Artemisia Leaf Extract protects against neuron toxicity by TRPML1 activation and promoting autophagy/mitophagy clearance in both in vitro and in vivo models of MPP+/MPTP-induced Parkinson's disease

Abstract

Background: Parkinson's disease (PD) is a neurodegenerative disorder involving the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc). Cellular clearance mechanisms, including the autophagy-lysosome pathway, are commonly affected in the pathogenesis of PD. The lysosomal Ca²⁺ channel mucolipin TRP channel 1 (TRPML1) is one of the most important proteins involved in the regulation of autophagy. Artemisia argyi Lev. et Vant., is a traditional Chinese herb, that has diverse therapeutic properties and is used to treat patients with skin diseases and oral ulcers. However, the neuroprotective effects of A. argyi are not explored yet.

Hypothesis: This study aims is to investigate the neuroprotective effects of A. argyi in promoting the TRPML1-mediated autophagy/mitophagy-enhancing effect METHODS: In this study, we used 1-methyl-4-phenyl-pyridinium (MPP+)-induced PD model established in an SH-SY5Y human neuroblastoma cell line as well as in a 1-methyl-4-phenyl-1,2,3,6-tetrahydro-pyridine (MPTP)-induced PD model in C57BL/6 J mice. MTT assay was conducted to measure the cell viability and further MitoSoX and DCFDA assay were used to measure the ROS. Western blot analysis was used to access levels of TRPML1, p-DRP1 (ser616), p-AKT, PI3K, and β-catenin, Additionally, IF and IHC analysis to investigate the expression of TRPML1, LC3B, β-catenin, TH+, α-synuclein. Mitotracker stain was used to check mitophagy levels and a lysosomal intracellular activity kit was used to measure the lysosomal dysfunction. Behavioral studies were conducted by rotarod and grip strength experiments to check motor functions.

Results: In our in vitro study, A. argyi rescued the MPP+-induced loss of cell viability and reduced the accumulation of mitochondrial and total reactive oxygen species (ROS). Subsequently, it increased the expression of TRPML1 protein, thereby inducing autophagy, which facilitated the clearance of toxic accumulation of α-synuclein. Furthermore, A. argyi played a neuroprotective role by activating the PI3K/AKT/β-catenin cell survival pathway. MPP+-mediated mitochondrial damage was overcome by upregulation of mitophagy and downregulation of the mitochondrial fission regulator p-DRP1 (ser616) in SH-SY5Y cells. In the in vivo study, A. argyi ameliorated impaired motor function and rescued TH+ neurons in the SNpc region. Similar to the results of the in vitro study, TRPML1, LC3B, and β-catenin expression was enhanced in the SNpc region in the A. argyi-treated mice brain.

Conclusion: Thus, our results first demonstrate that A. argyi can exert neuroprotective effects by stimulating TRPML1 and rescuing neuronal cells by boosting autophagy/mitophagy and upregulating a survival pathway, suggesting that A. argyi can further be exploited to slow the progression of PD.

Keywords: A. argyi; Autophagy; Mitophagy; Parkinson's disease; ROS; TRPML1; α-synuclein.