Potential effects and molecular mechanisms of melatonin on the dopaminergic neuronal differentiation of human amniotic fluid mesenchymal stem cells

Abstract

ABSTRACT Melatonin, a highly lipophilic molecule secreted by the pineal gland in the brain, plays a role in various biological functions. Previous studies reported that melatonin exerts its effect on mesenchymal stem cell (MSC) survival and differentiation into osteogenic‐ and adipogenic‐lineage. However, the effect of melatonin in neurogenic differentiation in amniotic fluid (AF)‐MSCs remains to be explored, thus we investigated the potential role of melatonin on dopaminergic neuron differentiation in AF‐MSCs. The results showed that various concentrations of melatonin did not affect cell viability and proliferative effects of AF‐MSCs. Increases in the levels of neuronal protein marker (&bgr;III‐tubulin) and dopaminergic neuronal markers (tyrosine hydroxylase, TH and NURR1), but decrease in the level of glial fibrillary acidic protein (GFAP), were observed in melatonin‐treated AF‐MSCs. Melatonin induced alteration in differential expression patterns of mesenchymal stem cell antigens by reducing CD29, CD45, CD73, CD90 and CD105, but no changing CD34 expressing cells. AF‐MSCs were sequentially induced in neurobasal medium containing standard inducing cocktails (ST: bFGF, SHH, FGF8, BDNF), 1&mgr;M melatonin, or a combination of ST and melatonin. The levels of TUJ1, TH, MAP2, NURR1 and dopamine transporter (DAT) were significantly increased in all treated groups when compared with control‐untreated cells. Pretreated AF‐MSCs with non‐selective MT1/MT2 receptors antagonist, luzindole and selective MT2 receptor antagonist, 4‐P‐PDOT diminished melatonin‐induced increase in dopaminergic neuronal markers and phosphorylated ERK but did not diminish increase in phosphorylated CaMKII by melatonin. Pretreatment with mitogen‐activated protein kinase (MEK) inhibitor, PD98059 and CaMKII inhibitor, KN‐93 were able to abolish increase in the levels of dopaminergic markers in melatonin‐treated AF‐MSCs. These findings suggest that melatonin promotes dopaminergic neuronal differentiation of AF‐MSCs possibly via the induction in ERK and CaMKII pathways through melatonin receptor‐dependent and ‐independent mechanisms, respectively. HIGHLIGHTSMelatonin induces neuronal protein markers but reduces GFAP expression in AF‐MSCs.Melatonin induces dopaminergic neuronal differentiation of human AF‐MSCs.Melatonin induces induction in ERK and CaMKII pathways in human AF‐MSCs.