin exerts substantial toxicity on the transplanted neuronal stem cells. Salsolinol has diverse neuropharmacological effects including inducing oxidative stress besides being able to inhibit the mitochondrial energy supply. Salsolinal also inhibits some key enzymes involved in the production of dopamine such monoamine oxidase, tyrosine hydroxylase and catechol-O-methyltransferase. Additionally, salsolinol also prevents the uptake of catecholamines. This study aims to evaluate neurotoxicity and apoptogenic effect of salsolinol on NE-4C neuronal stem cells through mammalian target of rapamycin signalling pathway. Salsolinol was added to NE-4C cells. Cell viability and apoptosis were evaluated by using trypan blue exclusion method and mitochondrial membrane potential staining assay, respectively. Additionally, some key regulatory proteins that could mediate cell apoptosis through mTOR signalling pathway was analysed. The relative expressions of mTOR, phospho-mTOR, raptor and GßL proteins were determined using enzyme- linked immunosorbent assay. Results revealed that when NE-4C cells were treated with salsolinol (0-100μM) for 24, 48 and 72 hours, salsolinol induced death in NE-4C cells mainly by alteration of mitochondrial membrane potential. Additionally, the change of the level of phospho-mTOR indicates the contribution of this protein in the death of the NE-4C cells. In conclusion, salsolinol induced neuronal cell death via mitochondrial membrane potential alteration and down-regulation of phospho-mTOR protein.