The neuritogenicity and the neuroregenerative potential of asiaticoside (AS) and its aglycone, asiatic acid (AA), has been generally reported. We recently identified the participation of extracellular signal-regulated protein kinases 1/2 (ERK1/2) and protein kinase B (Akt) in the neuritogenic mechanism of AS and AA. In this study, we further investigated the possible upstream target molecule and the associated downstream signaling of both triterpenoids in mouse neuroblastoma Neuro-2a cells. Our immunoblotting and immunofluorescence assays revealed that either AS or AA exerted neurite extension activity through inhibitory effect on glycogen synthase kinase 3β (GSK3β) and Ras homolog gene family member A (RhoA). AS appeared significantly more potent in promoting neurite elongation than AA, and concurrently expressed a higher degree of inhibition on GSK3β and RhoA activations. The mediation of GSK3β and RhoA activities in AS-treated cells involved Akt signaling. Moreover, when using GW441756, a specific tropomyosin receptor kinase A (TrkA) receptor signaling inhibitor, the ERK1/2 and Akt phosphorylation, the inhibitory effects on GSK3β and RhoA and the neurite outgrowth induced by AS, but not AA, were totally suppressed. In conclusion, our findings supported the different upstream regulators of AS and AA in promoting neuritogenicity in Neuro-2a cells. Although both AS and AA could enhance neurite elongation through the suppression of GSK3β and RhoA activities, only AS could modulate the effect through TrkA receptor signaling.
aDepartment of Biochemistry and Microbiology, Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok
bDrug and Health Product Research and Development Center, College of Pharmacy, Rangsit University, Pathum Thani
cChulalongkorn University Drugs and Health Products Innovation and Promotion Center, Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok, Thailand
Received 17 April 2019 Accepted 7 September 2019
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Correspondence to Boonsri Ongpipattanakul, PhD, Department of Biochemistry and Microbiology, Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok 10330, Thailand, Tel: +662 218 8366; fax: +662 218 8375; e-mail: Boonsri.firstname.lastname@example.org